In this lecture, we will delve into the physical layers defined in the IEEE 802.11 standard for wireless local area networks (WLAN). We will explore the various physical layers utilized in WLAN, focusing specifically on the IEEE 802.11-2020 standard. This standard outlines the physical characteristics that dictate data rates, channel widths, and frequency bands used in wireless communication.

 

Overview of IEEE 802.11-2020

The IEEE 802.11-2020 standard serves as a critical framework for WLAN technology, detailing the physical and data link layers responsible for wireless connectivity. The physical layers encompass essential factors such as modulation techniques, coding schemes, channel widths, and frequency usage. These elements collectively determine the performance and capabilities of a wireless network.

 

Impact of Channel Width and Modulation on Data Rates

Channel width and modulation are significant determinants of data rates in WLANs. As previously discussed regarding the Modulation and Coding Scheme (MCS) index, these factors contribute to the throughput experienced in wireless communication. Channel width refers to the amount of spectrum allocated for a specific communication channel. For instance, a standard 20 MHz channel can be combined with another to create a 40 MHz channel, enhancing throughput. However, it is crucial to note that wider channels may lead to reduced coverage.

Throughout this lecture, we will examine the different physical layers, including their respective channel widths, modulation techniques, and data rates.

Let’s begin with an in-depth analysis of each physical layer.

 

1. Direct Sequence Spread Spectrum (DSSS)

DSSS is one of the earliest physical layers defined in the 802.11 standard and continues to be supported in modern devices. Operating exclusively on the 2.4 GHz frequency band, DSSS employs a channel width of 22 MHz. This approach allows for the transmission of data over a defined frequency range.

In a DSSS configuration, a single spatial stream is used, meaning that only one antenna is required for both transmission and reception. This design limits data throughput to 1 and 2 megabits per second, making it relatively slow compared to newer standards. It is important to remember the key parameters of DSSS:

• Frequency: 2.4 GHz
• Channel Width: 22 MHz
• Data Rates Supported: 1 Mbps and 2 Mbps
• Spatial Streams: 1

2. High Rate Direct Sequence Spread Spectrum (HRDSSS)

Introduced with the 802.11b amendment in 1999, HRDSSS builds on the DSSS framework by introducing advanced modulation techniques to enhance throughput. HRDSSS operates within the same 2.4 GHz band and maintains a channel width of 22 MHz. However, it expands the data rates to include 5.5 Mbps and 11 Mbps, while still supporting the original DSSS rates of 1 Mbps and 2 Mbps.

Key characteristics of HRDSSS include:

• Frequency: 2.4 GHz
• Channel Width: 22 MHz
• Data Rates Supported: 1 Mbps, 2 Mbps, 5.5 Mbps, and 11 Mbps
• Spatial Streams: 1

This backward compatibility allows devices using the HRDSSS standard to communicate with those employing DSSS, ensuring a smooth transition as network infrastructure evolves.

3. Orthogonal Frequency Division Multiplexing (OFDM)

OFDM represents a significant advancement in WLAN technology, introduced with the 802.11a amendment, which also debuted in 1999. This physical layer operates on the 5 GHz frequency band and utilizes a channel width of 20 MHz. OFDM improves data rates substantially, with support for rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps.

Key attributes of OFDM include:

• Frequency: 5 GHz
• Channel Width: 20 MHz
• Data Rates Supported: 6, 9, 12, 18, 24, 36, 48, and 54 Mbps
• Spatial Streams: 1

It is important to note that OFDM is not backward compatible with DSSS or HRDSSS, as it operates in a different frequency band, making it crucial to assess network compatibility when deploying OFDM-based equipment.

 

4. Extended Rate Physical (ERP)

ERP was developed to extend the capabilities of OFDM for use in the 2.4 GHz band, operating under the 802.11g standard. This adaptation allows for the same modulation techniques used in OFDM while maintaining a channel width of 20 MHz. As a result, ERP supports data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps. Notably, ERP devices are backward compatible with both HRDSSS and DSSS, enabling seamless integration into existing networks.

Key features of ERP include:

• Frequency: 2.4 GHz
• Channel Width: 20 MHz
• Data Rates Supported: 6, 9, 12, 18, 24, 36, 48, and 54 Mbps
• Spatial Streams: 1

5. High Throughput (802.11n)

The 802.11n amendment introduced significant enhancements to WLAN technology by allowing devices to operate on both 2.4 GHz and 5 GHz bands. This standard supports channel widths of 20 MHz and 40 MHz, enabling the aggregation of two 20 MHz channels to improve throughput.

Key aspects of 802.11n include:

• Frequency: 2.4 GHz and 5 GHz
• Channel Widths: 20 MHz and 40 MHz
• Maximum Data Rates Supported: Up to 600 Mbps
• Spatial Streams: Up to 4

With the implementation of Multiple Input Multiple Output (MIMO) technology, 802.11n devices can utilize multiple spatial streams, significantly increasing data transmission capabilities.

6. Very High Throughput (802.11ac)

802.11ac, known for its very high throughput, is designed exclusively for the 5 GHz band and employs channel widths of 20 MHz, 40 MHz, 80 MHz, and 160 MHz. This standard enhances performance further by supporting up to 8 spatial streams and advanced modulation techniques, theoretically achieving data rates of up to 6,933 Mbps.

Key characteristics of 802.11ac include:

• Frequency: 5 GHz
• Channel Widths: 20 MHz, 40 MHz, 80 MHz, and 160 MHz
• Maximum Data Rates Supported: Up to 6,933.3 Mbps (theoretical)
• Spatial Streams: Up to 8

While 802.11ac devices can theoretically achieve incredible speeds, practical implementation may vary based on environmental conditions and device capabilities.

 

7. High Efficiency (802.11ax)

802.11ax, also known as Wi-Fi 6, introduces significant improvements to efficiency and performance, particularly in dense environments. This standard supports 2.4 GHz, 5 GHz, and 6 GHz bands, allowing for channel widths of 20 MHz, 40 MHz, 80 MHz, and 160 MHz. A notable feature of 802.11ax is the use of Orthogonal Frequency Division Multiple Access (OFDMA), enabling simultaneous transmissions to multiple devices.

Key features of 802.11ax include:

• Frequency Bands: 2.4 GHz, 5 GHz, and 6 GHz
• Channel Widths: 20 MHz, 40 MHz, 80 MHz, and 160 MHz
• Maximum Data Rates Supported: Up to 9.6 Gbps
• Spatial Streams: Up to 8

OFDMA allows for more efficient use of available bandwidth, facilitating improved performance for IoT devices and other low-bandwidth applications.

 

8. Sub 1 GHz (802.11ah)

The Sub 1 GHz standard, defined by 802.11ah, targets long-range and low-data-rate applications, primarily used in IoT scenarios. Operating in the 1 GHz band and below, it typically supports channel widths of 1, 2, 4, 8, and 16 MHz, with a maximum data rate of approximately 346.67 Mbps on a 16 MHz channel using 4 spatial streams.

Key points about 802.11ah include:

• Frequency: Sub 1 GHz (primarily 900 MHz)
• Channel Widths: 1, 2, 4, 8, and 16 MHz
• Maximum Data Rates Supported: Up to 346.67 Mbps (theoretical)
• Spatial Streams: Up to 4

This standard is particularly useful for applications requiring extended range and minimal power consumption, such as smart sensors and environmental monitoring.

Conclusion

In summary, the various physical layers defined in the IEEE 802.11 standards play a crucial role in shaping the performance and capabilities of wireless networks.