International Business Machines Corporation

Andrzej T Milewski

Dominique N Godard

Gerald Lebizay

Michel Demange

Alain Vedrenne

A 3-stage switching system is provided for generating, i.e. finding, reserving and setting, path from one switch entrance port (1) to at least one switch exit port (transmit side) for asynchronously received and buffered data cells. While an Nth cell is being transferred, control means (36) generate a control word including the switch exit port address for cell (N+1)th to be subsequently transferred. Said control word is used to find and reserve a path through the switch on a stage-by-stage basis, and then set said path, if any, using a fed back acknowledgement. The (N+1)th cell path generation is performed during cell N transfer, on a cycle stealing basis.

High speed digital packet switching system

An adaptive phase detection method and apparatus is described which provides an estimated value .phi..sub.n of the phase .phi..sub.n transmitted at a signalling instant nT in a data transmission system using a M-phase PSK modulation technique. The system compensates for the effects of the intersymbol interference created by not more than one leading lobe of a succeeding signal and an arbitrary number of trailing lobes of preceding signals caused by the impulse response of the transmission channel. The method of the present invention mainly comprises the steps of:

Adaptive phase detection method and apparatus

The invention provides a carrier detector for use in a multipoint communication system. In these systems a common communication link interconnects a master modem to a plurality of remote slave modems and a slave modem has to initialize itself without disturbing transmission of data between the master modem and another slave modem. Initialization is to be performed on such data, and the slave modem must be provided with a detector capable of detecting when data is being transmitted. The invention describes such a detector which is independent of the received signal power. The input signal is sampled at rate 6/T, T being the baud rate, and passed into two narrow band filters F1 and F2, centered at Nyquist frequencies f.sub.1 and f.sub.2, respectively. The sum of the outputs from filters F1 and F2 is sampled at a rate of 1/T for each of six different phases of the sampling rate 1/T. The energy of the six samples so obtained is measured. If only noise is received, the six measured energies must be theoretically equal; in practice, they will be of the same order of magnitude. When data is received, the six energies are very different. The indication 'data is being transmitted' is given if the largest energy E.sub.max is greater than a fixed multiple of the smallest one E.sub.min.

Carrier detector

A method for determining the initial values of the coefficients of a complex transversal equalizer in a synchronous data transmission system employing Double Side Band-Quadrature Carrier (DSB-QC) modulation on a transmission channel having variable distortion from message to message is disclosed. The coefficients are derived from training sequences which consist of periodic pseudo-random sequences of complex numbers having a periodic autocorrelation function, all the coefficients of which except the first are zero. The amplitude of all complex numbers of the sequence is constant. Sequences with these characteristics are identified as CAZAC sequences. With the exception of a training sequence generator and a coefficient generator the system utilized is a conventional data transmission system utilizing the DSB-QC modulation technique.

Method and apparatus for determining the initial values of the

A method for determining the initial values of the coefficients of a transversal equalizer for a synchronous data transmission system, wherein a training sequence is transmitted to allow the equalizer coefficients to be adjusted to optimum initial values. According to the method, a sequence (v.sub.i) of L elements v.sub.i, having a periodic autocorrelation function, only the first coefficient of which is not zero, is derived from a periodic binary pseudo-random sequence (u.sub.i) of L binary elements u.sub.i having a periodic autocorrelation function, the first coefficient of which is equal to L and each of the other coefficients are equal to -1. Then, the sequence (v.sub.i) is transmitted through the transmission channel and the initial values of the equalizer coefficients are derived from the received sequence. In a preferred embodiment of the invention the initial values of the equalizer coefficients are derived from the received sequence through a direct method which involves the calculation of the autocorrelation matrix of samples of the transmission channel impulse responses.

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Saint-Jeannet, France

Andrzej T Milewski