Wireless Technology For Non-Engineers

Transcription

1 ITU/BDT Regulatory Reform Unit G-REX Virtual Conference Wireless Technology For Non-Engineers Dale N. Hatfield Adjunct Professor, University of Colorado at Boulder March 17, 2005 Introduction Agenda Overview of Telecommunications Technology Trends Some Additional Groundwork Radio Communications Systems 1

2 Introduction Purpose: To provide non-engineers with a basic background in telecommunications technology in general and wireless technology in particular Overview of Telecommunications Technology Trends Outline Review of Basic Concepts Answer Seven Questions About Trends Analog versus Digital -- Why Digital? Voice versus Data -- What s the Difference? Circuit Switching versus Packet Switching -- Why Packet Switching? Narrowband versus Broadband -- Why Broadband? 2

3 Overview of Telecommunications Technology Trends Outline Answer Seven Questions About Trends (Cont d) High Latency versus Low Latency -- Why Low Latency? Intelligence Interior to the Network versus at the Edge of the Network -- Why at the Edge? Wired versus Wireless -- Why Wireless? The Network of the Future Review of Basic Concepts Analog Signal Intensity Time 3

4 Review of Basic Concepts Digital Signal Intensity Time Analog vs. Digital -- Why Digital? Analog to Digital and Digital to Analog Conversion Analog Signal Sequence of Numbers (Transmitted as a Sequence of Binary Numbers) Analog Signal A/D D/A On and Off Pulses Representing Binary Numbers 4

5 Analog vs. Digital -- Why Digital? Analog Amplification vs. Digital Regeneration INPUT AMP AMP AMP OUTPUT Analog Amplification: Noise Accumulates INPUT Repeater Repeater Repeater Digital Regeneration: Perfect Signal is Regenerated Analog vs. Digital -- Why Digital? Advantages Signal Regeneration Ease of Multiplexing Ease of Encryption Ease of Signaling Use of Modern Technology ( Moore s Law ) Performance Monitorability Operability at Low Signal/Noise or Signal/Interference 5

6 Analog vs. Digital -- Why Digital? Advantages (Cont d) Integration of Switching and Transmission Accommodation of Other Services Disadvantages: Larger Bandwidth Requirements Critical Timing Need for Analog to Digital Converters Source: Bellamy, Digital Telephony Voice vs. Data -- What s the Difference? Voice Information rate constant Intolerant of delays and variations in delay Tolerant of noise/distortion Symmetrical Data Information rate bursty/fractal Tolerant of delay Intolerant of noise/interference Often asymmetrical 6

7 Circuit Switching vs. Packet Switching -- Why Packet Switching? Types of Switching Circuit Switching: The practice of establishing an end-to-end connection between users of a network. The associated facilities are dedicated to the particular connection for the duration of the call. Message Switching: The practice of transporting complete messages from a source to a destination in non-real time and without interaction between the source and destination, usually in a store-and-forward fashion Packet Switching: The practice of transporting messages through a network, in which long messages are subdivided into short packets. The packets are then transmitted as in message switching (i.e, in a store-and-forward fashion) Source: Circuit Switching vs. Packet Switching -- Why Packet Switching? Traditional Circuit Switched Connection IXC POP IXC POP Key: LEC=Local Exchange Carrier IXC=Interexchange Carrier CO =Central Office POP=Point of Presence LEC CO LEC CO 7

8 Circuit Switching vs. Packet Switching -- Why Packet Switching? Traditional Packet Switched Network PS Dumb Terminal PS Host Computer "Dumb" Terminal Dumb Terminal PS PS PS M A M A PS Addressed Packets (e.g. collection of characters) PS = Packet Switch Functions: Error Control, Routing, Flow Control Circuit Switching vs. Packet Switching -- Why Packet Switching? Because of the differences between voice and data, in the past: Circuit switching and time division multiplexing were used in the public switched telephone network (PSTN) Packet switching and statistical multiplexing was used in public (and private) switched data networks 8

