U.S. patent application number 12/611964 was filed with the patent office on 2010-02-25 for wireless communication system.
Invention is credited to Kenzaburo Fujishima, Mikio Kuwahara, Masanori Taira, Koki UWANO.
Application Number | 20100046462 12/611964 |
Document ID | / |
Family ID | 37015843 |
Filed Date | 2010-02-25 |
United States Patent
Application |
20100046462 |
Kind Code |
A1 |
UWANO; Koki ; et
al. |
February 25, 2010 |
WIRELESS COMMUNICATION SYSTEM
Abstract
Wireless communication arrangements including: performing
scheduling of transmitting signal to each of the mobile stations so
that interference of radio waves sent from each of the remote units
to each of the mobile stations can be suppressed based on priority
level of the mobile station and the interference area information;
generating information to control the direction-variable antenna of
each of the plurality of remote units, so that the corresponding
remote unit forms beam according to scheduling result; and
transmitting the information to control the direction-variable
antenna to the plurality of remote units.
Inventors: |
UWANO; Koki; (Fujisawa,
JP) ; Taira; Masanori; (Yokohama, JP) ;
Fujishima; Kenzaburo; (Kobubunji, JP) ; Kuwahara;
Mikio; (Hachiouji, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
37015843 |
Appl. No.: |
12/611964 |
Filed: |
November 4, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11350111 |
Feb 9, 2006 |
7639984 |
|
|
12611964 |
|
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Current U.S.
Class: |
370/329 ;
455/63.4 |
Current CPC
Class: |
H04W 64/006 20130101;
H04B 7/0617 20130101; H04W 16/28 20130101; H04B 7/0408 20130101;
H04W 16/26 20130101; H04W 28/10 20130101 |
Class at
Publication: |
370/329 ;
455/63.4 |
International
Class: |
H04W 72/12 20090101
H04W072/12; H04B 15/00 20060101 H04B015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2005 |
JP |
2005-081930 |
Claims
1. A wireless communication method in a wireless communication
system comprising: a plurality of remote units for transmitting and
receiving wireless signals with a plurality of mobile stations,
each of the plurality of the remote units including a
direction-variable antenna of which directivity varies with an
electric signal supplied to a plurality of antenna elements; a
central base station connected with the plurality of remote units,
for transmitting signals from the plurality of mobile stations
through the plurality of remote units to a network side and
receiving signals for the plurality of mobile stations from the
network side, and performing scheduling of transmitting signals to
the plurality of mobile stations; wherein the central base station
executing operations of: storing an identification and an area
information of a remote unit in which each mobile station is
placed, for the plurality of remote units connected with the
central base station; storing a plurality of other area information
causing interference with a certain area of a certain remote unit
corresponding to each area of a remote unit; performing scheduling
of transmitting a signal to each of the mobile stations so that
interference of radio waves sent from each of the remote units to
each of the mobile stations can be suppressed based on priority
level of the mobile station and the interference area information;
generating information to control the direction-variable antenna of
each of the plurality of remote units, so that the corresponding
remote unit forms a beam according to scheduling result; and
transmitting the information to control the direction-variable
antenna to the plurality of remote units.
2. A wireless communication method according to claim 1, wherein
the central base station holds electric signals to be supplied to
the direction-variable antenna as a plurality of beam patterns, and
the directivity is changed by switching the beam pattern as
selected in accordance with the position of the mobile station.
3. A wireless communication method according to claim 2, wherein
the central base station estimates the position of the mobile
station by predicting the direction in which radio waves come from
the mobile station, and determines the beam pattern to be sent to
the mobile station.
4. A wireless communication method according to claim 2, wherein
each mobile station receives radio waves of all beam patterns from
the remote units and notifies the central base station of a beam
received with good quality, and the central base station determines
the beam pattern to be sent to the mobile station.
5. A wireless communication method according to claim 3, wherein
the central base station performs centralized management of the
beam patterns to be sent to all the mobile stations.
