Wireless Communication Systems

1
Wireless Communication Systems

• Lecture 1
• Overview of Wireless Communications

2

• Wireless is an old name for radio being used
  again to describe a wide variety of portable
  devices that rely on radio links for connectivity.

3
Types of Wireless Communications

• Microwave Link
• Satellite Link
• Mobile Cellular
• Infrared Links
• ISM applications
• Cordless phones
• Wireless LANs
• Military
• Marine
• Scientific

4
Why Wireless?

• Human freedom
• Portability and Mobility
• Objective anything, anytime, anywhere
• Mobility
• Size, weight, power
• Functionality
• Infrastructure required
• Cost

5
Definitions

• Definition of mobility
• user mobility users communicate anytime,
  anywhere, with anyone
• device portability devices can be connected
  anytime, anywhere to the network
• Definition of wireless
• Un-tethered, no physical wire attachment
• The need for mobility creates the need for
  integration of wireless networks into existing
  fixed network environments
• local area networks standardization of IEEE
  802.11
• Internet Mobile IP extension of the internet
  protocol IP
• wide area networks e.g., internetworking of 3G
  and IP

6
Technological Trends

• Advances in Technology
• more computing power in smaller devices
• flat, lightweight displays with low power
  consumption
• user interfaces suitable for small dimensions
• higher bandwidths
• multiple wireless interfaces wireless LANs,
  wireless WANs, home RF, wireless PANs
• New Electronic Computing Devices
• small, cheap, portable, replaceable and most
  important of all USABLE!

7
Why is Wireless Hard?The Wireless Channel

• Fundamentally Low Capacity C lt B log(1SNR)
• Spectrum scarce and expensive
• Received power diminishes with distance
• Self-interference due to multipath
• Multipath delayed more than a bit time causes
  self-interference (ISI)
• Channel changes as users move around
• Signal blocked by objects (cars, people, etc.)
• Broadcast medium everyone interferes

8
And The Wireless Network
Wireline Backbone

• Multiple access hard to coordinate
• Routing often multihop over multiple
  wireless/wired channels
• Topology is dynamic
• Link characteristics are dynamic
• Hard to allocate network resources according to
  needs
• Proliferation of standards and systems

9
An Integrated View
ad hoc
GSM, 3G, WLAN, Bluetooth, ...
PDA, laptop, cellular phones, GPS, sensors
10
(No Transcript)
11
Wireless vs Fixed

• Higher loss-rates due to interference
• other EM signals, objects in path (multi-path,
  scattering)
• Limited availability of useful spectrum
• frequencies have to be coordinated
• lower transmission rates
• local area 2 11 Mbit/s, -gt 50 - 70Mbit/s
• wide area 9.6 19.2 kbit/s -gt 384 - 2000Kbit/s
• Higher delays, higher jitter
• connection setup time for cellular in the second
  range, several hundred milliseconds for wireless
  LAN systems
• Lower security, simpler active attacking
• radio interface accessible for everyone
• base station can be simulated, thus attracting
  calls from mobile phones
• Always shared medium
• secure access mechanisms important

12
Wireless LANs Standards

• 802.11 (2M) -gt 802.11b (11M) -gt 802.11a (50-70M)
  -gt 802.11g (54M)
• Wider spectrum -gt Higher bit rates
• Generally used with access points
• Ad hoc component not used, has flaws
• Poor support for real-time communications
• HiperLAN
• European standard for high bit rate (25M) local
  transmission in 5GHz range over 50-300m

13
Infrastructure vs Adhoc
infrastructure network
AP Access Point
AP
AP
wired network
AP
ad-hoc network
14
Wireless Devices
Infrastructure
Pager
Satellite
Direct Broadcast Satellite Receiver
Interconnections may be copper, fiber, coax, or
wireless
Wireless Phone (cellular, PCS, satellite)
Cellular, PCS, Paging, Fixed Wireless
Public Switched Telephone Network
Fixed Broadband Wireless (gt10 Mbps)
Wireless Local Loop
Wireless systems have a whole lot of wire!
Portable Networking
15
Wireless Subscribers Worldwide
SOURCE UMTS FORUM
16
Radio waves are described by a frequency or
wavelength

• Frequency (f) is the number of oscillations
  (cycles) per second. Unit is Hertz or Hz
• Wavelength (l) is the distance covered by one
  oscillation (cycle) as the wave travels through
  space

Transmit
l Wavelength
Receive
Transmit
1 second, f 5 cycles per second or 5 Hz
17
Electromagnetic Spectrum
LIGHT
HARMFUL RADIATION
RADIO
SOUND
VHF VERY HIGH FREQUENCY UHF ULTRA HIGH
FREQUENCY SHF SUPER HIGH FREQUENCY EHF EXTRA
HIGH FREQUENCY
18
Wireless systems transmit and receive waveforms
that are outside of the spectrum of visible light
-- from about 800 to 30,000 MHz
Cellular, PCS, and Fixed Wireless Operate in this
range
19
(No Transcript)
20
Antennas

• All wireless devices have at least one antenna
  most use the same antenna to transmit and receive
• The antenna must be at least one quarter
  wavelength in size to work well.
• So, no matter how small you make a cellular
  phone, the antenna is going to have to be about
  this size!

