U.S. patent application number 11/065253 was filed with the patent office on 2006-01-05 for wireless communication method, wireless base station and wireless communication terminal.
Invention is credited to Kenzaburo Fujishima, Mikio Kuwahara, Masanori Taira.
Application Number | 20060002421 11/065253 |
Document ID | / |
Family ID | 35513861 |
Filed Date | 2006-01-05 |
United States Patent
Application |
20060002421 |
Kind Code |
A1 |
Kuwahara; Mikio ; et
al. |
January 5, 2006 |
Wireless communication method, wireless base station and wireless
communication terminal
Abstract
To reduce power consumption of a mobile station, this invention
provides a wireless communication method for communicating between
a base station and a plurality of terminals using a plurality of
channels, the channels being slots obtained by dividing
frequency-divided carriers by time, in which the base station
allocates a set of the channels which is composed of a plurality of
neighboring carriers and/or a plurality of successive slots for the
each terminal, and the base station allocates at least one of the
channels included in the channel sets for packet transmission the
terminals.
Inventors: |
Kuwahara; Mikio; (Hachioji,
JP) ; Fujishima; Kenzaburo; (Kokubunji, JP) ;
Taira; Masanori; (Yokohama, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
35513861 |
Appl. No.: |
11/065253 |
Filed: |
February 25, 2005 |
Current U.S.
Class: |
370/464 |
Current CPC
Class: |
H04W 72/1284 20130101;
Y02D 30/70 20200801; H04W 72/1231 20130101; H04W 52/0216 20130101;
H04L 5/0005 20130101; Y02D 70/00 20180101 |
Class at
Publication: |
370/464 |
International
Class: |
H04J 15/00 20060101
H04J015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2004 |
JP |
2004-193354 |
Claims
1. A wireless communication method for communicating between a base
station and a plurality of terminals using a plurality of channels,
the channels being slots obtained by dividing frequency-divided
carriers by time, characterized in that the base station allocates
a set of the channels which is composed of a plurality of
neighboring carriers and/or a plurality of successive slots for the
each terminal; and the base station allocates at least one of the
channels included in the channel sets for packet transmission to
the terminals.
2. The wireless communication method according to claim 1, wherein
the base station allocates the channels for the packet transmission
to the terminals by using results of channel state estimation
received from the terminals.
3. The wireless communication method according to claim 1, wherein
the base station sends notification of the channel sets to the
terminals.
4. The wireless communication method according to claim 3, wherein
each of the terminal receives the notification of the channel set
and determines which channels to monitor according to the channel
set notified.
5. The wireless communication method according to claim 1, wherein
the base station receives receiving abilities of the terminals and
allocates the channel sets to satisfy the receiving abilities.
6. The wireless communication method according to claim 1, wherein
the base station calculates deviations of the channels and
re-allocates the channel sets when the deviations are larger than a
predetermined value.
7. The wireless communication method according to claim 1, wherein
the base station receives receiving abilities of the terminals from
a base station controller that stores the receiving abilities of
the terminals.
8. A wireless base station for communicating between a base station
and a plurality of terminals using a plurality of channels, the
channels being slots obtained by dividing frequency-divided
carriers by ime, characterized in that the wireless base station
comprising: an information storage which stores information to be
transmitted to the terminals; a scheduler which determines a
destination terminals of the information; a modulator which
modulates signal according to the information to be transmitted; a
transmitter which transmits the modulated signal; and a channel
condition control unit which obtains receiving abilities of the
terminals, wherein a channel condition module allocates channel
sets each composed of a plurality of neighboring carriers and/or a
plurality of successive slots to satisfy the receiving abilities,
and stores the allocated channel sets.
9. The wireless base station according to claim 8, further
comprising a receiver which receives signals from the terminals,
wherein the wireless base station obtains the receiving abilities
from received signals sent from the terminals.
10. The wireless base station according to claim 8, further
comprising a receiver which receives signals from the terminals,
wherein the wireless base station obtains the receiving abilities
of the terminals from a base station controller that stores the
receiving abilities of the terminals.
11. The wireless base station according to claim 8, wherein the
scheduler allocates the channels included in the channel sets for
packet transmission to the terminals.
12. The wireless base station according to claim 8, further
comprising a control signal generator that generates a signal for
notifying the terminals of the channel sets.
13. A wireless communication terminal for communicating between a
base station and a plurality of terminals using a plurality of
channels, the channels comprising slots obtained by dividing
frequency-divided carriers by time, the wireless communication
terminal comprising: a receiver including a filter that extracts a
signal of particular frequencies from a signal received at an
antenna and an A/D converter that converts the signal to a digital
signal; a baseband unit which separates the signal into frequency
portions and demodulates the signal; and a controller that controls
an operation of the entirety of the wireless communication
terminal, wherein the receiver receives, from the base station, an
allocated channel set composed of a plurality of neighboring
carriers and/or a plurality of successive slots and notifies the
controller of the received channel set, and wherein the controller
which changes, according to the channel set, at least one of a
frequency range and a center frequency of the filter.
14. The wireless communication terminal according to claim 13,
further comprising a transmitter which modulates according to
information to be transmitted to the base station and transmits the
signal, wherein the controller generates notification of an ability
control signal including a receiving ability, and wherein the
transmitter transmits the ability control signal to the base
station.
15. The wireless communication terminal according to claim 13,
wherein the controller controls the receiver to operates in
channels included in the channel set and to be idle in channels not
included in the channel set.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese
application P2004-193354 filed on Jun. 30, 2004, the content of
which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a mobile wireless communication
system including a wireless base station and wireless communication
terminals, and more particularly to a technique for packet
scheduling.
[0003] In the downlink communication (from a base station to a
mobile station) in the cdma2000 1x-EV DO system, the base station
divides time into units (slots) of 1/600 second, and the base
station communicates only with a single mobile station in one slot
(channel) at a certain frequency and switches the communicating
station for each channel to communicate with a plurality of mobile
stations.
[0004] Mobile stations receive pilot signals from the base station,
estimate channel states from the pilot signals, and send the
results of channel state estimation (channel state information) to
the base station. The base station determines, on the basis of the
received channel state information, to which mobile station the
next channel should be allocated for packet transmission. The
allocation of channels is called packet scheduling. The packet
scheduling will be described referring to FIG. 30.
[0005] FIG. 30 shows a conventional channel schedule table, where
the vertical axis shows time and the horizontal axis shows
frequency. The frequency band is divided into carriers F1 to F4 and
a certain length of time is divided into slots S1 to S8, so as to
form time- and frequency-divided channels.
[0006] A mobile station A determines which of the carriers F1 to F4
it should use for communication. Specifically, the mobile station A
monitors a reference first carrier stored in SRAM of the mobile
station A and judges from broadcast information whether the first
carrier is filled up by other mobile stations. When the first
carrier is not filled, the mobile station A sends its own control
information to the base station to register its position.
