Mobile Radio Communications

Transcription

1 Course 3: Radio wave propagation Session 3, page 1

2 Propagation mechanisms free space propagation reflection diffraction scattering LARGE SCALE: average attenuation SMALL SCALE: short-term variations in position and time dx >> λ dt >> T S dx λ dt T S Session 3, page

3 Large-scale/small scale variations space PL (db) d Session 3, page 3

4 Large-scale/small scale variations time PL (db) t Session 3, page 4

5 Free-space propagation P: power G: antenna gain d: separation distance L: system loss P R ( d ) P G G = T T R λ ( ) 4π d L Session 3, page 5

6 Antenna gain isotropic: G=1 directional: G(θ) G = 4 π e λ A EIRP: effective isotropic radiated power (received power as if received from isotropic source) EIRP = G T P T Session 3, page 6

7 Free-space path loss PL =10log PT P R = 0 log 4π + λ ( d ) = PL + 0log 0 0log d d d 0 attenuation 0 db/dec dec Session 3, page 7

8 Ground wave reflection d 1 h t d h r E tot α α = cos c ct d d 1 ( ω t) + Γ cos( ω + θ ) Session 3, page 8

9 Ground wave reflection = d d 1 = d h t h r d + ( ) h + h d + ( h h ) t r d >> h t r θ 4πh t h r λd Session 3, page 9

10 Ground wave reflection θ α/d 1 α/d E E α = d α = d {( θ ) + θ } 1 cos sin α ( cos θ ) θ d ( ) Session 3, page 10

11 Ground wave reflection E α 4πht h d λd r P r = E Ae ( ht hr ) β 4 10π d A e G λ 4π Session 3, page 11

12 Two-ray path loss model PL = 40 log d ( 10logG t + 10logGr + 0log ht + 0log hr ) attenuation 40 db/dec dec Session 3, page 1

13 Path loss exponent Session 3, page 13

14 Log-distance path loss model P L = PL( d0) + 10n log d d 0 d: T-R distance d 0 : close-in reference distance n: path loss exponent ranging from 1 to 6 Session 3, page 14

15 Okumura path loss model L 50 = L + A ( f, d) G( h ) G( h ) F mu t r G AREA ht G ( ht ) = 0 log( ) 00 hr G ( hr ) = 10 log( ) 3 hr G ( hr ) = 0 log( ) 3 10m < h t < 1000m h r < 3m 3m < h t < 10m Session 3, page 15

16 Hata path loss model L = log 13.8 log h 50 c t r + ( log h t )log d + C( fc) f a( h ) Session 3, page 16

17 Coverage area actual coverage ideal cell boundary Session 3, page 17

18 Log-normal shadowing PL (db) d PL = PL(d) + Χ σ Session 3, page 18

19 Log-normal shadowing Χ = N ( 0, σ ) zero-mean Gaussion with standard dev. σ outdoor: σ=6-9db indoor: σ=-1db Session 3, page 19

20 Link budget P t P t : permitted transmit power P r : required receive power PL: path loss N: noise floor NF: noise factor FM: fading margin SNR: required signal-to-noise ratio PL FM SNR NF P R N Session 3, page 0

21 Multipath fading PL (db) d Session 3, page 1

22 Multipath effects d 1 d time delay fading in amplitude dispersion (echoes) Doppler spread speed angle of arrival Session 3, page

23 Delay space phenomenon Session 3, page 3

24 Fading d λ τ λ = c 1 f c θ π RF waves s = r 1 1 cosθ1 s = r cosθ s = r 3 3 cosθ3 Session 3, page 4

25 Time dispersion τ T S τ t t Session 3, page 5

26 Doppler spread d 1 d v λ ( φ ) cosφ f d = v 0 φ π v λ f d v λ Session 3, page 6

27 Doppler shifts Session 3, page 7

28 Doppler spread v (km/h) f c (MHz) f d (Hz) Session 3, page 8

29 Delay profile Session 3, page 9

30 Measured delay profile Session 3, page 30

31 Impulse response model time-variant, linear system: h( t, τ ) t: time variant due to motion (ms to s) τ: time dispersion (ns to µs) filter representation: y() t = x() t h( t, τ ) Session 3, page 31

