U.S. patent application number 11/665569 was filed with the patent office on 2007-12-20 for base station apparatus,wireless communication system,and wireless transmission method.
Invention is credited to Yasuhiro Hamaguchi, Hideo Nanba, Shimpei To.
Application Number | 20070291702 11/665569 |
Document ID | / |
Family ID | 36203002 |
Filed Date | 2007-12-20 |
United States Patent
Application |
20070291702 |
Kind Code |
A1 |
Nanba; Hideo ; et
al. |
December 20, 2007 |
Base Station Apparatus,Wireless Communication System,And Wireless
Transmission Method
Abstract
Allocation of transmission power is carried out adaptively
without affecting adjacent cells. There are comprised a reception
part (132) that receives information from a mobile station
apparatus, a transmission power determination part (125) that
determines transmission power when transmitting a wireless signal
to a mobile station apparatus based on the received information, an
acquisition part (120) that acquires information about
communication environment in each time channel or each frequency
channel from the received information, a scheduling part (120) that
identifies a time channel or frequency channel the relationship of
which between transmission power and communication environment
satisfies the condition for allocation and allocates transmission
data and transmission power for transmission to a mobile station
apparatus to a communication slot in the time channel or frequency
channel, and a transmission part (130, 131) that transmits a
wireless signal using the communication slot to which the
transmission data and the determined transmission power have been
allocated.
Inventors: |
Nanba; Hideo; (Chiba-shi,
JP) ; Hamaguchi; Yasuhiro; (Ichibara-shi, JP)
; To; Shimpei; (Chiba-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
36203002 |
Appl. No.: |
11/665569 |
Filed: |
October 19, 2005 |
PCT Filed: |
October 19, 2005 |
PCT NO: |
PCT/JP05/19195 |
371 Date: |
April 17, 2007 |
Current U.S.
Class: |
370/336 ;
455/561; 455/572 |
Current CPC
Class: |
H04J 3/00 20130101; H04L
5/023 20130101; H04W 72/0473 20130101; H04L 27/2608 20130101; H04W
52/346 20130101; H04W 52/243 20130101; H04W 72/085 20130101 |
Class at
Publication: |
370/336 ;
455/561; 455/572 |
International
Class: |
H04J 3/00 20060101
H04J003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2004 |
JP |
2004-303633 |
Claims
1. A base station apparatus that uses a plurality of slots and
performs wireless communication with a mobile station apparatus in
a cell, wherein said base station apparatus: receives information
from said mobile station apparatus; determines transmission power
to be allocated to a group of said slots as well as determining
transmission power when transmitting a wireless signal to said
mobile station apparatus based on said received information;
determines a group of slots or part of a group of slots for
transmitting transmission data based on the transmission power when
transmitting the wireless signal to said mobile station apparatus
and the transmission power allocated to said group of slots; and
transmits the wireless signal to said mobile station apparatus
using said determined group of slots or said determined part of
said group of slots.
2. The base station apparatus according to claim 1, which has a
plurality of time channels and performs wireless communication with
a mobile station apparatus in a cell using said time channel,
wherein said base station apparatus: receives information from said
mobile station apparatus; determines transmission power to be
allocated to said time channel as well as determining transmission
power when transmitting a wireless signal to said mobile station
apparatus based on said received information; determines a time
channel or part of time channel for transmitting transmission data
based on the transmission power when transmitting the wireless
signal to said mobile station apparatus and the transmission power
allocated to said time channel; and transmits the wireless signal
to said mobile station apparatus using said determined time channel
or said determined part of time channel.
3. The base station apparatus according to claim 1, which has a
plurality of frequency channels and performs wireless communication
with a mobile station apparatus in a cell using said frequency
channel, wherein said base station apparatus: receives information
from said mobile station apparatus; determines transmission power
to be allocated to said frequency channel as well as determining
transmission power when transmitting a wireless signal to said
mobile station apparatus based on said received information;
determines a frequency channel or part of frequency channel for
transmitting transmission data based on the transmission power when
transmitting the wireless signal to said mobile station apparatus
and the transmission power allocated to said frequency channel; and
transmits the wireless signal to said mobile station apparatus
using a frequency band corresponding to said determined frequency
channel or said determined part of frequency channel.
4. The base station apparatus according to either claim 2 or claim
3, wherein the condition for determining the allocation of time
channel or part of time channel, or frequency channel or part of
frequency channel for transmitting said transmission data is any
one of the following conditions that: the interference power at
said mobile station apparatus is the smallest; the magnitude of
transmission power and the magnitude of interference power at said
mobile station are associated in advance in a relationship of
inverse proportion and interference power corresponding to said
determined transmission power is possessed; and the ratio between
reception signal power and interference power at said mobile
station apparatus is the maximum.
5. The base station apparatus according to claim 4, wherein when
determining the allocation of time channel or part of time channel,
or frequency channel or part of frequency channel for transmitting
said transmission data, said base station apparatus: divides the
mobile station apparatus in said cell into a plurality of groups
based on the information received from said mobile station
apparatus; and allocates slots for transmitting transmission data
to the same time channel or the same frequency channel for a mobile
station apparatus in said same group.
6. The base station apparatus according to claim 45, wherein when
determining the allocation of time channel or part of time channel,
or frequency channel or part of frequency channel for transmitting
said transmission data, said base station apparatus: identifies
said group to which the transmission power for transmitting a
wireless signal to any one of the mobile station apparatus in said
cell belongs; and allocates, when there exists a vacant time
channel or a vacant frequency channel in all of the individual time
channels or the individual frequency channels or in the part
thereof to which transmission power corresponding to a group with
transmission power larger than that of said identified group has
been allocated, a slot for transmitting transmission data to said
mobile station apparatus to the vacant time channel or the vacant
frequency channel.
7. The base station apparatus according to claim 5, wherein when
determining the allocation of time channel or part of time channel,
or frequency channel or part of frequency channel for transmitting
said transmission data, said base station apparatus: determines
said group to which the transmission power for transmitting a
wireless signal to any one of the mobile station apparatus in said
cell belongs; and allocates, when transmission data is not
allocated to the time channel or the frequency channel allocated to
said identified group and when there exists a vacant time channel
or a vacant frequency channel in all of the time channels or the
frequency channels or in the part thereof to which transmission
power corresponding to a group with transmission power smaller than
that of said identified group has been allocated, a slot for
transmitting transmission data to said mobile station apparatus to
the vacant time channel or the vacant frequency channel.
8. The base station apparatus according to claim 5, wherein said
base station apparatus changes, after allocating a slot for
transmitting said transmission data, the transmission power of said
allocated slot based on said received information.
9. The base station apparatus according to claim 7, wherein said
base station apparatus changes the modulation scheme when
allocating transmission data to be transmitted to said mobile
station apparatus and said transmission power to said vacant time
channel or each vacant frequency channel.
10. The base station apparatus according to either claim 2 or claim
3, wherein said base station apparatus updates said allocated
transmission power at intervals of a certain period of time when
determining the allocation of time channel or part of time channel,
or frequency channel or part of frequency channel for transmitting
said transmission data.
11. The base station apparatus according to either claim 2 or claim
3, wherein said base station apparatus updates said allocated
transmission power when determining the allocation of time channel
or part of time channel, or frequency channel or part of frequency
channel for transmitting said transmission data, and if there
exists a mobile station apparatus that newly makes a request for
connection in the cell and if any one of the mobile station
apparatus moves, or if the situation of propagation path changes in
any one of the mobile station apparatus.
12. The base station apparatus according to claim 10, wherein said
base station apparatus allocates transmission power so that, when
updating said transmission power, the difference between the
transmission power immediately before the update and the
transmission power to be allocated at the time of update is equal
to or less than a fixed value.
13. The base station apparatus according to either claim 2 or claim
3, wherein said base station apparatus allocates, when determining
the allocation of time channel or part of time channel, or
frequency channel or part of frequency channel for transmitting
said transmission data: transmission power with which a wireless
signal can reach the entire range in the cell to at least one of
said time channels or frequency channels; and transmission power
the influence of which on the adjacent cells can be ignored to at
least one of said time channels or frequency channels.
14. The base station apparatus according to claim 13, wherein said
base station apparatus: acquires a level of interference received
from the adjacent cells based on information received from said
mobile station apparatus; and determines said time channel or part
thereof, or said frequency channel or part thereof to which the
transmission power with which the wireless signal can reach the
entire range in the cell is allocated in accordance with said
measured interference level in order to transmit data other than
said control data.
15. The base station apparatus according to claim 13, wherein said
base station apparatus: measures the number of adjacent cells based
on the information received from said mobile station apparatus; and
determines, when determining the allocation of time channel,
frequency channel, or communication slot for transmitting said
transmission data, a number L of said time channels or said part
thereof, or said frequency channels or said part thereof to which
transmission power with which the wireless signal can reach the
entire range in the cell is allocated in accordance with said
measured interference level in order to transmit data other than
said control data as such one that holds L.ltoreq.(total number of
time channels, frequency channels, or communication slots)/{(number
of adjacent cells)+1}.
16. The base station apparatus according to claim 13, wherein said
base station apparatus allocates, when determining the allocation
of time channel or part of time channel, or frequency channel or
part of frequency channel for transmitting said transmission data
and if, on one hand, there exists a mobile station apparatus
required to transmit a wireless signal with transmission power with
which the wireless signal can reach the entire range in the cell
and if, on the other hand, there exists no data to be transmitted
to said mobile station apparatus, dummy data to be transmitted to
said mobile station apparatus and the transmission power with which
the wireless signal can reach the entire range in the cell to said
time channel or said part thereof, or said frequency channel or
said part thereof.
17. The base station apparatus according to claim 5, wherein said
base station apparatus adds a hysteresis characteristic to the
condition for the change of groups when the group to which the
transmission power allocated to said mobile station apparatus
belongs is changed due to the information received from said mobile
station apparatus.
18. A wireless communication system configured by: the base station
apparatus according to either claim 2 or claim 3; and at least one
mobile station apparatus.
19. A mobile station apparatus that is applied to the wireless
communication system according to claim 18.
20. A wireless communication method of a base station apparatus
having a plurality of time channels and transmitting a wireless
signal to a mobile station apparatus using said time channel, said
method comprising at least: a step for receiving information from
said mobile station apparatus; a step for determining transmission
power when transmitting a wireless signal to said mobile station
apparatus based on said received information; a step for acquiring
information about communication environment in each time channel
from said received information; a step for determining the
allocation of time channel or part of time channel and transmission
power for transmission to said mobile station apparatus based on
said determined transmission power and said information about
communication environment; and a step for transmitting a wireless
signal to said mobile station apparatus using the time channel or
the part of time channel to which said transmission data and said
determined transmission power have been allocated.
21. A wireless communication method of a base station apparatus
having a plurality of frequency channels and transmitting a
wireless signal to a mobile station apparatus in a cell using said
frequency channel, said method comprising at least: a step for
receiving information from said mobile station apparatus; a step
for determining transmission power when transmitting a wireless
signal to said mobile station apparatus based on said received
information; a step for acquiring information about communication
environment in each frequency channel from said received
information; a step for determining the allocation of frequency
channel or part of frequency channel and transmission power for
transmitting transmission data to said mobile station apparatus
based on said determined transmission power and said information
about communication environment; and a step for transmitting a
wireless signal to said mobile station apparatus using the
frequency channel or the part of frequency channel to which said
transmission data and said determined transmission power have been
allocated.
Description
TECHNICAL FIELD
[0001] The present invention relates to a base station apparatus, a
wireless communication system, and a wireless transmission method,
which carry out the allocation of transmission power adaptively
without affecting adjacent cells.
BACKGROUND ART
[0002] In our country, the service of IMT-2000 (International
Mobile Telecommunication 2000) was started in October 2001 before
the rest of the world, and thus the transmission and access
technique in a mobile communication system is rapidly developing.
In addition, the technique of HSDPA (High Speed Down-link Packet
Access) and the like are standardized and the data transmission at
about 10 Mbps at maximum is now being put to practical use.
[0003] On the other hand, the standardization to realize a broad
band wireless Internet access that targets a transmission rate of
10 Mbps to 100 Mbps is in progress and various techniques have been
proposed. The condition required to realize high transmission rate
wireless communication is the improvement of frequency usage
efficiency. Since the transmission rate and the used bandwidth are
in a proportional relationship, a simple solution to increase the
transmission rate is to widen the frequency bandwidth to be used.
However, available frequency bands are in a tight situation and it
is unlikely that a sufficient bandwidth is allocated when
constructing a new wireless communication system. Consequently, it
becomes necessary to improve the frequency usage efficiency.
[0004] In addition, another required condition is to provide
service in a private area (isolated cell), such as a wireless LAN,
in a seamless manner while realizing service in a communication
area constituted by cells, such as a mobile phone.
[0005] Techniques having the possibility of solving these problems
include a technique called one-cell reuse OFDM/(TDMA, FDMA)
(Orthogonal Frequency Division Multiplexing/Time Division Multiple
Access, Frequency Division Multiple Access). This is a technique in
which communication is performed using the same frequency in all of
the cells in a communication area constituted by cells, the
modulation scheme when performing communication is the OFDM, and
the access scheme uses the TDMA and FDMA. This is a communication
system, without doubt, capable of realizing higher-speed data
communication in an isolated cell while maintaining a common
wireless interface with a cell area.
[0006] The OFDM, TDMA, and FDMA, which are constitutional
techniques of the OFDM/(TDMA, FDMA), are explained briefly.
[0007] First, the OFDM is a technique used for IEEE802.11a, which
is a wireless system of 5 GHz band, and a terrestrial digital
broadcasting. The OFDM is a system in which tens to thousands of
carriers are arranged at intervals of a minimum frequency that does
not cause interference theoretically and communication is performed
simultaneously. In the normal OFDM, such a carrier is called a
sub-carrier and each sub-carrier is modulated when performing
communication by a modulation scheme, such as the PSK, QAM, etc.
Further, with an error correction technique combined, it has grate
resistance to frequency selective fading. In the present
specification, the number of sub-carriers used in the OFDM is
assumed to be 768.
[0008] Next, the TDMA is an access system in which time is divided
when transmitting/receiving data. Normally, in a communication
system using the TDMA as an access system, a frame configuration is
used in which there are a plurality of slots, which is a unit of
communication time, and further, it is general to allocate a
control slot necessary for receiving a frame at the front of the
frame in the case of Down-link. In the present specification, it is
assumed that a frame is composed of nine slots and the front slot
is allocated as a control slot.
[0009] Next, the FDMA is an access system in which frequencies are
divided when transmitting/receiving data. Normally, in a
communication system using the FDMA as an access system,
frequencies are divided into several bands, which are frequency
bands for performing communication, and thus terminals (mobile
station apparatus) that access are classified. Normally, a
protective band called a guard band is prepared between divided
frequency bands, however, in the OFDM/(TDMA, FDMA), no guard band
is used because the frequency usage efficiency is decreased, or if
used, its band is very narrow, just for accepting several
sub-carries. In the present specification, 768 sub-carries used in
the OFDM are divided into 12 groups, each group including 64
sub-carries, for performing the FDMA.
[0010] Next, the OFDM/(TDMA, FDMA) is explained based on the
above-described introduction. FIG. 42 is a diagram showing a
two-dimensional frame configuration of the OFDM/(TDMA, FDMA). In
FIG. 42, the vertical axis represents the frequency and the
horizontal axis represents the time. One of a plurality of
rectangles shown in FIG. 42 is the minimum unit used for data
transmission, composed of a plurality of OFDM symbols, and is
referred to as a slot in the present specification. Among the
slots, those with diagonals are control slots. In this case, the
figure means that there are nine slots in the time direction and 12
slots in the frequency direction in one frame, that is, there exist
a total of 108 slots (among then, 12 slots are control slots) in
one frame. In addition, in the present specification, a group of
slots in the direction of the frequency axis at the same time
(composed of 12 slots in the case of FIG. 42) is referred to as a
time channel and a group of slots in the direction of the time axis
at the same frequency (composed of nine slots in the case of FIG.
42) is referred to as a frequency channel. In form, a slot is
denoted by (Tn, Fm), a time channel is denoted by Tn (n is a
natural number from 1 to 9), and a frequency channel is denoted by
Fm (m is a natural number from 1 to 12). For example, the hatched
slot in FIG. 42 is a slot denoted by (T4, F7).
