Reduced System-Time Overhead Parameter Length for Inter-RAT Handovers
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Solution Overview
Problem
Current methods for wireless access terminals to obtain system time of target radio access networks during active sessions are inefficient, consuming excessive overhead channel resources due to the need for precise timing resolution during handovers between different wireless technologies like LTE and CDMA.
Innovation Solution
Implementing a synchronous method for wireless access terminals to acquire system time, aligning it with the frame cycle boundary of the source network, reducing the required resolution and field size, such as reducing the system time field from 49 bits to 29 bits for LTE networks, allowing efficient handovers without dropping sessions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a 49-bit SYSTEM_TIME field is used to carry system time for target radio access technology, then the access terminal can accurately acquire the target network's system time with sufficient resolution, but the overhead channel resources are consumed excessively
Solution Approach 1:
The system time field is segmented into two parts: a 29-bit synchronized system time field that carries the actual system time information, and a 20-bit timing offset field that carries the difference between the source and target network timing. This segmentation allows the terminal to reconstruct the complete system time with full precision while using fewer total bits for transmission.
Solution Approach 2:
The patent changes the parameter representation by introducing a timing offset parameter instead of transmitting the complete system time with full resolution. The timing offset represents the difference between source network frame timing and target network system time, allowing the terminal to calculate the actual system time by combining the synchronized time with the offset, thereby reducing the total number of bits required.
2Measurement precision
If the access terminal acquires system time asynchronously from the target radio access technology, then the terminal can obtain timing information, but the overhead consumption increases significantly
Solution Approach 1:
The source radio access technology network performs preliminary synchronization with the target radio access technology network before handover. The source network obtains the target's system time in advance and includes this synchronized time information in the overhead parameters transmitted to the access terminal, eliminating the need for the terminal to perform asynchronous acquisition from the target network.
Solution Approach 2:
The source radio access technology network acts as an intermediary that has already synchronized with the target network and provides the synchronized system time information to the access terminal through overhead parameters. This intermediary approach allows the terminal to obtain accurate target network timing without directly interacting with the target network, reducing overhead consumption.
Data Source
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AI summary
A wireless communication system, a wireless access terminal and a method for a wireless access terminal to synchronize to system times in a wireless communication system are described. The method comprises: using a first timing hierarchy in a first wireless communication network to operate the wireless access terminal, the first wireless communication network having a first radio access technology, operating with the first timing hierarchy including determining a frame cycle for the first wireless communication network, the frame cycle having a frame cycle boundary; receiving broadcast parameters, within a system frame number "SFN" cycle, for a second wireless communication network having a second radio access technology different from the first radio access technology, the broadcast parameters including a system time of the second wireless communication network; aligning, from the perspective of the wireless access terminal, the system time of the second wireless communication network with the frame cycle boundary, wherein the frame cycle boundary is a beginning of a next SFN cycle; and engaging in a communication session using the second wireless communication network.