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. ***