21
Wireless Telephony
WIRELESS
AIR LINK
WIRED
PUBLIC SWITCHED TELEPHONE NETWORK
22
Cell Clusters
CELL 1 OVERLAPS 6 OTHERS DIFFERENT
FREQUENCIES MUST BE USED IN ADJACENT CELLS SEVEN
DIFFERENT SETS OF FREQUENCIES REQUIRED
SOURCE IEC.ORG
23
Hubs hand off the user as it passes from one
cell to the next. The Hub Base Stations transmit
the call back to the wired public switched
telephone network.
Public Switched Telephone Network
24
Cell Sizes
GSM 100m - 50 km 250 km/hr
25
Cellular Generations

• First
• Analog, circuit-switched (AMPS)
• Second
• Digital, circuit-switched (GSM, Palm) 10 Kbps
• Advanced second
• Digital, circuit switched, Internet-enabled (WAP)
  10 Kbps
• 2.5
• Digital, packet-switched, TDMA (GPRS,
  EDGE)40-400 Kbps
• Third
• Digital, packet-switched, wideband CDMA
  (UMTS)0.4 2 Mbps
• Fourth
• Data rate 100 Mbps achieves telepresence

26
Wireless LAN

• Idea just a LAN, but without wires
• Not as easy since signals are of limited range
• Uses unlicensed frequencies, low power
• 2.4 GHz
• IEEE 802.11 (wireless ethernet)
• WaveLAN 2 Mbps moving to 11 Mbps
• 5.2 GHz
• OFDM (orthogonal FDMA) modem technology (30 Mbps)
  IEEE 802.11

27
(No Transcript)
28
Wireless LAN Configurations
CLIENT AND ACCESS POINT
WIRELESS PEER-TO-PEER
BRIDGING WITH DIRECTIONAL ANTENNAS
MULTIPLE ACCESS POINTS ROAMING
UP TO 17 KM !
SOURCE PROXIM.COM
29
Bluetooth

• A standard permitting for wireless connection of
• Personal computers
• Printers
• Mobile phones
• Handsfree headsets
• LCD projectors
• Modems
• Wireless LAN devices
• Notebooks
• Desktop PCs
• PDAs

30
Bluetooth Characteristics

• Operates in the 2.4 GHz Industrial-Scientific-Me
  dical (ISM) (unlicensed)! band. Packet
  switched. 1 milliwatt. Low cost.
• 10m to 100m range
• Uses Frequency Hop (FH) spread spectrum, which
  divides the frequency band into a number of hop
  channels. During connection, devices hop from
  one channel to another 1600 times per second
• Bandwidth 1-2 megabits/second
• Supports up to 8 devices in a piconet (two or
  more Bluetooth units sharing a channel).
• Built-in security.
• Non line-of-sight transmission through walls
  and briefcases.
• Easy integration of TCP/IP for networking.

31
Bluetooth Devices
ALCATEL One TouchTM 700 GPRS, WAP
ERICSSON R520 GSM 900/1800/1900
ERICSSON BLUETOOTH CELLPHONE HEADSET
NOKIA 9110 FUJI DIGITAL CAMERA
ERICSSON COMMUNICATOR
32
WiMax

• WiMax, which is based on the IEEE 802.16
  standard, offers greater bandwidth and range than
  the 802.11 family of standards.
• Where Wi-Fi is intended to cover small areas,
  such as offices, homes, and hot spots.
• WiMax can theoretically extend a 70M-bps
  connection up to 50 km from a base station
  capable of supporting thousands of users (city
  hot zones).

33
802.16 for Broadband Wireless Access

• DSL complement
• DSL is not available, e.g. poor copper
  infrastructure
• DSL OPEX too high, e.g. low population density
• Central Office is too far away for DSL
• CLEC bypassing incumbent
• DSL competition
• If DSL is available, hard to beat

802.16
34
WPAN

• Wireless Personal Area Network (WPAN)
• Cable replacement
• Low-cost, short range networking scheme for PCs,
  laptops, PDA connectivity
• Benefits
• Expands connectivity users, locations and cost
• Provides mobility to users
• Quick installation
• Cost effective
• Scalable

35

• IEEE 802.15.3a
• An Ultrawideband (UWB) scheme.
• Up to 480 Mbps transfers.
• Only 3 meter radius for IEEE 802.15.3a.
• Provides for applications such as very fast
  digital camera to PCs transfers, connections
  between large screen TV monitors and your media
  centers and DVD camcorders, not general network
  use.
• The frequency spectrum considered is the 3.1 to
  10.6 GHz band, well above the fray where 802.11b
  and 802.11g reside.
• UWB may become a BIG DEAL. The concept is nothing
  short of using a UWB system to eliminate
  communication wiring! Wire may be on its way out.

