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Analogue and Digital Communication Systems

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Analogue and Digital Communication Systems Analogue comms Digital Comms Cellular systems WiFi, Bluetooth, Satellite JianGuo Zhang Ya Bao Assessment: – PowerPoint PPT presentation

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Title: Analogue and Digital Communication Systems


1
Analogue and Digital Communication Systems
  • Analogue comms
  • Digital Comms
  • Cellular systems
  • WiFi, Bluetooth, Satellite

JianGuo Zhang
Ya Bao
Assessment 2-hour written examination 70 TWO
Lab reports 30
2
Wireless Communications
  • 1). Wireless Communication Technology
  • 2). Cellular System Design Fundamental
  • (0G-5G)
  • 3). WiMAX,
  • 4). Wireless LANs (WiFi)
  • 5). Bluetooth
  • 6). Satellite (GPS)

3
Reading list
  • William Stallings, Wireless Communications and
    Networks 2/e. 2005. Prentice Hall.   
  • T.S. Rappaport. Wireless Communications. 2/e. 
    2002. Prentice Hall. 
  • Official websites of 3GPP, WiMAX, LTE, WiFi,
    Bluetooth, IEEE, etc.  

4
wireless communications
  • First demonstration in a room in 1896 by G.
    Marconi. 12 miles in 1897 and across the English
    Channel (21 miles) in 1899. in 1901 Marconi sends
    the first signal across an ocean.

5
Wireless Comes of Age
  • Guglielmo Marconi invented the wireless telegraph
    in 1896
  • Communication by encoding alphanumeric characters
    in analog signal
  • Sent telegraphic signals across the Atlantic
    Ocean
  • Communications satellites launched in 1960s
  • Advances in wireless technology
  • Radio, television, mobile telephone,
    communication satellites
  • More recently
  • Satellite communications, wireless networking,
    cellular technology, WPAN, WLAN, WMAN and WWAN

6
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7
Broadband Wireless Technology
  • Higher data rates obtainable with broadband
    wireless technology
  • Graphics, video, audio, HD, 3D
  • Shares same advantages of all wireless services
    convenience and reduced cost
  • Service can be deployed faster than fixed service
  • No cost of cable plant
  • Service is mobile, deployed almost anywhere

8
Introduction to wireless telephone systems
  • Early Mobile Telephone System Architecture (after
    WWII)0G
  • powerful transmitter
  • Single central antenna and coverage (radius 50km)
  • High power consumption of mobile station

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10
Mobile Telephone Service(MTS)
  • 1947 ATT 
  • 5,000 customers placing about 30 000 calls each
    week
  • Equipment weighed about 36 kg
  • 1965 Improved Mobile Telephone Service
  • 40 000 customers
  • In New York, 2 000 customers shared just 12 radio
    channels
  • Wait 30 minutes to place a call

11
  • Cellular
  • The world first automatic analogue cellular
    system was implemented by the Nippon Telephone
    and Telegraph company (NTT) in Japan in 1979. The
    cellular
  • standards for each of the countries is as
    follows
  • NMT (Nordic Mobile Telephone), used in Nordic
    countries, Switzerland, Netherlands, Eastern
    Europe and Russia. 1981
  • U.S AMPS (Advanced Mobile Phone System) 1983
  • TACS (Total Access Communications System) in the
    United Kingdom, 1985
  • C-450 West Germany, Portugal and South Africa,
  • Radiocom 2000 France,
  • RTMI, Italy
  •  Multiple systems in Japan

12
Cellular concept developed by Bell Laboratory
provides the wireless communications to an entire
population.
Cellular telephone system has developed from 1st
generation analog 2nd generation digital
communications GSM 3rd generation IMT-2000,
(UMTS and CDMA2000). 4th generation LTE (and
Wimax) 5th G on the way
13
Antennas and Propagation (William Stallings,
Wireless Communications and Networks 2nd Ed,
Prentice-Hall, 2005, Chapter 5)
14
Introduction
  • 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

15
Types of Antennas
  • Isotropic antenna (idealized)
  • Radiates power equally in all directions
  • Dipole antennas
  • Half-wave dipole antenna (or Hertz antenna)
  • Quarter-wave vertical antenna (or Marconi
    antenna)
  • Parabolic Reflective Antenna

