Aircraft systems

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Written at on English with a size of 112.13 KB.

Basic Concepts

  • Various Wireless Spectrums: range, data rate, frequency, technologies

  • Wireless technologies: WHAN, WPAN, WLAN, WMAN, WWAN

  • Cellular Networks: 0g, 1g, 2g, 3g, 4g

  • Bandwidth

Data rate, frequency, channel width

• Throughput
Bandwidth, data rate, output, goodput, as well as link, path, system throughput

  • Throughput is achievable data rate

  • Capacity is the maximum throughput

  • Wireless is primarily in Layers 1 and 1⁄2

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Wireless Communications versus Wireless Network

– Wireless Communications

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Wireless traditionally deals with layers 1 and 2

L1:signalstrength,propagations,fading,reflection,Modulationand Coding methods, , Antenna enhancements, Omnidirectional, MIMO

L2:MediumAccessmethods,TDMA,CDMA,FDMA,

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Wireless Communications versus Wireless Network

– Wireless Networks
More recently looking at other aspects of the network, L1 through L7 L3:Networking,adhoc,sensor,meshnetworks
L4L6: New protocols across all layers
L7: contemporary and future wireless and mobile applications

Spectrum
Wireless Spectrum, range, data rate, frequency, technologies

  • Range: Inside‐a‐room (meters), in‐the‐building(10's of meters), on‐ campus(100's of meters), in‐the‐city(Km's), outside‐the‐city(100's Km's), Satellite(1000's Km's)

  • Capacity: bps, Kbps, Mbps, Gbps

  • Frequencies (band, Hz): Radio ( 10K‐100M), Microwave (100M‐100G), Hz,

    MHz, GHz, ....

    Wireless technologies: W‐ HAN, PAN, LAN, MAN, WAN

Bluetooth, IR, ZigBee, RFID, WiFi, WiMAX, Cellular, Satellite, Adhoc, Mesh, Sensor

Cellular Networks: 0g, 1g, 2g, 3g, 4g

AMPS, GSM, GPRS, UMTS, CDMA2000, HSPA, LTE
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WPAN

Wireless Technology Spectrum

Bluetooth, IR, ZigBee, RFID
WLAN
WiFi, HIPERLAN, WaveLAN and RangeLAN, IR WMAN
WiMAX, LTEng
WWAN
Cellular, AMPS, GSM, GPRS, UMTS, CDMA2000, LTE Others
Satellite, Adhoc, Mesh, Sensor

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Range/rate

Network

Area

FreqSpectrum

Example

Modulation

Standard

Issues

5 – 10 m

8 devices

piconet

Wireless Technologies Spectrum

WPAN

Unlicensed/2.4GH

Bluetooth

FHSS

802.15

Same freq as .11

BSS/ESS

WLAN

~ 100 – 200 m/

100’s

Unlic/2.4, 5GH

WiFi .11

TDMA/CDMA

802.11

Low range, no QoS/sec

Cell

WMAN

City/ 50mbps

100’s

2‐11, 10‐66

WiMAX

OFDM/MIMD

802.16

Speed ↓ dist ↑

Cell

GSM/LTE

WWAN

City and more/ 15kb/s

1000’s

TDMA/CDMA

3GPP

Low data rate High cost

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WPANs

  • Bluetooth uses a radio modules and link Managers to establish communication among Peers

  • Typical range for the use of Bluetooth is inches To feet

  • Automatic connections between Bluetooth Devices create a piconet

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WLANs

  • WLAN uses an access point to facilitate communication Between wireless computers

  • The IEEE standard for WLAN is 802.11b/g/a/.....

  • The IEEE 802.11n is the latest WLAN standard

  • .11n provides data transmission speeds up to 600 Mbps with A range of over 300 feet

  • .11i: Wireless Networks including WLAN use WEP, WPA, and WPA2 protocol for security

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Wireless Cellular Networks (WCN)

  • Cellular telephone networks are built on lowpower transmitters built on towers that can reuse the same radio frequency channel

  • 4G cellular network uses digital transmission For voice and data and can reach rates up to 150 Mbps

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WPAN Others Bluetooth RFID Zigbee

