Principal Investigator: R. Freeman

Sponsor: National Science Foundation (NSF) CAREER Award, 6/97 – 5/99

A basic purpose of feedback is to reduce the effect of uncertainty on the behavior of a system. When applied inappropriately, however, feedback can also increase the risk of instability and other undesirable phenomena. An obstacle to the successful design of feedback controllers has long been the presence of nonlinearity in models and in real systems. The goal of this project is to develop innovative methods for designing feedback controllers for uncertain nonlinear systems and to educate future engineers and researchers in their application. During the course of this project, the PI will identify those flexibilities in new and existing nonlinear design methods which can be exploited to obtain good controllers for practical applications.

Investigators: A. Haddad and C. C. Lee

Sponsor: Motorola Center for Telecommunications Research, 8/98 – 8/99

This analytical and simulation project explores innovative means of dynamic-source data-rate control and bandwidth allocation in a wireless multimedia network. Besides traditional traffic sources such as voice and packet data, the next-generation wireless network must handle wideband, variable-bit-rate sources having rapidly fluctuating bandwidth demands. These are typically video sources. Significant research has been reported in the video-coding area in dealing with varying-bandwidth availability, and in the dynamic-channel-allocation area in dealing with fluctuating source-data rate. To achieve effective bandwidth allocation while delivering committed quality of service, we are designing and analyzing two-way control algorithms. Here, the bandwidth-allocation algorithm incorporates source-load information (e.g., the video-source outgoing buffer occupancy) in its allocation decisions. Concurrently, the video-source coding algorithm adapts its output data rate to the network-wide load information provided by the bandwidth-allocation algorithm.

Investigators: A. Haddad and C. C. Lee

Sponsor: Motorola, Inc., 7/97 – 7/99

This project studies analytical and simulation models for design, analysis, optimization, and comparison of current and future channel-allocation algorithms for wireless multimedia networks. While analytical models focus primarily on simplified traffic mixes such as constant-bit-rate (CBR) sources combined with bursty packet-data sources, simulation models incorporate all the multimedia traffic types. These include comprehensive source models for: CBR, ABR, VBR, and UBR traffic flows and addresses; call admission; traffic-flow policing; packet scheduling; quality-of-service (QoS) assignment; QoS monitoring; and general performance tracking on a flow-by-flow basis. The latest version of the model implements a token-bucket policing algorithm, a delay-earliest-due-date packet-scheduling algorithm, and a priority-driven RSVP based QoS mechanism. This enables the user to set bandwidth-allocation thresholds for the three QoS classes to achieve desired QoS goals.

Principal Investigator: M. Honig

Sponsor: Army Research Office (ARO), 8/96 – 8/99

The direct-sequence code-division multiple-access (DS-CDMA) communications protocol is attractive for military wireless communications; however, it must overcome the near-far problem. Because the transmitted waveforms are not orthogonal, a source of interference close to the receiver can disrupt communications from a transmitter relatively far away. This project studies the performance of linear minimum mean-squared-error (MMSE) estimation, which is robust with respect to near-far power variations. The focus of this research is on filter adaptation in the presence of time varying channel impairments such as dynamic fading and interference transients. The characteristics of reduced-rank, or subspace, techniques are being studied. Such techniques can significantly improve performance.

Principal Investigator: M. Honig

Sponsor: NSF, 9/96 – 8/99

Reliable communications within a mobile cellular network are hampered by detrimental phenomena such as: fading due to multipath; near-far effects causing power imbalance; multiuser interference; intersymbol interference; and additive thermal noise. Techniques such as multiuser detection and preprocessing at the transmitter can improve error performance and system capacity. This project studies the optimal design of multiuser-transmission schemes for a variety of cellular scenarios, and the adaptation of transmitter-spreading codes in the context of direct-sequence CDMA.

Principal Investigator: M. Honig

Sponsor: Center for Research on Applied Signal Processing, 9/97 – 8/99

This project studies multi-user demodulation of digital signals in the context of GSM and CDMA cellular systems. The receiver is assumed to be randomly located within a particular cell and unable to cooperate with the transmitters. The emphasis is on adaptive multi-user demodulation with limited side information. That is, training data may not be readily available, and near-far effects are likely due to the random location of the receiver relative to the transmitters. We have proposed linear and nonlinear (decision-feedback) types of multiuser detectors for this purpose, and are studying their performance.

