Monday, 9 January 2017

Planning & Optimization Solution for TDD-LTE-Reeastablishment through X2 inter Vendor issue

Based on LTE definition,reeastablishment through X2 interface is just private function,that is to say,this function between inter vendor not available unless IOT already done. 

SOLUTION

Two phases govern the behaviour associated to radio link failure as shown on Figure 10.1.6-1:
-     First phase:
-     started upon radio problem detection;
-     leads to radio link failure detection;
-     no UE-based mobility;
-     based on timer or other (e.g. counting) criteria (T1).
-     Second Phase:
-     started upon radio link failure detection or handover failure;
-     leads to RRC_IDLE;
-     UE-based mobility;
-     Timer based (T2).
 
Figure 10.1.6-1: Radio Link Failure
Table 10.1.6-1 below describes how mobility is handled with respect to radio link failure:
Table 10.1.6-1: Mobility and Radio Link Failure
Cases
First Phase
Second Phase
T2 expired
UE returns to the same cell
Continue as if no radio problems occurred
Activity is resumed by means of explicit signalling between UE and eNB
Go via RRC_IDLE
UE selects a different cell from the same eNB
N/A
Activity is resumed by means of explicit signalling between UE and eNB
Go via RRC_IDLE
UE selects a cell of a prepared eNB (NOTE)
N/A
Activity is resumed by means of explicit signalling between UE and eNB
Go via RRC_IDLE
UE selects a cell of a different eNB that is not prepared (NOTE)
N/A
Go via RRC_IDLE
Go via RRC_IDLE
NOTE:      a prepared eNB is an eNB which has admitted the UE during an earlier executed HO preparation phase, or obtains the UE context during the Second Phase.
In the Second Phase, in order to resume activity and avoid going via RRC_IDLE when the UE returns to the same cell or when the UE selects a different cell from the same eNB, or when the UE selects a cell from a different eNB, the following procedure applies:
-     The UE stays in RRC_CONNECTED;
-     The UE accesses the cell through the random access procedure;
-    The UE identifier used in the random access procedure for contention resolution (i.e. C‑RNTI of the UE in the cell where the RLF occurred + physical layer identity of that cell + short MAC-I based on the keys of that cell) is used by the selected eNB to authenticate the UE and check whether it has a context stored for that UE:
-     If the eNB finds a context that matches the identity of the UE, or obtainsthiscontextfrom thepreviously servingeNB,it indicates to the UE that its connection can be resumed;
-     If the context is not found, RRC connection is released and UE initiates procedure to establish new RRC connection. In this case UE is required to go via RRC_IDLE.
The radio link failure procedure applies also for RNs, with the exception that the RN is limited to select a cell from its DeNB cell list. Upon detecting radio link failure, the RN discards any current RN subframe configuration (for communication with its DeNB), enabling the RN to perform normal contention-based RACH as part of the re-establishment. Upon successful re-establishment, an RN subframe configuration can be configured again using the RN reconfiguration procedure.
NOTE:      If the recovery attempt in the second phase fails, the details of the RN behaviour in RRC_IDLE to recover an RRC connection are up to the RN implementation.

Budi Prasetyo

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