A new metric for space-time block codes with imperfect channel estimates

In this paper, a new metric for the decision rule of the space-time block (STB) codes having imperfect estimate of the channel fading parameters is derived. Estimation errors of these fading parameters have high impact on the performance of the STB code as the decision rule is dependent on these fading parameters. By including the variance of the channel estimation error in the decoder metric derivation of the STB codes, we derive an exact probability distribution function (pdf) of the received signals conditioned on the estimated channel parameters and transmitted symbol sequences. A modified decision rule is easily found from this and compared with the state-of-the-art scheme proposed by Tarokh. Performance comparison shows that significant improvement is achieved in terms of error rate and system complexity, especially for quadrature amplitude modulation (QAM). The derived decision rule converges to the ideal case for no estimation error and to Tarokh´s decision rule for high signal-to-noise ratio (SNR).