Adaptive equaliser

Details Adaptive equaliser Adaptive equaliser

1996-09-10

2000-08-08

Chin, Stephen

Pulse or digital communications

Equalizers

Automatic

375229, 375233, H03H 730

Patent

active

06101219&

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention refers to an equaliser of the adaptive type employed in transmission systems where the transmission channel does not have a flat transfer function, but where, due particularly to multipropagation effects, the signal at the receiver input includes linear distortion that considerably impairs its quality.
To correct these effects, use is made of channel equalisers, the purpose of which is to compensate these effects by means of certain mathematical algorithms. These algorithms converge towards an error signal with value zero or sufficiently small when the signals they receive are subject, during reception, to a linear process; however, the same does not occur, or at least not at the same speed, when the signals are subjected to a significantly non-linear process.


BACKGROUND OF THE INVENTION

The use of frequency modulation techniques of the GFSK type, like that employed in the Digital European Cordless Telecommunications (DECT) standard, make it advisable to use frequency demodulators based, for example, on discriminators; in this way it is possible to recover the data by means of a simple threshold detector in order to decide between the two logic states, 0 or 1.
In certain environments where these systems are applied, this type of receiver is sufficient because the maximum spread of the signal at the receiver is considerably less than one symbol and, consequently, the intersymbol interference produced in the channel is hardly appreciable. However in applications where radio coverage is greater, the latter is not true. In such situations it becomes advisable to make use of equalisers that remedy this signal-degrading effect resulting in the error probability of recovered symbols being notably enhanced.
For this reason, use is made of an equaliser of the type illustrated in the article "Adaptive equalisation for DECT systems operating in low time-dispersive channels" by J. Fuhl and G. Schultes, published in the magazine Electronics Letters of Nov. 25, 1993, vol. 29, No.24, pages 2076 and 2077.
In this article use is made of an equaliser of the well known type DFE (Decision Feedback Equaliser). In it, the training sequence employed is the 16-bit burst synchronisation as defined by the DECT. The training sequence is stored in a ROM and applied to the equaliser at the moment when the 16 bits appear at the receiver input, instead of the actually received signal. This prevents the possible errors produced in the detector, when the filter coefficients are still inexact, from being fed back to the equaliser and, therefore, a faster convergence occurs.
Nevertheless, when the demodulator is of the non-linear type like, for example, a frequency discriminator, even under ideal conditions of propagation, the demodulated signal can be considerably distorted due to the action of the demodulator. Under these conditions, adequate convergence does not occur, since no allowance is made for the non-linear process to which the received signals are subjected.


SUMMARY OF THE INVENTION

In the equaliser training phase, this sequence is applied to the equaliser simultaneously with that received in order to make thereby a first estimate of the coefficients of the filter or filters of the equaliser.
So as to make possible and hasten the convergence of the coefficients mentioned, the training sequence is not constituted by the digital symbols transmitted but, instead, it is formed by a cadence of samples that represents the training sequence just as it would be received at the output of the demodulator in the absence of noise and of multipropagation.
Thus, the new training sequence is obtained through the application of lowpass filter whose transfer function is the same as that of the premodulation filter employed in the modulator and, thereby, allowance is made for the prior linear distortion due to the filtering that occurs in the modulator.
Subsequently the non-linear distortion effects to which the data are subjected in the reception side during demodulation and prior to their detection or regene

REFERENCES:
patent: 4489416 (1984-12-01), Stuart
patent: 4747068 (1988-05-01), Voorman et al.
patent: 5434883 (1995-07-01), Kimoto et al.
patent: 5563911 (1996-10-01), Uesugi et al.

Affiliated with

Also associated with

Rating

Adaptive equaliser does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Adaptive equaliser, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Adaptive equaliser will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1157200