ec2043 notes

UNIT – I

INTRODUCTION

1.1 Introduction and Fundamentals of Wireless communication Technology

Objective

To explain the introduction about wireless networks

To describe the fundamentals of wireless communication.

References

1. Kaveh Pahlavan- Prashant Krishnamurthy “Principles of Wireless Networks”-

Pearson Education- Delhi- 2002 and PHI- 2005.

Introduction:

The cellular system employs a different design approach than most commercial

radio and television systems use. Radio and television systems typically operate at

maximum power and with the tallest antennas allowed by the regulatory agency of the

country. In the cellular system, the service area is divided into cells. A transmitter is

designed to serve an individual cell. The system seeks to make efficient use of available

channels by using low-power transmitters to allow frequency reuse at much smaller

distances. Maximizing the number of times each channel can be reused in a given

geographic area is the key to an efficient cellular system design. During the past three

decades, the world has seen significant changes in the telecommunications industry.

There have been some remarkable aspects to the rapid growth in wireless

communications, as seen by the large expansion in mobile systems. Wireless systems

consist of wireless wide-area networks (WWAN) [i.e., cellular systems], wireless local

area networks (WLAN) and wireless personal area networks (WPAN). The handsets used

in all of these systems possess complex functionality, yet they have become small, low

power consuming devices that are mass produced at a low cost, which has in turn

accelerated their widespread use. The recent advancements in Internet technology have

increased network traffi c considerably, resulting in a rapid growth of data rates. This

FRANCIS XAVIER ENGINEERING COLLEGE

www.francisxavier.ac.in

Department of ECE-FXEC

phenomenon has also had an impact on mobile systems, resulting in the extraordinary

growth of the mobile Internet.

Wireless data offerings are now evolving to suit consumers due to the simple

reason that the Internet has become an everyday tool and users demand data mobility.

Currently, wireless data represents about 15 to 20% of all air time. While success has

been concentrated in vertical markets such as public safety, health care, and

transportation, the horizontal market (i.e., consumers) for wireless data is growing. In

2005, more than 20 million people were using wireless e-mail. The Internet has changed

user expectations of what data access means. The ability to retrieve information via the

Internet has been “an amplifi er of demand” for wireless data applications. More than

three-fourths of Internet users are also wireless users and a mobile subscriber is four

times more likely to use the Internet than a nonsubscriber to mobile services. Such keen

interest in both industries is prompting user demand for converged services. With more

than a billion Internet users expected by 2008, the potential market for Internet-related

wireless data services is quite large. In this chapter, we discuss briefl y 1G, 2G, 2.5G, and

3G cellular systems and outline the ongoing standard activities in Europe, North

America, and Japan. We also introduce broadband (4G) systems (see Figure 1.2) aimed

on integrating WWAN, WLAN, and WPAN. Details of WWAN, WLAN, and WPAN are

given in Chapters 15 to 20.

First- and Second-Generation Cellular Systems

The fi rst- and second-generation cellular systems are the WWAN. The fi rst public

cellular telephone system (fi rst-generation, 1G), called Advanced Mobile Phone System

(AMPS) [8,21], was introduced in 1979 in the United States. During the early 1980s,

several incompatible cellular systems (TACS, NMT, C450, etc.) were introduced in

Western Europe. The deployment of these incompatible systems




resulted in mobile phones being designed for one system that could not be used with

another system, and roaming between the many countries of Europe was not possible.

The first-generation systems were designed for voice applications. Analog frequency

modulation (FM) technology was used for radio transmission.

The GSM (renamed Global System for Mobile communications) initiative gave the

European mobile communications industry a home market of about 300 million

subscribers, but at the same time provided it with a signifi cant technical challenge. The

early years of the GSM were devoted mainly to the selection of radio technologies for the

air interface. In 1986, fi eld trials of different candidate systems proposed for the GSM

air interface were conducted in Paris. A set of criteria ranked in the order of importance

was established to assess these candidates




Two digital technologies, Time Division Multiple Access (TDMA) and Code Division

Multiple Access (CDMA) (see Chapter 6 for details) [10] emerged as clear choices for

the newer PCS systems. TDMA is a narrowband technology in which communication

channels on a carrier frequency are apportioned by time slots. For TDMA technology,

there are three prevalent 2G systems: North America TIA/ EIA/IS-136, Japanese Personal

Digital Cellular (PDC), and European Telecommunications Standards Institute (ETSI)

Digital Cellular System 1800 (GSM 1800), a derivative of GSM. Another 2G system

based on CDMA (TIA/EIA/IS-95) is a direct sequence (DS) spread spectrum (SS) system

in which the entire bandwidth of the carrier channel is made available to each user

simultaneously (see Chapter 11 for details). The bandwidth is many times larger than the

bandwidth required to transmit the basic information. CDMA systems are limited by

interference produced by the signals of other users transmitting within the same

bandwidth GSM is moving forward to develop cutting-edge, customer-focused solutions

to meet the challenges of the 21st century and 3G mobile services. When GSM was fi rst

designed, no one could have predicted the dramatic growth of the Internet and the rising

demand for multimedia services. These developments have brought about new challenges

to the world of GSM. For GSM operators, the emphasis is now rapidly changing from

that of instigating and driving the development of technology to fundamentally enable

mobile data transmission to that of improving speed, quality, simplicity, coverage, and

reliability in terms of tools and services that will boost mass market take-up.

Traffic Usage:

A traffi c path is a communication channel, time slot, frequency band, line, trunk, switch,

or circuit over which individual communications take place in sequence. Traffi c usage is

defi ned by two parameters, calling rate and call holding.

Calling rate, or the number of times a route or traffi c path is used per unit time; more

properly defi ned, the call intensity (i.e., calls per hour) per traffic c path during busy

hour.




Call holding time: or the average duration of occupancy of a traffi c path by a call. The

carried traffi c is the volume of traffi c actually carried by a switch, and offered traffi c is

the volume of traffi c offered to a switch. The offered load is the sum of the carried load

and overfl ow (traffi c that cannot be handled by the switch).

Figure shows a typical hour-by-hour voice traffi c variation for an MSC. We notice that

the busiest period — the busy hour (BH) is between 10 A.M. and 11 A.M. We define the

busy hour as the span of time (not necessarily a clock hour) that has the highest average

traffic load for the business day throughout the busy season. The peak hour is defined as

the clock hour with highest traffic load for a single day. Since traffi c also varies from

month to month, we define the average busy season (ABS) as the three months (not

necessarily consecutive) with the highest average BH traffic load per access line.

Telephone systems are not engineered for maximum peak loads, but for some typical BH

load. The blocking probability is defined as the average ratio of blocked calls to total

calls and is referred to as the GoS.

Diversity

In a radio channel, it is subjected to fading, time dispersion, and other degradations.

Diversity techniques are employed to overcome these impairments and improve signal




quality. The basic concept of diversity is that the receiver has more than one version of

the transmitted signal available, and each version of transmitted signal is received

through a distinct channel. When several versions of the signal, carrying the same

information, are received over multiple channels that exhibit independent fading with

comparable strengths, the chances that all the independently faded signal components

experience the same fading simultaneously are greatly reduced. Suppose the probability

of having a loss of communications due to fading on one channel is p and this probability

is independent on all M channels. The probability of losing communications on all

channels simultaneously is then pM. Thus, a 10% chance of losing the signal for one

channel is reduced to 0.13 _ 0.001 _ 0.1% with three independently fading channels

[5,17]. Typically, the diversity receiver is used in the base station instead of the mobile

station, because the cost of the diversity combiner can be high, especially if multiple

receivers are necessary. Also, the power output of the mobile station is limited by the

battery. Handset transmitters usually lower power than mobilemounted transmitters to

preserve battery life and reduce radiation into the human body. The base station,

however, can increase its power output or antenna height to improve the coverage to a

mobile station.




Each of the channels, plus the corresponding receiver circuit, is called a branch and the

outputs of the channels are processed and routed to the demodulator by a diversity

combiner (see Figure 10.5). Two criteria are required to achieve a high degree of

improvement from a diversity system. First, the fading in individual branches should

have low cross correlation. Second, the mean power available from each branch should

be almost equal. If the cross-correlation is too high, then fades in each branch will occur

simultaneously. On the other hand, if the branches have low correlation but have very

different mean powers, then the signal in a weaker branch may not be useful even though

it has less fades than the other branches.

Types of Diversity

The following methods are used to obtain uncorrelated signals for combining:

1. Space diversity: Two antennas separated physically by a short distance d can provide

two signals with low correlation between their fades. The separation d in general varies

with antenna height h and with frequency. The higher the frequency, the closer the two

antennas can be to each other. Typically, a separation of a few wavelengths is enough to

obtain uncorrelated signals. Taking into account the shadowing effect (see Chapter 3),

usually a separation of at least 10 carrier wavelengths is required between two adjacent

antennas. This diversity does not require extra system capacity; however, the cost is the

extra antennas needed.

2. Frequency diversity: Signals received on two frequencies, separated by coherence

bandwidth (see Chapter 3) are uncorrelated. To use frequency diversity in an urban or

suburban environment for cellular and personal communications services (PCS)

frequencies, the frequency separation must be 300 kHz or more. This diversity improves

link transmission quality at the cost of extra frequency bandwidths.

3. Time diversity: If the identical signals are transmitted in different time slots, the

received signals will be uncorrelated, provided the time difference between time slots is

more than the channel coherence time (see Chapter 3). This system will work for an

environment where the fading occurs independent of the movement of the receiver. In a

mobile radio environment, the mobile unit may be at a standstill at any location that has a




weak local mean or is caught in a fade. Although fading still occurs even when the

mobile is still, the time-delayed signals are correlated and time diversity will not reduce

the fades. In addition to extra system capacity (in terms of transmission time) due to the

redundant transmission, this diversity introduces a signifi cant signal processing delay,

especially when the channel coherence time is large. In practice, time diversity is more

frequently used through bit interleaving, forward-error-correction, and automatic

retransmission request (ARQ).

4. Polarization diversity: The horizontal and vertical polarization components

transmitted by two polarized antennas at the base station and received by two polarized

antennas at the mobile station can provide two uncorrelated fading signals. Polarization

diversity results in 3 dB power reduction at the transmitting site since the power must be

split into two different polarized antennas.

