CA2100994A1 - Narrow band interference frequency excision method and means - Google Patents
Narrow band interference frequency excision method and meansInfo
- Publication number
- CA2100994A1 CA2100994A1 CA002100994A CA2100994A CA2100994A1 CA 2100994 A1 CA2100994 A1 CA 2100994A1 CA 002100994 A CA002100994 A CA 002100994A CA 2100994 A CA2100994 A CA 2100994A CA 2100994 A1 CA2100994 A1 CA 2100994A1
- Authority
- CA
- Canada
- Prior art keywords
- magnitude
- signal
- digitized signal
- spread spectrum
- transforming
- 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.)
- Abandoned
Links
Classifications
-
- 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
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7097—Interference-related aspects
- H04B1/71—Interference-related aspects the interference being narrowband interference
- H04B1/7102—Interference-related aspects the interference being narrowband interference with transform to frequency domain
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
- H04K3/00—Jamming of communication; Counter-measures
- H04K3/20—Countermeasures against jamming
- H04K3/22—Countermeasures against jamming including jamming detection and monitoring
- H04K3/224—Countermeasures against jamming including jamming detection and monitoring with countermeasures at transmission and/or reception of the jammed signal, e.g. stopping operation of transmitter or receiver, nulling or enhancing transmitted power in direction of or at frequency of jammer
- H04K3/228—Elimination in the received signal of jamming or of data corrupted by jamming
Abstract
ABSTRACT OF THE DISCLOSURE
In a preferred embodiment, a method for excising narrow band interferers in a spread spectrum signal communication which includes the steps of: receiving the spread spectrum signal; digitizing the spread spectrum signal; transforming the digitized signal from the time domain to the frequency domain; discarding the magnitude of the digitized signal and replacing it with a normalized value; and transforming the digitized signal back to the time domain.
In a preferred embodiment, a method for excising narrow band interferers in a spread spectrum signal communication which includes the steps of: receiving the spread spectrum signal; digitizing the spread spectrum signal; transforming the digitized signal from the time domain to the frequency domain; discarding the magnitude of the digitized signal and replacing it with a normalized value; and transforming the digitized signal back to the time domain.
Description
. 2 1 0 0 9 9 ~ PHA 40.655 NARROW BAND INTERFERENCE _REQUENCY EXCISION METHOD AND MEANS
1. Fiold of th~ Invention.
The present invention reldtes to r~dio ~ignal~
generally and, more particularly, but not by way of limitation, to no~el method and ~o~n~ ~or narrow band int~rf~rence frequency oxcision via phase domain normalization.
Z, Backaround Art.
Syre~d ~pectrum ~9S) communication ey6~0ms aro bocomlng more provalent ~or the securo trAnsmi6~ion of radio signal~l. SS or poeudonoi6e ~p~) modulation i9 ~mployed in digital communication ~y~tema to reduce the effect6 of interfero~ce due to other u~ers a~d intentional j~mming of the radio ~ignal~. Whon the interf~rence i~ ~arrow-band, the cro~ corrolation o~ tho rocei~ed ~ignal with the roplica o~ the PN code sequencoa redua~ the level of interference by ~preading it acro0~ tho requency band occupied by thc PN ~ignal. Thu~, the interf0rence is rondorod equi~alent to a lower lo~el noise with a relati~ely ~lat epoctrum. Simultaneou61y, the cro~6 correlation operatlon collapso~ the deGired signal to the bandwidth occupiod by the information ~ignal prior to ~preadi~g.
210099~ PHA 40.655 ~ he interferenco immunity of a PN SS communication ayet~m corrupted by narrow ~and interferonc~ can be further improved by filtering the ~ignal prior to cros~ correlation, ~here the objecti~e is to reduce the le~el o the interf er~nce at the expen60 of introducing 60me distortion to tho de0ired ~ignal. Such a ~echnigue i~ de6cribed i~ "~n FFT 3aec~ ~ochnique ~or Suppr~ ng ~arrow-3and interf~r~nce in PN Spread Sp~ctrum Commu~ications Sy6t~m~," by Robert C.
DiPietro, IE~E, CH2673-2/a9/0000-1360 February l9a9.
~ n a ~yplcal froquency epoctrum, a 6pread spectrum P~
aignal i3 placod at a level bolow a noi~e ~loor which makes detectlon or lnt0rceptio~ of the eignal significantly mo~e di~ficult. Thi~ ~proad ~ignal i~ recoverable in the pro~e~ce of typ~cal interferor~. When a ~trong interferinq ~ignal i6 pre~ent, tho desired ~ignal cannot be reco~ered.
