Uplink Performance Optimization of Limited-Capacity Radio Stripes

Cell-free (CF) massive multiple-input multiple-output (mMIMO) is a network architecture beyond fifth generation (B5G), which has the potential to deliver significantly higher spectral efficiency (SE) and energy conservation, when compared to the traditional cellular MIMO layout. Radio stripes form a particular realization of CF mMIMO topologies, which at a relatively modest deployment cost, promise to distribute part of the computational load of the centralized processing unit (CPU), while maintaining the same performance. However, the limited-capacity fronthaul (FH) network effect has not yet been adequately studied in this context. In this paper, we develop an uplink sequential processing algorithm that is optimal in the sense of locally minimizing the mean-squared error (MSE) at every antenna processing unit (APU). The performance is further enhanced by applying an effective Compare-and-Forward (CnF) strategy or by minimizing the compression error covariance trace, given the fronthaul capacity constraint. Additionally, we study the case where the radio stripe arrangement uses a distributed setup of access points (APs), aiming at minimizing path attenuation even more effectively. Based on analytical equations and simulation results, we conclude that throughput is maximized when the classic radio stripe setup is combined with the proposed algorithm and the CnF technique.