Improving concatenated coding communications by employing signal editing techniques

Signal editing (SE) is a technique used to locate and erase unreliable data before error correction decoding. Consider a concatenated coding (CC) communication system in which the inner code employs convolutional encoding with Viterbi decoding (CEVD) and the outer code could employ either a convolutional or a Reed-Solomon code. In this study, we show that useful information can be derived from the inner Viterbi decoding process to perform two special operations: (i) to locate and erase unreliable decoded data and (ii) to estimate the input channel noise level. As a result, the number of errors input to the outer decoder is reduced and the overall CC system performance is improved.     

Signal editing: A new approach to upgrade concatenated coding communications

Based on the property that correction coding is more sensitive to the number of errors than the number of erased code symbols, results of an analytical investigation to improve the performance of concatenated coding communications are presented. We propose a new tactic, ‘signal editing’, to estimate and erase unreliable data prior to the final outer decoding process. We show that signal editing has a capability to detect and delete individual erroneous digits that has not been achieved by other methods. As a result, system performance can be markedly improved. Specific recommendations for using the procedure are suggested and discussed. We illustrate how signal editing is implemented in the case of a convolutional code with Viterbi decoding. A new concatenated (or hybrid) coding technique is constructed integrating the code with interleaving and signal editing. Performance improvement is evaluated and analysed. In this study, signal editing is derived from the information available in the Viterbi decoding process. Not limited to convolutional code with Viterbi decoding, signal editing can be applied to other linear codes without any restriction.     

一种低译码复杂度的Turbo架构LDPC码

针对低密度奇偶校验(LDPC)码较大的译码复杂度和RAM占用,该文提出了一种低译码复杂度的Turbo架构LDPC码并行交织级联Gallager码 (Parallel Interleaved Concatenated Gallager Code,PICGC)。该文给出了PICGC的设计方法和编译码算法,并分析比较了PICGC译码器与LDPC译码器所需的RAM存储量,推导出RAM节省比的上界。理论分析和仿真结果表明,PICGC以纠错性能略微降低为代价,有效地降低译码复杂度和RAM存储量,且译码时延并未增加,是一种有效且易于实现的信道编码方案。     

Low earth orbit satellite communications experiments using the digital signal processing payload on the PoSAT-1 microsatellite

There is a growing interest in using networks of small satellites in low Earth orbit (LEO) to provide a variety of communications services in conjunction with small ground terminals. The only ’little LEO’ microsatellite digital store-and-forward communications network (HealthNet) in commercial operation at the time of writing uses microsatellites, communications payloads, and protocols designed and built at the University of Surrey, U.K. In order to provide an in-orbit research test-bed for improving communications with microsatellites in LEO by optimizing modulation and demodulation techniques, an advanced DSP payload, the digital signal processing experiment (DSPE), was included on board the latest Surrey microsatellite (PoSAT-1). In-orbit experiments using the PoSAT-1 DSPE first optimized the existing non-coherent CPFSK communication systems and then investigated the use of coherent MSK to provide a potential 3dB advantage while remaining compatible with the spacecraft systems. A novel DSP implementation of the Hodgart-Massey coherent MSK demodulator/decoder was developed by the authors and its behaviour compared with the classical de Buda demodulator undertypical LEO conditions through a sequence of rigorous computer simulations and laboratory bench tests. The simulations and bench tests quantified a practical 2dB improvement in BER performance when compared with non-coherent CPFSK, while also exhibiting considerable tolerance to the frequency and amplitude variations which are encountered in an LEO environment. These characteristics were subsequently confirmed by in-orbit demonstrations using the PoSAT-1 DSPE. The microsatellite, payload, modems and experimental results are presented in this paper and discussed with a view towards implementing an adaptable DSP-based communications system capable of optimizing data throughput with LEO microsatellites.     

