Introduction to basics of wireless networks such as • Radio waves & wireless signal encoding techniques • Wireless networking issues & constraints • Wireless internetworking devices

1. Introduction to Wireless
Communication
CS5440 Wireless Access Networks
Dilum Bandara
Dilum.Bandara@uom.lk

2. Outlines
 Elements of a wireless system
 Transmitter
 Frequency spectrum
 Modulation
 Antenna
 Medium
 Propagation
 Attenuation
 Receiver
 Antenna
 Demodulation
 Issues & constraints
2

3. Wireless Communication
 Transfer of data between 2+ points that aren’t
connected by an electrical conductor
 Typically use electromagnetic waves
 Why wireless?
 Running cables not always possible
 Low footprint
 Rapid (re)configuration
 Low cost
3

4. Wireless History
 Ancient systems – Smoke Signals, Carrier Pigeons, etc.
 Radio invented in 1880s by Marconi
 Many sophisticated military radio systems developed
during & after WW2
 Exponential growth in Cellular systems since 1988
 Ignited wireless revolution
 Voice, data, & multimedia ubiquitous
 6.8 billion subscribers worldwide as of Feb. 2013 (source ITU)
 Use in 3rd-world countries growing rapidly
 3.5 billion subscribers in Asia Pacific in 2013
 Wi-Fi enjoying tremendous success & growth
 Wide area networks (e.g., WiMax) & short-range systems other
than Bluetooth (e.g., UWB) less successful 4

5. 5

6. Future Wireless Networks
Next-generation Cellular
Wireless Internet Access
Wireless Multimedia
Sensor Networks
Smart Homes/Spaces
Automated Highways
In-Body Networks
IoT
Ubiquitous communication
among People & Devices
Source: Andrea Goldsmith, “Cross
Layer Design in Wireless
Networks”, Stanford University
6

7. Wireless Services
 Telemetry control & traffic control systems
 Infrared & ultrasonic remote control devices
 Professional LMR (Land Mobile Radio) & SMR (Specialized
Mobile Radio)
 Used by business, industrial & public safety entities
 Consumer 2-way radio
 Airband & radio navigation equipment
 Amateur Radio Service (Ham radio)
 Cellular telephones & pagers
 Global Positioning System (GPS)
 Cordless computer peripherals
 Cordless phones
 Satellite television 7
Source: www.access.kth.se

8. Medium
Elements of a Wireless System
8
Transmitter
Receiver 1
Receiver 2
Receiver n
Source: www.mikroe.com/old/books/rrbook/chapter2/chapter2.htm

9. Transmitter
 Elements depend on transmission technology
 Frequency & wavelength, c = f λ
 Modulation
 Antenna
9
AM Transmitter

10. Exercise
 Wavelength of an electromagnetic wave travelling
in space is 60 cm. What is its frequency?
 Assume speed of light is 3×108 m/s
a) 500 MHz
b) 3 GHz
c) 5 GHz
d) 15 GHz
10

11. Frequency Spectrum
 Range of available frequencies
 To avoid interference, various wireless
technologies use distinct frequency bands
 Signal power is well controlled
 Assigned by regulatory agencies
 e.g., FCC, ITU, TRC
11
Source: www.cosmosportal.org

12. 12
Government license not
required
Industrial, Scientific, &
Medical (ISM) band
VLF – very low frequency
LF – low frequency
MF – medium frequency
HF – high frequency
VHF – very high frequency
UHF – ultra-high frequency
SHF – super-high frequency
EHF – extremely high frequency
Source: P. Zheng et al., Wireless Networking Complete

13. Key Frequency Bands
 AM – 520 - 1650.5 KHz
 FM – 87.5 - 108 MHz
 Direct broadcast satellite – 10.9 - 12.75 GHz
 Global System for Mobile (GSM)
 890 - 960 MHz & 1710 - 1880 MHz
 Referred as 900 & 1800 bands
 Code Division Multiple Access (CDMA)
 900 & 1800 bands
 3G wideband CDMA (UMTS)
 1900 - 1980, 2020 - 2025, & 2110 - 2190 MHz bands
 Wireless LAN (IEEE 802.11)
 902 - 928 MHz, 2400 - 2483 MHz, 5.15 - 5.725 GHz
 ISM band – 2.4 GHz in US
13

