We consider a distributed medium access protocol, Opportunistic ALOHA, for reachback in sensor networks with mobile access
points (AP). We briefly discuss some properties of the protocol, like throughput and transmission control for an orthogonal
CDMA physical layer. We then consider the incorporation of necessary side information like location into the transmission
control and numerically demonstrate the loss in throughput in the absence of such information. Through simulations, we discuss
the robustness and sensitivity of the protocol under various modeling errors and propose strategies to allow for errors in
estimation of some parameters without reduction in the throughput. For networks, where the sensors are allowed to collaborate,
we consider three coding schemes for reliable transmission: spreading code independent, spreading code dependent transmission
and coding across sensors. These schemes are compared in terms of achievable rates and random coding error exponents. The
coding across sensors scheme has comparable achievable rates to the spreading code dependent scheme, but requires the additional
transmission of sensor ID. However, the scheme does not require the mobile AP to send data through the beacon unlike the other
two schemes. The use of these coding schemes to overcome sensitivity is demonstrated through simulations.
Parvathinathan Venkitasubramaniam was born in India in 1981. He received his B.Tech. degree from the department of Electrical Engineering, Indian Institute
of Technology, Madras in 2002. He joined the School of Electrical and Computer Engineering, Cornell University, Ithaca, NY,
in 2002 and he is working toward his Ph.D. degree. He is a recipient of the 2004 Leonard G. Abraham Award (with S. Adireddy
and L. Tong) from the IEEE Communications Society. His research interests include random-access protocols,sensor networks,
and information theory.
Srihari Adireddy was born in India in 1977. He received the B.Tech. degree from the Department of Electrical Engineering, Indian Institute
of Technology, Madras, and M.S. and Ph. D. degrees from the School of Electrical and Computer Engineering, Cornell University,
Ithaca, NY in 2001 and 2003 respectively. Currently, he is working at Silicon Laboratories, Austin, TX. He is a recipient
of the 2004 Leonard G. Abraham Award (with P. Venkitasubramaniam and L. Tong) from the IEEE Communications Society. His research
interests include signal processing, information theory, and random-access protocols.
Lang Tong received the B.E. degree from Tsinghua University, Beijing, China, in 1985, and M.S. and Ph.D. degrees in electrical engineering
in 1987 and 1990, respectively, from the University of Notre Dame, Notre Dame, Indiana. He was a Postdoctoral Research Affiliate
at the Information Systems Laboratory, Stanford University in 1991. Currently, he is a Professor in the School of Electrical
and Computer Engineering, Cornell University, Ithaca, New York.
Dr. Tong received Young Investigator Award rom the Office of Naval Research in 1996, and the Outstanding Young Author Award from the IEEE Circuits and Systems Society in 1991, the 2004 IEEE Signal Processing Society Best Paper Award (with M. Dong),
the 2004 Leonard G. Abraham Prize Paper Award from the IEEE Communications Society (with P. Venkitasubramaniam and S. Adireddy).
His areas of interest include statistical signal processing, adaptive receiver design for communication systems, signal processing
for communication networks, and information theory.