Wireless technology can provide many benefits to computing
including faster response to queries,
reduced time spent on paperwork, increased online time for
users, just-in-time and real time control,
tighter communications between clients and hosts. Wireless
Computing is governed by two general
forces: Technology, which provides a set of basic building
blocks and User Applications, which
determine a set of operations that must be carried out
efficiently on demand. This paper summarizes
technological changes that are underway and describes their
impact on wireless computing development
and implementation. It also describes the applications that
influence the development and
implementation of wireless computing and shows what current
Wireless computing is the topic of much conversation today.
The concept has been around for some
time now but has been mainly utilizing communication
protocols that exist for voice based
communication. It is not intended to replace wired data
communication but instead to be utilized in
areas that it would be otherwise impossible to communicate
using wires. Only recently has the industry
been taking steps to formulate a standard that is more
suitable to data transmission. Some the problems
to be overcome are:
(1) Data Integrity - relatively error free transmission,
(2) Speed - as close as possible to the speed of current
(3) Protection - making sure that the data now airborne is
encoded and cannot be tapped by
(4) Compatibility - ensuring that the many protocols that
sure to be created subscribe to a standard
to allow inter-operability,
(5) Environmentally safe - strengths of electromagnetic
radiation must be kept within normal levels.
In our study of the theories and implementation concerns of
wireless computing, we found that it is
being treated in an object oriented fashion. Scientists and
development crews, including the IEEE, are
doing their best to implement wireless connectivity without
changing the existing computer hardware.
As a result, a lot of focus is on using existing computer
hardware and software to convert data to a
format compatible with the new hardware which will be added
to the computer using ports or PCMCIA
connections that already exist. This means that wireless
communication will be transparent to the user
if and when wireless computing is utilized on a wide scale.
Wireless computing applications covers three broad areas of
computing today. Replacement of normal
wired LAN's need to retain the speed and reliability found
in wired LAN's. Creation of semipermanent
LAN's for quick and easy setup without the need for running
wires. This would be necessary for events
such as earthquakes. The last category is that of mobile
computing. With advent of PCMCIA cards,
notebook computers are being substituted for regular
desktop machines with complete connectivity of
the desktop machine. However, you lose the connectivity
when out of the office unless you have a
wireless means of communicating.
On the compatibility issue, the ability to mix wireless
brands on a single network is not likely to come
soon. The IEEE Standards Committee is working on a wireless
LAN standard -- 802.11, which is an
extension of the Ethernet protocol. Because the field of
wireless communication is so broad, the IEEE
was not able to set a standard by the time private
researchers were ready to test their theories hoping to
set the standard for others to follow.
There are a few methods of wireless communication being
theorized and tested.
(1) Radio: This is the method that makes use of standard
radio waves in the 902 MHz to 928 MHz
frequency range. Although these frequencies are well used,
methods have been developed to
ensure data integrity. Spread spectrum transmission of data
is a method where the transmitter
will send information simultaneously out over many
frequencies in the range increasing the
change that all data will eventually reach the receiver.
Frequency hopping is an additional
measure that also enables data security. The 26 MHz range
of frequencies is further divided in
to channels. The transmitter then sends out data hopping
from one channel to the next in a
certain pattern known to the receiver. Within each channel,
spread spectrum transmission can
be used to maintain interference avoidance. Some of this
transmission manipulation can be
avoided by transmitting at a frequency that is less used.
Some developers have tried
transmitting in the gigahertz range. The disadvantages here
are: 1) Higher frequencies mean
shorter wavelengths and shorter wavelengths do not
penetrate solid objects like walls and floors;
2) The same transmission strength employed by lower
wavelength transmitters yields a shorter
range at higher frequencies. This means that transmission
strength will need to be boosted
something hard to accomplish using portable tools and
potentially dangerous to humans; 3)
Transmission frequencies of 3 GHz and higher are licensed
by the Federal Communications
Commission. Developers in the range have the additional
hassle of obtaining a license every
time an installation is done.
(2) Laser: Laser-based communication is the fastest way to
communicate without wires.
Information travels at the speed of light. The drawbacks
however far outweigh the speed
advantage and prevent this method from becoming the
standard. The major drawback is that
communication is restricted to line of sight. Also, very
thick fog or blizzard conditions will
diffuse the laser beam and causing interference and
reducing data integrity.
(3) Infrared: This method is similar to Laser. High speed
communications are easy to achieve
using this method. However, it suffers from the same
problems that plague laser
communications. It requires line of sight transmission and
can be disrupted by strong ambient
light. Infrared wireless computing exists more commonly in
the form of peripheral connections
in a small area.
