Power Headroom Reporting in LTE-A Carrier Aggregation
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Solution Overview
Problem
The existing PHR MAC CE format in LTE Rel-8/9 systems is not applicable to LTE-A systems, which require reporting power headroom for multiple carriers with dynamic changes in the number of component carriers, distinguishing between Type 1 and Type 2 PHRs, and differentiating between real and virtual PHRs, leading to inconsistent understanding between the UE and base station.
Innovation Solution
A method and apparatus for reporting power headroom in carrier aggregation scenarios, where the terminal determines the length of the PHR MAC CE based on predetermined strategies and generates PHR MAC CE including power headroom for each carrier, and the base station identifies and acquires the power headroom from the PHR MAC CE, using length and type information to distinguish between virtual and real PHRs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the existing PHR MAC CE format from LTE Rel-8/9 is used, then the system maintains compatibility with legacy systems, but it cannot support reporting power headroom for multiple carriers in LTE-A carrier aggregation scenarios
Solution Approach 1:
The PHR MAC CE is segmented into multiple fields, each representing power headroom information for a specific component carrier. The MAC CE includes a first field for first component carrier PHR, a second field for second component carrier PHR, and additional fields for other component carriers, allowing independent reporting for each carrier while maintaining a unified MAC CE structure
Solution Approach 2:
The patent extends the PHR reporting from a single-dimension (one carrier) format to a multi-dimension format by adding carrier identification bits and multiple PHR value fields. Each PHR entry is associated with a component carrier index, creating a two-dimensional structure (carrier index × PHR value) that enables multi-carrier reporting
2Measurement precision
If the PHR MAC CE includes detailed information for each component carrier, then the reporting precision is improved, but the MAC CE length becomes variable and difficult to manage
Solution Approach 1:
The patent uses a predetermined MAC CE length that is calculated based on the maximum number of component carriers supported by the system. This preliminary determination of MAC CE length allows the base station and UE to agree on the structure in advance, eliminating the need for dynamic length negotiation and simplifying parsing operations
Solution Approach 2:
The patent introduces a parameter indicating the number of component carriers to be reported, which changes the interpretation of the MAC CE fields. Based on this parameter, the MAC CE structure adapts to include the appropriate number of PHR fields, balancing between providing detailed per-carrier information and maintaining manageable MAC CE sizes
3Loss of information
If the system reports both Type 1 and Type 2 PHRs for the primary cell, then the power headroom information is more comprehensive, but the MAC CE size and processing complexity increase
Solution Approach 1:
The patent dynamically includes or excludes Type 1 and Type 2 PHR fields based on the actual reporting scenario. The MAC CE structure allows for flexible configuration where Type 1 PHR (for PUSCH) and Type 2 PHR (for PUCCH) are included only when relevant to the current transmission situation, reducing unnecessary data volume while maintaining information completeness
Data Source
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AI summary
Disclosed are a method and an apparatus for reporting power headroom in a carrier aggregation context. By applying the technical solutions of the embodiments of the present invention, PHR MAC CE and a corresponding MAC sub-header are determined according to the number of uplink component carriers needing to report power headroom and a type of the power headroom to be reported, and indication information such as length information of the PHR MAC CE, type information of the power headroom, and information about whether the power headroom is virtual power headroom is carried therein, so that a base station can precisely obtain the power headroom of each uplink component carrier. In this way, the problem that the PHR MAC CE format in the current LTE Rel-8/9 is not applicable to an LTE-A system is solved.