Frequency band
2.2 WLAN STANDARDS
Standards for WLAN technology have been developed over the years by the IEEE under the 802.11 Work Group. IEEE 802.11™ (generally “802.11”) is a set of physical and MAC specifications for implementing WLAN communications. Part 11 is known as “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications” and is maintained and enhanced by the IEEE WG802.11 – Wireless LAN Working Group. These specifications provide the basis for wireless network products using the Wi‐Fi brand, managed and defined by the Wi‐Fi Alliance. The specifications define the use of the 2.400–2.500 GHz as well as the 4.915–5.825 GHz unlicensed bands. Each spectrum is subdivided into channels with a center frequency and a specified bandwidth. The 2.4 GHz band is divided into 14 channels spaced 5 MHz apart, though some countries regulate the availability of these channels. The 5 GHz band is more heavily regulated than the 2.4 GHz band and the spacing of channels varies across the spectrum, with a minimum of a 5 MHz spacing dependent on the regulations of the respective country of operation [4].
The IEEE 802.11 family of standards has gone through several iterations in recent years. In the 1990s, IEEE 802.11a and 802.11b were developed. IEEE 802.11b provided a transmission rate of 11 Mbps and IEEE 802.11a provided a transmission rate of 54 Mbps. In the 2000s, the IEEE 802.11 g was developed; it provides a transmission rate of 54 Mbps by applying OFDM at 2.4 GHz. To overcome the limits of WLAN communication speed, recent WLAN standards have introduced new schemes for increasing the speed and reliability of a network and extending a management distance of a wireless network. For example, IEEE 802.11n has introduced the standard of MIMO, using multiple antennas for both transmitter and receiver to support high throughput (HT), as depicted graphically in Figure 2.1. IEEE 802.11n provides a transmission rate of 300 Mbps with four spatial streams by applying MIMO‐OFDM; the standard also supports a channel bandwidth of up to 40 MHz and thus, provides a theoretical transmission rate of 600 Mbps with four spatial streams. These earlier standards have evolved into IEEE 802.11ac that can utilize a bandwidth of up to 160 MHz and supports a transmission rate of up to about 1 Gbps; it can make use of up to 8 spatial streams. The IEEE 802.11ax standard was under finalization at press time; the standard defines a high‐efficiency WLAN for enhancing the system throughput in high‐density environments; 802.11ax contemplates dynamically adjusting the energy level when a channel is clear, depending on whether the energy corresponds to its BSS signals or signals from another BSS [5, 6]. Such a scheme helps to promote spatial reuse between neighboring networks.
More broadly, a series of standards have been adopted as the WLAN evolved, including IEEE Std 802.11‐2012 (March 2012). This standard was subsequently amended by IEEE Std 802.11ae‐2012, IEEE Std 802.11aa‐2012, IEEE Std 802.11ad‐2012, IEEE Std 802.11ac‐2013, IEEE Std 802.11af‐2013, IEEE Std 802.11aj‐2018, IEEE Std 802.11ak‐2018, and IEEE Std 802.11aq‐2018 [2, 7, 8, 9]. Table 2.2 provides a list of IEEE 802.11 active projects at press time [10].
2.3 WLAN BASIC CONCEPTS
The transmission processes operate at the PHY layer and the Data Link layer. A WLAN device typically includes a baseband processor, a RF transceiver, an antenna unit, a storage device (e.g. memory), an input interface unit, and an output interface unit. The baseband processor performs baseband signal processing and includes a MAC processor and a PHY processor.
The MAC processor includes a MAC software processing unit and a MAC hardware processing unit. The PHY processor includes a transmitting signal processing unit and a receiving signal processing unit. The PHY processor implements a plurality of functions of the PHY layer. These functions may be performed in software, hardware, or a combination thereof according to implementation.
The PHY processor may be configured to generate Channel State Information (CSI), according to information received from the RF transceiver. The CSI may include one or more of an RSSI; a Signal to Interference and Noise Ratio (SINR); a Modulation and Coding Scheme (MCS); and the Number of Spatial Streams (NSS). CSI may be generated for one or more frequency blocks, a sub‐band within the frequency block, a subcarrier within a frequency block, a receiving antenna, a transmitting antenna, and combinations of a plurality thereof.
TABLE 2.2 IEEE 802.11 Active Projects at Press Time
| 802.11 Amendment | Description |
|---|---|
| P802.11ay – IEEE Draft Standard for Information Technology – Telecommunications and Information Exchange Between Systems Local and Metropolitan Area Networks – Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications – Amendment: Enhanced Throughput for Operation in License‐Exempt Bands Above 45 GHz | This amendment defines standardized modifications to both the IEEE 802.11 Physical Layers (PHY) and the IEEE 802.11 Medium Access Control layer (MAC) that enables at least one mode of operation capable of supporting a maximum throughput of at least 20 gigabits per second (measured at the MAC data service access point), while maintaining or improving the power efficiency per station. |
| P802.11ba – IEEE Draft Standard for Information Technology – Telecommunications and Information Exchange Between Systems Local and Metropolitan Area Networks – Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment: Wake‐up radio operation | This amendment defines modifications to both the IEEE 802.11 Physical Layer (PHY) and the Medium Access Control (MAC) sublayer for wake‐up radio operation. |
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P802.11 – IEEE Draft Standard for Information Technology
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