E-PDCCH Sequential Mapping for LTE Control Channel Detection
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Solution Overview
Problem
In LTE systems, user equipment (UE) incorrectly judges the start position of the Enhanced Physical Downlink Control Channel (E-PDCCH), leading to incorrect detection of control channel elements and subsequent errors in feedback information transmission, especially with the introduction of multi-user MIMO and CoMP technologies.
Innovation Solution
The E-PDCCH is mapped sequentially to resource elements in each OFDM symbol, and reference signals are sent using specific ports corresponding to aggregation levels, ensuring that different control channel elements do not have the same modulation symbols and allowing correct detection by the UE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If circular buffering based rate matching is used for PDCCH encoding, then the encoding rate can be less than 1/3, but different CCEs include the same modulation symbol causing UE detection errors
Solution Approach 1:
The patent segments the PDCCH encoding process by introducing a new rate matching method that divides the encoded bits into multiple groups corresponding to different CCEs. This ensures each CCE receives unique modulation symbols while maintaining the flexible encoding rate capability through controlled repetition patterns across segmented CCE groups.
Solution Approach 2:
The patent applies preliminary action by performing rate matching and bit grouping before CCE mapping. The base station pre-processes the encoded bits to ensure proper distribution across CCEs, preventing the detection error problem at the source rather than correcting it later at the UE side.
2Reliability
If PDCCH is transmitted at aggregation level 4, then control information redundancy is increased, but UE may incorrectly detect it as aggregation level 2 causing feedback channel errors
Solution Approach 1:
The patent applies local quality by making each CCE have distinct modulation symbol characteristics through the new rate matching method. This local differentiation within CCEs allows the UE to correctly identify the aggregation level by detecting the unique pattern across CCEs, preventing misinterpretation of AL4 as AL2.
Solution Approach 2:
The patent changes the parameter distribution pattern in rate matching to create distinguishable characteristics for different aggregation levels. By controlling how bits are mapped to modulation symbols across CCEs, the system creates unique signatures for AL2 and AL4 that prevent detection confusion.
3Device complexity
If PUCCH format 1a/1b channel is determined by implicit indexing of first CCE, then feedback channel allocation is simplified, but incorrect CCE start position detection leads to incorrect PUCCH channel determination
Solution Approach 1:
The patent segments the control channel structure into clearly defined CCE units with unique modulation patterns. This segmentation ensures the first CCE index is unambiguously identifiable, maintaining the simple implicit PUCCH indexing method while eliminating the reliability issue caused by detection errors.
Data Source
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AI summary
Embodiments of the present invention provide a method for communicating downlink control signal, a base station, and a user equipment. The method includes: mapping, by a base station according to an order of OFDM symbols used by an E-PDCCH of a user equipment UE, the E-PDCCH sequentially to resource elements used to transmit the E-PDCCH in each OFDM symbol; and sending, by the base station, the E-PDCCH to the UE by using the resource elements, where the E-PDCCH and a PDSCH invoked by the E-PDCCH are frequency-division multiplexed. In the present invention, the E-PDCCH can be mapped, according to an order of OFDM symbols used by an E-PDCCH of a UE, sequentially to resource elements used to transmit the E-PDCCH in each OFDM symbol, so that different control channel elements of E-PDCCHs at different aggregation levels will not include a same E-PDCCH modulation symbol, thereby avoiding that the UE judges a start position of the E-PDCCH incorrectly.