U.S. patent number RE36,591 [Application Number 09/231,111] was granted by the patent office on 2000-02-29 for transmission diversity for a cdma/tdd mobile telecommunication system.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Masaki Hayashi, Osamu Kato, Kazuyuki Miya.
United States Patent |
RE36,591 |
Hayashi , et al. |
February 29, 2000 |
Transmission diversity for a CDMA/TDD mobile telecommunication
system
Abstract
In a base station which has a plurality of antennas, each of a
plurality of comparison circuits operates to compare correlation
levels, which are obtained by despreading received signals for a
plurality of channels, with each other with respect to the
antennas. Each of a plurality of transmission antenna selecting
circuits operates to determine from which antenna a transmission
signal is to be transmitted for every channel. Each of a plurality
of multiplexing circuits operates to multiplex the transmission
signals of the individual channels, which are spread, for every
antenna. As a result, on the basis of the result of the comparison
of the correlation levels with respect to the antennas, a
transmission antenna is selected for every channel, and the signals
of the channels that are to be transmitted by a given antenna are
multiplexed, whereby the base station achieves transmission
diversity.
Inventors: |
Hayashi; Masaki (Yokohama,
JP), Miya; Kazuyuki (Machida, JP), Kato;
Osamu (Yokohama, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JP)
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Family
ID: |
26356195 |
Appl.
No.: |
09/231,111 |
Filed: |
January 14, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
388416 |
Feb 14, 1995 |
05598404 |
Jan 28, 1997 |
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Foreign Application Priority Data
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Feb 16, 1994 [JP] |
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6-019365 |
Sep 6, 1994 [JP] |
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6-212434 |
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Current U.S.
Class: |
370/342; 370/280;
375/267; 375/299; 455/101; 455/562.1 |
Current CPC
Class: |
H04B
7/04 (20130101); H04B 7/0608 (20130101); H04B
7/2618 (20130101) |
Current International
Class: |
H04B
7/26 (20060101); H04B 7/04 (20060101); H04J
013/04 (); H04J 003/00 (); H04B 007/216 () |
Field of
Search: |
;370/335,342,280,334,320
;375/200,207,267,299,347,349 ;455/504-6,562,101 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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582323-A1 |
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Feb 1994 |
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EP |
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WO92/10890 |
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Jun 1992 |
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WO |
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WO95/06365 |
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Mar 1995 |
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WO |
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Other References
Riaz Esmailzadeh et al, "Power Control in Packet Switched Time
Division Duplex Direct Sequence Spread Spectrum Communications",
IEEE, 1992, pp. 989-992. .
Nobuo Nakajima, "Micro/Pico Cellular Telecommunication and Network
Architecture", The 6th Karuizawa Workshop on Circuits and Systems,
Apr. 19-20, pp. 121-126. .
43rd IEEE Vehicular Technology Conference, May 1993, pp. 602-606,
"Linear Predictive Transmitter Diversity for Microcellular TDMA/TDD
Mobile Radio System", Y. Kondo et al. .
IEEE International Conference on Communications '93, vol. 3, May
1993, pp. 1775-179, "Diversity for the Direct-sequence Spread
Spectrum System Using Multiple Transmit Antennas", V. Weerackody.
.
Raymond Steele (Ed.), "Mobile Radio Communications", Pentech Press
(1992), pp. 70-77..
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Primary Examiner: Ton; Dang
Assistant Examiner: Vincent; David
Attorney, Agent or Firm: Venable Frank; Robert J. Wood;
Allen
Claims
We claim:
1. A mobile telecommunication system for performing communication
by utilizing a CDMA/TDD system, said mobile telecommunication
.[.System.]. .Iadd.system .Iaddend.including a base station which
comprises:
a plurality of antennas;
despreading means for subjecting signals, which are received by
said antennas, to despreading for a plurality of channels each of
which is assigned to a corresponding code, the received signals
being despread with each code assigned for each channel;
comparison circuits each of which serve to compare correlation
levels with respect to the code assigned for each channel, which
correlation levels are obtained by said despreading means, with
each other with respect to said antennas and to determine from
which antenna a signal is to be transmitted outwardly;
spreading means for spreading transmission data with each code
assigned for each channel
transmission antenna selecting means for selecting, on the basis of
an output signal from each of said comparison circuits, for every
channel, an antenna from which a transmission signal, which is
obtained by the spreading in said spreading means, is to be
transmitted outwardly; and
multiplexing means for multiplexing the transmission signals of the
associated channels, which are obtained by the spreading and which
are selected for transmission by the same antenna, for every
antenna.
2. A system according to claim 1, wherein said base station further
comprises means for composing the correlation levels of said
antennas with the code assigned for each channel, which correlation
levels are obtained by the despreading.
3. A system according to claim 1, wherein said base station further
comprises means for estimating, from changes in past values of the
correlation levels of said antennas with the code assigned for each
channel, which correlation levels are obtained by the despreading,
future values of the correlation levels with the code.
4. A system according to claim 1, wherein all of said plurality of
antennas of said base station are adjacently arranged in a central
portion of a cover area of said base station.
5. A system according to claim 1, wherein said plurality of
antennas of said base station are distributively arranged in a
plurality of locations within a cover area of said base
station.
6. A system according to claim 1, wherein said plurality of
antennas of said base station are divided into a plurality of
antenna groups, and the plurality of antennas in each of said
antenna groups are adjacently arranged, and also said antenna
groups are distributively arranged in a plurality of locations
within a cover area of said base station.
7. A system according to claim 1, wherein in said transmission
antenna selecting means, antennas are selected for individual
channels independently of the selection for other channels.
8. A system according to claim 1, wherein said transmission antenna
selecting means adjusts the selection of antennas for the channels
so as to avoid selecting only a subset of antennas out of all of
said antennas.
9. A system according to claim 1, wherein:
said multiplexing means has a multiplexing capability corresponding
to a number of channels which does not exceed a constant (M) that
is smaller than the total number of channels (L) within a cover
area of said base station;
said base station further comprises radio transmission/reception
means provided for every antenna which has an amplification
capability to accommodate the number of channels which does not
exceed said constant (M); and
said transmission antenna selecting means selects antennas for the
channels so that the number of channels selected for any one of the
antennas .Iadd.does .Iaddend.not .[.to.]. exceed said constant
(M).
10. A system according to claim 1, wherein said base station
further comprises transmission/reception switching means for
switching transmission/reception the antennas.
11. A mobile telecommunication system for performing communication
by utilizing a CDMA/TDD system adopting a direct spread method,
said mobile telecommunication system including a base station which
comprises:
a plurality of antennas
radio transmission/reception means provided for every antenna;
despreading means for subjecting received signals, which are
received by said antennas, to despreading for each of a plurality
of channels;
comparison means for comparing correlation levels, which are
obtained by the despreading, with respect to said antennas, for
every channel
decode means for decoding the received signals;
spreading means for spreading transmission data for every channel
in transmission;
transmission antenna selecting means for selecting an antenna for
every channel from which a transmission signal, which is obtained
by the spreading in said spreading means, is to be transmitted
outwardly and
multiplexing means for multiplexing the transmission signals of the
associated channels, which are obtained by the spreading, for every
antenna.
12. A system according to claim 11, wherein said base station
further comprises means for composing the correlation levels of
said antennas with the code assigned for each channel, which
correlation levels are obtained by the despreading.
13. A system according to claim 11, wherein said base station
further comprises means for estimating, from changes in past values
of the correlation levels of said antennas with a code assigned for
each channel, which correlation levels are obtained by the
despreading, future values of the correlation levels with the
code.
14. A system according to claim 11, wherein all of said plurality
of antennas of said base station are adjacently arranged in a
central portion of a cover area of said base station.
15. A system according to claim 11, wherein said plurality of
antennas of said base station are distributively arranged in a
plurality of locations within a cover area of said base
station.
16. A system according to claim 11, wherein said plurality of
antennas of said base station are divided into a plurality of
antenna groups, and the plurality of antennas in each of said
antenna groups are adjacently arranged, and also said antenna
groups are distributively arranged in a plurality of locations
within a cover area of said base station.
17. A system according to claim 11, wherein in said transmission
antenna selecting means, antennas are selected for individual
channels independently of the selection for other channels.
