CDMA has a number of advantages for a cellular network they are:

• Frequency diversity: Because the transmission is spread out over a larger bandwidth, frequency-dependent transmission impairments, such as noise bursts and selective fading, have less effect on the signal.

• Multipath resistance: In addition to the ability of DS-SS to overcome multi- path fading by frequency diversity, the chipping codes used for CDMA not only exhibit low cross correlation but also low autocorrelation. Therefore, a version of the signal that is delayed by more than one chip interval does not interfere with the dominant signal as much as in other multipath environments.

• Privacy: Because spread spectrum is obtained by the use of noise like signals, where each user has a unique code, privacy is inherent.

• Graceful degradation: With FDMA or TDMA, a fixed number of users can access the system simultaneously. However, with CDMA, as more users access the system simultaneously, the noise level and hence the error rate increases; only gradually does the system degrade to the point of an unacceptable error rate.

Drawbacks of CDMA for cellular networks:

• Self-jamming: Unless all of the mobile users are perfectly synchronized, the arriving transmissions from multiple users will not be perfectly aligned on chip boundaries. Thus the spreading sequences of the different users are not orthogonal and there is some level of cross correlation. This is distinct from either TDMA or FDMA, in which for reasonable time or frequency guard- bands, respectively, the received signals are orthogonal or nearly so.

• Near-far problem: Signals closer to the receiver are received with less attenuation than signals farther away. Given the lack of complete orthogonality, the transmis- sions from the more remote mobile units may be more difficult to recover. Thus, power control techniques are very important in a CDMA system.

• Soft handoff: A smooth handoff from one cell to the next requires that the mobile unit acquires the new cell before it relin- quishes the old. This is referred to as a soft handoff and is more complex than the hard handoff used in FDMA and TDMA schemes.