WLAN
WiFi
HomeRF

IR

Others
WLL
Cordeless HIPERLAN

Adhoc Mesh Sensor

Others WRAN WBA

WiMAX 802.16 802.16d 802.16e 802.16j 802.16m

Cellular
AMPS
GMS
GPRS
UMTS
CDMA2000. HSPA

Wireless Technology Spectrum

‐ ‐

IR

Satellite LEO

MEO GEO

IR
2m 4m 10m 100m 200m 300m 500m 1k 5K

LTE LEOMEO GEO 50K 70K 100K 1000K 6M 12M 16M

1g 2g 2.5 3g e.3g 4g

1
9
64K 3842M 20M1Gb

64144K

802.11n

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10Kb/s

384K20M

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Unified Wireless Spectrum Streams

WLAN IR UHF

2G 1G

(900MH, 2.4/5GH)

WiFi-ac/ad WiMAX-m nG HSPA/LTE-a

4G 3G

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λ = c/f, c ~=300k

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Frequency Spectrum

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Bandwidth Spectrum Wider bandwidth, higher data rate

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Wireless devices and applications

  • Wireless NIC (wNIC) is built into a laptop send data over Radio between devices

  • New applications can be used to run VoIP over WiFi and Avoid buying cellphones

  • Digital convergence refers to the combining of voice, Video and textprocessing and access to multiple network Platforms from a single device

  • Satellites, WLANs and Cellular systems often use Repeaters

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Wireless Issues

Wireless Issues

Signal propagation, fading, noise, interference, contention, LOS, medium Access, range, data rate, QoS, performance, ...

Layered related • Physical layer

Signals, channels, antenna • MAC layer

Medium access, Security, QoS • Network layer

Routing, IP
• Application layer

Applications, performance • Cross layer

Wireless Communications versus Networks

  • PHY‐MAC versus PHY‐APP layers

  • Signal versus equipment

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Resolving Wireless Issues

Research areas to mitigate issues and improve

  • Data rate (bandwidth, throughput, traffic), all means Capacity

  • Range, Coverage area, Reachability

  • Availability

  • Signal quality (SNR, SIR)

  • Security

  • Quality of Service

  • Applications

  • Price/Revenue

  • Easy deployment

  • Scalability, Robustness

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Wireless Standardization

  • Each type of technology there is 1standard groups (ieee, ietf,...) and a 2special interest group (industry, forums)

  • 1 is more concerned with lower layer 1, 2, 3, since must follow Rules/regulations, (the essence of technology)

  • 2 is more concerned with all layers (1‐7), commercial products, diff. Flavors, market... (applications...)

  • Standard bodies

  • Working Groups

  • Special Interest Groups

  • Forums

  • Alliances

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IEEE: Institute of Electrical and Electronics Engineers ETSI: European Telecommunications Standards Institute IETF: Internet Engineering Task Force
ITU: International Telecommunication Union
3GPP: 3rd Generation Partnership Project (based on UMTS)
3GPP2: 3rd Generation Partnership Project (based on UMTS(based on CDMA2000)
TTC: Telecommunications Technology Committee Local: Japanese, Chinese, Koreans, Brazilian’s ...... OMA: Open Mobile Alliance
LTE forum, WiMAX Forum

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Other wireless technologies

  • UWB uses a maximum range of about 10 meters, can Transmit up to 10 Gbps, for VoIPoW

  • WiMax is a communication technology that could Connect offices over 3 miles away from each other at Speeds over 70 Mbps using smart antennas

  • WiMAX is a replacement for ISDN technology ,

  • ISDN uses regular phone lines and transmits at speeds up

    to 256 Kbps

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Other wireless technologies

  • RFIDtagsareoftenfoundaroundthehouseon Product packages

  • NFC(NearFieldCommunication)isashortrange Wireless RFID technology

  • NFCmakesuseofinteractingelectromagneticradio Fields instead of the typical direct radio Transmissions used by other wireless technologies

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Basic Communication Concepts Signal: transmitter inside AP generate AC‐signalcreate wave

antenna  sin‐wav
Current changes electromagnetic field around antennasend

electric/magnetic signal

λ: the length between two repeating points

  • WLAN 15 cm

  • AM 500m

  • Satellite 6 cm (>SHF)

    F: rate of vibration of wave (sound, electromagnetic field, radio, light) A

A: amplitude is amount of energy put into a signal

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B

2 signals with Same F/ λ, more energy

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Hertz:

Basic Communication Concepts

  • Electromagnetic waves travel like light waves (carry electricity on them)

  • Idea for transferring data as electrical signal wirelessly

  • RF tries to send as much data as far as possible

    To send data over electromagnetic waves:

    • Use frequencies 3Hz – 10 Hz

3Hz 10KHz 100MHz 100GH 300GH 1012 1015 1024

|||||| ||||

Voice (phone) Radio Microwave IR IR

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Light/UV/X/

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Frequency vs. Channel bw
Each frequency range is divided into channelssub‐carriers

2.4 GHz: freq.Bw
Freq. Bw. (2.4GH = 2.48)

ch. Bw 2.4 ‐ 2.41 ‐ 2.42

.......
‐ 2.48

Ex: 900‐MH cordless = [902–928 MHz]
• 26MHz could be divided to several non‐overlapping ch. Frequencies

so in cordless phone could change the channel to avoid interfering Neighbors

changingthech.Issimplyusingdifffreqinthesamerange

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Channel Width and Bandwidth

  • Ex: .11b/g/n use 2.4GH‐freq = 2.4–2.4835 GH
    = 0.0835GH = 83.5MHz

  • If we divide 83.5 MHz to 11 channels/each 22MHz bandwidth

  • 1overlaps2,3,4,5,butnot6,Sowehave1,6,11non‐

    overlapping non‐interference

  • Why not use smaller ch. / more non‐overlap?

  • Because 22MHz gives higher speed / more data rate / better Quality so it’s trade‐off.

22 22 22

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Wider channel more bandwidth

More data on a signal more freq. Bw or bigger freq. spectrum Used (bitsMb, Gb)
bw = datarate and RFChwidth

= # of cycles/sec = Hz , 1Hz = 1 cycle/sec

More bw = higher Hz = more data rate = better quality signal

  • Smallest = CB (citizens’ band) = 3KHz, low quality

  • FM = better quality

  • TV = voice + video ~ 4.5MHz

  • New wireless tech = 20‐40MHz

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Use RF signal to deliver data

To get bw from RF signalsend data as an electrical signal using An emission method
Emission method like spread spectrum (ex: SS of 15MHz freq. Bands)

To place data on RF (carrier) use modulation

Modulation is adding data to a carrier signal using characteristics of the Wave such as frequency (FM) or Amplitude (AM)

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Transmission Fundamentals

  • Basic transmission topics

  • Data communications concepts
    Includestechniquesofanaloganddigitaldatatransmission Channelcapacity
    Transmission media
    Multiplexing

  • Electromagnetic Signal
    Functionoftime
    Canalsobeexpressedasafunctionoffrequency

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Signal consists of components of different frequencies

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TimeDomain Concepts

  • Analog signal:
    Signalintensityvariesinasmoothfashionovertime Nobreaksordiscontinuitiesinthesignal

  • Digital signal:
    Signalintensitymaintainsaconstantlevelforawhile Thenchangestoanotherconstantlevel

  • Periodic signal ‐ analog or digital signal pattern that repeats over time

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s(t +T ) = s(t ) 1< t < +1 where T is the period of the signal

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TimeDomain Concepts

  • Aperiodic signal:
    Analogordigitalsignalpatternthatdoesn'trepeatovertime

  • Peak amplitude (A):
    Maximumvalueorstrengthofthesignalovertime;typically

    measured in volts

  • Frequency (f ):
    Rate,incyclespersecond,orHertz(Hz)atwhichthesignalrepeats

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TimeDomain Concepts

  • Period (T ) ‐ amount of time it takes for one repetition of the signal

    T=1/f

  • Phase () ‐ measure of the relative position in time within a single period

of a signal

• Wavelength ()

  • –  Distanceoccupiedbyasinglecycleofthesignal

  • –  Distancebetweentwopointsofcorrespondingphaseoftwo Consecutive cycles

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Sine Wave Parameters

  • General sine wave
    s(t)=Asin(2ft+)

  • Effect of varying each of the three parameters (a)A=1,f=1Hz,=0;thusT=1s
    (b)Reducedpeakamplitude;A=0.5
    (c)Increasedfrequency;f=2,thusT=1⁄2
    (d)Phaseshift;=/4radians(45degrees)

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Sine Wave Parameters

Frequency-Domain Concepts

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Frequency-Domain Concepts

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Relationship between Data Rate and Bandwidth

• The greater the bandwidth, the higher the information-carrying capacity • Conclusions

Anydigitalwaveformwillhaveinfinitebandwidth(bw)
Butthetransmissionsystemwilllimitthebwthatcanbetransmitted
Foragivenmedium,thegreaterthebwtransmitted,thegreaterthecost Limitingthebandwidthcreatesdistortions
Soshouldfindabalance,orfindarangeofbwtobeused

