E445 Spring 2012 Lecture 1. Course TOPICS. Lecture 1 EE445 - Outcomes

Size: px

Start display at page:

Download "E445 Spring 2012 Lecture 1. Course TOPICS. Lecture 1 EE445 - Outcomes"

Randolph Bradford
5 years ago
Views:

1 E445 Spring 0 Lecture Andy V. Olson 63Cobl andyo@ece.montana.edu Lecture EE445 - Outcomes In this lecture you: will be introduced to the course grading elements should be able to define the process of communications and the elements in a communication system determine the tower height required on a perfect earth for LOS (line of sight) wireless communications communications Course Mechanics Prerequisites: EE30- Signal and Systems Analysis or equivalent or consent of the instructor Text: Digital and Analog Communications Systems, Prentice Hall, Leon W. Couch, 007, ISBN Other References: Modern Digital and Analog Communication Systems, B. P. Lathi Communication Systems, A. Bruce Carlson Fundamentals of Communications Systems, J. G. Proakis The Course Syllabus is available on the Class Website Course TOPICS Review of Signals and Spectra Analysis and Transmission of Signals Sampling and pulse code modulation Principles of Digital Baseband Signals Bandpass Signaling Principles and Circuits Bandpass Modulated Systems Introduction to the theory of probability Digital systems in the presence of noise Behavior of digital systems in the presence of noise Error correcting codes Example systems 3 4

2 $$$$$$$$ Spectrum is a limited resource Projections for the Wi-Fi market are among the rosiest in IT. At the 0. Planet Conference & Expo this week, an industry group said the $ billion Wi-Fi industry should expand at an compounded growth rate of 30 percent to nearly a $6 billion industry, putting it on par with household name brands like Budweiser and in line with growth in the mobile PC industry. Given spectrum is a limited resource we desire to pass the most information we can in the least bandwidth. What is the limiting factor? 5 6 What is Communications? INFORMATION SOURCE Communications is the Process of Transmitting Information from a Source to a Destination A Communication System Information v(t) Message Transmitter Telephone wired (electrons) FM/AM Radio wireless (EM) Fiber Optics light (photons) Speech acoustic Astronomy- light (photons) INFORMATION DESTINATION Channel Σ Additive Noise Receiver Transducer v(t)+n(t) Information Plus Noise 7

3 The Wireless Channel Figure Propagation of radio frequencies. Signal Propagation Channel Model is statistical, dependent on: the carrier frequency the signal bandwidth the terrain along and around the propagation path between the transmitter and receiver Signals follow the curvature of the earth 9 0 Couch, Digital and Analog Communication Systems, Seventh Edition 007 Pearson Education, Inc. All rights reserved Figure Propagation of radio frequencies. Figure Propagation of radio frequencies. Signals bounce between the earth and the Ionosphere Couch, Digital and Analog Communication Systems, Seventh Edition 007 Pearson Education, Inc. All rights reserved Couch, Digital and Analog Communication Systems, Seventh Edition 007 Pearson Education, Inc. All rights reserved

Line Of Sight - Tower Height to Clear a Spherical Earth Earth Bulge http://www.cisco.com/univercd/cc/td/doc/product/wireless/bbfw/ptop/ppspg0/spg0ch.

4 Line Of Sight - Tower Height to Clear a Spherical Earth Earth Bulge d = h d in miles h in feet Earth Bulge When planning for paths longer than seven miles, the curvature of the earth might become a factor in path planning and require that the antenna be located higher off the ground. The additional antenna height needed can be calculated using the following formula: D H = where H = Height of earth bulge (in feet) D = Distance between antennas (in miles) 3 Couch, Digital and Analog Communication Systems, Seventh Edition 007 Pearson Education, Inc. All rights reserved Plane Earth Loss-LOS Plane Earth Loss- Fresnel Diffraction When the wave interacts with the ground or some other obstruction we no longer have free space propagation to the Non-LOS communication involves an additional loss due to Diffraction receiver 5 6 4

