Areal spectrum utilization efficiency in digital radio link networks

Quadrature Phase Shift Keying (QPSK) is an important digital signal modulation method, which has the advantages of high spectrum efficiency and strong anti-interference. Coherent laser communication has the advantages of high speed, large capacity, light and small equipment as well as high sensitivity. In order to better introduce the QPSK modulation method into the space downlink coherent laser communication system, we give a bit error rate (BER) of QPSK modulation model with laser linewidth suitable for space downlink coherent laser communication system with QPSK modulation under atmospheric turbulence. Based on the model, we simulate and analyze the effects of atmospheric wind speed, zenith angle, gain of Erbium doped optical fiber amplifier (EDFA) and communication rate on the linewidth tolerance of space downlink coherent laser communication system with QPSK modulation. The results show that the linewidth tolerance of the system increases when the zenith angle decreases or the gain of EDFA increases or the wind speed decreases. And the effects of zenith angle, gain of EDFA and communication rate on the linewidth tolerance of the space downlink coherent laser communication system with QPSK modulation are large. The effect of wind speed on the linewidth tolerance of space downlink coherent laser communication system with QPSK modulation is smaller. And the larger the wind speed is, the smaller the effect of increasing wind speed on the linewidth tolerance. For the communication rate, the linewidth tolerance increases and then decreases with the increase of the communication rate. This work can be a reference for the design of space downlink coherent laser communication system with QPSK modulation.

The feasibility of a QPSK (quadrature-phase-shift-keying) optical heterodyne detection system for a high-speed and long-span coherent transmission is investigated. The key factors, which are the modulation method and the spectral linewidth requirement for optical light sources, are discussed. Through theoretical analysis and the simulation experiment, it is confirmed that the required beat spectral linewidth for QPSK coherent detection is less than 7.5*10/sup -5/*bit rate. It is also shown that the required spectral linewidth for QPSK differentially coherent detection is less than 2.5*10/sup -5/*bit rate. These results show that the gigabits-per-second range QPSK optical heterodyne detection can be realized with conventional external cavity laser diodes. >

Analogous to multiple symbol differential detection of quadrature phase-shift-keying (QPSK), a multiple bit differential detection scheme is described for offset QPSK that also exhibits continuous improvement in performance with increasing observation interval. Being derived from maximum-likelihood (ML) considerations, the proposed scheme is purported to be the most power efficient scheme for such a modulation and detection method. Extension of the result to shaped offset QPSK is also possible.

Orthogonal Frequency Division Multiplexing (OFDM) is an encoding method that are hugely utilized in wireless communication due to its high number of advantages such as tolerance for multipath delay spread, frequency selective fading channels immune and also power efficiency. The bad side of this method is it has high Peak Average Power Ratio (PAPR) that will generate nonlinear distortions and severe power penalty. In this research, Selective Mapping (SLM) method is proposed to solve the problem of high PAPR but from previous researches, it could be seen that in SLM, the search complexity increases as the number of phase sequence increase. To solve this issue, Firefly Algorithm (FA) is applied to optimize the function of SLM. The modulation method used is Quadrature Phase Shift Keying (QPSK). By the end of the process, CCDF and BER plots are computed. The performance of PAPR reduction in OFDM system are analyzed by different number of subcarriers, phase sequences, randomization parameters and iterations using CCDF graphs. The performance of OFDM channel through AWGN channel is studied with different number of subcarriers. By using SLM method only, the PAPR values manage to be reduced by 0.4–3 dB but with FA-SLM algorithm, the PAPR values can be reduced by 5–9.5 dB. With these results, it is concluded that the combination of SLM with FA can help to improve computational complexity in SLM and eventually reduce PAPR value in OFDM system.

