LPI in pulsed laser space communications

A basic low-probability of intercept (LPI) study for a pulsed-laser pulse position modulated (PPM) optical link with a colocated direct detection intercepting receiver is presented. The latter is considered to be a form of optical radiometer using continuous threshold testing to detect the presence of the transmitting laser. The various design alternatives for the coded PPM link, and their effect on the communication and LPI performance, are examined. It is shown that the use of optical pulse power spreading via multiple frame symbol coding is vital for avoiding interception. It can be achieved by transmitting message symbols as repeated PPM symbols using a laser pulse of sufficiently low peak power so that the detected pulse energy is much less than the detected background energy. The possibility of the use of both wideband and narrowband radiometers by the interceptor further limits the communicator's code design choices. Some equations defining effective LIP gain parameters for the communication link are developed     

无线光通信中PPM的RS级联编码调制研究

在脉冲位置调制(PPM)直接检测光通信系统中插入RS级联编码构成一种新的PPM光通信系统(RS-PPM),该方式对PPM直接检测光通信系统进行了改进,并用Mat l ab对编码系统和未编码系统的误比特率进行了仿真比较,仿真结果表明,基于RS级联编码的PPM系统具有较好纠错和抗干扰能力。     

Experimental error correction results for optical digital pulse-position modulation

Original practical and theoretical results are presented for the detection and correction of errors in a direct detection optical ( lambda =1.523 mu m) digital pulse-position modulation (digital PPM) system. These results show the degradation in system performance due to interframe interference and an original method of correcting this type of error is presented. This error correcting method was then used to enhance the performance of a Reed-Solomon (RS) coded, digital PPM system.<>     

Iterative Coded Modulation With Code Rate Flexibility for Optical Space Communications

We propose an iterative coded modulation technique with code rate flexibility for optical space communications. It is a modified version of the existing SCPPM, which consists of the serial concatenation of an outer convolutional code, an interleaver, a bit-accumulator, and pulse-position modulation (PPM), and has been demonstrated to give the best performance on an optical link modeled as PPM/Poisson channels. The primary modification is to add a single-parity-check (SPC) code. We refer to the coded modulation as SPC-SCPPM. The two codes are decoded with an iterative demodulator-decoder, using standard turbo-decoding techniques. We compare the two coded modulation techniques on a PPM/Poisson channel. The rate-1/2 SPC-SCPPM provides performance similar to the SCPPM of the same parameters. However, SPC-SCPPM has been shown to possess code rate flexibility for all rates higher than 1/2 in contrast to SCPPM.     

Network coding‐based channel quality indicator reporting for two‐way multi‐relay networks

This paper considers channel quality indicator (CQI) reporting for data exchange in a two‐way multi‐relay network. We first propose an efficient CQI reporting scheme based on network coding, where two terminals are allowed to simultaneously estimate the CQI of the distant terminal‐relay link without suffering from additional overhead. In addition, the transmission time for CQI feedback at the relays is reduced by half while the increase in complexity and the loss of performance are negligible. This results in a system throughput improvement of 16.7% with our proposed CQI reporting. Upper and lower bounds of the mean square error (MSE) of the estimated CQI are derived to study performance behaviour of our proposed scheme. It is found that the MSE of the estimated CQI increases proportionally with the square of the cardinality of CQI level sets although an increased number of CQI levels would eventually lead to a higher data rate transmission. On the basis of the derived bounds, a low‐complexity relay selection (RS) scheme is then proposed. Simulation results show that, in comparison with optimal methods, our suboptimal bound‐based RS scheme achieves satisfactory performance while reducing the complexity at least three times in case of large number of relays. Copyright © 2012 John Wiley & Sons, Ltd.     

