## 1 Introduction
In [26], authors proposed to use chaotic synchronization phenomena [27] for continuous time \"code acquisition\". In fact, any chaos shift keying (CSK)-based communication system can be considered as SS system, as chaos potentially can provide \"code gain\" similarly to discrete-time SS systems. In the publication [28], authors have added FM on top of CSK to provide better control over spectrum bandwidth and provide extra robustness against CFO issues. There is an interesting emerging research [29] which employs short continuous-time chaotic pulses, which are produced by the finite impulse response (FIR) filter with chaotic taps, which are controlled by the information sequence to be transmitted. On the receiving side, an adjustable bank of the matched filters with chaotic impulse responses is used as well. Considering SS nature, the proposed system demonstrates excellent results. Noticeably, synchronization for the predicting of the next symbol waveform can be implemented using artificial neural network (ANN) [30]. From the recent publications about the analog implementations of chaos-based communication systems, it is worth mentioning [31], where a completely analog system is studied [32], where chaos-based data transmission system, which employs analog chaos generators and STM32 microcontroller unit (MCU) for the data part [33], where the experimental study of analog frequency modulated chaos shift keying (FM-CSK)-based data transmission system with offline detection is employed. Digital implementations of chaos-based communication systems mostly employ off-the-shelf SDRs hardware, such as Universal Software Radio Peripheral (USRP). In one of the earliest papers [34], [PERSON] et al. presented the implementation of DCSK in GNURadio. In [35], authors presented the implementation of chaotic asynchronous code division multiple access (CDMA) in GNU Radio and USRP. In publication [36], authors presented National Instruments PXI(tm)-based implementation of frequency modulated differential chaos shift keying (FM-DCSK), where chaotic wavelets are frequency modulated and later keyed using DCSK. In publications [37; 38], authors demonstrated implementation of chaotic coherent DSSS in LabView(tm) and USRP. One of the issues with off-the-shelf SDRs is that they usually require an external computer to run the software part of the system. The computer, which is connected to the SDR by universal serial bus (USB) or Ethernet cable, represents a huge potential bottleneck, which limits the sample rate in the communication system. For the implementation of SS or ultra-wideband (UWB) systems, this can be a real issue as those modulation types require substantial bandwidth. In 2020 scientists from our research group started work on field-programmable gate array (FPGA)-based implementation of chaos-based antipodal chaos shift keying (ACSK) system [39], which potentially will allow using sample rates above 100 MHz. This paper is organized in a classical manner. Section 2 outlines the motivation of the research, Section 3 is devoted to the principles and models of ACSK, and the overall structure of the FM-ACSK transceiver. Section 4 is focused on the practical implementation of chaos generators, chaotic code synchronization and symbol synchronization. Section 5 is devoted to the description of techniques used for the evaluation of the transceiver's performance. Finally, Sections 6 and 7 discuss results and summarizes the work.