(4) Cellular connections although expensive to use now is
the area of much development by private
companies. Cellular computing can be likened to the current
wire-based internet network. Data
is packaged in to units, size of the unit is dependent on
the actual hardware, and is sent to the
nearest participating cell. That cell then forwards the
packet to the next cell and so forth until
the packet reaches its destination.
(5) Microwave: This method of communication has been
utilized for quite some time now.
However this method has makes little provision for data
aware transmission. It used extensively
in Europe where wired transmission of any type including
voice is poor. For data transmission,
a lot of technology is utilized in packaging the data into
a form that is compatible to voice
communication. On the receiving end, the process is
reversed. The advantage of this method
however is that communication can be accomplished using
existing satellite connections making
worldwide connectivity possible.
The IEEE 802.11 committee has voted to create a minimum
requirement for wireless computing
connections. In their consideration:
(1) Use the frequencies 2.4 to 2.5 GHz. This is in the low
end of the high frequency spectrum and
is currently not licensed by the FCC.
(2) Use spread spectrum technology. Compared to the current
bandwidth 26 MHz, 902 MHz to
928 MHz, the range 2.4 to 2.5 GHz yields a bandwidth of 100
MHZ. Spread spectrum
transmission now gives 385% percent increase in data
(3) Many more sub-channels can be formed in a bandwidth of
100 MHZ. This increases the
capability of frequency hopping which in turn yields
greater data security.
(4) Utilize Gaussian Frequency Shift-Keying. Frequency
shift-keying is a form of frequency
modulation in which binary signaling is accomplished by
using two frequencies separated by
some Df Hz. The frequency duration is small compared with
the carrier frequency, fc. A signal
received at frequency fc, would represent a digital low and
signals received at frequency fc + Df,
would represent a digital high. Note that this does not
interfere with spread spectrum or
frequency hopping capabilities since those function on
frequencies separated by 1 MHz or more.
As part of setting a wireless standard some modifications
of the standard set by the IEEE 802.3
committee have been adopted. The most significant of these
is the modification to the carrier sense
multiple access / collision detection, or CSMA/CD, protocol
used in wired networks today. This is a
method whereby any machine at any time, wishing to send a
message on the net, will first send a token
out to ensure that a carrier exists (network ready). After
establishing this, the message will be sent.
Because any machine may send at any time, collisions of
information will occur. If any machine detects
a collision, it will send out a jamming signal to all the
others. All machines will then wait on a random
interval timer after which they will try to send again.
For wireless networks however, since a machine is not in
constant communication with the rest of the
LAN, detecting a collision and notifying all other machines
on the net is impossible. A modification
in the way of the collision handling had to be made. A
method known as collision avoidance is
employed to create the
CSMA/CA standard. In a
collision avoidance strategy, the
net estimates the average time
of collisions and send a
jamming signal at that time. A
wireless transceiver will not
only sense a carrier but will also
listen out for the jamming
signal. When all is clear it then send its message. This
collision avoidance method has two drawbacks:
1) It cannot completely filter all collisions since it
operates on estimated times of collisions; 2) and if
it did, it slows the network significantly by sending
jamming signals whether or not a collision actually
4 Physical Layer
Much of the focus of wireless computing development is
centered on the physical and media access
control layers of a system. It is on this level of the LAN
protocol of which wireless products like
modems and transceivers
On the physical layer issue, the 802.11 is focusing on the
one proposed by Apple Computer
The Apple physical-layer protocol appears the most robust
of any considered to date in 802.11. Apple's
system is a full-duplex, slow frequency-hopping protocol.
By using a frequency-hop spread-spectrum
radio, the system fits with the spread-spectrum methods of
virtually all 802.11 specifications.
Apple splits the data-transport protocol into two layers:
- The RF Adoption Layer is similar in some respects to
cell-based data protocols, such as
Asynchronous Transfer Mode and IEEE 802.6 Switched
Multimegabit Data Services; like ATM and
802.6, the RF Adoption Layer includes
segmentation/reassembly functions and Protocol Data Unit
generation functions, and it also includes Forward Error
Correction (FEC) generation and verification
functions which substantially increase packet integrity in
wireless environments but adds FEC overhead.
- The RF Hopping Protocol Physical Layer consists of a
transmission convergence sublayer including
header generation, RF framing, and RF hopping protocol
functions and the physical- medium-dependent
sublayer, in which the actual characteristics of the RF
channel are handled.
