ECE4331_class27

ECE4331_class27 - ECE 4331, Fall, 2009 Zhu Han Department...

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ECE 4331, Fall, 2009 Zhu Han Department of Electrical and Computer Engineering Class 27 Nov. 24 th , 2009
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Cellular Systems and MAC Cellular Systems and MAC Cellular System Multiple Access Technique AMPS FDMA/FDD GSM TDMA/FDD USDC (IS-54 and IS-136) TDMA/FDD PDC TDMA/FDD CT2 Cordless Phone FDMA/TDD DECT Cordless Phone FDMA/TDD US IS-95 CDMA/FDD W-CDMA CDMA/FDD CDMA/TDD cdma2000 CDMA/FDD CDMA/TDD
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Random Access Random Access Packet Radio Protocols Multihop radio network that carries packets Not circuit oriented like GSM, CDMA, etc.  Example Protocols Pure Aloha Slotted Aloha CSMA Protocols 1-persistent CSMA non-persistent CSMA p-persistent CSMA CSMA/CD Reservation Protocols Reservation Aloha PRMA Others MACA, MACAW IEEE 802.11 MAC
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Pure Aloha Pure Aloha B M1 M2 M3 Ignoring the propagation delay between mobiles and base station: The time difference between the time a mobile send the first bit of packet and the time the base station receives the last bit of the packet is given by 2T. T = C/P T: packet time. C: channel data rate (bps) P: packet length (bits) During this 2T period of time, the packet may collide with someone else packet. Data Ack/Nack Algorithm : A mobile station transmits immediately whenever is has data. It then waits for ACK or NACK. If ACK is not received, it waits a random amount of time and retransmits .
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Contention for Aloha Contention for Aloha
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Throughput of Aloha Throughput of Aloha 0 0 .02 0 .04 0 .06 0 .08 0 .1 0 .12 0 .14 0 .16 0 .18 0 .2 0 0 .2 0 .4 0 .6 0 .8 1 Normalized Channel Occupancy Normalized Throughput ~0.185 0.5
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Slotted Aloha Slotted Aloha
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Reservation Protocols Reservation Protocols Reservation Aloha Packet Reservation Multiple Access
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PRMA PRMA Packet Reservation Multiple Access A combination of TDMA and reservation ALOHA Ask channel resource in the talkspurt Release channel resource in the silent gap Permission probability Effect of voice activity detector F r a m e N B - > M A C K B - > M B - > M A C K A C K . . . . . . . . . . . M - > B M - > B . . . M - > B
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PRMA PRMA NC-PRMA (Non-Collision Packet Reservation Multiple Access) The existing users inform the BS about their demands in a non- collision manner (time-frequency signaling scheme ) I i : Information slot CM i : Control minislot C : Control slot UID : Uplink user identifier DID : Downlink user identifier
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Improvements of PRMA Improvements of PRMA Wong and Goodman Allow data transmission to reserve a limited number of slots with reservation threshold Frame Reservation Multiple Access (FRMA) Divide a frame into voice and data slots Ratio of the number of voice and data slots is dynamic PRMA++ Separates the request and data channels C-PRMA QoS guarantee Schedules the uplink transmission (Earliest due date (EDD))
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CSMA: Carrier Sen CSMA: Carrier Sen s s e Multiple Access e Multiple Access Aloha does not listen to the carrier before transmission. CSMA listen to the carrier before transmission and transmits if
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ECE4331_class27 - ECE 4331, Fall, 2009 Zhu Han Department...

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