PHICH Allocation by Transmit Energy Sorting
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Solution Overview
Problem
In LTE systems, the assignment of Physical HARQ Indicator Channels (PHICHs) to mobile terminals does not adequately account for varying channel conditions, leading to unequal transmit energies across PHICH groups, which can result in suboptimal error rates and increased inter-cell interference.
Innovation Solution
A method where the base station generates a list of acknowledgement channels sorted in descending order of required Transmit Energy Per Resource Element (TEPRE) and assigns them to channel groups with the lowest cumulative transmit energy, ensuring more uniform energy distribution across groups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PHICHs are assigned to mobile terminals without considering varying channel conditions, then the assignment process is simple, but the transmit energies across PHICH groups become unequal leading to suboptimal error rates
Solution Approach 1:
The base station performs preliminary sorting of the PHICH list in descending order of required TEPRE before assignment. This preliminary ordering ensures that PHICHs requiring higher energy are assigned first to channel groups with lower cumulative energy, automatically achieving balanced energy distribution across groups without complex real-time adjustments during the assignment process.
2Reliability
If PHICHs are assigned without sorting by TEPRE, then the assignment is faster, but the variance in transmit energies across channel groups increases leading to stronger inter-cell interference
Solution Approach 1:
The PHICH list is pre-sorted by TEPRE requirements before the assignment process begins. This preliminary sorting enables a straightforward sequential assignment algorithm that achieves low inter-cell interference by ensuring higher-energy PHICHs are distributed to channel groups with lower cumulative energy, without requiring complex optimization algorithms that would slow down the assignment process.
Solution Approach 2:
The invention changes the assignment parameter from simple sequential indexing to TEPRE-based sorting. By ordering PHICHs according to their required transmit energy per resource element, the system transforms the assignment problem into a greedy optimization where each PHICH is assigned to the channel group with minimum cumulative energy, achieving both speed and low interference.
3Reliability
If channel groups have fixed TEPRE allocation, then resource management is simpler, but some mobile terminals may not receive sufficient energy for reliable acknowledgement detection
Solution Approach 1:
Instead of uniform TEPRE allocation across all channel groups, the invention applies local quality by assigning PHICHs with different TEPRE requirements to different channel groups based on their cumulative energy levels. This ensures that mobile terminals experiencing poorer channel conditions (requiring higher TEPRE) are assigned to channel groups that can provide sufficient energy, while terminals with better conditions are assigned to groups with lower energy allocation.
Data Source
AI summary
A method and apparatus is provided for assigning resources for an acknowledgement channel, such as the PHICH in LTE systems. A list of acknowledgement channels for a group of scheduled mobile terminals is generated. The list is sorted in descended order of the required transmit energies for the corresponding mobile terminals. The acknowledgement channels are then assigned to channel groups one at a time in sorted order to an available channel group with the lowest cumulative transmit energy. By sorting the channel list before assigning resources, the variance in the transmit energies for different channel groups is reduced. Given enough number of acknowledgement channel groups, the small variance in the transmit energies for different channel groups implies improved error rate performance.