Another vendor uses a smart-antenna architecture it says doesn't propagate energy in directions other than toward the receiving clients, keeping interference to a minimum that way. What is your argument against this architecture and in favor of your own approach to spectrum management?
Smart antennas , beam forming, MIMO can all help in getting some improvement to SNR, which helps with interference. But at the end of the day, interference signals are typically very hot, and “burning through” interference is not a reality. At best, these processing gains can be used to somewhat reduce the “zone of impact” of an interference device – ie. how much of the floorspace is taken out by the device. But there will always be a zone of impact, and the key is to understand and deal with the source of interference.
In a retail environment if a 100 Mw cordless phone is 4 feet away from a bar code scanner, the interference from the phone will drop the Wi-Fi connection between the scanner and the AP. CleanAir technology can solve this interference by changing channels away from the cordless phone , wheareas an antenna system will not be capable of resolving the interference.
With smart antennas the zone of impact may shrink a tiny bit but the interference is still there. So if wireless users are spread out the interference will go down a small amount but the interference will still impact the user closest to the source of interference.
replied to comment from Neil Diener, Cisco Systems
| July 12, 2010 5:55 PM
| Reply
Neil, you mention that CleanAir can solve interference problems by changing channels away from the source of the interference. What is the impact of such channel hopping on real-time traffic; namely, voice over IP over WLAN (VoWLAN) conversations?
CleanAir will not change channels unless the interference is severe -- and in this case VoIP and VoWLAN will be experiencing serious issues anyway.
After the channel change, there will be a brief loss of service as the client probes and finds the AP again, and then service should resume (with much better quality, since the AP has moved away from the interference).
Dilip,
Spectrum analysis doesn't fix or mitigate interference. It is a necessary part of a toolkit, but it is a reactive solution, not proactive like beam steering.
What would be the difference between increasing the SINR when the source of interference is wide band vs. only on one channel? None that I am aware of, but if I am wrong I will stand corrected. SNR/SINR is key to Wi-Fi connection and performance. I do agree that tools to detect, classify and locate are valuable for sure. However, having some extra signal to each STA does mitigate the effects of regular interference. (e.g. Bluetooth, low power cordless phones, microwave ovens etc)
Neil,
If you think about it, ALL Wi-Fi transmission burn through interference. Whether it is white Gaussian noise or a cordless phone, we are all overcoming interference of some type.
I'm not sure that I agree that most sources of interference are "hot" and disable the channel. In fact, I love it when the source of interference is so high that it basically acts as a DoS? Why? Easy to find and easy to shut down. What is a real killer is all of the general noise that is added from devices that slow down performance, but typically is just accepted by the net admin staff. Very few organizations have the resources to act on the information gained through system wide spectrum analysis.
Changing channels to avoid interference? I think that a spectrum analyzer in the AP is cool and all, but all vendors of significance have been able to change channels in response to interference for years without any special sauce.
One major problem is most vendors (including us) don't know if the channel they are moving to is actually better. You may be jumping from a room full of smoke to a room full of fire. Channel changes are necessary to combat strong noise, but should only be used as a last resort, not the only resort.
GT
It is critical for IT staff members to detect all possible sources of interference in the environment. By directing the RF energy from the AP to the receiving clients, vendors may claim to be effective in increasing the Signal to Noise Ratio at the client device, thus contributing to increased throughput or minimized interference in certain directions, but it cannot be the only mitigation method for dealing with RF interference. How does such a solution handle wide-band interference over the entire frequency band? Those wide-band sources wreak havoc in the RF environment, leaving WLAN networks unusable. It is better to find the problem and remove it from the environment, instead of just avoiding its path assuming that transmissions will not be interfered or interrupted. That can be achieved only with an RF spectrum management solution. “Detect, locate and classify” should be the anthem for any IT staff member to handle WLAN performance and security issues at layer 1.