18. A system according to claim 11, wherein said transmission
antenna selecting means adjusts the selection of antennas for the
channels so as to avoid selecting only a subset of antennas out of
all of said antennas.
19. A system according to claim 11, wherein:
said multiplexing means has a multiplexing capability corresponding
to a number of channels which does not exceed a constant (M) that
is smaller than the total number of channels (L) within a cover
area of said base station;
said radio transmission/reception means has an amplification
capability to accommodate the number of channels which does not
exceed said constant (M); and
said transmission antenna selecting means selects antennas for the
channels so that the number of channels selected for any one of the
antennas not to exceed said constant (M).
20. A system according to claim 11, wherein said base station
further comprises transmission/reception switching means for
switching the antennas.
21. A mobile telecommunication system for performing communication
over a plurality of channels by utilizing a CDMA/TDD system, each
channel having a spreading code assigned to it, said mobile
telecommunication system including a base station which
comprises:
a plurality of antenna means for receiving and radiating
signals;
despreading means for despreading signals received by each of the
antenna means using the spreading codes assigned to all of the
channels, to thereby generate for every antenna means a set of
despread signals for all of the channels;
comparison means for receiving the sets of despread signals and
ascertaining the power level of the received signal for each
channel at each of the antenna means;
spreading means for spreading transmission data for each channel
with the spreading code assigned to that channel, to thereby
generate a plurality spread data for all of the channels;
means, receiving signals from the comparison means, for selecting
one of the antenna means from among the plurality of antenna means
to radiate the spread data for each channel; and
multiplexing means for multiplexing spread data that have been
selected for radiation by the same antenna means.
22. A system according to claim 21, further comprising means,
responsive to despread signals received via each of the antenna
means, for composing the despread signals of each channel.
23. A system according to claim 21, wherein the means for selecting
comprises means for estimating, from past values of the power
levels of the received signals for each channel at each of the
antenna means, future values of the power levels.
24. A system according to claim 21, wherein all of the antenna
means are located at a central portion of a cover area of the base
station.
25. A system according to claim 21, wherein the antenna means are
distributed in a plurality of locations within a cover area of the
base station.
26. A system according to claim 25, wherein at least one of the
antenna means comprises a plurality of antennas arranged adjacent
one another.
27. A system according to claim 21, wherein the means for selecting
comprises means for selecting an antenna means to radiate the
spread data for each channel independently of the selection of
antenna means for other channels.
28. A system according to claim 21, wherein the means for selecting
comprises means for limiting the number of channels whose spread
data has been selected for radiating by the same antenna means.
.Iadd.
29. A CDMA/TDD (Code Division Multiple Access/Time Division Duplex)
base station, comprising:
a plurality of antennas;
despreading means for subjecting signals received by each of said
antennas to despreading for each of a plurality of channels;
comparison means for comparing correlation levels for each channel
with respect to each antenna, which correlation levels are obtained
by said despreading means, to determine which antennas have
received which channels best;
transmission antenna selecting means for selecting, on the basis of
output signals from said comparison means, for every channel, one
of said antennas from which a transmission signal is to be
transmitted outwardly; and
multiplexing means for multiplexing the transmission signals of
associated channels which are selected for transmission by the same
antenna, for every antenna..Iaddend..Iadd.30. A CDMA/TDD base
station according to claim 29, further comprising means for
estimating, from changes in past values of the correlation levels,
future values of the correlation levels with the
code..Iaddend..Iadd.31. A CDMA/TDD base station according to claim
29, wherein all of said plurality of antennas of said base station
are adjacently arranged in a central portion of a cover area of
said base station..Iaddend..Iadd.32. A CDMA/TDD base station
according to claim 29, wherein said plurality of antennas of said
base station are distributively arranged in a plurality of
locations within a cover area of said base
station..Iaddend..Iadd.33. A CDMA/TDD base station according to
claim 29, wherein said plurality of antennas of said base station
are divided into a plurality of antenna groups, each antenna group
having a plurality of antennas, wherein the plurality of antennas
in each of said antenna groups are adjacently arranged, and wherein
said antenna groups are distributively arranged at a plurality of
locations within a cover area of said base
station..Iaddend..Iadd.34. A CDMA/TDD base station according to
claim 29, wherein in said transmission antenna selecting means,
antennas are selected for individual channels independently of the
selection for other channels..Iaddend..Iadd.35. A CDMA/TDD base
station according to claim 29, wherein said transmission antenna
selecting means adjusts the selection of antennas for the channel
so as to avoid selecting only a subset of antennas out of all of
said antennas..Iaddend..Iadd.36. A CDMA/TDD base station according
to claim 29, wherein:
said multiplexing means has a multiplexing capability corresponding
to a number of channels which does not exceed a constant (M) that
is smaller than the total number of channels (L) within a cover
area of said base station;
said base station further comprises radio transmission/reception
means provided for every antenna which has an amplification
capability to accommodate the number of channels which does not
exceed said constant (M); and
said transmission antenna selecting means selects antennas for the
channels so that the number of channels selected for any one of the
antennas not to
exceed said constant (M)..Iaddend..Iadd.37. A CDMA/TDD base station
according to claim 29, in combination with a CDMA/TDD mobile
station that communicates with said base station..Iaddend..Iadd.38.
A CDMA/TDD mobile communication method, comprising the steps
of:
(a) subjecting signals received by each of a plurality of antennas
to despreading for each of a plurality of channels;
(b) comparing correlation levels for each channel with respect to
each antenna, which correlation levels are obtained by said
despreading, to determine which antennas have received which
channels best; and
(c) selecting, on the basis of said comparing step, for every
channel, one of said antennas from which a transmission signal is
to be transmitted outwardly..Iaddend..Iadd.39. A method according
to claim 38, further comprising the step of multiplexing
transmission signals that were selected in step (c) for
transmission by the same antenna..Iaddend..Iadd.40. A method
according to claim 38, wherein step (c) comprises estimating, from
changes in past values of the correlation levels, future values of
the correlation levels with the code..Iaddend..Iadd.41. A method
according to claim 38, wherein step (c) comprises adjusting the
selection of antennas for the channels so as to avoid selecting
only a subset of antennas out of all of said
antennas..Iaddend..Iadd.42. A method according to claim 38, wherein
step (c) comprises adjusting the selection of antennas for the
channels so as to avoid selecting the same antenna for more than a
predetermined number of channels..Iaddend..Iadd.43. A CDMA/TDD base
station for communication with mobile stations over a plurality of
channels, each channel having a code assigned to it,
comprising:
a plurality of antennas;
a plurality of receiving units, each receiving unit corresponding
to one of the antennas and receiving a signal via the corresponding
antenna during a sequence of reception time slots;
means for despreading the signal received by each receiving unit
using the codes assigned to all of the channels to thereby provide
a set of despread signals corresponding to each antenna;
a plurality of transmission units, each transmission unit
corresponding to one of the antennas;
means for spreading transmission data for each of the channels;
and
means, responsive to the sets of despread signals, for selectively
distributing the spread transmission data to the transmission units
for transmission via the corresponding antennas during transmission
time slots that are interspersed with the reception time
slot..Iaddend..Iadd.44. A CDMA/TDD base station according to claim
43, in combination with a CDMA/TDD mobile station that communicates
with said base station..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile telecommunication system
which is adapted to secure a communication link for a mobile unit
moving in a wide area by utilizing wireless communications, and
more particularly to a mobile telecommunication system which is
adapted to perform communication by utilizing a CDMA/TDD system
adopting the direct sequence spread spectrum (DS-SS) system.
2. Description of the Related Art
A system in which communication is established among a plurality of
stations in the same frequency band is called a multiple access
system. CDMA (Code Division Multiple Access) is a technology in
which the multiple access is performed on the basis of spread
spectrum communication, in which an information signal is
transmitted with the spectrum thereof spread into a sufficiently
wider band than the band width of the information signal of the
unit. A DS-SS system is a system wherein in the spreading, the
information signal is directly multiplied by a spreading code. TDD
(Time Division Duplex) means a system wherein the transmission/
reception of the signal is performed in the same band and is also
called a ping pong system, i.e., it means a system wherein the
communication is performed with the same radio frequency subjected
to time division in the transmission/reception. As for the
advantages of the TDD system, as shown in a paper entitled
"Micro/Pico Cellular Telecommunication and Network Architecture"
(N. Nakajima: the 6-th Karuizawa Workshop on Circuits and Systems
(Apr. 19 to 20, 1993) pp. 121 to 126), it is well known that since
transmission diversity can be applied to the base station, space
diversity becomes unnecessary in the mobile radio telephone, and as
a result, miniaturization can be realized.
