Problem
1. Suppose that, in a consideration of multiple-access interference, users are power controlled, but are not phase coherent; that is each user's bits bit have a random phase rotation I , relative to the other user bits. How will this affect the multiple-access noise? Assume that the phase rotation is constant over the period of the spreading code.
2. One suggested application of CDMA techniques is for overlaying a new ser-vice on top of an existing service. Suppose a point-to-point microwave link at 4 GHz currently exists. (This link may be referred to as the primary user.) This microwave link has a 1-MHz bandwidth and 40-dB margin to account for rain fades. A second service provider wants to reuse the same spectrum to distribute four 10-kHz audio channels with a total baseband bandwidth of 40 kHz (secondary user). Assume that the required transmit power of the second service is approximately 10 logio(40 kHz/1 MHz) lower than the first. If the audio channels are spread over the full bandwidth, what would be the degradation of the primary service under clear-sky conditions? What interference would the primary service cause in the secondary service. That is what would the signal-to-interference ratio (SIR) of the secondary user be? Should the primary user accept the application of the secondary user? Under what conditions, if any?