CA1230928A - Frequency management system - Google Patents
Frequency management systemInfo
- Publication number
- CA1230928A CA1230928A CA000443939A CA443939A CA1230928A CA 1230928 A CA1230928 A CA 1230928A CA 000443939 A CA000443939 A CA 000443939A CA 443939 A CA443939 A CA 443939A CA 1230928 A CA1230928 A CA 1230928A
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- Canada
- Prior art keywords
- channels
- frequency
- receiver
- sounding
- channel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT
Disclosed is a frequency management system to enhance communication reliability over HF channels in the 2 to 30 MHz band. Real time channel monitoring, evaluating, sounding and frequency allocating procedures are integrated into a single HF radio system using a single range of equipment. The best of available HF channels is automatically acquired by means of a single two-way exchange of unique sounding signals between members of an HF network.
Disclosed is a frequency management system to enhance communication reliability over HF channels in the 2 to 30 MHz band. Real time channel monitoring, evaluating, sounding and frequency allocating procedures are integrated into a single HF radio system using a single range of equipment. The best of available HF channels is automatically acquired by means of a single two-way exchange of unique sounding signals between members of an HF network.
Description
~3(~Z~3 T11~ PRIOR ART
lonospherically propagated radio signals are frequen~.ly subjected to soveL-e levels of amplitude and phase distortions from fadine, multipath and noise phenomena as well as man--r11ade inLc L' feronce ef~ct.s.
ln attempting to maximize the availability and relia-bility o~ communications through the HE' medium, it is TIUW
1.0 woll recognizod that the following two factors are predominant:
l. Ti1e determination of the optimum propagating frequency ~OL any selected path and time, and
lonospherically propagated radio signals are frequen~.ly subjected to soveL-e levels of amplitude and phase distortions from fadine, multipath and noise phenomena as well as man--r11ade inLc L' feronce ef~ct.s.
ln attempting to maximize the availability and relia-bility o~ communications through the HE' medium, it is TIUW
1.0 woll recognizod that the following two factors are predominant:
l. Ti1e determination of the optimum propagating frequency ~OL any selected path and time, and
2. rho validaLion that this sclocLed channol is also intorforcnco free, primarily at the recoiver's end.
'I'hQ most accu~aL~ mcans ~or sp~?cifying propagation conc1itions ovor a give11 1iF circuit is attained through r~?al-timc oblique path sounding. The incorporation of real time propagation data wiLh accurate spectrum-interference data at a receivcr provides the basis for a practical frequency manage-ment system. To be fully effective, however, HF frequency managemer1t would also require some means to rapidly disseminate reco~unendcd freql1cncios or spectrum information to multiple 11F
~S users. Moreovor, this distribution of frequency assignments should be roadily availablo, secure and not subject to the HF
oul.ages it is designed to avoid.
1ho bandwidth that will support skywave communication botwc~:!(1 any two points is normally much less than the 28 MHz-wide 11~ spectrum. The available bandwidth cha11ges cyclically Otl daily, annual, and eleven-year cycles and may be dislurbod by unpredictable short-term effects. Frequency assignn1ents aro commo11ly made using forecasts based on t.he slal.i;l.ical variations of propagation expectancy cycles, t.he path and the L`requencies available to the assi~ning authority.
"~
'I'hQ most accu~aL~ mcans ~or sp~?cifying propagation conc1itions ovor a give11 1iF circuit is attained through r~?al-timc oblique path sounding. The incorporation of real time propagation data wiLh accurate spectrum-interference data at a receivcr provides the basis for a practical frequency manage-ment system. To be fully effective, however, HF frequency managemer1t would also require some means to rapidly disseminate reco~unendcd freql1cncios or spectrum information to multiple 11F
~S users. Moreovor, this distribution of frequency assignments should be roadily availablo, secure and not subject to the HF
oul.ages it is designed to avoid.
1ho bandwidth that will support skywave communication botwc~:!(1 any two points is normally much less than the 28 MHz-wide 11~ spectrum. The available bandwidth cha11ges cyclically Otl daily, annual, and eleven-year cycles and may be dislurbod by unpredictable short-term effects. Frequency assignn1ents aro commo11ly made using forecasts based on t.he slal.i;l.ical variations of propagation expectancy cycles, t.he path and the L`requencies available to the assi~ning authority.
"~
3~
lntcr~erence may have cornponents due to external causes (Kalactic, atmospheric or receiver noise) but it is actually man-made noise and particularly the widespread interferences from distQnL HL~ stations, that accounts for the main source of errors in HL~' data con~,unications. The HE bandwidth is heavily ovorcrowded especially at night and msny observations have revealed that outages due to interferences from other users muy exceed t;hose due to propagation by a factor of five.
Knowledge of the level of interference present in a communi-cation~ channel is essential for channel optimization, ascommunications will take place on a channel showin~ the groatc!st value of signal-to--interference ratio.
The most advanced H~' frequency management system, typically consists of various combinations of three dedicated eqllipment items. Two of these items, an oblique sounder transmitter and sounder rece;ver provide an ionospheric "test set" measuring the propagation of an HF signal vs frequency over the communication path. The. third item, a spectrum monitor, provides the extent of interference measured across the entire 2 -- 30 Mllz bflnd during the past 5 - 30 minutes. Tn a typical chirpsounder system the sounder transmitter sends a linear lM/CW test signal (2 to 30 MHz chirp) and is track~d by fl time synchronized chirpsounder receiver at tho other end of the con~ nications paih.
SpocLrfll unalysis of the difference frequency between the soundoL receiver local oscillator and the incoming signQl yields a tirrle delay-vs-radio-frequency di~lay.
Specific conclusions with respect to tile operational utilization of such fl system indicate thflt:
L. A close oporationfll control and coordination is required I-ctween Tnultiple users of the system. Simultaneous soullding~ requires careful transmitter synchronization.
~23~
lntcr~erence may have cornponents due to external causes (Kalactic, atmospheric or receiver noise) but it is actually man-made noise and particularly the widespread interferences from distQnL HL~ stations, that accounts for the main source of errors in HL~' data con~,unications. The HE bandwidth is heavily ovorcrowded especially at night and msny observations have revealed that outages due to interferences from other users muy exceed t;hose due to propagation by a factor of five.
Knowledge of the level of interference present in a communi-cation~ channel is essential for channel optimization, ascommunications will take place on a channel showin~ the groatc!st value of signal-to--interference ratio.
The most advanced H~' frequency management system, typically consists of various combinations of three dedicated eqllipment items. Two of these items, an oblique sounder transmitter and sounder rece;ver provide an ionospheric "test set" measuring the propagation of an HF signal vs frequency over the communication path. The. third item, a spectrum monitor, provides the extent of interference measured across the entire 2 -- 30 Mllz bflnd during the past 5 - 30 minutes. Tn a typical chirpsounder system the sounder transmitter sends a linear lM/CW test signal (2 to 30 MHz chirp) and is track~d by fl time synchronized chirpsounder receiver at tho other end of the con~ nications paih.
SpocLrfll unalysis of the difference frequency between the soundoL receiver local oscillator and the incoming signQl yields a tirrle delay-vs-radio-frequency di~lay.
Specific conclusions with respect to tile operational utilization of such fl system indicate thflt:
L. A close oporationfll control and coordination is required I-ctween Tnultiple users of the system. Simultaneous soullding~ requires careful transmitter synchronization.
~23~
- 4 --2 When the pool of assigned frequencies is not very 1arge, tl-"~ use Or t.his system may prove to be counter-productive or over ~pcc;ficd.
3. Ln a mi].itary environmont, sounder transmitters havr-! a S VeLy 1.arr,o, identifiable si~nature and must, therefore, bo placcd some distance from communication conters to minimize tho risk of direction-finding, jamming or phys;cal destruit;on.
'1. rhll simultaneous radiation o~ multiple sounding trans 1.0 milters continuously scanning the entire 2 to 30 MHz bnnd pollutos tho HF spectrum, raises the R~ noise floor and consoquonlly se]r-jams friendly HF con~unicz~tion roceiving equipment.
S. Tho HF propagaLion path is not reciprocal, particularly LS wil.. h rospect to the extraordinary modes. Resorting to two way snunding per link will render the communication nelwl:,rk operat.iona].ly inlractable and oconomically inl-ler.lhle in view o~ tho magnitude and hi8h cost of such a systerll. 0 6. Hulllall judeement and analysis cannot entir~.31y be r~!E~laced. Intel].igent and exporienced asscssment o~ the dynamic iono~ram is Or paramount importance. This sy~l.t?m roquiros the continuous intervention of a sk;lled ~ o r .
S
A radica]ly di~erent concept is therefore needcd ~ tO
a singlo add-on torrn;nal contro1s and uses any standard rllodern H~ communicaLions oquipment to automatically probe a laTt~e number "r ~requoncy channels within an assigned HF sub-band.
:~0 lt sha].l perform sounding, 1.ink quality evaluations, select nnd socu(oLy disseminate thc besl; operating frequencies, to achiove rapid and re;iablc link connectivity.
~3~
Sl)MMAR~ 0~ Tli~ INVENTlON
Il is the priMary object of this invention to provide a new real time ~requency management system which will p~:rmit the automatic solection of optimum operational frequencies in H~ conunullication transmitters and receivers.
It will estab]ish communication links without the intervcTIt.ion of ski]led operators, eliminate the need to resort to propagation predictions~ and thus enhance the usefulness and reliability of high frequency communications systems.
ln accordancc with the fore&oing objects the invention hcrcill is directed to frequency programmable HF conm~unication systeins which employ transmitters and receivers capable, ;n response to control si&nals, of remote tuning and scanning a plura].ity Or channels. A high frequency communication network has onc controlling station and a plurality of controlled stulion.q. Moans are provided for all stations to continuously motliLor a larga group of randomly selected frequencies wit:nin a given band, measure and analy~e their noise and interf~reT?ce characterisTics and hard-label each channel as either 'noisy' or 'quiet', based on a set of criteria. The resulting b;TIarY
word is used by thc controlling station, in a prese]etted formaT., as the sounding message. Additional means are provided ~5 fcr lhe conl.rolling station to redundantly broadcast the same sounding mcqsage sequenTially over each one of the channels.
The radio trnnsmitters and receivers are synchronously hopped ~ccording to a pseudo-randomly coded sequ~rlce.
'I'he controL]cd station has the means for majority decoding Lhe highly redundant soundin& message and furl:her means for rncasuring the link quality of each channel on which that mc~ssagc was received. The link quality analysis includes mcalls ~or measuriny, bit-orror-rates (BER), multipath delays, fading rate~, inter~ercnce lcvels and distributions and signal-to noise ratios.
~f23C~
'IH~C! controlled station consequently generates another binary word in which each bit represents a hard-decision, bascd ~n a ~et of transmission quality criteria, as to whether thc corre~ponding, scanned channel is accepted as 'good' or S 'bad' ~or con~lunicat.iorls~
This link quality pattern is now used by the controlled stution as its answer--back soundin~ messages-rhe contro].l;ng station majority decodes the repetit.ive sounding broadcast made by the control.led station while iSsynchronously sequences tho ent.ire group of frequencies. It pcr~orrlls its own link quality analysis and compares the data processed at both ends of the link. The contro]ling station now derivcs tha optimal operating frequellcies. The selected 1.5 frequencies arc then ~utomatica].ly disseminated using the same fcequency hopping l.ransmission.
Accordinely, tho invention rclates to a high-frequency (H~) frequcncy-manngcment system wiLh ~t least two stations, a control.].ing stalion and one or more contro]led stations, each including an 11~ radio transmitter, HF radio receiver, a conlrol unit t`or controlling the operation of the transmitter and receivel and a frequency-management processor means for:
- continuously monitoring the interference and occupancy of a ~inito plurality o~ H~ channels, each channel tuned t.o a difrerent frequency;
-- hnrd-labeling of each one of the said channels as either a binaly"L" for a 'quiet' channel or a binary 1l0ll for a 'noisy' chanllel ~or vice versa?, based on a predetermined set of criteria;
-- storing and updating the resultin~ binary word wherein cucll bit represents an eva].uation of one of the freque7)c~ies visited:
-- using this binary word as a sounding sign;ll and tri~llsmitl..ing this signal repent.edly, once over each of the said finite ~roup of trequencies by having the transm;t.ter scun said ch~JIlrl~13;
~ ~3(~9;~3 -- synchronizing the remot0 station receiver so that it is scquenced through same said group of channels at an equal rate, bcing at each onc of the channels at the same period of timc as the transmitter, to allow the sounding message to be rcceived;
- majority-detecting said redundant sounding message by the remotc recciver proce~or;
- performing link quality measurements on each one of the scanned group of frequencies;
- hard-labeling Or each one of the said channels as either a binary"l" for a 'good' or 'acceptable', and a binary "O" for a 'ba~' or 'not-acceptable' con~unication quality ~or vice versa), based on another sct of crite~ia;
~S - storing the resulting binary word at the remote station rcceivor-processor, to be used by it in formi-l~ the answcr--back sounding signal;
- translllitting the answer-back sounding messa~e repeatedly, once ovcr each of the said group of channels by having the ~0 rcmolc sLation transmitter scan said channels;
- rnajority-detecting said redundant answer-back sounding mcssage by the first, controlling station receiver processor;
-- performing link quality measurements by the controlling station receiver-processor, on each one of the said scanned ~S group of frequencies;
-- selecting optimal frequencies by the controlling station processol, for reliable con~unications in both direct;ons, contrnlling-to controlled and controlled--to-controllin~
stations, based on the analysis of the received and der;ved link quality patt~rrls;
-- utilizing the synchronous frequency--hopping mode ~hich is maintaincd between the stations, to disseminate frequency informaticn by t~ansmitting, over the selected optimal frcqucncies, the relevant information for the remote station;
- automatica]ly tuning the communications transmitters and rcceivers to the selected preferred frequency or frequencies, to establish a reliable con~unication path between the stal;olls;
~;~3~
Thc timing and control means comprise:
--- mcans for randomly selecting N channels from within a specified IIF sub-band given its limits fl to fhi h;
S ---- mealls for storing said N channels as alternate colllTnuni-cal.ion channels with each channel having a predetern1;ned frcquency;
-- reccive/transmit means for placing the station in a transmiL mode;
1.0 --- mcans for sequencing and tuning the HF receiver and transmitter through the group of N channels;
--- means for providing timing for the overall system operation, bit synchronization, frame sync acquisition, sync cycl.e operation, sounding cycle operation and signal pro-cessin~ algorit.hllls;
- means for transmitting the sounding messages using an in cllannel diversity of two FSK modulators-demodulators;
- means ~or ~cneraLing a predetcrmined sequence based on the inpllt of a key variable and real time of day.
