Technical data

378 Chapter 12
GSM and EDGE Analyzer
Interpretation of GSM and EDGE Analyzer Measurement Results
GSM and EDGE Analyzer
standard specifies the Peak EVM not to exceed 11.0% during the useful part of the
EDGE burst, under all operating conditions, and excluding the effect of passive
combining equipment.
The EVM metrics are only reported for EDGE signals with their 8PSK modulation.
EVM is not reported for GSM signals, with their GMSK modulation, since this
measurement of signal quality is reported as the Phase Error metric.
95%tile EVM: This is the 95th Percentile of the EVM (Error Vector Magnitude). In
other words, it is the EVM value below which 95% of all measurements fall. EVM
is measured and calculated over the useful part of the burst, and is shown as a
percentage. The EVM figure represents the difference, in both phase and magnitude,
between a theoretically perfect signal and the actual signal received. The EDGE
standard specifies the 95th Percentile EVM not to exceed 11.0% during the useful
part of the EDGE burst, under all operating conditions, and excluding the effect of
passive combining equipment.
The EVM metrics are only reported for EDGE signals with their 8PSK modulation.
EVM is not reported for GSM signals, with their GMSK modulation, since this
measurement of signal quality is reported as the Phase Error metric.
Modulation Error Ratio (MER) and Carrier to Interference Ratio (C/I)
Modulation Error Ratio (also referred to as Carrier to Interference Ratio) is a
measure of signal quality that is similar to EVM. A measured signal can be modeled
as the sum of an ideal signal and an error signal. MER represents the ratio of the
ideal signal’s power and amplitude to the error signal’s power and amplitude. The
result is usually expressed in dB.
Although the Agilent E7495A/B base station test sets do not display the MER (or
Carrier to Interference Ratio) results, they can be calculated from the EVM result
using the following equation:
Modulation Error Ratio or Carrier to Interference Ratio = –20 * log(EVM/100) dB
Example: If you measure a signal and find its EVM to be 2.56%, the calculation to
find the MER or C/I is as follows:
MER (or C/I) = –20 * log(EVM/100) dB
= –20 * log(2.56/100) dB
= –20 * log 0.0256 dB
= –20 * –1.59176 dB
so EVM of 2.56% is equivalent to MER (or C/I) = 31.84 dB