In the downlink of a CDMA system, each users' signal is spread onto a pseudonoise sequence.13 Uncoded BPSK modulation is used, with a processing gain of G. Soft handoff is performed by sending the same symbol to the mobile from mul- tiple base-stations, the symbol being spread onto independently chosen pseudonoise sequences. The mobile receiver has knowledge of all the sequences used to spread the data intended for it as well as the channel gains and can detect the transmitted symbol in the optimal way. We ignore fading and assume an AWGN channel between the mobile and each of the base-stations.
1. Give an expression for the detection error probability for a mobile in soft handoff between two base-stations. You may need to make several simplifying assumptions here. Feel free to make them but state them explicitly.
2. Now consider a whole network where each mobile is already assigned to a set of base-stations among which it is in soft handoff. Formulate the power control problem to meet the error probability requirement for each mobile in the downlink.