Repeaters
Topics 1. 2. 3. 4. 5. 6.
Introduction to Repeaters Repeater Setup Considerations Procedure in Repeater Cell Setup Repeater Block Diagrams Frequency Shift Repeater Optical Repeater
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Introduction to Repeaters
Repeaters
Radio Repeaters • Radio repeaters, or Bi-Directional Amplifiers (BDA) Works as a bi-directional amplifier to increase the signal between mobiles and base stations, in uplink and downlink direction. −
Used for an area with poor coverage in outdoor and indoor environment, or for coverage enhancements in areas blocked by obstacles. − Uses a pick up (donor) antenna to receive and amplify the radio signal from a donor cell, and then retransmit from an antenna mounted near the area to be covered. − Complete local monitor function and powerful remote repeater network administration (OMC). −
• Typical applications include Indoor : conference centre, shopping mall, office building. Radio shadow areas : underground car parks, tunnels, valleys. − Coverage extension : motorways. − −
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Typical Repeater Setup BTS Donar antenna Repeater
Service area antenna
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Off-Air Repeater Application
Donor ANT Service ANT
BTS
Repeater Repeater Coverage
BTS Coverage
Extension of BTS Coverage
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Benefits of a Repeater • • • •
Fast rollout and fast coverage leads to fast return on investment Low build out costs No microwave link and No 2 Mbit- connection needed Less antennas and cable usage, and smaller space required for equipment.
• Easy to locate site for installation & coverage • Expands coverage areas in: rural, tunnels, in-building, canyons and highways • Platform for subscriber growth • Acts just like base station
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Types of Repeater Band Selective / Broadband • Pico repeater - Good for providing indoor coverage such as office, meeting room, function room and stairway etc. • In-line Booster - Boost signal power in feeder cables. Bandwidth Adjustable • Suitable for Inbuilding coverage.
dB
Typical 7 MHz
Typical 25 MHz
Typical 7 MHz
0 -3
-40 Centre frequency dB 0 -3
390 kHz
Operator's band
Frequency 390 kHz
• Outdoor coverage in rural and sub-urban areas. -40 Centre frequency
Repeaters
Frequency
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Types of Repeater Channel Selective • Suitable for providing coverage in high rise buildings. • Outdoor coverage in urban areas where frequencies reuse is tight.
approx 200 kHz
dB 0 -3
-40 190 kHz approx 200 kHz
dB
Hybrid Repeater • Suitable for use in synthesize frequency hopping network.
0 -3
190 kHz
Frequency
390 kHz
Operator's TCH band
390 kHz
-40 190 kHz
Centre 190 kHz
Frequency
frequency
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Repeater System Components
BDA To BTS
Yagi antenna
Panel antenna To MS service area
coaxial
coaxial Battery backup
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Donor Antennas • Donor antenna must be directed towards the donor cell (LOS) so that there is stronger received downlink power from BTS. − minimum downlink amplification needed. −
− −
minimum spurious or interfering signals; i.e. higher C/I. stronger uplink signals to the BTS.
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Donor Antenna • Popular belief that Yagis are best fitted as a donor antenna. −
Yagis have low gains and high horizontal sidelobe
levels.
Radiation pattern of a typical 12 dBi Yagi antenna Repeaters
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Donor Antenna •
30° - 40° corner reflector or log-periodic antennas are better suited with higher gain (~18dBi) and F/B ratio (> 40dB).
Radiation pattern of a 30 degree, 18 dBi corner reflector antenna
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Donor Antenna • Grid Parabolic Antennas are best suited for repeater applications. − −
Very high gain : 18 ~ 25 dBi Narrow beamwidth : < 10 deg
Radiation pattern of a typical 23 dBi grid parabolic antenna
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Service Antenna • Planar antenna with broad radiation pattern, depending on requirements lower gain antenna gives broader vertical beamwidth. − use radiating cable for better vertical fill. −
• • • •
Antenna is directed to the center of the coverage area. For tunnels, use Yagi antennas. For indoor, use special indoor antennas. Use minimum 7/8" coaxial cable to minimize loss
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Outdoor Repeater Applications • Most Repeaters Systems are interfaced with the common Outdoor and Indoor applications. We integrate Channel Selective Repeaters and Band Selective Repeaters to give coverage in rural and urban areas.