6. A wireless communication method according to claim 1, wherein
the performing scheduling selects such a mobile station that a
transmitted beam will not cause strong interference, in accordance
with the priority levels of the mobile stations and based on the
area information; and a combination of mobile stations are
determined so that interference will not occur between radio waves
sent by the remote units.
7. A wireless communication method according to claim 1, wherein
each mobile station measures radio waves sent from the remote unit,
determines a beam pattern causing interference, and notifies the
central base station of interference area information; and the
central base station, in accordance with the notified interference
area information, determines such a combination of mobile stations
that radio waves sent from the remote units will not cause
interference.
8. A wireless communication method according to claim 7, wherein
beam patterns of radio waves to be checked for interference are
selected in accordance with the communicating position of each
mobile station, in the radio wave measurement of the mobile
station.
9. A wireless communication method according to claim 4, wherein
the central base station performs centralized management of the
beam patterns to be sent to all the mobile stations.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of U.S. application Ser. No.
11/350,111, filed Feb. 9, 2006. This application relates to and
claims priority from Japanese Patent Application No. 2005-081930,
filed on Mar. 22, 2005. The entirety of the contents and subject
matter of all of the above is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to wireless communication
systems, and more specifically, to a wireless communication system
which includes a plurality of cells and is suited for suppressing
radio interference from adjacent base stations.
[0004] 2. Description of the Related Art
[0005] In a CDMA cellular system, the base stations of adjacent
cells use radio waves in the same frequency band. Radio
interference can occur between those cells. The degree of
interference depends on the propagation environment and the
positional relationship between the base stations. Interference
provides an insufficient signal-to-interference (S/I) ratio, and
high-speed data transmission becomes impossible sometimes.
Accordingly, stable communication must be established by increasing
the processing gain, using a modulation system having a high degree
of noise immunity, such as BPSK, or the like. A sufficiently high
S/I ratio allows the processing gain to be decreased or allows the
use of a multi-level modulation system having a low degree of noise
immunity, such as 16QAM, enabling high-speed data transmission.
Thus, interference from another cell greatly affects the
transmission data rate in the CDMA system.
[0006] The cdma2000 1xEV-DO system will be described below as an
example of the CDMA system. The system performs best-effort
control, and detailed specifications of the system can be obtained
from non-patent document 1. The best-effort system does not serve
all mobile stations uniformly but attempts to improve the radio
channel efficiency, giving a high priority to a mobile station
having a good channel quality. Each mobile station determines
parameters of communication channel modulation and encoding in
consideration of an observed degree of interference noise and
reports the parameters to the base station. The base station
receives the parameters and performs time-division packet
scheduling in such a manner that the radio channel is
preferentially allocated to a mobile station having a good
condition. Therefore, a smaller amount of interference noise
enables communication at a higher data rate. Minimizing the
interference noise is effective in improving the system
performance.
[0007] A method disclosed in Japanese Unexamined Patent Application
Publication No. 2002-232350 (patent document 1) has been proposed
to avoid interference between base stations in the cdma2000 1xEV-DO
system (former HDR system). The proposed method uses a
direction-variable antenna to narrow the aperture of the radio-wave
beam transmitted by each base station and to transmit the radio
waves in such a direction that strong interference will not
occur.
[0008] FIG. 1 shows a radio-wave transmission pattern with a
conventional technology.
[0009] The figure shows that three-sector base stations 1-1 to 1-7
transmit radio-wave beams in a common frequency band of f1. Shaded
portions represent the radio-wave beams, which are transmitted in
such directions that interference will not occur. The beam
transmission directions are switched at predetermined times so that
all directions are covered.
[0010] Patent Document 1
Japanese Unexamined Patent Application Publication No.
