U.S. patent application number 11/280254 was filed with the patent office on 2006-04-20 for mobile communication systems, mobile communication methods, base stations, mobile stations, and signal transmission methods in the mobile communication systems.
This patent application is currently assigned to NTT DoCoMo, Inc. Invention is credited to Shiro Kikuchi, Shinzo Ohkubo, Hitoshi Yoshino.
Application Number | 20060084475 11/280254 |
Document ID | / |
Family ID | 26616849 |
Filed Date | 2006-04-20 |
United States Patent
Application |
20060084475 |
Kind Code |
A1 |
Ohkubo; Shinzo ; et
al. |
April 20, 2006 |
Mobile communication systems, mobile communication methods, base
stations, mobile stations, and signal transmission methods in the
mobile communication systems
Abstract
A mobile station is configured to measure receiving qualities of
respective signals from a first antenna and a second antenna of a
base station (S3, S5), store the results of the measurement, and
request the base station to retransmit a signal from an antenna
with a higher receiving quality, based on the stored measurement
results, when an error is detected in received data thereafter
(S10, S11, S12). The base station retransmits the data, using the
antenna with the higher receiving quality (i.e., a base station
antenna to yield the higher receiving quality at the mobile
station) (S15). In another aspect, the mobile station measures a
receiving quality of a signal and notifies the base station of the
receiving quality. The base station selects a radio channel adapted
to a receiving quality on the basis of the measurement result and
transmits a signal, using the radio channel.
Inventors: |
Ohkubo; Shinzo;
(Yokosuka-shi, JP) ; Yoshino; Hitoshi;
(Yokosuka-shi, JP) ; Kikuchi; Shiro;
(Yokohama-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
NTT DoCoMo, Inc
Tokyo
JP
|
Family ID: |
26616849 |
Appl. No.: |
11/280254 |
Filed: |
November 17, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10166652 |
Jun 12, 2002 |
|
|
|
11280254 |
Nov 17, 2005 |
|
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Current U.S.
Class: |
455/562.1 ;
455/101; 455/277.1 |
Current CPC
Class: |
H04L 1/1671 20130101;
H04B 7/0608 20130101; H04B 7/0623 20130101; H04L 1/1867 20130101;
H04L 2001/0093 20130101; H04L 1/0025 20130101 |
Class at
Publication: |
455/562.1 ;
455/101; 455/277.1 |
International
Class: |
H04B 1/02 20060101
H04B001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 2001 |
JP |
2001-178999 |
Jun 20, 2001 |
JP |
2001-186910 |
Claims
1. A mobile station configured to perform signal
transmission/reception control including signal retransmission
control based on an automatic repeat request, with a base station
equipped with a plurality of antennas and configured to transmit a
signal on the basis of a signal transmission request from at least
one antenna out of the plurality of antennas, said mobile station
comprising: a quality measuring unit configured to measure
receiving qualities of signals transmitted from the plurality of
antennas of said base station; and a transmitter configured to
transmit an antenna use request to said base station that a signal
should be transmitted from at least one antenna out of said
plurality of antennas, based on the receiving qualities of the
signals from the respective antennas obtained by measurement.
2. A mobile station configured to perform signal
transmission/reception control including multicast signal
retransmission control based on an automatic repeat request, with a
base station equipped with a plurality of antennas and configured
to transmit a multicast signal on the basis of a signal
transmission request from at least one antenna out of the plurality
of antennas, said mobile station comprising: a quality measuring
unit configured to measure receiving qualities of signals
transmitted from the plurality of antennas of said base station;
and a transmitter configured to transmit an antenna use request to
said base station that a multicast signal should be transmitted
from at least one antenna out of said plurality of antennas, based
on the receiving qualities of the signals from the respective
antennas obtained by measurement.
3. The mobile station according to claim 1, wherein said quality
measuring unit measures said receiving quality by using a
synchronization signal, a signal of annunciation information, an
individual signal to the mobile station, a multicast signal, or a
combination of two or more out of these signals, transmitted from
at least one antenna of said base station.
4. The mobile station according to claim 1, wherein said receiving
quality is a received power, a value obtained by dividing a carrier
power by the sum of an interference power and a noise power, a
value obtained by dividing a signal power by the sum of an
interference power and a noise power, an error rate, a likelihood
obtained in decoding of error correction code, a C/N ratio, an S/N
ratio, a correlation value obtained by despreading of spreading
code, or a combination of two or more out of these.
5. A signal transmitting method in a mobile communication system
comprising a mobile station and a base station and configured to
perform transmission/reception of a signal while sending and
receiving an automatic repeat request, said signal transmitting
method being carried out as follows in the mobile communication
system: measuring at said mobile station a receiving quality of a
radio signal transmitted from the base station, notifying at said
mobile station the base station of the receiving quality of the
radio signal thus measured, and transmitting from said base station
a signal under a repeat request from said mobile station so as to
meet a required receiving quality of the mobile station, based on
the receiving quality thus notified of, wherein when a repeat
request for retransmission of a received signal is needed, said
mobile station notifies said base station of said repeat request,
together with said receiving quality of the radio signal
measured.
6. The signal transmitting method according to claim 5, wherein the
radio signal transmitted from said base station becomes at least
one radio channel.
7. The signal transmitting method according to claim 6, wherein
said mobile station uses, as a radio channel for measurement of the
receiving quality, an annunciation information channel or an
individual channel or a multicast channel or a combination of
these, among said at least one radio channel transmitted from said
base station.
8. The signal transmitting method according to claim 7, wherein
said receiving quality is one selected from at least one of the
following: a received power; C/(I+N) (Eq. 1) C: carrier power I:
interference power N: noise power; S/(I+N) (Eq. 2) S: signal power
I: interference power N: noise power; C/N (Eq. 3) C: carrier power
N: noise power; S/N (Eq. 4) S: signal power N: noise power; an
error rate; a likelihood obtained in decoding of error correction
code; a transmission power value of the base station; an increase
amount or an attenuation amount of the transmission power of the
base station.
9. The signal transmitting method according to claim 6, wherein
radio channels transmitted and received between said base station
and said mobile station are at least one of subcarrier channels,
orthogonal subcarrier channels, frequency channels, and frequency
channels in different frequency bands.
10. The signal transmitting method according to claim 5, wherein on
an occasion of notifying said base station of an acknowledgement of
arrival of a received signal, said mobile station notifies the base
station of the receiving quality of said at least one radio channel
measured.
11. The signal transmitting method according to claim 5, wherein
said mobile station notifies the base station of a number of at
least one radio channel and a receiving quality of the radio
channel, or of only a channel number of a receiving quality within
a predetermined range, as the receiving quality of said at least
one radio channel measured.
12. The signal transmitting method according to claim 5, wherein
said mobile station notifies said base station of a number of at
least one radio channel satisfying a required receiving quality,
including a radio channel with a maximum receiving quality at said
mobile station, together with the receiving quality achieved.
13. The signal transmitting method according to claim 5, wherein
said base station determines a radio channel satisfying the
required receiving quality at the mobile station on the basis of
notification from said mobile station, and the base station
transmits a signal under a repeat request from the mobile station,
using the radio channel determined.
14. The signal transmitting method according to claim 13, wherein
after transmitting the signal under the repeat request from said
mobile station, using said determined radio channel, said base
station also transmits a signal addressed to the mobile station,
using said determined radio channel.
15. The signal transmitting method according to claim 13, wherein,
based on the notification from said mobile station, said base
station determines a number of a radio channel which satisfies the
required receiving quality at the mobile station and through which
the signal is transmitted so that a transmission power from the
base station becomes a predetermined value, and also determines a
transmission power of the radio channel.
16. The signal transmitting method according to claim 15, wherein
when said base station transmits an identical multicast signal to a
plurality of mobile stations, the base station determines a number
of at least one radio channel which satisfies the required
receiving quality at each mobile station and through which the
multicast signal is transmitted so that a transmission power from
the base station becomes a predetermined value, and also determines
a transmission power of the radio channel, based on notification
from each mobile station.
17. The signal transmitting method according to claim 16, wherein
when said base station transmits the identical multicast signal to
the plurality of mobile stations, the base station determines a
number of a radio channel that can be assumed to have the greatest
number of repeat requests from the mobile stations, out of channel
numbers with receiving qualities within a predetermined range,
notified of by the respective mobile stations.
18. A mobile communication system comprising: a mobile station, and
a base station and configured to perform transmission/reception of
a signal while sending and receiving an automatic repeat request,
wherein said mobile station comprises: a quality measuring unit
configured to measure a receiving quality of a radio signal
transmitted from the base station; and a notifying unit configured
to notify the base station of the receiving quality of the radio
signal thus measured, wherein when a repeat request for
retransmission of a received signal is needed, said notifying unit
notifies said base station of said repeat request, together with
said receiving quality of the radio signal measured, and said base
station comprises: a transmitter configured to transmit a signal
under a repeat request from said mobile station so that a required
receiving quality is satisfied at the mobile station, based on the
receiving quality notified of by the mobile station.
19. The mobile communication system according to claim 18, wherein
said quality measuring unit measures a receiving quality of at
least one radio channel transmitted from the base station.
20. The mobile communication system according to claim 19, wherein
said quality measuring unit uses, as a radio channel for
measurement of the receiving quality at said mobile station, one
selected from an annunciation information channel, an individual
channel, a multicast channel, and a combination of these, among
said at least one radio channel transmitted from the base
station.
21. The mobile communication system according to claim 19, wherein
said receiving quality is one selected from at least one of the
following: a received power; C/(I+N) (Eq. 1) C: carrier power I:
interference power N: noise power; S/(I+N) (Eq. 2) S: signal power
I: interference power N: noise power; C/N (Eq. 3) C: carrier power
N: noise power; S/N (Eq. 4) S: signal power N: noise power; an
error rate; a likelihood obtained in decoding of error correction
code; a transmission power value of the base station; and an
increase amount or an attenuation amount of the transmission power
of the base station.
22. The mobile communication system according to claim 19, wherein
radio channels transmitted and received between said base station
and said mobile station are at least one of subcarrier channels,
orthogonal subcarrier channels, frequency channels, and frequency
channels in different frequency bands.
23. The mobile communication system according to claim 18, wherein
on an occasion of notifying said base station of an acknowledgement
of arrival of a received signal, said notifying unit notifies the
base station of the receiving quality of said at least one radio
channel measured.
24. The mobile communication system according to claim 18, wherein
said notifying unit notifies the base station of a number of at
least one radio channel and a receiving quality of the radio
channel, or of only a channel number of a receiving quality within
a predetermined range, as the receiving quality of said at least
one radio channel measured.
25. The mobile communication system according to claim 18, wherein
said notifying unit notifies said base station of a number of at
least one radio channel satisfying a required receiving quality,
including a radio channel with a maximum receiving quality at said
mobile station, together with the receiving quality achieved.
26. The mobile communication system according to claim 18, wherein
said base station comprises: radio channel determining unit
configured to determine a radio channel satisfying the required
receiving quality at the mobile station on the basis of
notification from said mobile station; and a transmitter configured
to transmit a signal under a repeat request from the mobile
station, using the radio channel determined by the radio channel
determining unit.
27. The mobile communication system according to claim 26, wherein
after transmitting the signal under the repeat request from said
mobile station, using said determined radio channel, said
transmitter in said base station also transmits a signal addressed
to the mobile station, using said determined radio channel.
28. The mobile communication system according to claim 26, wherein
said base station comprises: first radio channel number unit
configured to determine a number of a radio channel which satisfies
the required receiving quality at the mobile station and through
which the signal is transmitted so that a transmission power from
the base station becomes a predetermined value, based on the
notification from said mobile station; and first radio channel
transmission power determining unit configured to determine a
transmission power of the radio channel.
29. The mobile communication system according to claim 28, wherein
said base station comprises: second radio channel number
determining unit configured to, on an occasion of transmitting an
identical multicast signal to a plurality of mobile stations,
determine a number of at least one radio channel which satisfies
the required receiving quality at each mobile station and through
which the multicast signal is transmitted so that a transmission
power from the base station becomes a predetermined value, based on
notification from each mobile station; and second radio channel
transmission power determining unit configured to determine a
transmission power of the radio channel.
30. The mobile communication system according to claim 29, wherein
said base station comprises: third radio channel number determining
unit configured to, on an occasion of transmitting the identical
multicast signal to the plurality of mobile stations, determine a
number of a radio channel that can be assumed to have the greatest
number of repeat requests from the mobile stations, out of channel
numbers with receiving qualities within a predetermined range,
notified of by the respective mobile stations.
31. The mobile communication system according to claim 18, wherein
said base station comprises: a radio resource determining unit
configured to determine a radio resource satisfying the required
receiving quality at the mobile station on the basis of
notification from said mobile station; and a transmitter configured
to transmit the signal under the repeat request from said mobile
station, using the radio resource determined by said radio resource
determining unit.
32. The mobile communication system according to claim 18, wherein
said transmitter of said base station transmits the signal by using
radio resources in decreasing order of the number of repeat
requests from the mobile station.
33. The mobile communication system according to claim 31, wherein
said radio resource is at least one antenna, directivities of at
least one antenna, a radio channel, a transmission path, or either
of combinations of these.
34. A base station in a mobile communication system comprising a
mobile station and the base station and configured to perform
transmission/reception of a signal while sending and receiving an
automatic repeat request, said base station comprising: a
transmitter configured to transmit a signal under a repeat request
from said mobile station so that a required receiving quality is
satisfied at the mobile station, based on a receiving quality
notified of by the mobile station wherein said receiver quality is
included in the repeat request.
