Soft-decision phase detection with Viterbi decoding for CPM signals

It is known that continuous phase modulation (CPM) signals can be optimally detected by using coherent demodulation followed by Viterbi decoding. However, such a receiver is generally complicated, particularly at higher numbers of states, as it requires many correlators and many reference signals in the demodulator. In this study, a much simpler receiver, which employs a soft-decision phase detector followed by a Viterbi decoder, is proposed for the detection of CPM signals. The phase detector makes a decision in favor of one of the preselected phase subregions at the end of every interval, which is then used to calculate metrics for decoding. As in optimal detection, the Viterbi decoder decodes according to the trellis structure of CPM signals. The proposed receiver is analyzed in a narrow-band Gaussian channel with 2REC, 2-h, and trellis-coded continuous-phase frequency-shift keying signals. Numerical results show that the proposed receiver performs close to optimal detection with all types of signals considered in this study. The effect of the number of subregions in the phase detector is examined     

A diversity combining DS/CDMA system with convolutional encodingand Viterbi decoding

Averaged diversity combining is applied to an asynchronous DS/CDMA system using convolutional encoding and Viterbi decoding. A cyclic redundancy check (CRC) code is included in the scheme to trigger retransmission requests. Multiple received packets are combined on a bit by bit basis to form a single, more reliable packet. The error correcting decoder operates on the combined packet, as opposed to the most recently received individual packet (e.g., as in a type-I hybrid ARQ protocol), substantially increasing the probability of acceptance with each additional transmission. We show that the proposed technique allows a significant increase in the CDMA system capacity, throughput, and reliability     

Viterbi decoding for impulsive interference satellite channels

Data taken from real satellite channels point to the fact that such non-Gaussian behaviour as burst noise exists. Since the probability density function (p.d.f.) which minimizes the Fisher information (I_f) subject to the given variance of noise is Gaussian, performance can be improved by taking into account the non-Gaussian nature of the actual noise p.d.f. To achieve the higher efficiency, a modem, which consists of a maximum likelihood sequence detector (MLSD) implemented by an adaptive Viterbi algorithm (VA), is introduced in this paper. The new form of the algorithm, based on the m-interval polynomial approximation (MIPA) method, which adjusts the operation of the VA decoder to ensure its robustness to changing and/or non-Gaussian noise conditions, leads to an improvement of the error probability in operation of the receiver. In contrast to coding techniques, this improvement through digital signal processing is not obtained at the expense of bandwidth expansion. Monte Carlo simulation results involving bit error rate (BER) support theoretical conclusions.     

SBAS卫星信号的Viterbi译码优化方案

为了减少硬件处理的时间浪费,针对经由卷积编码的SBAS(Satellite-based Augmentation System )卫星信号,提出一种优化的Viterbi译码处理方案.该方案对译码数据流进行截断处理并进行性能补偿,通过Matlab平台对其进行建模仿真.仿真结果表明,该方案能够在节约硬件存储容量和减少数据处理压力的同时,获得与传统译码同等的译码性能,这为硬件实现提供了很好的参考依据.     

Satellite diversity in mobile satellite CDMA systems

The paper addresses the exploitation of satellite diversity in a satellite mobile network. In particular, we focus on the impact of diversity on service availability and on system capacity, considering the forward link of a CDMA system with a multisatellite and multibeam architecture. The analysis includes the effects of path blockage, intrabeam and interbeam interference, imperfect power control, and fading correlation in the time-domain due to nonideal interleaving. A closed-form solution is given for the estimation of system capacity. We show that satellite diversity is essential in providing service availability in urban and suburban areas, while the impact of satellite diversity on system capacity may be positive or negative, mainly depending on the fading channel characteristics. In particular, diversity becomes more and more beneficial for increasing fading time-domain correlation (i.e., for low mobile speed and/or limited interleaving depth). The analytical results have been validated by means of Monte Carlo simulation     

An improved authentication scheme for mobile satellite communication systems

Recently, Lee et al. proposed a simple and efficient authentication scheme for mobile satellite communication systems. However, we find that their scheme is vulnerable to the smart card loss attack, the denial of service attack and the replay attack. To overcome the weaknesses of Lee et al.'s scheme, we proposed an authentication scheme for mobile satellite communication systems to improve security. The proposed scheme possesses the essential properties and security requirements, which should be considered for the authentication scheme of mobile satellite communication systems. Copyright © 2014 John Wiley & Sons, Ltd.     

