Difference between maximum ratio combing and adaptive beamforming

On Fri, 20 Apr 2007 13:23:26 -0500, "philgo" <philgo@gmail.com> wrote:

>Let me try to rephrase the question.
>
>In traditional beam-forming, we are always talking about angles, angle of
>arrival, angle of departure, beam pattern pointing to a certain angle,
>etc.
>However, when we talk about the MRC, the concept of angle disappears and
>what we cared is only maximizing the SNR (or some other related metric). 
>
>Why we do not see/talk about the angles any more in MRC? I try to answer
>this question. Please share your comments and criticism.

I'll share my intuitive perspective and see whether it helps anything:

Beamforming requires coherence (i.e., phase alignment) between the
inputs to form and steer the beam as desired.

MRC only adjusts the inputs with a scale factor, so no beamforming is
taking place.   That's good because, as you've stated, each antenna
may be collecting energy from different reflected directions, so
forming a coherent beam may reduce the total amount of energy
collected and hurt rather than help.

Beamforming discriminates the direction in which energy is collected
by adjusting relative phases.   Some energy may be rejected in the
process.

MRC uses all of the energy collected by all antennas combined to
maximize SNR.

They're two very different techniques, but each have their purpose and
place.

I like the simplicity and elegance of MRC, though.   The fact that
it's more or less optimal in some conditions is just icing on the
cake.   ;)

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org