[0007] On the other hand, when the first carrier is filled up, the
mobile station A monitors another, second carrier. Similarly, when
the second carrier is filled, the mobile station A monitors a third
carrier, so as to determine which carrier to use for
communication.
[0008] In this example, the mobile station A determines to
communicate on the carrier F1. Then, the mobile station A estimates
channel states of the individual slots S1 to S8 of the carrier F1
and sends the channel state information to the base station. As
stated earlier, the base station allocates channels on the basis of
the channel state information from each mobile station. As for the
mobile station A, the base station judges that the channel state of
the slot S3 is good and allocates (schedules) the channel of the
slot S3 of the carrier F1 for the mobile station A.
[0009] The mobile station A may communicate using a plurality of
carriers. For example, JP 2003-9240 A describes a technique in
which a mobile station A communicates using a plurality of
carriers. The technique will be described referring to FIG. 31.
[0010] FIG. 31 shows a conventional channel schedule table, where
the vertical axis shows time and the horizontal axis shows
frequency.
[0011] The base station communicates with a plurality of mobile
stations using carriers F1 to F8. Here, the base station and the
mobile station A communicate at a low rate.
[0012] First, the base station determines to allocate three
carriers to the mobile station A for communication. The base
station may allocate the plurality of carriers F1, F4, and F8 to
the mobile station A so that the frequency differences between the
allocated carriers exceed a predetermined value. After that, the
base station sends packets to the mobile station A using the
carrier F1, the carrier F4, and the carrier F8. In this case, the
mobile station A sends, to the base station, channel state
information for each of the slots S1 to S8 on the carriers F1, F4,
and F8. The base station performs scheduling on the basis of the
channel state information from each mobile station. The base
station judges that the channel states of the channel of the slot
S3 of the carrier F1, the channel of the slot S4 of the carrier F4,
and the channel of the slot S7 of the carrier F8 are good and
schedules these channels for the mobile station A. The base station
then sends packets to the mobile station A over the scheduled
channels.
SUMMARY OF THE INVENTION
[0013] According to the conventional technique above, the mobile
station has to monitor a wide frequency band because the plurality
of carriers are allocated such that frequency differences between
the allocated carriers are over a predetermined value. This
requires that the mobile station be equipped with a plurality of RF
units or a wideband RF unit, for separation of carriers in the
baseband unit. Then the mobile station requires a large circuit
scale and consumes increased power.
[0014] An object of this invention is to reduce power consumption
of a mobile station while suppressing its circuit scale.
[0015] The embodiment of this invention provides a wireless
communication method for communicating between a base station and a
plurality of terminals using a plurality of channels, the channels
being slots obtained by dividing frequency-divided carriers by
time, characterized in that the base station allocates a set of the
channels which is sets each composed of at least a plurality of
neighboring carriers and/or a plurality of successive slots for the
each terminal; and the base station allocates at least one of the
channels included in the channel sets for packet transmission to
the terminals.
[0016] According to the embodiment of this invention, it is
possible to reduce power consumption of a mobile station.
[0017] This invention is applicable to carrier scheduling in mobile
communication systems and can be advantageously applied to a system
in which high-rate and low-rate mobile stations are present
together. Also, while the embodiments have shown examples adopting
the FDMA and OFDMA, this invention is applicable also to other
multiplexing systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The present invention can be appreciated by the description
which follows in conjunction with the following figures,
wherein:
[0019] FIG. 1 is a diagram showing a configuration of a wireless
communication system according to an embodiment of this
invention;
[0020] FIG. 2 is a block diagram of a base station according to a
first embodiment of this invention;
[0021] FIG. 3 is a block diagram of a mobile station according to
the first embodiment of this invention;
[0022] FIGS. 4A to 4D show spectra exhibited during a process of
extracting a signal of a particular carrier according to the first
embodiment of this invention;
[0023] FIG. 5 is a sequence chart of a channel set allocation
process according to the first embodiment of this invention, where
a mobile station A reports its receiving ability;
[0024] FIG. 6 is a sequence chart of a packet scheduling process
performed in the channel set allocation process according to the
first embodiment of this invention;
[0025] FIG. 7 is a channel schedule table according to the first
embodiment of this invention, where a channel set is allocated on
the basis of frequency;
[0026] FIG. 8 is a channel timing chart according to the first
embodiment of this invention;
[0027] FIG. 9 is a flowchart of a scheduling process according to
the first embodiment of this invention;
[0028] FIG. 10 is a flowchart of a process performed by the base
station after the scheduling process according to the first
embodiment of this invention;
[0029] FIG. 11 is a flowchart of a channel state estimation process
according to the first embodiment of this invention;
[0030] FIG. 12 is a flowchart of a scheduling result receiving
process according to the first embodiment of this invention;
[0031] FIG. 13 is a flowchart of a packet receiving process
according to the first embodiment of this invention;
[0032] FIG. 14 is a sequence chart of a channel set allocation
process according to the first embodiment of this invention, where
the mobile station A reports a change of its receiving ability;
[0033] FIG. 15 is a channel set sequence chart according to the
first embodiment of this invention, where the base station takes
the leadership;
[0034] FIG. 16 is a channel schedule table according to the first
embodiment of this invention, where a channel set is allocated on
the basis of time;
[0035] FIG. 17 is a channel timing chart according to the first
embodiment of this invention, where a channel set is allocated on
the basis of time and a result of scheduling is reported;
[0036] FIG. 18 is a flowchart of a channel state estimation process
according to the first embodiment of this invention, where a
channel set is allocated on the basis of time;
[0037] FIG. 19 is a flowchart of a scheduling result receiving
process according to the first embodiment of this invention, where
a channel set is allocated on the basis of time;
[0038] FIG. 20 is a flowchart of a packet receiving process
according to the first embodiment of this invention, where a
channel set is allocated on the basis of time;
[0039] FIG. 21 is a channel schedule table according to the first
embodiment of this invention, where a channel set is allocated on
the basis of frequency and time;
[0040] FIGS. 22A to 22C are graphs showing carrier channel states
according to the first embodiment of this invention;
[0041] FIG. 23 is a sequence chart of a packet scheduling process
according to a second embodiment of this invention;
[0042] FIG. 24 is a channel timing chart according to the second
embodiment of this invention;
[0043] FIG. 25 is a channel timing chart according to the second
embodiment of this invention, where a channel set is allocated on
the basis of time and the result of scheduling is not reported;
[0044] FIG. 26 is a block diagram of a base station 200 according
to a third embodiment of this invention;
[0045] FIG. 27 is a channel set sequence chart according to the
third embodiment of this invention;
[0046] FIG. 28 is a block diagram of a mobile station according to
a fourth embodiment of this invention;
[0047] FIGS. 29A to 29D show spectra exhibited during a process of
extracting a signal of a particular carrier according to the fourth
embodiment of this invention;
[0048] FIG. 30 is a conventional channel schedule table; and
[0049] FIG. 31 is a channel schedule table described in JP
2003-9240 A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] Embodiments of this invention will be described below
referring to the drawings.
