Imagine that you have two copies of a movie and two television sets. One copy is on Blu-ray and you pair that with a high-definition television — an HDTV. The other copy is on standard DVD, which you’ll watch on a standard-definition television. You synchronize both videos and watch the results.
The difference in image quality between the two sets should be obvious. The HDTV’s picture should look crisper and have colors far more vibrant than the standard counterpart. We’ve reached the peak of video quality — or have we?
When we talk about HDTVs, we’re really talking about image resolution. The picture on a television set is composed of millions of tiny dots of light called pixels. Standard-definition televisions have a resolution of 480. That means approximately 480 horizontal lines from the top of the screen to the bottom generate the images you see.
High-definition televisions pack more lines of pixels to create images. On the low end of the high-definition standard in the United States you have approximately 720 lines of pixels. On the high end, you have approximately 1,080 lines of pixels. Manufacturers are slowly phasing out the 720-line models in favor of the 1,080-line ones.
Using more pixels to create an image results in a smoother picture. Imagine you’re given a stack of green and brown squares of paper. You’re told you have to build a picture of a tree using the squares exactly as they are. If the squares of paper are large, your tree is going to look blocky with lots of jagged edges. But if you have smaller squares of paper, the tree will look smoother and more natural.
That’s what high-definition television does. It’s not just the number of pixels in the image — it’s the size of each individual pixel. As you pack more pixels into a screen, you have to make the pixels themselves smaller. In turn, the television will produce smoother images.
But is 1080 the best resolution possible? Could you buy a television set that packed even more pixels together? Would it make a difference? And would you be able to find programming that conformed to the higher resolution? Let’s find out.
There are few situations more terrifying than being trapped underground with no visible means of escape. Miners risk being caught in this situation every day they go to work. In the United States, the Mine Safety and Health Administration establishes guidelines and safety measures that help minimize the chance of a disaster. But sometimes that’s not enough.
According to the Bureau of Labor Statistics, the fatality rate for miners in 2007 was 24.8 per 100,000 people employed. Only the collective industries of agriculture, fishing, forestry and hunting had a higher fatality rate. Not every fatality was the result of a collapsed mine. An equipment failure or poor safety habits can also end in tragedy. Miners may encounter dangerous gases like methane as they move underground, too.
One of the biggest challenges in mine safety is communication. It’s difficult to create a network that works well underground. Most radio waves can’t penetrate rock — you need to have a line of sight between the two transmission points. That’s not feasible for most mining operations. A strong communications system underground could help reduce mining accidents and increase the effectiveness of rescue operations.
A wireless radio network would be a key component of an effective communications system. Using radio waves, miners could remain in contact with surface operations. Sensors hooked up to a wireless radio network could send back environmental information to the base of operations, alerting team leaders to potentially hazardous situations before an accident can happen. And with the right tracking system, leaders could keep tabs on where miners are within the mine. In the event of an accident, leaders could determine who was in the area at the time.
Wireless technology is pervasive — you can find hotspots in airports and coffee shops. Some cities have rolled out municipal wireless networks. You might think that every mine in the world would have them, too. But remember: Radio waves have a hard time penetrating through solid rock. When you design a wireless radio network for a mine, you have to take that into account. We’ll look at two of the most common approaches to implementing a wireless radio network in a mine.
First, we’ll focus on a system with a funny name: the leaky feeder.
