Site Survey
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 you’re using 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, which cause the Radio Frequency (RF) radiation pattern to be irregular and unpredictable. As a result, it’s often necessary to perform a RF site survey to fully understand the behavior of radio waves within a facility before installing wireless network access points.The ultimate goal of a RF site survey is to supply enough information to determine the number and placement of access points that provides adequate coverage throughout the area. In most implementations, “adequate coverage” means support of a minimum data rate. A RF site survey also detects the presence of interference coming from other sources that could degrade the performance of the wireless system.When conducting an RF site survey, we consider these general steps:
Visual inspection of the area.Walking through the area do reveal facts about the site plan. This is a good time to note any potential barriers that may affect the propagation of RF signals. For example, a visual inspection will uncover obstacles to RF such as metal tanks towers, mountains….
Identification of the user areas. It’s good habit to mark the areas of fixed and mobile users on the diagram as well as illustrating where mobile users may roam.
Determine preliminary access point locations.By considering the location of wireless users and range estimations of the wireless system used, approximation of the locations of spots that will provide adequate coverage throughout the user areas will be possible. Planning for some propagation overlap among adjacent access points may seem necessary when number of subscribers grow.
Mounting locations should be considered, which could be ground or rooftop towers. Recognizing suitable locations for installing the tower, antenna, cables, and power line is a vital task in any access point location phase.
Data gathering. Once the surveyor is satisfied that the planned location of access points will provide adequate coverage, data regarding site installation peripherals, covered spots and barriers should be gathered. Panoramic photos of site boundaries with steps of 45 degrees as well as photos in the direction of antenna azimuth predictions should be taken to provide an asset for the site planner. Such photos must be orderly placed in the site documentation. Data regarding existing and/or reusable site installations should also be included in the document. Any reusable container, room for indoor equipment or existing tower must be listed. The survey document should also contain information about the area, environment, site address, ways to access the site place and available access time to reach the place. A screen shot of a sample documentation is provided below.
Obstacle sketch must also be included in the final survey report to insure total clearance of the first Fresnel region. A screenshot of the obstacle sketch map is provided below:
The best way to connect two separate points to each other is wireless connection. Because in this way there is no need to use physical cable and so the problems such as maintenance and etc. will be removed.In the wireless methods, the last way is radio connection specially in the far distances. It means if you can find two points that can see each other, you can be sure your data transmission will be warranted .The radio connection has large capacity and high speed. Only optical fiber has capacity and speed more than microwave link.One of the most critical problems in microwave link is line of sight (LOS). It means for a certain secure connection between two points it is necessary that there may be a complete direct sight but it may not be sufficient so a suitable place in GSM view may not be suitable in microwave view. This problem will grow up when you use upper frequencies in 2 GigaHz or higher.Therefore in a good site survey both of BTS and microwave survey must reach an agreement. It is clear that these two fields need different engineers with different skills.But some of the activities will be equal in both fields like as finding the coordination, getting panoramic pictures and etc. in microwave survey it is too important to find the other end. In a good position that in the direct route there are no obstacles and some obstacles can not be seen by digital maps link as the other towers in the way.So microwave survey engineers use their telescopes to check the rout and compare the actual route information with nominal information to find the best location and if they can not see the other end they may use light flashing or sun light mirror to make sure about LOS.
