Satellite fog computing (SFC) achieves computation, caching, and other functionalities through collaboration among fog nodes. Satellites can provide real-time and reliable satellite-to-ground fusion ...services by pre-caching content that users may request in advance. However, due to the high-speed mobility of satellites, the complexity of user-access conditions poses a new challenge in selecting optimal caching locations and improving caching efficiency. Motivated by this, in this paper, we propose a real-time caching scheme based on a Double Deep Q-Network (Double DQN). The overarching objective is to enhance the cache hit rate. The simulation results demonstrate that the algorithm proposed in this paper improves the data hit rate by approximately 13% compared to methods without reinforcement learning assistance.
In traditional Stripmap SAR imaging, the platform motion error will bring the phase error in the azimuthal direction to the image, which will have a series of effects on the imaging quality. The ...traditional autofocus algorithm—Stripmap Phase Gradient Algorithm (SPGA)—can estimate any order phase error above the second order in theory, but it is difficult to estimate the linear phase error, which leads to the discontinuity of the estimated phase error. It usually needs multiple iterations to focus an image, which is inefficient. Moreover, because the linear phase error cannot be estimated, the traditional SPGA cannot eliminate the target offset in the image, resulting in the distortion of the image in the azimuthal direction. According to the continuity of phase error, we propose a modified iteration-free SPGA based on removing the linear phase. Without iteration, the proposed autofocus algorithm can achieve comparable or even better results than traditional SPGA. In the simulation experiments, piecewise linear errors are added to the images of multiple targets. SPGA still fails to focus the image after six iterations. The average ILSR and ILSR are −7.11 dB and −3.99 dB, respectively, and the average number of point target drift is 8.42 pixels. The proposed algorithm optimizes the average ILSR and ILSR to −12.34 dB and −9.87 dB and reduces the average number of point target drift to 0.16 pixels. In the actual data processing, using image entropy as the evaluation criterion, the time consumption is only 19.25% of SPGA under the condition of achieving the same focusing quality.
The measurement of the target azimuth angle using forward-looking radar (FLR) is widely applied in unmanned systems, such as obstacle avoidance and tracking applications. This paper proposes a ...semi-supervised support vector regression (SVR) method to solve the problem of small sample learning of the target angle with FLR. This method utilizes function approximation to solve the problem of estimating the target angle. First, SVR is used to construct the function mapping relationship between the echo and the target angle in beamspace. Next, by adding manifold constraints to the loss function, supervised learning is extended to semi-supervised learning, aiming to improve the small sample adaptation ability. This framework supports updating the angle estimating function with continuously increasing unlabeled samples during the FLR scanning process. The numerical simulation results show that the new technology has better performance than model-based methods and fully supervised methods, especially under limited conditions such as signal-to-noise ratio and number of training samples.
A dual-band circularly polarized complementary antenna loaded with adjusting stubs is presented. The antenna consists of a semi-circle shaped printed monopole fed by a 50- Ω microstrip and the ...complementary metal structure part connected to the ground plane. Due to the complement structure, this antenna can work in dual-band linearly. To achieve dual-band circular polarization, rectangular and L-shaped adjusting stubs are added. By adjusting the parasitic elements appropriately, the conventional complementary antenna can be converted into a dual band circularly polarized antenna. The antenna impedance bandwidths are 400 MHz centered at 2.5 GHz and 2000 MHz centered at 5.8 GHz. The 3-dB axial ratio (AR) bandwidths are 40 MHz centered at 2.41 GHz and 640 MHz centered at 5.38 GHz. The measured results agree well with the simulated results.
In this study, two types of cooling methods (vacuum cooling and air cooling) were used to cool cooked macro‐porous sausage. Alterations in the microbiological conditions, pH, instrumental color (L*, ...a*, and b*), total volatile nitrogenous bases (TVB‐N), lipid oxidation (TBARS), water activity (aW), moisture content, and texture indicators were evaluated to determine sausages' quality changes during storage under refrigeration for up to 10 days. In general, the shelf life of sausages chilled by vacuum cooling (8 days) was similar to that of sausages cooled by air cooling (9 days). For pH, no significant difference (p > .05) was obtained between two cooling methods. However, vacuum‐cooled sausages have lower L* value (p < .05), lower moisture content, and water activity compared with the air‐cooled sausages. However, sausages cooled by vacuum cooling showed a sharp increase in TBARS and TVB‐N values but maintained texture characteristics for a longer time compared with air‐cooled sausages. Although the results indicated that the quality of sausages treated by those two methods remarkably decreased after 7 days, characteristics of sausages cooled by vacuum cooling are better within accepted standards compared with air‐cooled sausages. In conclusion, vacuum cooling can be a feasible cooling method with great potential to be used in cooked macro‐porous sausages to maintain the quality and may provide reference experiences for the food with similar structure.
