Backscatter RFID Modulation Using Delta Sigma Variable Impedance
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Solution Overview
Problem
In RFID systems, tag collisions occur when multiple tags transmit data on the same frequency channel, leading to data transmission errors and reduced throughput, as the reader cannot differentiate overlapping signals from multiple tags.
Innovation Solution
The implementation of a complex modulation scheme using a variable impedance circuit and low pass delta sigma modulators to generate dedicated frequency channels for each tag, allowing for unique backscattering of RF signals by adjusting the reflection coefficient and phase, thereby reducing signal overlap and enabling distinct signal differentiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple tags transmit data on the same frequency channel using backscatter technology, then the system can maintain simple communication architecture and energy efficiency, but tag collisions occur leading to data transmission errors and reduced throughput
Solution Approach 1:
The patent segments the single shared frequency channel into multiple dedicated frequency channels by having each tag transmit on a unique frequency offset from the carrier frequency. This is achieved through frequency offset modulation where each tag is assigned a specific frequency deviation, effectively dividing the communication medium into separate channels that prevent signal overlap and collisions.
Solution Approach 2:
The patent changes the frequency parameter of the backscattered signal to differentiate between multiple tags. By varying the frequency offset of each tag's transmission, the system enables the reader to distinguish between simultaneous transmissions from different tags, thereby maintaining high data throughput while ensuring reliable data transmission without collisions.
2Reliability
If the reader sends gap pulse signals to reduce tag collisions, then collision errors are reduced, but the overall data throughput rate decreases due to waiting intervals
Solution Approach 1:
The patent applies preliminary action by pre-assigning unique frequency offsets to each tag before transmission begins. This allows tags to transmit simultaneously on different frequencies without causing collisions, eliminating the need for gap pulse signals and associated waiting intervals, thereby maintaining high data throughput while ensuring reliable transmission.
3Device complexity
If traditional modulation schemes like PSK or ASK are used, then the communication system remains simple, but tag collisions still occur due to overlapping backscattered signals on the given frequency channel
Solution Approach 1:
The patent transitions from modulation in the amplitude or phase domain to modulation in the frequency domain. By assigning unique frequency offsets to each tag, the system adds a frequency dimension to signal differentiation, allowing simultaneous transmissions to be distinguished without increasing modulation complexity at the tag level.
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 effectively reduces tag collisions by allowing each tag to transmit on a dedicated frequency channel, enhancing data throughput and accuracy in RFID systems, even when reading a large number of tags simultaneously.
Implementation Method 1
a variable impedance circuit, controlled by the modulator, having an output electrically connected to the antenna such that the varying impedance of the variable impedance circuit generates the varying reflection coefficient of the antenna
Implementation Method 2
Antenna backscatters an incoming radio frequency (RF) signal with a varying reflection coefficient
Data Source
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Figure 2
Figure 3~4
AI summary
A communication apparatus comprising an antenna for backscattering an incoming RF signal in accordance with a reflection coefficient of the antenna. The communication apparatus comprises at least one low pass delta sigma modulator which modulates the signal at its input and digitally controls the output of a variable impedance circuit, wherein the reflection coefficient of the antenna is varied based on the output of the variable impedance circuit. This communication device can be used in applications such as RFID tags.