Frequency shifting repeaters Application of the shifting concept in GSM 900
Connecting the Wireless World - 2004/01
Contents
The frequency shifting concept Technical description Application in the field Site selection Frequency planing
Connecting the Wireless World - 2004/01
Frequency Shifting
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When use frequency shifting
At sites with poor antenna isolation installations with high path loss (>100dB) very long distance from dedicated BTS (40 km have been realised so far) in rural areas with low traffic and low population
Connecting the Wireless World - 2004/01
Frequency Shifting
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System overview
The original signal f1 from the BTS is shifted to the link frequency f2 in the BTS unit. Then it is transmitted and received by the remote unit. There it is shifted back to the original frequency f1.
BTS
BTS Unit
Mobile
Due to the fact that the link frequency is inverted and not in the neighbour list, a mobile cannot log on the link frequency. Remote Unit
Connecting the Wireless World - 2004/01
Frequency Shifting
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Example: Levels in a shifting system
Direct coverage antenna (BTS)
Link antennas high gain, high f/b ratio
Coverage antenna
Path loss 120 dB (distance ca. 25 km) (for GSM 900 MHz)
BTS
BTS unit
Remote unit
Link budget DL: BTS unit ERP=43dBm; level at remote unit antenna: -77dBm Gain remote unit: 100 dB; input signal: -67 dBm=> output +33dBm Link budget UL: remote unit input =-70 dBm; output: +30 dBm; ERP: +40 dBm level at BTS unit: -80 dBm; input signal: -70 dBm=> output: -20 dBm
Connecting the Wireless World - 2004/01
Frequency Shifting
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Shifting concept principle
Conversion Steps : •Downconversion •Filtering •Upconversion (with Offset n*200 kHz) Offset is reversed after 2nd conversion
Connecting the Wireless World - 2004/01
fin
fout=fin +/- n * 200kHz offset
fo1+/- offset
fo1
Synthesiser
Control of local oscillator frequency and offset, locally or remotely
Frequency Shifting
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Frequency planning (1)
Aspects for coverage: Omni antennas can be used at remote unit for coverage Signal delay due to filtering: 11 - 12 Best solution: use dedicated sector or opposite BTS sector to avoid overlap
Connecting the Wireless World - 2004/01
Frequency Shifting
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Frequency planning (2)
At least 5 channels space between link and coverage channel. At least 3 channels below and above the link and coverage channels should be unused Multipath propagation should be avoided High gain narrow beam antennas should be used for the link to ensure best system performance In a two channel system the distance of the link channels should be different to the basic channels. The distance of a link channel to a original channel should not be same to the distance of the original channels p.e. if F1 of ch1 is 25 and F2 of ch1 is 35, neither F1 nor F2 of ch2 should be 15 or 45; and the distance of ch1 and ch2 should not be 10.
Connecting the Wireless World - 2004/01
Frequency Shifting
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Frequency spectrum
Other channel
Link channel
Other channel
Coverage channel
Other channel
Note:
At least 20 dB down
Max. the level of link and coverage channel
min. 5 channels space between link and coverage channel Best would be not to use 3 channels below and above link and coverage channel
Connecting the Wireless World - 2004/01
Frequency Shifting
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The BTS unit (MR351 BTS)
Frequency Range 890...915 MHz / 935...960 MHz Number of Channels: 2 Pout: + 33 dBm DL 5 dBm UL Gain: 50 dB min. DL 50 dB min. UL Noise Figure: 25 dB max DL 4 dB max UL Delay: < 6 µs typ.
Connecting the Wireless World - 2004/01
Frequency Shifting
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The remote unit (MR351 RU)
Frequency Range 890...915 MHz / 935...960 MHz Number of Channels: 2 Pout: + 33 dBm min. Gain: 100 dB min. Noise Figure: 6 dB max. DL / 3 dB max UL Delay: < 6 µs typ.
Connecting the Wireless World - 2004/01
Frequency Shifting
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Other types
MR350 former type, now replaced by MR351
Connecting the Wireless World - 2004/01
Frequency Shifting
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Block diagramm (DL)
Down-link channel of frequency shifting system. Note: frequency stability is very important for proper operation
Connecting the Wireless World - 2004/01
Frequency Shifting
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Location of modules
4
3
2 2
11
1
22
4
Conversion Module
Conversion Module Second Oscillator
3
Second Oscillator
Connecting the Wireless World - 2004/01
Frequency Shifting
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Donor BTS: Coupling the BTS unit
Antenna vs. directional coupler Significant for performance of both BTS and repeater system Levelling of BTS unit very important Take noise contribution into consideration
Connecting the Wireless World - 2004/01
Frequency Shifting
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Block diagramm of BTS unit
The BTS unit is normally equipped for combined connection. However, for separated connection (UL/DL) the input duplexer may be omitted.
Connecting the Wireless World - 2004/01
Frequency Shifting
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Block diagramm Remote Unit
The Remote unit is usually equipped with one RF connector for coverage antenna. Optionally a second RF connector with individual DL path may be equipped using air combining. Note that the two antennas have to be directed in the same direction as UL path is only received from one antenna. Connecting the Wireless World - 2004/01
Frequency Shifting
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Levelling a shifting system
Antenna Isolation not the limiting factor Gain vs. dynamic range Gain of remote unit should not exceed path loss Gain of BTS unit should not exceed coupling loss
Connecting the Wireless World - 2004/01
Frequency Shifting
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Operation & Maintenance
Standard ASCII User Interface O&M locally or remotely O&M remote Access through landline or wireless Modem O&M remote Facilities by Terminal Operation or automatically using OMC
Connecting the Wireless World - 2004/01
Frequency Shifting
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Operation & Maintenance Local access
Connect VT 100 Terminal Connector Communication parameters: 9600 Baud 8 Data Bits 1 Stop Bit No Parity Use ASCII command set
Connecting the Wireless World - 2004/01
Frequency Shifting
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Oeration & Maintenance GET commands
Interrogation of the Repeater’s parameters Examples: GET Displays all Parameters GET CHNL Displays set Channels GET ATT Displays set Attenuation GET TIME Displays System Time
Connecting the Wireless World - 2004/01
Frequency Shifting
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Operation & Maintenance Status Commands
Interrogation of the Repeater’s Status Examples: STATUS Displays all Info STATUS TEMP Displays Temperature STATUS AMP Displays Amplifier Stat. STATUS PWR Displays Power Supply Status
Connecting the Wireless World - 2004/01
Frequency Shifting
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Operation & Maintenance SET Commands
Setting the Repeater’s Parameters Examples: SET CHNL Set Channels SET ATT Set Attenuation SET TIME Set System Time
Connecting the Wireless World - 2004/01
Frequency Shifting
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Operation & Maintenance ACTION Commands
Perform certain Actions: Examples: STO SYNTH Store Synthesizer Status ALARMACKN Acknowledge Alarm manually BYE Log Out RES PW Reset Password
