A novel optical transmitting antenna based on free-form lens is proposed for visible light cellular network in order to improve the signal quality in the whole coverage area and communication performance of the system. Based on the energy mapping relation and Snell’s law, the optical transmitting antenna based on free-form lens is designed to realize rectangle light receiving areas. Using this optical transmitting antenna, the light signal from light emitting diodes (LED) source can be distributed uniformly in a square area of 0.8 m × 0.8 m. On this basis, a visible light cellular network with the novel optical transmitting antenna is applied, of which the quality of the receiving light signal and system performance are further investigated. It is demonstrated that in a 3 m × 3 m × 3 m room with 16 LEDs using the designed optical antenna, the uniformity of light distribution in the light network converage reaches 0.8. With the elimination of co-channel interference, the average signal to interference and noise ratio (SINR) is 12.6 dB, which can effectively improve the bit error ratio (BER) and ensure the communication performance of visible light cellular networks.

Based on the transmission characteristics of vortex beams and light scattering theory, the field distribution and interference characteristics of superposition vortex beams passing through the rotating random rough surface are studied. Two vortex beams with the same topological charge value and opposite signs are used for simulation and experiment of superimposition generation. Using angular spectrum diffraction theory, the influence of the root-mean-square roughness of the rotating random rough surface on the beam transmission is analyzed. As the superposition vortex beams with different topological charges pass through the rotating random rough surface and interfere with the reference light, the time-dependent curve of normalized intensity values at different rotational speeds can be obtained through numerical calculation. Then the frequency shift can be indirectly obtained by light intensity-time function and the speed of rotating target can be obtained through inversion. The results show that: the frequency is inverted by the period of the simulation curve, and when the rotational speed Ω is 2π/3 rad/s, 2π rad/s, 10π/3 rad/s, the corresponding frequency shift Δf is 2/3Hz, 2Hz, 10/3Hz, respectively. The results of this research can provide a theoretical reference for the regulation and application of superposition vortex beams.

In order to establish an accurate model of the hybrid radio frequency/free space optical(Radio Frequency/Free Space optical, RF/FSO) aviation relay communication system link under the condition of co-channel interference, a multi-user diversity(Multi-User Diversity, MUD) airborne platform RF/FSO hybrid link performance analysis method is proposed. The independent and identically distributed Nakagami-m fading channel is used to characterize the RF user signal and the co-channel interference(Co-Channel Interference, CCI) signal channel, while the FSO link between relay to destination is assumed to be affected by Exponentiated Weibull distributed atmospheric turbulence and the Rayleigh distributed pointing error. The decoding and forwarding protocol is adopted at the relay node to avoid accumulation of noise. Based on the cumulative distribution function of the system's end-to-end equivalent signal-to-noise ratio, the closed expressions for link outage probability and average bit error rate are derived. The research results show that when using coherent binary phase shift keying modulation, the system has the best error performance. The influence of interference signals can be reduced by increasing the number of users.

For improving the throughput and the fairness of user experience of indoor power line communications-visible light communications (PLC-VLC) system, an improved genetic algorithm based joint user pairing and subcarrier allocation (IGA-JUPSA) method is proposed in the paper. In the user pairing stage, a method of optimal non-orthogonal multiple access (NOMA) user pairing is designed to improve the throughput of PLC-VLC system. During the process of subcarrier allocation, the subcarrier allocation scheme combined NOMA with orthogonal multiple access (OMA) is proposed, and the improved genetic algorithm is used to optimize the subcarrier allocation for different NOMA groups for improving the system throughput and user fairness. Simulation results show that the proposed IGA-JUPSA can improve the throughput of PLC-VLC cascaded system and the fairness experience of users.

