Serial I/O Example 2: Networking and Communications: IEEE 802.11 Wireless LANWireless LAN

The IEEE 802.11 family of networking standards are serial wireless LAN standards and are summarized in Table 4.1. These standards defi ne the major components of a wireless LAN system.

Table 4.1: 802.11 standards.

IEEE 802.11 Standard Description

802.11-1999 Root Standard for The 802.11 standard was the fi rst attempt to defi ne the way Information Technology— wireless data from a network should be sent. The standard Telecommunications and defi nes operations and interfaces at the MAC (Media Access Information Exchange between Systems— Control) and PHY (physical interface) levels in a TCP/IP Local and Metropolitan Area Network— network. There are three PHY layer interfaces defi ned (one Specifi c Requirements—Part 11: Wireless IR and two radio: Frequency-Hopping Spread Spectrum LAN Medium Access Control (MAC) and [FHSS] and Direct Sequence Spread Spectrum [DSSS]), and Physical Layer (PHY) Specifi cations the three do not interoperate. Use CSMA/CA (carrier sense

multiple access with collision avoidance) as the basic medium access scheme for link sharing, phase-shift keying (PSK) for modulation.

802.11a-1999 “WiFi5” Amendment 1: Operates at radio frequencies between 5 GHz and 6 GHz High-speed Physical Layer in the to prevent interference with many consumer devices. Uses 5 GHz band CSMA/CA as the basic medium access scheme for link

sharing. As opposed to PSK, it uses a modulation scheme known as orthogonal frequency-division multiplexing (OFDM) that provides data rates as high as 54 Mbps maximum.

802.11b-1999 “WiFi” Supplement to Backward compatible with 802.11. 11Mbps speed, 802.11a-1999, Wireless LAN MAC and one single PHY layer (DSSS), uses CSMA/CA as the basic PHY Specifi cations: Higher-speed Physical medium access scheme for link sharing and

Layer (PHY) extension in the 2.4 GHz band complementarycode keying (CCK), which allows higher data rates and is less susceptible to multipath-propagation interference.

802.11b-1999/Cor1-2001 Amendment 2: To correct defi ciencies in the MIB defi nition of 802.11b.

Higher-speed Physical Layer (PHY) extension in the 2.4 GHz band—

Corrigendum 1

802.11c IEEE Standard for Information Designated in 1998 to add a subclass under 2.5 Support of Technology—Telecommunications and the Internal Sublayer Service by specifi c MAC Procedures information exchange between systems— to cover bridge operation with IEEE 802.11 MACs. Allows the Local area networks—Media access use of 802.11 access points to bridge across networks within control (MAC) bridges—Supplement for relatively short distances from each other (i.e., where there support by IEEE 802.11 was a solid wall dividing a wired network).

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IEEE 802.11 Standard Description

802.11d-2001 Amendment to IEEE Internationalization—defi nes the physical layer requirements 802.11-1999 (ISO/IEC 8802-11), (channelization, hopping patterns, new values for current MIB Specifi cation for Operation in Additional attributes, and other requirements) to extend the operation Regulatory Domains of 802.11 WLANs to new regulatory domains (countries).

802.11e Amendment to STANDARD [for] Enhance the 802.11 Medium Access Control (MAC) to Information Technology- improve and manage quality of service (QoS), provide classes Telecommunications and information of service and effi ciency enhancements in the areas of the exchange between systems-Local and Distributed Coordination Function (DCF) and Point metropolitan area networks-Specifi c Coordination Function (PCF). Defi ning a series of extensions requirements-Part 11: Wireless LAN to 802.11 networking to allow for QoS operation (i.e., to Medium Access Control (MAC) and allow for adaptation for streaming audio or video via a Physical Layer (PHY) specifi cations: preallocated dependable portion of the bandwidth.) Medium Access Method (MAC) Quality

of Service Enhancements

802.11f-2003 IEEE Recommended Standard to enable handoffs (constant operation while the Practice for Multi-Vendor Access Point mobile terminal is actually moving) to be done in such a Interoperability via an Inter-Access Point way as to work across access points from a number of Protocol Across Distribution Systems vendors. Includes recommended practices for an Inter-Supporting IEEE 802.11 Operation Access Point Protocol (IAPP), which provides the necessary

capabilities to achieve multivendor Access Point

interoperability across a distribution system supporting IEEE P802.11 Wireless LAN Links. This IAPP will be developed for the following environment(s): (1) a distribution system consisting of IEEE 802 LAN components supporting an IETF IP environment; (2) others as deemed appropriate.

