Adaptive channel direction quantization — Enabling multi user MIMO gains in practice

Many candidate technologies for future wireless communication systems (e.g., multi-user MIMO, interference alignment), rely on accurate Channel State Information (CSI) at the Transmitter (CSIT) to determine the appropriate multi-antenna pre-processing steps. Thus, in frequency division duplexing systems, a dedicated feedback link has to be provided to each attached user for CSI reporting. In order to keep the feedback rate moderate, CSI quantization is required. Additionally, CSI is typically only provided for a subset of all available time/frequency resources, implicating the need for an interpolation algorithm at the base station. Furthermore, to compensate for the processing delay of the feedback link, CSI prediction is required as well. In this work, we treat these problems by incorporating our previously presented CSI feedback algorithm in a 3GPP LTE-A compliant wideband OFDM simulation environment, and augmenting it with appropriate interpolators and predictors. As an example, the performance of multi-user zero-forcing beamfoming is investigated, under practical feedback delay- and time-frequency granularity-constraints, demonstrating substantial throughput gains, in case of low to moderate user mobility.