GSM Measurements for mobile station (UE)
This GSM measurements tutorial covers measurement performed by mobile station(UE) in idle and connected mode. It also covers conformance level measurements of GSM mobile.It also covers RSSI,BSIC measurements. Transmitter measurements include Frequency error,phase error,transmit output power,spectrum, modulation accuracy,I/Q gain offset.Receiver measurements include Frame Erasure ratio,Block Error measurement, Receiver Sensitivity ,Received signal strength,Co channel rejection,Adjacent channel rejection, Intermodulation rejection,RF Spurious emission,AM suppression.
GSM Mobile station is made of various layers and hence it requires extensive contents to cover measurements for each of these layers(layer 1(physical layer),RF part, layer 2, layer 3). This tutorial describes various GSM measurements which include measurement of Mobile station(UE) in idle and connected mode in layer 1. It also covers RF conformance measurements for GSM mobile.
When one switch on the GSM mobile it will be in idle mode until one connects with the network to bring the mobile in connected mode. There are two ways mobile can be brought to connected mode, viz. network initiated and mobile initiated.
In idle mode, mobile will perform frequency synchronization using frequency sync burst transmitted by BTS over FCCH.
It also does time synchronization with GSM hyperframe using synchronization burst transmitted by BTS over SCH.
SCH carries 25 useful bits, 19 is of reduced frame number(RFN)and 6 bits of BSIC. BSIC made of BCC(3bits) and NCC(3bits).
As mentioned RFN provides information on T1,T2 and T3' which provides information on frame number.
At the time of Radio Frequency planning in GSM network deployment, other than ARFCN, BSIC is uniquely alloted to each BTS. In GSM network each cell will be provided one broadcast downlink frequency and one broadcast uplink frequency. There are one or more downlink and uplink frequencies allocated for traffic channels. Remember that broadcast frequencies are used for signalling and traffic channels are used for voice/data packet.
RSSI measurements on ARFCNs (mainly broadcast frequencies) are performed. This is performed both in idle and connected mode on active and neighbour cells. BSIC(Base station identification and reconfirmation) is done on active and neighbour cells. BSIC helps mobile differentiate two similar broadcast frequencies from different cells.
In GSM systems, neighbour cells measurement are performed mainly in idle frames or during unused time slots.
GSM Mobile baseband/RF Conformance measurements
Following are the rf and baseband(layer-1) related measurements for GSM mobile as mentioned in the 3GPP published documents.
Frequency Error- It should be less than about 0.1ppm compare to Base station RF carrier frequency.
RMS Phase Error- It should not be greater than about 5 degrees. For detail refer 3GPP standard specified below.
Transmit Output power- The instantaneous power versus time depends on power class of UE(user equipment or mobile), modulation technique(GMSK/8PSK) and frequenct band(bands(GSM850,GSM900,DCS1800,PCS1900).
Output Power control limit- Output power control can be varied based on varying level of attenuation.
RF power spectrum - Power spectrum mask is defined in the standard which specifies various power limits at different frequency offsets from RF center frequency.
Modulation Accuracy in EVM(rms)- Measures accuracy of modulated baseband signal(symbol vector).
I/Q gain offset- Gain offset between real and imaginary signals in the modem.
For details on limit of the above refer 3GPP standard for conformance specifications.
Frame Erasure ratio or Bad Frame Indication
Block Error measurement
Received signal strength
Co channel rejection
Adjacent channel rejection
RF Spurious emission
GSM Measurements applications and equipment vendors
GSM/EDGE signal generation and analysis toolkit and measurements suite from NI refer following link,
Wireless communications test Equipment(model-8960,series-10) with GSM/GPRS/EGPRS test application suit(E1968A) from Agilent Technologies, www.agilent.com/
TEst and measurement solutions for GSM,GPRS and EGPRS (Model MD-8480C) from Anritsu corporation, www.anritsu.com/
VSG and VSA (various models: SMU200A,CMW-500 and CMU200 available) from R&S, www.rohde-schwarz.com
References: 3GPP,TS51.010-1, version 10.2.0,Release-10, MS conformance test document.