HARQ Indicator Determination via PHICH Symbol Segmentation
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Solution Overview
Problem
In LTE systems, erroneous determination of Hybrid Automatic Repeat Request (HARQ) indicators due to interference from Cell-specific Reference Symbols (CRS) transmitted by macro cells can lead to premature termination of data delivery or unnecessary retransmissions, affecting system performance and resource utilization.
Innovation Solution
A new Maximum Likelihood (ML) detector with reduced states is implemented at the UE, which separates and evaluates PHICH modulation symbols with and without CRS interference, combining metrics with appropriate scaling to accurately determine HARQ indicators, thereby reducing interference effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional HARQ indicator determination is used, then device complexity is low, but measurement precision deteriorates due to CRS interference
Solution Approach 1:
The patent segments the PHICH modulation symbols into two distinct data streams: one containing symbols with CRS interference and another containing symbols without CRS interference. This segmentation allows the system to process interfering and non-interfering symbols separately, improving measurement precision while managing complexity through structured separation rather than complete redesign.
Solution Approach 2:
The patent applies different evaluation methods to different parts of the received signal based on their interference characteristics. Symbols in the first data stream (with CRS interference) are evaluated using one set of metrics, while symbols in the second data stream (without CRS interference) are evaluated using another set of metrics. This local differentiation optimizes measurement precision for each segment's specific conditions.
2Measurement precision
If interference mitigation techniques are applied, then measurement precision improves, but device complexity increases
Solution Approach 1:
By dividing the PHICH modulation symbols into two data streams based on interference presence, the system can apply targeted mitigation techniques only where needed. This segmentation approach improves precision for interfering symbols without unnecessarily complicating the processing of non-interfering symbols.
Solution Approach 2:
The patent introduces an intermediary evaluation process that combines metrics from both data streams with appropriate scaling factors. This intermediary combining step mediates between the raw received signals and the final HARQ indicator determination, allowing interference effects to be managed systematically while maintaining overall system coherence.
3Reliability
If erroneous HARQ indicator determination occurs, then system performance deteriorates, but this is caused by interference rather than system failure
Solution Approach 1:
The patent converts the harmful CRS interference into a useful differentiation mechanism. By separating symbols into two data streams based on their interference characteristics, the system uses the presence of interference as a cue to apply appropriate evaluation methods. This transforms what would be a uniform source of error into a diagnostic feature that guides correct processing.
Solution Approach 2:
The system incorporates feedback through the evaluation process that compares and combines metrics from both data streams. The scaling factors applied during combination provide feedback about the relative strength and characteristics of interference versus signal, allowing the system to adjust its determination of HARQ indicators to compensate for CRS interference effects.
Data Source
AI summary
A system and method may provide user equipment (UE)-implemented inter-cell interference mitigation. In some implementations, a method in a user equipment for Hybrid Automatic Repeat Request (HARQ) indicator determination includes separating received Physical HARQ Indicator Channel (PHICH) modulation symbols into two data streams: (1) PHICH modulation symbols including interference from Cell-specific Reference Symbol (CRS) transmissions, and (2) PHICH modulation symbols including substantially no interference from the CRS transmissions. The UE separately evaluates the PHICH modulation symbols including interference and the PHICH modulation symbols including substantially no interference. The UE determines a Hybrid ARQ indicator based upon a combination of the separate evaluations of the PHICH modulation symbols including interference and the PHICH modulation symbols including substantially no interference.