16
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)
  • Measure of directivity of antenna

17
Radiation patterns
18
Three-dimensional antenna radiation patterns. The
top shows the directive pattern of a horn
antenna, the bottom shows the omnidirectional
pattern of a dipole antenna.
19
or as separate graphs in the vertical plane (E or
V plane) and horizontal plane (H plane). This is
often known as a polar diagram
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22
outdoor enclosure featuring a wide band 2.5GHz
panel antenna
Gain (max) 16 dBi (-0.5 dB)
Frequency 2300 - 2700 MHz
3 dB beamwidth 30 ( 5)
Front to back (F/B ratio) 20 dB ( 3 dB)
23
Patch (microstrip) antenna
24
Bent Patch Antenna
25
Helical Antenna
26
Horn Antenna
27
Conical Horn Antenna
openEMS
http//openems.de/index.php/TutorialsAntennas
28
Antenna Gain
  • Antenna gain
  • Power output, in a particular direction, compared
    to that produced in any direction by a perfect
    omnidirectional antenna (isotropic antenna)
  • Effective area
  • Related to physical size and shape of antenna

29
Antenna Gain
  • Relationship between antenna gain and effective
    area
  • G antenna gain
  • Ae effective area
  • f carrier frequency
  • c speed of light ( 3 ? 108 m/s)
  • ? carrier wavelength

30
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31
Propagation Models
  • Ground Wave (GW) Propagation lt 3MHz
  • Sky Wave (SW) Propagation 3MHz to 30MHz
  • Effective Line-of-Sight (LOS) Propagation gt 30MHz

32
Ground Wave Propagation
  • Follows contour of the earth.
  • Can propagate considerable distances.
  • Frequency bands ELF, VF, VLF, LF, MF.
  • Spectrum range 30Hz 3MHz, e.g. AM radio.

33
Sky Wave Propagation
  • Signal reflected from ionized layer of upper
    atmosphere back down to earth, which can travel a
    number of hops, back and forth between ionosphere
    and earths surface.
  • HF band with intermediate frequency range 3MHz
    30MHz.
  • e.g International broadcast.

34
Line-of-Sight Propagation
Tx. and Rx. antennas are in the effective line
of sight range. Includes both LOS and non-LOS
(NLOS) case For satellite communication, signal
above 30 MHz not reflected by ionosphere. For
ground communication, antennas within effective
LOS due to refraction. Frequency bands VHF,
UHF, SHF, EHF, Infrared, optical light Spectrum
range 30MHz 900THz.
35
LOS calculations
dr
do
optical horizon
radio horizon
earth
h
  • What is the relationship between h and d ?
  • For optical LOS

where h antenna height (m) d
distance between antenna and
horizon (km) K adjustment factor
for refraction, K 4/3
  • For effective or radio LOS

36
Line-of-Sight Equations
  • Effective, or radio, line of sight
  • d distance between antenna and horizon (km)
  • h antenna height (m)
  • K adjustment factor to account for refraction,
    rule of thumb K 4/3
  • Maximum distance between two antennas for LOS
    propagation

37
LOS Wireless Transmission Impairments
  • Attenuation and attenuation distortion
  • Free space loss
  • Noise
  • Atmospheric absorption
  • Multipath
  • Refraction
  • Thermal noise

38
Attenuation
  • Strength of signal falls off with distance over
    transmission medium
  • Attenuation factors for unguided media
  • Received signal must have sufficient strength so
    that circuitry in the receiver can interpret the
    signal
  • Signal must maintain a level sufficiently higher
    than noise to be received without error
  • Attenuation is greater at higher frequencies,
    causing distortion

39
Free Space Loss
  • Free space loss, ideal isotropic antenna
  • Pt signal power at transmitting antenna
  • Pr signal power at receiving antenna
  • ? carrier wavelength
  • d propagation distance between antennas
  • c speed of light ( 3 ? 108 m/s)
  • where d and ? are in the same units (e.g., meters)

40
Free Space Loss
  • Free space loss equation can be recast

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42
Free Space Loss
  • Free space loss accounting for gain of other
    antennas can be recast as

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44
Categories of Noise
  • Thermal Noise
  • Intermodulation noise
  • Crosstalk
  • Impulse Noise

45
Noise (1)
  • Thermal noise due to thermal agitation of
    electrons.
  • Present in all electronic devices and
    transmission media.
  • As a function of temperature.
  • Uniformly distributed across the frequency
    spectrum, hence often referred as white noise.
  • Cannot be eliminated places an upper bound on
    the communication system performance.
  • Can cause erroneous to the transmitted digital
    data bits.