[0011] Next, communication from a base station (referred to as AP
or base station apparatus) to a mobile station (referred to as MT,
mobile station apparatus, or simply "terminal") is considered. When
an AP allocates data of 15 slots to an MT, it is assumed that the
data is allocated to the slots with vertical lines in FIG. 42,
although there may be various cases. In other words, the data to be
received by the MT is allocated to (T2 to T4, F1), (T5 to T8, F4),
and (T2 to T9, F11). Further, in order to indicate that the AP has
allocated data to the MT, it is necessary to embed data indicative
of the allocation to the control slot of the frequency to be used.
In the case of this example, (T1, F1), (T1, F4), and (T1, F11)
correspond to the control slots.
[0012] The OFDM/(TDMA, FDMA) system is a system in which a
plurality of mobile stations transmit and receive data to and from
the base station by changing the frequency and time based on those
described above. In FIG. 42, the figure is drawn such that there
seems to be a gap between slots for convenience's sake, however,
the presence or absence of a gap is of no importance.
[0013] FIG. 43 is a block diagram showing a general configuration
of a transmission circuit used in the OFDM/(TDMA, FDMA). The
transmission circuit shown in FIG. 43 has a data multiplex part
431. In addition, the transmission circuit has 12 error correction
encoding parts 432-a to 432-l and at the same time, has 12
serial/parallel conversion parts (S/P conversion parts) 433-a to
433-l. A transmission power control part 435 exhibits a function of
changing transmission power for each frequency channel.
[0014] In the data multiplex part 431, information data is
separated into 12 groups in units of packets for transmission. In
other words, the data multiplex part 431 physically specifies the
ODFM/(TDMA, FDMA) slot to be specified by a module, such as a CPU
etc., not shown schematically here. After that, error correction
encoding is performed in the error correction encoding parts 432-a
to 432-l, separation into 64 groups is performed in the S/P
conversion parts 433-a to 433-l, and each carrier is modulated in a
mapping part 434. In the transmission power control part 435, power
control is performed into transmission power for each sub-channel
specified by a module, such as a CPU etc., not shown schematically
and IFFT (Inverse Fast Fourier Transform) processing is performed
in an IFFT part 436. When generating an OFDM signal of 768 waves,
the number of points of the IFFT normally used is 1,024.
[0015] After that, in a P/S conversion part 437, conversion into
serial data is performed and then a guard interval is inserted in a
guard interval insertion part 438. A guard interval is inserted in
order to reduce interference between symbols when receiving an OFDM
signal. Then, after converted into an analog signal in a D/A
conversion part 439 and converted into a frequency for transmission
in a radio transmission part 440, the data is transmitted from an
antenna part 441.
[0016] In addition, FIG. 44 is a block diagram showing a general
configuration of a reception circuit used in the OFDM/(TDMA, FDMA).
The reception circuit shown in FIG. 44 has a data demultiplex part
461 and further, has 12 error correction decoding parts 460-a to
460-l. In addition, the reception circuit has 12 parallel/serial
conversion parts (P/S conversion parts) 459-a to 459-l.
[0017] In the reception circuit, an operation reverse to that of
the transmission circuit is performed basically. The frequency of
the radio wave received by an antenna part 451 is converted into a
frequency in a frequency band in which A/D conversion is possible
by a radio reception part 452. With data having been converted into
a digital signal in an A/D conversion part 453, the OFDM symbols
are synchronized in a synchronization part 454 and the guard
interval is removed in a guard interval removal part 455. After
that, the data is paralleled into 1,024 data in an S/P conversion
part 456.
[0018] After that, the FFT of 1,024 points is performed in an FFT
(Fast Fourier Transform) part 457 and demodulation of the
sub-carrier of 768 waves is performed in a propagation channel
estimation and demapping part 458. Normally, propagation path is
estimated by the receiver by sending a known signal from the
transmitter to the receiver. After that, the necessary data is
serialized in the P/S conversion parts 459-a to 459-l, error
correction is performed in the error correction decoding parts
460-a to 460-l, and the data is input to the data demultiplex part
461. In the data demultiplex part 461, the data is processed into
information data and output.
[0019] Next, the outline of a communication system consisting of
cells is explained. FIG. 45(a) is an example of the case where
cells have a hexagonal shape and seven frequency bands are used. A
base station is arranged in the center of the cell and in cell B0,
communication is performed using a frequency band Fc0, in B1, Fc1
is used, and similar combinations follow in the rest of the cells.
In such a cell configuration in which the number of frequency bands
is sufficient, it is unlikely that the adjacent cells use the same
frequency and it is possible to perform communication in an
excellent condition without influence from the adjacent cells.
[0020] FIG. 45(b) is an example of the case where one-cell reuse
OFDM/(TDMA, FDMA) is used. Similarly, the configuration consists of
hexagonal cells, however, the same frequency Fc0 is used.
Consequently, when the one-cell reuse OFDM/(TDMA, FDMA) operates
ideally, it follows that a frequency usage efficiency seven times
that compared to the case in FIG. 45(a) can be attained. As a
result, it can be said that realization of one-cell reuse is a
indispensable technique in order to realize high speed
communication.
[0021] As obvious also from FIG. 45(b), the point that affects the
ideal operation of the one-cell reuse is to prevent interference
from other cells. Two techniques can roughly be thought as a method
for preventing interference from other cells. One method is to
establish a communication system in which each terminal removes
radio waves from other cells (interference removal) and the other
method is to prevent interference from affecting as much as
possible. Among these methods, the following two are explained with
respect to a specific technique of the latter method.
[0022] First, a wireless data communication system, a wireless data
communication method, and its program disclosed in Japanese
Unexamined Patent Publication No. 2003-18091 (Patent document 1)
are explained. A cell configuration relating to the invention
described in Patent document 1 is shown in FIG. 46. In FIG. 46, a
hexagon constructed by the dotted-line is shown in each cell in
comparison with FIG. 45(a). This means that one cell is divided
into two areas, one being near the base station and the other,
distant therefrom. When cell B0 is focused on, communication is
performed conventionally using a frequency Fc0 with terminals in
the area distant from the base station and communication is
performed using Fc1 to Fc6 with terminals in the area near the base
station. It is described that this increases the frequency usage
efficiency. Further, it is explained that the use of a sector
antenna within an area surrounded by the dotted-line increases the
efficiency. This is a technique that utilizes the fact that even
the use of the frequency bands Fc1 to Fc6 does not affect the
adjacent cells because it is possible to lower transmission power
when performing communication with terminals near the base
station.
[0023] Next, a mobile communication system, a base station
apparatus, and a control method of a mobile communication system
disclosed in Japanese Unexamined Patent Publication No. 2003-46437
(Patent document 2) are explained. A cell configuration relating to
the invention disclosed in Patent document 2 is shown in FIG. 47.
In FIG. 47, two hexagons constructed by the dotted-line are shown
in each cell in comparison with FIG. 45(a). When cell B0 is focused
on, the area most distant from the base station is denoted by Ts1,
the second most distant area is denoted by Ts2, and the nearest
area is denoted by Ts3. Ts represents time and Ts1 to Ts3
constitute one frame. This means that in B0, transmission power is
increased to the maximum during Ts1 and communication is performed,
and then, the transmission power is lowered in Ts2 and Ts3 and
communication is performed. Similarly, each cell performs
communication by changing transmission power in accordance with the
time, respectively.
[0024] In B0, when communication is being performed with increased
transmission power during Ts1, communication with transmission
power increased to the maximum is not being performed in other
adjacent cells, and therefore, it is possible to perform
communication in B0 in a state in which interference from other
cells is small. For the cells B1 to B6, the same advantage is
secured similarly.
[0025] Patent document 1: Japanese Unexamined Patent Publication
No. 2003-18091
[0026] Patent document 2: Japanese Unexamined Patent Publication
No. 2003-46437
DISCLOSURE OF THE INVENTION
[0027] However, even if the techniques described in Patent document
1 and Patent document 2 are used in the one-cell reuse OFDM/(TDMA,
FDMA), it is not possible to deal adaptively with the case of an
isolated cell or the case where the number of adjacent cells is
different, and further, the case where a base station is newly
installed after the base station has once been installed and the
service has been started. Further, in Patent document 2, that each
base station is synchronized with another is a tacit assumption and
there is no description on the solving means when not
synchronized.
[0028] The present invention has been developed the above-described
circumstances being taken into account and an object thereof is to
provide a base station apparatus, a wireless communication system,
and a wireless communication method capable of carrying out the
allocation of transmission power adaptively without affecting
adjacent cells.
[0029] (1) In order to attain the above-mentioned object, the
present invention has employed means as follows. In other words, a
base station apparatus according to the present invention is a base
station apparatus that uses a plurality of slots and performs
wireless communication with a mobile station apparatus in a cell,
characterized in that the base station apparatus receives
information from the mobile station apparatus, determines
transmission power to be allocated to a group of the slots as well
as determining transmission power when transmitting a wireless
signal to the mobile station apparatus based on the received
information, determines a group of slots or part of a group of
slots for transmitting transmission data based on the transmission
power when transmitting the wireless signal to the mobile station
apparatus and the transmission power allocated to the group of
slots, and transmits the wireless signal to the mobile station
apparatus using the determined group of slots or the determined
part of the group of slots
[0030] As described above, since the base station apparatus
determines the transmission power to be allocated to the group of
the slots as well as determining the transmission power when
transmitting the wireless signal to the mobile station apparatus
based on the received information and determines the group of slots
or the part of the group of slots for transmitting the transmission
data based on the transmission power when transmitting the wireless
signal to the mobile station apparatus and the transmission power
allocated to the group of slots, it is possible to carry out the
allocation of transmission power adaptively without affecting the
adjacent cells.
[0031] (2) In addition, a base station apparatus according to the
present invention is a base station apparatus that has a plurality
of time channels and performs wireless communication with a mobile
station apparatus in a cell using the time channel, characterized
in that the base station apparatus receives information from the
mobile station apparatus, determines transmission power to be
allocated to the time channel as well as determining transmission
power when transmitting a wireless signal to the mobile station
apparatus based on the received information, determines a time
channel or part of time channel for transmitting transmission data
based on the transmission power when transmitting the wireless
signal to the mobile station apparatus and the transmission power
allocated to the time channel, and transmits the wireless signal to
the mobile station apparatus using the determined time channel or
the determined part of time channel.
[0032] As described above, since the base station apparatus
determines the transmission power to be allocated to the time
channel as well as determining the transmission power when
transmitting the wireless signal to the mobile station apparatus
based on the received information and determines the time channel
or the part of time channel for transmitting transmission data
based on the transmission power when transmitting the wireless
signal to the mobile station apparatus and the transmission power
allocated to the time channel, for example, small transmission
power is allocated to a time channel with large interference power,
a time channel with small SINR, and a time channel with a large
error rate because those time channels are used only on the central
part of the cell as those not used on the peripheral part of the
cell because of their large interference. In addition, large
transmission power is allocated to a time channel with small
interference power, a time channel with large SINR, and a time
channel with a small error rate as those used on the peripheral
part of the cell because their interference is small even on the
peripheral part of the cell. Due to this, it is made possible to
carry out the allocation of transmission power adaptively without
affecting the adjacent cells.
[0033] (3) In addition, a base station apparatus according to the
present invention is a base station apparatus that has a plurality
of frequency channels and performs wireless communication with a
mobile station apparatus in a cell using the frequency channel,
characterized in that the base station apparatus receives
information from the mobile station apparatus, determines
transmission power to be allocated to the frequency channel as well
as determining transmission power when transmitting a wireless
signal to the mobile station apparatus based on the received
information, determines a frequency channel or part of frequency
channel for transmitting transmission data based on the
transmission power when transmitting the wireless signal to the
mobile station apparatus and the transmission power allocated to
the frequency channel, and transmits the wireless signal to the
mobile station apparatus using a frequency channel corresponding to
the determined frequency channel or the determined part of
frequency channel.
[0034] As described above, since the base station apparatus
determines the transmission power to be allocated to the frequency
channel as well as determining the transmission power when
transmitting the wireless signal to the mobile station apparatus
based on the received information and determines the frequency
channel or the part of frequency channel for transmitting
transmission data based on the transmission power when transmitting
the wireless signal to the mobile station apparatus and the
transmission power allocated to the frequency channel, for example,
small transmission power is allocated to a frequency channel with
large interference power, a frequency channel with small SINR, and
a frequency channel with a large error rate because those frequency
channels are used only on the central part of the cell as those not
used on the peripheral part of the cell because of their large
interference. In addition, large transmission power is allocated to
a frequency channel with small interference power, a frequency
channel with large SINR, and a frequency channel with a small error
rate as those used on the peripheral part of the cell because their
interference is small also on the peripheral part of the cell. Due
to this, it is made possible to carry out the allocation of
transmission power adaptively without affecting the adjacent
cells.
[0035] (4) In addition, a base station apparatus according to the
present invention is characterized in that the condition for
determining the allocation of time channel or part of time channel,
or frequency channel or part of frequency channel for transmitting
the transmission data is any one of the following conditions that:
the interference power at the mobile station apparatus is the
smallest; the magnitude of transmission power and the magnitude of
interference power at the mobile station are associated in advance
in a relationship of inverse proportion and interference power
corresponding to the determined transmission power is possessed;
and the ratio between reception signal power and interference power
at the mobile station apparatus is the maximum.
[0036] By determining the condition for allocation as described
above, it is made possible to carry out the allocation of
transmission power adaptively without affecting the adjacent
cells.
[0037] (5) In addition, a base station apparatus according to the
present invention is characterized in that when determining the
allocation of time channel or part of time channel, or frequency
channel or part of frequency channel for transmitting the
transmission data, the base station apparatus divides the mobile
station apparatus in the cells into a plurality of groups based on
the information received from the mobile station apparatus and
allocates slots for transmitting transmission data to the same time
channel or the same frequency channel for a mobile station
apparatus in the same group.
[0038] As described above, by grouping the mobile station apparatus
in the cell, the allocation of transmission power can be carried
out for each group, and therefore, it is made possible to perform
the allocation processing efficiently. In addition, it is possible
to efficiently carry out the allocation of transmission data and
transmission power for a mobile station apparatus that newly makes
a request for connection in the same cell. Due to this, it is made
possible to carry out the allocation of transmission power
adaptively without affecting the adjacent cells. By the way, the
transmission power of each group may assume discrete values or may
assume continuous values in the above-mentioned numerical value
range.
[0039] (6) In addition, a base station apparatus according to the
present invention is characterized in that when determining the
allocation of time channel or part of time channel, or frequency
channel or part of frequency channel for transmitting the
transmission data, the base station apparatus identifies the group
to which the transmission power for transmitting a wireless signal
to any one of the mobile station apparatus in the cell belongs, and
allocates, when there exists a vacant time channel or a vacant
frequency channel in all of the individual time channels or the
individual frequency channels or in the part thereof to which
transmission power corresponding to a group with transmission power
larger than that of the identified group has been allocated, a slot
for transmitting transmission data to the mobile station apparatus
to the vacant time channel or the vacant frequency channel.
[0040] With this configuration, it is possible to employ a form in
which, when there exists a vacant channel in the time channels or
the frequency channels that have been allocated to a group that
requires high transmission power, the allocation of a terminal that
requires low transmission power to the vacant slot of the time
channels or the frequency channels allocated to a terminal group
that requires high transmission power is allowed. This is because
the possibility is high that the time channel or the frequency
channel to which a terminal group that requires high transmission
power has been allocated is allocated a terminal group that
requires low transmission power in the adjacent cells and there
will occur no interference between the adjacent cells even when a
terminal that requires low transmission power is allocated to the
vacant communication slot of the time channel or the frequency
channel in question. Due to this, it is made possible to carry out
the allocation of transmission power adaptively without affecting
the adjacent cells.
[0041] (7) In addition, a base station apparatus according to the
present invention is characterized in that when determining the
allocation of time channel or part of time channel, or frequency
channel or part of frequency channel for transmitting the
transmission data, the base station apparatus identifies the group
to which the transmission power for transmitting a wireless signal
to any one of the mobile station apparatus in the cell belongs, and
allocates, when transmission data is not allocated to the time
channel or the frequency channel allocated to the identified group
and when there exists a vacant time channel or a vacant frequency
channel in all of the time channels or the frequency channels or in
the part thereof to which transmission power corresponding to a
group with transmission power smaller than that of the identified
group has been allocated, a slot for transmitting transmission data
to the mobile station apparatus to the vacant time channel or the
vacant frequency channel.
