3_W Ch_S_10

3_W Ch_S_10 - LAB 3 WLAN (04/15) 1. Introduction 2. Review...

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1 LAB 3 WLAN (04/15) 1. Introduction 2. Review of Modulation Techniques a. Principles of SS Transmission b. CDMA spreading. 3. Radio Waves and Basics of Antenna Theory a. Propagation theory b. Basic of antenna theory 4. Antenna Selection 5. Wireless Link Power Budget Analysis 6. MAC in Wireless 802.11b LANs 7. Motivation for a specialized MAC a, Hidden and exposed terminals; b. Classical Aloha; c. Slotted Aloha; 8. MACA a. MACAW 9. MAC 802.11 Sub-layer Protocol a. CSMA/CA 10. TCP/UDP over 802.11b 11. TCP Congestion Control a. Topology; b. MAC; c. Data transmission;
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2 Wireless Transmission The Electromagnetic Spectrum Radio Transmission Microwave Transmission Infrared and Millimeter Waves Lightwave Transmission In vacuum, all electromagnetic waves travel at the same speed, no matter what their frequency. This speed is the speed of light- c , is about 1 foot (30cm)/ns. In copper or fiber the speed slows to about 2/3 of this value and is slightly frequency dependent. The relation between frequency , wavelength , and speed – c is . As a rule of thumb, when is in meters and is in MHz- . f λ c f = f [ ] 300 = f
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3 Radio frequencies in the 100 kHz to 10 GHz range . 535 kHz AM Radio : 1705 kHz 2-way radio (cordless phones): 42-49.6 MHz TV Channels 2-4 : 54-72 MHz TV Channels 5-6 : 76-88 MHz FM Radio: 88-108 MHz TV Channels 7-13 : 174-216 MHz TV Channels 14-36: 470-608 MHz TV Channels 38-69 : 614-806 MHz Cellular Service: 806-902 MHz PCS Service: 1.850-1.990 GHz Unlicensed Usage: 5.725-5.850 GHz Unlicensed Usage: 2.390-2.4835 GHz Unlicensed Usage: 902-928 MHz 10 MHz 1 MHz 100 MHz 1 GHz 10 GHz 100 kHz microwave
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4 Microwave radio systems: 1. Microwave voice/data transmissions: No AM . 1.Data -modulate the carrier wave using : PM, FM, and SS modulation techniques . 2a. Links (channels) are separated with: FDMA. Voice data-to encode signal digitally use: PCM 3a. Several voice signals in one channel are separated by: TDMA
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5 Link characteristics of selected wireless network standards a IS-95, CDMA, GSM IS-95, CDMA, GSM Indoor Outdoor Mid range outdoor Long range outdoor 2G 3G 56 Kbps 384 Kbps 1 Mbps 4 Mbps 5-11 Mbps 54 Mbps 200 Mbps 802.15.1 UMTS/CDMA, CDMA2000 802.11b W/MAX 802.11a,g 802.11n 802.11a,g point-to-point 3G 10-30 m 50-200 m 200-4 Km 5 Km-20 Km
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6 Modulation Techniques A , φ , and f BPSK : 0° or 180°, QPSK 0°, 90°, 180°, 270° A higher K f value can be used in modulating the audio signal, Higher K f value decreases the signal error rate. However, decoding an FM signal becomes very difficult at high K f , So we cannot increase K f to use FM transmission in a wide frequency band. In the radio spectrum, the available bandwidth exceeds the necessary data rate. For instance , FM radio stations have about 100 kHz , bandwidth of an audio signal 20 kHz . Spread spectrum techniques are necessary to for efficient use of a wide frequency band at low error rates. ( 29 π + = f A t S c 2 sin ) (
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7 Shannon’s law shows the relationship between analog bandwidth and digital channel capacity. When the SNR < below 1 (wireless channel is noisy channel), less than 1 bit can be transferred by each sample.
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3_W Ch_S_10 - LAB 3 WLAN (04/15) 1. Introduction 2. Review...

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