194 research outputs found
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
Short-Packet Downlink Transmission with Non-Orthogonal Multiple Access
This work introduces downlink non-orthogonal multiple access (NOMA) into
short-packet communications. NOMA has great potential to improve fairness and
spectral efficiency with respect to orthogonal multiple access (OMA) for
low-latency downlink transmission, thus making it attractive for the emerging
Internet of Things. We consider a two-user downlink NOMA system with finite
blocklength constraints, in which the transmission rates and power allocation
are optimized. To this end, we investigate the trade-off among the transmission
rate, decoding error probability, and the transmission latency measured in
blocklength. Then, a one-dimensional search algorithm is proposed to resolve
the challenges mainly due to the achievable rate affected by the finite
blocklength and the unguaranteed successive interference cancellation. We also
analyze the performance of OMA as a benchmark to fully demonstrate the benefit
of NOMA. Our simulation results show that NOMA significantly outperforms OMA in
terms of achieving a higher effective throughput subject to the same finite
blocklength constraint, or incurring a lower latency to achieve the same
effective throughput target. Interestingly, we further find that with the
finite blocklength, the advantage of NOMA relative to OMA is more prominent
when the effective throughput targets at the two users become more comparable.Comment: 15 pages, 9 figures. This is a longer version of a paper to appear in
IEEE Transactions on Wireless Communications. Citation Information: X. Sun,
S. Yan, N. Yang, Z. Ding, C. Shen, and Z. Zhong, "Short-Packet Downlink
Transmission with Non-Orthogonal Multiple Access," IEEE Trans. Wireless
Commun., accepted to appear [Online]
https://ieeexplore.ieee.org/document/8345745
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