FMCW Radar Constant Envelope Modulation for Range Resolution
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Solution Overview
Problem
Current radar systems face challenges in achieving good range performance without excessive transmitter power, while also needing to share spectrum efficiently and balance instantaneous bandwidth occupancy with range resolution, especially in automotive applications where object recognition and hazard detection are critical.
Innovation Solution
The implementation of an FMCW radar system with constant envelope transmitters that use frequency modulation with shaped frequency pulses, optimized for low cross-correlation codes and efficient power amplification, allowing for improved range resolution and reduced spectral sidelobes, enabling effective object detection and hazard avoidance in automotive environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional radar waveforms are used to achieve good range performance, then range resolution is improved, but transmitter power consumption increases excessively
Solution Approach 1:
The patent applies parameter changes by transitioning from traditional amplitude-modulated waveforms to constant-envelope frequency-modulated waveforms. Specifically, it uses digital frequency modulation with shaped frequency transitions (not purely linear chirps) to achieve good range resolution while maintaining constant envelope, which enables efficient power amplification and reduces transmitter power consumption.
Solution Approach 2:
The patent replaces traditional mechanical/analog waveform generation with digital frequency modulation. By using digital codes to control frequency transitions and generating I/Q baseband vectors that are digitally processed before modulation, the system achieves precise waveform control with lower power consumption compared to traditional analog approaches.
2Measurement precision
If frequency modulation bandwidth is increased to improve range resolution, then range performance is improved, but spectral occupancy increases causing interference with other users
Solution Approach 1:
The patent changes the frequency modulation parameters by using shaped frequency transitions rather than pure linear chirps. The frequency deviation is limited to a specific range (e.g., ±25 kHz from carrier for 80 GHz radar) and the transitions are shaped using engineered I/Q waveforms. This allows achieving good range resolution within a controlled bandwidth, preventing excessive spectral occupancy that would interfere with other radar users.
Solution Approach 2:
The patent employs dynamic frequency modulation where the instantaneous frequency varies according to shaped transitions rather than constant linear sweeping. The frequency modulation is adaptive and controlled through digital processing of I/Q vectors, allowing optimal spectral efficiency while maintaining resolution.
3Use of energy by moving object
If constant envelope modulation is used to reduce transmitter power consumption, then power efficiency is improved, but waveform design complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-computing the I and Q baseband waveforms and storing them in lookup tables (memory). The waveform generation is simplified at runtime by simply reading pre-computed values from memory based on the current code state, rather than complex real-time calculation. This reduces the computational complexity burden during actual signal transmission.
Solution Approach 2:
The patent uses copying by creating lookup tables that store pre-computed I/Q waveform values. Instead of generating complex waveforms in real-time through complex calculations, the system copies pre-computed waveform data from memory during transmission, significantly simplifying the waveform generation process while maintaining constant envelope properties.
4Object-affected harmful factors
If shaped frequency transitions are used to reduce spectral sidelobes, then spectral efficiency is improved, but correlation loss increases for non-integral delay targets
Solution Approach 1:
The patent carefully adjusts the frequency transition parameters and shaping coefficients to optimize the balance between spectral sidelobe suppression and correlation performance. By engineering the I/Q waveforms with specific amplitude and phase characteristics, the system achieves reduced spectral sidelobes while maintaining acceptable correlation accuracy for targets with non-integral delays through optimized pulse shaping.
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 solution enables efficient object detection and hazard avoidance in automotive environments by achieving good range performance without excessive transmitter power, while optimizing spectral efficiency and reducing interference from strong targets, thereby enhancing the capability for multiple users to share the spectrum.
Implementation Method 1
The frequency modulation uses codes to deviate the frequency from a mean or center frequency according to one of a limited number of shaped frequency transitions
Implementation Method 2
The values are modulated on to a microwave carrier frequency for transmission by the radar transmitting antenna
Implementation Method 3
Mixing (multiplying) a waveform reflected from an object (also known as a target) with a replica of the transmitted signal results in a CW signal with a frequency that represents the distance
Implementation Method 4
By sweeping up in frequency and then down in frequency, the Doppler frequency can also be determined
Data Source
AI summary
A radar system for mobile applications includes transmitters and receivers. The transmitters are configured for installation and use in a mobile application. Each of the transmitters is configured to generate a radio signal. The receivers are configured for installation and use in the mobile application. Each of the receivers is configured to receive radio signals that include transmitted radio signals transmitted by the transmitters and reflected from objects in the environment. A first transmitter of the transmitters is configured to frequency modulate the transmitted radio signal using a shaped frequency pulse which is defined by a sequence of chips. The sequence of chips is selected to realize a selected frequency pulse shape.