Signal Guide

Service Description Selection GSM

Here you will find information about the selected service, along with measurement examples.

GSM Theory & Details
Communication
Typical Frequency Range:

Downlink 925 – 960 and 1805 – 1880 MHz
Uplink 890 – 915 and 1710 – 1885 MHz
Duplex spacing 45 bzw. 95 MHz

General:

The Global System for Mobile Communications (GSM) was developed by the Groupe Spécial Mobile (“GSM”). It is the standard for second generation (2G) mobile communications, being the first fully digital network to supplant the first generation analog systems. It is worldwide the most common mobile communications standard. Higher data transfer rates have been made possible by its further development, EDGE (enhanced data rates for GSM evolution) using an additional modulation method.

Modulation: TDMA, GMSK

Combination of frequency and time multiplexing. Frequency multiplex: MC (multi-carrier), RF channels 270 kHz wide, channel spacing 200 kHz (adjacent channels often unusable depending on level). Time multiplex: TDMA (time division multiple access), frame length 4.62 ms with 8 timeslots of 576.56 µs; 1 burst 546 µs, guard interval 30.4 µs. The bursts are GMSK modulated (Gaussian minimum shift keying with constant amplitude); 8PSK modulation is used for EDGE.

GSM Measurement Examples
Spectrum
Captures the entire downlink range of GSM-900 covering 925 – 960 MHz. Measured in »Stitched Mode«. Careful scrutiny allows TCHs (traffic channels) and BCCHs (broadcast control channels) to be differentiated: the BCCHs transmit continuously.
Spectrogram
Same range as Spectrum. The device delivers a “snapshot” every 169 ms. Capture is not simultaneous because the result in »Stitched Mode« is composed from several FFTs.
HiRes Spectrogram Full
The display shows several frames, covering 50 ms. Display width is 4 MHz, corresponding to 20 channels. Captured without time gaps.
HiRes Spectrogram Zoom
Section from HiRes Spectrogram Full. The time axis can be shifted as with a magnifier.
Persistence Spectrum
Light density display produced from the same data as HiRes Spectrogram Full.
Magnitude
The Scope display is more useful for GSM.
Scope
Display of 25 channels in parallel with 5 MHz CBW, without time gaps.