EIA NRSC DAR SYSTEMS SUBJECTIVE TEST .2. TRANSMISSION IMPAIRMENTS/

This paper describes the methods, results and conclusions of a series of subjective tests which were performed at the Communications Researc h Centre, Ottawa, Canada, to assess the audio quality of Digital Audio Radio (DAR) systems in the presence of transmission errors. Testing h ave been performed in a laboratory environment on the hardware impleme ntation of nine DAR systems. One of the systems operated in the AM bro adcast band, five in the FM broadcast band, two at L-band and one at S -band. Testing was done in the presence of transmission errors generat ed by additive white gaussian noise, co-channel interference and five different multipath mobile channels. In addition, one system was teste d with an interfering signal in the lower first adjacent DAR channel. The test results are presented and discussed, for each type of transmi ssion impairments, in terms of (a) the E-b/N-o ratios (D/U ratios for co-channel and adjacent channel interference) at the threshold of audi bility (TOA) of transmission errors and at the point where transmissio n errors are so important that the audio quality is unacceptable (poin t 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-SP/N-o, is proposed to quantify the power efficiency of the overall DAR systems (i.e. source coding plus channe l coding and modulation subsystems). The spectral efficiency of DAR sy stems is also presented and discussed.