5. Angle diversity: When the operating frequency is _10 GHz, the scattering of signals

from transmitter to receiver generates received signals from different directions that are

uncorrelated with each other. Thus, two or more directional antennas can be pointed in

different directions at the receiving site and provide signals for a combiner. This scheme

is more effective at the mobile station than at the base station since the scattering is from

local buildings and vegetation and is more pronounced at street level than at the height of

base station antennas. Angle diversity can be viewed

as a special case of space diversity since it also requires multiple antennas.

6. Path diversity: In code division multiple access (CDMA) systems, the use of direct

sequence spread spectrum modulation allows the desired signal to be transmitted over a

frequency bandwidth much larger than the channel coherence bandwidth. The spread

spectrum signal can resolve in multipath signal components provided the path delays are

separated by at least one chip period. A Rake receiver can separate the received signal

components from different propagation paths by using code correlation and can then

combine them constructively. In CDMA, exploiting the path diversity reduces the

transmitted power needed and increases the system capacity by reducing interference.




1.2 Electromagnetic Spectrum

Objective

To know the frequency allocated to particular bands.

References

1. Kaveh Pahlavan- Prashant Krishnamurthy “Principles of Wireless Networks”-

Pearson Education- Delhi- 2002 and PHI- 2005.

The electromagnetic spectrum is the range of all possible frequencies

of electromagnetic radiation. The "electromagnetic spectrum" of an object has a different

meaning, and is instead the characteristic distribution of electromagnetic radiation

emitted or absorbed by that particular object.

The electromagnetic spectrum extends from below the low frequencies used for

modern radio communication to gamma radiation at the short-wavelength (high-

frequency) end, thereby covering wavelengths from thousands of kilometers down to

a fraction of the size of an atom. The limit for long wavelengths is the size of

the universe itself, while it is thought that the short wavelength limit is in the vicinity of

the Planck length, although in principle the spectrum is infinite and continuous.

Most parts of the electromagnetic spectrum are used in science for spectroscopic and

other probing interactions, as ways to study and characterize matter.[3]

In addition,

radiation from various parts of the spectrum has found many other uses for

communications and manufacturing (see electromagnetic radiation for more

applications).

Electromagnetic waves are typically described by any of the following three physical

properties: the frequency f, wavelength λ, or photon energy E. Frequencies observed in

astronomy range from 2.4×1023

Hz (1 GeV gamma rays) down to the local plasma

frequency of the ionized interstellar medium (~1 kHz). Wavelength is inversely

proportional to the wave frequency.




http://en.wikipedia.org/wiki/Spectrum

http://en.wikipedia.org/wiki/Electromagnetic_radiation

http://en.wikipedia.org/wiki/Radio

http://en.wikipedia.org/wiki/Gamma_radiation

http://en.wikipedia.org/wiki/Wavelength

http://en.wikipedia.org/wiki/Kilometer

http://en.wikipedia.org/wiki/Fraction_(mathematics)

http://en.wikipedia.org/wiki/Atom

http://en.wikipedia.org/wiki/Universe

http://en.wikipedia.org/wiki/Planck_length

http://en.wikipedia.org/wiki/Infinity

http://en.wikipedia.org/wiki/Continuum_(theory)

http://en.wikipedia.org/wiki/Electromagnetic_spectrum#cite_note-em-spectrum-3

http://en.wikipedia.org/wiki/Electromagnetic_radiation

http://en.wikipedia.org/wiki/Frequency

http://en.wikipedia.org/wiki/Wavelength

http://en.wikipedia.org/wiki/Lambda

http://en.wikipedia.org/wiki/Photon

http://en.wikipedia.org/wiki/Energy

http://en.wikipedia.org/wiki/GeV

http://en.wikipedia.org/wiki/Plasma_frequency

http://en.wikipedia.org/wiki/Plasma_frequency

5

The Electromagnetic Spectrum

The electromagnetic spectrum and its uses for communication.

so gamma rays have very short wavelengths that are fractions of the size of atoms,

whereas wavelengths can be as long as the universe. Photon energy is directly

proportional to the wave frequency, so gamma ray photons have the highest energy




http://en.wikipedia.org/wiki/Atom

(around a billion electron volts), while radio wave photons have very low energy (around

a femtoelectronvolt). These relations are illustrated by the following equations:

where:

c = 299,792,458 m/s is the speed of light in vacuum and

h = 6.62606896(33)×10−34

J s = 4.13566733(10)×10−15

eV s is Planck's constant.[7]

Whenever electromagnetic waves exist in a medium with matter, their wavelength is

decreased. Wavelengths of electromagnetic radiation, no matter what medium they

are traveling through, are usually quoted in terms of the vacuum wavelength,

although this is not always explicitly stated.

Generally, electromagnetic radiation is classified by wavelength into radio

wave, microwave, terahertz (or sub-millimeter) radiation,infrared, the visible

region we perceive as light, ultraviolet, X-rays and gamma rays. The behavior of EM

radiation depends on its wavelength. When EM radiation interacts with single atoms

and molecules, its behavior also depends on the amount of energy per quantum

(photon) it carries.

Spectroscopy can detect a much wider region of the EM spectrum than the visible

range of 400 nm to 700 nm. A common laboratory spectroscope can detect

wavelengths from 2 nm to 2500 nm. Detailed information about the physical

properties of objects, gases, or even stars can be obtained from this type of device.

Spectroscopes are widely used in astrophysics. For example,

many hydrogenatoms emit a radio wave photon that has a wavelength of 21.12 cm.

Also, frequencies of 30 Hz and below can be produced by and are important in the

study of certain stellar nebulae and frequencies as high as 2.9×1027

Hz have been

detected from astrophysical sources.




http://en.wikipedia.org/wiki/Electron_volt

http://en.wikipedia.org/wiki/Femto

http://en.wikipedia.org/wiki/Speed_of_light

http://en.wikipedia.org/wiki/Planck%27s_constant

http://en.wikipedia.org/wiki/Electromagnetic_spectrum#cite_note-CODATA-7

http://en.wikipedia.org/wiki/Transmission_medium

http://en.wikipedia.org/wiki/Matter

http://en.wikipedia.org/wiki/Radio_wave


http://en.wikipedia.org/wiki/Microwave

http://en.wikipedia.org/wiki/Terahertz

http://en.wikipedia.org/wiki/Infrared

http://en.wikipedia.org/wiki/Visible_region

http://en.wikipedia.org/wiki/Visible_region

http://en.wikipedia.org/wiki/Ultraviolet

http://en.wikipedia.org/wiki/X-ray

http://en.wikipedia.org/wiki/Gamma_rays

http://en.wikipedia.org/wiki/Spectroscopy

http://en.wikipedia.org/wiki/Astrophysics

http://en.wikipedia.org/wiki/Hydrogen

http://en.wikipedia.org/wiki/Hydrogen

http://en.wikipedia.org/wiki/Emission_(electromagnetic_radiation)


http://en.wikipedia.org/wiki/Hertz

1.3 Radio Propagation Mechanisms

Objective

To describe refraction. Reflection, scattering, shadowing and diffraction.

References

1. C- Siva Ram Murthy and B- S- Manoj “Ad Hoc Wireless Networks Architectures

and Protocols”- Pearson Education -2nd Edition -Delhi -2004.

Exponential growth of mobile communications has increased interest in many topics in

radio propagation. Much effort is now devoted to refi ne radio propagation path-loss

models for urban, suburban, and other environments together with substantiation by fi eld

data. Radio propagation in urban areas is quite complex because it often consists of refl

ected and diffracted waves produced by multipath propagation. Radio propagation in

open areas free from obstacles is the simplest to treat, but, in general, propagation over

the earth and the water invokes at least one refl ected wave. For closed areas such as

indoors, tunnels, and underground passages, no established models have been developed

as yet, since the environment has a complicated structure. However, when the

environmental structure is random, the Rayleigh model used for urban area propagation

may be applied.

When the propagation path is on line of sight, as in tunnel and underground passages, the

environment may be treated either by the Rician model or waveguide theory. Direct wave

models may be used for propagation in a corridor. In general, radio wave propagation

consists of three main attributes: reflection, diffraction and scattering. Reflection occurs

when radio wave propagating in one medium impinges upon another medium with

different electromagnetic properties.

The amplitude and phase of the reflected wave are strongly related to the medium’s

instrinsic impedance, incident angle, and electric field polarization. Part of the radio wave




energy may be absorbed or propagated through the reflecting medium, resulting in a

reflected wave that is attenuated. Diffraction is a phenomenon by which propagating

radio waves bend or deviate in the neighborhood of obstacles.

11

Radio propagation Radio waves can be propagated and receiving power is influenced

in different ways:• Direct transmission (path loss, fading dependent on frequency)

• Reflection at large obstacles

• Refraction through different media

• Scattering at small obstacles

• Diffraction at edges

• shadowing

Propagation in free space is always like light (straight line).

Receiving power proportional to 1/d² (d = distance between sender and receiver)

reflection scattering diffractionshadowing refraction

Diffraction results from the propagation of wavelets into a shadowy region caused by

obstructions such as walls, buildings, mountains, and so on. Scattering occurs when a

radio signal hits a rough surface or an object having a size much smaller than or on the

order of the signal wavelength.

This causes the Signal energy to spread out in all directions. Scattering can be viewed at

the receiver as another radio wave source. Typical scattering objects are furniture, lamp

posts, street signs, and foliage. In this chapter, our focus is to characterize the radio

channel and identify those parameters which distort the information-carrying signal (i.e.,

base band signal) as it penetrates the propagation medium. The several empirical models

used for calculating path-loss are also discussed.




1.4 Wireless LANs and PANs

Objective

To describe the Wireless Local Area Networks and Personal Area Networks and

its applications.

References



Wireless network refers to any type of computer network that is not connected by cables

of any kind. It is a method by which homes, telecommunications networks and enterprise

(business) installations avoid the costly process of introducing cables into a building, or

as a connection between various equipment locations.[1]

Wireless telecommunications

networks are generally implemented and administered usingradio communication. This

implementation takes place at the physical level (layer) of the OSI model network

structure

Wireless LAN standards will also play an important role in the evolution of personal

communications. They are expected to cover local areas, generate pico-cells and provide

interconnectivity between Wireless PANs and broadband wireless/mobile networks.

