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Unformatted text preview: 4.1 Prof. Dr.Ing. Jochen H. Schillerwww.jochenschiller.deMC  2008 Mobile Communications Chapter 4: Wireless Telecommunication Systems • GSM • Handoff region • Frequency reuse • GSM Security Prof. Dr.Ing. Jochen H. Schillerwww.jochenschiller.deMC  2008 4.2 Powers of Two Received Signals as Functions of Distances from Two BSs BS Signal strength due to BS j X 1 Signal strength due to BS BS j X 3 X 4 X 2 X 5 MS P min P (x) P j (x ) • Observe: P j (X 1 ) ≈ 0 P(X ) ≈ 0 (Modified by LTL) Prof. Dr.Ing. Jochen H. Schillerwww.jochenschiller.deMC  2008 4.3 Signal Strength and Cell Parameters [http://en.wikipedia.org/wiki/DBm] • dBm (used in following slides) = an abbreviation for the power ratio in decibel (dB) of the measured power referenced to 1 mW (milliwatt) • dBm is an absolute unit measuring absolute power • Since it is referenced to 1 mW • In contrast, dB is a dimensionless unit, which is used when measuring the ratio between two values (such as signaltonoise ratio) • Examples : • 0 dBm = 1 mW • 3 dBm ≈ 2 mW • Since a 3 dB increase represents roughly doubling the power • −3 dBm ≈ 0.5 mW • Since a 3 dB decrease represents roughly cutting in half the power © 2007 by Leszek T. Lilien Prof. Dr.Ing. Jochen H. Schillerwww.jochenschiller.deMC  2008 4.4 Signal Strength and Cell Parameters – cont. [http://en.wikipedia.org/wiki/DBm] • Examples – cont. • 60 dBm = 1,000,000 mW = 1,000 W = 1 kW • Typical RF power inside a microwave oven • 27 dBm = 500 mW • Typical cellphone transmission power (some claim that users’ brains are being fried) • 20 dBm = 100 mW • Bluetooth Class 1 radio, 100 m range = max. output power from unlicensed FM transmitter (4 dBm = 2.5 mW  BT Class 2 radio, 10 m range) • −70 dBm = 100 pW (yes, “ ”!!!) • Average strength of wireless signal over a network • Average for the range: −60 to −80 dBm −60 dBm= 1 nW = 1,000 pW  −80 dBm= 10 pW © 2007 by Leszek T. Lilien Prof. Dr.Ing. Jochen H. Schillerwww.jochenschiller.deMC  2008 4.5 Land Propagation • The received signal power: where: G t is the transmitter antenna gain, G r is the receiver antenna gain, L is the propagation loss in the channel, i.e., L = L P L S L F L P G G P t r t r = Fast fading (longterm f.) Slow fading (shortterm f.) Path loss Prof. Dr.Ing. Jochen H. Schillerwww.jochenschiller.deMC  2008 4.6 Path Loss (for Land Propagation) • Path loss as a function of distance L p = A d α where: A and α : propagation constants d : distance between transmitter and receiver Value of α :...
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This note was uploaded on 11/03/2009 for the course COMPUTERS CS537 taught by Professor Salman during the Spring '09 term at Texas A&M University–Commerce.
 Spring '09
 SALMAN

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