[0042] As described above, since when allocating the transmission
power to the specific mobile station apparatus, the base station
apparatus allocates, when there exists a vacant communication slot
in the time channels or each of the frequency channels to which
transmission power corresponding to the group with transmission
power smaller than the group to which the transmission power for
the mobile station apparatus belongs has been allocated, the
transmission data to be transmitted to the mobile station apparatus
and the transmission power corresponding to the group with small
transmission power to the vacant communication slot, it is made
possible to carry out the allocation of transmission power
adaptively without affecting the adjacent cells.
[0043] (8) In addition, a base station apparatus according to the
present invention is characterized by changing, after allocating a
slot for transmitting the transmission data, the transmission power
of the allocated slot based on the received information.
[0044] As described above, since the base station apparatus
changes, after allocating the slot for transmitting the
transmission data, the transmission power of the allocated slot
based on the received information, it is made possible to use a
plurality of values as reception power on the mobile station
apparatus side in accordance with the variation in the propagation
path.
[0045] (9) In addition, a base station apparatus according to the
present invention is characterized by changing the modulation
scheme when allocating transmission data to be transmitted to the
mobile station apparatus and the transmission power to the vacant
time channel or each vacant frequency channel.
[0046] As described above, since the base station apparatus changes
the modulation scheme when allocating the transmission data to be
transmitted to the mobile station apparatus and the transmission
power to the vacant communication slot, it is possible to avoid the
influence on the adjacent cells while avoiding the occurrence of an
error by changing the modulation scheme to a lower one, that is, to
a modulation scheme for easier reception, as well as lowering the
transmission power when, for example, transmitting a wireless
signal to a mobile station apparatus that requires high
transmission power, and if the communication slot of each time
channel or each frequency channel to which low transmission power
has been allocated is vacant. On the contrary, it is possible to
avoid the influence on the adjacent cells while improving
transmission efficiency by changing the modulation scheme to a
higher one as well as raising transmission power when, for example,
transmitting a wireless signal to a mobile station apparatus that
requires low transmission power, and if the communication slot of
each time channel or each frequency channel to which high
transmission power has been allocated is vacant
[0047] (10) In addition, a base station apparatus according to the
present invention is characterized by updating the allocated
transmission power at intervals of a certain period of time when
determining the allocation of time channel or part of time channel,
or frequency channel or part of frequency channel for transmitting
the transmission data.
[0048] As described above, since the base station apparatus updates
the allocated transmission power at intervals of a certain period
of time, it is made possible to allocate transmission power in
accordance with the movement of the mobile station apparatus, the
change in the situation of propagation path, etc.
[0049] (11) In addition, a base station apparatus according to the
present invention is characterized by updating the allocated
transmission power when determining the allocation of time channel
or part of time channel, or frequency channel or part of frequency
channel for transmitting the transmission data, and if there exists
a mobile station apparatus that newly makes a request for
connection in the cell and if any one of the mobile station
apparatus moves, or if the situation of propagation path changes in
any one of the mobile station apparatus.
[0050] With this configuration, it is made possible to allocate
transmission power in accordance with the variation in the
situation of communication in the cell in real time.
[0051] (12) In addition, a base station apparatus according to the
present invention is characterized by allocating transmission power
so that, when updating the transmission power, the difference
between the transmission power immediately before the update and
the transmission power to be allocated at the time of update is
equal to or less than a fixed value.
[0052] As described above, since the base station apparatus
allocates the transmission power so that the difference between the
transmission power immediately before the update and the
transmission power to be allocated at the time of update is equal
to or less than a fixed value, it is made possible to keep the
variation in interference with the adjacent cells to a minimum.
Here, the difference shall be equal to or less than a fixed value
because of an attempt to define a range in which the transmission
power immediately before update does not change considerably after
the update. A specific numerical value range can be found from the
technical common sense in the communication technique.
[0053] (13) In addition, a base station apparatus according to the
present invention is characterized by allocating, when determining
the allocation of time channel or part of time channel, or
frequency channel or part of frequency channel for transmitting the
transmission data, transmission power with which a wireless signal
can reach the entire range in the cell to at least one of the time
channels or frequency channels and at the same time, transmission
power the influence of which on the adjacent cells can be ignored
to at least one of the time channels or frequency channels.
[0054] By thus allocating transmission power, it is made possible
to deal flexibly even with the case where there appears a mobile
station apparatus that newly makes a request for connection in the
cell and the mobile station apparatus requires high transmission
power or low transmission power.
[0055] (14) In addition, a base station apparatus according to the
present invention is characterized by acquiring a level of
interference received from the adjacent cells based on information
received from the mobile station apparatus and determining the time
channel or part thereof, or the frequency channel or part thereof
to which the transmission power with which the wireless signal can
reach the entire range in the cell is allocated in accordance with
the measured interference level in order to transmit data other
than the control data.
[0056] As described above, since the base station apparatus
determines the time channel or part thereof, or the frequency
channel or part thereof to which the transmission power with which
the wireless signal can reach the entire range in the cell is
allocated in accordance with the measured interference level, it is
possible to evaluate only the time channel or the part thereof, or
the frequency channel or the part thereof that is actually affected
by the interference from the adjacent cells and it is made possible
to improve the usage efficiency of the time channel or the part
thereof, or the frequency channel or the part thereof.
[0057] (15) In addition, a base station apparatus according to the
present invention is characterized by measuring the number of
adjacent cells based on the information received from the mobile
station apparatus and determining, when determining the allocation
of time channel, frequency channel, or communication slot for
transmitting the transmission data, a number L of the time channels
or part thereof, or the frequency channels or part thereof to which
the transmission power with which the wireless signal can reach the
entire range in the cell is allocated in accordance with the
measured interference level in order to transmit data other than
the control data as such one that holds L.ltoreq.(total number of
time channels, frequency channels, or communication slots)/{(number
of adjacent cells)+1}.
[0058] As described above, since the base station apparatus
dynamically changes the number of time channels or the part
thereof, or the number of frequency channels or the part thereof to
which the transmission power with which the wireless signal can
reach the entire range in the cell is allocated in accordance with
the number of adjacent cells, it is made possible to improve the
usage efficiency of the time channel or the part thereof, or the
frequency channel or the part thereof.
[0059] (16) In addition, a base station apparatus according to the
present invention is characterized by allocating, when determining
the allocation of time channel or part of time channel, or
frequency channel or part of frequency channel for transmitting the
transmission data and if on one hand, there exists a mobile station
apparatus required to transmit a wireless signal with transmission
power with which the wireless signal can reach the entire range in
the cell and if, on the other hand, there exists no data to be
transmitted to the mobile station apparatus, dummy data to be
transmitted to the mobile station apparatus and the transmission
power with which the wireless signal can reach the entire range in
the cell to the time channel or the part thereof, or the frequency
channel or the part thereof.
[0060] With such a configuration, it is made easy to detect a
channel with high interference power at each terminal of the
adjacent cells.
[0061] (17) In addition, a base station apparatus according to the
present invention is characterized by adding a hysteresis
characteristic to the condition for the change of groups when the
group to which the transmission power allocated to the mobile
station apparatus belongs is changed due to the information
received from the mobile station apparatus.
[0062] With such a configuration, it is made possible to perform
the grouping operation stably without being affected considerably
from situations in which the communication speed is not constant
and the communication speed needs to be changed frequently at the
mobile station apparatus.
[0063] (18) In addition, a wireless communication system according
to the present invention is characterized by being configured by
the base station apparatus according to any one of claim 1 to claim
17 and at least one mobile station apparatus.
[0064] According to the wireless communication system according to
the present invention, it is made possible to carry out the
allocation of transmission power adaptively without affecting the
adjacent cells.
[0065] (19) In addition, a mobile station apparatus according to
the present invention is characterized by being applied to the
wireless communication system according to claim 18.
[0066] According to the mobile station apparatus according to the
present invention, it is made possible to carry out the allocation
of transmission power adaptively without affecting the adjacent
cells.
[0067] (20) In addition, a wireless communication method according
to the present invention is a wireless communication method of a
base station apparatus having a plurality of time channels and
transmitting a wireless signal to a mobile station apparatus using
the time channel, characterized by comprising at least a step for
receiving information from the mobile station apparatus, a step for
determining transmission power when transmitting a wireless signal
to the mobile station apparatus based on the received information,
a step for acquiring information about communication environment in
each time channel from the received information, a step for
determining the allocation of time channel or part of time channel
and transmission power for transmission to the mobile station
apparatus based on the determined transmission power and the
information about communication environment, and a step for
transmitting a wireless signal to the mobile station apparatus
using the time channel or the part of time channel to which the
transmission data and the determined transmission power have been
allocated.
[0068] As described above, since the transmission power when
transmitting the wireless signal to the mobile station apparatus is
determined and at the same time, the transmission power to be
allocated to the time channel is determined based on the
information received from the mobile station apparatus, and the
time channel or part of time channel for transmitting transmission
data is determined based on the transmission power when
transmitting the wireless signal to the mobile station apparatus
and the transmission power allocated to the time channel, for
example, small transmission power is allocated to a time channel
with large interference power, a time channel with small SINR, and
a time channel with a large error rate because those time channels
are used only on the central part of the cell as those not used on
the peripheral part of the cell because of their large
interference. In addition, large transmission power is allocated to
a time channel with small interference power, a time channel with
large SINR, and a time channel with a small error rate as those
used on the peripheral part of the cell because their interference
is small also on the peripheral part of the cell. Due to this, it
is made possible to carry out the allocation of transmission power
adaptively without affecting adjacent cells.
[0069] (21) In addition, a wireless communication method according
to the present invention is a wireless communication method of a
base station apparatus having a plurality of frequency channels and
transmitting a wireless signal to a mobile station apparatus in a
cell using the frequency channel, characterized by comprising at
least a step for receiving information from the mobile station
apparatus, a step for determining transmission power when
transmitting a wireless signal to the mobile station apparatus
based on the received information, a step for acquiring information
about communication environment in each frequency channel from the
received information, a step for determining the allocation of
frequency channel or part of frequency channel and transmission
power for transmitting transmission data to the mobile station
apparatus based on the determined transmission power and the
information about communication environment, and a step for
transmitting a wireless signal to the mobile station apparatus
using the frequency channel or the part of time channel to which
the transmission data and the determined transmission power have
been allocated.
[0070] As described above, since the transmission power when
transmitting the wireless signal to the mobile station apparatus is
determined and at the same time, the transmission power to be
allocated to the frequency channel is determined based on the
information received from the mobile station apparatus, and a
frequency channel or part of frequency channel for transmitting
transmission data is determined based on the transmission power
when transmitting the wireless signal to the mobile station
apparatus and the transmission power allocated to the frequency
channel, for example, small transmission power is allocated to a
frequency channel with large interference power, a frequency
channel with small SINR, and a frequency channel with a large error
rate because those frequency channels are used only on the central
part of the cell as those not used on the peripheral part of the
cell because of their large interference. In addition, large
transmission power is allocated to a frequency channel with small
interference power, a frequency channel with large SINR, and a
frequency channel with a small error rate as those used on the
peripheral part of the cell because their interference is small
also on the peripheral part of the cell. Due to this, it is made
possible to carry out the allocation of transmission power
adaptively without affecting adjacent cells.
[0071] According to the present invention, since transmission power
when transmitting a wireless signal to a mobile station apparatus
is determined and at the same time, transmission power to be
allocated to a group of slots is determined based on information
received from the mobile station apparatus, and a group of slots or
part of a group of slots for transmitting transmission data is
determined based on the transmission power when transmitting the
wireless signal to the mobile station apparatus and the
transmission power allocated to the group of slots, it is possible
to carry out the allocation of transmission power adaptively
without affecting adjacent cells.
BRIEF DESCRIPTION OF THE DRAWINGS
[0072] FIG. 1(a) is a diagram showing an arrangement situation of a
cell and mobile station terminals, FIG. 1(b) is a diagram showing
transmission power required for Down-link in the cell, and FIG.
1(c) is a diagram showing an example of the allocation of
slots.
[0073] FIG. 2 is a diagram showing a configuration example of
slots.
[0074] FIG. 3 is a diagram showing an example of cell
arrangement.
[0075] FIG. 4 is a diagram showing transmission timing of a control
slot group.
[0076] FIG. 5 is a block diagram showing a general configuration of
a mobile station apparatus.
[0077] FIG. 6 is a block diagram showing a general configuration of
a base station apparatus.
[0078] FIG. 7 is a flow chart showing the operation of the
allocation of slot at a base station apparatus.
[0079] FIG. 8 is a flow chart showing the operation of the
allocation of slot at a mobile station apparatus.
[0080] FIG. 9(a) is a diagram showing an arrangement situation of
mobile station apparatus in cell 1 and cell 2, FIG. 9(b) is a
diagram showing transmission power required for Down-link in the
cell 2, and FIG. 9(c) is a diagram showing a situation of the
allocation of slot in the cell 2.
[0081] FIG. 10(a) is a diagram showing transmission power required
for Down-link in the cell 1 and FIG. 10(b) shows a diagram showing
transmission power required for Down-link in the cell 2.
[0082] FIG. 11 is a diagram showing a situation of the allocation
of mobile station apparatus in the cell 2 and interference power
affecting the cell 1.
[0083] FIG. 12 is a diagram showing a state in which slots have
been allocated to mobile station apparatus A to C in the cell
1.
[0084] FIG. 13 is a diagram showing transmission power required for
Down-link in the cell 1 and the cell 2 and a state in which slots
have been allocated to mobile station apparatus D to H in the cell
1.
[0085] FIG. 14 is a diagram showing how the transmission power
level and the interference level are associated with each
other.
[0086] FIG. 15(a) is a diagram showing the case where the
transmission timing of the control slot group is fixed and FIG.
15(b) is a diagram showing the case where the transmission timing
of the control slot group is variable.
[0087] FIG. 16 is a diagram showing an example in which the
transmission power required for Down-link and the allocation of
slot in the same group are changed.
[0088] FIG. 17 is a diagram showing the transmission power required
for Down-link and an example in which the allocation to the time
channel to which another group has been allocated is allowed.
[0089] FIG. 18 is a diagram showing a general configuration of a
mobile station apparatus.
[0090] FIG. 19 is a diagram showing a general configuration of a
base station apparatus.
[0091] FIG. 20 is a diagram showing an example of a sub-channel
used in Down-link.
[0092] FIG. 21 is diagram showing a configuration example of a
frame.
[0093] FIG. 22(a) is a diagram showing the configuration of a slot
and FIG. 22(b) is a diagram showing the outline of the topology of
a network.
[0094] FIG. 23(a) is a diagram showing the outline of a cell
arrangement and FIG. 23(b) is a diagram showing a structure example
of a control slot.
[0095] FIG. 24 is a diagram showing the relationship between the
cell boundary and the transmission power group.
[0096] FIG. 25 is a flow chart showing the outline of the operation
procedure of a mobile station apparatus.
[0097] FIG. 26 is a flow chart showing the outline of the operation
procedure of a base station apparatus.
[0098] FIG. 27 is a flow chart showing the operation of the
allocation of sub-channel that can be used.
[0099] FIG. 28 is a flow chart showing a connection process.
[0100] FIG. 29 is a flow chart of transmission power control.
[0101] FIG. 30 is a flow chart showing the determination of the
allocation of sub-channel.
[0102] FIG. 31 is a flow chart showing the operation of the
allocation of transmission data to slots.
[0103] FIG. 32 is a flow chart showing the operation of the
allocation of transmission data to slots.
[0104] FIG. 33 is a diagram showing the relationship between the
cell boundary and the transmission power group.
[0105] FIG. 34 is a diagram showing the relationship between the
cell boundary and the transmission power group.
[0106] FIG. 35 is a diagram showing the relationship between the
cell boundary and the transmission power group.
[0107] FIG. 36 is a diagram showing the relationship between the
cell boundary and the transmission power group.
[0108] FIG. 37 is a diagram showing the relationship between the
cell boundary and the transmission power group.
[0109] FIG. 38 is a diagram showing the relationship between the
cell boundary and the transmission power group.