In the RF Adoption Layer, a Protocol Data Unit is split
into three segments, and two error-correcting
data units are added. The RF Hopping segments, and two
error-correcting data units are added. The RF
Hopping Physical Layer builds special Burst Protocol Data
Units out of the data and FEC units and uses
carrier-sense methods borrowed from Ethernet to determine
whether an RF Hop Group is clear for
transmission. Each hop group consists of five separate
radio channels. The controller scans hop groups
via state-machine operation with four states: scan,
receive, carrier-sense, and transmit. In early tests at
Apple, the hop system showed 80-microsecond hop times,
57-microsecond clock recovery, and a
5-microsecond lapse between the time an empty channel is
sensed and transmission begins. Since each
cluster of wireless LANs can use different hop groups,
multiple LANs could operate in the same area
without interference. One concern is whether the overhead
for error correction for each packet, which
can be as much as 50% is too high to give the proposal a
The safety of those operating new equipment now plays a
larger role in determining the direction of
technological growth now more that ever. Factors under
consideration are the effect of infrared and
strong electromagnetic radiation that would pervade the
workplace on the workers. This limits the
strength of and communication device that would be used in
For the Personal Computer. The adapters have a small
attached antenna through which they send and
receive network traffic as radio signals. Some wireless
products are small boxes that attach to your PC's
parallel port. In either case, the signals may travel from
PC to PC, forming a wireless peer-to-peer
network, or they may travel to a network server equipped
with both wireless and standard Ethernet
adapters, providing notebook users a portable connection to
the corporate network. In either case,
wireless LANs can either replace or extend wired networks.
Standards are lacking. Wireless networking is still a
technology looking for a standard, which is why
very few wireless products can work with one another. Each
vendor uses a different protocol, radio
frequency, or signaling technology. If wired networks still
operated like wireless, you would have to
use the same brand of network interface card throughout
your network. Right now you are, for the most
part, tied to whichever brand of wireless LAN you pick.
Most of the products in this comparison listed
their wireless protocol as Ethernet carrier sense multiple
access/collision avoidance (CSMA/CA), a
variation of standard Ethernet. Unfortunately, each vendor
has put its own spin on CSMA/CA, which
means even their protocols are incompatible.
5 Wireless services
As technology progresses toward smaller, lighter, faster,
lower power hardware components, more
computers will become more and more mobile. For space
concerns this paper will exclude any further
discussion of the hardware developments toward mobility
except for devices directly related to wireless
connectivity such as modems.
A wireless computer is not connected via a wireline and
thus has mobility and convenience. A wireless
LAN provides the convenience of eliminating the wires, yet
is not necessarily mobile.
(What is mobility?)
Mobility is a characteristic where the wireless computer
may connect, loose the physical
communication (possibly due to interference) and reconnect
(possibly to another sub-network) and retain its virtual
connections and continue to operate its applications. The
network protocols will be discussed later.
(Then, what is portable?)
Portable is defined that the wireless computer may connect,
loose the connection and
then re-connect, as well. However, the mobile unit will
have to restart if it is
reconnected to another sub-network, requiring that running
processes be shut-down and
Mobility may be limited by the wireless service subscribed.
Four basic service zones are described:
Global/National service zone: Ubiquitous radio coverage
throughout a region, country or the
entire globe, low user densities, and minimal bandwidth
requirements. Typically satellite systems.
Mobile service zone: Radio coverage in urban, suburban and
populated rural areas,
medium to high user densities, low to medium bandwidth
requirements (tens of Kbps), and high vehicular speed.
(AMPS) system is a good example.
Local/micro service zone: Radio coverage in densely
populated urban areas, shopping
malls, and transportation centers. High enduser densities,
medium bandwidth requirements, hand-held portable terminals,
Indoor/pica service zone: in-building radio coverage, low
to high user densities, medium
to high bandwidth requirements (Mbps), very low mobility.
Prior to the cellular phone network, base station radio
covering a single cell geographic area with a fixed
number of channels was the only service available.
The cellular phone service divides the service area into
cells and assigns a subset of the available
channels to any given cell. This way the channels can be
reused and interference from neighboring cells
is reduced. The system tracks the active mobile unit,
delivers calls, and maintains connections as units
move between cells (Hand-off: a realtime transfer of a call
between radio channels in different cells).
This system is called Advanced Mobile Phone Service (AMPS).
