Abstract
With the development of wireless communications and internet of things (IoT), non-orthogonal multiple access (NOMA) has been considered as one of effective schemes to meet the rapidly growing user access requirements. Two types of NOMA, i.e., NOMA-2000 and power-domain NOMA (PD-NOMA), have been proposed in recent years. The first one is a superposition of a set of orthogonal frequency division multiple access (OFDMA) signals and a set of spread-spectrum multicarrier-code division multiple access (MC-CDMA) signals while the second one is a direct superposition of a MC-CDMA signal and an OFDMA signal. This paper proposes a dynamic user grouping method for classifying users and then compares the performance between NOMA-2000 and PD-NOMA over Rayleigh fading channels. Simulation results show that the PD-NOMA can always exhibit lower bit error rate (BER) than the NOMA-2000 under different signal-to-noise ratios. Under the Rayleigh fading environment, the performance of the PD-NOMA after user grouping is better than that of NOMA-2000.
Highlights
With the rapid development of mobile communications and internet of things (IoT), the demand for spectrum efficiency and system capacity has grown fast, and the traditional orthogonal multiple access (OMA) has been unable to meet the user needs [1]–[14]
SIMULATION RESULTS we show the comparisons of non-orthogonal multiple access (NOMA)-2000 and power-domain NOMA (PD-NOMA) with user grouping and without user grouping over uplink Rayleigh fading channels under different channel overload conditions
We introduce the concept of overloading factor (OF), that is OF = M /N
Summary
With the rapid development of mobile communications and internet of things (IoT), the demand for spectrum efficiency and system capacity has grown fast, and the traditional orthogonal multiple access (OMA) has been unable to meet the user needs [1]–[14]. NOMA uses non-orthogonal transmission at the transmitting end to actively introduce interference between users, and achieves correct demodulation through the successive interference cancellation (SIC) technology at the receiving end. NOMA-2000 detects two sets of orthogonal signals by iterative interference cancellation [24]. Non-orthogonal transmission between different users on the same sub-channel will cause interference between users, which is the reason why multi-user detection uses SIC technology at the receiving end. Within the OFDMA signal, there is no interference between users, as is the case in orthogonal MC-CDMA. The principle of SIC is to send the received signal to a threshold detector to get User signal because its symbol power is larger than User-2. Different with NOMA-2000, power-domain NOMA superposes MC-CDMA signal on OFDMA signal directly without spreading spectrum. When we allocate power to users, we should consider the accuracy of the receiver and the fairness between users at the same time
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