lhc noisc and interference measurement means comprise:
- mcans for measuring the radio receiver AGC level and radio receiver noisc output and distribllt.ion;
~5 --- means for measuring in-channel interferencc chatacteristics;
--- mcans for classifying noise and interference present on the COnmllJniCatiOn channel into a predetermined number oE
catc~ories, according to a predetermined set of criteria;
~- means for generating a corresponding number of binary words, each N-bit lon~, one for each category, wherein each bit represents a hard-decision qualifying each one of the N
communication channels monitored;
~,3~
_ 9 _ The link quality analysis means comprise:
--- means for de'ectin" noj~e representative of the noisr3 prcsent within the communication channel band as well as within two soparate ESK channels;
-- data detectors for prcviding a signal representative of thc data levels that are present on the con~lunication channel th~ the r~ceiver is tuned to;
-- means to measure the signal~to-noise r~-tio, the fading rato, and the rms multipath delay spread;
-- mean~ to UCf3 the demodulated rnd màjority-dete(ted sounding message to arrive at the actual bit-error-^rate;
-- mcans for quantizing tbe parameters: signal-to--noise-ratio and bit-error-rate, iC desired in combination witn one or more 15 of ~I1C! parameters: fading rate, delay spread, channel noise, datfl levels; measured on the communication channel to define tho dosirod predotermined number of link quality categories arcording to a predetermined set o~ criteria;
-- means for gcnerating a corresponding number o~ binary words, each N-bit long, one for each category, wherein each bit represents a hard-decision qualifying respectively one of the N communication channels sounded;
Jhe advanta~es and further objects of the invention, and 71 thc mc;lns by which they are achiev3d may be best appreciatr~d by referrin~ to ~hr3 detailod descripti~n which follows~
BRlEI` DUSCRIP'rION 0l~ Tll~ DRAWI~S
,~
~5 A more complete description of this invention may be had - ~ by re~erence to the ~ccompanying draw-ngs, iL.~rr~ing piererrr3d emhodilllf3rlt of the invention ts be drscribed in ~otail, wherein ~ Fig~ 1 depicts three ;J OCk diagralns ill~strating three r , ./ ~i frSJrell~ configurQtior~ of IJF e~ 3unications systems in wbich ~i? s~fS~ o~ ~he present invrl~iorl i integra~ed~
... . . .
,. . ,. ~,~
2~
.;,~. 2 outlines the format for soundi.ng messages between -not 5 tations.
~ ig. 3 outlines the format used in the network synchron-i~ation transmission cycle.
Fig. 4 ;s a simplified block diagram of the frequencymanagement system according to an embodiment of the pr~st~nt inve~ ion.
Fig. 5 is a functional block diagram of the system accnrdirl~ to an embodiment of the present invention.
I:)k'TIll l.r~:D VESCRIPl~ION 0~' TIIE PREF'ERRP:D EM80DIMENT
15`
~ orore going into a detailed description of the figures a brie~ overvicw will be given describing the environment and gt)neral ~eatures of the syxt.~m.
~rhc oporational situation typically assumes a network of HF radio USeL'S generally structured using a net controlling station in association with a plurality of widely scat.t.~red control.led stations, including relay stations.
~'ach controlled net station is expected to continuously 25 monitor the net traffic and to respond if polled by t.he contro].lin~ net station. Only one station at a time wnuld thon he transmitting, with transmit discipline being maintained by the controlling stat.inn.
Centralized fret~uency management and control, with full froquency assignment authority would normally be the rcspt~nsi-bility of the controlling station, within the single-net or thc multi--net configuration. Operational configurations, howcver, using one-way transmissions only, utili7e the capa-:~S bilil..y of the prescnt invention to assign the selection nf optimal IIF frcquencies to the controlled terminal.
1~3~ 2~3 ~ '~lC system according to the invention, can be used for the real-time management of HF communication networks having onc controlling station and one or more controlled (or rerllote) stations. The system is adapted to provide a frequerlcy S manaKometlt capability for any predetermined number of frcquencies. Practical considerations show that generally, a number of from about 50 to about 150 frequencies provides a suitable sysLern, depending on the conditions of use and the rcquirod speed and reliability. The operating sub-bands are 1.0 chosen to have an adequate width for accoEnodating the prodctermined numbor of frequencies, with an adequate spac;ng beLweon the frequencies used. In the eollowing, the invention is il.l.ustrated in an entirely arbitrary manner with reference to a system of 125 channels. It ought to be understood that
3. Ln a mi].itary environmont, sounder transmitters havr-! a S VeLy 1.arr,o, identifiable si~nature and must, therefore, bo placcd some distance from communication conters to minimize tho risk of direction-finding, jamming or phys;cal destruit;on.
'1. rhll simultaneous radiation o~ multiple sounding trans 1.0 milters continuously scanning the entire 2 to 30 MHz bnnd pollutos tho HF spectrum, raises the R~ noise floor and consoquonlly se]r-jams friendly HF con~unicz~tion roceiving equipment.
S. Tho HF propagaLion path is not reciprocal, particularly LS wil.. h rospect to the extraordinary modes. Resorting to two way snunding per link will render the communication nelwl:,rk operat.iona].ly inlractable and oconomically inl-ler.lhle in view o~ tho magnitude and hi8h cost of such a systerll. 0 6. Hulllall judeement and analysis cannot entir~.31y be r~!E~laced. Intel].igent and exporienced asscssment o~ the dynamic iono~ram is Or paramount importance. This sy~l.t?m roquiros the continuous intervention of a sk;lled ~ o r .
S
A radica]ly di~erent concept is therefore needcd ~ tO
a singlo add-on torrn;nal contro1s and uses any standard rllodern H~ communicaLions oquipment to automatically probe a laTt~e number "r ~requoncy channels within an assigned HF sub-band.
:~0 lt sha].l perform sounding, 1.ink quality evaluations, select nnd socu(oLy disseminate thc besl; operating frequencies, to achiove rapid and re;iablc link connectivity.
~3~
Sl)MMAR~ 0~ Tli~ INVENTlON
Il is the priMary object of this invention to provide a new real time ~requency management system which will p~:rmit the automatic solection of optimum operational frequencies in H~ conunullication transmitters and receivers.
It will estab]ish communication links without the intervcTIt.ion of ski]led operators, eliminate the need to resort to propagation predictions~ and thus enhance the usefulness and reliability of high frequency communications systems.
ln accordancc with the fore&oing objects the invention hcrcill is directed to frequency programmable HF conm~unication systeins which employ transmitters and receivers capable, ;n response to control si&nals, of remote tuning and scanning a plura].ity Or channels. A high frequency communication network has onc controlling station and a plurality of controlled stulion.q. Moans are provided for all stations to continuously motliLor a larga group of randomly selected frequencies wit:nin a given band, measure and analy~e their noise and interf~reT?ce characterisTics and hard-label each channel as either 'noisy' or 'quiet', based on a set of criteria. The resulting b;TIarY
word is used by thc controlling station, in a prese]etted formaT., as the sounding message. Additional means are provided ~5 fcr lhe conl.rolling station to redundantly broadcast the same sounding mcqsage sequenTially over each one of the channels.
The radio trnnsmitters and receivers are synchronously hopped ~ccording to a pseudo-randomly coded sequ~rlce.
'I'he controL]cd station has the means for majority decoding Lhe highly redundant soundin& message and furl:her means for rncasuring the link quality of each channel on which that mc~ssagc was received. The link quality analysis includes mcalls ~or measuriny, bit-orror-rates (BER), multipath delays, fading rate~, inter~ercnce lcvels and distributions and signal-to noise ratios.
~f23C~
'IH~C! controlled station consequently generates another binary word in which each bit represents a hard-decision, bascd ~n a ~et of transmission quality criteria, as to whether thc corre~ponding, scanned channel is accepted as 'good' or S 'bad' ~or con~lunicat.iorls~
This link quality pattern is now used by the controlled stution as its answer--back soundin~ messages-rhe contro].l;ng station majority decodes the repetit.ive sounding broadcast made by the control.led station while iSsynchronously sequences tho ent.ire group of frequencies. It pcr~orrlls its own link quality analysis and compares the data processed at both ends of the link. The contro]ling station now derivcs tha optimal operating frequellcies. The selected 1.5 frequencies arc then ~utomatica].ly disseminated using the same fcequency hopping l.ransmission.
Accordinely, tho invention rclates to a high-frequency (H~) frequcncy-manngcment system wiLh ~t least two stations, a control.].ing stalion and one or more contro]led stations, each including an 11~ radio transmitter, HF radio receiver, a conlrol unit t`or controlling the operation of the transmitter and receivel and a frequency-management processor means for:
- continuously monitoring the interference and occupancy of a ~inito plurality o~ H~ channels, each channel tuned t.o a difrerent frequency;
-- hnrd-labeling of each one of the said channels as either a binaly"L" for a 'quiet' channel or a binary 1l0ll for a 'noisy' chanllel ~or vice versa?, based on a predetermined set of criteria;
-- storing and updating the resultin~ binary word wherein cucll bit represents an eva].uation of one of the freque7)c~ies visited:
-- using this binary word as a sounding sign;ll and tri~llsmitl..ing this signal repent.edly, once over each of the said finite ~roup of trequencies by having the transm;t.ter scun said ch~JIlrl~13;
~ ~3(~9;~3 -- synchronizing the remot0 station receiver so that it is scquenced through same said group of channels at an equal rate, bcing at each onc of the channels at the same period of timc as the transmitter, to allow the sounding message to be rcceived;
- majority-detecting said redundant sounding message by the remotc recciver proce~or;
- performing link quality measurements on each one of the scanned group of frequencies;
- hard-labeling Or each one of the said channels as either a binary"l" for a 'good' or 'acceptable', and a binary "O" for a 'ba~' or 'not-acceptable' con~unication quality ~or vice versa), based on another sct of crite~ia;
~S - storing the resulting binary word at the remote station rcceivor-processor, to be used by it in formi-l~ the answcr--back sounding signal;
- translllitting the answer-back sounding messa~e repeatedly, once ovcr each of the said group of channels by having the ~0 rcmolc sLation transmitter scan said channels;
- rnajority-detecting said redundant answer-back sounding mcssage by the first, controlling station receiver processor;
-- performing link quality measurements by the controlling station receiver-processor, on each one of the said scanned ~S group of frequencies;
-- selecting optimal frequencies by the controlling station processol, for reliable con~unications in both direct;ons, contrnlling-to controlled and controlled--to-controllin~
stations, based on the analysis of the received and der;ved link quality patt~rrls;
-- utilizing the synchronous frequency--hopping mode ~hich is maintaincd between the stations, to disseminate frequency informaticn by t~ansmitting, over the selected optimal frcqucncies, the relevant information for the remote station;
- automatica]ly tuning the communications transmitters and rcceivers to the selected preferred frequency or frequencies, to establish a reliable con~unication path between the stal;olls;
~;~3~
Thc timing and control means comprise:
--- mcans for randomly selecting N channels from within a specified IIF sub-band given its limits fl to fhi h;
S ---- mealls for storing said N channels as alternate colllTnuni-cal.ion channels with each channel having a predetern1;ned frcquency;
-- reccive/transmit means for placing the station in a transmiL mode;
1.0 --- mcans for sequencing and tuning the HF receiver and transmitter through the group of N channels;
--- means for providing timing for the overall system operation, bit synchronization, frame sync acquisition, sync cycl.e operation, sounding cycle operation and signal pro-cessin~ algorit.hllls;
- means for transmitting the sounding messages using an in cllannel diversity of two FSK modulators-demodulators;
- means ~or ~cneraLing a predetcrmined sequence based on the inpllt of a key variable and real time of day.
lhc noisc and interference measurement means comprise:
- mcans for measuring the radio receiver AGC level and radio receiver noisc output and distribllt.ion;
~5 --- means for measuring in-channel interferencc chatacteristics;
--- mcans for classifying noise and interference present on the COnmllJniCatiOn channel into a predetermined number oE
catc~ories, according to a predetermined set of criteria;
~- means for generating a corresponding number of binary words, each N-bit lon~, one for each category, wherein each bit represents a hard-decision qualifying each one of the N
communication channels monitored;
~,3~
_ 9 _ The link quality analysis means comprise:
--- means for de'ectin" noj~e representative of the noisr3 prcsent within the communication channel band as well as within two soparate ESK channels;
-- data detectors for prcviding a signal representative of thc data levels that are present on the con~lunication channel th~ the r~ceiver is tuned to;
-- means to measure the signal~to-noise r~-tio, the fading rato, and the rms multipath delay spread;
-- mean~ to UCf3 the demodulated rnd màjority-dete(ted sounding message to arrive at the actual bit-error-^rate;
-- mcans for quantizing tbe parameters: signal-to--noise-ratio and bit-error-rate, iC desired in combination witn one or more 15 of ~I1C! parameters: fading rate, delay spread, channel noise, datfl levels; measured on the communication channel to define tho dosirod predotermined number of link quality categories arcording to a predetermined set o~ criteria;
-- means for gcnerating a corresponding number o~ binary words, each N-bit long, one for each category, wherein each bit represents a hard-decision qualifying respectively one of the N communication channels sounded;
Jhe advanta~es and further objects of the invention, and 71 thc mc;lns by which they are achiev3d may be best appreciatr~d by referrin~ to ~hr3 detailod descripti~n which follows~
BRlEI` DUSCRIP'rION 0l~ Tll~ DRAWI~S
,~
~5 A more complete description of this invention may be had - ~ by re~erence to the ~ccompanying draw-ngs, iL.~rr~ing piererrr3d emhodilllf3rlt of the invention ts be drscribed in ~otail, wherein ~ Fig~ 1 depicts three ;J OCk diagralns ill~strating three r , ./ ~i frSJrell~ configurQtior~ of IJF e~ 3unications systems in wbich ~i? s~fS~ o~ ~he present invrl~iorl i integra~ed~
... . . .
