TTI Bundling Control for Wireless Latency Reduction
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Solution Overview
Problem
The re-transmission approach in wireless communication systems, such as LTE, increases latency due to delays in receiving HARQ responses and re-transmitting data, especially in poor RF conditions, which can lead to increased latency and data errors.
Innovation Solution
Implementing TTI bundling in wireless communication systems, where the RAN determines and instructs the WCD to transmit data in multiple consecutive TTIs before waiting for a HARQ response, based on measurement reports, buffer status, and power headroom reports, to reduce latency and improve data robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is re-transmitted multiple times until successfully received, then data transmission reliability is improved, but transmission latency increases
Solution Approach 1:
The patent applies preliminary action by transmitting multiple copies of the same data packet in advance across different transmission time intervals before receiving acknowledgment. This allows the receiver to have multiple opportunities to successfully decode the data without requiring waiting periods for re-transmission decisions, thereby reducing latency while maintaining reliability.
Solution Approach 2:
The patent segments the data transmission into multiple parallel transmission attempts using different TTI bundles. Each bundle contains redundant copies of the data that can be independently received and decoded, allowing the system to achieve reliable transmission without sequential waiting for HARQ responses after each attempt.
2Reliability
If TTI bundling is used to transmit data four times in four consecutive TTIs, then data reception robustness is improved, but device power consumption increases
Solution Approach 1:
The patent implements dynamic adaptation by allowing the system to adjust the TTI bundle size based on current channel conditions, device power status, and traffic requirements. When channel conditions are good or power is constrained, smaller bundle sizes are used, reducing power consumption while maintaining adequate robustness. When conditions warrant, larger bundles provide enhanced reliability.
Solution Approach 2:
The patent changes the parameter of bundle size dynamically based on measured channel quality indicators and device state. By adjusting this key parameter, the system optimizes the trade-off between reception robustness and power consumption, using minimal redundancy when sufficient and maximal redundancy only when necessary.
3Reliability
If the UE waits for HARQ response after each data transmission, then transmission accuracy is maintained, but transmission speed decreases
Solution Approach 1:
The patent applies preliminary action by pre-transmitting multiple data copies across consecutive TTIs before awaiting HARQ feedback. This eliminates the need for the UE to wait for acknowledgment after each individual transmission, as the receiver can successfully decode from any of the pre-sent copies, thereby maintaining accuracy while significantly improving transmission speed.
Solution Approach 2:
The patent ensures continuity of useful action by keeping the transmission channel active with redundant data copies during the bundle period. Instead of idle waiting periods between transmissions, the system continuously utilizes the channel to deliver useful data, maintaining both accuracy through redundancy and speed through uninterrupted transmission flow.
Data Source
AI summary
A radio access network (RAN) determines whether transmission time interval (TTI) bundling is warranted for a wireless communication device (WCD) based on information contained in one or more reports from the WCD. The information may include a reference-signal value, such as a reference signal received power (RSRP) or a reference signal received quality (RSRQ), in a measurement report, an amount of data indicated in a buffer status report as being buffered by the WCD for transmission via one or more bearers in a bearer group, and a service class associated with the bearer group. If the RAN determines that TTI bundling is warranted for the WCD, the RAN may further select a TTI bundle size for the WCD. The RAN may select the TTI bundle size from among a plurality of values, which values may include a standard TTI bundle size and a smaller TTI bundle size.