## Advantages of CDMA

Spreading the user signal well beyond the frequency selective fading bandwidth is clearly advantageous for coping with this unique problem in wireless communications. It also provides protection from narrowband interfering signals (these are spread by the 'de-spreading' process in a direct sequence CDMA receiver). Perhaps the main advantage of CDMA as a multi-user system is the flexibility to accommodate variable user data capacity. Each user in a spread spectrum CDMA system can increase their modulation rate and local narrowband modulation bandwidth without affecting other users when it is spread, as long as the user does not increase the overall wideband energy of the composite multi-user signal and hence increase the chance of mutual interference when de-spreading beyond that tolerable to the system. |

By slightly over-subscribing the number of users and their 'spread energy quota' on a spread spectrum CDMA system, it is possible for an operator to exploit the fact that any individual user will not be using the 'corporate' channel all of the time, and provided that the transmitter is powered down when the user is not speaking, for example, the average overall energy will be at the acceptable 'under-subscribed' level.