Cloaking

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Taken from the following thread on the Star-OS forums:

http://forums.star-os.com/showthread.php?t=5419

The first thing that has to be understood is that both the AP and the CPE need to be able to "be cloaked". It doesn't work with one side only.

The second thing that has to be understood and is probably misunderstood by many is what channels or frequency range is used in typical 802.11b

A "typical" AP set up is using Channel *1*, Channel *6* and Channel *11* as "Center Channels" for a total of 3 AP's that are not overlapping.

Each sector actually uses 5 channels each. Channel 1 is Channels *1* ,2, 3 and the 2 before channel 1. Channel 6 is Channels 4, 5, *6*, 7, and 8 Channel 11 is Channel 9, 10, *11*, 12, 13


So each typical sector Ap using typical Channels 1, 6, and 11 are actually using "5" channels each, including 4 channels most aren't aware of, or rather frequency they don't see listed in their selection of channels. In each set of 5 channels the two outside channels are not full channels, but rather half channels with less power creating a buffer of unused frequency between the three typical AP sectors. Thus you have about 22MHz of space for each typical AP channels.

Star-OS V3 has 2 options for cloaking, using 1/4 the typical frequency range or 1/2 the typical frequency range.

Reducing the channel size from 22MHz to 5MHz (1/4) or 10MHz (1/2) wide is called cloaking.

With 1/4 th the typical frequency range channel size, you have 11 individual seperate channels and 1/2 gives you 6 seperate individual channels. Rather than the "typical" 3 channel layout of 802.11B


In addition to the 1/2 and 1/4 bandwidth used with each channel, there is also a 1/2 and 1/4 total throughput drop with each mode (as would be expected). A 1/4 (cloaking 4x) mode in 802.11g can produce speeds > 5Mbps (more than a typical 802.11b network), except that you now have 11 (or 13 depending on country) non-overlapping channels, instead of the standard 3.

This mode has the same effect with 802.11a.

With Cloaking, instead of the card's tx power being spread over the normal 20Mhz channel, it is focused on the 5, or 10Mhz band, and thus produces higher signal levels, which is great for those long-range links.

The cloaking modes also have a higher tolerance to interference, which is good for those RF congested areas.



You can think of it as an 'anti-turbo' in some ways. Using 2.4 for example, normal transmissions are 20 Mhz wide, provide X throughput, and require nobody noisy on the selected channel, plus two on each side of it. Turbo, is 40Mhx wide, provides about 2X the throughput (in theory) and requires pretty much the whole 2.4Ghxz band.

2x cloaking, are only 10Mhz wide, only have 1/2X throughput, but you can use twice as many channels. 4x is only 5Mhz wide, you can use every single one of the 11 channels without self interfering, and if there already are people on 1, 6 and 11, you can select channel 4 or 9 and sometimed sneak between their noise.

Everything is a tradeoff though - going from 5 to 10 to 20 to 40Mhz channels will increase throughput, but will increase the consumption and need for clear channels.


Cloaking cuts down on RF bandwidth and as a result it reduces the throuhgput. The X4 cloaking will still get more than a prism or orinoco card and it you can use compression it will get up to 10 mbps or almost double what you see with older 11B cards.

If you use X1 on channel 6 or 2437 MHz. This has 20 MHz RF bandwidth so the RF is 10 MHz on either side 2437, so it interferes with channels between 2427 and 2447.

If you use X2 on channel 6 or 2437 MHz. This has 10 MHz RF bandwidth so the RF is 5 MHz on either side 2437, so it interferes with channels between 2432 and 2442.

If you use X4 on channel 6 or 2437 MHz. This has 5 MHz bandwidth so the RF is 2.5 MHz on either side 2437, so it does not interfere with any channels because channels are 5 MHz apart. Of course this means it does not interfere with another X4 cloaked system but will still be seen as trouble for X2 or X1 systems, since they have the wider bandwidth.

There is no magic, just RF rules involved. You have to balance out the requirement for bandwidth and the desire for more channels and less interference.

2X cloaking requires 1 channel between, so your list is:

Channel 1 = uses 1,2

Channel 3 = uses 2,3,4

Channel 5 = uses 4,5,6

Channel 7 = uses 6,7,8

Channel 9 = uses 8,9,10

Channel 11 = uses 10,11

On 4X cloaking the non overlapping channels are: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11