Performance Analysis Of The Advanced SIC Receivers For NOMA Systems

With the development of the mobile network and the internet of things,the fifth generation(5G)wireless communication network aims to satisfy the various requirement for people from life,studying,industry and so on.Meantime,the number of connected equipment and the quality of service for users are growing larger.5G should support the requirements of low latency,massive connectivity,and high data rate.Non-orthogonal Multiple Access(NOMA)is regarded as a candidate for 5G multiple access technology because it can support massive connectivity and high spectral efficiency.Higher spectral efficiency in NOMA systems benefits from both of the superposition coding at the transmitters and the successive interference cancellation(SIC)which mitigates the multi-user interference at the receivers.With these attractive features,NOMA can offer a significant improvement in both spectrum efficiency and the reliability of communication.The theoretical performance analysis of multiple access system is one of the most essential system performance criteria.Therefore,it is important of the theoretical performance analysis of NOMA systems.In this paper,we investigate the outage performance of NOMA systems and propose the advanced SIC receiver schemes to improve the outage performance for NOMA users.In the previous work,the performance analysis of power domain NOMA(PD-NOMA)systems concentrated on the single cell scenarios.However,these research methods used to analyze the performance of single-cell NOMA systems could not be directly applied to multi-cell scenarios.Since NOMA is a full frequency reuse scheme in the power domain,the inter-cell interference inevitably impairs the performance of NOMA users.Therefore,the performance of NOMA systems in multi-cell scenarios should be investigated.In this paper,We proposed a modified Poisson cluster process method to model the distribution of base station(BS)and NOMA user pairs for multi-cell NOMA downlink system.Different from the previous work,the distribution of NOMA users location is correlated with the authorized BS.And a general method to analyze the outage performance of downlink NOMA systems is proposed.We first derive the closed-form outage probability for 2-user downlink NOMA systems.The theoretical results demonstrate that the NOMA users' outage probabilities increase with the intensity of BSs,the coverage area of accessed BS,and the target data rate.We further propose an optimal power allocation strategy for minimizing the maximal outage probability of NOMA users.Finally,the average area spectral efficiency is obtained to evaluate the network throughput.For uplink NOMA systems,signals from different users suffer from uncorrelated channel fading with different transmit power and different path loss.Hence,it is more practical to consider the independent nonidentical distributed Rayleigh fading environment for uplink NOMA systems.For the sake of simplifying,it is assumed that the uplink NOMA users under the independent identical distributed Rayleigh fading environment in the previous research work.Besides,more study of uplink NOMA is about 2 or 3 users NOMA systems.In this paper,we compare two advanced multiuser detection schemes in the interference-limited uplink NOMA system,the dynamic-ordered SIC receiver and the fixed-ordered one.We theoretically analyze the outage performance for the arbitrary number of users.We derive the closed-form outage probability expressions for the dynamic decoding mechanism.We expose a general method to analyze the outage performance when an arbitrary number of users are served simultaneously.We derive the closed-form outage probability expressions of any specific user with the fixed ordered decoding receiver for comparison.Finally,theoretical evaluations and numerical simulations are conducted,and reveal the superiority of the dynamic mode over the fixed one.Under the decoding scheme of conventional SIC receiver,the SIC receiver will not decode the remaining users' signals if any of the prior users fails in decoding,either the aforementioned dynamic order SIC receivers or the fixed order SIC receivers assume there will be 100% outage will occur for all the following users when the decoding for a user is unsuccessful.In this paper,we propose an advanced multiuser SIC decoding strategy based on the statistical channel state information in uplink NOMA systems.The decoding order is fixed according to each user's average received signal power.The BS attempts to decode the later users' information by regarding the unsuccessfully decoded users' signal as the interference.Consequently,there will be a significant gain in terms of the outage performance for the following decoded users even though the outage occurs on the previous users.We theoretically analyze the outage performance for the proposed SIC decoding scheme.The simulation results finally verify the accuracy of the theoretical results.