Obvioualy, the SS communication ey~tem can bo onhanced if the inter~oring ~iqnAl~ can be removed or 6uppre~aed.
There i~ a variety of mothod6 for exci6ing such intorfering ~ignal9. The6~ fall in~o t~o general catogori~: traneient excieion and frequoncy exci~ion.
In the transiont methods, the eignal ~usually analog) i8 paseed through a narro~ band notch filter or filters.
Thi~ method i~ typically implemented by sur~ace acou3tical wa~o-type technology (~ur~ace acou6tical waves, acou~tic :
1. Fiold of th~ Invention.
The present invention reldtes to r~dio ~ignal~
generally and, more particularly, but not by way of limitation, to no~el method and ~o~n~ ~or narrow band int~rf~rence frequency oxcision via phase domain normalization.
Z, Backaround Art.
Syre~d ~pectrum ~9S) communication ey6~0ms aro bocomlng more provalent ~or the securo trAnsmi6~ion of radio signal~l. SS or poeudonoi6e ~p~) modulation i9 ~mployed in digital communication ~y~tema to reduce the effect6 of interfero~ce due to other u~ers a~d intentional j~mming of the radio ~ignal~. Whon the interf~rence i~ ~arrow-band, the cro~ corrolation o~ tho rocei~ed ~ignal with the roplica o~ the PN code sequencoa redua~ the level of interference by ~preading it acro0~ tho requency band occupied by thc PN ~ignal. Thu~, the interf0rence is rondorod equi~alent to a lower lo~el noise with a relati~ely ~lat epoctrum. Simultaneou61y, the cro~6 correlation operatlon collapso~ the deGired signal to the bandwidth occupiod by the information ~ignal prior to ~preadi~g.
210099~ PHA 40.655 ~ he interferenco immunity of a PN SS communication ayet~m corrupted by narrow ~and interferonc~ can be further improved by filtering the ~ignal prior to cros~ correlation, ~here the objecti~e is to reduce the le~el o the interf er~nce at the expen60 of introducing 60me distortion to tho de0ired ~ignal. Such a ~echnigue i~ de6cribed i~ "~n FFT 3aec~ ~ochnique ~or Suppr~ ng ~arrow-3and interf~r~nce in PN Spread Sp~ctrum Commu~ications Sy6t~m~," by Robert C.
DiPietro, IE~E, CH2673-2/a9/0000-1360 February l9a9.
~ n a ~yplcal froquency epoctrum, a 6pread spectrum P~
aignal i3 placod at a level bolow a noi~e ~loor which makes detectlon or lnt0rceptio~ of the eignal significantly mo~e di~ficult. Thi~ ~proad ~ignal i~ recoverable in the pro~e~ce of typ~cal interferor~. When a ~trong interferinq ~ignal i6 pre~ent, tho desired ~ignal cannot be reco~ered.
Obvioualy, the SS communication ey~tem can bo onhanced if the inter~oring ~iqnAl~ can be removed or 6uppre~aed.
There i~ a variety of mothod6 for exci6ing such intorfering ~ignal9. The6~ fall in~o t~o general catogori~: traneient excieion and frequoncy exci~ion.
In the transiont methods, the eignal ~usually analog) i8 paseed through a narro~ band notch filter or filters.
Thi~ method i~ typically implemented by sur~ace acou3tical wa~o-type technology (~ur~ace acou6tical waves, acou~tic :
2 10 0 9 9 ~ PHA 40 .655 charged tran6ports, or charge-coupled devices). some e~timate of the interferi~g signal~s ~or signal~') frequonc~f (or frequencie~) is mado. Prom ~hi~ information, narrow band notche~ are placed at the inter~ering ~ignal~. (A ~et of pha~e lock loop~ could al~o be u~ed to track out the interfering signals~) ~ he frequency domain exciaion category usually involveo a digikal proc~ing approach. Tho tran~ient ~ignal i~ digitized and proce~od through a Pourier ~ran~form to tho frequency domain. ~ the froquency domain, there are ~evoral algorithm6 to auppre6s interfering ~ignals. Three type~ of algori~hms are generally recog~ized, the fir~t mothod i~ aimilar to ~ho time domain method. ~ ~ilter i5 appliod to ~he freguency data to suppr~ the interfering 3ignal~). The 60~0nd method eimply look~ at tho magnitute o~ the signal6 in the ~reguency domain, comparo~ the magnitude to a thr~hold o~
~he noi~e level, and eith0r zeroo~ the froquency bin~
corres~onding to the inter~ering ~ignals or adjusts the signal to the lovol relati~e to tho noi~e ~loor. Tho third algorithm involve~ calculating tho magnitudo of each frequency bin and di~iding e~ch ~requency bin by it3 magnitude. Since the inform~tion of the SS ~ignal i~
contained in the phase of the ~ignal, only the interfering signals are affected. The re~ultant ~pectrum i~ normalized 2 10 0 9 9 ~ PHA 40.655 to unity magnitude. The phaae remain~ unchanged. A plot o~
the magnitud~ respon~e is a rather uninterosting ~traight line.
