KEYWORDS: Light emitting diodes, Receivers, Error analysis, Received signal strength, Signal analyzers, Optical engineering, Testing and analysis, Transform theory, Signal detection, Signal to noise ratio
An analytical method to investigate the characteristics of the visible-light positioning using received signal strength (RSS) is proposed, and the formation mechanism of the positioning error is explored. The positioning error is studied in terms of two contributing factors being the original measurement noise of RSS and the dilution of precision (DOP), which transforms the measurement error to the positioning error. It is found that the DOP is related to light-emitting diode (LED) parameters, receiver parameters, and the geometric deployment of the LED beacons. In particular, the LED beacon geometric deployment in the form of triangle, square, and hexagon cell geometries are characterized and optimized. Numerical results show that the mean positioning error of the triangle deployment is smaller than the other two geometries under the same condition, and the side length of the cell should reduce as the half power angle of the LED decreases. The results of this paper provide a guideline to design the RSS-based visible-light positioning (VLP) systems.
A novel satellite on-board processing scheme based on photon frequency conversion is proposed for the purpose of realizing frequency conversion. For the received intermediate frequency signal, a Mach-Zehnder modulator is used to convert it into an optical signal. The modulated optical signal and an optical signal generated by a tunable laser enter the photodiode through a coupler to perform heterodyne beat frequency and generate an intermediate frequency signal of the target carrier frequency, thereby reducing the cost and power consumption of on-board processing. Simulation results show the spectrograms and constellation diagrams of frequency conversion from Q-band to V-band in 8PSK modulation format. The bit error rate(BER) obtained by simulation shows that in a satellite communication system, when the OSNR is higher than 5dB, the BER performance can meet the 2×10-2 threshold when using 8PSK modulation format, which indicates that error-free transmission can be achieved when using 20% soft-decision FEC. The Q factor obtained by simulation shows that when the OSNR is higher than 5dB, the Q factor can reach more than 6.5 when using QPSK modulation format, which indicates that reliable transmission can be achieved. Compared with existing solutions, this scheme has the advantages of lower cost, lower power consumption and more flexible frequency selection, it can also solve the inflexibility and improve the performance of radio frequency conversion in traditional scheme.
On the basis of multi-layer satellite network, this paper presents a GEO/LEO double-layer satellite optical network structure that can meet the global all-weather coverage. Due to the limited number of antennas on the satellite, the LEO satellites are divided into two categories according to the function. One of the categories, as cluster-head satellites, should both establish link with LEO satellites and GEO satellites. The cluster head satellites will also be grouped with the link distance as the index. Each group has the same number of satellites which communicate with the same GEO. A reasonable grouping method is used to avoid the problem of too many links being set up simultaneously with the same GEO satellite, which will affect the transmission delay and communication efficiency. In terms of route selection, the hop cost factor is introduced to improve the traditional KSP algorithm. Compared to the KSP algorithm at the cost of link distance, the designed algorithm limits the number of jumps during service transmission, so as to balance the link length and the number of hops well. Through MATLAB simulation, the proposed algorithm improves the efficiency of the utilization of interorbit link, reduces blocking rate, and makes the resource allocation more reasonable.
In this paper, Radio over Fiber (RoF) system of generalized frequency division multiplexing (GFDM) and orthogonal frequency division multiplexing (OFDM) based on geometric shaping (GS) 16QAM is established on MATLAB and Optisystem platform. The transmission signals consist of a GFDM signal and a OFDM signal with bandwidth of 5GHz and 2.5GHz respectively. The frequency interval between the two signals is 10GHz. They were then transmitted onto carriers with a frequency of 60GHz by a quadrature modulator, the central frequencies of the two signals are 60GHz, 70GHz respectively. The transmission distance through single mode fiber (SMF) is 16km. Furthermore, we study the bit error rate performance of the proposed scheme combined with low density parity check (LDPC) codes. In the end of the paper, we analyze the performance of the proposed RoF system and be verified through MATLAB and Optisystem joint simulation that the proposed GFDM scheme with LDPC-GS-16QAM outperforms GFDM scheme with regular 16QAM by at least 15.3dB at bit error rate (BER) of 10−5 .