,. . ,. ~,~
2~
.;,~. 2 outlines the format for soundi.ng messages between -not 5 tations.
~ ig. 3 outlines the format used in the network synchron-i~ation transmission cycle.
Fig. 4 ;s a simplified block diagram of the frequencymanagement system according to an embodiment of the pr~st~nt inve~ ion.
Fig. 5 is a functional block diagram of the system accnrdirl~ to an embodiment of the present invention.
I:)k'TIll l.r~:D VESCRIPl~ION 0~' TIIE PREF'ERRP:D EM80DIMENT
15`
~ orore going into a detailed description of the figures a brie~ overvicw will be given describing the environment and gt)neral ~eatures of the syxt.~m.
~rhc oporational situation typically assumes a network of HF radio USeL'S generally structured using a net controlling station in association with a plurality of widely scat.t.~red control.led stations, including relay stations.
~'ach controlled net station is expected to continuously 25 monitor the net traffic and to respond if polled by t.he contro].lin~ net station. Only one station at a time wnuld thon he transmitting, with transmit discipline being maintained by the controlling stat.inn.
Centralized fret~uency management and control, with full froquency assignment authority would normally be the rcspt~nsi-bility of the controlling station, within the single-net or thc multi--net configuration. Operational configurations, howcver, using one-way transmissions only, utili7e the capa-:~S bilil..y of the prescnt invention to assign the selection nf optimal IIF frcquencies to the controlled terminal.
1~3~ 2~3 ~ '~lC system according to the invention, can be used for the real-time management of HF communication networks having onc controlling station and one or more controlled (or rerllote) stations. The system is adapted to provide a frequerlcy S manaKometlt capability for any predetermined number of frcquencies. Practical considerations show that generally, a number of from about 50 to about 150 frequencies provides a suitable sysLern, depending on the conditions of use and the rcquirod speed and reliability. The operating sub-bands are 1.0 chosen to have an adequate width for accoEnodating the prodctermined numbor of frequencies, with an adequate spac;ng beLweon the frequencies used. In the eollowing, the invention is il.l.ustrated in an entirely arbitrary manner with reference to a system of 125 channels. It ought to be understood that
5 th i 5 i U by way of exaMple only, and that any reasonable and practical numbcr of channels can be mana~ed by such systems.
As stated above, the invention is illustrated with rofcrence to the system which provides a total capability of ~requcncy rnanaging a group of l25 frequencies, randomly distributed betwQen any sized sub--band fl to f2 f the H~
spectrum, for any sized time period tl to t2 of the day and night. The opcrating sub-band must be at least 500 kHz widc to accon~odate 125 channels at 4 kHz spacing. Thus, the system can bc pro~rammcd to process, excludinE, used or fo~bidden Croquencies, the entire HP band all of the time or any sma].l^r propagation windows of usable frequencies grossly prodicted to bc effective at certain correspondin~ t.ime pcriods. lt is to be clearly understood that this example is illustLativo and ought to be construed in a non-limitative malln"r. \, r This enscmble of 125 automatical.lv pre-assigned frequencles_constitutes_the frequency mana~ement sing].e, widcwband opeLatlnE cha_nel._ W_thin this channel information is timo a_d_ Lcqu_ncv m_lti~lexed, redundantly utilizinlg__he - '~ood' and tho 'bad'_available fre_uencies.
Thc system can be progran~led to operate in either one band or two separate ~ nds.
1. Onc Frequency Band: One pair of frequencies shall dc~inc the l.in)its of the expected operational band.
Within this band, 125 frequencies will always be available for evaluation, regardless of the size of the band, with 4--kHz minimum spacing. 0 2. Two Frequency Bands: Four frequencies shall define two scL~lrate 'VAY' and 'NIGHT' operational bands, which may havo ovorlapping regions. A single transition hour will be chosen for the transfer from the DAY band to the NIGHT band, or from 125 DAY frequencies to 125 NIGHT
f L`Cqll~Jlll' i l'S .
~ non-repeating, key-contro].led permutation of numbs~rs O
to l25, ds~Le~mines the actual frequency locations and their tcansmission scquence within the defined operational bands.
~0 WiLIl Lwo bands the system is actually processing 2.~0 I~F
t`rs~quencies, during the 24-hour period.
Thess~ 125 frequencies are continuously monitored by each of the net stations and the channel noise and intereerence is ~S eva].uated. The cs~ntro].ling-station initiates the sour)d;ng transmission. The sounding signal consists of local ns~;se information analyzed at the contro].ling-station location.
Vuring ~hc sounding cycle the controllingstation scans through a]l ot` the ].25 ~requencies in a random sequence.
lZ3~P92~
The spacing between frequencies shall be in multiples of 4 kH%. Given a band F1 to F2 then, for any subset o~
numl:)ers N= ~n~ 5~ randomly chosen from the set N-1,2,..... N l , where S max~
N = F~ - F (Fl and F2 being in MH~) Tho corresponding frequency set is ~ F~
lo F~ 2~;0 ~ ~2J
The net controlled-station step synchronously with the controlling--station and performs transmission quality evalu-a~ios~s pertaining to each of the 125 channels. The controlled-s~al.ioll wil]. sequentially respond by a repeat sounding cycle,scanning aeain al.l ].25 frequencies. The sounding signal will now carry ].ocal reception quality information back to ~he contLollin~-station, again frequency-hopping over all 12S
channels, in a random sequence. The controlling-station ~0 porforms its own transmission quality analysis and compounds it with the information received and processed through t.he sounding signal from the controlled station.
A single two-way exchange of real-time sounding trans--~S rnissiolls thus ~nables the controlling station to derive andreliably assign optimum operating HF frequoncies to each con~llunicating link.
lt is a central feature oE this invention that the fre-quency managelllent process acts as an automatic HF link controlto achieve an adaptive cl~annel and enhance communication reliabillty.
~ig. l illustrates in a block diagram form three of the many other possible configurations of HF radio communications sys~ms, incorporating the preferred embodiment of the p7esent invention. ~ freqency management terminal would normally be closely inte~ratoLI with the radio equipment..
-~ ~3~
In Fig. la a conventional HE' radio communications system i5 ShOWII that includes a radio remote control unit 21, the HF
Lranslllitter/receiver 24, and a matchin~ unit 26 to cou~le a narrowballd antenna 29. This matching unit need not be used S whon a broadband antenna 27 is available. The frequency management syst-:m is shown to comprise a remote control unit 22 and a processor 23 which is connected to another convenLional but dedicated HF radio system. The two control uniLs are interconnected by 25 to allow automatic freguency assignment and control. In this configuration the information channel is entirely independent from the frequency management sysLem channcl (22-23-20). The information channel ~21-24) which norrllally uses one frequency (half-duplex) or two froquencies (duplex) wi].l not be interrupted by the ~requ~ncy lS managelllent operation. The system channel which u~es l~S
frequencies operates simultaneously and continuously on a non-interference basis.
In Fig. lb the HF radio system 29 is shown to comprise separaLe IIF' transmitter system 30 and an Ht' receiver system 31. These may be physically widely separated. The frequency mallagemenL system, however, uses only a dedicated but convonLional ll~' receiver 32. The two receivers connect to a single receive antenna 37 through an antenna multicoupler 34.
In t,his configurat.ion thc system shares the COnQlUniCationS
transmitter only, which is therefore used both for information transfer as well as frequency management transmissions. The sysLem receiver can thus uninterruptedly monitor the l25 c~ n~ s.
ln Fig. lc a single remote control unit 33 combines t.he ConmlUniCation and frequency manaeement operations, audio and colll,rol, through the system processor 36 which coTIn~ts directly Lo the HF' radio receiver system 35 that serves both.
:3S
~ ~3~3~-As previously stated, each terminAl in the net shall maintain a continuous evaluation of all 125 channels by examining the prevailing interference in the normal comr~ ni-cation 3-kHz bandwidth. This monitoring process shall go on S at all availablo times, by means of the HF system communication eceivor. ~'ach tetDIinal shall sequentially scan the progra-nmed list of L25 freguL?ncies, continuously compiling and updating challn~l occupancy sTatistics.
The number of available operational channels will depend fiLst oL' all on the likelihood of finding any quiet ~requeneies (fLom tho pre-assigned group) during all hours of the day and night, while the rate at which the channel must be evaluated will dep-3nd on the likely variability of the noise spectrum lS allcl pcl:lpaGation conditions with time.
'l`hc torm 'qu;et channel' generally implies a c'nannel whose noise and interference level, inherently a variable quan~ity, only slightly exceeds some measured noise fl(~or avoL-~g(:~l within a liMited bandwidth, or a fixed noise level that corresponds to a low-level signal induc~d into the antorllla, OL~ the threshold of atmospheric noise.
Ilowever, the characteristics of the interference in the ~5 chanllcl, depcnding on the traf~ic and mode of operation, will determitle wllether the channel could be expected to support an accoptabl.e intelligibility of voice or an acceptable bit--erLor-rate. The power spectral density of interfererlce frotll oLheL IIF users may be significantly non-white within HF
voicc channels. Low frequency CW, ~orse Code or narrowband FSK may characterizL? an HF channel as 'noisy', while it may sl.ill support intelligible voice.
According to the invention, a predetermined number of :15 quAIltum !.tates is de~ined, respective to a predeterll-ined number of parameters, the main ones being signal--to-noise ~Z3~9~
- 1~
ratio and bit error-rate, the others being channel noise, data levcl~, ~ading rate, dclay ~pread. Advantageously, the para-mcLeLs mcasuted comprise at least the two main ones. These can be measured with one or more of the other parameters. Any combinution of one of the main parameters with two or more of the othor parameters can also be used.
As stated above, the invention is illustrated with rcrcrenco to a systom of 125 channels, and it i5 further illustrated with reference to eight guantum sl;ates classifying noise and interference present on thc communication channel.
~ l quanLum states of noise and interference power/
freqlJcncy distribution will be defined. Measurements will lS conlinuously indicate which of the eight thresholds has been crossed at oach of the 125 3-kHz channels. For each of these eighL s~ates a panoramic pattern will rapidly be formed, qual-irying a~ 'quiet' or 'noisy' each one of the 125 channels that . thc ontire net is currently evaluating. These patterns will bc cc~nlinuously updaLed throughout the monitoring periods.
Thc labcling of a channel as 'quiet' or 'noisy' will represent fl hard-decisio_, producing the bcst available choice and in-cluding a~wnys a fixed, minimum number of the 'quietest' ch~ nQ~s in cach pattcrn. With net stations dispecsed over a ; ~S widc gcographic expanse, di~ferent interference conditions will be cxperionced at different locations, which will most likely result in a very diffcrent Interference Measurement Pattc-.n (IMP).
Thi~: lMl' will thus constitute a sequence of binary mcasurcmcnts, ]25 bits long, whcre each "1" or "0" corresponds to a hard docision interference-state measurement. Each one of tho Illonitored channels is labeled Quiet ~"1") or Noisy ~"0") at lhe teTminal's location, based on the continuous monitl~rillg and updating of channel occupancy statistics, in 5 or 30 m;nute timo--scp~men~`s. Each bit position will correspond to the exact channcl position in an automatically produced coded table of l~S rroqu(~ s ~3L~32~
- ~7 -Tho process of real time HF channel s~l~ction normally involvos a single two-way transmission exchange between a conlLo]ling frcquency-management terminal and a controlled froquency-mana~f3ment torMinal. Howover, reliable channel assessmont may also be produced through a one-way transmiss;on ~J ~ 5 .
Thc IMl~, the continuously compiled and updatad inter forenco measuremcnt pattern, is used as the primary sounding signal by the controlling terminal. A soundin~ transmission will comprise a single cycle of 125 pseudo-randomly selected 11~ fcequency hops, repeating the same message in a buT-~t. of auliio data, once every hop. During each successive fr~me poriod tho samo frequencies are visited but according to a dil:Ceront, non ropetitive PN-coded permutation, con~rolled by a non-linoar sequence generator (NLSG).
Thc identical, redundant sounding message will be ~ent over each o~o Or these HE' frequencies by means of noncoherent LSK, using 2-nd order in-band diversity, at a rate of 224 ~its peL' second. The use of du l channel FSK contributes also to an incroased correlation between assessed channel quality and voico quality.
~IG. 2 is a timing diagram of the selected burst format of tho sounding framo 311~312~313 which has a hopping rate of l/r hops per second. Each frame starts with a frequency time guard pcriod 3]1 which is long enough to allow frequency ~ han~e ti~ , antenna match time and receiver AGC sottling time.
During thc ncxt timc period 312, the receiver doppler correc--tion loop (in the AFC circuit 35 in E'I~. 4) utilizes t;he dual-ESK tonos and filters to compensate for frequency dr;fts.
Tho ~ol]owing time poriod 313 is devoted to tho data block which CO!lSiStS oL a total of 210 bits. The first segmont 420 :~5 of 6~l bits each are tho synchroni~ation unique words used to provi(:le frallle sync. Tho next soemont 421 of 24 bits is used for I~s of sondor and destination. The foliowing segment 422 o~ 125 bi~s accon~lodates th~ sounding messa~.
J~Z3(~
- l8 -Sc~nlent /l23 of 3 bits indicates 1 of 8 quality states to which Ihc currollt soundin~ pattern belongs. The last segrnent 424 of 8 bits is the ollly one that varies with each frame as it indicates the frame numberl from 1 to lZ5. The sounding mc!ssage is sent by means of dual-FSK transmissions at 224 bps and tbc-n 125 times by hopping over eaeh of the 125 channels~
.
Thc soundin~ station (controlling or controlled~ trans-mits its mcssage on eaeh frequency in turn, and aIl the remote receivin~ net stations being synchroni~ed to the sounding staLiorl, repeatodly Leceive the identical message at each froquency. ~ unique Majority-logic decoclin~ al~orithm insllres a VCLy high probability o~ raceiving a].l messages error-free, undcr extremcly varying con~unications conditions. This ~apa-bil.iLy of socuro message transfer by redundant transmissions is a unique chacacteristic of the frequency management system ombodi~d in Ihe present inv~ntion.
