Deepen Sinha

Unequal error protection methods for perceptual audio coders

In most source coded bit streams certain bits can be much more sensitive to transmission errors than others. Unequal error protection (UEP) offers a mechanism for matching error protection capability to sensitivity to transmission errors. A UEP system typically has the same average transmission rate as a corresponding equal error protection (EEP) system but offers an improved perceived signal quality at equal channel signal to noise ratio. In this work we introduce methods of UEP to the perceptual audio coder (PAC). An error sensitivity classifier divides the bits in classes of different sensitivity. Different channel codes are then applied to each class. We show how punctured convolutional codes can be used for UEP of the PAC bitstream. Experimental results for channels with uniform as well as non-uniform noise/interference level indicate that the systems with UEP exhibit graceful degradation and extended range for applications such as digital audio broadcasting (DAB).

Multistream hybrid in band on channel FM systems for digital audio broadcasting

New approaches to hybrid in band on channel (HIBOC) FM systems for digital audio broadcasting based on multistream transmission methodology and multidescriptive audio coding techniques are introduced. These ideas combined with a lower per sideband audio coding rate and more powerful channel codes result in robust transmission and graceful degradation in variable interference channels. By also using orthogonal frequency division multiplexing techniques with a nonuniform power profile combined with unequal error protection and sideband time diversity, we arrive at new HIBOC FM schemes with extended coverage and better peak audio quality than previously proposed. The paper provides approximate performance analysis for potential systems including audio coding quality.

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

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.

Joint encoding and decoding methods for digital audio broadcasting of multiple programs

We introduce new methods for increasing the performance of multiprogram digital audio broadcast systems, e.g., satellite digital audio broadcasting. Joint multiprogram encoding is an attractive possibility for parallel broadcasting of a large number of programs. Joint coding extended over multiple audio frames in time give further improvements. The benefits of this kind of statistical multiplexing yield improved audio quality and/or higher capacity in terms of number of programs. We describe the new Joint Multiple Program Encoding Technique in the context of the perceptual audio coding (PAC) type of algorithms. We also describe methods for multi-program transmission including Equal Error Protection (EEP) as well as Unequal Error Protection (UEP) and improved error concealment for multiple program transmission. Some of the techniques described in this paper, are currently being used in satellite digital audio broadcasting in the United States.

Multi-stream transmission for spectrally and spatially varying interference AM-DAB channels

Hybrid in band on channel (IBOC) digital audio broadcasting (DAB) simultaneously with analog amplitude modulation (AM) has been proposed as a hybrid solution to digital audio broadcasting in the AM band. Adding digital transmission in the crowded AM band is a challenging proposition. To achieve FM like audio quality, an audio coder rate of 32-64 kbit/s may be required. One of the currently proposed hybrid IBOC-AM systems is 30 kHz wide. Severe second adjacent interference may occur in certain geographical areas. For coping with such harsh transmission conditions, we present a solution based on embedded/multi-descriptive audio coding with matched multistream transmission in separate frequency bands. With loss of one frequency band, the embedded system blends to a lower audio coder rate with still a better quality than analog AM. The non-embedded system without multi-stream transmission fails catastrophically causing a severe discontinuity in quality while blending directly to analog AM.