1.3.1 IEEE 802.11 Architecture

Wireless LANs (Wi-Fi) have revolutionized connectivity. The 802.11 architecture defines several key components.

• BSS (Basic Service Set): A group of stations communicating with each other.
• BSSID: The MAC address of the Access Point (AP).
• ESS (Extended Service Set): Multiple BSSs connected via a Distribution System (DS), allowing for roaming.

Study Deep: MIMO vs. Beamforming

While often used together, they solve different problems:

1. MIMO (Multiple Input Multiple Output): Uses multiple antennas to send multiple different data streams at once (Multiplexing).
2. Beamforming: Uses multiple antennas to focus the radio energy in the direction of a specific user, increasing range and signal strength (Directionality).

1.3.2 The MAC Layer: CSMA/CA

Unlike wired Ethernet which uses CSMA/CD, wireless uses CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) because wireless radios cannot usually listen while they transmit.

The Process:

1. DIFS: Station waits for a Distributed Inter-Frame Space.
2. Backoff: Station picks a random backoff time.
3. RTS/CTS (Optional): Request to Send / Clear to Send to solve the Hidden Node Problem.
4. Data: Send the actual data frame.
5. ACK: The receiver sent an acknowledgment. If no ACK, the sender assumes collision and tries again.

1.3.3 Evolution of 802.11 Standards:

• 802.11b (1999): 11 Mbps at 2.4 GHz.
• 802.11g (2003): 54 Mbps at 2.4 GHz (OFDM introduced).
• 802.11n (Wi-Fi 4): 600 Mbps, introduced MIMO (Multiple Input Multiple Output) and 40 MHz channels.
• 802.11ac (Wi-Fi 5): Multi-gigabit at 5 GHz, introduced beamforming and 160 MHz channels.
• 802.11ax (Wi-Fi 6/6E): Focuses on efficiency in crowded areas using OFDMA.

1.3.4 Physical Layer Techniques:

1. DSSS (Direct Sequence Spread Spectrum): Used in older 802.11b.
2. OFDM (Orthogonal Frequency Division Multiplexing): The standard for high-speed Wi-Fi, splitting the signal into multiple sub-carriers to combat interference.
3. MIMO: Using multiple antennas to transmit and receive multiple data streams simultaneously.

1.3.5 Wi-Fi 7: The Future of Wireless (802.11be)

Wi-Fi 7 is currently being deployed to handle Extreme High Throughput (EHT).

• 320 MHz Channels: Doubling the width of Wi-Fi 6.
• 4096-QAM: Packing more data into each signal.
• Multi-Link Operation (MLO): Allowing a device to send and receive data across different frequency bands (2.4, 5, and 6 GHz) at the same time for higher reliability.