[0110] FIG. 39 is a diagram showing the relationship between the
cell boundary and the transmission power group.
[0111] FIG. 40 is a flow chart showing the operation of the
allocation of sub-channel that can be used.
[0112] FIG. 41 is a flow chart showing the operation of the
allocation of sub-channel that can be used.
[0113] FIG. 42 is a diagram showing a configuration example of a
frame.
[0114] FIG. 43 is a diagram showing a general configuration of a
base station apparatus.
[0115] FIG. 44 is a diagram showing a general configuration of a
mobile station apparatus.
[0116] FIG. 45(a) is a diagram showing an example of a cell
arrangement and FIG. 45(b) is a diagram showing an example of a
cell arrangement.
[0117] FIG. 46 is a diagram showing an example of a cell
arrangement.
[0118] FIG. 47 is a diagram showing an example of a cell
arrangement.
[0119] FIG. 48 is a diagram showing how to give hysteresis to
grouping.
[0120] FIG. 49 is a diagram showing an example of a condition in
grouping.
[0121] FIG. 50 is a flow chart showing the operation of a base
station.
[0122] FIG. 51 is a flow chart showing the operation of a
terminal.
BEST MODES FOR CARRYING OUT THE INVENTION
First Embodiment
[0123] A method of allocation of slot according to a first
embodiment of the present invention is explained below. In the
method of allocation of slot according to the first embodiment of
the present invention, a plurality of terminals that require a
transmission power level of the same level in a base station are
allocated adaptively to different frequency channels of the same
time channel while taking into consideration the influence of
interference that comes from adjacent cells. An example of the
result of the allocation when such adaptive allocation of slot is
carried out is shown in FIG. 1. By the way, it is assumed that the
"base station" has the same meaning as the control station, AP, or
base station apparatus and the "mobile station" has the same
meaning as the MT, mobile station apparatus, or terminal.
[0124] FIG. 1(a) shows a cell and the arrangement of terminals in
the cell and FIG. 1(b) shows transmission power required for the
Down-link communication for the respective terminals in the cell.
However, in the first embodiment of the present invention, it is
assumed that the transmission of transmission power is so performed
that the reception power of all of the terminals in the cell is the
same. In such a situation, when the method of allocation of slot
according to the first embodiment of the present invention is
applied, the terminals whose transmission power required for the
Down-link is the same level are grouped. Here, grouping is such
that terminal A, terminal B, and terminal C are put into group 1,
terminal D, terminal E, terminal F, and terminal G are put into
group 2, and terminal H and terminal I are put into group 3. Then,
it follows that the terminals belonging to the same group are
allocated to different frequency channels of the same time channel.
Here, it is assumed that the group 1 is allocated to time channel
3, the group 2, to time channel 2, and the group 3, to time channel
5. As a result, such channel allocation as shown in FIG. 1(c) is
carried out and the transmission power required for the Down-link
communication to a terminal is maintained at the same level for
each time channel and therefore it is possible to keep the average
interference power affecting on adjacent cells substantially
constant for each time channel. A channel allocation procedure by
such adaptive allocation of slot is explained below.
[0125] First, a slot configuration according to the first
embodiment of the present invention is shown in FIG. 2. As shown in
FIG. 2, the slot configuration according to the first embodiment of
the present invention is assumed to be a configuration in which the
number of frequency channels is 12, the number of time channels
including control slots (hereinafter, a single time channel for
transmission of control information in a single frequency channel
is referred to as a control slot and the time channels for
transmission of control information over a plurality of frequency
channels are referred to as a control slot group) is 9, and the
same frequency band is used in all of the cells. In the following,
explanation is given with an example of a system in which base
stations are synchronized with each other, however, the present
invention is not limited to a system in which base stations are
synchronized with each other but can also be applied to a system in
which base stations are not synchronized with each other as in the
case of the synchronized system.
[0126] In addition, in the case of the system in which base
stations are synchronized with each other, it may also be possible
to assume that the cell arrangement is a state as shown in FIG. 3
and that the transmission timing of the control slot group is one
common to all of the cells as shown in FIG. 4(a), and further that
the configuration is such one in which timing is different for each
cell as shown in FIG. 4(b). Furthermore, it may also be possible to
assume a configuration in which the transmission timing of the
control slot is different from frequency channel to frequency
channel. A case where the control slot group is transmitted with
common timing determined in advance in all of the cells is
explained below.
[0127] First, a device configuration of terminals when the
allocation of slot according to the first embodiment of the present
invention is carried out is shown in FIG. 5. FIG. 5 is a block
diagram of a device configuration of terminals. In FIG. 5,
reference number 100 denotes an antenna part, 101 denotes a radio
reception part, 102 and 111 denote an A/D conversion part, 103
denotes a symbol synchronization part, 104 denotes a guard interval
removal part, 105 denotes an S/P part, 106 denotes an FET part, 107
denotes a propagation channel estimation and demapping part, 108
denotes a P/S part, 109 denotes an error correction decoding part,
110 denotes a demultiplex part, 112 denotes an RSS (Received Signal
Strength) measurement part, 113 denotes an interference power
measurement part, 114 denotes a control part, and 115 denotes an
Up-link transmission part.
[0128] As shown in FIG. 5, a terminal that carried out the
allocation of slot according to the first embodiment of the present
invention has the RSS measurement part 112, unlike the conventional
example, and performs measurement of a reception power level at
Down-link. In addition, measurement of interference power is
performed at the interference power measurement part 113. However,
in FIG. 5, the interference power measurement part is at the post
stage of the FFT part 106 and has a configuration in which the
transmission power of an interference signal after FFT is measured,
but, not limited to this, and a configuration may be possible in
which the transmission power of an interference signal before FFT
is measured.
[0129] The RSSI (Received Signal Strength Indicator) thus measured
is subtracted from the transmission power information of a base
station included in the control information transmitted from the
base station at the control part 114 and thereby a propagation loss
is calculated. The information about the propagation loss and the
interference power in each time channel is put together with other
information data as a packet at the control part 114 and
transmitted to the base station at the Up-link transmission part
15.
[0130] Processes other than the above (demodulation of information
data etc.) are performed in the same manner as that of the prior
art. First, the received signal is subjected to
symbol-synchronization at the synchronization part 113 via the A/D
conversion part 102. After that, the guard interval is removed at
the guard interval (GI) removal part 104 and after subjected to
serial/parallel conversion at the S/P conversion part 105, the
received signal is transmitted to the FFT part 106 and converted
from a signal in the time area into a signal in the frequency area.
For the received signal thus converted into one in the frequency
area, propagation channel estimation and demapping are performed at
the propagation channel estimation and demapping part 107, and
after the parallel/serial conversion at the P/S conversion part
108, the transmission data is decoded at the error correction
decoding part 109 and transmitted to the demultiplex part, as a
result.
[0131] FIG. 6 is a block diagram of a device configuration of a
base station. In FIG. 6, reference number 120 denotes a scheduling
part, 121 denotes a multiplex part, 122 denotes an error correction
encoding part, 123 denotes an S/P part, 124 denotes a mapping part,
125 denotes a transmission power control part, 126 denotes an IFFT
part, 127 denotes a P/S part, 128 denotes a guard interval
insertion part, 129 denotes a D/A conversion part, 130 denotes a
radio transmission part, 131 denotes an antenna part, and 132
denotes an Up-link reception part.
[0132] As shown in FIG. 6, a base station when the allocation of
slot according to the first embodiment of the present invention is
carried out transmits the propagation loss information and
interference information obtained from the Up-link reception part
to the scheduling part 120 unlike the conventional example, and
carries out the allocation of slot according to the first
embodiment of the present invention. Then, at a slot allocated by
the scheduling part 120, transmission of information data of each
terminal is performed as a result, and at the same time, the
transmission power control information for each terminal is
obtained from the scheduling part 120 and transmitted to the
transmission power control part 125.
[0133] Next, a flow chart of allocation of slot at a base station
according to the first embodiment of the present invention is shown
in FIG. 7 and FIG. 8. A control flow shown in FIG. 7 and FIG. 8 is
explained below, in which each terminal in cell 1 in FIG. 9(a) is
actually put into a group and channel allocation is carried out.
Here, it is assumed that in cell 2 (adjacent cell of the cell 1) in
FIG. 9(a), the allocation of channel and slot has already been
carried out and the situation of the channel allocation is such one
as shown in FIG. 9(c). At this time, it is also assumed that each
of terminals I to T in the cell 2 is at each of positions shown in
FIG. 9(a), respectively, and the transmission power (transmission
power required for Down-link) in the base station corresponding to
the respective terminals is such one as shown in FIG. 9(b).
[0134] In the situation as described above, when there occurs a
request for communication in the terminal A, terminal B, and
terminal C situated in the cell 1, first, as shown in FIG. 7 and
FIG. 8, the terminals A to C receive (step S21) the control
information of all of the frequency channels transmitted (step S2)
periodically in the control slot group from the base station in
each cell, and measures the RSSI of the received signal at each
terminal as shown in step S22. It is assumed that the control slot
group transmitted periodically from the base station in each cell
is transmitted with transmission power that can be received by even
a terminal situated at the edge of the cell and the contents of the
control information include transmission power information
(information indicative of the magnitude of transmission power used
for the transmission) when the base station transmits control
information, information about allocation of slot, etc.
[0135] After the measurement of the RSSI at each terminal, the
terminals A to C demodulate the received signal, as shown in step
S23 and obtain the transmission power information at the base
station when the control information is transmitted. Next, from the
transmission power information at the base station obtained in step
S24 and the RSSI obtained in step S22, the amount of attenuation of
radio waves on the propagation path (propagation loss: here it is
assumed that propagation loss=transmission power-RSSI) is
calculated (step S25).
[0136] Further, as shown in step S26, measurement of the
interference power that comes from the adjacent cells is performed
at each of the terminals (terminals A to C). The terminals A to C
notify the base station of the interference power thus obtained and
the propagation loss information of Down-link between the base
station and the terminal obtained in step S26 via the Up-link (step
S27).
[0137] By the procedure described above, it is possible for the
base station to obtain the propagation loss information of the
Down-link between the base station and the terminal and the
information about interference power that comes from the adjacent
cells necessary to carry out the adaptive allocation of slot
according to the first embodiment of the present invention for each
terminal.
[0138] Next, at the base station, as shown in step S5 to step S7 in
FIG. 7, the terminals are grouped based on the propagation loss
information at each terminal obtained via the Up-link. Here, the
grouping of terminals is a process, as shown in FIG. 10(a), in
which the transmission power required for performing Down-link
transmission for each terminal is calculated from the propagation
loss at each terminal (step S6) and the terminals having the same
transmission power as a result of the calculation are handled as a
group (step S7).
[0139] By the way, as shown in FIG. 9(b), FIG. 10(a), and FIG.
10(b), explanation is given on the assumption that the transmission
power of the Down-link for each terminal assumes discrete values,
however, not limited to this example, the present invention can
also be applied to the case where the transmission power of the
Down-link for each terminal assumes continuous values.
[0140] As shown in FIG. 10(a), here, the transmission power of the
Down-link for the terminal A is the same level as that of the
transmission power of the Down-link for the terminal C, and as a
result, they belong to the same group (here, the group 2). In
addition, the terminal B requires high transmission power and
therefore it belongs to a group (here, the group 1) different from
that of the terminals A and C.
[0141] As described above, after the terminals (here, the terminals
A to C) having a request for communication are put into a group,
the allocation of time channel to each group and the allocation of
frequency channel to each terminal belonging to the group are
carried out at the base station. By the method of allocation of
slot according to the first embodiment of the present invention,
the allocation of time channel is carried out in the order from the
group with higher transmission power of the Down-link (step S8).
Consequently, here, the allocation of time channel is carried out
from the group 1 (to which only the terminal B belongs) and as
shown in step S9, whether there exists a terminal to which a slot
has already been allocated in the selected group (group 1) is
determined. Here, only the terminal B that newly initiates
communication belongs to the group 1, and therefore, the procedure
moves to step S10 and the time channel with the lowest interference
power observed at the terminal B of the group 1 among the vacant
time channels (here, all of the time channels) is allocated to the
group 1.
[0142] As shown in FIG. 11, the interference power in the time
channel 4 is the minimum among the interference power of each time
channel observed in the cell 1 and the time channel 4 is allocated
to the group 1. As shown in FIG. 11, the interference power
affecting the cell 1 is the minimum in the time channel 4, and this
is because the terminals I to K situated near the base station of
the cell 2 and whose transmission power of the Down-link is set low
are allocated to the time channel 4.
[0143] By such a procedure, the allocation of time channel to the
group 1 is carried out and next, the allocation of frequency
channel to each terminal belonging to the relevant group is carried
out (step S11 to step S13). First, as shown in step S11, the amount
of data of Down-link for the terminal (terminal B) to which a slot
has not been allocated yet in the relevant group (here, the group
1) is calculated, and as shown in step S12, the number of frequency
channels necessary for one frame is calculated. Then, as shown in
step S13, the allocation of vacant frequency channel to the
relevant terminal in accordance with the number of necessary
frequency channels. Here, if the number of necessary frequency
channels of the terminal B is assumed to be three, it follows that
three frequency channels of the time channel 4 are allocated to the
terminal B, as shown in FIG. 12.
[0144] As above, the allocation of slot to the group 1 is
completed, however, since there remain other groups to which
allocation must be carried out in addition to the group 1, the
procedure returns to step 8 and the allocation of time channel to
the relevant group (here, the group 2) is carried out. If the
allocation of time channel to the group 2 is carried out in the
same manner as the above, the time channel 7 whose interference
power is the smallest of all but the time channel already allocated
to the group 1 is allocated to the group 2, as a result.
[0145] After the allocation of time channel for each group, in the
same manner as in the above, the allocation of frequency channel to
the terminals A to C belonging to the group 2 to which the time
channel has been allocated is carried out and thus the procedure of
the allocation of slot is completed. The result of such allocation
of slot is notified to the terminal in the cell by the control slot
group (step S16, step S17) and after that, each terminal occupies
the allocated slot for a fixed period of time and performs
communication.
[0146] Here, when the allocation of slot in the first embodiment of
the present invention is updated and the allocation to a certain
time channel is changed to a terminal group different from the
previous frame, it is desirable to operate the algorithm so as to
allocate, if possible, a terminal group that requires transmission
power close to that of the terminal group to which the relevant
time channel has been allocated in the previous frame in order to
keep the variation in the interference with the adjacent cells to a
minimum.
[0147] The result of the allocation of slot so far is shown in FIG.
12. As shown in FIG. 12, the terminal B that requires high
transmission power at the Down-link in the cell 1 is allocated to
the same time channel as that of the terminals I to K at which the
Down-link transmission is performed with the lowest transmission
power in the cell 2. In addition, the terminals A and C having
somewhat higher transmission power in the cell 1 are allocated to
the same time channel as that of the terminal L at which the
Down-link transmission is performed with low transmission power in
the cell 2.
[0148] As described above, by carrying out the allocation of slot
according to the first embodiment of the present invention, a
situation in which the terminals that require high transmission
power both in the adjacent cells are allocated to the same time
channel is eased and interference between cells can be
suppressed.
[0149] Further, as to the case where a request for communication
occurs newly at the terminals D to H in the cell 1, the process of
the allocation of slot by the same procedure is explained. First,
in the same manner as before (step S21 to step S29), each terminal
having received control information from the base station notifies
the base station of the propagation loss information of the
Down-link and the information about the interference power via the
Up-link. Here, if it is assumed that the Down-link transmission
power for the terminals D to H is that shown in FIG. 10(a),
respectively, the terminals D and F are added to the group 2 to
which the terminal A and the terminal C belong. In addition, the
terminal E is added to the group 1 to which the terminal B belongs
and it follows that the terminal G belongs to the group 3 and the
terminal H belongs to the group 4, respectively (step S5 to step
S7).
[0150] Next, as shown in step S8, if it is assumed that the time
channel is allocated in the order from the group having higher
transmission power at the Down-link, it follows that the time
channel is allocated to the group 1 to which the terminal E
belongs. At this time, the terminal B belongs to the group 1 and
the time channel 4 has already been allocated. Since the number of
vacant frequency channels of the time channel 4 is greater than the
number of necessary frequency channels of the terminal E, the
number of necessary frequency channels is allocated to the terminal
E among the vacant frequency channels of the time channel 4 as a
result (step S11 to step S16).
