Pulse or digital communications – Repeaters – Testing
Patent
1992-01-27
1993-12-28
Chin, Stephen
Pulse or digital communications
Repeaters
Testing
375 96, 375 54, 3647242, H03H 730
Patent
active
052746690
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a signal equalizing method in a receiver for digitally coded signals received over a transmission channel with multi-path reception.
2. Background Information
In wireless signal transmission in the higher frequency domain, the signal sometimes reaches the receiver in different ways, i.e., from different directions. In addition to a direct path, reflections from buildings or natural elevations may conduct the signal broadcast by the transmitter to the receiver on other than the direct path. Since the individual paths differ in length and attenuation, the receiver receives several signals which all contain the original information but may differ from one another in amplitude, delay and phase angle. The superposition of these signals results in a compound signal in which the original information is more or less distorted. This may result in considerable interference, particularly in digital signals.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a signal equalization method which eliminates the interferences caused by multi-path reception to the extent that the original signal is readable again.
This is accomplished in a method in which predetermined test sequences are transmitted, received and correlated to obtain a channel pulse response which is thereafter used to continue a filter arrangement for correcting for multi-path distortions.
In an embodiment of the method according to the invention, the transfer characteristics of the transmission channel are determined in order to obtain the composition of individual transmission paths at the location of the receiver The determination of these characteristics may be repeated at short time intervals so that changes occurring in the meantime, as they are encountered in particular with moving receivers, can be considered and adjusted to.
For this purpose, test sequences of an agreed-upon structure are broadcast and, due to the multi-path reception, they are of course subjected to the same distortions as useful data. However, in contrast to the useful data, the structure of the test sequences is known from the start so that conclusions regarding the distortions that took place in the transmission channel can be drawn. In detail, a correlation is performed between the test sequence which is also stored in the receiver and the received test sequence which is distorted due to superposition of multi-path signals.
The result, the channel pulse response, constitutes a correlation spectrum in which the individual spectral components represent the paths on which the original signal traveled from the transmitter to the receiver. This spectrum can be employed to control a filter arrangement which substantially simulates the inverse of the transfer function of the transmission channel. Once the superposed signal has passed through this filter arrangement, the distortions that occurred on the transmission path are cancelled out. This filter arrangement may be adjusted after each test sequence and then the adjustment remains in effect for the reception of useful data until the next test sequence, since it can be assumed that the determined transfer characteristics of the transmission channel remain constant for a certain period of time.
Modifications and advantageous features of the method according to the invention are defined in the claims, the further description of the invention and the drawing figures which depict one embodiment thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawing figures show the following:
FIG. 1 is a multi-path transmission model with equalization at the receiving end;
FIG. 2 is the configuration of a data frame in which useful data and test sequences are transmitted;
FIG. 3 is a section of a data stream to illustrate the cyclic correlation;
FIG. 4 is a cyclic correlation spectrum;
FIG. 5A-5B sow the sum sequences and a sum sequence function derived therefrom;
FIG. 6 is a possible filter arrangement for the inverse simulation of the transfer fu
REFERENCES:
patent: 4112370 (1978-09-01), Monsen
patent: 4392232 (1983-07-01), Andren et al.
patent: 4441192 (1984-04-01), Kita et al.
patent: 4599732 (1986-07-01), LeFever
patent: 4606045 (1986-08-01), Miller
patent: 4621366 (1986-11-01), Cain et al.
patent: 4731801 (1988-03-01), Hendrikson
Klank Otto
Laabs Jurgen
Chin Stephen
Deutsche Thomson-Brandt GmbH
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