From Analog to Digital
Every modern wireless system turns the message into bits before it modulates. Why did the whole world switch from analog?
Continuous vs. Discrete
Analog carries information in a continuously varying quantity — the exact voltage is the message. Digital carries it as discrete symbols (bits). A dimmer knob vs. a labelled switch.
Noise Immunity by Regeneration
The receiver only decides which symbol was sent. If noise is smaller than half the gap between symbols, it snaps back to a perfect copy — relayed across a continent, bit-for-bit identical. Analog degrades at every hop.
Error Correction & Compression
- Error correction — add redundant bits; the receiver detects and repairs corruption with no retransmit
- Compression — strip redundancy (JPEG, MP3, H.264) to fit far more in the same bandwidth
Neither has an analog equivalent — you cannot checksum a voltage.
Multiplexing & Security
- Multiplexing — many users’ bit streams interleave onto one channel and separate perfectly (one tower, thousands of phones)
- Encryption — bits can be secured with provable strength; a waveform cannot
The Shannon Limit
The maximum error-free rate depends only on bandwidth B and SNR. Every digital scheme aims toward this ceiling (Module 6 derives it).
Bits per Symbol
More symbols M → more bits each — but less tolerance for noise. And the catch: digital fails at a cliff, not a graceful fade.
What you learned
- Digital = discrete symbols; regeneration erases small noise instead of accumulating it
- Bits enable error correction, compression, multiplexing, and encryption
- Shannon–Hartley C = B log₂(1 + SNR) is the hard ceiling
- Bit rate = symbol rate × log₂M; the cost is an ADC and the cliff effect