Next‐generation global satellite system with mega‐constellations

Mega satellite constellations in low earth orbit (LEO) will provide complete global coverage; rapidly enhance overall capacity, even for unserved areas; and improve the quality of service (QoS) possible with lower signal propagation delays. Complemented by medium earth orbit (MEO) and geostationary earth orbit (GEO) satellites and terrestrial network components under a hybrid communications architecture, these constellations will enable universal 5G service across the world while supporting diverse 5G use cases. With an unobstructed line‐of‐sight visibility of approximately 3 min, a typical LEO satellite requires efficient user terminal (UT), satellite, gateway, and intersatellite link handovers. A comprehensive mobility design for mega‐constellations involves cost‐effective space and ground phased‐array antennas for responsive and seamless tracking. An end‐to‐end multilayer protocol architecture spanning space and terrestrial technologies can be used to analyze and ensure QoS and mobility. A scalable routing and traffic engineering design based on software‐defined networking adequately handles continuous variability in network topology, differentiated user demands, and traffic transport in both temporal and spatial dimensions. The space‐based networks involving mega‐constellations will be better integrated with their terrestrial counterparts by fully leveraging the multilayer 5G framework, which is the foundational feature of our hybrid architecture.     

Corona Based Optimal Node Deployment Distribution in Wireless Sensor Networks

This paper shows the trade off between different modulation techniques such as multi level quadrature amplitude modulation, multi level phase shift keying, and multi level differential phase shift keying for upgrading direct detection optical orthogonal frequency division multiplexing systems with possible transmission distance up to 15,000 km and total bit rate of 2.56 Tb/s. The 2.56 Tb/s signal is generated by multiplexing 64 OFDM signals with 40 Gb/s for each OFDM. Variations of optical signal to noise ratio (OSNR), signal to noise ratio (SNR), and bit error rate (BER) are studied with the variations of transmission distance. Maximum radio frequency power spectrum, and output electrical power after decoder are measured for different multi level modulation techniques with carrier frequency. It is observed that multi level QAM has presented better performance than multi level PSK and finally multi level DPSK in optical OFDM systems. Maximum output power after decoder is enhanced with both 32-PSK, and 64-QAM. Quadrature signal amplitude level at encoder is upgraded with 64-QAM. It is noticed that OSNR, SNR, and BER are improved using 4-QAM OFDM system than either QPSK or 4-DPSK.     

Effects of LDPC Code on the BER Performance of MPSK System with Imperfect Receiver Components over Rician Channels

In this letter, we study the influence of receiver imperfections on bit error rate (BER) degradations in detecting low‐density parity‐check coded multilevel phase‐shift keying signals transmitted over a Rician fading channel. Based on the analytical system model which we previously developed using Monte Carlo simulations, we determine the BER degradations caused by the simultaneous influences of stochastic phase error, quadrature error, in‐phase‐quadrature mismatch, and the fading severity.     

A high‐speed long‐haul wavelength division multiplexing–based inter‐satellite optical wireless communication link using spectral‐efficient 2‐D orthogonal modulation scheme

In this work, we propose a novel multi‐bit/symbol spectral‐efficient optical orthogonal modulation scheme based on simultaneously modulating differential quadrature phase shift keying (DQPSK)‐polarization shift keying (PolSK) in a 16‐channel wavelength division multiplexing (WDM)‐based inter‐satellite optical wireless communication (IsOWC) system. Through numerical simulations, we demonstrate a reliable transportation of 16 × 100 Gbps information over 25 000 km of transmission range with acceptable bit error rate (BER) using the proposed system. Further, the impact of space turbulences (ie, pointing error losses) on the BER performance of the proposed IsOWC link has been evaluated using numerical simulations. The simulation results report a successful transportation of information up to 2.7 μrad receiver pointing error angle with acceptable performance.     

