Random access preamble transmission First step in the random access procedre is the transmission o! a random access preamble
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"ndicates to the e#odeB the presence o! a random access attempt and to allo$s the e#odeB to estimate the delay bet$een the e#odeB and the UE Random access preamble is transmitted on Physical Random Access %hannel &PRA%H' "n a (rst step o! the random access procedre) the UE selects one preamble to transmit on the PRA%H
"n each cell) there are ./ preamble se*ences a0ailable Preamble se*ences are constrcted !rom one or se0eral root 1ado2-%h &1%' se*ences) by combining di2erent cyclic shi!ts o! each root se*ence
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3ogical root 1% se*ence inde is broadcasted as part o! the System "n!ormation +here are 454 di2erent root 1% se*ences sed !or random access and each 1% se*ence consists o! N1% 6 457 samples A ne$ parameter is introdced in the crrent release !or the Random access process,
rachRootSequence Planning "t can be bene(cial to plan rachRootSequence sch that the same root se*ences are not sed in neighboring cells
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"! the same root se*ences are sed in neighboring cells) and the PRA%H allocation o0erlaps) this $ill lead to an increased !alse alarm ratio) $here a random access preamble transmitted by a UE in the neighboring cell cold be detected by the e#odeB +his is mainly a problem $hen the random access load is high "n cells) $here UEs are tra0ersing $ith high speed) the restricted set o! root 1% se*ences shold be sed • "t cold be applicable !or cells that co0er rail$ays and high$ays • "t is not applicable in USA becase speeds on rail$ays and high$ays do not eceed 89: mph &limit !or 8799 MH;' 500
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rachRootSequence Planning RE%
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"t is recommended to set the parameter rachRootSequence to di2erent 0ales in neighboring cells to redce the probability !or !alse RA%H detections +he 0ales mst di2er by at least 89 bet$een any t$o neighbors &and at most 4>? since there is a $rap-arond bet$een the (rst and last 0ale in the 0ale range'
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rachRootSequence P3A##"#@ P# planning tool in Planet $ill be sed to generate a P# Process plan and then con0ert the P# plan to the rachRootSequence plan 8 Best ser0er layer $ill be generated > #eighbor list $ill be created by tili;ing best ser0er layer in Planet 5 A P# plan $ith an increment o! ? $ill be generated @i0es >/ grops) no reser0es rachRootSequence groping incldes >4 grops &see slide .' / +aCe the (rst >/ grops and replace the P# Plan created in Planet $ith 0ales listed on slide . / spare grops le!t