35. The base station according to claim 34, said base station
comprising: radio channel determining unit configured to determine
a radio channel satisfying the required receiving quality at the
mobile station, based on notification from said mobile station; and
said transmitter configured to transmit the signal under the repeat
request from the mobile station, using the radio channel determined
by the radio channel determining unit.
36. The base station according to claim 34, wherein after
transmitting the signal under the repeat request from said mobile
station, using said determined radio channel, said transmitter also
transmits a signal addressed to the mobile station, using said
determined radio channel.
37. The base station according to claim 34, said base station
comprising: first radio channel number determining unit configured
to determine a number of a radio channel which satisfies the
required receiving quality at the mobile station and through which
the signal is transmitted so that a transmission power from the
base station becomes a predetermined value, based on notification
from said mobile station; and first radio channel transmission
power determining means for determining a transmission power of the
radio channel.
38. The base station according to claim 34, said base station
comprising: second radio channel number determining unit configured
to, on an occasion of transmitting an identical multicast signal to
a plurality of mobile stations, determine a number of at least one
radio channel which satisfies the required receiving quality at
each mobile station and through which the multicast signal is
transmitted so that a transmission power from the base station
becomes a predetermined value, based on notification from each
mobile station; and second radio channel transmission power
determining unit for determining a transmission power of the radio
channel.
39. The base station according to claim 34, said base station
comprising: third radio channel number determining unit configured
to, on an occasion of transmitting an identical multicast signal to
a plurality of mobile stations, determine a number of a radio
channel that can be assumed to have the greatest number of repeat
requests from the mobile stations, out of channel numbers with
receiving qualities within a predetermined range, notified of by
the respective mobile stations.
40. The base station according to claim 34, wherein radio channels
used between said base station and said mobile station are at least
one of subcarrier channels, orthogonal subcarrier channels,
frequency channels, and frequency channels in different frequency
bands.
41. A mobile station in a mobile communication system comprising
the mobile station and a base station and configured to perform
transmission/reception of a signal while sending and receiving an
automatic repeat request, said mobile station comprising: a quality
measuring unit configured to measure a receiving quality of a radio
signal transmitted from the base station; and a notifying unit
configured to transmit a repeat request together with the receiving
quality of the radio signal thus measured to the base station.
42. The mobile station according to claim 41, wherein said quality
measuring unit measures a receiving quality of at least one radio
channel transmitted from the base station.
43. The mobile station according to claim 41, wherein said quality
measuring unit uses, as a radio channel for measurement of the
receiving quality at said mobile station, one selected from an
annunciation information channel, an individual channel, a
multicast channel, and a combination of these, among said at least
one radio channel transmitted from the base station.
44. The mobile station according to claim 41, wherein said
receiving quality is one selected from at least one of the
following: a received power; C/(I+N) (Eq. 1) C: carrier power I:
interference power N: noise power; S/(I+N) (Eq. 2) S: signal power
I: interference power N: noise power; C/N (Eq. 3) C: carrier power
N: noise power; S/N (Eq. 4) S: signal power N: noise power; an
error rate; a likelihood obtained in decoding of error correction
code; a transmission power value of the base station; and an
increase amount or an attenuation amount of the transmission power
of the base station.
45. The mobile station according to claim 41, wherein when a repeat
request for retransmission of a received signal is needed, said
notifying unit notifies said base station of said repeat request,
together with said receiving quality of the radio signal
measured.
46. The mobile station according to claim 41, wherein on an
occasion of notifying said base station of an acknowledgement of
arrival of a received signal, said notifying unit notifies the base
station of the receiving quality of said at least one radio channel
measured.
47. The mobile station according to claim 41, wherein said
notifying unit notifies the base station of a number of at least
one radio channel and a receiving quality of the radio channel, or
of only a channel number of a receiving quality within a
predetermined range, as the receiving quality of said at least one
radio channel measured.
48. The mobile station according to claim 41, wherein said
notifying unit notifies said base station of a number of at least
one radio channel satisfying a required receiving quality,
including a radio channel with a maximum receiving quality at said
mobile station, together with the receiving quality achieved.
49. The mobile station according to claim 41, wherein radio
channels used between said mobile station and said base station are
at least one of subcarrier channels, orthogonal subcarrier
channels, frequency channels, and frequency channels in different
frequency bands.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/166,652 filed Jun. 12, 2002, and further is based upon and
claims the benefit of priority from the Japanese Patent Application
Nos. 2001-178999, filed Jun. 13, 2001, and 2001-186910, filed Jun.
20, 2001, the entire contents of each of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to mobile communication
systems, mobile communication methods, base stations, and mobile
stations and, more particularly, to a mobile communication system
comprising a mobile station and a base station equipped with a
plurality of antennas and configured to perform signal
transmission/reception control including signal retransmission
control by the base station on the basis of an automatic repeat
request from the mobile station, a mobile communication method
executed by the mobile communication system, and the base station
and the mobile station constituting the mobile communication
system.
[0004] The present invention also relates to signal transmitting
methods and systems in mobile communication systems and, more
particularly, to a signal transmitting method and system in a
mobile communication system configured to perform
transmission/reception of a signal while transmitting and receiving
an automatic repeat request, the signal transmitting method and
system being configured to transmit the signal while changing
channels one from another so as to improve the receiving quality at
the mobile station.
[0005] Further, the present invention relates to base stations that
can perform communication according to the aforementioned signal
transmitting methods.
[0006] The present invention also relates to mobile stations
performing communication according to the foregoing signal
transmitting methods.
[0007] 2. Related Background Art
[0008] FIG. 1 is a block diagram of a conventional mobile
communication system 10, and FIG. 2 a chart for explaining the
cooperative operation of the conventional mobile communication
system with an automatic repeat request. At a base station 1, an
ARQ (Automatic Repeat Request) processor 2 accepts input data
addressed to a mobile station 11 through a data input terminal 6.
The ARQ processor 2 attaches error-detectable parity such as CRC
(Cyclic Redundancy Checking code) or the like to the data so as to
enable detection of an error occurring during transmission,
thereafter stores the data (A1 in FIG. 2), and outputs the data to
a transmitter 3. The transmitter 3 modulates the input data into a
transmitted signal and then transmits the signal through a
transmitted/received wave splitter 4 and from a first base station
antenna 7 to the mobile station 11 through a downlink 22 (A2).
[0009] At the mobile station 11, a receiver 12 receives the signal
from a mobile station antenna 17 through a transmitted/received
wave splitter 16. Then the signal received at the receiver 12 is
fed as received data to an ARQ processor 13 (A3). The ARQ processor
13 performs detection of error using the CRC (A4).
[0010] When no error is detected in the received data herein, the
ARQ processor 13 outputs the received data from a data output
terminal 14 and outputs an acknowledgement of arrival of the
received data to a transmitter 15. The transmitter 15 transmits the
acknowledgement of arrival of the received data to the ARQ
processor 2 of the base station 1 through an uplink 21 (A5).
Receiving the arrival acknowledgement, the ARQ processor 2 deletes
the data stored for retransmission (A7 and A8).
[0011] When an error is detected in the received data at A4 on the
other hand, the ARQ processor 13 sends a repeat request for
retransmission of the received data to the ARQ processor 2 of the
base station 1 through the uplink 21 (A6). Receiving the repeat
request, the ARQ processor 2 retransmits the requested data from
the first base station antenna 7 (A7 and A9).
[0012] FIG. 3 and FIG. 4 are a block diagram of another
conventional mobile communication system and a flowchart for
explaining the operation thereof. As shown in FIG. 3, the
conventional mobile communication system is comprised of a base
station 21 and a mobile station 31.
[0013] The base station 21 is generally comprised of an ARQ
(Automatic Repeat Request) processor 22, a transmitter/receiver 23,
a signal input terminal 24, and a base station antenna 25. The
mobile station 31 on the other hand is generally comprised of a
transmitter/receiver 32, an ARQ processor 33, a signal output
terminal 34, and a mobile station antenna 35.
[0014] The operation of the conventional mobile communication
system will be described below with reference to the flowchart of
FIG. 4.
[0015] At the base station 21, the ARQ processor 22 receives an
input signal addressed to the mobile station 31 through the signal
input terminal 24. The ARQ processor 22 attaches the
error-detectable parity such as the CRC (Cyclic Redundancy Checking
code) or the like to the data so as to enable detection of an error
occurring during transmission, thereafter stores the signal (B1),
and outputs the signal to the transmitter/receiver 23. The
transmitter/receiver 23 informs the mobile station of a start of
transmission of the signal (B2) and thereafter transmits the signal
to the mobile station 31 through a downlink 42 which is a frequency
channel determined for transmission of the signal addressed to the
mobile station (B3).
[0016] At the mobile station 31, the transmitter/receiver 32
receives the signal of the downlink 42 received by the mobile
station antenna 35 (B4) and thereafter the signal is fed into the
ARQ processor 33. The ARQ processor 33 performs the detection of
error in the received signal, using the CRC. When no error is
detected in the received signal (NO at B5), the received signal is
outputted from the signal output terminal 34 and an acknowledgement
of arrival of the received signal is transmitted to the ARQ
processor 22 of the base station through an uplink 41 (B6). After
that, the ARQ processor 22 receiving the arrival acknowledgement
deletes the signal stored for retransmission (NO at B8, and
B9).
[0017] When an error is detected in the received signal on the
other hand (YES at B5), the ARQ processor 33 sends a repeat request
for retransmission of the received signal to the ARQ processor 22
of the base station through the uplink 41 (B7). Then the ARQ
processor 22 receiving the repeat request retransmits the requested
signal in the frequency channel used for the preceding transmission
(YES at B8, and B10).
SUMMARY OF THE INVENTION
[0018] In the method of transmitting the high-quality signal with
the automatic repeat request in the conventional mobile
communication system described with reference to FIGS. 1 and 2,
however, since the signals were always transmitted with the use of
the same base station antenna, a low receiving quality state due to
fading or shadowing continued at a simple mobile station incapable
of implementing receiving antenna diversity or at a mobile station
staying long at an identical site, which posed the problem of
degradation of throughput because of repetition of repeat
requests.
[0019] An object of the present invention is therefore to decrease
the repetition of repeat requests from the mobile station, thereby
enhancing the throughput.
[0020] In order to achieve the above object, a mobile communication
system according to the present invention is, as set forth in claim
1, a mobile communication system comprising a mobile station and a
base station and configured to perform transmission/reception of a
signal while sending and receiving an automatic repeat request,
wherein the mobile station comprises: receiving quality measuring
means for measuring a receiving quality of a radio signal
transmitted from the base station; and request transmitting means
for transmitting to the base station a radio resource use request
for use of a radio resource adapted to a receiving quality, based
on the measured receiving quality of the radio signal. The base
station comprises: request receiving means for receiving the radio
resource use request; and signal transmitting means for
transmitting a signal addressed to the mobile station, including a
signal under a request for retransmission by the automatic repeat
request, using the radio resource requested by the radio resource
use request.
[0021] In the mobile communication system as set forth in claim 2,
the signal transmitting means transmits the signal by using radio
resources in decreasing order of the number of repeat requests from
the mobile station.
[0022] Further, in the mobile communication system as set forth in
claim 3, the receiving quality is one selected from the
following:
[0023] a received power; C/(I+N) (Eq. 1)
[0024] C: carrier power
[0025] I: interference power
[0026] N: noise power; S/(I+N) (Eq. 2)
[0027] S: signal power
[0028] I: interference power
[0029] N: noise power; C/N (Eq. 3)
[0030] C: carrier power
[0031] N: noise power; S/N (Eq. 4)
[0032] S: signal power
[0033] N: noise power;
[0034] an error rate;
[0035] a likelihood obtained in decoding of error correction
code;
[0036] a transmission power value of the base station;
[0037] an increase amount or an attenuation amount of the
transmission power of the base station;
[0038] a correlation value obtained by despreading of spreading
code;
[0039] either of combinations of these.
[0040] In the mobile communication system as set forth in claim 4,
the radio resource is at least one antenna, directivities of at
least one antenna, a radio channel, a transmission path, or either
of combinations of these. Here the antenna may be a single antenna
or a plurality of antennas, and in the case of a plurality of
antennas being used, directivities of the respective antennas may
be different from each other. The transmission path is intended for
a situation in which a signal is indirectly transmitted via a
mobile station as a relay station (multihop connection).
[0041] In order to achieve the above object, a mobile communication
system according to the present invention is, as set forth in claim
2, a mobile communication system comprising a mobile station, and a
base station equipped with a plurality of antennas, and configured
to perform signal transmission/reception control including signal
retransmission control by the base station on the basis of an
automatic repeat request from the mobile station, wherein the
mobile station comprises: quality measuring means for measuring
receiving qualities of signals transmitted from the plurality of
antennas of the base station; and request transmitting means for
transmitting to the base station an antenna use request that a
signal should be transmitted from at least one antenna out of the
plurality of antennas, based on the receiving qualities of the
signals from the respective antennas obtained by measurement, and
wherein the base station comprises: request receiving means for
receiving the antenna use request that the signal should be
transmitted from at least one antenna out of the plurality of
antennas; and signal transmitting means for transmitting a signal
addressed to the mobile station, including the signal under the
automatic repeat request for retransmission, from the antenna
requested by the antenna use request.
