GSM Conformance Testing: A Comprehensive Overview

This article outlines the fundamentals of GSM conformance testing, covering both the physical layer and radio conformance aspects. It also touches upon the tools used for testing physical and Radio Frequency (RF) layers.

GSM, short for Global System for Mobile Communications, represents the second generation of cellular technology and remains in use in many parts of the world. It operates across various bands, including GSM850, GSM900, GSM1800, and GSM1900, each with distinct uplink and downlink frequencies.

The GSM system primarily consists of two entities: the mobile station (MS) and the base station (BTS). The BTS connects to infrastructure elements like the BSC, MSC, PSTN, and PSDN to provide cellular service and various applications. Communication between the MS and BTS relies on FDMA/TDMA techniques. GSM employs different channels for specific functions, facilitating signal and data exchange between the MS and BTS.

In a GSM mobile phone, there are three primary layers. Layer-1 encompasses physical layer modules and RF. Layer-2 is responsible for LAPDm, and Layer-3 manages RR, MM, and CM. GSM conformance tests are essential for evaluating the PHY, RF, and protocol stack layers. Consequently, separate documents detail GSM radio conformance and GSM protocol conformance specifications.

GSM Physical Layer Conformance Testing

The following tests are conducted as part of physical layer evaluation in GSM conformance testing:

• GSM Channel Tests (Signaling and Traffic): These tests verify the mapping of information (control/data) onto different channels and their proper decoding. They assess all physical layer functions, including channel coding, interleaving, ciphering, burst formatting according to its structure, and modulation (GMSK). Traffic channels include TCH/F and TCH/H. Signaling channels comprise broadcast, common control, and dedicated types. Broadcast channels are FCCH, SCH, and BCCH. Common control channels include PCH, AGCH, RACH, and CBCH. Dedicated control channels are SDCCH, SACCH, and FACCH. Each channel has its own specific function within the GSM system.

GSM Radio Conformance Testing

These tests, performed according to ETSI TS 100-910, GSM 5.5 Version 5.12, evaluate both the transmitter and receiver components of the GSM radio.

GSM Transmitter Tests

• Output Power: Varies based on power classes and bands (e.g., 39 dBm for power class-2 in GSM-900).
• Power Control Range: Spans levels from level-0 (39 dBm) to level-31 (5 dBm).
• Output RF Spectrum: Specifications define the power profile and levels at different frequency offsets from the RF carrier for bands like GSM900 and DCS1800.
• Spurious Emission: Non-integer multiples of the RF carrier frequency must remain below specified levels to ensure efficient operation, as detailed in ETSI TS 100-910 V5.12.
• Radio Frequency Tolerance: GSM version 05.10 outlines the requirements for base station and mobile station synchronization.
• Output Level Dynamic Operation
• Phase Accuracy
• Intermodulation Attenuation: This is measured as the ratio of the power level of the intended signal to that of intermodulation components.

GSM Receiver Tests

• Blocking
• AM Suppression
• Intermodulation
• Spurious Emission

GSM Performance Tests (Transmitter and Receiver)

• 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 Before Release

Beyond conformance tests, other tests are commonly performed before the release of a GSM mobile phone:

• GSM MO (Mobile Originating) Calls: Both circuit-switched and packet-switched.
• GSM MT (Mobile Terminating) Calls: Both circuit-switched and packet-switched.
• Handover Tests: Evaluation of handovers between GSM and other Radio Access Technologies (RATs) like CDMA, LTE, and TD-SCDMA.
• SMS Tests: Both Mobile Originating (MO) and Mobile Terminating (MT).
• Drive Tests: Assessing mobile compatibility in various channel and interference conditions across different RATs, including handovers.

GSM Conformance Testing Tools

The following are some of the tools used for GSM conformance testing: