Impact of soft handoff threshold and maximum active group size on base station downlink transmit power in the UMTS system

We study the effect of two control parameters of the UMTS handoff algorithm on the outage probability of the forward link and the total average base station (BS) transmits power required per mobile station (MS) to satisfy a prescribed outage probability. Denoting the set of BSs supporting an MS in soft handoff (SH) as the active group, the first parameter, n_A, is the maximum allowed size of the active group. The second, denoted τ, is the upper limit on the difference between the path loss of the dominant BS and that of any other member of the active group, where the term "dominant" refers to the BS with the lowest path loss to the MS. We assume that the MS is equipped with a Rake receiver capable of performing "maximal ratio combining" of the signals it receives from the transmitting BSs. We present general analytical derivations along with results derived for specific situations through simulations and numerical integration.