Signal Propagation. Jie Gao 01/27/2010

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1 Signal Propagaion Jie Gao /7/

2 Signal Signal are generae as physial represenaions o aa A signal is a union o ime an loaion ieal igial signal a speial ype o signal, sine waves, also alle harmonis: s() = A sin( + ϕ) wih requeny, perio T=/, ampliue A, phase shi ϕ

3 FourierTransorm: Every Signal Can be Deompose as a Colleion o Harmonis g( ) = + n= a n sin(n) + n= b n os(n) ieal perioial igial signal eomposiion The more harmonis use, he smaller he approximaion error. 3

4 4

5 Time Domain v.s. Frequeny Domain Time omain Frequeny omain Knowing one an reover he oher. 5

6 Inererene Signalsa up Apply Fourier ransorm 6

7 Funamenal Quesion: Why No Sen Digial Signal in Wireless Communiaions? ieal igial signal 7

8 Funamenal Quesion: Why No Sen Digial Signal in Wireless Communiaions? May ause inererene suppose igial rame lengh T, hen signal eomposes ino requenies a /T, /T, 3/T, le T = ms, generaes raio waves a requenies o KHz, KHz, 3 KHz, 8

9 Banwih 9

10 Frequenies or Communiaions wise pair oax able opial ransmission Mm 3 Hz km 3 khz m 3 MHz m 3 MHz mm 3 GHz µm 3 THz µm 3 THz VLF LF MF HF VHF UHF SHF EHF inrare visible ligh UV VLF = Very Low Frequeny LF = Low Frequeny MF = Meium Frequeny HF = High Frequeny VHF = Very High Frequeny Frequeny an wave lengh: UHF = Ulra High Frequeny SHF = Super High Frequeny EHF = Exra High Frequeny UV = Ulraviole Ligh λ = / wave lengh λ, spee o ligh 3x 8 m/s, requeny

11 Sperum

12 Frequenies an Regulaions ITU-R hols auions or new requenies, manages requeny bans worlwie (WRC, Worl Raio Conerenes) Europe USA Japan Cellular Phones Corless Phones Wireless LANs Ohers GSM , /46-467, , 89-95/935-96, 7-785/85-88 UMTS (FDD) 9-98, - 9 UMTS (TDD) 9-9, - 5 CT , CT DECT 88-9 IEEE HIPERLAN , RF- Conrol 7, 8, 48, 433, 868 AMPS, TDMA, CDMA , TDMA, CDMA, GSM 85-9, PACS 85-9, PACS -UB I EEE , RF- Conrol 35, 95 PDC 8-86, , , PHS JCT IEEE RF- Conrol 46, 868

13 Anennas an Signal Propagaion

14 Anennas: Isoropi Raiaor Isoropi raiaor: a single poin equal raiaion in all ireions (hree imensional) only a heoreial reerene anenna Raiaion paern: measuremen o raiaion aroun an anenna y z x z y x ieal isoropi raiaor Q: how oes power level erease as a union o, he isane rom he ransmier o he reeiver? 4

ipole λ/ size o anenna proporional o wavelengh or beer

15 Real Anennas Real anennas are no isoropi raiaors Some simple anennas: quarer wave λ/4 on ar roos or hal wave ipole λ/ size o anenna proporional o wavelengh or beer ransmission/reeiving λ/4 λ/ Q: Assume requeny Ghz, λ=? 5

Dipole: Raiaion Paern o a Dipole hp://www.pub.

16 Dipole: Raiaion Paern o a Dipole hp:// hp://en.wikipeia.org/wiki/dipole_anenna 6

17 Why No Digial Signal (revisie) No goo or sperum usage/sharing The wavelengh an be exremely large o buil porable evies e.g., T = us -> =/T = MHz -> wavelengh = 3x 8 / 6 = 3m 7

18 Free-Spae Isoropi Signal Propagaion P P r = G r G P: r reeive power P : ransmie power λ 4 G r, G : reeiver an ransmier anenna gain λ(=/): wave lengh In ree spae, reeiving power proporional o /² ( = isane beween ransmier an reeiver) The oal raiaion power remains onsan, bu he surae area o a sphere wih raius r inreases like r. Someime we wrie pah loss in log sale: Lp= log(p) log(pr) 8

19 Signal Propagaion Reeiving power aiionally inluene by shaowing (e.g. hrough a wall or a oor) reraion epening on he ensiy o a meium releion a large obsales saering a small obsales iraion a eges iraion shaow aing reraion releion saering 9

20 Signal Propagaion: Senarios Deails o signal propagaion are very ompliae We wan o unersan he key haraerisis ha are imporan o our objeive

21 Reason I: Shaowing Signal srengh loss aer passing hrough obsales Some sample numbers i.e. reues o ¼ o signal log(/4) = -6.

