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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 co
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NR Bandwidth part (BWP) Concept

NR Bandwidth Part Concept : NR system supports much wider maximum CBW than LTE’s 20 MHz whereas In LTE in order to achieve wider bandwidth that can be done through Carrier Aggregation( CA) by adding extra Carriers (CC’s) .           So , what is the use of Wider BW ?             Answer is Wider bw will help to achieve higher data rates          Does UE really required wider BW always ?    Answer is UE doesn't always required to have high date rates , so the use of wide bw may imply power consumption in both RF and base band signal processing perspectives. New concept is designed in NR i.e. Band width part (BWP) and it addresses all issues as I mentioned above   - BWP concept in NR helps UE to access small BW than configured CBW which make NR energy efficient solution despite of having of wideband support This way UE can be configured different bandwidth parts out of those at a time UE can access only one BWP and that will be Chosen by network and subsequently
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MCG ,SCG, SPLIT Bearer and Use Case's

Talk about MCG /SCG and Split Bearers For EN-DC three bearer types exist those are 1.        MCG Bearer 2.        SCG Bearer 3.        Split Bearer In ENDC , Network can configure either E-utran PDCP or NR PDCP for MCG bearer whereas NR PDCP is must for SCG bearer and Split bearer Data Flow : MCG Bearer Using NR PDCP User plane data flow from the NR PDCP to LTE RlC Via MenB MCG Bearer using E-utran PDCP User plane data flow from the E-utran PDCP to LTE RlC Via MenB SCG bearer SCG bearer always Uses NR PDCP , and the data flow is from NR -PDCP to NR-RLC and NR-MAC via Senb Split Bearer Split bearer also Uses NR PDCP and the data flow is from NR-PDCP to LTE-RLC & NR-RLC For ex:  DRB -5 -LCID-4 (LTE-RLC ) and LCID-5(NR-RLC) NR PDCP can be created using R15 IE's i.e NR radio bearer config information -NRRadioBearerConfig will allow to configure DRB'
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NR Dual Connectivity (EN-DC)

Talk about Dual connectivity In a Simple words Dual connectivity means UE can get resources from two different enodeB's that is Master Enodeb and Secondary Enodeb . Sometime back in Rel12 of 3GPP has introduced this Dual connectivity concept but for NR deployment dual connectivity plays major role . In NR , E-Utran NR dual connectivity (EN-DC) will have two nodes 1.       First one is Master Enb i.e. Enb (LTE) and 2.       second one is Secondary Enb i.e. gNB (NR) So , First UE will connect to one Enb that acts as Master Enb and the other one will act as Secondary Enb . For EN-DC , UE will connect to LTE (i.e Menb ) and later UE will get an access to Senb via SCG addition procedure . For EN-DC 3GPP specifies three different types of bearer i.e. (MCG,SCG,SPLIT).  For more details about Multi Rat dual connectivity you can refer spec 37.340  
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