RFID Backscatter Channel Generation Using Band-Pass Delta-Sigma Modulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
RFID systems face tag collisions and data throughput issues due to overlapping backscattered signals on the same frequency channel, leading to errors and reduced performance, especially when reading multiple tags simultaneously, and existing solutions like separate antennas or adaptive tuners increase complexity and cost.
Innovation Solution
A band-pass delta sigma modulator is used to adjust the reflection coefficient of the antenna in RFID tags, allowing for backscattering on dedicated frequency channels by digitally controlling the variable impedance circuit, reducing DC offset and phase noise effects through complex modulation schemes like GMSK, QPSK, and OFDM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple tags transmit on the same frequency channel using backscatter technology, then the RFID system can read multiple tags simultaneously, but tag collisions occur and data throughput decreases
Solution Approach 1:
The patent segments the single 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 the band-pass delta-sigma modulator which spreads the tag's data across a bandwidth, creating distinct frequency signatures for each tag. The reader can then differentiate between tags by detecting their respective frequency offsets, eliminating collisions while maintaining simultaneous reading capability.
2Object-affected harmful factors
If separate transmit and receive antennas are used to reduce reflected signals, then DC offset effects are reduced, but device complexity and cost increase
Solution Approach 1:
The patent introduces an intermediary processing technique in the reader's signal processing chain that specifically targets and removes DC offset components. The reader applies a high-pass filter or DC offset cancellation algorithm to the received signal, separating the desired tag backscatter signal from the DC offset caused by antenna reflections. This allows the use of a single antenna configuration while maintaining signal quality comparable to bistatic systems.
3Measurement precision
If band-pass filtering is applied to reduce phase noise effects, then signal quality improves, but the system cannot handle low frequency modulations
Solution Approach 1:
The patent employs a dynamic modulation approach where the band-pass delta-sigma modulator adapts its frequency offset and bandwidth based on the specific tag and communication conditions. The modulator can dynamically adjust the frequency spread and modulation depth to optimize performance for different data rates and channel conditions. This dynamic adaptability allows the system to maintain high signal quality through band-pass filtering while simultaneously supporting a wide range of modulation schemes including low-frequency modulations when conditions permit.
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 clear differentiation of signals from multiple tags on dedicated channels, reducing collisions and improving data throughput while minimizing the impact of DC offset and phase noise, thus enhancing the overall performance of RFID systems without the need for additional antennas or complex tuners.
Implementation Method 1
an antenna for backscattering an incoming RF signal in accordance with a reflection coefficient characteristic of the antenna
Implementation Method 2
a band-pass delta sigma (ΔΣ) modulator coupled to an input of the variable impedance circuit to digitally control an output of the variable impedance circuit
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A communication apparatus comprising an antenna for backscattering an incoming RF signal in accordance with a reflection coeflicient of the antenna. The communication apparatus comprises at least one band-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 RFTD tags.