WiFi and Bluetooth

WiFi (802.11)

Generational Evolution

Key Concepts

Frequency Bands

2.4 GHz: Crowded (microwaves/BT/Zigbee all operate here), good wall penetration
  Channels 1~13 (China), only 3 non-overlapping channels (1/6/11)

5 GHz: Clean, many channels, large bandwidth, poor wall penetration
  Many channels, can bond 80/160 MHz

6 GHz (WiFi 6E/7): New spectrum, almost no interference
  But worse wall penetration, currently only for indoor use

OFDM / OFDMA

OFDM (WiFi 4/5): Occupies the entire channel for each transmission
  → Small packets also occupy the full channel, low efficiency

OFDMA (WiFi 6+): Divides the channel into RUs (Resource Units)
  → Multiple devices transmit simultaneously, similar to LTE
  → Significantly reduces latency and improves multi-device efficiency

Analogy: OFDM = single lane, OFDMA = multi-lane highway

MIMO / MU-MIMO

MIMO: Multiple antennas transmit and receive simultaneously
  2×2: 2 transmit, 2 receive (common in phones/laptops)
  4×4: 4 transmit, 4 receive (high-end routers)

MU-MIMO: Simultaneously sends data to multiple clients
  WiFi 5: Downlink only, WiFi 6: Supports both uplink and downlink

MLO (Multi-Link Operation) — WiFi 7

Simultaneously uses multiple bands (2.4G + 5G + 6G) for transmission
→ Higher throughput + lower latency + better reliability
→ If one band is interfered with, seamlessly switch to another

Bluetooth (Bluetooth)

Classic vs BLE

BLE Versions

4.0: Basic BLE
4.2: Security enhancements, packet length extension
5.0: 2M PHY, long-range coding, extended advertising
5.1: Direction finding (AoA/AoD → centimeter-level positioning)
5.2: LE Audio, Isochronous Channels (for TWS earbuds)
5.3: Channel classification, connection subevents
5.4: Periodic advertising sync (for electronic shelf labels)

Actually, BLE 4.2 is sufficient for most scenarios.
5.0+ mainly brings: faster, longer range, more power-efficient.

BLE Connection Flow

① Advertising

② Scan Request

③ Scan Response

④ Connection Request

Continuous Audio → Classic (A2DP)
Occasional Data + Low Power → BLE
Need iOS Background Communication → BLE (Apple favors BLE)
HID Keyboards/Mice → BLE (HID over GATT)
File Transfer → Classic (or WiFi Direct)
TWS Earbuds → BLE 5.2+ (LE Audio)

2.4GHz is the battlefield for WiFi + BT + Zigbee + Thread + Microwaves

WiFi and BT are in the same device:
  → Time Division Multiplexing (TDM): Alternating use of antennas
  → Coexistence Interface: Bluetooth tells WiFi "I'm about to send a packet", WiFi pauses

Implementation: Most WiFi/BT combo chips have internal coexistence mechanisms
     (MTK/Realtek/Broadcom/Qualcomm each have their own implementations)
Driver-side issues often cause coexistence failures (e.g., your MT7927)

In consumer electronics, WiFi and BT are almost always on the same chip
  MT7921/7925/7927 (MTK)
  AX200/AX210 (Intel)
  BCM series (Broadcom)

Connect to Host via PCIe/USB/SDIO
The Bluetooth part is usually exposed via a USB HCI interface