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MC-CDMA and SCMA Performance Evaluation in 100% and 200% Load Factor Scenarios

Abstract:

In fifth-generation (5G) wireless networks, the perspective of very large number of simultaneous connections is challenging. Hence, an overloaded system becomes a common scenario for new multiple access techniques. An overloaded scenario means that the number of active simultaneous users is greater than the number of system resources, and its ratio determines the load factor. Some multiple access techniques have been proposed for 5G systems and two of them are compared in this paper. These techniques are multi-carrier code division multiple access (MC-CDMA) and sparse code multiple access (SCMA). Their performance, in terms of the mean bit error rate (BER), and the decoding complexity, in terms of number of mathematical operations performed in the receiver, are evaluated considering quaternary constellations. In MC-CDMA, the optimum maximum-likelihood detector (MU-MLD), implemented via sphere decoding (SD), is considered. In SCMA, a near optimal message-passing algorithm (MPA) is used at the receiver. In the literature, SCMA is typically analyzed considering a 150% load factor scenario. Nevertheless, scenarios with lower (100%) and greater (200%) than 150% load factor are considered in this work. Results show that, for equivalent spectral efficiency and uncoded scenarios, MC-CDMA performs better than SCMA and the greater the load factor, SD algorithm becomes less complex than MPA.