多用户分集与能量受限非可信中继系统遍历安全性能分析

研究了一种能量受限的非可信中继与多用户分集技术相结合的两跳链路安全网络通信模型。为提升系统安全性能，本文采用混合时间-功率分配中继(time-power splitting-based relaying, TPSR)协议,并结合机会调度策略(opportunistic scheduling strategy, OSS)从多用户分集网络中选择一个最佳目的节点作为信息接收端。基于随机选择(random selection, RS)策略，该文中利用低复杂度的高斯Q函数分析系统的安全性能以及在协作中继上进行能量采集活动不中断的条件下推导了系统的遍历安全速率(ergodic secrecy rate, ESR)的近似闭合表达式。此外，将提出的OSS与RS通信方案下性能进行对比，证明本文所提出的OSS更适用于分布式多用户选择网络。      

Slot Synchronization in Optical PPM Communications

Maintaining slot clock synchronization in a baseband pulse position modulated (PPM) communication link is vital to its performance. This paper examines the slot clocking design associated with a direct detection, photodetecting optical PPM system. Although theoretical PPM synchronizers for optical links have been derived in the past, there is still interest in finding more practical, simpler, and easier-to-implement clocking subsystems. In this paper several types of practical slot synchronizers are considered. A basic design involving analog correlators and slot gating is presented, along with an indication of its performance. Several alternative designs are also presented, including digital synchronizers in which time samples are used for loop control. The advantage in digital systems is that more extensive processing can be handled in software, allowing the loop to perform closer to the ideal. Design procedures for digital clocking are presented, and optimal laser pulse shaping and filtering are discussed. Performance in terms of loop models and tracking error variance is included.     

空间激光通信网络中的全光相位再生技术

围绕空间激光通信网络中高速数据多跳传输应用需求,针对相位调制激光链路经过空间长距离传输后信号质量劣化的问题,研究了基于相位敏感四波混频参量效应实现二进制相位调制高速激光信号的全光相位再生技术。利用Matlab软件数值分析了全光相位再生系统的影响因素,并基于OptiSystem仿真平台搭建了全光相位再生系统。结合高轨-地面站空间激光通信系统链路预算,对速率为10 Gbit/s的DPSK信号光经背靠背、相位噪声劣化以及劣化后全光相位再生处理三种传输场景进了对比分析。模拟仿真结果与数值分析结果均表明,与劣化后未经再生处理的系统相比,全光相位再生处理后的系统误码率平均优化4个数量级,信噪比提升约3 dB,表明该空间激光通信全光相位再生技术可实现相位调制信号的全光相位再生,能够有效提升空间相干激光通信系统的性能,可以应用于空间高速激光通信网络中继节点处的全光数据中继等方向。     

A CSI Estimation Method for Wireless Relay Network

This letter proposes a method for channel state information (CSI) estimation in a wireless relay network, which consists of a base station (BS), a relay station (RS), and a mobile station (MS). The proposed method exploits the fact that the link condition between fixed BS and fixed RS tends to be stable, and the frequent CSI update is not necessary for this link. In order for the BS to obtain the CSI of the distant link (i.e. RS-MS link), RS amplifies a pilot signal received from MS with a pre-defined amplification factor, and forwards it to BS. This enables the BS to obtain the CSI of the RS-MS link based on the received pilot signal and pre-knowledge on the CSI of BS-RS link, which can reduce the required overhead to explicitly exchange CSI.     