KEYWORDS: Radio over Fiber, Orthogonal frequency division multiplexing, Modulation, Antennas, Radio optics, Demodulation, Roads, Distortion, Optical components, Complex systems
An amplitude-phase precode method that based on a high speed ROF-MIMO system is proposed to solve the distortion problem due to the features of optical devices and link damages. This method uses the digital predistortion algorithm model,which is based on Weierstrass theorem. This could precompensation to the ROF links and reduce the influence of nonlinear characteristics of optical devices such as erbium-doped fiber amplifiers on system signal transmission, and solve the sensitivity of QAM, OFDM and other non-constant envelope modulation signals to system distortion. Then the Minimum Mean Square Error (MMSE) precoding method is used to optimize the spatial characteristics of the MIMO transmission signal to solve the signal interference problem, so as to reduce the bit error rate of the system and reduce the complexity of digital signal processing at the user terminal. The simulation results show that the bit error rate (BER) performance of ROF system with the proposed amplitude-phase precode method is lower than 4*10-4 during the transmitting 10 Gb/s 16QAM-OFDM signal in 20km standard single model fiber. The proposed scheme has the obvious lower bit error rate than the non-precode high speed ROF-MIMO system. Therefore, the proposed scheme improves the base station and antenna array coverage, at same time, reduce the complexity of terminal unit and increase the stability of the system transmission.
A probabilistic shaping 64QAM scheme based on multilevel coded modulation is proposed, which combines the advantages of multilevel coded modulation and probabilistic shaping. The scheme combines several encoders with common rates through multilevel coded modulation. It can realize codewords with multiple code rates and save cost effectively. A simulation system is established to verify the performance of the proposed scheme. The results show that the proposed scheme requires lower SNR under the same BER while achieving higher code rate.
A modulation format identification (MFI) scheme based on orthogonal coding scheme is proposed to solve the modulation format identification problem in wavelength division multiplexing (WDM) systems. The scheme uses sidebands to carry orthogonally encoded modulation format information. The basic orthogonal codeword is generated by the Hadamard matrix, and the codewords that are not equal to other codewords after the cyclic shift are selected. The receiving end decodes the modulation format information by using mutual information. We calculate the difference between the maximum and minimum values of the mutual information between the received symbols after cyclic shifting and the standard codewords to make the proposed scheme more robust. We numerically simulated the proposed scheme in a wavelength division multiplexing system, where its channels carry 12.5 Gbaud 4/16/64 QAM and 8/16 PSK. The simulation results show that the modulation format information in the sideband has little effect on the main band information. In the absence of symbol calibration, the receiver can still recover modulation format information from the sideband information with a high accuracy rate. Compared with the MFI algorithm based on Stokes space and the MFI based on signal amplitude performance, the proposed MFI still performs well at low OSNR, although it occupies some bandwidth resources. Moreover, this solution only requires a small number of symbols for decision, so it can achieve fast response requiring little extra storage space.
A non-uniform QAM OFDM modulation system based on probabilistic shaping (PS) and geometric shaping (GS) is proposed in this paper, which can effectively resist the interference among signal waveforms and improve spectrum utilization and channel capacity. First, Huffman coding is used in the scheme for probability shaping to reduce the average energy of the signal. Uniform 16QAM is adjusted to non-uniform 12QAM and uniform 32QAM is adjusted to non-uniform 12QAM. Then geometric shaping is applied. Taking generalized mutual information (GMI) as the objective function, pairwise optimization (PO) algorithm is applied to continuously adjust the constellation. Finally, the coordinate point with the largest mutual information is obtained. The simulation results show the performance of non-uniform 12QAM and non-uniform 24QAM under different conditions, we obtain the signal-to-noise ratio (SNR) with generalized mutual information curve, signal-to-noise ratio with bit error rate (BER) curve under different QAM modulation formats and the bit error rate with the different length of the fiber under different transmission modes. The results show that the proposed non-uniform 12QAM-GS-OFDM has a gain of 0.02 bit/symbol over 12QAM-OFDM, the proposed non-uniform 24QAM-GS-OFDM has a gain of 0.02 bit/symbol over 24QAM-OFDM.
A Probabilistic Shaping (PS) 12-QAM scheme based on Set-Partitioned (SP) Two-Polarization (TP) is proposed to improve the effectiveness and reliability of Probabilistic Shaping 12-QAM (PS-12QAM). In this scheme, the Uniform 12- QAM constellation points are divided into two set partitions, and two polarization states are used to broaden the dimension between two set partitions. Moreover, the system capacity is further approached to Shannon limit by Probabilistic Shaping. The simulations on PS-8QAM, PS-12QAM, PS-16QAM and Probabilistic Shaping Set-Partitioned Two-Polarization 12- QAM (PS-SP-TP-12QAM) have been completed. The results show that, compared with PS-12QAM, the Euclidean distance between adjacent constellation points in PS-SP-TP-12QAM scheme is significantly optimized, and the bit error rate (BER) of this scheme is greatly improved up to 0.5dB. Compared with PS-8QAM and PS-16QAM, it brings a better balance between effectiveness and reliability performance.
