城市轨道交通CBTC系统使用1.8 GHz频段的研究

针对未来城市轨道交通使用1.8 GHz频段建设CBTC(列车控制系统)专网,对当前城市轨道交通线路上的1.8 GHz频段开展电磁环境测试,发现存在与同频段其他系统的干扰。对CBTC系统信号分别建立使用自由空间和泄漏同轴电缆的传输模型,以上海市相关标准指标为参数,通过确定性计算的分析方法,分别得到两种传输方式下的1.8GHz频段同频保护距离,可以保护CBTC系统不受同频段其他系统干扰。     

地铁CBTC与列车厢内便携Wi-Fi干扰共存性能研究

文章主要介绍地铁列车厢内便携Wi-Fi系统对地铁移动闭塞系统(CBTC)系统的干扰。考虑同样采用IEEE 802.11g制式的地铁CBTC系统和地铁列车厢内便携Wi-Fi设备在抢占2.4GHz频段同一信道时的干扰共存场景,理论推导便携Wi-Fi系统对CBTC系统中的车载无线吞吐量的影响;并通过蒙特卡洛仿真方法建立CBTC和车厢内便携Wi-Fi共存的系统模型,模拟IEEE 802.11g MAC层DCF协议,分析在便携Wi-Fi干扰下地铁CBTC系统上行链路的通信性能。通过仿真得到由于便携Wi-Fi的干扰导致CBTC系统上行链路信号的吞吐量、成功传输次数、碰撞次数以及时延的变化情况。     

基于Matlab的CBTC系统邻频干扰研究

针对IEEE 802.11g标准的特性,引入邻频干扰函数作为定量研究系统邻频干扰的方法。通过模拟一种实际运行场景,对采用不同信道方案时接收信号质量进行分析与计算,得出的增大信道间隔将有效提升接收信号的质量和系统吞吐量,为CBTC系统的信道规划提供理论依据和参考。     

IMT系统对1518～1525 MHz频段卫星移动系统的干扰

为分析在1 518～1 525MHz频段附近部署IMT系统的可行性,在梳理了国际电信联盟建议书和《无线电规则》的基础上,通过理论分析和仿真计算等手段,就1 492～1 518MHz频段IMT系统对1 518～1 525MHz频段卫星移动系统的干扰问题进行了深入分析.针对IMr系统基站对卫星移动系统终端在不同场景下的干扰链路,采用蒙特卡洛仿真方法对阻塞干扰与邻频干扰进行计算仿真.仿真结果给出了不同场景下的阻塞干扰概率以及两个系统邻频共存的条件.研究结果可为我国无线电管理部门对该频段邻频的未来规划提供理论支撑.     

2.6GHz频段内NR与LTE-FDD的共存干扰分析

当前通信过程中NR(新空口)与LTE-FDD(频分双工)共存时二者产生的干扰造成各自平均相对吞吐量损失过大,影响通信质量和用户体验。针对此问题,文章开展2.6 GHz频段内NR与LTE-FDD的共存干扰分析。规划、构建2.6 GHz频段内NR与LTE-FDD容量、传播模型,计算邻频干扰功率比,明确NR与LTE-FDD的共存干扰,并结合分析结果提出干扰规避与时隙对齐优化方案。通过实例应用证明,优化后NR与LTE-FDD通信过程中的平均相对吞吐量损失明显降低,且不会受到邻频干扰功率比变化的影响,提高通信质量。     

3.5 GHz频段5G系统对ATG系统干扰分析

为研究3.5 GHz频段地面5G系统对地空宽带通信(air to ground, ATG)系统同频同步干扰情况,对该频段中5G系统与飞机上ATG系统间的同频共存问题进行了系统间同频共存分析. 采用5G系统技术参数,在城区、城郊连续和郊区不同场景下,仿真5G系统基站(base station, BS)对机载ATG系统干扰情况及5G系统用户对ATG BS干扰情况,分别计算得到不同场景下5G系统BS对机载ATG系统及5G系统用户对ATG BS的平均干扰功率密度. 仿真结果表明,地面5G系统BS对机上ATG系统的同频干扰影响较小,可将该干扰视为可接受干扰. 同时,本文还给出了ATG BS的部署隔离距离参考值.     

基于返回散射探测和干扰监测的短波通信实时选频系统

 提出了一种基于HF电离层返回散射探测和干扰监测的短波通信实时选频系统.利用返回散射快速扫频及返回散射电离图自动判读技术,实时获取短波通信的可用频段信息,基于实时干扰监测结果,利用基于时间可用度的自动干扰分析技术得到干净信道信息,两种信息融合实时选择通信频率.文中给出了一些具体链路的通信选频试验结果,并对某些特殊情况下的实时选频效果进行了深入分析,试验结果表明了该系统的有效性.     

