Codes and Tracking Receiver for an Experimental Spread Spectrum Multiple Access System

Abstract

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.

Indexing Terms:

• SSMA
• Gold Codes
• ACF
• CCF

Additional information

Notes on contributors

K. Sudhakar

Sudhakar, K: Born at Kandukur in Prakasam district, Andhra Pradesh in November, 1956. He received his Bachelor's degree in Electronics and Communications Engineering from Regional Engineering College, Warangal in 1978 and Master's degree in Microwave and Radar Engineering from Indian Institute of Technology, Kharagpur in 1980. He worked as Senior Research Assistant in Radar and Communications Centre, I.I.T., Kharagpur for one year and was engaged in research and development work in Spread Spectrum Techniques and Fibre Optic Communication. At present he is in TTC, Jabalpur.

K. Ramamurthy

Ramamurthy, K: (b. 1955 Feb. 9). Received B Tech in Electronics & Comm. Engg. from Jawaharlal Nehru Technological Univ., Hyderabad in 1977 and MTech with specialization in Microwaves & Radar Engg. from IIT, Kharagpur in 1979. Currently associated with design & development of Avionics Communications Systems at Hindustan Aeronautics Ltd., Hyderabad.