Abstract
In this paper, we examine the robust beamforming design to tackle the energy efficiency (EE) maximization problem in a 5G massive multiple-input multiple-output (MIMO)-non-orthogonal multiple access (NOMA) downlink system with imperfect channel state information (CSI) at the base station. A novel joint user pairing and dynamic power allocation (JUPDPA) algorithm is proposed to minimize the inter user interference and also to enhance the fairness between the users. This work assumes imperfect CSI by adding uncertainties to channel matrices with worst-case model, i.e., ellipsoidal uncertainty model (EUM). A fractional non-convex optimization problem is formulated to maximize the EE subject to the transmit power constraints and the minimum rate requirement for the cell edge user. The designed problem is difficult to solve due to its nonlinear fractional objective function. We firstly employ the properties of fractional programming to transform the non-convex problem into its equivalent parametric form. Then, an efficient iterative algorithm is proposed established on the constrained concave-convex procedure (CCCP) that solves and achieves convergence to a stationary point of the above problem. Finally, Dinkelbach’s algorithm is employed to determine the maximum energy efficiency. Comprehensive numerical results illustrate that the proposed scheme attains higher worst-case energy efficiency as compared with the existing NOMA schemes and the conventional orthogonal multiple access (OMA) scheme.
Highlights
The demand for wireless traffic is expected to increase a thousandfold by 2020 for the 5G wireless networks due to the requirement of high speed data services, low latency, high spectral efficiency, massive connectivity and green communications [1,2]
The proposed joint user pairing and dynamic power allocation (JUPDPA) in Algorithm 1 and joint robust beamforming and EE maximization (JRBEE) algorithm given in Algorithm 2 are jointly labeled as proposed efficiency maximization (EEmax) Scheme
An efficient iterative algorithm based on the concave-convex procedure (CCCP) was proposed to optimize the transmit beamforming vectors for each pair
Summary
The demand for wireless traffic is expected to increase a thousandfold by 2020 for the 5G wireless networks due to the requirement of high speed data services, low latency, high spectral efficiency, massive connectivity and green communications [1,2]. In order to reduce the inter user interference (IUI), the impact of user pairing was examined for a MIMO-NOMA system in [22,23], where the authors exploit the fixed power allocation (FPA) scheme and pair the users with distinctive channel conditions assuming perfect channel state information (CSI) at the base station (BS). Several approaches for the EE maximization problem have been proposed in the literature [34,35,36,37] for the perfect CSI at the BSs. For instance, authors in [34] proposed an energy efficient optimal PA technique for a SISO-NOMA system that maximizes the EE subject to the minimum data rate requirement for each user. An EE resource allocation algorithm was proposed in [39] to maximize the secret EE and secret key EE for both MISO-single antenna eavesdropper and MIMO-multiple antennas eavesdropper systems considering perfect and statistical CSI at the base station. Motivated from the above observations, the major contribution of this work is summarized as follows
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