8GHz散射通信中扩频分离多径技术的应用

主要阐述8GHz散射通信系统的设计思路和采用线性调频扩频信号以及分离多径接收的合理性。对线性调频信号的形式和特点进行了分析,给出了分离多径技术的设计和实现方法。并以实际工程为例,给出了实测的通信链路试验波形和试验结果,用以说明扩频、分离多径技术应用于8GHz散射通信中获得的显著效果。实践表明,该系统有很强的实用价值。     

四种超宽带扩频方案的电磁兼容性能研究

由于保护距离有限,在满足功率谱密度限制的条件下超宽带信号仍然可能对其它通信系统产生一定的干扰。该文在直接序列扩频、跳时扩频、跳频扩频和线性调频扩频4种超宽带扩频信号通过AWGN信道时,推导了在超宽带扩频信号干扰下未扩频的其它通信系统误比特率的通用表达式,并通过蒙特卡罗仿真验证了理论推导的正确性。同时还给出了超宽带扩频信号通过IEEE 802.15.3a CM4信道时的仿真结果。这些结论为超宽带系统的电磁兼容性能评价和扩频方案选择提供了重要参考。     

引入直接序列扩频的线列阵通信信道均衡技术

在空间多径信道垂直线列阵通信中,由于多阵元码间干扰导致信道失衡,误码率较高,需要进行信道均衡设计。传统方法采用随机码扩频方法进行通信信道均衡,扩频信号经高放和混频后导致非线性失真,均衡效果不佳。文中提出一种基于直接序列扩频的线列阵通信信道均衡算法。基于PTRM技术构建了垂直线列阵通信的空间多径信道模型,采用直接序列扩频方法设计码间干扰抑制算法,利用垂直线列阵结构对PTRM时间压缩性能,接收到的扩频信号经高放和混频后,对中频扩频的调制信号进行相关解扩,重组多垂直线列阵的径分量,实现信道均衡。仿真结果表明,采用该算法进行垂直线列阵通信,信道均衡性能和码间干扰抑制性能较好,并有效降低了误比特率,改善了通信质量。     

基于直接序列扩频的WSN通信信道调制算法

无线传感器网络(WSN)通信是无线通信的重要应用领域,WSN通信信道受到码间干扰导致信道均衡度不高,需要进行信道调制提高信道均衡性能,降低误码率。提出一种基于直接序列扩频的WSN通信信道调制算法。进行WSN通信的信道模型构建,采用奈奎斯特码间干扰抑制原理进行波特间隔均衡器设计,对接收信号进行贯序处理,采用直接序列扩频技术实现WSN通信信道优化调制。仿真结果表明,采用该算法进行WSN通信,信道均衡性能较好,输出码元的误比特率较低,在通信质量改善方面比传统方法具有优越性能。     

基于频谱压缩接收的宽带/超宽带线性调频信号参数估计

该文提出了一种新的宽带/超宽带线性调频信号的接收方法, 它将宽带/超宽带线性调频信号通过射频通道的频谱压缩网络变成窄带信号,数字域用逆频谱压缩函数对压缩信号进行非线性重构,原线性调频信号的调制斜率和初始频率可通过重构信号精确估计。计算机仿真证实了算法的有效性。     

基于改进离散蝙蝠算法的无线Mesh网络部分重叠信道分配

针对应急通信背景下无线Mesh网络(WMN)中存在的信道干扰和频谱资源利用不充分的问题,该文提出一种改进的离散蝙蝠算法(IDBA)用于求解最优部分重叠信道(POCs)分配方案。该方法采用K-means聚类算法优化网络拓扑,引入樽海鞘群的链式行为提高局部搜索能力,建立以最小化链路加权干扰为目标的线性规划模型来解决流量汇聚情况可能造成的网络瓶颈链路问题。仿真结果表明,在不同网络规模下,相比于其他基于群智能优化算法的信道分配方法,该方法具有较快的收敛速度和较优的搜索能力。此外,该方法能够在节点密集时显著降低网络干扰并保持网络的稳定性。     

ETC系统中路侧单元下行链路的频谱特性研究

文章介绍了一种采用ADS软件数据流仿真获得射频电路频谱特性的方法，并采用该方法对ETC系统中路侧单元下行链路的频谱特性进行了分析，详细讨论了影响输出信号带外杂散电平的因素，给出了满足国标频谱模板的射频电路合理设计方法即中频调制法，通过解调信号与原信号对比一致性验证了该方法的正确性。该方法虽然稍微增加了射频电路的硬件成本，但给出的射频电路性能指标优异，可有效降低杂散发射电平及对临近信道的干扰，并且工程易实现。     