[0051] FIG. 1 is a diagram showing a configuration of a wireless
communication system according to a first embodiment of this
invention.
[0052] The wireless communication system of the embodiment includes
a base station 200, a mobile station A201(A), a mobile station
B201(B), a mobile station C201(C), a mobile station D201(D), and a
mobile station E201(E). The mobile station A201(A), the mobile
station B201(B), the mobile station C201(C), the mobile station
D201(D), and the mobile station E201(E) are within an area where
they can communicate with the base station 200.
[0053] All mobile stations 201 receive pilot signals from the base
station 200, estimate channel states of the downlinks (from the
base station to the mobile stations), and send the estimated
channel states (channel state information 203) to the base station
200. The base station 200 performs scheduling on the basis of the
channel state information 203 from the mobile stations 201. The
base station 200 sends packets to the mobile stations 201 according
to the scheduling (204).
[0054] FIG. 2 is a block diagram of the base station 200 of the
first embodiment.
[0055] An antenna 207 transmits or receives signals to or from the
mobile stations 201. A circulator 208 sends signals received at the
antenna 207 to a receiver 209 and sends transmit signals generated
in a transmitter 215 to the antenna 207.
[0056] The receiver 209 performs high-frequency and
intermediate-frequency amplification, detection, etc., and converts
a radio signal into a baseband signal. After that, the receiver 209
performs baseband signal demodulation, decoding, and error
correction. Then, when a signal from the antenna is receiving
ability information (MSAI) about a mobile station, the receiver 209
sends the information to a channel condition control unit 210, and
when the signal is channel state information (CSI), the receiver
209 sends the information to a scheduler 213, and when the signal
is user data, the receiver 209 sends the data through a network
interface 211.
[0057] The channel condition control unit 210 allocates channel
sets, as will be described later, on the basis of the receiving
ability information about mobile stations, and stores information
about the allocated channel sets (CCI). Also, the channel condition
control unit 210 sends the channel set information to the scheduler
213 when needed.
[0058] An information storage 212 obtains, from a network and
through the network interface 211, mobile station user data and
signals to be transmitted to the mobile stations, and stores the
data and signals. Also, the information storage 212 generates and
stores management information (TD) for the mobile stations using
past mean transmission rates of the mobile stations, and the like.
Also, the information storage 212 sends, to a modulator 214, the
stored mobile station user data and the stored signals to be
transmitted to the mobile stations.
[0059] The scheduler 213 performs scheduling on the basis of the
channel set information, referring to the channel state information
and the management information about the mobile stations. Then,
according to the scheduled packet transmitting timing, the
scheduler 213 sends coding information (MI) about the mobile
stations, information about signal transmitting carriers (F/S),
etc., to the information storage 212 and to the modulator 214.
[0060] A control signal generator 216 generates information for
controlling the transmitter 215 and sends the information to the
modulator 214.
[0061] The modulator 214 encodes a signal transmitted to a mobile
station on the basis of the coding information about the mobile
station, the information about transmitting carriers, etc. from the
scheduler. Also, the modulator 214 multiplexes the signal with the
control information from the control signal generator 216. The
modulator 214 then sends the multiplexed signal to the transmitter
215. The transmitter 215 converts the signal to an RF signal and
transmits the signal to the mobile station 201 through the
circulator 208 and from the antenna 207.
[0062] FIG. 3 is a block diagram of a mobile station according to
the first embodiment, which shows a configuration for FDMA.
[0063] An antenna 233 transmits or receives signals to or from the
base station 200. A circulator 217 provides signals received at the
antenna 233 to a radio receiver 218 and provides transmit signals
generated in a radio transmitter 228 to the antenna 233.
[0064] A receiving RF unit 230 includes the radio receiver 218, a
filter 219, an A/D converter 220, and a generator 231.
[0065] The generator 231 generates a high-frequency signal at a
particular frequency (a local oscillator signal) and provides the
signal to the radio receiver 218. The radio receiver 218 converts
frequencies of signals from the base station 200 using the local
oscillator signal.
[0066] The filter 219 removes unwanted frequency components other
than the signals from the base station 200 that have been converted
in frequency. The filter 219 may be capable of switching filters
219 for extracting different frequency ranges so that different
filters can be used for signals of different data transmission
rates (or according to the signal bandwidth) (e.g. when different
filters are used for call service and broadband communication
service). The A/D converter 220 converts the signal from the filter
to a digital signal.
[0067] A baseband processing unit 229 includes a filter bank 221, a
demodulator 222, a selector 223, and a channel state estimator
224.
[0068] The filter bank 221 extracts signals of individual carriers
from the digital-converted signal, using filters appropriate for
the carriers. Also, the filter bank 221 sends the extracted signals
of individual carriers to the demodulator 222 and the channel state
estimator 224.
[0069] The demodulator 222 demodulates the sent signals of
individual carriers. The selector 223 extracts destination
information from the demodulated signals, and when the own mobile
station is the destination, the selector 223 sends the signal to a
CPU 225. On the other hand, when the own mobile station is not the
destination, the selector 223 discards the signal.
[0070] The channel state estimator 224 estimates channel states
(S/I) from pilot signals inserted in signals of individual
carriers. However, as will be described later, the channel state
estimator 224 estimates channel states only about carriers
allocated as a channel set. This is because no packets are
transmitted on channels of other carriers.
[0071] When the mobile station 201 further obtains a data
transmission rate, the channel state estimator 224 obtains the data
transmission rate by referring to a table in which the channel
state information and data transmission rate are associated with
each other.
[0072] The CPU 225, controlling the entirety of the receiver 201,
controls reception or transmission of information from or to the
base station 200. The CPU 225 may be equipped with a timer. The
timer manages operating/idle times of the receiver. In an idle
period, the CPU 225 provides control to cut off the power to the RF
unit 230, the baseband processing unit 229, and a signal
transmitter unit 234. On the other hand, immediately before a
switch to an operating time, the CPU 225 provides control to supply
power to the RF unit 230, the baseband processing unit 229, and the
signal transmitter unit 234.
[0073] The signal transmitter unit 234 includes a modulator 226, a
D/A converter 227, and the radio transmitter 228.
[0074] The modulator 226 generates a modulated signal on the basis
of information input from the CPU 225 that is to be transmitted to
the base station, information about transmitting carriers (CI),
user ID (UI), and channel state (CSI) input from the channel state
estimator 224. The D/A converter 227 converts the modulated signal,
generated by the modulator 226, to an analog signal. The radio
transmitter 228 converts the analog-converted signal to the
frequency of the carrier sent to the base station and amplifies the
signal to required power. The amplified signal is transmitted to
the base station 200 from the antenna 233 through the circulator
217.