Repeater coverage for a main road
Island Coverage when microwave link is not possible / available
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Typical Coverage Improvements
Blk 135
Blk 135
Before
After
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Repeater Setup Considerations
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Antenna Isolation • A repeater can act as an oscillator if the signal feedback is greater than the gain. Isolation between donor & service antenna should be at least 10 - 15 dB more than system gain. − Fair distance from donor antenna for proper isolation is estimated to be 10-15m vertical spacing. −
• To measure, inject a known power into one antenna (or use tracking generator function), Spectrum & measure the Analyzer Donor level received by the other on a
Service
spectrum analyzer. isolation
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Factors Affecting Isolation • Antenna Pattern Antenna null should be pointing towards the other antenna. − Donor and Service antennas should have high F/B ratio. −
• Vertical Separation −
Narrow vertical aperture in the vertical antenna pattern.
• Environmental Separation Reflection and attenuation properties of materials near the antenna can influence isolation drastically. − Concrete towers improves isolation as signals are attenuated and reflected. −
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Effective Donor Path Loss (EDoPL) ERP
Donor
Repeater
Service
PLBTS-RR
PLRR-MS(max) Lcoax
Lcoax PLRR-MS(min)
EDoPL
MSmin
BTS
MSmax
• This comprises all losses and gains between the BTS output and the donor port of the repeater. • EDoPL is assumed to be equal for uplink and downlink. • EDoPL can be found by −
checking with the Switch the BTS power setting, PBTS;
connecting a spectrum analyzer to the end of the donot cable and reading the received level, Pin-rr; − EDoPL = PBTS - Pin-rr −
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Effective Donor Path Loss (EDoPL) • The uplink noise level arriving from the repeater to the BTS Nu = Nth-rr + Grr + NFrr - EDoPL where Nth-rr = thermal noise of a GSM channel (-121 dBm @ 20°C) Grr = uplink gain setting of repeater NFrr = repeater noise figure (typ 5 to 9 dB) • To minimize noise interference at the BTS, let Nu be 3 dB less than thermal noise of BTS, Nth-bts; i.e. Nu = -(121+3) = -124 dBm. • Assuming NFrr = 7 dB, the maximum repeater gain setting is determined by Nu = Nth-rr + Grr + NFrr - EDoPL -124 = -121 + Grr + 7 - EDoPL Grr = EDoPL - 10 Repeaters
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Repeater Saturation Downlink • Repeater input power (Pin) is too strong Pin (dBm) => Pout (dBm) - Minimum Gain (dB) − May need external attenuator −
• Repeater Gain set too High −
Maximum Gain (dB) <= Pout - Pin (dBm)
Uplink • Saturation is most important in indoor applications. MS goes into full power when switched on. The use of an indoor distribution network reduces the risk of saturation due to increased feeder and splitter losses. − −
• In outdoor, service antenna is usually mounted at a height. *Automatic Level Control will prevent repeater saturation Repeaters
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Timing Advance & Delay Spread • Repeaters have filters that cause delays of around 5 μs. reduces the maximum distance between MS and BTS from 35 km to 33.5 km. − Needs to be considered when implementation in rural areas. −
• Delay Spread can be compensated by the GSM system if the C/I > 9 dB or delay spread is less than 15.5 μs. − Placing the repeater between the donor BTS and the service area satisfies this requirement. −
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Interference & Handover • Band selective repeaters must be used with caution on sites close to the cell border Signal strength of donor and adjacent cells are close. May result in some calls being originated at an adjacent cell but outside its cell borders. − Donor antenna performance is important. − −
• Problem do not occur for channel selective repeaters Only the chosen GSM channels are repeated. − Superior to band selective for outdoor large area coverage. −
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Important Repeater Specifications • • • • • • •
Broadband, Band Selective, Channel Selective, Hybrid. Number of channels. Output power per carrier. Maximum gain and adjustable range. Noise figure. Automatic gain control. Spurious emission : ≤ 36 dBm in G9 band (ETS 300342). : ≤ 30 dBm in G18 band • Mean Time Between Failure (MTBF). • Other features remote connection via PSTN or GSM modem. − Interface to OMC. −
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Repeater Site Selection • Good LOS (Line Of Sight) with donor cell and intended coverage area. • Good donor signal level received at site. Example: A repeater with maximum 95dB gain and 37dBm output power requires a minimum input signal of -58dBm to produce max output power. −
• Sufficient antenna mounting space for good isolation. • Good air ventilation with shelter (preferred). • Easy access to repeater.
