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首页> 外文OA文献 >信頼性の高い大容量公共用移動通信システムを実現するためのソフトウェア無線およびコグニティブ無線に関する研究
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信頼性の高い大容量公共用移動通信システムを実現するためのソフトウェア無線およびコグニティブ無線に関する研究

机译：用于实现可靠的大容量公共移动通信系统的软件无线电和认知无线电的研究

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摘要

Public safety mobile wireless communication systems (PMCSs) are widely used by public safety personnel, such as firefighters and police, as well as local governments. PMCSs are crucial to protect safety and security of communities. Conventional PMCSs effectively cover underpopulated areas as well as urban areas by employing long-zone scheme. Since the PMCSs can cover areas that are not covered by commercial cellule systems, they play the important role as the only communication tool. Moreover, the conventional PMCSs have enhanced robustness and reliability. The conventional PMCSs can keep their services even if backbone lines are cut off. In contrast, short-zone scheme systems cannot offer stable and wide service area without backbone line connection. For example, the Great East Japan Earthquake in Japan, police mobile communication systems had kept their functions while cellular phones became disabled. PMCSs are required to be quite high robustness and reliability in order to save human life. Recently, conventional PMCSs are required to realize further expansion of service areas and high speed transmission although they have stably provided users with wide service areas so far. Nowadays, in order to solve complicated public affair quickly, more stable service areas and broadband communication are required. Compared with conventional PMCSs in urban areas, commercial wireless mobile communication systems (CWMCSs) such as cellular systems supply stable service areas and broadband communication in times of peace. In accordance with development of wireless technology, PMCSs need to keep pace with CWMCSs. However, conventional PMCSs can hardly realize further stable service areas and high speed transmission because of large-zone scheme. In terms of realization of further stable service areas, no-service areas cannot be eliminated easily. This is because no-service areas are mostly attributed to shadowing; in large-zone scheme, a no-service area that must essentially be covered by a certain base station is seldom covered by other neighboring base stations. Although new allocation of base stations is fundamental answer to solve no-service area problem in PMCSs, building new base stations of PMCSs that are not used for a commercial purpose is restricted by national and local budget. Realization of high speed transmission of PMCSs is also difficult because of large-zone scheme. To realize high speed transmission, increase of transmit power or shrinking of service area coverage is required to compensate Signal to Noise Power Ratio (SNR) deterioration caused by expanding bandwidth. Increase of transmission power of mobile station used in large-zone scheme systems is almost impossible because transmission power of mobile station is originally high. Thus, shrinking of service areas is necessary for high speed communication. Currently, to realize high speed transmission, next generation broadband PMCSs (BPMCSs) employing short-or middle-zone scheme are being developed. In the 3GPP, it is considered that the Long Term Evolution (LTE) is used for communication of public safety. In Japan, National Institute of Information and Communications Technology (NICT) has researched and developed Public Broadband Wireless Communication System (PBWCS), which employs 200MHz as carrier frequency. The PBWCS has already been equipped in national police agency in Japan. However, we consider that the conventional narrowband PMCSs (NPM-CSs) are not replaced with the BPMCSs completely. This is because the BPMCSs cannot cover all the areas that the conventional NPM-CSs have covered. Moreover, there are problems of robustness and