# Communication Systems IK2506

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Communication Systems IK2506
Anders Västberg

TEN1: 6 HEC. INL1: 1,5 HEC. 3 Problem Assignments Required reading: Carlson, B., et. al., Communication Systems, McGrawHill, 2002. Course Webpage:

Teachers Anders Västberg (Examiner) Svante Signell vastberg@kth.se
Svante Signell

Supplementary rules for examination
Rule 1: All group members are responsible for group assignments Rule 2: Document any help received and all sources used Rule 3: Do not copy the solutions of others Rule 4: Be prepared to present your solution Rule 5: Use the attendance list correctly For more information, see KTH rules at:

Mathematica and MATLAB

Carlson: Communication Systems
Signals and Spectra Signal Transmission and Filtering Random Signals and Noise Analog Modulation Analog Communication Systems Noise in Analog Modulation Systems Sampling and Pulse Modulation Digital Modulation Information Theory and Channel Coding [Stallings., 2005]

COS Wireless Courses IK2511 Wireless Network Project Research Project
Networks Radio Resource Management for Wireless Networks Data Transmission over Radio Channels, Error Control Coding for Radio Channels IK2508 Wireless Transmission IK2507 Wireless Communication Systems Radio Propagation, Link Design and Diversity, Spectrum Resource Management IK2506 Advanced Communication Systems Signals, Systems and Spectra Modulation, Stochastic Processes

Course Aim Give the student the ability to analyze the design parameters of a communication system. That means that the student should be able to: Explain the system structure of analogue and digital communication systems Use mathematical tools to analyse the performance of communication systems Use probability theory and stochastic processes in communication system applications.

Communication Systems
Main functionality: Information Transfer Can not cover all types of communication systems Can not cover the detailed implementation Look at system level

Types of Communication Systems
Analog Communication Systems Analog message: “Physical quantity that varies with time” Digital Communication Systems Digital message: “Ordered sequence of symbols selected from a finite set of discrete elements”

Communication Systems
Message signal Source of information Transmitter Transmitted signal Channel Estimate of message signal Received signal Receiver Information sink [Ahlin et. al., 2006]

Basic Structure Transmitter Transmission Channel Receiver Modulation
Coding Transmission Channel Loss or Attenuation Distortion Interference Noise Receiver Amplification Demodulation and decoding Filtering

Alteration of the Signal
Loss or Attenuation Can be compensated by amplification at the receiver Alteration of the Signal Shape Distortion Disappears when the signal is turned off Linear distortion may be corrected by the use of equalizers (special filter). Interference Contamination by other signals from human sources Noise Contamination by signals from natural processes both internal and external to the system

Types of Communication
Simplex (SX) One way communication Full-duplex (FDX) Two way communication at the same time Half-duplex (HDX) Two way communication, but not at the same time.

Fundamental Physical Limitations
Bandwidth If a signal changes rapidly in time, its frequency content or spectrum extends over a wide range, i.e. the signal has a large bandwidth Transmission bandwidth Noise Thermal noise

Analog Communication System
Source of information Signal Processing Modulator RF-Stage Channel Information sink Signal Processing Demodulator RF-Stage [Slimane]

Modulation Modulating signal Carrier Wave
Represent the message Carrier Wave Waveform the suits the application Modulation is a reversible operation Modulation – Demodulation Frequency translation

Modulation Modulation for Efficient Transmission
Antennas should have a dimension of at least 1/10 of the wavelength of the radio signal Modulation to Overcome Hardware Limitations Bandwidth should be at most 1/10 of the carrier frequency Modulation to Reduce Noise and Interference Wideband noise reduction – Increase bandwidth to reduce signal power Modulation for Frequency Assignment Modulation for Multiplexing Multiple Access

Digital Communication System
Source of Information Source Encoder Channel Encoder Digital Modulator Modulator RF-Stage Channel Information Sink Source Decoder Channel Decoder Digital Demodulator Demodulator RF-Stage [Slimane]

Coding Modulation – Signal Processing Operation
Coding – Symbol Processing Operation Encode – Decode Channel Coding Source Coding

decibels The bel is a logarithmic unit of power ratios. One bel corresponds to an increase of power by a factor of 10 relative to some reference power, Pref. The bel is a large unit, so that decibel (dB) is almost always used: The above equation may also be used to express a ratio of voltages (or field strengths) provided that they appear across the same impedance (or in a medium with the same wave impedance): [Saunders, 1999]

decibels Unit Reference Power Application dBW 1 W Absolute power dBm
1 mW P [dbW] = P [dBm] - 30 dBmV 1 mV Absolute voltage, typically at the input terminals of a receiver dB any Gain or loss of a network dBmV/m 1 mV/m Electric field strength dBi Power radiated by and isotropic reference antenna Gain of an antenna dBd Power radiated by a half-wave dipole 0 dBd = 2.15 dBi [Saunders, 1999]

Signals Deterministic Signals Stochastic Signals Periodic Signals
Non-Periodic Stochastic Signals Stationary Non Stationary