Soft selection combining for terrestrial digital audio broadcasting in the FM band

Abstract

Methods of adaptive soft combining and channel decoding are developed to combat the effects of multipath fading and nonuniform interference channels, with particular application to digital reception in hybrid in-band on-channel (HIBOC) digital audio broadcast (DAB) systems in the FM band. These systems transmit near CD quality digital audio and analog FM simultaneously within the same license band, requiring the digital audio to be protected with powerful channel codes and sophisticated decoding algorithms to provide broad coverage under a variety of fading and potentially severe interference conditions created by first adjacent FM stations. In an example HIBOC DAB system, digital transmissions are DQPSK/OFDM modulated in two sidebands of the analog FM host signal, and a complementary punctured pair convolutional (CPPC) inner coding scheme allows for higher diversity benefit than code combining when both sidebands are interference-free as well as full recovery of the audio information when one of the sidebands is severely corrupted by first adjacent interference. For the intermediate cases in which one of the sidebands is partially useful, we demonstrate via simulations that an unmodified receiver designed for a Gaussian channel and corresponding to equal-gain combining performs ineffectively for moderate to high interference levels. Motivated by a clear need for more sophisticated receivers, we examine soft combiners derived from the maximum-likelihood principle and provide simulated performance bounds for the case in which perfect channel parameter estimates are available. We then discuss more practical methods for performing adaptive soft combining and channel decoding, focusing in particular on an appealing soft selection combining technique, based on successive erasures and Viterbi decoding, that requires only coarse estimates of the channel parameters. An outer code used for error concealment may be further utilized to perform the selection function. The performance of this soft selection combining scheme under a variety of interference scenarios is also evaluated via simulation. Further improvements may be obtained with a list Viterbi decoder. Index Terms-Digital audio broadcasting (DAB), diversity combining, fading channel, interference mitigation, selection combining, successive erasure decoding. I. INTRODUCTION D IGITAL AUDIO BROADCAST (DAB) in the FM radio band promises near CD-quality audio, data services, and more robust coverage than existing analog FM transmission. However, before all-digital broadcasting can be made a reality,

Technical advances in digital audio radio broadcasting

“…Soft combining methods [91], [72] can be used to increase the efficiency of channel decoding, in particular for CPPC codes for single-stream systems. Complexity and robustness versus performance is an issue here.…”

Optimized Design of CPPC Parameters for IBOC DAB

“…In-band On-channel(IBOC) broadcasting uses orthogonal frequency-division multiplexing (OFDM) to emplace digital signals at the frequency bands which are the same as or adjacent to analog signals in an FM radio, thereby achieving the digitization of FM radio. It increases the sound quality and compatibility of the FM radio [1] [2].…”