[0042] A mobile communication method according to the present
invention is, as set forth in claim 11, a mobile communication
method which is executed by a mobile communication system
comprising a mobile station, and a base station equipped with a
plurality of antennas, and which is configured to perform signal
transmission/reception control including signal retransmission
control by the base station on the basis of an automatic repeat
request from the mobile station, the mobile communication method
comprising: a quality measuring step of, at the mobile station,
measuring receiving qualities of signals transmitted from the
plurality of antennas of the base station; a request transmitting
step of, at the mobile station, transmitting to the base station an
antenna use request that a signal should be transmitted from at
least one antenna out of the plurality of antennas, based on the
receiving qualities of the signals from the respective antennas
obtained by the measurement; a request receiving step of, at the
base station, receiving the antenna use request that the signal
should be transmitted from at least one antenna out of the
plurality of antennas; and a signal transmitting step of, at the
base station, transmitting a signal addressed to the mobile
station, including the signal under the automatic repeat request
for retransmission, from the antenna requested by the antenna use
request.
[0043] A base station according to the present invention is, as set
forth in claim 17, a base station which is equipped with a
plurality of antennas, constituting a mobile communication system,
together with a mobile station requesting to transmit a signal from
at least one antenna out of the plurality of antennas on the basis
of receiving qualities of signals transmitted from the plurality of
antennas, and which is configured to perform, with the mobile
station, signal transmission/reception control including signal
retransmission control based on an automatic repeat request from
the mobile station, the base station comprising: request receiving
means for receiving an antenna use request that a signal should be
transmitted from at least one antenna out of the plurality of
antennas; and signal transmitting means for transmitting a signal
addressed to the mobile station, including the signal under the
automatic repeat request for retransmission, from the antenna
requested by the antenna use request.
[0044] A mobile station according to the present invention is, as
set forth in claim 21, a mobile station which is configured to
perform signal transmission/reception control including signal
retransmission control based on an automatic repeat request, with a
base station equipped with a plurality of antennas and configured
to transmit a signal on the basis of a signal transmission request
from at least one antenna out of the plurality of antennas, the
mobile station comprising: quality measuring means for measuring
receiving qualities of signals transmitted from the plurality of
antennas of the base station; and request transmitting means for
transmitting to the base station an antenna use request that a
signal should be transmitted from at least one antenna out of the
plurality of antennas, based on the receiving qualities of the
signals from the respective antennas obtained by measurement.
[0045] Incidentally, the foregoing mobile communication system,
mobile communication method, base station, and mobile station
according to the present invention are based on the same technical
concept and they are aspects of the same technical concept as a
mobile communication system, as a mobile communication method, as a
base station, and as a mobile station.
[0046] The following will describe the means for solving the
problem in the mobile communication system according to the present
invention, but it is noted that the means for solving the problem
in the mobile communication method, the base station, and the
mobile station are also based on the same concept.
[0047] In the mobile communication system according to the present
invention, at the mobile station the quality measuring means
measures the receiving qualities of the signals transmitted from
the plurality of antennas of the base station and the request
transmitting means transmits to the base station the antenna use
request that the signal should be transmitted from at least one
antenna out of the plurality of antennas, based on the receiving
qualities of the signals from the respective antennas acquired by
the measurement. Namely, this request transmitting means transmits
to the base station the antenna use request that the base station
should transmit the signal from at least one antenna with the
receiving quality of the signal better than those from the other
antennas.
[0048] At the base station, the request receiving means receives
the antenna use request from the foregoing mobile station, and then
the signal transmitting means transmits the signal addressed to the
mobile station, including the signal under the automatic repeat
request for retransmission, from the antenna requested by the
antenna use request.
[0049] Through this operation, the signal addressed to the mobile
station is transmitted from at least one antenna with the receiving
quality relatively better, based on the receiving qualities of the
signals measured at the mobile station, and it is thus feasible to
improve the receiving quality of the signal at the mobile station,
to prevent the repetition of repeat requests from the mobile
station, and to enhance the throughput.
[0050] The foregoing mobile communication system can also be
applied to transmission of a multicast signal addressed to a
plurality of mobile stations.
[0051] Namely, a mobile communication system as set forth in claim
6 is configured so that at the mobile station the quality measuring
means measures receiving qualities of signals transmitted from the
plurality of antennas of the base station and the request
transmitting means transmits to the base station an antenna use
request that a multicast signal should be transmitted from at least
one antenna out of the plurality of antennas, based on the
receiving qualities of the signals from the respective antennas
acquired by the measurement. Namely, this request transmitting
means transmits to the base station the antenna use request that
the base station should transmit the multicast signal from at least
one antenna with the receiving quality of the signal better than
those from the other antennas.
[0052] At the base station the request receiving means receives the
antenna use request from the mobile station, and then multicast
signal transmitting means transmits a multicast signal addressed to
the mobile station, including the multicast signal under the
automatic repeat request for retransmission, from the antenna
requested by the antenna use request.
[0053] Through this operation, the multicast signal addressed to
the mobile station is transmitted from at least one antenna with
the receiving quality relatively better, based on the receiving
qualities of the signals measured at the mobile station, and it is
thus feasible to improve the receiving quality of the multicast
signal at the mobile station, to prevent the repetition of repeat
requests from the mobile station, and to enhance the
throughput.
[0054] In the foregoing configuration, however, there can occur
cases where the antenna use requests from a plurality of mobile
stations are present over two or more antennas, but the system can
be configured, as set forth in claim 7, so that when antenna use
requests from a plurality of mobile stations are present over two
or more antennas, the multicast signal transmitting means transmits
the multicast signal, using the antennas in descending order of the
number of requests. In this configuration, as the entire system, it
is feasible to improve the receiving quality of the multicast
signal at more mobile stations, to decrease the total number of
occurrences of repeat requests, and to enhance the total throughput
of the entire system.
[0055] The invention as set forth in claims 6 and 7 can be
described as follows from the view points of the mobile
communication method, the base station, and the mobile station.
[0056] Namely, a mobile communication method as set forth in claim
12 is a mobile communication method which is executed by a mobile
communication system comprising a plurality of mobile stations, and
a base station equipped with a plurality of antennas and which is
configured to perform signal transmission/reception control
including signal retransmission control by the base station on the
basis of an automatic repeat request from a mobile station, the
mobile communication method comprising: a quality measuring step
of, at the mobile station, measuring receiving qualities of signals
transmitted from the plurality of antennas of the base station; a
request transmitting step of, at the mobile station, transmitting
to the base station an antenna use request that a multicast signal
should be transmitted from at least one antenna out of the
plurality of antennas, based on the receiving qualities of the
signals from the respective antennas obtained by the measurement; a
request receiving step of, at the base station, receiving the
antenna use request that the multicast signal should be transmitted
from at least one antenna out of the plurality of antennas; and a
multicast signal transmitting step of, at the base station,
transmitting a multicast signal addressed to the mobile station,
including the multicast signal under the automatic repeat request
for retransmission, from the antenna requested by the antenna use
request.
[0057] A mobile communication method as set forth in claim 13 is
the mobile communication method according to claim 12, wherein in
the multicast signal transmitting step, when antenna use requests
from the plurality of mobile stations are present over two or more
antennas, the base station transmits the multicast signal by using
the antennas in descending order of the number of requests.
[0058] A base station as set fort in claim 18 is a base station
which is equipped with a plurality of antennas, constituting a
mobile communication system, together with a plurality of mobile
stations requesting to transmit a multicast signal from at least
one antenna out of the plurality of antennas on the basis of
receiving qualities of signals transmitted from the plurality of
antennas, and which is configured to perform, with the mobile
stations, signal transmission/reception control including multicast
signal retransmission control based on an automatic repeat request
from the mobile stations, the base station comprising: request
receiving means for receiving an antenna use request that a
multicast signal should be transmitted from at least one antenna
out of the plurality of antennas; and multicast signal transmitting
means for transmitting a multicast signal addressed to the mobile
station, including the multicast signal under the automatic repeat
request for retransmission, from the antenna requested by the
antenna use request.
[0059] A base station as set forth in claim 19 is the base station
according to claim 18, wherein when antenna use requests from the
plurality of mobile stations are present over two or more antennas,
the multicast signal transmitting means transmits the multicast
signal by using the antennas in decreasing order of the number of
requests.
[0060] A mobile station as set forth in claim 22 is a mobile
station which is configured to perform signal
transmission/reception control including multicast signal
retransmission control based on an automatic repeat request, with a
base station equipped with a plurality of antennas and configured
to transmit a multicast signal on the basis of a signal
transmission request from at least one antenna out of the plurality
of antennas, the mobile station comprising: quality measuring means
for measuring receiving qualities of signals transmitted from the
plurality of antennas of the base station; and request transmitting
means for transmitting to the base station an antenna use request
that a multicast signal should be transmitted from at least one
antenna out of the plurality of antennas, based on the receiving
qualities of the signals from the respective antennas obtained by
measurement.
[0061] The foregoing mobile communication system as set forth in
claim 5 or 6 is preferably configured, as set forth in claim 8, so
that when receiving the antenna use request, the request receiving
means of the base station performs antenna reception in a diversity
system. The diversity reception is generally classified under three
methods, the selection combining method using a signal from an
antenna with the maximum level out of a plurality of antennas, the
equal-gain combining method of combining outputs from the plurality
of antennas as they are, and the maximal-ratio combining method of
combining outputs with respective weights according to their
levels. The request receiving means of the base station may employ
any one of these methods. By performing the antenna reception by
these diversity methods, it is feasible to implement stable
reception of the antenna use request.
[0062] Likewise, a mobile communication method as set forth in
claim 14 is the mobile communication method according to claim 11
or 12 wherein in the request receiving step, when receiving the
antenna use request, the base station performs antenna reception in
a diversity system. A base station as set forth in claim 20 is the
base station according to claim 17 or 18 wherein when receiving the
antenna use request, the request receiving means performs antenna
reception in a diversity system.
[0063] In the mobile communication system as set forth in one of
claims 5 to 8, when at the mobile station the quality measuring
means measures the receiving qualities of the signals transmitted
from the plurality of antennas of the base station, the signals as
measured objects are not limited to specific signals, but can be
selected from various signals. Specifically, as set forth in claim
9, the quality measuring means can measure the receiving quality by
using a synchronization signal, a signal of annunciation
information, an individual signal to the mobile station, a
multicast signal, or a combination of two or more out of these
signals, transmitted from at least one antenna of the base
station.
[0064] Likewise, a mobile communication method as set forth in
claim 15 is the mobile communication method according to either one
of claims 11 to 14, wherein in the quality measuring step, the
mobile station measures the receiving quality by using a
synchronization signal, a signal of annunciation information, an
individual signal to the mobile station, a multicast signal, or a
combination of two or more out of these, transmitted from at least
one antenna of the base station. A mobile station as set forth in
claim 23 is the mobile station according to claim 21 or 22 wherein
the quality measuring means measures the receiving quality by using
a synchronization signal, a signal of annunciation information, an
individual signal to the mobile station, a multicast signal, or a
combination of two or more out of these signals, transmitted from
at least one antenna of the base station.
[0065] The physical quantity used as the receiving quality measured
at this time is not limited to a specific physical quantity,
either, but it can be selected from various physical quantities.
Specifically, as set forth in claim 10, the receiving quality can
be a received power, a value obtained by dividing a carrier power
by the sum of an interference power and a noise power (C/(I+N)), a
value obtained by dividing a signal power by the sum of an
interference power and a noise power (S/(I+N)), an error rate, a
likelihood obtained in decoding of error correction code, a C/N
ratio (Carrier to Noise Ratio), an S/N ratio (Signal to Noise
Ratio), a correlation value obtained by despreading of spreading
code, or a combination of two or more out of these.
[0066] Likewise, a mobile communication method as set forth in
claim 16 is the mobile communication method according to either one
of claims 11 to 15 wherein the receiving quality is a received
power, a value obtained by dividing a carrier power by the sum of
an interference power and a noise power, a value obtained by
dividing a signal power by the sum of an interference power and a
noise power, an error rate, a likelihood obtained in decoding of
error correction code, a C/N ratio, an S/N ratio, a correlation
value obtained by despreading of spreading code, or a combination
of two or more out of these. A mobile station as set forth in claim
24 is the mobile station according to either one of claims 21 to 23
wherein the receiving quality is a received power, a value obtained
by dividing a carrier power by the sum of an interference power and
a noise power, a value obtained by dividing a signal power by the
sum of an interference power and a noise power, an error rate, a
likelihood obtained in decoding of error correction code, a C/N
ratio, an S/N ratio, a correlation value obtained by despreading of
spreading code, or a combination of two or more out of these.
[0067] According to the present invention, as described above, the
signal addressed to the mobile station (including the multicast
signal) is transmitted from at least one antenna with the receiving
quality relatively better, based on the receiving qualities of the
signals measured at the mobile station, and it is thus feasible to
improve the receiving quality of the signal at the mobile station,
to prevent the repetition of repeat requests from the mobile
station, and to enhance the throughput.
[0068] When the present invention is applied in combination with
site diversity, use of plural base stations provides the effect of
increasing the diversity gain against shadowing, and the control
time can be unlimitedly shortened by the feature of the present
invention of using plural antennas in one base station. This makes
it feasible to realize large diversity gain against fading. The
maximum diversity gain can be achieved by applying the site
diversity to the present invention in this way.
[0069] In the conventional mobile communication system, as
described with reference to FIGS. 3 and 4, the base station
transmits the signal in only the determined frequency channel for
transmission of the signal addressed to the mobile station.
Therefore, a simple mobile station incapable of implementing
receiving antenna diversity, or a mobile station staying long at an
identical site remained in a low receiving quality state due to
fading or shadowing, thus posing the problem of degrading the
throughput because of the repetition of repeat requests.
[0070] An object of the present invention is therefore to decrease
the repetition of repeat requests from the mobile station to
enhance the throughput, as described above.
