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WLAN on the move: 802.11xyz

Posted: 15 Aug 2005 ?? ?Print Version ?Bookmark and Share

Keywords:wlan? 802.11xyz? 802.11? wifi? xytrans?

By Rob Howald, Xytrans Inc.

CommsDesign.com

The 802.11 standard (a.k.a. Wi-Fi) has been wildly successful and become a powerful tool in an always-connected world. It may play an even larger role in the future as it continues to evolve.

In a real-world example, this past week in my home, we added a fifth device that will regularly be accessing the household LAN (three through wireless access points). We now have two conventional PCs, a laptop, a VoIP adaptor, and a TiVo box. In addition, we are beginning to challenge the infrastructure's ability!be it our own or that of the cable company!to provide a high consistent download speed. It was adequate to file share and we could observe bursts of bandwidth, such as the very conclusive "six seconds left," followed two seconds later by "30 seconds left," as the percent complete bar crawled through bottlenecks along the route. Although the real-time data wasn't very informative, the average time for a download of a particular size was generally predictable.

The TiVo service is still a light user, accessing modest amounts of information in the background of daily activity without urgency. My laptop sits connected through the office VPN accessing files and services, having grown primarily in the sense that typical presentations and analysis tools have evolved considerably in parallel with faster computers. The two fixed-location PCs, however, have begun to stress our access capabilities. My daughter hangs out on the furthest-from-base station PC, located on the same floor but at the opposite end of the house, and three walls away. No matter how delicately I balance on one foot and hold the access point with capacitive body parts at unusual angles, I can't seem to cajole the unit to read anything but "signal strength low." So, my multi-tasking daughter!streaming AOL radio while surfing, building her website, answering her blog, and instant messaging!finds herself delayed, relatively speaking, with her portal being on the remote access point end of the network.

On the primary house PC, located at the router/wireless access point, the most important application runs almost daily from April through October, or from Opening Day to the start of the playoffs. Having relocated to the sunshine state, I don't often get to watch my home team, the Phillies, unless they happen to be playing on a nationally televised broadcast. Because they're not the Yankees and only play them every three years, they're eliminated from 80 percent of the national telecasts. However, through the wonders of broadband access, Major League Baseball offers a subscription service to every game (minus local blackout regulations). As a result, the master PC streams video at 350kbps!modest quality at best!most evenings. There are evenings that it struggles to stay afloat without an occasional freeze frame.

Growing with the times

When a design is finished and before it's put into the market, every engineer knows that the likely next steps are for product improvements, or the less exciting but often more important task of cost reduction. The 802.11 product line is no exception. Most consumers have little knowledge of the "plain" 802.11 systems that offered 1Mbps and 2Mbps data rates at 2.4GHz. This standard was published in 1997. The IEEE published the 802.11b standard in 1999, which runs at 2.4GHz, with a data rate of 11 Mbits/s. The latter two technical elements may not be meaningful to consumers, but they tend to be printed on the box. RF and network engineers may also be familiar with its physical layer (PHY) and MAC layer features, designed for robustness relative to unpredictable household environments, and with MAC layers able to mutually get along on the shared bandwidth.

The wow factor of reliable wireless LANs has worn off, and we expect them to turn on and work much the way we expect broadband to always be on, eliminating the hassles of dial-up issues, call drops, and sluggishness. While the primary functionality of 802.11 has been achieved, the first consumer equipment is beginning to fall short in some application areas. As a result, and ahead of any market clamor, engineers began to address some of the notable shortcomings in the standard. Initially, it was easy to keep abreast of the evolution. However, the alphabet soup has gotten difficult to keep pace with unless you are in the everyday 802.11 loop. Hence, I'll summarize these different 802.11 efforts and what problem they are trying to solve:

802.11a: The purpose of this task group is to create a physical layer system that operates in the unlicensed region of 5-GHz spectrum, also called the UNII band in the U.S. This standard, as the "a" designation implies, was the first published standard. The products just came after those of 802.11b.

The 802.11a working group created a physical layer based on Orthogonal Frequnecy Division Multiplexing (OFDM). Because of its ability coupled with advances in real-time signal-processing capability, OFDM has become a popular signaling technique. Basically, it allows wideband data-rate performance in difficult channels by slicing the spectrum into chunks for transmission, optimizing the chunks, and reassembling them at the receive site. The data rate capability of 802.11a is up to 54Mbps.