线性调频信号在散射通信中的应用

较详细地分析了线性调频信号的恒包络特性、矩形频谱特性以及匹配输出的窄相关特性;系统阐述了对流层散射通信的快衰落和大损耗特点;根据线性调频信号的窄相关性,设计散射通信的分离多径技术,还可以利用其扩频特性达到抗截获、抗干扰的作用。     

基于双光学频梳的超宽带射频信号信道化合成技术研究（特邀）

随着现代通信系统的发展,宽带和高频微波射频信号在雷达,通信和信号处理等领域的应用越来越广泛。基于微波光子信道化技术,文中通过两个自由频谱范围不同的光学频梳,实现了超宽带射频信号的信道化合成。在信道化合成系统中,多个独立的窄带信号输入各个信道进行上变频,并在多外差探测中被重组成为一个具有连续频谱的宽带射频信号。在多外差探测中,干扰抑制技术的使用提高了合成射频信号可达到的最高频率。在实验中,合成了一个覆盖频率范围8.4~12.4 GHz,瞬时带宽为4 GHz的宽带射频信号。实验结果显示,干扰的抑制率达到了21 dB,表明干扰抑制技术的使用提高了输出信号的最高频率的同时有效地提高了频谱利用率。     

基于发射功率自适应调节的无线通信网抗扰研究

为解决智能楼宇中ZigBee网络与WiFi网络之间的干扰问题,通过采用TI公司的CC2530芯片,设计了一种发射功率自适应调节的无线传感器网络节点。文中主要采用试验的方法对不同环境下的ZigBee节点之间通信的可靠性进行测试,得出通信距离、误包率和接收信号强度指示RSSI之间的关系。利用RSSI作为通信评价因子,根据实际应用环境的变化,自适应地改变ZigBee通信节点的发射功率。经实验测试,只需RSSI值＞-51 dBm,便可保证干扰环境下的误包率接近为0。     

Power and Channel Optimization for WiFi Networks Based on REM Data

The very high commercial exploitation of the WiFi based technologies in recent years and the absence of solutions for optimal WiFi orchestration, usually leads to suboptimal spectrum usage and user performances. The combination of WiFi based radio resource management (RRM) and the radio environmental maps (REMs) can provide an efficient solution for a Smart-WiFi technology, which improves the underlying spectrum usage as well as network performance. The REM facilitates efficient utilization of the radio environmental data, like device location, estimated channel models, real-time interference levels between the networks, WiFi channels occupancies etc. This information can be utilized for an intelligent and optimal RRM decision making in WiFi related scenarios. This paper proposes a novel REM based RRM approach for management and optimization of commercial WiFi devices that utilizes the available underlying radio environmental information. The paper demonstrates the proposed approach on a commercially available platform, conducting on-the-fly radio environmental data acquisition and optimized WiFi RRM allocation. The simulation analysis results also show that the proposed Smart-WiFi leverage noticeable performance gains for large scale scenarios, compared to conventional WiFi networks.     

移动互联网中的智能终端研究

移动互联网环境下,智能通信终端需要实现多模多待,具有智能化、开放化的平台和丰富的客户端。在这种情况下,功耗、两网射频的互扰、两网协同问题显得尤为突出,对此文章给出了相应的解决方案：通过视频增强器提升画质,减低功耗;通过避免带内泄漏干扰和带外阻塞干扰减少两网射频互扰;通过对通信架构、处理器、业务逻辑和用户界面几个方面重新设计实现双网双通有效协同。     

Geometry modeling in cellular network planning

To design a cellular radio network (GSM, UMTS, WiFi …) it is indispensable today to use a radio planning software. In current commercialized tools, radio network planning is based on a numerical evaluation of a set of radio metrics, directly linked to quality of service notion, such as interference, throughput, coverage, capacity … The network configurations produced by such tools are generally faced with the human expert judgment who attaches great importance to the organizational aspects such as cells size and the topology. In other words, all those concepts related to the visual cells shape and geometry. In this article we emphasize the simplicity and the strength by which the geometrical concepts helps to bring out good network properties which are not taken into account by conventional radio criteria. On one hand, well-formed cells lead to reduce the number of handover calls, and to form transition zones between cells allowing proper completion of the handover procedure. On the other hand, cell geometry optimization produce performing network schemes in which the frequencies reuse (frequencies planning in GSM, WiFi) is simplified. We describe in this paper an original and practical modeling of the cellular geometry criteria granting the integration of this concept into the automatic planning process of mobile radio networks. The relevance of this criterion is assessed on three different levels. On a local level, we first establish the correlation between the geometric criteria and the improvement of point-by-point radio quality indicators. We secondly show geometry impact on radio frequency planning and the improving of the handover zones. Finally we analyze the impact of geometric criterion on improving indoor positioning systems.     