Th0 convontional mothode of frequency excision noted above have several diaad~antage~. They ~annot be impl~monted in real timo hardwaro (i~e./ each data sa~plo i9 op~rated on for it~ i~terfering component3) or the uses of any r~al time implomentation~ ar~ ~ry llmlted. ~hey require that ostim~tos be m~d~ of the 6pectrum to ~djuet a clipping ~hre~hold) level or noi~o e~timation. They requiro computation proce~ses or comparison~ that require mathomatical ovorhoad, such ~ digi~al signal proce~sing procedure.
Accordingly, it 1~ a principal object of the present invontion to pro~ido method and me8~ for narrow band ~regueAcy ~xcision in real time.
It i~ a ~u~thor objoct o~ the i~ntion to provide ~uch mothod and m~an~ that do not requiro 0stima~0~ to bo made o~ the ~pectrum to adju~t a clipping level or noise estim~tion.
It i~ an ~dditional object o~ the in~ention to provide euch mothod and mean~ that do not require complex mathematical procedures~
210~g4 --- PHA 40.655 Other object~ o~ the pre~ent in~ention, as well a3 rticular feature~, elements, and ad~antage~ thereo~, will be elucidated in, or be apparent from, the fo~lowing doRcription and the accompanying drawing figure~.
210~994 PHA 40.655 SUMMARY OF TX~ INVENTION
The preuent in~0ntion achie~es th~ above object~, among other~, by provi~ing, in a pre~erred 0mbodiment, a method ~or exci3in~ narrow band inter~erer~ in a ~pread spectrum ~ignal communication, compri6ing the step~ of:
recoiving said spread ~pectrum signal; digitizing 3aid ~pread ~pectru~ signal; tran~orming ~aid digitized signal ~rom the time domain ~o the ~r~quoncy domain; di~carding the magnitude o ~aid digiti~ed ~ignal and repla~ing it with a normallzed value; and transorming ~aid digitized signal back to the time domain.
: -7-2~0~9~
PHA 40 . 655 Understanding of tho pre~ent in~ention and the variaus aspect~ thereof will be facilitated by re~erenc0 to the accompanying drawing figure~, submitted for purpos0s of illustration only and not intended to define the ~cope of the invention, on which:
Figur~ 1 illu~trates a typ~cal frequency ~poctrum with a SS ~ignal.
Figure 2 illu~trates the ~pectru~ of ~igure 1 after the correlation ~de~preading) of the SS aignal.
Figure 3 i~ a block diagram of a frequency excision ~y~tem according to the pro~ent i~ention.
Pigure 4 i5 a block diagra~ of the excision portion of the sy~tem o~ Fi~ure 3.
210099~ PHA 40.655 Referenc~ shou~d now be made to the drawing ~igure~, on which ~imilar or identical elements ar~ given con8i6~ent identifying numeral~ ~hroughout the variou0 figure~ theroo~, and which parenthetical referonce~ to ~igure ~um~ers direct ~h~ reader to the view~) on which tho ~lement( 8 ~ being de~crib~d i~ ~are) be~t ~een, although ths cloment~1 may be 0e~n al~o on othor ~iewc.
Tho pre~ent in~ention focuses on the above-mention~d third method to ~ccomplish freq~ency domain ex~ision. The ro~ultant frequency 6p~ct~um i6 ~ormalized to unity magnitude, with the phaoe romaining unchanged. A plot of the magnitude re~on~e i9 a rather unintere~ting ~traight lino, with the ~mplitude of any interferer~ no greator than that o the SS ~ignal.