Moreover, Wireless LANs in cooperation with higher layer protocols standardization

efforts are expected to solve the interoperability problems and offer an unprecedented

opportunity to increase the networking customer base beyond the satiated corporate

environment. In this section, we highlight the most important, mature and evolving

Wireless LAN (WLAN) standards.

A wireless local area network (WLAN) links two or more devices over a short distance

using a wireless distribution method, usually providing a connection through an access

point for Internet access. The use of spread-spectrum or OFDM technologies may allow




http://en.wikipedia.org/wiki/Computer_network

http://en.wikipedia.org/wiki/Telecommunications_network

http://en.wikipedia.org/wiki/Wireless_network#cite_note-1

http://en.wikipedia.org/wiki/Wireless

http://en.wikipedia.org/wiki/Radio_communication

http://en.wikipedia.org/wiki/Internet_access

http://en.wikipedia.org/wiki/Spread-spectrum

http://en.wikipedia.org/wiki/OFDM

users to move around within a local coverage area, and still remain connected to the

network.

Products using the IEEE 802.11 WLAN standards are marketed under the Wi-Fi brand

name. Fixed wireless technology implements point-to-point links between computers or

networks at two distant locations, often using dedicated microwave or modulated laser

light beams over line of sight paths. It is often used in cities to connect networks in two

or more buildings without installing a wired link.

Wireless personal area networks (WPANs) interconnect devices within a relatively small

area, that is generally within a person's reach. For example, both Bluetooth radio and

invisible infrared light provides a WPAN for interconnecting a headset to a laptop.

ZigBee also supports WPAN applications. Wi-Fi PANs are becoming commonplace as

equipment designers start to integrate Wi-Fi into a variety of consumer electronic

devices. Intel "My WiFi" and Windows 7 "virtual Wi-Fi" capabilities have made Wi-Fi

PANs simpler and easier to set up and configure

A Wireless PAN is a human centered network, connecting personal communication

devices in a spontaneous architecture, within a short-range, ‘‘personal’’ or ‘‘body’’

space. Data may be exchanged between devices carried by the same person (e.g. phone,

watch, PDA), between persons while in contact (e.g. during handshaking, business cards

may be exchanged) or between the user and the environment (e.g. the car may recognize

its driver, and start the engine). Various technologies have been proposed for PAN

networks.. The dominant communication method is the RF technology and Bluetooth is

the ad hoc standard. IEEE has started standardizing the Wireless PANs technologies in

the IEEE 802.15 working group. In more details, the IEEE 802.15 has defined the

following working subgroups:

1. 802.15.1, which is almost identical to Bluetooth standard;

2. 802.15.2, which works towards overcoming the interference between 802.11

WLANs and PANs

operating at the 2.4-GHz band;




http://en.wikipedia.org/wiki/IEEE_802.11

http://en.wikipedia.org/wiki/Wi-Fi

http://en.wikipedia.org/wiki/Fixed_wireless

http://en.wikipedia.org/wiki/Point-to-point_(telecommunications)

http://en.wikipedia.org/wiki/Microwave

http://en.wikipedia.org/wiki/Laser_light

http://en.wikipedia.org/wiki/Laser_light

http://en.wikipedia.org/wiki/Line-of-sight_propagation

http://en.wikipedia.org/wiki/Personal_area_network

http://en.wikipedia.org/wiki/Bluetooth

http://en.wikipedia.org/wiki/Infrared

http://en.wikipedia.org/wiki/ZigBee

http://en.wikipedia.org/wiki/Intel

http://en.wikipedia.org/wiki/Windows_7

http://en.wikipedia.org/wiki/Virtuality

3. 802.15.3, which provides higher data rates ad hoc networks; and

4. 802.15.4, which studies lower data rate and lower




1.5 IEEE 802.11 standard and HiPERLAN

Objective

To describe the IEEE 802.11 (Wireless LAN) standard and HiPERLAN.

References

C- Siva Ram Murthy and B- S- Manoj “Ad Hoc Wireless Networks Architectures


Wireless LAN:

The physical layer in a LAN deals with the actual physical transmission medium used for

communication.

a. Some commonly used physical media: twisted pair, coaxial cable, optical

fiber, and radio waves.

In IEEE 802 Logical Link Control (LLC) forms the upper half of the data link

layer. Medium access control (MAC) forms the lower sublayer.

a. error-controlled, flow-controlled

b. Adds an LLC header, containing sequence and acknowledgement numbers.

LLC provides three service options:

c. Unreliable datagram service

d. Acknowledged datagram service

e. Reliable connection-oriented service

A wireless LAN is one in which a mobile user can connect to a local area network

(LAN) through a wireless (radio) connection.

A standard, IEEE 802.11, specifies the technologies for wireless LANs.

It is designed to work in two modes:

a. In the presence of a base station: access point

b. In the absence of a base station: ad hoc networking

Physical Layer

a. It supports three different physical layers:

i. Frequency hopping spread spectrum (FHSS)




ii. Direct sequence spread spectrum (DSSS)

iii. Infrared

b. Clear channel assessment (CCA): It provides mechanisms for sensing the

wireless channel and determine whether or not it is idle.

MAC Sublayer follows carrier sense multiple access with collision avoidance

(CSMA/CA).

802.11 (WiFi)

WiFi is a common wireless technology used by home owners, small businesses, and

starting ISPs. WiFi devices are available “off the shelf” from computer stores, and

enhanced WiFi devices are designed for ISP use. Advantages of WiFi are as follows:

Ubiquitous and vendor neutral; any WiFi device will work with another regardless of the

manufacturer. Affordable cost. Hackable; many “hacks” exist to extend the range and

performance of a WiFi network.

Disadvantages are as follows:

Designed for LANs, not wide area networking (WAN).

Uses the CSMA mechanism. Only one wireless station can “talk” at a time, meaning one

user can potentially hog all of the network’s resources.

Applications such as video conferencing, Voice-Over Internet Protocol (VOIP), and

multimedia can take down a network.

HIPERLAN

HiperLAN (High Performance Radio LAN) is a Wireless LAN standard.[1]

It is

a European alternative for the IEEE 802.11 standards (theIEEE is an international

organization). It is defined by the European Telecommunications Standards

Institute (ETSI). In ETSI the standards are defined by the BRAN project (Broadband

Radio Access Networks). The HiperLAN standard family has four different versions.

Planning for the first version of the standard, called HiperLAN/1, started 1991, when

planning of 802.11 was already going on. The goal of the HiperLAN was the high data




http://en.wikipedia.org/wiki/Wireless_LAN

http://en.wikipedia.org/wiki/HiperLAN#cite_note-hiperlan-1

http://en.wikipedia.org/wiki/Europe

http://en.wikipedia.org/wiki/IEEE_802.11

http://en.wikipedia.org/wiki/IEEE

http://en.wikipedia.org/wiki/European_Telecommunications_Standards_Institute

http://en.wikipedia.org/wiki/European_Telecommunications_Standards_Institute

http://en.wikipedia.org/wiki/Bit_rate

rate, higher than 802.11. The standard was approved in 1996. The functional specification

is EN300652, the rest is in ETS300836.

The standard covers the Physical layer and the Media Access Control part of the Data

link layer like 802.11. There is a new sublayer called Channel Access and Control

sublayer (CAC). This sublayer deals with the access requests to the channels. The

accomplishing of the request is dependent on the usage of the channel and the priority of

the request.

CAC layer provides hierarchical independence with Elimination-Yield Non-Preemptive

Multiple Access mechanism (EY-NPMA). EY-NPMA codes priority choices and other

functions into one variable length radio pulse preceding the packet data. EY-NPMA

enables the network to function with few collisions even though there would be a large

number of users. Multimedia applications work in HiperLAN because of EY-NPMA

priority mechanism. MAC layer defines protocols for routing, security and power saving

and provides naturally data transfer to the upper layers.

On the physical layer FSK and GMSK modulations are used in HiperLAN/1.

HiperLAN features:

range 50 m

slow mobility (1.4 m/s)

supports asynchronous and synchronous traffic

sound 32 kbit/s, 10 ns latency

video 2 Mbit/s, 100 ns latency

data 10 Mbit/s

HiperLAN does not conflict with microwave and other kitchen appliances, which are on

2.4 GHz. HiperLAN/2 functional specification was accomplished February 2000. Version

2 is designed as a fast wireless connection for many kinds of networks. Those

are UMTS back bone network, ATM and IP networks. Also it works as a network at

home like HiperLAN/1. HiperLAN/2 uses the 5 GHz band and up to 54 Mbit/s data rate.




http://en.wikipedia.org/wiki/Physical_layer

http://en.wikipedia.org/wiki/Media_Access_Control

http://en.wikipedia.org/wiki/Data_link_layer

http://en.wikipedia.org/wiki/Data_link_layer

http://en.wikipedia.org/wiki/Packet_(information_technology)

http://en.wikipedia.org/wiki/Computer_network

http://en.wikipedia.org/wiki/Collision_(telecommunications)

http://en.wikipedia.org/wiki/Multimedia

http://en.wikipedia.org/wiki/Routing

http://en.wikipedia.org/wiki/Frequency-shift_keying

http://en.wikipedia.org/wiki/GMSK

http://en.wikipedia.org/wiki/UMTS

http://en.wikipedia.org/wiki/Asynchronous_Transfer_Mode

http://en.wikipedia.org/wiki/Internet_Protocol

The physical layer of HiperLAN/2 is very similar to IEEE 802.11a wireless local area

networks. However, the media access control (the multiple access protocol) is Dynamic

TDMA in HiperLAN/2, while CSMA/CA is used in 802.11a.

Basic services in HiperLAN/2 are data, sound, and video transmission. The emphasis is

in the quality of these services (QoS).[1]

The standard covers Physical, Data Link Control and Convergence layers. Convergence

layer takes care of service dependent functionality between DLC and Network layer (OSI

3). Convergence sublayers can be used also on the physical layer to connect IP, ATM or

UMTS networks. This feature makes HiperLAN/2 suitable for the wireless connection of

various networks. On the physical layer BPSK, QPSK, 16QAM or 64QAM modulations

are used.

