Codes and Tracking Receiver for an Experimental Spread Spectrum Multiple Access System
S.L. Maskara, K. Sudhakar, K. Ramamurthy · IETE Journal of Research · 1981
An experimental spread-spectrum system, with a band-width expansion of 100 times, to transmit 32 kbps ADM speech signals over a channel bandwidth of 3.2 MHz has been designed. The receiver, comprising of a delay-lock-loop tracking system has been built. The performance of the baseband portion of the DLL has been measured in the presence of noise and it is found that the speech can be recovered satisfactorily with an input SNR of—8.2 dB. The system has a capability of catering for 12 active subscribers simultaneously. For the purpose of allocating distinct codes and sequences to address the individual subscribers, the correlation functions of Gold codes have been computed. Out of the 129 possible Gold codes of length 127 each, 12 or more addresses can be selected for the subscribers. Techniques of generating the Gold codes and maintaining them have been discussed.