MCG ,SCG, SPLIT Bearer and Use Case's

5G NR PRACH - NR Random Access Procedure :-

Situation’s that trigger Rach process in NR :  As per 38.300-9.2.6 as follows.

Following use cases were used even in LTE case also  

i) Initial access from RRC_IDLE;

ii) RRC Connection Re-establishment procedure;

iii) Handover;

iv) DL or UL data arrival during RRC_CONNECTED when UL synchronisation status is "non-synchronised";

Following cases would be NR specific

v) Transition from RRC_INACTIVE;

vi) To establish time alignment at SCell addition;

vii) Request for Other SI

viii) Beam failure recovery.

How to find Time and Frequency resources to send RACH ?

After obtaining Rach information from signaling , UE should be able to calculate Time and frequency Domain location in order to send PRACH.

• Time resources used by PRACH indicated by prach-ConfigurationIndex

following parameters:

PRACH format : These are the available format’s { A1, A2, A3, B1, B2, B3, B4, C0 or C2 }

PRACH configuration period : PRACH is transmitted on system frame numbers based on the condition n_SFN mod x = y , here are the details about X and Y

• x indicates the number of SFN between PRACH configurations (i.e. PRACH is        configured each x·10 ms)
• y indicates the SFN within the PRACH configuration period containing PRACH occasions.

Slots with PRACH (expressed using 60 kHz subcarrier spacing) : A frame contains 40 60 kHz slots

This field indicates which of the 40 slots contain PRACH occasions

First PRACH symbol : First OFDM symbol in the 60 kHz slot containing PRACH

Number of PRACH slots in each 60 kHz slot

One if PRACH is using 60 kHz

Two if PRACH is using 120 kHz

Number of time-domain occasions within a PRACH slot (i.e. ) : Depends on the PRACH format duration

• Frequency resources for PRACH indicated by msg1-FrequencyStart and msg1-FDM

• msg1-FrequencyStart indicates the first frequency resource for PRACH
• msg1-FDM indicates the number of frequency resources for PRACH (can be 1, 2, 4 or 8)
• n_RA = {0, 1, … M-1}

M = msg1-FDM = {1, 2, 4, 8}

 For more information you can refer index 6.3.3.2-4 of TS 38.211

Followings IE’s information  based on 38.331 v15.3.0

RACH-ConfigGeneric ::=          SEQUENCE {

prach-ConfigurationIndex         INTEGER (0..255),

msg1-FDM                         ENUMERATED {one, two, four, eight},

msg1-FrequencyStart              INTEGER (0..maxNrofPhysicalResourceBlocks-1),

zeroCorrelationZoneConfig        INTEGER(0..15),

preambleReceivedTargetPower      INTEGER (-200..-74),

preambleTransMax                 ENUMERATED {n3,n4,n5,n6,n7,n8,n10,n20,n50,n100,n200},

powerRampingStep                 ENUMERATED {dB0, dB2, dB4, dB6},

ra-ResponseWindow                ENUMERATED {sl1, sl2, sl4, sl8, sl10, sl20, sl40, sl80}

}

PRACH Occasions :

Example to find out PRACH occasion 

  

From the above example