2002-232350
Non-Patent Document
[0011] The 3rd Generation Partnership Project 2 (3GPP2)
Specifications (online), The 3rd Generation Partnership Project 2
(found on Nov. 9, 2004), at
http://www.3gpp2.org/public_html/specs/index.cfm/
SUMMARY OF THE INVENTION
[0012] As described with FIG. 1, interference can be reduced by
providing each base-station apparatus with a direction-variable
antenna. This method requires that a mobile station be in the
region in which a directional beam is directed. Because each
base-station apparatus independently performs packet scheduling to
select a mobile station to be connected by wireless communication,
it is hard to consider the beam directions in other cells. If a
plurality of base stations determine the beam regions of the cells
by sharing information determining the radio-wave transmission
regions, it would be tough to perform real-time processing because
of delay and data amounts in data transfer between the
apparatuses.
[0013] Accordingly, it is an object of the present invention to
provide a wireless system that can determine the region of beam
transmission from each base station with high precision, in
consideration of the status of each mobile station in real time,
and can suppress the influence of radio interference between the
base stations.
[0014] The conventional wireless communication system requires a
base-station apparatus in each cell. Attention has been given to
radio-on-fiber technologies, which connect a central base station
and remote base stations by fiber-optic cables. The radio-on-fiber
technologies use the low loss and wide band of the optical fiber.
The central base station is given modulation and demodulation
functions and blocks performing call processing, and is connected
to the remote base stations equipped with an antenna by fiber-optic
cables. The siting cost can be reduced by simplifying the remote
base station, and the maintenance of the base stations can be
facilitated by concentrating all facilities that require
maintenance into the central base station. With this system, the
regions of beams can be determined with high precision because the
central base station can seize the statuses of all mobile stations
in wireless communication with the remote base stations below the
central base station.
[0015] The problems described above can be solved by a wireless
communication system in which a central base station and a
plurality of remote base stations are connected by communication
media such as a fiber-optic cable, and the remote base stations
perform wireless communication with a plurality of mobile stations,
the remote base stations are equipped with a direction-variable
antenna of which directivity varies with an electric signal
supplied to a plurality of antenna elements, and the central base
station performs packet scheduling of the mobile stations in such a
manner that interference of radio waves sent from the remote base
stations to the mobile stations can be suppressed.
[0016] The problems described above can be solved also by the
wireless communication system described above in which the central
base station holds electric signals to be supplied to the
direction-variable antenna as a plurality of beam patterns, and the
directivity is changed by switching the beam pattern as selected in
accordance with the position of the mobile station.
[0017] The problems described above can be solved also by the
wireless communication system described above in which each mobile
station receives radio waves of all beam patterns from the remote
base station and notifies the central base station of a beam
received with a good quality, and the central base station
determines the beam pattern to be transmitted to the mobile station
accordingly.
[0018] The problems described above can be solved also by the
wireless communication system described above in which the central
base station estimates the position of the mobile station by
predicting the direction in which radio waves come from the mobile
station, and determines the beam pattern to be sent to the mobile
station.
[0019] The problems described above can be solved also by the
wireless communication system described above in which the central
base station performs centralized management of the beam patterns
to be sent to all the mobile stations.
[0020] The problems described above can be solved also by the
wireless communication system described above in which the central
base station holds the information of a combination of beam
patterns causing interference between remote base stations and
determines such a combination of mobile stations that radio waves
sent from the remote base stations will not cause interference.
[0021] The problems described above can be solved also by the
wireless communication system described above in which each mobile
station measures radio waves sent from each remote base station,
judges a beam pattern causing interference, and notifies the
central base station of the beam pattern, and the central base
station determines such a combination of mobile stations that radio
waves sent from the remote base stations will not cause
interference.
[0022] The problems described above can be solved also by the
wireless communication system described above in which the beam
patterns of radio waves to be checked for interference are selected
in accordance with the communicating position of each mobile
station, in the radio wave measurement of the mobile station.
[0023] A wireless communication system according to the present
invention can suppress radio interference between base stations and
can improve the efficiency of the downstream radio channel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 shows a radio-wave transmission pattern with a
conventional technology.
[0025] FIG. 2 shows the configuration of a first embodiment of the
present invention.
