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MANs to Go Walkabout

The Institute of Electrical and Electronics Engineers Inc. (IEEE) is working on a new iteration of the 802.16 wireless metropolitan area network (MAN) standard that will enable base stations to connect with mobile as well as stationary devices (see IEEE Extends 802.16 Standard).

Current 802.16 standards define only how base stations can connect to stationary wireless modems. This "mobile" version, called 802.16e, will specify how devices equipped with compliant modems may wander about among base stations without losing their wireless connection.

Why does this matter? For one thing it would allow service providers to offer wireless "last mile" services to homes and offices at speeds up to 10 Mbit/s -- with the added bonus of mobility within the coverage area. (For instance, someone could access the Internet from their laptop from home, then take the device into White Castle for a steamed burger, then pop into the office for a dump -- all the while enjoying uninterrupted high-speed service).

For another, it means that carriers would have an alternative to 802.11 for large-scale public access rollouts: university campuses, city centers, sports arenas, and the like.

802.16e will be backwards compatible with the existing standard, allowing vendors to add mobility features to their existing fixed wireless network products, according to Dr. Roger Marks, chair of the IEEE 802.16 working group on broadband wireless access.

While the "mobile" version is still under development, the IEEE has just ratified the 802.16a version of the wireless MAN standard. Unlike the original 802.16 standard (for wireless line-of-sight deployments), this version supports fixed, non-line-of-sight usage for use in the 2GHz to 11GHz bands, although Marks says the "prime unlicensed bands for 802.16a are at 5 to 6 GHz."

Unstrung wondered (mused, really) if there could be interference issues if operators deploy both 802.11a wireless LAN and 802.16a wireless MAN systems in the same vicinity. "You could run into interference issues between 5 GHz 802.16 and 802.11a," says Marks. "This is one of the problems of unlicensed bands. However, there are several 5GHz bands, and with different preferences for indoor versus outdoor use. So, even in the 5GHz case, there are compatible scenarios."

However, there is currently no standard capability for 802.11 access points and 802.16 base stations to hand off to each other, so combining WLAN/MAN systems could prove to be tricky.

Marks says there were discussions at the IEEE in November about creating a generic 802. interface. This would enable handoff among wired Ethernet networks, wireless MAN, wireless LAN, and Bluetooth personal area networks (PANs). He expects more discussions on this topic this year.

The 802.16 specification is backed by equipment vendors such as Nokia Corp. (NYSE: NOK - message board) -- a company that is actually based in Finland, believe it or not -- as well as chipmakers such as Intel Corp. (Nasdaq: INTC - message board). "Intel has expressed very strong enthusiasm and support for the standard during the last few weeks," Marks comments.

So when will products using the standard arrive? "I'm not exactly sure," Marks clarifies. "They could be available by the end of 2003."

Marks expects typical implementations of the specification to provide data transfer rates of 10 Mbit/s and a coverage range of three to five miles. However, he stresses there are a lot of different variables with potential 802.16a rollouts, so the data transfer speeds and range offered by 802.16a networks may vary widely.

Hatim on Aug 2, 2001 -- "....there are a lot of variables. The current 802.16a standard proposal has many options; some are close to the 802.11a with the implied knowledge base and some closer to the DVB-T RC-T (a mouthful: digital video broadcasting - terrestrial reverse channel - terrestrial) with a more limited knowledge base. It is my guess that within a year from the approval of the standard products will appear that comply with one option or another. A product that can comply with all options may take longer (2 years or more)."

2/7/03 -- "We are confident we will be first to market with our 802.16a upgrade to our commercial W-OFDM based LIBRA products.

Hatim Zaghloul and Michel Fattouche founded Wi-LAN on the basis of a patent covering the use of OFDM for two-way data transmission with channel estimation and FEC. Since then the focus has been to develop OFDM to a level that optimizes the inherent NLOS benefits and at the same time translates the technology into useful products. There are several standards that have been accepted that incorporate OFDM in the manner described in the Wi-LAN patent.

All OFDM schemes divide the data stream into a number of carriers that are as close to each other as possible (the orthogonal part of OFDM) without interfering with each other. One of the most important parameters in an OFDM system is the number of sub-carriers used. Anywhere between 32 to 2000 subcarriers have been used or proposed. Using less than 128 sub-carriers significantly reduces the NLOS performance of OFDM. Using 2000 carriers is overkill and makes for an impossibly expensive product (requires a serious amount of processing power and very, very tight RF design). Based on field experience (Wi-LAN has built 64, 128 and 256 subcarrier systems), Wi-LAN has settled on using 256 subcarriers, which we believe offers the best blend of performance and cost. In addition to this we have included channel estimation, cyclic prefixes and FEC to produce what we believe to be the most robust OFDM solution available in our third generation OFDM product, the LIBRA 3000 series.

The recently ratified 802.16a standard includes OFDM with 256 subcarriers and the channel estimation, cyclic prefixes and FEC that are used in our products. All other OFDM based systems that we have seen in various stages of development have 64 sub-carriers, including the Redline system that Alvarion is OEMing. We believe we are the only company that has commercial 802.16a-like products, so we are confident that we will be first with 802.16a."

