Presentation on theme: "TELECOMMUNICATIONS Dr. Hugh Blanton ENTC 4307/ENTC 5307."— Presentation transcript:
TELECOMMUNICATIONS Dr. Hugh Blanton ENTC 4307/ENTC 5307
Dr. Blanton - ENTC 4307 - Wireless Technology 2 / 30 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 for RF and microwave circuits. Question: what relationship between d and exists for low frequency circuits?
Dr. Blanton - ENTC 4307 - Wireless Technology 3 / 30 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 4 / 30 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 5 / 30 Design Issue Operating Frequency Propagation Radiated Power
Dr. Blanton - ENTC 4307 - Wireless Technology 6 / 30 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 7 / 30 Allocated Spectra Operating frequency: Frequencies allocated by international standards bodies (e.g. FCC, CTRC, IEEE, etc.)
Dr. Blanton - ENTC 4307 - Wireless Technology 8 / 30 Typical FrequenciesApproximate Band Designations AM Broadcast Band 535 1605 kHzL-band 1 2 GHZ Shortwave radio 3 30 MHzS-band 2 4 GHz FM broadcast band 88 108 MHzC-band 4 8 GHz VHF TV (2 4) 54 72 MHzX-band 8 12 GHz VHF TV (5 6) 76 88 MHzKu-band 12 18 GHz UHF TV (7 13) 174 216 MHzK-band 18 26 GHz UHF TV (14 83) 470 890 MHzKa-band 26 40 GHz Microwave Oven 2.45 GHz U-band 40 60 GHz
Dr. Blanton - ENTC 4307 - Wireless Technology 10 / 30 Propagation Certain frequencies are very poor for long range communication.
Dr. Blanton - ENTC 4307 - Wireless Technology 11 / 30 Propagation (cont.) Power density of propagating wave in free space decreases as 1/R 2, 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 multipath interference or fading Spread spectrum systems, multiple antennas, and error- correcting codes can be used to reduce fading
Dr. Blanton - ENTC 4307 - Wireless Technology 12 / 30 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 13 / 30 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 14 / 30 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 15 / 30 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 16 / 30 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 17 / 30 Block Diagram Symbols Block diagram symbols for commonly used RF and microwave components Component SymbolComponent Name Antenna Amplifier Mixer Oscillator
Dr. Blanton - ENTC 4307 - Wireless Technology 18 / 30 Block Diagram Symbols (cont.) Component SymbolComponent Name 90 Power Divider Frequency Multiplier Frequency Divider Switch 90 22 22