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Soft Demodulation and Unequal Power Allocation for Digital Modulation Schemes

Authors:

Thomas Brüggen, Christina Schulte-Hillen, and Peter Vary

Book Title:

Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)

Venue:

Philadelphia, PA, USA

Organization:

IEEE

Date:

Mar. 2005

Pages:

1053–1056

Language:

English

Abstract

The quality of digital transmission of speech, audio and video signals over a noisy channel can be improved in many cases by error concealment, specifically by softbit source decoding (SBSD). It applies parameter estimation exploiting a priori knowledge on parameter level and reliability information on bit level. In this contribution we present a novel soft demodulation (SDM) method for higher order digital modulation schemes based on SBSD. The soft demodulator makes a soft decision on signal point level using a mean square (MS) estimator and can also exploit a priori knowledge about the source. Furthermore, we present a novel concept for unequal error protection (UEP) by higher order modulation with unequal power allocation (MUPA). Usually, the bits representing the quantized source codec parameters are protected by channel coding with UEP according to the individual bit error sensitivities. For communication systems where channel coding is not applicable, we propose the MUPA method with periodically time-varying power allocation. The average transmitted energy per bit remains unaffected. The significant SNR gains of the SDM combined with MUPA in comparison to systems with hard decision and a fixed signal constellation are demonstrated by simulation.

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