Due to a good trade-off between performance and complexity, a new class of decoding schemes, called soft-aided hard-decision (SA-HD) decoders, has become particularly interesting to optical communication fields in recent years. Soft-aided bit-marking (SABM) algorithm is one of the popular ones. To be friendly for hardware implementation, this paper proposes an improved SABM (iSABM) algorithm for staircase codes (SCCs), which we call iSABM-SCC. With the help of channel soft information, iSABM-SCC marks bits into three types according to their reliabilities using two thresholds. The marked information is then used to assist the staircase decoder to prevent miscorrections and to extend the error-correcting capability, thus improving the performance of SCCs. The simulation results for free-space optical communications show that the proposed iSABM-SCC scheme achieves higher performance gains over standard SCC (S-SCC) and RS code in turbulence channels. For instance, iSABM-SCC with code rate of 0.75 has been shown to yield up to 4.37 dB performance gain when compared to S-SCC for 4-PAM and up to 11.06 dB performance gain when compared to RS code for 8-PAM in a strong turbulence channel.

When the vortex beam carrying orbital angular momentum (OAM) is transmitted in the free space optical communication (FSO) channel, the turbulent medium in which will change the propagation characteristics of the vortex beam, destroy the spiral structure of the wave-front, and ultimately directly affect the stability and reliability of communication. To make up the shortcomings of the previously experimental research in the generalization, a high-power vortex beam array based on coherent beam combining (CBC) technology is selected as the research light source, and a complete system architecture is established from a theoretical point of view to analyze the impact of the amplitude and phase fluctuations caused by atmospheric turbulence on the performance of OAM based FSO communication systems. Applying the optical heterodyne detection (OHD), the random distribution of signal-to-noise ratio (SNR) under turbulent conditions is studied in detail. Based on this, the analytical expression of symbol error probability (SEP) under the condition of Mary Phase-Shift Keying (MPSK) has been derived, and the influence of different turbulence channel parameters, beam parameters and receiver parameters on SEP has been investigated. The results suggest that increasing the beam waist radius of the array sub-beams and the number of the array sub-beams, and reducing the ring radius of the array can improve the beam quality and optimize the system performance. In addition, the smaller topological charge, propagation distance and turbulence intensity, and larger receiver aperture diameter can make the symbol error probability lower and the corresponding communication performance better.

Nonlinear distortion is identified as a major factor affecting the operating bandwidth and spurious-free dynamic range (SFDR) of radio-over-fiber link. Combining with the RF power ratio, polarization multiplexing and bias control techniques, a multi-channel radio-over-fiber link with high dynamic range and octave-spanning bandwidth is constructed for distributed antenna system (DAS). A model of linearity optimization for the proposed link is developed using a Lagrange multiplier method optimization model, and the best trade-off among RF output power, polarization incident angle and RF power ratio can be obtained. Thus, the optimization of link linearity can be achieved on the premise that the third-order intermodulation distortion (IMD3) and second-order harmonic distortion (HD2) are suppressed simultaneously. The simulated and experimental results show the proposed scheme is effective and feasible.

In order to manage the inter-cell interference of the visble light communication-wireless fidelity (VLC-WiFi) heterogeneous network effectively, a dynamic carrier allocation method based on user centric access (DCAUCA) was designed in this paper, in which multi-AP cells were constructed for users according to user rates and the differences between user request rate and network service rate of each cell was sorted in descending order for the purpose of allocating carriers to each VLC AP sequentially. Furthermore, a strategy called residual interference suppression based on transmitting power control (RISPC) was proposed to further suppress residual interference. Simulation results show that, compared with the comparison method, the DCAUCA improves system throughput by up to 52.15% and user’s satisfaction by up to 7.10%. Compared with DCAUCA, the RISPC improves system throughput by up to 9.66%.

In this paper, a full-duplex radio over fiber system with high linearity is proposed. The system overcomes the influence of the third-order intermodulation distortion and the periodic power fading in the downlink. At the same time, wavelength reuse is used in the uplink, which simplifies the complexity of the base station. A full duplex radio over fiber system with high linearity is realized. The experimental results show that compared with the conventional system based on single Mach Zehnder modulator, the third-order intermodulation distortion in the downlink of the proposed system is obviously suppressed and the influence of fiber dispersion is overcome, the spurious free dynamic range of the system is improved by 17dB, and the constellation and error vector amplitude of broadband RF signal are improved significantly. In addition, the uplink can achieve stable wavelength reuse and modulation transmission.