多波束移动卫星系统的自适应开环预编码方法

对于卫星移动通信系统,由于卫星与地面终端之间的相对运动以及星地间传输延迟,传统的基于理想信道信息的预编码方法是不适用的。针对这一问题,提出了一种基于开环信道估计的预编码方法。卫星端利用开环获取的部分信道信息实现多波束联合预编码,并导出了系统传输速率的闭合解析表达式。此外,为了克服强干扰环境下多波束预编码系统性能恶化问题,提出了一种自适应预编码传输方法。卫星发射机依据开环获得的慢时变用户位置信道信息和信道统计量信息,自适应地选择预编码方法或传统频率复用方法,实现最优的系统性能。理论分析和仿真结果表明,与传统的干扰抑制方法相比,所提方法能实现更优的系统性能,同时也克服了传统预编码方法的局限性。     

A communication protocol for mobile satellite systems affected byrain attenuation

A protocol that supports real-time data rate selection and change during rain events is presented. The protocol is developed with emphasis on being efficient yet robust to the primary channel impairment in such mobile satellite systems. The system architecture is briefly presented and the analytical framework from which the protocol originates is pointed out. Link, connection, and packet types are introduced, and the protocol procedures and design rationale are discussed. The detailed presentation focuses on link setup with the appropriate data rate(s) and the real-time switching of data rates during a voice conversation to either preserve the link or enhance its quality during rain attenuation events     

Telemedicine using mobile satellite communication

With a view to providing paramedical care within moving vehicles, a telemedicine technique using mobile satellite communication was proposed. With this technique, the diagnosis from a specialist and the emergency care under his/her instructions would be available on the spot without unnecessary delay. The characteristic problems of this technique were identified as: channel capacity, size of the system, reliability of vital sign transmission, real-time operation and electromagnetic interference. Measures against these problems were devised, and their effectiveness was analyzed. A data format was designed and an experimental system was developed. The system can simultaneously transmit a color image, an audio signal, 3 channels ECG and blood pressures from a mobile station to a ground station. It can transmit an audio signal and error control signals from a ground station to a mobile station in a full duplex mode. Fundamental transmission characteristics were measured in a fixed station. Finally, experiments of medical data transmission were conducted with a navigating ship and an aircraft flying an international route. The measured threshold values of C/N_o to guarantee satisfactory data reception were well below the lower boundary of C/N_o of the communication link. Consequently, the feasibility of this technique was verified     

A simple and efficient authentication scheme for mobile satellite communication systems

In this article, the authors shall propose a simple and efficient authentication scheme for mobile satellite communication systems. The proposed scheme can achieve the following security requirements: (S1) withstand impersonation attacks; (S2) withstand denial server attacks; (S3) withstand smart card loss attacks; (S4) withstand replay attacks; and (S5) withstand stolen‐verifier attacks, and achieve the following functionality requirements: (F1) freely choose identity; (F2) provide mutual authentication; (F3) provide session key agreement; (F4) provide user anonymity; and (F5) provide perfect forward secrecy. In additional, the proposed scheme does not use the high complex computation, such as public key cryptosystem or secret key cryptosystem, for the mobile users' side. The proposed scheme is only based on hash functions and exclusive‐OR operations. Compared with other schemes, the proposed scheme has a lower computation cost. It is more simple and efficient scheme. Copyright © 2011 John Wiley & Sons, Ltd.     

Efficient dynamic authentication for mobile satellite communication systems without verification table

The mobile satellite system is an important wireless communication system widely used nowadays. The issue of protecting the transmission security in low‐earth‐orbit satellite networks thus becomes more and more critical. It is known that several authentication schemes for satellite communication systems have been proposed to deal with the issue. However, previous protocols either employ complicated public key computation or have to maintain a verification table. In this paper, the author will introduce a new dynamic authentication protocol for mobile satellite communication systems without using a verification table. The comparison results will also show that the proposed scheme has lower computational costs. Copyright © 2014 John Wiley & Sons, Ltd.     

Land mobile satellite systems

The general advantages and potential operating characteristics of the mobile satellite service (MSS) are described, and distinctions are made between radio telephone, which is interconnected to the public switched telephone network, and private mobile radio systems. Mobile satellite service offers voice, data, position location, and paging services, interconnection to the public switched telephone network, and the possibility of private networks. Performance and cost characteristics are given along with summaries of market needs and market demands. The space and ground systems of the MSS are described     

Performance analysis of coded communication systems on Nakagami fading channels with selection combining diversity

In this paper, we develop analytical tools for the performance analysis of coded, coherent communication systems on independent and identically distributed Nakagami-m fading channels with selection combining (SC) diversity. First, we derive an exact expression for the moment generation function (MGF) of the signal-to-noise ratio (SNR) of a code symbol at the output of the selection combiner. Next, based on Gauss-Chebyshev quadrature and Gauss-Laguerre quadrature rules, we propose a simple to compute, yet accurate, numerical solution for the pairwise error probability (PEP) of coded M-phase-shift keying (PSK) signals. Using the PEP expressions, we present the union bound-based bit-error performance of trellis-coded modulation schemes and turbo codes. Finally, we derive an exact expression for the computational cutoff rate of a coded system with M-PSK signaling and SC diversity, and show that the cutoff rate expression is a simple function of the MGF of the SNR at the output of the diversity combiner.     

