With wireless systems, it’s very difficult to predict the propagation of radio waves and detect the presence of interfering signals without the use of test equipment. Even if the system implements omni-directional antennas, radio waves don’t really travel the same distance in all directions. Instead walls, doors, elevator shafts, people, and other obstacles offer varying degrees of attenuation, causing the RF (radio frequency) radiation pattern to be irregular and unpredictable. As a result, it’s absolutely necessary to perform a wireless site survey to fully understand the behaviour of radio waves within the operating environment before installing access points.
Site survey
Tough Corp understand the ultimate goal of a wireless site survey is to determine the number and placement of access points (or mesh nodes) that provides adequate signal coverage throughout a site. With most implementations, “adequate coverage” means support of a minimum data rate or throughput. In order to perform a successful survey, Tough Corp need to relate the required performance to a value that survey tools measure, such as Signal to Noise Ratio (SNR). A wireless site survey conducted by Tough Corp also detects the presence of RF Interference emitting from other sources that could affect the ultimate performance of the wireless Network.
The complexity of each site survey will vary depending on the facility. For example, a small open space may not require a site survey. This scenario can probably suffice with a single Wi-Fi access point (or router) located anywhere within the site and still maintain adequate coverage. If the access point encounters RF interference from another nearby wireless LAN, Tough Corp would advise that you simply select another channel and eliminate the problem.
With larger facilities, such as an office complex, airport, hospital, or warehouse, or a large outdoor area like a city, Tough Corp would recommend an extensive wireless site survey. If this is not conducted users will probably end up with inadequate coverage and suffer from low performance in some areas.
When Tough Corp conduct a wireless site survey, the following consideration and steps are followed:
Understanding the wireless requirements. In order to identify optimum locations for access points or mesh nodes, Tough Corp must have a good understanding of your specific requirements for the network and the potential impacts signal coverage. For example, maximum range between a client device and the access point decreases as data rate bit increases the performance. It is important to know the target data rates (and throughput) to correctly interpret survey results. As the transmit power of devices varies significantly, it must be taken into consideration when using our site survey tools.
Understanding the Site
Before Tough Corp get too far with the site survey, we try and locate a set of site plans. If none are available, the preparation a drawing that depicts the location of walls, walkways, etc is required. The Site survey tools utilised by Tough Corp import diagrams in various image formats. Tough Corp obviously work with all the leading Geographic Information Systems such as ESRI or Pitney Bowles. Digital photos can be used as a last resort.
Visually inspecting the Site
Tough Corps’s engineers will walk through the site before performing any testing to verify the accuracy of the facility diagram. During this survey any potential attenuation barriers that may affect the propagation of RF signals will be identified. For example, our visual inspection will uncover obstacles to signals such as metal racks and partitions, items that site plans generally don’t show. During this phase possible the locations for mounting access points, such as above ceiling tiles or on pillars will be identified.
Assessing existing network infrastructure
Tough Corp need to determine the capacity of any existing wired networks that can interface the access points or mesh nodes. The majority of sites have Ethernet and in some cases optical fiber networks. Tough Corp will check how much of the existing networks can be made available for supporting the wireless network. This will aid designers later on in the deployment defining the architecture and bill of materials required for the wireless network.
Identifying required coverage areas
On the site diagram, jointly we will need to determine the areas where coverage is required, such as offices, hallways, stairwells, utility rooms, bathrooms, lunch rooms, patios, parking garages, and elevators. We will also identify where users will not wireless coverage to avoid wasting time surveying unnecessary areas.
Determining preliminary access point locations
When considering the location of wireless users and range estimations of the wireless LAN products Tough Corp recommend, approximate locations of access points that will provide adequate coverage throughout the user areas is selected. Tough Corp generally plan for some propagation overlap (usually 25 percent) with adjacent access points, but obviously keeping in mind that channel assignments for access points wil be required be far enough apart to avoid inter-access point interference.
Tough Corp carefully consider mounting locations, these could potentially be vertical posts or metal supports above ceiling tiles. It is important that we recognize suitable locations for installing the access point, antenna, and data / PoE cable. Different antennas may be specified for each access point depending on the location. For example a access point mounted near an outside wall a patch antenna with relatively high gain oriented within the facility may be the optimal option.
Verifying access point locations
Tough Corp utilise Wireless LAN Site Survey Software that identifies the associated access point, data rate, signal strength, and signal quality. This is loaded onto our rugged laptops that test the coverage of each preliminary access point location.
Tough Corp will install an access point at each preliminary identified location, monitor the site survey tool readings by moving varying distances away from the access point. We do not no need to connect the access point to the distribution system as the survey tests merely ping the access point and/or read the beacon signal strength. Tough Corp consider the SNR range and Uplink Signal strength when interpreting the results, these 2 factors determine the effectiveness of the network..
The performance or signal readings at different points as we move to the outer bounds of the access point coverage is recorded. In a multi-floor facility, we perform tests on the floor above and below the access point as a poor signal quality reading could indicate that RF interference is affecting the wireless LAN. Tough Corp would utilise a spectrum analyzer to characterize the interference, especially if there are no other indications of its source. Based on the results of our testing, Tough Corp may recommend the location of some access points be relocated and testing conducted again for the affected location.
Documenting findings
When your are satisfied that the location of access points will provide adequate signal coverage for your application, Tough Corp will document all findings on the site diagrams by depicting the location of each access point.
