Rateless space-time block code for mitigating pilot contamination effects in multi-cell massive MIMO system with lossy links

Massive multiple-input multiple-output (MIMO) is a breakthrough wireless transmission technique proposed for future wireless standards due to its spectrum and energy efficiencies. However, pilot contamination constitutes a particularly significant impairment in multi-cell systems that utilise reciprocity-based channel estimation. This phenomenon results from the non-orthogonality of the pilot sequences in different cells. Given a large number of antennas employed in massive MIMO systems, conventional channel estimation schemes cannot mitigate this problem effectively without high computational complexity. In this study, a simple rateless space-time block code (RSTBC) is employed in the downlink transmission of a lossy multi-cell massive MIMO system to mitigate the effects of signal-to-interference-and-noise ratio (SINR) degradation resulting from pilot contamination. Specifically, a robust optimisation problem is formulated to maximise the minimum downlink SINR among all users. Simulation and analytical results for large numbers of antenna elements at the base station (BS) are provided to demonstrate the usefulness of the proposed scheme. The SINR and spectral efficiency analyses indicate that RSTBC can effectively mitigate downlink SINR degradation that is caused by pilot contamination. Experimental results for the proposed scheme are also included for a 2 x 2 MIMO system, and it agrees closely with the simulation.