Communication Systems

Course Objectives
To introduce the student to analog and digital communication systems.

1.0 Analog and Digital Communication Systems: (2 hours)
1.1 Analog and digital communication sources, transmitters, transmission channels and receivers
1.2 Fundamental limitations due to noise, distortion and interference and the relationships between noise, bandwidth and information
1.3 Types and reasons for modulation

2.0 Representation of Communication Signals and Systems: (2 hours)
2.1 Review of signal transfer in linear systems, the ideal lowpass filter and distortionless transmission, the importance of channel bandwidth
2.2 The Hilbert transform and its properties
2.3 Bandpass systems and band-limited signals with examples
2.4 Complex envelope representation of band-limited signals, time domain expressions, rectangular representation (in-phase and quadrature components), polar representation (envelope and phase)

3.0 Continuous Wave Linear Modulators: (6 hours)
3.1 Amplitude modulation (AM), time domain expressions and modulation index, frequency domain (spectral). representations, transmission bandwidth for AM
3.2 AM modulation for a single tone message, phasor diagram of an AM signal, illustration of the carrier and sideband components
3.3 Transmission requirements for AM, normalized power and its use in communication, carrier power and sideband power
3.4 Double sideband suppressed carrier (DSB) modulation, time and frequency domain expressions
3.5 Transmission requirements for DBS, bandwidth and transmission power for DSB
3.6 Methods of generating AM and DSB, square modulators, balanced modulators, ring modulators
3.7 Single sideband modulation (SSB), generation of SSB using a sideband filter, indirect generation of SSB
3.8 Representation of SSB signals
3.9 Transmission requirements for SSB, transmit bandwidth and power, sideband filter examples
3.10 Vestigial sideband modulation (VSB)

4.0 Demodulators for Linear Modulation: (4 hours)
4.1 Demodulation of AM signals, square law and envelop detectors
4.2 The superheterodyne receiver for standard AM radio
4.3 Synchronous demodulation of AM, DSB and SSB using synchronous detection
4.4 Effects of frequency and phase errors in the local oscillator in DSB and SSB
4.5 Demodulation of SSB using carrier reinsertion and the use of SSB in telephony
4.6 Carrier recovery circuits
4.7 Introduction to the phase-locked loop (PLL)

5.0 Frequency Modulation (FM) and phase Modulation (PM): (4 hours)
5.1 Instantaneous frequency and instantaneous phase, time domain representations for FM and PM, phasor diagram for FM and PM
5.2 FM and PM signals for a single tone message, the modulation index and phasor diagrams
5.3 Spectral representation of FM and PM for a single tone message, Bessel’s functions and the Fourier series
5.4 Transmission bandwidth for FM, Carson’s rule, narrow-band and wide-band FM and PM signals
5.5 Generation of FM using Armstrong’s method, commercial FM requirements
5.6 Demodulation of FM and PM signals, the limiter discriminator
5.7 Commercial FM radio and stereo FM radio
5.8 Demodulation of FM using a phase-locked loop

6.0 Frequency Division Multiplexing (FDM) Systems: (1 hours)
6.1 FDM in telephony, telephone hierarchy and examples of group and super-group generation
6.2 Satellite systems and applications, frequency division multiple access (FDMA) systems
6.3 Filter and oscillator requirements in FDM

7.0 Spectral Analysis: (3 hours)
7.1 Review of Fourier transform theory, energy and power, parseval’s theorem
7.2 Power spectral density functions (pfsd), analog spectrum analyzers
7.3 The auto-correlation function, relationship between the pfsd and the auto-correlation function, pfsd’s of harmonic signals, psfd’s of uncorrelated (white) signals
7.4 Estimating psfd’s, the periodogram, psdf’s of harmonic signals
7.5 Effect of windowing on psdf estimates

8.0 Digital Communication Systems: (2 hours)
8.1 Digital communication sources, transmitters, transmission channels, and receivers
8.2 Distortion, noise, and interference
8.3 Nyquist sampling theory, sampling of analog signals, spectrum of a sampled signal
8.4 Sampling theorem for band-limited signals, effects of aliasing, reconstruction of sampled signals

9.0 Pulse Modulation Systems: (6 hours)
9.1 Pulse amplitude modulation (PAM), bandwidth requirements and reconstruction
methods, time division multiplexing
9.2 Pulse duration modulation (PDM), generation of PDM signals and reconstruction methods
9.3 Analog to digital conversion, quantization and encoding techniques, application to pulse code modulation (PCM)
9.4 Quantization noise in PCM, companding in PCM systems
9.5 Time division multiplexing (TDM), examples of PAM and PCM systems
9.6 The TI PCM system in telephony
9.7 The delta modulator and its operation
9.8 Quantization noise and slope overload in delta modulators, comparison of delta modulation and PCM
9.9 Introduction to linear prediction theory with applications in delta modulation