The san~e sounding message of N bits (N = 125) is being rcccivcd over N channels, each channel with its own bit-error-ra~e (8~R). One can make a first approximation and classify 8~ challnels as "blocked" when their 8ER ~ 1/2, or "open" when ~, ~l C i L' U ~ 2.
llllcl(:!L thcse simp].ifying assumptions if N = 2n+1 is the number o~ tcsted channels, N of which are blocked, the probability of error in any one bit under an N/2 majority dccision rule is:
.
p (B) ~ (2) ~ (~-e) ~
e-~ e ~ further approximation takes into eonsideration two typos o~ "open" channels: 'Good', when the BER -~ n2 ~nd 'Ufld', whell the BI~K ~ lO = Bl.
~.~3~9;~8 In additioll to the M blocked channels, the proportion of thc 'Good' ~nd 'l~ad' ch~nnels is known ~o vary considerably bcl.wcoll day and night. ~uring the day SOMO 20 to 30 percent Or l.hc N M cilanncls may be considered '8ad' while during the nighL 40 to 70 porcell~ of them may turn out to be 'Bad', on tlle avorage~
der these assumptions th& probability of error in any one hit, aL'tor majority decc)ding is (the nun~ber of B
~0 channol 5 boin~
p~ -M5(/~ J~L~M
B K (~_ g ~ -I / lc~
I.t sllould be omphasi~ed Ihat the above is derivod under thc assumptioll of uniformly distributed independent errors Wlli(`ll i9 a fair assumption. Namely, the bits received on cllal-lne]. i are indopcndcnt idontically distributed ti~i.d) with ~0 rc~:pect to the same bits (in the message) received on channel j (j - i)~ 'I`his assumpt;on would not be accurate under flat, vory widoband fading conditions of extremely lon& duration tLells of soconds), but these conditions are rarely encountered~
One can ovaluate the average bit error probability ou~r a discroto distribution of channel qualities for tho "open"
chanllc].s. ~.f a typical channel distribution is as follows:
Br':L~ ! 10 10- 2 ] 0 3 10--4 -5 ~ c,~
channols: S lO ' 30 40 lO 5 ~ rhe slverage bit crror probability after majority decoding for N-l.~S and M-SO percent would be: 5xlO , namely, even undc; vcry sovere conditions, with enough tested channels tho bil. crror rato o' the ro'erence sounding message is remark.a~ly low~
~ ~3~9~3 On~e ~he error probability for any one bit in the majori~y - decoded sounding message has been evaluated, one can ovaluate the probability of receiving an errored sounding mcssap,e, Pl, and then the probability of receiving an exact sounding mossa~c which is given by l-PE. For a totsl 3n bits of messap,e (2n~1 channels and n-l control bits), P~ ( 1 pM~ 3n This capability of secure acquisition o~ the sounding mcssage, through utilizing the highly redundant transmission sl~home, is a unique and a central aspect of the present i llV~-UIt~; on.
ro m~in~ain system synchronization all terminals must stop ~heir non--linear sequcnce generator (NLSG) clocks with t1lcir phasos directLy related to thc transmitting terminal c]ock which takes the lead. l`he NLSG has several special fcalures, in addition to the basic functions. It provides ~0 synchronizin~ or resynchronizing capability, the NLSG can be ro~llrned to a known starting poing and then stepped to a prclJet~:lmined point in tim~, in the process of initialization.
The YK bit st:ream is based on 8 key-variable contained ~5 witl~ ttlo NLSG. The NLSG is programmable with respect to t.he valiahle in Ihe sense that the current variable can be replaced with a new one as required, by means of a special ext.~rnal loader. ~ zeroizing function is also provided, should it bocomc necessary to clear all stored data in the NLSG, under cmcr&~:l"::~y condi~ions.
Th~ synchronized pseudo-random sequence generators at all froqu~ncy mana~oment torminals determine the same new frcqucncy for each successive frame. The freguencies are se~ected from the string of bits generated by the NLS~ each timc t.he frequoncy is to be changed.
L)uring rec~ption o~ the repeated sounding message, the sysl.cm maintains an elaborate Link Quality Analys;s, peLLorming sin~u]taneous measurements of a]l the paralI~eters co(Isiderod essenLial to the monitoring of con~unication S tLaf~ic. Link qual.ity analysis or in-band channel evaluation is a key process in enhancing HE` frequency selection and conununication sysLem performance estimation~projection.
Tj1C invention incorporates advanced signal processing a1goritl~ s that pcrmit measurcments of all essential paranIet.~rs within tIlc time constraints imposed by the time-varyin~ IJF
ch~;Irlel~ ~ fundamental n~easure of system channel performance dcL,rad~tioIl in a digital comn~unication system is the bit-~rror-rate ~L3IK). In the period of timc that the ~iF channel transfer ruIlction msly hc approxirnted as quasi-stationary, it is commonly di~:ricul~ to accumu1.a~ su~icient bit errors to characteri~ie noar-inslantaneous data performance. The invention us~s a modifiod approach of error rate extrapolation based upon pscIldo-errors (E~L3~R) to estimate the probability of error in 2 vf!Ly shorl. tirno. Pseudo errors may be generated by modifying thc eain or phase threshold criterion in the error decisions pL'OCe5S to obtain parameters which indicate apparently greater circuit degradation than raally exists. The measurement period is :hoLtened since the pseudo--error is designed to be larger ~S than the corLespoIlding actual error rate. The basic idea is that by narrowing the "good detection region" and wi-dening the "error detection region" one measures a highor BER than t.he acLual 13Ii.R of the detec'i.or. As a result, high accuracy low BIit vfllues can he measured from a) small data samples, and b) wilholII. actua]ly knowing the transmitted data.
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Thc l'L~I.R and Iho actual BER are related as ~o1io~s:
log P - K I loL,~
:~5 wheLc I' ;s tho bit pscudo-error probability arId PE i~ I.he actua1 ~:rrI7r probabi1ity.
%~3 ~
Ir Iho transmitted data is known, or derived from maJority decodin~ of repetitive soundings, as is donc in this illVelltiOIl, ono can "scale the channel" by calculatin~ K out of moasllrcd ~ and P~.
lt should be emphasized that the above was developed ma;nly for linoar, additive noise type fading channels. Since l.llis is not always the case with the HF channel, a cert.Rin cortoction should be made which will account for this discre-pancy. The channel BER model can he rewritteri as:
logP - K ~ logl'~ + KL
whore KL is a compensating factor whose value is derived ftolll l.ho burst orror statistics of the HF chal)nrJI.
Whrn the sounding cycle has ended, the contro3.1ed-Lcrminal recoivor has at its disposal a wide variety of information abou~ each of tho N sounded channels. The present invelltion takos advantage of its uniquo capability to fully rc~covor the soundin~ mossage bit-sequence. This original me SAI,O is usod ~or error counting, PBRR and 8ER dotermin~tion.
Moasurements are performed also of the rms multipath dolay spread, the fading rate, interference levels and distri-bution, and SN~. This data is processed and updated with every additional sounding transmission. A ve~y reliable characteriz-aliori of tho l~ conununication channel results. Knowledge of tllo channel conditions and parameters enables the prediction of channel perforn1ance aL high data rate transmissions based on lo~ rato d~ita transmissions.
Tested channels are also ranked for various uses: voice, rnulti-torlc D~'SK modem, wideband FSK, narrowband FSK, etc. The inL(3rldod oporational use clearly af~ects the link quality dClL'rnlinatiOIl Si.llCe interferences have different effect8 in di rr~ "~ applicat.io"s.
- ~3 -1~ascd on the link quality analysis and operational n1ode~
hnsd doci_ iOn5 are made by the receiving terminal, qualifying as ~Good" or "Uad" each one of the 125 channels tested. A
bin~1ry L;nk Quality Pattern (rJQp) of transmission performance S mC.l`SUrelllellt5 i5 gcnerated~ where each one of the tested chan-ncls is labeled "l" (Good) or "0" ~Bad). "l" to indicat.e an accoptable channel and "0" to indicate an unacceptable channel.
Accoptabi]ity is determined based on eight quantum states of pcrrormance characterizing eight separate link quality paller1ls~ These LQt's represent the best available choice and includc always a fixed, minimum number of the 'best' channels in f-~ach paLLern. ~`or example, in the ].imiting case, with all oLhcr. measured parameters equal, "Good" or "Bad" may indicRte, say, ~L1~ < 10 or BER ~ 10 following thc Doppler correction and AGC settling, the rcceiver mu5f porform the following functions:
a. ~ccover clock timing for bit detection.
20 b~ Kccognizc thc frame-sync unique synchroni~ing word to cslabli3h the basic frame timing reference and identify ncl. nllmbcr.
c. lde1lliry the I~ patterns. These bits enable the re(:f?iver to vcrify Lhe validity and legitimacy of the received ~5 bursL~
d~ ~ccopL 1he remaining portion of each message. Arrive at Lhc~ corrccf~ IME' or LQP and process the nec0ssary tests, evaluation3 and decisions.
To illu3trate the system's operation, let the controlling Lor1n;nal, C, init:iate a sounding braodcast cycle C uses ax a sol11(di11g signal its most recent IMP. The controlled-terminal, c, derivfs C~s ;'MP error-free, which provides it with the noise and inLer~crence levels measured at C's location, in each o~
j :~S Lhc 1~5 channcls n~onitored. In addition, c cafries out l~.~ r.QP
-~~ tcsts, during the sounding cycle, to sort out the "Good"
chnnnc]s. lhe final results can be tabulated as in Lhe fo]lowi1lr, siMplified exan~ple Chal~nal No. ~ 24 25 26 27 28 29 30 31 ~ - - -C's MI~ (Lclc~ived) - 0 0 1 0 1 1 0 1 ~
c's TMI' (maasured) - l 0 0 0 1 0 1 1 - - - -c's l.~P Decisions - G B B G U G 8 G - - - -~ 5 (G for "Good" and B for "Rad") :
~ ~rom the above data c can i~nediately deduce that:
., a. At th~ controlling terminal C, frequencies 24, 25, 27 and 30 are noisy. ~requencies 26, 28, 29 and 31 are quiet.
b. At the conLrolled terminal c, frequencies 25, 26, ?7 ar)d 29 are noisy, while fraquencies 24, 28, 30 and ~1 are c. Ltocep~ion quality was good at frequencies 24, 27, 29 and l.5 3l anl.l bad a~ erequencies 25, 26, 28 and 30.
d. At rreqllancies 27 and 29, although the channels were noisy a~ c's end, reception was good, probably because the signal over-powered the noise ]evel.
e. Al rreyuancies 28 and 30, although the channels were yuiet at c's end, reception was bad, probably because of no E~ropagation or a very low si~nal.
f. ~ur ~ransmission in the C--to-c direction, frequencies 24 and 31 may ba a good choice.
g. Ior ~ransmission in the c~to--C direction, ~requencies 29 and 3l ~nay be a good choice.
h. I.)oE)onl-lin~, on the nature and level of the noise at the roceiver's end other frequencies may also be considered whell the expccted received si~nal ].evel can be estimated.
.
~ Z3~D9;~3 - 2s -In ~pplications where, most of the time, only one-way transmissions are conducted (C-to-c), the frequency changing or al~ocatn~ function, over the communication link, may be asai~ncd to the controlled torm;nal c. Operation reli~ nn 5 just tho one-way sounding broadcasts (C-to-c). A reliable and rapid docision will be made, determinin,~ the best pair of trallSmit/locfaive operational frequencies, for cornmunication witll thf~ controlling terminal. This frequency allocation must bo sc~curely buLst-transmittf3d to the controlling terminal to 10 nl low norlllal Hf'~' con~lunications to prl)cf~d~
L~ollowin~ tho reception of the sounding transmission cyc]o, tile controlled terminal will wait a fixed number of tiUIlC! s].ots bo~ore attempting to respond to allow its communi-.5 catioo Lransmittf2r time to tune to the f~equency chosen fortho c-to-C transMisslon. Tn prepar~tion to respond, tbe conlLo:lled toralinal shall automatically construct a reporting m,3s-:age mado up of just tho one selected C-to-c communication freqllency (till the next update). Whan responding, only upon arrival at the time slot that coincides with the selected c-to-C froqu,3ncy (in the FH sequence) will the controlled ~rlll;nal turn--on its transmitter RF power for a bllrst-tranamission of this mossage. This will automatically reveal to C thf~ selected c~to-C irequency. Controlling and controlled tolrninals have now automatically tuned their fixed-channel HP
COnlmUniCatiOn roceivers and transmitters to tho selected pair ! of` oporal.ional frequenci es .
NoLmally the aystem operation over an HF link will :30 involvf3 a two--way sounding process, with the controlling torminal assuming frequency assignment authority~ Following tho fiL~t C-to-c soundine cycle, the controlled terminal, havine formod its I,ink Quality Pattern, automatically responds Wit~l a c to-C sounding broadcast. ~gain, within the single frallle Or 125 ~reguency hops, c's LQP sounding message will be repeat~cf onco ovory hop~ This two--way sounding process will take lf39S I:han S minutos.
:~3~ZI~ `
rho colltrolling terminal will now be lookin~ at two T.QPs which pLovide simultanQously the measured con~unie;lt.ion porrotmance at both ends oE the link and, therefore, enables a str~ight~orwald solection of optimal operating frequencies.
The dissemination of frequency information will be conducted using either a soundin~ broadcast burst-transmission or the current operating secure communications channel.
~efore a terminal can be used in an actual exchange of si~n~lls, somo preparatory operation is required. Necessary data n-ust be entered and stored: the frequency band or bands to be ~sod, operational modes, IDs of net sender destination, key variables, initial operating frequencies and a certain agreed-Lo cycle start time is also set in. This is used with the actual time to determine automatically the elapsed t;me of the op()~ation for frequencyhoppin~ and key synchroni~ation purE~oses. The actual time is acquired from a suit.ahle refeLence external source having second-accuracy, such as coordinated universal time, an electronic watch, a count down OVflt voice radio, etc.
To onsure proper net initiation under seach mode condiliolls, w11en a new number joins the net or transmissions havo not taken place for many hours, a special Synchronization Cycle is provided. During this cycle a unique sync message, bLoadcast by the controll.in~ terminal, is rspeated once over eacll o~ the 125 channels.
