Priority coding system

Claim 2

A communication system including a transceiver for transmitting and receiving a signal comprising a plurality of channels one of which consists of analogue speech signals and at least one other of which consists of data signals transmitted at intervals and interleaved with the speech signals, the data signals each comprising at least one complete cycle of a frequency or frequencies, which lie within the audio frequency spectrum wherein the significance of the data i.e. '0' or '1', is defined in dependence upon its phase or frequency and wherein the data signal transmission rate is determined in dependence upon error rate detected in relation to the data signals received at a remotely located transceiver

Claim 3

A communication system as claimed in claim 1 wherein the transceiver comprises a transmitter fed via a first switch either with speech signals from a speech transmission channel unit or with data signals from a data transmission channel unit in dependence upon the operative state of the first switch and a receiver comprising a second switch which is operatively associated with a sync control unit responsive to signals received from a remote transceiver for synchronising operation of the second switch so that data signals are fed . thereby to a data reception channel unit and speech signals are fed thereby to a speech reception channel unit, the data reception channel unit being operatively associated with a data error rate detector means for producing a local error rate signal indicative of the error rate appertaining to locally received data, which local error rate signal is fed to the data transmission channel unit for inclusion with the data signal for transmission and a data transmission rate controller responsive to a received error rate signal indicative of the received error rate sensed at the remote transceiver for controlling the rate of data transmitted in dependence upon the received error rate signal.

Claim 4

A communication system as claimed in claim 1 or claim 2 wherein as the detected error rate increases more data bits are used to define each data word whereby the data word transmission rate is decreased.

Claim 5

A communication system as claimed in any preceding claim wherein a frequency shift keying technique is utilised to define the significance of a data signal, i.e. the data significance '0' or '1' is indicated in accordance with the frequency of transmission.

Claim 6

f: 5. A communication system as claimed in any of claims 1 to 3 wherein data signals are transmitted utilising a phase shift keying technique-wherein the significance of data i.e. '0' or '1' is indicated in accordance with the phase of the transmitted signal.

Claim 7

A communication system as claimed in any preceding claim wherein data is derived from a light pen comprising means for scanning a bar coded pattern to provide a corresponding data digital signal.