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Wi-Fi: 802.11 WLAN

Wi-Fi White Papers

Overview

Users can design, model and simulate WiFi networks using devices such as Access Points (AP), Wireless Nodes (STA). A drag & drop GUI enables users to quickly create the network and set properties with a simple right click. The results of a simulation run are presented in a unified dashboard for convenient analysis. Graphics plots comprises of application throughputs, link throughputs, buffer occupancy and TCP congestion windows. The tabular presentation includes end-to-end delays, jitter, errors, packets generated / received / collided, route tables, TCP Acks, retransmissions etc.

WLAN Protocol Capabilities

NetSim WLAN

MAC Layer

  • Rate Adaptation – Minstrel, Generic
  • MCS Selection – Auto rate fallback, Fixed
  • CSMA/CA - protocol with RTS / CTS exchange, DIFS, Backoff and collisions, SIFS and ACK
  • Infrastructure - BSS mode and DCF mode
  • MPDU aggregation in 802.11n and 802.11ac
  • IEEE802.11e – Quality of Service based on EDCA

PHY Layer

  • 802.11a: 5 GHz frequency, 20MHz bandwidth, OFDM modulation, Upto 54 Mbps data rate
  • 802.11b: 2.4 GHz frequency, 20MHz bandwidth, DSSS modulation, Upto 11 Mbps data rate
  • 802.11g: 2.4 GHz frequency, 20MHz bandwidth, OFDM modulation, Upto 54 Mbps data rate
  • 802.11n (MIMO 4x4): 2.4 and 5 GHz frequencies, 20 and 40MHz bandwidths, HT modulation, Upto 600 Mbps data rate
  • 802.11ac (MIMO 8x8): 5 GHz frequency, 20, 40, 80 and 160MHz bandwidths, VHT modulation, Upto 6.933 Gbps data rate
  • 802.11p: 5.9 GHz frequency, 5, 10, 20MHz bandwidths, OFDM modulation, Upto 54 Mbps data rate
  • 802.11ax: Under Development

SNR/BER/PER Calculation Procedure

Understanding the Signal-to-Noise Ratio (SNR), Bit Error Rate (BER), and Packet Error Rate (PER) is crucial for evaluating wireless communication system performance. Below is a detailed breakdown of the calculation process:

  • Received Signal Strength (RSS) Calculation

    RSS = Transmit Power - RF Propagation Losses

    • RF Propagation Losses include:
      • Path loss
      • Fading
      • Shadowing

  • Interference Calculation

    Consider all co-channel transmissions occurring simultaneously:

    • Use propagation models to compute powers of all interfering signals
    • Account for interfering transmitters at various locations

  • Signal-to-Interference-plus-Noise Ratio (SINR) Calculation

    SINR = RSS / (Interference + Noise)

  • Bit Error Rate (BER) Computation

    Look up SINR-BER curves for the given Modulation and Coding Scheme (MCS)

  • Packet Error Probability (PEP) Calculation

    Derive PEP from the calculated BER

  • Rate-Error Abstraction for PHY Transmission

    Using the calculated rate and PEP, we create an abstraction for packet transmission and reception over the air. Important considerations:

    • Perform computations for each packet due to potentially time-varying channel conditions
    • Log all radio parameters in a CSV file for each packet transmission, enabling detailed analysis

This approach accounts for various factors that affect signal quality and transmission reliability in Wi-Fi.

Propagation Models

Pathloss models

  • File Based
  • Range Based
  • Log Distance
  • Friis Free Space
  • HATA Urban/Suburban
  • Indoor Office
  • Indoor Home
  • COST 231 HATA Urban/Suburban

Fading Models

  • Rayleigh
  • Nakagami
  • Rician

Shadowing Model

  • Lognormal
  • Constant

Application Traffic Generator

  • File Transfer Protocol (FTP)
  • Database Application
  • Voice Traffic
  • Video Traffic
  • Email
  • HTTP
  • Peer to Peer
  • CBR
  • Gaming
  • Custom Model: Users can develop custom application model based on Packet size and inter-arrival time available in the following probability distributions

Source Code

  • Protocol Source C code included

Simulation Results

Radio Measurements log

Results Dashboard

  • Network Metrics, Link metrics Application metrics, Protocol Specific metrics for each protocol, and Forwarding tables.
  • Metrics include throughputs, Delays, Data & control packet information and protocol specific Results
  • Graphical plots over time for link and application throughputs and TCP congestion window
Results

WLAN Traffic - Wireshark Packet Capture

Wireshark Packet Capture

Command Line Interface - CLI

  • CLI mode of running for more concise and powerful means of control
  • Facilitates use of automated scripts for running batch simulations
  • Model network configurations using XML based configuration files

Unsupported features/limitations

  1. Association, probing, beaconing
  2. MSDU aggregation
  3. Directional Antennas
  4. Beamforming
  5. PLCP preamble reception

Useful links