LASR Colloquia - Kun Tan/Microsoft Research Asia, "Improve Spectrum Efficiency using uACKs," ACES 6.336

Contact Name: 
Jenna Whitney
May 30, 2012 10:45am - 11:45am

There is a sign-up schedule for this event that can be found at

Type of Talk: LASR Colloquia

Speaker/Affiliation: Kun Tan/Microsof

t Research Asia

Talk Audience: UTCS Faculty, Graduate Students, Unde

rgraduate Students, and Outside Interested Parties

Date/Time: Wednesd

ay, May 30, 2112, 10:45 AM

Location: ACES 6.336

Host: Lili Qiu

Talk Title: Improve Spectrum Efficiency using uACKs


Wireless transmissions are lossy due to collision, interference, fading o

r noise. Traditional mechanisms to compact wireless loss is based on retran

smission. However, retransmissions reduce the efficiency of data communica

tion in wireless networks because of: (i) per-retransmission packet headers

, (ii)per-retransmission contention overhead, and (iii) redundant bits in
every retransmission. To improve spectrum efficiency in a lossy environmen

t, we propose a new in-frame retransmission scheme using uACKs. Instead of
waiting for the entire transmission to end before sending the ACK, the re

ceiver sends smaller uACKs for every few symbols, on a separate narrow fee

dback channel. Based on these uACKs, the sender only retransmits the lost

symbols after the last data symbol in the frame, thereby adaptively changi

ng the frame size to ensure it is successfully delivered. Further, uACK c

an also serve as an extension of busy-tone to help early detecting collisio

ns and mitigating the hidden/exposed terminal problem. We have implemented
uACK on the Sora platform. Experiments with our prototype validate the fea

sibility of symbol-level uACK. By significantly reducing the retransmistion
overhead, the sender is able to aggressively use higher data rate for a l

ossy link. Both improve the overall network efficiency. Our experiments fro

m a controlled environment and trace-based emulation over an 9-node softwar

e radio testbed show that uACK can significantly improve the network throug

hput compared to 802.11g and the best known retransmission scheme.


Kun Tan is a Lead Researcher at Microsoft Research Asia. He leads the d

evelopment of the Sora Software Radio system. His research interests includ

e transport protocols, congestion control, wireless networks and systems.
Previously, he has developed the Compound TCP, which has been implemente

d and deployed in latest Windows OS. Dr. Tan won the best paper award in NS

DI 2009, and also won best demo awards in NSDI 2009 and Sigcomm 2010. He i

s an associate editor of IEEE Transaction of Mobile Computing. He is also a

n adjunct professor of the department of Electronic Engineering of HUST, C


Dr. Tan received the B.E., M.E. and Ph.D. degree in Computer Sc

ience and Engineering from Tsinghua University, Beijing, China, in 1997

, 1999, and 2002 respectively.