Customizing Spectrum Analysis Graphs

Each Spectrum Analysis graph can be customized to display or hide selected data types. To view the available options for a graph type:

Figure 1  Viewing Spectrum Analysis Graph Options

Spectrum Analysis Graph Configuration Options

The following sections describe the customizable parameters and the default settings for each spectrum analysis graph.

Active Devices

This graph appears as a pie chart showing the percentages and total numbers of each device type for all active devices seen by the spectrum monitor or hybrid AP radio. This chart is useful for determining which types of devices are sending signals on the specified radio band or channel. The Active Devices graphs for spectrum monitors can be configured to show data for several different device types on a single radio channel or range of channels. Active Devices graphs for hybrid APs can show data for the single monitored channel only.

When you hover your mouse over any section of the pie chart, a tooltip displays the percentage and number of active devices classified into that device type. The example in Figure 2 shows that 99% of the active devices a spectrum monitor radio sees in the 2.4 GHz band are Wi-Fi APs.

Figure 2  Active Devices Graph

Click the down arrow in the upper right corner of this chart then click the Options menu to access the configuration settings for the Active Devices graph. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards.

Active Devices Table

This table lets you view, sort, and search for data about the devices that are sending signals on the specified radio band or channel. The Active Devices table for a spectrum monitor displays data for all channels on the selected band. The Active Devices table for a hybrid monitor displays data for the single monitored channel only. Click any of the column headings to sort the information in the table by that column criteria. Make a column wider or narrower by clicking the border of a column heading and dragging the border to a new position.

Figure 3  Active Devices Table

You can save the data in the Active Devices table for later analysis by exporting it as data file in .csv format, which can be viewed by spreadsheet and database management applications like Microsoft Excel. To export this table, click the down arrow in the upper right corner of this chart and select Export. A window opens and lets you browse to the location to which you want to save the file. Once you have identified the location where you want to save the file, click Save.

You can also filter table entries by signal strength, duty cycle, discovery time, activity duration, channels affected and device ID number by clicking the icon below any column heading and specifying the values or value ranges that should appear in the table. Table 2 describes each of the columns in the table and the filters that can be applied to the table output.

Active Devices Trend

The Active Devices Trend chart is a line chart that shows the numbers of Wi-Fi and non-Wi-Fi devices seen on each radio channel during the displayed time interval. When you hover your mouse over any line in the chart, a tooltip displays the number of active devices for the selected device type. The example in Figure 4 shows that there are 27 active Wi-Fi APs on channel 157 of the 5 GHz radio band.

Figure 4  Active Devices Trend Graph

An Active Devices Trend chart created by a hybrid AP displays data for the single channel monitored by that device. For spectrum monitors, the Active Devices Trend chart can display values for up to five different channels and device types. These graphs show the following data by default:

Table 3 describes the other values that can be displayed in the Active Devices Trend chart. Click the down arrow in the upper right corner of this chart then click the Options menu to access the Active Devices Trend configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards.

Channel Metrics

This stacked bar chart can show one of three different types of channel metrics; channel utilization, channel availability, or channel quality.

By default, this chart displays channel utilization data, showing both the percentage of each monitored channel that is currently being used by Wi-Fi devices, and the percentage of each channel being used by non-Wi-Fi devices and 802.11 adjacent channel interference (ACI).

The Channel Metrics graph can also show channel availability, the percentage of each channel that is available for use, or display the current relative quality of selected channels in the 2.4 GHz or 5 GHz radio bands. Spectrum monitors can display data for all channels in their selected band. Hybrid APs display data for their one monitored channel only.

In the spectrum analysis feature, channel quality is a relative measure that indicates the ability of the channel to support reliable Wi-Fi communication. Channel quality, which is represented as a percentage in this chart, is a weighted metric derived from key parameters that can affect the communication quality of a wireless channel, including noise, non-Wi-Fi (interferer) utilization and duty-cycles, and certain types of retries. Note that channel quality is not directly related to Wi-Fi channel utilization, as a higher quality channel may or may not be highly utilized.

When you hover your mouse over any bar in the chart, a tooltip displays the metric value for that individual channel. The example below shows that 61% of channel 3 is being consumed by non-Wi-Fi devices and 802.11 adjacent channel interference.

