Point to point Radiocommunication

Transcription

1 Point to point Radiocommunication SMS4DC training seminar 7 November 1 December Technical overview Content SMS4DC Software link calculation Exercise 1

2 Point-to-point Radiocommunication Link A Radio Link Terminal A Hop Isotropic antenna Transmitting antenna gain repeater repeater f 1 f f n Hop 1 Hop Propagation loss Isotropic antenna Receiving antenna gain Terminal Transmitter TX antenna cable lose Filters, feeder, etc. RX antenna cable lose Filters, feeder, etc. Receiver 3 Definition Point-to-point communication Radiocommunication between specified fixed stations Fading Fluctuation of signal level respect to stable condition for number of reasons Path Profile A vertical cut of terrain along propagation path between transmitter and receiver NFD Discrimination gained because of TX emission and RX reception masks Polarization The locus of electric field vector fluctuation SWR Standing Wave Ratio ([1+ Г ]/[1- Г ]) Minimum acceptable signal level 4

3 Link Budget Total Loss = [Free Space Loss] + [Atmospheric Gaseous Loss] + [Rain Attenuation] + [Clear Air Fading] + [Diffraction Loss] + [NFD] Flat Receive Level = P T + G T [Free Space Loss] [Atmospheric Gaseous Loss] [Diffraction Loss] G R [Receiver Insertion Loss] Fade Margin = [Flat Receive Level] [Receiver Threshold] Insertion Loss= [Cable Loss]+[Branching Loss]+[Mismatch Loss] 4 π d FreeSpaceLoss = λ 5 RF Signal Spectrum Power Spectral Density of x(t) : X ( f ) Out of band emission β % Occupied bandwidth f3 f f 1 f 4 f4 x( t) = X ( f ) df f f 3 1 f4 P X ( f ) df f3 Necessary bandwidth = f Y db (usually Y = 6dB to noise floor) spectrum floor noise floor β % frequency = Area of yellow color β X ( f ) df = P 00 Normally β = 0.5 % x( t) 6 3

4 Transmitting and Receiving Masks The power spectral density (PSD) Transmitter emission mask 0 db RF Signal x c (t) Spectrum floor Noise floor Necessary bandwidth Spurious emissions Assigned Frequency ~6 db Normally each TX has identical corresponding RX receiving masks Mismatched TX & RX masks cause additional loss (NFD) 7 Propagation Effects Diffraction fading due to obstruction of the path; Attenuation due to atmospheric gases; Fading due to atmospheric multipath or beam spreading (commonly referred to as defocusing) associated with abnormal refractive layers; Fading due to multipath arising from surface reflection; Attenuation due to precipitation or solid particles in the atmosphere; Variation of the angle-of-arrival at the receiver terminal and angle-of-launch at the transmitter terminal due to refraction; Reduction in cross-polarization discrimination (XPD) in multipath or precipitation conditions; Signal distortion due to frequency selective fading and delay during multipath propagation. 8 4

5 Propagation Loss Attenuation due to atmospheric gases, Diffraction fading due to obstruction or partial obstruction of the path, Fading due to multipath, beam spreading and scintillation, Attenuation due to variation of the angle-ofarrival/launch, Attenuation due to precipitation, Attenuation due to sand and dust storms 9 Gaseous Attenuation (ITU-R P.676) Considerable loss above 10 GHz A = γ d a a db High attenuation frequencies have special usages Pressure: hpa Temperature: 15 C Water vapour: 7.5 g/m 3 Specific attenuation (db/km) Frequency, f (GHz) Total H O Dry air H O Dry air

6 k-factor Electromagnetic wave bends while passing through nonhomogenous medium, Vertical profile of atmosphere is non-homogeneous, Median effective Earth radius factor : k50 = 157 /[157 N ] Effective radius of Earth in km: a e = 6371 k e See ITU-R P.453 for N (vertical refractivity gradient), Actual Modified Actual Modified k > 1 k < 1 11 Propagation by Diffraction (ITU-R P.56) Diffraction over a spherical earth for trans-horizon paths Diffraction by obstacles inside Fresnel zone LOS is possible Consideration of diffraction from round, wedge and sharp obstacles, single and multiple (in P.45 propagation model) shadow 1 6

7 Fresnel ellipsoids n =1 Fresnel Ellipsoids n = A M B AM + MB = AB + λ n Wavelength More than 90% of power, propagates inside first ellipsoid For Line of Sight (LOS) communication first Fresnel ellipsoid should be enough clear 13 Fresnel zone Radius of n th Fresnel zone R n R n d 1 d R n = 1/ 550 n d1 d ( 1 ) d + d f f is frequency in MHz and all distances are in km 14 7

8 Diffraction Fading Obstruction of the Path No LOS path Obstruction inside Fresnel zone 15 Diffraction loss and clearance 1 st Fresnel zone Positive h 0.6 F 1 clearance is necessary for tropical climate B: theoretical knife-edge loss curve D: theoretical smooth spherical Earth loss curve, at 6.5 GHz and k = 4/3 A: empirical diffraction loss for intermediate terrain F: radius of the first Fresnel zone h: amount by which the radio path clears the Earth s surface h Negative h Obstruct Diffraction loss relative to free space (db) B 0 A d 30 D Normalized clearance h/f

9 Antenna Height Determination (Single Antenna in tropical climate) Step 1: Determine antenna heights for 1.0F 1 clearance in median k- factor (k 50 = (157/(157- N)) or k =4/3) Step : Determine antenna heights for 0.6F 1 using effective k-factor from the following figure 1.1 Step 3: Select the larger 1 antenna heights 0.9 In temperate climate k e step will be down using 0.0F 1 for single isolated obstruction or 0.3F 1 for obstruction is extended along a portion of the map Path length (km) Multipath Fading atmospheric Multipath surface Multipath Antenna Decoupling (governs the minimum beamwidth) Beam Spreading (defocusing) 18 9