[0071] In order to accomplish the above object, the present
invention provides, as set forth in claim 25, a signal transmitting
method in a mobile communication system comprising a mobile station
and a base station and configured to perform transmission/reception
of a signal while sending and receiving an automatic repeat
request, the signal transmitting method being carried out as
follows in the mobile communication system: the mobile station
measures a receiving quality of a radio signal transmitted from the
base station, the mobile station notifies the base station of the
receiving quality of the radio signal thus measured, and the base
station transmits a signal under a repeat request from the mobile
station so as to meet a required receiving quality of the mobile
station, based on the receiving quality thus notified of.
[0072] According to the present invention, the base station
transmits the signal under the repeat request from the mobile
station so as to meet the required receiving quality at the mobile
station, based on the receiving quality of the radio signal
notified of by the mobile station, and it is thus feasible to avoid
the continuation of the low receiving quality state due to fading
or shadowing as suffered before. As a consequence, the repetition
of repeat requests from the mobile station can be decreased, and it
is feasible to enhance the throughput.
[0073] Concerning the radio signal from the base station measured
at the mobile station, as set forth in claim 26, the signal
transmitting method is configured so that the radio signal
transmitted from the base station becomes at least one radio
channel.
[0074] A type of the radio channel from the base station measured
at the base station is selected, for example, as set forth in claim
27, so that the mobile station uses, as a radio channel for
measurement of the receiving quality, an annunciation information
channel or an individual channel or a multicast channel or a
combination of these, among said at least one radio channel
transmitted from the base station.
[0075] According to the present invention, any radio channel can be
used for the measurement of the receiving quality at the mobile
station as long as it is a radio channel transmitted from the base
station.
[0076] The receiving quality of the radio channel measured at the
mobile station is selected as in the signal transmitting method, as
set forth in claim 28; the receiving quality is one selected from
the following:
[0077] a received power; C/(I+N) (Eq. 1)
[0078] C: carrier power
[0079] I: interference power
[0080] N: noise power; S/(I+N) (Eq. 2)
[0081] S: signal power
[0082] I: interference power
[0083] N: noise power; C/N (Eq. 3)
[0084] C: carrier power
[0085] N: noise power; S/N (Eq. 4)
[0086] S: signal power
[0087] N: noise power;
[0088] an error rate;
[0089] a likelihood obtained in decoding of error correction
code;
[0090] a transmission power value of the base station;
[0091] an increase amount or an attenuation amount of the
transmission power of the base station;
[0092] either of combinations of these.
[0093] Further, radio channels used in radio transmission between
the mobile station and the base station are selected as in the
signal transmission method, as set forth in claim 29, wherein radio
channels transmitted and received between the base station and the
mobile station are at least one of subcarrier channels, orthogonal
subcarrier channels, frequency channels, and frequency channels in
different frequency bands.
[0094] According to the present invention, the radio channels are
selected depending upon the transmission methods for
transmission/reception of signals between the base station and the
mobile station: the subcarrier channels in the multicarrier
transmission system; the orthogonal subcarrier channels in the OFDM
transmission system; the frequency channels in the FDM transmission
system; the frequency channels in different frequency bands in the
multiband transmission system.
[0095] From the viewpoint of enabling the notification of the
measured receiving quality on the occasion of the mobile station
sending the repeat request to the base station, the present
invention provides, as set forth in claim 30, the signal
transmitting method wherein when a repeat request for
retransmission of a received signal is needed, the mobile station
notifies the base station of the repeat request, together with the
receiving quality of the radio signal measured.
[0096] From the viewpoint of enabling the notification of the
measured receiving quality on the occasion of the mobile station
sending an arrival acknowledgement of a received packet to the base
station, the present invention provides, as set forth in claim 31,
the signal transmitting method wherein on an occasion of notifying
the base station of an acknowledgement of arrival of a received
signal, the mobile station notifies the base station of the
receiving quality of said at least one radio channel measured.
[0097] The information on the receiving quality sent from the
mobile station to the base station is one as in the signal
transmitting method, as set forth in claim 32, wherein the mobile
station notifies the base station of a number of at least one radio
channel and a receiving quality of the radio channel, or of only a
channel number of a receiving quality within a predetermined range,
as the receiving quality of said at least one radio channel
measured.
[0098] The information on the receiving quality is one as in the
signal transmitting method, as set forth in claim 33, wherein the
mobile station notifies the base station of a number of at least
one radio channel satisfying a required receiving quality,
including a radio channel with a maximum receiving quality at the
mobile station, together with the receiving quality achieved.
[0099] From the viewpoint of transmitting signals by changing radio
channels used for transmission of signals so as to improve the
receiving quality at the mobile station, the present invention
provides, as set forth in claim 34, the signal transmitting method
wherein the base station determines a radio channel satisfying the
required receiving quality at the mobile station on the basis of
notification from the mobile station, and the base station
transmits a signal under a repeat request from the mobile station,
using the radio channel determined.
[0100] According to the present invention, the base station
transmits the signal under the repeat request from the mobile
station by changing the radio channels one from another so as to
permit the mobile station receive the signal with the required
receiving quality, based on the receiving quality notified of by
the mobile station, and thus the base station does not always have
to use the predetermined radio channel for transmission of the
signal addressed to the mobile station, different from the
conventional systems. Namely, the base station adaptively changes
the radio channels one from another so as to improve the receiving
quality at the mobile station, so that the mobile station becomes
able to receive the signal with a better receiving quality,
resulting in decreasing the repetition of repeat requests. In
conjunction therewith, it becomes feasible to enhance the
throughput.
[0101] From the viewpoint that after the change of the radio
channel as described above the base station also transmits a signal
addressed to the mobile station through the use of the radio
channel, so as to enable maintenance of the required receiving
quality at the mobile station, the present invention provides, as
set forth in claim 35, the signal transmitting method wherein after
transmitting the signal under the repeat request from the mobile
station, using the determined radio channel, the base station also
transmits a signal addressed to the mobile station, using the
determined radio channel.
[0102] From the viewpoint of decreasing interference with other
mobile stations, the present invention provides, as set forth in
claim 36, the signal transmitting method wherein, based on the
notification from the mobile station, the base station determines a
number of a radio channel which satisfies the required receiving
quality at the mobile station and through which the signal is
transmitted so that a transmission power from the base station
becomes a predetermined value, and also determines a transmission
power of the radio channel.
[0103] According to the present invention, when receiving a repeat
request from the mobile station, the base station transmits the
signal requested by the repeat request, using the radio channel
satisfying the required receiving quality at the mobile station and
maintaining the transmission power from the base station at a
predetermined value. Accordingly, when the predetermined value is
set at a minimum value, the mobile station can receive the signal
requested by the repeat request, with the required receiving
quality even if the transmission power from the base station is
minimum. Namely, since the signal is transmitted at the minimum
transmission power from the base station, it is feasible to reduce
the interference with the other mobile stations not receiving the
signal under the repeat request.
[0104] From the viewpoint of improving the receiving quality of the
signal received at the mobile station even in the multicast
transmission of transmitting an identical signal to a plurality of
mobile stations, the present invention provides, as set forth in
claim 37, the signal transmitting method wherein when the base
station transmits an identical multicast signal to a plurality of
mobile stations, the base station determines a number of at least
one radio channel which satisfies the required receiving quality at
each mobile station and through which the multicast signal is
transmitted so that a transmission power from the base station
becomes a predetermined value, and also determines a transmission
power of the radio channel, based on notification from each mobile
station.
[0105] The present invention also provides, as set forth in claim
38, the signal transmitting method wherein when the base station
transmits the identical multicast signal to the plurality of mobile
stations, the base station determines a number of a radio channel
that can be assumed to have the greatest number of repeat requests
from the mobile stations, out of channel numbers with receiving
qualities within a predetermined range, notified of by the
respective mobile stations.
[0106] Further, the present invention provides, as set forth in
claim 39, a mobile communication system comprising a mobile station
and a base station and configured to perform transmission/reception
of a signal while sending and receiving an automatic repeat
request, wherein the mobile station comprises: receiving quality
measuring means for measuring a receiving quality of a radio signal
transmitted from the base station; and receiving quality notifying
means for notifying the base station of the receiving quality of
the radio signal thus measured, and wherein the base station
comprises: transmitting means for transmitting a signal under a
repeat request from the mobile station so that a required receiving
quality is satisfied at the mobile station, based on the receiving
quality notified of by the mobile station.
[0107] The mobile communication system as set forth in claim 1 is
different from the mobile communication system as set forth in
claim 39 in that the subject for determining the radio resource on
the basis of the receiving quality is on the mobile station side in
the former or on the base station side in the latter, and they both
belong to the same technical concept.
[0108] The present invention also provides, as set forth in claim
56, a base station in a mobile communication system comprising a
mobile station and the base station and configured to perform
transmission/reception of a signal while sending and receiving an
automatic repeat request, the base station comprising transmitting
means for transmitting a signal under a repeat request from the
mobile station so that a required receiving quality is satisfied at
the mobile station, based on a receiving quality notified of by the
mobile station.
[0109] Further, the present invention provides, as set forth in
claim 63, a mobile station in a mobile communication system
comprising the mobile station and a base station and configured to
perform transmission/reception of a signal while sending and
receiving an automatic repeat request, the mobile station
comprising: receiving quality measuring means for measuring a
receiving quality of a radio signal transmitted from the base
station; and receiving quality notifying means for notifying the
base station of the receiving quality of the radio signal thus
measured.
[0110] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not to be considered as limiting the present invention.
[0111] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
[0112] A mobile communication system according to the present
invention is configured, as set forth in claim 53, so that the base
station comprises radio resource determining means for determining
a radio resource satisfying the required receiving quality at the
mobile station on the basis of notification from the mobile
station; and signal transmitting means for transmitting the signal
under the repeat request from the mobile station, using the radio
resource determined by the radio resource determining means.
[0113] Further, in the mobile communication system as set forth in
claim 54, the transmitting means transmits the signal by using
radio resources in decreasing order of the number of repeat
requests from the mobile station.
[0114] In the mobile communication system as set forth in claim 55,
the radio resource is at least one antenna, directivities of at
least one antenna, a radio channel, a transmission path, or either
of combinations of these. Here the antenna may be a single antenna
or a plurality of antennas, and in the case of a plurality of
antennas being used, directivities of the respective antennas may
be different from each other. The transmission path is intended for
a situation in which a signal is indirectly transmitted via a
mobile station as a relay station (multihop connection).
BRIEF DESCRIPTION OF THE DRAWINGS
[0115] FIG. 1 is a block diagram of a conventional mobile
communication system.
[0116] FIG. 2 is a chart for illustrating the cooperative operation
of the conventional mobile communication system with the automatic
repeat request.
[0117] FIG. 3 is a block diagram of another conventional mobile
communication system with the automatic repeat request.
[0118] FIG. 4 is a chart for illustrating the operation of the
conventional mobile communication system.
[0119] FIG. 5 is a block diagram of a mobile communication system
in the first embodiment of the present invention.
[0120] FIG. 6 is a chart for illustrating the cooperative operation
of the mobile communication system with the automatic repeat
request in the first embodiment of the present invention.
[0121] FIG. 7A is a diagram for illustrating the procedure of data
transmission in application of the TDM system, and FIG. 7B a
diagram for illustrating the procedure of data transmission in
application of the CDM system.
[0122] FIG. 8 is a block diagram of a mobile communication system
in the second embodiment of the present invention.
[0123] FIG. 9 is a chart for illustrating the cooperative operation
of the mobile communication system with the automatic repeat
request in the second embodiment of the present invention.
[0124] FIG. 10 is a block diagram of a mobile communication system
in the third embodiment to which the signal transmitting method of
the present invention is applied.
[0125] FIG. 11 is a flowchart showing the operation in the third
embodiment of the present invention.
[0126] FIG. 12 is a block diagram of a mobile communication system
in the fourth embodiment to which the signal transmitting method of
the present invention is applied.
[0127] FIG. 13 is a flowchart showing the operation in the fourth
embodiment of the present invention.
[0128] FIG. 14 is a flowchart showing the processing procedure of
determining a number of a frequency channel and a transmission
power of the frequency channel in the fourth embodiment of the
present invention.
[0129] FIG. 15 is a diagram showing an example of receiving
qualities of respective frequency channels at each of mobile
stations in the fourth embodiment of the present invention.
[0130] FIG. 16 is a block diagram of a mobile communication system
in the fifth embodiment to which the signal transmitting method of
the present invention is applied.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0131] The first embodiment of the present invention will be
described with reference to FIGS. 5 to 7. The present embodiment
will describe an example in which a base station is equipped with
two base station antennas, but it is noted that the present
invention can be substantiated with any number of base station
antennas.
[0132] First, the configuration of the mobile communication system
will be generally described. As shown in FIG. 5, the mobile
communication system 100 is generally comprised of a base station
101 and a mobile station 111.
[0133] The base station 101 comprises a plurality of base station
antennas 7, 8; a plurality of transmitted/received wave splitters 4
provided corresponding to the respective antennas; an antenna
switching unit 109 for switching the transmitted/received wave
splitters 4 one from another to use either one; an ARQ processor
102 configured to perform various processes including a process of
attaching the error-detectable parity such as the CRC or the like
to the input data entering a data input terminal 6, a process of
retransmitting a signal in response to a repeat request from the
mobile station, a process of notifying a transmitter 103 of use of
an antenna based on an antenna use request, and so on; the
transmitter 103 configured to switch output of the antenna
switching unit 109 and transmit data from the ARQ processor 102;
and a receiver 5 configured to receive data from the outside
through the base station antennas 7, 8 and feed the data to the ARQ
processor 102.
