Aircraft systems

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, good‐put, 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, Omni‐directional, 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,ad‐hoc,sensor,meshnetworks
• L4‐L6: 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, Ad‐hoc, 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, LTE‐ng
WWAN
• Cellular, AMPS, GSM, GPRS, UMTS, CDMA2000, LTE Others
• Satellite, Ad‐hoc, Mesh, Sensor

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Range/rate

Network

Area

Freq‐ Spectrum

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 low‐ power transmitters built on towers that can re‐ use 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

Ad‐hoc ‐ 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 384‐2M 20M‐1Gb

64‐144K

n

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10Kb/s

384K‐20M

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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 Wi‐Fi and Avoid buying cellphones

• Digital convergence refers to the combining of voice, Video and text‐processing 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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Frequency vs. Channel bw
Each frequency range is divided into channelssub‐carriers

GHz: freq.BwFreq. 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 = data‐rate and RF‐Ch‐width

= # 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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Time‐Domain 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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Time‐Domain Concepts

• Aperiodic signal:
  – Analogordigitalsignalpatternthatdoesn’trepeatovertime

• Peak amplitude (A):
  – Maximumvalueorstrengthofthesignalovertime;typically

  measured in volts

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

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Time‐Domain 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(2ft+)

• 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 digital‐to‐analog 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  Blog21SNR

• 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

8106 2106log M 2

4log2 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

4A 4f2A 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:

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
 Acos2f t binary1

st Acos2fctbinary0  c

 Acos2f t binary1

 c Acos2fct binary0

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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 

 Acos2fct  4  11  3

stAcos2ft 4
c 01

 3 00 Acos2fct 4 

 Acos2f 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

DR R
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 st d1tcos2fct  d2 tsin 2fct

• 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

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Spread Spectrum DSSS and FHSS

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Spread Spectrum

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

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

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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

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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

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Frequency Hoping Spread Spectrum

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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 – FH‐TDD‐TDMA

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

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MAC layer concepts

Medium Access Approaches

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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, ….)

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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

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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)

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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

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Frequency, Time‐division Multiplexing

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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)

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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

TDMA‐OFDM TDMA‐OFDMA

Multiplexing Medium Access

Frequency

MUX/DMUX/MA FDM FDMA OFDM OFDMA SOFDMA

Code

SC‐FDMA CDMA OCDMA

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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

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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

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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

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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

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Frequency Division Multiple Access (FDMA)

• American Mobile Phone System (AMPS)

• Total Bandwidth 25 MHz

• Each Channel 30 KHz

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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

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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 sub‐carriers includes several sub‐channel

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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

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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 LTE‐Advanced
– HighSpeedOFDMPacketAccess(HSOPA),
– EvolvedUMTSTerrestrialRadioAccess(E‐UTRA)
– 3GPP2UltraMobileBroadband(UMB)
– IEEE802.22WirelessRegionalAreaNetworks(WRAN)

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Multiple Access Methods

• Radio waves analogous to light or voice

Source: Nortel

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