Pulse or digital communications – Receivers – Interference or noise reduction
Patent
1997-12-11
2000-08-01
Bocure, Tesfaldet
Pulse or digital communications
Receivers
Interference or noise reduction
375231, H04L 102, H04B 710, H03H 730
Patent
active
060977744
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL SCOPE
The present invention relates to an arrangement and a process in a base station for the demodulation of a received signal to a form suitable for decoding in a decoder.
PRIOR ART
In the spheres of radio communications and telecommunications, inter alia, signals are transmitted via channels with interference of unknown type. In an attempt to reduce this type of interference, so-called equalisers are used, which are operable to reproduce the undisturbed signal. The said equalisers are based on the principle of estimating the transmission function for the disturbed channel. This is usually done by making an estimate of the pulse response of the transmission medium. A known sequence, a so-called training sequence, which is usually transmitted in the middle of each time interval, is fed to the equalizer. The equalizer receives the said sequence and, with knowledge of the bit sequence which this represents, a transmission function can be estimated for the signal received. An inverted filter is then constructed through which the received signal can pass so that any interference, which has been introduced into the signal in the course of transmission, is reduced.
Since a mobile station in a mobile radio system moves, the interference on the allotted channel between a first base station and the mobile station ultimately becomes so great that it is no longer worthwhile trying to compensate for this interference with an equaliser in the base station. Instead the communication to the mobile station must pass by way of a second base station with better transmission conditions by performing a so-called handover between the first and second base stations.
In the GSM system, for example, so-called synchronous handover is used between base stations. A problem with this type of handover is that a signal received in the base station may consist both of a burst routine and a standard signal routine. When a mobile station has received a message that handover to a new base station is to be performed, the mobile station sends a predetermined number of burst routines corresponding to the number of successive TDMA frames on a new channel which is notified from the base station. In the GSM system four such burst routines are sent. After emitting the said burst routines, the mobile station proceeds to send normal signal routines via the designated channel. The receiving base station and an equaliser situated therein thus receive signal routines of two different types in connection with the handover. The said signal routines comprise training sequences of differing length.
A mobile telephone system receiver is already known from EP 0 457 448. The receiver comprises two receiver antennas which are connected by way of a first and a second channel to receiver circuits which each contain an equaliser. The two equalisers are separate from one another and correlation processes are performed therein independently of one another, which makes it possible to process different signals. After equalisation the signal which gives the best result is selected. The said signal is relayed for further processing. The known receiver, however, is not intended for a situation in which two different signal routines are received in connection with handover and does not provide a good solution to this problem. Another disadvantage with the known receiver is that the required signal processing capacity for the equalisers is high, since the latter function independently of one another.
DESCRIPTION OF THE INVENTION
The present invention is intended to solve this problem by providing an arrangement in a base station for the demodulation of a received signal to a form suitable for decoding, where the received signal may consist of both a burst routine and a standard signal routine. The invention is especially suited to use in a base station in a system with synchronous handover between base stations.
This problem is solved by the arrangement according to the invention which consists of a specially designed equaliser which is adapted to ident
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patent: 5121391 (1992-06-01), Paneth et al.
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Sohlman Ingemar
Stenvi Tommy
Bocure Tesfaldet
Telefonaktiebolaget LM Ericsson
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