1/28/10 1 MS in Telecommunications TCOM 500: Modern Telecommunications Dr. Bernd-Peter Paris George Mason University Spring 2009 MS in Telecommunications Outline • Digital Technology and its benefits • Digital and Analog Signals • A/D and D/A conversion • Binary and related number systems Paris 2 TCOM 500: Modern Telecommunications1/28/10 2 MS in Telecommunications DIGITAL TECHNOLOGY Paris 3 TCOM 500: Modern Telecommunications MS in Telecommunications Foundations of Digital Technology • The advent of digital technology has enabled the information revolution of the last three decades. • The technical corner-stone for enabling digital circuits is the transistor. • Invented 1947 at Bell Labs. • Large numbers of transistors can be combined into complex systems called Integrated Circuits (ICs). • First working integrated circuit produced by Jack Kilby in 1958 at Texas Instruments. Paris 4 TCOM 500: Modern Telecommunications1/28/10 3 MS in Telecommunications Very Large Integrated Circuits • Since the invention of integrated circuits, the number of transistors on an IC has increased by many orders of magnitude. • VLSI – Very Large Scale Integration • Hundreds of thousands of transistors in the early 1980s, • Several billion transistors as of 2009. Paris 5 TCOM 500: Modern Telecommunications ATMEL Diopsis 740 Dual-core DSP processor SoC MS in Telecommunications Moore’s Law • Moore’s law predicts that the number of transistors in integrated circuits doubles every two years. • Similar exponential growth is observed for processing speed, memory size, hard disk capacity, or number of pixels in digital cameras. Paris 6 TCOM 500: Modern Telecommunications1/28/10 4 MS in Telecommunications Benefits of Integrated Circuits • In comparison to circuits built from discrete components, ICs have two main advantages: • Cost: • Mass production enabled by “printing” the circuits via photolitography – not one transistor at a time. • Significantly less material required. • Performance: • Components can switch quickly because they are small and close together. Paris 7 TCOM 500: Modern Telecommunications MS in Telecommunications Impact on Telecommunications • For a field of technology to be successful, it must leverage the benefits enabled by digital integrated circuits. • The growth of Telecommunications has been and will be fueled by advances in digital hardware. • Today, virtually all exchange of information is in digital form. • This is the technological basis for providing telecommunications services at decreasing cost and increasing data rates. Paris 8 TCOM 500: Modern Telecommunications Cisco 805 Router1/28/10 5 MS in Telecommunications Central Questions for this Course • How is information represented in digital form? • Where do bits come from? • How is digital information processed and transmitted? • What is the best way to send digital information to a remote location? • How does one build large scale networks for exchanging digital information. • Using digital technology, of course! Paris 9 TCOM 500: Modern Telecommunications MS in Telecommunications ANALOG AND DIGITAL SIGNALS Paris 10 TCOM 500: Modern Telecommunications1/28/10 6 MS in Telecommunications Running Example • To make our discussion concrete, we focus on the problem of sending an audio signal between to locations. • As in telephony or audio broadcasting. Paris 11 TCOM 500: Modern Telecommunications Hi! How are you? Hi! How are you? Communication System MS in Telecommunications Transducers • The acoustical audio signal cannot be transmitted directly over long distances. • It must be converted into an electrical signal first. • At the receiving location, the electrical signal is converted back to an acoustical signal. • Devices that convert between electrical and non-electrical signals are called transducers. • The specific transducers, we need for our example are: • Microphone: converts an acoustic signal into an electric signal. • Speaker: converts an electrical into an acoustic signal. Paris 12 TCOM 500: Modern Telecommunications1/28/10 7 MS in Telecommunications Audio Transducer: Microphone • A microphone converts the audible changes in air pressure into a corresponding electrical signal. Paris 13 TCOM 500: Modern Telecommunications Hi! How are you? Oscilloscope Time Voltage MS in Telecommunications A Very Simple Communication System • With our transducers, we can build a very simple communications system. • The figure below shows (approximately) how the telephone system used to work. • Simple Intercom systems also work similarly. Paris 14 TCOM 500: Modern Telecommunications Hi! How are you? Hi! How are you? Electrical Cable1/28/10 8 MS in Telecommunications A Real Audio Signal Paris 15 TCOM 500: Modern Telecommunications MS in Telecommunications Analog Signals • The example signal is an analog signal. • Analog signals are continuous in time and amplitude. • That means: • The signal has an amplitude value for every instance of time, and • All amplitude values are possible. Paris 16 TCOM 500: Modern Telecommunications1/28/10 9 MS in Telecommunications Digital Signals • Analog signals are not suitable for processing by digital hardware. • For processing by digital hardware the signal must be discrete in time and amplitude. • Discrete-time: Instead of observing the signal at every instant of time, it is measured only at equally spaced sampling instances. This process is called Sampling. • Discrete-amplitude: The measured amplitudes must be rounded so that they can be represented in digital hardware. This process is called Quantization. • The process of converting an analog signal to a digital signal is called Analog-to-Digital conversion (ADC). • Digital signals are (quite literally) represented as a sequence of (integer) numbers in digital hardware. Paris 17 TCOM 500: Modern Telecommunications MS in Telecommunications ANALOG-TO-DIGITAL CONVERSION Paris 18 TCOM 500: Modern Telecommunications1/28/10 10 MS in Telecommunications From Analog Signal to Digital Samples Paris 19 TCOM 500: Modern Telecommunications … 6356 7497 8390 8956 9944 10892 10667 9601 8118 6498 5344 … MS in Telecommunications Sampling • The sampling process