Principal Investigator: M. Honig

Sponsor: European Space Agency, 9/97 – 9/98

CDMA is a strong contender for next-generation satellite communications systems. In this project, we study adaptive linear interference suppression techniques for the satellite forward link. To improve performance and capacity, other techniques are considered. These include convolutional coding and decoding, power control, and dual-satellite diversity. We have studied the trade-off between spreading gain and the convolutional code rate, and have evaluated the performance of a one-step power-control scheme with diversity. We conclude that adaptive linear interference suppression technique can significantly boost the quality of service and system capacity.

Principal Investigator: M. Honig

Sponsor: Army Research Office, 8/99-7/02

This project is concerned with signal processing and coding techniques for Direct-Sequence (DS)-Code-Division Multiple Access (CDMA) in a peer-to-peer network. Topics to be investigated include the performance of adaptive interference suppression algorithms in the presence of wireless channel impairments, combined coding and adaptive interference suppression, and joint adaptation of transmitters and receivers.

Investigators: M. Honig, S. Jordan, A. K. Katsaggelos and C. C. Lee

Sponsor: Motorola Center for Telecommunications Research, 8/98 – 8/99

This project investigates methods for supporting wireless multimedia communications. The work is aimed at enhancing the capabilities of current wireless technologies such as code-division multiple access, which is used for mobile cellular voice services.

Principal Investigator: S. Jordan

Sponsor: NSF, 9/96 – 8/99

This project is concerned with the allocation of specific network resources (buffer and bandwidth) to users and to virtual paths in an asynchronous transfer mode network. The research concentrates on developing a framework to analyze this resource-allocation problem. The goal is to efficiently allocate bandwidth and buffer to make the maximum number of users as happy as possible. Further, it is desirable that any such mechanism be distributed both hierarchically and geographically. Work is aimed at developing a framework to jointly allocate buffer and bandwidth, studying the use of priorities to replace explicit reservation of resources, and analyzing the resulting network dynamics.

Principal Investigator: S. Jordan

Sponsor: AT&T, 9/94 – 8/99

This grant upgrades and expands computer and networking equipment for the ECE Department’s Networks and Communications Laboratory. The equipment will be used for undergraduate telecommunications courses and research projects related to networked computing and wireless communications. The project addresses the integration of multiple heterogeneous services onto a single network.

Principal Investigator: C. C. Lee

Sponsor: Motorola, Inc., 10/96 – 12/99

This project involves performance modeling of Motorola’s EMX-2500 cellular switch and DMX switch network. The modeling strategy exploits accuracy, efficiency, configurability, and maintainability. The models provide performance-management capabilities such as: capacity analysis and planning; bottleneck projection and prevention; performance impacts by new switch features and / or applications; system parameter and message-handling logic optimization; overload control algorithm design and evaluation; etc. Simulations based on the models should reveal transient performance problems in addition to the average performance projected by conventional benchmarking.

Principal Investigator: C. C. Lee

Sponsor: U.S. Robotics, Inc., 9/96 – 12/99

This project is designing a simulation model to allow performance evaluation and design optimization for a communications system architecture that incorporates the interface of dial-up and packet-data networks. Specifically, the model deals with modem-based data traffic on one side and TCPIP-based Internet traffic on the other. Simulations designed and run based on this model have been successfully used to predict bottlenecks caused by unanticipated system architectural problems. The simulation results also reveal potential instability problems that can cause the system throughput to decline when the number of active lines increases.

Principal Investigator: C. C. Lee

Sponsor: Illinois Superconductor Corp., 5/93 – 12/99

This analytical and computational project evaluates cellular and PCS system capacity with conventional or superconducting RF front-end filters. It also explores the intersystem interference caused by insufficient front-end filtering, intermodulation due to nonlinearity in RF amplifiers and mixers, and system power differential due to power controls.

* (For ease of identification, each citation in this and the following sections will begin with the group faculty member(s)’ name(s))

R. Freeman, M. Krstic, and P.V. Kokotovic, "Robustness of adaptive nonlinear control to bounded uncertainties," Automatica, vol.34, no. 10, Oct. 1998, pp. 1227-1230.

S. Jordan, Y. Argyropoulos, and S.P.R. Kumar, "CDA in Interference-Limited Cellular Systems with Uneven Traffic Distributions", IEEE Transactions on Vehicular Technology, January 1999, pp. 224-232.