The most widely used technique for high-data-rate transmission is orthogonal frequency division multiplexing (OFDM). However, one disadvantage of OFDM systems is that the transmitted signals have a high peak-to-average power ratio (PAPR). High PAPR causes more interference and lower resolution in analogue to digital (A/D) and digital to analogue (D/A) converters. In this paper, Partial Transmit Sequence (PTS) technique using Improved Harmony Search (IHS) algorithm is proposed to solve the high PAPR problem. The PTS technique has a high search complexity because it involves an extensive random search over all possible phase vector combinations, which grows exponentially with the number of phase vectors. IHS improves the accuracy and convergence rate of conventional algorithms while requiring only a few parameters to be adjusted. The modulation method used is Quadrature Phase Shift Keying (QPSK). The performance of PTS and IHS-PTS are analyzed using CCDF graphs with different values of subcarriers and iterations. The PAPR reduction percentage increases more with using IHS-PTS compared to PTS only. To conclude, implementing IHS together with PTS can improve computational complexity in PTS and helps to reduce PAPR values even better in OFDM system.KeywordsImproved Harmony Search (IHS)Orthogonal frequency division multiplexing (OFDM)Peak average power ratio (PAPR)Partial Transmit Sequence (PTS)

This paper analyzes the influence of haze on the performance of ground space optical communication (GSOC). Firstly, the scattering model of haze aerosol is established based on the coated scattering theory of Christian Matzler. Then the fitting relationship between atmospheric visibility V and PM 2.5 is obtained according to the Meteorological Bureau of Beijing. In order to calculate the attenuation coefficient, the relationship between spectral distribution of aerosol particles and PM 2.5 Index is derived. Finally, the effect of haze on GSOC with different detectors and modulation modes are discussed. The result shows that with the increase of PM 2.5 Index, the received optical power, sign-to-noise (SNR) and channel capacity (CAP) decrease rapidly, and bit error rate (BER) increases rapidly. In terms of wavelength selection, under the same detector and modulation mode, the effect of haze on the GSOC of the 0.86um laser is greater than that of the 1.55um laser. In the modulation method, the use of Binary Phase Shift Keying (BPSK) modulation is better than the use of Quadrature Phase Shift Keying (QPSK) in order to reduce the BER, while the worst modulation is to use On-Off Keying (OOK). When the sensitivity of the detector is -35 dBm，the value of PM 2.5 corresponding to 1.55um is not higher than 557, and the value of PM 2.5 corresponding to 0.86um is not higher than 548.

Non-orthogonal multiple access (NOMA) is one of the most effective techniques for meeting the spectrum efficiency (SE) requirements of 5G and beyond networks. This paper presents two novel methods for improving the SE of the downlink (DL) NOMA power domain (PD) integrated with a cooperative cognitive radio network (CCRN) in a 5G network using single-input and single-output (SISO), multiple-input and multiple-output (MIMO), and massive MIMO (M-MIMO) in the same network and in a single cell. In the first method, NOMA users compete for free channels in a competing channel (C-CH) on the CCRN. The second method provides NOMA users with a dedicated channel (D-CH) with high priority. The proposed methods are evaluated using the Matlab software program using the three scenarios with different distances, power location coefficients, and transmitting power. Four users are assumed to operate on 80 MHz bandwidths (BWs) and use the quadrature phase shift keying (QPSK) modulation technique in all three scenarios. Successive interference cancellation (SIC) and unstable channel conditions are also considered when evaluating the performance of the proposed system under the assumption of frequency selective Rayleigh fading. The best four-user SE performance obtained by user U4 was 3.9 bps/Hz/cell for SISO DL NOMA, 5.1 bps/Hz/cell for SISO DL NOMA with CCRN with C-CH, and 7.2 bps/Hz/cell for SISO DL NOMA with CCRN with D-CH at 40 dBm transmit power. While 64 × 64 MIMO DL NOMA improved SE performance of the best-use U4 by 51%, 64 × 64 MIMO DL NOMA with C-CH CCRN enhanced SE performance by 64%, and 64 × 64 MIMO DL NOMA with D-CH CCRN boosted performance by 65% SE compared to SISO DL NOMA at 40 dB transmit power. While 128 × 128 M-MIMO DL NOMA improved SE performance for the best U4 user by 79%, 128 × 128 M-MIMO DL NOMA with C-CH CCRN boosted SE performance by 85%, and 128 × 128 M-MIMO DL NOMA with D-CH CCRN enhanced SE performance by 86% when compared to SISO DL NOMA SE performance at 40 dB transmit power. We discovered that the second proposed method, when using D-CH with CCR-NOMA, produced the best SE performance for users. On the other hand, the spectral efficiency is significantly increased when applying MIMO and M-MIMO techniques.

