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...     

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.     

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.     

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...     

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...     

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...     

Performance analysis of two-way relay mixed RF/FSO system with co-channel interference

In this paper,the performance of a two-way relay(TWR)mixed radio frequency/free space optical(RF/FSO)system with co-channel interference(CCI)is investigated.Different from interference-limited one-way relay(OWR)system,CCIs should be considered at both relay and users in TWR system.Additionally,opportunistic user schedule is applied to select the user with the largest signal to interference plus noise ratio(SINR).Exact and asymptotic outage probabil-ity(OP)is derived.Approximate bit error rate(BER)is further presented to evaluate the overall performance.Simula-tion results show that the performance of a TWR system is dominated by the uplink or downlink whose performance is severer.     

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.     

The Analysis of Multiuser Relaying Mixed RF/FSO Networks over Exponentiated Weibull Fading Channel

In this paper,the performance of multiuser relaying mixed radio frequency(RF)/free space optical(FSO)networks over exponentiated Weibull Fading Channel is studied.Based on the transmit opportunistic scheduling,a unified cumulative distribution function(CDF)of the end-to-end signal to noise ratio(SNR)for multiuser dual-hop relaying system is derived.Then the average symbol error rate(ASER),outage probability and ergodic channel capacity are analyzed in detail.Furthermore,in order to simplify the analysis of system performance,the asymptotic results for the outage probability and ASER are derived at high SNR regime.We also demonstrate Monte Carlo simulation to ensure the effectiveness of the results.The simulation results show that deploying the transmit opportunistic scheme can improve the proposed system performance.And aperture averaging and heterodyne detection technique can suppress the impact of turbulence on FSO networks.     

Performance Evaluation of FSO and MMW for the Uruguayan Weather Conditions

In this work the free space optics (FSO) and the millimeter waves (MMW) links are studied for the Uruguayan weather conditions. FSO availability is affected by fog significantly, while MMW availability is mainly affected by rains. Considering visibility and rain intensity data, these availabilities are estimated for the Uruguayan weather conditions. The results are extensible to other areas with similar weather. Finally the use of both links simultaneously, one as a backup of the other, is discussed.     

一种基于通信协议的RF无线通信

针对现有智能电子产品中无线传输效率低、可靠性不高的问题,以433.92MHz RF(Radio Freqency)发送模块和接收模块为例,提出了一种基于通信协议的点对点单向无线传输模式。介绍了其工作原理和主要特点,给出无线通信协议数据传输模式、接收和发射步骤。基于ATMAGE8单片机进行设计开发,提供了部分设计程序。通过在机器人上的测试,无线传输模块工作稳定可靠,达到预期设计目标。     

一种基于通信协议的RF无线通信

针对现有智能电子产品中无线传输效率低、可靠性不高的问题,以433.92MHz RF（Radio Freqency）发送模块和接收模块为例,提出了一种基于通信协议的点对点单向无线传输模式.介绍了其工作原理和主要特点,给出无线通信协议数据传输模式、接收和发射步骤.基于ATMAGE8单片机进行设计开发,提供了部分设计程序.通过在机器人上的测试,无线传输模块工作稳定可靠,达到预期设计目标.     

大气对近地面无线激光通信链路的影响

由于无线光通信有通信容量大,保密性好,抗电磁干扰,结构简单等优点,近年来随着适合无线光通信应用的先进通信电子设备等技术的成熟,又掀起了对其研究的热潮,无线光通信被视为下一代光通信的发展方向之一。首先指出了无线光通信的技术优势并回顾了其发展史,阐述了大气对近地面无线激光通信系统链路的影响,重点研究了大气的衰减和大气湍流效应中的光强(大气)闪烁、光束弯曲和漂移及光束展宽,并对大气闪烁进行了仿真。最后对近地面无线光通信进行了展望。