Ii'ig. 3 i]lustrates a simplified transmission timing di~l~ran~ of the Sync Cycle. In a typical frame, the first and lasL 64~bit data blocks are the two complementary unique words 501 and 505, designed to be detected as a doublet of a positive folLowed by a negative correlation peak. In the central data fiold the blocks 502, 503 and 504 of 96 bits comprise three ei~,ht--bil. characters, ~lpha or numeric, devoted to the sender's lUIL)esLillation, repeated three times.
1;~3~
I~ollowing initlalization, which includes loading the terminal's NI~SG with the common key, net synchronization is raEI;dly achicved i~ time-of-day internal clocks are all set to within maximum ~D (t~T) seconds of real time, where t is the syst~m hop-time between freguencies and T is the system dwell-timc at each frequency. The order in which the system is so(luenced through the gcoup of channels, is controlled by the NLSG's output.
upon entoring the search mode, the frequency management ~orlninals au~on~atically advance their set time-of-day by D
tin~o-sloLs in time. The terminals' NLSGs are therefore forced to ~o within (0, 2D) time-slots ahead of the real time of day.
1.5 ~hc sc!urch receiver will be taking unequal steps, jumping fllw~ys ahead of the sounding transmitter, and waiting for the tr.nnsmiLter to arrive. l'he receiver waits 2D+l time-slots on its present frequency, then jumps ahead 2D frequencies, then waits again 2D-Il time-slots, then jumps ahead 2D+2 frequencies, waits another 2D-~1 time-slot, then jumps ahead again 2D
f e oqucnc ios, etc .
Following an initial shift of ~D time-slots, and assusnill~ t 0 and T=l second, the optimal search procedure is:
wait . 2DIl alld S~arch = at 2D, then at 2Dt2. As a result of ~hi`: soarch pa~tern, the controlling-terminal and the conlrollod--terminal meet on various frequencies, in other words thoy criss-cross each other until acquisition is achi~ved and the search procedure ~nds.
~ ho averago waiting time (T~) between meetings of the tolminals during the search procedure is given by:
~.~3~9~28-~2)(2D~ = 2 P
The maximum waiting time until the first meeting for a giverl D, is l max = 2D.
DuriDg the synchroni~ation period, the terminals meet on 1 0 al- ~IVCL'-I~,C of .
MU different frequencies, where:
D ~) where N i5 the number of i 9 ~ (zp~/J2 ) assigned frequenr.ies, 1.5 N = 125.
Erame synchroni~ation exploits the systematic nature of the soarch detection process to realize a very reliable and raL~id frame--sync recovery.
~ digital correlator will detect arriving frame sync sequences and full utilization will be made of the so-called window tcchnique. This method takes advantage of the fact tha~ the Syllc sequences are periodic ~nd that legitimate co~relator outputs will have to be spaced in time according to thc (2V)-(~D-~l)-(ZD-~2)-~D+l)-... pattern. Acquisition will be dec]ared after detection of 3 sync sequences. The det~ct.ion thLesholds will determine the average synchronization time, as well as ~he n~ax. sync. time for specified miss/false-alarm probabilities. t I~ the probability of detecting a sync sequence on 8 channel is Ps, the averàge probability of detecting 3 consocutive syncs at proper spacings is~
' '` `
:~3~
P~ P5J
S Where Ps is given by the probability of detecting "over the threshold" number of correct bits in a PN sequence; it is a function of the channe] ~I~B.
Hence, the average s~nchroni2ation tiMe is p31 Whcn three successive hits are found, from among the channels crossed (before one scanning cycle is complete) the operation proceeds to the steady-state mode. In this mode the receiv~r is in full synchronism with the transmitter and hops witb it at the regular rate. The frame-sync detector maintains Q ' continuous trackin~ process and n~onitors the end of the sounding transmission.
- This unique synchronization algorithm is another impor-tant aspect of this inventiotl.
Re~erring to Fig. 4 which is a block diagram of the frequency mana~ement terminal, the system is shown to comprise four major modules:
1. Analog Module 12, which includes the terminal's data link and basic sensors.
2. Process Control Module 14, which generates the syst~lm's timing waveforms, and controls the sounding, and s~cllre radio functions.
3. Computer Module ll, which is responsible for the system signal processing, analysis and overall system control.
4. Front Panel Control Module 13, which includes all the operator's manual inter~ace controls and indicators.
~z~
Erom the radio interface connector 15 the radio receiver AGC signal is fed through conductor 71 to the computer modulQ
11. The received audio FSK signal is applied through conductor 73 to monitor filters 3l and R~T control device 32. The monitor filters are examining discrete segments in the 200-3200 audio band and signals present are delivered to the processor module 11 via conductor 72. When the terminal initiat0s a soundin~ transmission, a SEND/REC-ON ~ignal appears; thrqugh conductor 74, at the input of device 32. Out of the computer module the digital sounding message is applied, through conductor 75 to the dual FSK modulator 37. This device includes two widely spaced (in frequency) FSK modulators to which the same message is fed simultaneously. Two FSK output signals are then passed, via conductor 76, to the bi-directional analog gate 32 which applies them to the dualbandpass filters 33 for signal shaping and improved isolation.
Conductor 78 feeds the two FSK outputs to the radio modu]ator.
When the terminal reverts to the receiving mode, th~ R/T
control device 32 routes the two FSK signals received from the radio demodulator, through the dual bandpass filters 33, gating their output via conductor 79 to the dual FSK
demodulator 34. The output of this device which is now the restored digital message is fed through conductor 81 to the processor module.
The automatic frequency control device 35 provides a means of sensinK the doppler ~requency shift and applying an adaptive compellsation to improve the bit detection capability of the FSK demodulators. To help synchronize the local clock to the incoming digital burst, the bit synchronizer device 36 continuously interacts with the central timing source 41, throu~h conductor 85. The measured doppler shi~t QS well as the processed corrections are transferred via conductor 82 to the computer module interface 22.
I
z~
Under program control a multiple of unique algorithms and functions are simultaneously being processed in the micro-computer module 21. These deal with the rapid signal measure-ments, evaluations and frequency management decisions that must be accomplished in almost real time, while visiting 0ach of the lZ5 frequencies. Testing of noise and interf~ce characteristic parameters as well as actual communication quality parameters, the generation and grading of IMP and LQP
sounding signals, processing the synchronization acquisition scheme, message block-encryptioD/decryption, secure protocol, frequency assignments, etc., all these activities are computer controlled.
..
Timing-and-process-control device 41 disLributes all timing waveforms, stores and controls all initiali~ation data serially inputted, through conductor 94 and remote corltrol in~erface 48. .It receives the output of the non-linear-- sequence-generator device 44. By means of an external loader key variables are serially féd to the NLSG for the generation of a random sequence which is used for digital encryption, frequency translation and secure operation. The radio control device 42 receives control data from the timing device 41 via conductor 87, and couples frequency and SRND/REC control information to the radio system.
~5 ~ 'ront panel control module 13 provides a manually operated interface and comprises a time~of-day display and data indicator device 51, fl function switch 52 for testing, initialization, time settinK, b~nd selection, etc., and a mode switch 53 to select automatic/manual operation, one-way transmission, etc.
A functional block diaKram of the frequency management terminal is depicted in Fig. 5. It contains two functional ~5 groups: receiver group and transmitter group.
3.~3~
Functional modules numbered 601 to 610 are part of the transmitter, while functional modules 6ll and 625 ~excluding 616 and 617) are part of the receiver. The ti~ning of the teLminal originates from 616 which provides the required clocks to control box (617), to processing ~615) and to the modulator (608) and the demodulator (612) functions. Two inputs are provided by the external radio receiver, namely, tho received audio and the AGC. The audio is the iDpUt to ~.he receiver where the time recovery (611) and the detection (6l2 functions are being performed. ~uxillary functions like ~re-quency shi.ft corrections ~613) and pseudo -- BER measuremenL
(61~l) are also part of the receiver. The audio and the AGC
arc being monitored (604) and the lME' or LQP is generated (605). Pollowing the sync pattern transmission (606) the TMP
L5 or LQP as a sounding message is being transmitted (607) through the modulator (608). The frequency hopping of the radio un;ts (receiver and transmitter) is boing controlled by the control function (617). The sync search (618), acquisition (619) and tracking (620) are perÇormcd in the receiver on the received ~0 data. The hop-sync of the receiver (621) is initialized during the acguisition phase, while the crypto sync (622) is initiated from the control and timing units, the key value and time being loaded externally (623). The sync tracking unit : (620) tracks the frequency keys following acquisition. Once the sounding cycle has ended and the terminal receiver has anulysed (62~) the sounding message, a decision concerning t.he best frequcncy subset is pcrformed (625). This decision is conununicated to the operator (human or automatic) via t.he remole control I/O (627) and is displayed on the display (626). Via the control panel (626) or remote control port, a sel.f-test cycle can be initiali~ed (628), the results of which are stored ~for further statistics) and communicated t.o t.he operator as wel.l.
~LZ-3~928`
.
Any oE the functions descrihed herein, given t.he teaching of the invention may be implemented by those skilled in the art. Thus while a particular embodiment of the present invention has been shown and/or describecl, it is aparent t.hat changes and modifications may be made thereon without depar-ting from the invention in its broadest aspects. The foregoing Detailed Description is intended to be merely exemplary and not restrictive.
As stated above, the invention is illustrated with rofcrence to the system which provides a total capability of ~requcncy rnanaging a group of l25 frequencies, randomly distributed betwQen any sized sub--band fl to f2 f the H~
spectrum, for any sized time period tl to t2 of the day and night. The opcrating sub-band must be at least 500 kHz widc to accon~odate 125 channels at 4 kHz spacing. Thus, the system can bc pro~rammcd to process, excludinE, used or fo~bidden Croquencies, the entire HP band all of the time or any sma].l^r propagation windows of usable frequencies grossly prodicted to bc effective at certain correspondin~ t.ime pcriods. lt is to be clearly understood that this example is illustLativo and ought to be construed in a non-limitative malln"r. \, r This enscmble of 125 automatical.lv pre-assigned frequencles_constitutes_the frequency mana~ement sing].e, widcwband opeLatlnE cha_nel._ W_thin this channel information is timo a_d_ Lcqu_ncv m_lti~lexed, redundantly utilizinlg__he - '~ood' and tho 'bad'_available fre_uencies.
Thc system can be progran~led to operate in either one band or two separate ~ nds.
1. Onc Frequency Band: One pair of frequencies shall dc~inc the l.in)its of the expected operational band.
Within this band, 125 frequencies will always be available for evaluation, regardless of the size of the band, with 4--kHz minimum spacing. 0 2. Two Frequency Bands: Four frequencies shall define two scL~lrate 'VAY' and 'NIGHT' operational bands, which may havo ovorlapping regions. A single transition hour will be chosen for the transfer from the DAY band to the NIGHT band, or from 125 DAY frequencies to 125 NIGHT
f L`Cqll~Jlll' i l'S .
~ non-repeating, key-contro].led permutation of numbs~rs O
to l25, ds~Le~mines the actual frequency locations and their tcansmission scquence within the defined operational bands.
~0 WiLIl Lwo bands the system is actually processing 2.~0 I~F
t`rs~quencies, during the 24-hour period.
Thess~ 125 frequencies are continuously monitored by each of the net stations and the channel noise and intereerence is ~S eva].uated. The cs~ntro].ling-station initiates the sour)d;ng transmission. The sounding signal consists of local ns~;se information analyzed at the contro].ling-station location.
Vuring ~hc sounding cycle the controllingstation scans through a]l ot` the ].25 ~requencies in a random sequence.
lZ3~P92~
The spacing between frequencies shall be in multiples of 4 kH%. Given a band F1 to F2 then, for any subset o~
numl:)ers N= ~n~ 5~ randomly chosen from the set N-1,2,..... N l , where S max~
N = F~ - F (Fl and F2 being in MH~) Tho corresponding frequency set is ~ F~
lo F~ 2~;0 ~ ~2J
The net controlled-station step synchronously with the controlling--station and performs transmission quality evalu-a~ios~s pertaining to each of the 125 channels. The controlled-s~al.ioll wil]. sequentially respond by a repeat sounding cycle,scanning aeain al.l ].25 frequencies. The sounding signal will now carry ].ocal reception quality information back to ~he contLollin~-station, again frequency-hopping over all 12S
channels, in a random sequence. The controlling-station ~0 porforms its own transmission quality analysis and compounds it with the information received and processed through t.he sounding signal from the controlled station.
A single two-way exchange of real-time sounding trans--~S rnissiolls thus ~nables the controlling station to derive andreliably assign optimum operating HF frequoncies to each con~llunicating link.
lt is a central feature oE this invention that the fre-quency managelllent process acts as an automatic HF link controlto achieve an adaptive cl~annel and enhance communication reliabillty.
~ig. l illustrates in a block diagram form three of the many other possible configurations of HF radio communications sys~ms, incorporating the preferred embodiment of the p7esent invention. ~ freqency management terminal would normally be closely inte~ratoLI with the radio equipment..
-~ ~3~
In Fig. la a conventional HE' radio communications system i5 ShOWII that includes a radio remote control unit 21, the HF
Lranslllitter/receiver 24, and a matchin~ unit 26 to cou~le a narrowballd antenna 29. This matching unit need not be used S whon a broadband antenna 27 is available. The frequency management syst-:m is shown to comprise a remote control unit 22 and a processor 23 which is connected to another convenLional but dedicated HF radio system. The two control uniLs are interconnected by 25 to allow automatic freguency assignment and control. In this configuration the information channel is entirely independent from the frequency management sysLem channcl (22-23-20). The information channel ~21-24) which norrllally uses one frequency (half-duplex) or two froquencies (duplex) wi].l not be interrupted by the ~requ~ncy lS managelllent operation. The system channel which u~es l~S
frequencies operates simultaneously and continuously on a non-interference basis.
In Fig. lb the HF radio system 29 is shown to comprise separaLe IIF' transmitter system 30 and an Ht' receiver system 31. These may be physically widely separated. The frequency mallagemenL system, however, uses only a dedicated but convonLional ll~' receiver 32. The two receivers connect to a single receive antenna 37 through an antenna multicoupler 34.
In t,his configurat.ion thc system shares the COnQlUniCationS
transmitter only, which is therefore used both for information transfer as well as frequency management transmissions. The sysLem receiver can thus uninterruptedly monitor the l25 c~ n~ s.
ln Fig. lc a single remote control unit 33 combines t.he ConmlUniCation and frequency manaeement operations, audio and colll,rol, through the system processor 36 which coTIn~ts directly Lo the HF' radio receiver system 35 that serves both.
