MIMO Location Estimation via Direct Path SNR Filtering
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Solution Overview
Problem
In MIMO wireless networks, existing location estimation methods face challenges due to variable RSSI/SNR measurements across multiple chains, leading to inaccurate location determination, especially in environments with multipath and NLOS conditions.
Innovation Solution
The system determines path loss per RF subcarrier by obtaining feedback information, deriving received signal strength values, and calculating effective radiated power to accurately estimate location, while discarding unsuitable data and selecting suitable signal strength values to improve estimation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple chains are used for signal reception in MIMO networks, then communication reliability and performance are improved, but location estimation accuracy deteriorates due to variable RSSI/SNR measurements across chains
Solution Approach 1:
The patent segments the RSSI/SNR measurement process by analyzing each RF chain separately and identifying the specific chain that received the frame through the direct path. Instead of using aggregated or averaged measurements from all chains, the invention isolates and uses only the measurement from the chain that experienced the direct path condition, thereby eliminating the variability introduced by multipath reception on other chains.
Solution Approach 2:
The patent applies local quality by selecting the RSSI/SNR measurement from the specific RF chain that has the most favorable local condition (direct path) rather than using a global average or maximum across all chains. This localized measurement approach ensures that the location estimation is based on the highest quality signal available from any single chain, improving measurement precision while maintaining the benefits of multiple chains for communication reliability.
2Reliability
If all received chains are used to receive frames with maximal ratio combining, then signal reception robustness is improved, but RSSI/SNR measurement variability increases leading to location estimation error
Solution Approach 1:
The patent extracts and isolates the specific RSSI/SNR measurement from the RF chain that received the frame through the direct path, separating it from the other chains that may have experienced multipath conditions. This extraction allows the system to use MRC for robust signal reception while simultaneously using only the clean direct-path measurement for location estimation, thereby resolving the contradiction between reception robustness and measurement accuracy.
Solution Approach 2:
The patent performs preliminary identification of which RF chain received the frame through the direct path before using that chain's RSSI/SNR measurement for location estimation. This preliminary action of identifying the direct-path chain ensures that the subsequent measurement selection is based on accurate channel condition information, preventing the inclusion of corrupted measurements from multipath-affected chains.
3Loss of information
If per-chain RSSI/SNR measurements are reported for location estimation, then measurement data availability is improved, but measurement variability and location estimation error increase
Solution Approach 1:
The patent uses feedback information from the receiver to the transmitter about which RF chain received the frame through the direct path. This feedback mechanism allows the transmitter to identify and select the appropriate RSSI/SNR measurement from the correct chain for location estimation, ensuring that the most accurate measurement is used while maintaining full utilization of per-chain measurement data for overall system performance.
Data Source
AI summary
Disclosed herein, one embodiment of the disclosure is directed to a system, apparatus, and method for location estimation in the presence of multipath/non-line-of-sight (NLOS) conditions. Various methods have been contemplated to detect the level of multipath/NLOS propagation between two devices. A SNR variation method determines how the SNR of each chain/stream is varying over a time window in order to detect the chain/stream with least local scattering or multipath. A measure of coherence SNR is defined to measure the level of multipath/NLOS per-chain/stream. Moreover, since per-subcarrier SNR information is available at the one or both nodes, the coherence methods can be used on a per-subcarrier basis to detect multipath/NLOS for the entire channel, for the specific spatial stream or for the specific frequencies occupied by the subcarriers. Furthermore, a coherence bandwidth estimation method uses the SNR variation over subcarriers to detect the coherence bandwidth of the spatial stream. The amount of multipath/NLOS is inversely proportional to the coherence bandwidth.