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Remote Access and Site Connectivity: Wireless
Ceragon manufactures an extensive line of microwave radio systems (several of which are used successfully at Clear Channel in New York). For this topic I'll point out the FibeAir 4800, which is its product for the license-exempt ISM bands (2.4 and 5.8GHz). The FibeAir 4800 is specified to operate at data rates of up to 48Mb/s; modulation schemes are user-configurable (QPSK, 16QAM or 64QAM); it has native T1 interfaces, along with its Ethernet interface; and comes in three different physical versions - all indoor, all outdoor, or split indoor/outdoor units.
Ubiquiti (used successfully at Clear Channel in Los Angeles) is another manufacturer of license-exempt Ethernet radios. Its Rocket M2 (2.4GHz) and Rocket M5 (5.8GHz) radios are specified to hit data rates as high as 150Mb/s, though 54Mb/s (at -75dBm receive signal level) at 2.4GHz, and 5.8GHz are found from a perusal of the spec sheets. Ubiquiti's AirView software is included in all the M units, allowing the user to do remote spectrum analysis - clearly useful in setting up the links for the first time, and also troubleshooting later on should the need arise. (The unlicensed bands are subject to interference from other users, after all.) Ubiquiti also offers a line of small dishes that are made to easily integrate with the radios. The Rocket is an outdoor unit; installation consists of the mounting of the dishes, physically connecting the outdoor unit to the chosen antenna, and powering the device over the Ethernet cable.
Once you've established your radio LAN extension to your remote site, there may be one other problem to consider. What if you have more than one building at the site (say on top of a mountain)? What's the best way to add all the buildings to the network? The correct answer will depend upon the circumstances, of course. If the buildings are adjacent to one another, then it may be possible to simply connect them via CAT-5e or CAT-6 cables (made for outside and/or direct burial). On the other hand, they may be too far away from each other (or say, across the street) making direct cable connections impractical. Here again you could make use of the same sort of inexpensive ISM band radios we have already gone over to make a network. Obviously you'll need to make sure you can configure the radios to operate on different channels inside the ISM band choice so the various links can coexist with one another. Some amount of experimentation may be necessary in order to find the best ISM band for the site. Making use of the 900MHz ISM band for example, could be very problematic in the presence of other transmitters operating around 900MHz at a mountain top or other remote site.
Figure 1 illustrates an implementation. At the terminal site for your radio link you'll simply connect more of the radios up to ports on a Layer-2 switch. Each subsidiary radio link will act as a LAN bridge, so hosts in each of the other buildings will need to be addressed with the same network numbers.
Establishing high-speed Ethernet at a remote site can be very beneficial to the operation of a radio station; access to remote controls, computers, cameras, off-site servers and the like will give your system more functionality and probably make your job easier in the long run. It's well worth the investment in time and money.
Irwin is RF engineer/project manager for Clear Channel Los Angeles. Contact him at firstname.lastname@example.org.
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