Indoor Base Station Air Interface Synchronization via Reference Selection
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Solution Overview
Problem
In LTE systems, indoor femto cell base stations face challenges in synchronization due to penetrative radio signal loss and interference from outdoor macro cell base stations, leading to resource waste and reduced synchronization accuracy, especially in multi-hop scenarios where synchronization errors accumulate.
Innovation Solution
An air interface synchronization method where unsynchronized indoor base stations listen to synchronization sub-frames from outdoor and synchronized indoor base stations, select a synchronization reference base station based on priority information, and synchronize using a dedicated synchronization channel within existing sub-frames like MBSFN, avoiding resource waste and ensuring accurate synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If indoor base stations use GPS timing signal for synchronization, then synchronization accuracy is improved, but device complexity and cost increase due to GPS receiver requirements
Solution Approach 1:
The patent introduces an air interface as an intermediary medium for synchronization signal transmission between base stations. Instead of each base station requiring direct GPS reception, synchronization signals are transmitted through the air interface from reference base stations to other base stations, eliminating the need for GPS receivers in indoor base stations while maintaining synchronization accuracy
Solution Approach 2:
The patent creates copies of synchronization signals from GPS-synchronized reference base stations and transmits them through the air interface to other base stations. This allows indoor base stations to obtain synchronized timing information without directly receiving GPS signals, reducing device complexity while preserving synchronization precision
2Adaptability or versatility
If femto cell base stations are deployed indoors to provide high-rate data access, then service coverage is improved, but synchronization reliability deteriorates due to inability to acquire GPS timing signal
Solution Approach 1:
The air interface serves as a mediator to transmit synchronization signals from outdoor reference base stations to indoor femto cell base stations. This allows indoor base stations to reliably acquire synchronization information despite being unable to directly receive GPS signals through building penetrations
Solution Approach 2:
The patent replaces the GPS satellite-based synchronization mechanism with a terrestrial air interface-based synchronization mechanism. Instead of relying on satellite signals that cannot penetrate buildings, the system uses radio frequency signals transmitted through the air interface between base stations, ensuring reliable synchronization for indoor deployments
3Loss of information
If base stations transmit synchronization signals continuously, then synchronization information availability is improved, but resource waste increases due to occupying entire sub-frames
Solution Approach 1:
The patent segments the synchronization signal transmission from the entire sub-frame structure, extracting only the necessary synchronization elements (PSS, SSS, CRS) and transmitting them in a dedicated synchronization channel within the sub-frame. This allows partial use of sub-frame resources for synchronization while preserving other resources for data transmission, reducing overall resource waste
Solution Approach 2:
The patent applies partial action by transmitting only the essential synchronization components rather than occupying the entire sub-frame. The synchronization channel uses a portion of the available time-frequency resources just sufficient for synchronization signal transmission, avoiding excessive resource consumption while maintaining information availability
4Reliability
If HeNBs synchronize by listening to eNB synchronization signals, then synchronization is achieved, but synchronization accuracy deteriorates due to co-channel interference from adjacent HeNBs
Solution Approach 1:
The patent implements periodic synchronization signal transmission where base stations alternate between transmitting and listening phases. During each synchronization opportunity, only the reference base station transmits while others listen, then roles are rotated in subsequent periods. This periodic structure ensures that listening base stations do not experience interference from simultaneous transmissions by other base stations attempting to synchronize
Solution Approach 2:
The patent applies preliminary action by having base stations pre-coordinate their synchronization signal transmission times and frequencies before actual synchronization occurs. This preliminary coordination establishes an interference-free environment for each synchronization event, ensuring that listening base stations can accurately receive synchronization signals without co-channel interference from other base stations
Data Source
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AI summary
An air interface synchronization method is provided. The method includes that: a home-eNodeB which is not synchronized with an eNodeB, intercepts a synchronization subframe transmitted from the eNodeB and/or the home-eNodeB which was already synchronized with the eNodeB, a synchronization reference base station is selected from the base station which transmits the intercepted synchronization subframe, wherein the synchronization subframe includes a special synchronization channel for broadcasting synchronization sequence; the synchronization sequence is obtained, which is broadcasted in the special synchronization channel of the synchronization subframe transmitted by the synchronization reference station, and the synchronization with the synchronization base station is performed according to the synchronization sequence. Also, an air interface synchronization system, an eNodeB and a home-eNodeB are provided. The problem in prior art that the source is wasted in the process of synchronization is solved according to the method, the system, the eNodeB and the home-eNodeB.