:3S
~ ~3~3~-As previously stated, each terminAl in the net shall maintain a continuous evaluation of all 125 channels by examining the prevailing interference in the normal comr~ ni-cation 3-kHz bandwidth. This monitoring process shall go on S at all availablo times, by means of the HF system communication eceivor. ~'ach tetDIinal shall sequentially scan the progra-nmed list of L25 freguL?ncies, continuously compiling and updating challn~l occupancy sTatistics.
The number of available operational channels will depend fiLst oL' all on the likelihood of finding any quiet ~requeneies (fLom tho pre-assigned group) during all hours of the day and night, while the rate at which the channel must be evaluated will dep-3nd on the likely variability of the noise spectrum lS allcl pcl:lpaGation conditions with time.
'l`hc torm 'qu;et channel' generally implies a c'nannel whose noise and interference level, inherently a variable quan~ity, only slightly exceeds some measured noise fl(~or avoL-~g(:~l within a liMited bandwidth, or a fixed noise level that corresponds to a low-level signal induc~d into the antorllla, OL~ the threshold of atmospheric noise.
Ilowever, the characteristics of the interference in the ~5 chanllcl, depcnding on the traf~ic and mode of operation, will determitle wllether the channel could be expected to support an accoptabl.e intelligibility of voice or an acceptable bit--erLor-rate. The power spectral density of interfererlce frotll oLheL IIF users may be significantly non-white within HF
voicc channels. Low frequency CW, ~orse Code or narrowband FSK may characterizL? an HF channel as 'noisy', while it may sl.ill support intelligible voice.
According to the invention, a predetermined number of :15 quAIltum !.tates is de~ined, respective to a predeterll-ined number of parameters, the main ones being signal--to-noise ~Z3~9~
- 1~
ratio and bit error-rate, the others being channel noise, data levcl~, ~ading rate, dclay ~pread. Advantageously, the para-mcLeLs mcasuted comprise at least the two main ones. These can be measured with one or more of the other parameters. Any combinution of one of the main parameters with two or more of the othor parameters can also be used.
As stated above, the invention is illustrated with rcrcrenco to a systom of 125 channels, and it i5 further illustrated with reference to eight guantum sl;ates classifying noise and interference present on thc communication channel.
~ l quanLum states of noise and interference power/
freqlJcncy distribution will be defined. Measurements will lS conlinuously indicate which of the eight thresholds has been crossed at oach of the 125 3-kHz channels. For each of these eighL s~ates a panoramic pattern will rapidly be formed, qual-irying a~ 'quiet' or 'noisy' each one of the 125 channels that . thc ontire net is currently evaluating. These patterns will bc cc~nlinuously updaLed throughout the monitoring periods.
Thc labcling of a channel as 'quiet' or 'noisy' will represent fl hard-decisio_, producing the bcst available choice and in-cluding a~wnys a fixed, minimum number of the 'quietest' ch~ nQ~s in cach pattcrn. With net stations dispecsed over a ; ~S widc gcographic expanse, di~ferent interference conditions will be cxperionced at different locations, which will most likely result in a very diffcrent Interference Measurement Pattc-.n (IMP).
Thi~: lMl' will thus constitute a sequence of binary mcasurcmcnts, ]25 bits long, whcre each "1" or "0" corresponds to a hard docision interference-state measurement. Each one of tho Illonitored channels is labeled Quiet ~"1") or Noisy ~"0") at lhe teTminal's location, based on the continuous monitl~rillg and updating of channel occupancy statistics, in 5 or 30 m;nute timo--scp~men~`s. Each bit position will correspond to the exact channcl position in an automatically produced coded table of l~S rroqu(~ s ~3L~32~
- ~7 -Tho process of real time HF channel s~l~ction normally involvos a single two-way transmission exchange between a conlLo]ling frcquency-management terminal and a controlled froquency-mana~f3ment torMinal. Howover, reliable channel assessmont may also be produced through a one-way transmiss;on ~J ~ 5 .
Thc IMl~, the continuously compiled and updatad inter forenco measuremcnt pattern, is used as the primary sounding signal by the controlling terminal. A soundin~ transmission will comprise a single cycle of 125 pseudo-randomly selected 11~ fcequency hops, repeating the same message in a buT-~t. of auliio data, once every hop. During each successive fr~me poriod tho samo frequencies are visited but according to a dil:Ceront, non ropetitive PN-coded permutation, con~rolled by a non-linoar sequence generator (NLSG).
Thc identical, redundant sounding message will be ~ent over each o~o Or these HE' frequencies by means of noncoherent LSK, using 2-nd order in-band diversity, at a rate of 224 ~its peL' second. The use of du l channel FSK contributes also to an incroased correlation between assessed channel quality and voico quality.
~IG. 2 is a timing diagram of the selected burst format of tho sounding framo 311~312~313 which has a hopping rate of l/r hops per second. Each frame starts with a frequency time guard pcriod 3]1 which is long enough to allow frequency ~ han~e ti~ , antenna match time and receiver AGC sottling time.
During thc ncxt timc period 312, the receiver doppler correc--tion loop (in the AFC circuit 35 in E'I~. 4) utilizes t;he dual-ESK tonos and filters to compensate for frequency dr;fts.
Tho ~ol]owing time poriod 313 is devoted to tho data block which CO!lSiStS oL a total of 210 bits. The first segmont 420 :~5 of 6~l bits each are tho synchroni~ation unique words used to provi(:le frallle sync. Tho next soemont 421 of 24 bits is used for I~s of sondor and destination. The foliowing segment 422 o~ 125 bi~s accon~lodates th~ sounding messa~.
J~Z3(~
- l8 -Sc~nlent /l23 of 3 bits indicates 1 of 8 quality states to which Ihc currollt soundin~ pattern belongs. The last segrnent 424 of 8 bits is the ollly one that varies with each frame as it indicates the frame numberl from 1 to lZ5. The sounding mc!ssage is sent by means of dual-FSK transmissions at 224 bps and tbc-n 125 times by hopping over eaeh of the 125 channels~
.
Thc soundin~ station (controlling or controlled~ trans-mits its mcssage on eaeh frequency in turn, and aIl the remote receivin~ net stations being synchroni~ed to the sounding staLiorl, repeatodly Leceive the identical message at each froquency. ~ unique Majority-logic decoclin~ al~orithm insllres a VCLy high probability o~ raceiving a].l messages error-free, undcr extremcly varying con~unications conditions. This ~apa-bil.iLy of socuro message transfer by redundant transmissions is a unique chacacteristic of the frequency management system ombodi~d in Ihe present inv~ntion.
The san~e sounding message of N bits (N = 125) is being rcccivcd over N channels, each channel with its own bit-error-ra~e (8~R). One can make a first approximation and classify 8~ challnels as "blocked" when their 8ER ~ 1/2, or "open" when ~, ~l C i L' U ~ 2.
llllcl(:!L thcse simp].ifying assumptions if N = 2n+1 is the number o~ tcsted channels, N of which are blocked, the probability of error in any one bit under an N/2 majority dccision rule is:
.
p (B) ~ (2) ~ (~-e) ~
e-~ e ~ further approximation takes into eonsideration two typos o~ "open" channels: 'Good', when the BER -~ n2 ~nd 'Ufld', whell the BI~K ~ lO = Bl.
~.~3~9;~8 In additioll to the M blocked channels, the proportion of thc 'Good' ~nd 'l~ad' ch~nnels is known ~o vary considerably bcl.wcoll day and night. ~uring the day SOMO 20 to 30 percent Or l.hc N M cilanncls may be considered '8ad' while during the nighL 40 to 70 porcell~ of them may turn out to be 'Bad', on tlle avorage~
der these assumptions th& probability of error in any one hit, aL'tor majority decc)ding is (the nun~ber of B
~0 channol 5 boin~
p~ -M5(/~ J~L~M
B K (~_ g ~ -I / lc~
I.t sllould be omphasi~ed Ihat the above is derivod under thc assumptioll of uniformly distributed independent errors Wlli(`ll i9 a fair assumption. Namely, the bits received on cllal-lne]. i are indopcndcnt idontically distributed ti~i.d) with ~0 rc~:pect to the same bits (in the message) received on channel j (j - i)~ 'I`his assumpt;on would not be accurate under flat, vory widoband fading conditions of extremely lon& duration tLells of soconds), but these conditions are rarely encountered~
One can ovaluate the average bit error probability ou~r a discroto distribution of channel qualities for tho "open"
chanllc].s. ~.f a typical channel distribution is as follows:
Br':L~ ! 10 10- 2 ] 0 3 10--4 -5 ~ c,~
channols: S lO ' 30 40 lO 5 ~ rhe slverage bit crror probability after majority decoding for N-l.~S and M-SO percent would be: 5xlO , namely, even undc; vcry sovere conditions, with enough tested channels tho bil. crror rato o' the ro'erence sounding message is remark.a~ly low~
~ ~3~9~3 On~e ~he error probability for any one bit in the majori~y - decoded sounding message has been evaluated, one can ovaluate the probability of receiving an errored sounding mcssap,e, Pl, and then the probability of receiving an exact sounding mossa~c which is given by l-PE. For a totsl 3n bits of messap,e (2n~1 channels and n-l control bits), P~ ( 1 pM~ 3n This capability of secure acquisition o~ the sounding mcssage, through utilizing the highly redundant transmission sl~home, is a unique and a central aspect of the present i llV~-UIt~; on.
ro m~in~ain system synchronization all terminals must stop ~heir non--linear sequcnce generator (NLSG) clocks with t1lcir phasos directLy related to thc transmitting terminal c]ock which takes the lead. l`he NLSG has several special fcalures, in addition to the basic functions. It provides ~0 synchronizin~ or resynchronizing capability, the NLSG can be ro~llrned to a known starting poing and then stepped to a prclJet~:lmined point in tim~, in the process of initialization.
The YK bit st:ream is based on 8 key-variable contained ~5 witl~ ttlo NLSG. The NLSG is programmable with respect to t.he valiahle in Ihe sense that the current variable can be replaced with a new one as required, by means of a special ext.~rnal loader. ~ zeroizing function is also provided, should it bocomc necessary to clear all stored data in the NLSG, under cmcr&~:l"::~y condi~ions.
Th~ synchronized pseudo-random sequence generators at all froqu~ncy mana~oment torminals determine the same new frcqucncy for each successive frame. The freguencies are se~ected from the string of bits generated by the NLS~ each timc t.he frequoncy is to be changed.
L)uring rec~ption o~ the repeated sounding message, the sysl.cm maintains an elaborate Link Quality Analys;s, peLLorming sin~u]taneous measurements of a]l the paralI~eters co(Isiderod essenLial to the monitoring of con~unication S tLaf~ic. Link qual.ity analysis or in-band channel evaluation is a key process in enhancing HE` frequency selection and conununication sysLem performance estimation~projection.
Tj1C invention incorporates advanced signal processing a1goritl~ s that pcrmit measurcments of all essential paranIet.~rs within tIlc time constraints imposed by the time-varyin~ IJF
ch~;Irlel~ ~ fundamental n~easure of system channel performance dcL,rad~tioIl in a digital comn~unication system is the bit-~rror-rate ~L3IK). In the period of timc that the ~iF channel transfer ruIlction msly hc approxirnted as quasi-stationary, it is commonly di~:ricul~ to accumu1.a~ su~icient bit errors to characteri~ie noar-inslantaneous data performance. The invention us~s a modifiod approach of error rate extrapolation based upon pscIldo-errors (E~L3~R) to estimate the probability of error in 2 vf!Ly shorl. tirno. Pseudo errors may be generated by modifying thc eain or phase threshold criterion in the error decisions pL'OCe5S to obtain parameters which indicate apparently greater circuit degradation than raally exists. The measurement period is :hoLtened since the pseudo--error is designed to be larger ~S than the corLespoIlding actual error rate. The basic idea is that by narrowing the "good detection region" and wi-dening the "error detection region" one measures a highor BER than t.he acLual 13Ii.R of the detec'i.or. As a result, high accuracy low BIit vfllues can he measured from a) small data samples, and b) wilholII. actua]ly knowing the transmitted data.
.
Thc l'L~I.R and Iho actual BER are related as ~o1io~s:
log P - K I loL,~
:~5 wheLc I' ;s tho bit pscudo-error probability arId PE i~ I.he actua1 ~:rrI7r probabi1ity.
%~3 ~
Ir Iho transmitted data is known, or derived from maJority decodin~ of repetitive soundings, as is donc in this illVelltiOIl, ono can "scale the channel" by calculatin~ K out of moasllrcd ~ and P~.
lt should be emphasized that the above was developed ma;nly for linoar, additive noise type fading channels. Since l.llis is not always the case with the HF channel, a cert.Rin cortoction should be made which will account for this discre-pancy. The channel BER model can he rewritteri as:
logP - K ~ logl'~ + KL
whore KL is a compensating factor whose value is derived ftolll l.ho burst orror statistics of the HF chal)nrJI.
Whrn the sounding cycle has ended, the contro3.1ed-Lcrminal recoivor has at its disposal a wide variety of information abou~ each of tho N sounded channels. The present invelltion takos advantage of its uniquo capability to fully rc~covor the soundin~ mossage bit-sequence. This original me SAI,O is usod ~or error counting, PBRR and 8ER dotermin~tion.
Moasurements are performed also of the rms multipath dolay spread, the fading rate, interference levels and distri-bution, and SN~. This data is processed and updated with every additional sounding transmission. A ve~y reliable characteriz-aliori of tho l~ conununication channel results. Knowledge of tllo channel conditions and parameters enables the prediction of channel perforn1ance aL high data rate transmissions based on lo~ rato d~ita transmissions.
Tested channels are also ranked for various uses: voice, rnulti-torlc D~'SK modem, wideband FSK, narrowband FSK, etc. The inL(3rldod oporational use clearly af~ects the link quality dClL'rnlinatiOIl Si.llCe interferences have different effect8 in di rr~ "~ applicat.io"s.
