introduction to manet - institute of computer … to manet 5 hiperlan2 watm – ip-net ( 50 m)...

1Introduction to MANET

Introduction to MANETIntroduction to MANET

Safa Rahimi Movaghar


OutlineOutlinePART1 Introduction to MANET

• Goals of designing communication systems• Evolution of communication systems• Comparison of various Mobile Nets• MANET Definition, Requirements, Advantages and Applications • Difference between Cellular Networks and MANETs• Issues to Design MANET• Classification of MAC Protocols• Issues to Design MAC• Routing Protocol Challenges• Routing Protocol Requirements

PART2 Wireless Physical Technology• Electromagnetic spectrum, Frequency bands and uses• Radio propagation mechanisms• Modulation techniques• Multiple access techniques


Goals of designing Communication Goals of designing Communication SystemsSystems

Maximise:• Transmission bit rate (R)• System utilisation: providing reliable service for a

maximum number of users within minimum delayMinimise:• Probability of bit error• Power • System bandwidth (W)• System complexity, computational load, system

costSupport:• Handover• Asymmetric• Techniques (FDD, TDD)


EvolutionEvolution

•GSM/TDMA/CDMA: 9.6 – 28.8 kbps

2G: Low Speed Packet and Circuit Data

•GPRS/EDGE: 9.6 – 384 kbps

2.5G: High Speed Packet Data

•3GPP: 144 kbps – 2 Mbps

3G: Multimedia

•2 – 75 Mbps

•Interconnection with 3G, WiFi, fixed Networks

4G: Very High Speed Wireless Internet

2001

1999

1992

2006


Hiperlan2 WATM – IP-Net ( 50 m)Mobility & Range

Total data rate per cell [7]70 155 Mb/s

Indoor

Pedestrian

High Speed

Vehicular

Rural

Personal Area

Vehicular

Urban

BRAN:HiperaccessIEEE 802.11x

0.5 2

UMTS

DECT

BlueTooth

Fixed urban

BRAN Broad band Radio Access Network

Hiperaccess WATM (5 Km)

WATM Wireless ATM

WiMax Worldwide Interoperability for Microwave Access

WiMax:IEEE 802.16x

GSM GPRSEDGE

DECT

ComparisonComparison of of variousvarious Mobile NetsMobile Nets


• Dynamically reconfigurable, self-organising and rapidly deployable network which provides on-demand networking solutions

• Peer-to-peer• Multi-hop fashion• Dynamic topology

– Decision must be taken in a distributed manner.

MANETMANET


Advantages of MANETAdvantages of MANET

• Build very fast (No cable).• More efficient than cellular networks for local areas.

– Better use of the bandwidth.• For areas; placing wires may be impossible, or not necessary.• Higher capacity• Lower price• Cooperative functioning• Energy-efficient relaying• Support for multicast traffic• Fault-tolerant communication• Self-organization and maintenance• Scalability• Availability• Ubiquitous computing: Services without information about addresses or

positions.


MANET RequirementsMANET Requirements

• QoS• Reliability• Security• Fault-tolerant communication• Self-organization and maintenance• Scalability• Availability• Ubiquitous computing: request services without information

about service addresses or positions.


Many small hops are better than a big oneMany small hops are better than a big one

• Power Consumption

• Signal Interference

•Throughput

• Handoff

• Disconnection


Traffic

Area

avgtraffic

hot spottraffic

• Date rate• Traffic• High Mobility

Hybrid architectures, combine the benefits of cellular and ad hoc wireless networks, which improve capacity.