36
Relative coverage, mobility, and data rates of
generations of cellular systems and local
broadband and ad hoc networks.
37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
(No Transcript)
48
(No Transcript)
49
(No Transcript)
50
(No Transcript)
51
(No Transcript)
52
(No Transcript)
53
(No Transcript)
54
Multiple Access Systems

• Mobile phone systems must fit more and more users
  into limited spectrum. There are three main
  approaches
• Frequency Division Multiple Access (FDMA) users
  transmit on different frequencies
• Time Division Multiple Access (TDMA) users
  transmit at different times
• Code Division Multiple Access (CDMA) users have
  different codes like several conversations
  in same room in different languages

These three approaches are incompatible and the
source of much debate
55
Transmission Fundamentals
56
Electromagnetic Signal

• Function of time
• Can also be expressed as a function of frequency
• Signal consists of components of different
  frequencies

57
Analog and Digital Waveforms
58
Time-Domain Concepts

• Analog signal - signal intensity varies in a
  smooth fashion over time
• No breaks or discontinuities in the signal
• Digital signal - signal intensity maintains a
  constant level for some period of time and then
  changes to another constant level
• Periodic signal - analog or digital signal
  pattern that repeats over time
• s(t T ) s(t ) - ? lt t lt ?
• where T is the period of the signal

59
Examples of Periodic Signals.
60
Time-Domain Concepts

• Aperiodic signal - analog or digital signal
  pattern that doesn't repeat over time
• Peak amplitude (A) - maximum value or strength of
  the signal over time typically measured in volts
• Frequency (f )
• Rate, in cycles per second, or Hertz (Hz) at
  which the signal repeats

61
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 (?) - distance occupied by a single
  cycle of the signal
• Or, the distance between two points of
  corresponding phase of two consecutive cycles

62
Sine Wave Parameters

• General sine wave
• s(t ) A sin(2?ft ?)
• Figure 2.3 shows the effect of varying each of
  the three parameters
• (a) A 1, f 1 Hz, ? 0 thus T 1s
• (b) Reduced peak amplitude A0.5
• (c) Increased frequency f 2, thus T ½
• (d) Phase shift ? ?/4 radians (45 degrees)
• note 2? radians 360 1 period

63
Sine Wave Parameters
64
Time vs. Distance

• When the horizontal axis is time, as in Figure
  2.3, graphs display the value of a signal at a
  given point in space as a function of time
• With the horizontal axis in space, graphs display
  the value of a signal at a given point in time as
  a function of distance
• At a particular instant of time, the intensity of
  the signal varies as a function of distance from
  the source

65
Frequency-Domain Concepts

• Fundamental frequency - when all frequency
  components of a signal are integer multiples of
  one frequency, its referred to as the
  fundamental frequency
• Spectrum - range of frequencies that a signal
  contains
• Absolute bandwidth - width of the spectrum of a
  signal
• Effective bandwidth (or just bandwidth) - narrow
  band of frequencies that most of the signals
  energy is contained in

66
Frequency-Domain Concepts

• Any electromagnetic signal can be shown to
  consist of a collection of periodic analog
  signals (sine waves) at different amplitudes,
  frequencies, and phases
• The period of the total signal is equal to the
  period of the fundamental frequency

67
Relationship between Data Rate and Bandwidth

• The greater the bandwidth, the higher the
  information-carrying capacity
• Conclusions
• Any digital waveform will have infinite bandwidth
• BUT the transmission system will limit the
  bandwidth that can be transmitted
• AND, for any given medium, the greater the
  bandwidth transmitted, the greater the cost
• HOWEVER, limiting the bandwidth creates
  distortions

68
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

69
Examples of Analog and Digital Data

• Analog
• Video
• Audio
• Digital
• Text
• Integers

70
Analog Signals

• A continuously varying electromagnetic wave that
  may be propagated over a variety of media,
  depending on frequency
• Examples of media
• Copper wire media (twisted pair and coaxial
  cable)
• Fiber optic cable
• Atmosphere or space propagation
• Analog signals can propagate analog and digital
  data