2.4G频段WLAN与TD-LTE系统间干扰控制

当今频段资源已成为移动通信各大运营商相当稀缺的资源,各制式的通信系统之间的频率间隔变得很小,相邻频段的通信系统相互间容易形成杂散干扰和阻塞干扰。共同工作于2.4GHz频段的TD-LTE与WLAN系统,如果没有对相互间产生的杂散干扰和阻塞干扰进行控制,对彼此的通信质量有较大的影响,本文通过分析WLAN带外干扰对TD-LTE的影响,研究如何控制WLAN干扰值以保证TD-LTE系统的正常运行。     

同频异构femtocell联合子信道和功率分配算法

摘要：针对macro-femto同频融合网络中基于资源分配的干扰抑制问题,提出一种联合子信道和功率分配算法来抑制同频干扰。该算法通过对MU进行功率控制并采用跨层切换消除同频跨层干扰,对FU进行联合信道和功率分配消除同频层内干扰;跨层切换问题是在每一层网络目标中断概率约束下通过优化网络吞吐量实现,而基于联合信道和功率分配的同频干扰抑制问题是在切换MU的目标数据速率和其他MU以及FU干扰门限约束下,通过优化FU的和速率实现。理论分析和仿真结果表明,该算法能够提高FU的和速率,增大femtocell的网络容量,并可增加femtocell的部署数目。     

Ka频段卫星通信自适应传输技术

随着经济的日益发展,传统的C频段、Ku频段已经无法满足生活和社会活动的通信需求,因此带宽更大的Ka频段成为近年来的发展方向.由于通信信道条件对Ka频段卫星通信的影响很大,所以克服通信质量的干扰成为Ka频段通信的主要工作.本文在Ka频段卫星通信中给予LDPC码的自适应编码调制(ACM)技术及功率控制技术进行了研究.     

Performance improvements of communication-based train control (CBTC) systems with unreliable wireless networks

Communication-based train control (CBTC) uses wireless networks, such as wireless local area networks (WLANs), to transmit trains status and control commands. CBTC systems have stringent requirements for train-ground communications, as the train control system depends on the accurate, timely and reliable data over the communication links. However, since WLANs are not originally designed for high mobility environment, random packet delay and losses are inevitable in WLAN-based CBTC systems, which could result in unnecessary traction, brake or even emergency brake of trains, losses of line capacity and passenger satisfaction. In this paper, we study the impacts of random packet delay on the performance of CBTC systems, and propose a novel scheme to improve the CBTC performance by mitigating the impacts of random packet delay. Unlike the existing works that only consider a single train, we consider a group of trains in CBTC systems to improve the CBTC performance. Extensive field test and simulation results are presented. We show that the current adopted control scheme in CBTC systems needs to keep stability and performance under transmission delays through increasing the distance between trains in steady state which means cost of line capacity. By contrast, our proposed scheme can significantly improve the CBTC performance.     

PIS和CBTC共存WLAN干扰问题的研究

通过分析乘客信息系统(PIS)和列车自动控制系统(CBTC)的功能及无线局域网IEEE802.11a特点,以及通过无线局域网技术(WLAN)技术实现PIS与CBTC双向通信网络带宽需求,详细论证了PIS对CBTC系统的同频干扰、邻道干扰问题,并给出了在工程实现解决上述干扰问题的具体方案.     

Frequency-hopped multiple-access communication with nonorthogonalBFSK in Rayleigh fading channels

Nonorthogonal binary frequency-shift keying is considered in frequency-hopped multiple-access communication systems with Reed-Solomon coding. The effect of tone spacing on the average number of successfully transmitted information bits per unit time per unit bandwidth (called normalized throughput) is examined in Rayleigh fading channels. The tradeoff among tone spacing, code rate, and number of frequency slots in maximizing the normalized throughput is examined, keeping the total bandwidth fixed. The optimal tone spacing, code rate, and number of frequency slots in terms of the number of users and E¯_b/N₀ is also discussed. The throughput gain attained by using the optimal tone spacing becomes more significant as the number of users is increased     

基于WiFi6的城轨车地通信综合承载系统—系统设计与现场测试

2018年10月，IEEE发布了最新的WiFi标准协议802.11ax(WiFi6)，它同时支持2.4 GHz和5 GHz频段，传输速率可达9.6 Gbit/s^[1]。WiFi6的横空出世引起大量技术人员的研究，目前，WiFi6已应用在智能家居、广电、矿井建设等领域，但在轨道交通领域屈指可数。本文设计了基于WiFi6的城市轨道交通车地通信综合承载系统，通过将WiFi6赋能轨道交通车地通信系统，可以解决城市轨道交通的各项生产业务间严重的争抢频率资源问题，并在大连地铁13号线进行全国第一个WiFi6系统的真实地铁线路测试。结果表明，所设计的WiFi6系统具有网络吞吐能力大，传输速率快，覆盖范围广等特点，能够满足轨道交通业务需求，同时能够为CCTV和PIS等业务提供有效的传输通道。     

