What is space diversity and spatial multiplexing?

[vkekk]

Dear all ,

Pls help me to understand the below..

* What is Space diversity?

What is spatial multiplexing?

Why MIMO systems are popular? and their applications.

 

[toshine]

Re: Diversity.....

Hi,

First, I should confess that I am not very familiar with MIMO. However, I would like to give u my understanding.

* What is Space diversity?
Assume that there are two antennas in the transmitter end. Then, we can use the two antennas to send the same data. Since the two antennas are set far enough from each other, the same data are transmitted to the receiver via different paths, i.e., experiencing different fadings. This is referred to space diversity, or more clearly transmit diversity. Similarly, we could use two antennas in the receiver end to observe the corrupted data. This is called receive diversity.
In summary, space diversity is achieved by observing the data from different paths in the space. The main objecitve of space diversity is to combat channel fading and thus to provide reliable communications. This can be easily explained by realizing that the probability of two versions of the same data are both in deep fade is small.

* what is space multiplexing?
Different from space diversity, space multiplexing is used for high throughput. Again, assume that there are two antennas in the transmit end. Now, we send different data at the two antennas, then the total thoughput is doubled. However, data reliability is not guarenteed.

From above discussion, we can see that it is up to u to use antennas for space diversity or space multiplexing. Antennas can be used for diversity thus providing reliability, or for multiplexing to improve throughput.

In fact, there is a basic tradeoff between diversity and multiplexing. For more details, plz refer to David Tse and Lizhong Zheng's paper in IEEE Trans. IT.

*Why MIMO systems are popular? and their applications
Today, there are already many communicastions systems in use, which have occupy most of the available bandwidth. In another, customers ask for more communication services, such high quality movies via wireless channels. Hence, bandwidth efficient communications is required. With current technologies, which uses only one antenna at both communication ends, it is very difficult to achieve this goal. However, multiple antennas can achieve this goal.
Information theoretical analysis reveals that MIMO can greatly improve the capacity of communication systems, which grows almost linearly with the minimum number of the numbers of antennas in both ends.

 

[esfahanianboy]

Re: Diversity.....

Wireless communication, Tse, .. is the best ref on the topic

 

[vkekk]

Re: Diversity.....

Many thanks to ur reply...

That means Space multiplexing and spatial multiplexing are equal or different?

Why spatial multiplexing is only occured in BLAST(Bell layered space time) system.. Can you please give some information about BLAST and SISO systems....



Thanks in advance