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Graduate Exam Abstract


Xilin Cheng

Ph.D. Preliminary

November 14, 2014, 11:00 am - 1:00 pm

ECE Conference Room C101B

Energy Efficient Cooperative OFDM Communications over Underwater Acoustic Channels


Abstract: Underwater acoustic sensor networks (UWASN) have been attracting growing research interests in recent decades due to the emerging scientific, environmental, commercial and military applications. Underwater acoustic communications (UAC), which adopts acoustic waves as the information carrier, is the key communication technique to realize UWASN. However, UAC is very challenging. First, the acoustic signal is characterized by low carrier frequency and distance-dependent bandwidth. This significantly limits the capacity of UAC. Secondly, the large delay spread causes frequency selective fading and inter- symbol interference (ISI). Thirdly, the slow acoustic signal propagation (c = 1500) hinders the effective channel state information (CSI) feedback and accurate time synchronization. Finally, large Doppler shifts caused by motion lead to error-prone fast time-varying UAC channels. In this research, we will consider energy- efficient cooperative OFDM communications to improve the reliability of UAC. The first scenario we examined is the short-medium range communications, where the source can not directly communicate with the destination due to the blocking between them, and the relay is utilized to forward the signals from the source to the destination. Based on this scenario, we develop an adaptive amplify-and-forward (AF) relay-aided OFDM UAC (RA-UAC) protocol. We first derive the optimal power allocation between the source and the relay as well as the power distribution over all the subcarriers based on instantaneous channel state information (CSI). Then, to realize the benefits of the optimal power allocation, we implement channel prediction to compensate the channel variation during the CSI signal propagation and the Lloyd algorithm to quantize CSI efficiently. The benefits of the adaptive RA-UAC protocol is illustrated by comparing with the traditional RA-UAC protocol with the uniform power allocation. The second scenario we examined is the long range communications, where the direct-link (DL) between the source and the destination exists, and there are multiple potential relays between the source and the destination. For this scenario, we design an Asynchronous Amplify-and- forward relaying with Precoded OFDM (AsAP) protocol from the perspective of energy efficiency. The optimum power allocation between the source and the relays is investigated based on the knowledge of statistical channel state information (CSI). The analytical results suggest an AsAP scheme with Selective Relaying (SR-AsAP), where only the relay with maximum effective signal-to-noise ratio (SNR) forwards the source information. The performance of the SR- AsAP protocol is simulated, and its benefits are illustrated through comparison with the DL system and the AsAP protocol with all relay transmissions.

Adviser: Dr. Liuqing Yang
Co-Adviser: N/A
Non-ECE Member: Dr. Haonan Wang, Statistics
Member 3: Dr. Mahmood Azimi-Sadjadi, Electrical and Computer Engineering
Addional Members: Dr. Jie Luo, Electrical and Computer Engineering

Publications:
Student Publications:
[J1] X. Cheng, M. Wen, X. Cheng, and L. Yang, ``Effective Mirror-Mapping-Based Intercarrier Interference Cancellation for OFDM Underwater Acoustic Communications,'' Elsevier Ad Hoc Networks Journal, 2014.

[J2] X. Cheng, R. Cao and L. Yang, ``Relay-Aided Powerline Communications with Amplify-and-Forward,'' IEEE Transactions on Smart Grid, vol. 4, no. 1, pp. 265 - 272, March 2013.

[C1] X. Cheng, L. Yang, and X. Cheng ``Adaptive Relay-Aided OFDM Underwater Acoustic Communications,'' in Proceedings of 2015 IEEE International Conference on Communications. (Submitted)

[C2] Miaowen Wen, Xiang Cheng, Liuqing Yang and X. Cheng, ``Information-Guided Pilot Insertion for Capacity Improvement in OFDM Underwater Acoustic Communications,'' in Proceedings of the 48th Asilomar Conference on Signals, Systems and Computers, Pacific Grove, CA, November 2 - 5, 2014.

[C3] X. Cheng, B. Yu, X. Cheng and L. Yang, ``Two-Way Full-Duplex Amplify-and-Forward Relaying,'' in Proceedings of MILCOM Conference, San Diego, CA, Nov 18 - 20, 2013.

[C4] X. Cheng, M. Wen, X. Cheng and L. Yang, ``Effective Self-Cancellation of Intercarrier Interference for OFDM Underwater Acoustic Communications'' , in Proceedings of the International Conference on UnderWater Networks and Systems (WUWNet), Kaohsiung, Taiwan, November 11-13, 2013.

[C5] M. Wen, X. Cheng, X. Cheng, L. Yang and B. Jiao, ``Effective Intercarrier Interference Reduction Techniques for OFDM Underwater Acoustic Communications,'' in Proceedings of the 47th Asilomar Conference on Signals, Systems and Computers, Pacific Grove, CA, November 3 - 6, 2013 (invited).

[C6] X. Cheng, R. Cao and L. Yang, ``Practical Implementation of Hybrid DLT Codes for Cooperative Relay Communications,'' in Proceedings of MILCOM Conference, Orlando, FL, October 29- November 1, 2012.

[C7] X. Cheng, R. Cao, F. Qu and L. Yang, ``Relay-Aided Cooperative Underwater Acoustic Communications: Selective Relaying,'' in Proc. of MTS/IEEE Oceans Conference (OCEANS), Yeosu, Korea, May 21-24, 2012.

[C8] X. Cheng, R. Griffin, F. Qu and L. Yang, ``A Comparison of Multiband and Single-Band OFDM for Underwater Acoustic Communications,'' in Proc. of THE ACOUSTICS 2012 HONG KONG conference and exhibition, Hong Kong, May 13-18, 2012.

[C9] X. Cheng, F. Qu and L. Yang, ``Single Carrier FDMA over Underwater Acoustic Channels,'' in Proc. of 6th International ICST Conference on Communications and Networking in China, Harbin, China, August 17-19, 2011.

[C10] X. Cheng, R. Cao and L. Yang, ``On the System Capacity of Relay-Aided Powerline Communications,'' in Proceedings of IEEE International Symposium on Power Line Communications and Its Applications, Udine, Italy, April 3-6, 2011.


Program of Study:
ECE 520
ECE 568
ECE 799
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