Supporting cooperative transmission in massive multiple-input multiple-output (mimo) systems

Abstract

Embodiments of the disclosure relate to supporting cooperative transmission in massive multiple-input multiple-output (MIMO) systems, such as a wireless distribution system (WDS). A WDS includes a plurality of remote units each defining a home coverage cell. A selected remote unit can coordinate with a neighboring remote unit(s) to help mitigate inter-cell interference for a selected client device(s) located in an overlapping coverage area between the home coverage cell of the selected remote unit and a neighboring coverage cell(s) defined by the neighboring remote unit(s). The selected remote unit receives channel-data information from the selected client device(s) and forms a first radio frequency (RF) beam based on the channel-data information to distribute a downlink signal(s) to the selected client device. The selected remote unit coordinates with the neighboring remote unit(s) based on the channel-data information to form a second RF beam to distribute the downlink signal(s) to the selected client device.

What is claimed is: 
     
         1 . A communications system, comprising:
 a plurality of remote units comprising optical-to-electrical converters and electrical-to-optical converters, each configured to define a home coverage cell among a plurality of coverage cells in the communications system to communicate one or more downlink signals to one or more client devices located within a boundary of the home coverage cell; and   a central unit comprising electrical-to-optical converters and optical-to-electrical converters and communicatively coupled to the plurality of remote units over an optical fiber-based communications medium,   wherein a selected remote unit among the plurality of remote units is configured to:
 identify at least one selected client device located in at least one overlapping coverage area between the home coverage cell of the selected remote unit and at least one neighboring coverage cell defined by at least one neighboring remote unit among the plurality of remote units; 
 receive channel-data information from the at least one selected client device; 
 form a first radio frequency (RF) beam based on the channel-data information to distribute at least one first downlink signal among the one or more downlink signals to the at least one selected client device; and 
 coordinate with the at least one neighboring remote unit based on the channel-data information to form at least one second RF beam to distribute the at least one first downlink signal from the at least one neighboring remote unit to the at least one selected client device, and 
   the selected remote unit and the at least one neighboring remote unit are configured to form the respective first RF beam and the at least one second RF beam based on a defined time-frequency resource.   
     
     
         2 . The communications system of  claim 1 , wherein the selected remote unit is further configured to:
 identify at least one second selected client device located within the boundary of the home coverage cell of the selected remote unit and outside the at least one overlapping coverage area; and   distribute at least one second downlink signal among the one or more downlink signals to the at least one second selected client device.   
     
     
         3 . The communications system of  claim 2 , wherein the selected remote unit and the at least one neighboring remote unit are each configured to pre-code the first downlink signal based on the channel-data information to provide phase coherency between the at least one first RF beam and the at least one second RF beam. 
     
     
         4 . The communications system of  claim 2 , wherein the selected remote unit is further configured to receive the channel-data information based on at least one channel state information (CSI) provided by the at least one selected client device. 
     
     
         5 . The communications system of  claim 2 , wherein the selected remote unit is further configured to distribute the at least one first downlink signal and the at least one second downlink signal. 
     
     
         6 . The communications system of  claim 2 , wherein the selected remote unit is further configured to distribute the at least one second downlink signal based on the defined time-frequency resource. 
     
     
         7 . The communications system of  claim 6 , wherein the defined time-frequency resource comprises an identical number of RF carriers and an identical number of symbol streams. 
     
     
         8 . The communications system of  claim 2 , wherein the selected remote unit is further configured to pre-code the at least one second downlink signal to provide spatial separation from the at least one first downlink signal. 
     
     
         9 . A method for supporting cooperative transmissions in a communications system comprising a central unit and a plurality of remote units distributed over multiple floors of a building infrastructure, the method comprising:
 identifying at least one selected client device located in at least one overlapping coverage area between a home coverage cell of a selected remote unit among the plurality of remote units and at least one neighboring coverage cell defined by at least one neighboring remote unit among the plurality of remote units;   receiving channel-data information from the at least one selected client device;   forming a first radio frequency (RF) beam based on the channel-data information to distribute at least one first downlink signal to the at least one selected client device;   coordinating with the at least one neighboring remote unit based on the channel-data information to form at least one second RF beam to distribute the at least one first downlink signal from the at least one neighboring remote unit to the at least one selected client device;   identifying at least one second selected client device located within a boundary of the home coverage cell of the selected remote unit and outside the at least one overlapping coverage area; and   distributing at least one second downlink signal to the at least one second selected client device.   
     
     
         10 . The method of  claim 9 , further comprising forming the respective first RF beam and the at least one second RF beam based on a defined time-frequency resource. 
     
     
         11 . The method of  claim 10 , further comprising pre-coding the at least one first downlink signal based on the channel-data information to provide phase coherency between the first RF beam and the at least one second RF beam. 
     
     
         12 . The method of  claim 10 , further comprising receiving the channel-data information based on at least one channel state information (CSI) provided by the at least one selected client device. 
     
     
         13 . The method of  claim 11 , further comprising distributing the at least one first downlink signal and the at least one second downlink signal. 
     
     
         14 . The method of  claim 13 , wherein the communications system comprises a downlink optical fiber-based communications medium and an uplink optical fiber-based communications medium. 
     
     
         15 . The method of  claim 14 , wherein the central unit comprises electrical-to-optical and a plurality of optical-to-electrical converters.