Current cellular systems use analog
FM technology. However, implementation of digital radio
technology is being deployed now. These
systems utilize Time Division Multiple Access (TDMA) or
Code Division Multiple Access (CDMA)
to increase throughput up to ten times the previous analog
system. Additionally, end users will access
a wider range of telecommunications as the implementation
of integrated services digital network
(ISDN) principles are utilized. Personal Communication
Services, similar to the current cellular system,
will soon be available from the larger telecommunication
services, but with reduced price and wider
no restrictions on length
or type of data
bill by minute
congestions in urban
for data over cellular
bill by message size
integrated voice and
packet switching error
lack of applications
not fully developed
Dedicated packet switched
no call setup time
inherent reliability and
security of packet
coverage not full
limited packet size
Specialized mobile radio
voice and data
and service costs
The application of the wireless computing system determines
the type of wireless medium system to be
employed. Circuit switched or packet switched, both are
available through wireless technology and
provide connectivity. Circuit switched systems provide a
continuous connection established to the
destination by the switching system. The most popular
examples are the wireline public switched
telephone network (PSTN) and cellular telephones systems.
This method of communication can be
relatively expensive. If the phone systems offers voice
grade bandwidth, then a standard modem can
provide speed of 14.4 Kbps (at the time of this writing).
However, if a digital line is provided then
higher communication rates can be achieved with more
Packet switched systems provide a delivery system of
information packets. The packet contains the data
and an address to the destination. Packet switching is far
less expensive than circuit switching.
Examples would be RAM, ARDIS, and Internet networks. Packet
radio networks have been the target
of many studies since the military has a vested interest in
the communication medium. Concerns such
as reliability, throughput optimization and re-routing of
packets have been recent topics.
840 base stations
in 210 MSAs
8,000 cell sites
in 734 metro
upgrade in major
mid Sept 94
top 20 MSAs by
Cellular Digital Packet Data technology (CDPD)
utilizes the space between the voice segments on
cellular (AMPS) network channels and inserts a
data packet. The user pays only for the packet
sent as opposed to a cellular circuit switched
connection. CDPD cellular communications
systems such as the Ubiquity 1000 from PCSI,
offer packet burst rate of 19.2 Kbps with full
duplex. This CDPD modem offers the option to
use circuit switched cellular, wireline PSTN and
voice support. However, in a large urban area
with thousands of stations using any packet
switching service at current speeds, delay may be
Satellite can be used as long distance links within
wireless networks. Three major projects have
been proposed. The Teledesic system, composed
of 840 low orbit satellites, was proposed by Bill
Gates (Microsoft) and Craig McCaw (McCaw
Cellular). Second, the Pentagon, solicited a
system, using 1,000 smaller satellites, from TRW and Martin
Marietta. Both the Teledesic and the
Pentagon systems cost around $9 billion. The third system,
called Iridium, from Motorola, will use 66
satellites to offer mobile phone service all over the
globe. This project will begin this year and the rest
in place by 1996.
Software concerns in a wireless computing environment can
be broken into two areas, system and
7 System Software
Network operating systems must be able to handle the
uniqueness of a wireless computer. Advanced
operating systems utilizing distributed technology must be
adapted to the specific communication
media. The advancement of technology has provided that even
mobile computer systems the size of
notebooks are capable of internetworking as a host in
global networks. Mobile host protocols
compatible with TPC/IP have been developed to allow
continuous network connectivity where ever the
host may be. Due to the unpredictable nature of wireless
connections, even operating systems may have
to be written to provide support services for mobile
network. The WIN*OS, a micro kernel for a
wireless-compatible operating system, was developed to
"support concurrent and composable objects
and coordinated communication among groups of objects
through a process of agreements."
8 Application Software
Application software concerns in the wireless computing
environment vary depending on the type of
application and wireless medium used. For example, E-mail
software must know how to communicate
with the packet switched network as compared to the
traditional cellular network. Software developer
kits (SDK) and application programmers interfaces (API) are
usually available by the service provider.
Remote access software allows the remote user to connect to
a host workstation to view the screen and
control the keyboard as if the user was there. The data
does not have to be communicated to the remote
user and thus allows processing locally. Carbon copy and PC
anywhere are among the programs which
provide remote access for microcomputers. High baud rate is
needed especially when a graphical user
interface (GUI) is used.
9 Wireless Local Area Networks (WLAN)
WLAN offers the same features as a wireline LAN but without
the wires. Coverage can range from a
room to a building to a "campus" (wide-spread,
multi-building). Both stationary desktop systems and
mobile notebook computers can connect using specialized
wireless LAN adapter cards. Another
configuration allows wireless additions to current
networks. Wireless Hubs have been developed which
bridge the wireless units into the wireline network.
