Реферат: Wireless Technology Essay Research Paper Wireless Technology

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Wireless Technology Essay, Research Paper
Wireless Technology applied to Computer Processing
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 systems offer. II.
Introduction 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: a. Data Integrity -
relatively error free transmission, b. Speed – as close as possible to the speed
of current wired networks, c. Protection – making sure that the data now
airborne is encoded and cannot be tapped by unwelcome receivers, d.
Compatibility – ensuring that the many protocols that sure to be created
subscribe to a standard to allow inter-operability, e. 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
semi permanent 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. II. Methods There are a few methods of wireless
communication being theorized and tested. 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 ranges 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: a. Higher frequencies mean shorter wavelengths and
shorter wavelengths do not penetrate solid objects like walls and floors; b. 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. c. 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. d. 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. e. 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. f. 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. 3 Standards 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 reliability. (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 sends a jamming signal at that time. A wireless transceiver will not only
sense a carrier but will also listen 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) -If it did, it slows the network significantly by sending
jamming signals whether or not a collision actually occurs. IV. 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 Corporation. 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 Multi-megabit 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 chance. 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 accomplishing transmission. 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 windows closed. 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. Cellular (AMPS) system is
a good example. Local/micro service zone: Radio coverage in densely populated
urban areas, shopping malls, and transportation centers. High end user
densities, medium bandwidth requirements, hand-held portable terminals,
low-speed mobility. 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 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

Название: Wireless Technology Essay Research Paper Wireless Technology
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