Unlicensed 5G Synchronization Signaling Under LBT Timing Constraints
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Solution Overview
Problem
In the 5G NR system, sending synchronization signals in an unlicensed frequency band poses a challenge due to the need to comply with the Listen Before Talk (LBT) rule, which can result in failed transmissions and unfair access to the channel.
Innovation Solution
A network device performs LBT before the intended transmission time of synchronization signals and, if the channel is busy, delays the transmission by a preset time to retry LBT, ensuring the signals are sent when the channel is idle, using OFDM symbols or other time units as the granularity for the delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the network device performs LBT before the start time and transmits the synchronization signal when the channel is idle, then the transmission fairness is ensured, but the transmission delay increases when the channel is busy
Solution Approach 1:
The network device performs LBT in advance before the scheduled start time to determine channel availability. This preliminary channel assessment allows the device to prepare for transmission ahead of time, ensuring fairness by following LBT rules while minimizing delay by having the channel status determined beforehand.
Solution Approach 2:
The network device dynamically adjusts the transmission timing based on the LBT result. When the channel is busy at the scheduled start time, the device flexibly delays transmission and performs LBT again at a later time, adapting to changing channel conditions rather than adhering to a fixed transmission schedule.
2Loss of time
If the network device transmits the synchronization signal at the expected start time without retrying LBT, then the transmission timing is precise, but the transmission failure rate increases when the channel is busy
Solution Approach 1:
The network device uses the LBT result as feedback to determine whether to proceed with transmission. When the initial LBT at the scheduled start time indicates a busy channel, the device receives this negative feedback and responds by performing LBT again at a delayed time, thereby improving transmission success rate while maintaining timing precision through structured retry logic.
Solution Approach 2:
The network device performs a preliminary LBT check at the scheduled start time before actual transmission. This preliminary action allows the device to assess channel availability in advance and make an informed decision about whether to transmit immediately or delay, thus maintaining timing precision while reducing transmission failures.
3Reliability
If the network device performs LBT again within a preset time length after the start time when the channel is busy, then the synchronization signal can be sent in a timely manner, but the channel access complexity increases
Solution Approach 1:
The network device implements dynamic channel access by performing LBT again within a preset time length after the start time when the initial LBT indicates a busy channel. This dynamic approach allows the device to adapt to channel conditions and ensure reliable transmission while managing complexity through a structured, time-bounded retry mechanism with clear decision logic.
Solution Approach 2:
The network device changes the LBT execution parameter by performing LBT again at a delayed time within a preset time length rather than adhering strictly to the original start time. This parameter change (timing flexibility) ensures reliable transmission by allowing a second channel assessment opportunity while controlling complexity through defined time constraints.
Data Source
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AI summary
This application provides a synchronization signal sending method applied to an unlicensed frequency band. To ensure transmission fairness, a network device performs listen before talk LBT before a start time for transmitting a synchronization signal, to determine whether a channel is busy or idle. When the channel is busy, the network device cannot transmit the synchronization signal at the expected start time for transmitting the synchronization signal. Therefore, the network device performs LBT again within a preset time length after the start time, and sends the synchronization signal when determining that the channel is idle by performing LBT again. When the channel is idle, the network device preempts a channel resource, and sends the synchronization signal the expected start time for transmitting the synchronization signal.