Hybrid Digital–Analog transmission for wireless acoustic sensor networks

Abstract

A crucial task of a Wireless Acoustic Sensor Network (WASN) is the transmission of the acoustic signal to a central fusion node. Due to different microphone locations, the microphones may experience different or even varying radio channel qualities. Usually, the design of the digital transmission scheme is governed by the worst-case radio channel. For given radio resources, the end-to-end audio quality is specified by the compromise between the fidelity of the audio encoder and the required error protection capabilities of the channel encoder. The quantization noise of the audio encoder limits the end-to-end SNR even for increasing radio channel qualities. In the fusion node, the decoded signals are combined (fusion algorithm) and the overall output audio quality is limited due to the quantization noise even for error free transmission. In this paper it is shown that this unfavorable behavior can be avoided by using a Hybrid Digital-Analog (HDA) transmission concept. The key feature of HDA is that the audio output quality improves with increasing channel qualities. For typical fusion algorithms the HDA system supersedes purely digital transmission for all radio channel qualities.