How To Learn Wi-Fi
Published:
Learning Wi-Fi can be quite complicated for beginners. Wi-Fi physical layer has lots of features, including OFDM, OFDMA, MIMO and supports up to 160 MHz bandwidth. Start with the legacy Wi-Fi, which usually refers to 802.11a/g. Their physical layer is based on OFDM SISO with 20 MHz bandwidth, which is sufficient to understand the important Wi-Fi OFDM design.
This blog post focuses on the preamble-related parts.
0. OFDM
Reading materials:
- Read Section 4.1, 4.2 of Book MIMO-OFDM Wireless Communications with MATLAB.
- Read Chapter 2 of Book Next Generation Wireless LANs 802.11n and 802.11ac
Key learning points:
- FFT and IFFT
- Time domain and frequency domain signals
- CP
1. Wi-Fi Physical Layer
Transmitter
Reading materials:
- Chapter 4 of Book: Next Generation Wireless LANs 802.11n and 802.11ac (Focus on Section 4.1 in the beginning).
- Chapter Orthogonal frequency division multiplexing (OFDM) PHY specification of the IEEE 802.11 standard. Download it from IEEE Xplore
- Non-HT PPDU Structure
Key learning points:
- Preamble design including short training symbols and long training symbols
Channel
Reading materials:
- Chapters 1-3 of MIMO-OFDM Wireless Communications with MATLAB. Understand what is multipath channel. Focus on small-scale fading in the beginning.
- Matlab has modeled the fading channels, which can be found here
- Propagation Channel Models for WiFi/IEEE 802.11
Key learning points:
- Small-scale fading
- Modelling of multipath channel (frequency selectivity vs flat fading)
- Modelling of Doppler spread (fast vs slow fading)
Receiver
Reading materials:
- Paper Performance Assessment of IEEE 802.11p with an Open Source SDR-Based Prototype , which explains receiver algorithms design, including time synchronization, frequency offest estimation, channel estimation, etc.
Key learning points:
- Packet detection: How to use short training symbol for coarse time synchronization (autocorrelation)
- Symbol alignment: How to use long training symbol for fine time synchronization (cross correlation)
- Carrier frequency offset estimation and correction (autocorrelation)
- Channel estimation using long training symbols
2. Matlab Simulation
- Run 802.11n Packet Error Rate Simulation for 2x2 TGn Channel to understand physical layer algorithms. Setting the number of transmit antennas to 1 in the example.
- Model 802.11a/b/g/j/p-related signal reception functionality: Understand each receiver algorithm
3. Experimental Practice
- Software-defined radio (SDR): if you have SDR platforms (USRP or PlutoSDR), check Matlab WLAN SDR examples
- ESP32: try ESP32 CSI Toolkit to get CSI
Return to the Main Page of Wireless Communication Technologies.