Time-Aligned Handover Using Propagation Delay Offset
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Solution Overview
Problem
During handover in wireless communication networks, mobile devices often fail to align their transmissions with the target cell's frame timing, leading to interference, increased load on the Random Access Channel (RACH), and prolonged synchronization times due to varying propagation delays, which existing methods either delay synchronization or increase signaling overhead.
Innovation Solution
Calculating a target transmission time based on the determined target propagation delay, allowing the mobile device to time-align its signals with the target cell's frame timing, either by the serving access point or autonomously by the mobile device, reducing the need for timing measurements at the target base station and signaling overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the mobile device uses random access procedure to access the target base station during handover, then the mobile device can acquire physical layer synchronization, but the handover signals may interfere with adjacent slots/frames and cause high load on RACH due to retransmissions
Solution Approach 1:
The patent applies preliminary action by calculating and applying the propagation delay offset before the mobile device accesses the target base station. The serving base station determines the offset based on timing differences between serving and target cells, and provides this offset to the mobile device in advance through the handover command. This allows the mobile device to pre-adjust its transmission timing, ensuring that handover signals arrive at the target base station within the correct reception window, thereby preventing interference with adjacent slots/frames and reducing RACH retransmissions.
2Ease of operation
If the target base station calculates the uplink propagation delay and signals the offset to the mobile device, then the transmission timing can be adjusted, but this delays uplink synchronization especially in large cells
Solution Approach 1:
The patent applies preliminary action by performing the propagation delay calculation and offset determination before the mobile device actually accesses the target base station. The serving base station uses timing difference measurements between serving and target cells to compute the offset in advance, incorporating it into the handover command. This eliminates the need for the mobile device to perform timing adjustments after accessing the target base station, thereby avoiding synchronization delays that would occur if the calculation were performed after handover initiation.
Solution Approach 2:
The patent uses the serving base station as an intermediary to calculate and provide the propagation delay offset to the mobile device. Instead of the target base station directly measuring and signaling the offset (which would cause delays), the serving base station acts as a mediator that determines the offset based on available timing information and communicates it to the mobile device before handover. This intermediary approach enables timely timing adjustment without requiring post-access measurements at the target base station.
3Reliability
If the target base station estimates the propagation-related offset before handover and signals it to the serving base station, then proper timing can be achieved, but this increases signaling overhead on the transport network
Solution Approach 1:
The patent applies the taking out principle by extracting the propagation delay offset calculation from the target base station and performing it at the serving base station instead. The serving base station uses its existing timing measurements and the timing difference between serving and target cells to determine the offset locally. This eliminates the need for additional signaling messages between the target base station and serving base station, thereby removing the signaling overhead that would be required to transport the offset information across the network while still achieving accurate timing alignment.
4Reliability
If a longer reception window is implemented at the base station to capture signals, then signals arriving outside the reception window can be captured, but the complexity of the receiver increases due to more hardware and processing ability required
Solution Approach 1:
The patent applies preliminary action by adjusting the mobile device's transmission timing in advance so that signals arrive at the base station within the predetermined reception window. The serving base station calculates the propagation delay offset and provides it to the mobile device before handover, enabling the mobile device to transmit at the correct time. This ensures signals arrive within the standard reception window, eliminating the need for longer reception windows and the associated increase in receiver complexity.
Data Source
AI summary
Time-aligned handover for a mobile device is described herein. The time-aligned handover is achieved by determining a time difference between serving and target cells and determining a target propagation delay based on the time difference. In some cases, the target propagation delay may further be determined based on a serving propagation delay between the serving cell and the mobile device. A target transmission time is calculated based on the target propagation delay. The mobile device uses the target transmission time to time align transmissions to the target cell during handover.