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Network coded HARQ feedback

Event Date: January 14, 2014
Speaker: Dr. Besma Smida
Speaker Affiliation: Purdue University, Calumet
Hammond, Indiana
Sponsor: Communications, Networking, Signal & Image Processing
Time: 3:00 PM
Location: MSEE 239
Contact Name: Professor Mireille Boutin
Contact Phone: (765) 494-3538
Contact Email:

Feedback may improve data rates in several ways.  In wireless networks with perfect channel state information at the transmitter and receiver (CSITR), feedback may serve to increase rates by enabling the collaborative encoding or decoding of messages.  In practical networks without CSITR, feedback is used to either learn the channel state, or to request the re-transmission of a failed reception.  In this talk, I will review the role and the utility of feedback in wireless communications.  I will then analyze the combination of network coding (NC) and Hybrid-Automatic Retransmission request (HARQ) feedback in the context of networks without CSITR where re-transmissions are prevalent.  In particular, I will consider the broadcast channel where a base node wishes to 
transmit different messages to multi-terminal nodes.  The proposed scheme judiciously combines retransmissions to several users in a single resource block using NC.  If the combinations are correctly chosen, the end users
may exploit knowledge of the previously decoded packets to recover their designated packets from the combined ones.  My collaborators and I derive throughput expressions for network coded HARQ with an arbitrary number of users and symmetric Rayleigh channels. We obtain an expression that captures the gain of combining NC and HARQ for different SNR regimes and receiver feedback protocols.  We also introduce novel re-transmission strategies that make network coding more efficient at low SNR.  Finally, I will conclude my talk by discussing some open problems in the area of feedback in two-way communication.



Dr. Besma Smida is an Assistant Professor of Electrical and Computer Engineering at Purdue University Calumet. From 2006 to 2009, she was  a Post-Doc/Lecturer at Harvard University.  She received the M. Sc. and Ph.D. degrees in telecommunications from INRS-EMT, University of Quebec, Montreal, Canada, in 1998 and 2006.  From 1999 to 2002, she was a research engineer in the Technology Evolution and Standards group of Microcell Inc. (now Rogers wireless), Montreal, surveying and studying radio-communication technology evolution.  She took part in major wireless normalization committees (3GPP, T1P1).  Her research interests lie in the area of wireless communications. 

Dr. Smida has received a number of awards including the Governor General of Canada Academic Gold Medal 2007, the INRS Award of Academic Excellence 2007, NSERC Postdoctoral Fellowship award 2008, and FQRNT Postdoctoral Fellowship award 2006.  Recently, she has received an NSF-CIF (2013-2016) award, where she is the sole principal investigator.  She is a senior member of IEEE and was chair of IEEE Women in Engineering Chicago section from 2009-2013.