Method of grouping users to reduce interference in mimo-based wireless network

Abstract

In a system of MIMO communications in a wireless network, a number of wireless units are logically divided into a plurality of user groups, through operation of a semi-orthogonal user selection sub-system. For example, the user selection sub-system may implement a heuristic user selection algorithm based on near-orthogonality. Each user group is assigned a discrete transmission channel, which may be orthogonally defined in terms of frequency, time, or code. Data is transmitted over the channels (e.g., from network base stations) in a coherently coordinated manner, according to a zero-forcing beamforming operation. The system may be configured for operation in a time/frequency selective manner, e.g., over time/frequency selective fading channels. The wireless units may be allocated to the time/frequency slots based on prioritization of channel strength and considerations of fairness, in conjunction with the application of a semi-orthogonal user selection algorithm.

We claim: 
     
         1 . A method of MIMO communications for use in a wireless network including at least a first base station and a second base station, said method comprising:
 semi-orthogonally selecting a plurality of wireless units in the wireless network for assignment to a plurality of designated transmission channels; and   transmitting data signals to the plurality of wireless units over the assigned transmission channels, said data signals being transmitted from at least one of the first base station and the second base station according at least to a zero-forcing beamforming (ZFBF) operation.   
     
     
         2 . The method of  claim 1  wherein the data signals are transmitted also according to at least one designated transmission power constraint of the first and second base stations. 
     
     
         3 . The method of  claim 2  wherein:
 each of the first and second base stations has at least one transmit antenna; and 
 the at least one designated transmission power constraint comprises at least one of a per-transmit antenna transmission power constraint and a per-base station transmission power constraint. 
 
     
     
         4 . The method of  claim 2  wherein the transmission channels are discrete channels having equal bandwidths, and wherein the data signals are transmitted to the first plurality of wireless units at equal minimum rates. 
     
     
         5 . The method of  claim 4  wherein the semi-orthogonal selection results in a second plurality of wireless units being blocked from receiving transmissions, based at least in part on channel norms of the wireless units. 
     
     
         6 . The method of  claim 1  wherein the wireless units are semi-orthogonally selected for assignment to the transmission channels according to a greedy user selection algorithm that includes a near-orthogonality assessment of the wireless units. 
     
     
         7 . A method of MIMO communications in a wireless network including at least a first base station and a second base station, said method comprising:
 forming a plurality of user groups on a semi-orthogonal selection basis, wherein each of the user groups includes a different subset of the plurality of wireless units in the wireless network; and   for each of the user groups, transmitting data signals to the wireless units in the user group over a discrete transmission channel assigned to the user group, wherein the data signals are transmitted from at least the first base station and the second base station based on zero-forcing beamforming (ZFBF) of the data signals.   
     
     
         8 . The method of  claim 7  further comprising:
 blocking transmissions to wireless units not assigned to the user groups. 
 
     
     
         9 . The method of  claim 7  wherein the transmission channels have equal bandwidths, and wherein the data signals are transmitted to the wireless units in the user groups at equal minimum rates. 
     
     
         10 . The method of  claim 7  wherein the data signals are transmitted according to at least one designated transmission power constraint of the first and second base stations. 
     
     
         11 . The method of  claim 10  wherein:
 each of the first and second base stations has at least one transmit antenna; and 
 the at least one designated transmission power constraint comprises at least one of a per-transmit antenna transmission power constraint and a per-base station transmission power constraint. 
 
     
     
         12 . The method of  claim 7  wherein the wireless units are semi-orthogonally selected for forming the user groups according to a greedy user selection algorithm that includes a near-orthogonality assessment of the wireless units. 
     
     
         13 . A communications system for MIMO communications in a wireless network, comprising:
 a first base station having one or more transmit antennas for wireless communications with at least one user group of wireless units formed at least in part based on a semi-orthogonal selection of a subset of a plurality of wireless units in the wireless network;   wherein at least one of the first base station and a second base station is configured to transmit data to the wireless units in said at least one user group over an assigned transmission channel according to a zero-forcing beamforming (ZFBF) operation and according to at least one designated transmission power constraint applied to said at least one base station, the designated transmission power constraint comprising at least one of (1) a first transmission power constraint applied on a per-transmission basis for each transmit antenna of said at least one base station and (2) a second transmission power constraint applied on a sum transmission basis for all transmit antennas of said at least one base station.   
     
     
         14 . The communications system of  claim 13 , wherein data is transmitted from said at least one base station to a plurality of user groups, each of the user groups comprising a different subset of said plurality of wireless units, wherein the wireless units in each user group are semi-orthogonally selected from among the plurality of wireless units; and
 wherein a discrete transmission channel is assigned to each of the user groups so that data transmitted from said at least one base station to the wireless units in the user groups are transmitted over respective assigned transmission channels according to a ZFBF operation and at least one designated transmission power constraint applied to said at least one base station.   
     
     
         15 . The communications system of  claim 14 , wherein the transmission channels have equal bandwidth, and the data is transmitted to the wireless units in the user groups according to at least one equal minimum rate. 
     
     
         16 . The communications system of  claim 14 , wherein:
 the user groups comprise wireless units in a first subset of said plurality of wireless units; and   the wireless units in a second subset of said plurality of wireless units are blocked from receiving transmissions over the network, said second subset comprising all the wireless units in the plurality of wireless units other than those in the first subset, wherein the first and second subsets are formed based in part on channel norms of the plurality of wireless units.   
     
     
         17 . The communications system of  claim 14 , wherein the wireless units in each of the user groups are semi-orthogonally selected according to a greedy user selection algorithm that includes a near-orthogonality assessment of the wireless units. 
     
     
         18 . The communications system of  claim 13 , wherein the at least one designated transmission power constraint is imposed and met in an optimization procedure.