Figure 1 illuetratea a typical frequency ~pectrum. Aa ~hown on Figure 1, the desir~d SS ~ignal i~ deoir~bly ~elow the no~Go floor pro~n~ to make d~tection or intorc~ption o tho aign 1 01g~ificantly mor~ difficult th~n i~ the 6ignal wero above the noi~e floor. The "ST~ONG INTERFERER"
indicated could be a ~amming signal or t~o signal from a ~V
or radio etation or any co-located (i.e., n~arby) communicatione, The ~TY~ IM~ERF~R~RS" indicated could be producod ~rom low po~er ~ourcee, ~uch a~ ham radioe. The .
_g_ .
2100994 PHA 40.655 broken line titled ~PROCESSING GAIN" repre3en~-~ the level o the SS PN ~ignal when it i8 collap~ed (not ~pread).
Figure 2 illustrate~ tho ~pectrum ~hown on Figure 1 after thè correlation ~do~preading) of the 6ignal. As noted above, the collap~ed signal can be recovered in tho pre~ence o~ inter~erer~ by ono of the convontional method~ de~cribed abov~. A~ alw no~ed ~bove, tho~e convontional methods hdv~
c~rtain dieadvantages.
With re~erence now to F1gure 3, the present inven~ion overcom~ the~e dieadYantage~ through the u~e of real ~ime ad~ptive iltering through fa~t Fourier tra~orm (FFT~
technology. Thls i8 accompli~hed by providing the ~ignal proceesing ~y~tem ~hown as re4erence numeral 10. Sy~tem 10 compri3e# FFT circuitry 20, which recei~ input ~ignal~, and which i3 coupled to ~xCi~ion circuitry 22. Exci~ion circuitry 22 ie coupled to in~or~o FFT (I~FT) circuikry 2 whiCh pro~id0~ outpute to convention~l correlation circuitr ~not ~hown)~
In oporation, ~FT cirCuitry 20 reCei~e~ in-pha~e and quadrature ~I and Q) eignal input~ ~rom a digitizer 12 which, in turn~ rec~ivo~ an input rom an RF co~ertsr 1~.
FFT ~ircuitry 20 tran~form~ tho ~ignal~ to the ~requency domain. Once the data i~ in tho frequency domain, the magnitude thereo~ i3 dl~carded and roplaced with a normalization value and the narrow band interrerers are rejec~ed. Tho data is then . . . ~ - .
. 210 0 9 9 ~ PHA 40.655 ~ransformed back to the fre~uency d~main and proce~sed through IFF~ ~4 to the time domain.
~ he exciaion process works because of the ~anneri~m of ss ~ignal9. ss ~ignal6 are modulated by phase modulation.
Tho excision procees perform~ a type limiting operation commonly a~ociated with FM dotoction. By per~orming the exci610n operation in the ~roquency domain, all amplitude compone~ta, including tho~e of any intor~rorY, aro normalized to a common valu~. That i5 1 all ~ignals hAve the sam~ amplitude value and, thereforo, tho amplitude~ of the interferer~ are now rolatively inconeequ~ntial in~o~ar are tho correlation gain o the ~pread ~ignal i~ concerned. The ouput o~ FFT 20 is a set o~ co~plex (real and imaginary) munbera repre~enting the froquency component~ of tho dig~tized wa~e~orm. 3y utllizing a rectangular-to-polar conver~ion, the signal i~ re~olved into its magnitude and pha~e component~. Since the SS ~ignal in~ormation i~
contained ~olely in the phaae component, the magnltude component 1~ ~uperfluou~ and i6 di~carded. A polar-to-rectAngular con~ereion, with the mangitude ~et to ~ome arbitrary value ~unity i8 convenient) i9 all that i~
required to return a normalized ~pe~trum. Slnce there is no need to calculate any threshold or noise le~el, no o~erhead 210099~ PHA 40.655 in computat~on is required, E~ery data point i8 opera~ed on with no ~ime del~y (other than latoncy).
Mathematically, ~hi6 proces~ Can be described a~:
REAL~ut ~ co~arctan(IMAGINARY~ N /REALI N ) ~
IMAGINARYo U T 5 6in~arctan(IMAGINARYI N /REA~l~)], whor0 the trigonomotric function~ are modulo 2 PI.
FFT circuitry 20 ~nd IFFT circuitry 24 may be commercially available Ple~oy P~S~1615~ Stand Alono Proce~sor~ provided ~5 either a ~ingle chip or a two or ~ore ca~c~dod chipY.
Figure 4 urther illustrate~ the 6tructure o~ excision circuitry 22 whi~h ie indicated can bo implemented via a commercially a~ailable Ple~eey PDSP16330 Pythasoras Proce~ors or, alternati~oly, a TRW TMC2330 Coordinate Trangformo~s can be employed.
