## 1 Introduction  
The exponential growth of the wireless communication industry, producing billions of connected devices, has led to a severe problem of frequency spectrum congestion [1; 2; 3]. Unfortunately, new mobile network operators and emerging technologies are facing spectrum scarcity. Consequently, the auction prices of the wireless frequency spectra have risen sharply in recent years [4; 5; 6]. Therefore, different methods have been proposed to improve the coexistence between active sensing systems (i.e., spectrum sharing) [7; 8; 9; 10; 11]. On the other hand, the comprehensive studies have shown that the radar bands are mostly under-utilized and can be used for communication purposes. Therefore, the use of radar bands for communication purposes has increased in recent years. For example, the L-band (1-2 GHz) is shared by the long-range surveillance and air traffic control (ATC) radars with supported communication technologies, such as LTE and 5 G NR. Additionally, milli-meter wave (mmWave) bands (30-300 GHz) are shared by automotive and high-resolution imaging radars with supporting IEEE 802.11 ad/ay and WLAN communication technologies. Similarly, S-band (2-4 GHz) and C-band (4-8 GHz) are also being shared for communication purposes. These spectrum sharing methods gave birth to a new technology named as joint radar-communication designs, which is also called communication-radar spectrum sharing (CRSS) [12], RadCom [13], or integrated sensing and communication (ISAC) [14; 15] designs in a broader sense. The schemes, in which the radar and communication systemsutilize the same frequency bands but exist as separate systems, fall in the general category of radar-communication coexistence (RCC) [16]. Besides spectrum scarcity, multifunction antenna sensors are another motivation for the joint radar-communication designs [17]. Because a multifunction antenna sensor integrates communication, radar, and electronic counter-measure (ECM) subsystems on a single platform using shared antenna sensor arrays, the new designs based on multifunction antenna sensors facilitate flexible, robust, and adaptive processing for meeting the need of the day [18]. Importantly, by combining the radar and communication subsystems, the size, production/maintenance costs, and energy requirements of the devices can be significantly decreased. These systems are named as dual-function radar-communication (DFRC) [19; 20; 21], integrated radar and communication system (IRCS) [22] designs, etc., in the literature [23]. Precisely, the integrated radar-communication systems are particularly relevant to autonomous car networks and flying ad hoc networks (FANETs), in which vehicles sense and communicate with each other in order to know the traffic environment while simultaneously exchanging information with other vehicles [24; 25]. Because both the radar and communication technologies are based on the same foundations of antenna theory, the unification of radar and communication systems seems straightforward. However, the two systems have different requirements and their simultaneous operation poses serious challenges in the design of integrated waveforms. Therefore, the research community has focused special attention on the waveform design techniques in this regard. Different waveform design methods are used depending on the type of radar-communication scheme. In the coexistence scheme, the radar and communication waveforms have been designed independently such that mutual interference is minimized between the systems. A time-sharing scheme has been proposed in [26], in which both of the systems work in the same frequency bands but not simultaneously. A second scheme, based on spatio-spectral coexistence [27], involves radar and communication systems operating at different frequencies. However, this scheme reduces the communication data rate and the radar range resolution. There is an interference avoidance method based on null-space precoding [28; 29; 30]. This design, however, has an adverse effect on radar performance.