5 Earth Bulge with Fresnel Diffraction Minimum Antenna Height The minimum antenna height at each end of the link for paths longer than seven miles (for smooth terrain without obstructions) is the height of the First Fresnel Zone plus the additional height required to clear the earth bulge. The formula would be: D H = F D where H = Height of the antenna (in feet) D = Distance between antennas (in miles) Line of Sight Distance Between Antenna Towers Tower Height Miles 00 feet 3 5 F = Frequency in GHz 3 Miles 5 feet Miles 0 Miles Miles 4 Miles 6 Miles Miles 0 Miles Miles 4 Miles 6 Miles Height of Tower to Avoid Flat Earth Curvature 0 feet 5 feet 0 feet 5 feet 30 feet 40 feet 50 feet 60 feet 70 feet 0 feet Tower Height Required Over Tallest Obstacle In Line-of-Sight to Provide 60% Fresnel Zone Clearance.4GHz 0.b/g (Fresnel Zone Radius = 39 Feet) GHz 0.a (Fresnel Zone Radius = 5 Feet) Free Space vs Ground effects The EM wave interacting with the ground affects path loss EELE445- Lecture Information, Power, rms, db 9 0 5

Lecture EE445 - Outcomes In this lecture you: be able to sketch the block diagram of a communications system and describe it define the function of a communications engineer define Information and

6 Lecture EE445 - Outcomes In this lecture you: be able to sketch the block diagram of a communications system and describe it define the function of a communications engineer define Information and Shannon s Law will be able to work with db, dbm, dbw, dbv, dbuv,. Figure 4 General digital communication system. S( t) = R( t)cos( ω ct + θ ( t)) Information is in R(t) and θ(t) Couch, Digital and Analog Communication Systems, Seventh Edition 007 Pearson Education, Inc. All rights reserved Example of Received signal Power vs time for a Wireless channel Average power of S(t) at the receiver input vs time Figure 4 General digital communication system. The Communication Engineers Job is to maximize the amount of information transmitted though the channel using the least amount of spectrum i.e. the smallest bandwidth. System noise limits the information capacity of a communications system for a given bandwidth. This is defined by Shannon s Law for information channel capacity 3 4 Couch, Digital and Analog Communication Systems, Seventh Edition 007 Pearson Education, Inc. All rights reserved

7 Information Measure - I Average Information Measure- Entropy Example -bit word: see appendix B-3 for review possible outcomes O O = [0,0,0,0,0,0,0,0] 56 = [,,,,,,,] : O, m = P( O ) = = / 56 = = I = log = bits j, j =.. m 5 Entropy: 6 Shannon s Law for additive white noise Information Source Rate and Capacity: R, C H R = bits / s T Channel Capacity : S C = B log + N bits / s B = Bandwith in Hz S = Signal power in watts N = Noise power in watts Shannon s Capacity Example A communication system has a bandwidth of MHz. The signal power is picowatt. The noise power is 4 femtowatts. What is the channel capacity in Bits/sec? Signal power Σ Receiver Shannon s Law is the upper limit. Research into new modulation and coding techniques to approach this limit is very active Noise power 7 7

8 Shannon s Capacity Example S C = B log + bits / s N Figure Performance of digital systems with and without coding. N := S := 0 0 B := 0 6 C ln( ) B ln S := + C = Bits per second N Coding reduces the bit error rate 9 30 Couch, Digital and Analog Communication Systems, Seventh Edition 007 Pearson Education, Inc. All rights reserved db and Units db are used because of the extremely wide dynamic range of signals we encounter in communications. 0 6 Watts to 0-3 Watts P db 0log P V db = 0log V V P = R R V = 0log R V V P = R R + 0log R 3 So whenr = R : db and Units P V I db = 0log = 0log = 0log P V I We often set P to some reference power (or voltage) dbm = db relative to mw P in mw dbm = 0log P = mw 3

9 db and Units db and Units- Example dbw dbw db relative to Watt = 0log [ P in Watts], P = Watt dbv db relative to Volt dbv = 0log dbv = 0log [ V in rms Volts], dbuv db relative to μvolt V = Volt rms [ V in rms μvolts], V = μvolt rms P = in dbm : P = 0.0Watts = 0mW 50 0 mw = 0log = mw dbm 0 dbm

Link Budget Calculation

Link Budget Calculation Training materials for wireless trainers This 60 minute talk is about estimating wireless link performance by using link budget calculations. It also introduces the Radio Mobile