High-Density and De-Densified Smart Campus Communications. Daniel Minoli

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СКАЧАТЬ Area Networks – Specific Requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Technical corrections and clarifications to IEEE Std 802.11 for Wireless Local Area Networks (WLANs), as well as enhancements to the existing Medium Access Control (MAC) and Physical Layer (PHY) functions, are specified in this revision. P802.11ax – 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 Enhancements for High‐Efficiency WLAN This amendment defines modifications to both the IEEE 802.11 Physical Layer (PHY) and the Medium Access Control (MAC) sublayer for high‐efficiency operation in frequency bands between 1 and 7.125 GHz. P802.11az – 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 – Enhancements for Positioning This amendment defines modifications to both the IEEE 802.11 Physical Layer (PHY) and Medium Access Control (MAC) sublayer that enable determination of absolute and relative position with better accuracy with respect to the Fine Timing Measurement (FTM) protocol executing on the same PHY‐type, while reducing existing wireless medium use and power consumption and is scalable to dense deployments. This amendment requires backward compatibility and coexistence with legacy devices. Backward compatibility with legacy 802.11 devices implies that devices implementing this amendment shall (a) maintain data communication compatibility and (b) support the FTM protocol. P802.11bb – 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: Light Communications The scope of this standard is to define one Medium Access Control (MAC) and several Physical Layer (PHY) specifications for wireless connectivity for fixed, portable, and moving stations (STAs) within a local area. P802.11bc – 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 Broadcast Service The scope of this standard is to define one Medium Access Control (MAC) and several Physical Layer (PHY) specifications for wireless connectivity for fixed, portable, and moving stations (STAs) within a local area. P802.11bd – 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: Enhancements for Next‐Generation V2X The scope of this standard is to define one Medium Access Control (MAC) and several Physical Layer (PHY) specifications for wireless connectivity for fixed, portable, and moving stations (STAs) within a local area. P802.11be – 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: Enhancements for Extremely High Throughput (EHT) This amendment defines standardized modifications to both the IEEE Std 802.11 Physical Layers (PHY) and the Medium Access Control Layer (MAC) that enable at least one mode of operation capable of supporting a maximum throughput of at least 30 Gbps, as measured at the MAC data Service Access Point (SAP), with carrier frequency operation between 1 and 7.250 GHz while ensuring backward compatibility and coexistence with legacy IEEE Std 802.11 compliant devices operating in the 2.4, 5, and 6 GHz bands. This amendment defines at least one mode of operation capable of improved worst‐case latency and jitter.

Figure 2.2 illustrates a schematic block diagram of a wireless device at some level of specificity.

Each of the stations and the AP includes a processor and a transceiver and may further include a user interface and a display device. The processor is configured to generate frames to be transmitted through the wireless network, to process frames received through the wireless network, and to execute protocols of the WLAN. The processor performs some or all its functions by executing computer programming instructions stored on a non‐transitory computer‐readable medium. The transceiver represents a unit that is functionally connected to the processor and designed to transmit and receive frames through the wireless network. The transceiver may be defined using a single component that performs the functions of transmitting and receiving, or two separate components, each performing one of such functions [2]. As noted earlier, a station may typically include a desktop computer, a laptop computer, a tablet PC, a wireless phone, a mobile phone, a smartphone, an e‐book reader, a Portable Multimedia Player, a portable game console, a navigation system, a digital camera, and so on.

FIGURE 2.2 Block diagram of a WLAN device (example).

      WLAN devices are being deployed in diverse environments; these environments are characterized by the existence of many APs and non‐AP stations in geographically limited areas; increased interference from neighboring devices gives rise to performance degradation. Furthermore, WLAN devices are increasingly required to support a variety of applications such as video, cloud access, and cellular network offloading. In particular, video traffic is expected to be a major, if not the dominant type of traffic in many high‐efficiency WLAN deployments. With the real‐time requirements of some of these applications, WLAN users require improved performance in delivering their applications, including improved power consumption for battery‐operated devices [2].

      Some of the PHY techniques are discussed first, followed by a discussion of the Data Link layer techniques.

      2.3.1 PHY Layer Operation

Traditionally, at the PHY level, the 802.11 protocol uses a Carrier Sense Multiple Access (CSMA)/Collision Avoidance (CA) channel management method: WNs first sense the channel and endeavor to avoid collisions by transmitting a packet only when they sense the channel to be idle; if the WN detects the transmission of another node, it waits for a random amount of time for that other WN to stop transmitting before sensing again to assess if the channel is free. The process is based on the AP or the WN establishing signal detection energy on a given channel; specifically, the Received Signal Strength Index (RSSI) of the received PLCP (Physical Layer Convergence Protocol) Protocol Data Unit (PPDU)⁴: if the signal detection energy is less than a Clear Channel Assessment (CCA) threshold, the AP or the WN then contends for the channel and transmits its data.

      As described, a terminal in a WLAN checks whether a channel is busy or not by performing carrier/channel sensing before transmitting data. Such a process is referred to as CCA, and a signal level used to decide whether the corresponding signal is sensed, is referred to as a CCA threshold. When a radio signal is received by a terminal, it is processed to determine if it has a value exceeding the CCA threshold. When a radio signal having a predetermined or higher‐strength value is sensed, it is determined that the channel under consideration is physically busy, and the terminal delays its access to that channel. When a radio СКАЧАТЬ