2 research outputs found
Delay Violation Probability and Effective Rate of Downlink NOMA over - Fading Channels
Non-orthogonal multiple access (NOMA) is a potential candidate to further
enhance the spectrum utilization efficiency in beyond fifth-generation (B5G)
standards. However, there has been little attention on the quantification of
the delay-limited performance of downlink NOMA systems. In this paper, we
analyze the performance of a two-user downlink NOMA system over generalized
{\alpha}-{\mu} fading in terms of delay violation probability (DVP) and
effective rate (ER). In particular, we derive an analytical expression for an
upper bound on the DVP and we derive the exact sum ER of the downlink NOMA
system. We also derive analytical expressions for high and low signal-to-noise
ratio (SNR) approximations to the sum ER, as well as a fundamental upper bound
on the sum ER which represents the ergodic sum-rate for the downlink NOMA
system. We also analyze the sum ER of a corresponding time-division-multiplexed
orthogonal multiple access (OMA) system. Our results show that while NOMA
consistently outperforms OMA over the practical SNR range, the relative gain
becomes smaller in more severe fading conditions, and is also smaller in the
presence a more strict delay quality-of-service (QoS) constraint.Comment: 14 pages, 12 figure
Performance Analysis and Optimization of NOMA with HARQ for Short Packet Communications in Massive IoT
In this paper, we consider the massive non-orthogonal multiple access (NOMA)
with hybrid automatic repeat request (HARQ) for short packet communications. To
reduce the latency, each user can perform one re-transmission provided that the
previous packet was not decoded successfully. The system performance is
evaluated for both coordinated and uncoordinated transmissions. We first
develop a Markov model (MM) to analyze the system dynamics and characterize the
packet error rate (PER) and throughput of each user in the coordinated
scenario. The power levels are then optimized for two scenarios, including the
power constrained and reliability constrained scenarios. A simple yet efficient
dynamic cell planning is also designed for the uncoordinated scenario.
Numerical results show that both coordinated and uncoordinated NOMA-HARQ with a
limited number of retransmissions can achieve the desired level of reliability
with the guaranteed latency using a proper power control strategy. Results also
show that NOMA-HARQ achieves a higher throughput compared to the orthogonal
multiple access scheme with HARQ under the same average received power
constraint at the base station