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ECE4607_HW1_Solutions

ECE4607_HW1_Solutions - ECE4607 Mobile and Wireless...

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ECE4607: Mobile and Wireless Networks SPRING 2008 HOMEWORK I Solutions GIVEN: JANUARY 15, 2008 DUE: FEBRUARY 8, 2008 (MIDNIGHT) Prof. I. F. Akyildiz, Distinguished Chair Professor in Telecommunications Broadband and Wireless Networking Laboratory School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta, GA 30332 Tel.: 404-894-5141; Fax.: 404-894-7883 E_Mail: [email protected] QUESTION 1 (Power Consumption) Consider a sensor node with the following parameters. circle2 Basic consumption without radio (P c ) = 12.0 mA; circle2 Additional energy consumption for transmitting (Pt) = 12.0 mA; circle2 Additional energy consumption for receiving (Pr) = 4.5 mA; circle2 Energy needed to sleep (Ps) = 8uA (0.008 mA). The sensor should wake up once a second, measure a value and transmit it over the network. The battery provides an amount of energy of 2300mAh. The sensor node is driven with the same voltage that is provided by the battery. a) When the sensor wakes up, 5k instructions are needed for the measurement and preparation for sending. The CPU runs at a clock rate of 8 MHz, and one instruction needs an average of 3 clock cycles. Estimate the energy consumption for calculations in each wake up cycle.
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b) In each wake up cycle, the sensor sends 50 bytes of its own measurement and forwards 250 bytes of external data. The radio transmits at a speed of 19 200 bits/sec. Estimate the energy consumption for sending the data. c) According to the energy consumption in the calculation, sending and sleeping stage (ignore the receiving part), estimate the lifetime of the sensor. [Solution 1] (Power Consumption) a) One cycle of the CPU takes 1/ (8*10 6 ) seconds; the calculation needs 5K*3/ (8*10 6 ) = 15/ (8*10 3 ) = 1.875*10 -3 seconds; thus the energy consumption for calculation is 15/ (8*10 3 ) s*12mA = 0.0225mAs. b) Since 1 bit takes 1/19200 seconds to send, the transmission time is (250+50)*8/19200 = 0.125 seconds; thus the energy consumption for sending is 300*8/19200s*(12+12)mA = 3mAs.
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