HiperLAN/2 offers security measures. The data are secured with DES or Triple

DES algorithms. The wireless access point and the wireless terminal

can authenticate each other.




http://en.wikipedia.org/wiki/IEEE_802.11a

http://en.wikipedia.org/wiki/Media_access_control

http://en.wikipedia.org/wiki/Dynamic_TDMA

http://en.wikipedia.org/wiki/Dynamic_TDMA

http://en.wikipedia.org/wiki/CSMA/CA

http://en.wikipedia.org/wiki/Quality_of_Service

http://en.wikipedia.org/wiki/HiperLAN#cite_note-hiperlan-1

http://en.wikipedia.org/wiki/BPSK

http://en.wikipedia.org/wiki/QPSK

http://en.wikipedia.org/wiki/Quadrature_amplitude_modulation

http://en.wikipedia.org/wiki/64QAM

http://en.wikipedia.org/wiki/Data_Encryption_Standard

http://en.wikipedia.org/wiki/Triple_DES

http://en.wikipedia.org/wiki/Triple_DES

http://en.wikipedia.org/wiki/Wireless_access_point

http://en.wikipedia.org/wiki/Authenticate

1.6 Bluetooth

Objective

To describe the IEEE 802.15 (Bluetooth) and its specifications.

References

1. William Stallings- “Wireless Communication and Networks”- Pearson Education-

Delhi- 2002

Bluetooth is a high-speed, low-power, microwave wireless link technology designed to

connect phones, laptops, personal digital assistants (PDAs), and other portable equipment

with little or no work by the user. Unlike infrared, Bluetooth does not require line-of-

sight positioning of connected units. The technology uses modifications of existing

wireless LAN techniques but is most notable for its small size and low cost. Whenever

any Bluetooth-enabled devices come within range of each other, they instantly transfer

address information and establish small networks between each other, without the user

being involved.

Features of Bluetooth technology are as follows:

Operates in the 2.56 gigahertz (GHz) ISM band, which is globally available (no

license required)

Uses Frequency Hop Spread Spectrum (FHSS)

Can support up to eight devices in a small network known as a “piconet”

Omnidirectional, nonline-of-sight transmission through walls 10 m to 100 m range

Low cost

1 mw power

Extended range with external power amplifier (100 meters)

Bluetooth and IrDA are both critical to the marketplace. Each technology has advantages

and drawbacks, and neither can meet all users’ needs. Bluetooth’s ability to penetrate

solid objects and its capability for maximum mobility within the piconet allow for data

exchange applications that are very difficult or impossible with IrDA. For example, with

Bluetooth, a person could synchronize his or her




phone with a personal computer (PC) without taking the phone out of a pocket or purse;

this is not possible with IrDA. The omnidirectional capability of Bluetooth allows

synchronization to start when the phone is brought into range of the PC. On the other

hand, in applications involving one-to-one data exchange, IrDA is at an advantage.

Consider an application where there are many people sitting across

a table in a meeting. Electronic cards can be exchanged between any two people by

pointing their IrDA devices toward each other (because of the directional nature). In

contrast, because Bluetooth is omnidirectional in nature, the Bluetooth device will detect

all similar devices in the room and the user would have to select the intended person

from, say, a list provided by the Bluetooth device. On the security front, Bluetooth

provides security mechanisms which are not present in IrDA.




1.7 HomeRF

Objective

To describe the Home RF and its requirements

References

1. William Stallings- “Wireless Communication and Networks”- Pearson Education-

Delhi- 2002

HomeRF is a subset of the International Telecommunication Union (ITU) and primarily

works on the development of a standard for inexpensive radio frequency (RF) voice and

data communication. The HomeRF Working Group has also developed the Shared

Wireless Access Protocol (SWAP). SWAP is an industry specification that permits PCs,

peripherals, cordless telephones, and other devices to communicate voice and data

without the use of cables. SWAP is similar to the Carrier Sense Multiple Access with

Collision Avoidance (CSMA/CA) protocol of

IEEE 802.11 but with an extension to voice traffic. The SWAP system can operate either

as an ad hoc network or as an infrastructure network under the control of a connection

point. In an ad hoc network, all stations are peers, and control is distributed between the

stations and supports only data. In an infrastructure network, a connection point is

required so as to coordinate the system, and it provides the gateway to the public

switched telephone network (PSTN). Walls and floors do not cause any problems in its

functionality, and some security is also provided through the use of unique network IDs.

It is robust and reliable, and minimizes the impact of radio interference.

Features of HomeRF are as follows:

Operates in the 2.45 GHz range of the unlicensed ISM band.

Range: up to 150 feet.

Employs frequency hopping at 50 hops per second.

It supports both a Time Division Multiple Access (TDMA) service to provide delivery of

interactive voice and a CSMA/CA service for delivery of high-speed data packets.




The network is capable of supporting up to 127 nodes.

Transmission power: 100mW.

Data rate: 1 Mbps using 2 frequency-shift keying (FSK) modulation and

2 Mbps using 4 FSK modulation.

Voice connections: up to 6 full duplex conversations.

Data security: blowfish encryption algorithm (over 1 trillion codes).

Data compression: Lempel-Ziv Ross Williams 3 (LZRW3)-A Algorithm.

Comparison of Bluetooth with Shared

Wireless Access Protocol (SWAP)

Currently SWAP has a larger installed base compared to Bluetooth, but it is believed that

Bluetooth is eventually going to prevail. Bluetooth is a technology to connect devices

without cables. The intended use is to provide short-range connections between mobile

devices and to the Internet via bridging devices to different networks (wired and wireless)

that provide Internet capability. HomeRF SWAP is a wireless technology optimized for

the home environment. Its primary use is to provide data networking and dial tones

between devices such as PCs, cordless phones, Web tablets, and a broadband cable or

Digital Subscriber Line (DSL) modem. Both technologies share the same frequency

spectrum but do not interfere with each other when operating in the same space. As far as

comparison with IrDA is concerned, SWAP is closer to Bluetooth in its scope and

domain, so the comparison between Bluetooth and IrDA holds good to a large extent

between these two also.




1.8 Wireless Sensor Networks

Objective

To describe the Wireless Sensor Networks and its applications.

References



A wireless sensor network (WSN) consists of spatially

distributed autonomous sensors to monitor physical or environmental conditions, such

as temperature, sound,pressure, etc. and to cooperatively pass their data through the

network to a main location. The more modern networks are bi-directional, also

enabling control of sensor activity. The development of wireless sensor networks was

motivated by military applications such as battlefield surveillance; today such networks

are used in many industrial and consumer applications, such as industrial process

monitoring and control, machine health monitoring, and so on.

The WSN is built of "nodes" – from a few to several hundreds or even thousands, where

each node is connected to one (or sometimes several) sensors. Each such sensor network

node has typically several parts: a radio transceiver with an internal antenna or

connection to an external antenna, a microcontroller, an electronic circuit for interfacing

with the sensors and an energy source, usually a battery or an embedded form of energy

harvesting. A sensor node might vary in size from that of a shoebox down to the size of a

grain of dust, although functioning "motes" of genuine microscopic dimensions have yet

to be created. The cost of sensor nodes is similarly variable, ranging from a few to

hundreds of dollars, depending on the complexity of the individual sensor nodes. Size

and cost constraints on sensor nodes result in corresponding constraints on resources such

as energy, memory, computational speed and communications bandwidth. The topology

of the WSNs can vary from a simple star network to an advanced multi-hop wireless




http://en.wikipedia.org/wiki/Autonomous

http://en.wikipedia.org/wiki/Sensor

http://en.wikipedia.org/wiki/Temperature

http://en.wikipedia.org/wiki/Sound

http://en.wikipedia.org/wiki/Pressure

http://en.wikipedia.org/wiki/Radio

http://en.wikipedia.org/wiki/Transceiver

http://en.wikipedia.org/wiki/Antenna_(radio)

http://en.wikipedia.org/wiki/Microcontroller

http://en.wikipedia.org/wiki/Battery_(electricity)

http://en.wikipedia.org/wiki/Energy_harvesting


http://en.wikipedia.org/wiki/Sensor_node

http://en.wikipedia.org/wiki/Star_network

http://en.wikipedia.org/wiki/Mesh_networking

http://en.wikipedia.org/wiki/Wireless_mesh_network

mesh network. The propagation technique between the hops of the network can be

routing or flooding.

In computer science and telecommunications, wireless sensor networks are an active

research area with numerous workshops and conferences arranged each year.

The main characteristics of a WSN include

Power consumption constrains for nodes using batteries or energy harvesting

Ability to cope with node failures

Mobility of nodes

Communication failures

Heterogeneity of nodes

Scalability to large scale of deployment

Ability to withstand harsh environmental conditions

Ease of use

Power consumption

Sensor nodes can be imagined as small computers, extremely basic in terms of their

interfaces and their components. They usually consist of a processing unit with limited

computational power and limited memory, sensors or MEMS (including specific

conditioning circuitry), a communication device (usually radio transceivers or

alternatively optical), and a power source usually in the form of a battery. Other possible

inclusions are energy harvesting modules, secondary ASICs, and possibly secondary

communication devices (e.g. RS-232 or USB).

The base stations are one or more components of the WSN with much more

computational, energy and communication resources. They act as a gateway between

sensor nodes and the end user as they typically forward data from the WSN on to a

server. Other special components in routing based networks are routers, designed to

compute, calculate and distribute the routing tables.




http://en.wikipedia.org/wiki/Computer_science

http://en.wikipedia.org/wiki/Telecommunications

http://en.wikipedia.org/wiki/Microelectromechanical_systems

http://en.wikipedia.org/wiki/Smart_dust


http://en.wikipedia.org/wiki/Application-specific_integrated_circuit

http://en.wikipedia.org/wiki/RS-232

http://en.wikipedia.org/wiki/Universal_Serial_Bus

1.9 Optical Wireless Networks

Objective

To describe the optical wireless networks and network unit,

References



An optical network unit (ONU) is a device that transforms incoming optical signals

into electronics at a customer's premises in order to provide telecommunications services

over an optical fiber network.

An ONU is a generic term denoting a device that terminates any one of the endpoints of

a fiber to the premises network, implements apassive optical network (PON) protocol,

and adapts PON PDUs to subscriber service interfaces.[1]

In some contexts, an ONU

implies a multiple subscriber device. An optical network terminal (ONT) is a special case

of an ONU that serves a single subscriber.

An ONU closure is a mechanical compartment that houses the ONU equipment. The

outer closure faces the outside environment and provides physical, mechanical, and

environmental protection for cable (fiber and copper) components or equipment housed

within it.