Critical AreaCritical Area


Difference between Cellular Networks and Difference between Cellular Networks and MANETsMANETs

Cellular Networks MANETsFixed infrastructure Infrastructure-lessSingle-hop Multi-hopCentralised routing Distributed routingGood connectivity Frequent Path breaksHigh cost Low costEasy time-synchronisation Difficult time-synchronisation

Easy bandwidth reservation Complex bandwidth reservation

High cost of network maintenance

Self-organisation

Mobile hosts are relative low complexity

Mobile hosts are more intelligence


MANET ApplicationsMANET Applications• Wireless sensor networks:

– e.g. sensing forest fires, environment monitoring, studying wildlife;• Tactical military communications;• Networks of satellites (even around Mars);• Vehicular communications;• Rural areas or third world countries where basic communication

infrastructure is not well established.• Collaborative and distributed computing;

– Inventory tracking, Surveillance, Law enforcement operation, WLANs in conferences, Historical buildings, distributed file sharing

• Emergency operations;– rescue, crowd control, and commando operations. In environments

where the conventional infrastructure-based communication facilities are destroyed due to a war or earthquakes

• Wireless mesh networks;– e.g., residential zones for broadband Internet, highways, business

zones, important civilian regions, university campuses• Hybrid wireless networks.


Coverage area

Radio relay node

Lamp

Multi-hop ra

dio relay lin

k

Wired link to the Internet

Source [1]


Advantages of Hybrid StructureAdvantages of Hybrid Structure• Topology knowledge;• Failure-tolerant system:

– Increased flexibility in routing: It selects the best suitable nodes for routing.

– Exploiting spatial diversity through adaptive routing.• Reliability: It recognises failure in packet transmission and reaches other

nearby nodes or base station using multi-hop paths.• Better Coverage and connectivity in holes of a cell can be provided by

means of multiple hops;• Synchronise by cellular network;• Increasing robustness and scalability of the system;• Ubiquitous;• Real Time; • Bit rate; • Interference; • Consumed power;• Communication cost;• Higher capacity.


Wireless Network ProjectsWireless Network Projects• Internet Engineering Task Force (IETF)

– MANET working group [2] , was formed to standardize the protocols and functional specification of ad hoc wireless networks.

• Hybrid architectures– Multi-hop cellular networks (MCNs) [3][5]– Self-organizing packet radio ad hoc networks (SOPRANO) [4]– Integrated cellular ad hoc relay (iCAR) networks [6]

• Bluetooth: short-range, low-power, low-complexity, and inexpensive radio interface for ubiquitous connectivity among heterogeneous devices.

– Special Interest Group (SIG) formed by several companies such as 3com, Ericsson, IBM, Intel, Lucent, Microsoft, Motorola, Nokia, and, Toshiba.

• IEEE 802.11a,g: aka WiFi– wireless local area network (WLAN)– provides up to 54 Mbps @ 20 MHz bandwidth– 64 subcarriers– operates at 2.4 GHz (.11g) and 5 GHz (.11a)

• IEEE 802.16a,e: aka WiMax– wireless metropolitan area network (WMAN)– below 11GHz fixed wireless access (“last mile“)– supports up to 75 Mbps @ 20 MHz bandwidth– 256-2048 subcarriers

• Upcoming:– IEEE 802.11n (high-throughput extension of 11a,g)– IEEE 802.15.3 (multiband OFDM proposal for WPAN)


Bluetooth2 HomeRF2 802.11b 802.11a 802.11g 802.15.3 HiperLan2 5UP

Frequency 2.4GHz 2.4 GHz 2.4GHz 5 GHz 2.4 GHz 2.4 GHz 5 GHz 5 GHz

Technology FHSS FHSS DSSS OFDM DSS/OFDM OFDM OFDM OFDM

Max Range 10cm-10m 50m 150m 50m 150m 10m 80m 80m

Power Very Low Medium Medium Medium-High

Medium-High

Medium Medium N/A

Complexity 1x 1.5x 1.2x 4x ~3.5x 1.5x 2.5x 2x

QoS Yes Yes No No No Yes Yes Yes

Physical Bit Rate

<10Mbps

<10 Mbps

11Mbps

54 Mbps

22 -54Mbps

11-55 Mbps

54 Mbps

108Mbps

EffectiveBit Rate

<6 Mbps <6 Mbps <7Mbps

<31Mbps

<12 Mbps <30 Mbps

<31 Mbps

<72 Mbps

RegionalSupport

World USA/Asia

World USA/Asia

World World Europe/Japan

World

Comparison of Home Wireless Comparison of Home Wireless TechnologiesTechnologies


Issues to Design MANETIssues to Design MANET

• Medium access scheme• Routing• Multicasting• Transport layer protocol• Pricing scheme• Quality of service provisioning• Self-organization• Security• Energy management• Addressing and service discovery• Scalability• Deployment considerations


MACMAC• Nodes must decide when to access the

channel, i.e., transmit.• Two conflicting targets:

– Collisions of packets must be avoided.– Bandwidth must not be underutilized.

