Global System for Mobile Communications (GSM)

2G (GSM) Global System for Mobile Communications

Frequencies	450 MHz,850 MHz,900 MHz,1800 MHz,1900 MHz
Frequency Range	450 MHz - 1900 MHz
Mode	RAW, AM, FM
Modulation	GMSK
ACF	—
Emission Designator	—
Bandwidth	200 kHz
Location	Worldwide
Short Description	GSM (Global System for Mobile Communications) is a standard developed by ETSI to describe the protocols for second-generation (2G) digital cellular networks used by mobile phones. As of 2014, it has become the default global standard for mobile communications.
I/Q Raw Recording	—
Audio Sample

GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile), is a standard developed by ETSIEuropean Telecommunications Standards Institute. An independent, not-for-profit, standardization organization in the telecommunications industry in Europe, developing global telecommunications standards. to describe the protocols for second-generation (2G) digital cellular networks used by mobile phones, first deployed in Finland in July 1991. As of 2014 it has become the default global standard for mobile communications - with over 90% market share, operating in over 219 countries and territories. As the need for more low-band 5G and 4G networks grow, operators around the world began phasing out GSM to re-farm spectrum. In the U.S, AT&T shut down GSM in 2017 while T-Mobile GSM continues to operate until 2024. In Australia, Optus GSM was decommissioned in 2017.

Samples

GSM Traffic Channels (TCHs)

GSM Non-Hopping Downlink, received with NFMNarrowband Frequency Modulation:

GSM Non-Hopping Uplink:

GSM Hopping and Non-Hopping Downlink, received with AMAmplitude Modulation:

Frequencies

Info from Wikipedia page GSM Frequency Bands

System	Band	Uplink (MHzMegaHertz (MHz) 10^6 Hz)	Downlink (MHzMegaHertz (MHz) 10^6 Hz)	Channel number
GSM-850	850	824.2 – 849.2	869.2 – 893.8	128 – 251
PCS-1900	1900	1850.2 – 1909.8	1930.2 – 1989.8	512 – 810
E-GSM-900	900	880.0 – 915.0	925.0 – 960.0	975 – 1023, 0 - 124
DCS-1800	1800	1710.2 – 1784.8	1805.2 – 1879.8	512 – 885

GSM-850 and PCS-1900 (shaded in blue) have been deployed in NAR and CALA (North American Region [Canada and the US], Caribbean and Latin America)

E-GSM-900 and DCS-1800 (shaded in yellow) have been deployed in EMEA and APAC (Europe, the Middle East and Africa, Asia-Pacific)

Decoding Software

Hobby Level Software

• Airprobe
• gr-gsm
• Deka A5/1 cracker

Professional Software

• go2DECODE
• go2MONITOR

Decoding Tutorials

• Analyzing GSM with an RTL-SDR

Video Examples

• Analyzing Cellular GSM with RTL-SDR (RTL2832), Airprobe and Wireshark

• Optus GSM 900 SDR Recording before the shutdown

Additional Links

• GSM For Dummies

• ETSI GSM Part 1: General Description
• ETSI GSM Part 2: Logical Channels
• ETSI GSM Part 3: Modulation
• Tutorialspoint GSM - Specification

• GSM Specifications
• GSM Spench.net

Additional Images

Spectrum of E-GSM-900 Band E-GSM-900 GSM-850 GSM-850 Hopping GSM Cell phone uplinks Hopping GSM Cell phone uplinks Non-Hopping Uplink TCH GSM base non-hopping, E-GSM-900 band Spectrum of non-hopping GSM downlink signal, E-GSM-900 band Spectrum of non-hopping GSM downlink signal, E-GSM-900 band Old GSM-based phone GSM Cell Antenna