Uplink Data Buffering for Unlicensed Spectrum LBT Delays
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Solution Overview
Problem
The unpredictable nature of the first available slot in the unlicensed 5 GHz spectrum due to listen-before-talk (LBT) procedures complicates pre-computation of data payload in LTE uplink transmissions, especially when channel availability is delayed, leading to potential data transmission delays and incorrect ordering of data packets.
Innovation Solution
A wireless device retains previously scheduled data in a buffer and considers previously dropped transmissions when selecting data to transmit in subsequent subframes, ensuring data is sent in the next available slot, thereby minimizing delays and maintaining data order.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LBT procedure is applied in unlicensed spectrum, then channel sharing with other radios is enabled, but the first transmission slot becomes unpredictable
Solution Approach 1:
The system performs preliminary actions by buffering scheduled data transmissions and preparing transmission parameters in advance. When a transmission opportunity arises after LBT succeeds, the buffered data is immediately transmitted without waiting for re-scheduling, thus reducing the impact of unpredictable slot availability.
2Reliability
If data is buffered for subsequent transmission, then data order is maintained, but transmission delay increases
Solution Approach 1:
Data is preliminarily buffered with associated transmission parameters (resource allocations, modulation schemes) prepared in advance. When the channel becomes available, the pre-prepared data is transmitted immediately, maintaining order while minimizing delay compared to re-scheduling approaches.
Solution Approach 2:
The system dynamically adjusts transmission timing based on channel availability. Instead of fixed scheduling, transmissions are deferred to the next available slot while preserving the original data order, allowing the system to adapt to LBT outcomes without rigid timing constraints.
3Productivity
If transmission parameters are pre-computed, then processing efficiency is improved, but accuracy decreases due to channel uncertainty
Solution Approach 1:
Transmission parameters are pre-computed based on initial channel conditions and scheduling decisions. These parameters are buffered alongside the data and used directly when the channel becomes available, avoiding the need for re-computation and maintaining processing efficiency while accepting that parameters may need adjustment for actual transmission conditions.
Data Source
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AI summary
In one example embodiment, a method (1300) by a wireless device (710A-C) includes attempting to transmit (1302) a first data packet (1114) during a first transmission time interval (1110). During a second transmission time interval (1112) that is subsequent to the first transmission time interval (1110), a second data packet (1116) is transmitted if the transmission of the first data packet (1114) during the first transmission time interval (1110) was successful. The second data packet (1116) includes data that is exclusive of the data of the first data packet (1114). Alternatively, if the transmission of the first data packet (1114) during the first transmission time interval (1110) was not successful, a third data packet (1118) is transmitted. The third data packet (1110) includes data that includes at least a portion of the data of the first data packet (1114).