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


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


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.


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)


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 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 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 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


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.


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.


Other types

� MR350 former type, now replaced by MR351


Block diagramm (DL)

Down-link channel of frequency shifting system.

Note: frequency stability isvery important for proper operation


Location of modules

Conversion Module

Second Oscillator

2 1 24 3 2 1 1 2 3 4

Conversion Module

Second Oscillator


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


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.


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.


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


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


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


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


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


Operation & Maintenance SET Commands

� Setting the Repeater’s Parameters� Examples:

� SET CHNL Set Channels� SET ATT Set Attenuation� SET TIME Set System Time


Operation & Maintenance ACTION Commands

� Perform certain Actions:� Examples:

� STO SYNTH Store Synthesizer Status� ALARMACKN Acknowledge Alarm

manually� BYE Log Out� RES PW Reset Password

frequency_shift.pdf

Documents

wireless world

link frequency f2

link channels

frequency planning

coverage channels

theoriginal frequency

level of link

bts unit erp