Modul 6 antenna & related equipments


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Describe about GSM Physical hardwares. Antennas, BTS Module, etc...

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  • Antenna downtilt (mechanical or electrical): directional antennas may be tilted either mechanically or electrically in order to lower the main radiation lobe.
    By downtilting the antenna radiation pattern, field strength levels from this antenna at larger distances can be reduced substantially. Therefore antenna downtilting reduces interference to neighbouring cells while improving spot coverage also. Two types of downtilting exist:
    Mechanical downtilting means that the antenna is pointed towards the ground in the main beam direction. At the same time the back lobe is uptilted.
    Electrical downtilting has the advantage that the antenna pattern is shaped so that the main beam and the back lobe are downtilted. In order to be able to control the interference situation it is better to use electrical down tilting.
    With omnidirectional antennas, mechanical downtilting is not applicable, but only electrical. Electrical downtilting is performed by internal slight phase shifts in the feeder signals to the elementary dipoles of the antenna system.
  • Diversity techniques are based on the fact that receiving multiple uncorrelated copies of the same signal, at the same or delayed time, can reduce fast fading dips. When two received signals are combined, the achieved signal quality is better than either of the partial signals separately.
    There are different diversity reception schemes (see Figure 17): both the base station and the mobile station implement time diversity already by interleaving. Frequency diversity can be achieved with frequency hopping: since fast fading is frequency dependent, many frequencies are quickly and cyclically hopped so that if one frequency is in a fading dip, it is just for a very brief time. Traditionally two base station receiver antennas have been separated horizontally (usually) or vertically (seldom) to create space diversity. In urban environment, the same diversity gain can be achieved by using polarisation diversity: signals are received using two orthogonal polarisations at the reception end.
    In the mobile radio channel multipath propagation is present. The delayed and attenuated signal copies can be combined in a proper way to increase the level of the received signal (multipath diversity). In GSM it is performed by an equaliser, while in W-CDMA (Wideband-CDMA) a so called "rake receiver" is utilized. The most used methods in cellular network planning are space and polarisation diversity, as far as base station antennas are concerned.
    Space Diversity
    Space diversity is a traditional diversity method, especially used in macrocells. Spatial antenna array separation causes different multipath lengths between a mobile station and a base station. Partial signals arrive at the receiving end in different phases. The two antenna arrays must be separated horizontally in order to achieve uncorrelated signals. Space diversity performs very well with macrocells in all environments, giving diversity gain of about 4-5 dB.
    In microcells, the large antenna configurations are not often possible due to site acquisition and environmental reasons. Antennas must be small and easily hidden. The amount of physical antenna equipment must be minimised. Antennas are often placed on lampposts or other existing structures, in which spatial separation is not possible. On the other hand, arranging the antenna arrays within one physical antenna doesn’t provide big enough separation between the arrays. Therefore other means of providing diversity is required in urban microcellular environment.
    Polarisation Diversity
    Uncorrelated signals can be provided without physical separation by applying different orthogonal linear polarisation at the receiving end. Signals can be received using for example horizontal and vertical or 45 slanted polarisation in cross-polarised antennas. The performance of polarisation diversity technique depends on the environment and the reflections between mobile station and base station. The more the partial signals reflect and diffract along the route, the more uncorrelated the signals are at the receiver, and the more gain can be achieved.
    The polarisation diversity gain can be measured as improved bit error rate (BER) or frame erasure rate (FER) at the receiver. In very dense urban areas, where narrow streets and high buildings surround the site, more than 5 dB diversity gain – equal to that of space diversity – has been measured. On the other hand, in the open areas and LOS situations, signal does not reflect enough on the way and cross-polarisation would not give any additional gain. This must be taken into account as slightly decreased signal quality with low field strength levels. Since cross-polarised antennas are small and suitable for urban areas, cross-polarisation diversity is the preferred diversity method for microcells.
