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GSM conformance testing basics

This article describes basics of GSM conformance testing.It covers GSM physical layer conformance and GSM radio conformance test specifications. The GSM conformance testing tools to test physical and RF (Radio Frequency) layers are also mentioned.

GSM is the short form of Global System for Mobile Communications. It is the second generation of cellular technologies which exists even today in most part of the world. It uses various bands GSM850, GSM900, GSM1800 and GSM1900. In each of these there are uplink and downlink bands separated. There are two main entities in the GSM system viz. mobile and base station (i.e. BTS).

Base station gets connected with infrastructure such as BSC, MSC, PSTN, PSDN to provide cellular service with various applications. Both Mobile (i.e. MS) and BTS communicate using FDMA/TDMA concept. There are different channels defined for specific functions in the GSM for signal/data flow between MS and BTS.

GSM conformance testing

There are three main layers in GSM mobile phone. Layer-1 covers Physical layer modules and RF as depicted in the figure. Layer-2 covers LAPDm, Layer-3 covers RR, MM and CM.

GSM conformance tests have been defined to test PHY, RF and protocol stack layers. Hence there are different documents which defines GSM radio conformance and GSM protocol conformance specifications.

GSM Physical Layer Conformance testing

Following tests are performed as part of physical layer tests in GSM conformance testing.
• GSM channel tests both signaling and traffic. This will test mapping of information (control /data) on different channels and their decoding process. This will test all the physical layer modules such as channel coding, interleaving, ciphering, burst formation as per its dedicated structure and modulation (GMSK).

Traffic channels include TCH/F and TCH/H. Signaling channels include broadcast, common control and dedicated types. Broadcast channels include FCCH, SCH and BCCH. Common control channels include PCH, AGCH, RACH and CBCH. Dedicated control channels include SDCCH, SACCH and FACCH. Each of these channels have different meanings in the GSM system operation.

GSM radio conformance testing

Following tests are commonly performed as per reference ETSI TS 100-910, GSM 5.5 Version 5.12 as part of gsm radio conformance testing. This tests include both GSM radio transmitter part and GSM radio receiver part.

Following are the GSM transmitter tests.
• Output power : It is different as per different power classes and bands. For example, 39dBm (power class-2, GSM-900)
• Power control range : level-0 (i.e. 39 dBm) to level-31 (i.e. 5 dBm) different levels
• Output RF Spectrum : The standard defines power profile with power levels at different frequency offset from the RF carrier for GSM900, DCS1800 etc.
• Spurious emission : Spurious frequencies are the non integer multiples of the RF carrier frequency. They should be below certain level compare to RF carrier in order to make it work efficiently. Refer ETSI TS 100-910 V5.12.
• Radio Frequency tolerance : GSM version 05.10 defines BS and MS requirements for synchronization.
•  Output level dynamic operation
• Phase Accuracy
• Intermodulation Attenuation : It is the ratio of power level of wanted signal to power level of intermodulation component.

Following are the GSM receiver tests.
• Blocking
• AM suppression
• Intermodulation
• Spurious emission

Following are the GSM performance tests for transmitter and receiver testing.
• Nominal Error Rate
• Reference sensitivity level
• Reference Interference level
• Erroneous Frame Indication Performance
• Random Access and paging performance at high input
• Frequency hopping under interference

Other GSM tests performed before release

We have seen above conformance tests which are specific to different layers of protocol stack used inside GSM phone. Following are the tests commonly performed before release of the GSM mobile phone.
• GSM MO (Mobile Originating) call both circuit switched and packet switched
• GSM MT (Mobile Terminating) call both circuit switched and packet switched
• Handover tests (GSM to other RATs(e.g. CDMA, LTE, TD-SCDMA) and viceversa)
• SMS tests both MO and MT
• Drive tests in order to test mobile compatibility under channel and interference conditions with different RATs (Radio Access Technologies) including handover.

GSM conformance testing tools

Following are the GSM conformance testing tools.

Vendor or manufacturer GSM conformance testing tool
Rohde & Schwarz R&S®TS8980 conformance test system for GSM, WCDMA, LTE.
TS8950G RF conformance testing for GSM/EDGE
Keysight technologies GS-8852 2G RF Conformance Test

What is difference between or comparison between

Following links mention difference or comparison between various equipments:
comparison between VSG and VSA
DIfference between SNA ans VNA
Oscilloscope Bandwidth versus Rise time
Oscilloscope vs Logic Analyzer
Difference between Oscillscope types
Comparison between spectrum and network analyzer