蜂窝中继网络研究及其软件无线电实验

【作者】 黄琳；

【导师】 杨鸿文；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2010， 博士

【摘要】 中继技术是近几年无线通信的研究热点,然而现有的大多数研究主要集中在具体的物理层或其相近层的相关技术方面。若中继技术要得到实际应用,必须要分析它在实际多小区蜂窝环境中的性能。因此,本文从系统性能的角度出发,分别针对室外固定中继、室外车载中继和室内中继三种最典型的场景,研究了中继技术的应用问题,其中移动中继和室内中继场景下的研究是已有文献中少有涉及的。在研究中,以对理论模型的分析为基础,并用计算机仿真为辅助。重视理论结合实际,特别地利用了软件无线电(SDR, Software Defined Radio)平台对某些场景进行了测量和实验。本文具体工作可归纳如下：首先,对室外固定中继场景进行了研究。在此场景中,中继节点的位置固定不变。这类场景是较简单的一类,也是3GPP标准中着重研究的。本文分析了几种室外环境中固定中继设备给系统带来的容量增益,通过数值计算和动态仿真进行了评估。并且,与蜂窝网中的微基站和Wifi接入点相比较,分析了在网络中部署各种类型的中继设备的成本。根据仿真结果和成本分析,得出了结论：即层1中继设备大约能增加10-30%的容量；层2中继设备大约能增加30-100%的容量。层1中继设备的成本相当于相同发射功率的层2中继设备成本的34%左右。层1中继设备适合于解决覆盖空洞：而层2中继设备可用于热点区域增加容量。然后,本文研究了室外车载中继的相关问题。室外车载中继是指在公共交通工具上安装的,覆盖车内乘客的中继设备。车载中继设备不仅可以改善车上手机终端的信号质量,而且可以避免由终端频繁小区切换所带来的开销。本文通过模型分析、数值计算和系统级仿真验证了车载移动中继可以提高系统的平均吞吐量。当基站与中继之间链路的信噪比增益为3dB,车载用户占总用户的50%时,车载用户的平均吞吐量大约增加17%,总容量大约增加14%。此外,针对车载中继引入的新的干扰类型,提出了一种新的干扰协调方法。除了理论分析之外,还利用SDR平台实际测量了车载中继在室外某地区的信号强度增益,发现该场景下回程链路的信噪比增益非常有限,需通过提高处理增益来改善中继节点的接收性能。本文不仅关注了室外场景的问题,也对室内中继的应用场景、部署方式进行了讨论。分析了室内中继系统的容量,并通过系统级仿真验证了室内中继设备的部署可以大大提高室内用户的吞吐量。在不同的部署方式下,室内用户的平均吞吐量增益分别为50-200%左右。然后,分析了室内中继的适用范围,即：尽管室内中继站与宏基站复用相同的频谱资源,室内中继系统仍然能够带来明显的性能增益,室内中继系统在绝大部分地理区域内都适用。与其他场景类似,针对室内中继场景,也利用SDR平台测量了一个普通家庭室内的信号强度分布。在此实例中,窗户位置的信号强度相比室内其他位置有明显的增强,因此适合安装室内中继设备来改善室内覆盖。本文还讨论了室内中继场景中的干扰问题。针对室内中继场景的干扰情况,提出了一种改进的资源分配方式和功率控制方法,大大降低了干扰。在进行理论分析的同时,还使用SDR平台测量了某个学生宿舍内的内墙损耗和楼层间损耗,验证了仿真模型的有效性。最后,本文探讨了SDR在蜂窝中继系统中的应用；以及如何利用SDR技术来实现中继；在系统架构和技术上的主要挑战等问题。提出了利用SDR技术为固定中继自适应配置预编码码本,为车载中继配置切换策略等方案。本文还给出了一个利用Wifi作为回程链路实现GSM系统室内中继的实例,实验中成功的实现了中继小区中的手机与PSTN之间的通话。另外,对SDR在中继网络规划优化中的作用进行了探讨。在本论文研究过程中,利用了SDR平台进行多点同步测量和自定义统计分析。这些方法可用在网规网优软件中,与中继系统软件相配合,实现中继的自优化功能。更多还原

【Abstract】 Relay technology is one of the hot topics in wireless communication in recent years. Most of the existing works focus on the physical layer or MAC layer. But the performance and feasibility of relay technology should be investigated when we want to use relay in real celluar environment. This dissertation studies the performance of relay from the system level, in three possible scenarios: outdoor fixed relay, vehicle relay and indoor relay, and discussed the interference problems in these three scenarios.Based on the system model analysis and simulation, the system spectrum efficiencies are evaluated, and the corresponding novel interference avoidance algorithms are proposed then verified. In addition, some channel measurement experiments based on SDR (software defined radio) platform are performed to verify the system model parameters.In the first part, the outdoor fixed relay is studied. Here the fixed relay means the position of relay node is fixed. This type of relay is the simplest one, and widely discussed in acdamic works. Firstly, the capacity gains of different types of outdoor fixed relay are analyzed and simulated. Furthermore, the total cost of ownership when relay is deployed is estimated and compared with its capacity gain. The conclusion of this part is:one layer 1 relay per sector can bring 10-30% capacity gain; layer 2 relay can bring 30-100% capacity gain; the cost of layer 1 relay is around 34% cost of layer 2 relay. Layer 1 relay is suitable to solve coverage problem and layer 2 relay can be used to improve the hot spot capacity.The second part is about the vehicle relay. Vehicle relay is a kind of relay node equipped on the bus or train to provide service only for the passengers. Vehicle relay can not only increase the signal level at cellphone receiver, but also reduce the overhead of group handover and save cellphone battery power. In this part, firstly the performance of vehicle relay is analyzed and simulated. When the SNR gain of base station-relay link is 3dB, and the proportion of vehicle users is 50%, the average vehicle user throughput increases 17% and the total cell throughput increases 14%. Secondly one interference coordination method is proposed to solve the interference problem in this vehicle relay scenario. Third, one SDR experiment is performed to measure the signal level gain from vehicle relay. The experiment results show that such gain is very small then we have to optimize the backhaul performance through other way.The third part focuses on the indoor relay. Its application scenario and deployment methods are firstly discussed. The capacity of indoor relay is also analyzed. The simulation results show that there is 57.6～206.9% gain in the indoor user average throughput. After that, one problem is discussed to see when indoor relay is useful. The conclusion is indoor relay is useful in most of the area because indoor relay has rich reused radio resource but few users in its cell. Interference problem is also discussed in this part. One improved resource allocation method and power control scheme are proposed to solve the interference problem. In addition, the signal strength distribution in one apartment is measured by SDR experiment. In this apartment, we found indoor relay can be used to improve coverage. Furthermore, inner wall penetration loss and floor penetration loss are also measured in several dormitories. The measurement results show that the interference level in simulation model is high enough compared with the real situation.In the last part, the applications of SDR technology in relay network are discussed. The architecture of SDR-based relay is introduced and the corresponding challenges are clarified. One example of relay implementation on SDR is given, where one GSM relay with wifi backhaul is implemented. In the previous research work, SDR is used as a network dimensioning and optimization tool, so the novel measurement methods and functions are summarized in this part.更多还原