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Focus on Engineering & Design: Broadband Wireless Access – Promise and Reality

Contrary to predictions, Broadband Wireless Access has not become a serious competitor to telephone and cable TV networks in providing broadband services. What challenges must the technology overcome ...


February 1, 2002  


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Contrary to predictions, Broadband Wireless Access has not become a serious competitor to telephone and cable TV networks in providing broadband services. What challenges must the technology overcome to attain the success that once seemed a certainty?

The much ballyhooed promise of Broadband Wireless Access (BWA) as a serious competitor to telephone and cable television networks in the provision of broadband services, including the integration of telephony, data and fast Internet access, has been a profound disappointment — at least to this point in time.

To understand why this has occurred, it is necessary to examine the promises versus the realities which have emerged, and to underline the key challenges for this technology to attain the business success predicted by early proponents.

WHAT IS BWA?

There are significant differences between BWA and the narrowband versions of wireless technology, specifically Cellular Telephony and PCS. BWA is a “fixed” (as opposed to “mobile”) technology, intended to provide ubiquitous service to residential and business customers in a Point-to-Multipoint (PmP) configuration. The infrastructure is intended to serve many simultaneous business and residential users, each being provided with at least DS-1 (1.544 Mbps) symmetrical transmission — or at least two Mbps asymmetrical “download” capability.

BWA has promised video, voice and high-speed data integration, including fast Internet access, at higher bit rates than provided by either cable modems or telephony company Digital Subscriber Line (DSL) services.

Like all wireless communications technologies, BWA offers rapid deployment when compared to the hard-wire alternatives involving fiber optics and/or paired-wire. BWA also has the potential, depending upon the frequency band utilized, of providing rural service — an area where cable television and the telephone providers are severely handicapped.

There are a number of microwave frequency bands now allocated for BWA service provision (please see Table 1). Multipoint Communications Systems (MCS) and Industrial, Scientific and Medical (ISM) allocations provide frequencies in various bands throughout the microwave and millimetre wavelength spectral regions.

The higher frequency bands generally entail increased equipment costs, diminished power output and range, as well as susceptibility to rainfall and foliage attenuation; conversely, they offer more available bandwidth. Table 1 also associates the licensure processes implemented by Industry Canada for each of these bands. The differences between the processes are important, as they significantly impact economics.

LICENSING PROCESSES

Historically, Industry Canada awarded telecommunications licence frequency assignments on a “First-Come, First-Served” (FCFS) basis, with annual licence fees based on the amount of bandwidth occupied. While this FCFS process is still the most common form of Industry Canada licensure, use of a comparative or, more recently, an auction process, has now become a major element of spectrum licensing when the demand for spectrum is perceived to exceed its availability.

The comparative process is very similar to that utilized by the CRTC in awarding broadcasting licences. Competing applicants file proposals with Industry Canada outlining the social, economic and technical benefits of their plans, and hope to be favoured with a licence — either exclusively or with minimal competition. This process is often called the “beauty contest. While the process does not entail the substantial front-end costs associated with auctions, typical annual licence fees are in the range of one dollar per potential service household and are levied whether the operator has any customers or not.

Auctions are likely to displace the comparative alternative in most future actions, as these eliminate the need for Industry Canada to make any judgements on the quality of various competing applicants. Selection is exclusive and becomes quite simple: the applicant willing to pay the most money wins.

LOCAL MULTIPOINT COMMUNICATIONS SYSTEMS

The first impetus to BWA development in Canada occurred in the mid-nineties when a comparative process was used to select licensees for two 500 MHz spectral blocks at 28.5 GHz, to be used for local access services and multichannel TV distribution. Local Multipoint Communications Systems (LMCS) require the use of millimetre wave technology — the highest frequencies in use in the early 1990s.

LMCS’ foundation was based upon trials in New York City by a company called CellularVision, which was focused on the U.S. wireless cable market. With U.S. spectrum for “wireless cable” at 2.5 to 2.7 GHz heavily congested, 28 GHz became the first frequency band that provided enough capacity for a true multichannel offering. Yet, while Canada had allocated clear spectrum at 2.6 GHz for multichannel TV (MDS) broadcasting, Western International Communications (WIC) of Vancouver bought the Canadian rights to CellularVision’s technology and pushed hard for Canadian operational approval.

Industry Canada was encouraged to move quickly and provide Canada with a “world leadership” position in LMCS. It was suggested that LMCS licensure would generate 8,000 jobs and a $1 billion investment by 2000, making Canada the world leader in this exciting new technology.