Transmission performance analysis of Multi-Carrier Modulation in frequency selective fast Rayleigh fading channel

In this paper, we discuss the transmission performance of Multi-Carrier Modulation (MCM) in frequencyselective fast Rayleigh fading channels. First, we optimize the transmission parameters of MCM withM-ary differential phase shift keying/differential detection (DPSK):the guard duration andthe number of sub-carriers for frequency-selective fast Rayleigh fading channels, and then show the bit error rate (BER) performance of the optimizedM-ary DPSK MCM. Next, we propose an MCM with pilot-assistedM-ary quadrature amplitude modulation/coherent detection (QAM), and discuss the BER performance when we reduce the number of pilot signals from the view-point of frequency-time utilization efficiency. Finally, we propose a two-stage frequency offset compensation method.     

Performance analysis of hybrid transmit antenna selection/maximal‐ratio transmission in Nakagami‐m fading channels

Hybrid diversity systems have been of great importance because they provide better diversity orders and robustness to the fading effects of wireless communication systems. This paper focuses on the performance analysis of multiple‐input gle‐output systems that employ combined transmit antenna selection (TAS)/maximal‐ratio transmission (MRT) techniques (i.e., hybrid TAS/MRT). The probability density function, the moment generating function and the n ^th order moments of the output signal‐to‐noise ratio of the investigated diversity scheme are derived for independent identically distributed flat Nakagami‐m fading channels. The system capacity of the hybrid TAS/MRT scheme is examined from the outage probability perspective. Exact bit/symbol error rate (BER/SER) expressions for binary frequency shift keying, M‐ary phase shift keying and square M‐ary quadrature amplitude modulation signals are derived by using the moment generating function‐based analysis method. By deriving the upper bounds for BER/SER expressions, it is also shown that the investigated systems achieve full diversity orders at high signal‐to‐noise ratios. Also, by Monte Carlo simulations, analytical performance results are validated and the effect of feedback delay, channel estimation error and feedback quantization error on BER/SER performances are examined. Copyright © 2011 John Wiley & Sons, Ltd.     

Turbo‐coded APSK modulations design for satellite broadband communications

This paper investigates the design of power and spectrally efficient coded modulations based on amplitude phase shift keying (APSK) modulation with application to satellite broadband communications. APSK represents an attractive modulation format for digital transmission over nonlinear satellite channels due to its power and spectral efficiency combined with its inherent robustness against nonlinear distortion. For these reasons APSK has been very recently introduced in the new standard for satellite Digital Video Broadcasting named DVB‐S2. Assuming an ideal rectangular transmission pulse, for which no nonlinear inter‐symbol interference is present and perfect pre‐compensation of the nonlinearity, we optimize the APSK constellation. In addition to the minimum distance criterion, we introduce a new optimization based on the mutual information; this new method generates an optimum constellation for each spectral efficiency. To achieve power efficiency jointly with low bit error rate (BER) floor we adopt a powerful binary serially concatenated turbo‐code coupled with optimal APSK modulations through bit‐interleaved coded modulation. We derive tight approximations on the maximum‐likelihood decoding error probability, and results are compared with computer simulations. The proposed coded modulation scheme is shown to provide a considerable performance advantage compared to current standards for satellite multimedia and broadcasting systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Statistical channel modelling and performance evaluation in satellite personal communications

This paper is concerned with channel modelling for satellite personal communications and with the associated problem of performance evaluation. Channel characteristics for personal communications tend to differ from those traditionally accepted for vehicular communications. In this paper we report on modelling aspects for both wideband and narrowband personal communications. Then we consider performance evaluation for low-altitude earth orbit (LEO) satellite systems in terms of bit error probability and outage probability. To evaluate the outage probability for LEO systems, a tight and simple upper bound is finally provided. © 1998 John Wiley & Sons, Ltd.     

On the Transceiver Types of IR-UWB Systems at Sub-Nyquist Sampling Rates

In this paper, we present a unified performance analysis for different impulse radio (IR) ultra-wideband (UWB) transceiver types employing various modulation options and operating at sub-Nyquist sampling rates. Stored reference (SR), transmitted reference (TR), and energy detector (ED) receivers are considered employing one of the binary phase shift keying (BPSK), pulse position modulation (PPM), and on-off keying (OOK) modulation types. Realistic UWB channel models (the IEEE 802.15.4a channels) and practical pulse shapes (the root-raised cosine pulse) are used to characterize the statistics of the captured energies of different transceiver types at low sampling rates. The bit error rate (BER) expressions for different transceiver/modulation types are provided explicitly in additive white Gaussian noise channels. In multipath channels, the BER expressions are conditioned on the captured energies; then, the captured energy histograms at sub-Nyquist rates are used towards a semi-analytic evaluation of the BER for different transceiver/modulation combinations. The analyses are then verified via simulations using IEEE 802.15.4a channel models. The results show that in addition to their lower implementation complexities, the TR and ED receivers may be more favorable compared to SR receivers at low sampling rates in terms of their BER characteristics as well.

