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Satellite edge computing (SEC) is an important component for future network deployments. This article studies the task offloading in the SEC system with limited buffers (SEC–LB) and data dependencies among tasks. Due to the competition for LBs, a resource circular-waiting pattern may be formed, leading to a deadlock. To well analyze deadlocks, the Petri net model of SEC–LB is constructed for the first time. Then, a Petri-net-based modified Banker's algorithm (MBA) is proposed to determine the safety of a state, and a deadlock avoidance policy (DAP) $\rho_{\text{MBA}}$ with polynomial complexity is developed for SEC–LB. Moreover, we present an improved version of MBA, namely topology-based Banker's algorithm (TBBA), as well as its corresponding DAP $\rho_{\text{TBBA}}$. Compared with $\rho_{\text{MBA}}$, a scheme of simplifying the safety-determining is employed in $\rho_{\text{TBBA}}$. Simulation results demonstrate that $\rho_{\text{TBBA}}$ has higher efficiency and better performance than $\rho_{\text{MBA}}$ and the existing DAPs, especially for large-scale SEC–LB.

The global navigation satellite system (GNSS) is a critical infrastructure for positioning, navigation, and timing. Recently, vigorous implementation of low earth orbit (LEO) communication satellites has provided a new opportunity for developing GNSS. However, most of the existing navigation modulations are only applicable for narrow bandwidths; hence, broadband navigation modulation with good compatibility and scalability is needed. This paper presents a new broadband multicarrier navigation modulation, namely orthogonal frequency division multiplexing with binary offset carriers (OFDM-BOC), which uses orthogonal BOC signals as subcarriers. First, we derive the analytical expressions of the autocorrelation function (ACF) and power spectral density (PSD) based on the proposed signal model. Then, we discuss the relationship between the OFDM-BOC parameters and their time-frequency properties. This modulation can update existing BOC-like signals without affecting the original receiver. In addition, OFDM-BOC has a similar transmitter and receiver scheme to traditional modulation, so the update process only needs minor changes for the original navigation equipment. Compared with some representative navigation modulations such as AltBOC, BOC(10,5), and OFDM, the analysis reflects that OFDM-BOC has a flatter PSD main lobe, lower PSD maximum value, and smaller false lock probability. Moreover, it is shown that OFDM-BOC also has better spectrum efficiency, tracking performance, and anti-interference. Due to the excellent compatibility and navigation performance, OFDM-BOC provides a broadband modulation scheme for the next generation of navigation signals.

This article addresses the cooperative multiunmanned aerial vehicles task assignment problem (CMTAP) with temporally coupled constraints and aims to find a feasible assignment to minimize the equivalent distances of all tasks. We first present a mixed-integer linear programming model of CMTAP. To solve the undesirable deadlocks of CMTAP, a Petri net amender is constructed based on a candidate solution, and a deadlock-free solution is equivalent to a feasible transition sequence that can be fired sequentially in the corresponding amender. With this amender, we present a Petri net-based deadlock amending method (PDAM) with polynomial time complexity to convert a deadlocked solution into a deadlock-free solution. Also, a deadlock-free hybrid estimation of distribution algorithm (DHEDA) is developed for CMTAP by embedding PDAM into the original EDA. To further improve the solution quality, we establish a local exploitation method, and an adaptive operational probability is used to balance the computational burden and local exploitation ability. Then, a match-up-based reassignment method is proposed to cope with time-sensitive targets. Finally, extensive computational experiments demonstrate that PDAM is more effective at solving deadlocks than graph-based methods, particularly for large-scale CMTAP, and DHEDA outperforms existing algorithms when solving CMTAP.