[0026] FIG. 3 shows a layout of remote base stations placed in
cells according to the first embodiment of the present
invention.
[0027] FIG. 4 shows a block diagram of the remote base station.
[0028] FIG. 5 shows a block diagram of a downstream fixed-beam
forming circuit (DLFBF) in the remote base station.
[0029] FIG. 6 shows a block diagram of a central base station.
[0030] FIG. 7 shows a block diagram of an upstream fixed-beam
forming circuit (ULFBF) in the central base station.
[0031] FIG. 8 shows a block diagram of a demodulator (DEM) in the
central base station.
[0032] FIG. 9 shows a block diagram of a scheduling controller
(SCH) in the central base station.
[0033] FIG. 10 shows a flow chart for scheduling algorithm.
[0034] FIG. 11 shows a beam transmission pattern.
[0035] FIG. 12 shows an example of packet scheduling of the mobile
stations.
[0036] FIG. 13 shows an example of a mobile-station management
table.
[0037] FIG. 14 shows an example of an interference table of the
first embodiment of the present invention.
[0038] FIG. 15 shows one example of interference areas.
[0039] FIG. 16 shows a movement of a mobile station in the first
embodiment.
[0040] FIG. 17 shows a block diagram of a mobile station of a
second embodiment of the present invention.
[0041] FIG. 18 shows an example of an interference table of the
second embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] Embodiments of the present invention will be described below
with reference to the drawings, but the present invention is not
limited to those embodiments.
1. First Embodiment
[0043] FIG. 2 shows the configuration of a first embodiment of the
present invention. As shown in the figure, a central base station 6
is connected to a network 7 and also to a plurality of remote base
stations 4 through fiber-optic cables 5. The remote base station 4
perform wireless communication with a mobile station 2-1 selected
from a plurality of mobile stations 2-1 to 2-2, by using a
radio-wave beam formed by a direction-variable antenna 3.
[0044] FIG. 3 shows a layout of remote base stations 4 placed in
cells. The central base station 6 controls a plurality of remote
base stations 4-1 to 4-7 so that they send narrow-aperture
radio-wave beams in the same frequency band of f1 in such
directions that interference will not occur. The beam transmission
directions can be switched at predetermined times so that
communication can be performed with the mobile stations in all
directions.
[0045] FIG. 4 shows a block diagram of the remote base station 4,
which has the wireless control function of the conventional base
station functions. The remote base station 4 includes an antenna
module 3, duplexers (DUPS) 8, radio-frequency receivers (RXs) 9, a
multiplexer (MUX) 10, an electric-to-optic (E/O) converter 11,
fiber-optic cables 5, an optic-to-electric (O/E) converter 12, a
demultiplexer (DEMUX) 13, a downstream fixed-beam forming circuit
(DLFBF) 14, and radio-frequency transmitters (TXs) 15.
[0046] The upstream channel will be described first. The antenna
module 3 has an antenna array which can form a highly directional
beam pattern of 12 beams, for instance. The duplexer (DUP) 8
separates a transmission signal and a received signal. In a normal
mobile communication system, the duplexer (DUP) 8 includes band
selection filters for selecting the signals. The radio-frequency
receiver (RX) 9 brings a signal from the corresponding antenna
element of the antenna array to a certain level through
amplification, frequency conversion, and the like, then converts
the signal to a digital signal through A/D conversion. The
multiplexer (MUX) 10 performs time-division multiplexing of the
signal received by each antenna element and sent through the
duplexer (DUP) 8 and the radio-frequency receiver (RX) 9, and
converts the signal to serial data. The electric-to-optic (E/O)
converter 11 converts the electric signal to an optical signal for
fiber-optic transmission of the upstream signal to the central base
station 6.