802.11b: This is what consumers know best. The project of the task group responsible for the standard was to develop a PHY standard with a higher data rate in the 2.4GHz band. Recall, the original PHY had 1Mbps to 2Mbps rates, with PHY techniques identified as direct sequence spread spectrum (DSSS), frequency-hopping spread spectrum (FHSS), and infrared (IR). The higher rate 802.11b system is a DSSS system.

802.11c: This is a supplement to 802.1D to add requirements associated with bridging operation of the 802.11 MAC. 802.1 covers the management features (and 802.1D specific to bridging) section of the overriding 802 LAN specifications.

802.11d: This portion adds physical-layer requirements and definitions that permit compliance in other regulatory arenas (other countries). The current standard targets only a few countries, and this addendum extends the serviceable market.

802.11e: This is one of the new additions that widen the scope of applications for 802.11. It's designed to support LAN systems with quality of service (QoS) requirements. The example problem described above in my house represents a case where treatment of traffic classes may come into play as bandwidth demands grow on the network. In enterprise applications and VoIP, for example, many other examples exist.

802.11f: This spec was developed to provide interoperability between access points within distribution systems in a wireless LAN. Because of the flexibility left to the vendors in implementation, different concepts were developed for distribution systems. 802.11f describes the information exchange that must occur for interoperability.

802.11g: Another "biggie," 802.11g is an enhanced data rate version of 802.11b, but within the same 2.4GHz band and with compatibility to the 802.11b MAC, making systems backward compatible. 802.11g, which also settled on OFDM for the physical layer signaling standard, has up to 54Mbps capability.

802.11h: This segment targets the European regulatory bodies with respect to the 5GHz band used by 802.11a, which isn't convenient due to satellite bands as it is domestically. 802.11h provides the key elements of dynamic channel selection (DCS) and transmit power control (TPC), among other requirements.

802.11i: To enhance the security of the 802.11 MAC, this spec was developed. The current approach of wired equivalent privacy, or WEP, is relatively weak and can be broken by hackers. More robust, advanced encryption is available.

802.11j: PHY and MAC enhancements are added for regulatory approval in Japan in the now open 4.9GHz and 5GHz band.

802.11k: The development here is aimed at adding to resource management capabilities, such that external entities can view and enable coexistence. The original standard supports only resource management internally to the WLAN.

802.11m: Technical and editorial corrections are handled here.

802.11n: This spec evaluates improvements to 802.11 to achieve throughput greater than 100Mbps, which is a natural target, consistent with fast Ethernet speeds.

802.11p: Communications in mobile environments are handled here. The plan is to cover 1km at 125mph.

802.11r: This spec covers MAC development to reduce the time associated with the absence of connections. It supports the needs of real-time services, such as VoIP.

802.11s: Protocol development here will enable auto-configuration of access points and paths in multi-hop mesh distribution networks. It'll also support varying traffic types, such as unicast, multicast, broadcast.

802.11t: Here the metrics and test methods are provided to allow measurement and prediction of WLAN systems as a recommended practice. The purpose is to aid in deployment planning, and component and system comparison.

802.11u: This spec covers amendments to the PHY and MAC layers to support internetworking with other external networks.

802.11v: 802.11 is a task group with activity associated with network management. 802.11v goes beyond 802.11k in enhancing management interfaces of the PHY and MAC, including network configuration based on measurement and information exchange across a Layer 2 mechanism in an 802.11 network.

Work is taking place to determine what to do with Wi-Fi beyond what's described here. The next great movement in wireless will be the battle over the Wireless WAN, of which Wi-Fi expects to be a player.

About the author

Rob Howald is the vice president of engineering at Xytrans Inc. He is also the former director of systems engineering in the transmission network systems group of Motorola's Broadband Communications Sector in Horsham, Pa. He has a BSEE and an MSEE from Villanova University, a PhD from Drexel University, and an MBA from DeSales University.

References:

Gast, Matthew, 802.11 Wireless Networks, O' Reilly & Associates, Sebatopol, CA, 2002.

www.ieee.org

www.wi-fiplanet.com/tutorials/article.php/1439551




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