Questions abotu MIMO Receivers

[vkekk]

I require informations about the below querrys...

What will be the impact if we choose 4 transmit antenna and 6 receiver antennas in MIMO systems?

Also in the reverse case ?

What is precoded OFDM and their advantages and disadvantages?

 

[salam2000]

Re: MIMO Receivers...

The Spatial gain equal min(Nt,Nr)
the diversity gain is NtxNr
therefor you can get more diversity with two additional receiver antenna.

in reverse case also you can get more diversity, but I saw that some cramer-rao bound are dependent to Nr only.

 

[vkekk]

Re: MIMO Receivers...

Thanks..

Please give some more points to understand for both cases with respect to spatial and diversity....

 

[mimomod]

Re: MIMO Receivers...

I require informations about the below querrys...
What will be the impact if we choose 4 transmit antenna and 6 receiver antennas in MIMO systems?

You'll have 4 spatial multiplexing (min(4,6)), the excess receive antennas will be only usefull to get more diversity.

Also in the reverse case ?

You'll get 4 spatial multiplexing, and since the number of receive antenna is less, then you'll get no additional diversity if you don't resort to more advanced design of transmitter. To be able to improve the performance of the system you may introduce precoding at the transmitter.

What is precoded OFDM and their advantages and disadvantages?

Precoded system in general will reduce the computational burden at the receiver. This is very useful for downlink (base station to mobile) where the mobile device can be very simple.

Disadvantage: to design a good precoder, the transmitter has to know the channel state which is many cases in not possible or too costly to implement. This channel state information has to be fedback from receiver to transmitter which means you need an extra bandwidth. There are many schemes to reduce the additional bandwidth.

best[/quote]

 

[vkekk]

Re: MIMO Receivers...

Dear mimomod

First many thanks to ur reply...

In VBLAST System , 4 transmit antenna and 6 receiver antennas are used . My question is whether all transmit antennas are using same carrier frequency or different.
vblast system is used for which application.

What are the functions of ZF equalizer and MMSE equalizers in BLAST .

Why we are using rich scattering environment in VBlast.

I NEED INFO. for my project. please help me.

 

[mimomod]

Re: MIMO Receivers...

Dear mimomod

First many thanks to ur reply...

In VBLAST System , 4 transmit antenna and 6 receiver antennas are used . My question is whether all transmit antennas are using same carrier frequency or different.
vblast system is used for which application.

What are the functions of ZF equalizer and MMSE equalizers in BLAST .

Why we are using rich scattering environment in VBlast.

I NEED INFO. for my project. please help me.

1. Yes the same carrier.

2. The real commercial applications of VBLAST is not yet there. But theoretically, you can use it to any kind of system which can affort multiple antenna at transmitter and receiver. Logically, you may only use 2 antenna at the most at mobile phone.

3. BLAST needs a decoding scheme to separate multiple signals (one signal gets interference from other signals). For that you need multiuser detector, i.e. equalizer. ZF equalizer separates the multiple signals based on zero-forcing criterion (see for example proakis), whereas MMSE based on minimum mean square error criterion.

best

 

[vkekk]

Re: MIMO Receivers...

IN VBLAST , no coding, only spatial multiplexing. how can we decode a strongest signal without coding at the transmitter and why QAM only used as a modulation.

For what application VBLAST developed and their frequency ranges because VBLAST provide higher datarate than SISO .


Iam new to this mimo field . so excuse me if anything wrong in my question.

 

[mimomod]

MIMO Receivers...

1. To decode the strongest signal, you will assume that the other signals are interference. It is the same as when you have multiple users in single input single output (SISO) environment. That's why you have to employ multiple user decoder at the receiver (ZF or MMSE equalizer, instead of just rake or matched filter). It is highly probable that you will decode the strongest signal right, then you substract the strongest signal from the original received signal, then you decode the strongest signal from the left, etc.

2. VBLAST is a decoding scheme for the case where Tx and Rx have multiple antennas and you want to transmit several signals together within the same bandwidth and at the same time. The separation between the signals is dependent on the spatial dimension, i.e. the antenna array and multipath.

3. Frequency range of the VBLAST dependent on the applications, i.e. wireless standard.

4. VBLAST itself is just decoding mechanism. The use of multiple antennas at Tx & Rx is the one which responsible providing higher datarate than SISO.

best

 

[vkekk]

Re: MIMO Receivers...

1. VBLAST is a decoder or receiver or equalizer or whole system.

2. Why we are using rich scattering environment in VBlast.

3. what is maximum likelihood principle?

4. ZF , MMSE and SIC algorithms are the receiver algorithms or decoder algorithms .
Can we use all this algorithms for performance analysis of MIMO receivers for Blast system.

 

[vkekk]

Re: MIMO Receivers...

Any help......