9 Circuit Switching vs. Packet Switching -- Why Packet Switching? Circuit Switching and Time Division Multiplexing Advantages No transmission delay Disadvantages Only fixed increments of bandwidth provided Inefficient channel utilization for bursty traffic High call setup overhead Circuit Switching vs. Packet Switching -- Why Packet Switching? Packet Switching and Statistical Multiplexing Advantages User does not consume network resources when no information is being sent Bandwidth on demand Efficient utilization of transmission lines and ports Other Disadvantages Delay (high latency) 9

10 Circuit Switching vs. Packet Switching -- Why Packet Switching? Modern Packet Switching Advantages of traditional packet switching including; Not consuming bandwidth when idle Providing bandwidth on demand Capturing efficiencies associated with statistical multiplexing Efficiently handling asymmetric traffic Circuit Switching vs. Packet Switching -- Why Packet Switching? Modern Packet Switching (Cont d) Additional advantages including: Offering always on connectivity Offering lower delay (latency) Providing the ability to handle different types of signals -- voice, data, image, and video on common transmission and switching platforms 10

11 Narrowband vs. Broadband -- Why Broadband? In simple terms, bandwidth is just a measure of how fast information can be transmitted The larger the bandwidth, the more information that can be transmitted in a given amount of time Narrowband vs. Broadband -- Why Broadband? In the digital world, bandwidth is measured in bits per second Analogous measures: vehicles per hour or gallons per minute 11

12 Narrowband vs. Broadband -- Why Broadband? Illustration of the Importance of Bandwidth Computer Monitor High Latency vs. Low Latency -- Why Low Latency? In simple terms, latency just refers to delay Latency is the amount of time it takes information (e.g., a packet) to travel from source to destination In combination, latency and bandwidth define the speed and capacity of a network Low latency is critical in voice communications and certain real-time data communications applications 12

13 Intelligence Interior to the Network versus at the Edge of the Network -- Why at the Edge? Architecture of the Traditional Public Switched Telephone Network Circuit switching Dumb terminals with limited capabilities Intelligence residing in switches, intelligent peripherals, service control points, etc. interior to the network Services created inside the network Intelligence Interior to the Network versus at the Edge of the Network -- Why at the Edge? Architecture of Networks Based Upon the Internet Protocol (IP) Packet switching Dumb network Intelligent terminals (e.g., PCs) with a rich set of capabilities Services created in terminals/servers at the edge of the network 13

14 Wired versus Wireless -- Why Wireless? Motivation for Wireless Increased mobility of the workforce and society more generally Increased efficiency and convenience and safety Potentially lower infrastructure costs for certain fixed applications; more fungible investment Other Wired versus Wireless -- Why Wireless? Evolution of Commercial Mobile Radio Services First generation: analog, circuit switched, narrowband Second generation: digital, circuit switched, narrowband Third generation: digital, packet oriented, wideband/broadband 14

15 The Network of the Future Network Trends/Goals from a Technological Perspective: All applications -- voice, data, image, video, multimedia -- conveyed on an all digital, packet-switched, broadband, low latency network or platform A network of networks platform that uses common, open, non-proprietary standards and protocols (e.g., the Internet Protocol -- IP) The Network of the Future Network Trends/Goals from a Technological Perspective: (Cont d) Extension of this platform using wireless technology to allow users to communicate anyplace, anytime, in any mode or combination of modes. 15

16 The Network of the Future Integrated Network with Integrated Access Customer Node Edge Node IP Based Network Customer Premises Access Local/Regional Backbone Some Additional Groundwork Outline Characteristics of Analog Signals Concept of Bandwidth Filters Transmission Media 16

17 Some Additional Groundwork Characteristics of Analog Signals A periodic signal is a simple sort of signal in which the same fundamental pattern or shape repeats itself over and over in time A particularly important type of periodic signal is the sine wave Sine waves are associated with oscillatory actions or motions Some Additional Groundwork Characteristics of Analog Signals Oscillatory Motion Pendulum Tuning Fork Turning Wheel Radio Transmitter (Oscillator) 17

18 Some Additional Groundwork Characteristics of Analog Signals Sine Wave Intensity Time Some Additional Groundwork Characteristics of Analog Signals Parameters of Sine Waves Amplitude Frequency Phase The Above Three Parameters Completely Specify a Sine Wave 18