[0151] In addition, the terminals D and F are allocated to the
vacant frequency channel of the time channel 7 to which the group 2
has been allocated before, however, the number of vacant frequency
channels in the time channel 7 is only three as shown in FIG. 12.
If the number of necessary frequency channels of the terminal D is
assumed to be three, it is possible to allocate the terminal D to
the time channel 7, however, if the number of necessary frequency
channels of the terminal F is assumed to be five, it is not
possible to allocate the terminal F to the time channel 7. In such
a case, the terminal D is allocated to the remaining frequency
channels of the time channel 7 and the terminal F is allocated to
the time channel to which another group is not allocated. In this
manner, control is so executed that the number of time channels to
be allocated to the same group increases (steps S14 and 15).
[0152] As a result, in the time channels (the time channels 1 to 3,
5, 6, and 8) to which no group is allocated, the time channel 3
having the lowest interference power notified from the terminal F
is allocated to the terminal F (group 2) and the frequency channels
corresponding to the number of necessary frequency channels (five
frequency channels) of the terminal Fare allocated.
[0153] In addition, the time channel 8 having the lowest
interference power notified from the terminal G among the remaining
time channels is allocated to the group 3 to which the terminal G
belongs and the frequency channels corresponding to the number of
necessary frequency channels of the terminal G are allocated.
Similarly, the time channel 6 is allocated to the group 4 to which
the terminal H belongs and the frequency channels corresponding to
the number of necessary frequency channels of the terminal H are
allocated.
[0154] The result of the allocation of slot described above is
shown in FIG. 13. As shown in FIG. 13, the terminals B and E that
require high transmission power for the Down-link in the cell 1 are
allocated to the same time channel as that of the terminals I to K
in which Down-link transmission is performed with low transmission
power in the cell 2. In addition, the terminals A, C, D, and F that
require slightly higher transmission power for the Down link in the
cell 1 are allocated to the same time channel as that of the
terminals L to O in which Down-link transmission is performed with
low transmission power in the cell 2.
[0155] Further, the terminal G and the terminal H that do not
require high transmission power in the cell 1 are allocated to the
same time channel as that of the terminal T and the terminal S that
require high transmission power in the cell 2. As described above,
a situation in which the terminals having high transmission power
in the adjacent cells are allocate to the same time channel can be
eased and also in a situation in which two or more adjacent cells
exist, the same allocation is carried out by repeating the
above-mentioned procedure.
[0156] As described above, by repeating the procedure of the
allocation of slot according to the first embodiment of the present
invention, it is possible to group the terminals that require
transmission power of the same level for Down-link and allocate a
different time channel for each group, taking into consideration
the interference that comes from the adjacent cells. As described
above, by allocating the slot adaptively in accordance with the
required transmission power and the interference that comes from
the adjacent cells, a situation in which terminals having high
transmission power both in the adjacent cells are allocated to the
same time channel is eased and by executing the same control for
the terminal that newly starts communication, it is made possible
to suppress the average interference power affecting the adjacent
cells from varying much, and therefore, the interference between
cells can be reduced.
[0157] By setting in advance a time channel that can be used for
each cell, or by setting in advance the transmission power of each
time channel to a different value for each cell, separately from
the procedure of the allocation of slot according to the present
invention, it is made possible to reduce the interference between
adjacent cells, however, by such a method in which the time
channels that can be used are limited in advance, when there are
many terminals that require the same transmission power level in
the cell, a situation will arise in which the allocation of time
channel is not carried out despite that there are vacant time
channels and therefore efficiency decreases.
[0158] In contrast to this, in accordance with the allocation of
slot according to the present invention, the time channels that can
be used are not limited in advance and the allocation of time
channel is carried out dynamically in accordance with the required
transmission power and the interference power that comes from the
adjacent cells, and therefore, it is possible to flexibly deal with
an increase or decrease in the number of terminals and the addition
of cells by such a control executed autonomously and dispersedly by
the base station in each cell and thereby communication of high
efficiency can be realized while reducing the interference between
cells.
[0159] Next, a modification example of the first embodiment of the
present invention is shown. First, a form in which adaptive
modulation is applied is shown. In the procedure of the allocation
of slot according to the first embodiment of the present invention,
although the modulation scheme etc. of signals when user data is
transmitted is not referred to, when multi-carrier transmission
such as OFDM etc. is used, it may also be possible to employ the
same modulation scheme in all of the sub-carriers, or a form may be
possible in which a different modulation scheme is employed for
each sub-carrier, or a form may be possible in which a modulation
scheme different in terms of time is used in accordance with the
variation of the propagation channel instead of using the same
modulation scheme at all times.
[0160] Similarly, also when the OFDM is not used in each frequency
channel (when single carrier transmission is used for each
frequency channel), a form is possible in which a modulation scheme
different in terms of time in accordance with the propagation
channel variation is used. In a procedure in which the modulation
scheme is changed in accordance with the propagation channel
variation as described above, it follows that the reception signal
power and the interference power at the slot allocated to each
terminal are measured and after the reception SINR (Signal to
Interference plus Noise power Ratio) is calculated by finding its
ratio, a modulation scheme in accordance with the reception SINR is
selected. In this manner, by combining an adaptive modulation with
the allocation of slot according to the first embodiment of the
present invention, more efficient communication can be
realized.
[0161] Next, another modification example relating to the procedure
of the allocation of time channel is shown. In the procedure of the
allocation of slot according to the first embodiment of the present
invention, the allocation of time channel is carried out in the
order from the terminal group that requires the highest
transmission power among the terminal groups having made a request
for communication, however, on the contrary, a procedure is
possible in which the allocation of time channel is carried out in
the order from the terminal group capable of communication with the
lowest transmission power among the terminals having made a request
of communication. In this case, it follows that the time channels
having high interference power are allocated among the remaining
time channels for which allocation has not been carried out yet in
the order from the terminal group having the lowest transmission
power in the Down-link.
[0162] In addition, in the first embodiment of the present
invention, the time channels with the minimum interference power
measured at the terminal of the group are allocated among the
remaining time channels for which allocation has not been carried
out yet in the order from the terminal group that requires the
highest transmission power among the terminal groups having made a
request for communication. However, when the transmission power
required by the group having made a request for communication is
not so high, the time channel with the minimum interference power
is allocated to the group as a result, and after that, even if a
request for communication is made at a terminal situated near the
cell edge and a group that requires very high transmission power is
formed, it is not possible to allocate the time channel with the
minimum interference power to a new group that requires high
transmission power.
[0163] In order to avoid such a situation, a procedure may be
possible, separately from the first embodiment of the present
invention, in which, as shown in FIG. 14, the interference level of
each time channel is associated with one of the transmission power
levels in several steps set in advance and on the supposition of a
situation in which a group that requires a transmission power level
higher (lower) than that of the group of its own is formed, the
allocation of time channel based on the association between the
transmission power level and the interference power level is
carried out. In this case also, it is made possible to dynamically
deal with the circumstances because not only the time channels with
an interference level in accordance with the transmission power
level shown in FIG. 14 are targeted for allocation, but also the
time channels not in accordance with the transmission power level
are also targeted for allocation in the case of the situation in
which the number of terminals with the same transmission power
level is large and the allocation to the targeted time channels is
not possible.
[0164] In addition, a procedure may be used, separately from the
first embodiment of the present invention, in which arbitrary time
channels among the time channels with interference power equal to
or less than a threshold value which satisfies a predetermined
reception quality determined in advance are allocated among the
remaining time channels for which allocation has not been carried
out yet in the order from the terminal group that requires the
highest (lowest) transmission power among the terminal groups
having made a request for communication.
[0165] Next, the contents of the control information in the
Down-link, the contents of the information to be reported from each
terminal to the base station via the Up-link, and another form
relating to a method of the allocation of frequency channel are
shown. In the first embodiment of the present invention, such a
form is employed, in which the control slot group in the Down link
is used for transmitting the transmission power information of the
base station when the control information is transmitted, and at
the terminal, the propagation loss and the interference power found
from the RSSI are estimated and are reported to the base station by
the Up-link.
[0166] Separately from this, a form may be possible, in which the
control slot group in the Down-link is used for transmitting the
transmission power information of the base station as in the first
embodiment of the present invention, however, each terminal reports
the measured RSSI and interference power to the base station. In
this case, after the propagation loss in the propagation channel is
calculated at the base station from the difference between the
transmission power at the base station and the reported RSSI at the
terminal, the transmission power required for the Down-link
transmission to each terminal is calculated from the propagation
loss as in the first embodiment of the present invention and
grouping based on the transmission power of each terminal is
performed. By using this form, it is possible to eliminate the
procedure to find the propagation loss and the operation part at
the terminal.
[0167] In addition, separately from this, a form may be possible,
in which the same information as that in the first embodiment of
the present invention is transmitted in the control slot group in
the Down link, however, after measuring the RSSI and calculating
the propagation loss, each terminal finds the transmission power
control information and reports to the base station the
transmission power control information and interference power.
Here, the transmission power control information indicates the
transmission power obtained by subtracting the transmission power
when the control slot group is transmitted from the transmission
power required for performing the Down-link transmission found from
the propagation loss of each terminal and indicates how much the
power should be raised or reduced from the transmission power of
the control slot group.
[0168] In addition, a form may be possible, in which the same
information as that in the first embodiment of the present
invention is transmitted in the control slot group of the
Down-link, however, each terminal measures and averages the
reception signal power of each frequency channel instead of the
RSSI indicative of the reception power of the whole of the
frequency channels and reports to the base station this together
with the interference power. In this case, after the propagation
loss in the propagation channel is calculated at the base station
from the difference between the transmission power at the base
station and the reception power at each frequency channel, the
transmission power required for the Down-link transmission to each
terminal is calculated from the propagation loss, as in the first
embodiment of the present invention, and grouping based on the
transmission power of each terminal is performed.
[0169] Further, a form may be possible, in which the transmission
power information at the base station is transmitted in the control
slot group in the Down-link, as in the first embodiment of the
present invention, however, each terminal measures the reception
signal power of each frequency channel instead of the RSSI and
reports to the base station this together with the interference
power. In this case, the reception signal power of each frequency
channel is averaged at each base station and after the propagation
loss in the propagation channel is calculated at the base station
from the difference between the transmission power of the control
information transmitted from the base station and the average of
the reception power found before, the transmission power required
for the Down-link transmission to each terminal is calculated from
the propagation loss, as in the first embodiment of the present
invention, and grouping based on the transmission power of each
terminal is performed.
[0170] Alternatively, a form may also be possible, in which the
frequency channel to be allocated to the terminal is determined
first at the base station, and after the propagation loss (the
propagation loss that has taken into consideration the fading of
the channel to be allocated) is calculated from the difference
between the transmission power of the control information
transmitted from the base station and the reception power of the
frequency channel to be allocated to the terminal, the transmission
power required for the Down-link transmission to the terminal is
calculated based on the propagation loss and grouping is performed
based on the result.
[0171] As described above, in the form in which the reception
signal power of each frequency channel measured at the terminal is
reported to the base station via the Up-link, the amount of
information in the Up-link increases and the efficiency of the
Up-link decreases more or less. However, the base station grasps
the reception signal power for each frequency channel at each
terminal, and thereby, it is made possible to carry out the
allocation of frequency channel capable of obtaining the most
excellent reception power for each terminal among the frequency
channels that produce a difference in the reception power due to
the influence of fading when the frequency channel is allocated to
the terminal of each group after the allocation of time channel to
the group, and the efficiency in the Down-link increases.
[0172] In addition, by performing grouping that has taken fading
into consideration, it is possible to limit the transmission power
for each group to a certain range also when the transmission power
is so controlled that the reception power of all of the terminals
is constant, and it is made possible to reduce the amount of
variation in interference affecting the adjacent cells even in a
situation in which the allocation to the terminal is changed.
[0173] Further, unlike the first embodiment of the present
invention, a form may be possible, in which information indicative
of the transmission power of the control information is not
included in the control slot group of the Down-link. In this case,
it follows that the RSSI of the received control information or the
reception signal power of each frequency channel is measured at the
terminal and this is reported to the base station together with the
interference power via the Up-link. At this time, the reception
signal power of each frequency channel is may be averaged or a form
may also be possible in which it is not averaged and the
information corresponding to the number of frequency channels is
reported. By employing such a form, it is possible to eliminate the
control information in the Down-link.
[0174] When any one of the forms described above is used, the
period of report of the measurement result of the reception signal
power and the interference power at the terminal to the base
station by the Up-link may be for each frame or may be at
arbitrarily fixed intervals.
[0175] In addition, as described above, the transmission timing of
the control slot group in the Down-link may be common to all of the
cells or may be different from cell to cell (FIG. 4). Here, if the
transmission timing of the control slot group in the Down-link is
made common to all of the cells as shown in the first embodiment of
the present invention, the Down-link control slot group is
transmitted with the transmission power that can be received even
by a terminal situated at the cell edge, and therefore, there may
the case where the control information of the adjacent cells
interferes with each other at the terminal situated near the cell
edge. When such a problem arises, by making the transmission timing
of the control slot group in the Down-link differ from cell to
cell, the situation can be avoided, in which the control
information transmitted with the transmission power (the maximum
transmission power that can be transmitted) that reaches the cell
edge interferes with each other.
[0176] Further, when the allocation of slot according to the
present invention is carried out, in the time channel to which the
control information is allocated in the Down-link in the adjacent
cell, high interference power is measured, and therefore, it
follows that the terminal group with low transmission power of the
Down-link within the cell of its own is allocated dynamically to
the same time channel. Due to this, it is also made possible to
avoid the situation in which the control information and the user
data interfere with each other between cells.
[0177] As described above, by making the transmission timing of the
control slot group in the Down-link differ from cell to cell, it is
possible to avoid the situation in which the control information
transmitted with the transmission power that reaches the cell edge
interferes with each other and by allocating the terminal with low
transmission power to the time channel to which the control
information is transmitted in the adjacent cell, it is also
possible to avoid the interference between the control information
and the user data, however, there may be the case where trouble
occurs at the base station in the adjacent cell for some cause and
a signal having very high transmission power is transmitted in the
adjacent cell in the time channel for transmitting the control
information in the Down-link. In such a case, because the control
information is affected by the interference having high
transmission power, many terminals in the cell are disabled from
communication. As shown in FIG. 15, as a countermeasure to such a
problem, a form (FIG. 15(b)) may be employed, in which flexibility
is given so that the transmission timing is changed adaptively in
accordance with the interference of the adjacent cell, instead of a
form (FIG. 15(a)) in which the control slot group in the Down-link
is transmitted with a predetermined timing at all times.
[0178] This is a control in which that the interference power is
measured at the same time as the reception of the control
information in the Down-link (it may also be possible to measure
the SINR or detect a control information error) and when
interference having transmission power exceeding a certain
threshold value is observed (also when the control information is
erroneous successively etc.), the control slot group is moved to
the time channel with the lowest interference power among the
vacant time channels. When there is no vacant time channel, the
communication with the terminal allocated to the time channel with
the lowest interference power is disconnected (aborted) and the
control slot group is moved to the vacant time channel.
[0179] By employing such a form, the communication of some
terminals is disconnected forcedly, however, in the situation in
which the control information cannot be received correctly due to
the influence of interference, the communication of many terminals
in the cell is disconnected, and therefore, by employing the
above-described form, it is possible to maintain the communication
performed by many terminals in the cell. At this time, a form may
be possible in which notice to the effect that the control slot
group is moved is notified to the terminal in the frame immediately
before the control slot group is moved, or a form may be possible
in which such control is not executed but the terminal side is
caused to have a mechanism to detect the control slot group over
the entire the next frame when the control slot group cannot be
received at the terminal any longer.
[0180] Next, another form relating to the update timing of the
allocation of slot in accordance with the change in the surrounding
environment is shown. In the first embodiment of the first
invention, after the allocation of slot, each terminal performs
communication by occupying the allocated slot for an arbitrarily
fixed period of time and when the allocation to a certain time
channel is changed to a terminal group different from the previous
frame, a terminal group that requires the transmission power close
to that of the terminal group to which the time channel has been
allocated in the previous frame is allocated if possible.
