Multistream transmission for hybrid IBOC-AM with embedded/multidescriptive audio coding

Abstract

Hybrid in band on channel (IBOC) digital audio broadcasting simultaneously with analog amplitude modulation (AM) has been proposed as a solution to DAB in the AM band. Since the AM band is crowded and the available bandwidth per program is limited, adding digital transmission presents a challenge. To achieve FM-like audio quality, an audio coder rate of 32-64 kb/sec may be required. One currently proposed hybrid IBOC-AM system is 30 kHz wide. Severe second adjacent interference may occur in certain areas, leading to a possible 40% loss of the effective audio bit rate. To cope with such harsh transmission conditions, we present a solution based on embedded/multidescriptive audio coding with matched multistream transmission in separate frequency bands. With the loss of one frequency band, the embedded system blends to a lower audio coder rate with a much better quality than analog AM. The nonembedded system, without multistream transmission, fails catastrophically when a little more than one sideband is severely interfered with, causing a severe discontinuity in quality while blending directly to analog AM. Some detailed robust embedded systems are outlined. We also show how multistream transmission schemes can be used with nonembedded audio coders. Both daytime and nighttime scenarios are included. This paper contains a catalog of possible systems for different audio quality levels and interference scenarios, including systems with 20 kHz bandwidth rather than 30 kHz.