802.11n Increased Range - How?

[kfarrington]

Hi All,

All the blub in the market place talks about 802.11n increased range from using multiple antennas. I would have thought there would have to be an increased power level also?

Am I missing something here?

Also, is the max power setting for any AP 100mw and does anyone have any test results (lets say in open space) of 802.11b/g/n range comparisons?

Many thx indeed,

Ken

[Matthew Fowler · Accepted solution]

Hi Ken,

For legacy (a/b/g) clients the increase in range, or increase in the distance before rates shift down, is due to Maximal Ratio Combining (MRC) and ClientLink (legacy beamforming).

MRC is done on the receiver; hence how legacy clients can benefit. All three antennas receive the signal, which gets combined and adjusted so all are in phase. This effectively boosts the signal (gain).

With ClientLink, when the client sends a signal, each antenna is going to receive the signal at a slightly different time and therefore slightly out of phase. Say it hits the right antenna, then middle, then left. To get the signal back to the client in phase, we flip the order and send on the last to receive first. So, left then right (middle antenna is Rx only). Again, because the signals will arrive in phase, there will be gain.

Maximum range isn't increased all that much, but the range until rates shift down is increased - increasing overall cell throughput.

Check out:

http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps10092/white_paper_c11-516389_ns767_Networking_Solutions_White_Paper.html

-Matt

[kfarrington]

Matt, Many thx mate. MRC looks cool and have to do some research on this now :)

I was wondering how this was acheived.

Many thx

Ken

[Robert.N.Barrett_2]

I don't think it applies to 802.11b clients. All the MRC/ClientLink work is via OFDM (802.11g/a).

[Rob Huffman · Accepted solution]

Hey Ken,

Hope life is treating you well my friend!

Just to add a touch to the great explanation from Matt (+5 points here Matt :)

I thought that these presentations were excellent in explaining the "N" characteristics, especially the testing results! Have a look;

Cisco & Intel 802.11n Performance Results

http://tools.cisco.com/cmn/jsp/index.jsp?id=78662&redir=YES&userid=(none)

Hope this helps!

Rob

PS: My take on this is that the real "Buzz" is the "Throughput" improvements moreso than the "Range" improvements :)

[kfarrington]

Hey mate,

All is cool. How are you doing fella? Im needing a beer again :)

Rob, Excellent resources mate. Going thru them in detail now :)

Thx

Ken