Pat Calhoun Nov 6, 2007

I would recommend the following article:

An Overview of MIMO Communications—A Key to Gigabit Wireless
PAULRAJ, A.J.; GORE, D.A.; NABAR, R.U.; BOLCSKEI, H.;
Proceedings of the IEEE, Volume 92,  Issue 2,  Feb 2004 Page(s):198 - 218

William Burns Nov 28, 2007

re: 802.11n spatial diversity vs spatial multiplexing:
A bunch of questions:

Does the cisco 1250 series WAP use both techniques? Do you have to configure it to use one method vs. the other?

When it comes to spatial antenna diversity, is more better? Would greater spacing on 1250 antennas always be a good thing?

How would this be achieved, given that the only 2.4Ghz antennas officially for use w/ the 1250 are the AIR-ANT2430V-R triple-omni, and rubber-duck style antennas.

Is the dB loss from a TNC extender cable significant?

When you look at the 2.4Ghz TNC connectors on the 1250, which one is the receive-only connector?

Pat Calhoun Dec 2, 2007

William, it appears from the questions you are asking that you are trying to customize your AP 1250. I should note that Cisco does not endorse unauthorized modifications - further, there are certain FCC regulations that you should be aware of should this be your intent. It may be worth having a conversation with your Cisco wireless systems engineer.

In any case, to address your specific questions:

1. Does the cisco 1250 series WAP use both techniques? Do you have to configure it to use one method vs. the other?

The AP 1250 uses the basic mandatory MIMO technique in the 11n standard, it has a combination of both spatial diversity and multiplexing. The method used depends upon various channel feedback factors, including signal strength, and is handled on a per-station basis. Given Cisco’s focus on improving the overall wireless experience, I would expect this to be an area of significant innovation.

2. When it comes to spatial antenna diversity, is more better? Would greater spacing on 1250 antennas always be a good thing?

Spatial and antenna diversity are different, but related. The main contributions to performance gains from spatial antenna diversity include independent multipaths, number of antennas and, as you mention, antenna spacing. The higher the antenna count, the better. Similarly, the wider the antenna separation, the more the paths become uncorrelated, which increases diversity. It is, however, important to note that performance improvements do not continue to increase as either one of these factors are increased. You end up at a point where you get diminishing return on performance improvements.

3. How would this be achieved, given that the only 2.4Ghz antennas officially for use w/ the 1250 are the AIR-ANT2430V-R triple-omni, and rubber-duck style antennas.

I’m not quite sure where you got this information. The AP 1250 can be fitted with any TNC antenna. That said, I would point you to the Cisco webpage to look at the antennas we recommend, as well as their technical specifications: http://cisco.com/en/US/products/hw/wireless/ps469/products_data_sheet09186a008022b11b.html. Again, I would remind you on the FCC guidelines before you opt to deploy any custom antennas.

4. Is the dB loss from a TNC extender cable significant?

Losses incurred by cables are inevitable and an unfortunate fact of life.  But the amount of loss depends on the quality of cables and the freq.  You can find the dB losses from our ultra-low loss cables in the link above.  We have a 100 ft cable at Again, I would remind you on the FCC guidelines before you opt to deploy any custom antennas.

4. Is the dB loss from a TNC extender cable significant?

Losses incurred by cables are inevitable and an unfortunate fact of life.  But the amount of loss depends on the quality of cables and the freq.  You can find the dB losses from our ultra-low loss cables in the link above.  We have a 100 ft cable at <5 dB loss, which should not sacrifice any performance.

5. When you look at the 2.4Ghz TNC connectors on the 1250, which one is the receive-only connector?

It would be the middle of the three.

Shashindra kumar Singh Aug 28, 2008

When it comes to spatial antenna diversity, is more better? Would greater spacing on 1250 antennas always be a good thing?

How would this be achieved, given that the only 2.4Ghz antennas officially for use w/ the 1250 are the AIR-ANT2430V-R triple-omni, and rubber-duck style antennas.

Nancy Oct 31, 2008

Has Cisco released any adapters in the market to receive data from cisco aironet 1250 AP?