Multiple Access Techniques via Spatial Precoding

Abstract

The main goal of this work was to analyse the viability of Spatial Modulation as a technology to implement and support future 5G systems that are currently being developed. This was done by evaluating multiple access strategies applied with Spatial Modulation in multiple user scenarios, and finding a solution that may be viable for a real world implementation. The solution found to apply with Spatial Modulation is a Space-Time CDMA based one. The system's performance was analysed by testing the influence of its main parameters in multiple scenarios with various detectors. Some scenarios are from 5G projects to understand its viability for 5G systems. The main influential parameters were the number of receive antennas and the number of users, the first with a gain of approximately 4 dB. The second one shows only a negligible degradation for a Maximum Likelihood decoder. For the other non-optimal detectors used, it degrades the performance due to the presence of multiple access interference. The spatial diversity associated with transmit antennas was also analysed due to the existing trade-off between orthogonality and diversity. For the Matched filter detector, diversity does not compensate the loss of orthogonality, opposite to the other detectors, due to its vulnerability to multiple access interference. The presence of correlation between antennas also degrades performance in approximately 2 dB. For the 5G scenarios, the system shows negligible degradation for a higher number of users, demonstrating its potential to fit well in future 5G systems.