reliability when accidents happen. Hence, users of PMCSs will utilize both of NPMCSs and BPMCSs in accordance with the situation. In this case, users equipping several terminals feel inconvenient and also radio resources are not used effectively. The best solution to realize optimal PMCSs is employing heterogeneous cognitive radio (HCR) for PMCSs. By applying the HCR to PMCSs, service areas expansion and high speed transmission in PM-CSs will be realized effectively. We propose an integrated system combining NPMCSs with CWMCSs and BPMCSs to make communication quality of the PMCSs improve. The proposed HCR recognizes communication conditions of several systems and then provides PMCSu27s users with optimal communication quality. Although software defined radio techniques (SDR) are ideal to operate cognitive radio more flexibly, we deal with HCR mainly to realize combined systems in this thesis. We study advantages, problems, and their solution to realize the HCR for PMCSs. Firstly, we research service area expansion of NPMCSs using HCR. The proposed HCR is utilized for stabilization of NPMCSu27s service area. If communication quality of a NPMCS deteriorates owing to shadowing, the proposed HCR terminal obtains a part of NPMCSu27s data called subsidiary information (SI) from CWMCSs or BPMCSs. The proposed HCR terminal can improve PMCSu27s bit error rate (BER) performance by combining the SI with received signals of the NPMCS and then decoding the combined signals using forward error correction (FEC). Since convolutional codes are often used in FEC of NPMCSs, we consider BER improvement methods of the convolutional code. We derive modified Viterbi algorithm from maximum likelihood sequence estimation (MLSE) of the combined signals. Moreover, we introduce the distance spectrum to evaluate characteristics of the convolutional codes. The distance spectrum is used for estimating improvement of BER performances. Next, we consider synchronization methods to realize the proposed HCR. In the HCR, there are two types of synchronization method; one is the self-synchronization method to synchronize each system itself. The other is the co-synchronization method to combine different systems. In this thesis, we consider self-synchronization methods of NPMCSs mainly. This is because the HCR aims to improve communication quality of NPMCSs equipping conventional self-synchronization methods that are not probably available in low SNR environments. In this environment, since NPMCSs can hardly obtain their self-synchronization alone, powerful self-synchronization methods using HCR techniques are required. We propose two synchronization methods that are utilization of global portioning system (GPS) signals and utilization of the SI, respectively. The synchronization methods utilizing GPS signals can acquire timing synchronization. To obtain timing synchronization, the proposed HCR acquires accurate time and own location using the GPS signals. The HCR also gets the location of base stations and the frame timing by making the SI convey their information. Since the HCR can know accurate time and distance between the base station and the HCR, synchronization timing can be calculated. However, in GPS based method, preciseness of timing synchronization may be deteriorated by measurement error of GPS signals, diffraction caused by mountains, and propagation delay caused by reection. For this reason, we consider a mitigation method of the timing error and then evaluate BER performances using computer simulation. Moreover, we propose a SI based synchronization method that can obtain timing synchronization without GPS signals. The proposed method is employed when a NPMCS uses differential coded π/4 shift QPSK as the modulation scheme. The notable feature of the proposed method is to convey the phase rotation of the π/4 shift QPSK as the SI. The HCR can forecast PMCSu27s envelopes from the obtained SI and then obtain the timing synchronization by