COMETS experiments for advanced mobile satellite communications and advanced satellite broadcasting

The Communications and Broadcasting Engineering Test Satellite (COMETS) was developed to evaluate Ka‐band (31/21GHz) and millimetre‐wave (47/44 GHz) advanced mobile satellite communications systems, 21GHz advanced satellite broadcasting systems, and S‐band and Ka‐band inter‐orbit satellite communications systems. COMETS was launched because it was to become the new ‘bridge’ toward advanced satellite communications technologies in the next century, but the launch on 21 February 1998 regretfully failed due to premature shut down of the second stage engine of the H‐II launch rocket. After this accident, the initial low elliptic orbit of COMETS was improved by the apogee engine to a larger elliptic orbit with an apogee altitude of 17711km, a perigee altitude of 473 km, an inclination of 30.1°, and an orbital period of 319 min. Original and modified COMETS experimental plans, countermeasures in earth stations for the orbiting satellite, as well as an overview of the COMETS satellite and ground terminals are presented. Copyright © 2000 John Wiley & Sons, Ltd.     

卫星通信的近期发展与前景展望

从分析卫星通信的特点入手,综述了卫星通信的卫星平台、可用频率资源和主要相关技术的发展状况,概述了典型的卫星通信系统的性能特点,介绍了卫星通信的应用及产业化发展情况,并展望了发展前景。     

The use of digital circuit multiplication equipment in satellite communications

The use, within satellite communications, of low rate encoding (LRE) techniques, based on 24, 32 and 40 kb/s ADPCM coding, coupled with digital speech interpolation (DSI) to form a digital circuit multiplication equipment (DCME), is addressed in this paper. The need for a system simulation tool, in order to plan for and correctly use the DCME concept is identified. Results obtained with this simulation tool are presented. The simulation model makes it possible to predict the behaviour of the system from a quality point of view, with external conditions simulated to be very close to actual operating conditions.     

卫星通信技术的新发展

就当前卫星通信技术的若干热点作了一些概括和综述。首先,介绍了宽带卫星通信系统的有关概念和发展现状,提出了需解决的主要技术问题,给出了典型应用;然后,在介绍卫星移动通信的国内外发展现状的基础上,研究了系统的特点及需要突破的关键技术;最后,介绍了空间通信网的基本概念,给出了网络组成及功能,分析了需要解决的若干新技术。     

卫星激光通信中LDPC码构造方法的研究进展

激光因其单色性好、功率密度大等特性被提出应用于卫星通信系统中以应对未来通信业务需求,但激光通信在传输过程中受大气等因素影响会造成其传输可靠性降低.而低密度奇偶校验(Low-Density Parity-Check,LDPC)码因其灵活的构造方法、较低的编译码复杂度、纠错能力强等优点已被证明适用于卫星激光通信.本文从LD...     

浅谈数字卫星节目的接收

目前卫星数字压缩节目不断增加,中、小型有线台、站如何快速、有效地接收好这些节目？下文从初始计算,调整卫星接收天线,选择接收机等几个方面浅述了一些实用的方法。     

Simulation of an on-board hierarchical multistage digital FDM demultiplexer for mobile scpc satellite communications

This paper is focused on the finite-precision time-domain simulation of the hierarchical multistage method detailed in References 1 and 2 for demultiplexing of an FDM signal being composed of L = 32 slot signals. This approach to FDM demultiplexing is based on the processing of complex signals by linear-phase FIR filters, where at any stage of processing the respective signals are always oversampled by a factor of two. The simulation results fully confirm the system performance predicted in Reference 1 by modelling the distortions (spectral foldover and quantization noise) inherent in the system: assuming an ideal FDM signal at the input port of the analogue anti-aliasing bandpass filter in front of the analogue-to-digital converter, a minimum signal-to-distortion ratio (S/D) of 30 dB is achieved at all L output ports of the demultiplexer with {w, w_F, w_i} = {11,12,14}, as anticipated in Reference 1. The signal word length w apply to the A/D conversion, w_F to requantization between the filter stages, and w_i to filter internal signal processing.     

Improving satellite services with cooperative communications

This paper proposes new transmission schemes for the delivery of satellite services. In the proposed scenarios, mobile terminals are allowed to forward the signal received from the satellite. This scheme provides spatial diversity just like MIMO transmission schemes. Moreover, the coverage area is extended because masked terminals have an additional opportunity to get the service from neighboring terminals. We use the paradigm of cooperative communications to compare the advantages and limitations of several scenarios in hybrid terrestrial/satellite systems. In particular, we study the following basic transmission scheme: in a first time slot, the satellite sends its signal and, in a second time slot, mobile terrestrial terminals are relaying the satellite signal. An analysis framework is proposed and applied to this cooperation scenario at the destination terminal. The framework is modeling the cooperation process and clearly separates the control part from the data user part. The paper outlines the importance of the control part by evaluating the relay selection policy on a basic hybrid satellite/ad hoc system. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

