Direct-sequence spread spectrum in a shadowed Rician fading andland-mobile satellite channel

The performance of a direct-sequence spread-spectrum land-mobile satellite transmission system, using binary phase-shift keying (BPSK) modulation, is analysed. The satellite channel is modeled as having Rician fading characteristics. The bit-error probability is evaluated, considering both the envelope and the phase variation. Assuming a Gaussian approximation for the interference, numerical results are obtained for both spread-spectrum and narrowband land-mobile satellite communication systems with BPSK modulation. A comparison of the two systems is made for light, average, and heavy shadowing     

Statistical observations of data transmission over land mobilesatellite channels

It is shown how Rician fading limits the performance of the HDLC protocol. It is observed that for accurate reception, a packet must be transmitted entirely during an interfade interval. This means that packets ought to be sufficiently short so that most of them fall in the interfade time intervals. This leads to a high transmission efficiency. Consequently, the HDLC protocol is more efficient with shorter packets. However, a smaller packet size increases the overhead fraction of the packet and thereby reduces the effective throughput. In addition, the HDLC peak efficiency and optimum packet size increase with increasing fade margin and decrease with increasing vehicle velocity. Among other effects, the bit rate of the land-mobile satellite system channel is the most critical for optimum packet size and HDLC efficiency. Thus, a low bit rate implies long packet duration for a moderate packet size in bytes     

Issues in Terrestrial/Satellite Network Synchronization

This paper examines the key issues involved in choosing synchronization techniques applicable to both terrestrial and satellite switching networks. The terrestrial networks considered involve circuit switching, message switching, packet switching, and other integrated voice/data nodal configurations. The satellite networks considered involve time-division multiple access (TDMA) systems and their associated synchronization problems. Peculiar problems associated with satelliteswitched TDMA (SS/TDMA) network synchronization are also addressed. Finally, the issues involved in synchronizing integrated satellite/terrestrial networks are addressed. Emphasis will be placed on assessing the state of the art of current terrestial/satellite synchronization technology and projecting future trends.     

An improved π/4-QPSK with nonredundant error correction forsatellite mobile broadcasting

An improved π/4-quadrature phase-shift keying (QPSK) receiver that incorporates a simple nonredundant error correction (NEC) structure is proposed for satellite and land-mobile digital broadcasting. The bit-error rate (BER) performance of the π/4-QPSK with NEC is analyzed and evaluated in a fast Rician fading and additive white Gaussian noise. (AWGN) environment using computer simulation. It is demonstrated that with simple electronics the performance of a noncoherently detected π/4-QPSK signal in both AWGN and fast Rician fading can be improved. When the K-factor (a ratio of average power of multipath signal to direct path power) of the Rician channel decreases, the improvement increases. An improvement of 1.2 dB could be obtained at a BER of 10^-4 in the AWGN channel. This performance gain is achieved without requiring any signal redundancy and additional bandwidth. Three types of noncoherent detection schemes of π/4QPSK with NEC structure, such as intermediate frequency band differential detection, baseband differential detection, and FM discriminator, are discussed. It is concluded that the π/4-QPSK with NEC is an attractive scheme for power-limited satellite land-mobile broadcasting systems     

Packet radio performance of inhibit sense multiple access withcapture

Current portable and land-mobile radio systems employ frequency modulation which exhibits a distinct capture effect. Furthermore, multipath propagation, shadowing, and the spatial distribution of the terminal units create data packets with varying signal strength. We investigate the performance of nonpersistent inhibit sense multiple access (ISMA) applied to the forward channel of packet radio communication networks. We show that the aggregate capacity of ISMA substantially increases compared to the noncapture case for small capture ratios. The mean packet delay of ISMA is also reduced with capture. The effect of different signal strength distribution is explored, and the capacity and delay improvements discussed     

星地时钟同步方案设计及性能分析

在宽带卫星通信系统中,星载通信设备与地面通信设备间的时钟同步性能将会直接影响到整个卫星通信网络的性能。针对基于星上处理和星上交换的宽带卫星通信系统的技术特点,设计了3种星地时钟同步方案,并从链路传输滑动损伤、接收缓存容量、时钟信号的抖动和漂移等几个方面对星地时钟同步方案的性能进行了比较和分析,总结了上述几种同步方式的优缺点,最后给出了建议的星地时钟同步方式。     

Packet scheduling in MIMO satellite long term evolution networks

This paper deals with the performance evaluation of different packet scheduling schemes for Long Term Evolution mobile satellite systems based on the adoption of a multi‐user MIMO technique. The major breakthrough of MIMO technology in terrestrial networks has motivated the interest here for the adoption of MIMO in mobile satellite systems as well. In particular, a land mobile dual‐polarized GEO satellite system has been considered in this work. The aim of this paper is to propose new cross‐layer packet scheduling schemes that achieve a good trade‐off among throughput, QoS and fairness and to conduct performance comparisons with other scheduling schemes in the literature. This is the reason why this paper also proposes a new performance index that can be used to evaluate the overall performance of each scheduler. The work shows that the new cross‐layer scheduler, called channel‐based queue sensitive scheduler, attains the best performance in terms of the new comprehensive performance index, thus representing an interesting solution for future mobile satellite systems. Copyright © 2015 John Wiley & Sons, Ltd.     

