Rudra Dutta CSC Fall 2011, Section 001

Slides:



Advertisements
Similar presentations
Physical Layer: Signals, Capacity, and Coding
Advertisements

1 Transmission Fundamentals Chapter 2 (Stallings Book)
ECE 4321: Computer Networks Chapter 3 Data Transmission.
Physical Layer – Part 2 Data Encoding Techniques
Computer Communication & Networks Lecture # 06 Physical Layer: Analog Transmission Nadeem Majeed Choudhary
EE 4272Spring, 2003 Chapter 3 Data Transmission Part II Data Communications Concept & Terminology Signal : Time Domain & Frequency Domain Concepts Signal.
Chapter 3 Data and Signals
© Kemal AkkayaWireless & Network Security 1 Department of Computer Science Southern Illinois University Carbondale CS591 – Wireless & Network Security.
Department of Electronic Engineering City University of Hong Kong EE3900 Computer Networks Data Transmission Slide 1 Continuous & Discrete Signals.
Physical Layer – Part 2 Data Encoding Techniques
IS250 Spring 2010 Physical Layer IS250 Spring 2010
Physical Layer 1b session 1 TELE3118: Network Technologies Week 1: Physical Layer Some slides have been taken from:  Computer Networking: A Top.
William Stallings Data and Computer Communications 7th Edition (Selected slides used for lectures at Bina Nusantara University) Data, Signal.
Module 3.0: Data Transmission
Modulation                                                                 Digital data can be transmitted via an analog carrier signal by modulating one.
Modulation Modulation => Converts from digital to analog signal.
The Physical Layer: Data Transmission Basics
1 Physical Layer. 2 Analog vs. Digital  Analog: continuous values over time  Digital: discrete values with sharp change over time.
1 Long-Distance Communication. 2 Illustration of a Carrier Carrier –Usually a sine wave –Oscillates continuously –Frequency of carrier fixed.
COSC 3213 – Computer Networks I Summer 2003 Topics: 1. Line Coding (Digital Data, Digital Signals) 2. Digital Modulation (Digital Data, Analog Signals)
Review: The application layer. –Network Applications see the network as the abstract provided by the transport layer: Logical full mesh among network end-points.
Lecture 3-1: Coding and Error Control
1 Business Telecommunications Data and Computer Communications Chapter 3 Data Transmission.
1 Ch 6 Long-Distance Communication Carriers, Modulation, and Modems.
The Physical Layer Lowest layer in Network Hierarchy. Physical transmission of data. –Various flavors Copper wire, fiber optic, etc... –Physical limits.
Electromagnetic Spectrum
1 st semester 1436/  When a signal is transmitted over a communication channel, it is subjected to different types of impairments because of imperfect.
Shannon’s Theorem Nyquist Theorem Modulations Multiplexing
1 3. Data Transmission. Prof. Sang-Jo Yoo 2 Contents  Concept and Terminology  Analog and Digital Data Transmission  Transmission Impairments  Asynchronous.
Physical Layer Rudra Dutta ECE/CSC Fall 2007, Section 001.
Introductory Networking Concepts Introductory Networking Concepts Rudra Dutta CSC Fall 2013.
Advanced Computer Networks
1587: COMMUNICATION SYSTEMS 1 Digital Signals, modulation and noise Dr. George Loukas University of Greenwich,
1 CSCD 433 Network Programming Fall 2016 Lecture 4 Digital Line Coding and other...
Computer Communication & Networks
Data Encoding Data Encoding refers the various techniques of impressing data (0,1) or information on an electrical, electromagnetic or optical signal that.
Chapter 2: Physical Layer
Transmission Fundamentals
KOMUNIKASI DATA Materi Pertemuan 10.
Bandwidth Utilization
Bandwidth Utilization
William Stallings Data and Computer Communications 7th Edition
Introduction to electronic communication systems
Chapter 4: Digital Transmission
CS441 – Mobile & Wireless Computing Communication Basics
Physical Layer (Part 2) Data Encoding Techniques
Data Encoding Data Encoding refers the various techniques of impressing data (0,1) or information on an electrical, electromagnetic or optical signal that.
Physical Layer – Part 2 Data Encoding Techniques
2017 session 1 TELE3118: Network Technologies Week 1: Physical Layer
Lecture 4 Continuation of transmission basics Chapter 3, pages 75-96
2012 session 1 TELE3118: Network Technologies Week 1: Physical Layer
Unit 2.
Physical Transmission
فصل سوم: لایه فیزیکی (Physical Layer)
Important Concepts at the Physical Layer
Chapter 10. Digital Signals
Modulation Modulation => Converts from digital to analog signal.
Chapter 4 Transmission Impairments and Multiplexing
Signals, Media, And Data Transmission
CSCD 433 Network Programming
Chapter 3. Data Transmission
Physical Layer – Part 2 Data Encoding Techniques
REVIEW Physical Layer.
The Physical Layer Part 1
Computer Networks Bhushan Trivedi, Director, MCA Programme, at the GLS Institute of Computer Technology, Ahmadabad.
EEC4113 Data Communication & Multimedia System Chapter 2: Baseband Encoding by Muhazam Mustapha, September 2012.
Analog Transmission Example 1
(Digital Modulation Basics)
Chapter Three: Signals and Data Transmission
Multiplexing Simultaneous transmission of multiple signals across a single data link As data & telecomm use increases, so does traffic Add individual links.
Presentation transcript:

Rudra Dutta CSC 401 - Fall 2011, Section 001 Physical Layer Rudra Dutta CSC 401 - Fall 2011, Section 001

Context Lowest of OSI layers Provides a bit pipe More communications than networking We want to understand: General techniques Descriptive Theoretical results Analytical, problem solving Copyright Fall 2011, Rudra Dutta, NCSU

Communication Links Various technologies for physical communication Copper wire, coax, fiber, radio, satellites, … Single underlying phenomenon - EM waves One way to utilize the phenomenon - guide Copper, glass Another way – no guide Free space (“wireless cable”) Radio, optical (Smoke signal? Semaphore? Magnetic tapes? Carrier Pigeons ?) Copyright Fall 2011, Rudra Dutta, NCSU

EM Waves Energy can carry information More correctly, distribution of energy EM waves carry energy, hence information Amplitude, frequency, phase Modifications (“modulations”) of these carry information Copyright Fall 2011, Rudra Dutta, NCSU

Digital or Analog ? Digital – concept EM waves – analog by definition 010100… Digital – concept Information can be analog or digital EM waves – analog by definition Analog EM signal can be made to transfer digital data Thus we could (and usually do) have: “Digital interpretation of analog signal representing digital representation of analog data” Copyright Fall 2011, Rudra Dutta, NCSU

Propagation Media Guided Unguided Twisted pair Coax cable Optical fiber Unguided Radio (semi-guided follow curvature of earth) Radio bounced off ionosphere Fiberless optical (wireless optical) Communication satellites Copyright Fall 2011, Rudra Dutta, NCSU

Communication in the EM Spectrum Copyright Fall 2011, Rudra Dutta, NCSU

Modulation A “carrier” wave exists on the medium Own amplitude, frequency, phase Base energy pattern – no information Analog, of course A “signal” needs to be transmitted Time varying; analog, or digital The value of the signal from instant to instant is used to change the energy pattern of the carrier Copyright Fall 2011, Rudra Dutta, NCSU

Injection Baseband Broadband No carrier, modulation State of the medium (voltage) is made to follow signal one-to-one Uses “entire” medium Broadband Modulation of a carrier Carriers at different frequencies can carry different signals Sinusoidal advantages – remember harmonic analysis Natural frequencies of transmission Copyright Fall 2011, Rudra Dutta, NCSU

Synchronous vs. Asynchronous Various use of these terms Very multiply defined terms Can be used for traffic ITU-T and CCITT have different definitions Others such as FDDI possible In this transmission context With clock - asynchronous Can fall out of step - long string of zeros Synchronous - clock not needed Copyright Fall 2011, Rudra Dutta, NCSU

Synchronous Baseband Transmission “Self-synchronizing” codes Provide guaranteed transitions in clock ticks Rate suffers Manchester Transitions, not states, indicate bits Many others NRZI - Transitions indicate 1’s (needs line code) MLT-3 - Alternate 1’s are high and low (needs line code) Copyright Fall 2011, Rudra Dutta, NCSU

Broadband injection Amplitude, Frequency, or Phase may be modulated “Shift keying” Copyright Fall 2011, Rudra Dutta, NCSU

BPSK modulation PSK has excellent protection against noise Information is contained within phase Noise mainly affects carrier amplitude Copyright Fall 2011, Rudra Dutta, NCSU

QPSK Modulation, QAM Copyright Fall 2011, Rudra Dutta, NCSU

Multiplexing Techniques to employ same medium for multiple transmissions Requirement: over same reasonably short time, each transmission should receive some share of medium capability Two main methods Frequency division Time division Combinations thereof Code division – new concept Copyright Fall 2011, Rudra Dutta, NCSU

Frequency Division Multiplexing (a) The original bandwidths (b) The bandwidths raised in frequency (b) The multiplexed channel Copyright Fall 2011, Rudra Dutta, NCSU

Wavelength Division Multiplexing Copyright Fall 2011, Rudra Dutta, NCSU

Time Division Multiplexing The T1 carrier (1.544 Mbps) Copyright Fall 2011, Rudra Dutta, NCSU

