Graduate Exam Abstract
Xilin ChengPh.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
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
Adviser: Dr. Liuqing Yang
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
[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: