Energy Efficient Uplink Transmission in Cooperative mmWave NOMA Networks With Wireless Power Transfer

In 5G wireless networks, cooperative non-orthogonal multiple access (NOMA) and wireless power transfer (WPT) are efficient ways to improve the spectral efficiency (SE) and energy efficiency (EE). In this paper, a new cooperative NOMA scheme with WPT is proposed, where EE optimization with a constrained maximum transmit power and minimum required SE is considered for the user grouping and transmit power allocation of users. We obtain a sub-optimal solution by decoupling the original problem in two sub-problems: an iterative algorithm is considered for the user grouping, while, in addition, we utilize the Bat Algorithm (BA) for solving the power allocation problem, where BA was proved to be able to achieve a higher accuracy and efficiency with respect to other meta-heuristic algorithms. Furthermore, to validate the performance of the proposed system, analytical expressions for the energy outage probability and outage probability of users are derived, confirming the effectiveness of the simulation results. It is demonstrated that the proposed cooperative NOMA with WPT offers a considerable improvement in terms of SE and EE of the network compared to other methods. Finally, the effectiveness of BA in solving the EE optimization problem is demonstrated through a high convergence speed by comparing it with other methods.

I. Introduction

The demand for high data rate has increased rapidly in the last decade. This rapid growth in mobile data traffic should be accompanied with the same growth in the energy efficiency (EE) and spectral efficiency (SE) of the network [1]. To this end, several technologies have been introduced. One of the most promising technologies is millimeter-Wave (mmWave) communication which provides wide bandwidth and high SE. However, the deployment of mmWave in long-range communications is challenging due to the high path loss, low penetration, and high sensitivity to blockage. As stated in [2], SE and EE improvement of the network can also be afforded by resorting to the deployment of small-cell networks (SCNs). Short-range SCNs complement the macro-cell networks to provide coverage for both indoor and outdoor wireless networks [3], [4]. SCN is also an effective technology for deploying mmWave, therefore, a promising approach in 5G for supporting high data rate demand is combining SCNs and mmWave [5]. Non-orthogonal multiple access (NOMA) has been introduced as well for enhancing SE in 5G [6], [7]. The key concept in power domain NOMA is allocating each orthogonal resource block with different power levels to more than one user [6], where at the receiver side of NOMA systems, successive interference cancelation (SIC) is applied to detect the desired signal [8], [9]. Moreover, to improve the transmission reliability of users with poor channel gain, cooperative NOMA was introduced. Cooperative NOMA enhances the SE of the network by increasing the diversity gain [10]. Furthermore, the limited power of the mobile devices has attracted lots of attention when focusing on their impact in the cooperative wireless networks.