Patent GB-1156968-A (GB)
Title: Data Transmission System
IPC: H04L23/02
Filed: 1967-09-19
Abstract: 1,156,968. Multiplex systems; pulse signalling. INTERNATIONAL BUSINESS MACHINES CORP. 19 Sept., 1967 [7 Oct., 1966], No. 42495/67. Headings H4L and H4R. In a multiplex transmission system of the type described in Specification 1,129,373, in which orthogonal channel signals are formed by multiplying together selected harmonically related sinusoidal signals and selectively gating them to the line for a specific time, some of the channel signals are produced by multiplying together at least three of the harmonically related sinusoidal signals. By appropriate selection of the number and frequency of the component sinusoidal signals orthogonal product waveforms having particular characteristics may be produced, e.g. low bandwidth, flat frequency distribution, smooth transitions at the switching points, or abrupt transitions, the latter being particularly suitable for synchronizing signals. The actual orthogonal signals used may be changed during transmission if desired, e.g. in an adaptive system. Transmitter, Fig. 1. Comprises a coder 101 receiving input data in any form and providing, at its output, samples on a number of lines, the samples being either analogue or digital, simplex, or multiplex. The samples are fed to, and held in, buffer 100 for the duration of each timing period of the transmitter as regulated by timer 103. Timer 103 also synchronizes the production of harmonically related sinusoidal waves in frequency synthesizer 104 from which the waves are fed via matrix 114 to the multipliers M to provide the product waveforms to be fed to the gates G1 to G5, and hence to the summation network 119 and the outgoing channel in accordance with the signals stored in buffer 100. Since the power level may vary in accordance with the number of participating waveforms, the mode of operation, and the coding scheme employed, one product signal is modulated in gate Gp with the power level, as signalled by programmer 105, and the variable gain amplifier 120 is adjusted to maintain the power output constant. Gates GM and GS are utilized to transmit synchronizing signals. Matrix 114 may be some form of cross point switch controlled by controller 121 to vary the product waveforms used from time to time in accordance with a desired programme, or observations on transmission conditions. Receiver, Fig. 2.-Comprises a frequency synthesizer 135, matrix 136 and a multiplier tree similar to that at the transmitter to produce a similar set of product waveforms which are applied to respective multipliers M1 to Mp together with the incoming signal from the receiver 123. The outputs of the multipliers are applied to integrators 128 to 133, which are sampled and reset at the basic timing period of the system in order to recover the coded signals which, fed via buffer 162 to decoder 163 enable the original data to be reproduced. The synchronization may operate in a phase lock loop on the synchronizing channels, and the power level control signal for the receiver a.v.c. is derived from the power level control channel via programmer 164. As in the transmitter the connections of matrix 136 may be changed periodically according to a stored programme or adaptively in accordance with transmission conditions.