Satellite systems in a VSAT environment

The next generation of satellites is discussed and a Ka-band payload is proposed which will provide mesh connectivity at high data rates (e.g. 1 Mbit/s) directly between very small aperture terminals (VSATs) using a maximum antenna diameter of 1.5 m. It is demonstrated that there are no significant differences between Ku-band and Ka-band VSAT operations apart from propagation margins, which are analysed statistically over 650 European cities. It is shown that margins required for Ka-band operation are not excessive. A Ka-band satellite payload is proposed, based on frequency division multiple access, multibeam switching with dynamically controllable transponder bandwidths and gain. The payload adapts to traffic-loading requirements in its provision of multibeam connectivity and capacity. The signal format, modulation and coding technique used for transmission is unconstrained, except in terms of bandwidth, and this will allow advances in modulation and coding to take place during the lifetime of the satellite in orbit     

基于Ka波段DVB-S2卫星直播系统浅析

介绍了基于Ka波段DVB-S2卫星直播系统,分析了该系统的技术要点,讨论了Ka波段转发器及其关键部件技术的研究进展,并结合DVB-S2的传输特性分析了基于Ka波段DVB-S2的卫星直播系统的可行性.     

AN ADAPTIVE FEC SCHEME FOR Ka-BAND SATELLITE COMMUNICATIONS

Rain attenuation is the major problem for Ka-band satellite communications, and the fading due to rain can be well described by a lognormally distributed, first-order autoregressive model. Forward Error-control Coding (FEC) techniques can be used to reduce the effect of the rain attenuation, but the use of FEC causes a reduction in the bandwidth efficiency. In order to increase the bandwidth efficiency as well as maintain high link availability, an Adaptive Forward Error-control Coding (AFEC) scheme with rain fading prediction is proposed and analyzed in this paper. The results show that AFEC offers a good trade-off between link availability and bandwidth efficiency.     

Adaptive Coding and Modulation for the DVB-S2 Standard Interactive Applications: Capacity Assessment and Key System Issues

Point-to-point multibeam satellite systems based on the DVB-S standard are currently designed for link closure in the worst-case propagation and location conditions. The DVB-S standard, conceived for broadcasting applications, considers a fixed coding rate and modulation format that are selected according to the assumed coverage and availability requirements. This approach implies the occurrence of high margins in the majority of the cases, when interference and propagation conditions allow for higher signal-to-noise-plus-interference ratio. The adaptive coding and modulation (ACM) introduction in the new DVB-S2 standard for the interactive service profile opens up a number of appealing opportunities for the design and development of satellite broadband networks. In this article we show how the ACM introduction in the satellite downlink enables greatly enhanced system performance but also has a profound impact on the way the system and some of the key system components are designed.     

卫星通信中的信道编码与调制技术

本文首先研究了卫星通信中的信道编码与调制技术,并对广泛应用于卫星通信的DV B-S系列标准中的信道编码与调制技术进行了对比分析,最后提出了卫星通信采用更高级信道编码和调制技术的必然性。     

基于Ka频段的自适应MIMO调制算法

这里研究了一种应用于Ka频段卫星通信信道的自适应多输入多输出(MIMO,multiple-Input multiple-Out-put)调制算法,不同于一般Ka频段卫星通信的信道衰减补偿算法,该算法主要是能根据不同天气条件,利用MIMO系统的接收信噪比自适应的转换调制方式,以维持一定的目标比特率为目标,从而获取较高的系统吞吐量。仿真结果表明,该算法能有效应对Ka频段固定卫星通信信道下的严重信道衰落,兼顾系统性能和频谱效率,得到较高的吞吐量。     

QAM-OFDM卫星通信系统PAPR抑制方法研究

正交频分复用(OFDM)具有很高的频谱利用率和良好的抗多径衰落能力,是卫星通信备受关注的新技术之一。但OFDM信号峰值平均功率比(PAPR)较高的问题限制了其在卫星通信系统中的应用。针对卫星通信高数据率和高可靠性传输的要求,提出一种新的抑制QAM-OFDM信号PAPR的部分格状(PT)成形技术,分析了QAM-OFDM卫星通信系统在AWGN、频率选择性Rician衰落信道的误比特率性能。仿真实验表明,该技术不仅能有效降低QAM-OFDM信号PAPR,结合纠错编码还可大大改善OFDM卫星通信系统误比特率性能。     

