CA2195453A1 - Method for spread spectrum communications - Google Patents
Method for spread spectrum communicationsInfo
- Publication number
- CA2195453A1 CA2195453A1 CA002195453A CA2195453A CA2195453A1 CA 2195453 A1 CA2195453 A1 CA 2195453A1 CA 002195453 A CA002195453 A CA 002195453A CA 2195453 A CA2195453 A CA 2195453A CA 2195453 A1 CA2195453 A1 CA 2195453A1
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- Prior art keywords
- pulses
- frequency
- interval
- pulse
- transmission
- 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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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/713—Spread spectrum techniques using frequency hopping
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Dc Digital Transmission (AREA)
Abstract
A method for secure radio pulse transmission through varying atmospheric condition which chooses different frequencies for transmitting a series of pulses of energy dependent upon the digital data content to be transmitted, provides for determining the frequency choices for a subsequent pulse transmission in response to digital data content of at least one previously transmitted pulse. Application includes h.f. band, data and fax, wireless communications.
Description
2 ~ 9 5 4 5 3 PCTIUS96/07023 METHOD FOF SPREAD SPECTRUM COMMUNICATIONS
r ~c~. uu~ I of the lu.. ~--n Field of the l~,~. ~-The present invention generaily relates to spread spectnum, digital communications, and pdli' I' 1~' to a method for l~ " , Ig frequencies for frequency hopping lldll_,, ' ' .1:7.
S- ~ - ll of the Prlor Art Various ~lg i ""s exist for col~ 9 digital pulse, spread spectnum 10 communications. The principal goal is that of encoding frequency selection for providing communications which are effective in a fsding multipath e.,r;.ur""t",l and which are secure from both jamming and e -/~,sd~u~.~ ;"9. Spread spectrum t,al, ,:, typically tai-<e narrow ban 'v.' ill, symbols and spread them out over a much wider ban : ilh tlhan is neu,:.:.aly for the rate of data lldll~ O n.
15 Unfortunately, "ospl,efic multipath effects are frequency d~,an~ t and thus are acc~" ~ i by any spread spectnum approach.
In frequency hopping, spread spectnum systems, the carrier frequency is changed in acco,.ltl"..~ with a p,~ ' ,. ,ed sequence controlled by one of a variety of codes. The ~dll- Il.'-' ' III~U'~ iS thereby contained in eitherthe 2 0 1l an~l 1 l" ' ' frequency or in the frequency difference between the lldl _ "' pulses and a reference frequency. The spread spectnum signal may be received, decoded and demodulated by a receiver constnucted to employ the same frequency hopping code, once the same p,. , . ,ed code is sy~ lul ll ul liLed at the receiver with the ll al l~ code. In one prior art method 25 described in US Patent No. 4,612,652, a matched pair of pseudo random number ~ene, :. are used to '~: ,e the maric and space frequencies of both a transmitter snd a receiver. The direct generator output and a delayed version thereof are used to provide separate random frequency sequences for each of the mari< and space data signals, I--r ~ .31y. The separate gene, 30 are :~nl~:lllulliLud between llall~lll and recelver, rssulting in sy~n,ll,ul);~ l of both the mark and space frequencies. Unfortunately, the required _,.,-,hlull;...ll adds Col l I~ .Aity to the 1l dn' -.. ."' - and receiver and their i" lk n and can be the cause of lldns...:~.s;Jn failures.
WO 96/37060 !t f~ h ,~ PCT/US96/07023 2 1 9 ~ ~ 5 3 S ~y of the Invention AC~ ly, it is an object of ;he present inventiGn to provide a method of frequancy hopping, spread spectrum communications.
It is another object of the present invention to provide such a method 5 which is capable of co"".anl - ,9 for multipath and fadins lldll~ i env;, u, " "e1"ts.
It is a further object of the present invention to provide such a method which enables error correction and recovary of lost data.
It is a still further object of the present invention to provide such a method 10 which does not require v,, lvl "u"i~", or 5~ IUI ,i~ution between the lldllslllill and receiver.
In one form ths present invention provides a method for frequency shift keying l,d"s",;__;ans of the type including choosing different frequencies for ~I dl)SI I " ~- 19 a series of pulses of energy clt,l.encle, It upon the digital data content 15 to be lldl 1~1111-- ' d, wherein the improvement cu, l~ bes the step of . ",i";"g the frequency choices for a C~hserll~ent pulse l,d"~",i~ion l~pende"l upon digital data content of at least one previously l,d":,n, ' pulsa.
