The modulation error ratio or MER is a measure used to quantify the performance of a
digital radio (or digital TV) transmitter or receiver in a communications system using
digital modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...
(such as
QAM
Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signa ...
). 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 unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference aris ...
, low
image rejection ratio
Image response (or more correctly, image response rejection ratio, or IMRR) is a measure of performance of a radio receiver that operates on the Superheterodyne receiver, superheterodyne principle.
In such a radio receiver, a local oscillator ( ...
,
phase noise,
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 signa ...
, 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
*Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism
Vector may also refer to:
Mathematic ...
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 (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 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. 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 signa ...
, while noise is random by nature.
See also
*
Error vector magnitude
*
Carrier to Noise Ratio
*
Signal-to-noise ratio
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