FPGA implementation of closed‐loop compensation for LFMCW signal non‐linear distortions

Abstract

Linear-frequency-modulated continuous-wave (LFMCW) radars with deramping technique have several advantages such as compact size, low cost, and easy implementation, compared to traditional pulse radars; however, the non-linear distortions caused by analogue modules, particularly power amplifiers, may deteriorate the radar detection performance. To solve this problem, a digital closed-loop compensation scheme for the LFMCW signal is proposed, which can compensate the LFMCW signal in real time, when the non-linear distortions change with the working environment. The proposed compensation scheme improves the detection performance, noticeably. Considering the speed limitations of field programmable gate arrays (FPGAs), the proposed scheme is implemented in an FPGA at an intermediate-frequency level, using a polyphase processing structure.

A Survey on Vital Signs Detection Using Radar Techniques and Processing With FPGA Implementation

“…CW [1], [3], [8], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35] UWB-IR [2], [10], [21], [36], [37], [38], [39], [4], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50] FMCW [8], [7], [51], [52], [53], [54], SFCW [2], [9], [55], [56], [57] [58] A. CW Radar The authors in [1] used a CW Doppler and a pulse radar to wirelessly detect heart signal and breathing signal. Several sources of signal distortion were also...…”

“…Aimed at integration and size compactness, validations of this radar were performed on a target located 1 m away in different scenarios. Next, the work in [52] proposed a digital closed loop compensation architecture for LFMCW. It is aimed at solving nonlinear distortions caused by the analogue modules, which deteriorates detection accuracy.…”

“…This process is repeated over multiple periods. Next, as illustrated in Table 5, a radar for detection applications is designed with a center frequency of 600 MHz and a bandwidth of 300 MHz in [52]. These frequencies will possibly be too low if a higher range resolution is needed, especially when potentially detecting the small movements from the chest wall.…”

“…The classification of literature based on the processing platform is particularly useful when determining specific platforms for the implementation of different algorithms. [20], [22], [23], [25], [26], [28], [37], [35], [7], [38], [39], [55], [56], [57], [70], [71] FPGA [2], [21], [31], [54], [40], [43], [44], [45], [49], [62], [72], [73], [74], [75], [76] FPGA (not specifically for vital sign detection) [52], [53], [68], [77], [78], [79], [80], [81], [82], [83], [84] SoC [42] DSP [30] FPGA-GPU [69] PC-microcontroller [29], [27] DSP-microcontroller…”

“…For the LFMCW in [52], a DDS algorithm combined with CORDIC algorithm was used to build its nonlinear distortion compensation scheme, implemented on an FPGA. This implementation improved the peak side-lobe-ratio (PSLR) from 5.7 dB to 0.3 dB after applying the scheme.…”