There have been all sorts of possible explanations as to why WiMAX is not readily available. Most refer to business plans and political issues. Some recent news may very well point to the real reason for the slow rollout. Quite simply, providers are having problems trying to get "big enough pipes" to the cell towers. The InfoWorld article, "Backhaul woes slow Sprint's WiMAX rollout," mentions:
"What's holding Sprint back is simply the logistics of building the network, and specifically the problem of provisioning "backhaul" connections to the Internet. Mobile operators typically lease T-1 lines from their cell sites for these backhaul links, but those lines only provide 1.5Mbps. WiMax is designed to deliver more than that to every subscriber."Existing cell tower bandwidth
Some history might be in order here. A typical cell tower that was in a fairly active area would have 3 to 4 T1s aggregate bandwidth. If that particular tower was upgraded to 3G then usually one or two more T1's were added to the mix, bringing the total bandwidth to approximately 9Mbps.Bandwidth and range advertised by WiMAX
WiMAX has a theoretical maximum bandwidth of 75Mbps using 64QAM 3/4 modulation. WiMAX has a theoretical maximum range of 31 miles with a direct line of sight. It's not too hard to see why WiMAX backhaul may become a real issue. Requiring almost ten times the bandwidth that exists at each cell tower is a very significant increase. I also wonder if the increased range was factored in. A larger coverage area does not increase the bandwidth required per user, but it does increase the aggregate bandwidth as more users could be in each cell's coverage area.What's the solution?
As a network engineer, increasing bandwidth to a facility is my bread and butter. A typical solution is to jump up to the next T-carrier, which in this case would be a T3. The bandwidth supplied by a T3 is approximately 45Mbps. One challenge with T3 cabling is that it's not just your simple two twisted pairs of wire anymore. The copper solution for T3 is a pair of coaxial cables — one to transmit and one to receive — with BNC connectors. Another challenge is that T3 signals can only run short distances — standard distance is 380m-over copper.
Service providers are well aware of this and now have two challenges to overcome, increased bandwidth needs and expensive circuit extension challenges. There are two viable approaches being considered, and ultimately, it appears the answer will be a combination of both.
Since there is still some question as to what the ultimate bandwidth requirements will be, the logical choice is to just run fiber circuits to the cell tower. That will allow almost unlimited bandwidth, if implemented properly, by having extra dark fiber. There is major sticker shock with this approach, though. I have heard figures in the range of US$50,000 to $100,000 to run fiber to the cell tower, and that dollar amount is based on having a fiber network reasonably close to the cell tower.
A more logical and cost-effective approach would be to use microwave backhaul instead of fiber or even a composite of both. For example, one topology would have each remote cell tower connecting to a centrally located cell tower via an OC-3 microwave link. The distribution cell tower would be chosen or located so as to facilitate quality microwave links with all of the remote cell towers as well as the most cost-effective fiber run to the system's fiber network.
One interesting tidbit about this topic is that the rest of the world is significantly ahead of the U.S. when it comes to using microwave links for network backhaul. According to that same InfoWorld article:
"So the carrier wants to use point-to-point microwave wireless connections. Though these are used widely in other parts of the world -about half of all backhaul in Europe is microwave, and more than that in Asia, IDC analyst Godfrey Chua estimates-Sprint is practically treading on virgin territory by seeking it in the U.S., according to West. There are few engineers well-versed in setting it up, and Sprint has to overcome zoning issues for many installations, he said. The procedures of setting it up are also quite different, with the need to find an unobstructed line of sight through the air and deal with zoning issues."Final thoughts
One has to wonder why this is even an issue. Isn't it logical to think that this should have been looked at right away? Is it possible that a technical oversight may be turning into a major business headache for Sprint and others? The recent interest of Comcast and Time Warner Cable in Sprint and WiMax, as pointed out by TechRepublic Executive Editor Jason Hiner in his post, "Sprint CEO stays the course on WiMAX, but launch won't happen in April" may be coincidental, but both players have access to significant fiber networks and that might help Sprint's cause. Hmmmm.
I also did a little poking around, and I see that Clearwire — on and off WiMAX partner of Sprint — is advertising for microwave engineers. In fact, there seems to be a significant number of openings for microwave engineers. Hmmmm.
Information is my field...Writing is my passion...Coupling the two is my mission.