correlating the forecasted envelopes with real received envelopes. Since the proposed method can also be used for co-synchronization and BER improvement, CWMCSu27s resource consumption to convey the SI is suppressed. Finally, we consider HCRs combining several PMCSs. In this thesis, the combination of NPMCSs and the combination of a NPMCS and a BPMCS are researched. In the combination of NPMCSs, we consider that several PMCSs are integrated by SDR. In the combination of a NPMCS and a BPMCS, we propose site diversity based on HCR to improve uplink communication quality of the BPMCS. In this diversity, since uplink interference must be avoided, we employ combination of the adaptive array and HCR techniques. Moreover, we propose information compression methods for narrow band backbone lines so that received data can be conveyed to head office with little BER deterioration. PMCSs will have played an important role to ensure social safety. In the thesis, we consider the one of the next generation PMCSs employing SDR and HCR. Using this research, we can obtain a direction of optimal PMCSs. The next step that we need to perform is to apply our proposed method to actual radio systems. We must continue this research so that high reliable and compact PMCSs can be realized.
机译：公共安全移动无线通信系统（PMCS）已被消防人员，警察等公共安全人员以及地方政府广泛使用。 PMCS对于保护社区的安全至关重要。常规的PMCS通过采用长区方案有效地覆盖了人口稀少的地区以及城市地区。由于PMCS可以覆盖商业蜂窝系统无法覆盖的区域，因此它们作为唯一的通信工具发挥着重要作用。而且，常规的PMCS具有增强的鲁棒性和可靠性。即使切断骨干线，传统的PMCS仍可以保持其服务。相反，如果没有骨干线连接，短区方案系统将无法提供稳定且宽广的服务区域。例如，在日本的东日本大地震中，警察移动通信系统在手机瘫痪的同时保持了其功能。 PMCS必须具有很高的鲁棒性和可靠性，才能挽救生命。近来，需要常规的PMCS来实现服务区域的进一步扩展和高速传输，尽管到目前为止它们已经稳定地为用户提供了宽的服务区域。如今，为了快速解决复杂的公共事务，需要更稳定的服务区域和宽带通信。与市区的传统PMCS相比，诸如蜂窝系统之类的商用无线移动通信系统（CWMCS）在和平时期提供稳定的服务区域和宽带通信。随着无线技术的发展，PMCS需要与CWMCS保持同步。然而，由于大区域方案，传统的PMCS很难实现进一步稳定的服务区域和高速传输。在实现进一步稳定的服务区域方面，不能轻易消除无服务区域。这是因为无服务区域主要归因于阴影。在大区域方案中，基本上必须由某个基站覆盖的无服务区域很少由其他相邻基站覆盖。尽管新分配基站是解决PMCS中无服务区问题的基本答案，但是构建不用于商业目的的PMCS新基站受到国家和地方预算的限制。由于大区域方案，实现PMCS的高速传输也是困难的。为了实现高速传输，需要增加发射功率或缩小服务区域覆盖范围，以补偿由于带宽增加而引起的信噪比（SNR）下降。在大区域方案系统中使用的移动台的发送功率的增加几乎是不可能的，因为移动台的发送功率本来就很高。因此，缩小服务区域对于高速通信是必要的。当前，为了实现高速传输，正在开发采用短或中区方案的下一代宽带PMCS（BPMCS）。在3GPP中，考虑将长期演进（LTE）用于公共安全的通信。在日本，国立信息通信技术研究所（NICT）研究和开发了以200MHz为载频的公共宽带无线通信系统（PBWCS）。 PBWCS已在日本的国家警察局配备。但是，我们认为传统的窄带PMCS（NPM-CS）并未完全被BPMCS取代。这是因为BPMCS不能覆盖常规NPM-CS覆盖的所有区域。此外，当事故发生时，存在鲁棒性和可靠性的问题。因此，PMCS的用户将根据情况同时使用NPMCS和BPMCS。在这种情况下，装备有多个终端的用户感到不便，并且无线电资源也没有得到有效利用。实现最佳PMCS的最佳解决方案是为PMCS使用异构认知无线电（HCR）。通过将HCR应用于PMCS，PM-CS中的服务区域扩展和高速传输将得到有效实现。我们提出了一个结合了NPMCS与CWMCS和BPMCS的集成系统，以提高PMCS的通信质量。提议的HCR识别多个系统的通信条件，然后为PMCS用户提供最佳的通信质量。尽管软件定义无线电技术（SDR）是更灵活地操作认知无线电的理想之选，但本文还是主要针对HCR来实现组合系统。我们研究了实现PMCS的HCR的优点，问题及其解决方案。首先，我们研究了使用HCR扩展NPMCS的服务区域。提议的HCR用于稳定NPMCS服务区域。如果NPMCS的通信质量由于阴影而恶化，建议的HCR终端从CWMCS或BPMCS获得NPMCS数据的一部分，称为辅助信息（SI）。所提出的HCR终端可以通过将SI与NPMCS的接收信号组合，然后使用前向纠错（FEC）解码组合信号来提高PMCS的误码率（BER）性能。由于卷积码常用于NPMCS的FEC中，因此我们考虑了卷积码的BER改进方法。我们从组合信号的最大似然序列估计（MLSE）中得出改进的Viterbi算法。此外，我们介绍了距离谱以评估卷积码的特性。距离谱用于估计BER性能的提高。接下来，我们考虑采用同步方法来实现所提出的HCR。在HCR中，有两种类型的同步方法：一种是自同步方法，用于同步每个系统本身。另一种是组合不同系统的协同方法。本文主要考虑了NPMCS的自同步方法。这是因为HCR旨在提高NPMCS的通信质量，该NPMCS配备了在低SNR环境中可能无法使用的常规自同步方法。在这种环境下，由于NPMCS很难单独获得其自同步，因此需要使用HCR技术的强大的自同步方法。我们提出了两种同步方法，分别是利用全球分配系统（GPS）信号和利用SI。利用GPS信号的同步方法可以获得定时同步。为了获得定时同步，建议的HCR使用GPS信号获取准确的时间和自己的位置。 HCR还通过使SI传达其信息来获取基站的位置和帧时序。由于HCR可以知道基站和HCR之间的准确时间和距离，因此可以计算出同步定时。但是，在基于GPS的方法中，由于GPS信号的测量误差，山峰引起的衍射和反射引起的传播延迟，可能会使定时同步的精度下降。因此，我们考虑一种时序误差的缓解方法，然后使用计算机仿真评估BER性能。此外，我们提出了一种基于SI的同步方法，该方法无需GPS信号即可获得定时同步。当NPMCS使用差分编码的π/ 4移位QPSK作为调制方案时，将采用所提出的方法。该方法的显着特征是将π/ 4位移QPSK的相位旋转作为SI传递。 HCR可以从获得的SI预测PMCS的包络，然后通过将预测的包络与实际接收的包络相关联来获得定时同步。由于所提出的方法还可以用于同步和BER改善，因此抑制了CWMCS传递SI的资源消耗。最后，我们考虑结合了多个PMCS的HCR。本文研究了NPMCS的组合以及NPMCS和BPMCS的组合。在NPMCS的组合中，我们认为SDR集成了多个PMCS。通过结合NPMCS和BPMCS，我们提出了基于HCR的站点分集，以提高BPMCS的上行通信质量。在这种多样性中，由于必须避免上行链路干扰，因此我们采用了自适应阵列和HCR技术的组合。此外，我们提出了针对窄带骨干线的信息压缩方法，以便可以将接收到的数据传送到总公司，而BER的下降很少。 PMCS将在确保社会安全方面发挥重要作用。在本文中，我们考虑采用SDR和HCR的下一代PMCS之一。通过这项研究，我们可以获得最佳PMCS的方向。我们需要执行的下一步是将我们提出的方法应用于实际的无线电系统。我们必须继续进行这项研究，以便可以实现高度可靠和紧凑的PMCS。

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