Improved p0r~0rmance i~ gained by incorporating windowlng along wi~h overlap and add architecturo. The advantAgo~ o~ windowlng data i~ a well known and well documen~ed proce~s. S~e IEEE "On U~o o~ Window6 ~or H~rmonic Analy~is with the ~iscrete Fourier ~ran~orm," by Frede~ick ~arris, Proceedinas o~ t~ IE~E, vol. 66, no. 1, pag~ 51-~3, ~anuary 1978. It h~ boen ~ound that the H~mming window produce~ excoll~nt re~ults. The ~amming wlndow ha~ ~he bene~it that, when utilized with a 50-percen~
2 1 O 0 9 9 ~ PHA 40.655 overlap add archit~cture, the re~ultant tim~ dom~in wave~orm ha~ unity gain, although the add architecture imposeY t~ice a~ much proce~ing.
.~
2100994 PHA 40.655 It will thus be seen that th~ obje~t~ 6et forth abev~, among those elucidated ln, or made ~ppa~ent ~rom, the preceding description, are ef~icientLy attained and, since ce~tain change~ may be made in the abo~e construction without departing from tho ~copo of the inventio~, it 18 intended that all mattor contained in the above de~cription or ~hown on the accomp~nying drawing ~igures shall be lntorproted as 111ustr~ti~e only and ~ot in a limiting ~en~e.
It is al~o to be under~tood that the following claim~
are intcnd~d to co~er ~11 of th~ generic a~d ~p~ci~ic ature~ of the in~ontion herein described and all ~t~tement~ o~ the ~cop~ of the inYention which, as a matter o language, might bo said to fall therebetween.
~he noi~e level, and eith0r zeroo~ the froquency bin~
corres~onding to the inter~ering ~ignals or adjusts the signal to the lovol relati~e to tho noi~e ~loor. Tho third algorithm involve~ calculating tho magnitudo of each frequency bin and di~iding e~ch ~requency bin by it3 magnitude. Since the inform~tion of the SS ~ignal i~
contained in the phase of the ~ignal, only the interfering signals are affected. The re~ultant ~pectrum i~ normalized 2 10 0 9 9 ~ PHA 40.655 to unity magnitude. The phaae remain~ unchanged. A plot o~
the magnitud~ respon~e is a rather uninterosting ~traight line.
Th0 convontional mothode of frequency excision noted above have several diaad~antage~. They ~annot be impl~monted in real timo hardwaro (i~e./ each data sa~plo i9 op~rated on for it~ i~terfering component3) or the uses of any r~al time implomentation~ ar~ ~ry llmlted. ~hey require that ostim~tos be m~d~ of the 6pectrum to ~djuet a clipping ~hre~hold) level or noi~o e~timation. They requiro computation proce~ses or comparison~ that require mathomatical ovorhoad, such ~ digi~al signal proce~sing procedure.
Accordingly, it 1~ a principal object of the present invontion to pro~ido method and me8~ for narrow band ~regueAcy ~xcision in real time.
It i~ a ~u~thor objoct o~ the i~ntion to provide ~uch mothod and m~an~ that do not requiro 0stima~0~ to bo made o~ the ~pectrum to adju~t a clipping level or noise estim~tion.
It i~ an ~dditional object o~ the in~ention to provide euch mothod and mean~ that do not require complex mathematical procedures~
210~g4 --- PHA 40.655 Other object~ o~ the pre~ent in~ention, as well a3 rticular feature~, elements, and ad~antage~ thereo~, will be elucidated in, or be apparent from, the fo~lowing doRcription and the accompanying drawing figure~.
210~994 PHA 40.655 SUMMARY OF TX~ INVENTION
The preuent in~0ntion achie~es th~ above object~, among other~, by provi~ing, in a pre~erred 0mbodiment, a method ~or exci3in~ narrow band inter~erer~ in a ~pread spectrum ~ignal communication, compri6ing the step~ of:
recoiving said spread ~pectrum signal; digitizing 3aid ~pread ~pectru~ signal; tran~orming ~aid digitized signal ~rom the time domain ~o the ~r~quoncy domain; di~carding the magnitude o ~aid digiti~ed ~ignal and repla~ing it with a normallzed value; and transorming ~aid digitized signal back to the time domain.
