Performance analysis of energy harvesting relaying

Abstract

Recently, energy harvesting has been exploited as a key technique in wireless communications. Because conventional wireless systems are powered by batteries and cables, they tend to have restricted lifetime and flexibility. In order to solve these problems, wireless power has been investigated as a replacement for conventional batteries. This thesis focuses on energy harvesting in relaying. The data packet from the source to relay contains three parts: pilot for channel estimation, data symbols and pilots for harvesting. The data packet from the relay to the destination contains two parts: data symbols and pilots for estimation. To study energy harvesting, the performance of wireless powered communications is evaluated in terms of achievable rate and bit error rate, for applications where the downlink and the uplink are correlated, in contrast to previous works that assume independent uplink and downlink. Semi-closed expressions for the achievable rate and series expressions for the bit error rate are derived in Nakagami m fading channels, based on which the effect of link correlation is examined. Numerical results show that the link correlation has a significant impact on the achievable rate. Consequently, the optimum system parameter for correlated links is very different from that for independent links, showing the usefulness of our results. Also, the link correlation has a noticeable effect on the bit error rate, depending on the system parameters considered. Then, performance analysis has been performed for an AF relaying system with pilot-based channel estimation and time switching (TS) energy harvesting is conducted. Numerical results show the existence of the optimal values of the numbers of pilots for channel estimation and for energy harvesting, when the total size is fixed. Next, three novel structures using simultaneous wireless information and power transfer in energy harvesting amplify-and-forward (AF) relaying are investigated. Different combinations of time-switching (TS) and power-splitting (PS) energy harvesting protocols are studied. Closed-form expressions for the cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio (SNR) for the three structures are derived. Using these expressions, achievable rate (AR) and bit-error-rate (BER) are derived. Different parameters are examined. Numerical results show the optimal splitting ratio for channel estimation, energy harvesting and data transmission, when the packet size is fixed. Finally, the energy from the source and the energy from the ambient are merged together. The three ambient structures are studied. The closed-form expressions for the cumulative distribution function (CDF) of the end-to-end signal-to- noise ratio (SNR) for the three ambient structures are derived. Curve fitting has been used to achieve the approximately achievable rate (AR) and bit-error-rate (BER). The results provide the optimal values for channel estimation pilots and power splitting ratio series for these ambient RF added structures