A Passive Survey (also called Validation Survey) is used to evaluate existing wireless coverage and performance and is the most common form of wireless surveys. During a Passive Survey, the survey client silently listens to all Wi-Fi traffic on channels within the 2.4GHz and 5GHz bands.
The following are measured:
- Wi-Fi signal strengths
- Noise levels
- Signal-to-Noise Ratio (SNR)
- Predicted physical data rates
- Co-channel interference
- Channel overlap
- Rogue devices
The information gathered during a passive survey helps visualize the Radio Frequency (RF) environment. This imagery is key to understanding how to proceed with optimization of your wireless network. When performed as validation survey, it confirms the WLAN is performing as designed (predictive model).
This type of survey determines the RF signal propagation characteristics of pre-determined Access Points (AP). Although more time consuming, it is one of the most accurate surveys available.
A wireless engineer physically places an AP at a specified location within the office, warehouse or facility and captures the performance. The process is repeated until coverage and/or project quality is met.
The following are goals of AP-on-a-Stick (APoS) surveys:
- Determine the optimal locations for AP placement
- Verify coverage in all required areas at the desired minimum signal strength and SNR
- Ensure that adequate coverage overlap exists for client roaming
- Validate actual AP performance
This survey records the actual RF behavior in a facility, resulting in a more accurate WLAN design, by tailoring the outputs to the physical properties of the environment.
A Predictive (also called Planner Survey) Survey models the RF environment using simulation tools. It is essential that the correct environmental information is entered into the modelling tool, including facility construction types, heights and barriers like walls and large objects.
Predictive surveys are used to optimize AP placements and plan for proper channel allocation to avoid channel overlapping, interference and roaming.
The following variables can be simulated within the survey tool Curvature uses to allow for more accurate results:
- Most widely used AP models and antennas
- Band and channel settings
- Power settings, height, angle
- Attenuation zones and wall types
- Areas where coverage is saturated
A Predictive Survey is typically coupled with a Passive Survey. This combination allows Curvature to assess WLAN performance issues and develop a strategy to optimize the environment, for either a complete refresh or to enhance an existing deployment.
RF Spectrum Analysis
A RF Spectrum Analysis provides real-time detection and identification of several non-WLAN sources (non 802.11 traffic) that interfere and lower the performance of WLAN networks. Using specialized antenna and associated software, the Spectrum Analysis detects, identifies and helps locate individual sources of RF interference, including non-WLAN devices such as security cameras, wireless printers, projectors and many more. Several views of the data are available to determine the cause and source of RF interference.
- Real Time Fast Fourier Transform (FFT) providing a view of the RF signal levels
- Spectrum Density providing a long-term view into the network enabling the identification of infrequent transmissions
- Spectrogram graph provides a scrolling history of the RF environment and allows a visual understanding of the spectrum over time to see intermittent spikes or bursts of RF energy that may be causing WLAN network problems
- Interference Power – this graph displays the average power readings of interfering devices on the selected channel or channels