- ~3 -1~ascd on the link quality analysis and operational n1ode~
hnsd doci_ iOn5 are made by the receiving terminal, qualifying as ~Good" or "Uad" each one of the 125 channels tested. A
bin~1ry L;nk Quality Pattern (rJQp) of transmission performance S mC.l`SUrelllellt5 i5 gcnerated~ where each one of the tested chan-ncls is labeled "l" (Good) or "0" ~Bad). "l" to indicat.e an accoptable channel and "0" to indicate an unacceptable channel.
Accoptabi]ity is determined based on eight quantum states of pcrrormance characterizing eight separate link quality paller1ls~ These LQt's represent the best available choice and includc always a fixed, minimum number of the 'best' channels in f-~ach paLLern. ~`or example, in the ].imiting case, with all oLhcr. measured parameters equal, "Good" or "Bad" may indicRte, say, ~L1~ < 10 or BER ~ 10 following thc Doppler correction and AGC settling, the rcceiver mu5f porform the following functions:
a. ~ccover clock timing for bit detection.
20 b~ Kccognizc thc frame-sync unique synchroni~ing word to cslabli3h the basic frame timing reference and identify ncl. nllmbcr.
c. lde1lliry the I~ patterns. These bits enable the re(:f?iver to vcrify Lhe validity and legitimacy of the received ~5 bursL~
d~ ~ccopL 1he remaining portion of each message. Arrive at Lhc~ corrccf~ IME' or LQP and process the nec0ssary tests, evaluation3 and decisions.
To illu3trate the system's operation, let the controlling Lor1n;nal, C, init:iate a sounding braodcast cycle C uses ax a sol11(di11g signal its most recent IMP. The controlled-terminal, c, derivfs C~s ;'MP error-free, which provides it with the noise and inLer~crence levels measured at C's location, in each o~
j :~S Lhc 1~5 channcls n~onitored. In addition, c cafries out l~.~ r.QP
-~~ tcsts, during the sounding cycle, to sort out the "Good"
chnnnc]s. lhe final results can be tabulated as in Lhe fo]lowi1lr, siMplified exan~ple Chal~nal No. ~ 24 25 26 27 28 29 30 31 ~ - - -C's MI~ (Lclc~ived) - 0 0 1 0 1 1 0 1 ~
c's TMI' (maasured) - l 0 0 0 1 0 1 1 - - - -c's l.~P Decisions - G B B G U G 8 G - - - -~ 5 (G for "Good" and B for "Rad") :
~ ~rom the above data c can i~nediately deduce that:
., a. At th~ controlling terminal C, frequencies 24, 25, 27 and 30 are noisy. ~requencies 26, 28, 29 and 31 are quiet.
b. At the conLrolled terminal c, frequencies 25, 26, ?7 ar)d 29 are noisy, while fraquencies 24, 28, 30 and ~1 are c. Ltocep~ion quality was good at frequencies 24, 27, 29 and l.5 3l anl.l bad a~ erequencies 25, 26, 28 and 30.
d. At rreqllancies 27 and 29, although the channels were noisy a~ c's end, reception was good, probably because the signal over-powered the noise ]evel.
e. Al rreyuancies 28 and 30, although the channels were yuiet at c's end, reception was bad, probably because of no E~ropagation or a very low si~nal.
f. ~ur ~ransmission in the C--to-c direction, frequencies 24 and 31 may ba a good choice.
g. Ior ~ransmission in the c~to--C direction, ~requencies 29 and 3l ~nay be a good choice.
h. I.)oE)onl-lin~, on the nature and level of the noise at the roceiver's end other frequencies may also be considered whell the expccted received si~nal ].evel can be estimated.
.
~ Z3~D9;~3 - 2s -In ~pplications where, most of the time, only one-way transmissions are conducted (C-to-c), the frequency changing or al~ocatn~ function, over the communication link, may be asai~ncd to the controlled torm;nal c. Operation reli~ nn 5 just tho one-way sounding broadcasts (C-to-c). A reliable and rapid docision will be made, determinin,~ the best pair of trallSmit/locfaive operational frequencies, for cornmunication witll thf~ controlling terminal. This frequency allocation must bo sc~curely buLst-transmittf3d to the controlling terminal to 10 nl low norlllal Hf'~' con~lunications to prl)cf~d~
L~ollowin~ tho reception of the sounding transmission cyc]o, tile controlled terminal will wait a fixed number of tiUIlC! s].ots bo~ore attempting to respond to allow its communi-.5 catioo Lransmittf2r time to tune to the f~equency chosen fortho c-to-C transMisslon. Tn prepar~tion to respond, tbe conlLo:lled toralinal shall automatically construct a reporting m,3s-:age mado up of just tho one selected C-to-c communication freqllency (till the next update). Whan responding, only upon arrival at the time slot that coincides with the selected c-to-C froqu,3ncy (in the FH sequence) will the controlled ~rlll;nal turn--on its transmitter RF power for a bllrst-tranamission of this mossage. This will automatically reveal to C thf~ selected c~to-C irequency. Controlling and controlled tolrninals have now automatically tuned their fixed-channel HP
COnlmUniCatiOn roceivers and transmitters to tho selected pair ! of` oporal.ional frequenci es .
NoLmally the aystem operation over an HF link will :30 involvf3 a two--way sounding process, with the controlling torminal assuming frequency assignment authority~ Following tho fiL~t C-to-c soundine cycle, the controlled terminal, havine formod its I,ink Quality Pattern, automatically responds Wit~l a c to-C sounding broadcast. ~gain, within the single frallle Or 125 ~reguency hops, c's LQP sounding message will be repeat~cf onco ovory hop~ This two--way sounding process will take lf39S I:han S minutos.
:~3~ZI~ `
rho colltrolling terminal will now be lookin~ at two T.QPs which pLovide simultanQously the measured con~unie;lt.ion porrotmance at both ends oE the link and, therefore, enables a str~ight~orwald solection of optimal operating frequencies.
The dissemination of frequency information will be conducted using either a soundin~ broadcast burst-transmission or the current operating secure communications channel.
~efore a terminal can be used in an actual exchange of si~n~lls, somo preparatory operation is required. Necessary data n-ust be entered and stored: the frequency band or bands to be ~sod, operational modes, IDs of net sender destination, key variables, initial operating frequencies and a certain agreed-Lo cycle start time is also set in. This is used with the actual time to determine automatically the elapsed t;me of the op()~ation for frequencyhoppin~ and key synchroni~ation purE~oses. The actual time is acquired from a suit.ahle refeLence external source having second-accuracy, such as coordinated universal time, an electronic watch, a count down OVflt voice radio, etc.
To onsure proper net initiation under seach mode condiliolls, w11en a new number joins the net or transmissions havo not taken place for many hours, a special Synchronization Cycle is provided. During this cycle a unique sync message, bLoadcast by the controll.in~ terminal, is rspeated once over eacll o~ the 125 channels.
Ii'ig. 3 i]lustrates a simplified transmission timing di~l~ran~ of the Sync Cycle. In a typical frame, the first and lasL 64~bit data blocks are the two complementary unique words 501 and 505, designed to be detected as a doublet of a positive folLowed by a negative correlation peak. In the central data fiold the blocks 502, 503 and 504 of 96 bits comprise three ei~,ht--bil. characters, ~lpha or numeric, devoted to the sender's lUIL)esLillation, repeated three times.
1;~3~
I~ollowing initlalization, which includes loading the terminal's NI~SG with the common key, net synchronization is raEI;dly achicved i~ time-of-day internal clocks are all set to within maximum ~D (t~T) seconds of real time, where t is the syst~m hop-time between freguencies and T is the system dwell-timc at each frequency. The order in which the system is so(luenced through the gcoup of channels, is controlled by the NLSG's output.
upon entoring the search mode, the frequency management ~orlninals au~on~atically advance their set time-of-day by D
tin~o-sloLs in time. The terminals' NLSGs are therefore forced to ~o within (0, 2D) time-slots ahead of the real time of day.
1.5 ~hc sc!urch receiver will be taking unequal steps, jumping fllw~ys ahead of the sounding transmitter, and waiting for the tr.nnsmiLter to arrive. l'he receiver waits 2D+l time-slots on its present frequency, then jumps ahead 2D frequencies, then waits again 2D-Il time-slots, then jumps ahead 2D+2 frequencies, waits another 2D-~1 time-slot, then jumps ahead again 2D
f e oqucnc ios, etc .
Following an initial shift of ~D time-slots, and assusnill~ t 0 and T=l second, the optimal search procedure is:
wait . 2DIl alld S~arch = at 2D, then at 2Dt2. As a result of ~hi`: soarch pa~tern, the controlling-terminal and the conlrollod--terminal meet on various frequencies, in other words thoy criss-cross each other until acquisition is achi~ved and the search procedure ~nds.
~ ho averago waiting time (T~) between meetings of the tolminals during the search procedure is given by:
~.~3~9~28-~2)(2D~ = 2 P
The maximum waiting time until the first meeting for a giverl D, is l max = 2D.
DuriDg the synchroni~ation period, the terminals meet on 1 0 al- ~IVCL'-I~,C of .
MU different frequencies, where:
D ~) where N i5 the number of i 9 ~ (zp~/J2 ) assigned frequenr.ies, 1.5 N = 125.
Erame synchroni~ation exploits the systematic nature of the soarch detection process to realize a very reliable and raL~id frame--sync recovery.
~ digital correlator will detect arriving frame sync sequences and full utilization will be made of the so-called window tcchnique. This method takes advantage of the fact tha~ the Syllc sequences are periodic ~nd that legitimate co~relator outputs will have to be spaced in time according to thc (2V)-(~D-~l)-(ZD-~2)-~D+l)-... pattern. Acquisition will be dec]ared after detection of 3 sync sequences. The det~ct.ion thLesholds will determine the average synchronization time, as well as ~he n~ax. sync. time for specified miss/false-alarm probabilities. t I~ the probability of detecting a sync sequence on 8 channel is Ps, the averàge probability of detecting 3 consocutive syncs at proper spacings is~
' '` `
:~3~
P~ P5J
S Where Ps is given by the probability of detecting "over the threshold" number of correct bits in a PN sequence; it is a function of the channe] ~I~B.
Hence, the average s~nchroni2ation tiMe is p31 Whcn three successive hits are found, from among the channels crossed (before one scanning cycle is complete) the operation proceeds to the steady-state mode. In this mode the receiv~r is in full synchronism with the transmitter and hops witb it at the regular rate. The frame-sync detector maintains Q ' continuous trackin~ process and n~onitors the end of the sounding transmission.
- This unique synchronization algorithm is another impor-tant aspect of this inventiotl.
Re~erring to Fig. 4 which is a block diagram of the frequency mana~ement terminal, the system is shown to comprise four major modules:
1. Analog Module 12, which includes the terminal's data link and basic sensors.
2. Process Control Module 14, which generates the syst~lm's timing waveforms, and controls the sounding, and s~cllre radio functions.
3. Computer Module ll, which is responsible for the system signal processing, analysis and overall system control.
4. Front Panel Control Module 13, which includes all the operator's manual inter~ace controls and indicators.
~z~
Erom the radio interface connector 15 the radio receiver AGC signal is fed through conductor 71 to the computer modulQ
11. The received audio FSK signal is applied through conductor 73 to monitor filters 3l and R~T control device 32. The monitor filters are examining discrete segments in the 200-3200 audio band and signals present are delivered to the processor module 11 via conductor 72. When the terminal initiat0s a soundin~ transmission, a SEND/REC-ON ~ignal appears; thrqugh conductor 74, at the input of device 32. Out of the computer module the digital sounding message is applied, through conductor 75 to the dual FSK modulator 37. This device includes two widely spaced (in frequency) FSK modulators to which the same message is fed simultaneously. Two FSK output signals are then passed, via conductor 76, to the bi-directional analog gate 32 which applies them to the dualbandpass filters 33 for signal shaping and improved isolation.
Conductor 78 feeds the two FSK outputs to the radio modu]ator.
When the terminal reverts to the receiving mode, th~ R/T
control device 32 routes the two FSK signals received from the radio demodulator, through the dual bandpass filters 33, gating their output via conductor 79 to the dual FSK
demodulator 34. The output of this device which is now the restored digital message is fed through conductor 81 to the processor module.
The automatic frequency control device 35 provides a means of sensinK the doppler ~requency shift and applying an adaptive compellsation to improve the bit detection capability of the FSK demodulators. To help synchronize the local clock to the incoming digital burst, the bit synchronizer device 36 continuously interacts with the central timing source 41, throu~h conductor 85. The measured doppler shi~t QS well as the processed corrections are transferred via conductor 82 to the computer module interface 22.
I
z~
Under program control a multiple of unique algorithms and functions are simultaneously being processed in the micro-computer module 21. These deal with the rapid signal measure-ments, evaluations and frequency management decisions that must be accomplished in almost real time, while visiting 0ach of the lZ5 frequencies. Testing of noise and interf~ce characteristic parameters as well as actual communication quality parameters, the generation and grading of IMP and LQP
sounding signals, processing the synchronization acquisition scheme, message block-encryptioD/decryption, secure protocol, frequency assignments, etc., all these activities are computer controlled.
..
Timing-and-process-control device 41 disLributes all timing waveforms, stores and controls all initiali~ation data serially inputted, through conductor 94 and remote corltrol in~erface 48. .It receives the output of the non-linear-- sequence-generator device 44. By means of an external loader key variables are serially féd to the NLSG for the generation of a random sequence which is used for digital encryption, frequency translation and secure operation. The radio control device 42 receives control data from the timing device 41 via conductor 87, and couples frequency and SRND/REC control information to the radio system.
~5 ~ 'ront panel control module 13 provides a manually operated interface and comprises a time~of-day display and data indicator device 51, fl function switch 52 for testing, initialization, time settinK, b~nd selection, etc., and a mode switch 53 to select automatic/manual operation, one-way transmission, etc.
A functional block diaKram of the frequency management terminal is depicted in Fig. 5. It contains two functional ~5 groups: receiver group and transmitter group.
