HSDPA Power Control Strategy for Soft Handover
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Solution Overview
Problem
In WCDMA systems, soft handover for HSDPA channels is not specified, leading to poor HS-DPCCH reception performance and erroneous ACK/NACK messaging, which reduces throughput due to inappropriate power control and independent fading of UL and DL channels.
Innovation Solution
A user equipment (UE) adjusts its power control strategy by setting UL transmit power based only on TPC commands from the HSDPA serving cell when the up/down command ratio exceeds a certain threshold, indicating poor UL quality, to optimize trade-offs between HS performance and overall soft handover capacity gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TPC commands from all base stations in soft handover are combined to control UL transmit power, then overall soft handover capacity gain is optimized, but HS-DPCCH reception performance deteriorates due to inappropriate power control for HSDPA serving cell
Solution Approach 1:
The patent segments the power control mechanism by introducing a separate power control loop for the HSDPA serving cell. The UE determines UL transmit power based on TPC commands specifically from the HSDPA serving cell rather than combining commands from all base stations. This segmentation allows independent optimization of HSDPA channel power control while maintaining soft handover capacity through coordinated multi-cell operation.
2Reliability
If UL transmit power is increased to ensure sufficient reception quality, then reception reliability improves, but system efficiency deteriorates due to excessive power consumption and interference
Solution Approach 1:
The patent implements feedback-based power control where the UE monitors the quality of the UL channel to the HSDPA serving cell and adjusts transmit power accordingly. The UE determines whether to apply power control based on measured channel conditions and TPC command patterns from the serving cell. This feedback mechanism ensures power is increased only when necessary to maintain reliable reception, avoiding excessive power consumption during good channel conditions.
3Productivity
If conventional power control is used during soft handover, then multi-cell diversity gain is achieved, but synchronization performance deteriorates due to independent fading of UL and DL channels
Solution Approach 1:
The patent applies local quality by tailoring power control to the specific characteristics of the HSDPA serving cell connection. Instead of uniform power control across all soft handover cells, the UE adjusts power based on the UL channel quality specifically to the HSDPA serving cell. This localized approach accounts for independent fading conditions between UL and DL channels, maintaining synchronization performance while preserving multi-cell diversity gains through coordinated power control.
Data Source
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AI summary
In communication systems that send transmit power control (TPC) commands in one direction so that only enough transmit power is used to maintain sufficient quality in the opposite direction, the TPC commands can be used to obtain information about the quality of the opposite-direction link. If there is sufficient quality, the number of TPC "up" commands is about the same as the number of TPC "down" commands, and if there is poor quality, more TPC "up" commands are received than "down" commands. A user equipment can use this information to adjust its TPC strategy and reduce the risk of poor reception and loss of synchronization to a communication node, such as a serving node for high-speed downlink packet access.