Example: Approximate Digital signal,

1 and 0, Using analog

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Approximation using 3f, And f = 2MHz

  • Fundamental frequency = f

  • Absolute frequency = 3f – f = 2f

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Approximation using 3f, and f=2MHz Measure channel width and data rate

  • Fundamental frequency = f = 2MHz

  • Absolute frequency = 3*f – f = 2f= 4MHz channel width

  • T = 1/f = 1⁄2x 106 sec = 0.5 x 10-6 sec = 0.5 μs

  • Digital 1 and 0 takes 1⁄2(t)=1/2(0.5) = 0.25 μs for 1 bit, or

    4Mbps

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Approximation using 5f, and F=1MHz

  • Fundamental frequency = f=1MHz

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Approximation using 5f, and f=1MHz Measure channel width and data rate

  • Fundamental frequency = f = 1MHz

  • Absolute frequency = 5f – f = 4f=4MHz channel width

  • T = 1/f = 10-6 sec = 1 μs

  • Digital 1 and 0 takes 1⁄2(t)=1/2(1) = 0.5 μs for 1 bit, or 2Mbps

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Approximation using 5f, and F=2MHz

  • Fundamental frequency = 2MHz

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Approximation using 5f, and f=2MHz Measure channel width and data rate

  • Fundamental frequency = f = 2MH

  • Absolute frequency = 5*f – f = 4f=4*2MHz=8MHz channel

    width

  • T=1/2f=1⁄2(10-6)sec=0.5μs

  • Digital 1 and 0 takes 1/4(t)=1/2(0.5) = 0.25 μs for 1 bit, or 4Mbps

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Data Communication Terms

  • Data - entities that convey meaning, or information

  • Signals - electric or electromagnetic representations of data

  • Transmission - communication of data by the propagation and Processing of signals

  • Examples of Analog and Digital Data

  • Analog Video Audio

  • Digital Text

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Analog Signaling

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Digital Signaling

Reasons for Choosing Data and Signal Combinations

  • Analog data, analog signal

    Analog data easily converted to analog signal, example POTS

  • Digital data, analog signal
    Some transmission media will only propagate analog signals Examples include wireless, optical fiber and satellite

  • Analog data, digital signal
    Conversion permits use of modern digital transmission and switching

    equipment, example sending voice over IP

  • Digital data, digital signal
    Equipment for encoding is less expensive than digitaltoanalog equipment

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About Channel Capacity

• Impairments:
Noise,limitdataratethatcanbeachieved

  • Digital data:
    Towhatextentdoimpairmentslimitdatarate?

  • Channel Capacity:
    Maximumrateofdatatransmission

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Overcommunicationpathorchannel Undergivenconditions

Nyquist Bandwidth

  • For binary signals (two voltage levels)

    C=2B

  • With multilevel signaling C=2Blog2M

    M = number of discrete signal or voltage levels

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Signal-to-Noise Ratio

  • Ratio of the power in a signal to the power contained in the Noise:

    • –  At a particular point in the transmission

    • –  Typically measured at a receiver

    • –  Signal-to-noise ratio (SNR, or S/N)

  • A high SNR:

– –

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High-quality signal, low number of required intermediate repeaters SNR sets upper bound on achievable data rate

(SNR) 10 log dB 10

signal power Noise power

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Equation:

Shannon Capacity Formula C Blog21SNR

  • Represents theoretical maximum that can be achieved

  • In practice, only much lower rates achieved
    Formulaassumeswhitenoise(thermalnoise)
    Impulsenoiseisnotaccountedfor
    Attenuationdistortionordelaydistortionnotaccountedfor

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Example of Nyquist and Shannon Formulations

How many signaling levels are required?

C 2B log2 M

8106 2106log M 2

4log2 M M 16

PHY and MAC layer Concepts

Signals and Antenna Modulation and Coding

ASK, PSK, FSK

Spread Spectrum

DSSS, FHSS

Medium Access

TDM, FDM, OFDM, CDM

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PHY:

PHY and MAC layer concepts

  • How to use the medium, signals, and carry data over signal • Antenna

    • Modulation and Coding Schemes

    • ASK, FSK, BPSK, QPSK, QAM

  • How to spread the data over signal

DSSS and FHSS MAC:

