Understanding Wireless Network Performance

Aug 9, 2024

Wireless Networks Performance and Measurement

Key Challenges

  • Performance varies based on location, access point, and other variables.

Measuring Performance

  • Throughput: Amount of data transferred at any time.
  • Connection Speed: Proximity to the access point influences speed.

Received Signal Strength Indication (RSSI)

  • RSSI: Measures the signal strength received on a device.
    • Measured in dBm (decibels per milliwatt).
    • Negative values: closer to 0 is better.

  • RSSI Values:

    • -50 dBm or higher: Excellent
    • -70 dBm: Good
    • -80 dBm or lower: Low

Tools for Measuring RSSI

  • Wireless Survey Tools: Collect RSSI and noise values.
  • Spectrum Analyzers: Detailed frequency analysis.

Example Measurements

  • Good Connection: RSSI of -40 dBm, noise -90 dBm.
  • Poor Connection: RSSI of -85 dBm, noise close to -90 dBm.

Transmitted Signal Strength (EIRP)

  • EIRP: Effective isotropic radiated power.
    • Factors: Transmit strength, antenna gain, cable loss.
    • FCC Regulations: Max EIRP for 2.4 GHz is 36 dBm (4 watts).
  • Control Over EIRP:
    • Adjustable transmit power percentages (e.g., 100%, 75%).

Antenna Types

  • Omnidirectional Antennas:
    • Signal equally distributed in all directions.
    • Best for central locations.
  • Directional Antennas:
    • Focused signal, increases distance.
    • Types: Yagi, parabolic (used for long distances).

Antenna Polarization

  • Polarization: Orientation relative to the Earth.
    • Horizontal or vertical.
    • Both transmitter and receiver must match polarization for efficiency.

Access Point Association Time

  • Association Time: Time for devices to connect to access points.
    • Delays can occur with low/block signal or controller issues.
    • Measured via wireless controllers or SNMP.

Dealing with High-Density Environments

  • Challenges: Large number of users can use all available frequency.
    • Common in large gatherings (sports events, trade shows).
  • Metrics: Available air time percentage.
    • 100% usage indicates full capacity.
  • Solutions:
    • Disable legacy modes for faster speeds.
    • Check for interference and change frequencies if needed.
    • Adjust output power settings or add new access points to split load.

Site Surveys

  • Purpose: Identify wireless signals and interference.
    • Ongoing surveys recommended for changing environments.
  • Heat Maps: Use third-party software to map signal strength throughout a building.