GB2306723A

GB2306723A - Data communication

Info

Publication number: GB2306723A
Application number: GB9522243A
Authority: GB
Inventors: Peter John Garrard; Peter Hibbitt
Original assignee: ADVANCED TECH UK Ltd
Current assignee: ADVANCED TECH UK Ltd
Priority date: 1995-10-31
Filing date: 1995-10-31
Publication date: 1997-05-07
Also published as: WO1997016909A3; WO1997016909A2; GB9522243D0

Abstract

A device for the communication of noisy data comprises transmission means to encode a digital signal into at least two analogue tone frequency signals and transmit them, receiving means (6) sampling each analogue tone frequency over a period of time substantially greater than 40ms, the samples of the analogue tone frequency each being decoded when possible into a digital signal, and a valid digital signal being accepted for outputting when at least a predetermined number of samples taken in said period of time give rise to the same digital signal.

Description

DATA COMMUNICATION The present invention relates to low power communication of data signals within a noisy environment and in particular to the recovery of a required data signal from a noisy signal.

One known method of communicating data is a method where the digital data is converted into analogue dual tone multi frequencies (DTMF) which are then transmitted. Analogue signals are used because the recovery of an analogue signal is feasible at much lower levels than a digital signal. The DTMF signal is then detected by a receiver. To help ensure the tone received is a valid signal an analogue delay means is employed. This monitors the input tone signal for a period of typically up to 40ms until the signal is judged to be effective and only then is the input signal processed.

The tone detector is normally a phase-lock loop. We have found that the present communication method is not satisfactory for an electronically noisy environment and for the processing of a noisy signal.

According to one aspect of the present invention there is provided a device for the communication of noisy data comprising transmission means for the encoding of a digital signal into at least one analogue tone frequency signal and the transmission of the analogue tone frequency signal through a transmission medium, receiving means for detecting and decoding the analogue tone frequency into a digital signal, in which the detecting process comprises sampling the analogue tone frequency over a period of time substantially greater than 40ms, the samples of the analogue tone frequency each being decoded when possible into a digital signal, and a valid digital signal being accepted for outputting when at least a predetermined number of the samples taken in said period of time give rise to the same digital signal.

Thus, during the sampling period, due to noise some samples will not be capable of being decoded into a valid digital signal, but other samples will be successfully decoded. It is necessary for a predetermined number of samples to be successfully decoded during the sampling period, for the "average" of the successfully decoded digital signals (they should all be the same) to be taken as the valid digital signal.

The predetermined number is preferably greater than 50% of the samples.

Preferably the analogue tone frequency is in the form of a multi tone multi frequency. Alternatively the analogue tone frequency might be simplified to the form of a dual tone multi frequency.

Also preferably the analogue tone frequency signal is transmitted in the form of radio waves. Alternatively the analogue tone frequency signal is transmitted through electronic circuitry and/or electrical wiring.

Preferably the transmission unit comprises a microprocessor, a logic encoder and a transmitter.

Preferably the receiver means comprises a receiver and a microprocessor.

Also preferably the receiver device samples the analogue tone frequency signal ten times in one second.

By way of example only the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a representation of the flow of communication signals in a system in accordance with the invention; Figure 2 shows a dual tone multi frequency matrix; and Figure 3 shows how the transmission time or number of samples is increased in dependence on the signal to noise ratio.

With reference to Figure 1, a device 1 for the communication of noisy data comprises a dual tone multi frequency (DTMF) encoder 2 comprising a digital input 3 and an analogue output 4, a transmitter 5, a receiver 6 and a dual tone multi frequency decoder 7 comprising an analogue input 8 and a digital output 9.

The digital input 3 receives a digital signal. The digital signal is split into separate strings 10 containing four digital bits. Each string 10 comprises a different combination of digital bits.

With reference to Figure 2 the separate strings 10 may be represented by a combination of two of the tone frequencies of columns 11, 12 and 13 and rows 14, 15 and 16. The combination of the two tones forms an analogue dual tone multi frequency signal which is transferred from the analogue output 4 to the transmitter 5. The dual tone multi frequency encoder may be in the form of a telephone tone dialler such as a HoltekTM HT-9101.

The dual tone multi frequency signal is then transmitted by the transmitter 5. The encoder 4 is included within the HoltekTM HT-9101. The transmitter 5 could be in the form of a radio transmitter such as a ScantronicTM 4689-UK-00 module.

The receiver 6 receives the transmitted signal and supplies it to the analogue input 8. A typical receiver and decoder which may be used is a Holtek HT-9170 device. The receiver could be in the form of a radio receiver such as a ScantronicTM 4666-UK-00.

The receiver 6 device may be modified so that the dual tone multifrequency signal received is sampled over an extended period of data transmission time and the samples are then examined. Those samples of the dual tone multi-frequency signal that are capable of being decoded to give a digital signal are decoded. Other samples, due to noise, may be incapable of being decoded. A minimum requirement, say 50%, is set for the number of samples that must be successfully decoded in the extended period. Provided that this requirement is met, then the digital value of the successfully decoded samples is taken as the valid digital signal. This gives improved data recovery for a noisy signal over a greater distance of up to 1000 metres. This method also provides more reliable data recovery for noisy signals compared with conventional methods.

It will be appreciated that the number of digital bits contained in each separate string may vary and is not limited to 4 bits.

It will also be appreciated that each string may represent a predetermined command.

Figure 3 shows how the transmission time, or number of samples, is increased to deal with a reduction in the signal to noise ratio.

It will also be appreciated that the number of analogue tone frequencies transmitted concurrently is not limited to 2. That is, a multi tone multi frequency signal can with advantage be used.

Claims

1. A device for the communication of noisy data comprising transmission means arranged to encode a digital signal into at least one analogue tone frequency signal and to transmit the analogue tone frequency signal through a transmission medium, receiving means adapted to receive the analogue tone frequency signal from the transmission means and arranged to detect and decode the analogue tone frequency into a digital signal, the receiving means being arranged to perform a detecting process comprising sampling the analogue tone frequency over a period of time substantially greater than 40ms, the samples of the analogue tone frequency each being decoded when possible into a digital signal, and a valid digital signal being accepted for outputting when at least a predetermined number of the samples taken in said period of time give rise to the same digital signal.

2. A device as claimed in claim 1 in which the predetermined number is greater than 50% of the samples.

3. A device as claimed in claim 1 or claim 2 in which the analogue tone frequency is in the form of a multi tone multi frequency.

4. A device as claimed in claim 1 or claim 2 in which the analogue tone frequency is in the form of a dual tone multi frequency.

5. A device as claimed in any of the preceding claims in which the analogue tone frequency signal is transmitted by the transmission means in the form of radio waves.

6. A device as claimed in any of the preceding claims in which the transmission means is in the form of a unit comprising a microprocessor, a logic encoder and a transmitter.

7. A device as claimed in any of the preceding claims in which the receiving means is arranged to sample the analogue tone frequency signal ten times in one second.

8. A device for the communication of noisy data substantially as described herein with reference to Figure 1 of the accompanying drawings.