HARQ Timing for Mixed FDD TDD Carrier Aggregation
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Solution Overview
Problem
Current LTE systems face challenges in harmonizing HARQ operations and scheduling across different duplex modes, particularly when carrier aggregation involves a combination of FDD and TDD modes, leading to inefficiencies in resource utilization and acknowledgement timing.
Innovation Solution
The proposed solution involves flexible HARQ timing schemes that allow PDSCH HARQ-ACK timing to be reused across both TDD and FDD modes, with the option to use either TDD or FDD timing based on the primary cell's configuration, and specific TDD configurations for secondary carriers to optimize acknowledgement efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional FDD or TDD timing schemes are used separately, then the HARQ operation is straightforward within each mode, but the system cannot support carrier aggregation with mixed duplex modes
Solution Approach 1:
The patent applies universality by creating a unified HARQ timing framework that works across both FDD and TDD modes. The base station determines HARQ timing based on the primary cell's duplex mode, allowing the same timing mechanism to serve both FDD and TDD secondary cells. This multi-functional approach enables mixed-mode carrier aggregation without requiring separate HARQ procedures for each duplex mode.
Solution Approach 2:
The patent applies local quality by allowing different HARQ timing configurations for different cells based on their specific duplex mode requirements. The primary cell's duplex mode (FDD or TDD) determines the timing characteristics applied to secondary cells, enabling each cell to operate with appropriate timing while maintaining overall system coherence. This localized adaptation resolves the complexity of harmonizing different timing schemes.
2Productivity
If TDD mode is used with strict uplink-downlink subframe allocation, then interference is controlled, but a significant portion of downlink PDSCH subframes cannot be acknowledged
Solution Approach 1:
The patent applies dynamics by introducing flexible HARQ timing that adapts to the primary cell's duplex mode. When the primary cell is in FDD mode, the system can provide acknowledgements for all downlink subframes, dynamically adjusting the timing based on FDD's continuous uplink availability. This dynamic timing adjustment resolves the contradiction between maintaining TDD interference control and achieving reliable acknowledgements for all PDSCH subframes.
Solution Approach 2:
The patent applies parameter changes by modifying the HARQ timing parameters based on the primary cell's duplex mode configuration. The system changes the timing relationship between downlink PDSCH and uplink HARQ-ACK transmissions, allowing acknowledgements to be sent in appropriate uplink subframes determined by the primary cell's mode. This parameter adaptation enables both high throughput and reliable acknowledgements in mixed-mode carrier aggregation.
Data Source
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AI summary
A method at a user equipment for hybrid automatic repeat request (HARQ) operation, the user equipment operating on a primary carrier having a first duplex mode and on at least one secondary carrier having a second duplex mode, the method using HARQ timing of the first duplex mode if the timing of the first duplex mode promotes acknowledgement opportunities over using HARQ timing of the second duplex mode; and using HARQ timing of the second duplex mode if the timing of the second duplex mode promotes acknowledgement opportunities over using HARQ timing of the first duplex mode.