: -7-2~0~9~
PHA 40 . 655 Understanding of tho pre~ent in~ention and the variaus aspect~ thereof will be facilitated by re~erenc0 to the accompanying drawing figure~, submitted for purpos0s of illustration only and not intended to define the ~cope of the invention, on which:
Figur~ 1 illu~trates a typ~cal frequency ~poctrum with a SS ~ignal.
Figure 2 illu~trates the ~pectru~ of ~igure 1 after the correlation ~de~preading) of the SS aignal.
Figure 3 i~ a block diagram of a frequency excision ~y~tem according to the pro~ent i~ention.
Pigure 4 i5 a block diagra~ of the excision portion of the sy~tem o~ Fi~ure 3.
210099~ PHA 40.655 Referenc~ shou~d now be made to the drawing ~igure~, on which ~imilar or identical elements ar~ given con8i6~ent identifying numeral~ ~hroughout the variou0 figure~ theroo~, and which parenthetical referonce~ to ~igure ~um~ers direct ~h~ reader to the view~) on which tho ~lement( 8 ~ being de~crib~d i~ ~are) be~t ~een, although ths cloment~1 may be 0e~n al~o on othor ~iewc.
Tho pre~ent in~ention focuses on the above-mention~d third method to ~ccomplish freq~ency domain ex~ision. The ro~ultant frequency 6p~ct~um i6 ~ormalized to unity magnitude, with the phaoe romaining unchanged. A plot of the magnitude re~on~e i9 a rather unintere~ting ~traight lino, with the ~mplitude of any interferer~ no greator than that o the SS ~ignal.
Figure 1 illuetratea a typical frequency ~pectrum. Aa ~hown on Figure 1, the desir~d SS ~ignal i~ deoir~bly ~elow the no~Go floor pro~n~ to make d~tection or intorc~ption o tho aign 1 01g~ificantly mor~ difficult th~n i~ the 6ignal wero above the noi~e floor. The "ST~ONG INTERFERER"
indicated could be a ~amming signal or t~o signal from a ~V
or radio etation or any co-located (i.e., n~arby) communicatione, The ~TY~ IM~ERF~R~RS" indicated could be producod ~rom low po~er ~ourcee, ~uch a~ ham radioe. The .
_g_ .
2100994 PHA 40.655 broken line titled ~PROCESSING GAIN" repre3en~-~ the level o the SS PN ~ignal when it i8 collap~ed (not ~pread).
Figure 2 illustrate~ tho ~pectrum ~hown on Figure 1 after thè correlation ~do~preading) of the 6ignal. As noted above, the collap~ed signal can be recovered in tho pre~ence o~ inter~erer~ by ono of the convontional method~ de~cribed abov~. A~ alw no~ed ~bove, tho~e convontional methods hdv~
c~rtain dieadvantages.
With re~erence now to F1gure 3, the present inven~ion overcom~ the~e dieadYantage~ through the u~e of real ~ime ad~ptive iltering through fa~t Fourier tra~orm (FFT~
technology. Thls i8 accompli~hed by providing the ~ignal proceesing ~y~tem ~hown as re4erence numeral 10. Sy~tem 10 compri3e# FFT circuitry 20, which recei~ input ~ignal~, and which i3 coupled to ~xCi~ion circuitry 22. Exci~ion circuitry 22 ie coupled to in~or~o FFT (I~FT) circuikry 2 whiCh pro~id0~ outpute to convention~l correlation circuitr ~not ~hown)~
In oporation, ~FT cirCuitry 20 reCei~e~ in-pha~e and quadrature ~I and Q) eignal input~ ~rom a digitizer 12 which, in turn~ rec~ivo~ an input rom an RF co~ertsr 1~.
FFT ~ircuitry 20 tran~form~ tho ~ignal~ to the ~requency domain. Once the data i~ in tho frequency domain, the magnitude thereo~ i3 dl~carded and roplaced with a normalization value and the narrow band interrerers are rejec~ed. Tho data is then . . . ~ - .
. 210 0 9 9 ~ PHA 40.655 ~ransformed back to the fre~uency d~main and proce~sed through IFF~ ~4 to the time domain.
~ he exciaion process works because of the ~anneri~m of ss ~ignal9. ss ~ignal6 are modulated by phase modulation.
