As the volume, size and importance of Internet traffic increases, most highly connected people are finding cable modems, ISDN or DSL to be the minimum acceptable way to access e-mail, favorite Web sites and other services.

However, all of these systems are based on wired communications. Broadband wireless is aiming to provide an alternative to wired high-speed Internet for stationary users by attempting to merge concepts and technology from microwave communications systems with those from cellular and PCS. Microwave systems are point to point and thus are used for backbone network connectivity, not for connection to end users. LMDS and MMDS are based on similar technologies used to transmit data between a network and several terminals, providing bandwidth on a demand basis. Broadband wireless attempts to take this evolution one step further by solving the line-of-sight problem.

Line of Sight

Microwave systems are designed so that the antennas at each end of a communications link are clearly visible to one another. They can be placed on towers or on top of buildings and oriented so that as much of the radio energy as possible travels down the only communications direction that counts, the straight line between the antennas.

Cellular and PCS systems had to solve the problem of non-line-of-sight communications because terminals move around unpredictably, often being invisible to the cell site. In broadband wireless, it is not an issue of terminals moving, but of covering a large area with one cell site, where no one location for a cell site can see all homes and offices in its coverage area.

A related problem that cellular and PCS systems take in stride is in-building penetration, which often is quite good. This is important to broadband wireless because it eliminates the need for external antennas. Not only do the antennas cost money, but they also are a point of failure and are expensive to install, particularly if they have to be oriented carefully to pick up the signal from the broadband-wireless cell site.

Cost: The Ultimate Barrier

One of the biggest barriers to wireless-broadband penetration is price. Urban users already have DSL, ISDN and cable modems as choices, so prices for basic service have to be in the $40/month range in these areas. Many potential users of high-speed Internet access are not within a couple of miles of an LEC switch, meaning that DSL is not available, and they may not be serviced by cable either. In these areas, broadband wireless can be an available option, even outside the desired price point, assuming that the customer is within 4 to 8 miles of a cell site.

Standardization is one way to reduce prices and improve functionality. The most direct benefit would be reduced costs through higher volumes of equipment and the entry of companies with products that would not be cost effective if they had to be customized for each proprietary protocol. More effective test equipment, for example, might be a result of a widely accepted industry standard.

OFDM

If there ever is a widely accepted standard for broadband wireless, it probably will be based on orthogonal frequency division multiplexing (OFDM). It can break through the line-of-sight restrictions that plague older, single-carrier solutions. This radio divides a stream of data into multiple parallel parts, carrying each at a different frequency at different times. With diversity in both time and frequency, it is quite robust in the presence of noise, interference and multipath fading that occur when signals bounce off multiple objects.

Wideband OFDM

The wideband OFDM (W-OFDM) camp is led by Wi-Lan (www.wi-lan.com), which has patents on many aspects of this technology. Wi-Lan is one of the founders of the OFDM Forum (www.ofdm-forum.com), which has a number of major players behind it. Wi-Lan's W-OFDM, known as multicode direct-sequence spread spectrum, spreads the information being transmitted over a wider bandwidth than standard OFDM, allowing individual carriers to be spread farther apart, and therefore reduces the effects of frequency errors. Wi-Lan claims that its technology is thus more resistant to multipath fading and fading of portions of the frequency range.

W-OFDM is being considered for use in broadband wireless, but it is also incorporated in ETSI BRAN HiperLAN/2 and the 802.11a standard, which is a recently developed, higher-performance second generation of the popular 802.11b “wireless Ethernet” standard known as WiFi.

Vector OFDM

A competing group is the Broadband Wireless Internet Forum (BWIF) (www.bwif.org), led by Cisco (www.cisco.com), but also counting Texas Instruments (www.ti.com), Andrew (www.andrew.com), Analog Devices (www.analogdevices.com) and others as members. Its choice, vector OFDM (VOFDM), uses two antennas to add space diversity to the time and frequency diversity already provided by basic OFDM. Because signal fading often is very different at two places just a short distance apart, the use of two antennas significantly increases the possibility that a usable signal will be received at the other end of the channel.

Standardization

Paul Struhsaker, Raze Technologies (www.razetechnologies.com) CTO, former chair of IEEE 802.11 and an (www.ieee.org) active member of IEEE 802.16, said, “No wireless sector has ever taken off without an open standard to allow for interoperability. Good examples include IS-95 and GSM cellular, as well as IEEE 802.11b for wireless LANs.” Companies that agree with him have worked within IEEE's 802.16. They would like to repeat the IEEE's success with 802.11b, which is taking the wireless LAN marketplace by storm.

According to Roger Marks, technical contact for 802.16, the IEEE standards organization already has approved a single-carrier solution (i.e. not OFDM) in the 10GHz to 66GHz frequency bands for publication as 802.16.2. It is expected to be publicly available before the end of 2001. This will not, however, provide the needed non-line-of-sight and bit-rate capabilities.

OFDM proponents are happier about a second standard, known as 802.16a, which will provide for both single carrier and OFDM approaches in the unlicensed 2GHz to 11GHz bands. There is even a third standard in the works, 802.16b, which targets the 5GHz to 6GHz band and will support only OFDM. Both of these are scheduled for publication in 2002.

The W-OFDM camp was well represented at 802.16 meetings and provided extensive input. One industry group, known as the DSL Consortium, was so happy with this work that it closed up shop entirely. This organization, including Nortel (www.nortel.com), decided that its goal of ensuring an industry standard had been attained. The BWIF, however, made no official representations although, according to Struhsaker, its input still would be welcome.

There is some confusion over the status of the BWIF at the IEEE, because although it did not participate in 802.16 standardization, it is a program of IEEE-ISTO (Industry Standards and Technology Organization). However, this IEEE affiliate organization merely provides management services for BWIF and is not a participant in IEEE standardization, despite its name.

The basic problem appears to be intellectual property rights. BWIF requires that these be waived, something that W-OFDM proponents refuse to do. Standards often do have intellectual property associated with them and, therefore, cannot be used without paying licensing fees, although, standards organizations usually insist that they be fair and non-discriminatory.

BWIF is attempting to take the open-systems approach, believing that licensing fees are not the way for an industry to grow and make money. If VOFDM is accepted, its proponents will make money by selling lots of hardware and services, not from royalties.

Having a standard published is not the end of the story. If the broadband wireless industry cannot truly get a single standard, the confusion in the marketplace will not result in the lowered prices that it needs to become a real competitor in the high-speed Internet access space.

Crowe (crowed@cnp-wireless.com) is a wireless-standards consultant and editor of Cellular Networking Perspectives, a wireless-standards and -technology bulletin.