Joint user scheduling, link adaptation and space division multiplexing for the uplink of multi-cell distributed antenna systems with imperfect CSI

This paper proposes a joint user scheduling, linkadaptation and space division multiplexing algorithm for the up-link of distributed antenna systems (DASs) in a multi-cell scenario. Link adaptation includes power control and adaptive modulation and coding (AMC). The algorithm is based on an iterative least squares (LS) optimization, where power levels and beam-forming vectors are jointly calculated so as to comply with a different SINR (signal-to-interference-plus-noise ratio) for each scheduled user. This SINR level ensures the transmission of the selected modulation and coding scheme (MCS) with a value of BLER (block error rate). Whenever the SINR requirements are not met, then AMC and user scheduling are smoothly enabled so as to continue with another LS stage for further optimization. Each LS stage is solved by the method of gradient steepest descent, whose convergence speed is improved by reusing the solution of previous LS stages. An additional iterative loop is also used for a more efficient calculation of inter-cell interference. Imperfect channel state information is used throughout all system-level simulations. Results show considerable throughput gains when compared to conventional approaches.