[0134] The mobile station 111 comprises a mobile station antenna
17; a transmitted/received wave splitter 16; a receiving quality
measuring unit 118 configured to measure a receiving quality of a
received signal for measurement of receiving quality and store the
receiving quality in a memory 119; a receiver 12 configured to
receive a signal from the outside through the transmitted/received
wave splitter 16; an ARQ processor 113 configured to perform the
error detection using the CRC for the signal received at the
receiver 12 and output data from a data output terminal 14 and also
configured to, with detection of an error, output to a transmitter
15 notification of a repeat request for retransmission of received
data and a number of a base station antenna with a high receiving
quality; and a transmitter 15 configured to transmit the
notification of the repeat request and the number of the base
station antenna with the high receiving quality from the ARQ
processor 13.
[0135] The present embodiment will be described hereinafter,
supposing the receiving quality is a received power. However, as
explicitly stated in claim 10, it is also possible to employ as the
receiving quality a value obtained by dividing a carrier power by
the sum of an interference power and a noise power (i.e., C/(I+N)),
a value obtained by dividing a signal power by the sum of an
interference power and a noise power (i.e., S/(I+N)), an error
rate, a likelihood obtained in decoding of error correction code, a
C/N ratio, an S/N ratio, a correlation value obtained by
despreading of spreading code, or a combination of two or more out
of these.
[0136] The following will describe the operation of the mobile
communication system along FIG. 6.
[0137] At the base station 101, data addressed to the mobile
station 111, entering the data input terminal 6, is fed into the
ARQ processor 102. The ARQ processor 102 attaches the
error-detectable parity such as the CRC or the like to the data so
as to permit detection of an error occurring during transmission,
thereafter stores the data, and outputs the data to the transmitter
103 (step 1).
[0138] Prior to transmission of a transmitted signal of the input
data, the transmitter 103 switches the output of the antenna
switching unit 109 to the first base station antenna and outputs a
signal for measurement of receiving quality therefrom. The signal
for measurement of receiving quality is transmitted through the
transmitted/received wave splitter 4 and from the first base
station antenna 7 to the mobile station 111 (step 2).
[0139] At the mobile station 111, the signal for measurement of
receiving quality is fed through the transmitted/received wave
splitter 16 into the receiving quality measuring unit 118. The
receiving quality measuring unit 118 measures a received power
value of the signal for measurement of receiving quality and stores
the received power value as a receiving quality with the use of the
first base station antenna in the memory 119 (step 3).
[0140] Next, the output of the antenna switching unit 109 is
switched to the second base station antenna and a signal for
measurement of receiving quality is outputted. The signal for
measurement of receiving quality is transmitted through the
transmitted/received wave splitter 4 and from the second base
station antenna 8 to the mobile station 111 (step 4).
[0141] At the mobile station 111, in much the same manner as above,
the signal for measurement of receiving quality is fed through the
transmitted/received wave splitter 16 into the receiving quality
measuring unit 118 to measure a received power value thereof, and
the received power value is stored as a receiving quality with the
use of the second base station antenna in the memory 119 (step
5).
[0142] Thereafter, as shown in FIG. 7A, the output of the antenna
switching unit 109 is switched to the first base station antenna 7
and the transmitted signal of the data is outputted. The
transmitted signal is transmitted through the transmitted/received
wave splitter 4 and from the first base station antenna 7 to the
mobile station 111 (step 6).
[0143] The above described an application of the TDM (Time Division
Multiple) system, but it is also possible to apply the CDM (Code
Division Multiple) system. In this system, as shown in FIG. 7B,
signals for measurement of receiving quality are spread by
spreading codes uniquely corresponding to the respective antennas
and thereafter the signals are transmitted from the corresponding
antennas. The mobile station receives the signals, despreads the
signals by the spreading codes uniquely corresponding to the
antennas to obtain received powers, correlation values, or the
like, and can use them as receiving qualities.
[0144] The following will continue the description back into the
application case of the TDM system.
[0145] At the mobile station 111, the received signal is fed
through the transmitted/received wave splitter 16 into the receiver
12. Then the signal received at the receiver 12 is fed as received
data into the ARQ processor 113 (step 7). Then the ARQ processor
113 performs the error detection using the CRC. When no error is
detected in the received data herein, the received data is
outputted from the data output terminal 14 and an acknowledgement
of arrival of the data is sent through an uplink 21 to the ARQ
processor 102 of the base station 101 (step 8 and step 9).
[0146] The base station 101 can be configured to, on the occasion
of receiving notification of an arrival acknowledgement or a repeat
request from the mobile station 111, feed the outputs from the
first base station antenna 7 and the second base station antenna 8
into the receiver 5 and perform antenna reception in the diversity
system of two branches, thereby improving the receiving quality of
the uplink. Then the ARQ processor 102, receiving the notification
of the arrival acknowledgement, deletes the data stored for
retransmission (step 13 and step 14).
[0147] When at step 8 an error is detected in the received data on
the other hand, the ARQ processor 113 searches for a number of a
base station antenna with the higher receiving quality, i.e., the
higher received power value stored in the memory 119, and outputs
the number of the base station antenna together with a repeat
request for retransmission of the received data to the transmitter
15. The transmitter 15 sends the repeat request of the received
data and the number of the base station antenna through the uplink
21 to the ARQ processor 102 of the base station 101 (step 10, step
11, and step 12). The ARQ processor 102, receiving the notification
of the repeat request, first notifies the transmitter 103 of the
antenna number requested by the mobile station 111, and the
transmitter 103 controls the antenna switching unit 109 so as to be
ready for transmission through the use of the antenna to the mobile
station 111. Then the data under the repeat request is
retransmitted from the antenna requested by the mobile station 111
(step 13 and step 15).
[0148] Since the ARQ processor 102 stores the number of the antenna
requested by the mobile station 111, it becomes feasible to
transmit new data addressed to the mobile station 111, entering the
data input terminal 6 thereafter, through the use of the base
station antenna with the higher receiving quality at the mobile
station 111, without the need for transmitting the aforementioned
signals for measurement of receiving quality from the base station
101.
[0149] According to the first embodiment as described above, the
signal addressed to the mobile station 111 is transmitted from the
base station 101 through the use of the antenna with the receiving
quality relatively better, based on the receiving qualities of the
signals measured at the mobile station 111, and it is thus feasible
to improve the receiving quality of the signal at the mobile
station 111, to prevent the repetition of repeat requests from the
mobile station 111, and to enhance the throughput of the mobile
communication system 100.
[0150] The above described the transmission of the signals for
measurement of receiving quality prior to the transmission of data,
but the present invention can also be substantiated without the
transmission of the signals for measurement of receiving quality
prior to the data transmission, as stated in claim 9, by a
configuration wherein the mobile station 111 receives a
synchronization signal, a signal of annunciation information, an
individual signal to the mobile station, a multicast signal, or a
combination of two or more out of these and always updates the
contents stored in the memory 119.
[0151] The present embodiment can also be applied to the mobile
station functioning as a relay station instead of the base station,
supposing the situation of multihop connection. In this case, the
mobile station 111, which is a transmitting station of a repeat
request, preliminarily identifies existence of an adjoining mobile
station as relay station and requests retransmission of a signal by
designating a transmission path including the mobile station (relay
station). Similarly, the base station 101, which is a transmitting
station of the signal according to the repeat request,
preliminarily identifies existence of an adjoining mobile station
as a relay station and responds to the repeat request by
designating a transmission path including the mobile station (relay
station).
Second Embodiment
[0152] The configuration of the second embodiment of the present
invention will be described with reference to FIG. 8.
[0153] The present embodiment will describe an example of multicast
transmission wherein the base station transmits identical data
(which will be referred to as multicast data in the present
embodiment) to a plurality of mobile stations and a configuration
wherein an automatic repeat request is arranged so that
notification of a repeat request is given only when an error is
detected. There exist a plurality of mobile stations receiving the
multicast data, but the following will describe the operation of
only one mobile station out of them. It is a matter of course that
like operation is carried out at the other mobile stations being
multicast targets omitted to describe.
[0154] At the base station 201, multicast data addressed to the
mobile stations 211, entering the data input terminal 6, is fed
into the ARQ processor 202. The ARQ processor 202 stores the
multicast data for retransmission in the memory 210, thereafter
attaches the CRC to the data and performs error-correction code
coding thereof, and further attaches information about a number of
a base station antenna used for transmission and then outputs the
data to the transmitter 3. Then the transmitter 3 controls the
antenna switching unit 109 so as to implement transmission from the
antenna indicated by the information on the number of the base
station antenna thus attached. The transmitter 3 modulates the
input multicast data into a transmitted signal (multicast signal)
and thereafter outputs the signal to the antenna switching unit
109. The antenna switching unit 109 is configured to be able to
transmit the multicast signal through the transmitted/received wave
splitter 4 and from the base station antenna corresponding to the
aforementioned number information (either the first base station
antenna 7 or the second base station antenna 8).
[0155] In the present embodiment, it is assumed that the antenna
switching unit 109 is controlled so as to be able to transmit the
multicast signal, preferentially using a base station antenna with
the greatest number of requests from the mobile stations being the
multicast targets. Namely, before outputting the multicast data to
the transmitter 3, the ARQ processor 202 searches the information
stored in the memory 210 for the information on the number of the
base station antenna with the greatest number of requests from the
mobile stations, and controls the antenna switching unit 109 so as
to transmit the multicast signal from the base station antenna
corresponding to the number. The memory 210 is used for storing
correspondences between the numbers of requests from the mobile
stations and the numbers of the base station antennas.
[0156] At the mobile station 211 on the other hand, the multicast
signal received at the mobile station antenna 17 through the
downlink 22 is fed through the transmitted/received wave splitter
16 into the receiver 12. The receiver 12 demodulates the received
multicast signal and outputs the demodulated signal as received
multicast data to the ARQ processor 213. The ARQ processor 213
performs the decoding of error correction code and thereafter
performs the error detection using the attached CRC. At the same
time, the ARQ processor 213 stores a likelihood obtained in the
decoding of error correction code, together with the information on
the number of the base station antenna attached to the received
multicast data, in the memory 119. The foregoing likelihood can be
the number of corrected bits in the case of the error-correction
code coding being the block code such as the BCH code, the RS code,
or the like, or a metric in the case of the convolutional code.
[0157] When the foregoing error detection with the CRC finds no
error in the received multicast data, the ARQ processor 213 outputs
the received multicast data from the data output terminal 14,
without transmitting any signal to the base station 201 at all.
When an error is detected in the received multicast data on the
other hand, the ARQ processor 213 searches the information stored
in the memory 119 for the information on the number of the base
station antenna with the highest receiving quality and outputs the
information on the number of the base station antenna together with
a repeat request for retransmission of the received multicast data
to the transmitter 15. The transmitter 15 transmits the repeat
request of the received multicast data and the information on the
number of the base station antenna through the uplink 21 to the
base station 201.
[0158] At the base station 201, the receiver 5 receives the repeat
request of the received multicast data and the information on the
number of the base station antenna and the receiver 5 outputs the
data to the ARQ processor 202. The ARQ processor 202, as described
previously, measures the number of requests for the numbers of the
base station antennas requested by the mobile stations, stores the
correspondences between the numbers of the base station antennas
and the numbers of mobile stations requesting the respective
antennas, in the memory 210, and, on the occasion of retransmitting
the multicast data thereafter, retransmits the data, preferentially
using the base station antenna with the greatest number of
requests.
[0159] The following will describe the cooperative operation of the
base station 201 and a plurality of mobile stations (four mobile
stations A to D as an example herein) with reference to FIG. 9. The
configuration of the mobile stations A to D is substantially the
same as that of the mobile station 211 shown in FIG. 8, and they
are in an initial state in which no data is stored yet in the
memory 210 provided in the base station 201 and in the memories 119
provided in the respective mobile stations.
[0160] The base station 201 attaches the number information of the
first antenna 7 to multicast data, and transmits the multicast data
with the number information thus attached, to all the mobile
stations (the mobile stations A to D) as multicast targets. For
example, let us suppose the mobile stations A to C detect an error
in the received multicast data. Then the mobile stations A to C
send to the base station 201 a repeat request for retransmission of
the data and an antenna use request that the second antenna 8, an
error rate of which is not stored yet in the memory 119, should be
used. Since the mobile station D detects no error in the received
multicast data, it transmits nothing to the base station 201.
[0161] At the base station 201, the ARQ processor 202 then measures
the number of requests for the information on the number of each
antenna to be used for retransmission, from the mobile stations A
to C, and stores the results of the measurement, i.e., information
indicating that the number of requests for retransmission from the
second antenna 8 is three and that the number of requests for
retransmission from the first antenna 7 is zero, in the memory 210.
For this reason, based on the foregoing results of the measurement
stored in the memory 210, the base station 201 transmits the
multicast data to be retransmitted (hereinafter referred to as
retransmitted multicast data) to the mobile stations A to C from
the second antenna 8 with the maximum number of requests for
retransmission (this step corresponds to "first retransmission" in
FIG. 9).
[0162] In the reception of the first retransmitted multicast data,
the mobile stations A to C again detect an error, and then send a
repeat request to the base station 201. At the mobile station A, an
error rate is lower in the reception of the multicast data
transmitted from the second antenna 8, and the mobile station A
sends a use request for use of the second antenna 8, together with
the notification of the repeat request, to the base station 201. On
the other hand, at the mobile stations B and C, an error rate is
lower in the reception of the multicast data transmitted from the
first antenna 7, and thus they send a use request for use of the
first antenna 7, together with the notification of the repeat
request, to the base station 201.
