基于SC分集的混合FSO/RF航空通信系统性能分析

研究了基于选择合并(SC)分集的混合激光/射频(FSO/RF)航空通信系统性能,该系统设计简单且在发射端无需信道状态信息(CSI)。激光链路服从平均孔径效应下的Exponentiated Weibull大气湍流分布模型,射频采用Nakagami-m衰落信道模型,推导求出混合FSO/RF航空通信系统接收端信噪比的累积分布函数,进一步利用Meijer′s G函数推导了混合FSO/RF通信系统中断概率以及平均误码率的闭合表达式,通过仿真对比分析了不同湍流强度、调制方式及分集通信方案对系统中断、误码性能的影响。仿真结果表明,混合FSO/RF航空通信系统有效地利用了FSO及RF链路在不同大气信道条件下的互补性质,具有更优的中断和误码性能;采用BPSK调制能有效降低大气湍流对混合FSO/RF航空通信系统的影响;信噪比高时,并行传输、分集接收的通信方案对系统误码性能的改善要优于低阶调制对误码性能的改善。     

Performance and optimization of hybrid FSO/RF communication system in varying weather

Photonic Network Communications - Radio frequency (RF) spectrum is already dense enough and hard to add more broadband channels to meet the current user demands. Optical free-space communications...     

美军机载射频与FSO混合通信发展述评

机载光与射频混合通信系统概念是美国防先期研究计划局( DARPA)提出的创新性概念,用以为机载平台提供定向高速宽带数据链,支持空基骨干网等宽带通信应用。目前该概念已经进行了概念验证以及多次演示和测试。概述了美军机载光与射频混合通信研究进展,分析了相关关键技术,指出了发展趋势,并给出了相关的启示和建议。     

A new switching scheme for hybrid FSO/RF communication in the presence of strong atmospheric turbulence

Photonic Network Communications - Hybrid FSO/RF communication systems make use of an RF link with OWC link to achieve higher reliability along with high data rate communication. Both these (OWC and...     

基于大气信道链路的混合FSO/RF系统性能分析

提出了新的混合FSO/RF系统信道模型,此模型不仅克服了雾和雨对链路的严重影响,而且降低了系统的能量衰减,提高了系统的可用性.该系统在接收端探测器采用比较光电流大小来选择适合信道传输的链路,克服了各种天气状况的影响,最大限度地满足用户对通信性能的要求.     

Soft-switching hybrid FSO/RF links using short-length raptor codes: design and implementation

Free-space optical (FSO) links offer gigabit per second data rates and low system complexity, but suffer from atmospheric loss due to fog and scintillation. Radio-frequency (RF) links have lower data rates, but are relatively insensitive to weather. Hybrid FSO/RF links combine the advantages of both links. Currently, selection or ?hard-switching? is performed between FSO or RF links depending on feedback from the receiver. This technique is inefficient since only one medium is used at a time. In this paper, we develop a ?soft-switching? scheme for hybrid FSO/RF links using short-length Raptor codes. Raptor encoded packets are sent simultaneously on both links and the code adapts to the conditions on either link with very limited feedback. A set of short-length Raptor codes (k = 16 to 1024) are presented which are amenable to highspeed implementation. A practical Raptor encoder and decoder are implemented in an FPGA and shown to support a 714 Mbps data rate with a 97 mW power consumption and 26360 gate circuit scale. The performance of the switching algorithms is simulated in a realistic channel model based on climate data. For a 1 Gbps FSO link combined with a 96 Mbps WiMAX RF link, an average rate of over 472 Mbps is achieved using the implemented Raptor code while hard-switching techniques achieved 112 Mbps on average.     

Exponentiated Weibull大气湍流下混合RF/FSO系统容量分析

RF/FSO混合通信系统弥补了自由空间光通信受天气影响严重的问题,提高了系统的可用性。本文研究了Exponentiated Weibull大气湍流下双门限混合RF/FSO系统平均信道容量,考虑大气湍流和指向误差对平均信道容量的联合影响,利用MeijierG函数推导出平均信道容量的闭合表达式。根据平均信道容量闭合表达式进行了仿真,分析了在不同距离、大气湍流强度、抖动标准差和波束宽度条件下,平均信道容量随信噪比变化的关系。     

基于网络丢包率的混合FSO/RF系统切换技术研究

利用C++ Builder编程软件提供的相关网络组件,提出了基于网络丢包率的混合FSO/RF系统切换判决机制,在网络中实现了对链路的监控功能,并采用无线路由器、光纤收发器等器件搭建了混合FSO/RF测试系统,对基于网络丢包率的混合系统切换机制进行了测试,结果表明采用网络切换判决方案,能够自动选择链路通信,保证数据不间断...     

