Fixed Terrestial Wireless
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| - | == Introduction to Fixed | + | == Introduction to Fixed Terrestrial Wireless == |
: '''See [http://www.sprintbroadband.com/ Sprint Broadband Direct]''' | : '''See [http://www.sprintbroadband.com/ Sprint Broadband Direct]''' | ||
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| + | As of 3 Dec. 08 the link above does not work for me. Sprint Broadband Direct was taken off the air in the summer of 2008. See [http://www.dslreports.com/shownews/Sprint-Broadband-Direct-Goes-Offline-July-31-94556/ Sprint Broadband Direct Goes Offline]. | ||
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| + | Regardless, at the time of this writing, 3 Dec. 2008, fixed terrestrial wireless is alive and well in some locations, and is my present means of connecting to the internet. | ||
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| + | == Fixed Terrestrial Wireless Network Type and Infrastructure== | ||
| + | Fixed Terrestrial Wireless is a [[wikipedia:Point-to-multipoint|point-to-multipoint]] architecture, '[[wikipedia:Star network|star]]', with a single central hub radio that has internet connectivity, and a number of fixed client radios. | ||
| + | * Clients can connect to one and only one access point, and not to other clients. | ||
| + | * An access point can only connect to clients, not to other access points. | ||
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| + | == Wi-Fi Hardware == | ||
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| + | === Fixed Terrestrial Wireless Access Point === | ||
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| + | A Wireless Access Point (AP) is the central bridge device used in an Infrastructure wireless network. Traffic from the wireless side of the bridge is sent to the Internet side of the bridge, and ''vice versa''. The wireless access point controls all traffic with wireless client radios. The access point is normally pole or tower mounted at a location that provides good line of site coverage to as much of the desired service area as possible. The pole or tower mount will often contain two radios. One is the access point radio, the one that the client radios communicate with. The other is a point to point backhaul radio, that goes back to a central office and carries the traffic from the internet [http://en.wikipedia.org/wiki/Point_of_presence pop] to the pole top. | ||
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| + | === Client Radio === | ||
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| + | The subscriber installation is quite similar to that of a satellite TV receiver installation. Typically there is an radio/antenna unit mounted outside the house, in a location that has a clear view, or line of site, to the central hub radio. Depending on distance from the hub, the radio/antenna unit may be just a single weatherproof box, or for more distant locations, the radio/antenna may be mounted mounted on and pointed into a larger reflector that gives more gain. Unlike a satellite receiver system, the radio and the antenna are all located in the box mounted outside the home. The subscriber side of the radio/antenna is ethernet plus power for the radio. Add link here for power over cat5 cable. Putting the radio at the antenna eliminates radio to antenna coax losses, and therefore the length of the cable run from the outside equipment indoors is not a limiting factor for coverage area or receive signal strength. | ||
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| + | == Coverage Area == | ||
| + | === Overview === | ||
| + | Fixed Terrestrial Wireless is basically a cellular type configuration, as are Wi-Fi, WiMAX and Cellular. 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 miles from the hub. The coverage is therefore larger than WiMAX, 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. | ||
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| + | === 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 Wi-Fi in that section. 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. Note here if numbers are available. 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 won't work. | ||
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| + | The above notwithstanding, here are some comments about the radio path. | ||
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| + | As in the [http://wireless.navas.us/wiki/Wi-Fi#Wi-Fi_Hardware Wi-Fi] example, it is possible to do path calculations if you know the radio specs. The calculations follow the same format. However, since the radio is normally located at the antenna, you don't have to factor in coax losses at each end. Unlike in the case if Wi-Fi (which I would expect to be an exercise in futility doing link calculations) you should be able to get numbers that approach reality. If you know the transmit power and transmit antenna gain, and you know the receiver sensitivity and antenna gain, all that is left is the fade margin and the Path Loss. Once you calculate the Path Loss, you will then be able to calculate the fade margin. | ||
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| + | == Path Variables == | ||
| + | === 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. | ||
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| + | === Line of Sight === | ||
| + | If you have line of sight, then trees or someone building and consequently obstructing the line of sight WOULD be a problem. If you don't have line of sight, then the path may still work, and may change with the seasons if trees are the reason for it not being line of sight. | ||
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| + | === [http://en.wikipedia.org/wiki/Fresnel_zone Fresnel Zone Clearance] === | ||
| + | The remaining issue is one of ground clearance, commonly known as [http://www.afar.net/fresnel-zone-calculator/ fresnel zone clearance]. Fresnel zone clearance gives you an indication of what effect the ground along the path will have. If the path is very close to the ground, then you don't have much clearance, and will lose a few dB. But the path should be stable. If the path is high above the 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. I suspect this is seldom done for this type of service. Maybe this whole paragraph should be deleted. | ||
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| + | The only good thing to know about this fresnel zone topic is that the path will normally be short enough you don't have to worry about [http://en.wikipedia.org/wiki/K-factor K] changing the fresnel zone clearance. | ||
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| + | ==Service Speeds== | ||
| + | ===Typical=== | ||
| + | Since I have not had access to any hardware manuals, and I am writing this late at night, I will just offer up so observations. | ||
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| + | In my area at the current time, the data rate provided by my radio link is about 4.8 Mbps download, and about 1.8 Mbps upload. This can be controlled by the service provider by settings in the radio (I don't know which end) that pertain specifically to my link. This is about the same speed, if not faster, than I might get by a wired hookup by a cable or phone company provider. Ones upload and download speed to the internet can be checked at [http://www.speedtest.net/ SpeedTest]. | ||