A balance is needed.


• Random Access:– Nodes contend for the channel whenever they have a packet.– e.g. Slotted Aloha: Nodes transmit packets whenever they arrive.

• Transmission Scheduling:– Each node can transmit during a pre-assigned set of slots.– TDMA/FDMA/CDMA.

• Hybrid Protocols:– Nodes have pre-assigned slots but also contend.– e.g., Reservation Aloha: Nodes contend for a slot whenever they

need it, but then have priority in following frames.

Classification of MAC ProtocolsClassification of MAC Protocols

1Slot 2Slot n Slot

1st Frame

1Slot 2Slot n Slot

2nd Frame


Advantages of Each ApproachAdvantages of Each Approach

• Random access is preferable when:– traffic is bursty (e.g., data).– topology changes fast or is unknown.

• Transmission scheduling is preferable when:– traffic is periodic (e.g. voice traffic).– topology changes slowly.– quality guarantees are needed.

• Hybrid protocols are adaptable to the traffic/mobility conditions.


Random Access ProtocolsRandom Access Protocols

• Slotted Aloha.• Carrier Sense Multiple Access (CSMA).• Busy Tone Multiple Access (BTMA).• CSMA with Collision Detection

(CSMA/CD).• CSMA with Collision Avoidance

(CSMA/CA).• Dual Busy Tone Multiple Access

(DBTMA).


Issues to Design MACIssues to Design MAC

• Distributed operation: No centralized coordination; Minimum control overhead; • Synchronization: Mandatory for TDMA systems.

– The control packets used for synchronisation increase collisions.• Throughput: Minimise collisions and overhead, maximise channel utilisation.• Access delay: Average delay that any packet experiences to get transmitted. • Fairness: provide an equal share of the bandwidth to all competing nodes.

– Node-based: provide an equal bandwidth share for competing nodes;– Flow-based: Provides an equal share for competing data transfer sessions.

• Real-time traffic support: voice, video, and real-time data.• Resource reservation: QoS defined by parameters such as bandwidth, delay, and

jitter requires reservation of resources such as bandwidth, buffer space, and processing power.

• Ability to measure resource (bandwidth) availability to perform call admission control.

– Also used for making congestion-control decisions.• Capability for power control: Reduces the energy consumption, interference, and

increases frequency reuse. • Adaptive rate control: Variation in the data bit rate. High data rate when the sender

and receiver are near, and adaptively reduce the data rate when there is high noise.• Use of directional antennas: Increases spectrum reuse, reduces interference, and

power consumption.


Hidden/Exposed terminals ProblemHidden/Exposed terminals Problem

I E S D H J


Routing Protocol ChallengesRouting Protocol Challenges• Mobility results in frequent path breaks, packet

collisions, transient loops, stale routing information, and difficulty in resource reservation.

• Bandwidth constraint depends on the number of nodes and the traffic they handle.

• Error-prone and shared channel: Consideration of the state of the wireless link, SNR, and path loss for routing improves the efficiency of the routing protocol.

• Load location-dependent for channel contention: The high contention for the channel results in a high number of collisions. A good routing protocol should distribute the network load uniformly.

• Constraints on resources such as computing power, battery power, and buffer storage limit the capability of a routing protocol.


Routing Protocol RequirementsRouting Protocol Requirements

• Minimum delay for route discovery• Route reconfiguration must be fast (when topology changes).• Loop-free routing: Correct transient loops in the route, due to the

random movement of nodes.• Minimum control overhead for finding a new route and maintaining

existing routes. The control packets consume bandwidth and can cause collisions with data packets.

