SRS Transmission Power Scaling in Carrier Aggregation
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Solution Overview
Problem
In LTE mobile communication systems, the simultaneous transmission of SRS and other uplink channels in carrier aggregation poses challenges, particularly in managing power levels to avoid exceeding maximum allowed transmit power and maintaining single carrier properties, while also reducing signaling overhead and peak to average power ratio issues.
Innovation Solution
The solution involves defining cell-specific and UE-specific SRS subframe configurations for multiple carrier components, allowing flexible power management through methods like equal scaling, puncturing, or dropping of SRS transmission, and reducing signaling overhead by using offsets for UE-specific configurations, enabling efficient power utilization and simultaneous transmission of SRS and other uplink channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If SRS and other uplink channels are transmitted simultaneously in carrier aggregation, then uplink spectral efficiency is improved, but transmit power may exceed maximum allowed power
Solution Approach 1:
The patent changes the parameter of transmit power allocation by introducing scaling factors (w_c(i)) that dynamically adjust the power distribution among SRS and PUSCH transmissions across different component carriers. This allows the system to maintain simultaneous transmissions while adapting power levels to stay within maximum allowed power constraints.
Solution Approach 2:
The patent implements dynamic power management where the scaling factor w_c(i) is calculated based on real-time power conditions. When power exceeds the maximum limit, the system dynamically reduces SRS power proportionally while maintaining PUSCH power, creating a flexible power allocation mechanism that responds to changing transmission conditions.
2Measurement precision
If SRS transmission is configured for each uplink component carrier, then channel estimation accuracy is improved, but signaling overhead increases
Solution Approach 1:
The patent segments the SRS configuration into cell-specific parameters (common to all UEs in a cell) and UE-specific parameters (individual to each UE). This segmentation allows efficient resource allocation where cell-specific parameters reduce overhead while UE-specific parameters maintain precision for individual channel estimation requirements.
3Measurement precision
If multiple SRS transmissions are configured across different component carriers, then uplink channel quality monitoring is improved, but peak to average power ratio increases
Solution Approach 1:
The patent applies partial action by selectively scaling down SRS power only when and where needed to control PAPR, rather than uniformly reducing all SRS transmissions. The scaling factor w_c(i) is applied selectively to specific component carriers based on power conditions, maintaining sufficient SRS transmission quality while managing peak power consumption.
Data Source
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AI summary
A cell-specific sounding reference symbol (SRS) subframe configuration and UE-specific SRS configuration are defined for carrier aggregation. For the cell- specific SRS subframe configuration, the same cell-specific SRS subframes are configured for all uplink (UL) carrier components (CCs). For the UE-specific SRS configuration, different configurations are applied for UL CCs. Also, to reduce signaling overhead, the different UE-specific SRS configuration is signaled by using an offset on top of the UE-specific SRS configuration of a primary component carrier (PCC).