LPWAN Cellular Gateway Filtering for Miniature RF Isolation
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Solution Overview
Problem
Existing gateways connecting LPWAN and cellular networks face interference issues due to insufficient electromagnetic isolation between their RF chains, leading to degradation of the signal-to-noise ratio, especially in miniature designs.
Innovation Solution
Implementing a double filtering system with bandpass filters in the LPWAN RF chain and rejection filters in the cellular RF chain to attenuate interfering frequencies, ensuring at least 20 dB of isolation for each chain, while maintaining a compact size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the gateway is miniaturized to reduce size, then the gateway dimensions are reduced, but the electromagnetic isolation between RF chains deteriorates causing signal interference
Solution Approach 1:
The patent introduces filtering blocks as intermediary elements between the two RF chains. These filters act as mediators that selectively pass desired frequency bands while blocking interfering frequencies from the other chain, enabling compact design without sacrificing isolation performance
Solution Approach 2:
The patent applies frequency-selective filtering at specific locations within each RF chain. By placing bandpass filters in the LPWAN chain and rejection filters in the cellular chain at strategic points, the system achieves localized interference cancellation that maintains overall signal quality in a compact form factor
2Object-affected harmful factors
If antennas are separated by at least a quarter wavelength to achieve electromagnetic isolation, then the isolation level is sufficient, but the gateway dimensions increase
Solution Approach 1:
Instead of relying solely on physical separation distance, the patent introduces filtering blocks as intermediary elements that provide electromagnetic isolation through frequency-selective filtering. This allows adequate isolation to be achieved in a compact space where antenna separation would be insufficient
Solution Approach 2:
The patent changes the approach from spatial parameter (antenna separation distance) to frequency parameter (filtering characteristics). By manipulating frequency domain parameters through filtering, the system achieves isolation without requiring large physical dimensions
3Measurement precision
If receivers are designed with perfect bandpass filters, then the desired frequency band is perfectly received, but the receivers cannot be realized with current technology
Solution Approach 1:
The patent applies preliminary filtering action before the signal reaches the receiver. By placing filtering blocks upstream in the RF chains, interfering frequencies are attenuated before they can affect the receiver, compensating for the imperfections of real-world bandpass filters and achieving effective frequency selectivity
Solution Approach 2:
The filtering blocks perform preliminary frequency selection and interference rejection before the main receiver processing. This preliminary action prepares the signal by reducing spectral contamination, allowing standard receivers to achieve better performance than their inherent bandpass filtering would alone provide
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
The solution effectively isolates RF chains, preventing interference and maintaining signal quality, allowing the gateway to operate without interference even in miniature form factors.
Implementation Method 1
a part common to the uplink channel and to the downlink channel, the common part comprising a bandpass filter passing the frequencies in a frequency band of said at least one LPWAN network and attenuating the power of the frequencies outside of the band of said LPWAN network
Implementation Method 2
a second RF chain toward the cellular network, the second RF chain being suitable for establishing an uplink and downlink connection with the cellular network, a frequency band of the uplink and a frequency band of the downlink being outside of the frequency band of said LPWAN network, the second RF chain comprising an antenna, a modem and, installed in series between the modem and the antenna: at least one rejection filter attenuating the power of the frequencies within the frequency band of said at least one LPWAN network
Data Source
AI summary
A communication gateway for connecting an LPWAN network to a network for access to a cellular or RAN network, the LPWAN network and the RAN network using radio links. Such a gateway typically allows connected objects and servers on the Internet to communicate according to the Internet of Things (IoT) architecture. However, the proximity of the frequency bands used for the two radio links may lead to mutual interference between them, the transmitter of one interfering with the receiver of the other, especially when the gateway is miniature, of the order of magnitude of the connected objects (approximately 10 cm). The disclosed gateway electromagnetically isolates the two RF channels by means of double filtering: by a bandpass filter on the LPWAN RF channel combined with a rejection filter on the cellular RF channel.