Real-time implementation of distributed beamforming for simultaneous wireless information and power transfer in interference channels

In this paper, we propose one-bit feedback-based distributed beamforming (DBF) techniques for simultaneous wireless information and power transfer in interference channels where the information transfer and power transfer networks coexist in the same frequency spectrum band. In a power transfer network, multiple distributed energy transmission nodes transmit their energy signals to a single energy receiving node capable of harvesting wireless radio frequency energy. Here, by considering the Internet-of-Things sensor network, the energy harvesting/information decoding receivers (ERx/IRx) can report their status (which may include the received signal strength, interference, and channel state information) through one-bit feedback channels. To maximize the amount of energy transferred to the ERx and simultaneously minimize the interference to the IRx, we developed a DBF technique based on one-bit feedback from the ERx/IRx without sharing the information among distributed transmit nodes. Finally, the proposed DBF algorithm in the interference channel is verified through the simulations and also implemented in real time by using GNU radio and universal software radio peripheral.     

认知融合网络的关键技术

关注异构蜂窝网络和认知无线网络的发展,分别总结了认知异构蜂窝网络、认知家庭基站和认知WiFi 2.0网络的概念和相应研究,凝练了认知融合网络的概念。针对认知融合网络中宏站与多小站共存于相同频段,必然导致严重的干扰问题,提出了认知资源管理和认知干扰管理环路框架,实现资源和干扰的高效管理,有效提升端到端的用户体验质量。最后展望了认知融合网络的未来发展方向和关键技术问题。     

基于神经网络的多窗口频谱估计方法研究

干扰温度估计是认知无线电技术中的关键问题之一.多窗口频谱估计结合奇异值分解技术提供了一种估算射频环境中干扰温度功率谱的有效途径.提出基于神经网络的多窗口频谱估计结合奇异值分解的算法,与传统算法相比,该算法提高了干扰温度估计值的可靠性和准确度,降低了计算复杂度,同时能够适应复杂电磁环境下对干扰温度的实时性估值的要求.     

基于CC2430的无线传感器网络的实现

无线传感器网络是一项新兴的技术,具有广泛的应用领域。在简单介绍无线传感器网络的概念及其特点的基础上,着重讨论基于ZigBee技术和433 MHz无线射频技术的无线传感器网络的实现方法,包括无线传感器网络的硬件和软件设计。ZigBee是一种具有全球统一标准的自组织网状网,网络容量大、组网灵活。多个ZigBee网络的协调器节点通过433 MHz无线射频组成星型网,有效地扩大了传感器网络的地理覆盖范围。实验结果表明,网络节点及整体网络均获得了良好的性能,验证ZigBee是实现无线传感器网络的理想解决方案。     

Analysis of resource splitting scheme with cognitive based admission control for femto-WiFi wireless networks

The coexistence of femtocell and WiFi networks in a heterogeneous spectrum environment with licensed and unlicensed bands will support multi-mode femtocell users (FUs) to simultaneously transmit on both licensed and unlicensed bands. The efficient integration of both femtocell and WiFi technologies is seen as crucial for supporting the offloading of femtocell traffic to WiFi networks. To successfully deploy these integrated technologies, the overall licensed and unlicensed spectrum usage must be efficiently managed. Thus, we propose a new cognitive-based connection-level admission control with access retrial for a femtocell network that operates under a mixed spectrum of unlicensed and licensed bands. By deploying cognitive radio concepts, the FUs will utilize the unused spectrum of the existing unlicensed spectrum of the WiFi network in an opportunistic manner in addition to using the licensed spectrum. By using the retrial phenomenon policy, the blocked FUs can retry the access, which can reduce their loss probability. An analytical model using a three-dimensional continuous time Markov chain with a level-dependent quasi birth-and-death structure was developed to evaluate and study the performance of the proposed scheme. The matrix analytic method was used to obtain the steady state probability and performance measures. The result shows that the performance of FUs for integrated femtocell-WiFi networks using the proposed scheme significantly improved in terms of FUs throughput and loss probability. The results also show that the retrial phenomenon of FUs enhances their performance.     

Performance Analysis of Composite Fading Channel Based on Point Estimate Method

Existing spectrum sensing methods for cognitive radio do not consider the secondary network’s characteristics to obtain the frequency of spectrum sensing, i.e., the sensing period would be identical for secondary networks that have different traffic characteristics. In this paper, a hybrid sensing algorithm is proposed that finds the optimal sensing period based on both primary and secondary networks’ properties. A continuous-time Markov chain system is used to accurately model the spectrum occupancy, and a novel method is proposed that adaptively varies its parameters to avoid unnecessary sensing tasks, while guaranteeing the priority of the primary network. We conduct simulation work to evaluate the performance of the proposed method. It is shown that the proposed technique outperforms the non-hybrid approach with respect to sensing efficiency and energy consumption. A cognitive sensor network is also considered based on IEEE 802.15.4/ZigBee radios, and it is shown that significant energy savings can be achieved by the proposed method.