  • How to access the medium

  • Multiplexing and Multiple Access

  • TDM, TDMA

  • FDM, FDMA

  • CDM, CDMA

  • OFDM, OFDMA

    • IneachTechnologywhichPHYandMAClayerscheme
    Is used 74

  • FDM: Frequency Division Multiplexing

  • OFDM: Orthogonal Frequency Division Multiplexing

  • OFDMA: Orthogonal Frequency Division Multiple Access

  • SOFDMA: Scalable OFDMA

  • FFT: Fast Fourier Transform

  • IFFT: Inverse Fast Fourier Transform

  • ISI: Inter Symbol Interference

  • UL: UpLink

  • DL: DownLink

  • BS: Base Station

  • MS: Mobile Station

  • SNR: Signal‐to‐Noise Ratio

MIMO: Multiple Input and Multiple Output

MISO: Multiple Input and Single Output

SIMO: Single Input and Multiple Output

SISO: Single Input and Single Output

Modulation schemes:

  • ASK, FSK, BPSK, QPSK

  • PSK: Phase Shift Keying

  • QAM: Quadrature Amplitude Modulation

    Spread Spectrum Schemes:

    • DSSS • FHSS

Acronyms

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Antenna

  • An antenna is an electrical conductor or system of conductors Transmission - radiates electromagnetic energy into space
    Reception - collects electromagnetic energy from space

  • In two-way communication, the same antenna can be used for Transmission and reception

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Radiation Patterns

  • Radiation pattern
    Graphical representation of radiation properties of an antenna Depicted as two-dimensional cross section

  • Beam width (or half-power beam width)
    Angle of beam half of power of the direct beam Measure of directivity of antenna

  • Reception pattern
    Receivingantenna’sequivalenttoradiationpattern

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Types of Antennas

  • Isotropic antenna (idealized)

    Radiates power equally in all directions

  • Dipole antennas
    Half-wave dipole antenna (or Hertz antenna)
    Quarter-waveverticalantenna(orMarconiantenna)

  • Parabolic Reflective Antenna

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Radiation Pattern

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Radiation patter from different angles

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Parabolic Reflective Antenna

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• Antenna gain

Antenna Gain

Poweroutput,inaparticulardirection

Comparedtothatproducedinanydirectionbyaperfect Omnidirectional antenna (isotropic antenna)

• Effective area
Relatedtophysicalsizeandshapeofantenna

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Antenna Gain Calculation
Relationshipbetweenantennagainandeffectivearea

G=antennagain
Ae = effective area
f = carrier frequency
c = speed of light (3*108 km/s) = carrier wavelength

4A 4f2A ee

G
2 c2

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Propagation Modes

Ground-wave propagation Sky-wave propagation
Line-of-sight propagation

Transmit Antenna

Signal Propagation

Earth

Signal Propagation

Earth

Receiv Anten

Transmit Antenna

Signal Propagation

Earth

Receive Antenna

Transmit Antenna

Receive Antenna

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LOS Wireless Transmission Impairments

  • Attenuation and attenuation distortion

  • Free space loss

  • Noise

  • Atmospheric absorption

  • Multipath

  • Refraction

  • Thermal noise

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Multipath Propagation:

  • Three propagation mechanisms:

  • Reflection (R), Scattering (S), Diffraction (D)

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Coding and Modulations

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Signal Encoding Techniques

Modulation and Coding

  • Analog and digital data encoded to analog or digital signal

  • Optimize some characteristics, conserve bandwith, minimize Error, security, ......

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Modulation and Coding

4 different mapping or encoding:

1. Digital-to-digital 2. Digital-to-analog 3. Analog-to-analog 4. Analog-to-digital

2, 3, 4 in wireless communication
2 is most important in wireless networks

Analogdata(--digitized->)digitaldata
Digital data (--modulated->) analog signal

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Bits and bauds
Binary data transmitted by encoding each data bit into signal element

Data:

  • A one-to-one correspondence between bits and signal elements

  • Binary 0: represented by a higher voltage level, binary 1: lower voltage

    level

    Signal:

  • A digital bit stream encoded to analog signal as a sequence of signal Elements

  • Each signal element a pulse of constant frequency, phase, or amplitude

    One-to-one correspondence between: data elements (bits) and
    Analog signal elements (baud)

    » Not always, sometimes signals represent more bits

    Data rate: rate at which data are transmitted (bps)
    Modulation rate: rate at which the signal level is changed (sps or baud/s)

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Basic Encoding Techniques for Digital data to Analog signal

