Lecture on 802.11 Wireless Networks

Overview of 802.11 Technologies

• Different technologies and standards in 802.11 wireless networks.
• Frequencies used: 2.4 GHz and 5 GHz (sometimes both in the same access point).
• Channels: Sections of frequencies used by wireless networks, numbered and assigned by IEEE.
  • Example: Channel 6 in the 2.4 GHz range is consistent across all devices.
• Channel overlap: Important to use non-overlapping channels to avoid conflicts.
• Channel width (bandwidth): Refers to the amount of frequency used (e.g., 20 MHz, 40 MHz, 80 MHz, 160 MHz).

2.4 GHz and 5 GHz Frequencies

2.4 GHz

• In North America: 3 non-overlapping channels (1, 6, 11), grouped in 20 MHz blocks.

5 GHz

• Introduced more frequencies compared to 2.4 GHz.
• Wider bandwidths available: 20 MHz, 40 MHz, 80 MHz, 160 MHz.
• Examples of usage:
  • 802.11a, b, g: 20 MHz bandwidth (22 MHz for b).
  • 802.11n: Options for 20 MHz, 40 MHz, or 80 MHz.
  • 802.11ac: 20, 40, 80 MHz, and up to 160 MHz by bonding two 80 MHz channels.
  • 802.11ax: Same bandwidth options as 802.11ac.

Independent Basic Service Set (IBSS)

• Allows direct communication between two stations without an access point (ad hoc mode).
• Useful for temporary or permanent connections without requiring an access point.

Service Set Identifiers (SSID) and Basic Service Set Identifier (BSSID)

• SSID: Name of the wireless network (e.g., SGC1, Guest).
• BSSID: Physical/MAC address of the access point.
• ESSID: Extended SSID used across multiple access points, allowing seamless roaming.

Multi-user MIMO (Multiple-Input, Multiple-Output)

• Supported in 802.11n, 802.11ac, and 802.11ax.
• Allows multiple streams of data to be sent simultaneously.
• Examples of configurations:
  • 2x2:2 (2 antennas on AP, 2 on client, 2 streams).
  • 4x4:4 (4 antennas on AP, 4 on client, 4 streams).

802.11n

• Supports simple MIMO.

802.11ac

• Supports downstream multi-user MIMO.

802.11ax

• Supports both downstream and upstream multi-user MIMO.
• Introduces OFDMA (Orthogonal Frequency Division Multiple Access) for more efficient data distribution.

Antennas

Omnidirectional Antennas

• Common, distributes signal evenly in all directions.
• Good for central placement in buildings.

Directional Antennas

• Focuses signal for long-distance communication.
• Examples:
  • Yagi Antennas: High gain, compact.
  • Parabolic Antennas: Very high gain, focuses signal to a single point.