ECE8708_2010_ch6

ECE8708_2010_ch6 - ECE 8708 Wireless...

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ECE 8708 Wireless Communications :Multiple Access Techniques Wireless Communications ECE8708 ECE8708 - 2010 Spring 2010 Spring Chapter Chapter 6 ultiple Access Techniques Multiple Access Techniques FDMA, TDMA, CDMA Yimin Zhang, PhD Center for Advanced Communications Villanova University http://www.yiminzhang.com Yimin Zhang, Villanova University 1 p// y g ECE 8708 Wireless Communications :Multiple Access Techniques utlines Outlines DMA FDMA TDMA Spread Spectrum Communications Frequency Hopping Direct Sequence CDMA Spreading Codes Soft Handoff RAKE Diversity Yimin Zhang, Villanova University 2 ECE 8708 Wireless Communications :Multiple Access Techniques Comparing FDMA and TDMA What resource do you need to transmit information? Let’s look at Shannon’s capacity theorem… bps 1 log 2 N S B C it S T frequency hen multiple users request r bits 1 log 2 N BT I When multiple users request for resources of communications, we need to decide how to divide e ailable time and pectral time the available time and spectral resources to these users. Yimin Zhang, Villanova University 3 ECE 8708 Wireless Communications :Multiple Access Techniques Comparing FDMA and TDMA It is most desirable that we provide multiple channels that are orthogonal. g FDMA TDMA requency ivision Multiple Access Time ivision ultiple Access frequency frequency Frequency-Division Multiple Access Time-Division Multiple Access el 1 Channel 1 hannel 2 el 2 el 3 el 4 Chann Channel 2 Channel 3 Yimin Zhang, Villanova University 4 Channel 4 time time
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ECE 8708 Wireless Communications :Multiple Access Techniques Comparing FDMA and TDMA TDMA in practice… It’s really a FDMA/TDMA system. More channels can be provided thanks to data compression ade possible in digital communications. made possible in digital communications. frequency 1 2 3 1 2 3 4 5 6 7 8 9 4 5 6 7 8 9 Yimin Zhang, Villanova University 5 time 10 11 12 10 12 ECE 8708 Wireless Communications :Multiple Access Techniques ypes of Mobile Radio Transmission Systems Types of Mobile Radio Transmission Systems implex ommunication is possible only in one direction Simplex Communication is possible only in one direction, (e.g., paging systems). Half Duplex – Two way communication, but uses the same radio channel for both transmission and reception. User can only transmit or receive information. Full Duplex – Simultaneous two-way radio transmission and reception between subscriber and base station. – Two simultaneous but separate channels (FDD) or – Adjacent timeslots on a single radio channel (TDD) Yimin Zhang, Villanova University 6 ECE 8708 Wireless Communications :Multiple Access Techniques DMA d in irst Generation Systems FDMA Used in First Generation Systems AMPS: Advance Mobile Phone System - 1978 First cellular experimental analog systems - AT&T AMPS system (Chicago, IL); channel spacing is 30 KHz - 1983 First commercial analog system at Chicago, IL; total 40 MHz t i 800 MH b d spectrum in 800 MHz band -
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ECE8708_2010_ch6 - ECE 8708 Wireless...

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