Stability and Delay of Zero-Forcing SDMA with Limited Feedback - Computer Science > Information TheoryReport as inadecuate




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Abstract: This paper addresses the stability and queueing delay of Space DivisionMultiple Access SDMA systems with bursty traffic, where zero-forcingbeamforming enables simultaneous transmission to multiple mobiles. Computingbeamforming vectors relies on quantized channel state information CSIfeedback limited feedback from mobiles. Define the stability region for SDMAas the set of multiuser packet-arrival rates for which the steady-state queuelengths are finite. Given perfect CSI feedback and equal power allocation overscheduled queues, the stability region is proved to be a convex polytope havingthe derived vertices. For any set of arrival rates in the stability region,multiuser queues are shown to be stabilized by a joint queue-and-beamformingcontrol policy that maximizes the departure-rate-weighted sum of queue lengths.The stability region for limited feedback is found to be the perfect-CSI regionmultiplied by one minus a small factor. The required number of feedback bitsper mobile is proved to scale logarithmically with the inverse of the abovefactor as well as linearly with the number of transmit antennas minus one. Theeffects of limited feedback on queueing delay are also quantified. For Poissonarrival processes, CSI quantization errors are shown to multiply averagequeueing delay by a factor larger than one. This factor can be controlled byadjusting the number of feedback bits per mobile following the derivedrelationship. For general arrival processes, CSI errors are found to increaseKingman-s bound on the tail probability of the instantaneous delay by one plusa small factor. The required number of feedback bits per mobile is shown toscale logarithmically with this factor.



Author: Kaibin Huang, Vincent K. N. Lau

Source: https://arxiv.org/



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