Telecommunications – Transmitter and receiver at separate stations – Distortion – noise – or other interference prevention,...
Patent
1988-09-19
1990-12-25
Eisenzopf, Reinhard J.
Telecommunications
Transmitter and receiver at separate stations
Distortion, noise, or other interference prevention,...
455 67, 455185, 455226, H04B 110, H04B 1700
Patent
active
049809245
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to improvements of HF radio communications systems and in particular to the establishment of a reliable radio link in the congested HF spectrum when either normal or disturbed propagation conditions exist.
HF is generally recognised as the frequency range 3-30 MHz. However 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 that part of the radio frequency spectrum where the wanted signal and/or interfering signals may propogate by reflection from the regular E or F layers of the ionosphere.
HF stations have traditionally required skilled operators in order to establish reliable communication channels. However skilled operators are in short supply and proposals have been made to automate certain call establishment procedures so that unskilled operators may operate the transmission equipment. Thus in IEE Conference Proceedings No. 245, 1985, "Real-time Frequency Management in an Embedded Microcomputer", E. T. Clarke, a microcomputer which is normally present in modern HF transceivers is employed to store a mode of the ionosphere so that predictions of usable channel frequencies may be made automatically.
Nevertheless the need still exists for a fully automatic method of establishing reliable frequency channels, since such prior proposals have all required manual intervention to some degree.
The present invention provides an HF radio communications system comprising a plurality of radio stations, each radio station including a transceiver and a control means therefor, the control means including a processor and a memory, the memory storing a model of the ionosphere of a designated region in digital form, the processor being arranged to compute from the model a propagation frequency window for the required communication channels beween the stations, the transceiver being controlled by the control means to assess passively the allocated channels within the frequency window in order to reject those channels which are occupied by high levels of noise or interference, and the system being arranged such that a first station establishes communications with one or more further stations in order to actively sound those allocated channels which have not been rejected in order to establish which channels are suitable for trasmissions.
As preferred, there is an initialisation procedure which takes place within the system between the various radio stations which form part of the system in which one station assumes network control. This procedure is more full described in copending application U.S. Ser. No. 07/220,213 to Goodwin, filed 09/29/88, the contents of which are herein incorporated by reference.
The station which has assumed control is preferably arranged to carry out the procedure referred to above, in which the station computes the propagation window and passively assesses the allocated channels. The network control station then assumes the role of said first station and actively sounds the candidate channels for communication with a selected number of further stations. However it is envisaged that the procedure set fourth above will also be carried out prior to any message transmission in the network wherein the source station assumes the role of the first station and the destination station the role of the further stations.
Thus in order to carry out the procedure set forth above, the first radio station is provided with an HF propagation prediction model which may be used to compute the Maximum Usable Frequency (MUF) and Lowest Usable Frequency (LUF) for skywave propagation and, for example, path loss for both skywave and groundwave propagation. In more advanced implementations, it is envisaged that the model may, for example, also take account of predictions of noise and interference in the data link.
The prediction model is used to compute the frequency window or windows in which suitable channels may be found. For a single address message (SAM), i.e. for co
REFERENCES:
patent: 4520508 (1985-05-01), Reichert, Jr.
patent: 4524446 (1985-06-01), Sun et al.
1985 IEEE Military Communications Conference, 20-23 Oct. 1985, by D. O. Weddle et al., pp. 146-150.
IEEE Communications Magazine, vol. 24, No. 11, Nov. 1986, pp. 23-29, by K. J. Kokjer et al.
A.F.I.P.S. Proceedings of the National Computer Conference, 19-22, May 1975, by J. Burchfiel et al., pp. 245-251.
IEEE Conference Proceedings, No. 245, 1985, by E. T. Clarke.
Instruction Manual for FT-290R by Yaesu Electronics Corp., Front Page and pp. 21-24.
"Software for Amateur Radio", by Joe Kasser, 1984 TAB Books, Inc., Front Cover, pp. 69-118, 167-172.
Clarke Ernest T.
Goodwin Robert J.
Reed Allyson P. C.
Williams David J. S.
Eisenzopf Reinhard J.
Kuntz Curtis
Plessey Overseas Limited
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