ECE549_M1L6

ECE549_M1L6 - M1 L6 1 NC STATE UNIVERSITY ECE549 RF Design...

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M1 L6 1 NC STATE UNIVERSITY © M. B. Steer, 1995–2008 ECE549 RF Design for Wireless Professor Michael Steer http://www4.ncsu.edu/~mbs Module 1: RF Systems LECTURE 6 Radio Link
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M1 L6 2 NC STATE UNIVERSITY © M. B. Steer, 1995–2008 Lecture Goal The goal here is to understand propagation in wireless systems. You will be able to calculate loss in a radio link. You will also develop an understanding of fading and the schemes to overcome it. Lecture Outline Propagation •F a d i n g Methods to Overcome Fading Statistical Propagation Models Information Source Channel Information Destination
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M1 L6 3 NC STATE UNIVERSITY © M. B. Steer, 1995–2008 Propagation by Multiple Paths d h r d Any object which is half a wavelength ( λ /2) long can interfere with signal. λ /2 = 7.0 in., cellular radio (860 MHz) λ /2 = 3.2 in., PCS (1.9 GHz) Atmospheric Absorption, Line of Sight, and … h t h MULTIPATH h t d h r h MULTIPATH d h t h r h KNIFE-EDGE DIFFRACTION h t h r h TREE SCATTERING
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M1 L6 4 NC STATE UNIVERSITY © M. B. Steer, 1995–2008 Line of Sight (LOS) Propagation Free space - wave travels in a straight line atmospheric absorbtion (loss) reflections from the ground refraction in the atmosphere reflected wave direct (free space) wave refracted wave Tx Rx r Free Space “Spreading” Loss energy intercepted by the red square is proportional to 1/r 2
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M1 L6 5 NC STATE UNIVERSITY © M. B. Steer, 1995–2008 Free Space Path Loss Tx Rx d isotropic isotropic At a distance d the power density is P D P in G T d = 4 2 π P T is the transmitted power from the antenna G T is the transmitter antenna gain. The antenna gain G is the factor by which the power density is increased compared with the isotropic case. G is very large for antennas used in microwave point-to-point systems 100 (20 dB) to 10,000,000 (70 dB). Typical path loss: 140 dB for a 50 km link at 10 GHz (high gain antennas help offset loss ~ 60 dB) P T P in = η P in where is the power input to the antenna, is the efficiency of the antenna. η Note that includes the effect of finite antenna efficiency. G T
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M1 L6 6 NC STATE UNIVERSITY © M. B. Steer, 1995–2008 Free Space Path Loss If the receiving antenna has an effective area A R then the received power is P R P D A R = P R P T G T A R d = 4 2 π where A R G R = λ 2 4 G R is the receiver antenna gain. The received power is P R P T G T G R d = 4 2 Hence the transmission loss (ratio of transmitted power to received power) is: Tr Loss P T P R G T G R d . log log log log == + 10 10 10 20 4 dB Calculate the path loss and Tr. loss for antennas 50 km apart, for a 10 GHz system with antenna gains of 60 dB (answer 146 dB, 26.4 dB). path loss G T is the transmitter antenna gain. G R is the receive antenna gain. P R Is the output power from the receive antenna P T Is the power input to the transmit antenna (not the same the power transmitetd as on the previous slide.)
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M1 L6 7 NC STATE UNIVERSITY © M. B. Steer, 1995–2008 Example: Radio Link (Transmission Loss Calculation) Receiver Antenna Antenna Trans.
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ECE549_M1L6 - M1 L6 1 NC STATE UNIVERSITY ECE549 RF Design...

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