Fourteen applicants competed in 1995 for the first licences. While major entities such as Call-Net and Fonorola were among the applicants, only three firms were licensed by Industry Canada in October 1996: WIC Connexus, a WIC-associated company called Regional Vision Inc., and MaxLink of Montreal. WIC and MaxLink split 66 major markets, while Regional Vision took the remaining smaller markets.

While the initial LMCS driver had been provision of multichannel television to compete with cable TV, by the time the licences were sought the focus was shifting quickly to integrated, broadband telecommunications. Business analysis suggested that only large commercial or residential edifices could afford the costs of the wireless infrastructure. As a result, a close connection between the PmP wireless distribution and internal broadband cabling systems in apartment buildings and business edifices was visualized.

After several years of trials by WIC, MaxLink purchased the WIC licences and subsequently went out of business. In spite of substantial development costs and licence fees paid to Industry Canada, there were no significant revenues to any of the LMCS players, and no infrastructure of lasting value was established.

Industry Canada was blamed for many of the problems, having allocated spectrum without guard bands in a frequency range that differed from that selected in the U.S. However, the applicants got exactly what they asked for: a head start on the U.S. with all of the risks of band allocations and potential equipment incongruities.

24/38 GHZ MCS

Industry Canada used an auction process for the first time in the autumn of 1999 to award MCS spectrum at 24 and 38 GHz in 59 service areas (totalling 359 licences nationally). The band plans provided for guard bands and were fully aligned with those in the U.S.

There were 18 qualified bidders who registered with Industry Canada, depositing over $75 million. Major players included AT&T Canada, BCTel, and the Bell Mobility and Nexxia organizations. Results of the auctions saw a quick exit by the established carriers, with newcomers such as Stream, Wispra, Norigen and Dolphin Communications garnering major market spectrum at purchase prices exceeding $80 million.

After two years, many of the successful bidders have either expired (Norigen) or demonstrated very little wireless infrastructure establishment. U.S. and European experience has been identical, with the exception that there has been progressively less interest in BWA spectrum auctions in Europe.

The only significant Canadian utilization of 24 and 38 GHz auctioned spectrum has been via Dolphin’s TeraGo Networks Inc., which is currently developing eight Canadian markets in smaller cities lik
e Winnipeg. TeraGo utilizes a mixture of auctioned spectrum and licence-exempt ISM bands, with the licensed spectrum used for Point-to-Point (PtP) trunking and unlicensed spectrum used for PmP service cells.

2.5 GHZ MCS

A 96 MHz slice of bandwidth at 2.5 GHz, which was allocated for MCS services in the late 1960s and which had seen limited use by educational authorities and business interests for non-broadcast multichannel television distribution, was identified in 1999 for comparative licensing by Industry Canada. Commercial interests had recognized the advantages of the lower frequency spectrum in terms of equipment costs and coverage potential, pushing for national licensure of this band and promising provincial and regional system development for fast Internet access and other broadband services.

The 2.5 GHz spectrum is virtually impervious to the effects of rainfall, and has equipment available that supports relatively high transmit powers and use of linear modulations such as QAM and VSB, which provide high spectral efficiency.

Nine applicants filed for 2.5 GHz MCS licences, including major players such as Rogers Cantel, Telus, SaskTel and Inukshuk Internet, an entity with strong ties to TeleGlobe and Microcell. Licences were subsequently awarded to Inukshuk for the entire band in eight provinces, with SaskTel obtaining an exclusive licence in Saskatchewan, and Manitoba excluded from the licensing process because of existing educator use of the band throughout rural Manitoba. Licences were based on an annual charge for the number of households within each province.

While Inukshuk appears to have undertaken very little in terms of establishing infrastructure, SaskTel issued an RFP in August 2001, which has not yet been awarded. In Manitoba, SkyWeb, a unit of Craig Wireless Inc., has obtained MCS licences for some spectrum in Winnipeg and is offering fast Internet access using “migrated” cable TV transmission techniques — QAM downstream and QPSK return, with modified cable modems.

Some feel that limiting licensure, via the auction or comparative processes, to well-financed firms maximizes the possibility that significant infrastructure and new services will be developed — as opposed to the potential afforded by smaller firms incapable of handling the higher licence fees. However, given the large amount of currently licensed, but undeveloped, spectrum (which is no longer open to other users), one might hope for better results in the future.

LICENCE-EXEMPT ALTERNATIVES

Given the sizeable costs and time intervals associated with the auction comparative licence processes, there has been much interest in using Industrial, Scientific and Medical bands, which do not require Industry Canada licensure. The 902-928 MHz ISM band is relatively narrowband and is now virtually useless in major centres due to interference.