[0075] FIGS. 4A to 4D show spectra exhibited during a process of
extracting a signal of a particular carrier in the first
embodiment.
[0076] The antenna 233 receives a signal having a spectrum as shown
in FIG. 4A. The signal received at the antenna 233 includes signals
on all carriers.
[0077] With this signal, the filter 219, shown by the bold line in
FIG. 4B, extracts carriers necessary for the mobile station.
Specifically, as will be described later, the filter 219 extracts
signals such that all carriers in the allocated channel set are
included. Therefore, the output from the filter 219 is a wideband
signal including a plurality of carriers (e.g. in this embodiment,
a signal of a band including three carriers).
[0078] FIG. 4C shows the signal extracted by the filter. The filter
bank 221 has filters adapted to individual carriers as shown by
bold lines in FIG. 4C and extracts signals for the individual
carriers. FIG. 4D shows the spectrum of one of the signals of the
extracted carriers.
[0079] FIG. 5 is a sequence chart of a process of allocating a
channel set according to the first embodiment, which shows an
example in which the mobile station A reports the receiving
ability.
[0080] The receiving ability is the ability by which the mobile
station A201(A) communicates with the base station 200, which can
be a maximum communication rate of the mobile station A201(A), for
example.
[0081] The description below shows an example in which the mobile
station A201(A) uses a narrow band and a low rate.
[0082] First, the mobile station A201(A) notifies the base station
200 of the receiving ability using a control channel (309). For
example, the notification may be performed when the mobile station
A201(A) is powered up, or when the mobile station A201(A) starts
communication with the base station 200, and this shows an example
in which the mobile station A201(A) takes the leadership in the
channel set allocation.
[0083] The base station 200 receives the receiving ability of the
mobile station A201(A) (310) and allocates a channel set to satisfy
the receiving ability. As will be described in detail later, the
channel set means a plurality of channels in a sub-band formed of
carriers that are continuous on the frequency axis and/or a
sub-frame formed of slots that are continuous on the time axis.
[0084] The base station 200 notifies the mobile station A201(A) of
the allocated channel set using a control channel (312). Then, in
the subsequent communication with the mobile station A201(A), the
base station 200 performs packet scheduling using the allocated
channel set only (300). As will be described later, packet
scheduling methods include a method in which the mobile station
A201(A) is notified of the result of scheduling and a method in
which the mobile station A201(A) is not notified of the result.
[0085] The mobile station A201(A) receives the channel-set
notification (313) and then monitors only the allocated channel set
in the subsequent communication to receive packets from the base
station 200.
[0086] FIG. 6 is a sequence chart of the packet scheduling process
performed in the step 300 of the channel set allocation process
shown in FIG. 5, which shows an example in which the result of
scheduling is reported.
[0087] The base station 200 transmits pilot signals with constant
timing within the communicable area.
[0088] The mobile station A201(A) receives a pilot signal from the
base station 200 and estimates the channel state from the pilot
signal (301). For example, the channel state is estimated from
receive field strength (RSSI), carrier signal to interference wave
ratio (CIR), desired wave to interference wave ratio (SIR),
etc.
[0089] The mobile station A201(A) transmits the result of estimated
channel state (channel state information) to the base station 200
(302). The base station 200 receives the channel state information
(303) and allocates channels (performs scheduling) for packet
transmission on the basis of the channel state information (304).
During the scheduling, the base station 200 calculates an
evaluation function described later and allocates channels to
mobile stations of highest evaluation function values. The base
station 200 then notifies the mobile station A201(A) of the result
of the scheduling (305).
[0090] The mobile station A201(A) receives the result of the
scheduling (306). Then, according to the result of the scheduling,
the mobile station A201(A) waits for reception in the channels in
which the base station 200 transmits packets.
[0091] The base station 200 transmits packets on the scheduled
channels (307) and the mobile station A201(A) receives the packets
(308).
[0092] FIG. 7 shows a channel schedule table in an example of the
first embodiment in which a channel set is allocated on the basis
of frequency, where the vertical axis shows time and the horizontal
axis shows frequency.
[0093] The base station 200 communicates with a plurality of mobile
stations 201 using the carriers F1 to F8. The mobile station
A201(A) and the base station 200, which communicate at a low rate,
do not have to perform communication using all carriers.
[0094] Accordingly, the base station 200 allocates to the mobile
station A201(A) a channel set including the three carriers F6 to F8
at continuous frequencies. A plurality of carriers of continuous
frequencies, like the carriers F6 to F8, are called a sub-band. The
allocation of a channel set is achieved by determining the number
of carriers used for communication on the basis of the data
transmission rate between the mobile station 201 and the base
station 200.
[0095] The base station 200 transmits packets in the allocated
channel set, without scheduling the other carriers F1 to F5 for the
mobile station A201(A). Therefore, the mobile station A201(A)
monitors only a sub-band 101 (the carriers F6 to F8) in the
allocated channel set.
[0096] Specifically, the base station 200 transmits packets to the
mobile station A201(A) over the channel of the slot S3 of the
carrier F7, the channel of the slot S4 of the carrier F6, and the
channel of the slot S7 of the carrier F8 that are scheduled for the
mobile station A201(A).
[0097] FIG. 8 is a channel timing chart of the first embodiment.
The hatched portions in FIG. 8 show timing of communication between
the base station 200 and the mobile station A201(A).
[0098] The base station 200 transmits a pilot signal (Pilot) (500).
The mobile station A201(A) receives the pilot signal and estimates
the channel state from the received pilot signal. Then, the mobile
station A201(A) transmits the channel state information (CSI) to
the base station 200 in the slot next to the reception of the pilot
signal (501).
[0099] The base station 200 receives the channel state information
and performs scheduling. Then, the base station 200 transmits the
result of scheduling (RI) to the mobile station A201(A) in the slot
next to the reception of the channel state information (502). In
this process, in order to reduce overhead caused by the
transmission of the scheduling result, the base station 200
transmits the RI with increased spreading rate and reduced
transmission power, or transmits the RI by intermittent
transmission in a reduced transmission time.
[0100] Then, the base station 200 transmits data (Data) to the
mobile station A201(A) with the scheduled timing (503).
[0101] FIG. 9 is a flowchart of a scheduling process according to
the first embodiment, which is performed by the base station
200.
[0102] The base station 200 selects one of the plurality of
carriers (401). Next, the base station 200 specifies mobile
stations 201 allocated to the selected carrier by referring to the
channel condition module 210 (402). The channel condition module
210 allocates channel sets to all mobile stations 201 that
communicate with the base station 200 and stores the allocated
channel sets.
[0103] The base station 200 receives the channel state information
about the selected carrier for all of the specified mobile stations
and calculates the evaluation function (403).
