Separation of CDMA spread spectrum signals

Abstract

CDMA spread spectrum signaling techniques have gained increasing importance over the past few years. Long used in military systems such as GPS, they are finding increased usage in the burgeoning cellular communications market. From the view point of an interceptor, CDMA formats pose two problems. First is the spread spectrum nature of the format. This implies that the intercept receiver, without the benefit of the spreading code, must use the fully occupied bandwidth of the signal. This in turn implies that the received SNR can be considerably less than 0 dB. This is, of course, is one reason for using this technique. The second is that in the CDMA multiplexing all users occupy the same bandwidth, at the same time, with the same modulation format. Unless some form of spatial separation is possible, there is little information available from which separation can be obtained. We describe a procedure by which CDMA separation can be obtained. This algorithm is best considered as an initial detection concept by which basic information on the signal is obtained and perhaps handed off to an analysis receiver.<>