[0181] In other words, after the terminal group is once allocated
to a certain time channel, the allocation is not changed if
possible, or even when changed, the allocation is carried out to
the terminal group that requires nearly the same transmission
power. This is because a situation can be thought in which when the
terminal group to be allocated to the time channel is changed
frequently, the interference observed in the adjacent cell changes
frequently and therefore interference between adjacent cells occurs
and the receive performance are deteriorated.
[0182] In addition, this is because also when the allocation is
changed to a terminal group that requires transmission power (in
particular, transmission power extremely higher compared to the
previous frame) largely different from the transmission power
required to the terminal group having been allocated in the
previous frame, the performance are deteriorated due to the drastic
change in the interference observed in the adjacent cell. However,
it can be thought that excellent performance can be obtained by
employing a form in which the allocation of slot is updated in the
following case.
[0183] In general, since the terminal moves also during
communication, the distance from the base station changes because
of the movement and there may be the case where transmission power
different from that of the group to which the terminal has belonged
up to now is required. As described above, a form may be possible,
in which the allocation of slot is updated when the transmission
power required for the Down-link has changed accompanying the
movement of the terminal, that is, the group configuration has
changed from the previous one. In addition, a form may also be
possible, in which the slot allocation is updated when a situation
has been encountered etc., in which interference having high
transmission power is observed at the terminal (or when the
reception SINR is deteriorated, or when data is erroneous
successively) during the communication in the allocated slot.
[0184] In these cases, a review of the allocation of slot may be
done for all of the terminals in all of the groups or a form may be
possible, in which a review of the allocation of slot only to the
terminal encountered with a situation in which the transmission
power required for the Down-link changes etc. is done. However,
also when such a review of the allocation of slot is done, it is
desirable to allocate the terminal group or the terminal that
requires transmission power as close as possible to that of the
terminal group allocated in the previous frame to the relevant time
channel (slot) in order to suppress a drastic change in the
interference affecting the adjacent cells.
[0185] In addition, in a situation in which the number of cells,
such as an isolated cell, is small, it may also be possible to
perform the update of the allocation of slot frequently or to
allocate a terminal group with transmission power largely different
from that of the terminal group having been allocated in the
previous frame to the relevant time channel.
[0186] Next, another form relating to the case where a plurality of
time channels are allocated to one group to which a plurality of
terminals that require the same transmission power in the Down-link
belong is shown. In the first embodiment of the present invention,
the number of necessary frequency channels per frame for the
Down-link transmission is calculated for each terminal in the group
to which the time channel has been allocated and the vacant
frequency channels are allocated to the terminals in accordance
with the number of necessary frequency channels required of each
terminal. Then, when the number of vacant frequency channels of the
time channel is less than the number of necessary frequency
channels, allocation is carried out to another time channel and
allocation is carried out so that a plurality of terminals that
require the same transmission power are accommodated in one time
channel if possible.
[0187] Separately from such a form, another form may be possible,
in which the maximum number of time channels that can be allocated
to the terminal group that requires transmission power of certain
level in the Down-link is determined in advance and thereby it is
possible for the base station to carry out allocation freely in a
range that does not exceed the maximum number of time channels. At
this time, instead of determining in advance the maximum number of
time channels that can be allocated to the terminal group that
requires transmission power of certain level, it may also be
possible to cause the base station to have a mechanism for
adjusting the maximum number of time channels in accordance with
the number of adjacent cells by measuring the interference that
comes from the adjacent cells and estimating the number of adjacent
cells.
[0188] In addition, a form may also be possible, in which when a
plurality of time channels are allocated to one group, the terminal
belonging to the group may use any time channel among the plurality
of the allocated time channels and the change of the allocation to
a vacant frequency channel of a different time channel is allowed
during communication. An example of such a case is shown in FIG.
16. As shown in FIG. 16, the terminals A, C, and D are allocated to
the time channel 7 and the terminal F is allocated to the time
channel 3, however, these terminals belong to the same group and
therefore it may be allowed to reallocate the terminal D to the
time channel 3 to which the terminal F is allocated. This is
because the transmission power required for the Down-link to the
terminal D and the terminal F is the same level and even if the
time channel to which the terminal D is allocated is changed, the
influence imposed on the adjacent cells does not change.
[0189] Similarly, a form may also be possible, in which it is
allowed that one terminal is allocated to another time channel to
which another terminal belonging to the same group is allocated, in
addition to the time channel to which it has been allocated up to
now (that is, a plurality of time channels are allocated to one
terminal).
[0190] In addition, a form may also be possible, in which when
there is a vacant frequency channel in the time channel to which
the terminal group that require high transmission power is
allocated, it is allowed that the terminal that requires low
transmission power is allocated to the vacant frequency channel of
the time channel to which the terminal group that requires high
transmission power is allocated (FIG. 7).
[0191] This is because the possibility is high that the terminal
group that requires low transmission power is allocated to the time
channel to which the terminal group that requires high transmission
power is allocated in the adjacent cell, and even if a terminal
that requires low transmission power is allocated to the vacant
frequency channel of the time channel, no interference between
adjacent cells will occur.
[0192] On the contrary, however, in a situation in which there
exist vacant frequency channels in the time channel to which a
terminal group that requires low transmission power is allocated
and the number of frequency channels to be allocated to a terminal
that requires high transmission power is short, if a terminal that
requires high transmission power is allocated to the frequency
channel of the time channel to which a terminal group that requires
low transmission power is allocated, it follows that a large
interference occurs between adjacent cells. Because of this, a form
may also be possible, in which instead of allocating a terminal
that requires high transmission power to the vacant frequency
channel in the time channel to which a terminal group that requires
low transmission power is allocated as it is, after the modulation
scheme of the terminal that requires high transmission power is
changed to a lower one and at the same time, the transmission power
is also set to a lower value, the allocation to the vacant
frequency channel of the time channel to which the terminal group
that requires low transmission power is allocated is allowed. By
employing such a form, even when the allocation to the time channel
to which a different terminal group is allocated is carried out, it
is possible to suppress interference from affecting the adjacent
cells by setting transmission power to a lower value while avoiding
the occurrence of an error caused by the setting of the
transmission power to the terminal to a lower value.
[0193] Next, another form is shown, in which a vacant time channel
is reserved for a terminal that requires high transmission power.
As described above, in the first embodiment of the present
invention, the time channel of which the interference power
measured at the terminal of the group is the smallest is allocated
among the remaining time channels not allocated in the order from
the terminal group that requires the highest transmission power in
the terminal groups having made a request for communication.
However, when the transmission power required by a group having
made a request for communication is not so high, the time channel
the interference power of which is the smallest is allocated to the
group and after that, even if a request for communication is made
at a terminal situated near the cell edge and a group that requires
very high transmission power is formed, it is not possible to
allocate the time channel the interference power of which is the
smallest to a new group that requires high transmission power.
[0194] As a measure for this problem, a form may also be possible,
in which at least one vacant time channel is reserved for a
terminal group that requires high transmission power. On the
contrary, a form may also be possible, in which at least one vacant
time channel is reserved for a terminal group that requires low
transmission power. Further, a form may also be possible, in which
the number of time channels in which interference equal to or
greater than a certain value is observed (interfered time channels)
is counted and the resultant number of time channels, which is
obtained by subtracting the number of interfered time channels from
the total number of time channels, is reserved for a terminal group
that requires high transmission power.
[0195] As described above, even in a situation in which a terminal
that requires high (low) transmission power is not in
communication, it is made possible to deal with the case where a
terminal makes a request for communication in the future by
reserving a vacant time channel for a terminal group that requires
high (low) transmission power. However, just reserving a vacant
time channel is not an effective measure because there is the
possibility that a terminal group that requires high transmission
power in the adjacent cell is allocated to the reserved time
channel (this hardly leads to a problem when the terminal group
requires low transmission power).
[0196] Consequently, a form may also be possible, in which a time
channel for a terminal group that requires high transmission power
is reserved by transmitting dummy data with the same transmission
power as that when the control information is transmitted in the
time channel the interference power of which has been determined to
be the minimum by another terminal even when there exists no
terminal group that requires high transmission power. In addition,
it may also be possible to determine in advance a time channel to
be reserved to which dummy data is thus transmitted so as to differ
from cell to cell.
[0197] In a situation in which there exists a terminal that
requires high transmission power and a time channel is allocated,
however, the number of allocated frequency channels is small and
most of the frequency channels of the time channel in question are
vacant, a form may also be possible, in which dummy data is
transmitted in a vacant frequency channel of the time channel in
question. Such a form has the advantage that it is made easier to
detect a time channel with high interference power at each terminal
in the adjacent cells.
[0198] Further, as an optional form in which dummy data is
transmitted in order to reserve a time channel for a terminal group
that requires high transmission power, it may also be possible to
implement a function of terminating transmission of dummy data in
order to reduce interference affecting the adjacent cells in a
situation in which there is not at all any terminal in the
cell.
[0199] In addition, in a mobile communication system, transmission
and reception of control information (base station ID and terminal
ID) is performed generally between a base station and a terminal
even for a terminal that has not made a request for communication
and the base station has a grasp as to which terminal exists in the
cell of its own and the terminal has a grasp as to which cell the
terminal belongs to. At the base station in a system in which such
transmission and reception of control information is performed
between a base station and a terminal, it is possible to estimate
how much transmission power is required for the Down-link when the
data communication with the terminal is started. Consequently, as
an optional form in which dummy data is transmitted for the purpose
of reserving a time channel, it may also be possible to implement a
function of transmitting dummy data when there exists a terminal in
the cell, which is estimated to require high transmission power
when data communication is started, and of terminating transmission
of dummy data when there exists no terminal in the cell, which is
estimated to require high transmission power when data
communication is started.
[0200] As described above, it is possible to reserve a time channel
for a terminal that requires high transmission power in the cell of
its own while taking into consideration the prevention of
interference affecting the adjacent cells by estimating
transmission power required for the Down-link at the base station
and performing transmission of dummy data based on the estimation
result.
Second Embodiment
[0201] A second embodiment is explained below. FIG. 18 is a block
diagram showing the general configuration of a terminal device
(mobile station apparatus). Reference number 181 denotes a
reception antenna part, 182 denotes a radio reception part, 183
denotes an analog/digital conversion part (A/D conversion part),
184 denotes a synchronization part for synchronization of the OFDM
symbols, 185 denotes a guard interval (GI) removal part, 186
denotes a serial/parallel (S/P) conversion part, 187 denotes an FFT
part, 188 denotes a propagation channel estimation and demapping
part, 189-a to 189-l denotes parallel/serial conversion parts (P/S
conversion parts), 190-a to 190-l denote error correction decoding
parts, 191 denotes a demultiplex part, 192 denotes an SINR
measurement part, 193 denotes an RSS measurement part, 194 denotes
a control part, and 195 denotes an Up-link transmission part.
[0202] The frequency of the radio wave received by the antenna part
181 is converted into a frequency band in which A/D conversion is
possible in the radio reception part 182. The data converted into a
digital signal in the A/D conversion part 183 is synchronized with
the OFDM symbols in the synchronization part 184 and the guard
interval is removed in the guard interval removal part 185. After
that, the data is paralleled into 1,024 data in the S/P conversion
part 186. After that, in the FFT part 187, the FFT of 1,024 points
is performed and the demodulation of the sub-carrier of the 768
waves is performed in the propagation channel estimation and
demapping part 188. The necessary data is serialized in the P/S
conversion parts 189-a to 189-l, error correction is performed in
the error correction decoding parts 190-a to 190-l, and it is
divided into the data of each channel in the demultiplex part
191.
[0203] The SINR measurement part 192 is a block that measures the
SINR for each sub-channel, which will be described below, using the
output of the FFT part 187, the output of the propagation channel
estimation and demapping part 188, and the output of the error
correction decoding parts 190-a to 190-l. The RSS measurement part
193 is a block that measures the RSSI for each sub-channel from the
output of the radio reception part 182 and the output of the FFT
part 187. The control part 194 takes out necessary information from
the reception data output from the RSS measurement part 193, the
SINR measurement part 192, and the demultiplex part 191 and sends
the Up-link data to the Up-link transmission part 195 in accordance
with the procedure explained below. The Up-link transmission part
195 transmits the Up-link data sent from the control part 194 to
the base station.
[0204] FIG. 19 is a block diagram showing the general configuration
of the base station (base station apparatus). Reference number 260
denotes a scheduling part, 261 denotes a multiplex part, 262-a to
262-l denote error correction encoding parts, 263-a to 263-l denote
serial/parallel conversion parts (S/P conversion parts), 264
denotes a mapping part, 265 denotes a transmission power control
part, 266 denotes an IFFT part, 267 denotes a parallel/serial (P/S)
conversion part, 268 denotes a guard interval insertion part, 269
denotes a digital/analog conversion part (D/A conversion part), 270
denotes a radio reception part, 271 denotes an antenna, and 272
denotes an Up-link reception part.
[0205] Which sub-carrier and which time slot are used to transmit
the information data is determined in the scheduling part 260 and
the data is converted into a data stream in accordance with the
result thereof. The converted data is subjected to error correction
encoding in the error correction encoding parts 262-a to 262-l. For
example, when the number of sub-carriers is 768 waves and the
modulation scheme of each carrier is the QPSK, the data is
converted into the data in 768 lines in units of two bits. After
that, the data corresponding to the amount required for the
modulation of each carrier is converted in the S/P conversion parts
263-a to 263-l and each carrier is subjected to modulation in the
mapping part 264.
[0206] After that, by the direction from the scheduling part 260,
the amplitude of each carrier is adjusted in the transmission power
control part 265. After that, the IFFT is performed in the IFFT
part 266. In the following explanation, the number of points of the
IFFT is assumed to be 1,024 in order to generate the OFDM signal of
768 waves. Then, after the data is converted into serial data in
the P/S conversion part 267, a guard interval is inserted in the
guard interval insertion part 268. The guard interval is inserted
in order to reduce interference between symbols when the OFDM
signal is received.
[0207] Then, after converted into the analog signal in the D/A
conversion part 269, the data is converted into a frequency to be
transmitted in the radio reception part 270 and then, the data is
transmitted from the antenna part 271. By means of the transmission
power control information and the interference information received
by the Up-link reception part 272, the scheduling part 260 executes
the control properly. The method of the control is explained below
in detail.
[0208] The radio wave form used in the second embodiment is the
OFDM. It is assumed that the number of sub-carriers used in the
Down-link is 768 and 64 of sub-carriers are integrated into a
sub-channel. Consequently, it follows that the Down-link consists
of 12 sub-channels. This is shown in FIG. 20. In the second
embodiment, it is supposed that the number of sub-channels that can
be used is greater than the total number of adjacent cells.
[0209] The MAC has a fixed length frame configuration. In the
frame, nine slots are accommodated. This is shown in FIG. 21. Among
these slots, the front slot of the frame in each sub-channel is a
control slot, in which information about the control slot itself
and the following slots is stored. The control slots of all of the
sub-channels are together referred to as a control slot group.
[0210] To the front of each slot, a preamble is added and it is
possible for the reception terminal to perform demodulation of the
following data blocks by receiving the preamble and adjusting the
demodulation timing. The structure of the slot is shown in FIG.
22(a). The Up-link is not referred to in particular in the second
embodiment. Various techniques can be utilized. Irrespective
whether single carrier or multi carrier, and whether or not a frame
configuration is employed, various techniques can be utilized.
[0211] The topology of the network is a star type with the base
station as its center. The communication data of all of the
Down-links are transmitted directly from the base station to the
terminal. The outline of the topology is shown in FIG. 22(b).
[0212] It is assumed that the cells are arranged in a hexagonal
form. The base station is situated in the center and the base
stations are arranged equidistantly. It is assumed that the total
number of adjacent cells is six at the maximum. The outline of the
cell arrangement is shown in FIG. 23(a). The base station always
transmits the control slot to all of the sub-channels.
[0213] The following information is stored in the control slot.
That is, the network ID, the transmission power information of the
control slot of the sub-channel, and the terminal ID allocated to
each of the following slots. An example of the structure of the
control slot is shown in FIG. 23(b).
[0214] It is assumed that the control slot is sent by a modulation
scheme with higher reliability than that by which the data slot is
sent. This is because information of highly great importance is
transmitted by the control slot although the amount of information
is small. Although the modulation scheme is not specified in
particular, in the second embodiment, it is assumed that the BPSK
is used for the control slot and the QPSK is used for the data
slot.