10 Multipath Fading Elements Multipath fading depends on: Refractivity gradient in the lowest 65m of atmosphere Area terrain roughness Path inclination Exceedance time percentage Frequency Altitude of antennas Calculation method explained in ITU-R P Hydrometer Attenuation Can be ignored in frequencies below 5 GHz ITU gathered rain statistics during 15 year (ITU- R P.837), Specific attenuation γ R and frequency, γ R = kr depends on polarization Rain attenuation exceedance can be estimated within 0.001% to 1% of the time α db 0 10

11 XPD Degradation (XPD: Cross-polarization discrimination) XPD defined in ITU-R P.310 A measure of polarization diversification H V H V V H P XPD = P R, CoPol R, XPol TX RX TX RX Multipath occurrence and precipitation degrade XPD 1 Techniques to Reduce Multipath Fading Using inclined path to reduce flat fading due to atmospheric mechanisms (beam spreading, antenna decoupling, and atmospheric multipath); Reducing the occurrence of significant surface reflections; Using terrain shielding, Moving reflection point to poorer location Using vertical polarization over water Prevention of larger value of clearance Using diversities 11

12 Space diversity Diversity Technique To combat specular surface reflection To combat surface multipath fading Angle diversity (two antennas in different orientation, in same or different heights) Frequency diversity, more than one frequency used for transmission 3 Interference Mechanisms Long-term mechanisms Short-term mechanisms 4 1

13 Long-term Interference Propagation Mechanisms (P.45) FIGURE 1 Long-term interference propagation mechanisms Tropospheric scatter Diffraction Line-of-sight Short-term Interference Propagation Mechanisms (P.45) FIGURE Anomalous (short-term) interference propagation mechanisms Hydrometeor scatter Elevated layer reflection/refraction Ducting Line-of-sight with multipath enhancements

14 Exercising SMS4DC 7 Types of RF Channel Arrangements Homogeneous channel arrangement Uniform channel arrangement = f + n XS MHz, n Non-uniform channel arrangement References: fn = f0 + foffset + n XS MHz, n = 0,1,,... f = f + f + n XS MHz, n 0,1,,... n f n 0 offset = 0 = ITU-R Recommendations, F series, CEPT Recommendations, 0,1,,

15 Homogeneous RF Channel Arrangements (F.746) Alternated RF channel Arrangement (A) Polarization H(V) V(H) 1 3 XS XS 4 XS N YS YS N ZS Alternated pattern Main frequencies Channel number A B Co-channel RF channel Arrangement (B) Polarization H(V) V(H) XS r r 3r 4r A N Nr YS DS r r 3r 4r B N Nr ZS Main frequency pattern Band re-use in the co-channel mode Channel number Interleaved RF channel Arrangement (C) Polarization H(V) V(H) XS XS r r 3r 4r XS A A: go channels B: return channels N Nr YS r r 3r 4r B N Nr ZS Main frequency pattern Band re-use in the interleaded mode Channel number 9 Uniform Channel Arrangement Suitable for Simplex operation mode More common in the bands shared between Fixed and Mobile The only choice for TDD transmission Transmitting and receiving will be down in different time slots 30 15

16 Exercising SMS4DC software (1) Link Calculation provided for following models in the menu of Propagation Model: ITU-R P.370 ITU-R P.1546 ITU-R P.56 ITU-R P.45, and ITU-R P.530 Step 1: Lunch the SMS4DC software Step : Lunch the DEM view using toolbar push button 31 Exercising SMS4DC software () Step 3: Establish Fixed station A using set the frequency to 890 MHz Step 4: Choose antenna ant_ale8603_806.ant and check the antenna pattern Step 5: Establish an other Fixed station B using set the frequency to 880 MHz Step 6: Choose antenna ant_ale8603_806.ant and check the antenna pattern Step 7: Open the administrative part from Database- >Licensing Step 8: Select Anonymous Station and find station B, 3 16

17 Exercising SMS4DC software (3) Step 9: Open Antenna Information Table of station B Step 10: Push the Modify button, Step 11: Change the field Class of Antenna from T to R Step 1: Push the Save button, Step 13: Find the station A and go to the level of Frequency Step 14: Push the Add Receiver button top of the Frequency Information table of station A. The Add Receiver dialog box will appear. Step 15: Select the Point Radio button. All the selectable receivers will be displayed in relevant spreadsheet 33 Exercising SMS4DC software (4) Step 16: Choose the station B from table under POINT section and push ok Step 17: Close Administrative dialog box Step 18: Open the Database menu and select Display Link. Step 19: Select the record of new established hop Step 0: Push OK button to display stations of selected hop on map 34 17

18 Exercising SMS4DC software (5) Step 1: Open the menu Propagation Model and select Link item under the ITU-R P.370 propagation model Push button to save profile Changing direction of calculation Values with colored background can be tried respect to the editable values 35 Exercising SMS4DC software (6) Step 1: Repeat step 1 for P.45 and P.56 propagation model. See the different calculated results Step : Repeat step 1 for P.530 propagation model. See the different calculated results Step 3: Use mouse drag to change antenna height and manage reflection points Step 4: Push Reflection Points button to see spreadsheet of reflection points Profile data 36 18

19 Exercising SMS4DC software (6) Step 5: Push Availability button to see the availability calculation result 37 End 38 19