The light beam flicker and jitter caused by atmospheric turbulence will cause the point spread function (PSF) on the focal plane of the optical communication receiver to randomly fluctuate and drift, causing the photodetector to fail to effectively cover the signal light field. In order to minimize the bit error rate (BER) of free space optical communication (FSO) system under the limitation of multi-mode Gaussian background light noise field and received optical signal energy efficiency, an adaptive photoelectric array signal processing algorithm suitable for intensity modulation / direct detection (IM / DD) is proposed. In this method, the combined array path method is used to calculate the system BER of different array elements, and the minimum BER is used as the criterion to optimize the received photoelectric array element sequence. The analysis and simulation results show that under the same atmospheric turbulence and background light noise conditions, compared with the existing photoelectric array processing algorithm, the new method can greatly reduce the computational complexity of the system, while the system performance loss can be almost ignored.

To solve the problem of transceiver interference in the in-band full duplex (IBFD) system, a photonic radio frequency interference cancellation system based on phase modulators is proposed. Two phase modulators are used in a Sagnac loop to realize the modulation of the received signal and the local reference interference signal. Proper polarization control in the optical domain can finally cancel the self-interference signal. Experimental results show that the proposed scheme can achieve a single frequency interference suppression of more than 45 dB and a broadband interference suppression of more than 25 dB. The dynamic range of the system can reach 99.4 dB·Hz^2/3.

Pointing error in wireless optical communication system has an impact on the geometric attenuation of the received optical power, resulting in a decrease in the received optical power of the system and affecting the performance of the system. In order to accurately analyze the effect of pointing error on the performance of wireless optical communication system, based on the intensity distribution of Gaussian beam, the accurate analytical solution of the geometric attenuation model of received optical power in wireless optical communication system with circular aperture is derived. The influence of pointing error on the geometric attenuation of the system under different parameters is simulated, and the accuracy of the analytical solution is verified and compared with the existing model. The results show that there are errors in using the existing approximate model to calculate the geometric attenuation, and the existing errors cannot be ignored， therefore the model derivation under the circular aperture is more in line with the actual situation. In the point-to-point communication and networking communication of wireless optical communication, it is more accurate to use the Gaussian beam geometric attenuation analytical model under pointing error.

Optical vortex beam is a special beam that carries orbital angular momentum (OAM). Optical vortex beams with different OAMs are orthogonal to each other, and it’s numbers are infinite in theory, which can provide a new communication dimension for the optical communication systems. Therefore, it has attracted great attentions of worldwide scholars. With the in-depth investigations of OAM based optical communication technology, various OAM communication systems have been developed rapidly, but people seldom pay attention to the topic of energy-utilization efficiency in OAM based communication systems. This paper focuses on and summarizes energy-utilization efficiencies of OAM’s generation, detection, and the energy-utilization efficiency of whole communication systems in recent typical achievements. And the development trends and prospects for the energy-utilization efficiency of the future systems have been analyzed and prospected.

Aiming to fix the data loss problem of optical camera communication (OCC) data link resulted from the lack of sync between the camera and the LED signal lamp, as well as the gap time between every two consecutively captured pictures, the fundamental principle of LED-camera based OCC data link, camera parameters like pixel row number, pixel read out time, frame rate and shooting angle are analyzed in detail in this paper. Based on the characteristics of the OCC data link, a new data frame structure is proposed in this paper. When compared to the related data frame structure like interleaved Hamming coding and Raptor coding, the proposed date frame structure has a higher data transmission rate, and has the capability to fix both the inter-frame and intra-frame data loss problems. Numerical and measurement results both prove the validity of the theoretical analysis, finally.