The received radio wave via the mobile propagation path is
subjected to fluctuation called fading. This becomes a degradation
factor of the transmission system. In order to realize high quality
communication, as for the technology for reducing the influence of
the above-mentioned fading, diversity reception utilizing two or
more received radio waves is well known. Space diversity is one of
the above-mentioned diversity technologies in which, by using two
or more sufficiently spaced apart receiving antennas, a plurality
of fading received radio waves are obtained which change
independently of one another.
On the other hand, transmission diversity means a technology
wherein from the received radio waves received via space diversity,
the conditions of the path from the mobile station to the
respective antennas of the base station are estimated, and
transmission is performed in turn from the antenna having the
better transmission path or link state. In the case of the TDD
system, since the system of interest is a system wherein the
transmission/reception is performed in the same band, the frequency
correlation of the fading fluctuation of the transmitted radio wave
is the same as that of the received radio wave. Therefore, if the
interval of time required for the transmitted radio wave and the
received radio wave to be switched to each other is sufficiently
short, since the mutual time correlation of the fading fluctuation
is high, by the application of the above-mentioned transmission
diversity, a reduction of the influence by the fading fluctuation
of the transmitted radio wave can be relatively readily promoted.
As a result, for the individual channels, high transmission link
quality can be realized.
Heretofore, the application of transmission diversity in a base
station adopting the TDD system has been considered in a TDMA/TDD
system. TDMA (Time Division Multiple Access) is a system wherein
the radio frequency is subjected to time division, and a specific
time slot is assigned to a user, and in the time slot thus
assigned, the communication is performed.
The TDMA/TDD system is employed in a PHS (Personal Handy phone
System) as the Japanese next generation digital codeless telephone
system as well as in a DECT system which is in development in
Europe. FIG. 1 shows an example in which in the PHS system, a base
station BS is provided with two transmission/reception antennas A
and B, and communication is established between the base station BS
and four mobile terminals PS1 to PS4. The PHS system has a frame
structure as shown in FIG. 2 for example. In this connection, with
5 msec (transmission 2.5 msec/reception 2.5 msec) as one frame,
four channels are subjected to time division multiplexing. Each
subframe, in the figure, for accommodating a signal of the
associated channel is called a time slot, and the shadowed portions
represent gard time intervals which are provided in order to
prevent the transmitted signal and the received signal from
colliding with each other due to a lag between the transmission
timing and the receiving timing.
In addition, FIG. 3 is a view showing an example of a situation in
which the base station BS, having the two antennas A and B as shown
in FIG. 1, switches the transmission antenna every channel in
accordance with the levels of the received signals. The
transmission/reception frames and the time slots are shown. In FIG.
3, reference symbol TX represents transmission and reference symbol
RX represents reception. Then, it is assumed that the four mobile
terminals PS1 to PS4 perform their respective communications using
the channels 1 to 4. In the base where at time t0, the levels of
the received signals in the individual channels (the averages or
the like of the reception levels between the time slots) have the
relationship, as shown in the figure, with respect to the two
antennas A and B (the relation of A>B represents that the
reception level of the antenna A is higher than that of the antenna
B), when at the next time t1, the transmission is performed, the
antenna having the higher reception level is selected to transmit
the signal. In the figure, the reference symbol of the selected
antenna is shown. At time t1, it is shown that each of the channels
1 and 3 select the antenna A, and each of the channels 2 and 4
selects the antenna B. In the figure, a time slot for transmission
is represented by a shadowed portion. In addition, a portion having
no shadowing represents a time slot in which no transmission is
performed. Similarly, at time t3, on the basis of the results
(received power) at time t2, an antenna for transmission is
selected every channel. In such a way, the above-mentioned
transmission diversity can be realized.
As compared with such a TDMA system, the CDMA system is considered
as a system wherein, when used in a cellular system, a higher
frequency utilization efficiency than that in the TDMA system can
be realized, and hence a larger number of users can be
accommodated. Therefore, it is considered that in the future, the
CDMA system will be applied to a large number of cellular systems.
In addition, the TDD system is a system wherein the
transmission/reception is performed in the same frequency band on
the basis of time division, whereas as another communication
system, there is well known an FDD (Frequency Division Duplex)
system in which two frequency bands, which are sufficiently spaced
apart from each other, are respectively assigned to transmission
and reception. Heretofore, in the CDMA system, the CDMA/FDD system
employing the FDD system has been mainly developed.
However, in the conventional communication apparatus adopting the
CDMA/FDD system, there arise the following problems.
(1) Since the correlation between the fading of the forward link
and that of the reverse link is small, the space diversity
technique in the base station can be applied to only the reverse
link.
(2) In the case where the received power is reduced due to
frequency selective fading, the communication quality is degraded
and hence it is difficult to perform high quality
communication.
(3) In the case where the communication capacity has greatly
increased, since the interference of the communication radio waves
of other stations with the communication radio wave of the local
station becomes large, the communication quality is degraded, and
hence it is difficult to perform high quality communication.
(4) In the case where the communication capacity has greatly
increased, the requirements on the quadrature modulator and the
linear amplifier of the base station become severe.
SUMMARY OF THE INVENTION
The present invention was made in order to solve the
above-mentioned problems associated with the prior art, and it is
therefore an object of the present invention to provide a mobile
telecommunication system which is capable of applying the space
diversity technique to the forward link as well, and of stabilizing
the received power, and of greatly reducing interference of the
communication radio waves of other stations with the communication
radio wave of the local station, and of reducing the specifications
required for the modulator, the amplifier and the like.
In order to attain the above-mentioned object, according to the
present invention, in a mobile telecommunication system, a base
station includes: a plurality of antennas; means provided in each
of the antennas for subjecting a received signal on a reverse link
(transmission from a mobile terminal to the base station) to
despreading every channel; means for comparing correlation levels,
which are obtained by the despreading, with each other among the
antennas for the channels; means for selecting an antenna, from
which a transmission signal is to be transmitted, for every channel
in transmission; and means for multiplexing the transmission
signals of the individual channels, which are obtained by
spreading, every antenna.
Therefore, according to the present invention, in the reverse link,
an antenna by which an electric field having a good level is
received is selected, whereby it is possible to maintain always a
communication link in a good state. In addition, by increasing the
number of antennas, even the request for the high communication
quality can be satisfied. Further, since the correlation of the
transmission path of the reverse link and that of the forward link
is high, in the forward link as well, the same effects can be
obtained.