Secure anonymous authentication scheme without verification table for mobile satellite communication systems

An authentication scheme is one of the most basic and important security mechanisms for satellite communication systems because it prevents illegal access by an adversary. Lee et al. recently proposed an efficient authentication scheme for mobile satellite communication systems. However, we observed that this authentication scheme is vulnerable to a denial of service (DoS) attack and does not offer perfect forward secrecy. Therefore, we propose a novel secure authentication scheme without verification table for mobile satellite communication systems. The proposed scheme can simultaneously withstand DoS attacks and support user anonymity and user unlinkability. In addition, the proposed scheme is based on the elliptic curve cryptosystem, has low client‐side and server‐side computation costs, and achieves perfect forward secrecy. Copyright © 2013 John Wiley & Sons, Ltd.     

Predictive relay‐selection cooperative diversity in land mobile satellite systems

Cooperative diversity protocols promise a new dimension of diversity that provides better communication by engaging nearby relays in forming a ‘virtual’ array of antennas for combined signal transmission. The current incremental cooperative diversity algorithms incrementally select best relay(s) to cooperate based on the channel quality reported by the relays. However, the algorithms do not take into consideration the fact that the chosen best relay(s) at estimation may not always be the best at the time of communication. This is due to the time delay between the relay selection and its transmission of signal (problem of outdated channel quality information (CQI)). To solve this problem, the concept of channel prediction is introduced and employed whereby each relay determines a predicted value of its CQI based on its past measurements. The paper therefore develops a novel predictive relay‐selection (PRS) cooperative diversity model that seeks to improve land mobile satellite communication through prediction protocols. In the model, the chosen best relay is the one with the best predicted CQI value instead of the traditional outdated one. Performance analysis of outage probability and average bit error probability for the newly developed PRS cooperation shows that the PRS cooperation is better than direct and outdated CQI relay communication. Copyright © 2015 John Wiley & Sons, Ltd.     

LTE系统的Viterbi译码算法仿真及DSP实现

文章基于长期演进(LTE)系统的咬尾卷积码,通过对多种Viterbi译码算法的仿真比较,为时分长期演进(TD-LTE)测试系统选择了一种最优的Viterbi译码算法,并在TMS320C64x数字信号处理器(DSP)中实现了这种算法.提出了一些具体的软件优化策略和技巧,对加比选蝶形运算进行了大量简化.通过译码程序在CCS3.3中的运行结果,验证了该算法及优化策略和技巧的可行性和有效性.     

协作通信技术在卫星移动通信中的应用

卫星移动通信自逐渐发展以来,便因其覆盖范围广、地域限制弱、信号容量大等特点被广泛应用于通信网络当中,成为全球通信网络中不可或缺的有效信息传输手段之一,在军用领域和民用领域发挥着重要作用。但由于卫星移动通信的信道受多径效应、阴影效应以及多普勒效应的影响,严重的影响信号传输的有效性,因此必须采用相关的通信技术克服这一问题。协作通信技术作为提高通信质量的有效手段,因此研究其在卫星移动通信中的应用逐渐成为热门话题。     

Performance of M-PSK in mobile satellite communication over combined ionospheric scintillation and flat fading channels with MRC diversity

Combined scintillation and terrestrial fadings occur in mobile satellite communication channels as the signal passes through the ionosphere and the lower atmosphere. This results in a product fading channel, which negatively affects the performance of the system. The challenge is to evaluate the performance of the system, in terms of the average bit error probability (BEP). In this paper, through the use of the moment generating function, we derive expressions for the average BEP and an upper bound for M-ary phase-shift keying (M-PSK) modulation with maximal-ratio combining (MRC) diversity over the product RicianxRician channel. The results are expressed as double summations in terms of the generalized hypergeometric function, which can be computed using standard commercial software. For a large Rician factor, the expression is simplified to a single summation. Numerical results are obtained from the derived expressions and compared with simulation results. They show very good agreement for various Rician factors and the number of diversity branches. The upper bound is also evaluated and shown to be reasonably tight.     

Viterbi decoding algorithm for convolutional codes with repeat request

Using the Viterbi decoding algorithm with repeat request for convolutional codes is proposed, and the resulting performance is analyzed by random coding and generating function arguments and by simulation. It is shown that the reliability function of the proposed decoding algorithm is asymptotically twice that of the Viterbi decoding algorithm without repeat request, and that in certain practical situations the proposed algorithm can save about 50 percent in constraint length over the ordinary Viterbi algorithm for a given performance.     

Network management for mobile satellite systems

Mobile satellite systems (MSSs) are being developed around the world to provide voice and data services to large populations of mobile subscribers in rural and sparsely populated areas. To maintain efficient operation of an MSS, it is essential that a network management system (NMS) be incorporated into the design. This paper presents a comprehensive review of these issues in relation to the overall requirements of MSSs. Functions that need to be performed by the NMS are discussed in detail, under the categories of configuration, fault, performance, accounting, security, capacity, service, and administration management. An architecture for integrating NMS functions into the network control centre (NCC) and extending network management services to other network elements is presented. The roles of enabling technologies such as expert systems, fault tolerant processors, and objected‐oriented databases are examined. This revised version was published online in June 2006 with corrections to the Cover Date.