• Scalability• Provisioning of QoS: The QoS parameters can be bandwidth,

delay, jitter, packet delivery ratio, and throughput. – Supporting differentiated classes of service.

• Security and privacy to avoid resource consumption, denial-of-service, impersonation.


PART 2PART 2

Wireless Physical Technology


OutlineOutline

• Electromagnetic spectrum, Frequency bands and uses• Radio propagation mechanisms• Modulation techniques• Multiple access techniques


8

0 2 4 6 8 10 12 14 16 18 20 22 24

8 6 4 2 0 2 4 6 8 10 12 14 16

3 10

10 10 10 10 10 10 10 10 10 10 10 10 10

10 1

( )

0 10 10 10 10 10 10( ) 10 10 10 10

/

10

m

Frequency H z

W avelengt

s

h m

c fλ− − − − − − − −

= ×=

Band NameBand Name FrequencyFrequency WavelengthWavelength ApplicationsApplicationsExtremely Low Frequency (ELF)

30 to 300 Hz 10,000 to 1,000 Km

Power-line frequencies

Voice Frequency (VF) 300 to 3,000 Hz 1,000 to 100 Km Telephone communications

Very Low Frequency (VLF) 3 to 30 KHz 100 to 10 Km Marine communicationsLow Frequency (LF) 30 to 300 KHz 10 to 1 Km Marine communicationsMedium Frequency (MF) 300 to 3,000 KHz 1,000 to 100 m AM broadcastingHigh Frequency (HF) 3 to 30 MHz 100 to 10 m Long-distance aircraft/ship

communicationsVery High Frequency (VHF) 30 to 300 MHz 10 to 1m FM broadcastingUltra High Frequency (UHF) 300 to 3,000 MHz 100 to 10 cm Cellular telephoneSuper High Frequency (SHF)

3 to 30 GHz 10 to 1 cm Satellite communications, microwave links

Extremely High Frequency (EHF)

30 to 300 GHz 10 to 1 mm Wireless local loop

Infrared 300GHz to 400 THz 1 mm to 770 nm Consumer electronicsVisible Light 400THz to 900THz 770nm to 330nm Optical communications

Radio Microwave Infrared L U X-ray G-ray


Electromagnetic SpectrumElectromagnetic Spectrum

• Radio waves: – Easy to generate,– Ability to pass through buildings,– Ability to travel long distances.– At low frequencies the waves can pass

through obstacles easily,– At higher frequencies waves are more prone

to absorption by rain drops, and get reflected by obstacles,

– Interference problem.


LOS

Transmitter

Source [1]

RADIO PROPAGATION MECHANISMSRADIO PROPAGATION MECHANISMS


Characteristics of the wireless channelCharacteristics of the wireless channel

• Environmental conditions• Fast (Small-Scale) Fading • Slow (Large-scale) Fading

• Doppler Shift

• Path Loss• Interference• Reflection• Diffraction• Scattering• Blockage• Mobility

• Range• Data rate• Reliability

dfυλ

=


DiversityDiversity

• A diversity scheme refers to a method for improving the reliability of a message signal by utilizing two or more communication channels with different characteristics, in order to combat fading and interference. The independent paths can be distinct in T/F/S, or polarization.– Time: Direct sequence spread spectrum – Frequency: Frequency hopping spread spectrum– Space: Antenna array

• Aim at spreading the data over T/F/S so that the effects of burst errors are minimized.


DistributionDistribution

• Rayleigh: If there is no line-of-sight path between the transmitter and the receiver (outdoor).

• Ricean: if one such path is available (indoor).


• Ratio of the power of the transmitted signal to the power of the received signal on a given path.

