An example of a handwidth efficient Adaptive Multi Rate (AMR) system for Voice over IP (VolP) 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 h e s and parameter interpolation in conjunction with AMR codec mode adaptation, which secure the speech quality when using AMR for VoIP without increasing the handwidth substantially.
We propose a concept for public safety communication realized with IMS (IP Multimedia Subsystem), the cellular standards of 3GPP and packet switched transmission. Basing the solution on mainstream cellular technology leverages the economy of scale of today's commercial networks and enables migration of technical solutions and applications.Important requirements of the Public Safety sector are group communication, low latency, high capacity, security, reliability and interoperability for voice and broadband data services. Our analysis shows that the concept has the technology potential to meet these public safety requirements.
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