Distributed speech recognition (DSR) is motivated by the fact that codecs used in speech transmission usually reveal a degrading voice quality below some channel quality (carrier-to-interferer ratio C/I), which justifies efficient coding of features with an appropriate channel coding in the mobile terminal. The Adaptive Multi-Rate (AMR) speech codec standardized for GSM and UMTS however delivers an acceptable speech quality way down to C/I ratios of about 4 dB in the GSM full-rate speech channel.

In this paper we investigate network-based speech recognition (NSR) using a conventional speech channel with AMR coding as an alternative to a DSR system. This approach is natural and attractive since information services usually require a duplex channel for conversation anyway, furthermore no change to existing mobiles is required. For a GSM full-rate channel it turns out that an NSR system based on AMR coding indeed is comparable to DSR approaches.