In addition, since the transmission path or link states are
different among the mobile stations, a transmission/reception
antenna is selected for every link leading to the associated mobile
station, whereby the interference due to the communication radio
waves of other mobile stations is relatively reduced. As a result,
since the communication quality is improved, and also the
transmission power can be reduced, the mobile station can be
miniaturized and lightened.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing an example of an arrangement of
a base station and mobile terminal in a cellular radio
communication system;
FIG. 2 is a schematic view showing the frame structure of the PHS
system;
FIG. 3 is a schematic view showing an example of the base station
transmission diversity in a conventional TDMA/TDD system;
FIG. 4 is a block diagram showing the configuration of a main
portion of a base station of a mobile telecommunication system
according to a first embodiment of the present invention;
FIG. 5 is a schematic view showing an example of the base station
transmission diversity of the mobile unit communication system in
the first embodiment;
FIG. 6 is a block diagram showing the configuration of a main
portion of a base station of a mobile telecommunication system
according to a second embodiment of the present invention;
FIG. 7 is a schematic view showing an example of the base station
transmission diversity of the mobile telecommunication system in
the second embodiment;
FIG. 8 is a schematic view showing an arrangement of antennas of a
base station of a mobile telecommunication system according to a
third embodiment of the present invention;
FIG. 9 is a schematic view showing an arrangement of antennas of a
base station of a mobile telecommunication system according to a
fourth embodiment of the present invention;
FIG. 10 is a schematic view showing an arrangement of antennas of a
base station of a mobile telecommunication system according to a
fifth embodiment of the present invention;
FIG. 11 is a schematic view showing an arrangement of antennas of a
base station of a mobile telecommunication system according to a
sixth embodiment of the present invention;
FIG. 12 is a flow chart showing an algorithm for controlling a
comparison circuit in the sixth embodiment;
FIG. 13 is a schematic view showing an example of the base station
transmission diversity of a mobile telecommunication system
according to a seventh embodiment of the present invention;
FIG. 14 is a flow chart showing an algorithm for controlling a
comparison circuit in the seventh embodiment;
FIG. 15 is a schematic view showing an example of the base station
transmission diversity of a mobile telecommunication system
according to an eighth embodiment of the present invention; and
FIG. 16 is a flow chart showing an algorithm for controlling a
comparison circuit in the eighth embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
FIG. 4 shows the configuration of a base station of a mobile
telecommunication system according to a first embodiment of the
present invention, and in this example the base station has two
antennas and two channels a and b. In FIG. 4, reference numeral 101
designates a first antenna (an antenna A), reference numeral 201
designated a second antenna (an antenna B), reference numeral 102
designates a first transmission/reception switching switch for the
first antenna 101, reference numeral 202 designates a second
transmission/reception switching switch for the second antenna 201,
reference numeral 103 designates a first radio receiving unit for
the first antenna 101, and reference numeral 203 designates a
second radio receiving unit for the second antenna 201. Reference
numeral 105 designates a first despreading circuit for the first
antenna 101, and reference numeral 205 designates a second
despreading circuit for the second antenna 201. Each of the first
and second despreading circuits 105 and 205 operates to subject
received data to despreading using both spreading codes .alpha. and
.beta.. Reference numeral 301 designates a first comparison circuit
which operates to compare correlation levels (power levels of
received signals), which have been obtained by the despreading in
the first and second despreading circuits 105 and 205 using the
spreading code .alpha., with each other with respect to a first
channel a, and reference numeral 401 designates a second comparison
circuit which operates to compare correlation levels, which have
been obtained by the despreading in the first and second
despreading circuits 105 and 205 using the spreading code .beta.,
with each other with respect to a second channel b. Reference
numeral 302 designates a first composition circuit which operates
to compose the received signals, which have been subjected to
despreading in the first and second despreading circuits 105 and
205 using the spreading code .alpha., with respect to the first
channel a, and reference numeral 402 designates a second
composition circuit which operates to compose the received signals,
which have been subjected to the despreading in the first and
second despreading circuits 105 and 205 using the spreading code
.beta., with respect to the second channel b. Reference numeral 303
designates a first decode circuit for the first channel a which
operates to decode the composite signal which has been obtained by
the composition in the first composition circuit 302, and reference
numeral 403 designates a second decode circuit for the second
channel b which operates to decode the composite signal which has
been obtained by the composition in the second composition circuit
402.
Reference numeral 304 designates a first spreading circuit which
operates to spreading transmission data of the first channel a
using the spread code .alpha., reference numeral 404 designates a
second spreading circuit which operates to spread transmission data
of the second channel b using the spreading code .beta., reference
numeral 305 designates a first transmission antenna selecting
circuit for the first channel a which operates to select from which
antenna the transmission signal, which has been spread in the first
spreading circuit 304, is to be transmitted, and reference numeral
405 designates a second transmission antenna selecting circuit for
the second channel b which operates to select from which antenna
the transmission signal, which has been spread in the second
spreading circuit 404, is to be transmitted. Reference numeral 106
designates a first multiplexing circuit which operates to multiplex
the spread transmission signals with respect to the first antenna
101, reference numeral 206 designates a second multiplexing circuit
which operates to multiplex the spread transmission signals with
respect to the second antenna 201, and reference numeral 104
designates a first radio transmission unit for the first antenna
101 which has a first quadrature modulator 107 and a first linear
amplifier 108. Reference numeral 204 designates a second radio
transmission unit for the second antenna 201 which has a second
quadrature modulator 207 and a second linear amplifier 208. In
addition, reference numeral 501 designates a transmission/reception
switching timing signal which is used to operate the first and
second transmission/reception switching switches 102 and 202.
Next, the operation of the abovementioned first embodiment will be
described.
The received signals which have been received by the first and
second antennas 101 and 201, respectively, are subjected to first
order demodulation in the first and second radio receiving units
103 and 203 after passing through the first and second
transmission/reception switching switches 102 and 202,
respectively. Then, after down-conversion and detection, the
correlation of the first channel a and that of the second channel b
are detected by each of the first and second despreading circuits
105 and 205. With respect to the correlation detection results
which have been obtained from the two antennas 101 and 201
independently of each other, the frame mean powers of the
correlation levels (the power levels of the received signals) are
calculated for every channel in each of the first and second
comparison circuits 301 and 401. On the basis of those results, the
transmission path or link states (the transfer functions of the
transmission links) of the first and second antennas 101 and 201
are obtained, and then it is determined from which of the first and
second antennas 101 and 201 the signal of each channel is to be
transmitted at the next transmission timing, and then, first and
second transmission antenna selection signals 306 and 406 are
respectively output. The received signals which have been passed
through the first and second comparison circuits 301 and 401,
respectively, are composed by the first and second composition
circuits 302 and 402 to be decoded in the first and second decode
circuits 303 and 403, thereby obtaining the reception data of the
individual channels.
On the other hand, the transmission data of the first channel a and
the transmission data of the second channel b (the signals after
digital modulation) are respectively subjected to band spreading in
the first and second spreading circuits 304 and 404 using the
spreading codes .alpha. and .beta., which are assigned to the
respective channels, and then are multiplexed with respect to the
transmission antennas in the first and second multiplexing circuits
106 and 206 through the first and second transmission antenna
selecting circuits 305 and 405, which have been switched by the
first and second transmission antenna selection signals 306 and
406. The multiplexed signals are respectively up-converted in the
first and second radio transmission units 104 and 204, and then are
respectively transmitted outwardly from the first and second
antennas 101 and 201 through the first and second
transmission/reception switching switches 102 and 202, which are
switched by the transmission/reception switching timing signal
501.
FIG. 5 shows an example in which the CDMA/TDD system of the present
embodiment, the base station including the two antennas A and B,
switches the transmission antenna for every channel in accordance
with the levels of the received signals. The transmission/reception
frames are shown. In addition, FIG. 5 shows an example in the case
where four channels are provided. Similarly to the TDMA/TDD system
shown in FIG. 3, reference symbol TX represents transmission, and
reference symbol RX represents reception, and it is assumed that
the mobile terminals PS1 to PS4 (referring to FIG. 1) perform
respective communications using channels 1 to 4. In the case where
at time t0, the levels of the received signals of the individual
channels (the averages or the like of the levels of the received
signals for one frame) have the relationship, as shown in the
figure, with respect to the antennas A and B, it is assumed that
when the transmission is performed at the next time t1, the antenna
having the higher reception level is selected to perform the
transmission. In the figure, the reference symbol of the selected
antenna is shown. Then it is shown that at time t1, each of the
channels 1 and 3 selects the antenna A and each of the antennas 2
and 4 selects the antenna B, and after the signal of channel 1 and
the signal of channel 3 have been multiplexed, the resultant signal
is transmitted outwardly from the antenna A, and also after the
signal of channel 2 and the signal of channel 4 have been
multiplexed, the resultant signal is transmitted outwardly from the
antenna B. At time t3 and time t5 as well, on the basis of the
reception levels at time t2 and time t4, and antenna is selected
for every channel and multiplexing is performed before transmission
of the resultant signals.
As a result, in an environment in which fading changes depending on
the frequency band and varies in terms of time, the power levels of
the received signals of the reverse link and the forward link can
be stabilized, and high quality communication can be realized.
