為了實現綠能通訊，獵能是一項很有前景的技術，它能從環境資源中獵取能量，以維持長期且高自立性的合作式網路。與傳統具有穩定電源提供的中繼站不同，無線獵能中繼站使用由無線電訊號收集到的能量協助訊息轉傳至終端。然而，由於獵能的能量會受到通道衰減及無線電能量轉換效率影響，如何有效地使用收集到的能量是很值得研究的議題。本篇論文研究多天線中繼站並同時提升獵能效率及頻譜使用率。首先，針對單個中繼站系統進行研究並延伸至多個中繼站。在多個中繼站系統中，考慮了兩種不同中繼站選擇機制，分別為部分通道資訊及完整通道資訊。在完整通道資訊下，傳送端會知道確切地傳送端到中繼站及中繼站到終端的完整通道資訊，但在部分通道資訊下，中繼站僅回傳部分中繼站到終端的通道資訊。為了評估多天線中繼站的優勢，我們用模擬來呈現結果。在單中繼站系統，我們考慮了不同天線的配置；在多中繼站系統，使用不同的參數針對兩種中繼站選擇機制進行比較。

To enable green energy communication, energy harvesting (EH) is a promising technique which extracts energy from the ambient sources to maintain long-term and self-sustainable wireless networks. Unlike traditional battery relays, EH relays extract energy from the source signal and use the harvested energy to forward the source signal to the destination. However, the harvested energy by the EH relays is limited. How to effectively use the energy is worth investigating. In this thesis, we explore multi-antenna relays to improve the EH efficiency and maintain the high spectral efficiency at the same time. Firstly, we investigate the single-relay scenario and extend the system to the multi-relay. In the multi-relay system, we consider two relay selection schemes, called partial CSI and full CSI. In full CSI, the transmitter knows the exact the source-relay and relay-destination channel coefficients. As for partial CSI, the relays only feed back the relay-destination link channel gain. To evaluate the merit of multi-antenna relays, simulation results are presented, considering different antenna configurations in the single-relay scenario. In the multi-relay scenario, we compare relay selection scheme with partial CSI and that with full CSI in different parameters.

[1] D. Gunduz, K. Stamatiou, N. Michelusi, and M. Zorzi, “Designing intelligent energy harvesting communication systems,” IEEE Communications Magazine, vol. 52, no. 1, pp. 210–216, 2014.
[2] L. R. Varshney, “Transporting information and energy simultaneously,” in Proc. IEEE International Symposium on Information Theory, pp. 1612–1616, 2008.
[3] A. A. Nasir, X. Zhou, S. Durrani, and R. A. Kennedy, “Relaying protocols for wireless energy harvesting and information processing,” IEEE Transactions on Wireless Communications, vol. 12, no. 7, pp. 3622–3636, 2013.
[4] ——, “Throughput and ergodic capacity of wireless energy harvesting based df relaying network,” in Proc. IEEE International Conference on Communications (ICC), pp. 4066–4071, 2014.
[5] X. Zhou, R. Zhang, and C. K. Ho, “Wireless information and power transfer: Architecture design and rate-energy tradeoff,” IEEE Transactions on Communications,
vol. 61, no. 11, pp. 4754–4767, 2013.
[6] C. Zhai, L. Zheng, P. Lan, and H. Chen, “Wireless powered cooperative communication using two relays: Protocol design and performance analysis,” IEEE Transactions on Vehicular Technology, vol. 67, no. 4, pp. 3598–3611, 2017.
[7] A. A. Nasir, X. Zhou, S. Durrani, and R. A. Kennedy, “Wireless-powered relays in cooperative communications: Time-switching relaying protocols and throughput analysis,” IEEE Transactions on Communications, vol. 63, no. 5, pp. 1607–1622, 2015.
[8] R. Zhang and C. K. Ho, “Mimo broadcasting for simultaneous wireless information and power transfer,” IEEE Transactions on Wireless Communications, vol. 12, no. 5, pp. 1989–2001, 2013.
[9] A. N. Parks, A. P. Sample, Y. Zhao, and J. R. Smith, “A wireless sensing platform utilizing ambient rf energy,” in Proc. IEEE Topical Conference on Biomedical Wireless Technologies, Networks, and Sensing Systems, pp. 154–156, 2013.
[10] H. Mao, B. Xu, P. Zhu, J. Li, and X. You, “Downlink transmission strategies in power-splitting swipt distributed miso systems,” IEEE Access, vol. 6, pp. 52 997-53 005, 2018.
[11] C. Qin, W. Ni, H. Tian, and R. P. Liu, “Joint rate maximization of downlink and uplink in multiuser mimo swipt systems,” IEEE Access, vol. 5, pp. 3750–3762, 2017.
[12] C. Qin, W. Ni, H. Tian, R. P. Liu, and Y. J. Guo, “Joint beamforming and user selection in multiuser collaborative mimo swipt systems with nonnegligible circuit energy consumption,” IEEE Transactions on Vehicular Technology, vol. 67, no. 5, pp. 3909–3923, 2017.
[13] J. N. Laneman, D. N. Tse, and G. W. Wornell, “Cooperative diversity in wireless networks: Efficient protocols and outage behavior,” IEEE Transactions on Information Theory, vol. 50, no. 12, pp. 3062–3080, 2004.
[14] J. Liao, M. R. Khandaker, and K.-K. Wong, “Energy harvesting enabled mimo relaying through power splitting,” in Proc. IEEE 17th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), pp. 1–5, 2016.