Adaptation of CDMA soft handoff thresholds using fuzzy inference system

This paper proposes a new procedure to adjust soft handoff thresholds (T-DROP, T-ADD) by using a fuzzy inference system (FIS). The aims are to increase the value of T-DROP in order to release the traffic channel (TCH) at high traffic loads for increasing the carried traffic, and to decrease the value of T-DROP in order to add the TCH in active set at low traffic loads for increasing the quality of TCH. The system performance indicators consist of the quality of TCH (E_b/N ₀), outage probability, new call blocking probability (P_B), handoff call blocking probability (P_HO), expected number of base stations (BS) in active set (NO_BS), expected number of BS changes in active set (NO_update), trunking resource efficiency (TRE) and carried traffic (T_C). By comparison of all parameters among three algorithms, soft handoff (SHO) using the FIS tends to have higher performance (T_C, NO _BS, TRE, P_B, P_HO, NO_update) than those of IS-95A and IS-95B/cdma2000 SHO at high traffic loads or lower thresholds while the quality of TCH (E_b/N₀, outage probability) is still acceptable