The problem of data transmission over noisy discrete memoryless channels is considered when the arrival of data is bursty and is subject to a delay deadline. In this setting, the errors experienced by the source of information, concatenated with an infinite buffer and a noisy channel, are caused by either erroneous decoding at the receiver or violation of the delivery deadline. It is intuitive, then, that there is a trade off between reliability over the channel and timely delivery of information. Briefly revisiting the difficulty in quantifying the above trade-off in its classical Shannon Theoretic context, we have addressed this problem in particular instances with and without feedback:
R. Swamy and T. Javidi. Delay analysis of block coding over a noisy channel with limited feedback. Conference
Record of the Forty Second Asilomar Conference on Signals, Systems and Computers (ASILOMAR) Oct. 2008 [here]
R. Swamy and T. Javidi. Delay analysis of block coding over a noisy channel with limited feedback. Proceedings of
IEEE International Symposium on Information Theory (ISIT). July 2009 [here]
Unfortunately, the above analysis quickly become analytically intractable and not so elegant beyond the simple intuitions they provide. We have also taken advantage of the high SNR analysis of outage-limited channels to go around this difficulty. Hence, the focus of the work becomes to characterize the error performance of the overall system in the high SNR regime:
S. Kittipiyakul, P. Elia, and T. Javidi. High-SNR analysis of outage-limited communications with bursty and delay-limited information IEEE Trans. Inf. Theory, v. 55, no. 2, pp. 746-763, Feb 2009. [ .pdf]
S. Kittipiyakul and T. Javidi, Optimal operating point for MIMO multiple access channel with bursty traffic IEEE Trans. on Wireless Communications, v. 6, no. 12, Dec. 2007. [ .pdf]
S. Kittipiyakul and T. Javidi, Optimal operating point in MIMO channel for delay-sensitive and bursty traffic ISIT'06, July 2006. [ .pdf]
This characterization motives novel queuing theoretic work on a many source large deviation analysis of queues with batch service and/or multi-queue systems with Max-Weight scheduling policies. In particular, we use a recent extension of contraction principle, due to Garcia, to arrive at the appropriate large-deviation of a queue concatenated by a Max-weight scheduled multi-user channel, which is of independent interest.
Subramanian, V.G.; Javidi, T.; Kittipiyakul, S. Many-Sources Large Deviations for Max-Weight Scheduling. Information Theory, IEEE Transactions on , vol.57, no.4, pp.2151-2168, April 2 [here]
Many problems of information processing in networks are best modeled as a generalization of the classical multi-server multi-queue problem with scheduling constraints [1-5]. These problems are often mapped to a family of Markov decisions problems (MDPs) and partially observed MDPs (POMDPs). By identifying the optimal server allocation policies analytically or their salient structures, we can bypass the computational complexity and significantly improve the performance in terms of delay, blocking probabilities, or revenue/cost. My contributions in this area build on tractable models and are analytical in nature.
T. Javidi, N. Song, and D. Teneketzis. Expected Makespan Minimization in Two Interconnected Queues on Identical Parallel Machines. Journal of Probability in Engineering and Information Science, vol. 15, pp 409-443, 2001[pdf]
An extended version can be found here.
