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Transcript of Frequency_shift.pdf
Connecting the Wireless World - 2004/01
Frequency shifting repeaters
Application of the shifting concept in GSM 900
Frequency Shifting 2Connecting the Wireless World - 2004/01
Contents
� The frequency shifting concept� Technical description� Application in the field� Site selection� Frequency planing
Frequency Shifting 3Connecting the Wireless World - 2004/01
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
Frequency Shifting 4Connecting the Wireless World - 2004/01
System overview
BTS BTS Unit
Remote Unit
Mobile
The original signal f1 fromthe 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 theoriginal frequency f1.
Due to the fact that the link frequency is inverted and not in the neighbour list, a mobile cannot log on the link frequency.
Frequency Shifting 5Connecting the Wireless World - 2004/01
Example: Levels in a shifting system
BTSunit
RemoteunitBTS
Link antennashigh gain, high f/b ratio Coverage antenna
Path loss 120 dB(distance ca. 25 km)(for GSM 900 MHz)
Link budget DL: BTS unit ERP=43dBm; level at remote unit antenna: -77dBmGain remote unit: 100 dB; input signal: -67 dBm=> output +33dBm
Link budget UL: remote unit input =-70 dBm; output: +30 dBm; ERP: +40 dBmlevel at BTS unit: -80 dBm; input signal: -70 dBm=> output: -20 dBm
Direct coverageantenna (BTS)
Frequency Shifting 6Connecting the Wireless World - 2004/01
Shifting concept principle
Synthesiser
fo1 fo1+/- offset
fin fout=fin +/- n * 200kHz offset
Control of local oscillator frequency and offset, locally or remotely
Conversion Steps : •Downconversion•Filtering•Upconversion(with Offset n*200
kHz)
Offset is reversed after2nd conversion
Frequency Shifting 7Connecting the Wireless World - 2004/01
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
Frequency Shifting 8Connecting the Wireless World - 2004/01
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 besame to the distance of the original channelsp.e. if F1 of ch1 is 25 and F2 of ch1 is 35, neither F1 nor F2 of ch2 should be 15 or45; and the distance of ch1 and ch2 should not be 10.
Frequency Shifting 9Connecting the Wireless World - 2004/01
Frequency spectrum
Otherchannel
Otherchannel
Coverage
channel
Otherchannel
Link channel
At least 20 dB down
Note: min. 5 channels space between link and coverage channelBest would be not to use 3 channels below and above link and coverage channel
Max. the level of link and coverage channel
Frequency Shifting 10Connecting the Wireless World - 2004/01
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.
Frequency Shifting 11Connecting the Wireless World - 2004/01
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.
Frequency Shifting 12Connecting the Wireless World - 2004/01
Other types
� MR350 former type, now replaced by MR351
Frequency Shifting 13Connecting the Wireless World - 2004/01
Block diagramm (DL)
Down-link channel of frequency shifting system.
Note: frequency stability isvery important for proper operation
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Location of modules
Conversion Module
Second Oscillator
2 1 24 3 2 1 1 2 3 4
Conversion Module
Second Oscillator
Frequency Shifting 15Connecting the Wireless World - 2004/01
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
Frequency Shifting 16Connecting the Wireless World - 2004/01
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.
Frequency Shifting 17Connecting the Wireless World - 2004/01
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.
Frequency Shifting 18Connecting the Wireless World - 2004/01
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
Frequency Shifting 19Connecting the Wireless World - 2004/01
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
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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
Frequency Shifting 21Connecting the Wireless World - 2004/01
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
Frequency Shifting 22Connecting the Wireless World - 2004/01
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
Frequency Shifting 23Connecting the Wireless World - 2004/01
Operation & Maintenance SET Commands
� Setting the Repeater’s Parameters� Examples:
� SET CHNL Set Channels� SET ATT Set Attenuation� SET TIME Set System Time
Frequency Shifting 24Connecting the Wireless World - 2004/01
Operation & Maintenance ACTION Commands
� Perform certain Actions:� Examples:
� STO SYNTH Store Synthesizer Status� ALARMACKN Acknowledge Alarm
manually� BYE Log Out� RES PW Reset Password