Abstract
Fifth-generation of wireless cellular systems has the potential to increase capacity, spectral efficiency, and fairness among users. The Non-Orthogonal Multiple Access based wireless networks (NOMA) is the next generation multiplexing technique. NOMA breaks the orthogonality of traditional multiple access to allow multiple users to share the same radio resource simultaneously. The main challenge in designing NOMA is the selection of the resource allocation algorithms since user pairing and power allocation are coupled. This paper compares the performance of three power allocation schemes: fixed power allocation, fractional transmit power allocation and full search power allocation. The algorithms are analyzed in different simulation scenarios using three performance metrics of the spectrum efficiency and energy efficiency and sum rate. Additionally, the impact of user pairing algorithms studied through two user pairing schemes: random user pairing and channel state sorting based user pairing. Results indicate the superiority of NOMA to increase the capacity compared to traditional orthogonal multiple access. On the other hand, full search power allocation is the best performance compared to the other power allocation schemes though it is highly complex compared to fractional transmit power that gives a suboptimal performance.
Highlights
Smartphones nowadays are considered as a core of our lives, due to several services and applications provided, where phone calls are not the only applicable service
The capacity gain of both Non-Orthogonal Multiple Access (NOMA) and Orthogonal Frequency Division Multiple Access (OFDMA) systems versus transmitted power simulated in MATLAB with two users in the system, the channel gains given as 40 dB and 10 dB for UE1 and UE2, respectively
Fixed Power Allocation (FPA), Fractional Transmit Power Allocation (FTPA), and Full Search Power Allocation (FSPA) simulated with random user pairing and their performance compared based on system sum rate and spectral efficiency
Summary
Smartphones nowadays are considered as a core of our lives, due to several services and applications provided, where phone calls are not the only applicable service. Multiple accessing schemes that utilized over the past generations have relied on orthogonality that resembles exclusive usage of resources either in time, frequency, or code domain. OMA suffers from lacking the ability to support an increasing number of users due to the exclusive utilization of the orthogonal resource besides that it cannot provide an excellent experience to all users in the system that causes higher latency and bad cell-edge users’ experience [4]. Power domain NOMA works by superimposing the signals into the same frequency or time domain through Superposition Coding (SC) within distinctive power levels. To support multi-users to share the same time-frequency resources, user pairing and power allocation algorithms are necessary to allocate different power levels. The remaining sections of this paper discuss the mathematical model and different user pairing and power allocation algorithms.
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