Cross Layer Implementation of a Multi-User MIMO Test Bed

This paper describes an implementation of a realtime multi-user multiple-input multiple-output (MU-MIMO) communication system, with cross-layer channel-aware scheduling. The system is implemented using software reconfigurable nodes that may be configured as either user terminals, or as base stations, communicating in the GSM 1800 uplink band. Three different commonly used scheduling algorithms (based on channel state information fed back by the receiver nodes) are studied and compared experimentally for three different signal to noise ratios in an indoor non line of sight environment. It is shown that channel-aware scheduling increases not only the system throughput, but also the fairness. Further, using the possibility of changing antenna polarization through software controlled switches, the multiuser gains may be increased even further, both in total throughput as well as fairness.