宽带卫星通信中的ACM技术

采用自适应编码调制技术(ACM)的卫星数字视频广播新标准(DVB-S2)应用到宽带卫 星通信网中,将极大提升系统吞吐量,提供更丰富的交互式业务。从实际应用的角度,分析 了ACM的控制机制并提出其编码调制方案的简化方法。仿真结果表明,在几乎不影响系统性 能的前提下,该方案可以大幅降低ACM机制的复杂度。     

A generalized Chinese remainder theorem-based proactive multi-secret sharing scheme for global wide area network

Adaptive communication for is one of the hottest areas of research in the telecommunication systems including wireless broadcast systems. This is primarily accomplished for sake of boosting the transmission throughput with enhanced quality of service and ideal link utilization. In adaptive communication, various radio transmission parameters like modulation symbol, code-rate and power etc. are carefully chosen according to the erratic channel state information on the link. Digital video broadcast—second generation (DVB-S2) has an inbuilt support for adaptive coding and modulation (ACM). However, power adaptation is still a necessity because of power constraint in downlink where satellite has a limited power bank. Moreover, different downlinks have distinct transmit power requirements due to diverse ambient on earth receivers like rainy, foggy, stormy and with clear sky etc., hence flat transmit power distribution among all the ground receivers may not be a good idea at all. To utilize the ACM feature in DVB-S2 and to additionally adapt power, in this paper, an adaptive modulation, coding (MODCOD) and power scheme is proposed. By investigating a fuzzy system and differential evolution algorithm, to select the set of MODCODs and optimum power vector, respectively, for the next transmission interval. From the simulation results it is apparent that the proposed scheme is promising in terms of efficient link and transmit power utilization as well as quality of service compared to the schemes in the literature with flat power distribution.

     

DVB-S2: The Second Generation Standard for Satellite Broad-Band Services

DVB-S2 is the second-generation specification for satellite broad-band applications, developed by the Digital Video Broadcasting (DVB) Project in 2003. The system is structured as a toolkit to allow the implementation of the following satellite applications: TV and sound broadcasting, interactivity (i.e., Internet access), and professional services, such as TV contribution links and digital satellite news gathering. It has been specified around three concepts: best transmission performance approaching the Shannon limit, total flexibility, and reasonable receiver complexity. Channel coding and modulation are based on more recent developments by the scientific community: low density parity check codes are adopted, combined with QPSK, 8PSK, 16APSK, and 32APSK modulations for the system to work properly on the nonlinear satellite channel. The framing structure allows for maximum flexibility in a versatile system and also synchronization in worst case configurations (low signal-to-noise ratios). Adaptive coding and modulation, when used in one-to-one links, then allows optimization of the transmission parameters for each individual user,dependant on path conditions. Backward-compatible modes are also available,allowing existing DVB-S integrated receivers-decoders to continue working during the transitional period. The paper provides a tutorial overview of the DVB-S2 system, describing its main features and performance in various scenarios and applications.     

DVB-S2 LDPC Decoding Using Robust Check Node Update Approximations

Broadband satellite services to fixed terminals are currently offered in the forward link by the 2nd generation (2G) digital video broadcasting satellite (DVB-S2) standard. For this standard the use of powerful low-density parity-check (LDPC) error correcting codes has been adopted performing within approximately 1 dB from the Shannon capacity limit. This paper studies and compares for the first time in a systematic manner different approximation methods used in check node update computation of DVB-S2 LDPC decoding with the aim of reducing computational complexity. Various performance evaluation results are presented for a wide range of DVB-S2 parameters, such as LDPC codeword size, coding rate, modulation format and including several decoding algorithms. It is shown that the proposed check node update approximations have a robust behavior, i.e. the resulting performance is quite independent of the DVB-S2 modulation and coding parameters. It is further shown that these approximations perform very close to the optimal sum-product algorithm (SPA) in degradation, which is less than 0.2 dB. Despite this small degradation, the reduction in computational complexity compared to the optimal SPA is significant and can be as high as 40% in computational time savings.     