SP-QPSK: a new modulation technique for satellite and land-mobiledigital broadcasting

A new modulation technique, SP-QPSK (sinusoidal shaped π/4-QPSK), suitable for land-mobile and satellite digital-broadcasting systems applications is introduced. In digital data and/or sound broadcasting systems, which may have a relatively low bit-rate transmission requirement, the residual phase noise introduced by the Doppler shift of moving vehicles presents a high bit-error floor in coherently demodulated systems. The overall performance of noncoherent systems is frequently superior in a mobile radio environment. In addition, to satisfy the high-power and spectral-efficiency requirements of emerging digital-broadcast systems, nonlinear saturated amplifiers may become essential subsystems. The performance of the new generation of SP-QPSK systems is investigated experimentally and by computer simulations. Digital signal processing implementation techniques have been used in the experimental prototype design. The authors demonstrate that nonlinearly amplified SP-QPSK has a 10-dB-lower out-of-band radiated power than conventional QPSK and it is suitable for differential and discriminator detection     

Modeling and simulation of mobile satellite propagation

Mobile satellite systems are subject to severe fading due to blockage of the line-of-sight (LOS) path by roadside vegetation. A thorough understanding of the fading effects is necessary for the design of a reliable land-mobile satellite system. Analytical and empirical models are presented for predicting fade statistics for vegetative shadowing of mobile satellite terminals. A software simulator for generating simulated fade data is also presented. A physical model relating physical path parameters to propagation model parameters is presented, and results using the model are shown     

基于最大似然算法的OFDM同步技术研究

同步问题是卫星通信中的一个关键问题,直接关系到通信系统的性能。文中简要介绍了OFDM的同步技术,主要讨论了符号定时同步和载波同步。最大似然估计算法在OFDM符号定时同步和载波频率同步中得到了广泛的应用,通过最大似然估计方法,避免了基于导频符号的同步估计带来的频率和功率资源的浪费,通过仿真可以看到,能够很好地实现OFDM系统的符号同步和载波同步。     

Performance analysis of CFDAMA-PB protocol for packet satellitecommunications

Combined free/demand-assignment multiple-access (CFDAMA) schemes are suitable for broad-band packet satellite communications systems serving a finite number of bursty data sources. The performance analysis of the CFDAMA using piggy-backed (PB) reservation is presented. The probability generating function (PGF) of the packet delay is developed. The performance is evaluated in terms of three performance measures: average packet delay, variance of packet delay, and cumulative probability distribution of packet delay. Performance comparison with other pertinent schemes shows CFDAMA-PB to be superior for a wide range of user population sizes     

Admission control and handover management for high‐speed trains in vehicular geostationary satellite networks with terrestrial gap‐filling

Following a recent upgrade, the Digital Video Broadcasting—Return Channel Satellite (DVB‐RCS) standard sets up to support terminal mobility. In this scenario, integration with terrestrial systems becomes a primary concern to ensure network connectivity in urban areas. This article proposes an integrated satellite–terrestrial architecture for the provision of broadband services onboard high‐speed trains, in which terrestrial cellular networks are seen as viable gap‐fillers for discontinuous satellite coverage. We derive an analytical model of the hybrid DVB‐RCS‐cellular system by exploiting analogies between the mobility pattern predictability of LEO constellations and that of high‐speed trains. Terminals whose QoS cannot be guaranteed by the satellite segment are proposed to temporarily divert the connections towards the terrestrial infrastructure, where available. Using an iterative approach based on the Erlang fixed‐point approximation, we show performance improvements with respect to stand‐alone satellite systems in terms of handover failure probability and overall resource utilization. The analytical model is also validated via our ns2‐based DVB‐RCS packet‐level simulator. Detailed modelling of synchronization and signalling mechanisms confirms the accuracy of the analytical results, and shows that topology and mobility information can contribute to refine radio resource utilization optimality when used jointly. Copyright © 2009 John Wiley & Sons, Ltd.     