The space-based detection system is gradually indispensable into situational awareness systems such as near-celestial bodies and space debris because it has the characteristics of being unrestricted by factors such as climate and geography, and can be observed over a long period of time. At present, the international on-orbit detection of near-celestial bodies and space debris is widespread, that is, the lack of measurement system development and design means, and the lack of data sources. The paper focuses on the principle of space debris on-orbit imaging. Three image information extraction methods and two relative attitude determination methods are proposed. The simulation algorithm of space debris on-orbit imaging is constructed, and the feasibility of the simulation scheme is used. Performance, accuracy, data processing efficiency and other performance were evaluated. The results of the paper will contribute to the early analysis and assessment of space debris.
In order to achieve higher data transmission efficiency, a novel design of 64 state trellis coded modulation (TCM) based on three dimension 32QAM signal is presented in this paper. The simulation results show that when the BER is 10^-3, the Eb/N0 of the 64-state 32QAM-TCM scheme is 2.3dB smaller than that of the uncoded-16QAM scheme. The proposed scheme introduces significant performance improvement of bit error ratio over two dimension uncoded-16QAM scheme.
In this paper, a novel blind modulation format identification method is proposed based on fourth-power characteristic value, the effectiveness of this method is demonstrated and discussed in a 20GBaud long-haul coherent transmission system. It has been proved the usage of FFT peak value and variance is able to achieve accurate estimation among DP-QPSK/16QAM/32QAM/64QAM.
KEYWORDS: Phase shift keying, Extremely high frequency, Signal generators, Modulation, Signal detection, Modulators, Phase modulation, Radio over Fiber, Signal attenuation, Roads
The scheme of frequency tripled and quintupled phase shift keying (PSK) signal without phase multiplication based on two parallel phase modulators (PM) is proposed. To eliminate the impact of the reduction of the vector signals’ Euclidean distance induced by the phase-precoding, a novel phase precoding method is proposed and applied to the original PSK signal. A phase-precoded PSK signal with the same amplitude, same carrier frequency but opposite phase compared with the original PSK signal is generated and modulates the optical carrier via one PM. The original PSK signal modulate the same optical carrier via the other PM. A pair of proper harmonics from the output of the PMs is selected by the wavelength selective switch (WSS). Then the optical millimeter wave (MMW) signal is injected into the fiber. After certain distance of the fiber link transmission, the desired MMW PSK signal is generated after the Photodiode (PD) detection. To verify the feasibility of the proposed scheme, a radio over fiber (RoF) system with 1 Gbit⁄s rate data has been implemented and the tripled and quintupled frequency of QPSK signal has been generated by numerical simulation. The error vector magnitude (EVM) of the 60-GHz and 100-GHz QPSK signal has been measured versus the transmission distance of the fiber link and the launched power into PD with the optical signal noise ratio (OSNR) of 15 dB and 18 dB respectively. And the result shows that the proposed MMW PSK signal generation scheme could realize tripled and quintupled frequency upconversion of the QPSK signal and reliable transmission at least 80 km when the launched power into PD is higher than -5 dBm.
Orbital angular momentum (OAM) as a new degree of freedom, greatly improves the spectrum efficiency and channel capacity of optical communication system. It has become the research focus in the field of optical communications. Some scholars have demonstrated that the feasibility of two multiplexed groups of concentric rings of Laguerre-Gaussian (LG) beams with OAM multiplexing transmission in free space. Based on the point, this paper makes the further research on the propagation characteristics of LG beams with this spatial multiplexing structure in atmospheric turbulence. The random phase screen is established by using the modified von Karman power spectrum and the received power and crosstalk power of OAM modes of LG beams are obtained under the Rytov approximation. We investigate the characteristic parameters of LG beams with this spatial multiplexing structure for mitigating turbulence. Simulation results show that the system exists an optimum beam waist related to wavelength in which the received power of OAM modes reaches the maximum. Meanwhile, the BER and aggregate capacity of the system with two multiplexed groups of concentric rings of LG beams with OAM multiplexing are simulated and analyzed under different intensities of atmospheric turbulence. The results reveal that the system with larger mode spacing generally has lower inter-modal crosstalk and larger aggregate capacity than that with the smaller mode spacing. Finally, on the basis of above the analysis and research, some suggestions for efficient OAM multiplexing detection scheme are proposed.
In order to solve the problem of high speed, large capacity and limited spectrum resources of satellite communication network, a double-layered satellite network with global seamless coverage based on laser and microwave hybrid links is proposed in this paper. By analyzing the characteristics of the double-layered satellite network with laser and microwave hybrid links, an effectiveness evaluation index system for the network is established. And then, the fuzzy analytic hierarchy process, which combines the analytic hierarchy process and the fuzzy comprehensive evaluation theory, is used to evaluate the effectiveness of the double-layered satellite network with laser and microwave hybrid links. Furthermore, the evaluation result of the proposed hybrid link network is obtained by simulation. The effectiveness evaluation process of the proposed double-layered satellite network with laser and microwave hybrid links can help to optimize the design of hybrid link double-layered satellite network and improve the operating efficiency of the satellite system.
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