• Digital data to analog signal Amplitude-shiftkeying(ASK)

Amplitude difference of carrier frequency Frequency-shiftkeying(FSK)

Frequencydifferencenearcarrierfrequency

Phase-shiftkeying(PSK)
Phase of carrier signal shifted

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Basic Encoding Techniques

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Amplitude-Shift Keying

  • One binary digit represented by presence of carrier, at Constant amplitude

  • Other binary digit represented by absence of carrier

  • s(t) = cos 2 1

    0 0

    Where the carrier signal is Acos(2πfct), carrier frequency fc

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Binary Frequency-Shift Keying (BFSK)

  • Two binary digits represented by two different frequencies Near the carrier frequency

  • s(t) = cos 2 1 Cos 2 0

    where f1 and f2 are offset from carrier frequency fc by equal but Opposite amounts

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Multiple Frequency-Shift Keying (MFSK)

  • More than two frequencies are used

  • More bandwidth efficient but more susceptible to error • s(t)= cos2 1

    fi =fc +(2i–1–M)fd
    f c = the carrier frequency
    f d = the difference frequency
    M = number of different signal elements = 2 L L = number of bits per signal element

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Multiple Frequency-Shift Keying (MFSK)

• To match data rate of input bit stream, each output signal Element is held for:

Ts=LT seconds where T is the bit period (data rate = 1/T)

• So, one signal element encodes L bits

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Multiple Frequency-Shift Keying (MFSK) – Total bandwidth required : 2Mfd

Minimum frequency separation required: 2fd=1/Ts

– Therefore, modulator requires a bandwidth of BWd = 2L/LT = M/Ts

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Phase-Shift Keying (PSK) • Two-level PSK (BPSK)

Usestwophasestorepresentbinarydigits
Acos2f tbinary1

stAcos2fctbinary0 c

Acos2f tbinary1

c Acos2fctbinary0

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Phase-Shift Keying (PSK) • Differential PSK (DPSK)

Phase shift with reference to previous bit
Binary 0 – signal burst of same phase as previous signal burst
Binary 1 – signal burst of opposite phase to previous signal burst

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Phase-Shift Keying (PSK) • Four-level PSK (QPSK)

Eachelementrepresentsmorethanonebit

Acos2fct 4 11 3

stAcos2ft4
c 01

300 Acos2fct4


Acos2f t 4 10 c

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Phase-Shift Keying (PSK) • Multilevel PSK

– Using multiple phase angles with each angle Having more than one amplitude, multiple signals Elements can be achieved

DRR
L log2M

D = modulation rate, baud
R=datarate,bps
M = number of different signal elements = 2L L = number of bits per signal element

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Quadrature Amplitude Modulation • QAM is a combination of ASK and PSK

Twodifferentsignalssentsimultaneouslyonthesamecarrierfrequency std1tcos2fct d2 tsin 2fct

• Constellation diagram for PSK and QAM 8signalelement(0-2π)torepresent3bits
16QAMand64QAM

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Adaptive Modulation and Coding (AMC)

  • Modulations to add data to signal

  • Modulated signals are demodulated at the receiver to recover Original digital message

  • ASK, BFSK, FSK, BPSK, PSK, QPSK, MPSK, QAM, ......

    • Different order modulations to send more bits per symbol, higher

      throughput, better spectral efficiency

    • Trade off: distance, channel condition, complexity, throughput

    • QAM needs better SNR to overcome interference and maintain a certain Bit error ratio (BER)

    • The use of adaptive modulation allows a wireless system to choose the Highest order modulation depending on the channel conditions

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Adaptive Modulation and Coding (AMC)

  • General estimate of the channel Conditions needed for different Modulation techniques

  • Increased range, go to lower Modulations, such as BPSK

  • The closer to the BS, the higher order Modulations like QAM for increased Throughput

  • Adaptive modulation also overcome Fading and interference issues

105/80

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Spread Spectrum DSSS and FHSS

106/100

Spread Spectrum

  • What can be gained from apparent waste of spectrum? Immunityfromvariouskindsofnoiseandmultipathdistortion Hidingandencryptingsignals
    Severalusers:usesamehigherbandwidth,littleinterference

  • 2 types of SS:
    FrequencyHopingSpreadSpectrum(FHSS) DirectSequenceSpreadSpectrum(DSSS)

107/100

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Frequency Hoping Spread Spectrum (FHSS)