[0047] The downstream channel will be described next. The
optic-to-electric (O/E) converter 12 converts an optical signal
received from the central base station 6 to an electric signal. The
demultiplexer (DEMUX) 13 separates the received signal to a main
signal and array weight signals. The downstream fixed-beam forming
circuit (DLFBF) 14 combines the main signal with a beam pattern
having directivity in the radio-wave transmission direction as a
vector.
[0048] FIG. 5 shows a block diagram of the downstream fixed-beam
forming circuit (DLFBF) 14. The downstream fixed-beam forming
circuit (DLFBF) 14 assigns weight vector coefficients W1 to Wn
generated by the central base station 6 to the transmission signal
to generate signals to be supplied to the individual antennas.
Weight coefficients W1 to Wn are vector coefficients that change
the amplitude and phase simultaneously.
[0049] The radio-frequency transmitter (TX) 15 performs
amplification, frequency conversion, and other processing and sends
a downstream signal from the antenna module 3 through the duplexer
(DUP) 8.
[0050] FIG. 6 shows a block diagram of the central base station 6,
which has the modulation and demodulation functions of the
conventional base station functions. The central base station 6
includes optic-to-electric (O/E) converters 12, demultiplexers
(DEMUXs) 13, upstream fixed-beam forming circuits (ULFBFs) 16,
demodulators (DEMs) 17, decoders (DECs) 18, access line interfaces
(LIFs) 19, a scheduling controller (SCH) 20, encoders (CODs) 21,
modulators (MODs) 22, a weight control circuit (WC) 23,
multiplexers (MUXs) 10, and electric-to-optic (E/O) converters
11.
[0051] The upstream channel will be described first. The
optic-to-electric (O/E) converter 12 converts an optical signal
received from the remote base station 4 to an electric signal. The
demultiplexer (DEMUX) 13 separates the received signal into signals
for the antenna elements. The upstream fixed-beam forming circuit
(ULFBF) 16 combines the signals received by the antenna elements as
vectors and provides signals having a 12-beam radiation pattern in
a circumferential direction.
[0052] FIG. 7 shows a block diagram of the upstream fixed-beam
forming circuit (ULFBF) 16. A multiplier 24 assigns appropriate
weights to the signals for the antenna elements, an adder 25 adds
the signals, and a narrow-aperture beam is provided. Vector
coefficients are used as weight coefficients W11 to Wnn so that the
amplitude and phase are changed simultaneously.
[0053] The demodulator (DEM) 17 demodulates the received
signals.
[0054] FIG. 8 shows a block diagram of the demodulator (DEM) 17. A
channel separator (DES) 26 such as a despreading circuit separates
a signal sent from a desired mobile station, from the received beam
signals. Then, a comparator (COMP) 27 compares the beam signals,
and an optimum beam signal selected by a selector 28 is added for
multiple paths by a rake combination circuit (RAKE) 29, and is
demodulated by a demodulator (DET) 30.
[0055] The decoder (DEC) 18 performs error-correcting decoding and
sends the signal to a wired communication network via the access
line interface (LIF) 19.
[0056] The downstream channel will be described next. The access
line interface (LIF) 19 receives a signal from the wired
communication network. The scheduling controller (SCH) 20 selects a
mobile station to be connected by wireless communication.
[0057] FIG. 9 shows a block diagram of the scheduling controller
(SCH) 20. An operation block 38 of the scheduling controller (SCH)
20 calculates the base station ID, area ID, and transmission
priority level of each mobile station, on the basis of the beam
information, required data rate, and other schedule information of
each mobile station received from the demodulator (DEM) 17, and
stores the calculated items in a mobile-station management table
(MS_TBL) 31. The base station ID and area ID represent the current
location of the mobile station and correspond to an area in which a
narrow-aperture beam is sent in wireless communication. The
transmission priority level is calculated from the required data
rate, transmission throughput, and the like, in a best effort
manner. An interference evaluation table (I_TBL) 32 stores
information indicating with which area of a remote base station a
certain remote base station can cause strong interference. This
table is specified beforehand in consideration of the transmission
beam shape. A mobile station selection circuit (MS_SEL) 33
references the mobile-station management table (MS_TBL) 31 and the
interference evaluation table (I_TBL) 32, and selects mobile
stations so that the beams can be transmitted without causing
strong interference. A data buffer (BUF) 34 holds data to be sent
to each mobile station. Data of the mobile station selected by a
selector 39 is sent to the encoder (COD) 21. The transmission area
information of the selected mobile station is sent to the weight
control circuit (WC) 23.
