## 1 Introduction  
Due to the rapid development of communications, mobility adaptation has shown its importance in modern communication systems. In this case, the transmit signal is exposed in the wireless environment, which leads to severe security problems due to the lack of physical layer security (PLS) [1]. In order to gain effective security protection through wireless transmission, directional modulation (DM) has been proposed [2, 3, 4] which exploits spatial characteristics of the transmitter ([PERSON]), legitimate receiver ([PERSON]), and eavesdropper ([PERSON]), so as to transmit information to [PERSON] while interfering [PERSON]. Unfortunately, although DM has been widely researched, it is unwise to adopt DM directly if [PERSON] happens to locate in the same receive direction as [PERSON] [5, 6]. Because information can be extracted by [PERSON]. [PERSON] has no more obvious advantages in such a configuration, leading to the loss of wireless security [7, 8]. For the sake of further improving the achievable security, spatial and directional modulation (SDM) was designed with the aid of DM and spatial modulation (SM) [9], attempting to enhance the security weakened by the aforementioned traditional schemes. By utilizing multiple distributed receivers, it can not only convey part of information using the index of the activated receiver at [PERSON], but also keep considerable transmission security offered by DM [10, 11]. Therefore, SDM is capable to provide improved transmission security where some information is concealed in the receiver indices. However, [PERSON] will make every effort to achieve eavesdropping, then the security enhancement will suffer potential challenge whenever [PERSON] performs numerous distributed receivers and some of them are close to [PERSON]'s [12]. Recently, Refs. [13; 14] constituted an attractive security-enhanced scheme that combines SDM with covert information mapping (CIM) in the context of distributed receivers, called CIM-SDM, as integrating the idea of secret modulation to SDM. On the one hand, SDM can hide the information in the receiver indices. On the other hand, CIM is able to insert the covert information into the space-time antenna index mapping with a careful design and make [PERSON] suffer from severe interference [15]. Hence, significant improvement of transmission security can be achieved by this approach, even if [PERSON] has exactly the same multiple receiver distribution as Bob. Nevertheless, though SDM can prevent eavesdropping validly, it has an unavoidable limitation in low spectral efficiency due to activating only one receiver at a time. Moreover, the work of [16] has conceived a novel generalized spatial modulation (GSM) scheme for SM systems. Instead activating one receiver at a time, GSM can deliver multiple symbols by activating multiple activated receivers simultaneously [16; 17] while the conveyed information is hidden in indices of receiver subsets leading to a hybrid of SM and spatial multiplexing [18; 19]. The application of GSM will increase the spectral efficiency and rate effectively and it can improve the transmission obviously with the rising of the scale of distributed receivers [20; 21]. From a cross-layer point of view, it is appealing to combine GSM and SDM for making full use of both advantages. Against this backdrop, in this paper, we aim to enhance the security of transmission while improving transmission rate efficiently by jointly considering current CIM-SDM and GSM (CIM-GSDM), which is realized by the interference factor with the assistance of embedding the covert information, as well as concealing indices of receivers subsets, where multiple eavesdroppers exist. In particular, SDM and GSDM are both based on direction modulation, but SDM activates only one receiver in each transmission while GSDM can activate multiple receivers simultaneously which improves the transmission rate. In this scenario, CIM-GSDM can enhance transmission security effectively at Bob while decreasing unexpected eavesdropping at Eve simultaneously.