  • Signal is broadcast over seemingly random series of radio Frequencies

    AnumberofchannelsallocatedfortheFHsignal
    Widthofeachchannelcorrespondstobandwidthofinputsignal

  • Signal hops from frequency to frequency at fixed intervals Transmitteroperatesinonechannelatatime
    Bitsaretransmittedusingencodingschemes
    Ateachsuccessiveinterval,anewcarrierfrequencyisselected

    108/100

Frequency Hoping Spread Spectrum

  • Channel sequence dictated by spreading code

  • Receiver, hopping between frequencies in synchronization With transmitter, picks up message

    • Advantages

    Eavesdroppershearonlyunintelligibleblips

    Attemptstojamsignalononefrequencysucceedonlyatknocking Out a few bits

    109/100

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Frequency Hoping Spread Spectrum

110/100

Frequency Hopping

  • Total bandwidth divided into 1MHz physical channels

  • FH occurs by jumping from one channel to another in pseudorandom Sequence

  • Hopping sequence shared with all devices on BSS or piconet

  • Cell access:

    • –  Devices use time division duplex (TDD)

    • –  Access technique is TDMA FHTDDTDMA

Hopping from one frequency to the other, swap between master and slave

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MAC layer concepts

Medium Access Approaches

112/100

PHY/MAC/Medium Access/Interference

Various strategies and schemes in PHY and MAC layers to Deal with medium access and interference avoidance:

  • Contention based
    CSMA/DC and CA

  • Non-contention based

    • Polling

    • Scheduling(PHYandMAClayers)

    • Channelization

    • Multiplexing(Time,Code,Wavelengthand

      Frequency, ....)

113

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Methods for dividing and sharing the medium Duplexing Technique

• FDD/TDD

Multiplexing

• TDM/FDM/WDM

Multiple Access Method

  • TDMA, FDMA, CDMA

  • TDMA/OFDMA

  • OFDM Symbols allocated by TDMA

  • Sub-Carriers within an OFDM Symbol allocated by OFDMA

    Diversity

• Frequency, Time, Code (CPE and BS), Space Time Coding, Antenna Array

114/100

Medium Access categories

Medium Access

Contention based Non‐contention based

(ALOHA/CSMA)

Channelization

Multiplexing Multiple Access

(TDM/FDM) (TDMA/FDMA/CDMA)

Non‐channelization

Polling Scheduling

(rtPS, nrtPS) (PQ, WFQ)

115/100

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Contention-based Multiple Access(MA)

  • ALOHA

  • Slotted ALOHA

  • CSMA

  • CSMA/CD

  • CSMA/CA

  • PCF/DCF

  • RTS/CTS: Hidden Node and Exposed Node problem

  • Near and Far problem

116/100

Frequency, Timedivision Multiplexing

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117/100

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Multiple Access (MA)

  • General wireless cellular systems are multi-users systems

  • Radio resource are limited Limited Bandwidth
    Limitednumberofchannels

  • The radio resource must be shared among multiple users

  • Multiple Access Control (MAC) needed Contention-based
    Non-contention-based

Non-contention-based Multiple Access (MA)

  • A logic controller (BS or AP) is needed to coordinate the Transmissions of all the terminals

  • The controller informs each device when and on which Channel it can transmit

  • Collisions can be avoided entirely

  • Two Subdivisions

    • Non-channelization

    • Channelization

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Non-channelization Non-contention-based MA

• Terminals transmit sequentially using the same channel

• Example:
Pollingbasedmediumaccess

• Standard:

  • IEEE 802.15 (WPAN)

  • IEEE 802.11 (WLAN)

  • IEEE 802.16 (rtPS, ertPS, nrtPS)

120

Channelization Non-contention-based MA

  • Terminals transmit simultaneously using different channels

  • Most commonly used protocols in cellular systems

    • Example:

    1. Time Division Multiple Access (TDMA)

    2. Code Division Multiple Access( CDMA)

    3. Frequency Division Multiple Access (FDMA)

    • Standards

    1. GSM (TDMA)

    2. IS-95 (CDMA)

    3. AMPS (FDMA)

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Time

TDM TDMA

TDMAOFDM TDMAOFDMA

Multiplexing Medium Access

Frequency

MUX/DMUX/MA FDM FDMA OFDM OFDMA SOFDMA

Code

SCFDMA CDMA OCDMA

122

Multiple Access (MA)