Second Embodiment
FIG. 6 shows the configuration of a base station of a mobile
telecommunication system according to a second embodiment of the
present invention, and also shows an example in which the base
station has two antennas and two channels a and b. In FIG. 6,
reference numeral 101 designates a first antenna (an antenna A),
reference numeral 201 designates a second antenna (an antenna B),
reference numeral 102 designates a first transmission/reception
switching switch for the first antenna 101, reference numeral 202
designates a second transmission/reception switching switch for the
second antenna 201, reference numeral 103 designates a first radio
receiving unit for the first antenna 101, and reference numeral 203
designates a second radio receiving unit for the second antenna
201. Reference numeral 105 designates a first despreading circuit
for the first antenna 101, and reference numeral 205 designates a
second despreading circuit for the second antenna 201. In this
connection, each of the first and second despreading circuits 105
and 205 operates to subject received data to despreading using
spreading codes .alpha. and .beta.. Reference numeral 307
designates a first estimation circuit which operates to estimate
future values from past values of the correlation levels (the power
levels of received signals), of the first channel a, which have
been obtained by the despreading in the first and second
despreading circuits 105 and 205 using the spreading code .alpha.,
and reference numeral 407 designates a second estimation circuit
which operates to estimate future values from past values of the
correlation levels, of the second channel b, which have been
obtained by the despreading in the first and second despreading
circuits 105 and 205 using the spreading code .beta.. Reference
numeral 301 designates a first comparison circuit for the first
channel a which operates to compare the estimated values of the
correlation levels, which have been obtained from the first
estimation circuits 307, between the first and second antennas 101
and 201, reference numeral 401 designates a second comparison
circuit for the second channel b which operates to compare the
estimated values of the correlation levels, which have been
obtained from the second estimation circuit 407, between the first
and second antenna 101 and 201, reference numeral 302 designates a
first composition circuit which operates to compose the received
signals of the first channel a which have been obtained by the
despreading in the first and second despreading circuits 105 and
205 using the spreading code .alpha., reference numeral 402
designates a second composition circuit which operates to compose
the received signals of the second channel b which have been
obtained by the despreading in the first and second despreading
circuits 105 and 205 using the spreading code .beta., reference
numeral 303 designates a first decode circuit for the first channel
a which operates to decode the composite signal which has been
obtained by composing the received signals in the first composition
circuit 302, and reference numeral 403 designates a second decode
circuit for the channel b which operates to decode the composite
signal which has been obtained by composing the received signals in
the second composition circuit 402.
Reference numeral 304 designates a first spreading circuit which
operates to spread transmission data of the first channel using the
spreading code .alpha., reference numeral 404 designates a second
spreading circuit which operates to spread transmission data of the
second channel b using the spreading code .beta., reference numeral
305 designates a first transmission antenna selecting circuit for
the first channel a which operates to determine from which antenna
the transmission signal, which has been obtained by spreading in
the first spreading circuit 304, is to be transmitted, and
reference numeral 405 designates a second transmission antenna
selecting circuit for the second channel b which operates to
determine from which antenna the transmission signal, which has
been obtained by spreading in the second spreading circuit 404, is
to be transmitted. Reference numeral 106 designates a first
multiplexing circuit which operates to multiplex the spread
transmission signals with respect to the first antenna 101,
reference numeral 206 designates a second multiplexing circuit
which operates to multiplex the spread transmission signals with
respect to the second antenna 201, and reference numeral 104
designates a first radio transmission unit for the first antenna
101 which has a first quadrature modulator 107 and a first linear
amplifier 108. Reference numeral 204 designates a second radio
transmission unit for the second antenna 201 which has a second
quadrature modulator 207 and a second linear amplifier 208. In
addition, reference numeral 501 designates a transmission/reception
switching timing signal which is used to operate the first and
second transmission/reception switching switches 102 and 203.
Next, the operation of the abovementioned second embodiment will be
described.
The received signals which have been received by the first and
second antennas 101 and 201, respectively, are subjected to first
order demodulation in the first and second radio receiving units
103 and 203 after passing through the first and second
transmission/reception switching switches 102 and 202. Then, after
down-conversion and detection, the correlations of the first and
second channels a and b are detected by each of the first and
second despreading circuits 105 and 205. With respect to the
correlation detection results which have been obtained from the two
antennas 101 and 201 independently of each other, the frame mean
powers of the correlation levels (the power levels of the received
signals) are calculated every channel in the first and second
estimation circuits 307 and 407. On the basis of those results, the
transmission link states (the transfer functions of the
transmission links) of the first and second antennas 101 and 201
are obtained to estimate the future values from the past values,
and the estimated future values are compared with each other by
each of the first and second comparison circuits 301 and 401. Then
it is determined from which of the first and second antennas 101
and 201 the signal of each channel is to be transmitted outwardly
at the next transmission timing, and then first and second
transmission antenna selection signals 306 and 406 are respectively
output. The received signals which have been passed through the
first and second comparison circuits 301 and 401, respectively, are
composed in the first and second composition circuits 302 and 402
to be decoded in the first and second decode circuits 303 and 403
of the respective channels, thereby obtaining the reception data of
the individual channels.
On the other hand, the transmission data of the first channel a and
the transmission data of the second channel b (the signals after
digital modulation) are respectively subjected to band spreading in
the first and second spreading circuits 304 and 404 using the
spreading codes .alpha. and .beta., which are assigned to the
respective channels, and then are multiplexed with respect to the
transmission antennas in the first and second multiplexing circuits
106 and 206 through the first and second transmission antenna
selecting circuits 305 and 405, which are switched by the first and
second transmission antenna selection signals 306 and 406. The
multiplexed signals are respectively up-converted in the first and
second radio transmission units 104 and 204, and then are
respectively transmitted outwardly from the first and second
antennas 101 and 201 through the first and second
transmission/reception switching switches 102 and 202, which are
switched by the transmission/reception switching timing signal
501.
FIG. 7 shows an example in which the CDMA/TDD system of the present
embodiment, the base station including the two antennas A and B,
switches the transmission antenna for every channel in accordance
with the levels of the received signals. The transmission/reception
frames are shown. In addition, FIG. 7 shows an example in the case
where four channels are provided. Similarly to FIG. 5, reference
symbol TX represents transmission, and reference symbol RX
represents reception, and it is assumed that the mobile terminals
PS1 to PS4 (referring to FIG. 1) perform the respective
communication using the channels 1 to 4. In the case where at time
t0, the levels of the received signals of the individual channels
(the averages or the like of the levels of the received signals for
one frame) have the relationship, as shown in FIG. 7, with respect
to the antennas A and B, and are estimated at time t1, as shown in
FIG. 7, it is assumed that when at the next time t1, the
transmission is performed, the antenna having the higher estimated
value of the reception level is selected to perform the
transmission. In the figure, the reference symbol of the selected
antenna is shown. Then, it is shown that at time t1, each of the
channels 1 and 3 selects the antenna A and each of the channels 2
and 4 selects the antenna B, and after the signal of channel 1 and
the signal of channel 3 have been multiplexed, the resultant signal
is transmitted outwardly from the antenna A, and also after the
signal of channel 2 and the signal of channel 4 have been
multiplexed, the resultant signal is transmitted outwardly from the
antennas B. At time t3 as well, on the basis of the reception
levels at time t2 and the reception levels prior thereto, the
transmission link states at time t3 are estimated, and a
transmission antenna is selected for every channel and multiplexing
is performed, and then the multiplexed signals are transmitted
outwardly from the associated antennas. At time t5 as well,
similarly, the above-mentioned processings will be executed.
As a result, in an environment in which fading changes depending on
the frequency band and varies in terms of time, the states of the
transmission links can be estimated and the power levels of the
received signals of the reverse link and the forward link can be
stabilized, and high quality communication can be realized.
Third Embodiment
The configuration of a base station of a mobile telecommunication
system according to the present embodiment is the same as that in
the second embodiment. FIG. 8 shows an example of an antenna
arrangement of the base station of the mobile telecommunication
system in the present embodiment, and also shows an example in the
case where three antennas A, B and C are provided. With respect to
the antennas A, B and C, any two antennas are separated enough to
obtain independently fading transmission links, and they are
arranged in the central portion of the cover area of the base
station to provide generally concentric coverage.
In mobile telecommunication, the fluctuations in the power level of
the received signal are roughly due to the following three
factors.
(1) Change caused by distance: Fluctuations in the reception level
due to a change in the communication distance caused by movement of
the mobile station.
