20101 The Physical Layer Chapter 2. 20102 Bandwidth-Limited Signals.
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Transcript of 20101 The Physical Layer Chapter 2. 20102 Bandwidth-Limited Signals.
2010 1
The Physical Layer
Chapter 2
2010 2
Bandwidth-Limited Signals
2010 3
Maximal Data Rate
Shannon –Hartley law (1948):• a channel with a bandwidth of H Hz and random noise
• maximum bps (bits per second) is: H log2 (1+S/N)
• S/N: signal power to noise power (dB: 10 log10 (S/N) )
• current coding techniques approaches the limit
To achieve higher speed:• better cables and electronics
• higher bandwith (less attenuation of higher frequencies)
• lower internal noise
• decrease influence of external EM radiation
• light via fiber optics
2010 4
Coax, Twisted Pair, fiber
Category 5 UTP
Category 3 UTP
Signal is difference in voltage
2010 5
The Electromagnetic Spectrum
2010 6
The Telephone Local Loop: Modems
The use of both analog and digital transmissions for a computer to computer call. Conversion is done by the
modems and codecs.
2010 7
Modems
Binary signal
Amplitude modulation
Frequency modulation
Phase modulation
Modern methods combine these modulation modesand use more amplitudes, frequencies and phasesto approach the Shannon limit
2010 8
(Asymmetric)Digital Subscriber Lines
A typical (A)DSL equipment configuration.
2010 9
ADSL frequency bands
Operation of ADSL using discrete multitone modulation.
gap, larger for ISDN
In each channel a “modem: of maximal 56 kbps,reduced automatically when S/N is too highADSL2+ goes upto 2,2 GHz
2010 10
Internet over Cable
2010 11
TV Cable Spectrum Allocation
Frequency allocation in a typical cable TV system used for Internet access
2010 12
Wireless Local LoopsArchitecture of an LMDS (IEEE 802.16) system.
Superseded by ADSL and cable TV
WiMAX (IEEE 802.16) is more promising now
2010 13
Frequency Division Multiplexing
(a) The original bandwidths.
(b) The bandwidths raised in frequency.
(b) The multiplexed channel.
With fibers:different wavelength of light
2010 14
Time Division Multiplexing
2010 15
CDMA – Code Division Multiple Access
Each sender has an unique code of m bits, called chips“1”: chip sequence is send“0”: complement of it is send
2010 16
CDMA – Chip decoding
(a) Binary chip sequences(b) Bipolar chip sequences (c) Six transmissions(d) Recovery of C’s signal
2010 17
The Mobile Telephone System
• First-Generation Mobile Phones: Analog Voice
• Second-Generation Mobile Phones: Digital Voice (GSM)
• Third-Generation Mobile Phones:Digital Voice and Data (UMTS)
• Fourth-Generation:based on LTE ?
2010 18
Global System for Mobile Communications
GSM uses 2 * 124 frequency channels, each of which uses an eight-slot TDM system
2010 19
GSM data framing
other framing:
• Control (base to mobile) to manage the system
• Paging (base to mobile) to alert users to calls for them
• Access (bidirectional) for call setup and channel assignment
2010 20
Neighbouring cells
Different frequencies for neighbouring cells (fixed
sender / receiver)
2010 21
Energy, environment
Prediction over 4 year:•1/3 of IT budget goes to energy bills•2/3 of that for cooling
How to dispose of 512 million old PC’s