High-Speed Operation Takes Center Stage in WLAN Industry
Acceptance of the high-speed data extension allows WLAN technology to better compete with exiting wired Ethernet LANs.
By:Robert Keenan, Managing Editor
Contents
•High-Speed Operation
•Ethernet Speeds
•CCK Modulation
•Some Problems
•5.7 GHz Systems
•The Future
Industry experts agree that 1998 was a breakthrough year for the WLAN technology. Highly integrated chip sets were released. Lower-cost systems were rolled out. Interoperability was tested. Simply stated, the WLAN industry finally started to gain a foothold in the wireless market in 1998.
"Last year was absolutely a pivotal year for the WLAN industry," says Mack Sullivan, executive director of the Wireless LAN Alliance, a consortium of manufacturers that provide a clearinghouse of information about wireless local-area applications, issues, and trends. "There was a reduction in WLAN prices. New products opened WLAN technology to new areas. And there was a broadening of applications for which WLANs were used."
It was also a hot year on the standards front. The acceptance of a high-speed data rate, work in the 5 GHz range, a meeting of International standards bodies, and the emergence of personal area and home networking technologies fueled interest and excitement in the WLAN industry over the past year.
Although all of these events played a major roll in the emergence of the WLAN market last year, the new high-speed extension to the IEEE 802.11 standard seemed to take center stage in 1998. In fact, in the future, engineers look back to the ratification of high-speed standards as the key to mass acceptance of WLAN technology.
In July 1997, the IEEE 802.11 committee completed the final stages of the standardization process and ratified its specifications for WLAN operation. In this initial proposal, the standard specified WLAN operation at 1 and 2 Mb/s data rates.
As fast as people started to develop 1 and 2 Mb/s systems, companies formed new modulation techniques that pushed the WLAN market toward higher data rate operations. For example, just a few months after IEEE 802.11 was ratified, Lucent Technologies started touting a new modulation technique that raised the data rates in its WLAN systems to 10 Mb/s. Several months later, Harris Semiconductor also pushed the data rate envelope by releasing a new baseband processor that supported 11 Mb/s data rates.
This move to higher data rates raised many questions about the current IEEE 802.11 WLAN standard. One of the most prevalent questions was whether or not the 1 and 2 Mb/s data rates specified by 802.11 were sufficient to meet the demands of today's WLAN developers and end users.
The problem with the original IEEE 802.11 data rates was best seen in enterprise applications. In these environments, companies generally employ an Ethernet network, which deliver 10 Mb/s data rates, to provide Internet and intranet access. By only operating at 1 and/or 2 Mb/s, many WLAN manufacturers found it hard to complete with existing Ethernet LAN technology.
The IEEE 802.11 committee and industry companies realized the problem 1 and 2 Mb/s systems met in enterprise networking applications. To solve the problem, these industry members together to improve the data rate specifications of the current IEEE 802.11 standard. The result was a new high-speed extension for the 802.11 specification.
Initially, there was some disagreement about which modulation scheme to choose for the new high-speed data rate extension. This disagreement was solved in July, however, when Harris and Lucent teamed up to deliver a new high-speed data proposal to the IEEE 802.11 committee. Once received, the standards committee accepted the Harris/Lucent proposal for the new high-speed data extension.
To Harris/Lucent proposal is designed for direct sequence spread spectrum (DSSS) WLAN systems operating in the 2.4 GHz. This new technology employs a special coding scheme known as complimentary code keying (CCK) to deliver both 11 and 5.5 M/s data rates. It also uses the same bandwidth and channelization scheme defined in the current IEEE 802.11 standard for DSSS transmission. Thus, it is backward compatible with current 1 and 2 Mb./s data rates.
The acceptance of the high-speed standard, according to Al Petrick, senior manager of strategic marketing for Harris Semiconductor, was a big step for the WLAN industry. By moving to higher data rates, Petrick says that WLAN could finally address the Ethernet-type requirements that corporate customers required.
Sullivan agrees. Traditionally, WLAN technology has only found success and acceptance in vertical applications, such as healthcare environments, warehouses, and education facilities. According to Sullivan, speed was one of the main reasons WLAN technology did not find greater mass market success.
Through the new high-speed extension, Sullivan says the IEEE 802.11 committee is addressing the speed problems associated with WLAN technology. "This will make a huge difference in the WLAN market."
Despite the benefits, the new IEEE 802.11 high-speed data extension does have some drawbacks. One of the main challenges, according to Amos Young, applications engineer at American Microsystems, Inc. (AMI), is fitting the higher data rate into a narrowband.
Currently, 1 and 2 Mb/s WLAN systems can transmit three channels in the 2.4 GHz band. By moving to 11 Mb/s, engineers receive a 6X wider bandwidth. According to Young, this greater bandwidth does not leave engineers enough room to transmit even one channel over the 2.4 GHz range.
Higher data rate operation can also lead to multipath interference, power, and range problems in WLAN networks.
By increasing the data rate, engineers have to develop systems that operate at a higher frequency. At these higher frequencies, Young says WLAN systems may experience more multipath problems, must employ more power to operate, and feature a shorter operating range. In some environments, Young says these tradeoffs may not be beneficial for system designers.
Although 11 Mb/s data rates may be sufficient to meet the demands of today's WLAN applications, they may not provide enough bandwidth to handle emerging WLAN applications, such as multimedia and videoconferencing applications. So, today's WLAN designers are continually looking to push the WLAN envelope to higher and higher data rates.
There is one problem. Raising the data rates in the 2.4 GHz range may not be a feasible solution. According to Benno Ritter, product marketing manager at Philips Semiconductor, 11 Mb/s may be the top speed that WLAN systems can achieve in the 2.4 GHz range because of the cost associated with increasing this data rate even further.
To address this concern, the IEEE 802.11 committee has established a task group, designated Task Group A, to define future WLAN operation in the 5 GHz range. Once standardized, these systems will offer data rates of better than 20 Mb/s.
Over the past year, Task Group A has made significant advancements in defining WLAN operating in the 5.7 GHz band. In fact, the group has already chosen a modulation technique, called orthogonal frequency division multiplexing (OFDM), for transmission in the 5.7 GHz range.
In addition, the task group has sat down with the European Telecommunications Standards Institute (ETSI)-BRAN committee to establish a common physical layer (PHY) for worldwide WLAN systems operating in this band. The key to this meeting, according to Petrick, is that the international standards bodies have agreed to work together on bringing developing WLAN systems that can coexist in the 5.7 GHz range.
There are still many questions looming in the WLAN market. Will the 11 Mb/s standard open new areas for the market? What effect will Bluetooth and HomeRF have on the WLAN market? Will the common PHY provide true worldwide interoperability in the WLAN market? The biggest question, however, revolves around WLAN technology receiving mass acceptance.
According to AMI's Young, WLAN technology is close to receiving mass acceptance in certain applications. But to reach the mass levels, Young says the WLAN industry needs a large company to implement the technology and find success using it.
About the Author:
Robert Keenan is the Managing Editor of Wireless Design Online. In addition, he is the managing editor of RF Globalnet (http://www.rfglobalnet.com), a web community for RF/microwave design engineers. Keenan can be reached at 3257 N. Sheffield, Ste. 109, Chicago, IL 60657. Phone: 773-477-3574; e-mail: rkeenan@verticalnet.com