R. Freeman and H. Ito, "Generalized state-dependent scaling: backstepping for local optimality, global inverse optimality, and global robust stability," Proceedings of the 1999 European Control Conference, Karlsruhe, Germany, Aug. 1999.

R. Freeman and H. Ito, "A new look at robust backstepping through state-dependent scaling design," Proceedings of the 1999 American Control Conference, San Diego, June 1999.

R. Freeman, B. Miller, and J.E. Colgate, "Passive implementation for a class of static nonlinear environments in haptic display," Proceedings of the 1999 IEEE International Conference on Robotics and Automation, Detroit, May 1999.

Haddad, and K-S. Lee, "Stabilization of Stochastic Quantized Control Systems," Proc. 1999 American Control Conference, San Diego, CA, pp. 965-969, June 2-4, 1999.

A. Haddad and K-S. Lee, "Quantized Control of Stochastic Stable Linear Systems", Proc. 14^th IFAC World Congress, Beijing, CHINA, Vol. J., pp 265-270, July 5-9, 1999.

M. Honig, and R. Ratasuk, "Adaptive Multiuser Decision-Feedback Demodulation for GSM", Allerton Conference on Communication, Control, and Computing, Monticello IL, Sept. 1998.

M. Honig, "Review of Multiuser Detection and Interference Suppression Techniques for Satellite DS-CDMA", Proc. International Workshop on Digital Signal Processing Techniques for Space Applications, European Space Agency, Noordwijk, Holland, Sept. 1998.

M. Honig and J-B Kim, "Outage Probability of Multi-Code DS-CDMA With Linear Interference Suppression", IEEE Military Communications Conference, pp. 248-252, Bedford, Massachusetts, Oct. 1998.

M. Honig and J. S. Goldstein, "Adaptive Reduced-Rank Residual Correlation Algorithms for DS-CDMA Interference Suppression", Asilomar Conference on Signals, Systems, and Computers, Pacific Beach, Ca., Nov. 1998.

M. Honig, W. Xu, J. Zeidler, and L. B. Milstein, "Subspace Adaptive Filtering Techniques for Multi-Sensor DS-CDMA Interference Suppression in the Presence of a Frequency-Selective Fading Channel", Asilomar Conference on Signals, Systems, and Computers, Pacific Beach, Ca., Nov. 1998.

M. Honig, W. Phoel and B. Vojcic, "Coded Performance of MMSE Receivers for DS-CDMA", Conference on Information Sciences and Systems, The Johns Hopkins University, Baltimore, MD, pp. 249-254, March 1999.

M. Honig and W. Phoel, "MMSE Space-Domain Interference Suppression for Multi-Rate DS-CDMA", IEEE Vehicular Technology Conference, Houston, TX, May 1999.

M. Honig and G. Rajappan), "Multi-Dimensional Amplitude Control for DS-CDMA", IEEE Vehicular Technology Conference, Houston, TX, May 1999.

M. Honig and R. Ratasuk, "Multi-Stage Multiuser Decision Feedback Detection for DS-CDMA", IEEE International Conference on Communications, pp. 68-72, Vancouver, CA, June 1999.

C.C. Lee, and Y. C. Chen, "RF Front-end Nonlinearity and DS/CDMA Communication System Performance), Proc. 33^rd Annual Conference on Information Sciences and Systems, March 16-18, 1999, pp. 771-776.

R. Freeman "On the passivity of haptic displays of nonlinear virtual environments" University of California, Santa Barbara, March 1999.

M. Honig, "Adaptive Reduced-Rank Residual Correlation Algorithms for DS-CDMA Interference", Asilomar Conference on Signals, Systems, and Computers, Pacific Beach, Ca., Nov. 1998.

M. Honig, "Blind Adaptive Space-Time Multiuser Detection", Center for Research on Applied Signal Processing Semi-annual Research Review, Fort Meade, MD, March 1999.

M. Honig "Multiuser Detection for Satellite CS-DCMA", Sixth International Workshop on Digital Signal Processing for Space Applications, European Space Agency, Noordwijk, The Netherlands, September 1998.

M. Honig, " Adaptive Reduced-Rank Interference Suppression", University of South Australia, Adelaide, August 1999; Sydney University (Australia), August 1999; University of Newcastle, August 1999.

M. Honig, session chair, "Adaptive Techniques in Wireless Communications", Communication Theory Workshop, California, May 1999.