46
Noise (2) Noise on digital data
Error in bits
47
Thermal Noise
  • The noise power density (amount of thermal noise
    to be found in a bandwidth of 1Hz in any device
    or conductor) is

N0 noise power density in watts per 1 Hz of
bandwidth k Boltzmann's constant 1.3803 ?
10-23 J/K T temperature, in kelvins (absolute
temperature) 0oC 273 Kelvin
48
Thermal Noise
  • Noise is assumed to be independent of frequency
  • Thermal noise present in a bandwidth of B Hertz
    (in watts)
  • or, in decibel-watts (dBW),

49
Noise Terminology
  • Intermodulation noise occurs if signals with
    different frequencies share the same medium
  • Interference caused by a signal produced at a
    frequency that is the sum or difference of
    original frequencies
  • Crosstalk unwanted coupling between signal
    paths
  • Impulse noise irregular pulses or noise spikes
  • Short duration and of relatively high amplitude
  • Caused by external electromagnetic disturbances,
    or faults and flaws in the communications system

50
Signal to Noise Ratio SNR (1)
  • Ratio of the power in a signal to the power
    contained in the noise present at a particular
    point in the transmission.
  • Normally measured at the receiver with the
    attempt to eliminate/suppressed the unwanted
    noise.
  • In decibel unit,
  • where PS Signal Power, PN Noise Power
  • Higher SNR means better quality of signal.

51
Signal to Noise Ratio SNR (2)
  • SNR is vital in digital transmission because it
    can be used to sets the upper bound on the
    achievable data rate.
  • Shannons formula states the maximum channel
    capacity (error-free capacity) as
  • Given the knowledge of the receivers SNR and the
    signal bandwidth, B. C is expressed in bits/sec.
  • In practice, however, lower data rate are
    achieved.
  • For a fixed level of noise, data rate can be
    increased by increasing the signal strength or
    bandwidth.

52
Expression of Eb/N0 (1)
  • Another parameter that related to SNR for
    determine data rates and error rates is the ratio
    of signal energy per bit, Eb to noise power
    density per Hertz, N0 ? Eb/N0.
  • The energy per bit in a signal is given by
  • PS signal power Tb time required to send
    one bit which can be related to the transmission
    bit rate, R, as Tb 1/ R.
  • Thus,
  • In decibels

228.6 dBW
53
Expression of Eb/N0 (2)
  • As the bit rate R increases, the signal power PS
    relative to the noise must also be increased to
    maintain the required Eb/N0.
  • The bit error rate (BER) for the data sent is a
    function of Eb/N0 (see the BER versus Eb/N0
    plot).
  • Eb/N0 is related to SNR as

BER versus Eb/N0 plot
Higher Eb/N0, lower BER
where B Bandwidth, R Bit rate
54
Wireless Propagation Mechanisms
  • Basic types of propagation mechanisms
  • Free space propagation
  • LOS wave travels large distance with
    obstacle-free
  • Reflection
  • Wave impinges on an object which is large
    compared to the wave-length ?

reflection
Lamp post
diffraction
  • Diffraction
  • Occurs when wave hits the sharp edge of the
    obstacles and bent around to propagate further in
    the shadowed regions Fresnel zones.
  • Scattering
  • Wave hits the objects smaller than ? itself. e.g.
    street signs and lamp posts.

scattering
55
Spread Spectrum Technology
56
What is Spread Spectrum(SS)
  • Spread Spectrum (SS) technology was first
    introduced by military as a way of sending secure
    communications.
  • SS transmitter send their signals out over a
    multiple range of frequencies at very low power,
    in contrast to narrowband radio that concentrate
    all their power into a single frequency.
  • Spread data over wider frequency bandwidth
    Spread Spectrum

57
Spread Spectrum Techniques (2)
Intended army
Military Base
Enemy Base sending jamming signal
Enemy intercepting and stealing information
58
Spread Spectrum
  • What can be gained from apparent waste of
    spectrum?
  • Good noise or interferences rejection (or
    anti-jamming signals),
  • Resilient against unauthorized detection and
    interception,
  • High secrecy and security,
  • Robust towards multipath fading
  • Multiple access capability