基于双重调制技术的可见光通信系统研究

LED调制带宽制约着可见光通信(VLC) 系统的数据传输速率。为此,提出一种基于双重调制技术COB(chip on board)封装 的LED灯具,通过实现16级脉冲振幅 调制(PAM),将系统数据传输速率提升4倍;结合脉冲宽度调制(PWM)技术 进行调光,同时兼顾室内的照明及通信。采用Matlab软件模拟仿真视频传输试 验。结果表明,在相同信噪比(SNR)的情况下,基于双重 调制技术的VLC系统的误码率(BER)比传统使用开关键控(OOK)调控技术系 统的BER更低。本文系统在不增加器件带宽前提下,成倍提高了无线通信的 质量与 数据传输速率;从照明与通信的角度优化了VLC系统的信源,具有广阔的 应用前景。     

Performance comparisons for adaptive LEO satellite links

This paper considers the potential to achieve improved throughput in time‐varying satellite links which have flexibility in information bit rate and/or transmit power. We assume that other parameters of the link budget such as antenna gains and operating frequency are fixed. Simple results are derived, which illustrate what improvements in data throughput or power consumption are possible under two low‐earth orbit scenarios: inter‐satellite links and satellite to ground communications. Copyright © 2006 John Wiley & Sons, Ltd.     

Analyzing GPS signals to investigate path diversity effects of non‐geostationary orbit satellite communication systems

The concept behind path diversity is that a user who can access several satellites simultaneously will be able to communicate more effectively than a user who could only access one. The success of this method depends on the environment, the satellite constellation, and diversity combining technology. This paper explores the path diversity effects of non‐geostationary orbit (NGO) satellite personal communication services, for different degrees of user mobility, under various scenarios, using the constellation of the global positioning system (GPS). Measurements are taken near downtown Taipei. Three types of mobilities (fixed‐point, pedestrian, and vehicular) are examined, and the switch diversity and maximum ratio combining method are applied to determine the path diversity gain and calculate bit error probability. The error probability performance of applying diversity schemes in coherent binary phase shift keying (BPSK) and non‐coherent differential phase shift keying (DPSK) modulations over Rician fading channels are also analysed and evaluated by using the characteristic function method. The results show that fading can be significantly reduced and diversity greatly increased. A significant diversity gain and improvement in bit error rate (BER) can be expected in all cases by simply applying switch diversity scheme. Besides, for the maximum ratio combining method, the results imply that summing two satellite signals suffices to increase diversity and improve the bit error rate performance. Copyright © 2002 John Wiley & Sons, Ltd.     

Enhancing spectral efficiency of FSO system using adaptive SIM/M‐PSK and SIMO in the presence of atmospheric turbulence and pointing errors

This paper proposes an adaptive transmission modulation (ATM) technique for free‐space optical (FSO) links over gamma‐gamma turbulence channels.The ATM technique provides efficient utilization of the FSO channel capacity for improving spectral efficiency, by adapting the order of the phase‐shift keying modulation scheme, according to the channel conditions and the required bit error rate (BER). To overcome the channel degradation resulting from the turbulence effects as well as the pointing errors (PEs), single‐input multiple‐output (SIMO) system with maximal ratio combining (MRC) is proposed. Exact closed‐form expressions of BER and upper bound of the capacity are derived and verified by Monte Carlo simulations. The numerical results show that the proposed adaptive technique improves the spectral efficiency (SE) five times higher than the nonadaptive technique at the same BER threshold (10^?3).This improvement is achieved at signal‐to‐noise ratio (SNR) equals 27 and 42  dB in the case of atmospheric turbulence without and with PE, respectively. Furthermore, this SE could be obtained while the SNR = 30  dB by using ( 1 × 4 ) SIMO scheme with MRC and PE and having the same transmitting optical power.     