[0215] The mobile terminal (mobile station apparatus) demodulates
the control slot transmitted by the base station and makes a
request for connection by sending the terminal ID of its own to the
base station of the obtained network ID using the Up-link. When
allowing the connection, the base station having received the
request for connection transmits the terminal ID in the slot
allocation information in the control slot and orders the terminal
to use the slot in the Down-link.
[0216] The base station executes transmission power control in
order to keep the transmission power of the radio wave to be
transmitted to the mobile terminal to a minimum. Because of this,
the mobile terminal receives and demodulates the control slot group
of all of the sub-channels once in at least n (n: natural number)
frames and calculates the propagation loss of the sub-channel from
the information of the transmission power of each channel shown in
each control slot. At the same time, the mobile terminal calculates
the SINR of each sub-channel. The mobile terminal transmits the
calculated propagation loss and the SINR of each sub-channel to the
base station via the Up-link.
[0217] The base station obtains the propagation loss and the SINR
from all of the connected mobile terminals via the Up-link. After
that, the base station calculates transmission power required for
the transmission of the Down-link to each terminal from the
propagation loss of each terminal and classifies the terminals
connected to the base station into four levels (just an example,
not limited to four levels). One group is defined as a group in
which data is transmitted from the base station with transmission
power with which demodulation is possible even at the cell boundary
and two groups are defined as a group in which data is transmitted
from the base station with transmission power that sufficiently
attenuates at the cell boundary and that does not affects the
adjacent cells.
[0218] The other group is defined as a group in which data is
transmitted from the base station with transmission power with
which demodulation may not be possible at the cell boundary,
however, which may affect the adjacent cells. It is not required
for each group to include a terminal as a result of classification.
The relationship between the cell boundary and the transmission
power groups is shown in FIG. 24. In FIG. 24, the area in which
demodulation is possible even at the cell boundary is denoted by
2061 and the area that does not affect the adjacent cells is
denoted by 2062.
[0219] The outline of the operation procedure of the terminal is
shown along with a flow chart. The flow chart is shown in FIG. 25.
First, in step S2101, the terminal receives the signals of the
Down-link and searches for a base station that transmits the
control slot group. After a base station that transmits the control
slot group is found, the terminal demodulates the control slot
group in step S2102 and analyzes the contents of the control slot
group. In this step, the terminal acquires the base station ID of
the base station. Next, in step S2103, the terminal transmits the
acquired base station ID to the base station via an Up-link means
and makes a request for connection.
[0220] After step D2103, in step S2104, the terminal receives the
control slot group several times and determines whether or not the
connection is successful depending whether or not the ID of the
terminal of its own is transmitted in the control slot. If the
connection has failed, the procedure returns to step S2101 for
searching for a base station and when it has succeeded, the
procedure proceeds to step S2105 for measurement of the propagation
loss and the SINR. In step S2105 for measurement of the propagation
loss and the SINR, the terminal receives the Down-link signals from
the base station and measures the propagation loss from the base
station to the terminal for each sub-channel and the SINR (Signal
to Interference and Noise power of Ratio) at the position of the
terminal. Various measurement methods can be thought. Although the
detailed description is omitted because they do not related to the
contents of the second embodiment, the methods includes a method in
which the propagation loss is found from the RSSI (Receive Signal
Strength Indicator) of the control slot and the transmission power
in the control slot and the SINR is found from the difference
between the received waveform of the control slot and the ideal
waveform estimated from the demodulated data by demodulating the
control slot etc.
[0221] In the next step S2106, which is step for transmitting the
propagation loss and the SINR, the propagation loss and the SINR
found in the previous step S2105 are transmitted to the base
station via the Up-link means.
[0222] In the reception process in the next step S2107, the
Down-link data for the terminal of its own is received in
accordance with the contents of the received control slot. In the
next step S2108, the terminal determines whether or not the
reception of signals from base station is possible depending on
whether the next control slot can be received and when reception is
possible, the procedure returns to step S2105, which is step for
analyzing the propagation loss and the RSSI and when reception is
not possible, the procedure returns to step S2101, which is step
for searching for a base station. By repeating these steps, the
communication of the Down-link can be maintained.
[0223] Next, the outline of the operation procedure of the base
station is shown along with a flow chart. First, in step S2001, the
base station performs a process to allocate a sub-channel that can
be used to each transmission power group. Next, in step S2002, the
base station checks whether or not there exists a terminal that has
newly made a request for connection and performs the connection
process in step S2003 when there exists any. Irrespective of the
execution in step S2003, the base station performs the transmission
power control in step S2004. Then, the base station performs the
determination of a transmission sub-channel in step S2005 and the
procedure returns to step S2001 when the result is NG and the base
station allocates a sub-channel that can be used. When the result
is OK, the procedure proceeds to step S2007 for the allocation of
transmission data slot.
[0224] After the step for the allocation of transmission data slot,
the base station performs Down-link transmission in accordance with
the allocation in step S2008 and the procedure returns to step
S2002 in which whether or not there exists a terminal that has
newly made a request for connection is checked.
[0225] At the time of the transmission of the Down-link, the
transmission power for each sub-channel is controlled in accordance
with the transmission power of the transmission power group
allocated to the sub-channel. The control slot is also transmitted
in accordance with this control by displaying the transmission
power in the transmission power information in the control slot.
However, although explanation will be given later, there may be the
case where the data of a terminal of another transmission power
group is allocated to the data slot part. In this case, only the
slot shall be transmitted with the transmission power defined by
the transmission power group.
[0226] Next, the detail part of the operation procedure of the base
station is explained along with a flow chart. The contents of the
process of the step for the allocation of sub-channel that can be
used are explained. The flow chart is shown in FIG. 27. First, in
step S2201, the most recent propagation losses sent from all of the
terminals via the Up-link means are totalized. In the next step
S2202, the transmission power for each terminal is classified into
four levels according to the totalized propagation loss and all of
the terminals are classified into groups of transmission power. In
the next step S2203, the most recent SINR for each sub-channel sent
from all of the terminals via the Up-link means is totalized. In
the next step S2204, the minimum value of the SINR is found for
each sub-channel. In the next and subsequent steps, the allocation
of sub-channel that can be used is carried out actually for each
transmission power group.
[0227] In the second embodiment, it is assumed that one, four,
four, and three sub-channels are allocated to each group in the
descending order of the transmission power. Only one sub-channel is
allocated to the group with the strongest transmission power, and
this is because the value of the number of the total number of
sub-channels/(total number of adjacent cells+1) is prevented from
being exceeded.
[0228] In step S2205, first, the group with the largest
transmission power is focused on and allocation is carried out for
the group focused on in step S2206. The predetermined number of
sub-channels is allocated in the order from the sub-channels with
the largest minimum SINR among the sub-channels, that is, in the
order from the sub-channels with the smallest interference. In step
S2207, whether or not there remains a group to which a sub-channel
that can be used has not been allocated yet is checked and if there
remains any, a group with the second strongest transmission power
is focused on in step S2208 and step S2206, which is step for the
allocation of sub-channel, is repeated and when there remains no
group to which the sub-channel that can be used has not been
allocated yet, the allocation of sub-channel that can be used is
terminated.
[0229] Next, the detailed procedure of the step of connection
process is explained. A flow chart is shown in FIG. 28. First, in
step S2301, the terminal ID sent by a terminal via the Up-link
means is registered as one that can be used at the base station. At
this time, only once, the slot for the terminal is allocated for
the sub-channel allocated to the group with the maximum
transmission power. Due to this, the terminal knows that the
request for connection has been accepted. In addition, during the
allocation of the slot, the slot may be embedded with dummy data.
In the next step S2303, the base station waits until the terminal
sends the propagation loss and the procedure proceeds to the next
step. In the next step S2304, to which transmission power group
this terminal should belong is calculated from the sent propagation
loss. In the next step S2305, this terminal is added to the group,
as a result of the calculation, and the step of connection process
is terminated.
[0230] Next, the detailed procedure of the transmission power
control step is explained. A flow chart is shown in FIG. 29. First,
in step S2401, the most recent propagation losses sent from all of
the terminals are totalized. In the next step S2402, the
transmission power to each terminal is set to a four-level
transmission power based on the propagation loss obtained in the
previous step and in the next step S2403, grouping is performed
according to the set transmission power. Then, the transmission
power control step is terminated.
[0231] Next, the detailed procedure of the determination of the
allocation of sub-channel is explained. A flow chart is shown in
FIG. 30. First, in step S2501, the most recent SINR for each
sub-channel sent from all of the terminals is totalized. In the
next step S2502, whether or not the SINR of the sub-channel
allocated to the terminal satisfies a predetermined value is
checked for each terminal. Determination is made in step S2503 and
when the SINR satisfies the predetermined value at all of the
terminals, OK is issued as the result of determination in step
S2504 and when any one of the SINRs does not satisfy the
predetermined value, NG is issued as the result of determination in
step S2505, and then the step of the determination of the
allocation of sub-channel is terminated.
[0232] Next, the detailed procedure of the allocation of
transmission data slot is explained. A flow chart is shown in FIG.
31 and FIG. 32. First, in step S2601, the group with the largest
transmission power is focused on. In the next step S2602, the total
amount of data to be transmitted to the terminals included in the
focused-on group is checked and how many slots are required for the
data is calculated. In step S2603, when there is not data to be
transmitted and the number of necessary slots is zero, the
procedure proceeds to the determination as to whether or not there
is an unevaluated transmission power group in step S2613 and when
the number of necessary slots is one or more, the procedure
proceeds to the calculation of the number of unused slots in step
S2604. In step S2604 of the calculation of the number of unused
slots, the total number of vacant slots of the focused-on group and
the group to which transmission power larger than that of the
focused-on group is allocated is calculated.
[0233] In the next step S2605, the number of slots required for
transmission is compared with the calculated number of vacant slots
and whether or not the number of vacant slots is sufficient is
determined. When sufficient, all of the data for which a request
for transmission has been made as transmission data is regarded as
transmission data in step S2606, and when the number of vacant
slots is not sufficient, data corresponding to the number of vacant
slots is cut out from the data for which a request for transmission
has been made and regarded as transmission data in step S2607. At
this time, in order to prevent only the data bound for a specific
terminal from being cut out, the data is cut out by the round robin
method for all of the terminals in the group. Due to this, the
throughput of a specific terminal is prevented from reducing.
[0234] In the next step S2608, the prepared transmission data is
divided for each terminal. In the next step S2609, the priority of
the terminals is determined. The initial value of the process
method of the priority shall be the order of the terminal ID and
the terminal processed once with the highest priority will be
processed with the lowest priority next time, that is, the round
robin method shall be used.
[0235] By performing this process, it is avoided that only a
specific terminal is processed. In the next step S2610, data is
allocated to the vacant slots of the sub-channel allocated to the
focused-on group in the order of the priority set to the terminals.
At this time, when there are two or more sub-channels that can be
used, allocation is carried out in the order from the sub-channel
with the lowest SINR. When there remains transmission data that is
not allocated after the data is allocated to all of the vacant
slots of the sub-channel allocated in step S2611, the data is
allocated also to the vacant slots of the sub-channel allocated to
a group with transmission power larger than that of the focused-on
group until all of the transmission data is allocated in step
S2612.
[0236] In the next step S2613, whether or not there remains a group
with transmission power smaller than that of the transmission power
group currently focused on is checked, that is, whether or not
there remains an unprocessed group is checked, and when there
remains any, a group with transmission power second in magnitude to
that of the group currently focused on is focused on in step S2614
and then the procedure returns to step S2602 in which the number of
slots for the data to be transmitted to the terminals in the group
is calculated, and when there remains none, the step of the
allocation of transmission data slot is terminated.
[0237] Next, how interference between cells is avoided when there
exist the base station and the terminal group that operate as
described above is explained. First, a situation is supposed, in
which the allocation of the same sub-channel that can be used is
carried out by coincidence in adjacent cells. This situation is
shown in FIG. 33. Although this is a special situation, it can
occur depending on the position of the terminals in the cells, such
as when the terminals in one of the cells are arranged only in the
vicinity of the base station etc. Here, a case is considered, where
one of the terminals in the vicinity of the base station moves near
to the cell boundary. This case is shown in FIG. 34. Here, a
terminal b moves near to the position at which both the cells
neighbor each other. Since the adjacent cell also arranges the same
sub-channel, the SINR of a sub-channel (1) to be allocated newly to
the terminal that has moved will deteriorate. The terminal having
moved demodulates the control slot and reports the SINR and the
propagation loss of all of the sub-channels at the position to
which it has moved to the base station via the Up-link.
[0238] The base station learns that the classification of the
transmission power groups is correct no longer by the fact that the
propagation loss sent by the terminal that has moved becomes large.
The base station newly reconfigures the transmission power groups
and determines, by referring to the SINR sent from the terminals to
be added newly to the respective transmission power groups, whether
or not the sub-channel that can be used allocated to the
transmission power group to which the terminal is newly added can
be used without problem.
[0239] In this example, since the allocated sub-channel (1) is
affected by the adjacent cell, the SINR is below that which can be
used and it is determined that the sub-channel cannot be used. In
response to this, in the cell A, the reallocation of sub-channel
that can be use is carried out. At this time, evaluation is made in
the order from the group with the largest transmission power. Since
the allocation is carried out based on the SINR evaluated by the
terminal b belonging to the group, the sub-channel is selected from
among (10, 11, 12) with excellent SINR. Here, (12) is selected.
After that, sub-channels with excellent SINR are selected in the
descending order of the transmission power of the group and as a
result, a sub-channel with poor SINR is allocated to the group with
the smallest transmission power. The situation after the allocation
is shown in FIG. 35.
[0240] Here, the distance of the terminal in the group with small
transmission power from the other cell is sufficiently large and in
actuality, communication is possible without problem although the
evaluation of the SINR is poor more or less. In addition, the
transmission power is also small and therefore the signals of the
sub-channel used in this group hardly affects the other cell. As a
result, wireless interference does not occur between the two cells
and therefore the communication between the base station and the
terminals is enabled.
[0241] The operation is the same also when there are a plurality of
cells. Since up to one (total number of sub-channels that can be
used/(number of adjacent cells+1)) sub-channel that can be used is
allocated to the group with transmission power that can reach the
adjacent cell, even if most of sub-channels are affected by all of
the adjacent cells, it is unlikely that the system fails because it
is no longer possible to allocate transmission power that can reach
the adjacent cell in the cell.
[0242] Similarly, the adjacent cell is in a state in which it is
possible to prepare one or more sub-channels ((total number of
sub-channels-number of adjacent cells-1).gtoreq.1) that does not
affect the cell boundary, and therefore, it is made possible to
attain a sub-channel arrangement without interference in the cell
even when affected by all of the adjacent cells.
[0243] Even when the result of rearrangement is inconvenient to
other cells, if rearrangement of sub-channels is carried out each
time, the ratio of the number of sub-channels that can reach the
adjacent cells is set equal to or less than a certain value, and
therefore, the sub-channels that reach the adjacent cells become
dispersed gradually in the entire cell and the operation without
interference is enabled in the entire system.
[0244] Next, the operation when a cell is added newly is explained.
First, a situation is supposed, in which three cells (cell A, cell
B, cell C) are arranged and arrangement of sub-channels has already
been carried out properly between the cells. This state is shown in
FIG. 36. Next, a situation is supposed, in which a cell D is
arranged in such a manner as to be adjacent to the cell B and cell
C. This state is shown in FIG. 37. Here, a situation is supposed,
in which the cell C and the cell D have carried out the same
sub-channel arrangement due to the influence of the arrangement of
terminals after the arrangement. As shown in FIG. 37, it can be
thought that such a situation occurs when the arrangement state of
terminals in the cell D is a state in which a terminal, such as a
terminal f, is not affected by the cell C and only the influence
from the cell B can be detected.
[0245] In this state, when a terminal e in the cell C moves near to
the boundary with the cell D, interference from the cell D is
detected naturally. This state is shown in FIG. 38. In this case,
by performing the process in accordance with the above-described
procedure, the allocation of the sub-channels in the cell C is
changed. At this time, when a terminal is arranged between the cell
A and the cell B, the influence from the adjacent cells is detected
and arrangement of sub-channels is carried out in the cell such
that there is no interference among all of the cells. Since the
sub-channel that affects the adjacent cells is avoided with
priority, allocation is carried out as long as possible. An example
of the final allocation is shown in FIG. 39.