Figure 5  Channel Metrics Graph

Table 4 describes the parameters that can be displayed in the Channel Metrics graph. Click the down arrow in the upper right corner of this chart then click the Options menu to access these configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards.

Channel Metrics Trend

By default, this line chart shows the current relative quality of selected channels in the 2.4 GHz or 5 GHz radio bands over a period of time. The Channel Metrics Trend chart can also be configured to display trends for the current availability of selected channels, or the percentage of availability for those channels.Spectrum monitors can display data for up to five different channels. Hybrid APs display data for their one monitored channel only.

When you hover your mouse over any line in the chart, a tooltip displays channel quality or availability data for that individual channel at the selected time.

Figure 6  Channel Metrics Trend Chart

Table 5 describes the other parameters that can be displayed in the Channel Metrics Trend output. Click the down arrow in the upper right corner of this chart then click the Options menu to access these configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboard.

Channel Summary Table

The channel summary table provides a summarized or aggregated view of key statistics. Spectrum monitors display spectrum analysis data seen on all channels in the selected band, and hybrid APs display data from the one channel they are monitoring. The example in Figure 7 below shows that a spectrum monitor sees 44 Valid APs and 52% channel utilization on channel 40 in the 5GHz radio band.

Figure 7  Channel Summary Table

Spectrum monitor radios using the 5 GHz radio band can display channels using either 20 MHz or 40 MHz channel numbering. Spectrum Monitor radios that support 802.11ac can also display 80MHz channels. To toggle between these channel numbering modes, click the down arrow in the upper right corner of the graph titlebar, then click either Show 20 MHz Channels, Show 40 MHz Channels or Show 80 MHz Channels.

Click any of the column headings to sort the information in the table by that column criteria. Make a column wider or narrower by clicking the border of a column heading and dragging the border to a new position.

Table 6 describes the output of the Channel Summary table.

Device Duty Cycle

The Device Duty Cycle Chart is a stacked bar chart that shows the duty cycle of each device type on a channel. The duty cycle is the percentage of time each device type operates or transmits on that channel. Though Wi-Fi devices do not transmit if there is another Wi-Fi or non-Wi-Fi device active at that time, most non-Wi-Fi devices do not follow such a protocol for transmissions. Since these devices operate independently without regard to any other devices operating on the same channel, the total duty cycle of all device types may add up to more than 100% on a channel. For example, one or more video bridges may be active on a channel, each with 100% duty cycle. The same channel may have a cordless transmitter with 10% duty cycle and a microwave oven with 50% duty cycle. In this example, the Device Duty Cycle chart shows all three device types with their respective duty cycle percentages.

Spectrum monitors display spectrum analysis data seen on all channels in the selected band, and hybrid APs display data from the one channel they are monitoring. The example below shows data from a spectrum monitor monitoring all channels in the 2.4 Ghz band.

Figure 8  Device Duty Cycle

Table 7 describes the parameters you can use to customize the Device Duty Cycle chart. Click the down arrow in the upper right corner of this chart then click the Options menu to access these configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards.

Channel Utilization Trend

The Channel Utilization Trend chart is a line chart that shows the percentage of total utilization on each channel over a time interval. The channel utilization includes the utilization due to Wi-Fi as well as utilization due to non-Wi-Fi interferers and Adjacent Channel Interference (ACI).

This graph can show data recorded for the last ten, thirty, or sixty minutes. Spectrum monitors display spectrum analysis data seen on all channels in the selected band, and hybrid APs display data from the one channel they are monitoring. When you hover your mouse over any line in the chart, a tooltip shows the percentage of the channel being utilized at the specified time. The example in Figure 9 shows that channel 1 was 70% utilized at the selected time in the chart.

Figure 9  Channel Utilization Trend

Table 8 describes the parameters you can use to customize the Channel Utilization Trend chart. Click the down arrow in the upper right corner of this chart then click the Options menu to access these configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards.

Devices vs Channel

This stacked bar chart shows the current number of devices using each channel in the radio’s frequency band. This chart can show separate per-channel statistics for the numbers of Wi-Fi devices, cordless phones, bluetooth devices, microwaves, and other non-Wi-Fi devices.

