Module 1: System View
Wi-Fi 802.11 Generations
Learning objectives
- Explain the core mental model behind Wi-Fi 802.11 Generations
- Apply Wi-Fi 802.11 Generations within System View
- Identify important boundaries, trade-offs, and failure modes
- Produce concrete evidence from the practice exercise
Related: WIFI OFDM PLCP | WIFI MIMO Beamforming | WIFI Rate Control and MCS | WIFI Performance and Airtime | WIFI Index
Why Generations Matter to Hardware
Each 802.11 generation adds more than a higher number in marketing material. It changes PHY datapath width, clocking, memory, calibration, packet metadata, scheduler behavior, and verification scope.
| Family | Common name | Main hardware change |
|---|---|---|
| 802.11b | Wi-Fi 1 era | DSSS/CCK PHY, 2.4 GHz only |
| 802.11a/g | Wi-Fi 2/3 era | OFDM PHY, 20 MHz channels |
| 802.11n | Wi-Fi 4 | MIMO, HT preamble, A-MPDU, Block Ack importance |
| 802.11ac | Wi-Fi 5 | Wider channels, VHT, higher-order QAM, downlink MU-MIMO |
| 802.11ax | Wi-Fi 6/6E | OFDMA, trigger-based uplink, BSS coloring, HE preamble |
| 802.11be | Wi-Fi 7 | EHT, 320 MHz, 4096-QAM, multi-link operation, stronger multi-user pressure |
802.11a/g: OFDM Baseline
802.11a and 802.11g make OFDM the practical baseline for modern Wi-Fi hardware:
- 20 MHz channel
- OFDM symbols with subcarriers and pilots
- convolutional coding
- BPSK/QPSK/16-QAM/64-QAM
- legacy preamble and SIGNAL field
For MAC hardware, the important point is that the PHY can report a packet length and rate from the PLCP header, allowing the MAC to compute duration and NAV behavior.
802.11n: HT and MIMO
802.11n adds High Throughput (HT):
- multiple spatial streams
- optional 40 MHz operation
- short guard interval option
- A-MPDU aggregation becomes central
- Block Ack becomes essential for throughput
- MCS index encodes modulation, coding, and spatial streams
Hardware impact:
- RX must handle multiple RF chains and channel matrices.
- MAC needs reorder buffers and BA window tracking.
- TX scheduler must build aggregates without underrun.
- Rate control now chooses MCS and spatial stream count, not just a scalar rate.
802.11ac: VHT
802.11ac focuses on Very High Throughput:
- 80 MHz and optional 160 MHz channels
- 256-QAM
- more spatial stream scaling
- downlink MU-MIMO
- VHT-specific preamble and signaling
Hardware impact:
- FFT/IFFT size and datapath bandwidth increase.
- EVM requirements become tighter for high-order QAM.
- Beamforming feedback and steering matrix support become more important.
- MAC aggregation depth must grow to keep wide PHYs busy.
802.11ax: HE
802.11ax improves efficiency in dense networks:
- OFDMA resource units
- uplink trigger-based access
- BSS coloring
- target wake time
- more robust long OFDM symbols
- spatial reuse mechanisms
Hardware impact:
- PHY must support partial-band resource units, not only full-channel packets.
- MAC scheduler needs trigger frame handling and multi-user timing.
- CCA may include BSS color and spatial reuse decisions.
- More metadata crosses the MAC/PHY boundary.
802.11be: EHT
802.11be pushes Extremely High Throughput:
- wider channels up to 320 MHz
- 4096-QAM
- multi-link operation
- enhanced multi-user operation
- more aggressive aggregation and scheduling
Hardware impact:
- very high internal bandwidth
- larger reorder and aggregation structures
- tighter RF linearity and EVM requirements
- coordination across links for MLO-capable implementations
Design Rule
Do not design the MAC as if the PHY rate is the only variable. Modern Wi-Fi hardware must treat bandwidth, NSS, GI, coding, RU allocation, aggregation depth, BA window, queue priority, and channel occupancy as coupled design inputs.
Related
- WIFI OFDM PLCP — OFDM and PLCP details
- WIFI MIMO Beamforming — Spatial streams and beamforming
- WIFI Rate Control and MCS — MCS and feedback
- WIFI Performance and Airtime — Throughput and airtime math
Practice lab
Draw or encode one legal transaction trace for Wi-Fi 802.11 Generations. Annotate fields, channel events, ordering points, and completion conditions; then construct one illegal or adversarial trace and define the checker that should catch it.
Review questions
- What problem does Wi-Fi 802.11 Generations solve, and what assumptions does it rely on?
- Which boundary or failure case is easiest to miss, and how would you expose it?
- What alternative design would you consider, and what trade-off would change the decision?
- What artifact, trace, test, or metric proves that your implementation is correct?
Completion evidence
- A working artifact, annotated trace, or reproducible experiment
- At least one normal case and one deliberately failing or boundary case
- A concise explanation of the design choice and its trade-offs
- Saved output showing how correctness was evaluated