Wireless VisionWireless VisionWireless VisionWireless Vision

Wireless Vision

The vision of wireless communications supporting information exchange between people or devices is
the communications frontier of the next century. This vision will allow people to operate a virtual
office anywhere in the world using a small handheld device - with seamless telephone, modem, fax, and
computer communications. Wireless networks will also be used to connect together palmtop, laptop, and
desktop computers anywhere within an office building or campus, as well as from the corner cafe. In
the home these networks will enable a new class of intelligent home electronics that can interact with
each other and with the Internet in addition to providing connectivity between computers, phones, and
security/monitoring systems. Such smart homes can also help the elderly and disabled with assisted
living, patient monitoring, and emergency response. Video teleconferencing will take place between
buildings that are blocks or continents apart, and these conferences can include travelers as well, from
the salesperson who missed his plane connection to the CEO off sailing in the Caribbean. Wireless
video will be used to create remote classrooms, remote training facilities, and remote hospitals anywhere
in the world. Wireless sensors have an enormous range of both commercial and military applications.
Commercial applications include monitoring of fire hazards, hazardous waste sites, stress and strain
in buildings and bridges, or carbon dioxide movement and the spread of chemicals and gasses at a
disaster site. These wireless sensors will self-configure into a network to process and interpret sensor
measurements and then convey this information to a centralized control location. Military applications
include identification and tracking of enemy targets, detection of chemical and biological attacks, and
the support of unmanned robotic vehicles. Finally, wireless networks enable distributed control systems,
with remote devices, sensors, and actuators linked together via wireless communication channels. Such
networks are imperative for coordinating unmanned mobile units and greatly reduce maintenance and
reconfiguration costs over distributed control systems with wired communication links, for example in
factory automation.
The various applications described above are all components of the wireless vision. So what, ex-
actly, is wireless communications? There are many different ways to segment this complex topic into
different applications, systems, or coverage regions. Wireless applications include voice, Internet access,
web browsing, paging and short messaging, subscriber information services, file transfer, video telecon-
ferencing, sensing, and distributed control. Systems include cellular telephone systems, wireless LANs,
wide-area wireless data systems, satellite systems, and ad hoc wireless networks. Coverage regions in-
clude in-building, campus, city, regional, and global. The question of how best to characterize wireless
communications along these various segments has resulted in considerable fragmentation in the industry,
as evidenced by the many different wireless products, standards, and services being offered or proposed.
One reason for this fragmentation is that different wireless applications have different requirements. Voice
systems have relatively low data rate requirements (around 20 Kbps) and can tolerate a fairly high prob-
ability of bit error (bit error rates, or BERs, of around 10−3), but the total delay must be less than 100
msec or it becomes noticeable to the end user. On the other hand, data systems typically require much
higher data rates (1-100 Mbps) and very small BERs (the target BER is 10−8 and all bits received in
error must be retransmitted) but do not have a fixed delay requirement. Real-time video systems have
high data rate requirements coupled with the same delay constraints as voice systems, while paging and
short messaging have very low data rate requirements and no delay constraints. These diverse require-
ments for different applications make it difficult to build one wireless system that can satisfy all these
requirements simultaneously. Wired networks are moving towards integrating the diverse requirements
of different systems using a single protocol (e.g. ATM or SONET). This integration requires that the
most stringent requirements for all applications be met simultaneously. While this is possible on wired
networks, with data rates on the order of Gbps and BERs on the order of 10−12,itisnotpossibleon wireless networks, which have much lower data rates and higher BERs. Therefore, at least in the near
future, wireless systems will continue to be fragmented, with different protocols tailored to support the
requirements of different applications.
Will there be a large demand for all wireless applications, or will some flourish while others vanish?
Companies are investing large sums of money to build multimedia wireless systems, yet many multimedia
wireless systems have gone bankrupt in the past. Experts have been predicting a huge market for wireless
data services and products for the last 10 years, but the market for these products remains relatively
small, although in recent years growth has picked up substantially. To examine the future of wireless data,
it is useful to see the growth of various communication services, as shown in Figure 1.1. In this figure
we see that cellular and paging subscribers have been growing exponentially. This growth is exceeded
only by the growing demand for Internet access, driven by web browsing and email exchange. The
number of laptop and palmtop computers is also growing steadily. These trends indicate that people
want to communicate while on the move. They also want to take their computers wherever they go. It
is therefore reasonable to assume that people want the same data communications capabilities on the
move as they enjoy in their home or office. Yet exponential growth for high-speed wireless data has not
yet materialized, except for relatively stationary users accessing the network via a wireless LAN. Why
the discrepancy? Perhaps the main reason for the lack of enthusiasm in wireless data for highly mobile
users is the high cost and poor performance of today’s systems, along with a lack of “killer applications”
for mobile users beyond voice and low-rate data. However, this might change with some of the emerging
standards on the horizon.