Third Embodiment
[0246] In the above explanation, an embodiment in which the maximum
value of the number of adjacent cells is determined in advance is
explained. By changing part of the procedure described above, it is
made possible to deal with a case where the maximum number of
adjacent cells changes dynamically. If the maximum number of
adjacent cells is determined in advance, the number of sub-carriers
allocated to a group that performs transmission with transmission
power that reaches the cell edge is limited. In the above-described
example, since the six cells neighbor each another, only one
sub-carrier can be allocated to this group. Due to this, in the
case where terminals have gathered together near the cell edge, a
problem arises in that the usage efficiency of the sub-channels in
the cell decreases.
[0247] For this problem, it is made possible to improve the
efficiency by allocating more sub-channels to a group with
transmission power that can reach the cell edge in the case where
the number of adjacent cells is smaller or in the case of isolated
cell. A third embodiment is explained below.
[0248] In the third embodiment, a means for checking the number of
current adjacent cells is added to the base station in addition to
the case of the above-described second embodiment. The means for
checking the number of adjacent cells may use any method. For
example, such a method suggests itself, in which a high-gain
antenna is added in addition to the antenna the gain of which has
adapted to the cell radius normally used by the Up-link, and
thereby the Up-link communication of a terminal situated beyond the
cell radius is received, and the number of adjacent cells is
checked by checking which base station ID is used.
[0249] By the way, the operation of the terminal may be quite the
same as that in the second embodiment described above. The
operation of the base station is also the same basically. However,
part of the contents of the step of the allocation of sub-carrier
that can be used (FIG. 26, S2001) is changed. In the
above-described second embodiment, the number of sub-channels
allocated in step S2001 for the allocation of sub-channel that can
be used is set fixedly to one, four, four, and three in the
descending order of transmission power. This step is changed as
follows. A flow chart is shown in FIG. 40.
[0250] In the first step S2701, the number of adjacent cells is
checked. In the next step S2702, the number of sub-channels
allocated to a group with transmission power that reaches the cell
edge is calculated. This number is assumed to be (total number of
sub-channels/(number of current adjacent cells+1)) (decimal
fraction is rounded down). In the next step S2703, a group with
transmission power that reaches the cell edge is focused on. In the
next step S2704, a sub-channel is allocated to the focused-on group
with transmission power that reaches the cell edge. At this time,
the most recent minimum SINR for each sub-channel collected by the
base station is checked and allocation is carried out in the
descending order of the minimum SINR. In the next step S2705,
whether or not there is a transmission power group to which a
sub-channel has not been allocated yet is determined and when there
is any unallocated group, the procedure proceeds to step S2706 and
when there is no unallocated group, the step of the allocation of
sub-channel that can be used is terminated. In step S2706, a group
with transmission power second in magnitude to that of the
transmission power group currently focused on is focused on. In the
next step S2707, the number of sub-channels allocated to the
focused-on group is calculated.
[0251] Here, it is assumed that when the number of groups to which
a sub-channel is not allocated is one, that is, when the
unallocated group is only the group currently focused on, the
number shall be the total number of remaining sub-channels, and
when the number of groups to which a sub-channel has not been
allocated yet is more than one, the number shall be ((number of
unallocated sub-channels)/(number of groups to which the number of
sub-channels is not allocated) (decimal fraction is rounded up). In
the next step S2708, the number of sub-channels calculated in step
S2707 is allocated to the focused-on group. After that, the
procedure returns to step S2705, in which evaluation of the
remaining groups is continued.
[0252] By dynamically changing the number of sub-channels to be
allocated depending on the number of adjacent cells in this manner,
it is possible to avoid a situation in which the number of
sub-channels to be allocated to a specific group becomes less than
required.
Fourth Embodiment
[0253] In the above-mentioned embodiment, it is premised that there
is always interference from the adjacent cell. However, it is
possible to increase the number of sub-channels with transmission
power that reaches the adjacent cells by evaluating only the
sub-channels actually affected by the adjacent cells. An embodiment
in this case is shown below.
[0254] In a fourth embodiment, the operation of the terminal may
also be quite the same as that in the above-described second
embodiment. The operation of the base station is also the same
basically. However, part of the contents of the step of the
allocation of sub-channel that can be used (FIG. 26, S2001) is
changed as in the third embodiment described immediately above. A
flow chart is shown in FIG. 41.
[0255] In the first step S2801, the number of interfered
sub-channels is checked. A means for checking the number of
interfered sub-channels is not specified in particular. For
example, a method suggests itself, in which the SINR of each
sub-channel obtained from all of the terminals is checked and a
sub-channel in which the SINR is below a predetermined value at any
one of terminals is handled as an interfered sub-channel. In the
next step S2802, the number of sub-channels to be allocated to a
group with transmission power that reaches the cell edge is
calculated. It is assumed that this number is (total number of
sub-channels that can be used-currently interfered sub-channels),
however, when this number exceeds half the total number of
sub-channels that can be used (here, half is used, however, not
limited to half), this number is half the total number of
sub-channels that can be used. This is in order to cope with a case
where the number of interfered sub-channels is calculated as a
number less than the correct number and to leave the margin to
allocate a sub-channel to a group that does not affect the adjacent
cells in the cell of its own. In the next step S2803, a group with
transmission power that reaches the cell edge is focused on. In the
next step S2804, a sub-channel is allocated to the focused-on group
with transmission power that reaches the cell edge.
[0256] At this time, the most recent minimum SINR for each
sub-channel collected by the base station is checked and allocation
is carried out in the descending order of the minimum SINR. In the
next step S2805, whether or not there is a transmission power group
to which a sub-channel has not been allocated yet is determined and
when there is an unallocated group, the procedure proceeds to S2806
and when there is no unallocated group, the step of the allocation
of sub-channel that can be used is terminated. In step S2806, a
group with transmission power second in magnitude to that of the
transmission power currently focused on is focused on. In the next
S2807 step, the number of sub-channels to be allocated to the
focused-on group is calculated. Here, it is assumed that when the
number of groups to which a sub-channel is not allocated is one,
that is, when the unallocated group is only the group currently
focused on, the number is the total number of remaining
sub-channels, and when the number of groups to which a sub-channel
has not been allocated yet is more than one, the number is ((number
of unallocated sub-channels)/(number of groups to which the number
of sub-channels is not allocated))(decimal fraction is rounded up).
In the next step S2808, the number of sub-channels calculated in
step S2807 is allocated to the focused-on group. After that, the
procedure returns to step S2805, in which evaluation of the
remaining groups is continued.
[0257] By thus controlling and by increasing or decreasing the
number of sub-channels to be allocated to the group with
transmission power that reaches the adjacent cells depending on the
magnitude of the interference from the adjacent cells, it is made
possible to allocate more sub-channels to the group with
transmission power that reaches the adjacent cells. In this case,
even when many sub-channels are allocated to the group with
transmission power that reaches the adjacent cells, if the amount
of communication of this group is small, it is also possible to
allocate communication of a group with smaller transmission power,
and therefore, communication is performed almost without a decrease
in the efficiency in the cell.
[0258] In the above embodiments, control is performed in units of
sub-channels, a collection of sub-carriers, however, control can be
performed similarly in units of sub-carriers.
Fifth Embodiment
[0259] Next, a grouping method of terminals by a control station
(base station) when the quality of targeted communication differs
from group to group in a grouping method of terminals by the
control station according to distances from the terminals and the
control station etc. is explained. This corresponds to a system in
which communication of high speed is performed with a terminal that
is near the control station, that is, a terminal the reception SNR
of which can be thought to be high, and on the other hand,
communication of low speed is performed with a terminal that is at
the cell edge, that is a terminal the reception SNR (or SINR) of
which can be thought to be low.
[0260] When an adaptive modulation is used in the above-mentioned
system, there is a problem in that the communication speed of a
terminal having a subtle value with respect to the reference of
grouping is not constant or the communication speed needs to be
changed frequently.
[0261] In a fifth embodiment, therefore, a method for giving the
nature of hysteresis to grouping is explained. Using FIG. 48, the
grouping method is explained by an example. The horizontal axis in
FIG. 48 represents the transmission power level supposed to be
required by the respective terminals for reception (referred to a
supposed reception power) and the vertical axis represents the
destination of grouping according to the individual supposed
reception power. In the fifth embodiment, it follows that all of
the terminals are grouped into four groups. The solid line in FIG.
48 indicates the reference value of grouping in the case of
movement in the increasing direction of the supposed reception
power (in the rightward direction in the graph) and the dotted line
indicates the reference value of grouping in the case of movement
in the decreasing direction thereof (in the leftward direction in
the graph).
[0262] Here, for example, when the supposed reception power of a
terminal changes A to B, it follows that the terminal moves from
group B to group C when the supposed reception power is TC and when
the supposed reception power of a terminal from B to A, it follows
that the terminal moves from group C to group B moves when the
supposed reception power is TD. By performing such control, it is
possible to solve a problem in that the communication speed is not
constant and a problem in that the communication speed needs to be
changed frequently.
[0263] In addition, there may be a case where regrouping of
connected terminals is performed when a call is made to a new
terminal etc. At this time, by performing grouping of terminals
having supposed reception power in the hysteresis loop (In FIG. 48,
for example, where the supposed reception power is between TD and
TC) last, it is made possible to perform efficient regrouping even
in the case of crowded terminals. When there arises a need of
regrouping, the base station groups terminals in accordance with
the dotted line in FIG. 48. Following the dotted line results in
grouping that attains a transmission rate as high as possible. If
there remains unevenness in grouping after it is performed in
accordance with the dotted line, it is made possible to reduce the
unevenness by exchanging the terminals having the supposed
reception power on the dotted line. This utilizes the fact that
communication is possible even when the terminals in the hysteresis
loop belong to whichever group. By the way, after once grouped,
movement is made between groups as shown at the beginning of the
fifth embodiment.
[0264] As described above, according to the fifth embodiment, it is
also made possible to efficiently perform regrouping by setting the
hysteresis loop.
Sixth Embodiment
[0265] The grouping in the first to fifth embodiments premise that
the transmission power of the base station is controlled so that
the reception power is approximately constant irrespective of the
distance from the base station to the terminal.
[0266] However, when the transmission power control of the base
station as described above is performed, it follows that the
largest transmission power is allocated to the terminal near the
cell boundary. If it is assumed that the terminals are distributed
uniformly in the cell, the ratio of the terminals near the cell
boundary is large and therefore large transmission power is
allocated to many terminals and the interference power affecting
the adjacent cells increases as a result.
[0267] In the present embodiment, it is not required necessarily
for the reception power at the terminal to be constant. In a sixth
embodiment, a case is shown, where a plurality of values are used
as reception power at a terminal at the time of grouping according
to the propagation loss.
[0268] FIG. 49 shows an example of the grouping condition. In this
example, the whole is divided into five groups using the
propagation loss including the influence of the variation in the
propagation channel, such as fading, and three kinds of reception
target SNR are set for the respective groups. A control flow of a
base station is shown in FIG. 50 and a control flow of a terminal
is shown in FIG. 51 when grouping is performed in the
above-described manner.
[0269] First, the control flow of a base station is explained in
detail. By the way, the same frame format is used as that in FIG.
21.
[0270] First, in step S501, a signal for measuring SNR and
information of transmission power of the current control slot are
transmitted using the control slot. Any signal for measuring SNR
may be used. For example, a known signal may be used, in which part
of the OFDM sub-carrier is null carrier. In this case, it is
possible to find the SNR by comparing the strength of the
transmitted carrier and the null carrier on the reception side.
Next, in step S502, the propagation loss and information of SNR of
the control signal are acquired from each terminal via the Up-link.
Next, in step S503, the respective terminals are grouped according
to the propagation loss notified from each terminal. At this time,
it is assumed that the grouping in FIG. 49 is obeyed.
[0271] Next, in step S504, transmission power to be allocated to
each of the grouped terminals is determined. It is assumed that the
transmission power is a value determined in advance based on the
worst SNR in its group. After that, in step S505, Down-link data is
transmitted to each terminal using the slot for which allocation
has been determined in the previous frame. After that, in step
S506, the allocation of the slot to be used in the next frame is
determined as well as that of the transmission power found in step
S504 and the setting is so made that the contents are transmitted
using the next control slot. When the adaptive modulation is
performed, it is possible to set a modulation parameter by
referring to the SNR information obtained from the terminal when
the allocation is determined.
[0272] After that, the flow returns to step S501, where the above
procedure from the transmission of the control slot is
repeated.
[0273] Next, the control flow of a terminal is explained in detail.
First, in step S511, the control slot transmitted from the base
station is received. Next, in step S512, the propagation loss from
the base station to the terminal and the SNR of the received
control slot are measured. Any method for finding the propagation
loss and SNR may be used. For example, it is possible to use a
value as the propagation loss, which is the transmission power of
the control slot at the base station included in the control slot
minus RSSI. To be precise, this value is not the propagation loss,
however, since the relative value between terminals can be known if
the same measurement is performed at all of the terminals, it is
possible to use this value as the propagation loss. In addition, it
is possible to measure the SNR by transmitting a known signal in
which part of sub-carrier is null carrier to the base station and
by finding the transmission power ratio between a certain carrier
and the null carrier of the signal.
[0274] Next, the information of the propagation loss and SNR
measured in step S513 is transmitted to the base station via the
Up-link. After that, in step S514, the data is received based on
the allocated information included in the control slot. After that,
the flow returns to step S511 and the procedure from the reception
of the control slot is repeated.
[0275] Due to the above operation of the base station and the
terminal, the allocation of slot in accordance with the parameters
determined as shown in FIG. 49 and the transmission power control
are performed. By the way, the allocation of slot may be carried
out in the direction of time channel or in the direction of
frequency channel and it is possible to carry out by combining each
of the above-mentioned embodiments.
Seventh Embodiment
[0276] In the first to sixth embodiments, a configuration based on
the OFDM is employed. However, the present invention can be applied
to other than the OFDM. For example, in the case of SS (Spread
Spectrum), it is not possible to perform group control by the
frequency channel, however, group control can be performed by the
time channel and it is made possible to perform the present
invention.
INDUSTRIAL APPLICABILITY
Explanations of Letters or Numerals
[0277] 100 antenna part [0278] 101 radio reception part [0279] 102
A/D conversion part [0280] 103 synchronization part [0281] 104
guard interval removal part [0282] 105 S/P conversion part [0283]
106 FFT part [0284] 107 propagation channel estimation and
demapping part [0285] 108-a to 108-l P/S conversion part [0286]
109-a to 109-l error correction decoding part [0287] 110
demultiplex part [0288] 111 A/D conversion part [0289] 112 RSS
measurement part [0290] 113 interference power measurement part
[0291] 114 control part [0292] 115 Up-link transmission part [0293]
120 scheduling part [0294] 121 multiplex part [0295] 122-a to 122-l
error correction encoding part [0296] 123-a to 123-l S/P conversion
part [0297] 124 mapping part [0298] 125 transmission power control
part [0299] 126 IFFT part [0300] 127 P/S conversion part [0301] 128
guard interval insertion part [0302] 129 D/A conversion part [0303]
130 radio transmission part [0304] 131 antenna part [0305] 181
antenna part [0306] 182 radio reception part [0307] 183 A/D
conversion part [0308] 184 synchronization part [0309] 185 guard
interval removal part [0310] 186 S/P conversion part [0311] 187 FFT
part [0312] 188 propagation channel estimation and demapping part
[0313] 189-a to 189-l P/S conversion part [0314] 190-a to 190-l
error correction decoding part [0315] 190 demultiplex part [0316]
192 SINR measurement part [0317] 193 RSS measurement part [0318]
194 control part [0319] 195 Up-link transmission part [0320] 260
scheduling part [0321] 261 multiplex part [0322] 262-a to 262-l
error correction encoding part [0323] 263-a to 263-l S/P conversion
part [0324] 264 mapping part [0325] 265 transmission power control
part [0326] 267 IFFT part [0327] 267 P/S conversion part [0328] 268
guard interval insertion part [0329] 269 D/A conversion part [0330]
270 radio transmission part [0331] 271 antenna part [0332] 272
Up-link reception part
* * * * *