An ONU system consists of a closure that is a metallic or non-metallic enclosure that

provides physical and environmental protection for the active electronic, optoelectronics,

and passive optical components it houses. It terminates optical fibers from the ODN and

processes the signals to and from the Customer Premises Equipment (CPE). It is the NE

that provides the tariffed telecommunications as well as video service interfaces for

multiple residential and small business customers.

Services on the customer side of the ONU are communicated over metallic twisted pairs

and coaxial cable drops (in the future, possibly fiber cable or wireless) to a Network




http://en.wikipedia.org/wiki/Optical

http://en.wikipedia.org/wiki/Electronics

http://en.wikipedia.org/wiki/Telecommunications

http://en.wikipedia.org/wiki/Optical_fiber

http://en.wikipedia.org/wiki/Fiber_to_the_x

http://en.wikipedia.org/wiki/Passive_optical_network

http://en.wikipedia.org/wiki/Protocol_(computing)

http://en.wikipedia.org/wiki/Protocol_data_unit

http://en.wikipedia.org/wiki/Optical_network_unit#cite_note-0

Interface (NI) where they are handed off to the customer’s network (usually, inside

wiring). Depending on the deployment strategy, the ONU closure may provide one or

more of the following additional features:

1. Access to the fiber distribution cable

2. Management of slack fiber and fiber splices

3. Access to the Telephone Support Cable (TSC) for the purpose of powering the

ONU

4. Prevention of unauthorized entry.

Primary power for ONUs is derived from either an external DC or an external AC power

source. Back-up power for ONUs can either be derived from an external power source or

be internal to the ONU closure and be provided by the FITL system supplier. Primary

power and external back-up power can be delivered to ONUs over either copper twisted

pairs or coaxial cable facilities. These cable facilities are commonly referred to as the

TSC.

Deployment of an ONU system requires access to the fiber distribution cable, TSC, and

metallic customer drop wires. When access to these cables is provided internal to the

ONU closure (i.e., by looping each cable through the closure), it is necessary that the

ONU closure also provide splicing and storage facilities for each of these cables.

Telcordia GR-950, Generic Requirements for Optical Network Unit (ONU) Closures and

ONU Systems, contains complete proposed specifications for the ONU closures and

systems.




http://telecom-info.telcordia.com/site-cgi/ido/docs.cgi?ID=SEARCH&DOCUMENT=GR-950&

http://telecom-info.telcordia.com/site-cgi/ido/docs.cgi?ID=SEARCH&DOCUMENT=GR-950&

Wireless Networks- Introduction

1

- Introduction




Synopsis

Fundamentals of Wireless Communication Technology

Bluetooth

Home RF

2

Communication Technology

Electromagnetic spectrum

Radio propagation mechanisms

Characteristics of the wireless channel

IEEE 802.11 Standard

HIPERLAN standard

Home RF

Wireless Sensor Networks

Optical wireless networks




Fundamentals

A computer network is an interconnected collection of autonomous computers.

Networking Goals:• Resource sharing - e.g., shared printer, shared files.

• Increased reliability - e.g., one failure does not cause

3

• Increased reliability - e.g., one failure does not cause system failure.

• Economics - e.g., better price/performance ratio.

• Communication - e.g., e-mail.




Fundamentals of Wireless Communication Two aspects of mobility:

• User mobility: users communicate (wireless) “anytime, anywhere, with anyone”

• Device portability: devices can be connected anytime, anywhere to the network

Wireless vs. mobile Examples stationary (wired and fixed) computer notebook in a hotel wireless LANs in historic buildings wireless LANs in historic buildings Personal Digital Assistant (PDA)

The demand for mobile communication creates the need for integration of wireless networks into existing fixed networks:• Local area networks: standardization of IEEE 802.11,

ETSI (European Telecommunications Standards Institute) (HIPERLAN -combined technology for broadband cellular short-range communications and wireless Local Area Networks (LANs) )

• Internet: Mobile IP extension of the Internet Protocol IP• Wide area networks: e.g., internetworking of GSM and ISDNFRANCIS XAVIER ENGINEERING COLLEGE



The Electromagnetic Spectrum

5

The electromagnetic spectrum and its uses for communication.FRANCIS XAVIER ENGINEERING COLLEGE




ELF = Extremely Low Frequency (30 ~ 300 Hz) UHF = Ultra High Frequency (300 MHz ~ 3GHz)

1 Mm300 Hz

10 km30 kHz

100 m3 MHz

1 m300 MHz

10 mm30 GHz

100 m3 THz

1 m300 THz

visible lightVLF LF MF HF VHF UHF SHF EHF infrared UV

optical transmissioncoax cabletwisted pair

ELF VF

6

VF = Voice Frequency (300 ~ 3000 Hz) SHF = Super High Frequency (3 ~ 30 GHz)VLF = Very Low Frequency (3 ~ 30 KHz) EHF = Extremely High Frequency (30 ~ 300GHz)LF = Low Frequency (30 ~ 300 KHz) Infrared (300 GHz ~ 400 THz)MF = Medium Frequency (300 ~ 3000 KHz) Visible Light (400 THz ~ 900 THz)HF = High Frequency (3 ~ 30 MHz) UV = Ultraviolet Light (900 THz ~ 1016 Hz)VHF = Very High Frequency (30 ~ 3000 MHz) X-ray (1016 ~ 1022 Hz)

Gamma ray (1022 Hz ~)

Frequency and wave length: = c/f wave length , speed of light c 3x108m/s, frequency f




The Electromagnetic spectrum is used for information transmission by modulating the amplitude, frequency, or phase of the waves.

VLF, LF, and MF are called as ground waves. • Transmission range up to a hundred kilometers

• Used for AM radio broadcasting


7

• Used for AM radio broadcasting

HF and VHF• The sky wave may get reflected several times between the Earth and the

ionosphere.

• Used by amateur ham radio operators and for military communication.

VHF-/UHF-ranges for mobile radio• simple, small antenna for cars

• deterministic propagation characteristics, reliable connections




Radio Transmission

8

(a) In the VLF, LF, and MF bands, radio waves follow the curvature of the earth.

(b) In the HF band, they bounce off the ionosphere.FRANCIS XAVIER ENGINEERING COLLEGE



SHF and higher for directed radio links, satellite communication• small antenna, focusing• Microwave transmissions travel in straight lines. • High signal-to-noise ratio (SNR)• Line-of-sight alignment is required.• large bandwidth available

Wireless LANs use frequencies in UHF to SHF spectrum• some systems planned up to EHF• limitations due to absorption by water and oxygen molecules (resonance


9

• limitations due to absorption by water and oxygen molecules (resonance frequencies)– weather dependent fading, signal loss caused by heavy rainfall etc.

Infrared waves and waves in the EHF band are used for short-range communication.• Widely used in television, VCR, stereo remote controls

Visible light• Used in the optical fiber• Laser can be used to connect LANs on two buildings but can travel limited

distance and cannot penetrate through rain or thick fog.FRANCIS XAVIER ENGINEERING COLLEGE



Spectrum AllocationEurope USA Japan

CellularPhones

GSM 450-457, 479-486/460-467,489-496, 890-915/935-960,1710-1785/1805-1880UMTS (FDD) 1920-1980, 2110-2190UMTS (TDD) 1900-1920, 2020-2025

AMPS, TDMA, CDMA824-849, 869-894TDMA, CDMA, GSM1850-1910,1930-1990

PDC810-826, 940-956,1429-1465, 1477-1513

CordlessPhones

CT1+ 885-887, 930-932

PACS 1850-1910, 1930-1990

PHS1895-1918

10

ITU-R holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences)

Phones 932CT2864-868DECT 1880-1900

1990PACS-UB 1910-1930

1895-1918JCT254-380

Wireless LANs

IEEE 802.112400-2483HIPERLAN 25150-5350, 5470-5725

902-928IEEE 802.112400-24835150-5350, 5725-5825

IEEE 802.112471-24975150-5250

Others RF-Control27, 128, 418, 433, 868

RF-Control315, 915

RF-Control426, 868




Radio propagation Radio waves can be propagated and receiving power is influenced

in different ways:• Direct transmission (path loss, fading dependent on frequency)• Reflection at large obstacles• Refraction through different media• Scattering at small obstacles• Diffraction at edges

11

• shadowing

Propagation in free space is always like light (straight line). Receiving power proportional to 1/d² (d = distance between sender

and receiver)

reflection scattering diffractionshadowing refractionFRANCIS XAVIER ENGINEERING COLLEGE



Path loss: the ratio of the power of the transmitted signal to the power of the same signal received by the receiver.• Free space model: Assume there is only a direct-path between the transmitter

and the receiver.

• Two-way model: Assume there is a light-of-sight path and the other path through reflection, refraction, or scattering between the transmitter and the receiver

Characteristics of the Wireless Channel

12

• Isotropic antennas (in which the power of the transmitted signal is the same in all direction): The receiving power varies inversely to the distance of power of 2 to 5.

Fading: fluctuations in signal strength when received at the receiver.• Fast fading/small-scale fading: rapid fluctuations in the amplitude, phase, or

multipath delays.

• Slow fading/large-scale fading (shadow fading): objects that absorb the transmissions lie between the transmitter and receiver.




Measures used for countering the effects of fading are diversity and adaptive modulation.• Diversity modulation:

• Time diversity: spread the data over time.

• Frequency diversity: spread the transmission over frequencies. Example: the direct sequence spread spectrum and the frequency hopping spread spectrum.


13

spectrum.

• Space diversity: use different physical transmission paths. An antenna array could be used.

• Adaptive modulation: the transmitter adjusts the transmission based on the feedback from the receiver.

• Complex to implement




Interference• Adjacent channel interference: interfered by signals in nearby frequencies.

Solved by the guard bands.• Co-channel interference: narrow-band interference due to other systems

using the same frequency. Solved by multiuser detection machenisms, directional antennas, and dynamic channel allocation methods.

• Inter-symbol interference: distortion in the received signal caused by the temporal spreading and the consequent (neighbor) overlapping of individual pulses in the signal. Solved by adaptive equalization that involves


14

pulses in the signal. Solved by adaptive equalization that involves mechanisms for gathering the dispersed symbol energy into its original time interval.

Doppler Shift• The change/shift in the frequency of the received signal when the transmitter

and the receiver are mobile to each other.• Moving towards each other, the frequency will be higher; two moving away,

the frequency will be lower.




Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction.

Time dispersion: signal is dispersed over time

interference with “neighbor” symbols, Inter Symbol Interference (ISI)

The signal reaches a receiver directly and phase shifted

Multipath propagation

15

The signal reaches a receiver directly and phase shifted

distorted signal depending on the phases of the different parts

signal at sendersignal at receiver

LOS pulsesmultipathpulses




Transmission Rate Constraints• The number of times of signal changes is called the baud rate. Bit rate =

baud rate x bits per signal• Nyquist’s Theorem for noiseless channel:

• If the signal has L discrete levels over a transmission medium of bandwidth B , the maximum data rate C = 2B log2 L bits/sec

• Example: a noiseless 3-kHz channel cannot transmit binary signals at a rate exceeding 6000 bps (= 2 x 3000 log2 2).


16

rate exceeding 6000 bps (= 2 x 3000 log2 2).• Shannon’s Theorem for noisy Channel

• maximum data rate C = B log2 (1 + S/N) bits/sec B: bandwdith, S: signal power, N: noise power

• S/N (Signal-to-noise ratio, SNR), usually measured as 10 log10S/N in db = decibels, is called thermal noise ratio.

• Example: SNR = 20 db, 2 KHz bandwidth. The maximum data rate is 2000 x log2 (1 + 100) = 9230.241 bps




IEEE 802 Standards IEEE 802 standards defines the physical and data link layer for LANs.

17The important ones are marked with *. The ones marked with are hibernating. The one marked with † gave up.FRANCIS XAVIER ENGINEERING COLLEGE



IEEE 802 Standard

The physical layer in a LAN deals with the actual physical transmission medium used for communication.• Some commonly used physical media: twisted pair, coaxial cable, optical

fiber, and radio waves.

In IEEE 802 Logical Link Control (LLC) forms the upper half of the data link layer. Medium access control (MAC) forms the

18

the data link layer. Medium access control (MAC) forms the lower sublayer.• error-controlled, flow-controlled

• Adds an LLC header, containing sequence and acknowledgement numbers.

LLC provides three service options:

• Unreliable datagram service

• Acknowledged datagram service

• Reliable connection-oriented service




Wireless LAN: 802.11 A wireless LAN is one in which a mobile user can connect to a

local area network (LAN) through a wireless (radio) connection. A standard, IEEE 802.11, specifies the technologies for wireless

LANs. It is designed to work in two modes:

• In the presence of a base station: access point• In the absence of a base station: ad hoc networking

19

Physical Layer• It supports three different physical layers:

• Frequency hopping spread spectrum (FHSS)• Direct sequence spread spectrum (DSSS)• Infrared

• Clear channel assessment (CCA): It provides mechanisms for sensing the wireless channel and determine whether or not it is idle.

MAC Sublayer follows carrier sense multiple access with collision avoidance (CSMA/CA).FRANCIS XAVIER ENGINEERING COLLEGE



Wireless LANs

20

(a) Wireless networking with a base station.(b) Ad hoc networking.




Wireless Local Area Network (WLAN) The wireless Local Area Network (WLAN) is a type of local-area

network that uses radio waves to communicate between nodes.

A stationary node called an access point (AP) coordinates the communication between nodes.

The two main standards for WLANs are the IEEE 802.11 standard and European Telecommunications Standards Instititue (ETSI) HIPERLAN standard.

21

HIPERLAN standard.

Wireless personal area networks (WPANs) are short-distance wireless networks.

Bluetooth is a popular WPAN specification.• Work within 10 m.

• Bluetooth Special Interest Group (SIG) including Ericsson, Intel, IBM, Nokia, and Toshiba is the driving force for Bluetooth.

The IEEE 802.15 is a standard for WPAN.FRANCIS XAVIER ENGINEERING COLLEGE



What is HIPERLAN?

HIPERLAN - HIgh PErformance Radio LANHIPERLAN is a new standard for Radio

LANs developed in Europe by ETSIHIPERLAN is an interoperability standard HIPERLAN is an interoperability standard

which specifies a common air interface MAC and PHY layers in OSI modelHIPERLAN will be a family of standardsHIPERLAN 1 is described in detail




HIPERLAN - reference model

Medium Access Control

Application Layer

Presentation Layer

Session Layer

Transport Layer

higher layer protocols

Medium Access Control(MAC) Sublayer

Channel Access Control(CAC) Sublayer

Physical (PHY) Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

OSIReference Model

HIPERLANReference Model




Early wireless LANs operating in theISM bands (900MHz and 2.45GHz)Low data rate (~1Mbps) - an indirect result of the FCC spread spectrum rules part 15.247Severe interference environment - from unlike wireless

Origins of HIPERLAN

Severe interference environment - from unlike wireless LANs and other ISM band systemsLack of standards - IEEE 802.11 was initiated to satisfy this need but it was taking time to develop ETSI set up RES10 to develop a standard that would be equal in performanceto wired LANs such as Ethernet




HIPERLAN 1 - history

l ETSI set up RES10 group - mid 1991l RES10 start work on standard - early 1992

CEPT allocate spectrum - early 1993l CEPT allocate spectrum - early 1993l RES10 complete draft standard - mid 1995

l ETSI publish final standard - late 1995l RES10 start work on type approval - early 1996l HIPERLAN passes public enquiry - mid 1996




l Short range - 50mLow mobility - 1.4m/sNetworks with and without infrastructure

HIPERLAN 1 - requirements

Support isochronous trafficaudio 32kbps, 10ns latencyvideo 2Mbps, 100ns latencySupport asynchronous trafficdata 10Mbps, immediate access




High transmission rate - 23.5294MbpsModulation - non diff GMSK, BT = 0.3Error control - FEC, BCH(31,26)Packet failure rate - 0.01 (4160 data bits)Low transmission rate - 1.470588Mbps

HIPERLAN 1 PHY - specifications

Low transmission rate - 1.470588MbpsModulation - FSK, freq dev = 368kHzChannelisation - 5 channels, 5.15-5.30GHzTransmit power - +10, +20, +30dBmReceive sensitivity - -50, -60, -70dBm




HIPERLAN 1 PHY - packets

SYNCH SEQUENCE450bits

DATA BLOCK496 bits

LOW RATE HEADER35bits (560bits)MAC HEADER DATA BLOCK

496bits

LOW RATE 1.5Mbps HIGH RATE 23.5Mbps

DATA PACKET

450bits 496 bits35bits (560bits) 496bits

ACK PACKET

LOW RATE ACK23bits (368bits)

NO MAC HEADERIMMEDIATE TRANS

LOW RATE 1.5Mbps

1-47 BLOCKS




A HIPERLAN can only use one ChannelThere is no mechanism for changing channelAntenna diversity an option but...Must use same antenna for CCAand transmission for correct MAC function

HIPERLAN 1 PHY -

and transmission for correct MAC functionMust reduce transmit power by antenna gainto maintain EIRP as specified by CEPTPower saving with...Low rate header for modem power savingPower saving cycle strategies sleep/wake modes




Bluetooth•Bluetooth is a high-speed, low-power, microwave wireless link technology designed•to connect phones, laptops, personal digital assistants (PDAs), and other portable•equipment with little or no work by the user. •Unlike infrared, Bluetooth does not require line-of-sight positioning of connected units. •The technology uses modifications of existing wireless LAN techniques but is most notable •for its small size and low cost. •Whenever any Bluetooth-enabled devices come within range of each other, they instantly transfer address information and establish small networks between each other, without the user being involved.•Features of Bluetooth technology are as follows:

30

•Features of Bluetooth technology are as follows:•Operates in the 2.56 gigahertz (GHz) ISM band, which is globally available•(no license required)•Uses Frequency Hop Spread Spectrum (FHSS)•Can support up to eight devices in a small network known as a “piconet”•Omnidirectional, nonline-of-sight transmission through walls•10 m to 100 m range•Low cost•1 mw power•Extended range with external power amplifier (100 meters)




HomeRFHomeRF is a subset of the International Telecommunication Union (ITU) andprimarily works on the development of a standard for inexpensive radio frequency(RF) voice and data communication. The HomeRF Working Group has also developedthe Shared Wireless Access Protocol (SWAP). SWAP is an industry specificationthat permits PCs, peripherals, cordless telephones, and other devices tocommunicate voice and data without the use of cables. SWAP is similar to the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol of IEEE 802.11 but with an extension to voice traffic. Features of HomeRF are as follows:Operates in the 2.45 GHz range of the unlicensed ISM band.

31

Operates in the 2.45 GHz range of the unlicensed ISM band.Range: up to 150 feet.Employs frequency hopping at 50 hops per second.It supports both a Time Division Multiple Access (TDMA) service to providedelivery of interactive voice and a CSMA/CA service for delivery of high-speeddata packets.The network is capable of supporting up to 127 nodes.Transmission power: 100mW.Data rate: 1 Mbps using 2 frequency-shift keying (FSK) modulation and2 Mbps using 4 FSK modulation.Voice connections: up to 6 full duplex conversations.Data security: blowfish encryption algorithm (over 1 trillion codes).




Wireless Sensor Networks

Wireless Sensor Networks (WSNs)Wireless sensor networks consist of some nodes that have limited

processing capability, small memory and low energy source.These nodes are deployed randomly and often densely in theenvironment.

In monitoring applications, sensor nodes sense data from the

32

In monitoring applications, sensor nodes sense data from theenvironment periodically and then transmit them to a base stationwhich is called sink node.

Thereby data transmission consumes node’s energy based ontransmission distance




Design Goals of WSNs

Energy Efficiency

Node deployment

Energy consumption without losing accuracy

Fault Tolerance

Quality of Service

Data Aggregation/Fusion

Connectivity

Scalability

5/13/201533




INFRASTRUCTURELESS NETWORKS




Introduction and Issues in Ad Hoc Wireless Networks

� An ad hoc network is a collection of wireless mobile nodes (or routers)

dynamically forming a temporary network without the use of any existing

network infrastructure or centralized administration.

� The routers are free to move randomly and organize themselves arbitrarily;

thus, the network’s wireless topology may change rapidly andthus, the network’s wireless topology may change rapidly and

unpredictably.

� Some form of routing protocol is in general necessary in such an

environment, because two hosts Mobile users will want to communicate in

situations in which no fixed wired infrastructure is available.




