What is signal encoding?

Signal encoding is the process by which data bits (0 and 1) are converted into a physical signal suitable for transmission over a communication medium.

Put simply: signal encoding determines exactly how 0 and 1 will look "in reality", as voltage, light, or a radio wave.

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#Why signal encoding is needed

Computers work with bits, but:

• you cannot send an "abstract 0" over a cable
• you cannot send an "abstract 1" through the air

So bits need to be encoded into a physical signal that:

• can be transmitted
• can be received
• can be told apart from interference

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#What this looks like in practice

#In wired networks

• 0 and 1 are encoded as voltage levels
• or as a change in signal shape

Example:

• high level is 1
• low level is 0

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#In fiber optics

• 1 means there is a light pulse
• 0 means there is no light pulse (or the other way around, depending on the standard)

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#In wireless networks

Bits are encoded as changes in:

• frequency
• phase
• radio wave amplitude

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#What encoding actually determines

Signal encoding defines:

• what 0 looks like
• what 1 looks like
• how to tell bits apart from each other
• how the receiver understands where a bit starts and ends

This is a key task of the physical layer.

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#Important point for interviews

Encoding ≠ encryption

• encoding is needed to transmit the signal
• encryption is needed to protect the data

The physical layer encodes, but does not encrypt.

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#Simple analogy

Morse code:

• a dot and a dash are encoding
• the actual meaning of the message is not here yet

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#Briefly, for the interview

Signal encoding is the conversion of bits (0 and 1) into a physical signal of a specific form that can be transmitted over a cable or through the air.