[0104] For example, the calculation of the evaluation function uses
proportional fairness, according to Expression 1. .PHI.=DRC/R
[Expression 1]
[0105] Where DRC represents a data transmission rate based on the
channel state information from the mobile station 201. The DRC can
be determined by either of the base station 200 and the mobile
station 201. When the base station 200 receives channel state
information from a mobile station 201, the base station 200 refers
to a table associating the channel state information and the DRC to
obtain the DRC of that mobile station 201. Alternatively, the base
station 200 may receive DRC that the mobile station 201 has
obtained by referring to a given table.
[0106] The base station 200 divides DRC by the past mean data
transmission rate (R) of the corresponding mobile station 201. This
value is the evaluation function, which allows a judgement as to
whether the DRC is higher or lower as compared with the past mean
transmission rate. By making the allocation on the basis of the
evaluation function, the base station 200 can perform scheduling
while keeping fairness among all mobile stations 201.
[0107] The base station 200 compares evaluation function values of
all mobile stations 201 specified in the step 402, selects a mobile
station 201 with the highest evaluation function value, and
performs scheduling to that mobile station 201 (404). Through these
operations, the base station 200 completes the scheduling of the
selected carrier. The base station 200 then checks whether all
carriers have been selected, and when all carriers have not been
selected yet, the base station 200 performs scheduling of a carrier
not selected yet (405). When all carriers have been selected, the
scheduling about this slot is completed.
[0108] FIG. 10 is a flowchart of a process performed by the base
station 200 after the scheduling process of the first
embodiment.
[0109] The base station 200 selects one of the plurality of
carriers (406). Next, using the scheduling about the selected
carrier, the base station 200 obtains information about the mobile
station 201 to which a packet is transmitted, such as the ID and
data transmission rate of the mobile station 201 (407).
[0110] Also, the base station 200 obtains, using the information
storage 212, data to be transmitted to the mobile station 201 and
information about the selected carrier (408). Since the amount of
transmitted data depends on the data transmission rate, the
scheduler 213 indicates the data transmission rate to the modulator
214 (409). The modulator 214 then informs the information storage
212 of the amount of information to be sent to the modulator 214
per unit time.
[0111] The base station 200 checks whether all carriers have been
selected, and when all carriers have not been selected yet, the
base station 200 makes preparations for packet transmission over a
carrier not selected yet (405). When all carriers have been
selected, the preparations for packet transmission about this slot
are completed.
[0112] On the basis of these pieces of information, the base
station 200 transmits data to scheduled mobile stations 201 over
the channels of the selected carriers. The base station 200
transmits, to the mobile stations 201, data modulated according to
a proper modulation method on the basis of the channel state
information.
[0113] FIG. 11 is a flowchart of a channel state estimation process
according to the first embodiment, which is performed by the mobile
station A201(A).
[0114] The channel state estimation process is started and
performed with an interrupt timed for each slot. First, the mobile
station A201(A) checks whether there is any information to be
received from the base station 200 (411). That is, the mobile
station A201(A) checks whether it is being connected with the base
station. When there is no information to be received, the mobile
station A201(A) ends the process about this slot. On the other
hand, when there is information to be received (when it is in a
connected state), the mobile station A201(A) receives a pilot
signal of an allocated carrier by using hardware designed to
monitor carriers of the allocated channel set (412). For example,
the hardware is implemented with an FIR filter that performs
in-phase addition process of the pilot signal after FFT. Also in
the frequency direction, when frequency correlation is high (when
multi-path delay spread is small), correlation between adjacent
sub-channels is high and so in-phase addition is possible.
[0115] Then, the mobile station A201(A) estimates the channel state
of the allocated carrier from the received pilot signal (413). Now,
the mobile station A201(A) may further obtain a data transmission
rate from the estimated channel state by referring to a table
associating the channel state and the DRC. The mobile station
A201(A) transmits, to the base station 200, the result of channel
state estimation (channel state information) about the allocated
carrier, or the data transmission rate.
[0116] FIG. 12 is a flowchart of a process of receiving a result of
scheduling according to the first embodiment, which is performed by
the mobile station A201(A).
[0117] After transmitting the channel state information, the mobile
station A201(A) checks whether a result of scheduling has been sent
from the base station 200 (414). When no scheduling result has been
sent from the base station 200, the mobile station A201(A) ends the
scheduling result receiving process. On the other hand, when a
scheduling result has been sent from the base station 200, the
mobile station A201(A) checks the scheduling about the carriers of
the allocated channel set from the received scheduling result
(415).
[0118] The mobile station A201(A) checks whether the base station
200 sends a packet on a carrier allocated to the mobile station
A201(A) (416). When no packet is sent from the base station 200,
the mobile station A201(A) ends the scheduling result receiving
process. On the other hand, when the base station 200 sends a
packet, the mobile station A201(A) reserves packet reception in the
channel of the corresponding slot and corresponding carrier on the
basis of the scheduling result (417).
[0119] FIG. 13 is a flowchart of a packet receiving process
according to the first embodiment, which is performed by the mobile
station A201(A).
[0120] This receiving process is started and performed with an
interrupt timed for each slot. First, the mobile station A confirms
the scheduling reserved in the step 417 and checks whether there is
information to be received (418). When there is no information to
be received, the mobile station A201(A) ends the packet receiving
process in this slot. On the other hand, when there is information
to be received, the mobile station A201(A) receives the packet over
the scheduled channel (419).
[0121] While the description above has shown a packet scheduling
process that is performed when the mobile station is powered up and
starts operating, a similar packet scheduling process is performed
also when the mobile station 201 reports a change of its receiving
ability, as shown in FIG. 14.
[0122] FIG. 14 is a sequence chart of a channel set allocation that
is performed when the mobile station A201(A) of the first
embodiment reports a change of its receiving ability.
[0123] The change of receiving ability of the mobile station
A201(A) means a change of the data transmission rate of the mobile
station A201(A) that takes place, for example, when the mobile
station A201(A) switches from a voice call to a broadband
communication. Such a change is usually made after the call has
ended, but no problem arises when the change is made during the
communication. When the communication is switched to a
videoconference during a voice call, for example, the data
transmission rate must be changed during the call, and this
embodiment allows the data transmission rate to be changed as
desired. In this invention, absence of this procedure of making a
change during communication may cause inconvenience in use, because
the band is changed depending on the processing ability of the
mobile station and the service used. This embodiment solves this
problem. The example above has shown a change from narrowband to
wideband, it is clear that the same is true also with a change from
wideband to narrowband.
[0124] The mobile station A201(A) notifies the base station 200 of
the change of receiving ability through a control channel
(314).
[0125] The base station 200 receives the change of receiving
ability of the mobile station A201(A) (315) and allocates a channel
set that satisfies the changed receiving ability (311). The base
station 200 notifies the mobile station A201(A) of the allocated
channel set using a control channel (312). The base station 200
then performs packet scheduling only about the allocated channel
set (300).