The performance of cellular digital mobile radio systems is investigated using quadrature amplitude modulation (4-QAM) and differential phase shift keying (DPSK) in a frequency nonselective Rayleigh fading environment with lognormal shadowing, including the effects of (white) Gaussian noise, narrow-band impulsive noise/interference (Middleton's Class A model), and cochannel interference. The performance is analyzed in terms of probability of bit error. The UHF groundwave propagation law is introduced by considering the local mean power to be inversely proportional to the fourth power of propagation distance. To investigate the improvement in performance the influence of selection diversity and maximal ratio combining on the bit error probability is analyzed. It has been found that shadowing significantly affects the bit error performance. Application of selection diversity or maximal ratio combining results in important improvement of system performance. Selection diversity gives better results than maximal ratio combining for low signal-to-noise ratios. Results of our analysis show maximal ratio combining is not that sensitive to unequal branch signal-to-noise-plus-interference ratio.

An ultra-wide-band (UWB) signal is characterized by a radiated spectrum with a very wide bandwidth around a relatively low center frequency. In this paper, we study the reduced fading margin property of UWB signals. To evaluate the fading margin, we compare the performance of UWB signals in an environment with only additive white Gaussian noise (AWGN) versus the performance of UWB signals in a dense multipath environment with AWGN. The assumption here is that the presence of multipath causes a small increase in the signal-to-noise ratio required to achieve reasonable levels of bit error rate. A numerical example confirms this assumption, more specifically, the example shows that to achieve a bit error rate equal to 10/sup -5/, we require about 13.5 dB in the AWGN case and about 15 dB in the multipath case, resulting in a fading margin of just 1.5 dB. This small fading margin can be understood by the ability of the UWB signal to resolve the dense multipath.

In this paper, we improved the VPPM (Variable- Pulse-Position-Modulation) modulation mode referred to the PHY II based on the research about the short distance visible light communication IEEE 802.15.7 standard, and put forward a compound digital baseband modulation method named VPPM-DPAM (Variable-Pulse-Position-Modulation-Discrete Pulse-Amplitude-Modulation) which is suitable for indoor white Micro-LED array by introducing the DPAM based on the dispersion of light intensity, the modulated method we presented not only improves the communication speed of the system but also provides an accurate dimming mechanism for indoor adjustable luminance lighting which realizes the integration of communication lighting. What's more, we further discussed the constellation design in three-dimensional optimization of VPPM-DPAM which focused on the nonconvex optimization problem, found that the communication performance and lighting performance of the system have a constraint relation which was verified in both simulation and experiment. Finally, a visual light communication system based on DPAM-VPPM with compatible communication and lighting performance is obtained with certain anti-noise capability.

By using OPFs to transmit data in the form of light, fiber-optic communication has completely changed the way in-formation is transmitted. This technology's remarkable benefits, such as much lower attenuation, increased band-width capacity, and decreased crosstalk over extended distances, make it superior to conventional electrical trans-mission techniques. The deployment of Wavelength Division Multiplexing (WDM), which maximizes bandwidth usage by enabling several data channels to be carried simultaneously at various wavelengths, is one of the rapid breakthroughs in optical fiber (OPF) technology that are examined in this research. However, nonlinear event in-volved Self-Phase Modulation (S.P.M.), Four-Wave Mixing (FWM), and Stimulated Raman Scattering (S.R.S.) that are inherent in fiber optics frequently impair the performance of WDM systems. Signal distortion and energy loss may result from these causes. The study examines many digital modulation methods, such as Differential Phase Shift Keying (DPSK), Return-to-Zero (RZ), and Non-Return-to-Zero (NRZ), and evaluates how they affect system performance and efficiency at high bit-rates. The results point to a future path for optical communication system research and development, showing that DPSK provides improved sensitivity and lower bit error rates, while RZ modulation exhibits higher resilience to nonlinear effects.

