Per Synnergren

Bandwidth efficient AMR operation for VoIP

An example of a bandwidth efficient adaptive multi rate (AMR) system for Voice over IP (VoIP) is presented. In VoIP, packet losses cause degradation of the synthesized speech. The distortions may propagate over several consecutive frames, since predictors in the codec exploit inter-frame correlations to gain coding efficiency. To reduce the effects of packet loss, forward error correction (FEC) that adds redundant information to voice packets can be used. However, while FEC can reduce the effects of packet loss, it will increase the amount of bandwidth used by the voice stream, which is not desirable. In this paper we propose FEC methods like partial redundancy, selective redundancy for the most sensitive frames and parameter interpolation in conjunction with AMR codec mode adaptation, which secure the speech quality when using AMR for VoIP without increasing the bandwidth substantially.

Effects of QoS Scheduling Strategies on Performance of Mixed Services over LTE

3GPP is currently in the process of defining the long-term evolution (LTE) of 3G, which will be an all-IP network. Streamlining the system for packet services will lead to improvements in the form of higher bit-rates, lower latencies and a wider array of service offerings, but will also pose new challenges that need to be overcome. This paper investigates how call setup signaling will be affected as the load on the system increases and how the delivery of important signaling messages can be ensured. A traffic scenario where all users engage in both a voice over IP (VoIP) conversation and a video session is applied in an extensive network simulator. SIP signaling is used to set up the different media connections. We find that if all traffic is scheduled with equal priority, setup signaling might become heavily impaired and the delivery of signaling messages can not be ensured. However, if these messages are absolutely prioritized and always scheduled before other traffic, the length of call setups and terminations can be kept at almost constant values even if the system load is high. The results also indicate that other service qualities are not significantly affected by such a prioritization scheme.