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OSTBC transmission over cooperative diversity systems under nodes mobility impact

In this paper, we consider a wireless cooperative diversity system with Alamouti-type orthogonal-space-time-block-code (Alamouti-OSTBC) transmission at the source under the influence of the cooperating nodes' mobility, where the system's links are characterized by time-selective (rapidly time-varying) fading channels. We first employ the conventional Alamouti's decoder (ALD) at the system's destination, obtain its output's decision statistics, and show that, due to the time-selective fading, they are interfering and correlated. Then, we derive exact closed-form expressions for these statistics' conditional signal-to-interference-plus-noise-ratios (SINRs) and for the system's conditional symbol-error-probability (SEP) which experiences irreducible error floors as long as the fading is time-selective. Moreover, in order to overcome with this time-selective fading impact, we propose and derive a zero-forcing-decoder (ZFD) that could be applied at the system's destination instead of the ALD, which is capable of providing non interfering decision statistics. The error performance of this proposed ZFD is analyzed and closed-form conditional SEP expression is derived. Numerical results for the average SEP (obtained semi-analytically) along with practical link-level simulations of both ALD and ZFD are provided to validate the accuracy of the presented analysis and to demonstrate the system performance under several scenarios. The numerical results show considerable improvement of the ZFD error performance over that of the ALD that suppresses the impact of the time-selective fading. This improvement, however, comes at the expense of additional decoding complexity.