(2) Change in central value: Fluctuations in the reception level
due to a change in the environment, such as buildings.
(3) Instantaneous change: Fluctuations in the reception level due
to frequency selective fading.
In the case where three antennas are arranged in a manner as shown
in FIG. 8, the distances La, Lb and Lc between the mobile station
and the three antennas A, B and C are not largely different from
one another. In addition, since there is not a large difference
even in the environment such as the communication links, and hence
the instantaneous change becomes the predominant factor in the
fluctuations in the reception level, for the long term average,
there is no difference in the reception levels among the antennas.
Therefore, even if the reception level of the antenna A drops
instantaneously, the possibility is high that a higher reception
level can be obtained by antenna B or C, and thus in an antenna of
interest, good reception may be obtained. This is also applies to
the case where the reception level of antenna B or C drops. Thus,
the possibility is small that the reception levels of all of the
three antennas drop. Therefore, if the antenna having the higher
reception level is selected to perform the transmission/reception,
communication at a high reception level can be always performed. In
addition, by increasing the number of antennas, the possibility is
reduced more and more that the reception levels of all of the
antennas drop, and thus the fluctuation in the reception level
after selection of the antenna becomes small.
The result is that the communication quality is remarkably improved
on the reception side (in the reverse link of the base station) by
stabilizing the transmission/reception level. That is, high quality
communication in which the bit error rate is low in the reverse
link becomes possible.
Fourth Embodiment
The configuration of a base station of a mobile telecommunication
system according to the present embodiment is the same as that in
the second embodiment. FIG. 9 shows an example of an antenna
arrangement of the base station of the mobile telecommunication
system in the present embodiment, and also shows an example in
which three antennas A, B and C are employed. The three antennas A,
B and C are distributively arranged in a plurality of locations
within the cover area of the base station. With respect to the
three antennas A, B and C, any two antennas are separated enough to
obtain independently fading transmission links.
In the case where the three antennas A, B and C are arranged in a
manner as shown in FIG. 9, since the distances La, Lb and Lc
between the mobile station and the three antennas a, b and c are
greatly different from one another, the change caused by distance
becomes the predominant factor in the fluctuations in the reception
level. As a result, in accordance with the position of the mobile
station, the antennas by which the signals of the channels are to
be transmitted/received are substantially determined. In this case,
since the communication radio waves of other stations, which are
transmitted/received by the associated antennas, are greatly
attenuated as the distances further increase, as compared with the
communication radio wave of the local station, it is difficult for
those communication radio waves of other stations to interfere with
the communication radio wave of the local station. That is, the
communication radio waves of other stations which are
transmitted/received by the same antenna are the predominant factor
in the interference. In such a way, if the plurality of antennas
are widely distributively arranged within the cover area of the
base station, from the random nature of the positions of the mobile
stations, the number of mobile stations for which the
transmission/reception by individual antennas is predominant
becomes equal to one another in terms of probabilities. That is, as
compared with the case where the number of antennas is one, in the
case where the number of antennas is three, the number of mobile
stations for which transmission/reception by the same antenna is
predominant is reduced to 1/3, and the number of communication
radio waves of other stations other than the local station, which
cause interference, is approximately reduced to 1/3. Thus, the
interference is greatly reduced.
The effect is that the communication quality is improved remarkably
on the transmission side (in the forward link to the base station)
by reducing interference. That is, high quality communication in
which the bit error rate is low in the forward link becomes
possible.
Fifth Embodiment
The configuration of a base station of a mobile telecommunication
system according to the present embodiment is the same as that in
the second embodiment. FIG. 10 shows an example of an antenna
arrangement of the base station of the mobile telecommunication
system in the present embodiment, and also shows an example in the
case where ten antennas are employed. The ten antennas are divided
into four antenna groups a, b, c and d. The antenna group a has
three antennas, the antenna group b has three antennas, the antenna
group c has two antennas, and the antenna group d has two antennas.
Those antenna groups are arranged at four locations within the
cover area of the base station. The antennas in each antenna group
are arranged in the associated location so as to be separated
enough to obtain independently fading transmission links. The
distances among the antenna groups are sufficiently larger than
those among the antennas in each antenna group.
In the case where the antennas are arranged in a manner as shown in
FIG. 10, since the distances La, Lb, Lc and Ld between the mobile
station and the antenna groups a, b, c and d are largely different
from one another, the change caused by distance becomes the
predominant factor in the difference in the reception levels among
the antenna groups. Therefore, in accordance with the position of
the mobile station, the antenna group by which the
transmission/reception is to be performed is substantially
determined. In this case, since the communication radio waves of
other stations which are transmitted/received by the antennas of
the antenna groups are largely attenuated as the distances further
increase, as compared with the communication radio wave of the
local station, it is difficult for those communication radio waves
of other stations to interfere with the communication radio wave of
the local station. That is, the cause of the interference is
substantially limited to the communication radio waves of other
stations which are transmitted/received by the same antenna group.
In such a way, if the antenna groups are widely distributively
arranged in the cover area of the base station, from the random
nature of the positions of the mobile stations, the number of
mobile stations for which transmission/reception by the individual
antenna groups is predominant become equal to one another in terms
of probabilities. That is, as compared with the case where the
number of antenna groups is one, in the case where the number of
antenna groups is four, the number of mobile stations for which the
transmission/reception by the same antenna group is predominant is
reduced to 1/4, and the number of communication radio waves of
other stations other than the local station, which cause
interference, is approximately reduced to 1/4. Thus, the
interference is greatly reduced.
On the other hand, the distances between the mobile station and the
individual antennas in the same antenna group are not largely
different from one another. Since there is not a large difference
in the environment such as the communication links, and the
instantaneous change becomes the predominant factor in the
fluctuations in the reception level, for the long term average,
there is no difference in reception level between the antennas.
Therefore, even if the reception level of antenna A has an
instantaneous drop during communication with a mobile station for
which the transmission/reception by the antenna group d for example
becomes predominant, the possibility is high that a better
reception level can be obtained by antenna B or C, and hence with
an antenna of interest, good reception can be obtained. This also
applied to the case where the reception level of antenna B or C
drops. Thus, the possibility is small that the reception levels of
all of the three antennas are poor. Therefore, if the antenna
having the higher reception level is selected to perform the
transmission/reception, communication at the a reception level can
be always performed. In addition, by increasing the number of
antennas, the possibility is reduced more and more that the
reception levels of all of the antennas may drop, and hence
fluctuation in the reception level after selection of the antenna
becomes small.
The effect is that the communication quality is remarkably improved
on the reception side (in the reverse link of the base station) by
stabilizing the transmission/reception level. On the other hand,
the communication quality is also remarkably improved on the
transmission side (in the forward link of the base station) by
reducing interference. That is, high quality communication in which
the bit error rate is low in both the reverse link and the forward
link becomes possible.
Sixth Embodiment
FIG. 11 shows the configuration of a base station of a mobile
telecommunication system according to a sixth embodiment of the
present invention, and also shows an example in which the base
station includes two antennas and two channels a and b. In FIG. 11,
reference numeral 101 designates a first antenna (an antenna A),
reference numeral 201 designated a second antenna (an antenna B),
reference numeral 102 designates a first transmission/reception
switching switch for the first antenna 101, reference numeral 202
designates a second transmission/reception switching switch for the
second antenna 201, reference numeral 103 designates a first radio
receiving unit for the first antenna 101, and reference numeral 203
designates a second radio receiving unit for the second antenna
201. Reference numeral 105 designates a first despreading circuit
for the first antenna 101, and reference numeral 205 designates a
second despreading circuit for the second antenna 201. In this
connection, each of the first and second despreading circuits 105
and 205 operates to subject received data to despreading using both
spreading codes .alpha. and .beta.. Reference numeral 307
designates a first estimation circuit which operates to estimate
future values from past values of the correlation levels (the power
levels of received signals), of the first channel a, which have
been obtained by the despreading in the first and second
despreading circuits 105 and 205 using the spreading code .alpha.,
and reference numeral 407 designates a second estimation circuit
which operates to estimate future values from past values of the
correlation levels, of the second channel b, which have been
obtained by the despreading in the first and second despreading
circuits 105 and 205 using the spreading code .beta.. Reference
numeral 301 designates a first comparison circuit for the first
channel a which operates to compare the estimated values of the
correlation levels, which have been obtained from the first
estimation circuit 307, between the first and second antennas 101
and 201, and reference numeral 401 designates a second comparison
circuit for the second channel b which operates to compare the
estimated values of the correlation levels, which have been
obtained from the second estimation circuit 407, between the first
and second antennas 101 and 201. Reference numeral 302 designates a
first composition circuit which operates to compose the received
signals of the first channel a which have been obtained by the
despreading in the first and second despreading circuits 105 and
205 using the spreading code .alpha., reference numeral 402
designates a second composition circuit which operates to compose
the received signals of the second channel b which have been
obtained by the despreading in the first and second despreading
circuits 105 and 205 using the spreading code .beta., reference
numeral 303 designates a first decode circuit for the first channel
a which operates to decode the composite signal which has been
obtained by composing the received signals in the first composition
circuit 302, and reference numeral 403 designates a second decode
circuit for the channel b which operates to decode the composite
signal which has been obtained by composing the received signals in
the second composition circuit 402. In addition, reference numeral
502 designates a comparison circuits controlling circuit which
operates to be responsive to first and second transmission antenna
selection signals 306 and 406, which have been output from the
first and second comparison circuits 301 and 401, respectively, to
control the operations of the first and second comparison circuits
301 and 401.
