Excavating
Patent
1988-09-29
1990-07-03
Fleming, Michael R.
Excavating
371 55, G06F 1110
Patent
active
049397311
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCES TO RELATED APPLICATIONS
Reference is hereby made to copending U.S. application Ser. No. 07/220,211 to Reed et al. and copending U.S. application Ser. No. 07/220,213 to Goodwin, both assigned to the assignee of the present application.
FIELD OF THE INVENTION
The present invention relates to data transmission in an HF transmission system and in particular to a data transmission protocol.
BACKGROUND ART
HF is generally recognized as the frequency range 2-30 MHZ. For the purposes of this specification the term is intended to cover any frequency up to 30 MHZ and may include frequencies above 30 MHZ. The term is intended to designate a type of radio transmission usually involving ionospheric reflection, from the F-layer, the maximum usable frequency usually being somewhat less than 30 MHZ.
Commercial and military systems are known employing HF transmission between a large number of ground stations. For example, an army may possess portable transceivers carried on vehicles or as "man-packs" which rely on HF data transmission. Because of the nature of HF transmissions, usually involving ionospheric reflection, there is a high probability of errors in data transmission caused by bursts, rapid fading and gaussian noise. Further since a military system will be required to operate in all conditions and any geographic location, e.g. the Arctic circle, where disturbed ionospheric conditions of propagation may exist, these causes of transmission error may be compounded.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a data transmission protocol for data transmission in HF telecommunications systems which is reliable and can adapt to changing transmission conditions.
The invention provides in one aspect a data transmission system comprising a plurality of radio stations, each station including a transceiver with associated encoding/decoding means for transmitting/receiving data, wherein data signals are transmitted as packets including one or more blocks of data encoded with an error correcting code, wherein each station is arranged automatically to issue a request for repeat of a packet of data should it receive a packet containing errors which cannot be corrected, and wherein should the error rate in received packets be more than a predetermined amount over a predetermined interval of data transmission, the system is arranged automatically to reduce the rate of data transmission within each packet and/or change the channel frequency.
The invention provides in a further aspect a method of data transmission between a plurality of radio stations, each station including a transceiver with associated encoding/decoding means for transmitting/receiving data, the method comprising:
a first station transmitting data signals as a data packet to one or more receiving stations, the packet including one or more blocks of data each encoded with an error correcting code,
a receiving station receiving and decoding the transmitted data packet and transmitting an acknowledgement signal with a request for retransmittal of data should the packet contain more errors than can be corrected,
and the receiving station transmitting to the first station a request for change of data transmission rate and/or channel frequency should the error rate in the received packets be more than a predetermined amount over a predetermined interval of data transmission.
The invention provides in a further aspect apparatus for data transmission comprising a plurality of radio stations, each station including a transceiver with associated encoding/decoding means for transmitting/receiving data, wherein each station includes:
means for forming data packets for transmissions, each packet including one or more blocks of data each encoded with an error correcting code,
means for decoding transmitted data packets and for correcting detected errors, and means for transmitting an acknowledgement signal with a request for a repeat of a data packet should errors not be correctable,
and means for assessing the erro
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"Networked Meteor Burst Data Communications", by K. J. Kohjev et al., IEEE Communications Magazine, Vol. 24, No. 11, 11/86 (New York), pp. 23-29.
Hopkinson Jonathan N.
Reed Allyson
Fleming Michael R.
Plessey Overseas Limited
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