19 Some Additional Groundwork Characteristics of Analog Signals Parameters of Sine Waves - Amplitude Intensity Amplitude Time Some Additional Groundwork Characteristics of Analog Signals Parameters of Sine Waves - Frequency f = 1 cycle per second 1 Second f = 2 cycles per second 19

20 Some Additional Groundwork Characteristics of Analog Signals Parameters of Sine Waves - Phase Time φ Time Note that although the two sine waves are otherwise identical (in amplitude and frequency), they are shifted in time relatively to one another; the time difference (φ) is known as the phase Some Additional Groundwork Concept of Bandwidth The concept of bandwidth is used in two (interrelated) ways: To mean the range of signal frequencies that a circuit or channel will pass To mean the range of signal frequencies that are occupied or utilized by signal (e.g., an ordinary voice or an NTSC or PAL television signal) The amount of information that a circuit or channel can carry per unit of time depends upon its bandwidth and the strength of the desired signal relative to the noise in the channel (Shannon s Law) 20

21 Some Additional Groundwork Concept of Bandwidth (Cont d) Bandwidth is really an analog concept but it has been adopted in the digital world In the digital world, bandwidth is measured in bits per second Note that bandwidth (as measured in bits per second) is a rate, not a speed (despite the widespread use of the term) Some Additional Groundwork Concept of Bandwidth (Cont d) If the bandwidth of the information source is greater than bandwidth of the link or channel, then some of the information (e.g., quality) will be lost in transmission If the bandwidth of the information source is less than the bandwidth of the link or channel, then some of the bandwidth (capacity) of the link or channel will be wasted 21

22 Some Additional Groundwork Filters Filter: In electronics, a device that transmits only part of the incident energy and may thereby change the spectral distribution of energy: high-pass filters transmit or pass energy above a certain frequency low-pass filters pass energy below a certain frequency bandpass filters pass energy of a certain bandwidth; band-stop [or notch] filters transmit energy outside a specific frequency band Source: Federal Standard 1037C Some Additional Groundwork Filters (Continued) High-pass Filter f o Low-pass Filter Band-pass Filter f o f 1 f 2 Stop-band or Notch Filter f 1 f 2 Increasing Frequency 22

23 Some Additional Groundwork Filters (Continued) Filters shown on the previous page are ideal filters in that they exhibit: Zero attenuation where signals are to be passed Infinite attenuation where signals are to be rejected Perfect transitions from one to the other Perfect filters can only be approached and only at increasing cost Implications for spectrum management (e.g., guard bands) Some Additional Groundwork Transmission Media Twisted Pair Copper Cable Coaxial Cable Fiber-Optic Cable Wireless (Radio) 23

24 Radio Communications Systems Outline A Radio Communications Link Some Introductory Notes Modulation and Demodulation Building Blocks of Transmitters and Receivers Modulation Techniques General Modulation Techniques Digital Improving the Spectral Efficiency of a Link Multiple Access Techniques Radio Communications Systems A Radio Communications Link Transmission Line Antenna Antenna Transmission Line Transmitter Receiver Radio Waves 24

25 Radio Communications Systems Some Introductory Notes A pure carrier wave conveys no information and occupies no bandwidth A carrier can be used to convey information by changing one or more of the three basic characteristics of the wave i.e., amplitude, frequency or phase in a process called modulation Radio Communications Systems Some Introductory Notes (Continued) Modulation of a radio wave inevitably causes a spreading of the signal in frequency; a radio signal conveying information occupies a range of frequencies called a channel In general, the more information that is conveyed in a given amount of time, the wider the channel must be 25

26 Radio Communications Systems Some Introductory Notes (Continued) As a general proposition, signals that are spread over even wider channels (relative to the bandwidth of the information being conveyed) are more resistant to noise and interference. Radio Communications Systems Modulation and Demodulation Definitions Modulation is the process by which the information to be transmitted (e.g., voice or music) over a radio link is impressed upon the carrier wave More formally, modulation is the process, or result of the process, of varying a characteristic of a carrier, in accordance with an information-bearing signal (Fed. Std. 1037C) 26

