Robert A. Scholtz - US grants

VLSI design and test equipment will be provided for researchers at the University of Southern California for research in the Department of Electrical Engineering. This equipment is provided under the Instrumentation Grants for Research in Computer and Information Science and Engineering program. The research for which the equipment is to be used will be in the study of communication signal processing algorithm implementations on VLSI chips.

9400628 Scholtz Spread spectrum (SS) communications, once a military approach to jam-tolerant modulation design, is now being considered seriously for commercial purposes. The typical military design, using a form of SS modulation called code-division multiple access (CDMA), requires that each multiple access channel be assigned a distinct spreading code that makes a user's transmission look like wide-band noise to a receiver attempting to listen to another user's transmission. This noise, called multiple access noise, is generated in the receiver's correlator, and is related to the cross correlation properties of the signals employed by different users. It is a primary limitation to the multiple access system's capacity. Recently research has been directed toward a common code multiple access (CCMA) system in which all of the users employ the same wideband noise like carrier which is repeated every baud interval. Signals are separated at the receiver simply by their arrival times, because wide bandwidth signals have inherently a high time of arrival resolution capability. Hence two signals that are present at the same time do not catastrophically interfere (collide) with each other, unless their baud clocks are aligned to within the reciprocal of the common wideband carrier's bandwidth. If matched filter (correlation) reception is used in this environment ,then the system suffers degradation caused by both multiple access noise and collisions. In contrast to matched filter reception, inverse filter reception nearly eliminates multiple access noise in the receiver at the cost of a small delay (a few baud times) in the receiver. Inverse filters have been developed primarily for RADAR applications. One recent paper has proposed common code modulation with inverse filtering as a receiver. The objective of this project is to determine if CCMA systems with inverse filtering as a receiver component are competitive with or superior to traditional CDMA syst ems. Particular attention will be given to: (a) the tradeoff between the residual multiple access noise and processing delay in an inverse filter receiver, (b) signal design optimization, (c) the effects of multipath and impulsive noise on common code receiver design and system capacity, and (d) approaches to hybridizing CDMA matched filter systems with common code inverse filter systems to obtain a system that has the stronger points of each modulation. Potential payoffs include increased system capacity because of multiple access noise elimination, reduced power control requirements, and simpler central receivers, all in a system architecture with complexity comparable to current designs. If the payoffs turn to be real, a new paradigm for multiple access design will result. ***

9601804 Scholtz, Robert A. Choma, John J. University of Southern California Academic Research Infrastructure: Acquisition of Instrumentation for Testing of Ultra-Wideband Wireless and Wired Communications and Design of Enabling Instruments This Academic Research Infrastructure award supports the acquisition of very high speed analysis and test equipment for research on high speed communication networks. The research projects supported by the equipment are: 1. The design and implementation of ultra-wideband wireless and wired computer network systems. 2. An experimental research project on the design of an impulse radio wireless network for Ghz bandwidth base stations. 3. A research program in ultra high-speed circuit and test fixturing.

In this proposal a complete study of fundamental issues, both experimental and analytical, in ultra-wideband (UWB) radio is presented. The proposed work involves a strong interaction between experimental and analytical components, so that experimentally derived models can be used to design optimized algorithms, which can in turn be tested. For this purpose, radio, video, and test equipment is requested to complement existing facilities in the ultra-wideband radio lab (UltRa Lab). This equipment will be used for closely related research projects that support the development of fully mobile indoor video communication systems. The motivating wireless technology is spread-spectrum impulse radio which alleviates multipath problems, but must coexist in the same spectrum with signals in the frequency range from roughly 500 MHz to 2 GHz. The experiments are aimed at (1) quantifying the ability of different radio systems to coexist in the same band without mutually interfering, (2) quantifying the distortion properties of ultra-wideband antennas and propagation environments, and (3) measuring the effects of indoor radio performance anomalies on video transmissions. The equipment requested includes anechoic chamber components, a flexible software video compression system, high quality LANs that can be utilized in both the video and radio interference experiments, and a bit error-rate tester and other components necessary for interference and coexistence tests. These experiments will result in a database of channel measurements, which characterize propagation, antenna, and interference effects. The database will be used to extract statistical models which, in turn, will be used to develop algorithms for receiver signal processing and video rate control. This process of experimentation, model extraction, and algorithm development will be iterated throughout the duration of the requested support. Each of these experiments is briefly described below.

