Multi-Carrier Synchronization Signal Mapping for LTE-WiFi Coexistence
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Solution Overview
Problem
In LTE-WiFi coexistence scenarios, LTE's continuous transmission on unlicensed bands interferes with WiFi, leading to degraded performance due to lack of Clear Channel Assessment (CCA) in LTE, causing synchronization issues for receiving nodes due to opportunistic transmission patterns and frequency drift, resulting in inefficient resource utilization and potential loss of synchronization.
Innovation Solution
A transmitting device maps multiple synchronization signal sequences onto time and frequency resource elements of a single OFDM symbol, allowing for instant synchronization and reduced overhead, with centrally symmetric sequences for robust detection and compatibility with LTE systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If LTE performs continuous transmission on unlicensed bands, then transmission continuity is improved, but interference with WiFi and loss of synchronization occur
Solution Approach 1:
The patent implements periodic transmission with defined gaps instead of continuous transmission. The eNodeB transmits during defined time intervals and remains silent during gaps, allowing WiFi to access the channel periodically. This periodic action pattern resolves the contradiction by maintaining transmission continuity within intervals while preventing harmful continuous interference.
Solution Approach 2:
The patent maintains continuity of useful action by ensuring synchronization signals are transmitted continuously at defined positions within each transmission interval. Even though there are gaps between transmission intervals, the useful synchronization function remains continuous for devices that successfully acquire signals, as the periodic transmission ensures devices can maintain synchronization across gaps.
2Adaptability or versatility
If LAA performs opportunistic transmission with CCA, then fair coexistence with WiFi is improved, but synchronization stability deteriorates
Solution Approach 1:
The patent applies preliminary action by transmitting synchronization signals at predetermined positions within transmission intervals, before data transmission begins. This ensures devices can acquire and maintain synchronization in advance, stabilizing the synchronization state even though the overall transmission pattern is opportunistic and adaptive to channel conditions.
Solution Approach 2:
The patent changes the parameter of synchronization signal positioning from flexible/opportunistic to fixed/deterministic within each transmission interval. By anchoring synchronization signals at specific positions (e.g., beginning of transmission interval), the system maintains synchronization stability while preserving adaptability in the overall transmission timing through CCA-based channel access.
3Reliability
If synchronization signals are transmitted periodically in LTE, then synchronization is maintained, but resource overhead increases in LAA
Solution Approach 1:
The patent applies partial action by transmitting synchronization signals only during defined transmission intervals rather than continuously. This reduces the quantity of synchronization signal transmissions compared to continuous periodic transmission in licensed LTE, lowering resource overhead while maintaining sufficient synchronization reliability for devices that successfully acquire signals during active intervals.
4Object-generated harmful factors
If LAA transmits with maximum duty cycle of 5%, then interference with WiFi is reduced, but synchronization detection becomes more difficult
Solution Approach 1:
The patent applies local quality by concentrating transmission energy into specific defined positions within the 5% duty cycle window, rather than spreading it uniformly. By placing synchronization signals at predetermined locations (e.g., start of transmission interval) and using appropriate signal sequences, the patent improves detectability at these local positions while maintaining overall low duty cycle to minimize interference.
Data Source
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Figure 5a~5b
AI summary
84438224PCT01 33 ABSTRACT The present invention relates to a transmitting device and a receiving device. The transmitting device (100) comprises: a processor (102), and a transmitter (104); wherein the processor (102) is configured to map a plurality of synchronization signal sequences to time 5 and frequency resource elements of one Orthogonal Frequency Division Multiplex, OFDM, symbol, wherein at least two of the plurality of synchronization signal sequences are of a first kind; wherein the transmitter (104) is configured to transmit a multi-carrier signal comprising the one OFDM symbol. The receiving device (300) comprises: a processor (302), and a receiver (304); wherein the receiver (304) is configured to receive a multi-carrier signal 10 comprising a OFDM symbol, wherein time and frequency resource elements of the OFDM symbol comprises a plurality of synchronization signal sequences, and wherein at least two of the plurality of synchronization signal sequences are of a first kind; wherein the processor (302) is configured to detect the plurality of synchronization signal sequences comprised in the time and frequency resource elements of the OFDM symbol. Furthermore, the present 15 invention also relates to corresponding methods, a multicarrier wireless communication system comprising such a transmitting device, a computer program, and a computer program product. (Fig. 19)