RachRootSequence Planning

Prepared By RAJESH KUMAR

Random access preamble transmission

• First step in the random access procedure is the transmission of a random access preamble • Indicates to the eNodeB the presence of a random access attempt and to allows the eNodeB to estimate the delay between the eNodeB and the UE • Random access preamble is transmitted on Physical Random Access Channel (PRACH) • In a first step of the random access procedure, the UE selects one preamble to transmit on the PRACH

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Preamble sequence generation

– – – – – The preamble consists of two parts: Preamble sequence Cyclic prefix In each cell, there are 64 preamble sequences available Preamble sequences are constructed from one or several root Zadoff-Chu (ZC) sequences, by combining different cyclic shifts of each root sequence Logical root ZC sequence index is broadcasted as part of the System Information There are 838 different root ZC sequences used for random access and each ZC sequence consists of N ZC = 839 samples A new parameter is introduced in the current release for the Random access process:

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rachRootSequence Planning

– – – It can be beneficial to plan rachRootSequence such that the same root sequences are not used in neighboring cells If the same root sequences are used in neighboring cells, and the PRACH allocation overlaps, this will lead to an increased false alarm ratio, where a random access preamble transmitted by a UE in the neighboring cell could be detected by the eNodeB This is mainly a problem when the random access load is high In cells, where UEs are traversing with high speed, the restricted set of root ZC sequences should be used • It could be applicable for cells that cover railways and highways • It is not applicable in USA because speeds on railways and highways do not exceed 105 mph (limit for 1900 MHz) 500 450 400 350 300 250 200 150 100 50 0 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600

Carrier frequency [MHz]

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rachRootSequence Planning RECOMENDATION

It is recommended to set the parameter

rachRootSequence to different values in neighboring

cells to reduce the probability for false RACH detections › The values must differ by at least 10 between any two neighbors (and at most 827 since there is a wrap-around between the first and last value in the value range)

Group 1 4 5 2 3 8 9 6 7 10 11 12 13 14

rachRootSequence GROUPING

275 305 335 365 395 5 35 65 95 125 155 185 215 245

rachRootSequence

15 285 315 345 375 405 45 75 105 135 165 195 225 255 295 325 355 385 415 25 55 85 115 145 175 205 235 265 24 25 26 27 28 Group 15 16 17 18 19 20 21 22 23 695 725 755 785 815 425 455 485 515 545 575 605 635 665

rachRootSequence

435 705 735 765 795 825 465 495 525 555 585 615 645 675 715 745 775 805 835 445 475 505 535 565 595 625 655 685

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rachRootSequence PLANNING Process

PN planning tool in Planet will be used to generate a PN plan and then convert the PN plan to the rachRootSequence plan 1.

2.

3.

– – 4.

– Best server layer will be generated Neighbor list will be created by utilizing best server layer in Planet A PN plan with an increment of 7 will be generated Gives 24 groups, no reserves rachRootSequence grouping includes 28 groups (see slide 6) Take the first 24 groups and replace the PN Plan created in Planet with values listed on slide 6 4 spare groups left

THANKS