Earlier in this decade, the wireless industry began heating up over the immense promise of wireless
local loop applications. Predictions of an explosion of worldwide WLL system installations through the end of the
century were everywhere. Yet the number of lines actually deployed today is a token amount compared with the
International Telecommunication Union’s conservative estimate two years ago of a backlog of more than 50 million
potential telephone subscribers-those who could afford service but for whom it was unavailable.
Most would agree
the promise of an explosion of WLL applications throughout the world remains just that-a promise. More widely
contested, however, are the reasons why.
Was the original potential of WLL overestimated? I believe not. In terms
of simple economics, the demand for telephone lines continues to grow faster than new lines are installed. WLL
rightfully has been touted as the ideal source of fulfillment for this demand. WLL offers faster speed of deployment,
lower fixed and recurring costs and reliability that is even an improvement from wireline.
Was the demand among
emerging countries misperceived? No. It generally is recognized in emerging countries that telecommunications is a
crucial tool of economic expansion. Consider the fax machine, which has become an indispensable tool of commerce
for any business of substance on earth.
Those areas of the world for which the greatest growth in WLL applications
was predicted, particularly the Asia-Pacific region, recently were dealt a severe economic blow that may account for
some delays. For countries trying to emerge or keep up with other world economies, however, spending to establish or
maintain fundamental business/residential telephone service must be recognized as part of an economic cure, not
abandoned as a budgetary sacrifice.
Truly, the concept of WLL remains valid and viable. While there are numerous
reasons for the delay in its large-scale deployment, it is clearly only a delay. WLL will be the dominant solution for
voice and low-rate data (including fax and Internet access) for new construction in the emerging countries and
expansion in the developed countries.
What has caused the current stall in the WLL explosion, and what will it take
to re-ignite growth for this extremely important technology? Astonishingly, the very product that created strong initial
demand for WLL has slowed the introduction of such service internationally. By this I mean “re-labeled
cellular,” or cellular-based systems.
In the numerous field trials conducted in China, India, Malaysia, the
Philippines and elsewhere, almost every offering has been a cellular-like system. Such systems are simply not designed
for, and are not suitable for, WLL service. Let’s review why this is true, as well as the differences between mobile and
fixed systems, the unique requirements of fixed WLL, and this observer’s prediction of what will happen in the future
for WLL.
A matter of economics
WLL deployment will not accelerate until both fixed and recurring costs are
lower than those for wireline systems. Less clear are the ways to define and express these costs in a manner that can be
analyzed and compared. The most understandable measure of initial system cost is “cost per subscriber.”
However, assumptions of traffic carried per subscriber and density of deployment dramatically can affect this cost.
Also, recurring costs will be of the same order of magnitude as initial costs; they cannot be neglected. Consider that:
Traffic generated by a subscriber dictates the magnitude of dedicated infrastructure. In developed
countries, subscribers talk about 100 minutes per month on their wireless phones and about 1,000 minutes per month on
landline phones. While calling patterns in emerging countries may vary considerably, it is important that comparisons
of different systems use the same traffic assumptions.
Grade-of-service (GOS) assumptions influence costs. While
a GOS of 3 percent to 5 percent may be adequate for mobile service that is ancillary in nature, a more acceptable GOS
for fixed service is 1 percent or better.
Given the high costs associated with site rental and base-station
maintenance, an effective WLL system will require fewer base stations. More channels per base station is far more
important than the range of a base station. In most WLL situations, subscriber density is sufficiently high that
additional base stations are needed just to accommodate subscribers. Base-station capacity dictates the number of
stations required to cover a given area. This is different in rural areas, but since so few subscribers are involved, it is
often more economic to use special measures in these areas.
Cost-effective WLL systems must interface directly
into the switched network. The introduction of the mobile switching offices common in cellular systems raises costs to
unacceptable levels.
Systems and technologies that economically deliver high spectral efficiency hold the greatest
value. Cost per subscriber is, ultimately, closely related to the amount of spectrum available in each system. It does
little good to provide base stations with the capability to access a large number of channels if there is inadequate
spectrum available to accommodate all the channels.
System engineering demands are an important differentiator
between the candidates for WLL systems. Systems that require carefully engineered cell site locations will cost more,
both in engineering cost and cell acquisition, than systems that are self-organizing and not highly sensitive to site
locations. Interference-limited systems like Personal Handyphone System services are inherently favorable in this
regard.
For WLL, quality matters
Wireless users throughout the world have become inured to the variable
quality of today’s systems. Most of these users, however, have an alternative that provides reliable, high-quality
communications. WLL service creates a different situation. Subscribers whose only form of communications is
wireless will not be so tolerant. Carriers cannot expect to serve them with anything less than toll-quality voice or to
provide fax and exchange data service with high error rates. Digital wireless air-interface protocols that use high
compression to achieve communication with 13,000 bits per second or less do not deliver toll quality. This includes
offerings based upon Global System for Mobile communications and Code Division Multiple Access technologies.
