Chapter5-1

Chapter5-1 - Spring 2009 ELEC001 Electronic &...

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P.1 Chapter 5 - Transmission of Signals Wireless Communications Technology Spring 2009 ELEC001 Electronic & Information Technology
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P.2 Transmission of Information In the digital age, we commonly transmit information through mediums such as electrical wire and optical fiber , or by the means of radio/wireless communications In this chapter, using radio/wireless communication and cellular phone examples, we will cover topics including: Modulation of signals Design of the cellular network Methods for multiple access: FDMA, TDMA, CDMA
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P.3 I. Introduction to wireless communications - Radio as information carrier and frequency allocation - Wireless communications we are familiar with: 1G/2G/3G Cellular Systems
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P.4 Radio Wave for Wireless Communications Wireless communications is based on the wireless propagation of Radio wave which is electromagnetic wave in the frequency range of 10KHz – 300GHz to transmit analog or digital information such as audio, data, images and video. 300 GHz is the upper frequency limit from electrical circuitries/processes . 10 KHz is the practical lower limit for radio propagation in the earth environment . We are surrounded by radio signals! AM and FM radio, television broadcasting, cordless phone, CB radio, mobile/cellular, WiFi, bluetooth, RFID, “octopus” card, Global Positioning Systems (GPS), satellite communications, … Different radio signals are transmitted in different frequency bands within the radio spectrum. That is how these signals are kept separated and can be picked up properly by different devices.
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P.5 Spectrum Allocation Different radio signals use different frequency bands allocated by the government, based on many technical, economic and political considerations. Most countries are signatories of and bounded by the international radio treaty Different bands have different transmission characteristics in the earth environment - reflection by ionosphere, water absorption, scattering loss, etc., means some bands are good for indoor, some for long distances, bands below 500 KHz only good for marine environment, etc. Frequency spectrum is a valuable government asset. Companies have paid large sums to license spectrum usage. Yet, there are a few unlicensed bands scattered throughout the spectrum for use by citizens (e.g., ~27/28 MHz).
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P.6 Spectrum Allocation in the United States 10 KHz In Chapter 1, we presented the simplified US frequency allocation chart (shown at the right). The detailed chart (shown below) can be easily found from FCC (Federal Commission on Communications) 1 MHz 1 GHz
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P.7 Frequency Allocation in Hong Kong In Hong Kong, frequency band assignment is governed by the Office of the Telecommunications Authority (OFTA). http://www.ofta.gov.hk
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P.8 Baseband/Information Signals Baseband signal refers to the original signal carrying the audio, visual, or data information, with nothing done to it.
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Chapter5-1 - Spring 2009 ELEC001 Electronic &...

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