Two stage CCI/ISI reduction with space-time processing in TDMA cellular networks

We propose a two-stage, separate cochannel interference (CCI) and intersymbol interference (ISI) reduction technique using space-time processing. CCI and ISI are two major interference sources in wireless communication, and they are the limiting factors in the performance and capacity of a cellular network. However because of the different characteristics between CCI and ISI, algorithms designed to simultaneously reduce both interferences tend to combat ISI more and ignore CCI, which causes performance degradation of the equalizer. Further more, MLSE-type algorithms can effectively reduce ISI while MMSE-type algorithms are more robust to CCI. These considerations motivate us to derive two-stage interference reduction: the first stage uses a space-time MMSE equalizer to reduce CCI while preserving the ISI structure of the desired signal; the second stage uses a space-time Viterbi equalizer to reduce ISI. Space-time processing assures spatial and temporal diversities are fully captured and the difference of spatial and temporal properties between signals and interferences are fully explored. Simulation results show the proposed approach leads to good performance in a GSM scenario even at low carrier-to-interference ratio.