Performance Enhancement of Gaussian Minimum Shift Keying Using Optimum Phase Sampling Technique for Turbulent Free-Space Optical Communication

In this paper, analytical performances of Gaussian minimum shift keying (GMSK) are studied for free space optical communication system. Authors propose an innovative sampling technique called, optimum phase sampling technique to investigate the bit error performance of GMSK modulation. Subsequently, performances of GMSK like, bit error rate (BER), power spectral density, and adjacent carrier interference (ACI) have also been investigated and compared with other modulation techniques. Furthermore, return to zero (RZ) coding input bit stream prior to GMSK technique improves the ACI performance of GMSK. To end with, we present the improvement of degradation parameter (γ) in a tabular form through phase sampling technique. Moreover, both optimum phase sampling and narrow pulse shaping of RZ-GMSK obtains near optimal result of BER. The numerical results show, that the proposed phase sampled RZ-GMSK of 70% duty cycle at BT?=?0.6 has a degradation value of 0.979, which is comparable to GMSK at BT?=?∞. Moreover, the proposed RZ-GMSK achieves lower ACI value and has an error rate of 7?×?10^?7, which is lower than the GMSK of 1?×?10^?6 BER value.

     

Topological design,routing and capacity dimensioning for ISL networks in broadband LEO satellite systems

This paper considers the network design of intersatellite link (ISL) networks in broadband LEO satellite systems, where the major challenge is the topology dynamics. First, a general method to design convenient ISL topologies for connection‐oriented operation is presented, and a reference topology for numerical studies is derived. A permanent virtual topology is then defined on top of the orbiting physical one, thus forming a framework for discrete‐time dynamic traffic routing. On this basis, heuristic and optimization approaches for the combined routing and dimensioning task, operating on discrete time steps, are presented and their performance is numerically compared. It is shown that minimizing the worst‐case link capacity is an appropriate target function, which can be formulated as linear optimization problem with linear constraints. Using linear programming (LP) techniques, the dimensioning results are clearly better than with simple heuristic approaches. Copyright © 2001 John Wiley & Sons, Ltd.     

Low peak‐to‐average power ratio and efficient multicarrier spread spectrum transceivers using hybrid and quadrature cyclic shift orthogonal keying

This paper proposes two bandwidth and power efficient multicode multicarrier spread spectrum (MCSS) system modes based on a new cyclic shift orthogonal keying (CSOK) scheme that leads to low peak‐to‐average power ratio (PAPR) signals. Both system modes can improve the bandwidth efficiency by loading more data bits per symbol block. The first system mode is the hybrid CSOK (HCSOK) mode, which combines phase shift keying (PSK) or quadrature amplitude modulation (QAM) modulation symbol with the CSOK symbol, for example, the important hybrid quadrature PSK (QPSK)–CSOK case. The second is the quadrature CSOK (QCSOK) mode that transmits two parallel binary phase shift keying (BPSK)–CSOK branches at the same time. For both modes, maximum likelihood receivers are derived and simplified, leading to efficient fast Fourier transform‐based structures for maximum ratio combining and cyclic‐code correlation. Theoretical bit error rate (BER) analysis is conducted for the hybrid QPSK–CSOK case. Simulation results demonstrate that both the two system modes considerably outperforms the traditional Walsh‐coded MCSS system in terms of bandwidth efficiency, PAPR, BER, and antijamming capability. Furthermore, in indoor channel, QCSOK performs slightly worse than QPSK–CSOK, but it has almost twice the data rate when the code length is large. Copyright © 2011 John Wiley & Sons, Ltd.     

