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If you are like me, you remember the days of 300 baud acoustic coupler modems, the days when 2400 bps was blindingly fast, and later times when to live without a 28 kbps modem seemed like a return to the stone age. Now, as the volume, size and importance of internet traffic is increasing, most highly connected people are finding cable modems, ISDN or DSL to be the minimum acceptable way to access their email, favorite web sites and other services. Speeds are ranging from 100 kbps to 1 Mbps and higher!
However, all of these systems are based on wired communications. While 3G cellular systems are aiming to provide high speed wireless solutions for mobile users, broadband wireless is aiming to provide an alternative to wired high speed internet for stationary users.
Broadband wireless is 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 were 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.
Microwave systems are designed so that the antennas at each end of a communications link are clearly visible to each other. 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 needed to solve the problem of non-line-of-sight communications because terminals move around unpredictably, often being invisible to the cellsite. If systems do not take advantage of radio signals that bounce off buildings and other obstructions, communications would often be impossible. In broadband wireless, it is not an issue of terminals moving, but of covering a large area with one cellsite, where no one location for a cellsite 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 is often 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 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 cellsite.
One of the biggest barriers to penetration of wireless broadband 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 a LEC switch, which means 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 4-8 miles of a cellsite.
Standardization is one way that prices could be reduced and functionality improved. The most direct benefit would be reduced costs through higher volumes of equipment. Standardization would encourage 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.
If there ever is a widely accepted standard for broadband wireless, it will probably be based on OFDM (Orthogonal Frequency Division Multiplexing). 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 multi-path fading that occurs when signals bounce off multiple objects.
The Wideband OFDM (W-OFDM) camp is led by Wi-Lan of Calgary, 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, including Alcatel, Ericsson, Motorola and Nokia. Wi-Lan’s W-OFDM, known as Multi-code Direct Sequence Spread Spectrum (MC-DSSS) 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 their technology is thus more resistant to multi-path fading and fading of portions of the frequency range.
Wideband OFDM is not only 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.
A competing group is the Broadband Wireless Internet Forum (BWIF; www.bwif.org), led by Cisco, but also counting Texas Instruments, Analog Devices and Andrew Corp. 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. Since fading of signals is often 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.
According to Paul Struhsaker, CTO of Raze Technologies, former chair of IEEE 802.11 and an active member of IEEE 802.16, “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 has already approved a single carrier solution (i.e. not OFDM) in the 10-66 GHz 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 2-11 GHz bands. There is even a third standard in the works, 802.16b, which targets the 5-6 GHz band and will only support OFDM. Both of these are scheduled for publication in 2002.
The Wideband OFDM camp was well represented at 802.16 meetings, and provided a great deal of input. One industry group, known as the DSL Consortium, was so happy with the work that they were doing, that they closed up shop entirely. This organization, including Nortel, decided they had attained their goal of ensuring an industry standard was developed. The BWIF forum, however, made no official representations, although according to Struhsaker, their input would still 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 Wideband 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 are fair and non-discriminatory.
The 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 V-OFDM 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 they need to become real competitors in the high speed internet access space.
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