AFDM Chirp Carrier Multiplexing for Low-Complexity ISAC Sensing
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Solution Overview
Problem
Existing wireless communication systems face challenges in efficiently integrating sensing and communication functions, particularly in 6G waveforms, due to resource inefficiencies and high complexity in self-interference cancellation, especially with conventional chirp-based frequency modulated continuous-wave (FMCW) radars and orthogonal frequency-division multiplexing (OFDM) solutions.
Innovation Solution
The implementation of orthogonal chirp division multiplexing (OCDM) and affine frequency division multiplexing (AFDM) using discrete affine Fourier transform (DAFT) to generate multi-chirp waveforms, allowing for orthogonal chirp carriers that are used as pilots or nulled, enabling efficient resource utilization and low-complexity MIMO sensing with self-interference cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional FMCW radar is used for sensing, then good sensing performance is achieved, but resource utilization efficiency is poor and self-interference cancellation is complex
Solution Approach 1:
The patent transforms the FMCW radar signal parameters by using OCDM/AFDM modulation to generate multiple orthogonal chirp carriers with different frequencies and time shifts. This parameter transformation enables efficient resource multiplexing while maintaining the excellent sensing performance of conventional FMCW radar.
Solution Approach 2:
The patent segments the single FMCW chirp signal into multiple orthogonal chirp carriers, each carrying different sensing or communication data. This segmentation allows parallel transmission of multiple signals without mutual interference, improving resource utilization efficiency while maintaining individual signal integrity for sensing operations.
2Adaptability or versatility
If TDM is used to integrate FMCW sensing with data communications, then both functions are supported, but overhead is high
Solution Approach 1:
The patent merges sensing signals and communication data into a single OCDM/AFDM modulated waveform by assigning different orthogonal chirp carriers to different functions. This merging eliminates the need for separate time slots or frequency bands, thereby supporting integrated sensing and communication without the high overhead associated with TDM.
Solution Approach 2:
The patent creates a universal waveform structure where each OCDM/AFDM signal can simultaneously serve multiple functions (sensing, communication, channel estimation) through different chirp carriers. This multi-functionality reduces the need for separate dedicated signals, thereby reducing overall system overhead.
3Measurement precision
If OFDM or OTFS waveforms are used for ISAC, then range and velocity resolution are achieved, but full duplex analog cancellation operation is costly
Solution Approach 1:
The patent extracts and removes the direct-path self-interference component from the received signal using simple DC blocking, separating it from the useful reflected signals. This extraction approach avoids the need for complex full-duplex analog cancellation operations while preserving the range and velocity resolution capabilities.
Solution Approach 2:
The patent replaces the expensive and complex full-duplex analog cancellation operation with a simple and inexpensive DC blocking module. This substitution uses a low-complexity solution that is sufficient for the specific requirements of OCDM/AFDM-based ISAC, thereby reducing device complexity while maintaining measurement precision.
4Area of stationary object
If multiple devices use sensing service in the same cell area, then sensing coverage is improved, but interference between sensing signals increases
Solution Approach 1:
The patent introduces an additional dimension of orthogonality by using OCDM/AFDM modulation with multiple orthogonal chirp carriers. This dimensional expansion allows multiple devices to transmit sensing signals simultaneously in the same time-frequency resource without mutual interference, thereby improving sensing coverage while eliminating signal interference.
Solution Approach 2:
The patent uses orthogonal chirp carriers as intermediaries to transmit sensing signals from multiple devices. These carriers act as mediators that enable simultaneous transmission by differentiating signals in the orthogonal domain, allowing multiple devices to operate in the same cell area without generating harmful interference.
Data Source
AI summary
The present disclosure relates to sensing and/or communication in a network. The disclosure proposes a sensing device, a sensing device transmitter, a sensing device receiver, a network device, a network, and corresponding methods for operating said devices. The sensing device is configured to generate an affine frequency division multiplexing (AFDM) signal comprising a set of chirp carriers that are orthogonal in a discrete affine Fourier transform (DAFT) domain, and transmit the AFDM signal, wherein the set of chirp carriers is generated based on an inverse discrete affine Fourier transform (IDAFT) and wherein the set of chirp carriers comprises a first subset of chirp carriers that are pilot signals for sensing, and a second subset of chirp carriers that are nulled.