Networks Essay, Research Paper

Survey of Wireless Computing

School Of Computer Science

Florida International University

Abstract

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.

1 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:

(1) Data Integrity – relatively error free transmission,

(2) Speed – as close as possible to the speed of current wired networks,

(3) Protection – making sure that the data now airborne is encoded and cannot be tapped by

unwelcome receivers,

(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.

2 Methods

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.

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 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

occurs.

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

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 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 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 enduser 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 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

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 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 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

In-building

coverage

yes

top 20 MSAs by

June 1993

limited

limited

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

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 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.

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

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.

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. “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” ope