[0126] The mobile station A201(A) receives the channel-set
notification (313). The mobile station A201(A) then monitors only
the allocated channel set in the subsequent communication to
receive packets from the base station 200.
[0127] Receiving the channel-set notification, the mobile station
A201(A) changes the local oscillating frequency outputted from the
generator 231. Also, when the mobile station A201(A) changes the
band depending on the received signal, the mobile station A201(A)
switches the band limiting filter 219 and varies the sampling clock
supplied to the A/D converter 220. Also, the filter bank 221 of the
mobile station A201(A) changes the number of filters used for
monitoring.
[0128] While an example of the first embodiment has been shown in
which the mobile station 201 takes the leadership in the channel
set allocation, the base station 200 may take the leadership in the
channel set allocation.
[0129] FIG. 15 is a channel-set sequence chart in an example in
which the base station 200 of the first embodiment takes the
leadership.
[0130] The base station 200 measures a utilization rate for each
channel and detects a channel deviation (316). The channel
deviation shows non-uniformity of channel utilization rates, where
a larger channel deviation lowers the channel utilization rate.
[0131] The base station 200 allocates a channel set to an arbitrary
mobile station 201 in a manner that reduces the channel deviation
(311). For example, the base station 200 notifies the mobile
station A201(A) of a change of channel set (312). The mobile
station A201(A) receives the channel-set notification (313). Then,
the base station 200 performs packet scheduling only about the
allocated channel set (300).
[0132] The mobile station A201(A) receives the channel-set
notification (313). The mobile station A201(A) then monitors only
the allocated channel set in the subsequent communication to
receive packets from the base station 200.
[0133] While this embodiment has so far shown examples in which
channel sets are allocated on the basis of frequency, channel sets
may be allocated on the basis of time in the first embodiment.
[0134] FIG. 16 is a channel schedule table in an example of the
first embodiment in which a channel set is allocated on the basis
of time, where the vertical axis shows time and the horizontal axis
shows frequency.
[0135] The base station 200 transmits packets to all mobile
stations 201 by using the entire frame including the slots S1 to
S8. In FIG. 11, when the base station 200 and the mobile station
A201(A) communicate at a low rates the base station 200 allocates
carriers for communication to the mobile station A201(A), but the
base station 200 may allocate time (slots) for communication in
order to reduce power consumption.
[0136] The base station 200 allocates to the mobile station A201(A)
the two slots S2 and S3 that are continuous in time. Here, a group
of time-continuous plural slots, like S2 and S3, is called a
sub-frame 102.
[0137] The base station 200 transmits packets to the mobile station
A201(A) in the slots of the allocated channel sets. Specifically,
in the first frame, the base station 200 transmits packets to the
mobile station A201(A) over the carrier-F3 slot-S2 channel and the
carrier-F1 slot-S3 channel. In the next frame, the base station 200
transmits packets to the mobile station A201(A) over the carrier-F6
slot-S2 channel and the carrier F8 slot-S3 channel.
[0138] In this process, the mobile station A201(A) does not cause
its circuitry to uselessly operate in the slots not allocated (S1
and S4 to S8), thereby achieving reduction of power
consumption.
[0139] When starting operation, the mobile station A201(A) must
perform overhead processing, such as initialization, and therefore
allocating discontinuous slots causes power consumption for
initialization etc. for every allocated slot. In order to reduce
such power consumption, the base station 200 allocates continuous
slots to the mobile station A201(A). That is, though the mobile
station A201(A) has to perform initialization for the slot S2, it
does not have to perform initialization for the slot S3, and
allocating continuous slots thus reduces power consumption.
[0140] FIG. 17 is a channel timing chart according to the first
embodiment, which shows an example in which a channel set is
allocated on the basis of time and the result of scheduling is
reported. The portions surrounded by bold lines indicate slots in
which the base station 200 and the mobile station A201(A) associate
with each other. The hatched portion shows a slot 514 in which the
base station 200 transmits a packet to the mobile station
A201(A).
[0141] The channel set is allocated on the basis of time and so the
mobile station A201(A) receives packets only in the channel-set
sub-frame 513. Therefore, the mobile station A201(A) estimates the
channel state using the pilot signal 510 that precedes the
sub-frame 513 by a given number of slots (e.g. six slots).
[0142] The mobile station A201(A) transmits the result of channel
state estimation (channel state information) to the base station
200 in the slot next to the reception of the pilot signal 510
(511). The base station 200 performs scheduling on the basis of the
channel state information and transmits the result of scheduling to
the mobile station A201(A) (512). The base station 200 transmits
data to the mobile station A201(A) according to the scheduling
(514).
[0143] FIG. 18 is a flowchart of a channel state estimation process
according to the first embodiment where a channel set is allocated
on the basis of time, which is performed by the mobile station
A201(A) in place of the process of FIG. 11.
[0144] The channel state estimation process is started and
performed with an interrupt timed for each slot. First, the mobile
station A201(A) checks whether it is time to receive a pilot signal
(420). The reception of pilot signal (e.g., 510 in FIG. 17) is
timed to precede the allocated channel-set sub-frame (e.g., 513 in
FIG. 17) by a given length of time (e.g. six slots).
[0145] When it is not time to receive a pilot signal, the mobile
station A201(A) ends the channel state estimation process. On the
other hand, when it is time to receive a pilot signal, the mobile
station A201(A) checks whether there is information to be received
in this slot (421).
[0146] When the check shows that there is no information to be
received, the mobile station A201(A) ends the channel state
estimation process. On the other hand, when there is information to
be received, the mobile station A201(A) receives the pilot signal
of the allocated carrier (422). The mobile station A201(A) then
estimates the channel state of the allocated carriers from the
received pilot signal (423).
[0147] FIG. 19 is a flowchart of a scheduling result receiving
process according to the first embodiment where a channel set is
allocated on the basis of time, which is performed by the mobile
station A201(A) in place of the process of FIG. 12.
[0148] After transmitting the channel state information, the mobile
station A201(A) checks whether it is time to receive a result of
scheduling from the base station 200 (424). The reception of a
scheduling result (e.g., 512 in FIG. 17) is timed to be a given
time (one slot) after the transmission of the channel state
information (511 in FIG. 17).
[0149] When it is not time to receive a scheduling result, the
mobile station A201(A) ends the scheduling result receiving
process. On the other hand, when it is time to receive a scheduling
result, the mobile station A201(A) receives a scheduling result and
checks the scheduling of the allocated carriers (all carriers when
the channel set is not allocated on the basis of frequency)
(426).
[0150] The mobile station A201(A) checks whether the base station
200 transmits a packet over the allocated carriers (427). When no
packet is transmitted from the base station 200, the mobile station
A201(A) ends the scheduling result receiving process. On the other
hand, when the base station 200 sends a packet, the mobile station
A201(A) reserves reception of the packet in the channel of the
corresponding slot and the corresponding carrier, on the basis of
the scheduling result (428).
