TTI Bundling Collision Avoidance in LTE Uplink HARQ
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Solution Overview
Problem
Current wireless communication technologies, such as LTE, do not effectively handle collisions between bundled uplink radio resource grants, which can disrupt Hybrid Automatic Repeat Request (HARQ) processes, particularly when a new grant overlaps with an ongoing transmission time interval (TTI) bundle, leading to inefficiencies in data re-transmissions and potential loss of data.
Innovation Solution
A method and apparatus for determining collisions between later and earlier received grants of bundled uplink resources, where the radio device flushes the re-transmission buffer associated with the earlier grant, allowing for recalculating bundling start offsets and continuing with new bundle boundaries to prevent data loss and maintain HARQ process integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the network schedules multiple consecutive subframes with a single resource grant to reduce control signaling overhead, then capacity is improved, but collisions occur when a new grant overlaps with an ongoing TTI bundle
Solution Approach 1:
The UE performs preliminary actions by detecting grant collisions before they disrupt HARQ processes. The method proactively identifies when a new uplink grant overlaps with an ongoing TTI bundle by comparing grant timing and bundle duration, allowing the system to prepare for and handle the collision before it causes data loss or transmission errors.
2Area of stationary object
If TTI bundling is used to improve coverage at the cell edge, then coverage is improved, but HARQ process integrity is compromised when grants collide
Solution Approach 1:
The method extracts and isolates the colliding grant from the normal HARQ process flow. When a collision is detected, the affected HARQ process is identified and separated from the regular transmission sequence, allowing the system to handle the collision case specially without disrupting other ongoing HARQ processes, thus preserving overall HARQ integrity while maintaining extended coverage benefits.
Solution Approach 2:
Upon detecting a grant collision, the method discards the corrupted or conflicting data in the re-transmission buffer associated with the colliding grant. This deliberate discarding prevents propagation of errors, and the system recovers by re-establishing the HARQ process with corrected timing or re-scheduling, thereby recovering from the collision while maintaining the coverage extensions provided by TTI bundling.
3Reliability
If the UE flushes the re-transmission buffer to recover from collision, then HARQ process integrity is restored, but data loss occurs
Solution Approach 1:
The method converts the harmful effect of grant collision into a beneficial recovery opportunity. By detecting the collision and deliberately flushing the re-transmission buffer, the system transforms a potential data loss scenario into a controlled reset that restores HARQ process integrity. The collision event itself becomes the trigger for a clean state transition, allowing the HARQ process to restart from a known good state rather than propagating corrupted transmissions.
Data Source
AI summary
A radio device/user equipment determines that a later received grant of bundled uplink resources collides with an earlier received grant of bundled uplink resources. The earlier received grant has associated with it an active re-transmission process. In response to that collision determination, at least a re-transmission (HARQ) buffer associated with the earlier received grant is flushed. In one embodiment all HARQ buffers are flushed; in another the HARQ buffer associated with the earlier received grant is flushed while the one associated with the later received grant is not. Several ways are described to determine whether there is a collision: whether the later received grant aligns with a boundary of the resources granted by the earlier received grant, and whether there is an actual collision among the different HARQ processes. Calculating HARQ process numbers is also described where an offset is used to account for the grants allocating bundled TTIs.