[0058] The encoder (COD) 21 performs error-correcting encoding. The
modulator (MOD) 22 performs modulation of a certain method. The
weight control circuit (WC) 23 selects a weight coefficient to be
used as a multiplier of each antenna array for forming the beam to
be transmitted to the selected mobile station 2. The weight pattern
of each area is specified in a table beforehand and is selected in
accordance with the transmission area information given by the
scheduling controller (SCH) 20. The multiplexer (MUX) 10 multiplies
the modulated signal with the array weight signal. The
electric-to-optic (E/O) converter 11 converts the electric
downstream signal to an optical signal for fiber-optic transmission
to the remote base station 4.
[0059] FIG. 10 shows an algorithm for mobile station scheduling. An
appropriate processing block or the mobile station selection
circuit (MS_SEL) 33 in the scheduling controller (SCH) 20 executes
this algorithm, by using the two tables mentioned above. First, the
mobile-station management table (MS_TBL) 31 is sorted in descending
order of priority levels assigned to the mobile stations (S101).
One mobile station having the highest priority level is selected
(S105). The remote base station to communicate with the selected
mobile station is checked to see whether a specified number of
mobile stations has already been allocated (S107). If yes, the
selected mobile station cannot be allocated additionally. So, the
mobile station is not allocated (S109), and a next mobile station
is selected (S105). If the specified number of mobile stations has
not yet been allocated, the selected mobile station is kept as a
candidate mobile station that can be allocated, and an interference
check (S111) is carried out. In the interference check step (S111),
it is checked whether the beam to be sent to the candidate mobile
station and the beam to be sent to an allocated mobile station will
cause strong interference, in accordance with the interference
evaluation table (I_TBL) 32. If it is determined that interference
will occur, the allocated terminal takes precedence over the
candidate mobile station, and the candidate mobile station is not
allocated (S113). A next mobile station is selected (S105). If it
is determined that no interference will occur, the candidate mobile
station is allocated (S115). It is checked whether all the remote
base stations already have a specified number of mobile stations
(S117). If not, a next mobile station is selected, and the
scheduling steps (S103 to S119) are repeated. If the specified
number of mobile stations has been allocated, scheduling is
finished. When all the mobile stations are evaluated, scheduling
ends even if the specified number of mobile stations has not yet
been allocated.
[0060] FIG. 11 shows an example beam transmission pattern.
[0061] Mobile station scheduling will be described in further
detail with reference to a mobile station layout shown in FIG.
11.
[0062] FIG. 12 shows a result of scheduling. In the figure, T0 to
T3 represent time slots of data transmission, and shaded slots
indicate selected mobile stations. As the priority levels of the
mobile stations and the interference status vary with time, the
selected mobile stations are switched.
[0063] FIG. 13 shows an example of the mobile-station management
table (MS_TBL) 31 at time T0, and FIG. 14 shows an example of the
interference evaluation table (I_TBL) 32. The mobile-station
management table (MS_TBL) 31 lists the areas containing the mobile
stations 2-1 to 2-6 and the priority levels. The interference
evaluation table (I_TBL) 32 lists areas where beam transmission can
cause interference with each area of each remote base station. For
instance, area <6> of base station 4-1 can cause strong
interference with areas <11> and <12> of base station
4-2 and area <2> of base station 4-3, so that these areas are
stored in the interference table. (The numbers in the angle
brackets corresponds to the circled area numbers in the
drawings.)
[0064] FIG. 15 shows the interference status in the above example
case. Strong interference can occur in shaded portions.
