Channel Estimation Using Cyclic Shifted Reference Signals
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Solution Overview
Problem
Current channel estimation methods in wireless local access networks (WLAN) based on OFDM technology, such as 802.11ax, suffer from high signaling overhead and low resource utilization due to the use of long training fields (HE-LTF) which are inefficient, especially in outdoor applications with multiple spatial flows.
Innovation Solution
A channel estimation method that divides the HE-LTF into two parts: one part carries a reference signal, and the other part carries useful information, allowing for orthogonal subcarrier distribution across OFDM symbols, reducing the number of OFDM symbols required for channel estimation and improving resource utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If long training fields (HE-LTF) are used for channel estimation in OFDM-based WLAN systems, then channel estimation accuracy is improved, but signaling overhead increases and resource utilization decreases
Solution Approach 1:
The patent segments the channel estimation process by dividing the available subcarriers into multiple groups and using different cyclic shifts for different spatial flows. This allows multiple spatial flows to share the same time-frequency resources with orthogonal codes, eliminating the need for separate reference signals for each flow and reducing signaling overhead while maintaining estimation accuracy.
Solution Approach 2:
The patent makes the reference signal universal by using the same base sequence for multiple spatial flows with different cyclic shifts. This single reference signal structure serves all spatial flows simultaneously, eliminating the need for separate reference signals and reducing the overall signaling overhead while maintaining the ability to estimate channels for all flows accurately.
2Measurement precision
If long training fields (HE-LTF) are used for channel estimation in OFDM-based WLAN systems, then channel estimation accuracy is improved, but resource utilization decreases
Solution Approach 1:
The patent segments the reference signal resources by using code division multiplexing with cyclic shifts. This allows multiple spatial flows to be multiplexed on the same time-frequency resources, effectively increasing resource utilization while maintaining the ability to provide accurate channel estimates for each flow through orthogonal code separation.
Solution Approach 2:
The patent merges the reference signals of multiple spatial flows into a single unified structure by using different cyclic shifts of the same base sequence. This combination allows all spatial flows to share the same time-frequency resources, improving resource utilization while maintaining channel estimation accuracy through orthogonal code separation at the receiver.
3Measurement precision
If subcarrier interleaving is used to distribute reference signals across OFDM symbols, then channel estimation performance is improved, but the number of OFDM symbols required increases
Solution Approach 1:
The patent uses periodic cyclic shifts of the base sequence across different spatial flows, creating an orthogonal code structure that allows all spatial flows to be estimated within a single OFDM symbol. This periodic code structure eliminates the need for multiple OFDM symbols while maintaining channel estimation performance through the orthogonal properties of the cyclically shifted sequences.
Data Source
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AI summary
Embodiments of the present invention provide a channel estimation method, a communications node, and a communications system. The method includes: obtaining a preamble in a signal packet sent by a first communications node, where the preamble includes at least a first field and a second field, a subcarrier of an orthogonal frequency division multiplexing OFDM symbol of the first field is used to carry a first reference signal, the first reference signal is a determined signal that is known to both a second communications node and the first communications node, a subcarrier of an OFDM symbol of the second field is used to carry useful information, and the useful information is physical layer control information and/or data; and obtaining, by using the first field and the second field, a first channel estimate, of each spatial flow, on all subcarriers of a multiple-input multiple-output transmission frequency band. Technical solutions provided in the embodiments of the present invention reduce a signaling overhead and improve resource utilization while ensuring performance of channel estimation.