Space–Time Trellis Codes Based on Channel-Phase Feedback

Space-time coding (STC) has been proposed recently for multiple-antenna wireless communication systems. Most of the proposed STC schemes use the assumption that either no channel-state information, or the channel mean/covariance information, is available at the transmitter. In this paper, we propose a new STC scheme for a closed-loop transmission system, where quantized channel-phase information is available at the transmitter. A new performance criterion is derived for the quasi-static fading channel. This design criterion is then used to construct a new class of space-time trellis codes (STTCs). The proposed code construction is based on the concatenation of a standard multiple trellis-coded modulation outer code with an inner code. The inner code is selected from a series of inner codes using the channel-phase feedback. The series of inner codes are constructed based on the systematic set partitioning of several classes of space-time signal designs. Simulation results show significant performance improvement over the other STTCs in the literature. In addition, the proposed coding scheme enjoys low peak-to-average-power ratio, simple decoding, and power-efficient low-cost implementation     

Performance of DS/CDMA systems with differential M-ary orthogonal modulation and RS-coding for LEO satellite communications

This paper presents a coded modulation scheme based on M-ary orthogonal modulation by means of Walsh–Hadamard (WH) sequences, suitable for low-earth-orbit (LEO) direct sequence/code division multiple access (DS/CDMA) satellite communication systems. Based on the IS-95 scheme, we consider Reed–Solomon (RS)-coded M-ary orthogonal modulation with error or erasures decoding, which presents good performance enhancement with low complexity. LEO satellite links are characterized by large Doppler frequency shifts caused by the difference in velocity between the satellite and the earth mobile terminal, which make conventional non-coherent detection ineffective. In order to overcome the phase shift variations during the symbol period, which result in orthogonality loss of the WH sequences, we applied a differential encoding process to the spreading sequences or the WH chips prior to transmission. A special diversity process suitable for the environment under consideration is also applied. Simulation results show that the proposed diversity/coding/modulation scheme attains very good performance at low transmitter/receiver complexity. © 1998 John Wiley & Sons, Ltd.     

基于MP-WFRFT的多维联合调制卫星隐蔽通信研究

为进一步提高卫星信号的隐蔽性能,该文结合加权分数阶傅里叶变换(WFRFT)的星座混淆特性与混沌映射轨迹的抗截获特性,提出一种基于物理层安全的双极化卫星联合调制方案。借鉴“相位扰码”思想和“联合设计”理念,通过扩展4-WFRFT加权项参数,增加了卫星信号处理的多样性,在此基础上嵌入Logistic映射加密,提高了信息破解的难度。建立双极化卫星混沌安全传输系统模型,提出基于MP-WFRFT一体多维的组合隐蔽新概念,探索双极化卫星信号星座优化设计和裂变融合机理。仿真结果验证了所提方案的有效性。     

Efficient video transmission over correlated Nakagami fadingchannels for IS-95 CDMA systems

This paper deals with the problem of efficient transmission of video signals over generalized fading channels in direct sequence-spread spectrum (DS-SS) code division multiple access (CDMA) systems. We first propose a modified version of the H.263 video codec incorporating a selective forward error correction (FEC) coding scheme combined with a forced intra-frame update mechanism. The modified codec results in the improvement of the average video and frame-to-frame performance. We further consider a coherent DS-CDMA system for the forward link (base-to-mobile) in both single-cell and multiple-cell environment. We provide performance evaluation results by both analysis, employing the Gaussian approximation, and computer simulations, using Monte Carlo error counting techniques. By integrating the proposed video codec with a coherent DS-CDMA system based upon the IS-95 standard, we investigate the performance of the video transmission over frequency-selective, correlated Nakagami fading forward-link channels employing a RAKE receiver. To simulate the fading channel, we have implemented in software a correlated Nakagami fading simulator based upon the principle of superposition of complex partial waves, an approach which replicates the wave propagation process in actual physical situations. A variety of performance evaluation results, both in single-cell and multiple-cell environment, are presented for a different number of resolving paths, cell user capacity, signal propagation characteristics, as well as for the presence of channel estimation errors. Heuristic explanations and interpretations of the trend of the obtained results are also given     

Dynamic uplink frame optimization with adaptive coding and modulation in DVB‐RCS2 satellite networks

In the current generation of satellite networks, modulation and coding schemes can be dynamically changed in real‐time to face different link conditions. Therefore, the link budget is not anymore required to be computed under the worst case, with relevant advantages in terms of efficiency. The new digital video broadcasting‐return channel via satellite 2 standard extends the dynamic modulation and coding to the return link: by using different modulation and coding schemes within the uplink frame, the terminals experiencing good link conditions transmit at very high bitrates, whereas the terminals experiencing fade events transmit at lower bitrates. This paper addresses the problem of optimizing the uplink frame modulation and coding schemes based on the current link conditions experienced by the terminals and on their transmission capacity requirements. The problem is formulated as an Integer Program and an efficient Linear Program approximation is proposed. Simulation results validate the proposed approach. Copyright © 2013 John Wiley & Sons, Ltd.     