14. Key Frequency Bands (Cont.)
 Bluetooth – 2.402 - 2.480 GHz in US
 WiMax – 2 - 11 GHz (includes both licensed &
unlicensed)
 Ultra-wideband (UWB) – 1.1 - 10.6 GHz
 Radio-frequency IDentification (RFID)
 LF (120 – 140 KHz), HF (13.56 MHz), UHF (868 – 956 MHz), &
Microwave (2.4 GHz)
 IrDA – 100 GHz
 Wireless sensors
 300 - 1000 MHz & 2.4 GHz ISM band
 Global Positioning System (GPS)
 1575.42 MHz (referred to as L1) & 1227.60 MHz (L2)
14

15. Antenna
15
 Converts signal to electromagnetic waves
 Size must be consistent with wavelength
 Types
 Directional
 Satellite communication
 Omnidirectional
 Cell phones, car radios
 MIMO
 Wireless routers
Source: www.flann.com

16. Antenna Gain
 How well an antenna converts input power into
radio waves headed in a specified direction
 Depends on antenna's directivity & electrical
efficiency
 Gain
 Ratio of power produced by antenna to power
produced by a hypothetical lossless isotropic antenna
 Unitless
 Usually expressed in decibels (dB)
 Directional  high gain
 Omnidirectional  low gain
16

17. Attenuation
 Reduction in signal strength with distance,
propagation medium, & atmospheric conditions
 Typically high for high frequencies
 Friis free-space equation
 PR, PT – Power at receiver (in Watts or Milliwatts)
 GT, GR – gain of antenna
 λ – wavelength (in meters)
 d – distance (in meters) 17
22
2
)4(
=)(
d
GGP
dP RTT
R



18. Example
 Transmission frequency is 881.52 MHz & antenna gains
are 8 dB & 0 dB for base station & mobile station
 What is the signal attenuation at a distance of 1,500 m?
 c = 299 792 458 m/s
 Solution
 c = f λ  λ = 299 792 458/881.52×106 = 0.34 m
 8 dB = 100.8 = 6.3
 0 dB = 100 = 1
 Loss = PT – PR
 Loss = 86.89 dB
18
8
9-
22
2
22
2
22
2
22
2
10×8788.4=
)(
10×0497.2=
)(
1500)4(
34.0×1×3.6
=
)(
1500)4(
34.0×1×3.6
=
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)4(
=
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)4(
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dP
P
P
dP
P
dP
P
dP
d
GG
P
dP
d
GGP
dP
R
T
T
R
T
R
T
R
RT
T
R
RTT
R







19. Attenuation (Cont.)
 Based on empirical evidence, more reasonable to
model PR as a log-distance path-loss model
 np – path loss exponent
 Xσ – zero-mean Gaussian random variable with STD σ
 All power values are in dBm
19
 )/log(10)()( 000 ddndPdP pR
Source: S. Rao, “Estimating the ZigBee
transmission-range ISM band,” EDN, May 2007.

20. Complex Attenuation
 When signal encounters obstacles
 High-frequency signals experience
1. Absorption
2. Shadowing
 When object >> λ
3. Reflection
 When object >> λ
4. Refraction
5. Diffraction
6. Scattering
 When object ≤ λ
20

21. Complex Attenuation (Cont.)
21
Source: http://computer-help-
tips.blogspot.com/2011/04/radio-frequency-
behaviors.html
Absorption
Source: http://elmag.org/en/propagation-modeling-
of-shadowing-by-vegetation-for-mobile-satcom-%26-
satnav-systems
Shadowing

22. Complex Attenuation (Cont.)
22
Reflection
Source: http://wireless.navigator.co.uk/radio_link.htm
Refraction
Source: http://computer-help-
tips.blogspot.com/2011/04/radio-frequency-
behaviors.html

23. Complex Attenuation (Cont.)
23Scattering
Diffraction
Source: http://newhorizons.bg/blog/2010/12/wireless-
101-terminology-part-2-implementing-cisco-unified-
wireless-networking-essentials-iuwne/
Source: http://www.astrosurf.com/luxorion/qsl-
propa.htm

24. Example – Attenuation Experienced by
Mobile Phones
24
Source: www.intechopen.com/books/matlab-a-fundamental-tool-for-scientific-computing-and-engineering-
applications-volume-2/mobile-radio-propagation-prediction-for-two-different-districts-in-mosul-city

