Technology Brief

This is a gentle introduction to the technology of broadband distribution. We have tried to make it as simple as possible, and we shall use our own project as an example.

In order to get broadband to your house, some kind of connection needs to be made to the backhaul. The backhaul is the network that connects the country (in fact the world) together. Think of it as the water mains or the electricity grid – it’s where you get your broadband “supply” from. In cities, many people connect to the backhaul at the telephone exchange over their copper telephone wire, but for reasons we shall describe shortly, this may not be possible in the country. It’s important to understand that the company that provides the backhaul is not necessarily the company that connects you to the backhaul.

To connect to the backhaul, there are two general methods: through some kind of cable and using wireless. Let’s look at the cable options first.

• Copper wire. This 150 year old technology has served telephone communications very well, but speech transmission requires rather low data rates. Telephone wires are not good for the data rates required by broadband. The longer the line, the slower the transmission. If you are above 5 miles it’s unlikely that the wire will carry any kind of broadband and above 2 miles, the transmission speeds are not likely to be good.

  In Arnisdale, the telephone connection comes from Glenelg (where there is backhaul) but the cable has been dropped along the roadside by British Telecom and is nine miles long. This is too long for broadband. In fact people at the end of the cable even have difficulty in getting a dial-up connection. Copper wire is not only bad for broadband, it is unecological. The cable between Arnisdale and the exchange in Glenelg probably contains more than three tons of copper!

• Optic fibre. This has excellent transmission properties. In fact this is how the huge amounts of data are carried over long distances (e.g., under the Atlantic). Optic fiber is also being used for last mile transmission in some urban areas. Many businesses use it internally. While the cost of fibre may be comparable to copper, the higher deployment costs come in the way of its universal adoption. A possibility is to use mixture of optic fibre and copper (FTTC) that obviates the need for re-wiring individual homes while still delivering high-speed Internet access.

• Coaxial cable. We mention it here for completeness. Many cities have been wired with coax for cable TV. It can also be used to carry high data rates, but optic fibre is better. Of course, remote communities haven’t been wired with coax.

The other form of transmission is wireless. There are two kinds:

• Satellite. Here you have a dish pointing at a satellite which connects you with the backhaul back on the ground. Currently the only form satellite broadband that is affordable by most of us is one in which the signals coming into your house come via satellite, but the outgoing signal goes by telephone cable. This works if you are browsing the Web when a few keystrokes go out and lots of data comes back, but it won’t support internet telephony and it won’t support businesses that send out as much data as they receive. Also, the affordable packages provide download rates that are little better than a good dial-up connection.

  Another possibility is two-way satellite, in which both the inward and outward signals go via satellite. First, these packages are much more expensive – hundreds of pounds a month – and the data rate still isn’t that great.

  But there is another problem with any kind of satellite transmission. To get to the backhaul, the signal has to travel a huge distance – almost half way to the moon. Even though the rate of data transmission may be adequate, there is a noticeable delay in the signal getting to its destination. This makes internet telephony difficult, and some programs that require direct interaction over the internet become almost unusable.

• Wireless. We should say terrestrial wireless, to distinguish it from satellite, which is also wireless. In this form, the signal is relayed via masts. Wireless is already used (microwave links) for the backhaul. It is also used (wifi) for local transmission in your house. The commercial-grade kit that is used for backhaul is very expensive, so what we are doing is adapting the technology that is used in your house to work over long distances.

  A challenge with terrestrial wireless in the Scottish Highlands is that the transmission relays, usually small masts, have to have line-of-sight; they have to “see” each other. Now it can be quite difficult in mountainous terrain to arrange this. Also the weather is not friendly and our masts have some appeal to amourous or bellicose stags. This is where the fun starts

The conclusion of this story is that terrestrial wireless is the only option open to us, and our research is aimed at making this cheap, reliable and high speed. If you want to learn more about how we are doing this, please turn to our research page.