[0163] At the base station 201, the ARQ processor 202 stores
information that the number of requests for retransmission from the
second antenna 8 is one and the number of requests for
retransmission from the first antenna 7 is two, in the memory 210.
For this reason, based on the results of the above measurement
stored in the memory 210, the base station 201 transmits the
retransmitted multicast data to the mobile stations A to C from the
first antenna 7 with the maximum number of requests for
retransmission (this step corresponds to "second retransmission" in
FIG. 9).
[0164] The mobile stations B and C detect no error in the reception
of the second retransmitted multicast data, and thus they transmit
nothing to the base station 201. On the other hand, the mobile
station A detects an error, but it sends no repeat request to the
base station 201, because the base station antenna used for the
transmission is not the antenna requested by the mobile station A.
This is because in the next transmission the retransmitted
multicast data is expected to be transmitted using the second
antenna 8 requested by the mobile station A.
[0165] Thereafter, based on the results of the measurement stored
in the memory 210, the base station 201 transmits the retransmitted
multicast data to the mobile station A from the second antenna 8
with the second highest number of requests for retransmission (this
step corresponds to "third retransmission" in FIG. 9).
[0166] The mobile station A detects no error in the reception of
the third retransmitted multicast data, and thus transmits nothing
to the base station 201, thus completing the multicast transmission
from the base station 201.
[0167] By the operation as described above, it becomes feasible to
implement the transmission of high-quality signals with the
automatic repeat request of the present invention in the
transmission of multicast data.
[0168] According to the second embodiment described above, the base
station 201 transmits the retransmitted multicast data, using the
base station antennas in descending order of the number of antenna
use requests based on the receiving qualities of signals measured
at the respective mobile stations, and it is thus feasible as a
whole of the mobile communication system to improve the receiving
qualities of retransmitted multicast data at more mobile stations,
to decrease the total number of occurrences of repeat requests, and
to enhance the total throughput of the entire system.
[0169] The above first and second embodiments described the
examples in which the mobile station transmitted the antenna use
request for use of one antenna out of the plurality of base station
antennas, but it is also possible in the case of a number of base
station antennas being provided, to employ a configuration wherein
the mobile station transmits an antenna use request designating two
or more base station antennas with better receiving qualities, as
antennas to be used.
[0170] Incidentally, while the present invention can be mentioned
as a so-called diversity system wherein one base station uses
plural antennas, site diversity is known as a diversity system
wherein a plurality of base stations use one antenna.
[0171] This site diversity has the advantage of great diversity
gain because of no correlation with shadowing (variation of local
median value), but it has the following disadvantages against the
fading (instantaneous variation), though demonstrating some great
diversity gain because of no correlation therewith: the delay in
control time is too large to realize the satisfactory diversity
gain because of transmission of control signals between plural base
stations; the efficiency is low, because radio resources and
devices for the plural base stations are preliminarily occupied for
the control in order to adapt to the instantaneous variation.
[0172] When the present invention is applied in combination with
the above site diversity, it can provide the effect of increase in
the diversity gain thanks to the use of the plural base stations
against the shadowing. Since the control time can be unlimitedly
shortened by the feature of the present invention of using plural
antennas in one base station, satisfactorily large diversity gain
can be realized against the fading. By applying the site diversity
to the present invention as described, it is feasible to attain the
maximum diversity gain.
[0173] The present embodiment can also be applied to the mobile
station functioning as a relay station instead of the base station,
supposing the situation of multihop connection. In this case, the
mobile station 211, which is a transmitting station of a repeat
request, preliminarily identifies existence of an adjoining mobile
station as relay station and requests retransmission of a signal by
designating a transmission path including the mobile station (relay
station). Similarly, the base station 201, which is a transmitting
station of the signal according to the repeat request,
preliminarily identifies existence of an adjoining mobile station
as a relay station and responds to the repeat request by
designating a transmission path including the mobile station (relay
station).
Third Embodiment
[0174] The third embodiment of the present invention will be
described with reference to FIGS. 10 and 11. The present embodiment
will describe an example in which the base station transmits the
signal to the mobile station in the multiband transmission
system.
[0175] FIG. 10 is a block diagram of the mobile communication
system in the present embodiment, which is generally comprised of a
base station 301 and a mobile station 311. The base station 301
comprises an ARQ processor 302, a transmitter/receiver 303, a
signal input terminal 304, a base station antenna 305, and a
channel determiner 306. The mobile station 311 comprises a
transmitter/receiver 312, an ARQ processor 313, a signal output
terminal 314, a mobile station antenna 315, a receiving quality
measuring unit 316, and a memory 317.
[0176] The following will describe the operation with reference to
the flowchart of FIG. 11.
[0177] At the base station 301, a signal addressed to the mobile
station 311, entering the signal input terminal 304, is fed into
the ARQ processor 302. The ARQ processor 302 attaches the
error-detectable parity such as the CRC or the like to the signal
so as to permit the detection of an error occurring during
transmission, thereafter stores the signal for retransmission (T2),
and outputs the signal to the transmitter/receiver 303. The
transmitter/receiver 303 informs the mobile station 311 of a
transmission start of the signal addressed to the mobile station
311 and a number of a frequency channel in a frequency band for
transmission of the signal (T3) and thereafter transmits the signal
to the mobile station 311 (T4).
[0178] If candidates are preliminarily known for the number of the
frequency channel in the frequency band for transmission of the
signal, it is also possible to omit the informing step of the
number of the frequency channel in the frequency band.
[0179] On the other hand, at the mobile station 311, the receiving
quality measuring unit 316 continuously, constantly measures C/I
(Carrier-to-Interfere ratio: carrier power to interference power
ratio) of individual channels transmitted from the base station
301, as receiving qualities (T1), and stores relations between
numbers of frequency channels in frequency bands Measured, and
C/I's of the frequency channels in the memory 317.
[0180] As described above, the receiving quality measuring unit 316
continuously, constantly measures the C/I's of individual channels
or the like transmitted from the base station 301. Therefore, the
relations are always updated between numbers of frequency channels
in frequency bands, and C/I's of the frequency channels in the
memory 317.
[0181] At the mobile station 311 in this configuration, the signal
addressed to the mobile station, transmitted from the base station
301, is received through the downlink 322 by the
transmitter/receiver 312 (T5), and thereafter the signal is fed
into the ARQ processor 313. The ARQ processor 313 performs the
error detection of the received signal using the CRC. When no error
is detected in the received signal (NO at T6), the ARQ processor
313 outputs the received signal from the signal output terminal 314
and also sends an acknowledgement of arrival of the received signal
through the uplink 321 to the ARQ processor 302 of the base station
301 (T7). Then the ARQ processor 302, receiving the notification of
the arrival acknowledgement from each mobile station, deletes the
signal addressed to the mobile station, stored for retransmission
(T9 and T10). In this respect, it is also possible to employ a
configuration without the notification of the arrival
acknowledgement (T7), wherein the process of detecting the repeat
request (T9) is provided with a time-out judging function and the
operation of T10 is carried out when no repeat request is detected
within a certain period of time.
[0182] When at T6 an error is detected in the received signal (YES
at T6) on the other hand, the ARQ processor 313 sends a repeat
request for retransmission of the received signal through the
uplink 321 to the ARQ processor 302 of the base station 301 and
also sends to the channel determiner 306 of the base station 301 a
number of a frequency channel in a frequency band with the maximum
C/I out of those measured and stored in the memory 317, and the C/I
of the frequency channel (T8).
[0183] When the ARQ processor 302 receives the repeat request, it
is determined at T9 whether the input signal is a repeat request.
When a repeat request is detected at the determination of T9 (YES
at T9), the channel determiner 306 is notified of the result of the
detection. Receiving the notification of the detection of the
repeat request from the ARQ processor 302, the channel determiner
306 calculates such a transmission power that the receiving quality
at the mobile station 311 becomes a required value, based on the
C/I thus notified of (T11), and then controls the
transmitter/receiver 303 so that the signal under the repeat
request is retransmitted by the frequency channel number notified
of and the transmission power calculated. Then the signal
retransmitted from the ARQ processor 302 is fed into the
transmitter/receiver 303, and the transmitter/receiver 303 informs
the mobile station of the number of the frequency channel in the
frequency band used for retransmission (T12) and thereafter
transmits the retransmitted signal thereto (T13).
[0184] The base station 301 also transmits a new signal addressed
to the mobile station, entering the signal input terminal 304
thereafter, by using the number of the frequency channel in the
frequency band and the transmission power acquired in the above
operation.
[0185] When candidates are known in advance for the number of the
frequency channel in the frequency band used for retransmission,
the base station omits the informing step of the number of the
frequency channel in the frequency band used for retransmission and
the mobile station receives the retransmitted signal by the use of
the number of the frequency channel in the frequency band with the
maximum receiving quality out of the candidates for the number of
the frequency channel in the frequency band.
[0186] As described above, the present embodiment showed the
example using the multiband transmission system as an example of
the transmission system between the base station 301 and the mobile
station 311, and besides, it is also possible to use the FDM
(Frequency Division Multiplexing) transmission system, the
multicarrier transmission system, or the OFDM (Orthogonal Frequency
Division Multiplexing) transmission system as a transmission system
between the base station 301 and the mobile station 311. For
example, the base station 301 is notified of a number of a
frequency channel and a receiving quality of the frequency channel
in the case of the FDM transmission system being used; of a number
of a subcarrier channel and a receiving quality of the subcarrier
channel in the case of the multicarrier transmission system being
used; or of a number of an orthogonal subcarrier channel and a
receiving quality of the orthogonal subcarrier channel in the case
of the OFDM transmission system being used, whereby the receiving
quality at the mobile station 311 can be improved by the operation
similar to that in the present embodiment.
[0187] According to the third embodiment of the present invention,
as described above, the base station 301 calculates the
transmission power to achieve the required receiving quality at the
mobile station, based on the number of the frequency channel and
the C/I of the frequency channel notified of by the mobile station
311, and retransmits the signal under the repeat request from the
mobile station 311, using the number of the frequency channel
notified of and the transmission power thus calculated, whereby the
mobile station 311 can be prevented from being kept in the low
receiving quality state because of fading or shadowing. As a
consequence, the repetition of repeat requests from the mobile
station 311 can be reduced, so as to enhance the throughput. Since
the retransmission of the retransmitted signal is carried out after
changeover into the frequency channel with the minimum transmission
power from the base station 301, interference can be reduced with
mobile stations 311 not receiving the retransmitted signal.
[0188] The present embodiment can also be applied to the mobile
station functioning as a relay station instead of the base station,
supposing the situation of multihop connection. In this case, the
mobile station 311, which is a transmitting station of a repeat
request, preliminarily identifies existence of an adjoining mobile
station as relay station and requests retransmission of a signal by
designating a transmission path including the mobile station (relay
station). Similarly, the base station 301, which is a transmitting
station of the signal according to the repeat request,
preliminarily identifies existence of an adjoining mobile station
as a relay station and responds to the repeat request by
designating a transmission path including the mobile station (relay
station).
Fourth Embodiment
[0189] The fourth embodiment of the present invention will be
described below with reference to FIGS. 12 to 15. The present
embodiment will describe an example in which the base station
transmits a multicast signal to each mobile station in the FDM
transmission system.
[0190] FIG. 12 is a block diagram of the mobile communication
system in the fourth embodiment, which is generally comprised of a
base station 401 and a mobile station 411, as in the third
embodiment described above. The base station 401 comprises an ARQ
processor 402, a transmitter/receiver 403, a signal input terminal
404, a base station antenna 405, and a channel determiner 406. The
mobile station 411 comprises a transmitter/receiver 412, an ARQ
processor 413, a signal output terminal 414, a mobile station
antenna 415, a receiving quality measuring unit 416, and a memory
417.
[0191] The following will describe the operation of the mobile
communication system in the present embodiment with reference to
the flowchart of FIG. 13. There exist a plurality of mobile
stations in a group receiving one multicast signal, but only one
mobile station in the group will be described below as a typical
example. The other mobile stations belonging to the group also
perform the operation similar to that of the mobile station
described below.
[0192] At the base station 401, a multicast signal addressed to the
mobile stations 411, entering the signal input terminal 404, is fed
into the ARQ processor 402. The ARQ processor 402 attaches the
error-detectable parity such as the CRC or the like to the signal
so as to permit the detection of an error occurring during
transmission, thereafter stores the multicast signal for
retransmission (T22), and outputs the signal to the
transmitter/receiver 403. The transmitter/receiver 403 informs each
mobile station of a start of transmission of the multicast signal
and a number of a frequency channel for transmission of the
multicast signal, and thereafter transmits the multicast signal to
the mobile station 411 (T23 and T24).
[0193] When candidates are known in advance for the number of the
frequency channel used for transmission of the multicast signal, it
is also possible to omit the informing step of the frequency
channel number.
[0194] On the other hand, at the mobile station 411, the receiving
quality measuring unit 116 continuously, constantly measures C/I of
an individual channel or the like transmitted from the base station
401 as a receiving quality (T21), and stores the relation between
the number of the frequency channel and the C/I of the frequency
channel thus measured, in the memory 117.
[0195] As described above, the receiving quality measuring unit 416
continuously, constantly measures the C/I's of the individual
channels or the like transmitted from the base station 401.
Therefore, the relations are always updated between the numbers of
the frequency channels, and the C/I's of the frequency channels in
the memory 117.
