Bands tell you where a signal sits. This track is about what the signal is: how bits become a radio wave, why each technique was invented, and what it looks like when it goes wrong. Each topic is about one technique only, so you can go as deep as you like without losing the thread.
The vocabularyFive words people mix up
| Term | What it is | Examples |
|---|---|---|
| Frequency band | Where the signal sits in the spectrum | 2.4, 5 and 6 GHz |
| Waveform (PHY technique) | How the signal is built in time and frequency | DSSS, FHSS, CCK, OFDM |
| Modulation | How bits are mapped onto phase and amplitude | DBPSK, DQPSK, BPSK, QPSK, QAM |
| Coding | Extra bits added so errors can be corrected | Convolutional coding, LDPC |
| Standard (amendment) | The document that defines all of the above for one generation | 802.11b, g, n, ac, ax, be |
The common mistake. “2.4 GHz” is a band, not a modulation. “OFDM” is a waveform, not a standard. “802.11ax” is a standard, not a band. When a question mixes these up, it usually cannot be answered until they are pulled apart.
The pathFrom bits to radio
- Bits from the MAC layer.
- Coding adds protection (not all waveforms use it).
- Modulation turns bits into phase and amplitude values.
- The waveform arranges those values in time and frequency: spread over chips, hopped across channels, or spread over subcarriers.
- The radio sends the result on the band and channel the regulator allows.
TopicsStart with any of these
802.11 and 802.11bDSSSSpreading with a code, processing gain and why 1 and 2 Mbit/s are so robust.802.11-1997 onlyFHSSHopping across channels, and where the idea lives on today.802.11bCCKHow 8 bits choose one of 256 code words: 11 Mbit/s without a wider channel.802.11a, g and laterOFDMSubcarriers, orthogonality, the IFFT and the guard interval, step by step.802.11a to 802.11beQAMConstellations from BPSK to 4096-QAM, and what noise does to them.802.11ax and 802.11beOFDMAResource units: sharing one channel between several clients.802.11n and laterMIMOSpatial streams, beamforming and multi-user MIMO.