CDMA系统中基于FPGA的DAGC实现-豆柴文库

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CDMA系统中基于FPGA的DAGC实现
CDMA(CodeDivisionMultipleAccess)isadigitalcellulartechnologythatemploysspreadspectrumtechniquestoenablemultipleuserstosharethesamefrequencyspectrumwithoutinterference.Toensureefficientutilizationofthelimitedfrequencyresourcesavailable,CDMAsystemsincorporateseveraltechnologiessuchaspowercontrolanddiversitytechniquestoimprovethequalityofserviceforusers.Inparticular,powercontroliscriticalinCDMAsystemssinceitdeterminesthetransmitpowerofthemobilestationbasedonthereceivedpowertominimizeinterference.
OneofthekeytechnologiesusedinCDMAsystemstoachievepowercontrolistheDigitalAutomaticGainControl(DAGC)mechanism.DAGCoperatesbyadjustingthereceiver'sgaindependingonthereceivedsignalpowerlevels.TheDAGCalgorithmisimplementedusingdigitalsignalprocessingtechniques,whichmeansthatitcanbeimplementedusingFPGAs(FieldProgrammableGateArrays).FPGA-basedimplementationsofferseveraladvantagessuchashighthroughput,lowpowerconsumption,andlowlatencycomparedtosoftware-basedimplementations.
TheDAGCalgorithmaimstomaintainaconstantsignalamplitudeattheoutputofthereceiver,regardlessofthesignalpowerlevel.Thegoalistoavoidsignalclippingorsaturation,whichcanintroducedistortionandaffectthequalityofthereceivedsignal.TheDAGCblockconsistsofanumberofsub-blocksthatworktogethertoachievethedesiredoutputsignalamplitude.Thesesub-blocksincludethepowerdetector,thegaincontrolcircuit,andthefeedbackloop.
Thepowerdetectormeasuresthereceivedsignalpowerandprovidesavoltagelevelproportionaltothesignalpowertothegaincontrolcircuit.Thegaincontrolcircuitadjuststhegainoftheamplifierdependingontheinputvoltagelevel,whichinturnadjuststheoutputsignalamplitude.Thefeedbackloopadjuststhegainoftheamplifierinreal-timebasedonthedifferencebetweenthedesiredoutputamplitudeandtheactualoutputamplitude.
TheimplementationofDAGCusingFPGAsinvolvesdesigningahardwareblockthatperformsthevarioussub-blockfunctions.ThehardwareblockisprogrammedusingspecializedhardwaredescriptionlanguagessuchasVerilogorVHDL.Thehardwareblockitselfcanbedivid