Space-time precoding for mean and covariance feedback: application to wideband OFDM

摘要: We consider optimization of the capacity a multi-input single-output wideband cellular "downlink," in which base station has estimates statistics spatial channel. Our main focus is on orthogonal frequency-division multiplexed (OFDM) systems, although some our results apply to single-carrier as well. Prior work shown that channel covariance can be obtained without overhead for both duplex (FDD) and time-division (TDD) systems by suitably averaging uplink measurements. In this paper, we investigate benefits supplementing "free" feedback with mean feedback, where latter refers realization each subcarrier. Mean using reciprocity TDD requires explicit FDD systems. first devise strategies mainly restricting attention beamforming, optimal or near-optimal many outdoor channels narrow spread. Second, since degrades rapidly delay mobile channels, develop quantitative rules thumb regarding accuracy required useful supplement already available, robust, feedback. validate following intuition: requirements are more relaxed larger spread, number transmit elements.