Why Rr >Tr in MIMO ?

[vkekk]

In MIMO Concepts, we are using more no of receiver antenna than no of transmitter antennas. ( eg. Tr = 4 , Rr =7 where Rr is no of receiver antennas).

Can anybody help me to understand, why Rr >Tr ? because iam thinking equal no of Rr and Tr is enough to achieve good performance in terms of gain..

Please share yours suggestion ...

 

[A.Anand Srinivasan]

Re: Rr >Tr ....MIMO

the correlation between the different signals received leads to effectively finding the correct signal... so more number of receivers means better noise rejection...

 

[vkekk]

Re: Rr >Tr ....MIMO

How more number of receiver antennas provides better noise rejection? because at the receiver we received a signal which is interfered with other signals, so in what way it achieves better noise rejection .( for example take, V-BLAST architecture have Rr>Tr )..

 

[farzad_m]

Rr >Tr ....MIMO

the answer is that we always assume that we can achieve channel parameter at the receiver so we can exploit receive diversity and the more the number of Rx antennas the better diversity we have at the receiver but in the transmitter we dont have channel estimation unless we feedback it from the receiver so Tx antenna cannot provide diversity.
this is also obvious from shannon capacity formula for MIMO systems that shows that MISO has the same capacity as SISO.

 

[A.Anand Srinivasan]

Re: Rr >Tr ....MIMO

it is principally done assuming that more than 50% of the receiver antenna will decide on the correct output... the more the number of receiver the more the probability of right answer.... assuming the channel is not that highly noisy...

 

[vkekk]

Re: Rr >Tr ....MIMO

what do you mean ''assuming the channel is not that highly noisy''.

 

[A.Anand Srinivasan]

Re: Rr >Tr ....MIMO

they usually assume some boundary conditions while using a expression or distribution.... a highly noisy environment would definitely violate these conditions,,,...

 

[mkhan]

Re: Rr >Tr ....MIMO

In MIMO Concepts, we are using more no of receiver antenna than no of transmitter antennas. ( eg. Tr = 4 , Rr =7 where Rr is no of receiver antennas).

Can anybody help me to understand, why Rr >Tr ? because iam thinking equal no of Rr and Tr is enough to achieve good performance in terms of gain..

Please share yours suggestion ...

Hi,

I did not read all the discussion on this topic, but here is my answer.
Lets assume DL. BS is Transmitter and MS are receivers. Now NT (number of transmit antennas at BS) can be and usually are more than One. NR (number of receive antennas at each MS) can be more than ONE there is no restriction BUT due to some practical factors they r considered as ONE, so NR = 1. NU(number of user) in the system are usually more than the NT, and as each NU has NR =1, so does NR > NT.
Hence in conclusion the scenerio will be:
NT > 1
NR = 1
NU > NT
and NR*NU > NT.

Thats why when u model ur channel its dimensions are usually (NU*NR \times NT).

BR,

MAK

 

[behy]

Re: Rr >Tr ....MIMO

if u review the capasity formulations of MIMO systems, u can see that useing T>R have no effect on the capasity but if u choose R>T u can improve the capasity