Wi-Fi | Курс "Компьютерные сети"

Introduction to Wi-Fi Technology

Overview of Wi-Fi

• The speaker introduces himself as Andrey Sazykhin and presents the course on networks and telecommunications, focusing on Wi-Fi technology.

• Wi-Fi is described as the most popular wireless data transmission technology. The term "Wi-Fi" is a trademark owned by the Wi-Fi Alliance, which ensures compliance with standards.

• Unlike Ethernet, which allows manufacturers to create devices without certification, Wi-Fi requires equipment to pass tests for compliance with IEEE 802.11 standards.

Technical Standards

• Wi-Fi operates at both physical and data link layers in the OSI model, utilizing two sub-layers: MAC (Medium Access Control) and LLC (Logical Link Control).

• There are two main modes of operation: infrastructure mode (using access points connected to wired networks) and ad-hoc mode (direct communication between devices).

Wi-Fi vs. Ethernet

Addressing and Data Transmission

• Both Wi-Fi and Ethernet use MAC addresses for device identification; however, they differ in their transmission mediums—Wi-Fi uses electromagnetic radiation while Ethernet uses cables.

• The frame format at the data link layer is similar for both technologies, allowing tools like Wireshark to capture packets regardless of their source.

Evolution of Standards

• The first standard, IEEE 802.11, was established in 1997 with speeds of 1 or 2 Mbps; modern standards have significantly increased this capacity.

• Current standards utilize electromagnetic radiation exclusively from the second generation onward (802.11b), operating primarily at 2.4 GHz and 5 GHz frequencies.

Frequency Management in Wi-Fi

Channel Utilization

• Data transmission employs Orthogonal Frequency Division Multiplexing (OFDM), allowing parallel data transfer across different frequencies.

• There are a limited number of channels available (14), leading to potential interference when multiple networks operate within close proximity—a phenomenon known as "Wi-Fi jungle."

Bandwidth Considerations

• Wider channels allow for higher data rates; newer standards support channel widths up to 160 MHz but depend on manufacturer implementation.

Advanced Features in Modern Standards

MIMO Technology

• Multiple Input Multiple Output (MIMO) technology enables simultaneous signal transmission through multiple antennas, enhancing throughput significantly.

• With three transmitting antennas sending distinct spatial streams, MIMO can triple data transfer rates by effectively managing these signals at the receiving end.

Understanding Wi-Fi Signal Quality and Speed

Signal Quality and Speed Variability

• The signal quality for each spatial stream in Ethernet is fixed, with speeds such as 100 Mbps or 1 Gbps being uniform across all devices in the network.

• In contrast, Wi-Fi allows speed adjustments based on signal quality; higher signal quality results in increased speed, while lower quality leads to decreased speed.

Parameters Affecting Wi-Fi Speed

• Various parameters can be adjusted to modify Wi-Fi speed, including channel width (ranging from 20 MHz to 160 MHz) and different modulation techniques that transmit data at varying speeds and reliability.

• The lowest achievable speed of 6.5 Mbps occurs with binary phase modulation using a 20 MHz channel and an 800 ns guard interval; conversely, the highest speed of 866 Mbps is achieved through quadrature amplitude modulation with a 160 MHz channel and a 400 ns guard interval.

Spatial Streams and Data Transmission

• Utilizing multiple antennas allows for several spatial streams, which can significantly enhance data transmission rates.