Brief Dc~ r o~ the D._: _ The present invention is illustratively described in reference to the 20 appended drawings in which:
Fg. 1 is a diagram of an encoding method configurad in ac- ("dance with one e"ll,udi",~,lt of the present invention; and Fg. 2 is a diagram of a received lldll~l~lis:,io" decoded in accor.ld"ce with another e" IbG~ l 11 of the present invention.
Detalled De.. v.i, of the D,_. ~ s In one el,ll,oli",e"lt of the present invention, a wide frequency bdll :llh is divided into a p,. '~ -",; ,ad number of fraquency channels or bins which areused to distribute sequentially lldll:-lll'-- ' pulses of a signal. The frequency selection or hopping pattern is partially p,t:d~lt~ .""ed and includes alternate3 o sl Ihseql ~4nt frequency paths d~,al ,ui"g upon the data content of each llul)~lllill~d pulse. Normally the lldll:,lllitltld frequency ~u~ ,u"ts a logical data value such as "1 " or "O". In the s~ Ihseql IQnt fraquency hop there ara two pairs of frequencies with each pair cc~ uùl,di, ,g to one of the possible data values of its i""" p,~de~e ~ol hop. Which pair of frequencies are used to transmit the ............. .. . ..... _ . . .. .. _ .. . .... _ ............. ... .... _ ... ... _ .... .... _ .. _ . _ .. _ .. _ ... ..
WO 96/37060 ' ~ , PCTIUS96/07023 21 ~5~53 s, IhSQr;nQnt data bit depends upon the data content of the previous hop. A ~1 sent on the previous hop wiil dictate use of one of the pairs and a O will dictate use of the other of the pairs. The individual channels in each frequency pair ofy the s~hseq~ ~snt hop represent the same logical "1 and O and the data content 5 of the subsequent hop deten " ,es which channel of the d~ ~.. " ~ ed pair is used.
The present method is l,~F ~ to the l,d"a",is5ion of more than one data bit at a time. Trdnal, ,9 two data bits at once requires four possible pulse frequencies to represent the four possible .;on iilions of two data bits. The 5llh5erjllent pulse lldnsllli~si(", uses foursets of fourfrequencies, orsixteen in 10 all, and d~ '~ . ",i";.,g which set of four is used in response to the four possible data cor ti~ ~s of the previous bit.
Fg 1 is a diagram showing a simplified encoding method in ac(~or id"~
with one ~",i,odi",t",l of the present invention. Each row of the diagram se";~ a sequential pulse 1, dl ,~",is:.ion intervai. The diagram Itl,ul tlsel ,.s a 15 single bit lldnsllli:,:,ion rate meaning that only one logic bit is l,tu~sr" ~ 3d in each interval. The diagram is repetitive so that the four lldllslllia~ion intervals are repeated in sequential passes.
Each logic value shown ,t"J,t,:,e"ts a separate frequency bin within a full lldnSIIIi:~.iOII bdn 'I ,. Logical pairs of bins are shown in pd,ar,~i,t3ses,( ). The 2 0 example shows a total of thirty different frequency bins. Within each of thelldll'llli:~aiull intervals, rows, only one of the co,,~,uol,di,,g frequency bins is used to transmit a pulse. Which frequency bin is used depends upon the data content of the current bit and the data content of the bits l~d";.~;lled in the previous intervais. The specific pair of frequency bins which is avaiiable for the 25 .cllhseqll-Qrlt lldllSIIIia:,iOn interval from each frequency bin is co""e..tt,d thereto by dotted lines. From the fourth lldn~lllia ,iUn interval, each pair of frequency bins is treated as if it cor,t,:",ol,"~ to the first lldll~llli~aioll interval and the sequence repeats from the second lldll~ ion interval.
Thus in the first intervai, a puise is lldll:,lllillttd in either of the bins shown 30 l~ sell ,9 the ,t,:",e~.ti~o logic vaiue. in the second lldnallli:,~ion interval shown, which pair of bins is available depends upon the data content of the first interval. Which bin of the availabie pair is used depends upon the logic vaiue to be lldnallF i in that second interval. This scheme continues to the l~dn~ aion of a puise in the fourth intervai. The ,t ~,e~.live iogic vaiue of the pulse actually _ _ _ _ _ _ _ . .
