In this paper, a T-shaped piezoresistive multi-axis force sensor fabricated by the semiconductor technology is developed. The sensor's design, simulation, piezoresistors arrangement, and characterization are discussed. Fourteen piezoresistors are arranged on silicon beams and used as independent strain gauges. The three components (F _x , F _y , and F _z ) of an applied force and two components of a moment (M _x , and M _y ) can be simultaneously resolved from the piezoresistance changes induced by the stresses. The sensor was first characterized using a gravity mass reference test bench. The results show the properties of linearity (0.99), sensitivity (force: 1.5 mN; moment: 0.003 Nmm), and small crosstalk (≈5%) between the dominant force component and other components. The fabricated sensor was also verified against a commercial six degree of freedom load cell, and found to perform reliably with high repeatability, low hysteresis (0.5%), and good dynamic response (4 ms).

A novel metamaterial-based and broadband planar integrated Luneburg lens antenna is designed, fabricated, and measured. A substrate integrated waveguide (SIW) horn antenna is applied as the source to illuminate the operation of the Luneburg lens. In particular, air-via metamaterial structures are loaded in front of the SIW horn aperture to realize broadband performance. Meanwhile, the feeding structure by the SIW horn antenna and the Luneburg lens are integrated through this air-via metamaterial transition. Accordingly, the air-via unit cells are designed and arranged in an array with an equivalent gradient refractive index through diameters to achieve good wave focusing effects. Besides, a good agreement is observed between simulations and experiments. The measured results indicate that a wide bandwidth from 16 to 28 GHz is realized with the return loss below -10 dB. Moreover, high end-fire gains varying from 12.5 to 17 dBi are obtained in the band of 18-27 GHz.

The usable satellite spectrum is becoming scarce due to static spectrum allocation policies. Cognitive radio approaches have already demonstrated their potential towards spectral efficiency for providing more spectrum access opportunities to secondary user (SU) with sufficient protection to licensed primary user (PU). Hence, recent scientific literature has been focused on the tradeoff between spectrum reuse and PU protection within narrowband spectrum sensing (SS) in terrestrial wireless sensing networks. However, those narrowband SS techniques investigated in the context of terrestrial CR may not be applicable for detecting wideband satellite signals. In this paper, we mainly investigate the problem of joint designing sensing time and hard fusion scheme to maximize SU spectral efficiency in the scenario of low earth orbit (LEO) mobile satellite services based on wideband spectrum sensing. Compressed detection model is established to prove that there indeed exists one optimal sensing time achieving maximal spectral efficiency. Moreover, we propose novel wideband cooperative spectrum sensing (CSS) framework where each SU reporting duration can be utilized for its following SU sensing. The sensing performance benefits from the novel CSS framework because the equivalent sensing time is extended by making full use of reporting slot. Furthermore, in respect of time-varying channel, the spatiotemporal CSS (ST-CSS) is presented to attain space and time diversity gain simultaneously under hard decision fusion rule. Computer simulations show that the optimal sensing settings algorithm of joint optimization of sensing time, hard fusion rule and scheduling strategy achieves significant improvement in spectral efficiency. Additionally, the novel ST-CSS scheme performs much higher spectral efficiency than that of general CSS framework.

In spacecraft networks, the time-varying topology, intermittent connectivity, and unreliable links make management of the network challenging. Previous works mainly focus on information propagation or routing. However, with a large number of nodes in the future spacecraft networks, it is very crucial regarding how to make efficient network topology controls. In this article, we investigate the topology control problem in spacecraft networks where the time-varying topology can be predicted. We first develop a model that formalizes the time-varying spacecraft network topologies as a directed space–time graph. Compared with most existing static graph models, this model includes both temporal and spatial topology information. To capture the characteristics of practical network, links in our space–time graph model are weighted by cost, efficiency, and unreliability. The purpose of our topology control is to construct a sparse (low total cost) structure from the original topology such that (1) the topology is still connected over space–time graph; (2) the cost efficiency ratio of the topology is minimized; and (3) the unreliability parameter is lower than the required bound. We prove that such an optimization problem is NP-hard. Then, we provide five heuristic algorithms, which can significantly maintain low topology cost efficiency ratio while achieving high reliable connectivity. Finally, simulations have been conducted on random space networks and hybrid low earth orbit/geostationary earth orbit satellite-based sensor network. Simulation results demonstrate the efficiency of our model and topology control algorithms.

Network architecture analysis is a curial issue for a large scale Machine-To-Machine (M2M) network. Considering an M2M backbone network which consists of distributed satellite clusters in geosynchronous orbit (GEO), a new distributed satellite cluster network (DSCN) hybrid topology architecture is proposed in this paper. To the best of the authors' knowledge, the conceptions of domains, strong/weak link, hubs, small world, and degree realizability are proposed for the first time in the DSCN based M2M backbone networks. How these features affect the network is given through analysis and simulation. By employing Network Science Theory, a strong constraint DSCN topology is presented. In addition, we compare the DSCN with several typical network topologies. Results show that the proposed hybrid architecture realizes a stunning trade-off between the efficiency and robustness.

Space Information Network (SIN) has recently become prevalent as a promising approach to solve the collaboration difficulty among current space programs. However, due to large scale, high component complexity and dynamic characteristics of the SIN, the task of proper SIN architecture design is challenging. We propose a novel architecture of SIN, which composed of Geostationary Earth Orbit (GEO) satellites as backbone network nodes, Low Earth Orbit (LEO) or Incline Geosynchronous Orbit (IGSO) satellites as enhanced coverage nodes, and high altitude platforms to meet the service requirements of emergency or hot-spot applications. Compared with most existing studies, the proposed architecture is autonomous system (AS) based. The complex and dynamic SIN is decoupled into semi-static subnetworks constituted by similar nodes which are easier to control.