We present three methods of weighting N-bit μ-law Pulse Code Modulation (PCM) with binary modulation, and evaluate their performances theoretically for transmission over Rayleigh fading and Gaussian channels. The digital modulation methods considered are noncoherent frequency shift keying and coherent phase shift keying. Ideal selection combining and ideal maximal ratio combining diversity techniques are employed when the transmission is over fading channels. Weighting System 1 is the conventional weighted pulse code modulated system, where the bits in every PCM word have the same weighting profile. Weighting System 2 has 2N unique weighting profiles, while System 3 has an addendum to System 2, where every bit in a particular word is further weighted by a unique multiplicative factor. For Rayleigh fading channels and the encoder operating at an input level that provided maximum signal-to-quantization noise-ratio, we obtained gains in overall signal-to-noise ratio (s/n) over unweighted μ-law PCM of 3, 4.5, and 6 dB for Systems 1, 2, and 3, respectively. When the systems were used in conjunction with Gaussian channels, the corresponding gains were 10, 12, and 17 dB, for a channel s/n of 10 dB. In addition to the theoretical results, we conducted computer simulations using four concatenated speech sentences transmitted via our weighted μ-law PCM systems over mobile radio channels. The simulation performances were in good agreement with our theoretical results, which were based on input signals having an exponential distribution.

We investigated and compared the performances of three different types of optical twin-single sideband (twin-SSB) modulation methods. Twin-SSB can transmit two different signals on lower side-band (LSB) and upper side-band (USB), and has been studied as a technique to improve spectral efficiency. Twin-SSB arranges the spectra side-by-side without any spectral spacing. Dispersion tolerance of twin-SSB is as high as that of conventional SSB schemes. The twin-SSB modulation can be performed by using a dual-polarization quadrature phase shift keying (DP-QPSK) modulator, a QPSK modulator, or a single Mach-Zehnder modulator (MZM). The twin-SSB with the three modulation methods need to be modulated at a limited linear domain of the optical field output function of the modulator. Therefore, if we apply a large electrical modulation signal to the modulators to decrease the optical loss, the nonlinear characteristics of the modulators degrade the performance of the twin-SSB signals. We investigated the modulation performance by changing the amplitude of the electrical modulation signal for the modulators, and investigated the optimal conditions of the twin-SSB modulation methods. We also performed numerical simulations of 50-km standard single mode fiber (SSMF) transmission of the twin-SSB signals with the optimal modulation conditions, and evaluated the error vector magnitude (EVM) performances of the transmitted signals. The results revealed that the EVM performances of the twin-SSB signals using a DP-QPSK modulator and a QPSK modulator were superior to that of a single MZM.

Electrogoniometers are used to collect continuous information on postural distributions among workers. Enormous quantities of data are generated that have to be reduced to meaningful parameters (angle, frequency, and duration). In this study we propose statistical models to determine these essential characteristics of postural load on nurses, housekeepers, and office workers. A direct registration of the lumbar posture was made over a workday with an inclinometer. An exposure variation analysis was used to summarize information on the angle of trunk flexion, the time period of maintained postures, and the percentage of worktime in a data matrix. A hierarchical regression analysis was used to compare these characteristics among nurses (N=64), housekeepers (N=16), and office workers (N=27). The occupational groups did not differ for either frequency or duration of trunk flexion over 30 degrees since frequency and duration were inversely related. Nurses experienced longer worktimes than the office workers did for trunk flexion between 30 and 70 degrees maintained <5 seconds, whereas office workers experienced longer worktimes in smaller angles (< 30 degrees) for longer periods. Comparable differences in the distributions of postural load were found between housekeepers and office workers. This study describes the use of hierarchical models in analyses of the exposure level, frequency, and duration of postural load simultaneously and offers an alternative to conventional ergonomic analysis in which the dynamics of exposure are often ignored. The distinction in postural load between nurses or housekeepers and office workers is best determined by the combination of trunk angle and time period.

This article provides an overview of the technologies for generating radio signals, such as orthogonal frequency division multiplexing and its modifications: universal filtered multicarrier and filter bank multi-carrier currently used in wireless communication networks. Subject of research: methods of multicar-rier modulation. Main results: Overview of modern methods of forming multicarrier signals in radio communication systems. A number of computational experiments have been performed to compare the characteristics of signal localization, peak-to-average ratios and spurious emissions. Practical implica-tions: the results can be used in choosing the type of modulation in the case of the development of digi-tal radio communication systems.