59
Spread Spectrum
  • Input fed into channel encoder
  • Produces narrow bandwidth analogue signal around
    central frequency
  • Signal modulated using sequence of digits/codes
  • Spreading code/sequence
  • Typically generated by pseudo-noise/pseudorandom
    generator
  • Increases bandwidth significantly Spreads
    spectrum
  • Receiver uses same sequence to demodulate signal
  • Demodulated signal fed into channel decoder

60
Frequency Hoping Spread Spectrum (FHSS)
  • Signal is broadcast over seemingly random series
    of radio frequencies
  • A number of channels (e.g., Bluetooth 79)
    allocated for the FH signal
  • Width of each channel corresponds to bandwidth
    (Bluetooth 1MHz) of input signal
  • Signal hops from frequency to frequency at fixed
    intervals (Bluetooth 1600hops/sec, 0.625ms/hop)
  • Transmitter operates in one channel at a time
  • Bits are transmitted using some encoding scheme
  • At each successive interval, a new carrier
    frequency is selected

61
Frequency Hoping Spread Spectrum
  • Channel sequence dictated by spreading code
  • Receiver, hopping between frequencies in
    synchronization with transmitter, picks up
    message
  • Advantages
  • Good noise or interferences rejection (or
    anti-jamming signals),
  • Resilient against unauthorized detection and
    interception,
  • High secrecy and security,
  • Robust towards multipath fading
  • Multiple access capability

62
Frequency Hoping Spread Spectrum
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64
FHSS Using MFSK
  • MFSK signal is translated to a new frequency
    every Tc seconds by modulating the MFSK signal
    with the FHSS carrier signal
  • For data rate of R
  • duration of a bit T 1/R seconds
  • duration of signal element Ts LT seconds (L
    number of bits per signal element)
  • Tc ? Ts - slow-frequency-hop spread spectrum
  • Tc lt Ts - fast-frequency-hop spread spectrum

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67
FHSS Performance Considerations
  • Large number of frequencies used
  • Results in a system that is quite resistant to
    jamming
  • Jammer must jam all frequencies
  • With fixed power, this reduces the jamming power
    in any one frequency band

68
Direct Sequence Spread Spectrum (DSSS)
  • Each bit in original signal is represented by
    multiple bits in the transmitted signal
  • Spreading code spreads signal across a wider
    frequency band
  • Spread is in direct proportion to number of bits
    used
  • One technique combines digital information stream
    with the spreading code bit stream using
    exclusive-OR (XOR )

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70
Code-Division Multiple Access (CDMA)
  • Basic Principles of CDMA
  • D rate of data signal
  • Break each bit into k chips
  • Chips are a user-specific fixed pattern
  • Chip data rate of new channel kD
  • Receiver knows senders code and performs
    electronic decode function
  • ltd1, d2, d3, d4, d5, d6gt received chip pattern
  • ltc1, c2, c3, c4, c5, c6gt senders code

71
Categories of Spreading Sequences
  • Spreading Sequence Categories
  • PN sequences
  • Orthogonal codes
  • For FHSS systems
  • PN sequences most common
  • For DSSS systems not employing CDMA
  • PN sequences most common
  • For DSSS CDMA systems
  • PN sequences
  • Orthogonal codes

72
PN Sequences
  • PN generator produces periodic sequence that
    appears to be random
  • PN Sequences
  • Generated by an algorithm using initial seed
  • Sequence isnt statistically random but will pass
    many test of randomness
  • Sequences referred to as pseudorandom numbers or
    pseudonoise sequences
  • Unless algorithm and seed are known, the sequence
    is impractical to predict

73
Important PN Properties
  • Randomness
  • Unpredictability

74
Gold Sequences
75
Orthogonal Codes
  • Orthogonal codes
  • All pairwise cross correlations are zero
  • Fixed- and variable-length codes used in CDMA
    systems
  • For CDMA application, each mobile user uses one
    sequence in the set as a spreading code
  • Provides zero cross correlation among all users
  • Types
  • Walsh codes
  • Variable-Length Orthogonal codes

76
Walsh Codes
  • W1 (0)

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