EIA/NRSC DAR systems subjective tests. II. Transmission impairments

Abstract

For pt.I see ibid., vol.43, no.3, p.261-7 (1997). This paper describes the methods, results and conclusions of a series of subjective tests which were performed at the Communications Research Centre, Ottawa, Canada, to assess the audio quality of digital audio radio (DAR) systems in the presence of transmission errors. Testing has been performed in a laboratory environment on the hardware implementation of nine DAR systems. One of the systems operated in the AM broadcast band, five in the FM broadcast band, two in the L-band and one in the S-band. Testing was done in the presence of transmission errors generated by additive white gaussian noise, co-channel interference and five different multipath mobile channels. In addition, one system was tested with an interfering signal in the lower first adjacent DAR channel. The test results are presented and discussed, for each type of transmission impairments, in terms of (a) the E/sub b//N/sub 0/ ratios (D/U ratios for co-channel and adjacent channel interference) at the threshold of audibility (TOA) of transmission errors and at the point where transmission errors are so important that the audio quality is unacceptable (point of failure or POF) and (b) the failure margin which is a measure of how quickly DAR systems fail when the received signal power is reduced. A new parameter, labeled C/sub SP//N/sub 0/, is proposed to quantify the power efficiency of the overall DAR systems (i.e. source coding plus channel coding and modulation subsystems). The spectral efficiency of DAR systems is also presented and discussed.