27 Radio Communications Systems Modulation and Demodulation Definitions (Cont d) Demodulation is the process by which the information that is transmitted over a radio link is extracted from the carrier wave More formally, demodulation is the recovery, from a modulated carrier, of a signal having substantially the same characteristics as the original modulating signal (Fed. Std. 1037C) Radio Communications Systems Transmitter and Receiver Basic Building Blocks OSC MOD AMP AMP DE- MOD INFO INFO Transmitter Receiver 27

28 Radio Communications Systems Modulation Techniques (Time Domain) Amplitude Time Unmodulated Carrier (e.g., 900 MHz) Modulation (e.g., 1 khz) Audio Amplitude Modulation Radio Communications Systems Modulation Techniques (Time Domain) Amplitude Time Unmodulated Carrier (e.g., 900 MHz) Modulation (e.g., 1 khz) Audio Frequency Modulation 28

29 Radio Communications Systems Modulation Techniques (Frequency Domain) Amplitude Frequency Amplitude UnmodulatedCarrier Carrier and Sidebands Amplitude Amplitude Modulation Carrier and Sidebands Frequency Modulation Radio Communications Systems Digital Modulation (Frequency Shift Keying) Amplitude Unmodulated Carrier (e.g., 900 MHz) Time Modulation (Digital Signal) Frequency Shift Keying (FSK) 29

30 Radio Communications Systems Digital Modulation (Phase Shift Keying) Amplitude Unmodulated Carrier (e.g., 900 MHz) Time Modulation (Digital Signal) Phase Shift Keying (PSK) Radio Communications Systems Digital Modulation Techniques Amplitude Shift Keying or Modulation (ASK) Frequency Shift Keying or Modulation (FSK) Phase Shift Keying or Modulation (PSK) Combination/Refinements of Above (Examples) Gaussian Minimum Shift Keying (GMSK) Quadrature Amplitude Modulation (QAM) - a combination of phase shift modulation and amplitude modulation 30

31 Radio Communications Systems Improving the Spectral Efficiency of a Link Semaphore Example Code: = 1 = 0 Signals Sent sec 2 sec 3 sec 4 sec 5 sec Time Note in this example there is one change (symbol) per second and each symbol is encoded with one bit (zero or one); one symbol per second = one baud Radio Communications Systems Improving the Spectral Efficiency of a Link Semaphore Example (Cont d) 00 Code: Signals Sent sec 2 sec 3 sec 4 sec 5 sec Time Note in this example there is one change (symbol) per second and each symbol is encoded with two bits; one symbol per second but two bits second 31

32 Radio Communications Systems Improving the Spectral Efficiency of a Link Semaphore Example (Cont d) The transmission rate can be increased by encoding more bits per movement (symbol) but at the penalty of making it more difficult to discern the actual change; hence encoding more bits per symbol makes the signal more susceptible to interference such as fog or atmospheric variations Radio Communications Systems Improving the Spectral Efficiency of a Link Link spectral efficiency is specified in terms of the number of bits-per-second per Hertz of bandwidth The link spectral efficiency can be increased by encoding more bits per symbol (as in the case of the semaphore example) Improving the link spectral efficiency in this manner is referred to as going to higher level modulation 32

33 Radio Communications Systems Improving the Spectral Efficiency of a Link As in the case of the semaphore, going to higher level modulation makes the link more sensitive to errors caused by noise or interference Greater susceptibility to interference may mean that the links (stations) must be moved further apart which may reduce system spectrum efficiency (less frequency reuse) Since spectrum is scarce, spectrum efficiency is an important topic for regulators and operators of radio systems Radio Communications Systems Multiple Access Techniques Multiple access techniques allow multiple users to share a common communications medium (e.g., a block of radio spectrum or the bandwidth on a coaxial or fiber optic cable) Different methods Frequency Division Multiple Access Time Division Multiple Access Code Division Multiple Access Carrier Sense Multiple Access Polling Protocols 33

34 Summary and Final Comments Contact Information Dale N. Hatfield Adjunct Professor Interdisciplinary Telecommunications Program University of Colorado at Boulder Engineering Center - ECOT-311 Campus Box 530 Boulder, CO Main Tel: Direct Dial: Fax: dale.hatfield@ieee.org or hatfield@spot.colorado.edu 34