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.

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.