W096/37060 21~4~ PCT/US96/07023 l,d"a", ' in the fourth interval is treated as the logical equivalent of the first intorval and the pairs of frequency bins used in the actual fifth Ll~ blll;abiuninterval ars selected from the second ~,dnb",iabion interval shown.
By the method described, an actual lldl IblllibbiOn signal is identitied by 5 d~ r",i" ,9 the length of the sequence of lldllbllliabiUn intervals in which pulses are detected in the proper frequency bins. Sequences of pulses which are not sufficiently sustained are discarded as non-signals. Further, an actual pulse lldns",illt,d in the fourth interval may be used to reconstnuct pulses missing from the second and third intervals by simply following the dotted lines back through10 the intervals.
The actual frequencies which represent the frequency bins shown in Fig. 1 may be perio.lically l~dbbiylled to further prevent decoding of an illttll~ d message.
Fig. 2 is a diagram ,~,ur~be, ,9 an example of potential signal pulses 15 received overa portion of a message lldllblllilled in ac~iuldd"ce with one e",~u.li",er,l of the present invention. The horizontal axis It~,ulubellts a portion of the total bdl ' ;dll~ of the lldlls",ission with different horizontal positions ,~.,t,se" ,9 different frequency bins or channels within that total ban ' :-ll,. The vertical axis of the diagram is labeled with successive pulse l,d"b",ibbion intervals 20 to represent the successive frequency hops of the l,d"s",ibsiun. Each circle shown on the chart ~ bel IS energy detected in the ll~b,UUUti~rO frequency bin and l,d"a",ibbiùn interval, by a wideband receiver ,,w,, i"g at least the portion of the bdr, ' :dll~ shown. The lldl IblllibbiUn shown in Fig. 2 is a two bit Il dl Ibl llibbil)n rate for each frequency hop or 1, dnS~ I ~ission interval. That is, two 25 binary bits of datamtl~ belllillg a total of four possible logical states are lldllblllilltld in each interval.
The first lldllblllibbiUn interval shows energy detected in bins 10 and 12.
The second l,d"s",i~bion interval shows energy detected in the nine frequency bins for which there are circles shown. Those bins which are logical successors 3 0 to the bins 10 and 12 are respectfully conneultld thereto by dotted lines and are labeled in quotes (7 with their logical value, i.e. ~01". Because energy, ,t,l.,~se, ~ ~ by the circles, is shown to be present in all of the logical successors in the second interval as well as bins 10 and 12 of the first interval, s~ ~hss~llJsnt lldnblllibbiun intervals are neu~bbdly to detennine the correct data sisnal tor the WO 96/37060 ~2 1 9 5 4 5 3 PCT/US96/07023 ~;: 5 first and second intervals. In the third interval, ensrgy is detected in the five frequency bins shown. Because the detected energy in the third interval can onlybe a logical successor to the energy in bin 14 of the second interval, it is known that bin 14 is the corred data signal for the second l,d"a",iaaion interval. All of r 5 the remaining energy detected in the second interval can be discounted because none of the detected frequency bins have a logical successor in the third interval.
Likewise the proper signal pulses may be traced back to bin 10 of the firs interval. Also, the correct signal path continues to develop through s~hse~ snt lld"s",isaion intervals in frequency bins 16-22.
Simultaneously, another data path is shown to be received in ener~qy detection circles 23-26. Because energy is continually detected in the proper frequency bins of 5llhceqllent intervals, it is ~l~t~r",i"ecl to be a valid signal. In this manner simultaneous signals may be l, dr,s",;tl~d in a multi-user network.
This second signal also d~llluilall - that the encoding is not time def,ende"l 15 and, therefore, does not require_)"~il"~., ~ 1.
The logical sequence of frequencies to be used is cl~tt,r", ,ed in response to the l,dnsi"i~ion bit rate and the available spectrum to be used, in a manner with makes full use of the available spectnum prior to allowing any frequency repetition. Such repetition limits the number of frequency hops which can be 20 reconstnucted if lost. The number of sequential pulses which can be lldns",ill~d prior to any frequency repetition is the number of hops that can be reconstnucted from the method of the present invention. The use of frequency bins in this manner allows discontinuity of the full l,d"~",isaiùn ban ~' : 'Ih. Thus continuous emitters, located in the middle of the full lldllalll;~iùll spectnum, only block their 25 limited balid~kllll portion of the spectnum.
