Spectrum Analysis - RF interference in WLANs is inevitable and unpredictable. It can originate from neighboring Wi-Fi networks or non-Wi-Fi sources, such as 2.4-GHz cordless phones, microwave ovens, analog video cameras, gaming consoles and wireless telemetry systems. The characteristics and severity of RF interference varies based on the type and location of the device and may have an impact on client access and performance of the WLAN.
All Aruba 802.11n APs utilize Wi-Fi chipsets with integrated high-definition spectrum analysis capabilities, enabling alwayson, simultaneous spectrum analysis and wireless security monitoring. Simultaneous scanning of the RF spectrum for interference and intrusion protection eliminates the cost and complexity of separate dedicated hardware or handheld analyzers with client software. As a result, the Aruba solution is less than half the cost of other products and reduces the time spent by IT staff to manually capture RF interference events.
The ArubaOS RFProtect module includes spectrum analysis capabilities used in conjunction with Aruba’s Adaptive Radio Management (ARM) technology. RFProtect Spectrum Analyzer identifies and classifies interference sources in up to 13 categories, then provides administrator analysis of the interference via 12 graphical charts, including FFT and spectrogram graphs. Aruba’s Adaptive Radio Management (ARM) employs infrastructure-based controls to optimize Wi-Fi client behavior and automatically ensures that APs stay clear of Wi-Fi and non-Wi-Fi interference.
Core spectrum reporting capabilities include:
- Active Devices by Device Type, Active Devices by Channel, Active Devices Trend
- Channel Quality, Channel Quality Trend, Channel Utilization, Channel Utilization Trend
- FFT Power, FFT Duty Cycle, Interference Power
- Swept Spectrogram, Channel Quality Spectrogram
Aruba 802.11n access points are based on the Atheros XSpan technology. The Wi-Fi chipset was developed from the ground-up with integrated high definition spectrum analysis capabilities as one of the key objectives and leapfrogs the architecture model currently used in competing solutions. Add to it the custom-built processor and dedicated TPM, Aruba’s 802.11n hardware platforms are capable of performing multi-purpose access point, air-monitor and spectrum monitor function without compromising security and without added costs.
As opposed to competing solutions that require three or more separate management servers or consoles, new AP hardware, or dedicated sensor deployments, Aruba adds software-based spectrum analysis to existing hardware, preserving capital investments, and leaving the network undisturbed.
- Software-based, runs with AP-92/93, AP-105, AP-135, AP-175 and AP-120 Series 802.11n Aruba APs
- Integrated into any new 802.11n APs announced by Aruba in the future
- Enabled/disabled from Mobility Controller console on a per radio basis; enabled with WIP license
- Radios continue to scan for wireless security events while in the spectrum mode
- Enables interference charts, channel quality and availability metrics
- Provides recording/playback capability for extended unattended data capture
- (Future) Enables ARM channel optimization based on interference classification
- (Future) Continues to run while the radios are serving Wi-Fi clients
- ([[AP-92/93], AP-105, AP-175, AP-134/135 only) Provides FFT displays, spectrograms, interference classification
Spectrum and AirWave
AirWave fully supports spectrum from both instant and the controller. Note, the AP needs to be in SM mode or have hybrid scanning turned on for the inforamtion to be sent to AirWave.
Where to look in AirWave:
- Radio detail page - Table that lists all current and historic interferers classified by the radio. It displays signal strength, duty cycle, affected channel and time heard. This is everything you need to determine the impact of an interferer.
- RF health report - identifies the radios that are hearing the most interferers
- VisualRF - Locate interferers with 5-10 meters of accuracy
AMON needs to be enabled so that the controller sends the spectrum data to AirWave. To enable AMON, run 'mgmt-server type amp' from the CLI or navigate to Configuration-->Management-->General and add the server in the 'airwave server section'.
Instant will send the data to the controller as part of the standard info.
Spectrum Analysis and the AP-125
AP-125 shipped in Nov 2007. That was eons ago….so it’s fortuitous that it at least supports SOME spectrum. The AP-125 is from some of the first-gen 11n chipsets, and even the AP-125s in their current form have been out for at least a two years (likely longer).
The AP-125 does not support FFT charts, swept spectrograms of interference source classification.
The AP-125 will not get classification support or the FFT charts. We will add new features to it when we can but classification, FFTs and swept spectrograms will never be added.
The 125 has a different and older radio chipset than the AP-105, AP-92/93, AP-134/135, AP-175. It does not provide the same data that the modern radios provide. We supported what we could on as much hardware as we could.
