Shaye Communications Limited

David J McCabe

Graham E Beesley

Jasjit S Saini

Corruption in digital data communications systems is detected, at the receiving end, by taking a number of samples of the received signal within each bit period. Flip flops (4, 7 and 8) are used to take samples from the digitized received signal as follows: flip flop (4), a mid bit sample indicative of the value of the center of the bit; flip flop (7), a pre-mid sample taken within the bit period before the mid-bit sample; and flip flop (8), a post-mid sample taken within the bit period after the mid-bit sample. Gating circuitry (23, 24, 25) is used to analyse the three samples and give a 'good' or 'bad' output signal to register 11 as a result of the analysis. Corruption is judged to be present if any one of the samples has a different value to the others.

Digital communications systems

A method of establishing a digital time-division duplex radio communication link between one of a plurality of portable units and a base unit in a cordless telephone system, transmissions from the base unit are allowed only on a ping-pong basis with transmission bursts from all the active transmitters in the base unit being synchronized with one another. This prevents blocking of receiver sections due to co-sited transmitters transmitting at the same time on a different channel. The difficulty of synchronizing the transmission bursts of the active portable units with their respective transceivers within the base unit is overcome by allowing the portable unit to make an initial continuous call comprising multiple identical sequences of data containing units small enough to be completely received within the limited reception windows of the base unit. After the initial call has started communication, an exchange of signals takes place on a ping-pong basis to establish synchronism between the portable unit and base unit. Finally, if all is well, the system reverts to a speech mode in which voice signals rather than data signals are exchanged between the portable unit and base unit.

Duplex communications method and system

A waveform encoder/decoder includes an encoder having an input for an audio signal to be encoded, and an output whereby the digitally encoded signal is passed to a transmission link and then to a corresponding decoder. The encoder includes detectors for monitoring the digital output signal for slope overload and idle pattern respectively and setting a corresponding value in a state machine. The value stored in the state machine is used to control a pulse width generator which in turn controls the enable time of a tri-state gate connected in the feedback path from the output back to the input. An R.C. filter is used to reconstruct the digital output from the gate to form an estimate of the audio input signal, and this estimated signal is compared with the actual input signal in a comparator. A D-type flip-flop is used to digitize the output from comparator to generate the signal to be output to the transmission link. The circuit, being fully digital, ensures improved repeatability and is particularly convenient and low in cost.

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Winchester, United Kingdom

David J McCabe