As ",e"tiol)ed, spread spectrum techniques in the H.F. band (3-30 MHz.) are readily sl~ ~Fr ~ '. to cornuption from frequency cle~,end~"l ionospheric con.litio"s. Different frequencies penetrate the ionoaphe,~ to different altitudes prior to reflection back to earth and the same frequency may also be reflected 3 o from different altitudes. The first condition upsets the sequence of pulses l,d,,ar,, ~ at different frequencies and the second condition introduces additional, or multipath, signals which are likewise differently timed and out of sequence. The practice of the present invention therefore includes the periodic sounding of the iouua~.l,er~ with a p,~ tt"",;"ed sequence of lldnsllliaaioil WO 96i37060 t P ~ PCT/U596107023 21954,53 pulses in as many as all of the separate frequency bins used in the full lldllallliaail:)ll bar, ;JII,. ne . Ii~ ,i"9 each of the received pulses with the p,. ",i"ad sequence provides delay and multipath cor,~ctions for the lldllal"iaaiun er,~r;,u"l"e"l. In one ~",bodi",t:"l, this sounding may be executed 5 every second to thereby allow COI I ~I~an- n for the vast majority of varying k"~o:,ulla~ic .;ur, ~ns. After the sounding, the actual data signal is lldllaulilled and the received pulses are realigned in time in response to the sounding results and prior to decoding in acco"~d"ce with the present invention.
The encoding method of the present invention is also colllr with bit 10 dia~J~Iaiùn, which is an o,ll,ùgor,dl or i"d~Jel"~tl"l rnethod of encoding. By example the data bits of a sisnal to be lldilalllitt~d are first aligned, at laast ~I,eo,tlticall), as sequential rows of a matrix. The data is then read from the matrix, for encoding in acco" d".~a with the present invention, as sequential columns of bits. Thus an entire missing column of data may be lost in 15 lldnsllliasiun and it will show up in the recaived and decoded signal as single bits lost in sequential data strings. Such i".la~,anJ~, It or ol Ihogu, Idl decoding techniques may be taken dliV... ' ~ of to iteratively decode, correct recode rmd re-decode the signal and thereby reduce gaps in lost data.
Cor,~v; 101~
2 0 The present invention provides a method for encoding spread spectnum pulse l,d"s",i~aiùns which are cor"uer - d for varying dlllloa~Jllalic conditions.
The present invention further provides for recovery of lost signals which operates both ill.l~.alldr~"lly and in co"lb;r,dtiun with other known techniques to provide :,y~ ~uO :ir results when compared to the recovery ability of individual techniques.
25 The present invention does not require any frequency or time sequence alignment between l,d"a",;tt~r and receiver priorto l,d"a",iaaiun thus reducing complexity and lldllal"iasion delay and failure. This l,dns",illt"/lt,caiver i"depel "~t"lce further enables the reception of simultaneous signals by the same receiver thareby supporting radio network ~ ns.
The r~",l.odi",~"ts described above are intended to be taken in an illustrative and not a limiting sense. Various ". ~.la and changes may be made to the above e"lbodi",6rlta by persons skilled in the art without departingfrom the scope of the present invention as defined in the appended clairns.
r ~c~. uu~ I of the lu.. ~--n Field of the l~,~. ~-The present invention generaily relates to spread spectnum, digital communications, and pdli' I' 1~' to a method for l~ " , Ig frequencies for frequency hopping lldll_,, ' ' .1:7.
S- ~ - ll of the Prlor Art Various ~lg i ""s exist for col~ 9 digital pulse, spread spectnum 10 communications. The principal goal is that of encoding frequency selection for providing communications which are effective in a fsding multipath e.,r;.ur""t",l and which are secure from both jamming and e -/~,sd~u~.~ ;"9. Spread spectrum t,al, ,:, typically tai-<e narrow ban 'v.' ill, symbols and spread them out over a much wider ban : ilh tlhan is neu,:.:.aly for the rate of data lldll~ O n.
15 Unfortunately, "ospl,efic multipath effects are frequency d~,an~ t and thus are acc~" ~ i by any spread spectnum approach.
