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My situation: there are 7 profiles being used in a controller and distribute to several APs and ARM feature enabled. By using InSSIDer, there are 7 different Virtual MAC address map to corresponding virtual SSID but come from one nearby AP, and they are all assigned a channel 1.
My question: will different virtual SSID with the same channel have co-channel interference problem?

Many thanks!

Sure!

If I understand your description correctly, any AP on channel one will interfere with another AP on the same channel ... IF they are too close together for the power levels they are using.

All devices on the same AP will share the channel bandwidth, but that is not co-channel interference.

I agree with wlanman, and perhaps the situation bears more explanation. I believe what you are describing is an AP with multiple SSIDs (and thus, multiple BSSIDs), and they all show up on the same channel. This is the expected normal behavior. These SSIDs are all tied to one 2.4 GHz radio, and that radio must tune to a specific channel, so all BSSIDs for that AP will show up on the same channel. Client devices connected to this radio will all contend with one another for the same limited bandwidth.

May I ask more... what is the difference between one AP (w/ one antenna) with multiple SSID and one AP (w/ 3x3 MIMO) with multiple SSID regarding to the above situation? Thank you!

Let's say we have two APs. Both can operate in 2.4ghz ad 5ghz simultaneously. Both aps have 3 different ssids. One is a single antenna ap and the other is a 3x3 mimo.

Both APs will broadcast 6 different bssids.

I believe an AP will only broadcast beacons on a single antenna no matter how many antennas. This is why we can not aim the antennas in different direction. They must cover the same area.

It isn't recommended to have so many SSIDs on one AP.... Just saying.

Sean

802.11n utilizes some very sophisticated digital processing and electronics to help "make sense" of the modulated ( "modulated" being the key term here ) RF signals which are "picked up" by the particular device's antennae. The signal processing systems within the client device or AP are able to "look" at the waveforms which are incoming and try to "combine them"( the term "combine" is used very loosely here without getting into the mathematics of how the processing operates ) in order to maximize the received carrier to noise ratio.

Imagine an office scenario in which 802.11n is being utilized. People are moving around, doors are being opened and closed etc. The entire RF environment ( temperature, humidity, objects which reflect, diffract etc ) is changing on both a microscopic and a macroscopic level, minute by minute, second by second, millisecond by millisecond etc.

Imagine that we have an 802.11n AP somewhere in the office space, with say, two antennas and a bunch of clients. Without getting into complications of asymmetry here, let?s imagine that each client has two antennae with two radios.

Beacons are the ?lifeblood? or ?heart? of a Wi-Fi system. They are an absolutely essential component, providing all sorts of information from ?I?m alive !! My name is XYZ !!? to ?Here?s what I?m capable of doing?let me know what you?re capable of doing. If we can both do the same things?great !! If not, for example if you cannot transmit as fast as me, let?s talk about it and come up with a mutually agreeable speed??

Now let?s imagine that the AP transmits and the client listens. The AP transmits some data over both it?s antennas. The data has been modulated and an analog ( not digital as many texts wrongly state ) RF signal has been transmitted out both antennae. The signals spead, and bounce and refract and reflect and diffract and do all the stuff that RF signals do. They are then picked up by the client radios and the internal processing begins to ?get the best signal mix?.

In other words, modulated RF signals have been sent from both AP antennas.

Now let?s imagine that we only sent beacon signals over one antenna. We could have a number of options here. Beacon out one antenna, nothing out the other. Beacon out one antenna and ?regular? ( spreadsheet, e-mail, VOIP etc ) data out the other. Beacon out one antenna and a clean carrier out the other.

In the latter two scenarios, the receive electronics would become totally confused, as in the second case interference would occur between two signals at the same frequency but carrying different data ( beacon data in one and e-mail data, say, in the other ). In the third case, we would have a modulated RF carrier ( beacon data ) being interfered with, by a clean carrier.

This now leaves us with the first scenario of having the beacon data going out one antenna only. You could do this. There is absolutely no reason ( electrically ) why not. However, we would be sort of ?shooting ourselves in the foot? here, as we would ?miss out on? all the benefits of multi-transmission that 802.11n brings to the table.

So, if we are going to transmit data ( be it beacon or regular old ?data? data ) we need to make sure that the same signal is broadcast from all antennas. If we have a ?mix? as previously mentioned, we will be causing interference in our own network. If we only use one antenna, we are not getting the most for our money from 802.11n.

Hope that makes things a little clearer.

Dave

By the way, in satellite communication systems, we CAN transmit beacons from one antenna and have data coming simultaneously from another antenna. However, a special receiver is needed to receive and interpret the data coming in from the beacon ( satellite temperature, fuel reserves etc ). That beacon signal is on a dedicated frequency and antenna. Many satellites use parabolic antennas to focus their beams on earth. When the satellite is first deployed from the launch vehicle, it will be spinning and may be tumbling. If we used a parabolic antenna at that point, the ground tracking stations ( TTC+M...Tracking, Telemetry, Command and Monitoring ) would only see a "pulse", then dead time, then a "pulse" as the satellite was spinning and tumbling. In that initial stage, we would normally use an omnidirectional antenna so that irrespective of the satellite's physical position, we would always be able to "see it" from the ground. Once communications are established between the ground station and the spacecraft, the spinning can be regulated ( not all satellites are meant to spin normally ) and any tumbling can hopefully be corrected by firing thrusters for example. Once the spacecraft is stable and it's communications antennas are pointed to earth, the beacon is usually switched to an earth pointing horn type antenna ( for example ) as opposed to the omni which was used in the initial acquisition phase.

How does the satellite know it is pointing to the earth ? Special sensors output a pulse when they detect the edge of warm earth ( the earth radiates electromagnetic energy ) verus cold space. Some satellites utilize star trackers ( onboard memory contains celestial maps of where certain bright stars are and their relation to earth at any point in time ). Others utilize sun sensors, tuned to the electromagnetic spectrum of the sun.

Dave