Wireless Technology


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

"convenience" to a necessity.

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