In frequency hopping, spread spectnum systems, the carrier frequency is changed in acco,.ltl"..~ with a p,~ ' ,. ,ed sequence controlled by one of a variety of codes. The ~dll- Il.'-' ' III~U'~ iS thereby contained in eitherthe 2 0 1l an~l 1 l" ' ' frequency or in the frequency difference between the lldl _ "' pulses and a reference frequency. The spread spectnum signal may be received, decoded and demodulated by a receiver constnucted to employ the same frequency hopping code, once the same p,. , . ,ed code is sy~ lul ll ul liLed at the receiver with the ll al l~ code. In one prior art method 25 described in US Patent No. 4,612,652, a matched pair of pseudo random number ~ene, :. are used to '~: ,e the maric and space frequencies of both a transmitter snd a receiver. The direct generator output and a delayed version thereof are used to provide separate random frequency sequences for each of the mari< and space data signals, I--r ~ .31y. The separate gene, 30 are :~nl~:lllulliLud between llall~lll and recelver, rssulting in sy~n,ll,ul);~ l of both the mark and space frequencies. Unfortunately, the required _,.,-,hlull;...ll adds Col l I~ .Aity to the 1l dn' -.. ."' - and receiver and their i" lk n and can be the cause of lldns...:~.s;Jn failures.
WO 96/37060 !t f~ h ,~ PCT/US96/07023 2 1 9 ~ ~ 5 3 S ~y of the Invention AC~ ly, it is an object of ;he present inventiGn to provide a method of frequancy hopping, spread spectrum communications.
It is another object of the present invention to provide such a method 5 which is capable of co"".anl - ,9 for multipath and fadins lldll~ i env;, u, " "e1"ts.
It is a further object of the present invention to provide such a method which enables error correction and recovary of lost data.
It is a still further object of the present invention to provide such a method 10 which does not require v,, lvl "u"i~", or 5~ IUI ,i~ution between the lldllslllill and receiver.
In one form ths present invention provides a method for frequency shift keying l,d"s",;__;ans of the type including choosing different frequencies for ~I dl)SI I " ~- 19 a series of pulses of energy clt,l.encle, It upon the digital data content 15 to be lldl 1~1111-- ' d, wherein the improvement cu, l~ bes the step of . ",i";"g the frequency choices for a C~hserll~ent pulse l,d"~",i~ion l~pende"l upon digital data content of at least one previously l,d":,n, ' pulsa.
Brief Dc~ r o~ the D._: _ The present invention is illustratively described in reference to the 20 appended drawings in which:
Fg. 1 is a diagram of an encoding method configurad in ac- ("dance with one e"ll,udi",~,lt of the present invention; and Fg. 2 is a diagram of a received lldll~l~lis:,io" decoded in accor.ld"ce with another e" IbG~ l 11 of the present invention.
Detalled De.. v.i, of the D,_. ~ s In one el,ll,oli",e"lt of the present invention, a wide frequency bdll :llh is divided into a p,. '~ -",; ,ad number of fraquency channels or bins which areused to distribute sequentially lldll:-lll'-- ' pulses of a signal. The frequency selection or hopping pattern is partially p,t:d~lt~ .""ed and includes alternate3 o sl Ihseql ~4nt frequency paths d~,al ,ui"g upon the data content of each llul)~lllill~d pulse. Normally the lldll:,lllitltld frequency ~u~ ,u"ts a logical data value such as "1 " or "O". In the s~ Ihseql IQnt fraquency hop there ara two pairs of frequencies with each pair cc~ uùl,di, ,g to one of the possible data values of its i""" p,~de~e ~ol hop. Which pair of frequencies are used to transmit the ............. .. . ..... _ . . .. .. _ .. . .... _ ............. ... .... _ ... ... _ .... .... _ .. _ . _ .. _ .. _ ... ..
WO 96/37060 ' ~ , PCTIUS96/07023 21 ~5~53 s, IhSQr;nQnt data bit depends upon the data content of the previous hop. A ~1 sent on the previous hop wiil dictate use of one of the pairs and a O will dictate use of the other of the pairs. The individual channels in each frequency pair ofy the s~hseq~ ~snt hop represent the same logical "1 and O and the data content 5 of the subsequent hop deten " ,es which channel of the d~ ~.. " ~ ed pair is used.
