Radio Front End Carrier Cancellation for FDD Frequency Hopping
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Solution Overview
Problem
Conventional wireless communication systems face challenges in achieving sufficient self-interference cancellation in Frequency Division Duplex (FDD) systems, particularly due to the large and complex filter-based duplexers required for high isolation, which are cumbersome and inefficient, especially with the increased interference and bandwidth demands of 4G technology.
Innovation Solution
The implementation of a software-configurable radio front end that uses a combination of feed-forward cancellation and digital residual interference cancellation methods, including phase shifting and infinite impulse response filtering, to eliminate the need for large filters and achieve high isolation levels, allowing for operation across multiple frequencies and bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If filter-based duplexers are used to achieve high isolation between transmit and receive bands, then self-interference attenuation is improved, but device size and weight increase significantly
Solution Approach 1:
The patent replaces mechanical filter-based duplexers with electronic self-interference cancellation mechanisms. Specifically, it uses a canceller circuit that generates an inverted version of the transmit signal and subtracts it from the receive signal path, eliminating the need for heavy air-cavity filters while achieving the required 100 dB isolation between transmit and receive bands
Solution Approach 2:
The invention creates a copy of the transmit signal through a feedback path, inverts its phase by 180 degrees, and injects it into the receive path to cancel the self-interference. This copying approach allows electronic cancellation without requiring physical filter structures
2Adaptability or versatility
If multiple duplexers are used for multi-band operation, then frequency band versatility is improved, but device complexity and size increase
Solution Approach 1:
The patent implements a universal self-interference cancellation architecture that can operate across multiple frequency bands without requiring separate duplexers for each band. The electronic cancellation mechanism is bandwidth-agnostic and can be reconfigured through software to support different bands, enabling multi-band operation with a single transceiver design
Solution Approach 2:
The invention uses dynamically reconfigurable components including voltage-controlled oscillators and software-defined radio techniques to adjust the cancellation mechanism for different operating bands. This dynamic adaptation allows the system to switch between bands without physical reconfiguration
3Reliability
If larger duplexers are used to meet increased isolation requirements, then transmit-to-receive isolation is improved, but manufacturing cost and device size increase
Solution Approach 1:
The patent replaces complex mechanical filter assemblies with integrated circuit-based cancellation mechanisms. The canceller uses standard electronic components including amplifiers, phase shifters, and subtractors that can be manufactured using conventional PCB or integrated circuit techniques, dramatically simplifying production compared to precision-machined air-cavity filters
4Reliability
If frequency hopping is implemented for security, then communication security is improved, but system complexity increases
Solution Approach 1:
The patent implements frequency hopping through software control of the local oscillator in the mixer stage. The system automatically changes operating frequencies according to a pseudorandom sequence known to both transmitter and receiver, providing security without requiring complex hardware reconfiguration. The self-interference cancellation mechanism adapts automatically to each frequency hop
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 efficient self-interference cancellation, reducing the size and cost of transceivers, enabling operation in multiple bands without the need for traditional filters, and supports advanced wireless standards like LTE-Advanced through band aggregation and frequency hopping, while maintaining high security and performance.
Implementation Method 1
phase shifting the transmit signal in a second path in the radio front end, the second path being different from the first path
Implementation Method 2
digital residual interference cancellation methods, including phase shifting and infinite impulse response filtering
Data Source
AI summary
The present application describes a computer-implemented method for frequency hopping including configuring a radio front end to operate on a first frequency; receiving a transmit signal in a first path in the radio front end; amplifying a transmit signal in the first path; phase shifting the transmit signal in a second path in the radio front end, the second path being different from the first path; coupling the amplified transmit signal to a third path in the radio front end; coupling the phase-shifted transmit signal in the second path to the amplified transmit signal in the third path to form a carrier-cancelled signal in a fourth path in the radio front end in the radio front end; phase shifting the carrier-cancelled signal in the fourth path; coupling the phase-shifted carrier-cancelled signal in the fourth path to the amplified transmit signal in the first path; and reconfiguring the radio front end to operate on a second frequency.