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Procedure in Repeater Cell Setup
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Steps In Setting Up Repeater Cell Pre-Installation Drive Test Repeater Design
Repeater Installation Repeater Commissioning
Post-Installation Drive Test Optimization
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Pre-Installation Drive Test • Determine drive test route for existing coverage area. • Identify weak spots. • Repeater Coverage Design
Before
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Repeater Installation Optimize Donor Antenna Spectrum Analyzer Service Donor
Isolation Measurement isolation
Configure Repeater
Test Calls
Optimize Coverage
Repeaters
Repeater Installation • Optimize Donor Antenna Direct Donor antenna towards donor cell. Scan for optimum donor carrier strength using spectrum analyzer. − Adjust antenna until maximum donor signal strength is achieved. − −
• Measurement of Coupling Loss (Isolation) Measure the signal received by the other antenna on a spectrum analyzer. − Isolation (coupling loss) is the difference between the 2 power levels. − Inject a signal of known power level into one antenna. −
• Configure Repeater Set to carrier frequency/bandwidth. Adjust Attenuation to achieve optimum DL & UL output power. − Set appropriate threshold for alarms. − −
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Repeater Installation • Test Calls − − −
Calls set up and voice quality. Test for any abnormal drop calls. Handovers between neighbour cells.
• Optimize Service Antenna −
Orientate antenna to achieve desired network coverage.
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Post-Installation Drive Test • Perform drive test on pre-determined route. • Verify coverage enhancement at weak spots. • Optimize repeater coverage Repeater Cell Blk 135
After
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Impact on Donor Cell • • • • •
Enhanced network coverage at affected areas. Increase in cell traffic. Possible congestion due to increase in traffic. Higher handover in donor cell due to increase in traffic. Higher drop calls due to more handover and traffic congestion.
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Repeater Block Diagrams
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Channel Selective Repeater ALC
C-ATT PA1 Channel Filter
M-ATT
20dB
f1
LNA1
f1 ALC
40dB
C-ATT PA2
Downlink -30dB Test
Donor Ant
f2
DT
Channel Filter
20dB
Mobile
DL Freq Select Module
f2
MT
ALC
C-ATT PA3
Ant
-30dB Test
20dB Mobile
Channel f1
Filter
M-ATT
f1
ALC
Uplink
PA4 C-ATT 20dB
OMT Computer with Data card
Channel
UL Freq Select Module
f2
Filter
Alarm Modem
Wireless Modem
LNA2
40dB
f2
Main Control Unit
Power Supply
Indicator
Li-ion BATT
External Power
OMC OMT
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Bandwidth Adjustable Repeater
ALC M-ATT
C-ATT
LNA1
PA1 Band
Test
Donor
Downlink
f1
Band
Filter f1 f2 Filter DL Freq Select Module
f2
Mobile
Ant
Ant DT
ALC
Test
C-ATT
M-ATT
PA2
LNA2
f2
OMT Computer with Data card
Modem
MT
Alarm Indicator
Band
Band
Filter
Filter
f2 f1 UL Freq Select Module
Main Control Unit
Uplink
Mobile
f1
Power Supply
Li-ion BATT
Wireless Modem External Power
OMT
OMC
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Band Selective Repeater
ALC M-ATT CDMA Freq FC1, FC2
C-ATT
LNA1 Downlink
-30dB Test
fC1, fC2
CDMA Freq PA1
Band
30dB f1
Donor Ant
FC1, FC2
15dB
Filter
f1
fC1, fC2
Mobile Ant
DL Freq Select Module -20dB Test
ALC C-ATT
M-ATT
Mobile
PA3
LNA2 15dB f2
Channel Filter
30dB Uplink
f2
UL Freq Select and PA Module OMT Computer with Data card
Alarm Modem
Indicator
Main Control Unit
Power
Li-ion
Supply
BATT
Wireless Modem
External Power
OMC
OMT
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Hybrid Repeater ALC
C-ATT
PA1
-30dB Test
M-ATT LNA1 40dB
Downlink
20dB
C-ATT 20dB
f1
Band Filter
f1+fo
f2
Band Filter
f2+fo
DL Band Freq Select Module ALC
PA2 Channel f3
Filter
f3+fo
DL Channel Freq
Donor Ant
Mobile Ant
Select Module ALC
DT
-30dB Test
C-ATT PA3
Mobile Band f2+fo
Filter
20dB
Band f2
f1+fo
Filter
f1
M-ATT
UL Band Freq Select Module
LNA2 40dB
ALC
C-ATT PA4 OMT Computer with Data card
UL Channel Freq Select Module
Wireless Modem
Alarm Indicator Modem
MT
f3+fo
Downlink
20dB
Channel Filter f3
Power Supply
Main Control Unit
Li-ion BATT
External Alarm Sensors
OMC External Power
OMT
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Indoor Band Selective Repeater