The present method is l,~F ~ to the l,d"a",is5ion of more than one data bit at a time. Trdnal, ,9 two data bits at once requires four possible pulse frequencies to represent the four possible .;on iilions of two data bits. The 5llh5erjllent pulse lldnsllli~si(", uses foursets of fourfrequencies, orsixteen in 10 all, and d~ '~ . ",i";.,g which set of four is used in response to the four possible data cor ti~ ~s of the previous bit.
Fg 1 is a diagram showing a simplified encoding method in ac(~or id"~
with one ~",i,odi",t",l of the present invention. Each row of the diagram se";~ a sequential pulse 1, dl ,~",is:.ion intervai. The diagram Itl,ul tlsel ,.s a 15 single bit lldnsllli:,:,ion rate meaning that only one logic bit is l,tu~sr" ~ 3d in each interval. The diagram is repetitive so that the four lldllslllia~ion intervals are repeated in sequential passes.
Each logic value shown ,t"J,t,:,e"ts a separate frequency bin within a full lldnSIIIi:~.iOII bdn 'I ,. Logical pairs of bins are shown in pd,ar,~i,t3ses,( ). The 2 0 example shows a total of thirty different frequency bins. Within each of thelldll'llli:~aiull intervals, rows, only one of the co,,~,uol,di,,g frequency bins is used to transmit a pulse. Which frequency bin is used depends upon the data content of the current bit and the data content of the bits l~d";.~;lled in the previous intervais. The specific pair of frequency bins which is avaiiable for the 25 .cllhseqll-Qrlt lldllSIIIia:,iOn interval from each frequency bin is co""e..tt,d thereto by dotted lines. From the fourth lldn~lllia ,iUn interval, each pair of frequency bins is treated as if it cor,t,:",ol,"~ to the first lldll~llli~aioll interval and the sequence repeats from the second lldll~ ion interval.
Thus in the first intervai, a puise is lldll:,lllillttd in either of the bins shown 30 l~ sell ,9 the ,t,:",e~.ti~o logic vaiue. in the second lldnallli:,~ion interval shown, which pair of bins is available depends upon the data content of the first interval. Which bin of the availabie pair is used depends upon the logic vaiue to be lldnallF i in that second interval. This scheme continues to the l~dn~ aion of a puise in the fourth intervai. The ,t ~,e~.live iogic vaiue of the pulse actually _ _ _ _ _ _ _ . .
W096/37060 21~4~ PCT/US96/07023 l,d"a", ' in the fourth interval is treated as the logical equivalent of the first intorval and the pairs of frequency bins used in the actual fifth Ll~ blll;abiuninterval ars selected from the second ~,dnb",iabion interval shown.
By the method described, an actual lldl IblllibbiOn signal is identitied by 5 d~ r",i" ,9 the length of the sequence of lldllbllliabiUn intervals in which pulses are detected in the proper frequency bins. Sequences of pulses which are not sufficiently sustained are discarded as non-signals. Further, an actual pulse lldns",illt,d in the fourth interval may be used to reconstnuct pulses missing from the second and third intervals by simply following the dotted lines back through10 the intervals.
The actual frequencies which represent the frequency bins shown in Fig. 1 may be perio.lically l~dbbiylled to further prevent decoding of an illttll~ d message.
Fig. 2 is a diagram ,~,ur~be, ,9 an example of potential signal pulses 15 received overa portion of a message lldllblllilled in ac~iuldd"ce with one e",~u.li",er,l of the present invention. The horizontal axis It~,ulubellts a portion of the total bdl ' ;dll~ of the lldlls",ission with different horizontal positions ,~.,t,se" ,9 different frequency bins or channels within that total ban ' :-ll,. The vertical axis of the diagram is labeled with successive pulse l,d"b",ibbion intervals 20 to represent the successive frequency hops of the l,d"s",ibsiun. Each circle shown on the chart ~ bel IS energy detected in the ll~b,UUUti~rO frequency bin and l,d"a",ibbiùn interval, by a wideband receiver ,,w,, i"g at least the portion of the bdr, ' :dll~ shown. The lldl IblllibbiUn shown in Fig. 2 is a two bit Il dl Ibl llibbil)n rate for each frequency hop or 1, dnS~ I ~ission interval. That is, two 25 binary bits of datamtl~ belllillg a total of four possible logical states are lldllblllilltld in each interval.
