electrical communications systems ece.09.331 spring 2009

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

Electrical Electrical Communications SystemsCommunications Systems

ECE.09.331ECE.09.331 Spring 2009Spring 2009

Shreekanth MandayamECE Department

Rowan University

http://users.rowan.edu/~shreek/spring09/ecomms/

Lecture 1bLecture 1bJanuary 21, 2009January 21, 2009


ECOMMS: TopicsECOMMS: Topics

Probability

Inform ation

Entropy

Channel Capacity

Discrete

Pow er & Energy S ignals

Continuous Fourier T ransform

Discrete Fourier T ransform

Baseband and Bandpass S ignals

Com plex Envelope

G aussian Noise & SNR

Random VariablesNoise Calculations

Continuous

Signals

AMSw itching M odulator

Envelop Detector

DSB-SCProduct M odulatorCoherent Detector

Costas Loop

SSBW eaver's M ethodPhasing M ethod

Frequency M ethod

Frequency & Phase M odulationNarrow band/W idebandVCO & S lope Detector

PLL

Analog

Source EncodingHuffm an codes

Error-control EncodingHam m ing Codes

Sam plingPAM

QuantizationPCM

Line Encoding

T im e Division M uxT 1 (DS1) Standards

Packet Sw itchingEthernet

ISO 7-Layer Protocol

BasebandCODEC

ASKPSKFSK

BPSK

QPSK

M -ary PSK

QAM

BandpassM ODEM

DigitalDigita l Com m T ransceiver

System s

Electrical Com m unication System s


PlanPlan• Baseband and Bandpass Signals

• Recall: Comm. Sys. Block diagram • Aside: Why go to higher frequencies?• International & US Frequency Allocations

• Intoduction to Information Theory• Recall: List of topics• Probability• Information• Entropy

• Signals and Noise


Comm. Sys. Bock DiagramComm. Sys. Bock Diagram

)(~ tmTxs(t)

Channelr(t)

m(t)

Noise

RxBaseband

SignalBaseband

SignalBandpassSignal• “Low” Frequencies

• <20 kHz• Original data rate

• “High” Frequencies• >300 kHz• Transmission data rate

ModulationDemodulation

orDetection

Formal definitions will be provided later


Aside: Why go to higher Aside: Why go to higher frequencies?frequencies?

Tx /2

Half-wave dipole antenna

c = f c = 3E+08 ms-1

Calculate for

f = 5 kHz

f = 300 kHz

There are also other reasons for going from baseband to bandpass


Frequency AllocationsFrequency Allocations

• International Frequency Allocations: http://www.fcc.gov/oet/spectrum/table/Welcome.html

• US Frequency Allocation Chart: http://www.ntia.doc.gov/osmhome/allochrt.html


InformationInformationInfo

SourceInfo

SourceInfo Sink

Info Sink

CommSystem

• Recall:

• Information Source: a system that produces messages (waveforms or signals)

• Digital/Discrete Information Source: Produces a finite set of possible messages

• Digital/Discrete Waveform: A function of time that can only have discrete values

• Digital Communication System: Transfers information from a digital source to a digital sink


Another Classification of Another Classification of Signals (Waveforms)Signals (Waveforms)

• Deterministic Signals: Can be modeled as a completely specified function of time

• Random or Stochastic Signals: Cannot be completely specified as a function of time; must be modeled probabilistically

• What type of signals are information bearing?


Signals and NoiseSignals and Noise

• Strictly, both signals and noise are stochastic and must be modeled as such

• We will make these approximations, initially:• Noise is ignored• Signals are deterministic

Comm. Waveform

Signal(desired)

Noise(undesired)

Lab 1


Measures of InformationMeasures of Information

• Definitions• Probability• Information• Entropy• Source Rate

• Recall: Shannon’s Theorem• If R < C = B log2(1 + S/N), then we can have error-

free transmission in the presence of noise

MATLAB DEMO:entropy.m


SummarySummary

electrical communications systems ece.09.331 spring 2009

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