ece 442 c ommunication s ystem d esign l ecture 1. m odulation husheng li dept. of eecs the...

ECE 442 COMMUNICATION SYSTEM DESIGNLECTURE 1. MODULATIONHusheng Li

Dept. of EECS

The University of Tennessee

COURSE INFORMATION

Lecturer: Husheng Li Time: 12:40pm --- 1:55pm Location: MK404 Office time: 3pm --- 4pm, everyday Office: MK644 Course website http://web.eecs.utk.edu/~husheng/ECE442_2012.htm

TEXTBOOK

A. B. Carlson and P. B. Crilly, Communication Systems, 5th edition, McGraw Hill, 2010

REFERENCE BOOK (1)

J.Proakis and M. Salehi, Digital Communications, 5th Edition, McGraw Hill, 2008

REFERENCE BOOK (2)

A. Goldsmith, Wireless Communications, Cambridge, 2005

REFERENCE BOOK (3)

D. Tse and P. Viswanath, Fundamentals of Wireless Communication, Cambridge, 2005

LOGISTICS

Grading: midterm/final tests (50%), homework (4 problems each week, 25%), projects (totally 3, 25%)

Projects: Project 1: Use Matlab Simulink to simulate the

performance of a communication system (deadline: midterm)

Project 2: Use Matlab to implement the coding and decoding algorithms of convoulutional codes. Evaluate the performance (deadline: April 15th).

Project 3: A report about 4G systems (deadline: Final exam)

COVERAGE

DIGITAL MODULATION / DEMODULATION

Modulation means loading digital information bits into the continuous waveforms at the transmitter. Demodulation is the inverse procedure.

When a sinusoidal signal is used for radio emission, the information can be carried at the three elements: amplitude (amplitude-shift keying: ASK), frequency (frequency-shift keying: FSK) and phase (phase-shift keying: PSK).

)sin()( wtAtx

ILLUSTRATION

BANDPASS SIGNAL

Any modulated bandpass signal can be writtend in the following quadratic-carrier form:

The equivalent lowpass spectrum is defined as

)sin()()cos()()( twtxtwtxAtx cqcic

)()()( fGfGfG qilp

AMPLITUDE MODULATION

An M-ary ASK signal can be written as

A special case is called OOK.

k

Dk kDtpatx )()(

SPECTRUM EFFICIENCY The spectrum efficiency is given by

HzbpsM /log2

QAM

Quadrature-carrier AM (QAM) achieves twice the spectrum efficiency of binary ASK

Signal Constellation

PHASE MODULATION

An M-ary PSK signal is expressed in general by

which can be decomposed into the quadrature form.

k

Dkccc kDtptwAtx )()cos()(

QPSK 8-PSK

FREQUENCY MODULATION

In FSK, the frequency is given by

kdck afff

SPECTRUM OF FSK

The i and q elements of Sunde’s FSK are mutually independent.

Sunde’s FSK has very little spillover.

M-ARY ORTHOGONAL FSK AND CPFSK

For the M-ary orthogonal FSK, the M keyed frequencies are spaced by

In CPFSK, the information signal is

the RF signal is then given by

2/2/12 rDfd

0

)()(k

Dk kDtpatx

t

dccc dxwtwAtx0

cos)(

COHERENT BINARY SYSTEMS

A coherent bandpass system employs information about the carrier frequency and phase at the receiver to detect the message.

A noncoherent system does not need synchronization with the carrier phase, thus causing performance degradation compared with coherent bandpass system.

BANDPASS BINARY RECEIVER

The filter for optimum binary detection should be matched to the difference between the two signaling waveforms.

TWO ALTERNATIVE APPROACHES

Parallel matched

filter

Correlation detector

HOW TO ANALYZE THE BIT ERROR RATE?

When the two possible outputs are z1 and z0, the bit error rate is given by

2

|| 01 zzQPe