Fixed Terrestial Wireless
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=== Overview === | === Overview === | ||
- | Fixed Terrestrial Wireless is basically a [[wikipedia:Cellular network|cellular network]], as are [[Wi-Fi]], [[WiMAX]] and [[Cellular|cellular telephone]]. The hub defines the 'central' point of the cell, and the distance covered will depend on antennas used, transmitter powers, receiver sensitivity, and the terrain and any interfering obstacles. This type of system can easily cover an area where subscribers are 5 or more miles from the hub. The coverage is thus similar to | + | Fixed Terrestrial Wireless is basically a [[wikipedia:Cellular network|cellular network]], as are [[Wi-Fi]], [[WiMAX]] and [[Cellular|cellular telephone]]. The hub defines the 'central' point of the cell, and the distance covered will depend on antennas used, transmitter powers, receiver sensitivity, and the terrain and any interfering obstacles. This type of system can easily cover an area where subscribers are 5 or more miles from the hub. The coverage is thus similar to WiMAX, much larger than Wi-Fi, but limited to fixed subscriber side installations. The deployment of this system would usually be designed to cover a predetermined area of land, which may or may not be circular. Therefore, the hub may not be at the actual center of the cell, and the cell may not be circular. |
=== Link Calculations === | === Link Calculations === | ||
- | For an idea of how to calculate the area covered, you need to know the specifications of the hardware at each end, and the specifics of the radio path. You can check example calculations | + | For an idea of how to calculate the area covered, you need to know the specifications of the hardware at each end, and the specifics of the radio path. You can check example calculations in [[Wi-Fi#Link_Calculations]]. (Coax loss is normally zero for Fixed Terrestial Wireless since the antenna is normally attached to the radio.) However, in nearly all cases, you will be using equipment provided by the wireless service provider, and you probably won't have access to the radio specifications. The service provider will probably not make any path calculations, but will ask your location, and if it sounds possible, come out and 'take a look'. If line of sight seems OK, or even close, and the distance is OK, then they will likely just give it a try and see what they get. You should not expect your salesman or installer to be a radio engineer. You should expect the installer to be familiar with the area and know what normally will or will not work. |
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== Path Variables == | == Path Variables == | ||
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=== Line of Sight === | === Line of Sight === | ||
- | If you have line of sight, then | + | If you have line of sight, then tree growth or someone building and consequently obstructing the line of sight might well create a problem. If you don't have line of sight, then the path might still work, but might change with the seasons if trees are the reason for it not being line of sight. |
- | === | + | === Fresnel Zone === |
- | The remaining issue is one of ground clearance, commonly known as [http://www.afar.net/fresnel-zone-calculator/ fresnel zone clearance] | + | The remaining issue is one of ground clearance, commonly known as [http://www.afar.net/fresnel-zone-calculator/ fresnel zone clearance], which gives you an indication of what effect ground along the path will have. If the path is very close to ground, then you probably won't have enough clearance, and will lose a few dB, but the signal should be stable. |
- | + | === Ground Reflection === | |
+ | If the path is high above ground, and crosses over a flat area along the path that can be seen from the antennas at both ends, then you have the possibility of signal reflections off the ground arriving at the receive antenna delayed and out of phase with the direct path, and the two signals can cancel. It is an unfortunate fact of life that the reflectivity of the ground can change drastically. If you have a rough surface, or a nice crop of corn, it will attenuate any signal that would otherwise be reflected. But at another time of year, the ground can be bare, maybe have a nice coating of dew or water, and be very reflective. The solution to this type of problem normally is to alter the height of one antenna and change the reflection from a cancelling mode to an additive mode. | ||
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+ | === Rain Attenuation === | ||
+ | With a radio path of less than 10 miles, the path should not normally be subject to too many variables. Rain attenuation would not normally be a problem. | ||
==Service Speeds== | ==Service Speeds== | ||
- | + | High speeds of 4.8 Mbps downlink and 1.8 Mbps uplink are quite possible. Actual speeds can vary greatly depending on provider, geography, and class (cost) of service. | |
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