Two types of cooling methods (vacuum cooling and air cooling) were used to cool cooked macro‐porous sausages, which will store almost 10 days at 4°C. Storage stability is primarily assessed by physical, chemical, and microbial parameters.
In this letter, a three-port omnidirectional cylindrical dielectric resonator antenna (DRA) is presented. The design makes use of the TM 01 δ and two degenerate HEM 21 δ modes of the cylindrical DRA. ...The resonant features of the two modes are investigated and their resonant frequencies are different. The TM 01 δ mode is fed with horizontal magnetic current, which is obtained by four slots. The input impedance of the antenna is affected by the length of the open-circuit stub, which is the end of the feed network. Thus, the resonant frequency of the TM 01 δ mode can be moved to that of the HEM 21 δ one through the proposed exciting method. Two HEM 21 δ modes are excited simultaneously by a 90° hybrid coupler to realize right- and left-hand circularly polarized omnidirectional radiation. Based on the three modes, a three-port three-polarization DRA with omnidirectional radiation for indoor communication applications is fabricated and measured. The results indicate that the S -parameters, field characteristics, and communication performance are satisfactory in the operating band.
This paper presents a novel design method for a tri‐band multiple in multiple out (MIMO) antenna. The antenna consists of four sets of identical antenna pairs arranged on the two side frames. Three ...resonant modes can be obtained using a microstrip coupling feed structure by employing different branches in antenna unit design. The working frequencies of the modes can be adjusted independently. Moreover, in each pair of antennas, two antenna units were closely arranged and a decoupling grounding branch was employed between the adjacent antennas to ensure good isolation. The tri‐band eight‐element MIMO antenna operates at 3.5, 4.9, and 5.6 GHz and the isolations were better than 14 dB. The proposed antenna had a low profile of 0.06λ
0 ${\lambda }_{0}$ and good isolation so it has potential applications in 5G mobile terminals.
Programmable metasurfaces are two-dimensional electromagnetic structures characterized by a low profile, conformability, and the ability to flexibly manipulate the amplitude and phase of ...electromagnetic waves. For high-quality beam scanning with the metasurface, it is essential that the metasurface possesses high-precision phase response quantization characteristics. This paper constructs a reflection-type metasurface unit cell featuring four P-I-N diodes and six operating states. To address the unit cell’s complexity and optimization challenges, we developed an automatic optimization algorithm, derived from the genetic optimization algorithm, for the metasurface unit cell. This algorithm was used to optimize a six-phase reflective 2.5 bit programmable metasurface cell operating at 5 GHz. The unit cell’s prototype was fabricated and measured to verify the design. Additionally, a metasurface comprising 16 × 16 unit cells was designed and simulated. The results highlight the metasurface unit cell’s excellent phase response quantization characteristics, and investigate the impact of quantization accuracy on beam scanning.
A one-dimensional active broadband phased array based on microwave photonics that works in the Ku band is proposed to achieve a large instantaneous bandwidth. The phased array uses a feeding network ...based on microwave photonics to provide the true time delay and a wide operating bandwidth. The array is mainly composed of a broadband horn antenna, an RF transmitting/receiving module, an optical network module, and a temperature control module. The form of a horn was selected for the antenna unit, and it was fed through a waveguide to obtain a wide operating bandwidth. An optical fiber delay line that could realize the true time delay at different frequencies was adopted for the time-delay module of the optical network. To obtain a large time delay and small quantization error, a hybrid time-delay diagram utilizing electrical and optical time delays was used in the design. In addition, a temperature control module was added to the antenna system to enhance the stability of the photonic time-delay module. For verification, a prototype of the presented antenna system was designed, fabricated, and measured. The experimental results showed that the optical phased array antenna was able to scan ±20° from 12 GHz to 17 GHz, and the beam pointing did not appear to be offset over the wide operating bandwidth.
In this paper, a co-aperture dual-polarized antenna array is proposed. The frequency band covers the P-band (0.4–0.7 GHz) and the X-band (9.3–9.9 GHz). The P-band array is designed in the form of an ...all-metal Vivaldi, while minimizing the impact of the P-band antenna array structure on the X-band electrical performance. The final profile design for the dual-band antenna structure is only 0.12 λ0 (λ0 corresponds to the wavelength of 0.4 GHz). The X-band design adopts the miniaturized waveguide slot structure, which can be well embedded in the P-band array structure. In order to verify the feasibility of the scheme, prototype processing and testing were carried out, and the test results are consistent with the simulation results. The active VSWRs of the overall design are less than 2.0. Additionally, the dual-band antenna array has favorable radiation performance in each frequency band. It can be used in forest biomass measurements and other interferometric applications.
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