In
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than tha ...
s, maximum-ratio combining (MRC) is a method of
diversity combining Diversity combining is the technique applied to combine the multiple received signals of a diversity reception device into a single improved signal.
Various techniques
Various diversity combining techniques can be distinguished:
* Equal-gain co ...
in which:
#the signals from each
channel are added together,
#the
gain
Gain or GAIN may refer to:
Science and technology
* Gain (electronics), an electronics and signal processing term
* Antenna gain
* Gain (laser), the amplification involved in laser emission
* Gain (projection screens)
* Information gain in d ...
of each channel is made
proportional
Proportionality, proportion or proportional may refer to:
Mathematics
* Proportionality (mathematics), the property of two variables being in a multiplicative relation to a constant
* Ratio, of one quantity to another, especially of a part compare ...
to the rms
signal level
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 dec ...
and inversely proportional to the mean square
noise level in that channel.
#different proportionality constants are used for each channel.
It is also known as ratio-squared combining and predetection combining. Maximum-ratio combining is the optimum combiner for independent
additive white Gaussian noise
Additive white Gaussian noise (AWGN) is a basic noise model used in information theory to mimic the effect of many random processes that occur in nature. The modifiers denote specific characteristics:
* ''Additive'' because it is added to any nois ...
channels.
MRC can restore a signal to its original shape. The technique was invented by American engineer
Leonard R. Kahn in 1954.
MRC has also been found in the field of neuroscience, where it has been shown that neurons in the retina scale their dependence on two sources of input in proportion to the signal-to-noise ratio of the inputs.
Example: Least Squares estimate in the case of Rx diversity
We consider an example of which the receiver is endowed with N antennas. In this case, the received vector
is
where
is noise vector
. Following the ML detection criterion the detection procedure may be written as
where
is the considered constellation of
and
is the least square solution to the above model.
The least square solution in this case is also known as maximum-ratio-combining (MRC). In the case of N antennas the LS can be written as
which means that the signal from each antenna is rotated and weighted according to the phase and strength of the channel, such that the signals from all antennas are combined to yield the maximum ratio between signal and noise terms.
References
*
External links
Siae Microelettronica patent">Siae Microelettronica">Siae Microelettronica
patent
Telecommunications techniques
Radio resource management
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