Abstract
Wireless-powered communication networks (WPCNs) consist of wireless devices (WDs) that transmit information to the hybrid access point (HAP). In this situation, there is interference among WDs that is considered to be noise and causes information loss because of adjacent signals. Moreover, power is limited and can be lost if transmission distance is long. This paper studies sum-throughput maximization with sectored cells for WPCN. We designed a downlink (DL) energy beamforming by sector based on the hybrid space division multiple access (SDMA) and nonorthogonal multiple access (NOMA) approach to maximize the sum throughput. First, a cell is divided into several sectors, and signals from each sector are transmitted to each antenna of the HAP, so that the signals are not adjacent. Further, the HAP decodes the overlapping information of each sector. Next, power allocation is optimized by sector. To optimize power allocation, a constrained optimization problem is formulated and then converted into a nonconstraint optimization problem using the interior penalty method. The optimal solution derives the maximal value to the problem. Power for each sector is optimally allocated according to this optimal solution. Under this consideration, sum-throughput maximization is performed by optimally allocating DL energy beamforming by sector. We analyzed sum throughput and fairness, and then compared them according to the number of sectors. Performance results show that the proposed optimal power allocation by sector using hybrid SDMA/NOMA outperforms the existing equal power allocation by sector in terms of the sum throughput while fairness is also maintained. Moreover, the performance difference between the hybrid approach and SDMA, which optimally allocates power by sector, was about 1.4 times that of sum throughput on average, and the hybrid approach was dominant. There was also no difference in fairness performance.
Highlights
Wireless-powered communication networks (WPCNs) consist of wireless devices (WDs) that transmit information to the hybrid access point (HAP)
WDs with a short distance to HAP in order to optimize power allocation by sector. This is because minimizing power loss due to long distances can increase the total amount of power transmitted with a sectored cell and improve sum throughput; (3) we perform information reception by sector from each antenna of the HAP to reduce interference between multiple WDs, and we use nonorthogonal multiple access (NOMA) to superimpose signals from multiple WDs. This is because sum throughput can be improved by dividing cells and by separating overlapping signals according to signal strength differences to reduce information loss due to interference between multiple WDs; (4) in performance evaluation, we demonstrated the effectiveness of optimal power allocation, and the hybrid space division multiple access (SDMA) and NOMA approach
The HAP performs DL energy beamforming for each sector, and each WD transmits information to the HAP after harvesting energy
Summary
In analog beamforming (ABF), the traditional way to form beams is to use attenuators and phase shifters as part of the analog RF circuitry where a single data stream is divided into separate paths. One beam is created for the entire frequency band, which is sufficient for line-of-sight (LoS) beamforming [6]. The advantage of this method is that only one RF chain is required. The disadvantage is the loss from the cascaded phase shifters at high power
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