[0065] The scheduling operation at time T0 will be described with
reference to the algorithm shown in FIG. 10. It is supposed here
that the allocation count of each remote base station is
predetermined to 1. When the mobile stations to be scheduled are
sorted in descending order of priority level, the ranking of mobile
stations, from highest to lowest, is 2-2, 2-5, 2-6, 2-1, 2-3, and
2-4. Mobile station 2-2 having the highest priority level is
selected as a first candidate mobile station. Because no mobile
station has been allocated to remote base station 4-1, mobile
station 2-2 is allocated to the remote base station. Mobile station
2-5 is selected next. No mobile station has been allocated to
remote base station 4-3, but area <2> thereof will cause
interference with area <7> of base station 4-1, containing
allocated mobile station 2-2. Accordingly, mobile station 2-5 is
not allocated. Then, mobile station 2-6 is selected. No mobile
station has been allocated to remote base station 4-3, and area
<4> of remote base station 4-3 will not cause interference
with area <7> of base station 4-1, containing allocated
mobile station 2-2. Accordingly, mobile station 2-6 is allocated to
remote base station 4-3. Mobile station 2-1 is selected next.
Because mobile station 2-2 has been allocated to remote base
station 4-1, mobile station 2-1 is not allocated. Then, mobile
station 2-3 is selected. No mobile station has been allocated to
remote base station 4-2, but area <9> of remote base station
4-2 will cause interference with area <4> of base station
4-3, containing allocated mobile station 2-6. Accordingly, mobile
station 2-3 is not allocated. Mobile station 2-4 is selected next.
No mobile station is allocated to remote base station 4-2, and area
<12> of remote base station 4-2 will not cause interference
with the areas including allocated mobile stations 2-2 and 2-6.
Accordingly, mobile station 2-4 is allocated to remote base station
4-2. Now, all the base stations have allocated mobile stations, and
scheduling is completed. As a result of scheduling, packet
scheduling to the mobile stations can be determined in such a
manner that strong interference will not be caused by beams
transmitted among the remote base stations.
[0066] If any of the mobile stations moves to a different area, the
mobile station management table is updated as described below.
[0067] FIG. 16 shows a movement of a mobile station to a different
area in the present embodiment. If mobile station 2-1 moves from
area <6> of remote base station 4-1, as shown in FIG. 15, to
area <7> of remote base station 4-1, as shown in FIG. 16, the
signal from mobile station 2-1 received in area <7> and
demodulated by the demodulator (DEM) 17 of the central base station
6 has the highest intensity. The demodulator (DEM) 17 notifies the
scheduling controller (SCH) 20 that mobile station 2-1 is in area
<7> of remote base station 4-1. The scheduling controller
(SCH) 20 updates the positional information in the mobile station
management table (MS_TBL) accordingly, and performs subsequent
scheduling in accordance with the updated table.
[0068] This system monitors the positions of mobile stations in
real time and can control the beams transmitted from the remote
base stations so that strong interference will not occur.
2. Second Embodiment
[0069] Another embodiment of the present invention will be
described. The second embodiment differs from the first embodiment
in that the central base station performs scheduling on the basis
of information calculated by a mobile station. More specifically,
the mobile station generates area information for the mobile
station management table and also generates interference evaluation
information.
[0070] This enables a table to be created in accordance with the
quality of radio waves received by the mobile station and thus
enables the precision of scheduling for avoiding interference to be
improved. The mobile station calculates the information by using a
pilot signal sent by the remote base station periodically in each
area.
[0071] FIG. 17 shows a block diagram of a mobile station of the
second embodiment. The mobile station includes an antenna module 3,
a duplexer (DUP) 8, a radio-frequency receiver (RX) 9, a
demodulator (DEM) 17, a decoder (DEC) 18, an encoder (COD) 21, a
modulator (MOD) 22, a radio-frequency transmitter (TX) 15, an area
measurement circuit (AREA) 35, an interference measurement circuit
(I_MSR) 36, and a data processing block (DATA) 37.