Review and comparison of tropospheric scintillation prediction models for satellite communications

An overview of the origin and characteristics of tropospheric scintillation is presented and a measurement database against which scintillation models are to be tested is described. Maximum likelihood log‐normal and gamma distributions are compared with the measured distribution of scintillation intensity. Eleven statistical models of monthly mean scintillation intensity are briefly reviewed and their predictions compared with measurements. RMS error, correlation, percentage error bias, RMS percentage error and percentage error skew are used in a comprehensive comparison of these models. In the context of our measurements, the ITU‐R model has the best overall performance. Significant difference in the relative performance of the models is apparent when these results are compared with those from a similar study using data measured in Italy. Copyright © 2006 John Wiley & Sons, Ltd.     

用于卫星通信系统的空间通信协议网关设计

针对卫星通信系统中传输控制协议(TCP)传输性能不理想的问题,设计并实现了一种基于空间通信协议的网关。在网关设计中,优化了Vegas拥塞控制算法的参数,并通过空间通信协议连接表实现了对多连接的支持。卫星通信模拟系统中的测试结果表明,当卫星链路具有高误码率和大传输延时(大于1 000 ms)情况下,该网关的性能与直接使用TCP相比,平均吞吐量提高比达10∶1,且多连接情况下各连接之间竞争带宽的公平性表现较为满意。     

Performance of a turbo‐coded CDMA system in a mobile satellite channel

The bit error rate (BER) performance of a turbo‐coded code‐division multiple‐access (CDMA) system operating in a satellite channel is analysed and simulated. The system performance is compared for various constituent decoders, including maximum a posteriori probability (MAP) and Max‐Log‐MAP algorithms, and the soft‐output Viterbi algorithm. The simulation results indicate that the Max‐Log‐MAP algorithm is the most promising among these three algorithms in overall terms of performance and complexity. It is also shown that, for fixed code rate, the BER performance is improved substantially by increasing the number of iterations in the turbo decoder, or by increasing the interleaver length in the turbo encoder. The results in this paper are of interest in CDMA‐based satellite communications applications. Copyright © 2005 John Wiley & Sons, Ltd.     

An on-board processing satellite payload for european mobile communications

The paper considers the application of satellite on-board processing (OBP) technology for land mobile applications for possible introduction in the late 1990s. Initially a system outline is presented followed by a discussion considering the merits of OBP over conventional transparent payloads. The paper then presents an overview of the work being carried out as part of an ESA study. Some details on the critical parts of the system are also included.     

Adaptive non-linear equalisation of digital communications channels

Non-linear distortion introduced by communications channels increases the probability of error. In this paper, an adaptive non-linear canceller is presented which attempts to remove non-linear interference from the output of a feedforward or decision feedback equaliser, improving the error rate. It may be implemented using a memory look-up table architecture, making it suitable for high speed real time operation.     

Exploiting cognitive radios for reliable satellite communications

Satellite transmissions are prone to both unintentional and intentional RF interference. Such interference has significant impact on the reliability of packet transmissions. In this paper, we make preliminary steps at exploiting the sensing capabilities of cognitive radios for reliable satellite communications. We propose the use of dynamically adjusted frequency hopping (FH) sequences for satellite transmissions. Such sequences are more robust against targeted interference than fixed FH sequences. In our design, the FH sequence is adjusted according to the outcome of out‐of‐band proactive sensing, carried out by a cognitive radio module that resides in the receiver of the satellite link. Our design, called out‐of‐band sensing‐based dynamic FH, is first analyzed using a discrete‐time Markov chain (DTMC) framework. The transition probabilities of the DTMC are then used to measure the ‘channel stability’, a metric that reflects the freshness of sensed channel interference. Next, out‐of‐band sensing‐based dynamic FH is analyzed following a continuous‐time Markov chain model, and a numerical procedure for determining the ‘optimal’ total sensing time that minimizes the probability of ‘black holes’ is provided. DTMC is appropriate for systems with continuously adjustable power levels; otherwise, continuous‐time Markov chain is the suitable model. We use simulations to study the effects of different system parameters on the performance of our proposed design. Copyright © 2014 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.