T. Javidi and D. Teneketzis. An Approach to Connection Admission Control in Single-hop Multi-service Wireless Networks with QoS Requirements. IEEE Transactions on Vehicular Technology, July 2003 [pdf]
N. Ehsan and T. Javidi, Delay Optimal Transmission Policy in a Wireless Multi-access Channel. IEEE Transactions on Information Theory, Volume 54, Issue 8, pp. 3745 – 3751, August 2008 [pdf]
S. Kittipiyakul and T. Javidi, Delay-Optimal Server Allocation in Multi-Queue Multi-Server Systems with Time-Varying Connectivities. IEEE Transactions on Information Theory. Volume 55, Number 5, April 2009 [pdf]
T. Javidi. Cooperative and Non-cooperative Resource Sharing in Networks: A Delay Perspective. IEEE Transactions on Automatic Control, Volume 53, Number 9, pp 2134-2142, October 2008 [pdf]
Subramanian, V.G.; Javidi, T.; Kittipiyakul, S. Many-Sources Large Deviations for Max-Weight Scheduling. Information Theory, IEEE Transactions on , vol.57, no.4, pp.2151-2168, April 2 [here]
But more importantly, they enable simple-to-implement heuristics, e.g., practical subcarrier allocations for OFDMA, or new buffered architecture for throughput optimal scheduling for switching:
S. Kittipiyakul and T. Javidi, Resource allocation in OFDMA with time-varying channel and bursty arrivals, IEEE Communications Letters, v. 11, no. 9, pp. 708-710, Sept 2007 [pdf]
T. Javidi, R Magill, and T. Hrabik. A High Throughput Scheduling Algorithm for a Buffered Crossbar Switch Fabric. In Proceedings of IEEE International Conference on Communications, vol. 5, pp. 1586-1591, 2001 [.pdf]
With the success of wireless communication techniques many novel applications and issues have emerged. One such application is communication under secrecy constraints. The maximum rate of information transfer from a transmitter, Alice, to a receiver, Bob, secret from an eavesdropper, Eve, known as secrecy capacity between Alice and Bob, has been a topic of study for multiple decades. We have studied the secrecy capacity of a communication systems where there is an additional rate-limited secret feedback channel from Bob to Alice. The work sheds light on the significance of secret feedback channel and its role in increasing secrecy.
Ardestanizadeh, E.; Franceschetti, M.; Javidi, T.; Young-Han Kim. Wiretap Channel With Secure Rate-Limited Feedback. IEEE Transactions on Information Theory, vol.55, no.12, pp.5353-5361, Dec. 2009 [here]
Another area of interest is in the domain of coordinated multi-vehicle motion planning and control. Prior to joining UCSD, I collaborated with Prof. K. Morgansen at the University of Washington, Seattle, to develop an integrated communication and control architecture for coordinated control of multi-vehicles. Along with our graduate students, D. Klein and P. Lee, we established a trade-off between communication costs and cost of control in the control of vehicles with Kuromoto under-actuated controllers. We further extended the heading control problem by considering a randomized scheme for achieving consensus in a network.
D. Klein, P.Lee, K. Morgansen and T. Javidi, "Integration of Communication and Control using Discrete Time Kuramoto Models for Multivehicle Coordination over Broadcast Network," IEEE Journal on Selected Areas in Communications, v. 26, no. 4, pp. 695-705, May 2008. [pdf]
R. Pagliari, M.E. Yildiz, S. Kirti, K. Morgansen, T. Javidi, and A. Scaglione. A Simple and Scalable Algorithm for Alignment in Broadcast Networks. in IEEE Journal on Selected Areas in Communications, August 2010 [here]
Wired and wireless networks can be viewed as economies where the goods are bandwidth, buffer size, and power. The goals and characteristics of network design and management also match the requirements and characteristics usually associated with economic markets in many aspects such as scalability, efficiency, and decentralization. My former PhD student, Jennifer Price, and I used simple and basic ideas in microeconomics to design and analyze wireless and wired networking protocols.
J. Price and T. Javidi. Decentralized Rate Assignments in a Multi-Sector CDMA Network. IEEE Transactions on
Wireless Communications, December 2006 [pdf]
J. Price and T. Javidi, Leveraging Downlink for Efficient Uplink Allocation in a Single-Hop Wireless Network. IEEE Transactions on Information Theory, v. 53. no. 11, Nov 2007. [pdf]
J. Price and T. Javidi, Distributed Rate Assignments for Simultaneous Interference and Congestion Control in CDMA-Based Wireless Networks. IEEE Transactions on Vehicular Technology, Volume 57, Issue 3, May 2008 [pdf]
J. Price and T. Javidi. Network Coding Games with Unicast Flows. IEEE Journal on Selected Areas in Communications, Volume 26, Issue 7, pp. 1302 – 1316, September 2008 [pdf]