Tho excision procees perform~ a type limiting operation commonly a~ociated with FM dotoction. By per~orming the exci610n operation in the ~roquency domain, all amplitude compone~ta, including tho~e of any intor~rorY, aro normalized to a common valu~. That i5 1 all ~ignals hAve the sam~ amplitude value and, thereforo, tho amplitude~ of the interferer~ are now rolatively inconeequ~ntial in~o~ar are tho correlation gain o the ~pread ~ignal i~ concerned. The ouput o~ FFT 20 is a set o~ co~plex (real and imaginary) munbera repre~enting the froquency component~ of tho dig~tized wa~e~orm. 3y utllizing a rectangular-to-polar conver~ion, the signal i~ re~olved into its magnitude and pha~e component~. Since the SS ~ignal in~ormation i~
contained ~olely in the phaae component, the magnltude component 1~ ~uperfluou~ and i6 di~carded. A polar-to-rectAngular con~ereion, with the mangitude ~et to ~ome arbitrary value ~unity i8 convenient) i9 all that i~
required to return a normalized ~pe~trum. Slnce there is no need to calculate any threshold or noise le~el, no o~erhead 210099~ PHA 40.655 in computat~on is required, E~ery data point i8 opera~ed on with no ~ime del~y (other than latoncy).
Mathematically, ~hi6 proces~ Can be described a~:
REAL~ut ~ co~arctan(IMAGINARY~ N /REALI N ) ~
IMAGINARYo U T 5 6in~arctan(IMAGINARYI N /REA~l~)], whor0 the trigonomotric function~ are modulo 2 PI.
FFT circuitry 20 ~nd IFFT circuitry 24 may be commercially available Ple~oy P~S~1615~ Stand Alono Proce~sor~ provided ~5 either a ~ingle chip or a two or ~ore ca~c~dod chipY.
Figure 4 urther illustrate~ the 6tructure o~ excision circuitry 22 whi~h ie indicated can bo implemented via a commercially a~ailable Ple~eey PDSP16330 Pythasoras Proce~ors or, alternati~oly, a TRW TMC2330 Coordinate Trangformo~s can be employed.
Improved p0r~0rmance i~ gained by incorporating windowlng along wi~h overlap and add architecturo. The advantAgo~ o~ windowlng data i~ a well known and well documen~ed proce~s. S~e IEEE "On U~o o~ Window6 ~or H~rmonic Analy~is with the ~iscrete Fourier ~ran~orm," by Frede~ick ~arris, Proceedinas o~ t~ IE~E, vol. 66, no. 1, pag~ 51-~3, ~anuary 1978. It h~ boen ~ound that the H~mming window produce~ excoll~nt re~ults. The ~amming wlndow ha~ ~he bene~it that, when utilized with a 50-percen~
2 1 O 0 9 9 ~ PHA 40.655 overlap add archit~cture, the re~ultant tim~ dom~in wave~orm ha~ unity gain, although the add architecture imposeY t~ice a~ much proce~ing.
.~
2100994 PHA 40.655 It will thus be seen that th~ obje~t~ 6et forth abev~, among those elucidated ln, or made ~ppa~ent ~rom, the preceding description, are ef~icientLy attained and, since ce~tain change~ may be made in the abo~e construction without departing from tho ~copo of the inventio~, it 18 intended that all mattor contained in the above de~cription or ~hown on the accomp~nying drawing ~igures shall be lntorproted as 111ustr~ti~e only and ~ot in a limiting ~en~e.
It is al~o to be under~tood that the following claim~
are intcnd~d to co~er ~11 of th~ generic a~d ~p~ci~ic ature~ of the in~ontion herein described and all ~t~tement~ o~ the ~cop~ of the inYention which, as a matter o language, might bo said to fall therebetween.
Claims (8)
1. A method for excising narrow band interferers in a spread spectrum signal communication, comprising the steps of:
(a) receiving said spread spectrum signal;
(b) digitizing said spread spectrum signal;
(c) transforming said digitized signal from the time domain to the frequency domain;
(d) discarding the magnitude of said digitized signal and replacing it with a normalized value; and (e) transforming said digitized signal back to the time domain.
(a) receiving said spread spectrum signal;
(b) digitizing said spread spectrum signal;
(c) transforming said digitized signal from the time domain to the frequency domain;
(d) discarding the magnitude of said digitized signal and replacing it with a normalized value; and (e) transforming said digitized signal back to the time domain.
2. A method, as defined in Claim 1, wherein (d) comprises the steps of:
(d1) utilizing a rectangular-to-polar conversion to resolve said digitized signal into its magnitude and phase components;
(d2) discarding said magnitude component; and (d3) utilizing a rectangular-to-polar conversion with the magnitude set to an arbitrary value to return said digitized signal to a normalized spectrum.