25. Exercise
 Reflection of wireless signals occurs when
a) wavelength is constant
b) object size << wavelength
c) object size ≈ wavelength
d) object size >> wavelength
25

26. Noise
 Disturbances introduced to wireless signals
26Source:
www.cisco.com/en/US/prod/collateral/video/ps8806/ps5684/ps2209/prod_white_paper0900aecd805738f5.html

27. Noise (Cont.)
 Sources
 Thermal (white) noise
 From electronic circuit
 PThermal = KTB
 K – Boltzmann constant, T - Ambient temperature, B - receiver BW
 Intermodulation noise
 When 2 frequencies of signals are transmitted over same medium
27
2 signals at 270 & 275 MHz
Source:
http://en.wikipedia.org/wiki/Inter
modulation

28. Noise (Cont.)
 Crosstalk between channels
 Impulse noise
 Due to instantaneous electromagnetic changes
28
Source: http://volpefirm.com/impact-of-
impulse-noise-on-adaptive-pre-equalization-
part-ii/impulse-noise/
Source: www.chalmers.se/en/departments/s2/research/
Pages/Hardware-constrained-communication.aspx

29. Signal-to-Noise Ratio
 To cope with noise, transmitted signal > noise
 High Signal-to-Noise Ratio (SNR)
 Or use spread spectrum technology
 Embed signal over wide range of frequencies with low power
29

30. Example
 PT = 10 W, free space loss 117 dB, antenna gains 8 dB
& 0 dB, total system losses 8 dB, receiver antenna
temperature 290 K, & receiver bandwidth 1.25 MHz
 Find PR
 Find thermal noise, K = 1.38×10-23 W/Kelvin-Hz
 Find SNR at receiver
 Solution
 PR = -107 dBW
 PThermal = KTB = 1.38×10-23 × 290 × 1.25×106 = -143 dBW
 SNR = -107 + 143 = 36 dB
30

31. Multipath Propagation
 Receive same signal through different paths
 Different arrival times
 Inter Symbol Interference (ISI)
 Different levels of attenuation
 Different levels of distortion
31
Source: http://www.ni.com/white-paper/6427/en/

32. Signal Propagation
 Amplitude domain
 Amplitude change with
time
 Frequency domain
 Frequency change
with time
 Phase domain
 Phase change with
time
 Frequency & phase
modulation require high-
frequency carriers 32
Source: www.ni.com/white-paper/4805/en

33. AM & FM
33
Amplitude Modulation
Frequency Modulation

34. Phase Modulation
34

35. Phase Modulation (Cont.)
 Amplitude-Shift Keying (ASK)
 Binary ASK
 1 – By presence of a signal
 0 – No signal
 Pros
 Bandwidth efficient
 Simple to implement
 Cons
 Low power efficiency
 Susceptible to noise & multipath propagation
 Unclear absence of a signal vs. binary 0
35

36. Phase Modulation (Cont.)
 Frequency-Shift Keying (FSK)
 Binary FSK
 1 – High frequency
 0 – Low frequency
 Pros
 Better SNR
 Simple decoding
 Long distance
 Cons
 Slightly less bandwidth efficient than ASK & PSK
 More complicated circuitry than ASK
36

37. Phase Modulation (Cont.)
 Phase-Shift Keying (PSK)
 Encode based on phase of carrier wave
 Binary PSK
 1 – 180o
 0 – 0o
 Quadrature PSK
 0o, 90o, 180o, 270o
 Pros
 Power efficient
 Cons
 Low-bandwidth efficiency
 More complicated circuitry than FSK
37

38. Phase Modulation (Cont.)
 Quadrature Amplitude Modulation (QAM)
 Combines ASK & PSK
 Widely used
38
Source:
www.physics.udel.edu/~watson/scen103/projec
ts/96s/thosguys/qam.html
Source:
www.scicos.org/ScicosModNum/modnum_web/sr
c/modnum_421/interf/scicos/help/eng/htm/MODQ
AM_f.htm

39. Multiplexing
 Transmitting multiple signals simultaneously
 Maximize capacity
 Time Division Multiplexing (TDM)
 Multiple channels occupy same frequency in
alternating slices
 Frequency Division Multiplexing (FDM)
 Use different carrier frequencies
 Code Division Multiplexing (CDM)
 Same frequency & same time but different codes
 Code – like Tx & Rx speak different languages
39