• Function of:– propagation distance,– Frequency

• Propagation Model– Free Space Model

– Two Path Model

– General case:Isotropic Antennas

2

22

2

( )4

( )

1( ) 2 54

r t t r

t rr t t r

r t t r

P PG Gd

h hP PG Gd

P PG Gd γ

λπ

λ γπ

=

=

= ≤ ≤

Path LossPath Loss


InterferenceInterference• Adjacent channel interference: Avoided by guard bands. • CO-channel (Narrow-band) interference: due to other

nearby systems (say, AM/FM broadcast) using the same transmission frequency.– Minimized with the use of multi-user detection mechanism,

directional antennas, and dynamic channel allocation methods.• Inter-symbol interference: When distortion in the

received signal (caused by the temporal spreading and the consequent overlapping of individual pulses) in the signal goes above a certain limit (symbol detection time), the receiver unable to reliably distinguish between changes of state in the signal. – Adaptive equalization: Correct, or make equal, the frequency

response of a signal (applied as a general term for filters). Estimate channel pulse response to periodically transmitted well-known bit patterns, known as training sequences.


Maximum Data RateMaximum Data Rate

• Nyquist's theorem: Used for a noiseless channel. Maximum data rate (channel capacity) possible on a

channel: C = 2B log2L bits/sec

– L is the number of discrete signal levels/voltage– B is the bandwidth of the channel (in Hz)

• Shannon's theorem: Used for noisy channel. SNR = 10 log10(S/N)C = B ld(1+ (S/N)) bits/sec


Transceiver/ReceiverTransceiver/Receiver

CodingInter-leaving

Symbol mapping

Pilot insertion S/

P

IFFT

CP/

Win

dow

ing

Ove

rlap/

Add

DAC RF TX

DecodingDeinter-leaving

Symbol demapping S/

P

FFT

Equa

liser

Synch ADC RF RXP/

S

TransmitterTransmitter

Coherent ReceiverCoherent Receiver


Modulation TechniquesModulation Techniques

• Analog Modulation:– AM: Creates sidebands (additional unwanted signals in

frequencies on either side of the carrier), lead to poor spectrum utilization, and they consume additional power.

• SSB (Single Side Band): sidebands are stripped away on one side, used in place of plain AM & Broadcast radio.

– FM: Random interference affects more the amplitude of a signal rather than its frequency. Thus the SNR for an FM wave is higher than that for an AM wave. Used in radio broadcasts and first-generation cellular phones.

– PM• Digital Modulation: ASK, FSK, PSK


FMS

Ф’(t) α information signal/modulating signal nf: frequency modulation index

'

( ) [cos(2 ) ( )]

( ) ( )c c

f

s t A f t t

t n x t

π= +Φ

Φ =

( ) (1 ( )) cos(2 ) sa c a

c

As t n x t f t nA

π= + =

Amplitude Modulation Signal

Carrier Signal

Information Signal

( ) cos(2 )cc t f tπ=

( )x t

40Introduction to MANETDPSK Modulation

BPSK Modulation

BFSK Modulation:

BPSK Modulat

( ) cos(2 ), 10, 0

( ) cos(2 ( ) ), 1cos(2 ( ) ), 0

( ) cos(2 ), 1cos

ASK Modu

(2 )

lation

io :

:

,

n

c c

c c

c c

c c

c c

s t A f t for binaryfor binary

s t A f k t for binaryA f k t for binary

s t A f for binaryA f t for binary

π

ππ

π ππ

==

= += −

= += 0

BFSK Modulation

ASK Modulation

Bit String

Differential PSK: 1 is represented by the presence of a carrier signal whose phase has been changed relative to the phase of the carrier used for representing the previous bit.


Gaussian MSK (GMSK)Gaussian MSK (GMSK)

• Minimum Shift Keying (MSK): FSK modulation with a minimum tone distance of 1/2T, where T is the duration of each transmitted bit.

• GMSK: In order to reduce side bands, the baseband signal to be transmitted is filtered (with Gaussian filters) before the frequency shift keying process. – Used in GSM.

• GFSK is an FSK technique in which the data to be transmitted is first filtered in the baseband by means of a Gaussian filter, and is then modulated by simple frequency modulation. – A two-level or four-level GFSK is used in the IEEE 802.11


( ) c o s ( 2 ) , 1 043c o s ( 2 ) , 1 14

5c o s ( 2 ) , 0 14

7c o s ( 2 ) , 0 04

c c

c c

c c

c c

s t A f fo r b in a r y

A f t fo r b in a r y



ππ

ππ

ππ

ππ

= +

= +

= +

= +

• Uses four different phases each separated by radians.