PHS, PACS, and Digital Enhanced Cordless Telephone technologies use a mild form of compression that can provide
toll quality. Similarly, minimum data rates of 9,600 bps for fax and 28.8 bps for data are essential.
Again,
measurement criteria are important. In the real world, ambient noise and a variety of languages and accents are
expected. Be wary of claims of “mean opinion scores” where no mention is made of the conditions under
which testing is done. With very quiet environments, strong signals, and professional speakers, most systems offer
acceptable voice quality. The real world is seldom so ideal. With the addition of background noise and introduction of
regional accents, the penalty for compression becomes apparent.
Availability of spectrum is a key
Most
countries are making radio-frequency spectrum available for more than one air interface. This is consistent with the
profusion of offerings and the lack of widespread deployment of any one system. Since roaming has no real
significance in fixed WLL systems, compatibility between
various systems is not a requirement. Yet the spectrum is,
very properly, being meted out sparingly. Regulators and carriers are sensitive to the efficient use of spectrum as well
as the total amount of sp
ectrum needed to achieve stated cost and capacity goals. To reach significant market
penetration, WLL systems must be spectrally efficient.
The added expense of mobility
Almost all of the wireless
local loop offerings today are, effectively, cellular systems that have been adapted to the WLL market. In most cases,
the air-interface-the complex set of protocols and signaling that allows a radio system to act like a wired connection-is
exactly that used for systems that have a requirement for mobile subscribers. The demands placed upon a cellular
system by the requirement for mobility are both complex and costly. For example, hand-off-the ability to maintain
communications with the subscriber as a subscriber moves from cell to cell-is mandatory in mobile systems. Hand-off
involves interaction between cell sites and the cellular switch. This adds cost in the mobile switching office, the base
station controllers, the base stations and even in the subscriber handsets.
More importantly, a subscriber’s location is
known before a call is initiated. This knowledge can be extremely valuable in reducing the cost of the system design
and in increasing capacity. Smart antenna systems use this information to increase a WLL system’s efficiency, i.e.,
increase the number of channels that can be deployed in a single base station for a given amount of radio spectrum. The
more channels served in a single base station, the fewer base stations required. As a result, the fixed cost of creating the
sites, acquiring the site locations, maintaining the equipment, bringing connections to the public switch network and
other factors are reduced.
Technology to the rescue
Numerous systems and technologies exist today designed
specifically for WLL. Ultra-linear power amplifiers, intelligent antennas and very high voice quality compression are
becoming basic to WLL offerings in the unrelenting battle to reduce system costs and to exceed the performance of
wireline systems. For the same reason, effective WLL equipment uses the most advanced radio designs, incorporating
digital signal processors and microprocessors to replace traditional analog components. The steep reduction in the price
of these computer-related components only can accelerate the cost reduction of WLL systems.
Is there a role for
wireline?
While it is unlikely in the not-too-distant future there will be few, if any, wireline systems built for
personal voice communications, there is still an important role for wireline systems in the telecommunications world.
As an example, communications from one computer to another, where very large amounts of data are involved, can be
handled much more effectively with wires (including fiber) than wirelessly. Similarly, in high-density applications such
as office and apartment buildings, it is more effective to provide personal voice communications using wire.
Wire
and fiber will continue to be the technology of choice for long-haul broadband communications, although, even here,
satellite communications are taking an ever-increasing role.
As wireless technology advances, wireless systems will
encroach further on wired territory. The more efficiently a wireless technology can handle large amounts of data (i.e.,
in a small frequency band and at very low cost), the less need there is for costly, high-maintenance wires. While it will
be some years before very heavy data traffic can be handled effectively using the radio spectrum, the age of wireless
communications for voice and low-rate data is already upon us.
A strong future ahead
A trillion dollars will be
spent worldwide on the local loop during the next 25 to 30 years. Almost all of that will be spent on wireless local loop.
There is no way to accelerate the acquisition or spending of such a huge amount of money.
Taking China as one
example, an annual growth in gross national product of 10 percent for 20 years will be required to achieve a telephone
line penetration of 20 percent in that country, assuming a large fraction of capital spending is applied to the
telecommunications market. Should this optimistic scenario materialize, there will be an expenditure of $300 billion in
China for equipment alone during that period.
Conclusion
Wireless local loop is poised to become the basis for a
new level of productivity and efficiency in telecommunications. In Southeast Asia alone, more than $5 billion is likely
to be spent in the next five years, creating more than 7 million wireless local loop lines. This will happen only if the
cost for WLL systems drops well below the cost of both today’s cellular systems and wired systems. New technologies
already are appearing in products designed for WLL applications; these technologies and products will launch this
exciting new industry. Certainly wireline will continue to play an important role in telecommunications. Yet, in the not-
too-distant future, new systems aimed at bringing voice, fax and data services to the masses will be almost exclusively
WLL.
Martin Cooper is co-founder and chairman of ArrayComm Inc., San Jose, Calif.
