Variable Coherence Integration for Weak Signal Location
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Solution Overview
Problem
Network-based wireless location systems face challenges in detecting weak signals due to decreasing radio power levels and the introduction of advanced spread spectrum coding schemes, which reduce their ability to detect radio signals at neighboring receivers, especially when coherence over longer integration lengths is compromised by mobile oscillator drift and Doppler shifts.
Innovation Solution
The system employs parallel processing in correlation processing to maximize coherence by segmenting signals into multiple paths, allowing for a fully coherent estimate and non-coherent summation, thereby increasing processing gain and improving signal detection in noisy conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If longer integration length is used to increase TDOA and AoA accuracy, then location accuracy is improved, but coherence is compromised due to mobile oscillator drift and Doppler shifts
Solution Approach 1:
The patent divides the integration period into multiple segments (e.g., 10 segments) and processes each segment separately through correlation with reference signals. This segmentation allows the system to maintain coherence within each shorter segment while achieving location accuracy through aggregation of results from multiple segments, thereby resolving the contradiction between long integration length and coherence stability.
Solution Approach 2:
The patent applies partial coherence processing by processing only portions of the full integration length through multiple segments rather than requiring full coherence across the entire integration period. This partial action approach enables the system to achieve sufficient processing gain and location accuracy without demanding perfect coherence throughout the complete integration length, accommodating oscillator drift and Doppler shifts.
2Use of energy by moving object
If radio power levels are decreased for power control, then energy efficiency is improved, but signal detection capability deteriorates
Solution Approach 1:
The patent combines multiple correlation results from different segments and multiple receivers through non-coherent summation. By merging the processing gains from multiple segments (each contributing to the total processing gain) and combining results across multiple receivers, the system achieves enhanced signal detection capability that compensates for reduced individual signal power levels, enabling detection despite decreased radio power.
Solution Approach 2:
The patent creates multiple copies of the reference signal and processes them through parallel correlation paths. Each segment uses a reference signal copy that is correlated with the received signal segment. This copying approach multiplies the processing gain by creating multiple independent correlation paths that can be combined, thereby enhancing detection capability even when individual signal power levels are reduced for power control.
3Adaptability or versatility
If advanced spread spectrum coding schemes are introduced, then communication security and capacity are improved, but signal detection difficulty increases
Solution Approach 1:
The patent performs preliminary correlation processing by correlating received signal segments with reference signals before final location calculation. This preliminary action of correlation helps to despread the signal and extract timing information even in the presence of advanced spread spectrum coding. The correlation process effectively reverses the spreading operation, making the signal detectable despite the complexity of codes like CDMA, W-CDMA, OFDM, and SC-CDMA.
Data Source
AI summary
In a network-based Wireless Location System (WLS), geographically distributed Location Measurement Units (LMUs) must be able to detect and use reverse channel (mobile to network) signals across multiple BTS coverage areas. By using Matched Replica correlation processing with the local and reference signals subdivided into discrete segments prior to correlation, the effects of mobile clock drift and Doppler shifts can be mitigated allowing for increased processing gain.