802.11g-2003 Amendment 4: Further A higher-speed(s) PHY extension to 802.11b—offering wireless Higher-Speed Physical Layer Extension transmission over relatively short distances at up to 54 Mbps in the 2.4 GHz Baud compared to the maximum 11 Mbps of the 802.11 standard and operating in the 2.4 GHz range. Uses CSMA/CA as the basic medium access scheme for link sharing.

802.11h-2001 Spectrum and Transmit Enhancing the 802.11 MAC standard and 802.11a High Power Management Extensions in the Speed PHY in the 5 GHz Band supplement to the standard;

5 GHz band in Europe to add indoor and outdoor channel selection for 5 GHz license exempt bands in Europe; and to enhance channel energy measurement and reporting mechanisms to improve spectrum and transmit power management (per CEPT and subsequent EU committee or body ruling incorporating CEPT Recommendation ERC 99/23).

Looking into the tradeoffs involved in creating reduced-power transmission modes for networking in the 5 GHz space—

essentially allowing 802.11a to be used by handheld computers and other devices with limited battery power available to them. Also, examining the possibility of allowing access points to reduce power to shape the geometry of a wireless network and reduce interference outside the desired infl uence of such a network.

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Table 4.1: (continued)

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802.11i Amendment to STANDARD Enhances the 802.11 MAC to enhance security and [for] Information Technology- authentication mechanisms and improve the PHY-level Telecommunications and information security that is used on these networks.

exchange between systems-Local and metropolitan area networks-Specifi c requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifi cations:

Medium Access Method (MAC) Security Enhancements

802.11j Amendment to STANDARD The scope of the project is to enhance the 802.11 standard [for] Information Technology- and amendments, to add channel selection for 4.9 GHz Telecommunications and information and 5 GHz in Japan to additionally conform to the Japanese exchange between systems-Local and rules for radio operation, to obtain Japanese regulatory Metropolitan networks-Specifi c approval by enhancing the current 802.11 MAC and 802.11a requirements—Part 11: Wireless LAN PHY to additionally operate in newly available Japanese Medium Access Control (MAC) and 4.9 GHz and 5 GHz bands.

Physical Layer (PHY) specifi cations:

4.9–5 GHz Operation in Japan

802.11k Amendment to STANDARD This project will defi ne Radio Resource Measurement [for] Information Technology- enhancements to provide interfaces to higher layers for radio Telecommunications and information and network measurements.

exchange between systems-Local and Metropolitan networks- Specifi c requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifi cations: Radio Resource Measurement of Wireless LANs

802.11ma Standard for Information Incorporates accumulated maintenance changes (editorial Technology–Telecommunications and and technical corrections) into 802.11-1999, 2003 edition information exchange between systems– (incorporating 802.11a-1999, 802.11b-1999, 802.11b-1999 Local and Metropolitan networks–Specifi c corrigendum 1-2001, and 802.11d-2001).

requirements–Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifi cations–

Amendment x: Technical corrections and clarifi cations

802.11n Amendment to STANDARD The scope of this project is to defi ne an amendment that [for] Information Technology- shall defi ne standard modifi cations to both the 802.11 Telecommunications and information physical layers (PHY) and the 802.11 Medium Access Control exchange between systems-Local and Layer (MAC) so that modes of operation can be enabled that Metropolitan networks- Specifi c are capable of much higher throughputs, with a maximum requirements-Part 11: Wireless LAN throughput of at least 100 Mbps, as measured at the MAC Medium Access Control (MAC) and data service access point (SAP).

Physical Layer (PHY) specifi cations:

Enhancements for Higher Throughput

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The fi rst step is to understand the main components of an 802.11 system, regardless of whether these components are implemented in hardware or software. This is important because different embedded architectures and boards implement 802.11 components differ-ently. On most platforms today, 802.11 standards are made up of root components that are implemented almost entirely in hardware. The hardware components can all be mapped to the physical layer of the OSI model, as shown in Figure 4.12. Any software required to enable 802.11 functionality maps to the lower section of the OSI data-link layer but will not be dis-cussed in this section.