[0151] FIG. 20 is a flowchart of a packet receiving process
according to the first embodiment where a channel set is allocated
on the basis of time, which is performed by the mobile station
A201(A) in place of the process of FIG. 13.
[0152] This receiving process is started and performed with an
interrupt timed for each slot. First, the mobile station A201(A)
checks whether the slot is in the sub-frame of the allocated
channel set (e.g., 513 in FIG. 17) (429).
[0153] When it is not in the sub-frame, the mobile station A201(A)
ends the packet receiving process in this slot. On the other hand,
when it is in the sub-frame, the mobile station A201(A) powers up
packet receiving hardware and receives the packet over the
allocated channel (430).
[0154] Also, in the first embodiment, a channel set may be
allocated on the basis of both of frequency and time.
[0155] FIG. 21 is a channel schedule table according to the first
embodiment, in the case where a channel set is allocated on the
basis of frequency and time. In the channel schedule table, the
vertical axis shows time and the horizontal axis shows
frequency.
[0156] When the base station 200 and the mobile station A201(A)
perform low-rate communication, the base station 200 allocates to
the mobile station A201(A) a channel set 103 including the carriers
F6 to F8 and the times S2 and S3.
[0157] Subsequently, as described earlier, the base station 200
transmits packets to the mobile station A201(A) in the allocated
channel sets. Specifically, in the first frame, the base station
200 transmits packets to the mobile station A201(A) over the
carrier-F6 slot-S2 channel and the carrier-F8 slot-S3 channel. In
the next frame, the base station 200 transmits packets to the
mobile station A201(A) over the carrier-F7 slot-S2 channel and the
carrier F6 slot-S3 channel.
[0158] As described so far, the first embodiment allocates channel
sets on the basis of frequency and/or time, so the mobile station
A201(A) receives packets only in the slots where packets may be
received, which allows the mobile station A201(A) to reduce power
consumption.
[0159] Conventionally, even when the mobile station A201(A)
performs low-rate communication, packets may be communicated on all
the carriers F1 to F8. This requires the mobile station A201(A) to
perform the channel state estimation (301) and the channel state
information transmission (302) about all the carriers.
[0160] In contrast, according to the first embodiment, the channel
state estimation 301 and the channel state information transmission
302 are performed only about the carriers F6 to F8 included in the
allocated sub-band 101. Reducing the number of carriers requiring
the channel state estimation 301 and the like reduces power
consumption for the pilot signal reception, the channel state
estimation (301), etc.
[0161] Also, reducing the number of carriers requiring the channel
state information transmission (302) reduces the amount of channel
state information data transmitted to the base station, which can
reduce the amount of processing and the power consumption for the
data transmission.
[0162] Also, the power consumption of the mobile station A201(A) is
reduced as compared with the example (FIG. 31) in which the
frequencies of carriers scheduled for the mobile station A are
discontinuous.
[0163] In other words, in performing the channel state estimation
(301) about a plurality of carriers, the mobile station A201(A)
requires the AD converter 220 which is capable of dealing with a
sampling clock covering all carrier frequencies that might bring
packets. Enlarging the range of sampling clock for the AD converter
220 increases power consumption.
[0164] Thus, in a case where carrier frequencies scheduled for the
mobile station A are discontinuous as shown in the conventional
example (FIG. 31), the mobile station A201(A) uses a wider range of
carrier frequencies even with the same number of carriers
allocated. Accordingly, a range of sampling clock becomes wider,
leading to lessen the power consumption reduction effect. In
contrast, according to the first embodiment, carriers at continuous
frequencies are allocated to the mobile station A201(A), so the
sampling clock range of the AD converter 220 can be minimized. The
mobile station A201(A) of the embodiment thus consumes less
power.
[0165] Also, in the first embodiment, a channel set is allocated on
the basis of time, so the mobile station A201(A) expects to receive
packets only in channels of particular slots which allows the
mobile station A201(A) to perform the carrier channel state
estimation (301) and the channel state information transmission
(302) only about the particular slots. Thus the mobile station
A201(A) consumes less power.
[0166] FIGS. 22A, 22B, and 22C are graphs showing carrier channel
states in the first embodiment, where the vertical axes show time
and the horizontal axes show channel state.
[0167] In wireless communication, a higher value of channel state
S/(I+N) allows signal transmission with higher coding rate or
larger multi-value modulation, which offers higher carrier
utilization rate. The channel states S/(I+N) vary in time because
of movements of the mobile stations 201 and environmental
variations, and the channel state of each mobile station 201 varies
independently.
[0168] FIG. 22A is a graph showing carrier channel states in a case
where three mobile stations A201(A), B201(B), and C201(C)
communicate with the base station 200. The base station 200 selects
a mobile station 201 that presents a highest value among the values
of channel state S/(I+N) reported from the three mobile stations
201 and allows that mobile station 201 to use the carrier.
[0169] FIG. 22B is a graph showing carrier channel states in a case
where two terminals A201(A) and B201(B) communicate with the base
station 200, and FIG. 22C is a graph showing a carrier channel
state in a case where a single mobile station A201(A) communicates
with the base station 200.
[0170] It is appreciated, by comparing these graphs, that the
carrier channel state S/(I+N) increases as the number of mobile
stations 201 increases, causing user diversity effect. Thus, the
carrier utilization rate is enhanced.
[0171] In the first embodiment, the base station 200 allocates a
same carrier to a plurality of mobile stations 201 and thus
increases the carrier utilization rate.
[0172] Next, a second embodiment of the invention will be
described.
[0173] FIG. 23 is a sequence chart showing a packet scheduling
process according to the second embodiment, which is performed in
the step 300 of the channel set allocation process (FIG. 5).
[0174] The packet scheduling process of the second embodiment
differs from the packet scheduling process (FIG. 6) of the first
embodiment in that the step (305) in which the base station 200
notifies the mobile station A201(A) of the result of scheduling and
the step (306) in which the mobile station A201(A) receives the
result of scheduling are omitted. The other steps are the same as
those of the packet scheduling in which the result of scheduling is
reported. The same steps are denoted by the same reference
characters and are not described again here.
[0175] It should be noted that, unlike in the case where the result
of scheduling is reported, the mobile station A201(A) constantly
waits for reception from channels that may bring packets and
monitors to see whether any packet destined for the mobile station
A201(A) is transmitted.
[0176] In other words, in the second embodiment, where the result
of scheduling is not reported, the mobile station A201(A) is always
waiting for reception and therefore consumes more power than when
the mobile station A201(A) is notified of the result of
scheduling.
