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TELECOMMUNICATIONS

TELECOMMUNICATIONS. Dr. Hugh Blanton ENTC 4307/ENTC 5307. What is wireless. Free space communication (no wire, no waveguide, no fiber optic cable) Indoor/outdoor/space Concentrating on most active frequency bands - RF and microwave frequencies

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TELECOMMUNICATIONS

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  1. TELECOMMUNICATIONS Dr. Hugh Blanton ENTC 4307/ENTC 5307

  2. What is wireless • Free space communication (no wire, no waveguide, no fiber optic cable) • Indoor/outdoor/space • Concentrating on most active frequency bands - RF and microwave frequencies • RF – “radio frequency” - hundreds of MHz to several GHz • Microwave - several GHz to approx 30 GHz • Circuit theory / transmission lines / electromagnetics all needed • Circuit dimensions d l for RF and microwave circuits. • Question: what relationship between d and l exists for low frequency circuits? Dr. Blanton - ENTC 4307 - Wireless Technology 2 / 30

  3. Wireless Protocols • Mobile wireless • Advanced Mobile Phone Service (AMPS) - 1st generation cellular (800 MHz) • Personal Communications Services (PCS) - 2nd generation mobile phones, pagers (900 MHz-2 GHz) • Bluetooth (short-range wireless connections) (2.4 GHz) • Mobile satellite services (Iridium, GlobelStar) (1.6,19,23,29 GHz) • Fixed wireless • Wireless local-area-network (IEEE 802.11) (2.4 - 2.5 GHz) • LMCS/LMDS/BWA (27-30 GHz) Dr. Blanton - ENTC 4307 - Wireless Technology 3 / 30

  4. Why Wireless • Mobility • Available channels • Cost • 1 in 5 in U.S. live in areas too remote for fast wire-line internet access • Construction:equipment = • 20:80 for wireless • 90:10 for burried line • Half new fixed phone lines installed by 2003 will be wireless Dr. Blanton - ENTC 4307 - Wireless Technology 4 / 30

  5. Design Issue • Operating Frequency • Propagation • Radiated Power Dr. Blanton - ENTC 4307 - Wireless Technology 5 / 30

  6. Operating Frequency • Transmit and receive frequencies (T/R) must lie within allocated bands • Various physical considerations when allocating frequency bands for protocols: • Noise power much higher below 100 MHz due to lights, lightning, and electrical equipment, and above 10 GHz due to thermal noise of atmosphere and interstallar radiation • Antenna gain increases with frequency for fixed antenna size • Maximum data rate increases with increasing frequency • Transistor efficiency decreases with increasing frequency, and cost increases • Atmosphere significantly attenuates propagation in certain frequency bands (will look at this later) • High frequency signals require unobstructed line-of-sight path Dr. Blanton - ENTC 4307 - Wireless Technology 6 / 30

  7. Allocated Spectra • Operating frequency: • Frequencies allocated by international standards bodies (e.g. FCC, CTRC, IEEE, etc.) Dr. Blanton - ENTC 4307 - Wireless Technology 7 / 30

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  10. Propagation • Certain frequencies are very poor for long range communication. Dr. Blanton - ENTC 4307 - Wireless Technology 10 / 30

  11. Propagation (cont.) • Power density of propagating wave in free space decreases as 1/R2, where R is the distance from the source. • Atmosphere and other objects may cause much faster decrease in power density • Reflections may interfere with direct line-of-sight path, leading to multipathinterference or fading • Spread spectrum systems, multiple antennas, and error-correcting codes can be used to reduce fading Dr. Blanton - ENTC 4307 - Wireless Technology 11 / 30

  12. Radiated Power and Safety • Organic tissue absorbs RF and microwave energy and converts it to heat (e.g. microwave oven) • This is not a good thing when the tissue is you! • Heating is dangerous to areas such as brain, eyes, genitals, and stomach organs • Radiation may cause cataracts, cancer, and sterility • ANSI/IEEE standard sets safety standard for exposure limits (e.g. limited to 10 mW/cm2 above 15 GHz where radiation is absorbed by the skin) • Hand held cell phones limited to maximum radiated power of 0.76 W, while base stations are limited to 500 W Dr. Blanton - ENTC 4307 - Wireless Technology 12 / 30

  13. Case Study: PCS • Second generation cellular protocol • North American PCS systems use IS-136 (TDMA), IS-95 (CDMA, QPSK) or European Global System Mobile (GSM) (which is also TDMA) systems • Most modern cell phones are dual mode, meaning that they can not only communicate on digital PCS networks, but also the older first generation Advanced Mobile Phone Service (AMPS) system Dr. Blanton - ENTC 4307 - Wireless Technology 13 / 30

  14. Case Study: GPS • Global Positioning Satellite (GPS) system uses 24 satellites in medium earth orbit (MEO) 20,200 km above the Earth to provide position information • A minimum of four satellites must have a line-of-sight view of the positioning receiver • Propagation delay between satellites and receiver used to determine position of receiver relative to the satellites (for which position is known) • Low gain antennas are used for the receivers, so receivers must be able to receive signals around -130 dBm • Timing pulses transmitted as spread spectrum signals with BPSK modulation. Dr. Blanton - ENTC 4307 - Wireless Technology 14 / 30

  15. Case Study: Bluetooth • Bluetooth specifications • Short range radio link intended to replace cable(s) connecting portable and / fixed electronic devices • Operates in the 2.4 GHz ISM (Industrial Scientific Medicine) band • 78 1-MHz channels • Gaussian Frequency Shift Keying (GFSK) Dr. Blanton - ENTC 4307 - Wireless Technology 15 / 30

  16. Case Study: Bluetooth • Bluetooth specifications (cont.) • Transmitter • Three power levels (1, 2.5, 100 mW) • In-band and out-of-band spurious emissions • Frequency accuracy of 75 kHz from center of channel • Receiver • Sensitivity  70 dBm • Maximum usable level 20 dBm Dr. Blanton - ENTC 4307 - Wireless Technology 16 / 30

  17. Block Diagram Symbols • Block diagram symbols for commonly used RF and microwave components Dr. Blanton - ENTC 4307 - Wireless Technology 17 / 30

  18. 90 2 2 Block Diagram Symbols (cont.) Dr. Blanton - ENTC 4307 - Wireless Technology 18 / 30

  19. Filter Block Symbols Dr. Blanton - ENTC 4307 - Wireless Technology 19 / 30

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