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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:
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Cooperative Communications and Relay Networks.
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Cognitive radio and coexistence between wireless
services.
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Multi-user Information Theory.
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Space-time processing (MIMO and MU-MIMO)
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Multi-carrier modulations (OFDM, MC-CDMA) .
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Adaptation of Wireless Transceivers.
Research
Projects
Current:
Relay Networks:
Relay channels have recently witnessed a
renaissance due to the interest in wireless networks with no or
minor infrastructure. Relaying is one way to
increase a network's spectral efficiency given power, size and cost
constraints on 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.
My major research accomplishments so
far in the area of relay networks are:
1-
Proposing relay selection algorithms that achieve
the best reported
diversity-multiplexing tradeoff for the class of decode-and-forward
multi-relay networks
(Project Digest).
2- Proposing the use of MIMO relay to manage the
interference in Interference Networks. We reported the first case of
achieving full
degrees-of-freedom.
3- Proposing a bandwidth efficient three-node
channel model, “Relay channel with private messages” and performed a
capacity analysis
(Project Digest).
This project is funded in part by the "National
Science Foundation (NSF)" (check UTD's
announcement).
Visit
Ramy's collection of: Resources for Relay Channels and Cooperative
Communications.
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.
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