[CPCC] SEMINAR Wireless Multicast/Ad-Hoc Networks April 6 10 AM

Ender Ayanoglu ayanoglu at uci.edu
Thu Apr 2 16:35:04 PDT 2009


                               SEMINAR

The Throughput-Delay Tradeoff for Wireless Multicast Using Hybrid-ARQ
Protocols and Transmission of Confidential Messages In Ad-Hoc Networks

                                 by
                             Jianqi Wang
                              UC Irvine

                            April 6, 2009
                               Monday
                                10 AM
                       Engineering Gateway 3161

                              ABSTRACT

We present a hybrid automatic repeat request (ARQ) scheme for wireless
multicast, i.e., common information broadcast, with incremental
redundancy channel coding and packet retransmission.  With this
scheme, we can reliably deliver the same copy of information to
different users with mild delay. In addition, the design of the
feedback channel for this scheme can be greatly simplified as no
effort must be expended to combat cross user interference. We assume
that there is always a packet for the transmitter to send whenever the
channel is available. The transmitter is assumed to have a buffer of
infinite length so that there is no packet-dropping.  Three specific
schemes are studied, including generalized slotted ALOHA (GSA),
repetition time diversity (RTD), and general incremental redundancy
(INR). The scaling laws of the average delay and average throughput
with respect of the number of users are derived.  In addition, we also
derive a condition to obtain a linear scaling for both the throughput
and the delay with respect to the number of users. Since every user
can achieve no more than the ergodic capacity, we actually achieve the
optimal scaling law in this case. Simulation results confirm our
findings.

In the second part of the talk we discuss our investigation of the
cooperative jamming schemes for the transmission of confidential
messages in ad-hoc networks. By letting the mobile units (the helpers)
in the vicinity of the legitimate receiver send out jamming signals
while the transmitter communicates with the receiver, an environment
that is hostile to any eavesdroppers can be established.  Meanwhile,
the jamming signals are designed in an intelligent way such that the
interferences that the legitimate receiver experiences are kept
low. Two particular approaches are considered. In the first approach,
the jamming subspace was broadcasted to all the participants including
the eavesdroppers before the transmitter starts the
communication. With the knowledge of the publicized jamming subspace,
the helpers can aligned their jamming signals perfectly at the
legitimate receiver, while the legitimate can remove these
interferences completely. At the eavesdropper, due to the randomness
in the channels from the helpers, the interferences it sees occupy the
whole space. In the second approach, we assume such publicized jamming
subspace is not available.  For this case, complete removal of the
interference from the helpers at the legitimate receiver is very
difficult if not impossible. We propose a way to minimize the
interferences the legitimate receiver receives from the helpers. For
both approaches, we will present the asymptotic behavior of the
secrecy rate with respective to the node density of the network, the
area the helpers occupy, and the number of transmit/receive antennas.

                              SPEAKER'S BIOGRAPHY

Jianqi Wang received the B.Eng. degree in automation from Tsinghua
University, Beijing, China, in 1997, the M.S. degree in electrical and
computer engineering from Colorado State University, Fort Collins, in
2002, and the Ph. D. degree in electrical and computer engineering
from Purdue University, West Lafayette, IN. His research interests are
in communication theory and statistical signal processing.


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