|
Research Interests
I am interested in the theory and design of wireless communications at
the physical layer. I use tools from information theory, communications theory and signal
processing.
Specifically, I have been interested in the following topics:
-
Cooperative Communications.
-
Relay Networks.
-
Multi-user Information Theory.
-
Multi-carrier modulations (OFDM, MC-CDMA) .
-
Adaptation of Wireless Transceivers.
Research
Projects
Current:
Relay Networks:
Relay channels has recently witnessed a
renaissance due to the interest in
infrastructureless wireless networks. Relaying is one way to
increase a network's spectral efficiency given power, size and cost
constraints of individual nodes. Even for networks with fixed
infrastructure, on top of increasing throughput and enhancing
network reliability, relaying can provide a feasible solution
to coverage extension to dead spots. We are currently
studying new aspects of a three-terminal relay channel which is a
building block of larger networks. We propose a model where
peer-to-peer communications is allowed on top of the relayed signal.
Performance limits and capacity characterization have been
investigated. This project is funded in part by the "National
Science Foundation (NSF)".
Visit
Ramy's collection of: Resources for Relay Channels and Cooperative
Communications. New!
Past:
Doppler Spread Estimation:
Doppler spread is a parameter that provides a
measure of the fading rate of the channel. It's estimation provides
adaptation capabilities to wireless transceivers resulting in better
performance (QoS, BER, etc.). The project was centered around obtaining
a reliable Doppler spread estimate and using this estimate for adapting
mobile OFDM systems. The target application was mobile Wimax
(IEEE802.16e). An algorithm for reliable Doppler estimation in OFDM
systems was developed and reported in a conference paper. This
project was supported by "Logus
Broadband Wireless Solutions".
Interference Cancellation in MC-CDMA:
MC-CDMA or OFDM-CDMA is a multi-user OFDM scheme
that provides frequency diversity against the fading channel. Data of each user is spread in frequency using a unique spreading code. The
codes are chosen to be orthogonal. However, in the uplink, signals
coming from different users are no longer orthogonal since each of them
face a different channel to the base station. This severely
degrades the BER performance, and interference cancellation / multi-user detection
(MUD) techniques become necessary.
Since MC-CDMA performance suffers due to carrier
frequency offsets between receiver and transmitter (as in all OFDM-based
systems), it is of interest to study how this affects a MC-CDMA system
employing interference cancellation at base station. Successive
ineterference cancellation was chosen due to its low complexity
compared to other MUD techniques. Closed form expressions for BER were
obtained showing the performance at various offsets and loads (number of
users). Results were reported in two conference papers.
|
