620 research outputs found
On the Power Allocation Limits for Downlink Multi-user NOMA with QoS
The fundamental power allocation requirements for NOMA systems with minimum
quality of service (QoS) requirements are investigated. For any minimum QoS
rate , the limits on the power allocation coefficients for each user are
derived, such that any power allocation coefficient outside of these limits
creates an outage with probability equal to 1. The power allocation
coefficients that facilitate each user's success of performing successive
interference cancellation (SIC) and decoding its own signal are derived, and
are found to depend only on the target rate and the number of total users
. It is then proven that using these power allocation coefficients create
the same outage event as if using orthogonal multiple access (OMA), which
proves that the outage performance of NOMA with a fixed-power scheme can
matched that of OMA for all users simultaneously. Simulations confirm the
theoretical results, and also demonstrate that a power allocation strategy
exists that can improve the outage performance of NOMA over OMA, even with a
fixed-power strategy.Comment: Presented at Internation Conference on Communications (ICC) 2018
Wireless Communication Symposium, 5 pages long, 2 figure
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
A Survey of Physical Layer Security Techniques for 5G Wireless Networks and Challenges Ahead
Physical layer security which safeguards data confidentiality based on the
information-theoretic approaches has received significant research interest
recently. The key idea behind physical layer security is to utilize the
intrinsic randomness of the transmission channel to guarantee the security in
physical layer. The evolution towards 5G wireless communications poses new
challenges for physical layer security research. This paper provides a latest
survey of the physical layer security research on various promising 5G
technologies, including physical layer security coding, massive multiple-input
multiple-output, millimeter wave communications, heterogeneous networks,
non-orthogonal multiple access, full duplex technology, etc. Technical
challenges which remain unresolved at the time of writing are summarized and
the future trends of physical layer security in 5G and beyond are discussed.Comment: To appear in IEEE Journal on Selected Areas in Communication
- …