71
Acoustic Spectrum of Speech and Music
72
Digital Signals

• A sequence of voltage pulses that may be
  transmitted over a copper wire medium
• Generally cheaper than analog signaling
• Less susceptible to noise interference
• Suffer more from attenuation
• Digital signals can propagate analog and digital
  data

73
Attenuation of Digital Signals
74
Analog Signaling
75
Digital Signaling
76
Reasons for Choosing Data and Signal Combinations

• Digital data, digital signal
• Equipment for encoding is less expensive than
  digital-to-analog equipment
• Analog data, digital signal
• Conversion permits use of modern digital
  transmission and switching equipment
• Digital data, analog signal
• Some transmission media will only propagate
  analog signals
• Examples include optical fiber and satellite
• Analog data, analog signal
• Analog data easily converted to analog signal

77
Analog Transmission

• Transmit analog signals without regard to content
  
• Attenuation limits length of transmission link
• Cascaded amplifiers boost signals energy for
  longer distances but cause distortion
• Analog data can tolerate distortion
• Introduces errors in digital data

78
Digital Transmission

• Concerned with the content of the signal
• Attenuation endangers integrity of data
• Digital Signal
• Repeaters achieve greater distance
• Repeaters recover the signal and retransmit
• Analog signal carrying digital data
• Retransmission device recovers the digital data
  from analog signal
• Generates new, clean analog signal

79
About Channel Capacity

• Impairments, such as noise, limit data rate that
  can be achieved
• For digital data, to what extent do impairments
  limit data rate?
• Channel Capacity the maximum rate at which data
  can be transmitted over a given communication
  path, or channel, under given conditions

80
Concepts Related to Channel Capacity

• Data rate - rate at which data can be
  communicated (bps)
• Bandwidth - the bandwidth of the transmitted
  signal as constrained by the transmitter and the
  nature of the transmission medium (Hertz)
• Noise - average level of noise over the
  communications path
• Error rate - rate at which errors occur
• Error transmit 1 and receive 0 transmit 0 and
  receive 1

81
Nyquist Bandwidth

• For binary signals (two voltage levels)
• C 2B
• With multilevel signaling
• C 2B log2 M
• M number of discrete signal or voltage levels

82
Signal-to-Noise Ratio

• Ratio of the power in a signal to the power
  contained in the noise thats present at a
  particular point in the transmission
• Typically measured at a receiver
• Signal-to-noise ratio (SNR, or S/N)
• A high SNR means a high-quality signal, low
  number of required intermediate repeaters
• SNR sets upper bound on achievable data rate

83
Effect of Noise on a Digital Signal.
84
Shannon Capacity Formula

• Equation
• Represents theoretical maximum that can be
  achieved
• In practice, only much lower rates achieved
• Formula assumes white noise (thermal noise)
• Impulse noise is not accounted for
• Attenuation distortion or delay distortion is not
  accounted

85
Example of Nyquist and Shannon Formulations

• Spectrum of a channel between 3 MHz and 4 MHz
  SNRdB 24 dB
• Using Shannons formula

86
Example of Nyquist and Shannon Formulations

• How many signaling levels are required?

87
Classifications of Transmission Media

• Transmission Medium
• Physical path between transmitter and receiver
• Guided Media
• Waves are guided along a solid medium
• E.g., copper twisted pair, copper coaxial cable,
  optical fiber
• Unguided Media
• Provides means of transmission but does not guide
  electromagnetic signals
• Usually referred to as wireless transmission
• E.g., atmosphere, outer space

88
Unguided Media

• Transmission and reception are achieved by means
  of an antenna
• Configurations for wireless transmission
• Directional
• Omnidirectional

89
General Frequency Ranges

• Microwave frequency range
• 1 GHz to 40 GHz
• Directional beams possible
• Suitable for point-to-point transmission
• Used for satellite communications
• Radio frequency range
• 30 MHz to 1 GHz
• Suitable for omnidirectional applications
• Infrared frequency range
• Roughly, 3?1011 to 2?1014 Hz
• Useful in local point-to-point multipoint
  applications within confined areas

90
Terrestrial Microwave

• Description of common microwave antenna
• Parabolic "dish", 3 m in diameter
• Fixed rigidly and focuses a narrow beam
• Achieves line-of-sight transmission to receiving
  antenna
• Located at substantial heights above ground level
  
• Applications
• Long haul telecommunications service
• Short point-to-point links between buildings

91
Broadcast Radio

• Description of broadcast radio antennas
• Omnidirectional
• Antennas not required to be dish-shaped
• Antennas need not be rigidly mounted to a precise
  alignment
• Applications
• Broadcast radio
• VHF and part of the UHF band 30 MHZ to 1GHz
• Covers FM radio and UHF and VHF television

92
Optical Telepoint LOS Cellular System