1.1 An Overview of IEEE 802.11

1.1.1 The 802.11 MAC Layer

• The 802.11 MAC adopts CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) for medium access, differing from Ethernet's CSMA/CD due to wireless constraints.
• Stations sense the medium before transmitting and back off randomly if the medium is busy.
• Wireless collisions are inferred by the absence of acknowledgments, unlike wired networks where collisions are detected electrically.

1.1.2 The 802.11 PHY Layers

• The original IEEE 802.11 standard (1997) defined three physical layers (PHYs):
• Infrared (IR)
• Frequency Hopping Spread Spectrum (FHSS)
• Direct Sequence Spread Spectrum (DSSS)
• Later amendments added:
• 802.11b: Improved DSSS with CCK (11 Mbps in 2.4 GHz).
• 802.11a: Introduced OFDM (54 Mbps in 5 GHz).
• 802.11g: Combined OFDM in 2.4 GHz with backward compatibility to 802.11b.
• 802.11n and 802.11ac introduced wider channels and MIMO.

Key Data Rate Progression:

• 802.11n: Up to 600 Mbps using 40 MHz channels.
• 802.11ac: Up to 6.933 Gbps with 160 MHz channels and 8 spatial streams.

1.1.3 Network Architecture

• Basic Service Set (BSS): A foundational unit of 802.11, either:
• Independent BSS (IBSS): Ad-hoc, peer-to-peer communication.
• Infrastructure BSS: Managed by an access point (AP).
• Extended Service Set (ESS): Multiple BSSs connected via a distribution system (DS), typically Ethernet.

1.1.4 Wi-Fi Direct

• Enables peer-to-peer communication without an AP.
• One device acts as a Group Owner (GO), similar to an AP but without infrastructure dependency.

1.2 History of High Throughput and 802.11n

1.2.1 High Throughput Study Group

• Formed in 2002 to address the need for higher data rates (e.g., 100+ Mbps).
• Explored technologies like spatial multiplexing and wider bandwidth.

1.2.2 Formation of Task Group n (TGn)

• Task Group n (TGn) was created in 2003 to develop the 802.11n standard.
• Goals:
• Minimum 100 Mbps throughput.
• Support for backward compatibility (802.11a/b/g).
• Spectrum efficiency: At least 3 bps/Hz.

Key Challenges:

• Balancing higher throughput with backward compatibility and coexistence.
• Developing functional requirements and comparison criteria for proposals.

1.3 Applications and Environments for 802.11n

• Home, enterprise, and public spaces (e.g., hotspots) require higher data rates for applications like:
• HD video streaming
• Voice over IP (VoIP)
• Online gaming

1.4 Major Features of 802.11n

• MIMO (Multiple Input Multiple Output): Improves throughput by transmitting multiple spatial streams.
• Channel Bonding: Combines two 20 MHz channels into a 40 MHz channel for higher data rates.
• Frame Aggregation: Groups smaller frames into larger ones to reduce overhead.
• Short Guard Interval (GI): Reduces the gap between symbols to improve efficiency.

1.5 History of 802.11ac

• Built as an evolution of 802.11n, offering:
• Wider bandwidths (80 MHz and 160 MHz).
• Support for MU-MIMO (Multi-User MIMO), enabling simultaneous transmissions to multiple devices.
• Higher-order modulation (256-QAM) for improved spectral efficiency.

1.6 Outline of the Book

• The book is structured to provide:
• A detailed explanation of the physical (PHY) and medium access control (MAC) layers.
• Insights into enhancements like beamforming and MU-MIMO.
• Guidance on coexistence and interoperability with legacy standards.

Key Mathematical Insights in Chapter 1:

1. Data Rate Progression:
   R=M⋅Subcarriers⋅Modulation Bits⋅Coding Efficiency
• MMM: Spatial streams.
• Highlights exponential growth in data rates (up to 6.933 Gbps for 802.11ac).
2. Spectral Efficiency:
   Efficiency = Throughput \ Channel Bandwidth
• 802.11n: At least 3 bps/Hz.

1. CSMA/CA Collision Avoidance:
   
• Random backoff algorithm reduces the chance of simultaneous retransmissions.