What does "Diversity" exactly mean?

[ks1267]

I have come across a word "Diversity" so many times when I read a paper in communication areas e.g. wireless, mimo-ofdm. There seems to be various definitions depending on the topic. This made me really confused what it exactly is.

e.g. I read in some MIMO paper below...

Two main advantages of MIMO systems:
1 Multiplexing
2 Diversity: the same signals sent through different parallel channels; the reliability of signal detection (bit error rate) improves.

However there is something like Diversity schemes and else.

Could anyone explain me what "diversity" exactly means. Thank you.

 

[kel8157]

I understand it this way, if you point a laser beam directly at a receiver, and another laser beam 45 degrees then reflect over a mirror and receive it at the same receiver, then at the receiver you have same signal from two sources, phase shifted. If the receiver has the capability so separate the two sources (aka equalization) then align them and add the two sources together, you get better receiption. Without equalization, the two signals add together and becomes interference to each other.. Of course in reality there are infinitely number of paths for RF waves..

then again, if the receiver can separate the two sources, it's better to transmit different data on the two paths, thus doubling data rate..

 

[Mazz]

there is a clear explanation of the diversity schemes on wikipedia:
https://en.wikipedia.org/wiki/Diversity_scheme

I hope it can help.

Mazz

 

[saeddawoud]

Simply, if you have, say, two antennas seperated several times the wavelength, then the sub-channels of these two antennas will be independent. So, if you transmit the same data stream on the two antennas, then you decrease the probability of error by a power of 2, and you got MIMO diversity .

However, if you send different data streams on the two antennas, then you got MIMO multiplexing by which you increase the data rate.

Of courcse, which to use depends on the enviroment itself, and you may switch between the two schemes of MIMO adaptively.

 

[amdyang]

maybe u can turn to D.tse `s famous paper in 2003
diversity and multiplexing: a tradeoff ...