Resolving DCI Search Space Ambiguity via RRC Configuration
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Solution Overview
Problem
In wireless communication systems, particularly in LTE, ambiguity arises when a downlink control information (DCI) message has a common payload size and the same first control channel element index in both common and UE-specific search spaces, leading to unclear interpretation of bit fields, which impairs the coverage and scheduling of secondary cells compared to primary cells.
Innovation Solution
The use of Radio Resource Control (RRC) to configure user equipment (UE) to assume whether a DCI message with a common payload size and same first control channel element index, but different bit fields, is transmitted in the common or UE-specific search space, based on specific parameter values in RRC messages, thereby resolving the ambiguity and improving secondary cell coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If DCI messages with common payload size and same first CCE index are transmitted in both common search space and UE-specific search space, then search space utilization is improved, but bit field interpretation ambiguity arises
Solution Approach 1:
The patent applies local quality by configuring different search spaces (common search space and UE-specific search space) with different bit field interpretations for DCI messages, even when they have the same payload size and first CCE index. This allows the system to maintain multiple transmission modes while resolving ambiguity through localized configuration differences.
Solution Approach 2:
The patent uses preliminary action by configuring the UE in advance through RRC signaling about which search space (common or UE-specific) a DCI message belongs to, before the actual decoding process. This pre-configuration eliminates ambiguity during message interpretation by establishing the correct bit field mapping beforehand.
2Reliability
If UE monitors all control channel candidates, then complete DCI detection is achieved, but monitoring complexity increases
Solution Approach 1:
The patent segments the control channel candidates into different search spaces (common search space and UE-specific search space), each with its own set of CCEs and DCI message characteristics. This segmentation allows the UE to monitor only relevant candidates for each search space type, reducing overall complexity while maintaining detection completeness.
Solution Approach 2:
The patent changes parameters such as payload size and CCE index ranges for different search spaces, creating distinguishable characteristics that help the UE efficiently identify and monitor only the relevant DCI messages for each search space type, thereby reducing monitoring complexity.
3Adaptability or versatility
If DCI messages are scheduled in overlapping search spaces, then scheduling flexibility is improved, but secondary cell coverage is impaired
Solution Approach 1:
The patent applies local quality by configuring different search spaces with different bit field interpretations, allowing the system to maintain scheduling flexibility while ensuring proper secondary cell coverage through localized configuration differences that prevent ambiguous scheduling.
Solution Approach 2:
The patent uses preliminary action by configuring the UE in advance through RRC signaling about search space assignments and bit field interpretations before scheduling occurs. This pre-configuration ensures that DCI messages scheduled in overlapping search spaces are correctly interpreted, maintaining secondary cell coverage while preserving scheduling flexibility.
Data Source
AI summary
A user equipment, UE, is configured to receive downlink control information, DCI, transmitted to the UE by a primary cell in a wireless communication system. The UE comprises one or more processing circuits that shall assume that a DCI message which has a common payload size and the same first control channel element index, but different bit fields, in a common search space and a UE-specific search space is transmitted by the primary cell in the common search space or the UE-specific search space, based on radio resource control, RRC, configuration of the UE.