Abstract
This paper investigates a cooperative uplink system where two users wish to send messages to a base station with the help of a buffer-aided relay. Transmission modes in terms of both non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) are considered. For the considered system, the probability for the user-to-relay channels to successfully perform NOMA is first theoretically derived in two scenarios of dynamic and fixed power controls (PCs) at users. Then, an efficient buffer-aided hybrid NOMA/OMA based mode selection (MS) scheme is proposed, which adaptively switches between the NOMA and OMA transmission modes according to the instantaneous strength of wireless channels and the buffer state. The state transmission matrix probabilities of the corresponding Markov chain is also derived, and the performance of the proposed hybrid NOMA/OMA scheme is analyzed with closed-form expressions, in terms of sum throughput, outage probability, diversity gain, and average packet delay. For both the dynamic and fixed PCs, the proposed scheme is proved to achieve a diversity gain of two when the buffer size is not smaller than three, which means that fixed PC will not lead to a loss of diversity gain.
Highlights
Non-orthogonal multiple access (NOMA) technology, using successive interference cancellation (SIC) and multiplexing in power-domain, can improve spectrum efficiency, which is considered to be a promising fifth-generation mobile communication technology [1]
We propose an efficient buffer-aided hybrid NOMA/ OMA based mode selection (MS) scheme, which adaptively switches between the NOMA and OMA transmission modes according to the instantaneous channel state information (CSI) and the buffer state
One can observe that, when r0 = 2 bits per channel use (BPCU), the hybrid NOMA/OMA and NOMA schemes achieve the maximum sum throughput of 2 BPCU at high SNR, whereas the OMA scheme can only achieve about 1.3 BPCU in this case
Summary
Non-orthogonal multiple access (NOMA) technology, using successive interference cancellation (SIC) and multiplexing in power-domain, can improve spectrum efficiency, which is considered to be a promising fifth-generation mobile communication technology [1]. The performance of the proposed hybrid NOMA/OMA MS scheme is derived with closedform expressions for sum throughput, outage probability, and average packet delay. It is demonstrated that the proposed scheme can achieve a diversity gain of two as long as the buffer size is not smaller than three, for both two scenarios of dynamic and fixed PCs. the performance of the proposed hybrid NOMA/OMA MS scheme is derived with closedform expressions for sum throughput, outage probability, and average packet delay. It is assumed that each user u and the relay are constrained by the maximum transmit power P, and each receiver has the same noise power σ 2 This implies that individual power constraints at the users are considered in the uplink system, which is more practical than the assumption of the sum power constraint at the users in many existing works for uplink NOMA (e.g., [3], [12]). M4 denotes the relay-toBS mode, where the relay selects a packet from each user’s buffer and blends the two packets into a mixed packet with 2r0 bits and transmits it to the BS1; and M5 denotes the silent mode
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