As mentioned before, during the recent natural
disasters in California, the Federal Emergency
Management Agency (FEMA) set up field offices
with WLAN very quickly. Here is a great example
of how WLAN can be used: An ETHERNET
connection over a radio link provided data from a
low-power PC in a buoy to a PC on a ship. The
system provided a megabyte/sec data rate for four
days while guaranteeing error-free delivery of
data. Even more incredible is the MBARI
acoustic LAN. Since under water, radio waves
travel only a few feet but sound waves can travel
for miles, the acoustic LAN uses the better carrier
of wireless data signals. The acoustic LAN has
two 5Kbps data channels and two slow-speed
command channels. The LAN is used to
communicate with tilt meters and buoys.
Personal Data Assistants (PDA) are the new
handheld computers which also have wireless options. Using
a pen-based GUI operating system, the
applications are accessed from local storage. Fax, data and
voice can be transferred to and from the
PDA via cellular phone system. The AT&T EO can run a
program called Gnosis which when also
loaded on a remote server host will allow the user to
search for documents and have them downloaded
in minutes including graphics.
Even though all these nifty devices such as radio
modems and PDAs are developed and marketed,
a recent study of mobile professionals shows that
currently relatively few spend time far from their
desks. In fact, only 13 percent of mobile users
spend time outside their metro area and just 1
percent outside the country. As the technology
becomes more common place, more users will
find themselves moving further out of their wired
areas and into the wireless field.
Security becomes essential in wireless
computing. Especially since the data is
broadcast to the receiving unit. International
Standards Organization (ISO) has published
security services which provide for secure data
and computer systems on standard wireline
networks. However, these must be modified to
meet the needs of mobile users and systems. Data encryption
and Two possible solutions include
exchanging security information between a small number of
entities, or even more complex involving
an information center.
Infrared offers the least problem of security due fact that
stations must be in the line-of-sight and the
limited area of coverage, usually one room. Spread spectrum
RF transmissions spread the data over a
range of frequencies making interception extremely
difficult. Also, low power limits the coverage area,
although the signal will penetrate walls. Cellular phone
networks offer no security of their own. Even
though listening to these transmissions has been made
unlawful, the signals can be overheard by a radio
scanner. Data encryption is left up to the connecting unit.
Packet radio offers inherent data security by
scrambling the data packets.
Clipper chip will replace the digital encryption statndard
(DES). The Clipper chip boasts to be 16
million times stronger with 80-bits as compared to the old
DES, which has a 56-bit binary key. This
chip will be used in many communication products,
especially wireless. The Department of Justice and
AT&T will be installing them in their telephone products.
The controversy about these chips stems from
the fact that they are programmed with a back door. The
government can, with a court order, access
the chip and monitor the communication.
In the relatively short time of the Information Revolution,
the world has seen several technologies, first
introduced as "convenient", become "essential" the basic
structure of the modern lifestyle. The
automobile, telephone, and the refrigerator are easy
examples to cite. The wireless revolution will
transform another "convenience" to a necessity. "Emerging
wireless systems will provide the technology
to allow people and machines to communicate anytime,
anywhere, using voice, [video,] data and
messaging services through telecommunications." The
wireless revolution began with the introduction
of the cellular phone networks. This coupled along with the
reduction in size of the microcomputer and
an increase in the applicable technologies.
After surveying the many aspects of wireless computing,
several areas stand-out and appearently require
further research and development. Among those are mobile
internetworking protocols, which would
allow a mobile host to connect to any part of the network.
Mobile "aware" operating systems would
further allow more features catering to mobile users.
Features such as built-in APIs in the OS kernel
available for specific applications which would provide
services pertaining to suspend/resume and store
and forward operations. Standardized mobile networking
protocol will allow interoperability between
open wireless systems. Advanded signal processing and
speech coding techniques will allow more
efficient use of bandwidth and data transfer speed.
Security research at all levels will continue to remain
an issue and must stay one step ahead of the criminal
elements. All of these areas will help to bring
about the wireless computing revolution.
12 About the authors
Christopher xxxxx is a first year Computer Science graduate
student of Florida International
University. He is also an operations systems analyst for
xxxxxxxx xxxxxxxx xxxxxxxxxxx
xxxxx of Florida where he participates in the
implementation of a DB2/Client-Server operating
system. He graduated with a Bachelors in Computer Science
from FIU in 1992. His current
interests in research include mobile computing and visual
object oriented programming.
David R. Xxxxxxxxx
David R. xxxxxxxxx is currently a Master's degree candidate
at Florida International University
where he originally graduated with a Bachelors degree in
Computer Science in 1986. He also
designed cirriculum and taught lower and upper division
computer classes for the School of
Computer Science at FIU. For six years he has been employed
at xxx xxxx xxxxx as
Accounting/Informations systems manager. He is an avid user
of mobile computers and
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