## Disadvantages of CDMA

Wideband spreading of signals, whether it be with 'frequency hopping' or 'direct sequence' techniques, has a penalty in terms of the signal processing overhead involved with such high rate and bandwidth transmission. Power control has also been identified as a critical issue in maximizing the number of users that can be supported on a given common frequency channel. CDMA also requires a large amount of bandwidth to be available in a contiguous block (spread spectrum only) in order to ensure that sufficient spreading can be obtained to mitigate the frequency selective fading and to ensure that there is sufficient coding gain in the system. Typically bandwidths of 5 MHz upwards are desirable for best communications performance in a typical cellular environment, although regulatory constraints have forced smaller bandwidths (1.25 MHz for IS-95) to be used in some circumstances.

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