The modulation error ratio or MER is a measure used to quantify the performance of a
digital radio
Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services.
Types
In digital broadcasting syst ...
(or digital TV) transmitter or receiver in a communications system using
digital modulation (such as
QAM). A signal sent by an ideal transmitter or received by a receiver would have all
constellation points precisely at the ideal locations, however various imperfections in the implementation (such as
noise, low
image rejection ratio,
phase noise
In signal processing, phase noise is the frequency-domain representation of random fluctuations in the phase of a waveform, corresponding to time-domain deviations from perfect periodicity (jitter). Generally speaking, radio-frequency engineers ...
,
carrier suppression,
distortion, etc.) or signal path cause the actual constellation points to deviate from the ideal locations.
Transmitter MER can be measured by specialized equipment, which
demodulates the received signal in a similar way to how a real radio demodulator does it. Demodulated and detected signal can be used as a reasonably reliable estimate for the ideal transmitted signal in MER calculation.
Definition
An error vector is a
vector in the I-Q plane between the ideal constellation point and the point received by the receiver. The Euclidean distance between the two points is its magnitude.
The modulation error ratio is equal to the ratio of the
root mean square
In mathematics and its applications, the root mean square of a set of numbers x_i (abbreviated as RMS, or rms and denoted in formulas as either x_\mathrm or \mathrm_x) is defined as the square root of the mean square (the arithmetic mean of the ...
(RMS) power (in Watts) of the reference vector to the power (in Watts) of the error. It is defined in
dB as:
:
where P
error is the RMS power of the error vector, and P
signal is the RMS power of ideal transmitted signal.
MER is defined as a
percentage
In mathematics, a percentage (from la, per centum, "by a hundred") is a number or ratio expressed as a fraction of 100. It is often denoted using the percent sign, "%", although the abbreviations "pct.", "pct" and sometimes "pc" are also us ...
in a compatible (but reciprocal) way:
:
with the same definitions.
MER is closely related to
error vector magnitude (EVM), but MER is calculated from the average power of the signal. MER is also closely related to
signal-to-noise ratio
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in deci ...
. MER includes all imperfections including deterministic
amplitude imbalance
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...
,
quadrature error
Quadrature may refer to:
In signal processing:
*Quadrature amplitude modulation (QAM), a modulation method of using both an (in-phase) carrier wave and a 'quadrature' carrier wave that is 90° out of phase with the main, or in-phase, carrier
*Qua ...
and
distortion, while noise is random by nature.
See also
*
Error vector magnitude
*
Carrier to Noise Ratio
*
Signal-to-noise ratio
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in deci ...
References
* ''ETSI technical report ETR 290: "Measurement guidelines for DVB systems"'', Errata 1, May 1997
{{Noise
Quantized radio modulation modes
Radio electronics
Digital radio
Telecommunications