Motivated by the previous works in this field , , we solve the optimization problem P1 via Lyapunov optimization method, as it develops a low complexity algorithm to achieve the mode selection and power allocation scheme, while revealing the throughput-delay tradeoff in buffer-aided WPCCN.
As a result, the adaptive joint mode selection and power allocation protocol of the buffer-aided WPCCN is given by
For the buffer-aided WPCCN, the optimal time-averaged achievable rate achieved by the joint mode selection and power allocation is denoted by R*.
Hence, at the beginning of each time slot, the buffer-aided WPCCN may work as follow:
Hence, buffer used in WPCCN can bring a certain throughput gain.
Therefore, we can come to an conclusion that the throughput performance of the buffer-aided WPCCN can be improved further by joint mode selection and power allocation strategy.
In this subsection, we examine the positions of the PB and the relay node how to affect the throughput performance of the WPCCN. The transmit power of the PB is set to P = 30 Watt; the overall distance between the PB with S and R is fixed at 20 meters, i.e., [d.sub.1] + [d.sub.2] = 20 meters; similarly, the sum distance of the S - R link and R - D link is fixed at 20 meters, i.e., [d.sub.3] + [d.sub.4] = 20 meters.
5 that in order to achieve a higher throughput of the considered WPCCN, buffer-aided relaying with joint mode selection and power allocation scheme should be adopted, meanwhile, the PB should be located close to S , while R should be located close to D ; or the PB is located close to R , while R is located close to S.
7 shows that for the buffer-aided WPCCN with JMSPA scheme, the larger the time-averaged delay, the higher time-averaged throughput is obtained, which presents a throughput-delay tradeoff of the buffer-aided JMSPA protocol.
In this paper, we have investigated a buffer-aided WPCCN which consists of S, R, D, and a dedicated PB.
After transforming optimization problem several times in last section, we adopt iterative algorithm to maximize system average transmission rate for a multiple relay WPCCN with jointly subcarrier pairing, power allocation and time-slot assignment subject to total network power constraint.
In this paper, we considered a WPCCN where multiple relays and one source node harvest energy from a HAP and then transmit signals using the harvested energy with the HTC protocol.