Abstract
This paper studies a multi-user network model based on sparse code multiple access (SCMA), where both unicast and multicast services are considered. In the direct transmission scheme, the communication between the base station (BS) and the users is completed with one stage, in which the relay is inexistent. In the two-stage cooperative transmission scheme, any number of relays are placed to improve the reliability of wireless communication system. The BS broadcasts the requested message to users and relays in the first stage, and the successful relays forward the message to unsuccessful users in the second stage. To characterize the performance of these two schemes, we derive the exact and approximate expressions of average outage probability. Furthermore, to take full advantage of the cooperative diversity, an optimal power allocation and relay location strategy in the high signal-to-noise ratio (SNR) regime is studied. The outage probability reaches the minimum value when the first stage occupies half of the total energy consumed. Simulation and analysis results are presented to demonstrate the performance of these two schemes. The results show that the two-stage cooperative scheme effectively reduce the average outage probability in SCMA network, especially in the high SNR region.
Highlights
IntroductionAs an efficient method of physical resource management, non-orthogonal multiple access (NOMA)
As an efficient method of physical resource management, non-orthogonal multiple access (NOMA)is considered as a promising technology to achieve the targets of the fifth generation (5G) wireless communication systems [1]
Among the available NOMA technologies, sparse code multiple access (SCMA) [2] is a code domain multiplexing scheme, which can achieve an obvious increase in spectral efficiency compared to orthogonal multiple access (OMA)
Summary
As an efficient method of physical resource management, non-orthogonal multiple access (NOMA). In [16], the application of NOMA to multicast cognitive radio networks is investigated, and a dynamic cooperative transmission scheme is proposed These studies are all focused on the power domain NOMA, and their results are not suitable for the SCMA system. Considering a delay constraint network, the BS transmits the message with a target rate for each unicast user/multicast group, the average outage probability is used to indicate the performance of the proposed network model. We propose a network model of hybrid unicast-multicast based on SCMA, in which two transmission schemes (direct transmission and relay-assisted two-stage cooperative transmission) are discussed. We first obtain an asymptotic approximation of average outage probability in the high signal-to-noise ratio (SNR) regime Based on this tight asymptote, we are able to determine the optimal relay locations and power allocation for the cooperative scheme.
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