GSM Measurements of mobile station (UE) as per 3GPP conformance tests
GSM measurements provide critical data about network performance, helping operators optimize services and troubleshoot issues. This page describes measurements for GSM mobile station (i.e. UE) in idle and connected mode in layer 1 (Physical Layer). 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 and 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 and 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, RF part, layer 2, layer 3). We will cover measurements related to RF (Radio Frequency) and physical layer of Mobile Station.
RSSI Measurements in IDLE and Connected Mode
• When user 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 (Radio Frequency) and baseband (layer-1) related measurements for GSM mobile as mentioned in the 3GPP conformance and other documents.
GSM Mobile Transmitter measurements
1. Frequency Error : It should be less than about 0.1ppm compare to Base station RF carrier frequency.
2. RMS Phase Error : It should not be greater than about 5 degrees. For detail refer 3GPP standard specified below.
3. Transmit Output power : The instantaneous power versus time depends on power class of UE (user equipment or mobile),
modulation technique (GMSK, 8PSK) and frequenct bands including GSM850, GSM900, DCS1800 and PCS1900.
4. Output Power control limit : Output power control can be varied based on varying level of attenuation.
5. RF power spectrum : Power spectrum mask is defined in the standard which specifies various power limits at different frequency offsets from RF center frequency.
6. Modulation Accuracy in EVM(rms) : Measures accuracy of modulated baseband signal(symbol vector).
7. I/Q gain offset : Gain offset between real and imaginary signals in the modem.
➨Note : For details on limit of the above refer 3GPP standard for conformance specifications.
GSM Mobile Receiver measurements
1. Frame Erasure ratio or Bad Frame Indication
2. Block Error measurement
3. Receiver Sensitivity
4. Received signal strength
5. Co channel rejection
6. Adjacent channel rejection
7. Intermodulation rejection
8. RF Spurious emission
9. AM suppression
Equipments for GSM measurements
➨GSM/EDGE signal generation and analysis toolkit and measurements suite from NI refer following link,
Refer : https://sine.ni.com/nips/cds/view/p/lang/en/nid/209228
➨Wireless communications test Equipment(model-8960,series-10) with GSM/GPRS/EGPRS test application suit(E1968A)
from Agilent Technologies, Refer : www.agilent.com/
➨Test and measurement solutions for GSM,GPRS and EGPRS (Model MD-8480C) from Anritsu corporation, Refer : www.anritsu.com/
➨VSG and VSA (various models: SMU200A,CMW-500 and CMU200 available) from R&S, Refer : www.rohde-schwarz.com
References :
• 3GPP,TS51.010-1, version 10.2.0,Release-10, MS conformance test document.
Conclusion
GSM measurements are indispensable for maintaining high-quality mobile services, offering valuable insights into signal strength, quality, and network efficiency. By monitoring these key metrics, network operators can make informed decisions to optimize performance and address any issues, ensuring seamless communication for users. These measurements play a crucial role in sustaining the reliability and effectiveness of GSM networks.