GSM – A Combined Approach GSM uses 124 frequency channels, each of which uses an eight-slot TDM system Copyright Fall 2011, Rudra Dutta, NCSU

CDMA – A New Approach Combines multiplexing and collision issues New approach lies in treating collisions - may extract some data Multiplexing is more like FDM Binary “chip” sequences assigned to stations May appear that bit rate increase should not result - in fact does Power control an essential part We discuss later (in MAC) Copyright Fall 2011, Rudra Dutta, NCSU

The Issue of Bitrate Consider simple AM (ASK) 00 01 10 11 1 Consider simple AM (ASK) Transmit one of two distinct amplitudes (voltages)  transmission of one bit How soon after can we transmit another bit? How fast can transmitter change its state? How fast can receiver recognize line state? Appears to limit bit rate, but - Does not have to be just two states Why not transmit one of four distinct amplitudes? Why not more?  No limit to bit rate Copyright Fall 2011, Rudra Dutta, NCSU

Channel Characteristics Channel modifies the EM wave Copyright Fall 2011, Rudra Dutta, NCSU

Phenomena Hindering Transmission Interference with energy (pattern) Attenuation (entropy loss) Distortion (variable delay of different energy packets) Dispersion Noise (unpredictable) All but noise can be guarded against With the ideal infinite data transfer rate Copyright Fall 2011, Rudra Dutta, NCSU

A Little Communication Theory The road to EM transmission: Fourier: Harmonic analysis Nyquist: Sampling theorem – bit rate Shannon: Bit rate in presence of noise Briefly, Most signals can be represented by sinusoid combinations Discrete time sampling can reconstruct signals Noiseless channel has limited maximum bit rate Noise reduces maximum bit rate Copyright Fall 2011, Rudra Dutta, NCSU

Bandwidth-Limited Signals (a) A binary signal and its root-mean-square Fourier amplitudes, (b-c) successive approximations Copyright Fall 2011, Rudra Dutta, NCSU

Bandwidth-Limited Signals (2) (d) – (e) Successive approximations to the original signal Copyright Fall 2011, Rudra Dutta, NCSU

Sampling – Nyquist’s Theorem Twice the highest frequency  no reconstruction loss Copyright Fall 2011, Rudra Dutta, NCSU

Nyquist’s Result – Intuitive View Fitting a sinusoid Low-rate sampling  wrong sinusoid Half-rate sampling  wrong sinusoid Full-rate sampling  still could be wrong Double rate  no possibility of wrong sinusoid “Highest frequency” Naturally introduced by device characteristics Medium carries all frequencies between a lowest and highest frequencies (“frequency band”) Hence “band” “width” Copyright Fall 2011, Rudra Dutta, NCSU

Bandwidth limited Bit rate Nyquist’s theorem Maximum bit rate = 2H log2 V bits/sec H = bandwidth V = number of discrete states Shannon’s theorem Maximum bit rate = H log2 (1 + S/N) bits/sec Introduces signal-noise ratio Insight: random characteristic limits bit rate Note on application SNR in Shannon’s theorem - ratio of power content (PS/PN) Usual unit of SNR - dB, a logarithmic unit dB = 10 log10 (PS/PN) Copyright Fall 2011, Rudra Dutta, NCSU

Examples A digital signal is sent over a 7.5-kHz channel whose signal-to-noise ratio is 20 dB. What is the maximum achievable data rate? Since 20 dB is the same as 100:1 (because 20 = 10 log10(100/1)), we apply Shannon’s theorem to obtain 7500 (log2101) = 50 Kbps.   A binary signal is sent over a 6 MHz channel with SNR 30 dB. What data rate will be achieved? Again, the theoretically maximum bitrate of the channel is available as 6000000 (log21001) = 59.8 Mbps. But in this case, we are already told that the signal is binary, that is only two discrete states of the medium can be used. We may not be able to utilize the full SNR of the medium with only two states; to check, we must apply Nyquist’s theorem with V = 2. Indeed, we get 2 * 6000000 * log22 = 12 Mbps. Thus this is the maximum bitrate that will be achieved by a binary signal. Copyright Fall 2011, Rudra Dutta, NCSU

Comparing Results Both results give bitrates, but Nyquist’s theorem With different assumptions and input Nyquist’s theorem Bit rate IF exactly V states are successfully used Mo-Dem equipment already decided Noise must allow V states Often stated as perfect channel assumption Shannon’s result Estimation of what value of V will be successful Noise level decides, so need noise level as input Either might be larger, depending on input Copyright Fall 2011, Rudra Dutta, NCSU

What Have We Learned? EM communication links provide bit pipes – lowest layer of networking Various transmission methodologies Theoretical results providing channel bit rates At higher layers, bit rate is what we are primarily interested in Validation of layering concept Copyright Fall 2011, Rudra Dutta, NCSU