In a 5G wireless communication system, demands of massive connectivity, ultra-low latency, higher data rates, higher reliability, and many more are fulfilled by NOMA (non-orthogonal multiple access) which is one of the potential candidates that can carry multiple users at the same time and frequency. As NOMA uses the power allocation method to transmit signals, a problem of mismatch between quality of service (QoS) and channel conditions of the users occurs. To resolve this issue, a scheme cooperative rate-splitting non-orthogonal multiple access (C-RS-NOMA) has been proposed in this work to enhance the performance of downlink power-domain NOMA in terms of outage probability, system capacity, spectrum efficiency, and energy efficiency. The performance of the proposed techniques has also been compared with the existing cooperative-NOMA and traditional NOMA techniques. The simulation results showed the improvement in different key parameters of C-RS-NOMA with respect to the existing NOMA and cooperative NOMA schemes.
TopIntroduction
A wireless communication network in which information is carried over a well-defined channel. Each channel has a fixed frequency bandwidth and bit rate. In a cellular mobile communication system, the first wireless network was created over four decades ago in the early 1980s when the 1G mobile network was introduced at that time the demand for more connections grows worldwide which directs the evolution of mobile communication more rapidly. Various networks are developed starting with 1G and going up to 4G all these distinct generations of wireless communication are differentiated based on multiple access schemes used.
For 1G, the frequency division multiple access (FDMA) scheme was used, offering a maximum speed of up to 2.4 Kbps. Then a time division multiple access (TDMA) scheme had been used for 2G mobile communication which offers a maximum speed of up to 50Kbps with general packet radio service (GPRS) and 1Mbps with enhanced data rates for GSM evolution. code division multiple access (CDMA) Technology had been used in 3G wireless communication, offering speeds up to 14Mbps. And for 4G an orthogonal frequency division multiple access (OFDMA) scheme was used that offered speeds up to 1Gbps. All these are the orthogonal multiple access (OMA) Techniques where the spectrum allocation of users was differentiated based on frequency, time, and code. In OMA maximum number of supported users are limited. As demands for wireless communication increase in terms of higher data rates, massive connectivity, lower latency, advanced multimedia functions, and higher spectral efficiency to satisfy these requirements, various enhanced technology for 5G has been proposed such as massive MIMO, mm-wave communication and NOMA (non-orthogonal multiple access) that allows multiple users to share a spectrum at the same time and frequency which is well known in multiple access techniques used for 5G wireless communication and offers increase system throughput. NOMA uses superposition-coded signals at the transmitting side and SIC (Successive Interference Cancellation) at the receiving side, making it possible to decode complete interference. In power-domain NOMA, each user was allotted many different power levels according to their channel conditions so that maximum user fairness exists (Boccardi et al., 2014; Dai et al., 2015). As in the fixed power allocation scheme of downlink NOMA without considering the channel conditions of the user, power levels for far and near users are set on a fixed value. This causes a dissimilarity between the user’s service quality and the channel conditions (Joe, 2020).
Other than the NOMA technique, there is one more multiple access was introduced in downlink scenarios which were RSMA (Rate-Splitting Multiple Access) which demonstrates various performance benefits over NOMA (Non-Orthogonal Multiple Access) and SDMA (Space-Division Multiple Access) techniques. As SDMA completely considers interference as noise. As linear-precoded rate-splitting was used at the transmitter of RSMA (Rate-Splitting Multiple Access) with SIC (Successive Interference Cancellation) at the receiving end making it possible to treat a few parts of interference as noise and decode a few parts of interference. And this advantage of RSMA (Rate-Splitting Multiple Access) over SDMA and NOMA makes improvements in QoS (Quality of Service) also reduces complexity and gives enhancements in parameters like Spectral Efficiency (SE) and Energy Efficiency (EE) (Mao, Clerckx, & Li, 2018; Mao, Clerckx, & Li, 2018). RSMA technique simply splits the user signals into two parts, which we can call virtual inputs to splits the signal's rate and enables the user to achieve any rate partition that gives the user flexibility.
This work proposed a C-RS-NOMA (Cooperative-Rate-Splitting Non-Orthogonal Multiple Access) techniques for the future generation mobile communication systems to fulfill the ultra-high requirements of achievable data rates, system capacity, higher SE, and higher EE, and this scheme also solves the problem of dissimilarity between users’ quality of service (QoS) and the channel conditions.