Troubleshooting (GSM/EDGE/EDGE Evolution)

This topic contains information to help you troubleshoot measurements when using the GSM Global System for Mobile Communications: Originally developed as a pan-European standard for digital mobile telephony, GSM has become the world’s most widely used mobile system. It is used on the 900 MHz and 1800 MHz frequencies in Europe, Asia and Australia, and the 1900 MHz frequency in North America and Latin America./EDGE Enhanced Data for Global Evolution: A technology that gives GSMA and TDMA similar capacity to handle services for the third generation of mobile telephony. EDGE was developed to enable the transmission of large amounts of data at a high speed, 384 kilobits per second. (It increases available time slots and data rates over existing wireless networks.)/EDGE Evolution demodulator. Also see Setting up a GSM/EDGE/Edge Evolution Measurement for additional measurement information.

PROBLEM	POSSIBLE CAUSE	SOLUTION
Demodulation fails to lock on signal	Signal not present	Check connections
	Carrier too far from center frequency	Adjust Center Frequency
	Input is over-loaded or under ranged	Adjust Input Range
	Frequency span is too narrow	Increase frequency span
	Wrong symbol rate	Enter correct Symbol Rate
	Wrong modulation scheme	Specify correct modulation scheme, or set Modulation Scheme to Auto Select
	I/Q offset too large	Reduce LO feedthrough (or DC offset for I+jQ receiver)

Spectrum Disappears	Spectrum not present or digital demodulation not configured correctly.	View the spectrum trace (Trace > Data Spectrum) and also examine the time and search time traces (Trace > Data > Time or Trace > Data > Search Time). Use these traces to determine whether the spectrum is present and whether the digital demodulator is configured properly.

Eye diagrams show incorrect symbol timing	I and Q are misaligned using I+jQ receiver	Check cable lengths Adjust for delay using external calibration

SYNC NOT FOUND	Search length too short	Increase Search Length
	Incorrect filter selection for HSR signal	Make sure that the HSR Pulse Shape Filter parameter is set to Wide for high symbol rate signals.

PULSE NOT FOUND
	Search length too short	Increase Search Length or adjust triggering to ensure that leading and trailing edges of pulse are fully within search length
	Signal length not optimized	Try the following method to determine Search Length when performing a Pulse Search: SL = (2*MaxOn) + MaxOff Where:SL is search length in seconds. MaxOn is the maximum on time of a pulse in seconds. MaxOff is the maximum off time between pulses in seconds.

Pulse found but incorrectly aligned	Poor signal-to noise ratio or on/off ratio	Check Input Range setting Reduce span to eliminate excess noise and interfering signals.
	Time corrections disabled	Enable time corrections
	Span is too narrow	Increase span to prevent degradation of pulse edges

Error Vector Time shows regions of large errors	Distortion or a poor signal to-noise ratio causing bit errors	Check Input Range
	Large frequency errors interfering with carrier lock	Adjust Center Frequency
	Large I/Q offsets causing bit errors	Reduce LO feedthrough (or DC offset if using I+jQ receiver)

EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format. larger than expected and Error Vector Time shows errors that increase towards beginning and end of result length	Wrong symbol rate	Make fine adjustments to the Symbol Rate

EVM is high at the very start and very end of Error Vector Time, but good everywhere else	Signal has incorrect tail bits	Set the Synchronization Mode to RF Amp, or change the tail bits to match the GSM/EDGE/EDGE Evolution standards. Background: The tail bits are not shown but can affect EVM of neighboring bits when the Synchronization Mode is set to TSC or Polar Mod. In these synchronization modes, the VSA uses a Viterbi decoder with built-in knowledge of both the TSC sequence and the tail bits in order to provide robust demodulation of noisy signals. The decoder will cause errors from the tail bits to "leak" into neighboring bits.

EVM larger than expected and Error Vector Time shows a uniform distribution of errors	Frequency span too narrow	Increase span
	Incorrect filter selection for HSR signal	Make sure that the HSR Pulse Shape Filter parameter is set to Wide for high symbol rate signals.
	Input is overloaded or under ranged	Adjust Input Range
	Signal too close to DC	Increase carrier frequency
	I and Q misaligned using I+jQ receiver	Check cable lengths Adjust for delay using external calibration
	AC coupling when using I+jQ receiver	Select DC Coupling on both input channels
	I and Q imbalance	Ensure impedance is identical for both inputs

The trace data constellation symbol location shape, such as dots, is not properly displayed.	The display driver is not functioning correctly.	Contact your PC manufacturer to see if a newer version of the display driver is available. If not, try decreasing the hardware acceleration. See the Windows documentation for instructions.