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 real-time 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 availability. Wireless Advantages Limitations Traditional Cellular no
restrictions on length or type of data transmission, national coverage, bill by
minute potential line interruptions, congestions in urban areas limited
throughput CDPD enhanced technology for data over cellular bill by message size
integrated voice and data packet switching error correction techniques lack of
applications development not fully developed Dedicated packet switched mobile
networks integrated applications and communications no call setup time inherent
reliability and security of packet switching coverage not full nationwide
limited packet size require specialized modems data only Specialized mobile
radio voice and data vehicle based limited coverage Satellite-enabled networks
geographic reach expensive equipment 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 wire-line 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 specialized equipment. 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. Packet Switched Systems ARDIS RAM
Mobile Data Circuit Cellular CDPD Network Capacity 1,300 base stations in
approx. 325 metro service area (MSA) 840 base stations in 210 MSAs 8,000 cell
sites in 734 metro areas potentially entire cellular network Coverage (cities
and towns) 10,700 6,300 NA NA Transmission speed 4.8Kbps. 19.2Kbps upgrade in
major metro areas 8Kbps 38.4Kbps to 56Kbps 19.2Kbps Message capacity 256 bytes
512 bytes NA 114 bytes National roaming completed by mid Sept 94 yes no yes
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, wire line 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 unacceptable. 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. 6 Software Software
concerns in a wireless computing environment can be broken into two areas,
system and application. 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 exampleof 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.
10 Security 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 ad computer systems on standard wire line 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. 11 Conclusion 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.