基于比特交织编码调制的短波瞬间通信系统关键技术研究
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摘要
短波通信由于设备简单、成本低廉、抗摧毁性好、可维修性强及超视距传输等一系列优点一直是军事通信重要手段之一。但是随着现代高科技战争的发展,传统的短波通信很难摆脱现代电子对抗技术的威胁,因此发展抗干扰、抗窃听、抗截获等目标的短波通信系统就变得尤为重要。
本论文是以中国工程院陆建勋院士提出的新型短波抗干扰通信系统——短波自适应瞬间通信系统(ABCS)为基本指导思想,探讨比特交织编码调制(BICM)技术在短波瞬间通信系统中的应用及相关关键技术研究。
论文首先介绍了现代短波通信中的新技术,重点介绍了陆建勋院士提出的ABCS通信系统,分析了ABCS的理论基础、主要特点及相对于传统短波通信体制的优势。然后探讨了比特交织编码调制技术在ABCS中的应用,论文主要包括以下内容:
1.系统的编码调制方案的实现。比特交织编码调制(BICM)通过把传统的二进制纠错码和一组独立的比特交织器连接起来以增加分集级数,是一种带宽有效的编码技术。论文将BICM技术应用到短波瞬间通信系统中,分别实现了基于LDPC码的BICM系统、基于硬判决的BICM-ID系统和基于软判决的BICM-ID系统,并对其性能进行分析和仿真。为ABCS-Ⅱ系统编码调制技术方案的选择提供了依据。
2.系统的同步方案的实现。同步是猝发通信的关键,它直接关系到系统性能的好坏。论文实现了系统的位同步和载波同步(包括相偏和频偏),重点探讨了载波同步:实现了基于Turbo原理的迭代相位同步,较传统的相位同步方法,提高了系统误码率(BER)性能;提出一种载波频偏估计方法,该方法能有效抑制传统频偏估计后的残留频偏的波动,有效提高了系统的误帧率和误码率性能。
3.系统的均衡方案的实现。短波信道是频率选择性衰落信道,严重的码间干扰是限制短波通信速率的主要障碍之一。要在一定的误码率条件下,提高系统的通信速率,就必须采用信道均衡技术来消除码间干扰的影响。论文主要实现了基于硬判决的BICM-ID系统的Turbo均衡,将软干扰抵消算法(SIC)应用到系统中,并对其进行两次改进,有效提高了系统性能:1)针对传统SIC均衡中第一次迭代盲信息概率分布传递的方式,提出通过接收信号对发射信号的先验概率分布做出估计,提高了系统性能。2)将其与MAP算法结合,提出一种复合型MAP-SIC算法,即在迭代初始,应用MAP均衡算法对发射信号的先验概率分布做出更加精确的估计,较传统的SIC算法具有更优越的性能。论文还实现了基于软判决的BICM-ID系统的Turbo均衡,提出了一种加权外信息概率的迭代检测方法,能够更有效地控制系统中波动过大的位概率,提高了系统性能。
4.系统的信道估计方案的实现。Turbo均衡系统是建立在接收端已知信道参数的假设上的。实际应用中,信道冲激响应、信噪比等信道参数一般是未知的,因此需要信道估计技术来估计这些参数。论文实现了一种BICM系统中的半盲迭代信道估计算法,利用译码产生的判决信息,通过迭代地在信道估计和解码之间交换信息来完成联合信道估计和解码。借助极少量的训练序列来辅助识别,就能达到较好性能,有效提高了频谱利用率。
High frequcency (HF) communication is an important communication method, especially in military communication; this is attributed to its simplity, moderate cost, ability to provide near global connectivity without repeaters, beyond line-of-sight, and ease of proliferation. But with the development of modern high technolgy war, traditional HF communication is threatened by modern electronic countermeasures, so it is very useful to develop efficient anti-jamming measures in HF communicaiton. The object of this dissertation is to study the applicaiton of Bit interleave coded modulation (BICM) in HF communication and relevant key techniques based on the model of a new HF adaptive burst communication system (ABCS) proposed by academician Lu Jianxun in China Engineering Academy.