    Two main combining methods are used to take advantage of the signals in space or polarisation diversity:
    Selection combining: every antenna signal branch is demodulated, C/I and bit error rates (BER) are calculated and then all signal branches are sampled at regular time intervals, always the best signal branch is selected for further processing. This method passes only a single branch and rejects all other signals.
    Maximal ratio combining: antenna signals are individually amplified at the same amplitudes, the signal phasing is assessed. Signal samples are added (vector addition) with correct phase adjustments. Then the combined signal is demodulated and further processed. This diversity method achieves a C/I improvement due to the fact that the wanted information (carrier signal) from different antenna branches are strongly correlated, while the additive noise components are uncorrelated (assuming white Gaussian noise process). In the superposition of both signals the wanted components will constructively add, while the noise components eliminate each other. (Note: If antennas are not sufficiently separated from each other, also the noise processes of both antennas will be correlated and the C/I improvement therefore decreases to zero.)
  • In link budget calculations, antenna diversity brings a signal improvement of ~ 5 dB. Note that this is not a physical improvement, i.e. a signal that is stronger by 5 dB (physically impossible), but rather an equivalent gain. The improvement in signal quality, i.e. in bit error rate, is the same as could be expected by a signal stronger by 5 dB. It is an “indirect gain”. This higher equivalent gain allows for a higher tolerable path loss, i.e. a larger communication range.
    One supplier company claims that by 3 dB more allowable path loss they could provide 20% more coverage range, i.e. 40% more coverage area per cell. Conclusion was, that therefore they need 40% less base stations to cover the same area size. This cunningly simple calculation is also stunningly wrong. It would be in theory true if the environment were infinitely large and flat, if there were exactly zero overlap between cells and the cells were placed exactly regularly and there were absolutely no obstacles within the entire area. This obviously is not the case in real life.
  • Modul 6 antenna & related equipments

    1. 1. GSM-GPRS Operation Antenna And Equipment Related Module 6
    2. 2. 2 Outline  Base station antenna specification and meanings  Antenna types and trends  Antenna Type And Developments  Other Elements
    3. 3. 3 BTS Logic Structure BSC Baseband subsystem Power supply subsystem RF subsystem Abis interface Um interface MS Antenna & feeder subsystem -48V/+24V
    4. 4. 4 Antennas Categories Omnidirectional antennas  radiation patterns is constant in the horizontal plain  useful in flat rural areas Directional antennas  concentrate main energy into certain direction  larger communication range  useful in cities, urban areas, sectorised sites
    5. 5. 5 RF Antenna and Feeder Sector¦A Sector¦A Sector¦A Antenna Feeder Jumper Jumper BTS cabinet Inner cable TX/RX MANT RXD
    6. 6. 6 Antennas - Antenna Gain  Measures the antenna´s capability to transmit/extract energy to/from the propagation medium (air)  dB over isotropic antenna (dBi)  dB over dipole (dBd)  Antenna gain depends on  mechanical size: A  effective antenna aperture area: w  frequency band  Antenna Gain: G A w= 4 2 π λ Pt Gain (Dbi) Isotropic radiated Power Equivalent isotropic radiated power: EIRP = Pt+Gain(Dbi) radiated power
    7. 7. 7 Technical Data B l a h b l a h b la h b l a h
    8. 8. 8 Antenna Properties Electrical properties  Operation Frequency Band  Input impedance  VSWR  Polarization  Gain  Radiation Pattern  Horizontal/Vertical beamwidth  Downtilt  Front/back ratio  Sidelobe suppression and null filling  Power capability  3rd order Intermodulation  Insulation Mechanical properties  Size  Weight  Radome material  Appearance and color  Working temperature  Storage termperature  Windload  Connector types  Package Size  Lightening