A Scenario for Infrastructure less Networks




Issues in Ad Hoc Wireless Networks

� Ad hoc networks inherit some of the traditional problems of wireless

communication and wireless networking:

� The wireless medium does not have proper boundaries outside of which

nodes are known to be unable to receive network frames.

� The wireless channel is weak, unreliable, and unprotected from outside� The wireless channel is weak, unreliable, and unprotected from outside

signals, which may cause lots of problems to the nodes in the network.

� The wireless channel has time-varying and asymmetric propagation

properties. Hidden-node and exposed-node problems may occur.




Contd..

� Medium Access Control (MAC) Protocol Research Issues

� Networking Issues

� Ad Hoc Routing and Forwarding

� Unicast Routing

� Proactive Routing Protocols

� Reactive Routing Protocols

� Multicast Routing

� Location-Aware Routing




Transmission Control Protocol (TCP) Issues

� TCP is an effective connection-oriented transport control protocol that

provides the essential flow control and congestion control required to ensure

reliable packet delivery.

� The main research areas and open issues include the following:

� Impact of mobility� Impact of mobility

� Nodes interaction MAC layer

� Impact of TCP congestion window size

� Interaction between MAC protocols

� Network Security




Different Security Attacks

� Impersonation� Denial of service� Disclosure attack� Man in the middle attack� Black hole attack� Black hole attack� Wormhole attack




Medium Access Scheme and Transport Layer Protocols

� Random access will be suitable for ad hoc networks because of lack of

infrastructure support.

� The use of Bluetooth and IEEE 802.11 is not optimized in a multi-hop

environment.

� The Multiplicative Increase–Multiplicative Decrease (MIMD) rate� The Multiplicative Increase–Multiplicative Decrease (MIMD) rate

adaptation algorithm causes the periodic TCP packet retransmissions.




Contd..

� TCP is unable to distinguish between losses due to route failures and network congestion.

� TCP suffers from frequent route failures. � The contention on wireless channel.� TCP unfairness.� TCP unfairness.




Transport Layer Protocols




Pricing Scheme

� The use of pricing as a means for allocating resources in communication

networks has received much attention in recent years.

� Some of them proposed a scheme where a network provider charges users

as a function of the traffic load on the individual links in the network, and

users accessing the network decide on their transmission rate as a functionusers accessing the network decide on their transmission rate as a function

of these network prices.




Quality of Service Provisioning

� Quality of service (QoS) is a measure of the level of service that a

particular data gets in the network.

� The network is expected to guarantee a set of measurable pre-

specified service attributes to the users in terms of end-to-end

performance such as delay, bandwidth, probability of packet loss,performance such as delay, bandwidth, probability of packet loss,

delay variance (jitter), and so forth.

� Traditional Internet QoS protocols like Resource Reservation

Protocol (RSVP) cannot be easily migrated to the wireless

environment due to the error-prone nature of wireless links and the

high mobility of mobile devices.




Self Organizing and Security

� Self-organization is a great concept for building scalable systems consistingof huge numbers of subsystems.

� self-organization is especially important in ad hoc networking because ofthe spontaneous interaction of multiple heterogeneous components overwireless radio connection.

� Security goals

� Availability� Availability

� Confidentiality

� Integrity

� Authentication

� Non-repudiation




Addressing and Service Discovery

� In MANETs, some of the connected hosts might have, in addition to the ad hoc

network interface, an external connection to the Internet. Such nodes may announce

this ability as a service to the participating ad hoc nodes. Using service discovery,

members of the MANET are then able to use such a gateway service.

� - In an electronic parking system, a service is defined differently. In such a scenario,

implemented as a sensor network, each parking slot is equipped with a sensor.

Whenever the slot is not occupied, the sensor announces a parking service and a

guidance system able to route the car to the parking slot.

� - Using their wireless hand-held device or not ebook, participants in collaborative

applications or distributed gaming environments need to discover application or

game servers before participating in a session.




Energy Management

� The main reasons for energy management in ad hoc networks are as follows:

� Limited energy reserve:

� Difficulties in replacing the batteries

� Lack of central coordination

� Constraints on the battery source� Constraints on the battery source

� Selection of optimal transmission power:




Scalability

� A set of properties are identified that a scalable and efficient solution must have:

� • Localization of overhead: a local change should affect only the immediate

neighborhood, thus limiting the overall overhead incurred due to the change.

� • Lightweight, decentralized protocols: we would like to avoid concentrating

responsibility at any individual node, and we want to keep the necessary state to be

maintained at each node as small as possible.

� • Zero-configuration: we want to completely remove the need for manual

configuration beyond what can be done at the time of manufacture.




Ad hoc wireless internet

� An ad hoc network typically refers to any set of networks where all

devices have equal status on a network and are free to associate with

any other ad hoc network devices in link range.




MAC Protocols

Introduction Contention-based Protocols Introduction

Issues

Design Goals

Classifications

Contention-based Protocols

Contention-based Protocols with reservation mechanisms

Contention-based Protocols without Scheduling mechanisms

MAC Protocols that use directional antennas

Other MAC Protocols




Issues

The main issues need to be addressed while designing a MAC protocol for ad hoc wireless networks:• Bandwidth efficiency is defined at the ratio of the bandwidth used for actual

data transmission to the total available bandwidth. The MAC protocol for ad-hoc networks should maximize it.

• Quality of service support is essential for time-critical applications. The MAC protocol for ad-hoc networks should consider the constraint of ad-hoc MAC protocol for ad-hoc networks should consider the constraint of ad-hoc networks.

• Synchronization can be achieved by exchange of control packets.




Issues The main issues need to be addressed while designing a MAC

protocol for ad hoc wireless networks:• Hidden and exposed terminal problems:

• Hidden nodes: – Hidden stations: Carrier sensing may fail to detect another station.

For example, A and D.– Fading: The strength of radio signals diminished rapidly with the

distance from the transmitter. For example, A and C.distance from the transmitter. For example, A and C.• Exposed nodes:

– Exposed stations: B is sending to A. C can detect it. C might want to send to E but conclude it cannot transmit because C hears B.

– Collision masking: The local signal might drown out the remote transmission.

• Error-Prone Shared Broadcast Channel• Distributed Nature/Lack of Central Coordination• Mobility of Nodes: Nodes are mobile most of the time.




Wireless LAN configuration

WirelessLAN

Laptops

radio obstruction

A B C

D

LAN

Server

LAN

Base station/access point

Palmtop DE




The 802.11 MAC Sublayer Protocol

(a) The hidden station problem.(b) The exposed station problem.




Design goals of a MAC Protocol Design goals of a MAC protocol for ad hoc wireless networks

• The operation of the protocol should be distributed.

• The protocol should provide QoS support for real-time traffic.

• The access delay, which refers to the average delay experienced by any packet to get transmitted, must be kept low.

• The available bandwidth must be utilized efficiently.

• The protocol should ensure fair allocation of bandwidth to nodes.• The protocol should ensure fair allocation of bandwidth to nodes.

• Control overhead must be kept as low as possible.

• The protocol should minimize the effects of hidden and exposed terminal problems.

• The protocol must be scalable to large networks.

• It should have power control mechanisms.

• The protocol should have mechanisms for adaptive data rate control.

• It should try to use directional antennas.

• The protocol should provide synchronization among nodes.FRANCIS XAVIER ENGINEERING COLLEGE



Classifications of MAC protocols Ad hoc network MAC protocols can be classified into three types:

• Contention-based protocols• Contention-based protocols with reservation mechanisms• Contention-based protocols with scheduling mechanisms• Other MAC protocols

MAC Protocols for Ad Hoc Wireless Networks

Contention-BasedProtocols

Contention-based protocols with

reservation mechanisms

Other MAC Protocols

Contention-based protocols with

scheduling mechanisms

Sender-InitiatedProtocols

Receiver-InitiatedProtocols

SynchronousProtocols

AsynchronousProtocols

Single-ChannelProtocols

MultichannelProtocols

MACAW

FAMA

BTMA

DBTMA

ICSMA

RI-BTMA

MACA-BI

MARCH

D-PRMA

CATA

HRMA

RI-BTMA

MACA-BI

MARCH

SRMA/PA

FPRP

MACA/PRRTMAC

DirectionalAntennas

MMAC

MCSMA

PCM

RBAR




Classifications of MAC Protocols Contention-based protocols

• Sender-initiated protocols: Packet transmissions are initiated by the sender node.

• Single-channel sender-initiated protocols: A node that wins the contention to the channel can make use of the entire bandwidth.

• Multichannel sender-initiated protocols: The available bandwidth is divided into multiple channels.

• Receiver-initiated protocols: The receiver node initiates the contention resolution protocol.

Contention-based protocols with reservation mechanisms• Synchronous protocols: All nodes need to be synchronized. Global time

synchronization is difficult to achieve.

• Asynchronous protocols: These protocols use relative time information for effecting reservations.




Classifications of MAC Protocols Contention-based protocols with scheduling mechanisms

• Node scheduling is done in a manner so that all nodes are treated fairly and no node is starved of bandwidth.

• Scheduling-based schemes are also used for enforcing priorities among flows whose packets are queued at nodes.

• Some scheduling schemes also consider battery characteristics.

Other protocols are those MAC protocols that do not strictly fall Other protocols are those MAC protocols that do not strictly fall under the above categories.




Contention-based protocols MACAW: A Media Access Protocol for Wireless LANs is based

on MACA (Multiple Access Collision Avoidance) Protocol

MACA• When a node wants to transmit a data packet, it first transmit a RTS

(Request To Send) frame.

• The receiver node, on receiving the RTS packet, if it is ready to receive the data packet, transmits a CTS (Clear to Send) packet. data packet, transmits a CTS (Clear to Send) packet.

• Once the sender receives the CTS packet without any error, it starts transmitting the data packet.

• If a packet transmitted by a node is lost, the node uses the binary exponential back-off (BEB) algorithm to back off a random interval of time before retrying.

The binary exponential back-off mechanism used in MACA might starves flows sometimes. The problem is solved by MACAW.




MACA Protocol

The MACA protocol. (a) A sending an RTS to B.

(b) B responding with a CTS to A.




