Uplink Channel Estimation via Time Domain Tap Feedback
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Solution Overview
Problem
In orthogonal frequency division multiplexing (OFDM) systems, especially for sparse channels like mmWave, frequency domain channel estimation is inefficient, and achieving effective uplink channel estimation with a limited number of pilots is challenging due to the difficulty in time domain estimation.
Innovation Solution
The base station performs channel estimation using feedback from user equipment on tap positions, employing a least-squares method for downlink channel estimation and matching pursuit for uplink channel estimation, while optimizing pilot density and feedback overhead to improve estimation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency domain channel estimation is used in OFDM systems, then the estimation can be performed using conventional methods, but the estimation efficiency is poor for sparse channels like mmWave
Solution Approach 1:
The patent inverts the conventional approach by performing channel estimation in the time domain instead of the frequency domain. The base station receives pilots in the frequency domain, transforms them to the time domain, and performs estimation there. This inversion is particularly effective for sparse channels like mmWave, achieving both high accuracy and efficiency by exploiting the sparsity characteristic in the time domain.
2Measurement precision
If time domain channel estimation is performed, then angle estimation can be done simultaneously and estimation performance improves, but the number of pilots required increases significantly
Solution Approach 1:
The patent changes the parameter of pilot density by optimizing the number and distribution of pilots in the time domain. Instead of using a large number of pilots as in conventional frequency domain methods, the patent determines an optimized pilot density that is sufficient for time domain estimation, thereby reducing the total number of pilots required while maintaining or improving estimation performance.
Solution Approach 2:
The patent performs preliminary determination of channel tap positions and sparsity characteristics before final channel estimation. By first identifying the significant taps and their positions in the time domain, the system can then focus estimation resources on these specific locations, reducing the overall pilot requirement while achieving accurate channel estimation.
3Quantity of substance
If uplink channel estimation is performed with a limited number of pilots, then pilot overhead is reduced, but achieving performance targets becomes problematic
Solution Approach 1:
The patent applies local quality by concentrating pilot resources on the most significant channel taps identified through time domain analysis. Instead of uniformly distributing pilots across all frequency subcarriers, the system identifies the dominant propagation paths and places pilots strategically at locations that provide maximum information about the channel, thereby achieving high estimation performance with reduced overall pilot overhead.
Data Source
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AI summary
A method for uplink channel estimation in time domain is disclosed. A base station transmits downlink signals to a user equipment before estimating uplink channel. The user equipment estimates downlink channel based on the received signals and feeds back channel tap positions of the estimated downlink channel. Finally, the base stations estimate the uplink channel based on the channel tap positions and pilots transmitted by the user equipment. A system and apparatus employing the method are also disclosed.