WIRELESS TRANSMITTER FOR OPTICAL COMMUNICATION WITH FREQUENCY-MODULATED LASER CARRIER

Wide-band digital indoor and future mobile communication systems are being developed in the quasi-millimeter and millimeter wave frequency bands. In such high-speed systems, the degradation of transmission quality by multipath fading constitutes a limiting barrier. Multipath fading, which results from reflection, refraction and scattering of radio waves by buildings and other structures, gives rise to more than one path reaching the receiver and produces a distorted version of the transmitted signal. In mobile and indoor communication systems it cannot be eliminated, therefore the multipath channel must be well characterized in order to reduce its effect in the design of such systems. The objective of this research is to study the multipath fading and delay spread effects due to buildings in an urban propagation channel. In particular, the effects of the building materials, shapes and number of buildings on multipath fading are being studied.

The subject of research in this article is the process of building a mobile communication system that operates under electronic countermeasures. The aim is to develop recommendations for building a wireless mobile communication system that operates effectively in a complex interfering electromagnetic environment. The strategy for building a mobile wireless communication system is based on the use of a grouping of low-altitude UAVs with ultra-wideband signal technology circulating in control and communication channels, with the integration of artificial intelligence elements into its structure. The objective of this study is to ensure the stable and secure operation of a wireless mobile communication system despite electronic countermeasures. The methods of analytical, temporal positional pulse coding, and fuzzy logical inference were used to make decisions on the transfer of service in the network. The following results were obtained. A strategy for building a wireless mobile communication system despite electronic countermeasures has been developed. It is shown that in order to obtain high noise immunity of control and communication channels and to protect information from interception, wireless ultra-wideband communication technology should be used. This will provide large volumes and speeds of information transmission. A technical solution for the design of an ultra-wideband transceiver antenna system is proposed. Moreover, it is recommended to use the results of data processing in a fuzzy decision-making system for the transfer of service between mobile network nodes in conditions of interference. Conclusions. The scientific novelty of the obtained results is as follows. The use of ultra-wideband channels makes it possible to increase the number of control and communication channels in a wireless mobile system almost unlimitedly. The preliminary distribution of orthogonal codes between the channels realizes the process of control and communication without the interception of information and mutual interference. The use of the time-position-pulse coding method prevents the occurrence of intercharacter distortions of the encoding ultrashort pulses. This also reduces the level of distortion of information signals caused by multipath propagation, which guarantees the security of information in the system. The use of a fuzzy decision-making system for the transfer of services between mobile network nodes allows dynamically changing the network topology in real time and maintaining high quality of service under electronic countermeasures.

Nowadays, the coherent optical communication system plays an important role in communication field because of large capability and bandwidth. A coherent optical communication, based on high-order modulation and digital signal processing technologies, consists of optical transmitters, optical fiber lines, optical amplifiers and optical receivers. In the high-speed coherent optical communication system, the phase noise from the transmitter laser and the local oscillator laser can significantly degrade the performance of the signal transmission and detection, especially for the systems using high-order modulation format, such as m-ary phase shift keying (mPSK) and m-ary quadrature amplitude modulation (m-QAM). Therefore, investigations on laser phase noise compensation algorithm based on digital signal processing technologies has become more and more significant. In this work, a multi-ring carrier phase recovery algorithm is developed for compensating the laser phase noise in optical fiber communication systems using high-order modulation formats. Degradations on the performance of communication systems due to the laser phase noise have been investigated. The system performance using the proposed algorithm and the conventional Viterbi-Viterbi algorithm were also evaluated in 9-channel and 15- channel, 32-Gbaud, Nyquist-spaced QPSK, 16-QAM, 64-QAM and 256-QAM coherent transmission systems with considering the impact of the laser phase noise. It is found that the phase noise leads to stricter constraints on the linewidths of transmitter-side and receiver-side lasers, and it can greatly degrade the achievable information rates in communication systems. Besides, compared to the conventional Viterbi-Viterbi algorithm, which is usually applied in the QPSK system, our proposed algorithm can also well mitigate the laser phase noise in 16-QAM, 64-QAM and 256-QAM optical communication systems.
\n

Abstract. Currently, there is a need to develop new technical solutions for antenna systems for mobile radio communication systems with improved electrical and mass-dimensional characteristics. As a result of the analysis of the currently conducted fundamental and applied research, it was found that the use of various composite structures (metamaterials) can improve the characteristics of antennas and antenna-feeder path devices. At the same time, there is an urgent scientific and technical problem of developing adequate electrodynamic and mathematical models of antennas and antenna-feeder path devices based on metamaterials for the correct calculation of their characteristics. The purpose of the work is theoretical and experimental studies of the characteristics of a two-element common-mode antenna array with a reflector made of a spiral metamaterial for mobile radio communication systems. The above research results have shown that the use of such antenna arrays is advisable when both types of polarization (vertical and horizontal) are required. Such an antenna array can increase the efficiency of communication systems, for example, in a wooded area. The proposed common-mode antenna array with a chiral metamaterial reflector can be used on mobile objects of digital and analog radio communication systems operating, including in the mode of pseudorandom tuning of the operating frequency.

