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This paper investigates a satellite-terrestrial system employing the non-orthogonal multiple access (NOMA) scheme over Shadowed-Rician fading channels. The effects of both imperfect channel state information (CSI) and imperfect successive interference cancellation (SIC) on the NOMA based satellite-terrestrial system are taken into account. First, the outage performance of the proposed system is evaluated, and the closed-form expressions for the exact and asymptotic outage probabilities are obtained. Next, the expressions of the ergodic sum rate and system throughput are derived in the presence of channel estimation errors and residual interference. Moreover, we analyze the impacts of different residual interference levels on the energy efficiency. Finally, the numerical simulation results are conducted to verify the correctness of theoretical analysis and the advantages of the proposed NOMA scheme. At medium-high SNR region, the NOMA users are capable of outperforming orthogonal multiple access (OMA) users in terms of outage behaviors and system throughput with imperfect CSI and imperfect SIC. The ergodic sum rate decreases as the level of residual interference $\varpi $ increases, and is even lower than that of OMA once $\varpi $ goes beyond a certain value. Additionally, the energy efficiency of NOMA scheme is sensitive to the imperfect SIC.

This study investigates the performances of cooperative pattern division multiple access (PDMA) technology with a half-duplex amplify-and-forward (AF) relaying over Rayleigh fading channels. To characterise the performances of the AF-PDMA system, the closed-form expressions of the exact outage probabilities, system throughput and diversity order are derived, respectively. The particle swarm optimisation algorithm based on penalty function is used to obtain the optimum power allocation coefficients by maximising the system throughput. By setting different values on the target data rate for users to analyse the AF-PDMA system throughput performance, simulation results demonstrate the performance enhancement of the considered AF-PDMA compared with orthogonal multiple access with AF relaying and PDMA with decode-and-forward relaying.

As a novel non-orthogonal multiple access scheme for fifth generation mobile networks, pattern division multiple access (PDMA) can support more connectivity and significantly improve spectral efficiency compared with conventional orthogonal multiple access (OMA). In order to further to improve the system transmission reliability and spectrum efficiency for PDMA, a novel PDMA framework combined with multiple-input multiple-output (MIMO) technology by using space–frequency block coding scheme for downlink transmission is proposed in this study. The performance analysis expressions of system capacity for MIMO-PDMA and MIMO-OMA are derived. The detailed MIMO-PDMA design diagrams for transmitting and receiving end are presented and the equivalent space and frequency channel matrix for each user are derived to facilitate the performance evaluation of the proposed framework. The simulation results are provided to demonstrate that the integration of the two technologies can achieve better performance compared with traditional PDMA and MIMO-OMA.

A simultaneous wireless information and power transfer non-orthogonal multiple access assisted satellite-terrestrial system is investigated, where a terrestrial source communicates with a pair of users via a regenerative satellite harvesting energy from the source radio frequency signals. The impacts of imperfect channel state information (CSI), hardware impairments and imperfect successive interference cancellation (SIC) on system performance are taken into account from the perspective of realistic scenarios. Based on these, we derive the expressions for the exact and asymptotic outage probabilities. In addition, the sum throughput and energy efficiency in the delay-limited transmission mode are investigated to characterize the system performance. Numerical results are provided to validate the accuracy of the analytical results and show the effects of the three imperfections brought in the considered system.

There is greater flexibility in selecting the direct-current (DC) bus voltage in a two-stage photovoltaic (PV) grid-connected structure than in a single-stage one. The independent DC/DC and DC/alternating current (AC) control in traditional control methods changes the duty cycle of the first-stage DC/DC, which affects the control of the secondary DC/AC and even stabilises the DC bus voltage between the two stages. Therefore, two-stage converters should be considered and controlled in a unified manner. Here, the authors introduce a robust μ value control method based on the hybrid sensitivity theory to control a two-stage PV power generation system. Considering the effect of parameter perturbation on the modelling of the DC/DC average state model, the proposed method improves the DC bus voltage stability of a PV system and the power quality of the grid-connected current while achieving the maximum power point tracking performance of the PV. MATLAB simulations using three PV operating conditions demonstrate that the proposed control method can effectively reduce the fluctuation of the DC bus voltage between the two stages, the harmonic distortion rate of the grid-connected current, and the power oscillation time when the working conditions change.