    9. 9. GSM-GPRS Operation Antenna Electrical properties
    10. 10. 10 Wavelength 1/2 Wavelength 1/4 Wavelength 1/4 Wavelength 1/2 Wavelength Dipole Dipoles 1800MHz 166mm 900MHz 333mm
    11. 11. 11 1 dipole (received power) 1mW Multiple dipole matrix Received power 4 mW GAIN = 10log(4mW/1mW) = 6dBd
    12. 12. 12 Gain = 10log(8mW/1mW) = 9dBi “Sector antenna” Received power 8mW “Omnidirectional array” Received power 1mW (Overlook Antenna
    13. 13. 13  GSM 900 : 890-960MHz  GSM 1800 : 1710-1880MHz  GSM dual band : 890-960MHz & 1710-1880MHz  eg.824-960MHz 1710-1900MHz  CDMA2000 1x Frequency Range
    14. 14. 14 Impedance  50Ω Cable 50 ohms Antenna 50 ohms
    15. 15. 15 9.5 W 80 ohms 50 ohms Forward: 10W Backward: 0.5W Return Loss 10log(10/0.5) = 13dB VSWR (Voltage Standing Wave Ratio) VSWR
    16. 16. 16  <1.5  Γ=(VSWR-1)/(VSWR+1)  RL=-20lg Γ
    17. 17. 17 Polarization Vertical Horizontal + 45degree slant - 45degree slant
    18. 18. 18 V/H (Vertical/Horizontal) Slant (+/- 45°)
    19. 19. 19  Linear,vertical  ±45 °dual linear ±45 ° slant
    20. 20. 20 Dipole Ideal radiating dot source (lossless radiator) eg: 0dBd = 2.15dBi dBd and dBi 2.15dB
    21. 21. 21 Pattern
    22. 22. 22 Beamwidth 120° (eg) Peak Peak - 10dB Peak - 10dB 10dB Beamwidth 60° (eg) Peak Peak - 3dB Peak - 3dB 3dB Beamwidth
    23. 23. 23 3dB Beamwidth Horizontal  Directional Antenna 65°/90°/105°/120 °Omni 360°
    24. 24. 24 Directional Omni-directional 3dB Beamwidth Vertical
    25. 25. 25  Mechanical down tilt  Fixed electronic down tilt  Adjustable electronic down tilt Downtilt
    26. 26. 26 Demonstration of Electronic Downtilt
    27. 27. 27 Non down tilt Electronic downtilt Mechanical downtilt
    28. 28. 28 Electronic and mechanical downtilt
    29. 29. 29 Antenna Downtilit – Whats goal ?
    30. 30. 30 Antenna Downtilt Consideration
    31. 31. 31  Ratio of maximum mainlobe to maximum sidelobe F/B = 10 log(FP/BP) typically 25dB Back power Front power Front to back ratio
    32. 32. 32 Upper Side lobes Suppression & Null Fill
    33. 33. 33 Sidelobes (dB) (dB)
    34. 34.
    35. 35. 35  Continuous :25-1500 watts  peak :n2 ×p Permitted Power
    36. 36. 36  IMD@2×43dBm  f1, f2, 2f1-f2, 2f2-f1 913MHz,936MHz,959MHz,982MHz Third Order Intermodulation
    37. 37. 37 Intermodulation  Intermodulasi  Terjadi akibat penguatan sistem yang non linier  Hanya orde ke-3 dan kadang-kadang orde ke-5 yang signifikan  Sinyal dengan amplituda yang sama menghasilkan level IM yang sama pada frek tinggi dan rendah  Sinyal dengan amplituda berbeda memberikan level IM yang berbeda pula  Untuk mencegah intermodulasi,penguat dioperasikan pada penguatan bukan- maksimum
    38. 38. 38 Intermodulation  Intermodulasi  Komp. Orde 1 : diharapkan linier  Komp. Orde 2 : frek 2ω  diredam oleh filter  Komp. Orde 3 : frek 3ω  diredam dengan filter Penguat Non-linier ( ) ( )tB tAv B Ai ω ω cos cos + = ++ += 3 2 i iio cv bvavv  Yang bermasalah :  Komponen yang lain  amplituda kecil ( ) ( )ABBA ωωωω −− 2,2
    39. 39. 39 1000mW ( 1W) 1mW 10log(1000mW/1mW) = 30dB Isolation
    40. 40. 40 10 Simple Guidelines for RF Safety  All personnel should have EME awareness training  All personnel entering the site must be authorized  Obey all posted signs  Assume all antennas are active  Before working on antennas, notify owners and disable appropriate transmitters  Maintain minimum 3 feet clearance from all antennas  Do not step in front of antennas  Use personal RF monitors while working near antennas  Never operate transmitters without shields during normal operation  Do not operate base station antennas inside equipment rooms
    41. 41. 41  PVC, Fiberglass  Anti-temperature, water-proof, anti-aging, weather resistant Radome Material
    42. 42. 42  Good-looking, environment- protecting Colour
    43. 43.