The first lldllblllibbiUn interval shows energy detected in bins 10 and 12.
The second l,d"s",i~bion interval shows energy detected in the nine frequency bins for which there are circles shown. Those bins which are logical successors 3 0 to the bins 10 and 12 are respectfully conneultld thereto by dotted lines and are labeled in quotes (7 with their logical value, i.e. ~01". Because energy, ,t,l.,~se, ~ ~ by the circles, is shown to be present in all of the logical successors in the second interval as well as bins 10 and 12 of the first interval, s~ ~hss~llJsnt lldnblllibbiun intervals are neu~bbdly to detennine the correct data sisnal tor the WO 96/37060 ~2 1 9 5 4 5 3 PCT/US96/07023 ~;: 5 first and second intervals. In the third interval, ensrgy is detected in the five frequency bins shown. Because the detected energy in the third interval can onlybe a logical successor to the energy in bin 14 of the second interval, it is known that bin 14 is the corred data signal for the second l,d"a",iaaion interval. All of r 5 the remaining energy detected in the second interval can be discounted because none of the detected frequency bins have a logical successor in the third interval.
Likewise the proper signal pulses may be traced back to bin 10 of the firs interval. Also, the correct signal path continues to develop through s~hse~ snt lld"s",isaion intervals in frequency bins 16-22.
Simultaneously, another data path is shown to be received in ener~qy detection circles 23-26. Because energy is continually detected in the proper frequency bins of 5llhceqllent intervals, it is ~l~t~r",i"ecl to be a valid signal. In this manner simultaneous signals may be l, dr,s",;tl~d in a multi-user network.
This second signal also d~llluilall - that the encoding is not time def,ende"l 15 and, therefore, does not require_)"~il"~., ~ 1.
The logical sequence of frequencies to be used is cl~tt,r", ,ed in response to the l,dnsi"i~ion bit rate and the available spectrum to be used, in a manner with makes full use of the available spectnum prior to allowing any frequency repetition. Such repetition limits the number of frequency hops which can be 20 reconstnucted if lost. The number of sequential pulses which can be lldns",ill~d prior to any frequency repetition is the number of hops that can be reconstnucted from the method of the present invention. The use of frequency bins in this manner allows discontinuity of the full l,d"~",isaiùn ban ~' : 'Ih. Thus continuous emitters, located in the middle of the full lldllalll;~iùll spectnum, only block their 25 limited balid~kllll portion of the spectnum.
As ",e"tiol)ed, spread spectrum techniques in the H.F. band (3-30 MHz.) are readily sl~ ~Fr ~ '. to cornuption from frequency cle~,end~"l ionospheric con.litio"s. Different frequencies penetrate the ionoaphe,~ to different altitudes prior to reflection back to earth and the same frequency may also be reflected 3 o from different altitudes. The first condition upsets the sequence of pulses l,d,,ar,, ~ at different frequencies and the second condition introduces additional, or multipath, signals which are likewise differently timed and out of sequence. The practice of the present invention therefore includes the periodic sounding of the iouua~.l,er~ with a p,~ tt"",;"ed sequence of lldnsllliaaioil WO 96i37060 t P ~ PCT/U596107023 21954,53 pulses in as many as all of the separate frequency bins used in the full lldllallliaail:)ll bar, ;JII,. ne . Ii~ ,i"9 each of the received pulses with the p,. ",i"ad sequence provides delay and multipath cor,~ctions for the lldllal"iaaiun er,~r;,u"l"e"l. In one ~",bodi",t:"l, this sounding may be executed 5 every second to thereby allow COI I ~I~an- n for the vast majority of varying k"~o:,ulla~ic .;ur, ~ns. After the sounding, the actual data signal is lldllaulilled and the received pulses are realigned in time in response to the sounding results and prior to decoding in acco"~d"ce with the present invention.
The encoding method of the present invention is also colllr with bit 10 dia~J~Iaiùn, which is an o,ll,ùgor,dl or i"d~Jel"~tl"l rnethod of encoding. By example the data bits of a sisnal to be lldilalllitt~d are first aligned, at laast ~I,eo,tlticall), as sequential rows of a matrix. The data is then read from the matrix, for encoding in acco" d".~a with the present invention, as sequential columns of bits. Thus an entire missing column of data may be lost in 15 lldnsllliasiun and it will show up in the recaived and decoded signal as single bits lost in sequential data strings. Such i".la~,anJ~, It or ol Ihogu, Idl decoding techniques may be taken dliV... ' ~ of to iteratively decode, correct recode rmd re-decode the signal and thereby reduce gaps in lost data.
