Efficient client-server based implementations of mobile speech recognition services

The purpose of this paper is to demonstrate the efficiencies that can be achieved when automatic speech recognition (ASR) applications are provided to large user populations using client-server implementations of interactive voice services. It is shown that, through proper design of a client-server framework, excellent overall system performance can be obtained with minimal demands on the computing resources that are allocated to ASR. System performance is considered in the paper in terms of both ASR speed and accuracy in multi-user scenarios. An ASR resource allocation strategy is presented that maintains sub-second average speech recognition response latencies observed by users even as the number of concurrent users exceeds the available number of ASR servers by more than an order of magnitude. An architecture for unsupervised estimation of user-specific feature space adaptation and normalization algorithms is also described and evaluated. Significant reductions in ASR word error rate were obtained by applying these techniques to utterances collected from users of hand-held mobile devices. These results are important because, while there is a large body of work addressing the speed and accuracy of individual ASR decoders, there has been very little effort applied to dealing with the same issues when a large number of ASR decoders are used in multi-user scenarios. Preprint submitted to Elsevier Science 5 May 2006