Range Extension in IEEE 802.11ah Systems Through Relaying

A great number of Internet of Things (IoT) and machine-to-machine (M2M) based applications, which are telecommunication areas with the highest foreseen growth in the future years, require energy efficient, long range and low data rate wireless communication links. In order to offer a competitive solution in these areas, IEEE 802.11 standardization group has defined the “ah” amendment, the first sub-1 GHz WLAN standard, with flexible channel bandwidths, starting from 1 MHz, up to 16 MHz, and many other physical and link layer improvements, enabling long-range and energy efficient communications. However, for some regions, like Europe, the maximum transmitted power in dedicated frequency band is limited to only 10 mW, thus disabling the achievement of ranges which would be close to targeted of up to 1 km. In this paper we examine possibilities for range extension through implementation of half-duplex decode-and forward (DF) relay station (RS) in communication between an access point (AP) and an end-station (ST). Assuming a Rician fading channel between AP and RS, and a Rayleigh fading channel on RS–ST link, we analytically derive results on achievable ranges for the most robust modulation and coding schemes (MCSs), both on downlink (DL) and uplink (UL). Analyses are performed for two different standard adopted deployment scenarios on RS–ST link, and variable end-to-end link outage probabilities. Moreover, we have analyzed whether the considered most robust MCSs, known for supporting the longest range, but the lowest data rates, can meet the defined requirement of at least 100 kb/s for the greatest attainable AP–RS–ST distances. We examine data rate enhancements, brought by coding and using of short packets, for both DL and UL. Finally, we present bit error rate results, obtained through simulations, of a dual-hop DF IEEE 802.11ah relay system for the considered MCs. All presented results confirm that IEEE 802.11ah systems through deployment of relay stations, become an interesting solution for M2M and IoT based applications, due to flexibility they offer in many aspects, meeting requirements for wide transmission ranges in such applications.     

Load-Based Power Saving in IEEE 802.16j Multi-Hop Relay Networks

In this paper, our previous work of Load-Based Power Saving (LBPS) for energy saving at the user side is extended to support integrated sleep scheduling for BS, RS, and MSS in the IEEE 802.16j Multi-Hop Relay Network. Topology-dependent time frame structure is adopted in our design to reduce the transmission delay in the relay network, in which the number of relay zone (for transmission over the relay link) depends on the hop count of RS in the network. Focused on non-real-time traffic, two LBPS schemes, namely LBPS-Aggr-MR and LBPS-Merge-MR, are proposed. Simulation study shows the proposed LBPS schemes significantly outperform the standard Type I PSC in terms of power saving efficiency.     

Efficient CQI feedback via network coding for wireless relay networks

For the efficacy of radio resource management in downlink wireless relay networks, the channel quality indicator (CQI) between a mobile station (MS) and a relay station (RS) should be fed back from the RS to its base station (BS), at the cost of additional feedback overhead. In this letter, we propose an efficient feedback scheme based on network coding between a pilot sequence and the CQI of MS-RS link, through which the BS can have both CQIs of MS-RS and RS-BS links without overhead. Numerical results reveal that the proposed CQI reporting scheme has as good feedback performance as conventional one which generally requires additional feedback burden.     

星际激光链路中的前向纠错编码技术研究

建立了简化的星际光通信链路模型,将背景光噪声和光放大器自发辐射噪声引入星际光通信链路中,提出利用前向纠错编码技术来改善星际光通信误码性能的方法。介绍了喷泉码的编译码特点,将喷泉码引入链路模型中。通过仿真研究表明,喷泉码相比于RS码对链路的抗误码性能有很大提高,且随着信噪比的增大改善更加明显。     

星际激光链路中的前向纠错编码技术研究

建立了简化的星际光通信链路模型, 将背景光噪声和光放大器自发辐射噪声引入星际光通信链路中, 提出利用前向纠错编码技术来改善星际光通信误码性能的方法。介绍了喷泉码的编译码特点, 将喷泉码引入链路模型中。通过仿真研究表明, 喷泉码相比于RS码对链路的抗误码性能有很大提高, 且随着信噪比的增大改善更加明显。     

大气无线光通信调制方式性能分析

在对三种典型大气无线光通信调制方式--OOK、PPM和DPIM的调制结构进行分析的基础上,结合大气无线光信道特点,分析比较了这三种调制方式的带宽需求、传输容量、功率需求和差错性能.理论分析与仿真结果表明,OOK方式实现简单,不需要符号同步,带宽需求最小,但功率利用率太低;PPM方式大大提高了功率利用率,但带宽利用率最低,而且需要符号同步;DPIM相比于OOK具有更高的功率利用率,相比于PPM具有更高的带宽利用率,而且不需要符号同步,应用于无线光通信系统具有显著的优势.     