At the beginning the dissertation introduced the new techniques in modern HF communication, and put emphasis on the introduction of ABCS, including its basic theories, main characters and advantages over traditional HF communication system. Then BICM and its applications in ABCS was discussed. The following items give the summarization of the main work:
1. The modem scheme was realized. BICM is a bandwidth-efficient code technology which adds the diversity order. BICM was applied to ABCS in this dissertation. The LDPC coded BICM system, BICM-ID(BICM with iterative decoding) based on hard decision and BICM-ID based on soft decision was respectively implemented and the performance was analyzed and simulated, which applied the bases to the choice of modem scheme.
2. The synchronization scheme was realized. Synchronization is a key of burst communication, which has an influence on the system performance. Our scheme performed timing recovery and carrier recovery and we put the emphases on carrier recovery. An iterative phase recovery method based on Turbo principle was performed, which outperforms the traditional methods. A carrier frequency estimation method was proposed, which can effectively control the fluctuation of the rudimental frequency brought by the conventional estimator and get better performance of FER(frame error rate) and BER(bit error rate), compared with the classical estimator.
3. The equalization scheme was realized. In HF communication the intersymbol interference (ISI) is serious and is the main obstacle of HF high rate communication. So we must use the channel equalization technology to eliminate the influence of ISI if we want to improve the communication rate over certain BER. We performed the Turbo equalization and applied SIC(Soft Interference Canceller) algorithm to BICM-ID based on hard decision and improved its performance by making use of two methods: Firstly, we used the priori probability of transmitted signal as input on the first iteration and improved the performance of equalization, compared with the traditional method which uses the uniform probability distribution as input on the first iteration. Secondly, we combined SIC with MAP and proposed a combined MAP-SIC algorithm, which applied the MAP equalization algorithm to get more precise priori probability of transmitted signal on the first iteration. It outperformed the conventional SIC algorithm. We also performed the Turbo equalization in BICM-ID based on soft decision and proposed an improved iterative detection method based on the exchange of weighed extrinsic information probability, which can control the bit probabilities with large dynamics effectively and improve the system performance.
4. The channel estimation scheme was realized.Turbo equalization is based on the hypothesis of the known channel parameters. In actual application, Channel Impulse Response and SNR are unknown, so we have to use the channel estimation technology to estimate these parameters. We proposed a semi-blind channel estimation algorithm in BICM system, which makes use of the decision information provided by the decoder and gets good channel estimation by iteratively exchanging information between the channel estimator and the decoder. This method works well with rough initialization of channel parameters obtained from very short train sequence, which leads to high spectrum efficiency.
本论文是以中国工程院陆建勋院士提出的新型短波抗干扰通信系统——短波自适应瞬间通信系统(ABCS)为基本指导思想,探讨比特交织编码调制(BICM)技术在短波瞬间通信系统中的应用及相关关键技术研究。
论文首先介绍了现代短波通信中的新技术,重点介绍了陆建勋院士提出的ABCS通信系统,分析了ABCS的理论基础、主要特点及相对于传统短波通信体制的优势。然后探讨了比特交织编码调制技术在ABCS中的应用,论文主要包括以下内容:
1.系统的编码调制方案的实现。比特交织编码调制(BICM)通过把传统的二进制纠错码和一组独立的比特交织器连接起来以增加分集级数,是一种带宽有效的编码技术。论文将BICM技术应用到短波瞬间通信系统中,分别实现了基于LDPC码的BICM系统、基于硬判决的BICM-ID系统和基于软判决的BICM-ID系统,并对其性能进行分析和仿真。为ABCS-Ⅱ系统编码调制技术方案的选择提供了依据。
2.系统的同步方案的实现。同步是猝发通信的关键,它直接关系到系统性能的好坏。论文实现了系统的位同步和载波同步(包括相偏和频偏),重点探讨了载波同步:实现了基于Turbo原理的迭代相位同步,较传统的相位同步方法,提高了系统误码率(BER)性能;提出一种载波频偏估计方法,该方法能有效抑制传统频偏估计后的残留频偏的波动,有效提高了系统的误帧率和误码率性能。
3.系统的均衡方案的实现。短波信道是频率选择性衰落信道,严重的码间干扰是限制短波通信速率的主要障碍之一。要在一定的误码率条件下,提高系统的通信速率,就必须采用信道均衡技术来消除码间干扰的影响。论文主要实现了基于硬判决的BICM-ID系统的Turbo均衡,将软干扰抵消算法(SIC)应用到系统中,并对其进行两次改进,有效提高了系统性能:1)针对传统SIC均衡中第一次迭代盲信息概率分布传递的方式,提出通过接收信号对发射信号的先验概率分布做出估计,提高了系统性能。2)将其与MAP算法结合,提出一种复合型MAP-SIC算法,即在迭代初始,应用MAP均衡算法对发射信号的先验概率分布做出更加精确的估计,较传统的SIC算法具有更优越的性能。论文还实现了基于软判决的BICM-ID系统的Turbo均衡,提出了一种加权外信息概率的迭代检测方法,能够更有效地控制系统中波动过大的位概率,提高了系统性能。
