nader(mat) - Multiple Access Techniques for Wireless...

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Multiple Access Techniques for Wireless Communication Submitted to : Dr. Mohab Mangoud Submitted by: Nader Ahmed Abu Al Arraj
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Outline 1. Introduction 2. Spread Spectrum Multiple Access (SSMA) 2.1 Frequency Hopped Multiple Access (FHMA) 2.2 Code Division Multiple Access (CDMA) 2.3 Hybrid Spread Spectrum Techniques 3. Space division Multiple (SDMA) 4. Packet Radio 4.1 Packet Radio Protocols 4.2 Carrier Sense Multiple Access (CSMA) Protocols 4.3 Reservation Protocols 5. Conclusion 6. References
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Multiple Access Techniques for Wireless Communications Multiple access schemes are used to allow many mobile users to share simultaneously a finite amount of radio spectrum. The sharing of spectrum is required to achieve high capacity by simultaneously allocating the available bandwidth (or the available amount of channels) to multiple users. For high quality communications, this must be done without severe degradation in the performance of the system. Introduction . 1 In wireless communications systems, it is often desirable to allow the subscriber to send simultaneously information to the base station while receiving information from the base station. For example, in conventional telephone systems, it is possible to talk and listen simultaneously, and this effect, called duplexing, is generally required in wireless telephone systems. Duplexing may be done using frequency or time domain techniques. Frequency division duplexing (FDD) provides two distinct bands of frequencies for every user. The forward band provides traffic from the base station to the mobile, and the reverse band provides traffic from the mobile to the base station. In FDD, any duplex channel actually consists of two simplex channels (a forward and reverse), and a device called a duplexer is used inside each subscriber unit and base station to allow simultaneous bidirectional radio transmission and reception for both the subscriber unit and the base station on the duplex channel pair. The frequency separation between each forward and reverse channel is constant throughout the system, regardless of the particular channel being used. Time division duplexing (TDD) uses time instead of frequency to provide both a forward and reverse link. In TDD, multiple users share a single radio channel by taking turns in the time domain. Individual users are allowed to access the channel in assigned time slots, and each duplex channel has both a forward time slot and a reverse time slot to facilitate bidirectional communication. If the time separation between the forward and reverse time slot is small, then the transmission and reception of data appears simultaneous to the users
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at both the subscriber unit and on the base station side. Figure -1- illustrates FDD and TDD techniques. TDD allows communication on a single channel (as opposed to requiring two separate simplex or dedicated channels) and simplifies the subscriber equipment since a duplexer is not required. Figure-1-
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nader(mat) - Multiple Access Techniques for Wireless...

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