Uplink Timing Advance Calculation for IRAT Handover
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Solution Overview
Problem
Current inter-radio access technology (IRAT) handover procedures in wireless communication systems face challenges in ensuring successful handovers without random access configuration, leading to potential failures due to inaccurate uplink timing advances during transitions between different radio access technologies like LTE and TD-SCDMA.
Innovation Solution
The method modifies the current uplink timing advance of the source cell based on the differences between uplink and downlink timings of both the source and target cells, allowing the user equipment to determine an accurate uplink timing advance for the target cell, thereby facilitating successful handovers without requiring a random access configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional IRAT handover procedure is used without random access configuration, then handover speed is improved, but handover reliability deteriorates due to inaccurate uplink timing advance
Solution Approach 1:
The patent calculates and prepares the uplink timing advance value before the handover occurs. By using the formula TA_target = TA_source + (DL_offset_target - UL_offset_target) - (DL_offset_source - UL_offset_source), the system pre-determines the correct timing advance for the target cell, eliminating the need for random access procedures and ensuring both fast and reliable handover execution.
2Measurement precision
If random access configuration is included in handover command, then uplink timing accuracy is improved, but handover complexity and time increase
Solution Approach 1:
The patent extracts the uplink timing advance calculation from the random access procedure by directly computing it using the offset differences between source and target cells. This removes the need for complex random access configuration and multiple signaling exchanges, achieving accurate timing synchronization through a simplified direct calculation approach.
3Ease of operation
If uplink timing advance is not adjusted during handover, then handover simplicity is maintained, but uplink synchronization is lost
Solution Approach 1:
The patent changes the timing advance parameter during handover by calculating the difference in offset parameters between source and target cells. This parameter adjustment ensures that uplink synchronization is maintained in the target cell while keeping the handover procedure simple and direct, avoiding the need for complex random access procedures.
Data Source
AI summary
A user equipment (UE) determines an uplink timing advance of a target NodeB, such as an uplink dedicated physical channel (DPCH) transmit timing, during handover transition when the UE receives a handover command without a random access configuration. In one instance, the UE modifies a current timing advance of a source eNodeB based on a difference between an uplink timing of the source eNodeB and a downlink timing of the source eNodeB and a difference between an uplink timing of the target NodeB and a downlink timing of the target NodeB. In another instance, the UE determines the uplink timing advance of the target NodeB based on the modified current uplink timing advance of the source eNodeB.