Interference Studies Between Adjacent Satellite Communications Systems operating Above 10 GHz and Using Power Control as Fade Mitigation Technique

Interference problems are arising from the spectral coexistence between satellite communication networks that operate at frequencies above 10 GHz and particularly when they employ power control as fade mitigation technique. This situation is aggravated due to tropospheric propagation phenomena. In this frequency range, rain attenuation is considered to be the dominant tropospheric fading mechanism. The conditional acceptable intersystem interference probability of the Carrier-to-Interference Ratio of a satellite terminal interfered by an adjacent satellite network is defined as a figure of merit and analytically calculated taking into account a physical-mathematical model for the rainfall medium. The correlated propagation fading phenomena over multiple slant paths are accurately incorporated. The proposed model is flexible and can be applied on a global scale since it incorporates the local climatic conditions concerning the point rainfall rate and the spatial rainfall inhomogeneity. Useful numerical results of the proposed model are obtained and the impact of various crucial operational and geometrical parameters of satellite networks’ coexistence is examined. The numerical results have been also verified through simulations using a multi-dimensional rain attenuation synthesizer. Finally, simple and easy-calculated formulas for the satellite communication designers for back of the envelope computations are given.     

基于无速率码的遥感数据自适应传输技术

基于自适应编码调制的遥感数据传输方案实现了传输速率阶梯式换挡,但未能充分利用链路余量。为进一步提高遥感卫星数据传输过程中的频谱效率,提出了基于无速率码的遥感数据自适应传输技术。将无速率码与QPSK、8PSK、16QAM、64QAM调制方式结合,通过设定译码成功概率阈值得到离散信噪比下的最佳译码开销和最佳码率值。采用多项式拟合求得卫星过境期间码率值的变化情况,进而得到有效数据率变化曲线,实现了遥感卫星过境时段内有效数据率随仰角的无缝切换。通过求解有效数据率曲线的积分值,得到了采用联合译码算法的Raptor码在4种方案下的传输数据量。分析结果表明,与第二代数字卫星电视广播标准（DVB-S2）中的自适应编码调制方案相比,所提出的传输方案使传输数据量提高了10.29%~27.65%,且在信噪比低至-5 dB的情况下也可以进行数据自适应传输。     

Link adaptation and SINR errors in practical multicast multibeam satellite systems with linear precoding

The application of linear precoding at the gateway side enables broadband multibeam satellite systems to use more aggressive frequency reuse patterns increasing the overall capacity of future high-throughput satellites (HTS). In any practical precoded system, receivers can estimate only a few coefficients of the channel state information (CSI), while the others, in what is known as nullification, are set to zero. In this paper, the impact of the CSI nullification to the SINR estimation is analyzed statistically and geographically for a multicast multibeam satellite system. The errors in the SINR calculated by the gateway affect to the modulation and coding schemes (MCSs) selection, increasing the rate of erroneous frames or leading to an underutilization of the available resources. Therefore, as countermeasure, a link adaptation algorithm based on an adaptive margin per user is proposed, helping to achieve the error rate constraints of DVB-S2X systems without compromising the throughput, even under severe CSI degradation due to nullification and Rician fading.     

DVB-S2及其相关技术

论述了卫星数字广播标准DVB-S2制定的必要性及其技术特点。DVB-S2采用高阶调制,信道编码采用LDPC码与BCH码相结合,信道纠错能力可达到Es/N0优于10-7。介绍了香浓极限以及DVB-S2系统的结构组成,并详细介绍了各模块的功能。由于DVB-S2适用于单码流或多码流输入,故它支持多种业务,给卫星数字广播开辟了新的应用领域。为了不使DVB-S接收机作废,DVB-S2采用了向后兼容广播模式。