Abstract:
The unabated growth in the use of wireless communication is continuing and new services are being introduced. The wireless users access or share to a resource using multiple access techniques. There are three multiple access techniques namely, Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA). FDMA is a technique whereby spectrum is divided up into frequencies and then assigned to users. The number of users are restricted by the number of available frequency channels. TDMA improves spectrum capacity by splitting each frequency into time slots. This allows each user to access the entire radio frequency channel for the short period of a call. Other users share this same frequency channel at different time slots. The number of users are restricted by the number of time slots in a frame. The CDMA is based on "spread" spectrum technology. It increases spectrum capacity by allowing all users to occupy all channels at the same time. Transmissions are spread over the whole radio band, and each voice or data call is assigned a unique code to differentiate from the other calls carried over the same spectrum. The number of users can be increased as large as the number of available orthogonal codes. The capacity of CDMA system is limited by interference. Capacity of a communication network is the maximum number of the subscribers that can be accommodated for a given quality of service parameters. The quality of service (QoS) parameters are signal to noise ratio, signal to interference ratio, bit energy to noise ratio and bit error rate etc.