Throughput and delay analysis for hybrid radio-frequency and free-space-optical (RF/FSO) networks

In this paper the per-node throughput and end-to-end delay of randomly deployed (i.e. ad-hoc) hybrid radio frequency - free space optics (RF/FSO) networks are studied. The hybrid RF/FSO network consists of an RF ad hoc network of n nodes, f(n) of them, termed ‘super nodes’, are equipped with an additional FSO transceiver with transmission range s(n). Every RF and FSO transceiver is able to transmit at a maximum data rate of W ₁ and W ₂ bits/sec, respectively. An upper bound on the per node throughput capacity is derived. In order to prove that this upper bound is achievable, a hybrid routing scheme is designed whereby the data traffic is divided into two classes and assigned different forwarding strategies. The capacity improvement with the support of FSO nodes is evaluated and compared against the corresponding results for pure RF wireless networks. Under optimal throughput scaling, the scaling of average end-to-end delay is derived. A significant gain in throughput capacity and a notable reduction in delay will be achieved if \(f(n) = \Upomega\left(\frac{1}{s(n)}\sqrt{\frac{n}{\log n}}\cdot \frac{W_1}{W_2} \right)\). Furthermore, it is found that for fixed W ₁, f(n) and n where f(n) < n, there is no capacity incentive to increase the FSO data rate beyond a critical value. In addition, both throughput and delay can achieve linear scaling by properly adjusting the FSO transmission range and the number of FSO nodes.     

Mixed RF/FSO bidirectional system achieving spectral efficiency

The performance of two-way relay (TWR)-assisted mixed radio-frequency/free-space optical (RF/FSO) system is evaluated in this letter. The proposed system employs decode-and-forward relaying phenomena where the relay is basically an interfacing node between two source nodes \(S_1\) and \(S_2\), where \(S_1\) supports RF signal, while \(S_2\) supports FSO signal. The TWR-assisted system helps in achieving spectral efficiency by managing bidirectional communication in three time slots, thus maximizing the achievable rate of the network. The RF link is subjected to generalized \(\eta -\mu \) distribution, and the optical channel is affected by path loss, pointing errors and gamma–gamma (gg) distributed atmospheric turbulence. The novel expressions for the probability density function and cumulative distribution function of the equivalent end-to-end signal-to-noise ratio (SNR) are derived. Capitalizing on these derived statistics of end-to-end SNR, the expressions of outage probability and the bit-error rate for different binary modulations and M-ary modulations are provided.     

Availability Evaluation of Ground-to-Air Hybrid FSO/RF Links

Recently, a hybrid architecture that utilizes the complementary nature of free-space optics (FSO) and radio frequency (RF) links with respect to their individual weather sensitivities was proposed to significantly increase availability for terrestrial broadband links. Based on this architecture, we developed a channel model integrating both the RF and FSO channels. Using the model and cloud distribution data obtained from the International Satellite Cloud Climatology Project, availability of an airborne hybrid FSO/RF link is evaluated. From the results, we conclude that if the FSO link alone is used, availability is greatly hampered by clouds due to attenuation and temporal dispersion. Contrarily, the RF signals are relatively immune to cloud influence, thus improving the hybrid link availability significantly. Furthermore, because of the significant temporal dispersion caused by multiple scattering of cloud particles, availability of FSO links can be improved by using frequency division schemes, though far from compensating for losses incurred by clouds.     

Threshold optimization for modified switching scheme of hybrid FSO/RF system in the presence of strong atmospheric turbulence

Photonic Network Communications - Translucent optical networks use sparsely located regenerator nodes to increase the optical reach, otherwise limited by the physical layer impairments. Routing in...     

