An integrated sensing and communication (ISAC) aided dynamic resource allocation is proposed for random access (RA) in Internet-of-Things (IoT) oriented satellite terrestrial relay networks (STRNs). Specifically, we design an ISAC aided RA architecture, which consists of sensing phase and RA phase. Relays can sense the number of active users by wireless sensing and assist RA with the sensed results. Active users are grouped into orthogonal clusters in the spectrum domain according to relays that they belong to. To appropriately utilize the bandwidth resources, a dynamic resource allocation optimization problem is formulated and solved, which is able to dynamically allocate bandwidth to each cluster according to the number of intra-cluster active users. Based on allocated bandwidth, active users can always perform optimal uplink RA, which maximizes the total system throughput. Simulation results show that the proposed scheme greatly outperforms the existing schemes in terms of total system throughput and packet loss rate (PLR).

Multisatellite cooperative random access (MSC-RA) scheme is proposed in low earth orbit (LEO) satellite networks. In the scheme, a packet structure based on single carrier interleaved frequency division multiple access (SC-IFDMA) is designed to overcome the effect of users’ propagation delays on the received signals at satellite nodes, which ensures the synchronization of received signals. The transmission model from multiple terminals to multiple satellite nodes in a slot can be equivalent to a virtual multi-input multioutput model, and MSC detection is employed to decode multiple collided packets. The MSC detection can be applied to slotted ALOHA (SA), contention resolution diversity slotted ALOHA (CRDSA), CRDSA-3, and irregular repetition slotted ALOHA (IRSA) protocols, which are dubbed MSC-SA, MSC-CRDSA, MSC-CRDSA-3, and MSC-IRSA, respectively. At the gateway station, the MSC detection and iterative interference cancellation processing are alternately conducted for multiple collided packets at satellite nodes. The performance of these MSC-RA schemes is evaluated via mathematical analysis and computer simulation in terms of throughput, stability and energy efficiency. Simulation results show that MSC-SA, MSC-CRDSA, MSC-CRDSA-3, and MSC-IRSA schemes significantly outperform conventional ones, and the MSC-CRDSA scheme is superior to MSC-SA, MSC-CRDSA-3 and MSC-IRSA schemes.

As a key technology of 6G, integrated sensing and communication (ISAC) has attracted much attention, and its security issues are becoming increasingly severe. In this letter, we enhance the physical layer security (PLS) of ISAC systems using rate-splitting multiple access (RSMA). To ensure specific security requirements, we formulate a joint optimization problem that involves the precoding matrix and the common rate. The goal is to maximize the communication-sensing weighted secure sum rate (SSR), thereby enhancing the overall system performance while maintaining security. To solve the non-convex optimization problem, we adopt the staged algorithm named successive convex approximation with penalty (SCA-P) algorithm. Firstly, the original non-convex problem is transformed into a series of more tractable convex problems. Then, penalty terms are introduced to deal with complex constraints. Finally, we gradually approach the optimal solution of the original problem by iteratively solving these convex problems. Simulation results show that the proposed scheme has better security performance than the state-of-the-art schemes.

In this letter, non-orthogonal multiple access based coded slotted ALOHA (NOMA-CSA) for machine-type communications (MTC) is proposed, in which encoded segments are transmitted with discrete power levels. Most collided segments can be successfully decoded by using the successive interference cancellation (SIC) and maximum-a-posteriori (MAP) erasure decoding. To further improve performance, the code degree distribution and the power distribution for the different number of power levels are jointly optimized, which leads to considerable performance improvement. Numerical results verify our analysis and show that the NOMA-CSA greatly outperforms conventional schemes in terms of throughput and packet loss rate (PLR).

In this letter, we propose a distributed Q-learning (DQL) based joint relay selection and access control (JRSAC) scheme for Internet of Things (IoT)-oriented satellite terrestrial relay networks (STRNs) with massive IoT devices and multiple relays. Firstly, a semi-random access (SRA) architecture is proposed to improve the learning efficiency of the DQL algorithm. Subsequently, a JRSAC optimization problem is formulated and solved by the proposed DQL algorithm. Simulation results show that the proposed DQL based JRSAC scheme significantly outperforms conventional schemes in terms of the medium access control (MAC) throughput, total access delay, and sum rate.

In this paper, we propose an optimal irregular repetition slotted ALOHA (IRSA) under total transmit power constraint for random access (RA) in Internet-of-Things (IoT)-oriented satellite networks, which is named as an optimal power-limited IRSA (PL-IRSA). In this proposal, the total transmit power for each satellite machine-type device (SMD) within a frame is considered to be the same and equally allocated into its multiple packet replicas. Due to a variant number of packet replicas, the transmit power of each packet replica for different SMDs may be different. The difference of transmit powers of packet replicas and path loss enhance the received power diversity, which is able to improve the throughput by using the capture effect. At the receiver side, we introduce a semi-analytical (SEA) model to approximate the physical-layer decoding, and derive an asymptotic packet loss rate (PLR) based on this SEA model. From the derived results, an optimization problem is formulated and solved to find out the optimal degree distributions for different total transmit powers and code rates, which maximize the normalized system throughput. Simulation results demonstrate that the proposed optimal PL-IRSA can lead to significant performance improvement with respect to conventional ones.