Random Access Procedure for Dual Connectivity Backhaul Latency
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Solution Overview
Problem
In dual connectivity LTE systems, the conventional random access procedures for mobile terminals to acquire resources from multiple base stations are inefficient, particularly due to latency issues in backhaul connections between master and secondary eNBs, which affect the timing synchronization and resource allocation during handovers and initial access.
Innovation Solution
The proposed solution involves modifying the random access procedure in dual connectivity contexts by allowing the UE to transmit a random access preamble to the secondary eNB, with the master eNB providing a timing advance command and uplink resource allocation, and using a modified RNTI (RA-RNTI2) for decoding the random access response, and adjusting the RAR window duration to compensate for backhaul latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conventional random access procedure is used in dual connectivity, then the UE can acquire resources from multiple base stations, but the backhaul latency causes timing synchronization issues and increases handover failures
Solution Approach 1:
The master eNB performs preliminary actions by providing timing advance commands to the UE before the random access procedure completes. This allows the UE to adjust its transmission timing in advance, compensating for backhaul latency and ensuring proper synchronization with the secondary eNB, thereby reducing handover failures.
Solution Approach 2:
The master eNB acts as an intermediary between the UE and the secondary eNB. It receives the random access preamble from the UE, processes the timing advance information, and provides corrected timing advance commands to the UE. This intermediary role allows the system to compensate for backhaul latency without requiring direct low-latency communication between UE and secondary eNB.
2Measurement precision
If the random access procedure is modified to work with backhaul latency, then timing synchronization is improved, but the procedure complexity increases
Solution Approach 1:
The master eNB performs multiple functions within the random access procedure: it receives the random access preamble, calculates timing advance based on the preamble reception time, provides timing advance commands to the UE, and manages uplink resource allocation. This multi-functionality consolidates complexity into a single node rather than requiring complex coordination between multiple nodes.
3Productivity
If dedicated uplink resources are allocated to the UE, then resource acquisition efficiency is improved, but the procedure is more complex when backhaul latency is present
Solution Approach 1:
The master eNB provides feedback in the form of timing advance commands to the UE based on the random access preamble reception. This feedback mechanism allows the UE to adjust its transmission timing, ensuring efficient resource utilization even in the presence of backhaul latency, while the feedback itself is managed through existing signaling procedures.
Data Source
AI summary
In dual connectivity, a UE is served by cells are operated in different eNBs with one eNB designated as the master eNB (MeNB) and the other as a secondary eNB (SeNB). A random access procedure is described by which a UE connected to an MeNB may attempt to acquire access to an SeNB cell. The procedure may utilize the backhaul connection between the SeNB and the MeNB so that the random access response may be transmitted over an MeNB cell.