ALC
M-ATT LNA1
PA1 30dB
Band
Downlink
-30dB
f1
Test
Donor
Filter
f1+fo
Mobile
DL Freq Select and PA Module
Ant
Ant DT
MT
ALC
M-ATT PA2
LNA2 Band Filter
f1+fo
30dB
Mobile
Uplink
f1
UL Freq Select and PA Module
OMT Computer with Data card
Alarm Indicator Wireless
Power Supply
Main Control Unit
Modem
Li-ion BATT
Modem External Alarm Sensors
OMC
External Power 220VAC
OMT
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Indoor Wideband Booster
ALC
M-ATT LNA1
PA1 Downlink
Mobile Ant
Donor Ant
MT
DT
ALC
M-ATT PA2
LNA2 Mobile
Uplink
Computer with OMT Data card
Modem
Alarm
Main Control
Power
Li-ion
Indicator
Unit
Supply
BATT
Wireless Modem Power 220VAC External
OMT OMC
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Frequency Shift Repeater
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Limitations of a Conventional Repeater • High uplink noise, especially for band-selective and wideband repeaters Repeater coverage is uplink limited, based on thermal noise level reaching the BTS − Requires careful uplink gain setting −
• Difficulty in deploying high power repeaters Minimum isolation requirements or risk of oscillation − Requires careful choice of donor and service antenna −
• Requires large tower for effective implementation • Dependent on best donor traffic conditions • Mainly suited for use in indoor coverage
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FSR vs Repeater • A conventional repeater can act as an oscillator if the signal feedback is greater than the gain. −
−
Isolation between donor and service antenna should be at least 10 - 15 dB more than system gain. Fair distance from donor antenna for proper isolation; e.g. 15-20 m vertical separation and at least 120 degree horizontal separation for normal repeater setup for high gain operation
Isolation
Vertical Separation
• The FSR works on the principle that the output signal frequency of a channel selective repeater is shifted from the input frequency − −
lower antenna isolation requirement (e.g. 70dB for inband FSR regardless the system gain) Fair distance from donor antenna for proper isolation; e.g. 1-2 m vertical separation; less stringent horizontal separation requirement
Repeater
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Frequency Shift Repeater (FSR) • The FSR is a point-to-multipoint, frequency-shifting repeater system that overcomes antenna isolation problem in conventional repeater system. • Supports 2 or 4 channel frequencies. • Available in 2W, 10W or 20W. • Comprises of Master Unit (Direct or Wireless Coupling) and Remote Unit. • Available in GSM-DCS, GSM-GSM, DCS-DCS, GSM-CDMA, GSM-1.5GHz. • Wireless remote and local monitor function (OMT). • Optional powerful remote repeater network administration (OMC).
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System Applications • Point-to-Point using Direct Coupling Main Unit.
1800MHz RU
MU 900MHz 900MHz 900MHz
GSM BTS
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System Applications • Point-to-Point using Wireless Coupling Main Unit.
Internal or Ext Antenna
Internal or Ext Antenna
Wireless Coupling Main Unit
Remote Unit
GSM Mobile
GSM BTS
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System Applications • Point-to-Multipoint using Direct Coupling Main Unit. RU
F1
F2 MU
F2
F1
F2
F1 GSM BTS
F1
RU
RU
F1 F1
F1 F1 F1
F1
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System Applications • Point-to-Multipoint using Wireless Coupling Main Unit. RU
WC MU
F1
F1 F2
F1 F2 GSM BTS
F2
F1
RU
RU
F1 F1
F1 F1 F1
Repeaters
F1
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Optical Repeater
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System Block Diagram
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Main Unit Block Diagram
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Remote Unit Block Diagram
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Optical Repeater Applications • Fiber optic coupled Repeaters are often used for In- Buildings and also for some outdoor systems. • Airports and underground exhibition halls are some of the common areas where fiber optic repeaters are used.
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Summary 1. Introduction to Repeaters 2. Repeater Setup Considerations 3. Procedure in Repeater Cell Setup 4. Repeater Block Diagrams 5. Frequency Shift Repeater 6. Optical Repeater
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