Different AP Configuration Modes
There are two modes for spectrum analysis, Hybrid AP and Spectrum Monitor.
Hybrid AP – While serving clients the AP will perform spectrum analysis on the home channel. The AP will classify interferers, display FFT charts and send summary information up to AirWave.
The AP-135 and 105 are the only APs that support spectrum analysis in the home channel during Access Point (aka. Hybrid) configuration in FCS ArubaOS 6.1.3.
- AP 105 and 135 support the same radio serving clients and processing spectrum information at the same time. The second radio can be in whatever mode it wants to be (AM,SM or AP).
- Try not to call it ‘Hybrid Scanning’. We don’t perform spectrum scanning in hybrid mode. There is no time slicing. We gather the data on the home channel while serving clients. The AP does not change channel to gather spectrum info. ARM/WIDS scanning continues as usual. That scanning doesn't give us enough info for spectrum classifications.
- Note: In our most recent testing the Cisco 3600 took a bit of a performance hit when hybrid spectrum (CleanAir) was enabled.
‘Hybrid AP’ doesn’t refer to the hardware abilities to be an AM, SM or AP. It refers to the ability of the physical radio to be in AP mode and perform ARM, WIP and Spectrum duties. Traditionally radios in AP mode just serve clients. Some of our competitors(Moto) still have limitations in this respect.
Hybrid spectrum processing (while serving clients) is enabled by checking the ‘spectrum monitoring’ checkbox in the radio profile. It only takes effect when the radio is in AP mode. This will be clear in the 6.2 UI. I wouldn’t call it ‘hybrid scanning’ when talking about the spectrum monitoring. Unlike the rogue detection and WIP functions, spectrum analysis while serving clients does not ‘scan’ channels. It processes the data that is coming into the AP while the AP is serving clients on the home channel. Scanning implies going off channel to look or interrupting client service to tune the radio specifically for spectrum. We don’t do either of those things. AP Mode:
Spectrum Monitor – This mode is dedicated to spectrum scanning and scans multiple channels. Spectrum Monitors do not serve clients as they focus on spectrum. Spectrum monitors will classify interferers, display FFT charts and send summary information up to AirWave.
AM or SM Mode Performance
There is a bit of a performance hit but it is not because the radio is time slicing. It has to do with how the data is processed. The radio does most of the FFT and preprocessing for us but the network cpu does some of the final classifications. That is the custom code we have written. The performance hit only comes in when the AP is already maxed out and the network CPU is starting to be a bottleneck. There is no performance hit on an AP that isn’t near max throughput. 10% loss is a cautious estimate. In the last round of testing that the TME team did, they saw no performance loss on a 135 in hybrid mode. That was a bit of a surprise. There is a good chance that the spectrum load is getting lost in the performance variation between test runs.
|AP Radio Config in ArubaOS 6.1 / Radio Functions Enabled||Air Monitor (aka. AM)||Spectrum Monitor (aka. SM)||Access Point (aka. Hybrid)|
|Wireless Access||No||No||Home Channel|
|Spectrum Analysis||No||All regualatory Channels||Home Channel|
|Intrusion Detection||All Channels including 4.9||All regulatory Channels||All regulatory Channels|
|Intrusion Containment||Regulatory Domain Channels||No||Home Channel|
Supported Modes and Devices in 6.1 and 6.1.1:
Support in AOS 6.1.3
Planned support in AOS 220.127.116.11 AP-93 is scheduled to get hybrid support. RAP-3 is scheduled to get Spectrum Monitor mode support. Plans are subject to change without notice.
Hybrid spectrum on the 92/93/93-h, 104, 175 was not ready for 6.1 or 6.1.3.x.
Spectrum enhancements AOS 6.2
- Can scan entire band (Today limited to viewing each UNI band)
- ARM to consider spectrum learn information in its ARM calculations (non wifi duty cycles, error rates, etc)
- Spectrum playback without being connected to controller
- 6.2 is scheduled to add hybrid support for the 92/93
Note: Originally we had hoped to get hybrid support on all spectrum capable APs in 6.2. Unfortunately we don’t have time to test all of the APs for 6.2. Because of that the 92/93 was prioritized and will be getting hybrid support in 6.2. We hope to get additional APs hybrid support in 6.2.1 but nothing is committed yet.
Spectrum and RAPs
RAP-5WN does not support spectrum, and there are no plans to add it.
Spectrum on RAP-108/109 is currently not targeted to be added in 6.4.
Not 100% sure about the plans for AP-104, but expect Hybrid Spectrum to be added in 6.3.