The last few years have witnessed a tremendous growth of the demand for wireless services and a significant increase of the number of mobile subscribers. A recent data traffic forecast from Cisco reported that the global mobile data traffic reached 1.2 zettabytes per year in 2016, and the global IP traffic will increase nearly threefold over the next 5 years. Based on these predictions, a 127-fold increase of the IP traffic is expected from 2005 to 2021. It is also anticipated that the mobile data traffic will reach 3.3 zettabytes per year by 2021, and that the number of mobile-connected devices will reach 3.5 per capita.
With such demands for higher data rates and for better quality of service (QoS), fifth generation (5G) standardization initiatives, whose initial phase was specified in June 2018 under the umbrella of Long Term Evolution (LTE) Release 15, have been under vibrant investigation. In particular, the International Telecommunication Union (ITU) has identified three usage scenarios (service categories) for 5G wireless networks: (i) enhanced mobile broadband (eMBB), (ii) ultra-reliable and low latency communications (uRLLC), and (iii) massive machine type communications (mMTC). The vast variety of applications for beyond 5G wireless networks has motivated the necessity of novel and more flexible physical layer (PHY) technologies, which are capable of providing higher spectral and energy efficiencies, as well as reduced transceiver implementations.
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In this paper, we propose a novel non-orthogonal multiple access (NOMA) scheme with beamwidth control for hybrid millimeter wave communication systems and study the resource allocation design to maximize the system energy efficiency. In particular, NOMA transmission allows more than one user to share a single radio frequency chain, which is beneficial to enhance the system energy efficiency. More importantly, the proposed beamwidth control can increase the number of served NOMA groups by widening the beamwidth that can further exploit the energy efficiency gain brought by NOMA. To this end, two beamwidth control methods, based on the conventional beamforming and the Dolph–Chebyshev beamforming, respectively, are proposed. We first characterize the main lobe power losses due to the two beamwidth control methods and propose an effective analog beamformer design to minimize the power loss. Then, we formulate the energy-efficient resource allocation design as a non-convex optimization problem, which takes into account the minimum required user data rate. A NOMA user grouping algorithm based on the coalition formation game theory is developed and a low-complexity iterative digital precoder design is proposed to achieve a locally optimal solution utilizing the quadratic transformation. Simulation results verify the fast convergence and effectiveness of our proposed algorithms. In addition, our results demonstrate the superior energy efficiency achieved by our proposed beamwidth controlling NOMA scheme compared to the conventional orthogonal multiple access and NOMA schemes without beamwidth control.
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