R.F. Synchronization in DSPN-SSMA Systems

The presence of additive Narrow-band Gaussian noise at the input of an SSMA receiver will result in a disturbance which is analogous to that which causes ´spikes´ in FM systems. This disturbance will not manifest itself as a ´spike´ at the output of an SSMA receiver but may cause loss of r.f. synchronization and hence erroneous chip detection. Most Direct-Sequence Pseudo-Noise-SSMA (DSPN - SSMA) receivers operate at low or negative input Carrier-to-Noise Ratios (CNRs). At such low CNRs the frequency of occurence of this disturbance is high. Below a ´threshold´ CNR the frequency and nature of this disturbance may result in the number of chips in error exceeding the permissible number for a given PN code resulting in degradation of system performance. The Zero-crossing Analysis [1] offers a definite clue to the nature of this disturbance and predicts a higher frequency of its occurance than is given by Rice´s model. It is believed that the study of r.f. synchronization in DSPN-SSMA systems using the Zero-crossing Analysis presented in this paper is a new approach.