IS-95 CDMA CDMA offers some advantages over TDMA and FDMA ...

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EE5401 Cellular Mobile CommunicationsEE5401 Cellular Mobile Communications Quadrature modulation :- The in-phase and quadrature spreading is performedby the same pair of M-sequences as in the forward link.These pilot sequences are used for synchronizationpurpose.- Modulation is offset quadrature PSK (OQPSK). Thedata spread by of Q-pilot PN sequence is delay by halfa chip (406.901ns) with respect to the data spread bythe I pilot PN sequence. This delay is to improvespectral shaping and synchronization.CodingForward linkRate ½, constraintlength 9Reverse linkRate 1/3, constraintlength 9Interleaving 1 frame, 384 symbols 1 frame, 576 symbolsWalshmodulationLong PN codeRepeatedsymbolsDistinguishes aparticular userScrambles data,decimated to symbolrateAll symbol transmittedProvides 64-arymodulationModulation QPSK OQPSKDistinguishes users, noneed to change rateRepeated symbols gatedoffInstitute for Infocomm Research 233National University of SingaporeInstitute for Infocomm Research 234National University of Singapore
EE5401 Cellular Mobile CommunicationsEE5401 Cellular Mobile CommunicationsPower controlThree different power control mechanism- Uplink open loop power control- Uplink closed loop power control- Downlink slow power controlOpen loop power controlClosed loop power control- Adjusts the initial access channel transmission powerof the MS and compensates large abrupt variations inthe pathloss attenuation.- MS estimate the pathloss by measuring received signalstrength at the mobile. Parameters are initiallytransmitted on the synchronization channel. Theparameters are used to adjust the open-loop control fordifferent cell sizes and parameters.- Since uplink and downlink have a frequencyseparation of 20MHz, their fading processes are notstrongly correlated. Even though the average power isapproximately the same, the short term power isdifferent, therefore, the open loop power control cannotcompensate for the uplink fading.- The BS measures the received SIR over 1.25ms period(equivalent to 24 bits at 19.2 kpbs), compares that tothe target SIR, and decides whether the MStransmission power needs to be increase or decreased.The power control bits are transmitted on thedownlink traffic channel every 1.25ms (800 bps) bypuncturing the data symbols. The placement of apower control bit is randomized within the 1.25mspower control group.Institute for Infocomm Research 235National University of SingaporeInstitute for Infocomm Research 236National University of Singapore
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IS-95 CDMA CDMA offers some advantages over TDMA and FDMA ...

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