Performance Analysis of the Hybrid MMW RF/FSO Transmission System

Wireless Personal Communications - In this paper, an exact performance analysis for the hybrid radio frequency/free space optical (RF/FSO) communication system based on receiver diversity combining...     

Relay selection in mixed RF/FSO system using DF relaying

In this paper, we carry out the performance analysis of relay selection in decode-and-forward (DF)-based mixed radio frequency/free-space optical (RF/FSO) system. We consider two relay selection schemes, namely max-select and distributed switch and stay, and compare their performance with the system having all relays active. The selected DF relay decodes the received RF signal from source and converts it into an optical signal using the subcarrier intensity modulation scheme for transmission over FSO links. The RF links follow generalized \(\eta -\mu \) distribution, while the FSO links are subjected to pointing errors and are assumed to follow gamma–gamma distribution. Novel analytical expressions for cumulative density function and the moment generating function of the equivalent end-to-end signal-to-noise ratio are derived. Capitalizing on the derived statistics, we provide the new closed-form expressions of the outage probability for different relay selection schemes.     

Steerable reflector-assisted communication in obstructed line-of-sight FSO link with optimal mitigation of dust-induced signal fading

Photonic Network Communications - This paper introduces an effective technique for bridging free-space optical (FSO) communication between end-to-end nodes with obstructed direct line-of sight...     

具有能量收集的双向RF/FSO中继系统性能分析

设计了一种在大气湍流和指向误差影响下的带有能量收集的混合双向RF/FSO中继传输系统。RF信号部分采用能量分割的方式进行能量收集,FSO信号部分则将其信号中的直流电分量所携带的能量收集起来存储在中继器中。其中射频RF链路采用Nakagamim信道衰落模型,自由空间光FSO链路采用Gamma Gamma信道衰落模型。并且计算出了两条链路各自的累积分布函数CDF。采用DF的中继协作方式,并利用Meijei G函数推导出系统中断概率的闭合表达式,最终通过仿真来验证结果的正确性。     

Distributed topology control in large‐scale hybrid RF/FSO networks: SIMT GPU‐based particle swarm optimization approach

The tremendous power of graphics processing unit (GPU) computing relative to prior CPU‐only architectures presents new opportunities for efficient solutions of previously intractable large‐scale optimization problems. Although most previous work in this field focused on scientific applications in the areas of medicine and physics, here we present a Compute Unified Device Architecture‐based (CUDA) GPU solution to solve the topology control problem in hybrid radio frequency and free space optics wireless mesh networks by adapting and adjusting the transmission power and the beam‐width of individual nodes according to QoS requirements. Our approach is based on a stochastic global optimization technique inspired by the social behavior of flocking birds — so‐called ‘particle swarm optimization’ — and was implemented on the NVIDIA GeForce GTX 285 GPU. The implementation achieved a performance speedup factor of 392 over a CPU‐only implementation. Several innovations in the memory/execution structure in our approach enabled us to surpass all prior known particle swarm optimization GPU implementations. Our results provide a promising indication of the viability of GPU‐based approaches towards the solution of large‐scale optimization problems such as those found in radio frequency and free space optics wireless mesh network design. Copyright © 2011 John Wiley & Sons, Ltd.     

基于FPGA的FSO通信误码测试仪的设计

提出了一种基于FPGA的FSO通信误码测试方案.该方案中,误码测试主要是由伪随机序列发生模块、同步模块、误码统计模块以及LCD显示模块来实现,对这些模块进行了详细的论述.误码测试的关键技术之一是比特同步,该方案利用FIFO实现误码仪内部数据与接收数据之间的同步.利用该方案研制了一套10 Mbit/s的误码测试仪.大量实...     

FSO通信误码测试仪硬件设计

介绍了一种基于AT89S52单片机和EP1K30 FPGA的FSO通信误码测试系统的设计与实现方案.系统以FPGA为处理核心,实现高速误码检测;单片机完成控制逻辑.详细讨论了伪随机码发生模块、同步模块、误码检测模块及单片机与FPGA接口的软硬件设计.并利用设计的样机进行了本地光纤环回和实验室内近距离无线激光通信的误码测试实验,实验结果表明此设计工作稳定可靠,可以实现对FSO通信质量进行检测的设计要求.