40. Multiplexing (Cont.)
40Source: http://m.ztopics.com/Time%20division%20multiple%20access/

41. CDMA
41
Source: http://electronicdesign.com/communications/fundamentals-communications-access-technologies-
fdma-tdma-cdma-ofdma-and-sdma
Source:
www.umtsworld.com/technology/cdmabasics.htm

42. Exercise
 Which of the following multiplexing technique
allow signals to use different frequencies at the
same time?
a) Amplitude Division Multiplexing
b) Frequency Division Multiplexing
c) Code Division Multiplexing
d) Time Division Multiplexing
42

43. Narrowband Transmission
 Pros
 Efficient use of frequency
 Cons
 Require regulation
 Easier to intercept & jam
43
Source: www.tapr.org

44. Spread Spectrum
 Spread signal over a large range of frequencies
 Low power density (power per frequency)
 Signal appear as background noise 44
www.intercomsonline.com/Spread-Spectrum-Technology_a/162.htm

45. Spread Spectrum (Cont.)
 Only receivers that know the spreading scheme
can reconstruct original signal
 Spreading scheme defined by a code
 Only designated receiver knows the code
 Pros
 Improved channel capacity
 Resistance against interference
 Security against tapping & jamming
 Cons
 Complex circuits
45

46. Signal With & Without Noise
46
Source: www.sciencedirect.com/science/article/pii/S0888327009003756

47. Types of Spread Spectrum Systems
1. Direct Sequence Spread Spectrum (DSSS)
2. Frequency-Hopping Spread Spectrum (FHSS)
3. Orthogonal Frequency-Division Multiplexing
(OFDM)
47

48. Direct Sequence Spread Spectrum (DSSS)
 Spread signal over
broader frequency
band
 Chipping technique to
spread signal
 Transmitter & receiver
needs to be
synchronized
 Used in WiFi
48
Source: www.maximintegrated.com/app-notes/index.mvp/id/1890

49. Frequency-Hopping Spread Spectrum
(FHSS)
 Hoping sequence of
frequencies
 Only subset of the available
frequencies are used to hop
 Transmitter & receiver needs
to be synchronized
 Relatively simple to implement
than DSSS
 Relatively easier to recover Tx
signal than DSSS
 Relatively less robust to signal
distortion & multipath effects
 Used in Bluetooth 49
Source: www.maximintegrated.com/app-
notes/index.mvp/id/1890

50. Orthogonal Frequency-Division
Multiplexing (OFDM)
 Utilize orthogonal multiple subcarriers in parallel
 Much higher data rates
 Low multipath interference
 Used in IEEE 802.11 a/g
50
Source: http://wiki.hsc.com//Main/OFDM

51. Challenges
 Wireless channels are a difficult & capacity-
limited communications medium
 Typically less efficient
 Traffic patterns, user locations, & network
conditions are constantly changing
 Applications are heterogeneous with hard
constraints that must be met by networks
51

52. More Challenges
 Network challenges
 Scarce spectrum
 Demanding/diverse applications
 Reliability
 Ubiquitous coverage
 Seamless indoor/outdoor operation
 Device challenges
 Size, power, cost
 Multiple antennas in Silicon
 Multi-radio Integration
 Coexistance
Cellular
Apps
Processor
BT
Media
Processor
GPS
WLAN
Wimax
DVB-H
FM/XM
52

53. Growth in mobile data, massive spectrum deficit & stagnant revenues
require technical & political breakthroughs for ongoing success of cellular
Careful what you wish for…
53
Source: Unstrung Pyramid Research 2010Source: FCC

54. Software-Defined (SD) Radio
 Wideband antennas & A/Ds span BW of desired signals
 DSP programmed to process desired signal: no specialized
HW
Cellular
Apps
Processor
BT
Media
Processor
GPS
WLAN
Wimax
DVB-H
FM/XM A/D
A/D
DSP
A/D
A/D
Is this the solution to the device challenges?
Today, this isn’t cost, size, or power efficient
54

55. Summary
 Bandwidth & QoS is in demand
 Many applications & services
 Spectrum is scare
 Many elements & solutions
 Still not enough
 It’s only going to be even more interesting...
55