If a device affects more than one channel, it is recorded as a device on all channels it affects. For example, if a 20Mhz Wi-Fi AP has a center frequency of 2437 Mhz (channel 6) it is counted as a device on channels 3-9 because it affects all those channels. Similarly, if a channel-hopping device uses all channels within a frequency band, it is counted as a device on all channels in that band.

When you hover the mouse over any part of the chart, a tooltip shows the numbers of the device type currently using that channel. The example in Figure 10 shows that the spectrum monitor can detect 42 APs on channel 5.

Figure 10  Devices vs Channel

Table 9 describes the parameters you can use to customize the Devices vs Channel chart. Click the down arrow in the upper right corner of this chart then click the Options menu to access these configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards.

FFT Duty Cycle

The FFT Duty Cycle chart is a line chart that shows the duty cycle for each frequency bin. The width of the each frequency bin depends on the resolution bandwidth of the spectrum monitor. The spectrum analysis feature considers a frequency bin to be utilized if the detected power in that bin is at least 20 dB higher than the nominal noise floor on that channel. The FFT Duty Cycle provides a more granular view of the duty cycle per bin as opposed to the aggregated channel utilization reported in the Channel Metrics chart.

This chart can show the duty cycle over the last second, the maximum FFT duty cycle measured for all samples taken over the last N sweeps, and the greatest FFT duty cycle recorded since the chart was last reset.

Figure 11  FFT Duty Cycle

By default, this chart shows the current duty cycle for devices on all channels being monitored by the spectrum monitor radio. Table 10 describes the other optional parameters you can use to customize the FFT Duty Cycle table. Click the down arrow in the upper right corner of this chart then click the Options menu to access these configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards.

Interference Power

The Interference Power chart displays various power levels of interest, including the Wi-Fi AP with maximum signal strength, noise, and interferer types with maximum signal strength. The ACI displayed in the Interference Power Chart is the ACI power level based on the signal strength(s) of the Wi-Fi APs on adjacent channels. A higher ACI value in Interference Power Chart does not necessarily mean higher interference since the AP that is contributing to the maximum ACI may or may not be very actively transmitting data to other clients at all times. The ACI power levels are derived from the signal strength of the beacons.

This chart displays the noise floor of each selected channel in dBm. The noise floor of a channel depends on the noise figure of the RF components used in the radio, temperature, presence of certain types of interferers or noise, and the width of the channel. For example, in a clean RF environment, a 20 MHz channel has a noise floor around -95 dBm and a 40 MHz channel has a noise floor around -92 dBm. Certain types of fixed-frequency continuous transmitters such as video bridges, fixed-frequency phones, and wireless cameras typically elevate the noise floor seen by the spectrum monitor. Other interferers such as frequency-hopping phones, Bluetooth and Xbox may not affect the noise floor of the radio. A Wi-Fi radio can only reliably decode Wi-Fi signals that are a certain dB above the noise floor and therefore estimating and understanding the actual noise floor of the radio is critical to understanding the reliability of the RF environment.

The chart also includes information about the AP on each channel with the highest power level. You can hover your mouse over an AP on the chart to view the AP’s name, SSID and current power level. The example below shows that the AP with the maximum power on channel 157 has the SSID qa-ss, and a power level of -55dBm.

Figure 12  Interference Power

Table 11 describes the other optional parameters you can use to customize the interference power chart. Click the down arrow in the upper right corner of this chart then click the Options menu to access these configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards.

Quality Spectrogram

This plot shows the channel quality statistics for selected range of channels or frequencies. This chart can also be configured to show channel availability, the percentage of each channel that is unused and available for additional traffic.

Channel Quality is a weighted metric derived from key parameters which include noise, non-Wi-Fi (interferer) utilization and duty-cycles and certain types of retries. Quality levels are indicated by a range of colors between dark blue, which represents a higher channel quality, and red, which represents a lower channel quality. Channel availability is indicated by a range of colors between dark blue, which represents 100% channel availability, and red, which represents 0% availability.

The Spectrum Analysis Quality Spectrogram chart measures channel data each second, so after every 5-second sweep, the newest data appears as a thin colored line on the bottom of the chart. Older data is pushed up higher on the chart until it reaches the top of the spectrogram and ages out. The example below shows the Aruba Quality Spectrogram chart after it has recorded over 1500 seconds of FFT data.