MACA avoids the problem of hidden terminals• A and C want to

send to B

• A sends RTS first

• C waits after receiving CTS from B

MACA examples

A B C

RTS

CTSCTS

MACA avoids the problem of exposed terminals• B wants to send to A, C

to another terminal

• now C does not have to wait for it cannot receive CTS from A

A B C

RTS

CTS

RTS




MACAW Variants of this method can be found in IEEE 802.11 as

DFWMAC (Distributed Foundation Wireless MAC), MACAW (MACA for Wireless) is a revision of MACA.

• The sender senses the carrier to see and transmits a RTS (Request To Send) frame if no nearby station transmits a RTS.

• The receiver replies with a CTS (Clear To Send) frame.• Neighbors• Neighbors

• see CTS, then keep quiet.• see RTS but not CTS, then keep quiet until the CTS is back to the

sender.• The receiver sends an ACK when receiving an frame.

• Neighbors keep silent until see ACK.• Collisions

• There is no collision detection.• The senders know collision when they don’t receive CTS.• They each wait for the exponential backoff time.




MACA variant: DFWMAC in IEEE802.11

idle

sender receiver

packet ready to send; RTS

time-out; RTS

RxBusy

idle

RTS;

data; ACK

wait for the right to send

wait for ACK

RTS

CTS; data

ACK

wait fordata

RTS; RxBusy

RTS; CTStime-out

data; NAK

ACK: positive acknowledgementNAK: negative acknowledgement

RxBusy: receiver busy

time-out NAK;RTS




Contention-based protocols

Floor acquisition Multiple Access Protocols (FAMA)• Based on a channel access discipline which consists of a carrier-sensing

operation and a collision-avoidance dialog between the sender and the intended receiver of a packet.

• Floor acquisition refers to the process of gaining control of the channel. At any time only one node is assigned to use the channel.

• Carrier-sensing by the sender, followed by the RTS-CTS control packet • Carrier-sensing by the sender, followed by the RTS-CTS control packet exchange, enables the protocol to perform as efficiently as MACA.

• Two variations of FAMA

• RTS-CTS exchange with no carrier-sensing uses the ALOHA protocol for transmitting RTS packets.

• RTS-CTS exchange with non-persistent carrier-sensing uses non-persistent CSMA for the same purpose.




Contention-based protocols Busy Tone Multiple Access Protocols (BTMA)

• The transmission channel is split into two: • a data channel for data packet transmissions• a control channel used to transmit the busy tone signal

• When a node is ready for transmission, it senses the channel to check whether the busy tone is active. • If not, it turns on the busy tone signal and starts data transmissions• Otherwise, it reschedules the packet for transmission after some random • Otherwise, it reschedules the packet for transmission after some random

rescheduling delay.• Any other node which senses the carrier on the incoming data channel

also transmits the busy tone signal on the control channel, thus, prevent two neighboring nodes from transmitting at the same time.

Dual Busy Tone Multiple Access Protocol (DBTMAP) is an extension of the BTMA scheme. • a data channel for data packet transmissions• a control channel used for control packet transmissions (RTS and CTS

packets) and also for transmitting the busy tones.FRANCIS XAVIER ENGINEERING COLLEGE



Contention-based protocols Receiver-Initiated Busy Tone Multiple Access Protocol (RI-

BTMA)• The transmission channel is split into two:

• a data channel for data packet transmissions

• a control channel used for transmitting the busy tone signal• A node can transmit on the data channel only if it finds the busy tone to be absent

on the control channel.on the control channel.

• The data packet is divided into two portions: a preamble and the actual data packet.

MACA-By Invitation (MACA-BI) is a receiver-initiated MAC protocol. • By eliminating the need for the RTS packet it reduces the number of

control packets used in the MACA protocol which uses the three-way handshake mechanism.

Media Access with Reduced Handshake (MARCH) is a receiver-initiated protocol.FRANCIS XAVIER ENGINEERING COLLEGE



Contention-based Protocols withReservation Mechanisms

Contention-based Protocols with Reservation Mechanisms • Contention occurs during the resource (bandwidth) reservation phase. • Once the bandwidth is reserved, the node gets exclusive access to the

reserved bandwidth. • QoS support can be provided for real-time traffic.

Distributed packet reservation multiple access protocol (D- Distributed packet reservation multiple access protocol (D-PRMA) • It extends the centralized packet reservation multiple access (PRMA)

scheme into a distributed scheme that can be used in ad hoc wireless networks.

• PRMA was designed in a wireless LAN with a base station.• D-PRMA extends PRMA protocol in a wireless LAN.• D-PRMA is a TDMA-based scheme. The channel is divided into fixed- and

equal-sized frames along the time axis.




Access method DAMA: Reservation-TDMA

Reservation Time Division Multiple Access • every frame consists of N mini-slots and x data-slots

• every station has its own mini-slot and can reserve up to k data-slots using this mini-slot (i.e. x = N * k).

• other stations can send data in unused data-slots according to a round-robin sending scheme (best-effort traffic)

N mini-slots N * k data-slots

reservationsfor data-slots

other stations can use free data-slotsbased on a round-robin scheme

e.g. N=6, k=2




Contention-based protocols withReservation Mechanisms

Collision avoidance time allocation protocol (CATA) • based on dynamic topology-dependent transmission scheduling

• Nodes contend for and reserve time slots by means of a distributed reservation and handshake mechanism.

• Support broadcast, unicast, and multicast transmissions.• Support broadcast, unicast, and multicast transmissions.

• The operation is based on two basic principles:

• The receiver(s) of a flow must inform the potential source nodes about the reserved slot on which it is currently receiving packets. The source node must inform the potential destination node(s) about interferences in the slot.

• Usage of negative acknowledgements for reservation requests, and control packet transmissions at the beginning of each slot, for distributing slot reservation information to senders of broadcast or multicast sessions.





Hop reservation multiple access protocol (HRMA) • a multichannel MAC protocol which is based on half-duplex, very slow

frequency-hopping spread spectrum (FHSS) radios• uses a reservation and handshake mechanism to enable a pair of

communicating nodes to reserve a frequency hop, thereby guaranteeing collision-free data transmission.collision-free data transmission.

• can be viewed as a time slot reservation protocol where each time slot is assigned a separate frequency channel.

Soft reservation multiple access with priority assignment (SRMA/PA)• Developed with the main objective of supporting integrated services of

real-time and non-real-time application in ad hoc networks, at the same time maximizing the statistical multiplexing gain.

• Nodes use a collision-avoidance handshake mechanism and a soft reservation mechanism.




Five-Phase Reservation Protocol (FPRP)• a single-channel time division multiple access (TDMA)-based broadcast

scheduling protocol.• Nodes uses a contention mechanism in order to acquire time slots.• The protocol assumes the availability of global time at all nodes.• The reservation takes five phases: reservation, collision report, reservation


• The reservation takes five phases: reservation, collision report, reservation confirmation, reservation acknowledgement, and packing and elimination phase.

MACA with Piggy-Backed Reservation (MACA/PR)• Provide real-time traffic support in multi-hop wireless networks• Based on the MACAW protocol with non-persistent CSMA• The main components of MACA/PR are:

• A MAC protocol• A reservation protocol• A QoS routing protocol




Real-Time Medium Access Control Protocol (RTMAC)• Provides a bandwidth reservation mechanism for supporting real-time traffic

in ad hoc wireless networks

• RTMAC has two components

• A MAC layer protocol is a real-time extension of the IEEE 802.11 DCF.– A medium-access protocol for best-effort traffic


– A medium-access protocol for best-effort traffic

– A reservation protocol for real-time traffic

• A QoS routing protocol is responsible for end-to-end reservation and release of bandwidth resources.




Protocols in this category focus on packet scheduling at the nodes and transmission scheduling of the nodes.

The factors that affects scheduling decisions• Delay targets of packets

• Traffic load at nodes

Contention-based protocols withScheduling Mechanisms

• Traffic load at nodes

• Battery power

Distributed priority scheduling and medium access in Ad Hoc Networks present two mechanisms for providing quality of service (QoS)• Distributed priority scheduling (DPS) – piggy-backs the priority tag of a

node’s current and head-of-line packets to the control and data packets

• Multi-hop coordination – extends the DPS scheme to carry out scheduling over multi-hop paths.




Distributed Wireless Ordering Protocol (DWOP)• A media access scheme along with a scheduling mechanism

• Based on the distributed priority scheduling scheme

Distributed Laxity-based Priority Scheduling (DLPS) Scheme• Scheduling decisions are made based on

Contention-based protocols withScheduling Mechanisms

• The states of neighboring nodes and feed back from destination nodes regarding packet losses

• Packets are recorded based on their uniform laxity budgets (ULBs) and the packet delivery ratios of the flows. The laxity of a packet is the time remaining before its deadline.




MAC protocols that use directional antennas have several advantages:• Reduce signal interference• Increase in the system throughput• Improved channel reuse

MAC protocol using directional antennas• Make use of an RTS/CTS exchange mechanism

MAC Protocols that use directionalAntennas

• Make use of an RTS/CTS exchange mechanism• Use directional antennas for transmitting and receiving data packets

Directional Busy Tone-based MAC Protocol (DBTMA)• It uses directional antennas for transmitting the RTS, CTS, data frames, and

the busy tones.

Directional MAC Protocols for Ad Hoc Wireless Networks• DMAC-1, a directional antenna is used for transmitting RTS packets and

omni-directional antenna for CTS packets.• DMAC-1, both directional RTS and omni-directional RTS transmission are

used.FRANCIS XAVIER ENGINEERING COLLEGE



Other MAC Protocols

Multi-channel MAC Protocol (MMAC)• Multiple channels for data transmission

• There is no dedicated control channel.

• Based on channel usage channels can be classified into three types: high preference channel (HIGH), medium preference channel (MID), low preference channel (LOW)

Multi-channel CSMA MAC Protocol (MCSMA) Multi-channel CSMA MAC Protocol (MCSMA)• The available bandwidth is divided into several channels

Power Control MAC Protocol (PCM) for Ad Hoc Networks• Allows nodes to vary their transmission power levels on a per-packet basis

Receiver-based Auto rate Protocol (RBAR)• Use a rate adaptation approach

Interleaved Carrier-Sense Multiple Access Protocol (ICSMA)• The available bandwidth is split into tow equal channels

• The handshaking process is interleaved between the two channels.FRANCIS XAVIER ENGINEERING COLLEGE



ec2043 notes

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