[0072] The downstream channel will be described first. The antenna
module 3 includes an antenna which can receive a signal in every
direction, like an omni antenna. The duplexer (DUP) 8 separates a
transmission signal and a received signal. The radio-frequency
receiver (RX) 9 brings the received signal to a certain level
through amplification, frequency conversion, and the like, then
converts the signal to a digital signal through A/D conversion. The
demodulator (DEM) 17 demodulates the received signal. The
demodulator (DEM) 17 also calculates S/I of the pilot signal sent
to each area of the remote base station and notifies the calculated
result to the area measurement circuit (AREA) 35 and the
interference measurement circuit (I_MSR) 36. The decoder (DEC) 18
performs error-correcting decoding of the demodulated signal and
sends the resultant signal to the data processing block (DATA) 37.
The area measurement circuit (AREA) 35 selects an area of the best
reception quality in accordance with the S/I information of the
pilot signal of each area received from the demodulator (DEM) 17,
and sends the selection result as area information to the modulator
(MOD) 22. The interference measurement circuit (I_MSR) 36 checks
whether S/I of the pilot signal of the area received from the
demodulator (DEM) 17 reaches a certain threshold level, if so,
judges the area as being an interference area, and notifies the
modulator (MOD) of the judgment.
[0073] The upstream channel will be described next. The data
processing block (DATA) 37 sends a signal, and the encoder (COD) 21
performs error-correcting encoding of the signal. The modulator
(MOD) 22 receives the signal transmitted from the data processing
block (DATA) 37, area information from the area measurement circuit
(AREA) 35, and interference information from the interference
measurement circuit (I_MSR) 36, and performs modulation of a
certain method. The radio-frequency transmitter (TX) 15 performs
amplification, frequency conversion, and other processing, and
sends an upstream signal from the antenna module 3 through the
duplexer (DUP) 8.
[0074] The demodulator (DEM) 17 of the central base station 6
demodulates the area information and interference information sent
from the mobile station, and sends the result to the scheduling
controller (SCH) 20, which includes a setting block for setting a
table and other means (not shown). The scheduling controller (SCH)
20 stores the area information in the mobile-station management
table (MS_TBL) 31 and the interference information in the
interference evaluation table (I_TBL) 32.
[0075] FIG. 18 shows an example of the interference table of the
second embodiment. The table stores information indicating in which
area of which remote base station the beam from each mobile station
causes interference. In the shown table, mobile station 2-1 has
found that strong interference occurs only by the beam sent to area
<11> of base station 4-2. The central base station 6 performs
scheduling in accordance with the mobile-station management table
(MS_TBL) 31 and the interference evaluation table (I_TBL) 32, as in
the first embodiment.
[0076] Supposing that the mobile stations are placed as shown in
FIG. 11, scheduling of the second embodiment will be compared with
scheduling of the first embodiment. As shown in FIG. 14, mobile
station 2-1 in area <6> of base station 4-1 considers areas
<11> and <12> of base station 4-2 and area <2> of
base station 4-3 to be strong interference areas, in the first
embodiment. In the second embodiment, radio waves transmitted to
just area <11> of base station 4-2 are considered to cause
strong interference at mobile station 2-1. In the first embodiment,
mobile station 2-1 cannot be simultaneously scheduled with a mobile
station in area <12> of base station 4-2 or in area <2>
of base station 4-3 although strong interference does not actually
occur. In the second embodiment, mobile station 2-1 can be
simultaneously scheduled with the mobile station in area <12>
of base station 2-4 or in area <2> of base station 4-3. This
means that the accuracy of evaluation information is improved by
using the interference status measured by the mobile station.
According to the second embodiment, the system can control the
beams transmitted from the remote base stations while monitoring
the interference status of the mobile stations in real time.
[0077] According to the present invention, the wireless
communication system can suppress radio interference between base
stations and can improve the efficiency of the downstream radio
channel.
* * * * *
References