19. Modulation: Carrying data on radio waves

A good and brief article describing how to transmit (computer) binary data over the air using an airwave as a transport medium is included below for anybody, who is interested in a quick understanding of signal modulation.

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1. Modulation: Carrying data on radio waves

http://www.secureidnews.com/news-item/contactless-101-modulation-lets-radio-waves-carry-data/

2. Illustrated charts taken from Internet.

2a. Amplitude Modulation and Frequency Modulation

Source: https://commons.wikimedia.org/wiki/File:Amfm3-en-de.gif

2b. Amplitude Shift Keying

Source: https://www.tutorialspoint.com/digital_communication/digital_communication_amplitude_shift_keying.htm

2c. Phase shift key

Source: https://payatu.com/getting-started-with-radio-waves-hacking/

2d. Phase shift modulation

Source: https://dsp.stackexchange.com/questions/42803/relation-between-normal-phase-shift-of-a-wave-and-phase-modulation

2e. Phase modulation

Source: http://www.carritech.com/news/what-is-modulation-in-telecommunications/

2f. Different types of modulation

Figure 1. Analog modulation

Figure 2. Digital Modulation

Source: https://www.edgefx.in/types-of-modulation-techniques-with-applications/

3. Binary presentation of data

Our (computer) data are presented in binary codes, i.e. 0 and 1. For example,

Digits:

- 0000 0000: is zero

- 0000 0001: is one

- 0000 0010: is two

Characters:

Letter	ASCII Code	Binary
a	097	01100001
b	098	01100010
c	099	01100011
d	100	01100100

In section 1 and 2, you can see that binary data are converted in different types of wave forms, i.e. modulation techniques to transmit in sine waves, and then receiver to demodulate and sample receiving data in order to convert those back into square waves based on the technology used in the transmitter. The square waves will be converted into binary data, which would be processed by a computer.

Figure 3. Diagram illustrates the process described above.

4. Sharing a frequency band by different service providers

Usually telecom providers or operators used the different frequency bands to provide wireless services. 

However many operators could use "frequency modulation" or "phase shift key modulation" to provide services to their users using the same frequency band as long as they provided different amplitude in carrier waves. The wireless receiver would extract data from wave carriers with expected amplitude, i.e. allocating different amplitudes to adjacent operators in an area.