[0196] The present embodiment will be described hereinafter,
supposing the receiving quality is C/I. It is, however, also
possible to use as the receiving quality a received power, C/(I+N),
S/(I+N), C/N, S/N, an error rate, a likelihood obtained in decoding
of error correction code, a base station transmission power value,
an amount of increase or attenuation of the base station
transmission power, or a combination of these. The character "C" in
C/(I+N) above represents the carrier power, and "S" in S/(I+N)
above the signal power. Further, the character "I" in above C/(I+N)
and above S/(I+N) represents the interference power, and "N" the
noise power.
[0197] In the present invention, as described, it is possible to
use any signal for the measurement of receiving quality as long as
it is a signal transmitted from the base station 401 configured to
transmit the multicast signal.
[0198] At the mobile station 411, the multicast signal transmitted
from the base station 401 is received through the downlink 422 at
the transmitter/receiver 412 (T25) and thereafter is fed into the
ARQ processor 413. The ARQ processor 413 performs the error
detection of the received multicast signal using the CRC. When no
error is detected in the received multicast signal (NO at T26), the
ARQ processor 413 outputs the received multicast signal from the
signal output terminal 414 and sends an acknowledgement of arrival
of the received multicast signal to the ARQ processor 402 of the
base station 401 through the uplink 421 (T27).
[0199] The ARQ processor 402, receiving only the notification of
the arrival acknowledgement from each mobile station, deletes the
multicast signal stored for retransmission (NO at T29, and T30). In
this respect, it is also possible to employ a configuration without
the foregoing notification of the arrival acknowledgement (T27),
wherein the process of detecting the repeat request (T29) is
provided with a time-out judging function and the operation of
(T30) is executed when no repeat request is detected within a
certain period of time.
[0200] When an error is detected in the received multicast signal
on the other hand (YES at T26), the ARQ processor 413 sends a
repeat request for retransmission of the received multicast signal
through the uplink 421 to the ARQ processor 402 of the base station
401. The ARQ processor 413 also makes access to the memory 417 and
notifies the channel determiner 406 of the base station 401, of the
latest frequency channel number and the C/I of the frequency
channel measured and stored in the memory 417 (T28).
[0201] When the repeat request is fed into the ARQ processor 402,
it is determined at (T29) whether the input signal is a repeat
request. When a repeat request is detected at the determination of
T29 (YES at T29), the channel determiner 406 is notified of the
result of the detection. When the channel determiner 406 receives
the notification that the repeat request is detected by the ARQ
processor 402, it determines a number of a frequency channel for
retransmission and a transmission power of the frequency channel on
the basis of the frequency channel number and the C/I of the
frequency channel notified of by each mobile station (T31), and
thereafter controls the transmitter/receiver 403 so as to
retransmit the signal by the use of the frequency channel number
and the transmission power thus determined.
[0202] Then the multicast signal stored for retransmission at the
ARQ processor 402 is fed into the transmitter/receiver 403, and the
transmitter/receiver 403 informs the mobile station of numbers of
frequency channels or a number of a single frequency channel used
for retransmission (T32) and thereafter transmits the input
retransmitted multicast signal (T33).
[0203] Each mobile station to receive the retransmitted multicast
signal, receives the retransmitted multicast signal in a channel of
a frequency channel number with the maximum receiving quality at
the mobile station out of the frequency numbers thus informed of.
When candidates are known in advance for the numbers of the
frequency channels or the number of the single frequency channel
used for retransmission, the informing step of the frequency
channel number for retransmission of the multicast signal is
omitted, and each mobile station receives the retransmitted
multicast signal in a channel of a frequency channel number with
the maximum receiving quality out of the candidates for the
frequency channel numbers.
[0204] The base station 401 can also transmit a new multicast
signal entering the signal input terminal 404 in processing
thereafter, using the numbers of the frequency channels or the
number of the single frequency channel and the transmission power
determined above.
[0205] As described above, the fourth embodiment described the case
using the FDM transmission system as an example of the transmission
system between the base station 401 and the mobile station 411, and
besides, it is also possible to use the multicarrier transmission
system, the OFDM transmission system, or the multiband transmission
system as a transmission system between the base station 401 and
the mobile station 411. For example, the base station 401 is
notified of a number of a subcarrier channel and a receiving
quality of the subcarrier channel in the case of the multicarrier
transmission system being used; of a number of an orthogonal
subcarrier channel and a receiving quality of the orthogonal
subcarrier channel in the case of the OFDM transmission system
being used; or of a number of a frequency channel in a frequency
band and a receiving quality of the frequency channel in the
frequency band in the case of the multiband transmission system
being used, whereby the receiving quality at the mobile station 411
can be improved by the operation similar to that of the present
embodiment.
[0206] According to the fourth embodiment of the present invention,
as described above, the base station 401 determines the frequency
channel number for retransmission of the multicast signal and the
transmission power of the frequency channel on the basis of the
frequency channel number and the C/I of the frequency channel
notified of by each mobile station and thereafter retransmits the
signal by the frequency channel number and transmission power thus
determined. Therefore, the mobile station 411 can receive the
retransmitted multicast signal with the required receiving quality
even in a state under the influence of fading or shadowing. As a
consequence, the repetition of repeat requests from the mobile
station 411 is reduced, so as to enhance the throughput. The
interference can be reduced with mobile stations not receiving the
retransmitted multicast signal.
[0207] The following will describe an example of the procedure of
determining the number of the frequency channel in the radio
channel and the transmission power on the assumption of the mobile
communication system in the present embodiment and with reference
to FIG. 14.
[0208] The determination of the frequency channel number and the
transmission power is done at the channel determiner 406 of the
base station. FIG. 14 is a flowchart (algorithm) showing the
processing procedure of determining the frequency channel number
and the transmission power. FIG. 15 shows an example of receiving
qualities of respective frequency channels at each of mobile
stations 1 to 3.
[0209] For convenience of explanation, the following will describe
an example in which the number of frequency channels available is
three (f=0, 1, or 2). Since it is possible to select an arbitrary
number of frequency channels up to three, there are seven
combinations (c=0-6) of frequencies accordingly. The following
description will be given on the presumption that the channel
determiner 406 is already notified of the receiving qualities of
the respective frequency channels at each of the mobile stations.
For example, as shown in FIG. 15, the channel determiner 406 is
assumed to be notified of the receiving qualities at the respective
mobile stations 1-3.
[0210] FIG. 15 is a graph showing an example in which each mobile
station 1-3 is monitoring the receiving qualities of signals of the
first to third frequency channels transmitted from the base station
401, as described previously. In FIG. 15, the horizontal axis
represents the frequency (f) and the vertical axis the receiving
quality (dB). As shown in FIG. 15, for example, the mobile station
1 is in a state in which the receiving quality of the first
frequency channel (f=0) is 0 dB, the receiving quality of the
second frequency channel (f=1) -1 dB, and the receiving quality of
the third frequency channel (f=2) -15 dB.
[0211] Similarly, the mobile station 2 is in a state in which the
receiving quality of the first frequency channel (f=0) is -20 dB,
the receiving quality of the second frequency channel (f=1) 0 dB,
and the receiving quality of the third frequency channel (f=2) -10
dB. The mobile station 3 is in a state in which the receiving
quality of the first frequency channel (f=0) is -15 dB, the
receiving quality of the second frequency channel (f=1) -20 dB, and
the receiving quality of the third frequency channel (f=2) 0 dB. In
the present example, the required receiving quality (Qreq) at each
mobile station 1-3 is assumed to be 0 dB.
[0212] As a premise of describing the flowchart of FIG. 14 herein,
the following presents correspondence relations between the
combinations of frequency channels f assumed to be used for
retransmission, and c representing classes of the combinations.
[0213] c=0: f=0 (the first frequency channel being used)
[0214] c=1: f=1 (the second frequency channel being used)
[0215] c=2: f=2 (the third frequency channel being used)
[0216] c=3: f=0, 1 (the first and second frequency channels being
used)
[0217] c=4: f=1, 2 (the second and third frequency channels being
used)
[0218] c=5: f=0, 2 (the first and third frequency channels being
used)
[0219] c=6: f=0, 1, 2 (the first, second, and third frequency
channels being used)
[0220] In FIG. 14, the first step is to assume c=0, i.e., that only
the first frequency channel is used, and set the mobile station 1
(i=0) as a mobile station (T41). Then calculation of (T42) is
executed. At T42, MAX{q(i,f)} is calculated. Here q(i,f) indicates
the receiving quality of the frequency channel f at the mobile
station i. Further, MAX{q(i,f)} indicates maximum q(i,f) among all
the frequency channels f in the combination class c of the
frequency channels at the mobile station i. In the present example,
at i=0, the maximum receiving frequency in the case of c=0 is given
at f=0, and thus the calculation is done as follows:
Q(0,0)=q(0,0)=0 dB (reference is made to 1 in a circle in FIG.
15).
[0221] After q(0,0) is acquired in this way, the flow proceeds to
next (T43) to increment i by "1" (i=1, the mobile station 2). At
this (T43), the modulo arithmetic is carried out, and thus i is
incremented until a remainder in division of (i+1) by M (the number
of all mobile stations sending a request) becomes zero. Therefore,
1 mod 3(=M) at this point, which results in i.noteq.0. Thus the
determination at T44 is NO, so that the processing from T42 is
carried out again. This means that the processing of T42 to T43 is
repeatedly carried out until i becomes equal to M (before i=3).
[0222] Accordingly, since the determination at T44 is NO, the flow
returns to T42 to execute the calculation of MAX{q(i,f)} for the
mobile station 2 (i=1). Then the result below is obtained
(reference is made to 2 in a circle in FIG. 15).
Q(1,0)=MAX{q(1,0)}=-20 dB Further, the calculation for i=2 (mobile
station 3) is also carried out in much the same manner as the above
procedure, and the following result is obtained.
Q(2,0)=MAX{q(2,0)}=-15 dB (reference is made to 3 in a circle in
FIG. 15).
[0223] After T42 is executed in this way (c=0) for all the mobile
stations (i=0-2), the determination at T44 results in i=0 (YES at
T44), and then the flow proceeds to next T45.
[0224] At this T45, P(c)=.SIGMA.{Qreq-MIN(Q(i,f))} is calculated as
follows. In this equation, Qreq represents the required receiving
quality, and P(c) the transmission power from the base station in
the case of the combination class of frequency channels being
c.
[0225] In the case of c=0, the calculation is carried out as
follows. P .function. ( 0 ) = .times. Qreq - MIN .times. { Q
.function. ( 0 , 0 ) , Q .function. ( 1 , 0 ) , Q .function. ( 2 ,
0 ) } = .times. 0 .times. .times. dB - MIN .times. { 0 .times.
.times. dB , - 20 .times. .times. dB , - 15 .times. .times. dB } =
.times. 0 .times. .times. dB - ( - 20 .times. .times. dB ) =
.times. + 20 .times. .times. dB ##EQU1##
[0226] Accordingly, for c=0, the calculation results in P(0)=+20
dB.
[0227] After completion of the calculation of P(c) in the case of
c=0 in this way, the flow proceeds to next T46 to increment the
combination class c of frequency channels. At this point, c becomes
1 mod 6 (Nc) and thus c.noteq.0, leading to NO as the result of the
determination at (T47). Thus the processing from (T42) is executed
again. Namely, the processing of T42 to T46 is repeatedly carried
out until c becomes equal to Nc (before c=6 in the present
example).
[0228] The following presents the results of the calculations of
Q(i,f) and P(c) executed in much the same manner as the
above-stated procedure, for c=1 to c=6.
[0229] In the case of c=1) Q(0,1)=MAX{q(0,1)}=-1 dB (cf. 4 in a
circle in FIG. 15) Q(1,1)=MAX{q(1,1)}=0 dB (cf. 5 in a circle in
FIG. 15) Q(2,1)=MAX{q(2,1)}=-20 dB (cf. 6 in a circle in FIG. 15) P
.function. ( 1 ) = .times. Qreq - MIN .times. { Q .function. ( 0 ,
1 ) , Q .function. ( 1 , 1 ) , Q .function. ( 2 , 1 ) } = .times. 0
.times. .times. dB - MIN .times. { - 1 .times. .times. dB , 0
.times. .times. dB , - 20 .times. .times. dB } = .times. 0 .times.
.times. dB - ( - 20 .times. .times. dB ) = .times. + 20 .times.
.times. dB ##EQU2##
[0230] In the case of c=2) Q(0,2)=MAX{q(0,2)}=-15 dB (cf. 7 in a
circle in FIG. 15) Q(1,2)=MAX{q(1,2)}=-10 dB (cf. 8 in a circle in
FIG. 15) Q(2,2)=MAX{q(2,2)} 0 dB (cf. 9 in a circle in FIG. 15) P
.function. ( 2 ) = .times. Qreq - MIN .times. { Q .function. ( 0 ,
2 ) , Q .function. ( 1 , 2 ) , Q .function. ( 2 , 2 ) } = .times. 0
.times. .times. dB - MIN .times. { .times. - 15 .times. .times. dB
, - 10 .times. .times. dB , 0 .times. .times. dB } = .times. 0
.times. .times. dB - ( - 15 .times. .times. dB ) = .times. + 15
.times. .times. dB ##EQU3##
[0231] In the case of c=3) Q(0,0)=MAX{q(0,0), q(0,1)}=q(0,0)=0 dB
Q(1,0)=MAX{q(1,0), q(1,1)}=q(1,1)=0 dB Q(2,0)=MAX{q(2,0),
q(2,1)}=q(2,0)=-15 dB P .function. ( 3 ) = .times. Qreq - MIN
.times. { Q .function. ( 0 , 0 ) , Q .function. ( 2 , 0 ) } + Qreq
- MIN .times. { Q .function. ( 1 , 1 ) } = .times. 0 .times.
.times. dB - MIN .times. { 0 .times. .times. dB , - 15 .times.
