脉冲位置调制光谱切片传输中英文翻译

Pulse position modulation for spectrum-sliced transmission

Proponents of ultra-wideband (UWB) technology promise todeliver large amounts of data with very lowpower spectral density. The ultra-wideband radio concept is very attractive as it promises to open large amounts of spectrum to a variety of user sand at the same time it claims little interfere nice between users. Unlike conven tional wire less communications systems that are carrier based,UWB-based communications is baseband .It use sase ries of short pulses that spread thee nergy of thes ignal from near DC to a few GHz. One typical technique is to as sign a window in time and shif the position of the pulse with in that window. This is classical pulse position modulation. With band width restrictions effectively removed, UWB promises to speed upwire less data trans ferrates. Some pub lished work has addressed the issue of how many users can the UWB channel support[2][3].This work considered one type of capacity-the capacity interms on the number of users. The capacity was derived from signal-to-no is eratio (SNR)consi derations. Acer tain SNR is required to achieve a specified biterr or probability(BEP).The no is eflo or raises with the number of users.

A more fund amentalty peofcapacity is the well known Shannon capacity in bits/s. Our go a list odevelopanunderstanding of thero leofvar iouspara me terso nthe Shannoncapac it yo fUW

B commun ications.The well known Shannon!s form ulC=Wlog(l+SNR),where SNR is the 2 signal-to-noiseratio and Wist hechannel band width, predicts the channel capacity Cfor an additive white Gaussiannoise (AWGN) channel with continuousal uedinput sand outputs. This express iondoesnot apply to communications with PPM signals. PP mis a modul ation with discret e-valuedi nputsan dcon tinu ous-val uedoutput s.Further more,P Pmsignalsa reorthogo nal,whichi mposesa naddition alconst raintont hecapacityc alcul ations. Newcapacitycal culations arerequi red,which htakeint oaccountthes econstrain ts.PPMcap acitywas studiedint hecontex tofwireles sinfra reda nd optic alcha nnels[4].The capacityo fPPM modul ationservesas thestarti ngpointtow hichUWB- speci ficcons traintsar eadded.Thec onstraints arethepow erspectr umdensityl imitation underF CCPar t15r ulesand thes preadingra tiocons train t.Sincegiga hertzunoc cupiedslice sofbandwidth arenotavailable atmic rowavef requencies,underFCCreg ulations,U Wbradiomust betreat eda ss p uriousint erferenc etoallother communicat I

onsystems.

The FCC is currently assessing whether to allow UWB emission son an unlicensed basis. Un in tend edout of bande missionsa regov ernedb yFCCPart15ru les.Inthisp aper,weassumetha tUWBtransmiss ionscomplywi ththisFCCrul e.Thespreading ratioconst raintisinte ndedtosatisfyi nterferences uppressionre quirements[5 ][6].Thispape risorgani zedasfollows. Sectionintrodu cesthesi gnalmodel.The linkbudgetcalculati onforUWBunde rFCCPart 15rules isdevel opedinsectio n.AnalysisofU WBM-ary PPM capacity is carried out insection IV.Finally,conclusionsarep rovidedinse ctionV..SIGNALMODEL Considera single-user UWB pulse position modulated communication ssystem. The M-ary PPM signal setis {S1(t),S2(t),SM(t)}, where Sm(t), (mM) Canbewrit tenas: (t)=p(t-j). Inthisexpr ession, p(t)is the UWB puls eofduration Tp (normalizedsuchthat), Episthee nergyperp ulse,Tis the puls erepetition time, thesequencecj frepresents thet imehoppi ngcode,withcj Tanadditional times hiftto the jthpul seof the ccomm unication burst. Fora fixedT ,the symbolrate R=1/(N,Tf) determinesN, the fnumbero fpulsestha tformasymbol. The symbolduration is then T,=N,Tf. The parameter is the additional times hift corresponding to the pulseposition modulation, mwith T=0, T100.

Theband widthrequ irementso fM-aryPPMca nbeestim atedfromth eLandau- Pollak theorem[8], which hstates that the band width of as ignalt imelimitedto T,(symboldu ration)andof dimensionali tyMisappro ximatelyB = .Thisval uecanbeint erpretedasthe minimumbandw idthrequire dtotransmi tuncodedM -aryPPM.UWB using Mary PPM is spread spect rumin thesense that theUWBbandwidthW>>B.From (2),W=c/Tp,andT,=NT,the spread spectrumcondition Wsf>>Bismet for aspread ingratio=>>M.Themot ivationfor spreadspe ctrumUWBPPMis twofold:(1)atta inspecifie dleveloftr ansmittedpower subjecttopower densityconstra intssetb yFCCPart1 5regulat ion,(2)attai nspecif iedlev elofresist anceto othe remissi onsintheb and(jamresistance).The transmitted powerre quirementis deter m ine dbythedis tanceb etweenthe transmitte randthere ceiver.Thi sissueisdi scusse dinthenextse ction.Jamre sistance of U WB isanalyzed .

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