3.~3~
Functional modules numbered 601 to 610 are part of the transmitter, while functional modules 6ll and 625 ~excluding 616 and 617) are part of the receiver. The ti~ning of the teLminal originates from 616 which provides the required clocks to control box (617), to processing ~615) and to the modulator (608) and the demodulator (612) functions. Two inputs are provided by the external radio receiver, namely, tho received audio and the AGC. The audio is the iDpUt to ~.he receiver where the time recovery (611) and the detection (6l2 functions are being performed. ~uxillary functions like ~re-quency shi.ft corrections ~613) and pseudo -- BER measuremenL
(61~l) are also part of the receiver. The audio and the AGC
arc being monitored (604) and the lME' or LQP is generated (605). Pollowing the sync pattern transmission (606) the TMP
L5 or LQP as a sounding message is being transmitted (607) through the modulator (608). The frequency hopping of the radio un;ts (receiver and transmitter) is boing controlled by the control function (617). The sync search (618), acquisition (619) and tracking (620) are perÇormcd in the receiver on the received ~0 data. The hop-sync of the receiver (621) is initialized during the acguisition phase, while the crypto sync (622) is initiated from the control and timing units, the key value and time being loaded externally (623). The sync tracking unit : (620) tracks the frequency keys following acquisition. Once the sounding cycle has ended and the terminal receiver has anulysed (62~) the sounding message, a decision concerning t.he best frequcncy subset is pcrformed (625). This decision is conununicated to the operator (human or automatic) via t.he remole control I/O (627) and is displayed on the display (626). Via the control panel (626) or remote control port, a sel.f-test cycle can be initiali~ed (628), the results of which are stored ~for further statistics) and communicated t.o t.he operator as wel.l.
~LZ-3~928`
.
Any oE the functions descrihed herein, given t.he teaching of the invention may be implemented by those skilled in the art. Thus while a particular embodiment of the present invention has been shown and/or describecl, it is aparent t.hat changes and modifications may be made thereon without depar-ting from the invention in its broadest aspects. The foregoing Detailed Description is intended to be merely exemplary and not restrictive.
Claims (14)
1. A high frequency (HF) frequency-management system with at least two stations, a controlling station and one or more controlled stations, each including an HF radio transmitter, HF radio receiver, a control unit for control-ling the operation of the transmitter and receiver and a frequencymanagement processor means for:
continuously monitoring the interference and occupancy of a finite plurality of HF channels, each channel tuned to a different frequency:
hard-labelling of each one of the said channels as either a binary "1" for a 'quiet' channel or a binary "0" for a 'noisy' channel (or vice versa), based on a predetermined set of criteria:
resulting in a binary word, and storing and updating the binary word wherein each bit represents an evaluation of one of the frequencies visited:
using the binary word as a sounding signal and transmit-ting this signal repeatedly, once over each of the said finite group of frequencies by having the transmitter scan said channels:
synchronizing a controlled station receiver so that it is sequenced through same said group of channels at an equal rate, being at each one of the channels at the same period of time as the transmitter, to allow the sounding message to be received:
majority-detecting said redundant sounding message at a controlled station receiver processor:
performing link quality measurements on each one of the scanned group of frequencies:
hard-labelling of each one of the said channels as either a binary "1" for a 'good' or 'acceptable', and a binary "0" for a 'bad' or 'not-acceptable' communication quality (or vice versa), based on another set of criteria:
storing the binary word at the controlled station receiver processor, to be used by it in forming the answer-back soun-ding signal:
transmitting the answer-back sounding message repeatedly, once over each of the said group of channels by having a controlled station transmitter scan said channels:
majority-detecting said redundant answer-back sounding mes-sage by a receiver processor at a first controlling station:
performing link quality measurements by the receiver pro-cessor at the first controlling station, on each one of the said scanned group of frequencies:
selecting optimal frequencies by the receiver processor at the first controlling station, for reliable communi-cations in both directions, controlling-to-controlled and controlled-to-controlling stations, based on the analysis of the received and derived link quality patterns:
utilizing the synchronous frequency-hopping mode which is maintained between the stations, to disseminate frequency information by transmitting, over the selected optimal fre-quencies, the relevant information for the remote station:
automatically tuning the communications transmitters and receivers to the selected preferred frequency or frequen-cies, to establish a reliable communication path between the stations.
continuously monitoring the interference and occupancy of a finite plurality of HF channels, each channel tuned to a different frequency:
hard-labelling of each one of the said channels as either a binary "1" for a 'quiet' channel or a binary "0" for a 'noisy' channel (or vice versa), based on a predetermined set of criteria:
resulting in a binary word, and storing and updating the binary word wherein each bit represents an evaluation of one of the frequencies visited:
using the binary word as a sounding signal and transmit-ting this signal repeatedly, once over each of the said finite group of frequencies by having the transmitter scan said channels:
synchronizing a controlled station receiver so that it is sequenced through same said group of channels at an equal rate, being at each one of the channels at the same period of time as the transmitter, to allow the sounding message to be received:
majority-detecting said redundant sounding message at a controlled station receiver processor:
performing link quality measurements on each one of the scanned group of frequencies:
hard-labelling of each one of the said channels as either a binary "1" for a 'good' or 'acceptable', and a binary "0" for a 'bad' or 'not-acceptable' communication quality (or vice versa), based on another set of criteria:
storing the binary word at the controlled station receiver processor, to be used by it in forming the answer-back soun-ding signal:
transmitting the answer-back sounding message repeatedly, once over each of the said group of channels by having a controlled station transmitter scan said channels:
majority-detecting said redundant answer-back sounding mes-sage by a receiver processor at a first controlling station:
performing link quality measurements by the receiver pro-cessor at the first controlling station, on each one of the said scanned group of frequencies:
selecting optimal frequencies by the receiver processor at the first controlling station, for reliable communi-cations in both directions, controlling-to-controlled and controlled-to-controlling stations, based on the analysis of the received and derived link quality patterns:
utilizing the synchronous frequency-hopping mode which is maintained between the stations, to disseminate frequency information by transmitting, over the selected optimal fre-quencies, the relevant information for the remote station:
automatically tuning the communications transmitters and receivers to the selected preferred frequency or frequen-cies, to establish a reliable communication path between the stations.
2. A system according to claim 1, wherein the frequency information is disseminated by burst transmission on the selected frequency.
3. A high frequency (HF) frequency management system according to claim 1 wherein the timing and control means comprise:
means for randomly selecting N channels from within a specified HF sub-band given its limits flow to fhigh;
means for storing said N channels as alternate communication channels with each channel having a predetermined frequency;
receive/transmit means for placing the station in a transmit mode;
means for sequencing and tuning the HF receiver and transmitter through the group of N channels;
means for providing timing for the overall system operation, bit synchronization, frame sync acquisition, sync cycle operation, sounding cycle operation and signal processing algorithms;
means for transmitting the sounding messages using an in-channel diversity of two FSK modulators-demodulators;
means for generating a predetermined sequence based on the input of a key variable and real time of day.
means for randomly selecting N channels from within a specified HF sub-band given its limits flow to fhigh;
means for storing said N channels as alternate communication channels with each channel having a predetermined frequency;
receive/transmit means for placing the station in a transmit mode;
means for sequencing and tuning the HF receiver and transmitter through the group of N channels;
means for providing timing for the overall system operation, bit synchronization, frame sync acquisition, sync cycle operation, sounding cycle operation and signal processing algorithms;
means for transmitting the sounding messages using an in-channel diversity of two FSK modulators-demodulators;
means for generating a predetermined sequence based on the input of a key variable and real time of day.
4. A system according to claim 3 wherein there are provided means for pseudo-randomly sequencing and tuning the HF
receiver and transmitter through the group of N channels, means being provided for generating a pseudorandom sequence based on the input of a key variable and real time of the day.
receiver and transmitter through the group of N channels, means being provided for generating a pseudorandom sequence based on the input of a key variable and real time of the day.
5. The high frequency (HF) frequency management system according to claim 1 wherein the noise and interference measurements means comprise:
means for measuring the radio receiver AGC level and radio receiver noise output and distribution;
means for measuring in-channel interference characteristics;
means for classifying noise and interference present on the communication channel into a predetermined number of categories, according to a predetermined set of criteria;
moans for generating a corresponding number of binary words, each N-bit long, one for each category, wherein each bit represents a hard-decision qualifying each one of the N communication channels monitored.
means for measuring the radio receiver AGC level and radio receiver noise output and distribution;
means for measuring in-channel interference characteristics;
means for classifying noise and interference present on the communication channel into a predetermined number of categories, according to a predetermined set of criteria;
moans for generating a corresponding number of binary words, each N-bit long, one for each category, wherein each bit represents a hard-decision qualifying each one of the N communication channels monitored.
6. A system according to claim 5, wherein the number of categories used is from 3 to 10, and which comprises means for generating a corresponding number of binary words, one for each category.
7. A high frequency (HF) frequency management system according to claim 1 wherein the link quality analysis means comprise:
- means for detecting noise representative of the noise present within the communication channel band us well as within two separate FSK channels;
- data detectors for providing a signal representative of the data levels that are present on the communication channel that the receiver is tuned to;
- means for determining the signal-to-noise ratio;
- means for measuring the fading rate and its spread;
- means for measuring the rms multipath delay spread;
- means for using the demodulated and majority-detected sounding message to arrive at the actual bit-error-rate;
- means for quantizing the parameters:
signal-to-noise-ratio and bit-error-rate, if desired in combination with one or more of the parameters: fading rate, delay spread, channel noise, data levels, measured on the communication channel, to define the desired predetermined number of link quality categories according to a predetermined set of criteria;
- means for generating a corresponding number of binary words, each N-bit long, one for each category, wherein each bit represents a hard-decision qualifying.
respectively one of the N communication channels sounded.
- means for detecting noise representative of the noise present within the communication channel band us well as within two separate FSK channels;
- data detectors for providing a signal representative of the data levels that are present on the communication channel that the receiver is tuned to;
- means for determining the signal-to-noise ratio;
- means for measuring the fading rate and its spread;
- means for measuring the rms multipath delay spread;
- means for using the demodulated and majority-detected sounding message to arrive at the actual bit-error-rate;
- means for quantizing the parameters:
signal-to-noise-ratio and bit-error-rate, if desired in combination with one or more of the parameters: fading rate, delay spread, channel noise, data levels, measured on the communication channel, to define the desired predetermined number of link quality categories according to a predetermined set of criteria;
- means for generating a corresponding number of binary words, each N-bit long, one for each category, wherein each bit represents a hard-decision qualifying.
respectively one of the N communication channels sounded.
8. A system according to claim 7, wherein the categories used are signal-to-noise ratio and bit-error rate.
9. A system according to claim 5 wherein the number of channels is from 25 to 130, and the number of categories used is from 2 to 8.
10. A system according to claim 9, wherein the sub-band used is about 500 kHz wide, and the number of channels used is 25 to 130 with about 4 kHz spacing .
11. A high frequency (HF) frequency management system accor-ding to claim 1 wherein the receiver synchroni-zation means comprise - means for transmitting B N-frame sync cycle, pseudo-randomly hopping over the group of N channels, where each frame includes a unique sync format;
- when the receiver reverts to the 'search' mode, means are adapted to step the receiver at an irregular rate but in a unique pattern of 'skipping X channels and then waiting Y time-slots, etc.', designed to keep the receiver always ahead of the regularly stepping transmitter; maintaining this search pattern until a predetermined number of syncs is detected, indicating sync acquisition;
- means for maintaining a continuous process of tracking frame syncs during the sounding cycles.
- when the receiver reverts to the 'search' mode, means are adapted to step the receiver at an irregular rate but in a unique pattern of 'skipping X channels and then waiting Y time-slots, etc.', designed to keep the receiver always ahead of the regularly stepping transmitter; maintaining this search pattern until a predetermined number of syncs is detected, indicating sync acquisition;
- means for maintaining a continuous process of tracking frame syncs during the sounding cycles.
12. A high frequency (HF) frequency management system according to claim 1 wherein the channel selector means comprises:
- comparison means for evaluating and comparing the Interference Measurement Patterns (IMPs) received and locally measured, and the Link Quality Patterns (LQPs) locally measured, at the controlled station, to allow the controlled station to deduce, based on a single sounding cycle, optimal operating frequencies for the controlled-to-controlling and controlling-to-controlled directions;
- comparision means for evaluating and comparing the LQPs received and the LQPs measured at the controlling station, to allow the controlling station to derive, based on the answer-back sounding cycle, optimal operation frequencies for the controlling-to-controlled and controlled-to-controlling directions.
- comparison means for evaluating and comparing the Interference Measurement Patterns (IMPs) received and locally measured, and the Link Quality Patterns (LQPs) locally measured, at the controlled station, to allow the controlled station to deduce, based on a single sounding cycle, optimal operating frequencies for the controlled-to-controlling and controlling-to-controlled directions;
- comparision means for evaluating and comparing the LQPs received and the LQPs measured at the controlling station, to allow the controlling station to derive, based on the answer-back sounding cycle, optimal operation frequencies for the controlling-to-controlled and controlled-to-controlling directions.
13. A HF frequency management system according to claim 12 further comprising:
- frequency disseminating means for the distribution of frequency allocation information.
- frequency disseminating means for the distribution of frequency allocation information.
14. A HF frequency management system according to claim 13 wherein the frequency disseminating means comprises:
- means for selecting and storing optimal communication frequencies in the storage means of each channel according to the discrete address of the remote and near stations;
- means for the near or remote station to transmit on the selected outgoing frequency, to the remote or near station respectively, information preceded by a unique sender's identity and address, regarding the selected incoming frequency.
- means for selecting and storing optimal communication frequencies in the storage means of each channel according to the discrete address of the remote and near stations;
- means for the near or remote station to transmit on the selected outgoing frequency, to the remote or near station respectively, information preceded by a unique sender's identity and address, regarding the selected incoming frequency.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000443939A CA1230928A (en) | 1983-12-21 | 1983-12-21 | Frequency management system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000443939A CA1230928A (en) | 1983-12-21 | 1983-12-21 | Frequency management system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1230928A true CA1230928A (en) | 1987-12-29 |
Family
ID=4126801
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000443939A Expired CA1230928A (en) | 1983-12-21 | 1983-12-21 | Frequency management system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1230928A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11647550B2 (en) | 2020-04-17 | 2023-05-09 | Rockwell Collins, Inc. | 4G automatic link establishment (ALE) with improved two-way link quality analysis (LQA) exchange |
-
1983
- 1983-12-21 CA CA000443939A patent/CA1230928A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11647550B2 (en) | 2020-04-17 | 2023-05-09 | Rockwell Collins, Inc. | 4G automatic link establishment (ALE) with improved two-way link quality analysis (LQA) exchange |
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