Performance analysis of cooperative cognitive radio networks based on hybrid NOMA/OMA and best relay selection

Abstract

In non‐orthogonal multiple access (NOMA) systems, it may not be advisable to send the superimposed signal of all users to individual users with retransmission requirements during the retransmission phase. This paper investigates a novel cognitive radio network based on hybrid NOMA/orthogonal multiple access (CR‐H‐NOMA/OMA) in underlay spectrum sharing, whereby a hybrid NOMA/OMA cooperative mechanism is proposed for the secondary network by considering that the access modes of secondary users (SUs) and relays can be switched between NOMA and OMA. In order to compensate the loss of throughput caused by successive interference cancellation (SIC) during the cooperative phase, one or two relays with the best channel quality between themselves and the destination users are selected according to the states of the initial signal decoded by SUs, using truncated automatic repeat request (T‐ARQ) to retransmit only the desired signal of SU instead of the entire superimposed signal. Exact closed‐form expressions for outage probabilities of SUs and system throughput of the secondary network are derived under the interference constraint of the primary network to evaluate the performance of the proposed cooperative scheme. Numerical and simulation results demonstrate the superiority of the proposed hybrid NOMA/OMA cooperative scheme when compared with conventional pure NOMA and pure OMA based on time division multiple access (TDMA) in terms of secondary throughput. Also, the outage and throughput performance depend critically on the choices of key paraments such as power allocation factor and target rate.

Outage of cooperative NOMA with an energy harvesting relay in an underlay cognitive radio network

“…From Equation (17), we can write P s 1 f ailure = PðΓ s 1 SD 2 < θ 1 Þ = P(A), P s 1 success = PðΓ s 1 SD 2 > θ 1 Þ= 1-P(A), and P s 2 f ailure = PðΓ s 2 SD 2 < θ 2 Þ= P(B). So, Equation ( 17) can be written as…”

“…The performance of a decode‐and‐forward underlay CR‐NOMA network under cooperative scheme with imperfect channel state information is studied in Arzykulov et al 15 Probability of outage of an underlay network considering imperfect SIC is studied in Im and Lee 16 . A hybrid NOMA/OMA cooperative CR network with relay selection using truncated automatic repeat request (T‐ARQ), which causes the transmission of only the UU's desired signal from the selected relay instead of the total superimposed signal, is investigated in Li et al 17 Here, the base station transmits NOMA signal to two UUs and relays first; next one or two best relays are selected using T‐ARQ. A study is done on the effectiveness of a NOMA system in an underlay CR scenario using partial relay selection (PRS) in Aswathi et al, 18 where the secondary network receives NOMA signal and the secondary base station transmits information to the UUs using K‐half duplex, decode‐and‐forward relays.…”

Bio-inspired hybrid lyrebird optimization-based power allocation and relay-selection scheme

“…Recently, different relay selection methods have been presented in cognitive relay networks for preserving the secrecy and delay constraints of the NOMA system. But, to satisfy the needs of multiple users, enhanced PA is indispensable for the NOMA network relay to function effectively [8][9].…”

User grouping and resource management in efficient NOMA‐OMA transmission scheme for infotainment message dissemination in VANETs

“…Non‐orthogonal multiple access (NOMA) 5 is identified as a promising technology to meet the challenges in spectral utilization. NOMA serves multiple users over the same transmission by linear superposition of signals corresponding to the users in power domain which is known as superposition coding (SC) 6,7 . The users sharing the same NOMA transmission form a cluster.…”

“…NOMA serves multiple users over the same transmission by linear superposition of signals corresponding to the users in power domain which is known as superposition coding (SC). 6,7 The users sharing the same NOMA transmission form a cluster. The near user with the best channel gains from the transmitter is given less power than the far users with the worst channel gains.…”