On the Impact of the Soft Handoff Threshold and the Maximum Size of the Active Group on Resource Allocation and BS Transmit Power in the UMTS System

We study the effect of two control parameters of the UMTS handoff algorithm on resource allocation and base station [BS] transmit power. We provide information on the effect of the parameters on the probability distribution of the number of BSs supporting a mobile station [MS], the number of MSs supported by a single BS (per carrier), and the total average BS transmit power required per MS to satisfy a prescribed outage probability. Denoting the set of BSs supporting an MS in soft handoff as the active set, the first parameter, nA, is the maximum allowed size of the active set. The second, denoted X , is the upper limit on the difference between the path loss of the dominant BS and that of any other member of the active set, where the term "dominant" refers to the BS with the lowest path loss to the MS. We assume that the mobile 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.