Traditional non-linear (dirty paper coding) and linear (beamforming) precoding techniques that maximize the sum rate in the multi-antenna broadcast channel often suffer severe performance degradation when the channel state information (CSI) at the transmitter is erroneous or outdated. This has motivated the recent development of a linear precoding algorithm that uses the channel distribution information (CDI) rather than channel state to provide more stable performance in time-varying environments. This paper extends the prior analysis by using simulations with measured multi-user multi-antenna broadband channel responses to examine the effect of frequency selective channel characteristics on the behavior of the traditional CSI-based strategies as well as the more recent CDI-based approach. The results show that the CDI-based beamformer can offer superior performance with reduced feedback communication requirements.
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