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Method for the demodulation of pulse-shaped modulated signals with the partial estimation of metrics

IP.com Disclosure Number: IPCOM000124277D
Publication Date: 2005-Apr-14
Document File: 3 page(s) / 93K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for the demodulation of pulse-shaped modulated signals with the partial estimation of metrics. Benefits include improved functionality and improved performance.

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Method for the demodulation of pulse-shaped modulated signals with the partial estimation of metrics

Disclosed is a method for the demodulation of pulse-shaped modulated signals with the partial estimation of metrics. Benefits include improved functionality and improved performance.

Background

              The demodulation of a signal with intersymbol interference (ISI) is conventionally performed using the well-known Viterbi algorithm. However, its calculation is extremely complex. A simpler solution is required. Additionally, the Viterbi algorithm with ISI requires that the number of calculations required not be less than the depth of ISI. This requirement adds complexity and processing time.

General description

              The disclosed method is the demodulation of pulse-shaped modulated signals with the partial estimation of metrics. The method can be used in receivers for a standard enhanced general packet radio service and as the demodulator for 8 phase-shift keying modulated signals. The method uses only the first part of the symbol duration with partial estimation of the symbols for calculating Euclidian metrics. Additionally, the demodulator removes the influence of previous symbols using subtraction of the restored signal from the received signal.

Advantages

The disclosed method provides advantages, including:

•             Improved functionality due to enabling signal demodulation/ISI with performance close to optimal

•             Improved functionality due to providing a signal demodulator with low computational complexity

•             Improved functionality due to eliminating the depth limitation on ISI processing

•             Improved performance due to providing an algorithm that simplifies processing

•             Improved performance due to not requiring preliminary signal processing

Detailed description

              The disclosed method includes delayed decision feedback (DDF) to reduce ISI, which arises from multipath propagation of signal. In-phase and quadrature components from an analog-to-digital converter (ADC) are input to the subtracter of the DDF.

              DDF is comprised of a modulator with combined modulation and channel pulse-shaping. The DDF modulator uses previously demodulated symbols from the output of the demodulator to remove its effect on the currently demodulated symbol. Each curve

of the pulse-shaped modulated signal represents a symbol. The solid line represents the currently demodulated symbol. Dash-dotted lines represent symbols for which their influence is re...