Survey Procedures

wireless-computersIntroduction:
Implementation of a WiFi wireless LAN (WLAN) network, within or between buildings, requires performing a site survey. No one can tell exactly how wireless equipment will operate in every circumstance without a survey. This is especially true in an intra-building application where there are load bearing or asbestos-lined walls, or inter-building links where obstacles such as trees are involved.

Site surveys for wired and wireless LAN networks are similar. Wireless surveys also analyze the conditions required to provide an optimal radio link. The complexity and details of the survey depend on the complexity of the proposed network. The most important details are the number of sites involved, the terrain and the distance between sites.

Site Qualification:
This is the first step required to determine if a WiFi wireless LAN (WLAN) network is a feasible solution. With the assistance of our vendors, NAS has assembled a set of forms to help determine the feasibility of a wireless system.

Once these forms are completed, they should be emailed or faxed to NAS engineers, who will determine if a wireless network is a practical solution. These forms will also help determine how complex the site survey needs to be.

Site Survey:
The site survey will ensure the proper wireless LAN solution can be designed for the application. This survey is required if there is any question as to how the proposed wireless system will operate, or to determine if it is feasible for the application.

The complexity of the site survey required depends on which of the following typical system configurations is proposed:

  • Simple Wireless LAN Network Configuration: This is normally a point-to-point link under six miles where the open space between the two locations is free of obstructions. In an intra-building system, this would be a predominately open space with few structural walls. This configuration requires a basic site survey.
  • Complex Wireless LAN Network Configuration: This is a point-to-point system in excess of six miles; a point-to-point system with obstructions in or near the path; a multi-site inter-building system; or an intra-building system with multiple rooms and/or load-bearing walls.

Who Should Perform the Survey:
A team of persons should perform the site survey with expertise in wireless LANs and RF links. RF expertise is not widely available. For this reason, NAS has assembled a team of certified RF engineers and installers who are qualified to perform complex site surveys nationwide. To assure a successful design and implementation, it is critical that persons with RF link expertise participate in the wireless system site survey.

Purpose of the Site Survey:
The main items the site survey will determine include…

  • The system’s configuration and performance objectives.
  • The costs, advantages and disadvantages of alternative configurations to meet performance objectives.
  • The recommended design to meet the cost and performance objectives.

The site survey should provide all of the information needed to ensure that the wireless LAN system is properly designed. The site survey should always review and determine the following:

  • The users, applications and equipment on the wireless LANs that are to be inter-networked. This details the configurations of the wired LANs already installed or that are planned for Installation in the buildings or rooms that will be linked.
  • The wireless LAN system best suited for the application. Wireless LAN (WLAN) systems are combinations of routers, bridges, hubs, and clients, as well as cables and antennas. The site survey will determine the right combination of these components for the application.
  • The free space path requirements between antennas (External P2P or P2MP). A clear RF line of site must exist between the antenna locations. If no visible barriers exist between the LAN locations where antennas are to be erected, normally the sites can be linked. However, in some instances, a terrain analysis may be needed to ensure that the minimum required free space is available, and to determine how high the antennas must be to avoid obstructions and out-of-phase deflections.
  • The specific places where each component should be located. Antennas must be positioned high enough for a clear RF line of sight. The wireless LAN bridges, routers or hubs are normally placed in a computer room or wiring closet, collocated with the servers. The FCC has certified a specific cable and antenna set for each wireless manufacturer. However, NAS as a qualified/certified professional installation group, may customize the cables and antennas for any installation as required.
  • Whether to use a point-to-point or multipoint configuration. Most WiFi wireless LAN systems provided by NAS can be configured with an option for multipoint operation. There are specific exceptions, which will be noted by your NAS wireless engineer.
  • Potential sources of interference in the alternative RF bands. For complex WiFi wireless LAN connections in environments where the airways tend to be busy, it may also be necessary to check for competing signals with a Spectrum Analyzer. Spectrum analysis can detect and measure potential sources of interference in any selected RF band.
  • The federal, state, and local regulations. It is important to follow FCC and National Electrical Codes in the construction of masts and towers, and the electrical grounding of the WiFi wireless LAN system. All designs and installations must comply with the appropriate regulations. NAS engineers will work with your staff to determine any special compliance issues for local regulations