    44. 44. GSM-GPRS Operation Antenna Types and Development
    45. 45. 45 Antenna Types By frequency band: GSM900, GSM1800, GSM900/1800 By polarization: Vertical, Horizontal, ±45º linear polarization, circle polarization By pattern: Omni-directional, directional By down-tilt: Non, mechanical, electronic adjustment, remote control By function: Transmission, receiving, transceiving
    46. 46. 46 Broad band Multifunctional High Integrity Antenna Development Trend
    47. 47. 47  def = Attenuation between TX & RX antenna connectors  Horizontal separation  needs approx. 5λ distance for sufficient decoupling  antenna patterns superimposed if distance too close  Vertical separation  distance of 1 λ provides good decoupling values  good for RX /TX decoupling  Minimum coupling loss main lobe 5 .. 10 λ 1λ Antennas Decoupling
    48. 48. 48 Installation Examples  Recommended decoupling  TX - TX: ~20dB  TX - RX: ~40dB  Horizontal decoupling distance depends on  antenna gain  horizontal rad. pattern  Omnidirectional antennas  RX + TX with vertical separation (“Bajonett”)  RX, RX div. , TX with vertical separation (“fork”) Vertical decoupling is much more effective 0,2m
    49. 49. 49 •Time diversity •Frequency diversity •Space diversity •Polarisation diversity •Multipath diversity •interleaving •frequency hopping •multiple antennas •crosspolar antennas •equaliser •rake receiver t f Diversity Diversity Technics
    50. 50. 50 Diversity gain depends on environment Is there coverage improvement by diversity ?  antenna diversity  equivalent to 5dB more signal strength  more path loss acceptable in link budget  higher coverage range R R(div) ~ 1,3 R A 1,7 A ?? 70% more coverage per cell ?? needs less cells in total ?? True only (in theory) if the environment is infinitely large and flat Diversity Coverage Improvement?
    51. 51. 51 Network Elements MHA MastHead Amplifier (Low Noise Amplifier)  RX signal amplified near the antenna in the top of the mast  Offers better coverage  Eliminates the antenna cable loss  Increased receiver sensitivity of the BTS and cell size  Increased network quality Noise Figure £ 2.0 dB (typical) RX Gain: Up to 12 dB Dimensions : 266 x 130 x 123 mm Weight : 5.6 kg (duplexed) Volume : 4.2 l IP 65 Enclosure Protection Power Feeding Through Antenna Coax Alarms handled in BTS
    52. 52. 52 Booster • TX signal amplified • Nokia Booster Configuration • Booster (PA) Unit (TBU) • Booster Filtering Unit (AFH) • Masthead Preamplifier equipment (MHA) • Output power before combining can be up to 49 dBm  Isolator + combiner + filter (AFH) give roughly 2.5 dB losses  Booster BTS is suitable for all the environments where enhanced coverage or high output power is needed  Theoretically, cell radius is enhanced up to 60% and the coverage area is roughly the triple Network Elements Booster TRXTBUAFH
    54. 54. GSM-GPRS Operation End of Section 6 Antenna And Equipment Related