Power spectrum, anti–intercept and SN ratio characteristics of direct sequence spread spectrum communication systems using FIR and IIR filters
Hiroji Kusaka, Fujio Nishida, Yoshihito Simazaki · Electronics and Communications in Japan (Part I Communications) · 1987
Abstract The time series generated from a direct sequence spread spectrum (DS‐SS) signal can be expressed in terms of an auto‐recursive (AR) model. An all‐zero FIR filter (FIRF) and an all‐pole IIR filter (IIRF), which are the inverse to each other, consist of the parameters of the AR model. We propose a spread spectrum communication system using an FIRF on the transmission side and an IIRF on the receiving side as well as a system using an IIRF on the transmission side and an FIRF on the receiving side. The former is called the DS‐SS communication system using FIR‐IIR filters and the latter using IIR‐FIR filters. When the order and the delay time in the delay element (the order and the sampling time interval, respectively, of the AR model of filters are selected properly by the former system, the power spectral density (psd) of the transmission signal can be spread more than that of the DS signal so that the density is lower and the peak value is suppressed. By the latter system, an optimum transmission becomes possible in the sense that the SN ratio is maximum within the main lobe of the psd of the DS signal. Further, the pulse duration time of the rectangular pulse train of the transmitted signal in both systems is transformed to the selected delay time. Since the amplitude of the pulse train changes randomly, both systems have an anti‐intercept property such that interception is almost impossible.