(d1) utilizing a rectangular-to-polar conversion to resolve said digitized signal into its magnitude and phase components;
(d2) discarding said magnitude component; and (d3) utilizing a rectangular-to-polar conversion with the magnitude set to an arbitrary value to return said digitized signal to a normalized spectrum.
3. A method, as defined in Claim 1, wherein step (c) is accomplished utilizing a Fast Fourier Transform.
4. A method, as defined in Claim 1, where step (e) is accomplished utilizing a Fast Fourier Transform.
5. An apparatus for excising narrow band interferere in a spread spectrum signal communication, comprising:
(a) receiving means to receive said spread spectrum signal;
(b) digitizing means coupled to said receiving means to digitize said spread spectrum signal;
(c) first transforming means coupled to said digitizing means to transform said digitized signal from the time domain to the frequency domain;
(d) rejection means coupled to said first transforming means to discard the magnitude of said digitized signal and replace it with a normalized value; and (e) second transforming means coupled to said rejection means to transform said digitized signal back to the time domain.
(a) receiving means to receive said spread spectrum signal;
(b) digitizing means coupled to said receiving means to digitize said spread spectrum signal;
(c) first transforming means coupled to said digitizing means to transform said digitized signal from the time domain to the frequency domain;
(d) rejection means coupled to said first transforming means to discard the magnitude of said digitized signal and replace it with a normalized value; and (e) second transforming means coupled to said rejection means to transform said digitized signal back to the time domain.
6. An apparatus, as defined in Claim 5, wherein said rejection means comprises:
(d1) first rectangular-to-polar conversion means to resolve said digitized signal into its magnitude and phase components and to discard said magnitude component; and (d2) second rectangular-to-polar conversion moans with the magnitude set to an arbitrary value to return said digitized signal to a normalized spectrum.
(d1) first rectangular-to-polar conversion means to resolve said digitized signal into its magnitude and phase components and to discard said magnitude component; and (d2) second rectangular-to-polar conversion moans with the magnitude set to an arbitrary value to return said digitized signal to a normalized spectrum.
7. An apparatus, as defined in Claim 5, wherein said first transforming means is a Fast Fourier Transform device.
8. An apparatus, as defined is Claim 5, where said second transforming means is a Fast Fourier Transform device.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/920,215 US5263048A (en) | 1992-07-24 | 1992-07-24 | Narrow band interference frequency excision method and means |
| US920,215 | 1992-07-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2100994A1 true CA2100994A1 (en) | 1994-01-25 |
Family
ID=25443365
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002100994A Abandoned CA2100994A1 (en) | 1992-07-24 | 1993-07-21 | Narrow band interference frequency excision method and means |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5263048A (en) |
| EP (1) | EP0580243A3 (en) |
| JP (1) | JPH06197093A (en) |
| KR (1) | KR940006368A (en) |
| CA (1) | CA2100994A1 (en) |
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| FR2742896B1 (en) * | 1995-12-22 | 1998-03-20 | Centre Nat Etd Spatiales | METHOD AND DEVICE FOR INTERFERENCE SIGNAL ELIMINATION IN A DIRECT SEQUENCE SPREAD SPECTRUM LINK |
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| EP0386418B1 (en) * | 1989-03-06 | 1994-12-21 | Robert Bosch Gmbh | Method for data reduction of digital audio signals and for approximate recovery of same |
| DK0486554T3 (en) * | 1989-08-11 | 1994-12-27 | Siemens Ag Oesterreich | Method and apparatus for converting digitally modulated receive signals from the high frequency range |
| US5018088A (en) * | 1989-10-02 | 1991-05-21 | The Johns Hopkins University | Adaptive locally-optimum detection signal processor and processing methods |
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-
1992
- 1992-07-24 US US07/920,215 patent/US5263048A/en not_active Expired - Lifetime
-
1993
- 1993-07-20 EP EP19930202128 patent/EP0580243A3/en not_active Withdrawn
- 1993-07-21 JP JP5180474A patent/JPH06197093A/en active Pending
- 1993-07-21 CA CA002100994A patent/CA2100994A1/en not_active Abandoned
- 1993-07-23 KR KR1019930013988A patent/KR940006368A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0580243A3 (en) | 1994-02-09 |
| US5263048A (en) | 1993-11-16 |
| EP0580243A2 (en) | 1994-01-26 |
| JPH06197093A (en) | 1994-07-15 |
| KR940006368A (en) | 1994-03-23 |
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