A Generalized Method of Moments Detector for Block Fading SIMO Channels

In this letter, we apply the generalized method of moments (GMM), widely used in econometrics, to receivers operating with imperfect channel state information (CSI) in single-input-multiple-output (SIMO) block-fading channels, where a single pilot symbol is used. The GMM results in the standard maximum ratio combining (MRC) receiver, but with an improved channel estimate. Although not our goal at the outset, this result reveals an inherent capability of the GMM to improve any channel estimate through filtering of the initial channel estimate with a matrix that is constructed from the received signals. The filtering involves a matrix inverse of size min{T, M}, where M is the number of receive antennas and T + 1 is the coherence interval of the channel. The gain over an MRC receiver, using a scaled version of the pilot observation as channel estimate, lies in the range 0.1-3 dB depending on the system configuration. A coherence interval of about five symbol intervals is sufficient to reach these gains.