  • General wireless systems are multi-users systems

  • Radio resource are limited

    • Limited Bandwidth

    • Limited number of channels

  • The radio resource must be shared among multiple users

  • Multiple Access Control (MAC) needed

    • Contention-based

    • Non-contention-based

123

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Time Division Multiple Access (TDMA)

• GSM

  • Time slot 0.577 ms

  • Frame 4.6 ms

  • 8 time slots per frame

  • Frequency band 20 KHz

124

Code Division Multiple Access (CDMA)

• IS-95

  • Orthogonal codes

  • 64 codes (channels)

    • –  One pilot channel

    • –  Seven paging channels

    • –  56 traffic channels

  • Each carrier 1.25 MHz

125

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Code-Division Multiple Access (CDMA)

  • Basic Principles of CDMA D=rateofdatasignal
    Breakeachbitintokchips

  • Chips are a user-specific fixed pattern Chipdatarateofnewchannel=kD

126/100

Frequency Division Multiple Access (FDMA)

• American Mobile Phone System (AMPS)

  • Total Bandwidth 25 MHz

  • Each Channel 30 KHz

127

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FDM

  • Signals from multiple transmitters are transmitted

    • At the same time slot

    • Over multiple frequencies

  • Each frequency range (sub-carrier):

    • Modulated separately for different data stream

    • Spacing (guard band) is placed between sub-carriers to avoid Signal overlap

      Spacing between adjacent sub‐carriers Frequency
      128

• • • • •

• •

OFDM

OFDM also uses multiple sub-carriers
Sub-carriers are closely spaced without causing interference Removes guard bands between adjacent sub-carriers

Frequencies (sub-carriers) are orthogonal

i.E. The peak of one sub-carrier coincides with the null of adjacent sub-carrier

High rate data stream is divided into multiple parallel low rate data Streams

Each smaller stream mapped to individual data sub-carrier Modulated using BPSK, QPSK, 16-QAM, or 64-QAM

Frequency
Closely spaced Sub‐carriers

129

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OFDMA

  • Multi-user version of OFDM digital modulation scheme

  • Multiple access is achieved in OFDMA using sub-channels

  • Sub-channel is a subset of subcarriers assigned to each user

  • This allows simultaneous low data rate transmission from several Users

    Frequency

    Each subcarriers includes several subchannel

130

OFDMA

  • OFDMA also uses multiple closely spaced sub-carriers

  • Sub-carriers are divided into groups (channels/sub-channels)

  • DL sub-channel: intended for different receivers

  • UL sub-channel: transmitter assigned one or more sub-channels

  • Pilots: measure channel condition, time and freq. Sync. (avoid ISI)

Pilot Sub‐Carrier

Sub‐Carrier for User 1

OFDMA Symbols

Source: Wikipedia

Sub‐Carrier for User 2

Guard band

131

Guard band: avoid overlap and interference

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OFDMA Operation

Sub-channels and Multiple Access:

  • Multiple access method based on OFDM signaling

  • Allows simultaneous transmissions to/from several users

  • Subcarriers are assigned to sub-channels that in turn can be allocated To different users

Provides high-granularity bandwidth allocation

Time

Frequency

Sub‐channel

132

  • Each terminal occupies a subset of Sub-carriers

  • Subset is called an OFDMA traffic Channel (sub-channel)

  • Each traffic channel is assigned Exclusively to one user at any time

    Example:

    The IEEE 802.16e/ WiMax uses OFDMA for Multiple Access:

user4 User3 User2

user1

OFDM-FDMA (OFDMA)

  • –  Bandwidth options 1.25, 5, 10, or 20 MHz

  • –  Entire bandwidth divided into 128, 512, 1024 or 2048 sub carriers

  • –  A subset of these sub-carriers is grouped into a sub-channel

  • –  20 MHz bandwidth with 2048 sub carriers has 9.8 KHz spacing between sub Carriers

    133/100

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OFDMA widespread

  • OFDMA is adopted by various new 4G wireless technologies

  • WiMAX air interface is based on OFDM/OFDMA PHY layer

• It is also used by:
IEEE802.16m,mWiMAX
IEEE802.20,mBWA
3GPP LTEAdvanced
HighSpeedOFDMPacketAccess(HSOPA),
EvolvedUMTSTerrestrialRadioAccess(EUTRA)
3GPP2UltraMobileBroadband(UMB)
IEEE802.22WirelessRegionalAreaNetworks(WRAN)

134/100

Multiple Access Methods

• Radio waves analogous to light or voice

Source: Nortel

135/100

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