This array of communication technologies can be confusing but the basic idea is quite simple. These are all members of the family of Electromagnetic Waves. Other members of this family include
- TV and radio signals
- Microwaves in your oven
- Gamma rays (from radioactive decay)
- Ultraviolet and Infrared rays
- And the ever popular visible light rays in a variety of colors that surround us every day
The only difference in these waves is their frequency. If you could change the frequency of light rays, they might become microwaves and you'd be cooked like a hamburger when you turned on a lamp to read.
To communicate using electromagnetic radiation we have created devices like radio and TV transmitters coupled with sending and receiving antennas so we can hear or view the signals. Our antennas pick up all the signals and the tuner in a radio or TV set picks out a very precise frequency - 91.1 for example - so we hear a specific station.
Our cell phones have the capability to communicate using the parts of the spectrum listed in the title above. There is an antenna built into your cell phone for each type of signal it can handle. Obviously the 3G phone signal coming from a cell tower is included or it wouldn't be a cell phone. 3G means the third generation cell phone technology; 4G is coming soon. 3G and 4G signals are designed primarily for voice transmission but can be used for data if you don't have a wi-fi connection available. The other signals are designed for data but services like Skype allow voice signals to be be handled also.
Wi-fi signals are generated by a wi-fi router in your home, office, coffee shop or collection of devices in a city-wide system. 3G signals can be transmitted for miles but your wi-fi router only has a range of a few hundred feet. Your neighbor may be able to pickup your signal and use your Internet connection if she is in the right part of her house. Most modern cell phones can receive GPS signals from satellites eleven thousand miles above the earth (see "range" below). The GPS signal is not related to the 3G signals so a cellphone connection is not required.
Bluetooth signals are short range signals used so nearby devices such as a keyboard and computer or cell phone and ear piece can communicate. Even shorter range signals will be used by NFC - Near Field Communication system - being developed now for credit card applications. That signal can only be transmitted for an inch and a half; very low power indeed. Every signal differs from all others in two respects - frequency and amplitude (power).
The range a signal can travel is determined by its power - also referred to as amplitude. There are strict regulations on what frequency and amplitude someone can use to broadcast or transmit. A certain frequency can be used in one location by one radio station. That same frequency can be used in another distant city provided the strength of the signals are set so they don't extend into each others territories.
An entirely new system consisting of thousands of high-powered wi-fi towers is under development by LightSquared. These towers would blanket the US with high powered wi-fi signals for nearly universal Internet access across the country. There is controversy, however, because these wi-fi signals are very close to the frequencies assigned to GPS. and could interfere with navigation. This could be very serious since airline navigation systems are at long last being converted to GPS.