Pulse or digital communications – Repeaters – Testing
Patent
1992-02-20
1993-06-01
Cangialosi, Salvatore
Pulse or digital communications
Repeaters
Testing
380 34, H04L 2730
Patent
active
052166910
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a digital receiver for spread-system signals generated by multiplication of an information-carrying signal by an auxiliary function, having a correlator for the correlation of the received signal with a reference code, and having a digital signal processor for evaluating the results of the correlation.
European Patent Application No. 89,117,388.2 describes a digital radio transmission system which uses the spread-spectrum technique in which digital signal processing is used bu the correlators of the receives are constructed discretely with analog components and are thus relatively costly in terms of space and power requirements. In addition, the analog components have the known drifting and aging problems and they also restrict the application possibilities of the digital signal processing.
By means of the invention, the implementation of digital correlators with sufficiently high time-bandwidth products will now be made possible, so that receives can be built which are compact and economical in terms of power consumption and which do not have any drifting and aging problems.
This object is achieved according to the invention by means of a digital, time-integrating, multistage correlator, the individual stages of which are connected on the one hand to a digital delay line fed with the reference code and to which on the other hand a digital signal recovered from the received signal is applied, the length of the delay line being adapted to the maximum expected length of the impulse response of the transmission channel.
The correlator according to the invention can be integrated monolithically and is therefore economical in terms of space and power and is easy to install. The receives equipped with correlators of this kind do not have the drifting and aging problems of the known analog solutions and are extremely flexible. The receives are particularly suitable for radio transmission systems with multipath propagation, but they also permit multiple use of the transmission channel by means of multiple access (code division multiple access=CDMA). Such receivers are used advantageously for radio systems with microcell arrangement in locally limited areas such as factory premises, houses or multistory buildings.
The invention is explained in greater detail below with reference to an exemplary embodiment and the drawings, in which:
FIG. 1 shows a block circuit diagram of a digital multipath receiver for spread-spectrum signals,
FIG. 2 shows a block circuit diagram of the correlator of the receiver of FIG. 1; and
FIGS. 3a, 3b, 4a, 4b are diagrams for the purpose of functional explanation .
The multipath receiver according to the invention is a digital receiver for spread-spectrum signals according to the so-called direct sequence method and it is particularly suitable for radio transmission systems on channels with multipath propagation. A system of this kind is described in European Patent Application No. 89,117,388.2 by the Ascom Zelcom AG, reference being hereby explicitly made to the disclosure of said patent application. The digital receiver described below constitutes an improvement of the correlation receiver described in this patent application, the improvement concerning primarily the employed correlators of the receiver, in that now digital correlators are proposed.
FIG. 1 shows a block diagram of a digital multipath receiver which includes, according to the illustration, three blocks: a converter 1, a so-called I/Q processor 2 and of a digital stage 3. In the converter 1, the received broad-band signal which arrives at the aerial of the receiver via paths Pl to Px is filtered in a band-pass filter 4 in order to suppress signals outside the employed frequency band. The output signal of the band-pass filter 4 is amplified in an amplifier 5 and mixed in a mixer 6, at whose other input a local oscillator 7 is connected, to an intermediate frequency f.sub.IF. This intermediate frequency signal now passes into the I/Q processor 2 where it is filtered in a further band-pass filt
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Ascom Zelcom AG
Cangialosi Salvatore
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