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History of Cellular Phones
Cellular: A type of wireless communication that is most familiar to mobile phones users. It’s called ‘cellular’ because the system uses many base stations to divide a service area into multiple ‘cells’. Cellular calls are transferred from base station to base station as a user travels from cell to cell. – definition from the Wireless Advisor Glossary.
The basic concept of cellular phones began in 1947, when researchers looked at crude mobile (car) phones and realized that by using small cells (range of service area) with frequency reuse they could increase the traffic capacity of mobile phones substantially. However at that time, the technology to do so was nonexistent.
Anything to do with broadcasting and sending a radio or television message out over the airwaves comes under Federal Communications Commission (FCC) regulation. A cell phone is a type of two-way radio. In 1947, AT&T proposed that the FCC allocate a large number of radio-spectrum frequencies so that widespread mobile telephone service would become feasible and AT&T would have a incentive to research the new technology. We can partially blame the FCC for the gap between the initial concept of cellular service and its availability to the public. The FCC decided to limit the amount of frequencies available in 1947, the limits made only twenty-three phone conversations possible simultaneously in the same service area – not a market incentive for research.
The FCC reconsidered its position in 1968, stating “if the technology to build a better mobile service works, we will increase the frequencies allocation, freeing the airwaves for more mobile phones.” AT&T and Bell Labs proposed a cellular system to the FCC of many small, low-powered, broadcast towers, each covering a ‘cell’ a few miles in radius and collectively covering a larger area. Each tower would use only a few of the total frequencies allocated to the system. As the phones traveled across the area, calls would be passed from tower to tower.
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Why is a cell phone called a cell phone?
One of the most interesting things about a cell phone is that it is really a radio. Before cell phones, people who needed mobile communications ability installed radio telephones in their cars. In the radio telephone system, there was one central antenna tower per city, and perhaps 25 channels available on that tower. The cellular phone system divides the area of a city into small cells. This allows extensive frequency reuse across a city, so that millions of people can use cell phones simultaneously.
Here’s how it works: The carrier chops up an area, such as a city, into cells. Each cell is typically sized at about 10 square miles (perhaps 3 miles x 3 miles). Cells are normally thought of as hexagons on a big hexagonal grid. Each cell has a base station that consists of a tower and a small building containing the radio equipment. Cell phones have low-power transmitters in them and the base station is also transmitting at low power. Low-power transmitters have two advantages:
- The power consumption of the cell phone, which is normally battery-operated, is relatively low. Low power means small batteries, and this is what has made handheld cellular phones possible.
- The transmissions of a base station and the phones within its cell do not make it very far outside that cell. Therefore, cells can use the same 56 frequencies. The same frequencies can be reused extensively across the city.
The cellular approach requires a large number of base stations in a city of any size. A typical large city can have hundreds of towers. But because so many people are using cell phones, costs remain fairly low per user. Each carrier in each city also runs one central office called the Mobile Telephone Switching Office (MTSO). This office handles all of the phone connections to the normal land-based phone system, and controls all of the base stations in the region.
As you move toward the edge of your cell, your cell’s base station will note that your signal strength is diminishing. Meanwhile, the base station in the cell you are moving toward (which is listening and measuring signal strength on all frequencies, not just its own one-seventh) will be able to see your phone’s signal strength increasing. The two base stations coordinate themselves through the MTSO, and at some point, your phone gets a signal on a control channel telling it to change frequencies. This hand off switches your phone to the new cell.
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