The objective of this presentation is to illustrate that an electromagnetic macro modeling can properly predict the path loss exponent in a mobile cellular wireless communication system. This represents the variation of the path loss with distance from the base station antenna. Specifically, it will be shown that the path loss exponent is 3 preceded by a slow fading region and followed by the fringe region where the path loss exponent is 4. The size of these regions is determined by the height of the base station antenna. The relevant theory starts from the analysis of radiation from a vertical electric dipole situated over a horizontal imperfect ground plane as first considered by Sommerfeld in 1909. The various methods used to evaluate the Sommerfeld integrals are described for different regions. Then, accurate numerical analyses and experimental data will illustrate the above statements, validating the theory. Moreover, the experimental data reveal that a macro modeling of the environment using an appropriate electromagnetic analysis can accurately predict the path loss exponent for the propagation of radio waves in a cellular wireless communication system scenario without needing to recourse to other types of micromodeling.

In order to solve the problems of low-risk assessment accuracy and long time-consuming assessment of current wireless mobile communication systems, a wireless mobile communication system based on artificial intelligence algorithms is proposed. First, the research status of risk assessment of wireless mobile communication system at home and abroad is analyzed, and the risk assessment index system of wireless mobile communication system is established; then, the learning samples are collected according to the risk assessment index system of wireless mobile communication system, and artificial intelligence algorithm is used to optimize the neural network. Build the wireless mobile communication system risk assessment model; finally, carry out the wireless mobile communication system risk assessment simulation comparison test. The experimental results show that the accuracy rate of the risk assessment of the wireless mobile communication system by the artificial intelligence algorithm is over 95%, and the assessment error is smaller than in other models. The risk assessment time of the wireless mobile communication system is significantly reduced, the real-time performance is better, and it has a higher practical application value.

The next-generation wireless personal and mobile communication systems are expected to accommodate not only high-quality voice services, but also a broad range of other multirate services. Of the various multiaccess techniques, wide-band code-division multiple access (CDMA) has been regarded as an important part of the third-generation wireless communication systems because of its high frequency utilization efficiency and suitability for handling multimedia and multirate services. In this paper, we consider a system with a simplified receiver structure for direct-sequence CDMA (DS/CDMA) wireless communication handsets, in which improved performance is demonstrated when compared to a conventional DS/CDMA system with a RAKE receiver at the mobile station. We arrive at this system by finding the optimal solution to a general multiple-input single-output (MISO) DS/CDMA smart antenna system. We find that this solution reduces to a pre-RAKE with space transmit diversity system under the assumption that a simple one-finger matched filter is used at the receiver. This system combines the advantages of pre-RAKE diversity and transmit antenna diversity. It is shown that significant system performance and capacity improvements are possible. The numerical results also reveal that this system is not too sensitive to channel estimation errors.

The design of a mobile or portable radio communications system requires the consideration of a number of unique engineering factors which do not necessarily apply to the design of a fixed, or point-to-point system. The design procedure is a combination of theoretical and empirical methods, which when taken with measured data, produce a system design meeting the required specifications. This paper will treat that portion of the system design pertaining to radio frequency propagation and system coverage. It stresses a realistic measurement program which will provide coverage data in support of the system design.

The statement is substantiated that for the design of mobile radio communication systems at short distances up to 1 000 m, the main recommended calculation models have a significant error, since they were created for calcula-tions of long distances (as a rule, from 1 to 50 km) and have limitations in application. Due to the fact that at the present stage of development of mobile radio communication systems, the frequency ranges are in intensive research and use not only 900 and 1 800 MHz, but also 450-800 MHz sections, as well as from 2 100 to 6 000 MHz, which were not previously used for cellular communication systems, it is necessary to propose additional models necessary for the preliminary design of 3-5 generation systems in the range from 2 100 MHz. The range of radio waves in the ranges from 2 100 to 6 000 MHz is significantly reduced compared to the ranges of 1 800 or 900 MHz. The use of classical calculation models such as the Okumura and COST-231–Hata models at distances less than 1 km is characterized by significant errors and is not recommended by the authors of the models themselves for use at short distances. To solve this problem, new models have been developed for calculating the attenuation of radio signals designed to estimate attenuation at short distances.

