Subject : Mobile Communication

Topic : CDMA

Difficulty : Medium

• Of all the 2G cellular systems,IS-95 is the most complex because of the use of spread spectrum,that brings advantage not available with TDMA based systems.
• The CDMA which is helping in performing soft hand-offs which improved the voice quality during hand-off.
• Mobility outside the soft hand-offs is based on general mobility management procedures.
• There are three types of hand-offs defined as IS-95.

• The system level objectives of maximum utilization of available radio spectrum in cellular communication system often translate into maximum number of simultaneous mobile users served bye the system with acceptable signal quality,which is directly related to minimizing the transmitted power of each mobile users at all time of its operation.
• In IS-95, a slow mobile assisted power control is employed on forward channel therefore Non coherent detection is employed on reverse channel and hence power control implementation is a must on the reverse channel.
• There are mainly two types of power control mechanism an open loop and close loop.
• Because all the voice channel occupy the same frequency and time slot, the received signal from multiple mobile user located anywhere within the periphery of the serving cell must all have the same receive signal strength at the base station for detection.
• The advantage of implementing strict power control is that the mobile user can operate at minimum required $\frac{E_{b}}{N_{o}}$ for adequate performance.This increase battery life and reduces the size of weight of mobile users phone equipment.