| The rapid growth of the cellular telephone industry has presented the wireless communications market with the challenge of overcoming the capacity and quality limitations of the present AMPS (Advanced Mobile Phone Systems) analog system. The growing number of users and a limited broadcast spectrum designated for cellular communications causes overcrowding in the spectrum, which in turn causes dropped calls, blocked calls, and overlapping conversations, or "cross talk". CDMA technology provides a 10-to-20 fold increase in capacity over the present system, better voice quality, and more privacy.In this paper, the fundamentals of spread spectrum code-division-multiple-access are reviewed and related to the advantages of CDMA listed above. A simulation is made using a 16-bit signal and a 31-chip PN code sequence in order to test the principles behind CDMA. The model used for the simulation is based on a basic spread spectrum system composed of multipliers, adders, a matched filter, and a decision device that are realized through the use of C programming. Knowledge of the PN code characteristics both at the transmitter and the receiver and the use of a matched filter at the receiver are shown to be essential factors in the recovery of the information signal from the noisy spread spectrum signal. |