.times. dB } + 0 .times. .times. dB - MIN .function. ( 0 .times.
.times. dB ) = .times. ( + 15 .times. .times. dB ) + ( 0 .times.
.times. dB ) .apprxeq. .times. + 15.1 .times. .times. dB
##EQU4##
[0232] The above sum of (+15 dB) and (0 dB) is given by a logarithm
of the sum of antilogarithms of (+15 dB) and (0 dB).
[0233] The antilogarithm of (0 dB) is "1" and the antilogarithm of
(+15 dB) is ".apprxeq.31.6." Thus the sum x of these is given as
follows. x=1+31.6=32.6 10 log x=10 log 32.6.apprxeq.+15.1 dB.
[0234] In the case of c=4) Q(0,1)=MAX{q(0,1), q(0,2)}=q(0,1)=-1 dB
Q(1,1)=MAX{q(1,1), q(1,2)}=q(1,1)=0 dB Q(2,2)=MAX{q(2,1),
q(2,2)}=q(2,2)=0 dB P .function. ( 4 ) = .times. Qreq - MIN .times.
{ Q .function. ( 0 , 1 ) , Q .function. ( 1 , 1 ) } + Qreq - MIN
.times. { Q .function. ( 2 , 2 ) } = .times. 0 .times. .times. dB -
MIN .times. { - 1 .times. .times. dB , 0 .times. .times. dB } + 0
.times. .times. dB - MIN .function. ( 0 .times. .times. dB ) =
.times. ( + 1 .times. .times. dB ) + ( 0 .times. .times. dB )
.apprxeq. .times. + 3.5 .times. .times. dB ##EQU5##
[0235] Just as in the above case, the sum of (+1 dB) and (0 dB) is
given by a logarithm of the sum of antilogarithms of (+1 dB) and (0
dB).
[0236] The antilogarithm of (0 dB) is "1" and the antilogarithm of
(+1 dB) is ".apprxeq.1.26." Thus the sum x of these is given as
follows. x=1+1.26=2.26 10 log x=10 log 2.26.apprxeq.+3.5 dB.
[0237] In the case of c=5) Q(0,0)=MAX{q(0,0), q(0,2)}=q(0,0)=0 dB
Q(1,2)=MAX{q(1,0), q(1,2)}=q(1,2)=-10 dB Q(2,2)=MAX{q(2,0),
q(2,2)}=q(2,2)=0 dB P .function. ( 5 ) = .times. Qreq - MIN .times.
{ Q .function. ( 0 , 0 ) } + Qreq - MIN .times. { Q .function. ( 1
, 2 ) , Q .function. ( 2 , 2 ) } = .times. 0 .times. .times. dB -
MIN .function. ( 0 .times. .times. dB ) + 0 .times. .times. dB -
MIN .times. { - 10 .times. .times. dB , 0 .times. .times. dB } =
.times. ( 0 .times. .times. dB ) + ( + 10 .times. .times. dB )
.apprxeq. .times. + 10.4 .times. .times. dB ##EQU6##
[0238] Just as in the above case, the sum of (0 dB) and (+10 dB) is
given by a logarithm of the sum of antilogarithms of (0 dB) and
(+10 dB).
[0239] The antilogarithm of (0 dB) is "1" and the antilogarithm of
(+10 dB) is "10.1" Thus the sum x of these is given as follows.
x=1+10=11 10 log x=10 log 11.apprxeq.10.4 dB.
[0240] In the case of c=6) Q(0,0)=MAX{q(0,0), q(0,1),
q(0,2)}=q(0,0)=0 dB Q(1,1)=MAX{q(1,0), q(1,1), q(1, 2)}=q(1,1)=0 dB
Q(2,2)=MAX{q(2,0), q(2,1), q(2,2)}=q(2,2)=0 dB P .function. ( 6 ) =
.times. Qreq - MIN .times. { Q .function. ( 0 , 0 ) } + Qreq - MIN
.times. { Q .function. ( 1 , 1 ) } + Qreq - MIN .times. { Q
.function. ( 2 , 2 ) } = .times. 0 .times. .times. dB - MIN
.function. ( 0 .times. .times. dB ) + 0 .times. .times. dB - MIN
.function. ( 0 .times. .times. dB ) + 0 .times. .times. dB - MIN
.function. ( 0 .times. .times. dB ) = .times. ( 0 .times. .times.
dB ) + ( 0 .times. .times. dB ) + ( 0 .times. .times. dB )
.apprxeq. .times. + 4.8 .times. .times. dB ##EQU7##
[0241] Just as in the above case, the sum of (0 dB), (0 dB), and (0
dB) is given by a logarithm of the sum of antilogarithms of (0 dB),
(0 dB), and (0 dB).
[0242] Since the antilogarithm of (0 dB) is "1," the sum x is given
as follows. x=1+1+1=3 10 log x=10 log 3.apprxeq.+4.8 dB.
[0243] After completion of the calculations of P(0) to P(6) as
described above, the flow proceeds to T48 to calculate
MIN{P(c)}.
[0244] The following presents the calculation method of MIN{P(c)}.
MIN .times. { P .function. ( c ) } = .times. MIN .times. { P
.function. ( 0 ) , P .function. ( 1 ) , P .function. ( 2 ) , P
.function. ( 3 ) , P .function. ( 4 ) , P .function. ( 5 ) , P
.function. ( 6 ) } = .times. MIN .times. { + 20 .times. .times. dB
, + 20 .times. .times. dB , + 15 .times. .times. dB , + 15.1
.times. .times. dB , + 3.5 .times. .times. dB , + 10.4 .times.
.times. dB , + 4.8 .times. .times. dB } ##EQU8## Accordingly, the
calculation at T48 obtains the following. MIN{P(c)}=P(4)=+3.5
dB.
[0245] The above processing results in finally selecting the
combination of frequency channels in c=4. Therefore, while the
second frequency channel is set at the transmission power of +1 dB
and the third frequency channel at the transmission power of 0 dB,
the same multicast signal is retransmitted at each of the
frequencies (the second and third frequencies).
[0246] As described above, the above processing permits the
frequency channel number(s) minimizing the transmission power from
the base station, and the transmission power(s) thereof to be
determined while satisfying the required receiving quality at the
mobile stations.
[0247] The present embodiment can also be applied to the mobile
station functioning as a relay station instead of the base station,
supposing the situation of multihop connection. In this case, the
mobile station 411, which is a transmitting station of a repeat
request, preliminarily identifies existence of an adjoining mobile
station as relay station and requests retransmission of a signal by
designating a transmission path including the mobile station (relay
station). Similarly, the base station 401, which is a transmitting
station of the signal according to the repeat request,
preliminarily identifies existence of an adjoining mobile station
as a relay station and responds to the repeat request by
designating a transmission path including the mobile station (relay
station).
Fifth Embodiment
[0248] Lastly, the fifth embodiment of the present invention will
be described with reference to the block diagram of FIG. 16. The
present embodiment employs the NACK base automatic repeat request
not to send an arrival acknowledgement but to send only a repeat
request, and the base station is configured to receive multicast
signals of packet units and send them in the multicarrier
transmission system. The following will describe an example of
combination with a method using spreading codes for repeat requests
and thereby permitting detection of repeat requests and numbers of
packets under the repeat request even with occurrence of collision
between repeat request signals at the base station.
[0249] The method capable of detecting the repeat requests even
with occurrence of collision between repeat requests is disclosed
in International Patent Application (PCT/JP01/02923).
[0250] FIG. 16 is a block diagram of the mobile communication
system in the present embodiment, which is generally comprised of a
base station 501 and a mobile station 511, as in the first
embodiment and the second embodiment described above. The base
station 501 comprises an ARQ processor 502, a transmitter/receiver
503, a signal input terminal 504, a base station antenna 505, a
channel determiner 506, and a repeat request signal quality
measuring unit 507. The mobile station 511 comprises a
transmitter/receiver 512, an ARQ processor 513, a signal output
terminal 514, a mobile station antenna 515, a receiving quality
measuring unit 516, and a memory 517.
[0251] At the base station 501, packets of a multicast signal
entering the signal input terminal 504 are fed into the ARQ
processor 502. The ARQ processor 502 attaches the CRC to the input
packets and outputs them to the transmitter/receiver 503. The
transmitter/receiver 503 informs each mobile station of a start of
transmission of the packets and a number of a subcarrier used for
the transmission of the packets and thereafter transmits the
packets through the downlink 522 to the mobile station 511.
[0252] On the other hand, at the mobile station 511, the receiving
quality measuring unit 516 continuously, constantly measures as the
receiving quality, S/(N+I) of each subcarrier transmitted from the
base station 501 and stores the correlation between the subcarrier
number and S/(N+I) of the subcarrier thus measured, in the memory
517.
[0253] At the mobile station 511 in this configuration, the packets
transmitted from the base station 501 are received through the
downlink 522 by the transmitter/receiver 512 and thereafter are
outputted to the ARQ processor 513. The ARQ processor 513 performs
the error detection of the received packets using the CRC. When no
error is detected in the received packets, the ARQ processor 513
outputs the packets from the signal output terminal 514. Since the
NACK base automatic repeat request is employed, no arrival
acknowledgement is sent to the base station 501 when no error is
detected.
[0254] When an error is detected in the received packets, the ARQ
processor 513 notifies the base station 501 through the uplink 521
of a repeat request for retransmission of a requested packet and
the subcarrier number with the maximum receiving quality stored in
the memory 517. The present embodiment will describe an example of
a method of selecting a channel number with a receiving quality
within a certain range as a subcarrier number with the maximum
receiving quality at each mobile station and notifying the base
station of only the subcarrier thereafter. Spreading codes are used
for packet numbers under repeat requests and numbers of subcarriers
used for transmission of retransmitted packets. For example, in the
case where 256 spreading codes are available, 128 spreading codes
can be allocated to identification of packet numbers, and 128
spreading codes to identification of subcarrier numbers. Namely, in
this case, a number of a spreading code transmitted from the mobile
station 511 to the base station 501 can be determined by the
following calculation. Number of spreading code=(packet
number)+(subcarrier number).times.16
[0255] For example, in the case where the retransmitted packet
number is "8" and the subcarrier number for the repeat request of
the retransmitted packet is "3," 8+3.times.16=56, and thus the
mobile station transmits the fifty sixth spreading code as a repeat
request signal. This makes a judgment on a repeat request feasible
using a correlation value by the spreading code or a level of a
signal obtained by the despreading operation as a receiving quality
even if collision occurs between repeat request signals at the base
station 501. Accordingly, the base station 501 can detect the
repeat request for retransmission of the eighth packet through the
use of the third subcarrier.
[0256] For the spreading code transmitted from the mobile station
511, the repeat request signal quality measuring unit 507 of the
base station 501 detects the retransmitted packet number and
subcarrier number. The repeat request signal quality measuring unit
507 notifies the ARQ processor 502 of the retransmitted packet
signal detected and notifies the channel determiner 506 of the
subcarrier number requested to use in retransmission. Then the ARQ
processor 502 searches for a packet number with the largest number
of repeat requests and thereafter controls the transmitter/receiver
503 so as to retransmit the packet by the subcarrier number thus
searched for. The transmitter/receiver 503 informs the mobile
station of the retransmission using the subcarrier number and
thereafter transmits the retransmitted packet fed from the ARQ
processor 502, using the subcarrier.
[0257] As described above, the receiving quality at the mobile
station can be improved by the configuration and operation of the
mobile communication system in the present embodiment.
[0258] According to the mobile communication system in the present
embodiment, the base station 501 receives from the mobile station
511 the repeat request signal assigned by the spreading code and
thus, even with occurrence of collision between repeat request
signals at the base station 501, the base station 501 can detect
each repeat request for retransmission of which packet using which
subcarrier, by determining the correlation value of the spreading
code. Since the packet with the greatest number of repeat requests
is retransmitted using the subcarrier with the greatest number of
requests (the subcarrier with the maximum receiving quality), the
mobile station can receive the packet with the required receiving
quality under the repeat request. As a consequence, the repetition
of repeat requests from the mobile station can be reduced, so as to
enhance the throughput.
[0259] The present embodiment can also be applied to the mobile
station functioning as a relay station instead of the base station,
supposing the situation of multihop connection. In this case, the
mobile station 511, which is a transmitting station of a repeat
request, preliminarily identifies existence of an adjoining mobile
station as relay station and requests retransmission of a signal by
designating a transmission path including the mobile station (relay
station). Similarly, the base station 501, which is a transmitting
station of the signal according to the repeat request,
preliminarily identifies existence of an adjoining mobile station
as a relay station and responds to the repeat request by
designating a transmission path including the mobile station (relay
station).
[0260] In each of the above embodiments, the receiving quality
measuring function of the receiving quality measuring unit 316,
416, 516 in the mobile station 311, 411, 511 corresponds to the
receiving quality measuring means, and the receiving quality
transmitting function of the transmitter/receiver 312, 412, 512 to
the receiving quality notifying means.
[0261] The transmitting function of the transmitter/receiver 303,
403, 503 in the base station 301, 401, 501 corresponds to the
transmitting means; the channel determining function of the channel
determiner 306, 406, 506 corresponds to the radio channel
determining means and to the first, second, and third channel
number determining means. Further, the transmission power
calculating function of the channel determiner 306, 406, 506
corresponds to the first and second radio channel transmission
power determining means.
[0262] From the invention thus described, it will be obvious that
the embodiments of the invention may be varied in many ways. Such
variations are not to be regarded as a departure from the spirit
and scope of the invention, and all such modifications as would be
obvious to one skilled in the art are intended for inclusion within
the scope of the following claims.
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