Beamforming Techniques for Non-Orthogonal Multiple Access in 5G Cellular Networks

In this paper, we develop various beamforming techniques for downlink transmission for multiple-input single-output (MISO) non-orthogonal multiple access (NOMA) systems. First, a beamforming approach with perfect channel state information (CSI) is investigated to provide the required quality of service (QoS) for all users. Taylor series approximation and semidefinite relaxation (SDR) techniques are employed to reformulate the original non-convex power minimization problem to a tractable one. Further, a fairness-based beamforming approach is proposed through a max-min formulation to maintain fairness between users. Next, we consider a robust scheme by incorporating channel uncertainties, where the transmit power is minimized while satisfying the outage probability requirement at each user. Through exploiting the SDR approach, the original non-convex problem is reformulated in a linear matrix inequality (LMI) form to obtain the optimal solution. Numerical results demonstrate that the robust scheme can achieve better performance compared to the non-robust scheme in terms of the rate satisfaction ratio. Further, simulation results confirm that NOMA consumes a little over half transmit power needed by OMA for the same data rate requirements. Hence, NOMA has the potential to significantly improve the system performance in terms of transmit power consumption in future 5G networks and beyond.Comment: accepted to publish in IEEE Transactions on Vehicular Technolog

MIMO Truncated Shannon Bound for System Level Capacity Evaluation of Wireless Networks

We outline a general method for modelling the capacity of a MIMO link within a wireless, assuming that capacity of a link is a random function of SNR and signal to interference ratio (SIR), since the maximum link throughput depends on the random channel of both the user's signal and the interference. We show how a look-up table for the CDF of this random function can be obtained by link-level simulation in the presence of interference having the same characteristics as the interference found in the target network. We also exploit the Truncated Shannon Bound (TSB) to estimate the resulting capacity obtained in practice in a system using adaptive modulation and coding on the link level