• Enable transmission of two bits per phase shift.

2π

QuadratureQuadrature Phase Shift Keying (QPSK)Phase Shift Keying (QPSK)


• DPSK Advantage: Used for self-clocking, since phase differences occur continuously for long runs of 1s.

• In standard DQPSK, a long run of 0s at the data input would result in a signal with no phase shifts at all, which makes synchronization at the receiver very difficult. If -DQPSK is used in such a situation, the phase shift of ensures that there is a phase transition for every symbol, which would enable the receiver to perform timing recovery and synchronization.

• -PSK: 4-level PSK technique, each phase shift represents two bits. – Used for self-clocking, since there is always a phase shift

between the transmissions of consecutive bits. • Quadrature Amplitude Modulation (QAM): Possible to

encode several bits (16-QAM, 64-QAM).– Susceptible to errors, due to noise and distortion.

OtherOther PSK TechniquesPSK Techniques

/4π/ 4π

/4π


/45 /4

/45 /4

ππππ

−−

shifted PSK mechanism for a bit string 110001.

0001

10

11

/4π

5 / 4 / 4 5 / 4phaseshift phaseshift phaseshiftπ π π−

Constellation pattern in 8-QAM

111 110 000 001

010

011

101

100


Multiple Access TechniquesMultiple Access Techniques

• Multiple access techniques are used to control access to the shared channel.

• SDMA: uses directional transmitters/antennas to cover angular regions (best suited to satellite systems).

• FDMA• TDMA• CDMA


FDMAFDMA• Available bandwidth is divided into multiple

frequency channels/bands. A transmitter-receiver pair uses a single dedicated frequency channel for communication.– Disadvantage: Frequency bands are separated from

each other by guard frequency bands in order to eliminate inter-channel interference.

Source [1], [8]


Cellular NetworkCellular Network--FDMAFDMA

• BS dynamically allocates a different carrier frequency to MS.

• Used for two-way Communication (uplink and downlink), is called frequency division duplex (FDD).

• Since high-frequency transmissions suffer greater attenuation when compared to low-frequency transmissions, high transmission power is required for high-frequency channels for compensating the transmission losses.

• Power available at an MS is limited. Hence, the uplink frequency is always lower than the downlink frequency.


Orthogonal Frequency Division MultiplexingOrthogonal Frequency Division Multiplexing• OFDM spreads data over multiple simultaneous carriers, each of

them being modulated at a low rate. • It reduces the signal distortion at the receiver caused due to multi-

path propagation of the transmitted signal. • By appropriately choosing the frequency spacing between the sub-

carriers; the subcarriers are made orthogonal to each other.– Orthogonality of the sub-carriers ensures error-free reception at the

receiver. • Used in WLANs and digital broadcasting.• Facilitates use of adaptive modulation techniques• Simple integration with MIMO Source [8]


Time Division Multiple AccessTime Division Multiple Access

• TDMA shares the available bandwidth in the time domain. Each frequency band is divided into several time slots (channels).

• Each node is assigned one or more time slots in each frame, and the node transmits only in those slots.

• Uplink and downlink time slots, used for transmitting and receiving data, respectively, – can be on the same frequency band, called time division duplex - TDMA

(TDD-TDMA);– or on different frequency bands, called frequency division duplex -

(FDD-TDMA). • Require perfect synchronization.• High Overhead: To prevent synchronization errors and inter symbol

interference due to signal propagation time differences, guard intervals are introduced between time slots.

• TDMA is widely used in second generation cellular systems such as GSM, because of low cost.


Code Division Multiple AccessCode Division Multiple Access

• Each transmitter has a unique code that is independent of the data being transmitted.

• The orthogonality of the codes enables simultaneous data transmissions from multiple users using the entire frequency spectrum.– Frequency hopping spread spectrum;– Direct sequence spread spectrum.