Correlation model for shadow fading in land-mobile satellitesystems

A simple yet accurate correlation model for shadow fading in land-mobile satellite systems, derived from L and S-band channel recordings, is proposed. The model has been developed for heavily wooded and suburban environments and covers elevation angles of 60-80°. It is demonstrated that in such environments the effective correlation distance of shadowing is in the order of a few tens of meters     

Analysis of a new multiaccess/switching technique for multibeamsatellites in a prioritized ISDN environment

A performance analysis to compute the packet loss, call blocking, and packet delays of a typical user in an integrated voice-data-video satellite internetworking environment is discussed. The uplink technique used is a hybrid packet/circuit switched approach of the demand assignment type, while the downlink is a time-division-multiplexing (TDM) technique. Onboard the satellite, a baseband nonblocking switch is used to route the packets from input to output ports. Various amounts of input and output buffering as well as priority rules and blocking resolution algorithms are used. The authors conduct a performance analysis for the problems at hand and identify the best ranges for the different parameters involved     

Standardization on performance objectives of satellite systems using adaptive coding and modulation

The radiocommunication part of the International Telecommunication Union (ITU‐R) establishes the standards for wireless communications. Recommendation ITU‐R S.1062 specifies the performance objectives for satellite communication systems providing constant bit rate service. However, this is not applicable to most modern satellite communication systems utilizing adaptive coding and modulation (ACM) schemes to compensate for channel impairments, especially for systems operating in high frequency bands. For this reason, ITU‐R recently developed Recommendation ITU‐R S.2131 that is suitable for satellite systems with ACM. The developed Recommendation provides a method to determine performance objectives for satellite systems using ACM. Two possible objective parameters are presented, including packet error rate and spectral efficiency. This paper presents the standardization process, and the background used to establish new performance objectives. In addition, interpretations of the objectives are given by using estimation results for two different propagation characteristics.     

The simulation modelling and performance analysis of low earth orbit satellite communication networks for personal communications

This paper extends previous research efforts related to the simulation performance modelling and analysis of satellite communication networks. Specifically, the use of low earth orbit (LEO) satellite networks for personal communications is examined. Six different satellite constellation configurations are investigated in a packet‐switched operating environment. Performance metrics examined are the end‐to‐end packet delay and the utilization of satellite channels in the dynamic environment. Realistic and accurate models of the physical satellite network and its terrestrial transmitters require that numerous operating characteristics and assumptions be specified. These are based on proposed design requirements of commercial systems, such as Iridium. Via the use of simulation, we show the relative delay and utilization performance of differing satellite network architectures. From these simulation models, mathematical metamodels are derived for the system delays. These innovative models are used to predict the delay performance of different network architectures not previously simulated. Comparison of these metamodels with simulation results show that metamodels provide an accurate means for performance prediction. Copyright © 1999 John Wiley & Sons, Ltd.     

Performance evaluation of channel-sensitive, stabilized multipleaccess schemes for land-mobile satellite services using a hybridsimulation tool

A hybrid simulation tool for real-time performance measurements of complete networks is presented. The simulation tool combines the advantages of software and hardware modules. Recorded channel data are included. They allow the reproduction of realistic situations in the laboratory. Synchronization problems and noise are considered. As an example, stabilized slotted ALOHA access protocols were implemented and investigated in land-mobile satellite environments. A slotted ALOHA-based modified channel access strategy for highly unreliable channels is proposed requiring all mobile stations to estimate the link quality before starting a transmission. The different strategies are analyzed by simulation as well as the analytical methods. Transmission parameters are determined and optimized using a combination of analysis and simulation. The results show the power of the simulation tool and the better performance of stabilized slotted ALOHA with link-quality estimation in city channels     

Physical model of shadowing probability for land mobile satellitepropagation

A physical model of shadowing probability for a land-mobile satellite system is derived from a simple geometrical model. The resulting model exhibits physically reasonable behaviour, in good agreement with empirical measurements and allows the variation of shadowing states with both satellite elevation and azimuth to be predicted     

Decoder-assisted frame synchronization for packet transmission

This paper proposes a novel frame synchronization methodology for packets with convolutionally encoded data. Rather than by placing sync bits in a separate header, the sync bits are placed in a midamble and encoded as part of the data sequence, using the error correction encoder to resolve time ambiguities. The scheme is based on the principle that an error in trellis termination may result in decoding a wrong information bit sequence, while the starting portion of the sequence can be decoded as error free. This frame synchronization technique is extended to the synchronization of turbo-coded systems using a list-based approach, where the first synchronizer provides a list of potential packet starting positions, and the following synchronizer makes the final decision. The performance improvement over conventional synchronization techniques is quantified via simulation     

Proposal and performance evaluation of an efficient multiple-access protocol for LEO satellite packet networks

This paper deals with a modified version of the packet reservation multiple-access (PRMA) protocol suitable for integration of real-time (voice) and best effort (data) traffic in low Earth orbit (LEO) satellite communication systems. The proposed scheme differs from previous alternatives on the method adopted to handle access requests for voice and data terminals, and to transmit data messages. An analytical approach is proposed and validated in the case of voice and classical (i.e., geometric distributed) data traffic in order to derive system performance in terms of mean data message delay and voice packet dropping probability. However, in order to better highlight the advantages of the proposed approach typical interactive and background traffics types have been also considered. Performance comparisons with previous proposed PRMA protocols for voice and data transmission in LEO satellite communication systems are also shown in order to highlight the better behavior of the proposed scheme. Finally, a brief discussion concerning the extension of the proposed S-PRMA protocol to the case of different satellite communication systems is also provided.