Classical space-time coding methods, such as BLAST, STTC, and STBC, are coding methods based on perfect channel state information, and are decoded by coherent detection. In order to obtain the utilization rate of high-frequency bands and the gain of spatial diversity and multiplexing. However, when the network nodes move rapidly, the periodic pilot symbol channel estimation method has a large time delay. Especially when the number of transmitting antennas is relatively large, the channel training time is highly complex, and it is difficult to meet the requirements of coding accuracy. Based on the above considerations, this paper proposes a space-time-frequency coding method based on MIMOOFDM system. Compared with space-time coding, this space-time-frequency coding method makes full use of the frequency diversity gain of the MIMO-OFDM system to improve the performance of the system.
Visible light communication has advantages such as high speed, broadband, green, safety, and low cost. Moreover, visible light communication is not subject to electromagnetic interference, so it is useful in a wide range of application scenarios such as aviation, hospitals, and mines. However, due to the limited spectrum and coverage provided by a single LED, multiple LED coverage is adopted in the indoor layout to provide seamless connection, which also brings spectrum interference in overlapping areas. This paper proposes an indoor visible light interference suppression method based on the backward forward markup (BFM) algorithm. This method not only solves the problem of spectral interference, but also improves throughput while ensuring user fairness. The simulation results show that the BFM algorithm has brought significantly improvements in various aspects, with system throughput increased by 75% and fairness factor increased by 0.3.
It is suggested and designed to use Terfenol-D magnetostrictive material in a fiber extrinsic F-P interferometric magnetic field sensor. The two reflective end faces of the F-P cavity are, respectively, the copper reflective layer and the fiber end face. As a result, changes of the magnetic field have an impact on the F-P cavity's cavity length, and the environmental magnetic field can be detected by measuring the variation in cavity length. The typical relationship between magnetic field and spectral drift of the sensor is theoretically analyzed. The sensitivity is measured experimentally to be 0.82 nm/mT for a magnetic field intensity of 0 mT to 70 mT at room temperature. The sensor has a compact structure, and the complexity of the low-level interference signal demodulation makes it suitable for use in engineering.
Optical fiber bus technology is an important research direction in communication systems of electronic devices in special vehicle platforms. According to the requirements for communication quality between devices in special vehicle platforms, an optical fiber bus based on gigabit passive optical network topology is proposed. A data cache-based predictive weighted interpolated polling dynamic bandwidth allocation method is presented and investigated for the optical fiber bus’s upstream bandwidth allocation. The network controller establishes a weighted buffer area for the communication requirements in the polling period according to the type and data volume of the network terminal (NT) data stream and dynamically allocates the bandwidth of each optical NT to better meet the communication requirements for different data within the special device platform. Verification is done by means of OPNET software simulation and the establishment of a NT simulation test system in the laboratory. This proves that the proposed dynamic bandwidth allocation algorithm can reduce the end-to-end delay of RS422 port data by more than 50% and meet the Ethernet and controller area network port data delay requirements.
To simplify the structure and improve the sensitivity of the optical fiber Fabry-Perot (FP) magnetic field sensor (MFS),
an optical fiber extrinsic FP interferometric MFS based on Terfenol-D magnetostrictive material (TDMM) was designed
and fabricated. Insert a TDMM with the diameter of 8mm and a length of 30mm into the cavity, and vapor-deposit 20%
aluminum film on one end surface, and vapor-deposit 60% transmission inducing film on the fiber end surface. The two
film layers are used as a FP with the cavity length of 1.7mm. The relationship between spectral drift and magnetic field
sensing was theoretically analyzed. When the magnetic field intensity is 10~30mT, the sensitivity of magnetic field
sensing is 0.081nm/mT and the interference signal extinction ratio is as high as 9dB at room temperature. The sensor is
featured as the interferometric signal demodulation is simple and potentially can be used in engineering field.
In the indoor visible light communication (VLC) system, the light source has the dual function of illumination and communication. Due to the different size of indoor space and indoor facilities, it will inevitably lead to different indoor light power distribution. In order to achieve the optimal communication effect, the layout of the light source must be reasonably designed so that the receiving power distribution is relatively uniform on the same horizontal plane in the room. The current layout methods are mostly based on the square plane three-dimensional space, while the layout methods of the rectangular plane three-dimensional space are rarely studied. In this paper, a room with size 5m×4m×3m is used as a model. Firstly, according to the shock response principle, the optimal layout of four LED lights is obtained through theoretical calculations, so that the received light power fluctuation in the z=h plane in this room is minimized. Then, according to a set of simulation parameters, the theoretical optimal layout with the minimum fluctuation of receiving optical power in the h=0.75m plane in the room is calculated, and then Matlab is used to simulate the received optical power distribution of the plane under different layouts. The simulation results are consistent with the theoretical calculations. Finally, the illumination distribution under the optimal layout is calculated to verify that the designed optimal layout meets the international illumination standards. The light source layout model designed in this paper not only meets the illumination standards, but also ensures the reliability of communication. It provides an optimization method for the layout of indoor visible light communication LED light source.
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