基于无线通信的CBTC研究综述

对基于通信技术的列车控制系统进行了全面研究,分析了CBTC系统通过车地设备间的连续、高速、双向的数据通信技术,实现列车的高精定位和控制的关键作用,并进一步介绍了CBTC的基本原理、特点和系统结构,对CBTC系统中几种常用的无线通信解决方案进行了分析和比较,总结得出采用漏泄同轴电缆和无线电台混合组网的最优解决方案,同时指出CBTC系统由于采用了先进的通信技术,其必将引领现代城市轨道交通与铁路通信信号发展的未来方向.     

Service availability analysis in communication‐based train control systems using wireless local area networks

Data communication technology is one of the key subsystems in communication‐based train control (CBTC), which is an automated train control system for railways that ensures safe operation of rail vehicles using data communications. In CBTC systems, less service availability could cause train derailment, collision or even catastrophic loss of lives or assets. Therefore, the availability of data communication should be carefully considered in designing CBTC systems. In this paper, we propose two wireless local area network (WLAN)‐based data communication systems with redundancy in CBTC systems. The availability is analyzed using continuous time Markov chain (CTMC) model. We also model the WLAN‐based data communication system behavior with deterministic and stochastic Petri net (DSPN). The DSPN solution is used to show the soundness of our proposed CTMC model. Numerical examples illustrate that the proposed systems with redundancy can significantly improve service availability in CBTC systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Novel Fairness Improved Radio Resource Management Schemes for Best-Effort Service in OFDMA Systems

In this paper, we propose a complete radio resource management procedure for best-effort service in OFDMA systems, which improves the system fairness with graceful throughput degradation compared to the upper bound of the system throughput. By the proposed bandwidth and power allocation algorithms, the user in the worst channel environment has almost the same probability of accessing the system as the user in the best channel environment. Furthermore, a novel sub-channel allocation algorithm is proposed to exploit frequency selectivity and multi-user diversity gains simultaneously in OFDMA systems, which is able to achieve the highest system throughput given each user’s channel environment.     

城轨CBTC系统中数据通信子系统的研究

随着无线通信技术的飞速发展,无线通信的可靠性、可用性大大提高,基于通信的列车运行控制系统（CBTC）是今后轨道交通列车运行控制系统的发展趋势。数据通信系统（DCS）实现CBTC系统地面设备之间和车地设备之间的双向信息交换,是CBTC系统的核心。研究了数据通信系统的骨干网络,对其系统的硬件配置进行了理论分析,讨论了网络容量,噪声及干扰控制,并对数据通信系统的安全性能进行了分析。     

非完备功控CDMA无线网络上行准入控制算法及性能分析

本文研究了非完备功控宽带CDMA无线网络上行准入控制问题。首先为非完备功控CDMA网络上行链路建立了系统模型，然后设计相应的准入控制算法，其中无线资源被划分为供各类用户专用的部分和在各类用户之间共享的部分。为了利用非实时用户可以容忍延时的特点，又引入了队列结构以降低阻塞率。通过对算法进行Markov分析，从理论上计算了用户阻塞率和平均吞吐率性能。仿真结果验证了理论模型的正确性。     

Efficient MAC protocol design and performance analysis for dense WLANs

In this paper, we analytically study the dense basic service set network transmission problems in very high throughput (VHT, namely IEEE 802.11ac) wireless local area networks (WLANs) due to nervous bandwidth resources. Our contributions are threefold as follows. Firstly, we derive the closed-form expressions of throughput gains for primary channel establishment from multi-band selection using the optimal skipping rule, which balances the throughput gain from finding a good quality band with the overhead of measuring multiple bands. Secondly, in order to satisfy the quality of service of overlapping BSS users, we design a space interference avoidance mechanism, which can improve the system throughput for the whole dense WLANs. Thirdly, in order to further improve the transmission performance of dense BSS networks, we propose an unequal bandwidth transmission mechanism based on the VHT WLANs, which can not only clear the redundant network allocation vector duration timely but also use the limited bandwidth efficiently. The proposed protocols and mechanisms exploit both time and frequency diversity sufficiently, and are shown to result in typical throughput gains compared with the traditional IEEE 802.11 MAC protocol.