10.0 Digital Data Communication Systems: (8 hours)
10.1 Introduction to information theory, definition of information, examples of simple sources
10.2 Information rate and Shannon's channel capacity theorem
10.3 Baseband digital communication systems, multilevel coding using PAM
10.4 Pulse shaping and bandwidth considerations, intersymbol interference (ISI)
10.5 Nyquist conditional for zero ISI, band-limited Nyquist pulses, the eye diagram
10.6 Correlative coding techniques, reducing transmission bandwidth with duobinary encoding
10.7 Spectral shaping using bipolar and modified duobinary encoding techniques
10.8 Bandpass (modulated) digital data systems, digital modulation, PSK, DPSK and FSK
10.9 M-array data communication systems, quadrature amplitude modulation (QAM) systems, four phase PSK
10.10 Applications of modems for transmission over telephone lines

11.0 Representation of Random Signals and Noise in Communication Systems: (8 hours)
11.1 Signal power and spectral representations, the auto-correlation and power spectral density (pfsd) functions
11.2 White noise, thermal noise, the psdf of white signals
11.3 Input and output relationships for random signals and noise passed through a linear time invariant system, band-limited white noise, RC filtering of white noise
11.4 The noise bandwidth of a linear time invariant system and its use in communications
11.5 Optimum detection of a pulse in additive white noise, the matched filter
11.6 Matched filter detection in baseband data communication systems
11.7 Comparison of the matched filter for rectangular pulses with first and second order suboptimum Butterworth filters
11.8 Performance limitation of baseband data communications due to noise,
probability of error expressions for multilevel data signals
11.9 Relationship between signal power, noise and channel bandwidth, comparison of systems using Shannon capacity
11.10 Narrowband noise representation, generation of narrowband noise and psdf, time domain expressions for narrowband noise

12.0 Noise Performance of Analog and Digital Communication Systems: (8 hours)
12.1 Signal-to-noise ratio in linear modulation, synchronous detection of DSB
12.2 Signal-to-noise ratios for AM and SSB, comparison of DSB, SSB and AM
12.3 Effect of noise in envelope and square law detection of AM, threshold effects in nonlinear detectors
12.4 Signal-to-noise ratio for FM, SNR improvements using preemphasis and deemphasis networks
12.5 FM threshold effects, noise clicks in FM systems
12.6 Comparison of linear and exponential modulation systems for additive white band-limited noise channels
12.7 Effects of noise in modulated digital communication systems, optimum binary systems
12.8 Probability of error expressions for binary communications
12.9 Probability of error in QAM systems, comparison of digital modulation systems

13.0 Introduction to Coding Theory: (5 hours)
13.1 Block coding for error detection and correction, parity check bits and block coding
13.2 Examples of single cyclic error correcting codes
13.3 Introduction to convolution codes

Laboratory: Following Ten experiments are recommended:
1.0 Lowpass and bandpass filters with applications in communications. The student will be required to design and test a 4th order filter constructed using two 2nd order sections. The filter chips used will be the Burr-Brown UAFAI and the implementation could be Butterworth, Chebyshev or Bessel.

2.0 and 3.0 Linear modulation. This experiment will familiarize the student with linear modulation methods including double sideband modulation (DBS) and amplitude modulation (AM). will be compared to envelope detection.

4.0 Power spectral density (psdf) measurement of signals. A digital spectrum analyzer will be used to measure the psdf of signals. In particular, the power spectral density of frequency modulated signals will be analyzed and compared with theory.

5.0 Demodulation of frequency modulated signals using a phase locked loop (PLL). A second order PLL to demodulate an FM signal will be designed and tested in the laboratory. The PLL chip to be used is the CD4046B.

6.0 The delta modulator. In this experiment the effects of sampling rate, number of bits in the up-down counter are quantized and measured. The resulting family of SWR curves are compared with expected theoretical results.

7.0 Baseband data communications. A baseband communication system using NRZ signals and 2nd order transmit and receive filters is investigated. The measurements include the eye diagram and probability of error.

8.0 Correlative encoding. A correlative encoder is designed by the student and implemented in hardware. Commonly used encoders include duobinary, bipolar and modified duobinary. A corresponding digital simulation can also be used to illustrate the difference between analog and digital filtering.

9.0 Demodulation of frequency shift keying (FSK) using a phase locked loop (PLL). This is the digital counter-part of Laboratory #5 in COMMUNICATION SYSTEMS I. The PLL is designed to provide a good EYE while still ensuring that the loop stays in lock.

Note: A computer package can be used to replace most of the above hardware experiments. One such package is marketed by: Icucom Corporation, 48 Ford Avenue, Troy, New York 12080, (518) 247-7711 and is called "The Workstation Communications Simulator".

References:
1.0 S. Haykin, "An Introduction to Analog and Digital Communication", Wiley, New York, 1989.
2.0 L. W. Couch II, "Digital and Analog Communication Systems", 2nd Edition, Macmillan Publishing Company, New York, 1987.