CDF and MGF based analysis over Rayleigh TWDP shadowed fading channel for indoor communication

Recently, the two-wave with diffuse power (TWDP) distribution has been extensively used to model the shadowing in multipath-faded/shadowed indoor environment. In this article, novel expressions for joint moments, mean, second moment, variance and cumulative distribution function for Rayleigh TWDP shadowed fading model are derived. By using the derived expression of mean and variance, the expression for amount of fading is obtained. Also, the outage probability, moment generating function and average bit error rate (ABER) for various modulation schemes namely binary phase shift keying (BPSK), binary frequency shift keying (BFSK), minimum shift keying (MSK), differentially coherent phase shift keying (DCPSK) and non-coherent frequency shift keying (NCFSK) are calculated. The derived expressions for cumulative distribution function, outage probability and ABER are presented in analytical format and have been numerically evaluated. Moreover, the numerical results of ABER using MSK and DPSK modulation schemes is compare with results of Rayleigh Gamma composite fading model. The study shows that better outage probability (0.01) is observed at 40dB average signal to noise ratio (SNR) with 5dB lowest threshold SNR, however, at higher threshold SNR (>5dB) with fixed average SNR (40dB), poor outage probability performance are obtained. Further, at higher shadowing (10dB), for fixed average SNR (15dB), minimum error probability (10^?4) is observe, while at lower shadowing (less than 10dB), higher error probability (greater than 10^?4) is observed that represents poor BER performance.     

Performance analysis of impulse‐radio ultra‐wideband energy detector system using cooperative dual‐hop amplify and forward strategy

A novel analytical representation of bit error rate (BER) performance of an impulse‐radio ultra‐wideband energy detector on–off keying system using cooperative dual‐hop amplify and forward relay technology, with various diversity combining schemes over IEEE 802.15.4a environment is presented in this paper. In particular, the approximate expressions based on energy detection principle are derived for various diversity combining cases, namely linear optimal combining, linear combining, and selective combining. Simulation results depict an improvement in BER performance, with increase in number of relay paths (L ) and decrease in number of frames per symbol (N _f ). Furthermore, the BER performance of the impulse‐radio ultra‐wideband energy detector on–off keying system improves substantially using dual‐hop cooperative amplify and forward scheme, compared with that of non‐cooperative or single link scenario. Among the diversity combining schemes, linear optimal diversity combining performs better when compared with linear diversity combining and selective combining. The analytical BER expressions are validated with the simulation results, which confirm the accuracy and precision in approximation used in the investigation of BER. Copyright © 2015 John Wiley & Sons, Ltd.     

Cross‐level PRC transmitter for TH‐PAM UWB systems

A cross‐level pre‐RAKE combining (PRC) scheme for time hopping pulse amplitude modulation ultra wideband (TH‐PAM UWB) transmitter is studied in this paper. A two‐stage cross‐level PRC (CL‐PRC) scheme is proposed. The conventional PRC schemes suppress all the chip‐wise interference. However, the proposed scheme suppresses only the specific frame‐wise inter‐symbol interference (ISI) by exploiting the characteristic that the information bits are transmitted only at ultra short time slots. This results in a low complexity pre‐equalizer without bit error rate (BER) performance degradation. Furthermore, an order selection rule is presented to achieve the tradeoff between signal‐to‐interference ratio (SIR) and computational complexity. Simulation results illustrate the superior SIR and BER performance of our proposal. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance of zero cross correlation resultant weight spectral amplitude codes in lower Earth orbit‐based optical wireless channel system

A consolidated performance investigation and design of newly constructed zero cross correlation resultant weight (ZCCRW) code is presented without mapping over optical wireless channel (OWC) in lower Earth orbit (LEO). Multiple access interference (MAI) is suppressed by incorporating proposed 1‐D code at 10 Gbps with an algorithm. A further state of the art comparison of diverse optical code division multiple access (OCDMA) codes such as multi diagonal codes and diagonal double weight codes is accomplished with proposed code in terms of root mean square (RMS) jitter, extinction ratio, MAI, quality factor (QF), and bit error rate (BER) at different linewidths, chip sizes, link lengths, and active users. It is perceived that for ZCCRW code, QF obtained is 16.5 for chip size (0.1 ns), and at 4000 km, BER 10^‐9 is achieved using the forward error correction (FEC) technique. OWC system in LEO with lasers in spectral amplitude code (SAC) OCDMA is proposed for the first time as per the author's best knowledge.