Off-the-shelf wireless hardware modules supporting one or some combination of the 802.11 standards (i.e., 802.11a, 802.11b, 802.11g, etc.) have in many ways complicated the efforts to commit to one wireless LAN standard. These modules also come in a wide variety of forms, including embedded processor sets, PCMCIA, Compact Flash, and PCI formats. In general, as shown in Figures 4.13a and b, embedded boards need to either integrate 802.11 functional-ity as a slave controller or into the master chip or the board needs to support one of the stand-ard connectors for the other forms (PCI, PCMCIA, Compact Flash, etc.). This means that either (1) 802.11 chipset vendors can produce or port their PC Card fi rmware for an 802.11 embedded solution, which can be used for lower volume/more expensive devices or during product development, or (2) the same vendor’s chipset on a standard PC card could be placed on the embedded board, which can be used for devices that will be manufactured in larger volumes.

On top of the 802.11 chipset integration, an embedded board design needs to take into consid-eration wireless LAN antenna placement and signal transmission requirements. The designer

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Figure 4.12: OSI model.

IR DS FH

Infrared (IR) Pulse Position Modulation. This PHY provides 1 Mbit/s with optional 2 Mbit/s. The 1 Mbit/s version uses Pulse Position Modulation with 16 positions (16-PPM) and the 2 Mbit/s version uses 4-PPM.

Direct Sequence Spread Spectrum operating in the 2 400 - 2 483.5 MHz band (depends on local regulations). This PHY provides both 1 and 2 Mbit/s operation. The 1 Mbit/s version uses Differential Binary Phase Shift Keying (DBPSK) and the 2 Mbit/s version uses Differential Quadrature Phase Shift Keying (DQPSK).

Frequency Hopping Spread Spectrum operating in the 2 400 - 2 483.5 MHz band (depends on local regulations). This PHY provides for 1 Mbit/s (with 2 Mbit/s optional) operation. The 1 Mbit/s version uses 2 level Gaussian Frequency Shift Keying (GFSK) modulation and the 2 Mbit/s version uses 4 level GFSK.

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must ensure that there are no obstructions to prevent receiving and transmitting data. When 802.11 is not integrated into the master CPU, such as with the System-on-Chip (SoC) shown in Figure 4.13b, the interface between the master CPU and the 802.11 board hardware also needs to be designed.

Figure 4.13a: 802.11 sample hardware confi gurations with PCI card.

Diversity Antennas

PRISM 3 miniPCI 802.11a, g, and b

Low

Figure 4.13b: 802.11 sample hardware confi gurations with SoC.

PA

ARM9 Based WiSoC for 802.11a, g, and b

PA

PCI 802.3 802.3 802.11 uAP

Driver

MVC

802.11a, b, g Baseband

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Embedded Board Buses and I/O 153

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Components that transmit data in parallel are devices that can transfer data in multiple bits simultaneously. Just as with serial I/O, parallel I/O hardware is also typically made up of some combination of six main logical units, as introduced at the start of this chapter, except that the port is a parallel port and the communication interface is a parallel interface.

Parallel interfaces manage the parallel data transmission and reception between the master CPU and either the I/O device or its controller. They are responsible for decoding data bits received over the pins of the parallel port (transmitted from the I/O device) and receiving data being transmitted from the master CPU, then encoding these data bits onto the parallel port pins.

They include reception and transmission buffers to store and manipulate the data being transferred. In terms of parallel data transmission and reception schemes, like serial I/O transmission, they generally differ in terms of the direction in which data can be transmitted and received as well as the actual process of transmitting/receiving data bits within the data stream. In the case of direction of transmission, as with serial I/O, parallel I/O uses simplex, half-duplex, or full-duplex modes. Also, as with serial I/O, parallel I/O devices can transmit data asynchronously or synchronously. However, parallel I/O does have a greater capacity to transmit data than serial I/O, because multiple bits can be transmitted or received simultane-ously. Examples of board I/O that transfer and receive data in parallel include IEEE 1284 con-trollers (for printer/display I/O devices—see Example 3), CRT ports, and SCSI (for storage I/O devices). A protocol that can potentially support both parallel and serial I/O is Ethernet, presented in Example 4.