Backward Compatible PHICH Resource Mapping in TDD Carrier Aggregation
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Solution Overview
Problem
In LTE TDD systems, when carriers have different TDD uplink/downlink configurations, the base station cannot always feed back a PHICH (Physical Hybrid Automatic Repeat Request Indicator Channel) due to a lack of identifiable PHICH resources, leading to increased overhead from reserving non-backward compatible PHICH resources.
Innovation Solution
The method involves using a sub-frame with a backward compatible PHICH resource on either the first or second carrier to transmit and receive the PHICH, ensuring that the PHICH can be identified by the UE, even if the carriers have different TDD uplink/downlink configurations, thereby avoiding the need to reserve non-backward compatible resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If cross-carrier scheduling is used with carriers having different TDD configurations, then carrier aggregation capability is improved, but PHICH feedback becomes unreliable due to lack of identifiable resources
Solution Approach 1:
The patent introduces a mapping relationship as an intermediary between the secondary carrier's uplink sub-frame and the primary carrier's downlink sub-frame. This mapping enables the UE to identify the correct PHICH resource on the primary carrier, which has backward compatible resources, thereby mediating between the scheduling on secondary carrier and feedback on primary carrier with different TDD configurations
Solution Approach 2:
The patent makes the primary carrier serve multiple functions: it acts as both a carrier for data transmission and as a carrier for carrying PHICH resources that can serve multiple secondary carriers with different TDD configurations. This universal approach allows the primary carrier's backward compatible PHICH resources to support feedback for multiple secondary carriers
2Reliability
If non-backward compatible PHICH resources are reserved on primary carrier, then PHICH feedback can be provided for secondary carrier, but system overhead increases
Solution Approach 1:
The patent uses copying by having the UE determine PHICH resource indices on the primary carrier based on uplink resource indices from the secondary carrier through a mapping relationship. This allows the system to reuse existing backward compatible PHICH resources on the primary carrier rather than creating new non-backward compatible resources, effectively copying the resource identification mechanism across carriers with different TDD configurations
Data Source
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AI summary
The present invention discloses a method for transmitting information in a TDD system, a user equipment, and a base station, and belongs to the TDD field. The method for transmitting information includes: receiving, by a UE and on a first carrier of a TDD system, an uplink scheduling grant sent by a base station; sending, by the UE and in a first sub-frame on a second carrier, a scheduled PUSCH; and receiving, by the UE and in a second sub-frame, a PHICH, where the first carrier and the second carrier have different TDD uplink/downlink configurations; the second sub-frame has a backward compatible PHICH resource; and on the first carrier or the second carrier, the backward compatible PHICH resource is a PHICH resource which is identifiable to a UE in a TDD system whose version is lower than that of the TDD system. The present invention solves a problem in the prior art that a PHICH cannot be fed back because there is no PHICH resource, and may save an overhead of a PHICH resource.