Jitter Management in Circuit Switched Voice over HSPA Networks
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چکیده
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. This variance is called jitter. This jitter can lead to significant degradation of quality in real-time services if it is not properly handled. High Speed Packet Access (HSPA) is an extension to the third Generation W-CDMA cellular network that provides significantly increased bandwidth and network capacity by introducing a High Speed-Downlink Shared Channel (HS-DSCH) for downlink and an Enhanced-Dedicated Channel (E-DCH) for uplink. Both HS-DSCH and E-DCH use re-transmissions in order to ensure a low block error rate, as a result jitter is induced in both channels. Moreover, HS-DSCH also uses channel dependent scheduling between users adding additional jitter. Since HSPA uses IP and the voice service is provided by voice over IP (VoIP), jitter management is performed at the destination end-point. However, 3GPP has also specified transportation of circuit switched voice over HSPA (CSoHS), where jitter management needs to be performed separately, at both the entry point to the core network and in the receiving 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. It introduces two schemes for jitter management: a fixed jitter buffer and an adaptive jitter buffer. 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 maximum permitted jitter) and the buffering time. The results show that the adaptive jitter buffer can achieve better performance in balancing the trade-off between jitter loss and buffering delay when dealing with various network conditions. In contrast, the fix jitter buffer is not capable of tracking variations in the network conditions, as the performance of the fixed jitter buffer is determined solely by the configuration of the initial buffer level. The adaptive jitter buffer is able to consistently provide equal or better quality of service than the fixed jitter buffer.
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تاریخ انتشار 2009