Effects of channel distortion on code tracking error in DS spread spectrum systems

The delay locked loop tracking circuit of a typical direct sequence spread spectrum system has been analysed to find an analytical expression of the tracking error bias due to the presence of linear channel distortions, independently of their origin (for instance, due to band limitations and/or multipath propagation). Moreover, the influence of the tracking error on system performance, in terms of variation of received energy per bit at the input of the data demodulator, has been determined. A real multipath indoor transmission channel with band limitations due to transmitter and receiver filters has been considered as an application example of the formulas described. In this context, both multipath components with delays shorter and longer than the chip time have been examined, and results have been compared with those achievable considering an ideal synchronisation on the first path.