22 Disane power relaionship in praie Reeive power ereases proporional o / r where r varies rom o 6. Long orrior, big inoor environmen: r= Mealli builing: r=6. Slow aing

23 Reason II: Mulipah Signal an ake many ieren pahs beween sener an reeiver ue o releion, saering, iraion 3

24 Mulipah Can Reue Signal Srengh Example: releion rom he groun: reeive power ereases proporional o / 4 insea o /² ue o he esruive inererene beween he ire signal an he signal relee rom he groun groun For eail, see page 9: hp:// 4

25 Mulipah Faing Due o onsruivean esruiveinererene o muliple ransmie waves, signal srengh may vary wiely as a union o reeiver posiion Lisen o raio on a ar. 5

26 Mulipah Ee (ixe reeiver loaion) Channel haraerisis hange over loaion, requeny example os( ) phase ierene: α ( [ ) os ] ( ) + = + = + λ α ( [ ) os ] 6

27 Mulipah (ixe reeiver loaion) Suppose a - he wo waves oally esru. (wha oes i mean?) λ = = ineger Q: an we in plaes where he wo waves onsru? + = + λ 7

28 Opion : Change Loaion I reeiver moves o he righ by λ/4: = + λ/4; = - λ/4; ' ' λ = λ = λ -> + λ / ( λ / 4) λ + By moving a quarer o wavelengh, esruive urns ino onsruive. 8

29 Opion : Change Frequeny ' ± = Change requeny: 9 The hange epens on elay sprea λ + = +

30 Mulipah Faing: A Simple Two-pah Example reeiver -Wavelengh is abou.3 m or GHz ellular 3

31 Mulipah Faing wih Mobiliy: A Simple Two-pah Example r r() = r + v, assume ransmier sens ou signal os( ) More eail see page 6 Eqn. (.3): hp:// 3

32 Mulipah Ee (moving reeiver) Channel haraerisis hange over ime (loaion) example os( ) Suppose =r +v =-r -v α ( [ ) os ] α ( [ ) os ] 3

33 Derivaion ]) [ ])sin( [ sin( ) )sin( sin( ]) [ os( ]) [ os( ) ( ] [ ] [ ] [ ] [ v r v r v r v r v r v r v r v r v r v r = = ]) [ ])sin( [ sin( ]) [ ])sin( [ sin( ]) [ ])sin( [ sin( ]) [ ])sin( [ sin( ) ( v r v v r v r v r v r v r v r = = = = See hp:// or os(u)-os(v)

34 Reeive Waveorm ms v r sin( [ ])sin( [ v ]) eep ae v = 65 miles/h, = GHz: v/ = 9 * 3 / 3x 8 = Hz Why is as mulipah aing ba? 34

35 Small-Sale Faing 35

36 Mulipah Can Sprea Delay signal a sener Time ispersion: signal is isperse over ime LOS pulse mulipah pulses signal a reeiver LOS: Line O Sigh 36

37 Delay Sprea RMS: roo-mean-square 37

38 Mulipah Can Cause ISI isperse signal an ause inererene beween neighbor symbols, Iner Symbol Inererene (ISI) Assume 3 meers elay sprea, he arrival ime ierene is 3/3x 8 = ms i symbol rae > Ms/se, we will have serious ISI LOS pulse signal a sener mulipah pulses In praie, raional ISI an alreay subsanially inrease loss rae signal a reeiver LOS: Line O Sigh 38

39 Summary: Wireless Channels Channel haraerisis hange over loaion, ime, an requeny Reeive Signal Power (B) pah loss power Large-sale aing log (isane) small-sale aing ime requeny 39

Outline. Wireless PHY: Modulation and Demodulation. Admin. Page 1. g(t)e j2πk t dt. G[k] = 1 T. G[k] = = k L. ) = g L (t)e j2π f k t dt.

Outline. Wireless PHY: Modulation and Demodulation. Admin. Page 1. g(t)e j2πk t dt. G[k] = 1 T. G[k] = = k L. ) = g L (t)e j2π f k t dt. Outline Wireless PHY: Modulation and Demodulation Y. Richard Yang Admin and recap Basic concepts o modulation Amplitude demodulation requency shiting 09/6/202 2 Admin First assignment to be posted by this