Delay constrained communication over wireless fading channels
The design of communication systems for wireless channels is very challenging because of time-varying nature and low reliability of
wireless channels. The design is especially challenging for
applications that demand both, high data rate and stringent delay
bounds. Delay constrained communication require reliability of
communication in terms of low decoding error probability, as well as
guarantees on delay violation probability. Traditionally, low
decoding error probability is ensured through the design of the
physical layer, while low delay violation probability is ensured
through the design of the link layer. The two layers are designed
separately, even though the defining performance (quality of service)
constraints span two different layers.
In this work, we present a cross-layer framework for a joint design of
the physical and link layers. This framework combines ideas from coding
theory and queuing theory, resulting in the 'queued-code'. Theoretical
analysis has shown the benefit of using the queued-code, for delay
constrained communication over fading wireless channels. The analysis
shows that the queued-code must balance the requirements of queuing and
coding, leading to a satisfying symmetric result. We have also
implemented queued-codes based on low density parity check (LDPC) codes
to show the practicality of our approach.
Physical layer security using 'artificial noise' The broadcast nature of the wireless medium makes
communication over this medium extremely convenient, by allowing for
untethered access to voice, multimedia and data services. However, the
broadcast nature also makes it easy to eavesdrop on any communication
over this medium. The traditional approach for ensuring privacy of
communication is to use encryption (typically, symmetric). The
difficulty in decoding the secret message is based on a known difficult
problem, e.g., prime factorization. This approach requires the exchange
of a shared secret key, between the transmitter and the receiver. In
contrast, provable secrecy can be obtained using a coding approach
(where information theoretic analysis provides a proof of secrecy).
This form of secrecy is called information theoretic secrecy, and the
secrecy remains intact regardless of the time and computational
resource utilized by the eavesdropper in attempting to decode the
secret message.
The motivation of this research is to use the properties of the
wireless medium, to enhance the secrecy of communication at the
physical layer. The key idea in this research is to transmit
'artificial noise' along with the information bearing signal, using
multiple transmit antennas. The transmission scheme is designed such
that the artificial noise is canceled at the receiver, but not at the
eavesdropper (since, in general, the eavesdropper's channel is different from the receiver's channel).
Thus, the receiver only receives the information bearing signal, while
the eavesdropper receives both, the information bearing signal as well
as the artificial noise. Thus, the eavesdropper's channel is
selectively degraded, and hence, secrecy is guaranteed using
information theoretic results. A key result of this research shows that
the behavior of 'MIMO Secrecy Capacity' and 'MIMO Capacity' is
different, thus showing that secrecy constraints can modify the
behavior of channel capacity.
The following colleagues have graduated. It was a pleasure working with them.
Arjunan
Rajeswaran
Gyouhwan
Kim
Sungchul
Han
Xun Zhang
Yaron
Rachlin
Papers
R. Negi,
and S. Goel, "An information-theoretic
approach to queuing in wireless channels with large delay bounds,"
Proc. IEEE Globecom, vol. 1, pp. 116-122, Dallas, USA, Dec. 2004. (pdf)
R. Negi
and S. Goel, "Secret Communication using
Artificial Noise," Proc. IEEE Vehicular Tech. Conf, vol. 3, pp.
1906-1910, Dallas, Sept. 2005. (pdf)
S. Goel
and R. Negi, "Secret Communication in
Presence of Colluding
Eavesdroppers," Proc. IEEE Military Communication
(MILCOM), vol. 3, pp.
1501-1506, Atlantic City, Oct. 2005. (pdf)
S. Goel and R. Negi, "The Queued-Code
in Finite-State
Markov Fading Channels with Large Delay Bounds," Proc. IEEE ISIT, pp.
30-34, Seattle, USA, July 2006. (pdf)
S. Goel and R. Negi, "A Queued-Code
Based on LDPC Block
Codes," Proc. IEEE Globecom, pp. 3255-3259, Washington, DC, USA, Nov.
2007. (pdf)
S. Goel and R. Negi, “Guaranteeing Secrecy using Artificial Noise,” IEEE Trans. Wireless Communications, vol. 7, no. 6, pp. 2180-2189, June 2008.
S. Goel and R. Negi, “Multiuser Diversity in Cellular Downlink using the Queued-code,” to appear in Proc. IEEE Globecom 2008.
Contact
Email
satashug
"at" ece.cmu.edu
Phone
412-268-4488
Mailing Address
HH 1111,
Hamerschlag Hall
Carnegie Mellon University
5000 Forbes Avenue
Pittsburgh, PA 15213-3890, USA