Pulse or digital communications – Equalizers – Automatic
Patent
1997-04-30
1999-06-29
Ghebretinsae, Temesghen
Pulse or digital communications
Equalizers
Automatic
375353, 370292, H03H 730
Patent
active
059178566
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for establishing a data communication connection in a data channel where PAM signals are utilized, the transmitter transmitting a training sequence, formed of predetermined symbols, a predetermined number of times, in which method: the data channel is monitored in order to detect a predetermined signal, samples are taken from the data channel, and the amplification of the receiver is adjusted in such a way that the received signals settle at a predetermined level.
The invention relates especially to multipoint modem networks utilizing PAM (Pulse Amplitude Modulation) signals and comprising one master modem which transmits the same data to several slave modems. The slave modems alternately transmit data to the master modem by reserving the channel in turn for their own use. In addition to transmission rate, training time also significantly affects the amount of data that can be transmitted in a time unit in such a network. In this connection, training time refers to the time required for establishing a connection. During the training time, synchronization is performed with the remote clock, and a descrambler and amplification are set, among other things.
In a previously known arrangement for establishing a datacommunication connection, fixed correction coefficients, dependent on the data channel used, are determined beforehand for the receiver, and, by means of the coefficients, the interference resulting from the data channel, between the symbols to be transmitted, is compensated for. A typical known equalizer of this type is a FIR (Finite Impulse Response) equalizer by means of which both the front part and the tail part can be removed from a pulse response. Since the correction coefficients are fixed, a connection can be established by setting correct amplification, synchronizing the receiver with the transmitter clock, and by setting a descrambler.
The major drawback of the aforementioned known solution is that when it is applied, the pulse response of the data channel must be known, so that the fixed correction coefficients can be set correctly. For example, when a multipoint network is set up, the assembler must manually adjust the correction coefficients of each modem to a suitable value. This is due to the fact that, for example when a copper cable is used, the pulse response of the data channel changes according to the cable length, so that the correction coefficients must always be set specifically for each case.
SUMMARY OF THE INVENTION
The purpose of the present invention is to eliminate the aforementioned drawback and to provide a method of establishing a datacommunication connection, which method requires no manual adjustments of the type described above. This object is achieved with the method according to the invention, characterized in that when the transmitter starts repeating the training sequence, during a time period it takes to transmit one training sequence the samples taken from the data channel are buffered in order to form a sample sequence, a channel pulse response estimate is calculated by convoluting the buffered samples with a predetermined symbol sequence, a main sample is selected from the pulse response estimate, correction coefficients are calculated from the pulse response estimate on the basis of the samples preceding and following the main sample, in order to minimize the interference on the data channel. And when the transmitter stops transmitting the training sequence and starts transmitting data, the samples taken from the data channel are corrected by utilizing the correction coefficients calculated.
The invention is based on the idea that when the receiver is adapted to calculate the pulse response estimate, on the basis of a predetermined training sequence transmitted through the data channel, by convoluting samples taken from the received training sequence with a predetermined sample sequence, and when the correction coefficients are set on the basis of the calculated pulse response estimate, there
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Benndorf, J. et al.: "Application of Fast convolution Algorithms Using Sampling Frequency change in Digital High-Speed Modems".
Ghebretinsae Temesghen
Nokia Telecommunications Oy
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