Best regards,

Ken Wetherell
Vice President, Corporate Communications & Investor Relations
Wi-LAN Inc.

Still no bright spot for Alvarion
Alvarion CEO Zvi Slonimsky: Our situation is relatively good, given
the state of the industry.

XCAD Corporation has developed a Capsim simulation of the physical
layer of the IEEE 802.11a Wireless LAN and IEEE 802.16 Wireless MAN.
We have focussed on the algorithms for receiver training and robust
performance over fading multi-path channels, large carrier offsets
and low SNR conditions. Moreover, XCAD is in the unique position to
simulate both the MAC layer and Physical layer simultaneously. This
is very important in designing MAC layer protocols that optimize
performance over various physical layer impairements. See the Capsim
application note on combined link and physical layer simulation for
details of an ARQ system.

IEEE Communications Magazine • March 2003

Increasing demand for high-performance 4G broadband wireless mobile
calls for use of multiple antennas at both the base station and
subscriber ends. Multiple antenna technologies enable high capacities
suited for Internet and multimedia ser-vices, and also dramatically
increase range and reliability. This design is motivated by the
growing demand for broadband wireless Internet access. The challenge
for wireless broadband access lies in providing a comparable quality
of service for similar cost as competing wireline technologies. The
target frequency band for this system is 2–5 GHz due to favorable
propagation characteristics and low radio frequency (RF)equipment
cost. The broadband channel is typically a non-line-of-sight (LOS)
channel and includes impairments such as time-selective and frequency-
selective fading. Multiple antennas at the transmitter and receiver
provide diversity in a fading environment. By employing multiple
antennas, multiple spatial channels are created, and it is unlikely
all the channels will fade simultaneously.

Orthogonal frequency-division multiplexing (OFDM) is chosen over a
single carrier solution due to lower complexity of equalizers for
high delay spread channels or high data rates. A broadband signal is
broken down into multiple narrowband carriers (tones), where each
carrier is more robust to multipath. In order to maintain
orthogonality among tones, a cyclic prefix is added that has length
greater than the expect-ed delay spread. With proper coding and
interleaving across frequencies, multipath turns into an OFDM system
advantage by yielding fre-quency diversity. OFDM can be implemented
efficiently by using fast Fourier transform (FFT) at the transmitter
and receiver. At the receiver, FFT reduces the channel response into
a multiplicative constant on a tone-by-tone basis. With multiple
input multiple output (MIMO), the channel response becomes a matrix.
Since each tone can be equalized inde-pendently, the complexity of
space-time equalizers is avoided. Multipath remains an advantage for
a MIMO-OFDM system since frequency selectivity caused by multipath
improves the rank distribution of the channel matrices across
frequency tones, thereby increasing capacity

Full document is in the Files section under the OFDM Folder. (Yahoo Wi-Lan Club)

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Wi-comm Communications Review

Wi-Comm Communications Co. Ltd. (Wi-Comm), is a Chinese joint venture
company owned 51% by Ray Scientific and Technology Development Co.
Ltd. of China (Ray Scientific), 20% by Wi-LAN Inc., and 29% by
Wincomm Communications Inc. (Wincomm), of Beijing. Wi-LAN has granted
Wi-Comm a non-exclusive license to manufacture (initially comprised
of final assembly of core components) and sell Wi-LAN products in
China, in exchange for a 20% equity interest in Wi-Comm and royalties
on Wi-Comm's sales. Any increase in the scope of manufacturing will
be based on market demand and subject to the mutual agreement of the
parties. Wi-LAN continues to retain exclusive title to and ownership
of its patented and proprietary technologies and is the exclusive
supplier to Wi-Comm of broadband wireless equipment.

The joint venture brings Wi-LAN closer to its strong Chinese business
partners, with the objective of offering the best price-to-
performance wireless access solutions in the 2-11GHz band. Using Wi-
LAN's Advanced Wireless Ethernet Bridges (AWE) and Broadband Wireless
Systems (BWS) products and key components, Wi-Comm will be able to
offer its customers high-capacity broadband wireless point-to-
multipoint systems that are rapidly deployable, scaleable, easily
expandable, and cost-effective.

"Having Wi-LAN's products, expertise and patented technologies at our
disposal gives us a significant advantage toward growing our
successful business in China," said Lok Chow, General Manager of the
Wi-Comm joint venture. "As our customers are expecting non-line-of-
sight capabilities, Wi-LAN's W-OFDM technology is the perfect
solution to meet their demands."

In 2001 the State Regulatory Radio Commission (SRRC), the Chinese
government agency responsible for regulating spectrum allocation,
certified Wi-LAN's AWE 120-24, AWE 120-58 and BWS 3500 products for
use in China. With these certifications, Wi-LAN has a full product
offering available for sale in China for the license-exempt 2.4 GHz
and 5.8 GHz bands, as well as the 3.5 GHz licensed frequency.

Lok Chow

Mr. Lok Chow is the President of both Wincomm Communications (Canada)
Inc. and Beijing Wi-Comm United Communications Inc. He is also the
General Manager of the Beijing Wi-Comm Communications, a joint
venture between Beijing Ray Investments Co. Ltd and Wi-LAN Inc. of
Calgary Canada.

