What Are the Advantages of Digital Transmission?
- Any transmitted signal, be it digital or analog, must go through several electronic devices such as modulators, demodulators and amplifiers, in both the transmitter and receiver. None of these devices are perfect and add some degree of noise and distortion. Also, as the signal passes over its wire or through the air, it picks up more noise and interference from power lines, other transmitted signals and even the sun. So any signal will always arrive at its destination in a weak and distorted condition.
- In an analog signal, the information desired is equally affected by all of these external factors. At the receive end, filters and demodulators can clean up some of this noise, but never all of it. But in the digital system at the originating end, the desired information has been coded into a series of 1's and 0's which only represent the original signal. Even in a highly distorted receive signal, the digital decoder need only pick the 1's and the 0's out of the noise to completely recreate the signal.
- Assume a professor wants to distribute a lecture to college campuses across the nation. In the analog example, he makes analog tape and gives it to one college. That college keeps the tape, but makes a copy and forwards it on to the next college, which does the same, and so on. After multiple generations, copies will become so distorted they are no longer usable. However, a digital tape would be the same as if he had written a letter (a code) and sent it in the same manner. At each college, a professor (decoder) "reads" the letter aloud to an audience, copies it and passes it along. But even if the letter gets crumbled, rained on, discolored or stained as it is copied, as long as it is readable, the lecture can be regenerated by any professor without adding the noise or distortion to the actual speech.
- In any receive signal, the ratio between the wanted and unwanted part is called the signal to noise ratio. With equal signal to noise ratios, the digital signal will outperform the analog system because the decoder need only be able to distinguish 0's and 1's, whereas the analog signal will need to pick up far more complex information out of the mess of wanted and unwanted signals. It could be compared with picking black and white marbles out of muddy water as opposed to filtering out different colored oils. The marbles can be found in the water more easily, and then clearly identified.
- The threshold of a receiver such as a TV set lets us know how weak of a signal can be received and still give a usable sound and picture. In an analog system, as the received signal decreases in strength, the noise (or static on the audio and snow on a TV screen) increases, until it is all static and snow. But in a digital signal, the snow won't even begin to appear until the signal is almost gone. Therefore, you will get cleaner sound and picture with hardly any signal at all.
- Some other more technical advantages of digital transmission include that it can be more easily encrypted for better security, can carry more data on a given system, can integrate voice, video and data more easily, can be checked for errors easily, and can go longer distances because the noise and distortion do not increase. The signals are not repeated; they are regenerated. When transmitted over fiber optic systems, digital signals can carry tremendous amounts of traffic over far greater distances.