FHSSFHSS

• The transmission switches across multiple narrow-band frequencies in a pseudo-random manner, that is, the sequence of transmission frequencies is known both at the transmitter and the receiver, but appears random to other nodes in the network.

• Fast FHSS: The rate of change of frequencies is much higher than the information bit rate, resulting in each bit being transmitted across multiple frequency hops.

• Slow FHSS: Multiple bits are transmitted on each frequency hop.

• FHSS is used mainly for short-range radio signals.


FHSSFHSS• The transmission switches across multiple narrow-band

frequencies in a pseudo-random manner. Sequence of transmission frequencies is known both at the transmitter and the receiver, but appears random to other nodes in the network.

• Fast FHSS: The rate of change of frequencies is much higher than the information bit rate.

• Slow FHSS: Multiple bits are transmitted on each frequency hop.

• FHSS is used mainly for short-range radio signals.

Transmission 1

Transmission 2

Source [1]


DSSSDSSS

• Like conversation with different languages in a room.• In DSSS, each node is assigned a specific n-bit code,

called a chipping code. n is known as the chipping rate of the system. These codes assigned to the nodes are orthogonal to each other, that is, the normalized inner product of the vector representations of any two codes is zero. Each node transmits using its code. At the receiver, the transmission is received and information is extracted using the transmitter's code.

• DSSS is used in all CDMA cellular telephony systems.


DSSSDSSS• Like conversation with different languages in a room.• In DSSS, each node is assigned a specific n-bit code,

called a chipping code. n is known as the chipping rate of the system. These codes assigned to the nodes are orthogonal to each other, that is, the normalized inner product of the vector representations of any two codes is zero. Each node transmits using its code. At the receiver, the transmission is received and information is extracted using the transmitter's code.

• DSSS is used in all CDMA cellular telephony systems.

Bit pattern to be transmitted

Chipping sequence

DSSS signal

Source [1]


Complementary code keying (CCK)Complementary code keying (CCK)

• A modulation technique used in conjunction with DSSS. • A set of 64 8-bit code words is used for encoding data

for the 5.5 Mbps and 11 Mbps data rates in the 2.4 GHz band of the IEEE 802.11 wireless networking standard.

• Sophisticated mathematical formulas are applied to the DSSS codes, which permit the codes to represent a greater amount of information in each clock cycle. The transmitter can now send multiple bits of information through each DSSS code, which makes it possible to achieve the 11 Mbps data rate.


ReferenceReference

[1] C. Siva Ram Murthy and B.S. Manoj: Ad Hoc Wireless Networks - Architecture and Protocols. Prentice Hall PTR, 2004.

[2] "IETF MANET Working Group Information," http://www.ietf.org/html. charters/manet-charter.html

[3] Y. D. Lin and Y. C. Hsu, "Multi-Hop Cellular: A New Architecture for Wireless Communications," Proceedings of IEEE INFOCOM 2000, pp. 1273-1282, March.

[4] A. N. Zadeh, B. Jabbari, R. Pickholtz, and B. Vojcic, "Self-organizing Packet Radio Ad Hoc Networks with Overlay," IEEE Communications Magazine, vol. 40, no. 6, pp. 140-157, June 2002.

[5] R. Ananthapadmanabha, B. S. Manoj, and C. Siva Ram Murthy, "Multi-Hop Cellular Networks: The Architecture and Routing Protocol," Proceedings of IEEE PIMRC 2001, vol. 2, pp. 78-82, October 2001.

[6] H. Wu, C. Qiao, S. De, and 0 . Tonguz, "Integrated Cellular and Ad Hoc Relaying Systems: iCAR," IEEE Journal on Selected Areas in Communications, vol. 19, no.10, pp. 2105-2115, October 2001.

[7] Dipl. Ing. SINGER Michael, Mobile Computing, Vienna University of Technology, Institute for Information system.

[8] Gerald Matz, Wireless OFDM Systems, Institute of Communications and Radio-Frequency Engineering, Vienna University of Technology.

http://www.ietf.org/html

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