Cor,~v; 101~
2 0 The present invention provides a method for encoding spread spectnum pulse l,d"s",i~aiùns which are cor"uer - d for varying dlllloa~Jllalic conditions.
The present invention further provides for recovery of lost signals which operates both ill.l~.alldr~"lly and in co"lb;r,dtiun with other known techniques to provide :,y~ ~uO :ir results when compared to the recovery ability of individual techniques.
25 The present invention does not require any frequency or time sequence alignment between l,d"a",;tt~r and receiver priorto l,d"a",iaaiun thus reducing complexity and lldllal"iasion delay and failure. This l,dns",illt"/lt,caiver i"depel "~t"lce further enables the reception of simultaneous signals by the same receiver thareby supporting radio network ~ ns.
The r~",l.odi",~"ts described above are intended to be taken in an illustrative and not a limiting sense. Various ". ~.la and changes may be made to the above e"lbodi",6rlta by persons skilled in the art without departingfrom the scope of the present invention as defined in the appended clairns.
Claims (4)
1. In a method for frequency shift keying transmissions of the type including choosing different frequencies for transmitting a series of pulses of energy dependent upon the digital data content to be transmitted, wherein the improvement comprises the step of determining the frequency choices for a improvement pulse transmission dependent upon digital data content of at least one previously transmitted pulse.
2. The method of claim 1, wherein the step of detecting the frequency choices for a subsequent pulse transmission are dependent upon a plurality of previously transmitted pulses.
3. The method of claim 2, wherein the different frequencies used for transmitting pulses are spread out over a predetermined spectrum, and further comprising the step of periodically determining characteristic transmission conditions of a transmission medium over the predetermined spectrum.
4. The method of claim 3, wherein the step of periodically determining transmission conditions includes transmitting, over the transmission medium, a predetermined sequence of pulses at predetermined frequencies spread over the predetermined spectrum, receiving the transmitted predetermined sequence of pulses and comparing the received pulses to the predetermined sequence to determine characteristic transmission conditions of the transmission medium.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US44460895A | 1995-05-19 | 1995-05-19 | |
| US08/444,608 | 1995-05-19 | ||
| PCT/US1996/007023 WO1996037060A1 (en) | 1995-05-19 | 1996-05-16 | Method for spread spectrum communications |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2195453A1 true CA2195453A1 (en) | 1996-11-21 |
Family
ID=23765604
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002195453A Abandoned CA2195453A1 (en) | 1995-05-19 | 1996-05-16 | Method for spread spectrum communications |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0771495A1 (en) |
| AU (1) | AU5794896A (en) |
| CA (1) | CA2195453A1 (en) |
| WO (1) | WO1996037060A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI20205091A1 (en) * | 2020-01-29 | 2021-07-30 | Nokia Technologies Oy | Apparatus and method for communication |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4583231A (en) * | 1983-11-02 | 1986-04-15 | General Electric Company | Method of, and apparatus for, frequency-hopped frequency-shift-keyed digital data communications |
| SE445698B (en) * | 1984-11-19 | 1986-07-07 | Ericsson Telefon Ab L M | PROCEDURE TO REDUCE THE IMPACT OF SMALL-STANDARD STORARS IN RADIO COMMUNICATION BETWEEN TWO STATIONS, WHICH USE FREQUENCY HOPE |
| US5412687A (en) * | 1993-10-15 | 1995-05-02 | Proxim Incorporated | Digital communications equipment using differential quaternary frequency shift keying |
-
1996
- 1996-05-16 AU AU57948/96A patent/AU5794896A/en not_active Abandoned
- 1996-05-16 EP EP96914652A patent/EP0771495A1/en not_active Withdrawn
- 1996-05-16 CA CA002195453A patent/CA2195453A1/en not_active Abandoned
- 1996-05-16 WO PCT/US1996/007023 patent/WO1996037060A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO1996037060A1 (en) | 1996-11-21 |
| EP0771495A1 (en) | 1997-05-07 |
| AU5794896A (en) | 1996-11-29 |
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