Reference numeral 304 designates a first spreading circuit which
operates to spread transmission data of the first channel a using
the spreading code .alpha., reference numeral 404 designates a
second spreading circuit which operates to spread transmission data
of the second channel b using the spreading code .beta., reference
numeral 305 designates a first transmission antenna selecting
circuit for the first channel a which operates to select from which
antenna the transmission signal, which has been obtained by
spreading in the first spreading circuit 304, is to be transmitted,
and reference numeral 405 designates a second transmission antenna
selecting circuit for the second channel b which operates to
determine from which antenna the transmission signal, which has
been obtained by spreading in the second spreading circuit 404, is
to be transmitted. Reference numeral 106 designates a first
multiplexing circuit which operates to multiplex the spread
transmission signals with respect to the first antenna 101,
reference numeral 206 designates a second multiplexing circuit
which operates to multiplex the spread transmission signals with
respect to the second antenna 201, and reference numeral 104
designates a first radio transmission unit for the first antenna
101 which has a first quadrature modulator 107 and a first linear
amplifier 108. Reference numeral 204 designates a second radio
transmission unit for the second antenna 201 which has a second
quadrature modulator 207 and a second linear amplifier 208. In
addition, reference numeral 501 designates a transmission/reception
switching timing signal which is used to operate the first and
second transmission/reception switching switches 102 and 202.
Next, the operation of the abovementioned sixth embodiment will be
described.
The received signals which have been received by the first and
second antennas 101 and 201, respectively, are subjected to first
order demodulation in the first and second radio receiving units
103 and 203 after passing through the first and second
transmission/reception switching switches 102 and 202. Then, after
down-conversion and detection, the correlation of the first and
second channels a and b are detected by each of the first and
second despreading circuits 105 and 205. With respect to the
correlation detection results which have been obtained from the two
antennas 101 and 201 independently of each other, the frame mean
powers of the correlation levels (the power levels of the received
signals) are calculated for every channel in each of the first and
second comparison circuits 307 and 407. On the basis of those
results, the transmission link states (the transfer functions of
the transmission links) of the first and second antennas 101 and
201 are obtained to estimate future values from the past values.
The estimated future values are compared with each other by each of
the first and second comparison circuits 301 and 401, and then it
is determined, due to an instruction issued from the comparison
circuits controlling circuit 502, from which of the first and
second antennas 101 and 201 the signal of each channel is to be
transmitted outwardly at the next transmission timing. Then first
and second transmission antenna selection signals 306 and 406 are
respectively output. The first and second transmission antenna
selection signals 306 and 406 are fed back to the comparison
circuits controlling circuit 502, which is responsive to the first
and second transmission antenna selection signals 306 and 406 to
determine whether or not a transmission antenna is to be selected
over again and to issue instructions to both of the first and
second comparison circuits 301 and 401. The received signals which
have been passed through the first and second comparison circuits
301 and 401, respectively, are composed by the first and second
composition circuits 302 and 402 to be decoded in the first and
second decode circuits 303 and 403 of the respective channels,
thereby obtaining the reception data of the individual
channels.
On the other hand, the transmission data of the first channel a and
the transmission data of the second channel b (the signals after
digital modulation) are respectively subjected to band spreading in
the first and second spreading circuits 304 and 404 using the
spreading codes .alpha. and .beta., which are assigned to the
respective channels, and then are multiplexed with respect to the
transmission antennas in the first and second multiplexing circuits
106 and 206 through the first and second transmission antenna
selecting circuits 305 and 405, which are switched to each other by
the first and second transmission antenna selection signals 306 and
406. The multiplexed signals are respectively up-converted in the
first and second radio transmission units 104 and 204, and then are
respectively transmitted outwardly from the first and second
antennas 101 and 201 through the first and second
transmission/reception switching switches 102 and 202, which are
switched by the transmission/reception switching timing signal
501.
The operation for switching the antennas in the CDMA/TDD system of
the present embodiment is the same as that shown in FIG. 7. In the
case where at time t0, the levels of the received signals of the
individual channels (the averages or the like of the levels of the
received signals for one frame) have the relationship, as shown in
FIG. 7, with respect to the antennas A and B, and are estimated, at
the next time t1, as shown in FIG. 7, when transmission is
performed, the individual channels select the antennas each having
the higher reception level independently of one another to transmit
therefrom outwardly the associated signals. This algorithm is shown
in FIG. 12.
In FIG. 12, firstly, the antenna from which the signal of channel 1
is to be transmitted outwardly is selected (Step 901), and next the
antenna from which the signal of channel 2 is to be transmitted
outwardly is selected (Step 902), and next the antenna from which
the signal of channel 3 is to be transmitted outwardly is selected
(Step 903), and finally, the antenna from which the signal of
channel 4 is to be transmitted outwardly is selected (Step 904).
Those antennas are selected perfectly independently of one another,
and from which antennas the signals of other channels are to be
transmitted outwardly does not exert an influence on the selection
of the transmission antenna of each channel. In FIG. 7, reference
symbols of the selected antennas are shown. In this connection, it
is shown at time t1 that each of the channels 1 and 3 selects the
antenna A and each of the channels 2 and 4 selects the antenna B,
and then after the signals of channel 1 and the signal of channel 3
have been multiplexed, the resultant signal is transmitted
outwardly from the antenna A, and also after the signal of channel
2 and the signal of channel 4 have been multiplexed, the resultant
signal is transmitted outwardly from the antenna B. At time t3 as
well, on the basis of the reception levels at time t2 and the
reception levels prior thereto, the transmission link states at
time t3 are estimated, and a transmission antenna is selected for
every channel and multiplexing is performed with respect to every
antenna, and then the resultant signals are transmitted outwardly
from the associated antennas. At time t5 as well, similarly, the
abovementioned processings will be executed.
From the random nature of the positions of the mobile stations and
the independency of the fading of the transmission links associated
with the antennas, even by such a simple transmission antennas
selecting algorithm, the selected transmission antennas for the
individual channels are not concentrated, in terms of
probabilities, on a subset of the antennas, but are distributed to
the individual antennas. That is, even without complicated control,
the transmissions are distributed to the individual antennas in a
manner that reduces the number of signals which are multiplexed in
one antenna, and as a result the performance which is required for
the first and second quadrature modulators 107 and 207 can be
reduced, along with the performance which is required for the first
and second linear amplifiers 108 and 208 of the first and second
radio transmission units 104 and 204.
Seventh Embodiment
The configuration of a base station of a mobile telecommunication
system according to the present embodiment is the same as that in
the sixth embodiment. FIG. 13 shows an example in which the
CDMA/TDD system of the present embodiment, the base station having
two antennas A and B, switches the transmission antenna for every
channel in accordance with the levels of the received signals. The
transmission/reception frames are shown in FIG. 13, and also an
example in the case where four channels are provided. In this
connection, similarly to FIG. 5, reference symbol TX represents
transmission and reference symbol RX represents reception, and it
is assumed that the mobile terminals PS1 to PS4 (referring to FIG.
