SAW Sensor Tag Coding for Low Cross-Correlation Identification
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Solution Overview
Problem
Current passive wireless coded Surface Acoustic Wave (SAW) sensors and sensor-tags face limitations due to code collision interactions, which restrict the number of simultaneously operable sensors and cause interference issues due to cross-correlation problems, making it difficult to achieve large sets of independently identifiable devices within commercially useful spectral bandwidths.
Innovation Solution
The use of direct sequence spread spectrum (DSSS) coding combined with both time and frequency diversity to construct sets of individually identifiable SAW sensor tag devices, employing codes with good autocorrelation properties and low cross-correlation properties to reduce code collision interference, and incorporating techniques such as amplitude weighting and fractal-like code construction to achieve zero cross-correlation over desired time ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If coded SAW sensors use traditional coding methods, then device identification is achieved, but code collision and cross-correlation interference occur, limiting the number of simultaneously operable sensors
Solution Approach 1:
The patent transitions from traditional single-dimensional coding to multi-dimensional diversity coding by combining code diversity, time diversity, and frequency diversity. This allows sensors to be distinguished along multiple dimensions simultaneously, exponentially increasing the number of uniquely identifiable devices while reducing cross-correlation interference through orthogonal code sets designed with zero cross-correlation properties.
Solution Approach 2:
The invention changes the fundamental parameters of the coding system by using orthogonal codes with specific mathematical properties (zero cross-correlation) rather than traditional coding sequences. By carefully selecting and designing code sets where the cross-correlation between any two codes is zero, the system eliminates code collision interference and enables a larger number of sensors to operate simultaneously without mutual interference.
2Quantity of substance
If more sensors are deployed in a wireless sensor system, then sensing coverage increases, but code collision and cross-correlation problems worsen, causing interference
Solution Approach 1:
The patent fundamentally changes the code parameters by using orthogonal sequences with zero cross-correlation properties. This mathematical property ensures that when multiple sensors transmit simultaneously, their signals do not interfere with each other, allowing high-density sensor deployment without the cross-correlation interference that plagues traditional systems.
Solution Approach 2:
The system performs preliminary action by pre-designing and assigning orthogonal code sets to each sensor before deployment. These codes are mathematically constructed to have zero cross-correlation, so when sensors are deployed at high density, the interference problem is already solved by the pre-established orthogonal relationships, rather than attempting to manage interference after the fact.
3Quantity of substance
If traditional coding schemes are used to identify sensors, then identification is possible, but the number of identifiable devices is limited within commercially useful spectral bandwidths
Solution Approach 1:
The patent adds multiple dimensions to the identification space by combining code diversity (different orthogonal code sequences), time diversity (different time slots or delays), and frequency diversity (different carrier frequencies). This multi-dimensional approach allows a vast number of unique device identifiers to be packed into a limited spectral bandwidth, as each device is identified by a combination of parameters rather than relying solely on frequency separation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the operation of larger sets of sensors with reduced interference, improving sensor identification and measurement accuracy by minimizing code collision and cross-correlation issues, allowing for more sensors to be used in a wireless sensor system without significant interference.
Implementation Method 1
Sensors based on surface-launched acoustic wave devices have been developed since the 1980's
Implementation Method 2
The device incorporates a piezoelectric substrate
Data Source
AI summary
A surface-launched acoustic wave sensor tag system for remotely sensing and/or providing identification information using sets of surface acoustic wave (SAW) sensor tag devices is characterized by acoustic wave device embodiments that include coding and other diversity techniques to produce groups of sensors that interact minimally, reducing or alleviating code collision problems typical of prior art coded SAW sensors and tags, and specific device embodiments of said coded SAW sensor tags and systems. These sensor/tag devices operate in a system which consists of one or more uniquely identifiable sensor/tag devices and a wireless interrogator. The sensor device incorporates an antenna for receiving incident RF energy and re-radiating the tag identification information and the sensor measured parameter(s). Since there is no power source in or connected to the sensor, it is a passive sensor. The device is wirelessly interrogated by the interrogator.