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# HW6_Sol - Telcom 2110 Network Design Homework#6 Spring 2010...

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Telcom 2110 Network Design Homework #6 Spring 2010 1. Consider the design of a point to point link of .5 Km distance using 802.11a equipment in the 5GHz band. Assume a line of sight exists between the transmitter and receiver and the link uses channel 36 (i.e., carrier frequency is 5.180 GHz). The transmit power is 15dBM and the required signal receiver signal strength for 54 Mbps operation is -78 dBm. If the build in antenna on the 802.11 equipment has a antenna gain of 2.2 dB at both the transmitter and receiver will the link operate at 54 Mbps while allowing for a 10 dB system margin? If not what must the gain of external antennas be to operate the link? Given: d = .5km = 500 m f = 5.180 GHz = 5.180 x 10 9 Hz P t = 15 dBm Required P r = -78 dBm G t = G r = 2.2 dB From Free Space Loss model we have Path Loss(P L ) = 21.98 – 20log( ) + 20log(d) = 21.98 – 20log( 3*10 8 5.18*10 9 ) + 20log(500) = 100.704 dB Since P r = P t + G t – P L + G r = 15 + 2.2 – 100.704 + 2.2 = -81.304 dB The expected received power is -81.304 dB Then we have expected system margin of -81.304 – (-78) = -3.304 dB which is less than 10 dB Therefore, the system will not be able to operate at 54Mbps. In order to effectively operate the system at 54Mbps we need 10dB system margin. Thus, we need to have received power of 10 + (-78) = -68 dB which means we need to have additional gain from implementation of external antenna. So, from P r = P t + G t – P L + G r + G external antenna -68 = 15 + 2.2 – 100.704 + 2.2 + G G = 13.304 dB Therefore, external antennas need to have gain of at least 13.304 dB in order that the system will be able to operate at 54Mbps

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2. The Figure below shows the layout of the 4 th floor of the SIS building. The scale is 1 cm. in the drawing represents 2.5 m. The power levels and frequency channels of the IEEE 802.11b wireless LAN access points are given in the table below. Assuming a loss of 6 dB per wall and shadow fading of 13 dBm. Use the partition dependent path loss model to answer the following Power level Channel AP1 20 dBm 2.412 GHz (ch1) AP2 20 dBm 2.437 GHz (ch6) a.
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HW6_Sol - Telcom 2110 Network Design Homework#6 Spring 2010...

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