The band at 2.45-2.5 GHz is the current prime focus of ISM activity, but is also experiencing interference problems in metropolitan markets. Interference stems not only from multiple users, but also the growing proliferation of consumer wireless equipment such as cordless phones, garage door openers and television “senders”. The latest frontier for ISM, which is developing quickly, is at 5.8 GHz.

Along with the avoidance of costs associated with the licensing process, there are other cost benefits to ISM band usage, stemming from the mandated use of CDMA (spread-spectrum) techniques and relatively low power. Low power CDMA can be implemented with significantly lower cost equipment than is utilized for licenced implementations. And there is enough robustness in the CDMA process to support multiple users (at least initially) in PtP applications.

PmP implementations are vulnerable to interference and there is no protection afforded by any regulatory agency to users of these bands. The growth of users in some metropolitan areas has been significant, raising the level of interference correspondingly. This leads to the use of increased power, illegal amplifiers and excessive antenna gains — techniques that create more problems than they solve. Many consider this entire area of technology to be of interim interest, perhaps having a somewhat longer service life in rural areas.

In the meantime, the licence-exempt operators have succeeded in “cream-skimming” some of the users that were anticipated to be customers by firms that obtained licences at considerable expense.

TWIN CHALLENGES

There are two fundamental challenges that have hampered the successful implementation of BWA. One major challenge has been that of providing robust, reliable transmission in an environment that is subject to multipath reflections, variations in attenuation and, at the higher frequencies, substantial signal fading due to rainfall and vegetative effects. Robust transmission must be provided in both the forward and return directions, with most current implementations requiring “clear” (60 per cent Fresnel zone), Line-of-Sight (LOS) paths. Adequate clearance is difficult in the presence of trees, buildings and other obstructions in metro areas, as well as in rural implementations. Effective transmission reliability for PmP systems likely requires technology that will support Near-Line-of-Sight (NLOS) configurations.

Ignoring the cost of obtaining a licence, the cost effectiveness of the transmission infrastructure — particularly the Media Access Control (MAC) and customer site equipment — represents another major challenge.

While Industry Canada licenses are not required for the use of ISM bands, there is a requirement for all wireless systems with regard to the registration of towers with Transport Canada. There is also a requirement for registration with municipal authorities (Land Use Consultation) to conform with Safety Code 6, which pertains to health issues related to emitted signal field intensity. Many ISM band implementations ignore all regulatory requirements.

A proliferation of standards, including IEEE 802.11a/b, ETSIBRAN, DOCSIS, Wi-Fi and many proprietary alternatives — along with competing user organizations such as BWIF, OFDM, N-West, Wireless DSL Consortium, Single Carrier Forum and the Free Space Alliance — have hampered the attainment of cost economies that clearly result from the adoption of universal, open standards. Many BWA implementations have implemented DOCSIS-based MAC and customer equipment components, given that DOCSIS (a cable television industry standard) has fostered equipment interoperability. This has created competition and driven down equipment costs.

However, DOCSIS has been developed for the relatively friendly and stable environment of a cable distribution system. DOCSIS’ use of QAM and QPSK modulations does not provide NLOS performance. Moreover, Cable Modem Termination System (CMTS) equipment used for MAC at hub sites is still relatively expensive, particularly in rural or small town implementations.

Nevertheless, there are modulation formats and MACs that can provide the required NLOS robustness, as well as diminished hub costs — alternatives provided by major players who are well established and have deep pockets.

Making a BWA system function is not enough; it must satisfy business plan requirements in the face of well-established and well-financed competition. The BWA industry is still wrestling with these challenges.

Bill Evans, has more than 30 years of experience in the cable television, broadcast engineering, business telecom and microcomputer networking industries. He is president of Winnipeg-based EB Systems Ltd, an engineering consulting, system design and project management/implementation firm that he formed in 1989.

TABLE 1: BWA BAND ALLOCATIONS IN CANADA

Frequency Classification Licensing Status
24 / 38 GHz MCS Auction 1999
26 / 28 GHz LMCS Comparative 1996
23 GHz MCS FCFS plus Auction
18 GHz MCS Not Promulgated
5.8 GHz ISM Licence-Exempt
3.4 / 3.6 GHz MCS Rural-Auction likely
2.5 GHz MCS Comparative 1999
2.45 GHz ISM Licence-Exempt
902 MHz ISM Licence-Exempt

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