TDD-FDD Carrier Aggregation Feedback Bottleneck Resolution
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Solution Overview
Problem
The existing carrier aggregation systems in TDD-FDD communication face a feedback bottleneck, leading to increased air interface delay due to mismatched short transmission time intervals (sTTIs) between FDD and TDD carriers.
Innovation Solution
The proposed communication method for a carrier aggregation system uses an sTTI that occupies two OFDM symbols as the minimum scheduling unit for the TDD carrier, balancing scheduling delays between TDD and FDD carriers and enhancing feedback opportunities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the TDD carrier uses seven OFDM symbols as the minimum sTTI division pattern and the FDD carrier uses two or three OFDM symbols as the sTTI division pattern, then the scheduling flexibility of the FDD carrier is improved, but a feedback bottleneck occurs because the TDD carrier cannot provide enough feedback opportunities
Solution Approach 1:
The invention segments the feedback transmission by dividing it into multiple feedback opportunities within the TDD uplink subframe. Instead of treating the TDD carrier as a single feedback channel, the patent creates multiple discrete feedback opportunities (at least two) within each TDD uplink subframe, allowing feedback information to be transmitted in segments across different time instances. This segmentation resolves the contradiction by providing sufficient feedback capacity while maintaining the seven-symbol sTTI structure.
Solution Approach 2:
The invention introduces a new dimension to feedback transmission by utilizing multiple feedback opportunities within a single TDD uplink subframe. Rather than increasing feedback capacity through time (more subframes), the patent expands the feedback dimension within the subframe structure itself, creating multiple feedback slots or opportunities. This dimensional approach allows the TDD carrier to match the feedback capacity of FDD carriers without changing the fundamental sTTI length.
2Productivity
If the FDD carrier generates one uplink feedback opportunity every two or three OFDM symbols while the TDD carrier provides only two feedback opportunities per uplink subframe, then the FDD feedback rate is improved, but the TDD carrier becomes the limiting factor causing air interface delay
Solution Approach 1:
The invention applies preliminary action by pre-configuring multiple feedback opportunities within each TDD uplink subframe structure. Before actual feedback transmission occurs, the system establishes at least two feedback opportunities in advance within each subframe, ensuring that feedback capacity is prepared and available. This preliminary structuring of feedback opportunities eliminates the bottleneck by ensuring sufficient capacity exists before the feedback rate requirement arises.
Solution Approach 2:
The invention changes the feedback transmission parameter by increasing the number of feedback opportunities per TDD uplink subframe from two to at least two (with potential for more). This parameter change in the feedback structure allows the TDD carrier to match or exceed the feedback rate of FDD carriers, resolving the contradiction between feedback rate and air interface delay by adjusting the feedback opportunity count rather than the sTTI length.
Data Source
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AI summary
This application discloses a communication method for a carrier aggregation system. The carrier aggregation system is a carrier aggregation system including a TDD carrier and an FDD carrier, and method includes: A terminal device receives downlink information by using a secondary component carrier; and the terminal device sends feedback information for the downlink information by using a primary component carrier. When the primary component carrier or the secondary component carrier is a TDD carrier, at least one first subframe that includes P consecutive sTTIs exists in the TDD carrier, and at least one sTTI that occupies two OFDM symbols exists in the P sTTIs, where P is an integer greater than 1. Embodiments of the present invention further provide a corresponding terminal device and network device. In technical solutions of the present invention, because a minimum scheduling unit of the TDD carrier in the carrier aggregation system is an sTTI that occupies two OFDM symbols, balance can be achieved between a scheduling delay of the TDD carrier and a scheduling delay of the FDD carrier to some extent, so that a feedback bottleneck in the carrier aggregation system is decreased, and an air interface delay is reduced.