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SIMPLIFIED DATA DEMODULATION SCHEME USING DECIMATION PHASE CONTROL

IP.com Disclosure Number: IPCOM000005594D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2001-Oct-18
Document File: 2 page(s) / 82K

Publishing Venue

Motorola

Related People

Lester Longley: AUTHOR

Abstract

An important operation in data demodulation is sampling the filtered, received waveform at the decision instant, so that intersymbol interference is minimized and so that the signal-to-noise ratio of the sampled out- put is maximized. Most conventional datademodulation systems operate on a continuous-time analog signal, performing pulse-shaping filtering followed by a threshold unit to obtain adata sample. Alternatively, an integrate- and-dump operation may be used toobtain the datasample. In either case, the decision instant is continuously controlled by time-synchronization circuitry.

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MO7WROLA Technical Developments Volume 6 October 1966

SIMPLIFIED DATA DEMODULATION SCHEME USING DECIMATION PHASE CONTROL

by Lester Longley

   An important operation in data demodulation is sampling the filtered, received waveform at the decision instant, so that intersymbol interference is minimized and so that the signal-to-noise ratio of the sampled out- put is maximized. Most conventional datademodulation systems operate on a continuous-time analog signal, performing pulse-shaping filtering followed by a threshold unit to obtain adata sample. Alternatively, an integrate- and-dump operation may be used toobtain the datasample. In either case, the decision instant is continuously controlled by time-synchronization circuitry.

   However, in a discrete-time demodulator, such continuously-variable timing control is not generally possi- ble. Usually, the decision value can only be obtained at discrete instants of time. In fact, when the sampling rate is only a few multiples of the symbol rate, the timing control is very coarse. To achieve finer time resolution than that of the sampling clock, a phase shifter may be required. This may be very important to overall system performance when the horizontal eye opening is narrow. One solution may be an adaptive digital filter, which, in effect, adds avariable delay which may be only a fraction of the sampling time, thus providing relatively fine time resolution.

   Figure 1 shows a simpler method of allowing finer specification of the decision instant in discrete-time systems. The data demodulator is comprised of adatadetection unit (60) possibly preceded by a pre-detection filter (40). When the input to t...