随机存取通道rach ) looks over-complicated，why do we still need it？ themainpurposecanbedescribedasfollows。
achieveuplinksynchronizationbetweenueandenbobtaintheresourceformsg3itisnotefficientifueisusingbroadcasting/always-onsynchronizationmechanism.theuplinksynchronizationprocessshouldmeetfollowingcriteria 3360
1.thesynchronizationprocessshouldhappenonlywhenthereisimmediatenecessary
2.thesynchronizationshouldbededicatedtoonlyaspecificue
fundamentaldifferencefromlterachthemajordifferencebetweenlterachandnrrachwouldliejustbeforerachpreamblegetstransmittted.itis dis esupportedbydefaultinnr.whennrisoperatinginbeamformingmode，ueneedtodetectthaselectabestbeamforrachprocess.thebeamselectictiod
howtodeterminewhichpreambleformattouse？
howdoesnetworkknowsexactlywhenuewilltransmittherach？ itis simple.networkknowswhenuewillsendtherachevenbeforeuesendsitbecausenetworktellsuewhentheueissupposedtotransmittherach。
How many RACH-Preamble can be used？ theoretically 64 prachpreamblesareavailableintotal，butthenumberofthepreamblesavailableinaspecificconditionaredeterminedbyacoupoupoup
how to generate 64 prachpreamblesequence？ I ) generateazaddoffchusequenceusingrootsequenceindex wecancallitasbasedsequence )。
ii ) generate 64 differentsequencebydoingcyclicshiftofthebasesequence.thecyclicshiftintervalisdeterminedbyncsandthencsisissdetetetermm
howtogeneraterachsignalyoudonothavetoknowthedetailsofthisprocedureunlessyouarethedsporfpgaengineerimplementingxxdkn/phowistherachpreamblepowerdeterminedtherachpreamble prach ) powervariesdependingoncasesasdecribedbelow。
basicallyprachpowerisdeterminedbyopenlooppowercontrolalgorithm。
watistherachprocessoverviewitispresentedinthebelowdiagrams
stepuplinkordownlinkprocess0UE-bs sib 21u e-bsprachpreamble msg1) 2UE-bsrachresponse-rar ) msg2) ) ) ) ) 3 ) 4ue—bsharqackformsg 35ue—bscrrcconnectionsetup msg4) ) ) ) ) ) ) 452 6ue—bsharqackformsg 47ue—BSD
内容解决时间： step3to step 5
RRC delay: step 5 to step 7
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