(1) Interference Rejection and Coexistence Experiments and Analysis (Scholtz and Chugg). This experimental work will explore the ability of impulse radio with power spectrum thinly spread roughly from 500 MHz to 2 GHz to coexist over short range channels with the myriad of other electronic systems in that broad spectrum. This effort will test coexistence with LANs, cordless phones, microwave ovens, wireless TV links, etc. The processing gain of the spread-spectrum techniques employed in the impulse radio will be checked and the dynamic range of current impulse radios will be tested. These experiments will determine the direction of research efforts on impulse radio implementation.

(2) Characterization of ultra-wideband antennas and propagation environment (Prata, Chugg, Scholtz). The experimental work to be carried out in the controlled environment of an anechoic chamber supports the characterization of ultra-wideband antennas for impulse radio, and the characterization of narrower-band antennas to evaluate their ability to receive/reject impulses. This environment will be used to evaluate new UWB antenna designs that provide more robust spatial coverage, better pulse shaping characteristics, polarization diversity, and to study the propagation of UWB signals through different kinds of materials. The equipment purchased under this grant is destined for an anechoic chamber atleast 15' (w) x 15' (h) x 30' (l) to be constructed in the near future (architectural work on the building containing this chamber is beginning now).

(3) Experiments with Software-Compressed Asynchronous Video over UWB Wireless Links (Ortega, Chugg). Two stages are planned in the experimental work with robust asynchronous video transmission. In a first stage, laptops and wireless LAN equipment will be used to test techniques, which are currently under study for rate control over a time varying channel. All video functions (compression, rate control, error correction, retransmission, etc.) will be implemented in software. In a second stage the algorithms will be adapted to operate over an experimental impulse radio link. At that point the results from the initial stage will be incorporated and also changes needed for the particular transmission conditions of impulse radio will be implemented.

Each of the student researchers supported under the requested funding will be involved in all three of these aspects. This research will be further supported by the UltRa Lab infrastructure, which has been developed recently under the support of NSF and through the Integrated Media System Center ERC and our industrial sponsors. The infrastructure includes laboratory space, equipment, a team of undergraduate merit scholars to assist in laboratory procedures, and access to circuit and semiconductor process expertise from both USC collaborators and industrial partners. The research described in this proposal is a portion of the fundamental investigations required to develop and demonstrate UWB indoor radio multimedia systems (complementary investigations into integrated circuit design are also necessary, but are not part of the research proposed herein). The original equipment budget for this proposal has been revised to reflect equipment acquisitions from other sources and no other proposals for this work are currently pending.

Research Objectives and Approaches:
The objective of this research is the development of measurement instrumentation that will enable (i) measurement of distributed wireless propagation channels with ultra-wide bandwidth and (ii) design, measurement and validation of distributed wireless systems for communications, localization, and radar. The instrumentation is thus intended to explore both the fundamental principles of distributed wireless propagation channels and systems, as well as to enable the development and testing of practical distributed wireless systems that go far beyond current systems. The approach is based on a combination of state-of-the array channel sounding with electro-optical signal conversion. By converting wideband microwave signals to optical signals, which are transmitted via optical fibers, widely separated antennas can be operated by a single high-precision signal source/receiver in a synchronized manner.

Intellectual Merit:
Firstly, the development activity will push the frontiers of electro-optical modulation. Secondly, the instrument enables many measurements that will for the first time answer some of the fundamental questions related to wireless propagation in distributed systems, such as the correlation of shadowing, delay spread, and angular spread at widely separated transmitters/receivers. Further intellectual merit is obtained from the use of these measurement results to stimulate and test novel theoretical ideas.

Broader impact:
Measurements with the developed instrumentation will help to enable novel applications of distributed wireless systems (many of which are ?Grand Challenges? defined by the National Academy), such as wireless health and remote monitoring of vital signs, distributed localization for emergency responders, high-efficiency video distribution systems, and many more.