## 1 Introduction
Later research [14, 15] demonstrated that bringing in cooperative jamming achieves a positive secrecy rate in scenarios involving single untrusted relaying in the absence of a direct connection between the source and destination. Another study [16] showed that increasing the number of relays in a bidirectional untrusted relay system could enhance the ergodic secrecy sum rate, even without the aid of jamming signals. Additionally, this study proposed a relay selection method to optimize the instantaneous total secrecy rate with multiple bidirectional untrusted relaying. However, the method focused on selecting the relay with the highest gain from channels to the destination, disregarding the security levels of untrusted relaying. A recent advancement introduces a cooperative communication strategy based on the traditional DF protocol that accommodates intra-link errors, termed lossy-forward (LF) relaying [17]. LF relaying ensures the relay forwards decoded information to the destination despite decoding errors during the RF transmission stage. This study presents an LF relaying approach for an air-to-ground network with two untrusted relays, considering factors like atmospheric absorption, scattering, and other terrestrial propagation challenges. By allowing for errors, LF relaying reduces the risk of unauthorized access to confidential data, making it a promising candidate for enhancing PLS in air-to-ground communications. The relay nodes, essential for the relay process, are also potential security threats. LF relaying is utilized to maintain data transmission integrity and confidentiality against these untrusted nodes. In this context, we propose incorporating cooperative jamming [18] in a diamond-shaped network featuring two untrusted relays. The jamming signals are deliberately sent from the mobile terminal to safeguard confidential information from being compromised by untrusted relays. To evaluate the effectiveness of our approach, we introduce the reliable and secure probability, which is referred to as RSP in this work, which measures the likelihood that the mobile terminal can correctly retrieve the original information while keeping it confidential from the untrusted relays. Analytical results indicate that optimal outcomes are achieved with balanced power distribution between the source and untrusted relays. This paper focuses on the optimal power allocation problem to maximize the RSP. Given a fixed transmission power, we investigate how to distribute power among the source, untrusted relays, and destination (which sends jamming signals) to achieve the highest RSP. Our findings reveal strategies for optimal power distribution that maximize the RSP, providing a theoretical foundation for enhancing network reliability and security. This optimization framework contributes significantly to understanding secure and reliable communication in networks involving untrusted relays. The rest of this article is organized as follows: Section 2 describes a number of related studies and the discussed outcomes. An overview of the system model for analyzing the PLS in an air-to-ground diamond network is presented in Section 3. Section 4 introduces the definition of the acceptable rate region and derivation of reliable and secure probability with a formulation of the CEO (chief executive officer) problem for transmissions from untrusted relays to the destination. An optimal power allocation solution in terms of the RSP of diamond untrusted relay networks is presented in Section 5. Section 6 concludes this article with some recommendations.