1) perform their respective communications using the channels 1 to
4. In the case where at time t0, the levels of the received signals
of the channels (the averages or the like of the levels of the
received signals for one frame) have the relationship, as shown in
FIG. 13, with respect to the antennas A and B, and then the levels
at next time t1 are estimated as shown in FIG. 13, when
transmission is performed at next time t1, the individual channels
select respective antennas each having the higher estimated value
of the reception level independently of one another to transmit
therefrom outwardly the associated signals. This algorithm is shown
in FIG. 14.
In FIG. 14, firstly, the relation of X=100 is set. Then, out of the
antenna having the highest reception level and the antenna having
the second highest reception level, the antenna having the highest
reception level is selected at a probability of X%, and the antenna
having the second highest reception level is selected at a
probability of (100-X)% (Step 1101). First, the antenna from which
the signal of channel 1 is to be transmitted outwardly is selected
(Step 1102), and next the antenna from which the signal of channel
2 is to be transmitted outwardly is selected (Step 1103), and next
the antenna from which the signal of channel 3 is to be transmitted
outwardly is selected (Step 1104), and finally, the antenna from
which the signal of channel 4 is to be transmitted outwardly is
selected (Step 1105). Then, it is checked whether or not the
antennas from which the signals of the individual channels are to
be transmitted outwardly are concentrated on a subset of the
antennas (e.g., one antenna) (Step 1106). Then, if not, the process
of selecting the transmission antennas is completed. On the other
hand, if so, the value of X is gradually decreased (Step 1107) and
the transmission antennas for the individual channels are selected
over again in accordance with the above-mentioned algorithm. In
FIG. 13, reference symbols of the selected antennas are shown. In
addition, it is shown at time t1 that each of the channels 1 and 3
selects the antenna and each of the channels 2 and 4 selects the
antenna B, and that after the signal of channel 1 and the signal of
channel 3 have been multiplexed, the resultant signal is
transmitted outwardly from the antenna A, and also after the signal
of channel 2 and the signal of channel 4 have been multiplexed, the
resultant signal is transmitted outwardly from the antenna B. Then,
it is shown at time t3 that each of the channels 1, 2 and 3 selects
the antenna A and only channel 4 selects the antenna B, and that
after the signal of channel 1, the signal of channel 2 and the
signal of channel 3 have been multiplexed, the resultant signal is
transmitted outwardly from antenna A, and also the signal of
channel 4 is transmitted outwardly from antenna B (after the
multiplexing). Then, at time t5, since for all of the channels,
antenna A has a larger estimated value than antenna B, in the first
selection at a probability of X=100, all of the channels select the
antenna A, and hence the channels concentrate on one antenna. As a
result of decreasing slightly the value of X to perform the
selection over again, it is shown that channel 4 selects the
antenna B.
From the random nature of the positions of the mobile stations and
the independency of the fading of the transmission links associated
with the antennas, even in the selection at a probability of
X=100%, though small in terms of probabilities, the selected
transmission antennas for the associated channels may concentrate
on one of the antennas in some cases. In such cases, there is
provided the effect that even if the channel(s) selecting the
antenna(s), in which the reception level is not maximum, may be
more or less present, by selecting the antennas over again, the
transmission antennas are distributed to the individual antennas so
that the number of channels the signals of which are multiplexed
can be reduced, and also the performance can be reduced which is
required for the first and second quadrature modulators 107 and 207
and the first and second linear amplifiers 108 and 208 of the first
and second radio transmission units 104 and 204 in the base
station.
Eighth Embodiment
The configuration of a base station of a mobile telecommunication
system according to the present embodiment is the same as that in
the sixth embodiment. But, an example is considered in which the
total number of accommodation channels within the cover area of the
base station is four (L=4). As for the performance of the first and
second quadrature modulators 107 and 207 and the first and second
linear amplifiers 108 and 208 of the first and second radio
transmission units 104 and 204, the radio transmission unit for one
antenna has a transmission capability up to two channels (M=2).
FIG. 15 is an example in which the CDMA/TDD system, the base
station having two antennas A and B, switches the transmission
antenna for every channel in accordance with the levels of the
received signals. The transmission/reception frames, and also an
example in which four channels are provided. In this connection,
similarly to FIG. 5, reference symbol TX represents transmission
and reference symbol RX represents reception, and also it is
assumed that the mobile terminals PS1 to PS4 (referring to FIG. 1)
perform their respective communications using channels 1 to 4. In
the case where at time t0, the levels of the received signals of
the channels (the averages or the like of the levels of the
received signals for one frame) have the relationship, as shown in
FIG. 15, with respect to the antennas A and B, and then are
estimated, when the transmission is performed at the next time t1,
the individual channels select the respective antennas each having
the higher estimated value of the reception level independently of
one another to transmit therefrom outwardly the associated signals.
This algorithm is shown in FIG. 16.
In FIG. 16, firstly, the relation of X=100 is set. Then, out of the
antenna having the highest reception level and the antenna having
the second highest reception level, the antenna having the highest
reception level is selected at a probability of X%, and the antenna
having the second highest reception level is selected at a
probability of (100-X)% (Step-1301). First, the antenna from which
the signal of channel 1 is to be transmitted outwardly is selected
(Step 1302), and next the antenna from which the signal of channel
2 is to be transmitted outwardly is selected (Step 1303), and next
the antenna from which the signal of channel 3 is to be transmitted
outwardly is selected (Step 1304), and finally, the antenna from
which the signal of channel 4 is to be transmitted outwardly is
selected (Step 1305). Then, it is checked whether or not an antenna
which has been selected as the transmission antenna by three or
more channels is present (Step 1306). If not, the process of
selecting the transmission antennas is completed. On the other
hand, if so, the value of X is gradually decreased (Step 1307), and
then the transmission antennas for the individual channels are
selected over again until such an antenna becomes absent. In FIG.
13, reference symbols for the selected antennas are shown. In
addition, it is shown at time t1 that each of the channels 1 and 3
selects the antenna A and each of the channels 2 and 4 selects the
antenna B, and that after the signal of channel 1 and the signal of
channel 3 have been multiplexed, the resultant signal is
transmitted outwardly from the antenna A, and also after the signal
of channel 2 and the signal of channel 4 have been multiplexed, the
resultant signal is transmitted outwardly from the antenna B. Since
at time t3, for the channels 1, 2 and 3, antenna A has a larger
estimated value than that of antenna B, and for channel 4, antenna
B has a larger estimated value than antenna A, in the first
selection at a probability of X=100, each of the channels 1, 2 and
3 selects the antenna B, and also channel 4 selects the antenna B.
Thus, three channels concentrate on the antenna A. As a result of
decreasing slightly the value of X before performing the selection
over again, it is shown that the channel 2 selects the antenna B.
Then, at time t5, since for all of the channels, the antenna A has
a larger estimated value than antenna B, in the first selection at
a probability of X=100, all of the channels select the antenna A,
and hence the channels concentrate on one antenna. As a result of
decreasing slightly the value of X to before performing the
selection over again, it is shown that the channels 3 and 4 select
the antenna B.
From the random nature of the positions of the mobile stations and
the independency of the fading of the transmission links associated
with the antennas, even in the first selection at a probability of
X=100%, the selected transmission antennas for the associated
channels are not concentrated, in terms of probabilities, on one of
the antennas, but are distributed to the individual antennas. But,
though small in terms of probabilities, the selected transmission
antennas for the associated channels may be concentrated on one of
the antennas in some cases. In such cases, even if the channels may
be more or less present which select the antenna(s) in which the
reception level is not maximum, when the antennas are selected over
again so that the transmission antennas are distributed to the
individual antennas, the system can suppress interference more
effectively. In addition, even in the case where the performance of
the first or second quadrature modulator 107 and 207 and the first
or second linear amplifiers 108 and 208 of the first or second
radio transmission unit 108 or 208 for one antenna in the base
station is inferior to the mobile station accommodation capability
of the whole base station, by distributing the transmission
antennas to the individual antennas to decrease the number of
channels the signals of which are multiplexed, the system can be
readily configured.
* * * * *