Jitter Management in Circuit Switched Voice over HSPA Networks

Abstract: When a shared channel or packet switched network is used for transmission (e.g.WLAN, HSPA (Turbo-3G), LTE (4G)), it introduces variance in the delay of packets. Thisvariance is called jitter. This jitter can lead to significant degradation of quality inreal-time services if it is not properly handled. High Speed Packet Access (HSPA) is an extension to the third Generation W-CDMAcellular network that provides significantly increased bandwidth and network capacity byintroducing a High Speed-Downlink Shared Channel (HS-DSCH) for downlink and anEnhanced-Dedicated Channel (E-DCH) for uplink. Both HS-DSCH and E-DCH usere-transmissions in order to ensure a low block error rate, as a result jitter is induced inboth channels. Moreover, HS-DSCH also uses channel dependent scheduling betweenusers adding additional jitter. Since HSPA uses IP and the voice service is provided by voice over IP (VoIP), jittermanagement is performed at the destination end-point. However, 3GPP has also specifiedtransportation of circuit switched voice over HSPA (CSoHS), where jitter managementneeds to be performed separately, at both the entry point to the core network and in thereceiving end-point as jitter is introduced both in the uplink and downlink. This report studies CSoHS, with a focus on its delay and jitter characteristics. Itintroduces two schemes for jitter management: a fixed jitter buffer and an adaptive jitterbuffer. These jitter buffer designs are evaluated mainly by looking at the jitter loss (i.e.,the proportion of packets that have to be discarded because they exceed the maximumpermitted jitter) and the buffering time. The results show that the adaptive jitter buffer canachieve better performance in balancing the trade-off between jitter loss and bufferingdelay when dealing with various network conditions. In contrast, the fix jitter buffer is notcapable of tracking variations in the network conditions, as the performance of the fixedjitter buffer is determined solely by the configuration of the initial buffer level. Theadaptive jitter buffer is able to consistently provide equal or better quality of service thanthe fixed jitter buffer.i