32 FIR representation h b ( t, τ ) N 1 = i= 0 a i () t exp{ jθ () t } δ ( τ τ ) i i a 0,θ 0 a 1,θ 1 a,θ a 3,θ 3 a 4,θ 4 t 0 τ 0 τ 1 τ τ 3 τ 4 h b (t,τ) BW signal < 1/( τ) τ0: excess delay reference N τ: maximum excess delay Session 3, page 3

33 FIR representation t t h b (t,τ) t 1 h b (t 1,τ) t 0 τ 0 τ 1 τ τ 3 τ 4 h b (t 0,τ) Session 3, page 33

34 Power delay profile h b ( t, τ ) measured in local area spatial averaging (-6m) Session 3, page 34

35 Time dispersion parameters τ = k k P( τ ) τ k P( τ ) k k τ = k k P( τ ) τ k P( τ ) k k mean excess delay: τ rms delay spread: σ τ = τ (τ ) maximum excess delay: τ where P P max Session 3, page 35

36 Time dispersion example normalized RX power (db) σ τ τ = 55ns = 70ns τ excess delay (ns) Session 3, page 36

37 Time dispersion values environment f (MHz) σ τ urban suburban indoor µs ns 70-90ns Session 3, page 37

38 Coherence bandwidth h(t,τ) H(f) B c : f where frequencies become uncorrelated corr.>0.5 B c 1 5σ τ Session 3, page 38

39 Flat fading All frequency components fade identically. B s << B c T s >>σ τ S(f) H(f) f f Session 3, page 39

40 Frequency-selective fading Different frequency components fade differently. B s > B c T s <σ τ S(f) H(f) f f Session 3, page 40

41 Rayleigh fading Amplitude fading N i.i.d. components: resultant Normally (Gaussian) distributed Gaussian distribution on I and Q gives Rayleigh on envelope Q I Session 3, page 41

42 Rayleigh distribution p r r r) = exp ( r σ σ ( 0) p(r) /σ r = 1.533σ σ r = 0.49σ 0 σ σ 3σ 4σ r Session 3, page 4

43 Rician fading Amplitude fading One dominant component + N i.i.d. components: resultant Rician distributed Session 3, page 43

44 Rician distribution p r r + A Ar r) = exp 0 (, I A r σ σ σ ( 0) A: amplitude of dominant component I 0 : zero-order Bessel function Rician factor: K = A σ Session 3, page 44

45 Rician distribution K - : K : approaching Rayleigh approaching N(A,σ) p(r) K - K=3dB 0 σ σ 3σ 4σ r Session 3, page 45

46 h(τ) Modeling: flat fading a, φ t F f s(t) a exp(jφ) a: Rayleigh dist. φ: uniform (0,π] Session 3, page 46

47 Modeling: -ray fading h(τ) a 1, φ 1 a, φ 0 τ t F f s(t) Σ a 1 exp(jφ 1 ) τ a exp(jφ ) Session 3, page 47

48 Doppler spread d 1 d v λ ( φ ) cosφ f d = v 0 φ π v λ f d v λ Session 3, page 48

49 Doppler power spectrum S D ( f ) = f m 1 α f f m f c f m = v λ f c -f m f c f c +f m Session 3, page 49

50 Coherence time S D (f) h D (t) T c : t where samples become uncorrelated T c 1 f m Session 3, page 50

51 Slow and fast fading Fast fading: B s < B D T s >Τ c Slow fading: B s >> B D T s <<Τ c Session 3, page 51

52 Slow/fast - flat/freq freq-sel.. fading Flat / frequency selective fading: Echo pattern h(t,τ) Fast / slow fading: Motion effects h(t,τ) Session 3, page 5

53 T s Slow/fast - flat/freq freq-sel.. fading flat, slow fading flat, fast fading σ τ frequency selective, slow fading frequency selective, fast fading T c T s Session 3, page 53

54 B s Slow/fast - flat/freq freq-sel.. fading frequency selective, fast fading frequency selective, slow fading B c flat, fast fading flat, slow fading B D B s Session 3, page 54

55 Multipath time scales dt Amplitude fading: (i.e. dt=1ns) Time dispersion: (i.e. dt=1µs) dt dt Doppler spread: (i.e. dt=10ms) 1 f c d c 1 f d Session 3, page 55

56 FOR NEXT WEEK Read: Chapter 5: 5.1, 5. (not 5.., 5..3), 5.3 (not 5.3., 5.3.3) (not 5.7.8) Solve problems: Chapter 4: 4., 4.3, 4.5, 4.18, 4.1 Session 3, page 56