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. This should not be confused with In ...
(or digital TV) transmitter or receiver in a communications system using
digital modulation
Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information.
The process encodes information in form of the modulation or message ...
(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
Noise is sound, chiefly unwanted, unintentional, or harmful sound considered unpleasant, loud, or disruptive to mental or hearing faculties. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrat ...
, 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 enginee ...
,
carrier suppression,
distortion
In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...
, 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
Vector most often refers to:
* Euclidean vector, a quantity with a magnitude and a direction
* Disease vector, an agent that carries and transmits an infectious pathogen into another living organism
Vector may also refer to:
Mathematics a ...
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, the root mean square (abbrev. RMS, or rms) of a set of values is the square root of the set's mean square.
Given a set x_i, its RMS is denoted as either x_\mathrm or \mathrm_x. The RMS is also known as the quadratic mean (denote ...
(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 () is a number or ratio expressed as a fraction (mathematics), fraction of 100. It is often Denotation, denoted using the ''percent sign'' (%), although the abbreviations ''pct.'', ''pct'', and sometimes ''pc'' are ...
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 noise power, often expressed in deci ...
. MER includes all imperfections including deterministic
amplitude imbalance,
quadrature error and
distortion
In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...
, while noise is random by nature.
See also
*
Error vector magnitude
*
Carrier to Noise Ratio
In telecommunications, the carrier-to-noise ratio, often written CNR or ''C/N'', is the signal-to-noise ratio (SNR) of a modulation, modulated signal. The term is used to distinguish the CNR of the radio frequency passband signal from the SNR of ...
*
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 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