199 research outputs found
A Tutorial on Nonorthogonal Multiple Access for 5G and Beyond
Today's wireless networks allocate radio resources to users based on the
orthogonal multiple access (OMA) principle. However, as the number of users
increases, OMA based approaches may not meet the stringent emerging
requirements including very high spectral efficiency, very low latency, and
massive device connectivity. Nonorthogonal multiple access (NOMA) principle
emerges as a solution to improve the spectral efficiency while allowing some
degree of multiple access interference at receivers. In this tutorial style
paper, we target providing a unified model for NOMA, including uplink and
downlink transmissions, along with the extensions tomultiple inputmultiple
output and cooperative communication scenarios. Through numerical examples, we
compare the performances of OMA and NOMA networks. Implementation aspects and
open issues are also detailed.Comment: 25 pages, 10 figure
Multi-points cooperative relay in NOMA system with N-1 DF relaying nodes in HD/FD mode for N user equipments with energy harvesting
Non-Orthogonal Multiple Access (NOMA) is the key technology promised to be applied in next-generation networks in the near future. In this study, we propose a multi-points cooperative relay (MPCR) NOMA model instead of just using a relay as in previous studies. Based on the channel state information (CSI), the base station (BS) selects a closest user equipment (UE) and sends a superposed signal to this UE as a first relay node. We have assumed that there are N UEs in the network and the N-th UE, which is farthest from BS, has the poorest quality signal transmitted from the BS compared the other UEs. The N-th UE received a forwarded signal from N - 1 relaying nodes that are the UEs with better signal quality. At the i-th relaying node, it detects its own symbol by using successive interference cancellation (SIC) and will forward the superimposed signal to the next closest user, namely the (i + 1)-th UE, and include an excess power which will use for energy harvesting (EH) intention at the next UE. By these, the farthest UE in network can be significantly improved. In addition, closed-form expressions of outage probability for users over both the Rayleigh and Nakagami-m fading channels are also presented. Analysis and simulation results performed by Matlab software, which are presented accurately and clearly, show that the effectiveness of our proposed model and this model will be consistent with the multi-access wireless network in the future.Web of Science82art. no. 16
Improving performance of far users in cognitive radio: Exploiting NOMA and wireless power transfer
In this paper, we examine non-orthogonal multiple access (NOMA) and relay selection strategy to benefit extra advantage from traditional cognitive radio (CR) relaying systems. The most important requirement to prolong lifetime of such network is employing energy harvesting in the relay to address network with limited power constraint. In particular, we study such energy harvesting CR-NOMA using amplify-and-forward (AF) scheme to improve performance far NOMA users. To further address such problem, two schemes are investigated in term of number of selected relays. To further examine system performance, the outage performance needs to be studied for such wireless powered CR-NOMA network over Rayleigh channels. The accurate expressions for the outage probability are derived to perform outage comparison of primary network and secondary network. The analytical results show clearly that position of these nodes, transmit signal to noise ratio (SNR) and power allocation coefficients result in varying outage performance. As main observation, performance gap between primary and secondary destination is decided by both power allocation factors and selection mode of single relay or multiple relays. Numerical studies were conducted to verify our derivations.Web of Science1211art. no. 220
Coordinated direct and relay transmission with NOMA and network coding in Nakagami-m fading channel
Although the use of coordinated direct and relay transmission (CDRT) in non-orthogonal multiple access (NOMA) can extend the coverage, its duplicated transmission reduces the spectrum efficiency (SE) of NOMA. To improve the SE, we propose a spectrum-efficient scheme for NOMA-based CDRT over Nakagami-m fading channels. In this scheme, the base station (BS) connects with a cell-center user (CCU) directly while communicating with a cell-edge user (CEU) via a relay and the CCU. Then, the relay and the CCU use network coding to process and retransmit the signals sent by the BS first and the CEU later. Finally, the BS and the relay simultaneously broadcast downlink signals. We derive the closed-form expressions for the average SE, the user fairness index and the energy efficiency (EE) as well as the asymptotic average SE using both perfect and imperfect successive interference cancellation (SIC). Simulations verify the correctness of our theoretical analysis and the superiority of the proposed scheme in SE and EE
Outage Performance of RIS-aided Cooperative FD-SWIPT-NOMA in Nakagami-m Channels
In this work we {derive new} analytical expressions for the outage
probability (OP) of the downlink (DL) cooperative full-duplex (FD) simultaneous
wireless information power transfer (SWIPT) non-orthogonal multiple access
(NOMA) system aided by reconfigurable intelligent surfaces (RIS). The
expressions for both the strongest and weakest NOMA users are devised assuming
Nakagami- channel fading. The derived analytical OP expressions are simple
to compute yet accurate for a wide range of RIS passive elements
configurations, energy harvesting (EH) coefficient, and residual
self-interference (SI) levels, being extensively validated by numerical
simulations, demonstrating the correctness and accuracy of the proposed
analytical method. The OP expressions reveal how paramount is to mitigate the
SI in the FD relay mode, since for reasonable values of residual SI coefficient
(dB), it is notable its detrimental effect over the
system performance; hence, new SI reduction methods for FD relays are useful
for low number of passive elements. Also, applying the proposed OP expressions
to predict the behaviour of the RIS-NOMA system equipped with a higher number
of passive elements () reveals a substantial reduction of the SI
effect, motivating the implementation of the cooperative FD communications.
Furthermore, we found the asymptotic behavior of outage probability of both
clustered users, as well as the equal diversity order for both users, given by
if the fraction of the harvest energy or
if , indicating the influence of channel parameters and number
of RIS elements in the performance.Comment: 23 pages, 8 figures, full pape
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