Abstract
In this paper, we propose user grouping, subcarrier allocation, and bit allocation schemes in multicarrier nonorthogonal multiple access (NOMA) systems on downlink beamforming to reduce the total transmit power while considering the data-rate and the error-rate constraints of practical modulation types. Power control is also considered. In this system, each subcarrier can be assigned to multiple users for data transmission. Each subcarrier is allocated to a cluster that contains groups of two users for data transmission. A subset of subcarriers is assigned to the same cluster for sharing. The system is based on orthogonal frequency division multiple access (OFDMA), in which a primary user (PU) is more important than a secondary user, and we ensure that all assigned subcarriers transmit data to the PU in the system. In the proposed schemes, the user-grouping operation is performed first and the subcarrier allocation along with the bit loading and power assignment are performed subsequently based on the user-grouping results. The simulation results obtained using the proposed schemes in conjunction with the nonorthogonal multiple access to allocate bits, subcarriers, and transmit power show that the proposed schemes outperform the conventional OFDMA system in terms of transmit power.
Highlights
In the light of recent technological advances, nonorthogonal multiple access (NOMA) is considered a promising technology for fifth-generation (5G) multiple access and beyond [1]–[4]
Given that a NOMA scheme comprises many signals of different users in a cell and these signals are multiplexed in the power domain at the transmitter side [4], the multiuser signals are separated by executing successive interference cancellation (SIC) and the beamforming
The system consisted of one base station (BS), which was equipped with two transmit antennas, M = 2
Summary
In the light of recent technological advances, nonorthogonal multiple access (NOMA) is considered a promising technology for fifth-generation (5G) multiple access and beyond [1]–[4]. In [17], an optimization problem involving minimization of the total transmit power under a QoS with a minimum rate constraint was studied for downlink orthogonal frequency-division multiplexing (OFDM)-based NOMA systems. In [24], by using a singular-valuedecomposition (SVD)-based interference alignment technique for downlink multiuser MIMO-NOMA systems, where users shared the same frequency channel, an optimization problem was formulated to maximize the sum rate under the total power and proportional fairness constraints. The resource allocation problem with rate and error-rate constraints considering the aggregation of multiuser, multicarrier, NOMA, and downlink beamforming in systems has not been investigated far. We investigate the user selection problem and design resource-allocation algorithms for downlink beamforming in OFDMA-based NOMA systems.
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