The multipath fading and Doppler effect are well-known phenomena affecting channel quality in mobile wireless communication systems. Within this context, the emergence of reconfigurable intelligence surfaces (RISs) brings a chance to achieve this goal. RISs as a potential solution are considered to be proposed in sixth generation (6G). The core idea of RISs is to change the channel characteristic from uncontrollable to controllable. This is reflected by some novel functionalities with wave absorption and abnormal reflection. In this paper, the multipath fading and Doppler effect are characterized by establishing a mathematical model from the perspective of reflectors and RISs in different mobile wireless communication processes. In addition, the solutions that improve the multipath fading and Doppler effect stemming from the movement of mobile transmitter are discussed by utilizing multiple RISs. A large number of experimental results demonstrate that the received signal strength abnormal fluctuations due to Doppler effect can be eliminated effectively by real-time control of RISs. Meanwhile, the multipath fading is also mitigated when all reflectors deployed are coated with RISs.

We investigate a velocity estimation algorithm for orthogonal frequency division multiplexing (OFDM) based communication systems. Since OFDM is a strong candidate for future mobile broadband wireless communication systems, the channel estimation, in this case two dimensional Wiener filtering, should work in a wide range of user velocities (0 to 350 km/h) and different delay spreads. To keep the channel estimation errors as small as possible, an adaptation of the filter coefficients to the current channel state must be realized. We present a modified version of a previously published velocity estimator and present error estimations to predict the reliability of the estimator. It is shown, that the estimator is very reliable compared to the accuracy requirements of the adaptive Wiener filter in a wide range of channel states. The algorithm can be applied directly to OFDM systems with transmit diversity (TD) and to OFDM MIMO systems.

The so-called irreducible error due to frequency-selective fading is known to have a serious effect on mobile radio communication systems. Thus, the analysis of such errors is a prerequisite for making high-speed digital signal transmission over a fading channel feasible. The authors attempted to elucidate the physical mechanisms causing such errors using laboratory measurements of microscopic bit error rate. The results clarified some sources of burst errors in a multipath fading channel. In particular, large and rapid timing fluctuations of eye pattern due to severe delay distortion of the multipath channel was found to be the most dominant source of error.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Near the ground laser communication systems must operate in the presence of strong atmospheric turbulence. The effects of atmospheric turbulence on the laser beam which are relevant to optical communications are a broadening of the laser footprint, random jitter of the laser beam, and high spatial frequency intensity fluctuations referred to as scintillation. The overall goal of our program is to improve the performance and extend the range of optical communications systems by exploring the use of adaptive optics and channel coding. Knowledge of the turbulence conditions and the ability to describe its properties are the key aspects to make these improvements effective. The multi-phase approach described here is directed to statistically describe atmospheric turbulence based on results derived from experimentally collected data. To model the performance of a real world system, we have developed an outdoor path partially over water, spanning 3 km turbulence measurement and monitoring system. The system described in this paper has two transmitters and two receivers. The transmitter side is equipped with a laser and a bank of 14 horizontally, in-line mounted LEDs. The laser transmitter and LED operate at 808 nm with laser power of 2mW. The receiver side consists of two channels. The WFS channel captures the signal from the laser transmitter and is specifically designated for the wavefront sensing. The wavefront sensor channel consists of relay optics, a Hartmann WFS, and a CCD camera. The PSF channel is designed to capture the signal from LED bar and consists of relay optics and a CCD camera. The data collected from the PSF channel is used for measurements of anisoplanetic effects. In this paper we emphasize the data collection and consecutive analysis from the WFS channel only. Statistics of the Fried parameter r 0 are derived from 6TB of data collected over 50 days under various day and night atmospheric conditions. Significant fluctuations of r 0 are found with the values ranging from 2mm and up to 15cm.

Guest Editorial

Location management is one of the most important issues in mobile radio communication systems. This paper presents an intelligent paging scheme which uses geographical information to help in searching for the target mobile terminal. Since the characteristics of geography, such as street placement, mountain areas, lack locations, etc., influences the distribution of mobile users, the probability of user distribution among each registration zone is quite different. According to the probability information, we may track a mobile user by utilizing the geographical background information. Three different paging policies are proposed. Simulation results demonstrate that the proposed schemes significantly improve the location management performance.