There is no “typical”
Let’s start by saying that there is no typical onsite engagement, every environment is unique. Building construction whether it is concrete, brick, sheetrock, steel girder. Type of enterprise, school, office, home, marina, outdoor sport stadium, museum, etc. Obstructions, mirrors, equipment, restrooms, fish tanks, window tinting, people. These can dramatically affect the way RF behaves.
The first part of any engagement needs to be a meeting with the customer to determine what needs to be done. Why is the customer interested in a site survey? Are they looking to install a new wireless system? Is there an issue with their currently installed system? are they looking to refresh hardware? We need to know how to identify success.
During this phase, it should be determined by both parties if the wireless engineer will have access to the wireless LAN controller. Only engineers certified by the manufacturer should be allowed access. All the information required to identify the performance of a wireless LAN can be determined “in the air”. Remediation recommendations can be general like, “there are too many radios using the same 5 GHz channel”, or “these 5 radios should have their 2.4GHz radios turned off”. A certified wireless engineer can then take this information and make the configuration changes on the WLC.
Radio Frequency Spectrum Analysis
The medium that WiFi uses is the air, more specifically two radio frequencies that are transmitted through the air. 802.11 b/g/n (2.4GHz) uses 14 channels from 2.412 to 2.484GHz. 802.11 a/n/ac (5GHz) uses 27 channels (in three discrete bands) from 5.170 – 5.805. “WiFi” analysis tools only look at 802.11 data packets transmitted in these bands. These tools have access to a lot of valuable information such as SSID names, channelization, signal strength, channel utilization, data rates, and much more. However, this is only 802.11 data, there can be other devices using or interfering with these frequencies that these tools cannot measure.
RF spectrum analysis test equipment will monitor the entire frequency for any signal in these bands that may interfere with 802.11 traffic.
The key difference it these two types of test equipment is in what is being listened to. With the WiFi test equipment 802.11 packets are being analyzed for the informational data that they contain. With RF spectrum analysis tools, the entire band is being analyzed for whatever is being transmitted.
Site survey means many things to many people. In the most general terms, a site survey is:
“The process of planning and designing a wireless network, to provide a wireless solution that will deliver the required wireless coverage, data rates, network capacity, roaming capability and Quality of Service (QoS).”
Let’s talk about the different types of site surveys.
- Determine existing RF conditions
- Determine building construction type, materials, RF obstruction dB levels
- Locate wired LAN physical plant
- Create a design model using real world measurements vs. software assumptions
- Identify and document physical locations for access point installation
- Identify coverage areas and locate any gaps in coverage
- Channel utilization / width
- Confirm access point installation locations are providing coverage as designed
- Document current 802.11 coverage
- Confirm wireless LAN is performing as configured
- Find any non 802.11 signal or interference in the area
- Identify existing access point installation methods conform to manufacturer’s requirements
Radio Frequency Analysis:
- Graphically identify any transmitting device using either the 2.4 or 5 GHz bands
- RF Survey – A wireless engineer will use hardware and software to measure and record RF conditions throughout the entire in scope area. RF analysis solutions include, MetaGeek’s Wi-Spy and Chanalyzer, AirMagnet Spectrum XT
- Post Installation – A wireless engineer will import an accurate floor plan and calibrate into a wireless design software program such as NETSCOUT’s Air Magnet Survey, Ekahau Site Survey and Planner, TamoGraph and others. The wireless engineer will then walk the entire site taking measurements at many locations to determine the actual RF properties of the site.
- Pre-Installation – One or many RF transmitters will be activated onsite and measurements will be taken to determine the attenuation properties of structures within the site. This information will be added to a predictive wireless design to greatly improve the accuracy of the design.
- Troubleshoot – Identify the root cause of any issues determined during the assessment phase with any RF tools necessary, packet capture, RF analyzer, heat map, transmitter locator. Tools such as, Wireshark, NETSCOUT’s AirCheck G2.
After the onsite the wireless engineer will analyze the data collected and create a report that will communicate the results to the customer. All phases of the onsite engagement will be reported separately in a way that will allow the customer to put together a complete picture of the survey.
For estimate purposes, typically the off site work will take the same amount of time that the actual onsite takes. If the wireless engineer is onsite for 8 hours, then it will likely take 8 hours to analyze the data and create the required reports. There can be some economy of scale here, if it is a very large project the analysis and reporting time required will probably be reduced.
Onsite time is determined using a formula including square footage and time factors for each type of survey. Minimum time on site is used for smaller engagements.
Elements of a report:
- Summary of results
- Pre-installation predictive heat maps
- Post installation actual heat maps
- Access point installation locations and methods
- Radio frequency analysis, identify and locate any interfering devices
- Remediation recommendations
- Present results visually and through explanatory test
The keys to a successful site survey are, properly identify customer concerns, identify success parameters, accurately perform specific test and measurement methodologies, clearly and concisely report results.
Note: Throughout this article 2.4 and 5GHz bands were used. The Public Safety band 4.9 is very similar but not used as much. Most WiFi and RF tools can be used for this band also. Some require additional hardware or licensing but all the same theories apply.
VP Wireless Engineering