## 1 Introduction  
Vehicle-to-vehicle (V2V) communications comprise a wireless network wherein automobiles send each other information about their actions. These data include speed, location, direction of travel, braking, and loss of stability. Traffic accidents worldwide cause around 1.2 million fatal accidents annually. According to the World Health Organization (WHO), this corresponds to a quarter of deaths caused by injuries [1]. New technologies in wireless communications can provide mobile users with the information to anticipate possible accidents. In this way, it is possible to reduce the number of deaths that occur each year due to this cause [2]. In this sense, it is important to understand the characteristics of the communication channel. With this, adequate system design can be obtained. In particular, the characteristics of the V2V channel make proper system design challenging. The V2V channel has apparent differences compared with the traditional cellular communication channel, such as lower antenna height, faster moving speed of transmitters (TXs) and receivers (RXs), different frequency bands, etc. Therefore, it is important to conduct targeted research on the V2V channel [3, 4, 5, 6, 7]. In V2V scenarios with high mobility and multipath propagation, two significant factors come into play: the Doppler effect caused by high mobility and the delay spread caused by multipath propagation. When both phenomena impact the received signal, it leads to the so-called dual selective channel (DSC) [8, 9]. In multi-carrier systems operating in such a scenario, two types of interference become inevitable: inter-symbol interference (ISI) and inter-carrier interference (ICI). These interferences severely impact the system performance, leading to a degradation in overall system performance. Multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems have been widely recognized to satisfy the increasing demand for high-data-rate wireless communications systems. OFDM is one of the most popular multi-carrier technologies and is part of many standards such as long-term evolution (LTE) and IEEE 802.11x wireless local area network (LAN). MIMO is an antenna technology for wireless communications that use multiple TX antennas and multiple RX antennas, which can be used for transferring more data at the same time (multiplexing) or to create multiple versions of the same signal, increasing the total energy at the receiver (diversity) [2; 10; 11; 12; 13]. Although systems based on MIMO-OFDM have been used successfully in communication systems such as those mentioned above. It is not known what the performance of these systems could be in more complex scenarios such as high-mobility V2V networks or in systems such as massive MIMO. Future communication systems must be improved by fast, efficient transmission technologies through a high mobility wireless communication medium for [14]. Communication systems of the sixth generation (6G) will be enhanced by the combination of new technologies, such as intelligent reflective surfaces (IRS) in massive MIMO systems, artificial intelligence, terahertz-hertz (THz) communications, and new cell-free architectures [14; 15]. Recently, index modulation (IM) has emerged as one of the promising MIMO solutions for spectral- and energy-efficient next-generation communications systems [16]. The most widely studied IM technique is spatial modulation (SM). In spatial modulation (SM), each Tx and/or Rx antenna can be used as a point in the spatial constellation [17; 18]. In this way, in SM, the complete array of Tx antennas is used to convey extra information in addition to transmission of the conventional quadrature amplitude modulation (QAM) symbol transmission. However, in addition to the spatial dimension, other features of a conventional communication system can be used to modulate.