Fly Through Air With Greatest of Ease
One of the coolest aspects of the Convergence Wave is being able to adapt new technologies to old problems. While wireless transmission of video is not necessarily a new solution, recent technology advances have made it much more affordable and flexible.
In ancient times, you know, six to seven years ago, if you needed to put a camera or other device out at a location without infrastructure, you only had a couple of choices. You could trench at great cost, or you could put up a fixed, licensed microwave wireless system … also at great cost.
With the advent of wireless networking devices, our lives have become much easier, in some respects. It has also introduced many new choices, technologies and terms that we need to sort through. Let’s take a look at the basics of the new Wireless Wave.
Deciphering the Alphabet Soup
As mentioned, the new wireless options available to us are a direct result of developments in the networking industry. Like all other advances in that world, wireless technology adheres to standards. These standards are specified under IEEE 802.11 Wireless LAN (WLAN) protocols. The sections we are most concerned with fall under three (now four) letter designations: a, b, g and the proposed n.
Probably the most common WLAN standards in use today are 802.11 b and g. They don’t require licensing, and the wireless access points used for these standards are very affordable and available everywhere (as we’ll see in a bit, this is a double-edged sword).
The main differences between all these standards are the frequencies they operate on and the (theoretical) data rate across the link. Operating at 2.4GHz, 802.11b states a data rate of 11Mbps. I mentioned theoretical because the actual throughput is approximately 4Mbps. An important point to remember about wireless links is the stated data rate and the actual throughput are two very different numbers!
On the consumer market, 802.11b was the first wireless standard that really became widely available. This made it very prevalent, very quickly. Consequently, the 2.4GHz wireless network channels used by b are extremely crowded. This, coupled with the small actual throughput, makes it fairly undesirable for wireless video.
The next standard to hit the mass market was 802.11g. Also operating at 2.4GHz, g does offer greater throughput and higher availability of empty space. At 54Mbps theoretical and approximately 19Mbps actual, it is an acceptable choice for your digital video project.
There is another standard available, 802.11a. It operates at 5GHz, and has a stated rate of 54Mbps and effective throughput of 23Mbps (slightly better than g). Because of the overcrowding of the 2.4GHz band, 802.11a offers much more flexibility of installation locations, due to its use of the 5GHz band. This lack of overcrowding is due in part to 802.11a equipment being more expensive, and not being as readily available as its b and g counterparts.
Unfortunately, as wireless networked video systems become more widespread, the 802.11a space will suffer the same crowded fate as the others. Enjoy it while you can.
The newest kid on the block technically hasn’t arrived yet, but that doesn’t seem to be stopping vendors from making equipment for it. Offering vast improvements over b, g and even a, 802.11n allows for operation in both 2.4 and 5GHz, making it backward compatible with the others. It also gives you a stated theoretical rate of 248Mbps, with an actual rate (with today’s equipment) of approximately 74Mbps.
Only one problem … the 802.11n standard has not been ratified yet. Everything you see on the market today with “n” in the name is a pre- or draft-n standard. Even the MIMO (multiple-in-multiple-out) technology devices are based on drafts of the n standard. Here’s the problem: Even though the standard is close to being stable and finalized (sometime next year, supposedly), if anything in that standard is changed, there’s a chance some of that gear won’t work. Most of the gear you are going to run into for high-end commercial wireless systems will fall into the 802.11a standard.
Site Survey Critical Prior to Work
I mentioned previously that the availability and inexpensiveness of wireless network equipment is a double-edged sword. Add that to the fact that these systems don’t require licenses and we have a problem. Anyone can, at any time, put up a wireless link, anywhere.
I want to stress two important things at this point. The first is in order to have a successful wireless installation, a site survey must be performed before equipment is purchased or even specified to make sure there is space available in the spectrum in that location.
The second is no matter how good the site survey, your link can be interrupted at any time by someone in the area throwing up their own wireless system. Be prepared for the phone calls.
The wireless site survey, or spectrum analysis, can be done at a couple of levels. Most higher-end wireless systems offer built-in spectrum analyzers. Only one problem: You have to have the product purchased and installed in order to use it.
True spectrum analyzer packages come in various flavors, and most are expensive. They can be purchased as a standalone device, which is basically an elaborate oscilloscope. More recently, laptop-based packages have become more readily available and affordable. The laptop systems are also more portable and flexible.
Portable analyzer packages are probably not worth the cost if you only do the occasional point-to-point wireless link. If you do systems of any size, or point-to-multipoint systems, it may be a wise investment.
Sharing the Love
One trend starting to emerge in wireless network systems is the appearance of municipal, city-wide wireless networks. These systems are being used for everything from transmission of network data to police and fire vehicles to public Wi-Fi access points.
This dual use may be a good way for an integrator to upsell a wireless video system to a municipality. Unfortunately, the bandwidth used by streaming video is too large to share a link with most other applications.
A new solution to this bandwidth problem has been showing itself in the marketplace. Several wireless manufacturers are now offering dual-radio transceivers. For some of the products, the two radios can be joined together to offer increased throughput for backhaul applications.
Other systems, however, have the ability to put each radio on a different frequency, isolating the two into different networks. This would allow one side to be used for video streaming, and the other for public or municipal access points. The dual-radio hardware allows several different configurations for your system. Each device can be an access point, bridge, backhaul or a combination. Access points allow a device to be connected to the network itself.
A bridge can be used to couple multiple nodes together, in some cases bypassing obstacles such as buildings. A backhaul is generally a high bandwidth link used to get multiple streams back to a central point.
Vast Subject Demands More Study
We have covered some of the basic wireless concepts as they pertain to networked systems. For more general wireless information, see “10 Tips to Reliable Wireless Systems” on page 42. In addition, many manufacturers offer training on this complex subject.
Wireless is an excellent way to get signals where wired infrastructure just won’t go or would be expensive to get there. Unwire yourself and your video; just make sure you do your homework first.
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