Enhanced HSDPA Mobility Performance: Quality and Robustness for Voice over HSPA Service

Legacy High Speed Downlink Shared Channel (HS-DSCH) Serving Cell Change (SCC) procedures in deployed HSPA networks (3GPP Release 5 and 6) may lead to unacceptably high call drop rates in realistic Urban Canyon conditions when Signaling Radio Bearers (SRBs) are mapped on the HS-DSCH. Mapping SRB on HS-DSCH is necessary to enable high capacity voice over HSPA (Circuit Switched Voice or VoIP over HSPA) since it eliminates the code limitation that arises when SRBs are mapped on DCH. To address the above robustness issue, Enhanced SCC (ESCC) was introduced in 3GPP Release 8. In this paper we highlight the first ever implementation of the E-SCC algorithm in a HSPA prototype system. A comprehensive evaluation of the E-SCC algorithm for voice over HSPA is performed through measurements made over a prototype network. We show that under tough urban canyon conditions, the ESCC procedure provides significant gains compared to the legacy USCC procedure in terms of call drop rates, packet drops and duration of serving cell change, thus allowing robust high quality voice service under mobility conditions. To conclude, this paper provides evidence that E-SCC algorithm implementation is feasible and when implemented, robust mobility for voice over HSPA can be achieved.