14 research outputs found
Hybrid Successive Interference Cancellation and Power Adaptation: a Win-Win Strategy for Robust Uplink NOMA Transmission
The aim of this paper is to reveal the importance of hybrid successive
interference cancellation (SIC) and power adaptation (PA) for improving
transmission robustness of uplink non-orthogonal multiple access (NOMA).
Particularly, a cognitive radio inspired uplink NOMA communication scenario is
considered, where one primary user is allocated one dedicated resource block,
while M secondary users compete with each other to be opportunistically served
by using the same resource block of the primary user. Two novel schemes are
proposed for the considered scenario, namely hybrid SIC with PA (HSIC-PA)
scheme and fixed SIC with PA (FSIC-PA) scheme. Both schemes can ensure that the
secondary users are served without degrading the transmission reliability of
the primary user compared to conventional orthogonal multiple access (OMA)
based schemes. Rigorous analytical results are presented to evaluate the
performance of the proposed two schemes. It is shown that both schemes can
avoid outage probability error floors without any constraints on users' target
rates in the high SNR regime. Furthermore, it is shown that the diversity gain
achieved by the HSIC-PA scheme is M, while that of the FISC-PA scheme is only
1. Numerical results are provided to verify the developed analytical results
and also demonstrate the superior performance achieved by the proposed schemes
by comparing with the existing HSIC without PA (HSIC-NPA) scheme. The presented
simulation results also show that HSIC-PA scheme performs the best among the
three schemes, which indicates the importance of the combination of HSIC and PA
for improving transmission robustness.Comment: arXiv admin note: substantial text overlap with arXiv:2307.0151
Novel Time Asynchronous NOMA schemes for Downlink Transmissions
In this work, we investigate the effect of time asynchrony in non-orthogonal
multiple access (NOMA) schemes for downlink transmissions. First, we analyze
the benefit of adding intentional timing offsets to the conventional power
domain-NOMA (P-NOMA). This method which is called Asynchronous-Power
Domain-NOMA (AP-NOMA) introduces artificial symbol-offsets between packets
destined for different users. It reduces the mutual interference which results
in enlarging the achievable rate-region of the conventional P-NOMA. Then, we
propose a precoding scheme which fully exploits the degrees of freedom provided
by the time asynchrony. We call this multiple access scheme T-NOMA which
provides higher degrees of freedom for users compared to the conventional
P-NOMA or even the modified AP-NOMA. T-NOMA adopts a precoding at the base
station and a linear preprocessing scheme at the receiving user which
decomposes the broadcast channel into parallel channels circumventing the need
for Successive Interference Cancellation (SIC). The numerical results show that
T-NOMA outperforms AP-NOMA and both outperform the conventional P-NOMA. We also
compare the maximum sum-rate and fairness provided by these methods. Moreover,
the impact of pulse shape and symbol offset on the performance of AP-NOMA and
T-NOMA schemes are investigated