Plextek Ltd - Wireless LAN

Plextek's WLAN design services include: WLAN PC card design, 802.11b WLAN product design, combined WLAN and GPRS PC card design, VHDL-based COFDM modem design for 802.11a WLAN, HIPERLAN WLAN transceiver design, WLAN firmware development, radio channel propagation measurement for WLAN design, supply of WLAN reference designs, custom WLAN system design.

Wireless LAN (WLAN)

Although other WLAN standards exist, the term has become synonymous with the IEEE 802.11 family of standards. 802.11 is by far the dominant WLAN technology, offering system flexibility, rapid deployment, high data rates and multi-vendor equipment inter-operability.

The standards have evolved from the original 802.11b which offered 11Mbits/s through 802.11g at 54Mbits/s to the latest Multiple In Multiple Out (MIMO) systems offering 108Mbits/s and beyond. In parallel, improvements in technology have achieved more integrated solutions that are cheaper and lower power. With the advent of wireless broadband access to the office and home a new market of Voice Over IP (VoIP) handsets has emerged using services from Skype, Vonage, Net2Phone, etc..

Plextek is experienced in designing products incorporating 802.11 and has undertaken a range of client specific WLAN design and development programmes including:

Dual-mode 802.11b/802.11a PC Card for an IC Vendor, with particular emphasis on a low-cost 5.8GHz radio implementation

Antenna beam steering for improved performance

VHDL-based COFDM modem implementation, available to IC vendors targeting 802.11a and 802.11g platforms

Firmware development for encoding/decoding, encryption, authentication, integrated configuration management

Driver development for MS Windows, CE, etc.

Software development for MMI and user-applications

Linear RF power amplifier design using digital pre-distortion and analogue feedforward techniques, to accommodate the non-constant-envelope modulations schemes

Propagation measurement and channel-sounding for input to cell planning, antenna diversity design, modem definition, etc.

802.11 Standards Overview

802.11 comprises a large collection of related standards, each identified by the IEEE Task Group responsible for its production. The following 802.11 standards define the core 802.11 functionality of Media Access Control (MAC) and physical layer interfaces (PHY):

802.11 This is the original 802.11 standard, which defines the MAC and three different PHYs: Frequency Hopping Spread Spectrum (FHSS), Direct Sequence Spread Spectrum (DSSS) and Infra-Red (IR). FHSS and DSSS operate in the 2.4GHz ISM band and support Data rates of 1 and 2Mbps. All three are now obsolete, although the DSSS PHY has been absorbed into the 802.11b and 802.11g standards. All subsequent 802.11 standards incorporate the original MAC and also define extensions that support their specific features.

802.11a This defines a PHY operating in the unlicensed 5.15 - 5.825GHz ISM band, offering data rates up to 54Mbps using Orthogonal Frequency Division Multiplexing (OFDM). It uses 20MHz wide channels each carrying 52 sub-carriers. This PHY is not compatible with 802.11b or 802.11g due to the use of a different frequency band, although some products do support all three.

802.11b This PHY is an evolution of 802.11-DSSS supporting dynamic data rate shifting up to 11Mbps using DSSS and Complimentary Code Keying (CCK). It defines a set of overlapping 22 MHz wide channels in the unlicensed 2.4GHz ISM band. It is backward compatible with 802.11-DSSS up to 2Mbps.

802.11g Effectively a hybrid of 802.11a and 802.11b, providing data rates up to 54Mbps in the 2.4GHz band. It uses OFDM encoding for rates above 20Mbps, but also supports backward compatibility with 802.11b for data rates up to 11Mbps.

802.11n This Task Group has been created in response to the development of proprietary PHYs that can deliver higher bit rates that the existing standards. The Task Group is charged with standardising a new PHY that can support bit rates significantly higher than those supported by 802.11a/g.

In addition to the core standards, there are a number of further standards that have been defined in order to enhance 802.11:

802.11d International roaming extensions defining mechanisms for an 802.11 terminal to adapt to the different national requirements.

802.11e
A MAC layer enhancement, defining support for Quality of Service. This offers improved support for time sensitive traffic such as audio and video.

802.11f A MAC layer enhancement defining support for Inter Access Point roaming. This offers the ability for portable equipment (e.g. PDAs) to move between Access Points as the users move around without breaking connections.

802.11h This is a "spectrum managed" enhancement to 802.11a. It defines Dynamic Frequency Selection (DFS) and Transmitter Power Control (TPC) mechanisms to reduce interference between users and to prevent conflict with other users of the 5GHz bands such as satellite links and radars.

802.11i Also know as Wi-Fi Protected Access version 2 (WPA2), this standard enhances the security of radio traffic by means of improved authentication and encryption algorithms. It was designed to correct crucial weaknesses in the security mechanisms contained in the original 802.11 standard. WPA2 offers backward compatibility with the earlier WPA standard, which was a stopgap measure, designed to plug some of the gaps in the original standard while 802.11i was still under development. The key difference between WPA and WPA2 is that WPA2 it is based on the latest AES encryption, in place of the older RC4 encryption employed by both WEP and WPA.

802.11j Extensions for Japan

802.11k Radio resource measurement - this enhances support for features such as steerable antennas, which need to be aware of the real-time performance of the radio link.

802.11p Wireless Access for Vehicle Environment (WAVE) defines enhancements to 802.11 to support transportation applications including data exchange between moving vehicles and between these vehicles and the roadside infrastructure in the 5.9 GHz band

802.11r
Fast Roaming. Defines mechanisms for seamless roaming between Access Points and will be applicable to mobile VoIP and 802.11p.

802.11s Mesh Networking

802.11t Wireless Performance Prediction (WPP). This group aims to create a set of measurement methods, performance metrics, and test recommendations that enable measurement of the performance of IEEE 802.11 standard equipment and networks.

802.11u This group addresses interworking issues between an 802.11 access network and any external network to which it is connected. Areas covered are enrolment, network selection, security, authorisation and handover.

802.11v Wireless network management

802.11w Protected management frames. WLAN systems send system management information in unprotected frames, making them vulnerable. This standard will prevent disruption caused by malicious systems.

Equipment designed to conform to the 802.11 family of standards may optionally carry the WiFi logo. The WiFi Alliance (formerly known as WECA) has set up this branding scheme in order to provide customers with a means to determine whether equipment from different manufacturers will work together. Before it can carry the WiFi logo, equipment must pass a set of interoperability tests defined by the Alliance and undertaken by independent laboratories.