4.系统的信道估计方案的实现。Turbo均衡系统是建立在接收端已知信道参数的假设上的。实际应用中,信道冲激响应、信噪比等信道参数一般是未知的,因此需要信道估计技术来估计这些参数。论文实现了一种BICM系统中的半盲迭代信道估计算法,利用译码产生的判决信息,通过迭代地在信道估计和解码之间交换信息来完成联合信道估计和解码。借助极少量的训练序列来辅助识别,就能达到较好性能,有效提高了频谱利用率。
High frequcency (HF) communication is an important communication method, especially in military communication; this is attributed to its simplity, moderate cost, ability to provide near global connectivity without repeaters, beyond line-of-sight, and ease of proliferation. But with the development of modern high technolgy war, traditional HF communication is threatened by modern electronic countermeasures, so it is very useful to develop efficient anti-jamming measures in HF communicaiton. The object of this dissertation is to study the applicaiton of Bit interleave coded modulation (BICM) in HF communication and relevant key techniques based on the model of a new HF adaptive burst communication system (ABCS) proposed by academician Lu Jianxun in China Engineering Academy.
At the beginning the dissertation introduced the new techniques in modern HF communication, and put emphasis on the introduction of ABCS, including its basic theories, main characters and advantages over traditional HF communication system. Then BICM and its applications in ABCS was discussed. The following items give the summarization of the main work:
1. The modem scheme was realized. BICM is a bandwidth-efficient code technology which adds the diversity order. BICM was applied to ABCS in this dissertation. The LDPC coded BICM system, BICM-ID(BICM with iterative decoding) based on hard decision and BICM-ID based on soft decision was respectively implemented and the performance was analyzed and simulated, which applied the bases to the choice of modem scheme.
2. The synchronization scheme was realized. Synchronization is a key of burst communication, which has an influence on the system performance. Our scheme performed timing recovery and carrier recovery and we put the emphases on carrier recovery. An iterative phase recovery method based on Turbo principle was performed, which outperforms the traditional methods. A carrier frequency estimation method was proposed, which can effectively control the fluctuation of the rudimental frequency brought by the conventional estimator and get better performance of FER(frame error rate) and BER(bit error rate), compared with the classical estimator.
3. The equalization scheme was realized. In HF communication the intersymbol interference (ISI) is serious and is the main obstacle of HF high rate communication. So we must use the channel equalization technology to eliminate the influence of ISI if we want to improve the communication rate over certain BER. We performed the Turbo equalization and applied SIC(Soft Interference Canceller) algorithm to BICM-ID based on hard decision and improved its performance by making use of two methods: Firstly, we used the priori probability of transmitted signal as input on the first iteration and improved the performance of equalization, compared with the traditional method which uses the uniform probability distribution as input on the first iteration. Secondly, we combined SIC with MAP and proposed a combined MAP-SIC algorithm, which applied the MAP equalization algorithm to get more precise priori probability of transmitted signal on the first iteration. It outperformed the conventional SIC algorithm. We also performed the Turbo equalization in BICM-ID based on soft decision and proposed an improved iterative detection method based on the exchange of weighed extrinsic information probability, which can control the bit probabilities with large dynamics effectively and improve the system performance.
4. The channel estimation scheme was realized.Turbo equalization is based on the hypothesis of the known channel parameters. In actual application, Channel Impulse Response and SNR are unknown, so we have to use the channel estimation technology to estimate these parameters. We proposed a semi-blind channel estimation algorithm in BICM system, which makes use of the decision information provided by the decoder and gets good channel estimation by iteratively exchanging information between the channel estimator and the decoder. This method works well with rough initialization of channel parameters obtained from very short train sequence, which leads to high spectrum efficiency.
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