In wireless communications, the channel conditions vary over time due to signal fading and multipath propagation. If a wireless device can transmit simultaneously over different channels, there is a chance that some of these channels may have better conditions than others; therefore the overall performance will improve. The widely known Multiple Input-Multiple Output (MIMO) technology works on this principle. While MIMO provides spatial diversity through multiple antennas on the same wireless device, user cooperation does so through a partner's antenna. This means that spatial diversity can be obtained in small size wireless devices which cannot have more than one antennas. The idea behind cooperation is, when a wireless device transmits signal, the signal is "overheard" by another wireless device (the partner). If the partner also sends a copy of that signal to the destination, spatial diversity is achieved.
In order for cooperative diversity to benefit a particular application, such as wireless video, there are many questions to be answered. For example:
- How do we allocate bandwidth between partners to optimize end to end source quality?
- Since resources are limited, a partner may not be able to retransmit the entire signal that it "overhears". How can partners selectively retransmit a portion of each other's signal to optimize overall performance?
- Since only a portion of the signal is transmitted cooperatively (given the above bullet), how does a higher layer application divide its transmission session into cooperative and non-cooperative? And how would this affect the end to end quality of service for the underlying application?
In this project we are interested in answering the above questions both from an information theoretic perspective and also for practical source and channel coders. In particular, we investigate real-time multimedia communications over wireless. We will include video simulations and channel simulations while jointly optimizing parameters at both layers. We will gather performance measures from simulation to determine how cooperation can benefit wireless multimedia communications.
This research is partially funded by NSF, Philips, WICAT, CATT.
- O. Alay, E. Erkip and Y. Wang, "Cooperative Transmission of Correlated Gaussian Sources", in Proceedings of IEEE 41st Annual Asilomar Conference on Signals, Systems and Computers, Pacific Grove, CA, November 2007.
- H.Y. Shutoy, D. Gunduz, E. Erkip and Y. Wang, "Cooperative source and channel coding for wireless multimedia communications", IEEE Journal on Selected Topics on Signal Processing, Special Issue on Network-Aware Multimedia Processing and Communications, vol. 1, no. 2, pp. 295-307, August 2007.
- O. Alay, H. Shutoy, D. Gunduz, E. Erkip, Y. Wang, "Cooperative source and channel coding for wireless video transmission", in Proceedings of 16th Annual Wireless and Optical Communications Conference, NJ, April 2007
- H. Shutoy, Y. Wang and E. Erkip, "Cooperative Source and Channel Coding for Wireless Multimedia Communications", in Proceedings of IEEE International Conference on Image Processing, Atlanta, Georgia, October 2006 (invited paper).