Figure 13  Quality Spectrogram

When you hover your mouse over any part of the spectrogram, a tooltip shows the devices the spectrum monitor detected on that frequency, the BSSID of the device (if applicable), the power level of the device in dBm, the time the device was last seen by the spectrum monitor, and the channels affected by the device.

The following table describes the other optional parameters you can use to customize the Quality Spectrogram. Click the down arrow in the upper right corner of this chart then click the Options menu to access these configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards

Real-Time FFT

The Real-time FFT chart displays the instantaneous Fast Fourier Transform (FFT) signature of the RF signal seen by the radio. The Fast Fourier Transform (FFT) converts a RF signal from time domain to frequency domain. The frequency domain representation divides RF signals into discrete frequency bins; small frequency ranges whose width depends on the resolution bandwidth of the spectrum monitor (i.e., how many Hz are represented by a single signal strength value). Each frequency bin has a corresponding signal strength value. Since there may be a large number of FFT signatures received by the radio every second, an algorithm selects one FFT sample to display in the Real-time FFT chart every second.

This chart can show an average for all samples taken over the last second, the maximum FFT power measured for all samples taken over ten channel sweeps, and the greatest FFT power recorded since the chart was last reset. When you hover your mouse over any line, a tooltip shows the power level and channel or frequency level represented by that point in the graph. When you hover your mouse over a frequency level (within the blue brackets on the graph), a tooltip shows the types of devices seen on that frequency, as well as each device’s BSSID, power level, channels affected and the time the device was last seen by the spectrum monitor.

Figure 14  Real-TIme FFT

By default, this chart shows the maximum power level recorded for any device on all channels or frequencies monitored by the spectrum monitor radio.

Table 13 describes the other parameters you can use to customize the Real-time FFT chart. Click the down arrow in the upper right corner of this chart then click the Options menu to access these configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards.

Swept Spectrogram

A spectrogram is a chart that shows how the density of the quantity being plotted varies with time. The spectrum analysis Swept Spectrogram chart plots real-time FFT Maximums, real-time FFT Averages or the FFT Duty Cycle. In this swept spectrogram, the x-axis represents frequency or channel and the y-axis represents time. Each line in the swept spectrogram corresponds to the data displayed in the Real-Time FFT or FFT Duty Cycle chart.

The power or duty cycle values recorded in each sweep are mapped to a range of colors. In the average or maximum FFT power Swept Spectrogram charts, the signal strength levels are indicated by a range of colors between dark blue, which represents -90 dBm, and red, which represents a higher -50 dBm. The duty cycle Swept Spectrogram chart shows the percentage of the time tick interval that the selected channel or frequency was broadcasting a signal. These percentages are indicated by a range of colors between dark blue, which represents a duty cycle of 0% percent, and red, which represents a duty cycle of 100%.
A spectrogram plot is a complex chart that can display a lot of information. If you are not familiar with these types of charts, they may be difficult to interpret. The following illustrations can help explain how FFT power data is rendered in a spectrogram format.

The example in Figure 15 shows how an FFT Power chart could appear if a single data measurement was plotted as a simple line graph.

Figure 15  Simple Line Graph of FFT Power Data

Now, suppose that each channel’s FFT power level was also represented by a color that corresponded to that specific FFT power level. In the example below, channel 12 has a FFT power level of -50 dBm, so it is represented by the color red. Channel 1 has a FFT power level of -85 dBm, so it is represented by dark blue.

Figure 16  FFT Power Line Graph with Color

If the graph was then flattened so each channel’s FFT power for that single1-second sweep was represented only by a color (and not by a value on the y-axis), the graph could then appear as follows:

Figure 17  FFT Power Spectrogram Sample

The spectrum analysis Swept Spectrogram measures FFT power levels or duty cycle data each second, so after every 1-second sweep, the newest data appears as a thin colored line on the bottom of the chart. Older data is pushed up higher on the chart until it reaches the top of the spectrogram and ages out. The example below shows the Swept Spectrogram chart after it has recorded over 300 seconds of FFT data.

Figure 18  Swept Spectrogram

Table 14 describes the parameters you can use to customize the Swept Spectrogram chart. Click the down arrow in the upper right corner of this chart then click the Options menu to access these configuration settings. Once you have configured the desired parameters, click OK at the bottom of the Options menu to save your settings and return to the spectrum dashboards.