Space Division Multiple Access with a Sum Feedback Rate Constraint
Background For a multiple-input-multiple-output (MIMO) communication system, by exploiting the spatial degrees of freedom, space division multiple access (SDMA) supports simultaneous uplink/downlink communication between a base station and multiple users in the same time and frequency slots. This technology presents multiple algorithms intended for use in a SDMA wireless communication network, to enable a sum feedback rate of the CSI (Channel State Information) for each user without overloading the transfer rate of the network. All users would share a finite-rate feedback channel, a feature which doesn’t exist in currently implemented SDMA algorithms.
Invention Description The proposed SDMA design consists of a (i) a limited feedback algorithm for CSI quantization and feedback control, (ii) the downlink joint scheduling and beamforming algorithm for scheduling users and selecting transmit beamforming vectors for downlink transmission, and (iii) the uplink joint beamforming and scheduling algorithm. The proposed limited feedback algorithm is used by each user for quantizing the estimated downlink CSI into a finite number of bits. Moreover, to constrain the sum feedback rate, this algorithm applies a set of feedback thresholds to admit users into feedback of quantized CSI.
At the base station, using multi-user feedback CSI, the proposed downlink joint scheduling and beamforming algorithm is executed for jointly selecting downlink users and their transmit beamforming vectors so as to maximize the downlink throughput. This algorithm effectively reduces the mutual interference between scheduled users caused by inaccuracy of feedback CSI, which results in a high downlink throughput.
An uplink joint scheduling and beamforming algorithm is also proposed, which exploits channel reciprocity and hence uses feedback downlink CSI to select uplink users and receive beamforming vectors for separating multi-user data streams at the base station.
The proposed algorithms enable constraining of sum feedback rate for SDMA with multiuser diversity without decreasing the throughput, making it suitable for use in a practical communication system such as 3GPP LITE where all users share a finite-rate feedback channel. The proposed SDMA design provides a low-complexity joint beamforming and scheduling algorithm, which avoids exhaustive search of an optimal set of beamforming vectors and schedule users as well as the more complicated zero-forcing beamforming.
These algorithms are in alignment with IEEE 802.16e and 3GPP LTE standards.
Market Potential/Applications Companies working on wireless mobile communication, wireless local area networks (WLAN) such as IEEE 802.11, wireless metropolitan area networks (WMAN) such as IEE 802.16e/WIMAX, and cellular wireless systems (3GPP).
IP Status One U.S. patent application filed
UT Researcher Robert W. Heath, Jr., Ph.D., Electrical and Computer Engineering, The University of Texas at Austin Jeffrey G. Andrews, Ph.D., Electrical and Computer Engineering, The University of Texas at Austin Kaibin Huang, The University of Texas at Austin
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