Joint power,subcarrier and subframe allocation in Multihop relay networks

In this paper we study the problem of subframe, subchannel and power allocation in OFDMA‐based multihop relay networks. The system consists of a base station (BS), a number of relay stations (RS) and mobile stations (MS). We consider frame by frame scheduling, where the frame is divided into two subframes such as BS‐RS and RS‐MS subframes. We study two different problems, satisfying link rate requirements with minimum‐weighted total power and maximizing proportional fairness. For the first problem, we find the optimal solution and also propose a less complex subframe and bandwidth allocation scheme with good performance. For the second problem, we propose an algorithm that outperforms an existing scheme with less feedback. Copyright © 2009 John Wiley & Sons, Ltd.     

Adaptive Cooperative Decode-and-Forward Transmission with Power Allocation Under Interference Constraint

In this paper, we examine an adaptive decode-and-forward cooperative protocol under interference constraint. In the proposed protocol, relying on the obtained instantaneous signal-to-noise ratios (SNRs), a direct link or relay link is used to transmit data from the secondary source to the secondary destination. In addition, once the relay link is used, the secondary source and relay must adapt their transmit power to maximize the instantaneous SNR of this link. To evaluate the performance of the proposed protocol, we derive closed-form lower-bound and upper-bound expressions for the outage probability over Rayleigh fading channel. Finally, various Monte-Carlo simulations are presented to verify our analysis and compare the performance of the proposed protocol with that of the direct transmission protocol in underlay cognitive network.     

Practical Coarse Relay Site Planning: Performance Analysis Over Composite Fading/Shadowing Channels

Relay deployments promise to alleviate the limitations of conventional macrocell networks, such as poor indoor penetration and coverage holes in a cost-efficient way. In this context, the capacity of the wireless relay link between a relay node (RN) and its serving base station has a crucial impact on the end-to-end performance. The deployment flexibility of RNs, which mainly stems from the wireless relay link, compact physical characteristics, and low-power consumption, can be exploited by relay site planning (RSP) to overcome the limitations of the relay link and, thus, enhance the system performance. To this end, RSP is carried out via selecting an RN deployment location from a discrete set of alternatives considering the signal-to-interference-plus-noise ratio (SINR) on the relay link as the selection criterion. In practice, the so-called coarse RSP takes into account only large-scale fading due to shadowing. Nevertheless, as RNs are stationary, the wireless channels pertaining to relay deployments are subject to simultaneous impairments by both shadowing and multi-path fading, i.e., composite fading/shadowing. In this paper, we present the performance of coarse RSP that can be used for planning and dimensioning of two-hop cellular relay networks in composite fading/shadowing environments, where co-channel interference is also present. The relay link is modeled by Nakagami-lognormal distribution while the access link between a mobile terminal and its serving RN is modeled by Rician-lognormal distribution. Further, we provide an accurate analytical framework through closed-form expressions for relay link SINR, link rates, and end-to-end rate. Results show that coarse RSP can still yield high performance improvements in terms of both SINR and rate considering composite fading/shadowing channels. Moreover, coarse RSP is shown to effectively decrease the amount of fading on the relay link and, thus, mitigate the detrimental effects of composite fading/shadowing.     

弱湍流下基于PPM调制和RS码的ALC系统差错性能分析

引入了RS码作为大气光通信的信道编码,讨论了在高斯信道和弱湍流信道下,基于PPM调制和RS编码大气光通信系统的性能,仿真比较了未编码与编码系统的差错性能,仿真结果表明,在相同的差错性能条件下,编码增益提高2～3 dB,在高斯信道中的差错性能优于弱湍流信道.     

Optical PPM CDMA Communication System with Optical Hard Limiter

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