Optimal Power Allocation in Downlink Non-Orthogonal Multiple Access (NOMA)

Wajd Fahad Alghasmari,Laila Nassef

doi:10.14569/ijacsa.2021.0120240

Abstract

Fifth generation of wireless cellular networks promise to enable better services anytime and anywhere. Non-orthogonal multiple access (NOMA) stands as a suitable multiple accessing scheme due to the ability to allow multiple users to share the same radio resource simultaneously via different domains (power, code, etc.). Through the introduced power domain, users multiplexed at the radio resource within different power levels. This paper studies power allocation in downlink NOMA, an optimization problem formulated that aims to maximize the system's sum rate. To solve the problem, a genetic algorithm based power allocation (GAPA) was proposed that uses genetic algorithm (GA) that employs heuristics to search for suitable solutions. The performance of the proposed power allocation algorithm compared with full search power allocation (FSPA) that gives an optimal performance. Results show that GAPA reaches a performance near to FSPA with lower complexity. In addition, GAPA simulated with various user paring algorithms. Channel state sorting based user pairing with GAPA achieves the best performance comparing to random user pairing algorithm and exhaustive user pairing.

Highlights

Conventional orthogonal multiple access (OMA) takes an incredible role starting from the first generation of wireless cellular networks (1G) to the fourth generation (4G) that uses orthogonal frequency division multiple access (OFDMA) for downlink network and single carrier (SC-OFDMA) for the uplink network [1]
System's sum rate, spectral efficiency, and energy efficiency are evaluated for genetic algorithm based power allocation (GAPA) with exhaustive search user pairing in downlink Non-orthogonal multiple access (NOMA) system
In a downlink NOMA system, power allocation optimization problem is formulated where total subchannel power and minimum user's data rate are taken in consideration

Summary

INTRODUCTION

Conventional orthogonal multiple access (OMA) takes an incredible role starting from the first generation of wireless cellular networks (1G) to the fourth generation (4G) that uses orthogonal frequency division multiple access (OFDMA) for downlink network and single carrier (SC-OFDMA) for the uplink network [1]. Reducing SIC execution can be established through the user pairing scheme that widely studied in different researches over the past years Another designing aspect of downlink NOMA is power allocation which in addition helps boosting the performance of the system due the power domain multiplexing strategy. In the downlink NOMA system, a resource allocation algorithm using GA is proposed for pairing users that share the same frequency resource with an optimal power allocation strategy [22], results show that through the proposed algorithm a fast coverage to the target solution is achieved. The proposed GA power allocation algorithm aims to maximize the achievable sum rate, results show that GA based NOMA overcome the performance of OMA. From the discussed works, reaching optimality in power allocation is still very challenging task especially with higher number of users sharing a single RB.

SYSTEM MODEL

PROBLEM STATEMENT

RESULTS AND DISCUSSION

CONCLUSION