Channel error protection scheme for distributed speech recognition

Abstract

This paper describes ongoing research preparing for the widespread deployment of spoken language processing in networks encompassing wired and wireless transmission channels. The paper gives a brief overview of the standardized bit-error protection scheme aimed at minimising channel transmission errors and used within the distributed speech recognition (DSR) paradigm. Within the ETSI-DSR standard, two quantised mel-spectral frames – each of 10 ms duration are grouped together and protected with a 4-bit Cyclic Redundancy Checking (CRC) forming a frame-pair. However, this causes the entire frame-pair erroneous if a one-bit error only occurs in the frame-pair packet. Over an error-prone transmission channel this format will cause severe problems. To overcome this, the paper presents a one-frame architecture in which a 4-bit CRC is calculated to protect each frame independently. This scheme results in that the overall probability of one frame in error is lower, or that an error occurring in one frame does not affect another frame. A number of simple recognition experiments have been conducted to verify the introduction of the one-frame CRC protection scheme for a number of simulated transmission channel biterror rates (BER) ranging from 0 (no transmission channel involved) to 2٠10. Experimental results show that the one-frame protection scheme is more robust to channel errors although a slight increase in the errorprotection overhead is needed.