As a novel non-orthogonal multiple access scheme, pattern division multiple access (PDMA) has been proposed for the fifth generation mobile communication technology (5G) to enhance spectrum efficiency and increase connexion capability. This study analyses the theory performance of uplink PDMA. The exact closed-form expressions for outage probability (OP) are derived in the Rayleigh fading channel, and the OPs of each user with different pattern and target signal-to-interference-plus-noise ratio are evaluated. In addition, the comparison between PDMA and conventional orthogonal multiple access (OMA) in terms of sum data rate (SDR) is conducted. Numerical simulation results verify the authors' analysis and show that PDMA outperforms OMA in terms of OP and SDR.

Massive machine type communication (mMTC) is one of the key application scenarios for the fifth generation mobile communication (5G). Grant-free (GF) transmission can reduce the high signaling overhead in mMTC. Non-orthogonal multiple access (NMA) can support more users for mMTC than orthogonal frequency division multiple access (OFDMA). Applying GF transmission in NMA system becomes an active topic recently. The in-depth study on applying GF transmission in pattern division multiple access (PDMA), a competitive candidate scheme of NMA, is investigated in this paper. The definition, latency and allocation of resource and transmission mechanism for GF-PDMA are discussed in detail. The link-level and system-level evaluations are provided to verify the analysis. The analysis and simulation results demonstrate that the proposed GF-PDMA has lower latency than grant based PDMA (GB-PDMA), possesses strong scalability to confront collision and provides almost 2.15 times gain over GF-OFDMA in terms of supporting the number of active users in the system.

Massive multiple-input multiple-output (MIMO) is envisioned to meet the growing spectral efficiency (SE) requirement in next generation cellular systems. However, it has been recognized that the unaffordable channel state information reference signal (CSI-RS) overhead required for acquiring CSI is a major challenge in frequency division duplexing (FDD) massive MIMO systems. To tackle the challenge of this CSI-RS overhead limitation, certain attempts, which have been designed for the scenarios with dispersive locations of users and sparse nature of channels, suffer from inaccurate channel estimation when the nature of channels for different users becomes highly correlated and rich. In this paper, we propose an enhanced CSI acquisition scheme for FDD multi-user massive MIMO systems, which exploits beamformed CSI-RS transmission mechanism to reduce the CSI-RS overhead. We present two limited feedback algorithms which provide different tradeoffs between system performance and CSI feedback overhead, where the multistage CSI acquisition strategy is adopted to avoid prohibitive computational complexity and amount of feedback requirement. The simulation results show that our CSI acquisition scheme, without additional CSI-RS overhead and enormous CSI feedback overhead, achieves higher SE performance as compared to conventional scheme.

This paper studies the application of cooperative techniques for pattern division multiple access (PDMA) in downlink (DL) network. More particularly, the performance of joint decode-and-forward (DF) relaying and PDMA (DF-PDMA) is investigated over Rayleigh channel, where the direct links are existent between the base station and users. To characterize the performance of the considered scenarios above, the closed-form expressions for outage probability and sum data rate are derived. Based on the derived results, the diversity orders achieved by users are obtained. The analysis results manifest that those users with DF relaying can achieve higher diversity order, in addition, the users selecting the PDMA pattern with higher column weight can further obtain higher diversity order. Simulation results unveil that DF-PDMA outperforms PDMA and orthogonal multiple access with DF relaying (DF-OMA) in terms of outage probability and system throughput. It is also worth noting that DF-PDMA can provide better fairness compared to DF-OMA.

As a promising candidate non-orthogonal multiple access scheme for the fifth generation (5G) wireless communication system, pattern division multiple access (PDMA) has received considerable attention recently. Using pattern matrix ( $\text {G}_{\text {PDMA}}^{[{2,3}]}$ , as an example, is used in this paper), PDMA directly maps the information bits of different users to radio resources, such as code, power, time and frequency, and space resource. PDMA can meet the requirements of massive connectivity and higher spectral efficiency for the 5G mobile network. In order to further improve transmission reliability and enhance the coverage, an uplink cooperative PDMA (Co-PDMA) scheme with half-duplex decode and forward relay is proposed. The analytical expressions of outage probability (OP) and sum data rate are derived to characterize the performance of the proposed scheme. The results show that the proposed Co-PDMA scheme achieves superior outage performance, with gains of 8 and 12 dB over the non- Co-PDMA and cooperative orthogonal multiple access (Co-OMA), respectively, @ OP = 0.1. Besides, the scheme is found to outperform two other schemes in terms of higher sum data rate and achieve an almost maximum 50% gain over Co-OMA when every user has the same target data rate.

