Outage behavior of slow fading channels with power control using noisy quantized CSIT

The topic of this study is the outage behavior of multiple-antenna slow fading channels with quantized feedback and partial power control. A fixed-rate communication system is considered. It is known from the literature that with error-free feedback, the outage-optimal quantizer for power control has a circular structure. Moreover, the diversity gain of the system increases polynomially with the cardinality of the power control codebook. Here, a similar system is studied, but when the feedback link is error-prone. We prove that in the high-SNR regime, the optimal quantizer structure with noisy feedback is still circular and the optimal Voronoi regions are contiguous non-zero probability intervals. Furthermore, the optimal power control codebook resembles a channel optimized scalar quantizer (COSQ), i.e., the Voronoi regions merge with erroneous feedback information. Using a COSQ, the outage performance of the system is superior to that of a no-feedback scheme. However, asymptotic analysis shows that the diversity gain of the system is the same as a no-CSIT scheme if there is a non-zero and non-vanishing feedback error probability. Index terms Outage probability, noisy feedback, channel optimized quantizers, bit-mapping, diversity.