[0177] However, for example, when the carrier frequency is 2 GHz
and the moving rate is 60 Km/h, the channel state varies at about
1110 Hz. Thus, the scheduling must be performed every several ms,
so it is technically difficult to notify the mobile station 201 of
the result of scheduling in advance. Therefore, the
third-generation mobile communication system, cdma2000 1xEV-DO,
adopts a packet scheduling scheme not involving notification of
scheduling results.
[0178] FIG. 24 is a channel timing chart according to the second
embodiment. The hatched portions in FIG. 24 show timing of
communication performed between the base station 200 and the mobile
station A201(A).
[0179] The base station 200 transmits a pilot signal within the
communication area (500). The mobile station A201(A) receives the
pilot signal and estimates the channel state from the received
pilot signal. Then, the mobile station A201(A) transmits the result
of channel state estimation (channel state information) to the base
station 200 in the slot next to the slot in which mobile station
A201(A) received the pilot signal (501).
[0180] The base station 200 receives the channel state information
and performs scheduling. Then, when the base station 200 makes a
schedule for the mobile station A201(A), the base station 200
transmits data to the mobile station A201(A) in the slot next to
the slot in which the base station received the channel state
information (503).
[0181] FIG. 25 is a channel timing chart according to the second
embodiment, in a case where a channel set is allocated on the basis
of time and the result of scheduling is not reported. The portions
surrounded by bold lines show slots in which the base station 200
and the mobile station A201(A) associate with each other. The
hatched portion denotes a slot 514 in which the base station 200
transmits a packet to the mobile station A201(A).
[0182] The channel set is allocated on the basis of time, so the
mobile station A201(A) receives packets only in the sub-frame 513.
Therefore, the mobile station A201(A) estimates the channel state
using the pilot signal 510 that precedes the sub-frame 513 by a
given number of slots (two slots).
[0183] The mobile station A201(A) transmits the result of channel
state estimation (channel state information) to the base station
200 in the slot next to the slot in which the mobile station
A201(A) received the pilot signal (511). Since the base station 200
does not have to notify the mobile station A201(A) of the result of
scheduling, the base station 200 performs scheduling of the slot
513 next to the slot in which the channel state information was
received. Then, the base station 200 transmits packets to the
mobile station A201(A) according to the scheduling (514).
[0184] When the result of scheduling is not reported, in a
conventional example, the mobile station A201(A) cannot tell when a
packet is transmitted and therefore has to wait for reception in
all slots.
[0185] According to the second embodiment, as described above, the
base station 200 allocates to the mobile station A201(A) a channel
set of a sub-frame (a frame formed of slots that are continuous in
time), to thereby allowing the mobile station A201(A) to receive
packets only in the slots included in the allocated channel set.
This allows the mobile station A201(A) to save the amount of
processing and consumption power for reception.
[0186] Next, a third embodiment of this invention will be
described.
[0187] FIG. 26 is a block diagram of a base station 200 according
to the third embodiment.
[0188] In the third embodiment, the base station 200 differs from
the base station 200 of the first embodiment shown in FIG. 2 in
that information about the receiving abilities of mobile stations
is transmitted from the network to the channel condition control
unit 210.
[0189] When a signal from the network is information about the
receiving ability of a mobile station 201, the network interface
211 sends the information to the channel condition control unit
210. In other respects, the configuration of the base station 200
of this modification is the same as that of the base station 200 of
the first embodiment. Therefore the same components are denoted by
the same reference characters and are not described again here.
[0190] FIG. 27 is a channel set sequence chart according to the
third embodiment, where the base station 200 is notified of the
receiving ability of the mobile station A201(A) from a base station
controller.
[0191] First, the mobile station A201(A) sends a control signal
including an ID, position registration, etc. (317). The base
station 200 receives the control signal from the mobile station
A201(A). Then, the base station 200 transfers the received control
signal to the base station controller (318).
[0192] The base station controller receives the control signal
about the mobile station A201(A) (319). Then, using the ID of the
mobile station included in the received control signal, the base
station controller searches receiving ability information stored in
a storage device for the receiving ability of the mobile station
A201(A). Then, the base station controller notifies the base
station 200 of the obtained receiving ability (320).
[0193] The base station 200 receives the receiving ability of the
mobile station A201(A) (321) and allocates a channel set that
satisfies the receiving ability (322). The base station 200
notifies the mobile station A201(A) of the allocated channel set
using a control channel (323). The base station 200 then performs
scheduling only about the allocated channel set (300).
[0194] The mobile station A201(A) receives the channel-set
notification (313). The mobile station A201(A) then monitors only
the allocated channel set in the subsequent communication to
receive packets from the base station 200.
[0195] Next, a fourth embodiment of this invention will be
described.
[0196] FIG. 28 is a block diagram of a mobile station 201 according
to the fourth embodiment, which adopts the OFDMA.
[0197] In the case of the OFDMA, the mobile station 201 includes an
FFT unit 232 in place of the aforementioned filter bank 221 of the
FDMA mobile station 201 (FIG. 3) of the first embodiment. The FFT
unit 232 performs the Fourier transform to separate signals into
sub-carriers. The sampling frequency for the signal inputted to the
FFT unit 232 is varied depending on the number of frequency
channels (bandwidth) of the previously allocated channel set. The
number of taps of the FFT unit 232 is also varied according
thereto. Since the sub-carrier band is (sampling frequency/number
of taps of the FFT unit), the sampling frequency and the number of
taps of the FFT unit are varied so that this value is constant,
whereby particular frequencies can be extracted without changing
the sub-carrier band.
[0198] In other respects, the configuration is the same as that of
the FDMA mobile station 201 of the first embodiment. The same
components as those of the FDMA mobile station 201 (FIG. 3) are
denoted by the same reference characters and are not described
again here.
[0199] FIGS. 29A to 29D show spectra exhibited during a process of
extracting a signal of a particular carrier according to the fourth
embodiment, which shows an example that adopts the OFDMA.
[0200] The antenna 233 receives a signal having a spectrum as shown
in FIG. 29A. In the OFDMA signal, the signals of sub-carriers
partially overlap with each other.
[0201] With these signals, the filter 219 denoted by the bold line
in FIG. 29B extracts a portion necessary for the mobile station
201. The filter 219 extracts the signal portion so that it includes
the allocated channel set. Therefore, the output from the filter
219 is a wideband signal including a plurality of sub-carriers
(e.g., in this embodiment, a wideband signal including seven
sub-carriers).
[0202] FIG. 29C shows the signal extracted by the filter. The FFT
232 separates the signal into individual sub-carriers. FIG. 29D
shows the spectrum of one of the separated sub-carrier signals. In
the OFDMA system, one channel may be formed of one sub-carrier, or
one channel may be formed of a plurality of sub-carriers.
[0203] While the present invention has been described in detail and
pictorially in the accompanying drawings, the present invention is
not limited to such detail but covers various obvious modifications
and equivalent arrangements, which fall within the purview of the
appended claims.
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