Pattern division multiple access (PDMA) is a promising non-orthogonal multiple access scheme for the fifth generation mobile communication system. Link performance estimation technique is the key to ensure accurate performance evaluation of the PDMA uplink system. Although the belief propagation (BP) receiver with near-optimal performance is normally considered for PDMA uplink system, it remains a big challenge for the estimation of the link performance for the PDMA uplink system with the BP receiver. In this paper, we first propose a novel link performance estimation technique for the PDMA uplink system with the BP receiver. The performance of the BP receiver is estimated by utilizing the genie-aided interference cancellation receiver as an upper bound with a single fitting parameter. Then, we provide a simple search process of finding the fitting parameter. Finally, the simulation results show that the proposed method achieves greater link performance estimation accuracy over the conventional method in the PDMA uplink evaluation.

In this paper, a multiple parameters weighted fractional Fourier transform (MP-WFRFT) and constellation scrambling (CS) method based physical layer (PHY) security system is proposed. The proposed scheme is executed by two steps. In the first step, MP-WFRFT, implemented as the constellation beguiling (CB) method, is applied to change the signal's identity. In the second step the additional pseudo random phase information, regarded as the encryption key, is attached to the original signal to enhance the security. Typically, the pseudo random phase information can be removed effectively by the legitimate receiver. In contrast to the cryptography based encryption algorithms and the conventional PHY secrecy techniques, the main contribution of the proposed scheme is concentrated on the variation in signal's characteristics. Simulation results show that the proposed scheme can prevent the exchanging signal from eavesdroppers' classification or inception. Moreover, the proposed scheme can guarantee the BER performance at a tolerate increasing in computational complexity for the legitimate receivers.

As one of promising non-orthogonal multiple access scheme, pattern division multiple access (PDMA) scheme is considered to be one competitive multiple access technology for the fifth generation (5G) communications. The detection algorithm is the key technology to improve the system performance. Due to the PDMA patterns sparse nature, belief propagation (BP) become one effective receiver algorithm to achieve close to maximum likelihood (ML) detection performance with lower complexity. However, the complexity order is still exponential with the row weight of the PDMA pattern and the modulation index. A novel receiver based on expectation propagation (EP) algorithm is proposed in this paper to reduce the complexity order from exponential to linear. This paper makes a comparison on the two algorithms above in terms of system performance and complexity. Link-level simulation results show that the proposed EP receiver achieves nearly the same performance as the BP receiver with orders less complexity.

As a key technology of 5G, non orthogonal multiple access (NOMA) technology can significantly improve the spectrum efficiency compared with the traditional orthogonal multiple access technology. In addition, grant-free transmission technology can further reduce the transmission delay of the system and effectively improve the number of service users in the cell. In this paper, the pattern division multiple access (PDMA) technology (a typical NOMA technology) is taken as an example, PDMA technology based on Grant-free transmission (GF-PDMA) is studied, the uplink GF-PDMA pilot’s structure is designed and a user activation detection algorithms based on the received pilot’s power is proposed. The simulation results reviews that the algorithm proposed in this paper can fully meet the detection requirements of PDMA.

Reflectors used for light-emitting-diode (led) light source are designed in three-dimensional space to produce uniform illuminance effect. reflector's surfaces are calculated by the source-target mapping method in geometrical optics. ignoring scattering and absorption loss of the material, reflectors' performances are investigated. the simulation results show that the light efficiency which is the ratio of light flux in the target surface to that from led light source can reach above 95%. and the illuminance uniformity which is the ratio of minimum illuminance (min e) to average illuminance (aye e) also can reach above 95%. finally, the array of reflectors is investigated and the result shows it still has good performance. (c) 2015 elsevier gmbh. all rights reserved.

The anticipated 1000 fold increase in traffic demand over the next decade and the explosion of new services and applications, such as the internet of things (IoT), pose great challenges for the current 4G mobile network. Pattern division multiple access (PDMA), as a novel non-orthogonal multiple access scheme, has been proposed recently to address these challenges. The performance of PDMA uplink system mainly depends on the receiver algorithm. The conventional message pass algorithm (MPA) cannot fully exploit the benefits of the coded PDMA system. In this paper, we devise an advanced receiver via iterative detection and decoding (IDD) algorithm which fully exploits coding potentials and diversity gains of the PDMA. The simulation results show that IDD based advanced receiver obtains a performance improvement about 1.6 dB at block error rate (BLER) of 0.01 for 300% overload compared with the MPA based approach.