Lok received his B. Sc. degree from the National Taiwan University
and a M. Sc. from the University of Manitoba, Canada, both in
Electrical Engineering. He continued his graduate studies in a Ph.D
program concerned the optical properties of amorphous
semiconductors. In 1981, Lok joined Canada Wires and Cables Co.
During his tenure at Canada Wire, Lok was the Group Leader for
Optical Fiber Development and also Optical Cable Development. Later
Canada Wires was purchased by the Alcatel Communications. After
leaving Alcatel, Lok founded Wincomm Communications in 1994. Since
then, Lok has cooperated with several major wireless engineering
firms on broadband access network technologies including BNI of
Winnipeg Canada and Wi-LAN Inc. of Calgary, Canada.

From 1996, Lok teamed up with the Hong Kong based Huaneng Basic
Industry Investment Co. Ltd., and established Wi-Comm United
Communications (WCU) in Beijing. Under Lok's leadership, Wincomm
Communications has established itself as one of the major players in
the wireless enterprise network and BWA market in China. In 2001,
Wincomm formed a Joint Venture called Wi-Comm Communications with Wi-
LAN and Ray Investments Co. The Joint Venture provides hardware
support and OEM of Wi-LAN's products in China. Lok is an advocate
of the W-OFDM, an innovative wireless technology developed by Wi-
LAN. Wi-Comm United has won two BWA projects in Nanjing, China. WCU
is working actively in the Metropolitan FWA market as well as the
future wireless applications with mobile terminals. Lok has organized
a W-OFDM Strategic Alliance in China to provide a business forum for
system integrators, BWA vendors and users who are interested in the W-
OFDM solutions.

W-OFDM, as Described by the INVENTOR

To:Peter Ecclesine who wrote (5766)
From: Bernard Levy Sunday, Oct 31, 1999 3:36 PM
View Replies (2) | Respond to of 12365

Hi Peter and Jim:

Could you enlighten us as to what aspects
of OFDM are covered by patents? OFDM itself
was proposed in a 1964 by J. Holsinger in a
MIT RLE report, so that as a modulation
scheme, OFDM should be in the public domain.

Also, at the implementation level, aren't some
of the DMT patents relevant to OFDM? Is this why
TXN is part of the group working with CSCO on

Best regards,

Bernard Levy

To:Bernard Levy who wrote (5771)
From: Hatim Zaghloul Sunday, Oct 31, 1999 8:52 PM
View Replies (4) | Respond to of 12365


OFDM is as you said, primarily a public domain technology. However all attempts to operate wideband OFDM in the late eighties had failed for three known shortcomings of OFDM: the peak to average ratio, synchronization since there are too many carriers to lock on only one and selective fading.

Wi-LAN introduced and a simple method of whitening to reduce the peak to average ratio. This was patented in the Canadian patent.

Wi-LAN introduced the concept of using an estimate of the frequency response of the channel as means to remove the effects of selective fading.
This aspect is the main claim in the US and Canadian patents.

Synchronization was solved by a number of companies. Wi-LAN opted for using a direct sequence header for OFDM.

Wi-LAN has filed another patent on the use of the channel estimator to improve the performance of the forward error corrector.

This was disclosed in a submission to the IEEE802.11 working group.

As for DMT, Cisco itself published a paper indicating that OFDM is principally different than DMT:

I hope this gives some answers.


To:Bernard Levy who wrote (5775)
From: Hatim Zaghloul Monday, Nov 1, 1999 10:25 AM
Respond to of 12365

I do not know if you are familiar with the patent dates.
Our patent is earlier than the first DMT patent. Our solution for the peak to average problem is the one adopted in the IEEE802.11a

(I remind everyone that Wi-LAN did not develop the standard and only had one submission to it relating to the forward error correction).

Also, I am not certain that DMT had any intentions of being wideband. We gave a number of definitions of wideband in our patent. These definitions include: 1. if bandwidth occupied is wide enough that the propagation channel is frequency selective meaning different subchannels are subjected to different channel characteristics, or 2. if the subchannels are far enough apart from each other that an implementation can be made without discrete (rf hardware) carrier recovery.

As you must know, I cannot carry this debate much further since, ultimately, this is what courts are for.


To:ftth who wrote (5779)
From: Hatim Zaghloul Monday, Nov 1, 1999 10:35 AM
Respond to of 12365


We have not taken a formal position with regard to COFDM; please excuse that I cannot comment on it at this stage.

I gave some definitions of wideband in an earlier post today.

The carriers issue was an issue in the past (and unfortunately for most engineers patents solve old problems so that they are not problems any more). Everyone now knows the concept of synchronizing on a header that is not a OFDM (or multicarrier) header.

Using a simple or a complex channel estimator with OFDM was not as apparent in the late 1980s as it is now (again that patents describe it in detail). OFDM is not a classical single carrier communications scheme and most concepts from the past did not lend themselves to OFDM in an obvious way.

Thank you for your interest.


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