对准误差对前置光放大卫星激光通信系统性能的影响

发射机及接收机的对准误差都会引起前置光放大卫星激光通信系统信号的衰落,在同时考虑发射机、接收机对准误差的条件下优化系统性能非常重要。将接收机对准误差引起的空间光耦合损耗用一个高斯函数近似,并同时考虑发射机对准误差引起的对准损耗,推导出了接收光功率概率密度的近似解析表达式,应用该概率密度函数,建立了基于平均误码率原则的前置光放大卫星激光通信系统的优化模型。仿真结果表明,在给定平均误码率要求及对准误差一定时,存在一个最佳发射光束宽度、接收天线直径及空间光耦合参数,使所需的发射功率最小,采用更大的接收天线并不能降低对发射功率的要求。     

EGSM/TD-LTE双模双连接手机近场电磁兼容的研究

针对EGSM/TD-LTE双模双连接手机,研究了手机近场的电磁兼容问题。首先构建了EGSM和TD-LTE两个模式的手机近场电磁兼容问题的评估模型;其次基于该评估模型研究了近场射频干扰与双模双连接手机接收性能的关系,当EGSM的发射功率为30dBm,TD-LTE系统的接收灵敏度会恶化2dB;最后给出了一种提高多频段双天线隔离度的解决方案,并通过仿真表明,该方法能够有效提高双模双连接手机的天线隔离度,从而克服双模双连接手机的电磁兼容问题。     

On the Link Performance of a Proposed Compact Antenna System

In this paper we consider an antenna system, that consists of one active and one parasitic antenna element. Different antenna patterns may be created by loading the parasitic element with appropriate reactive impedances on each symbol period. We demonstrate the performance of a communication link that uses the proposed antenna system at the transmitter and two omnidirectional antennas at the receiver. The Arimoto-Blahut algorithm is used to find the capacity achieving distribution on the channel symbols. The capacity of the antenna system is compared to the capacity obtained by a single transmitter antenna.     

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...     

Antenna combining for the MIMO downlink channel

A multiple antenna downlink channel where limited channel feedback is available to the transmitter is considered. In a vector downlink channel (single antenna at each receiver), the transmit antenna array can be used to transmit separate data streams to multiple receivers only if the transmitter has very accurate channel knowledge, i.e., if there is high-rate channel feedback from each receiver. In this work it is shown that channel feedback requirements can be significantly reduced if each receiver has a small number of antennas and appropriately combines its antenna outputs. A combining method that minimizes channel quantization error at each receiver, and thereby minimizes multi-user interference, is proposed and analyzed. This technique is shown to outperform traditional techniques such as maximum-ratio combining because minimization of interference power is more critical than maximization of signal power in the multiple antenna downlink. Analysis is provided to quantify the feedback savings, and the technique is seen to work well with user selection and is also robust to receiver estimation error.     

近距离无线激光通信系统的设计

研究了一种用于传输数字图像信号的近距离无线激光通信系统,对系统的发射机和接收机部分进行了电路设计,搭建了实验系统并进行了系统调试,得到了合适的电路结构和器件参数,为实用的无线激光通信系统的研究和设计提供了参考依据。     

Intra-chip wireless interconnect for clock distribution implementedwith integrated antennas, receivers, and transmitters

A wireless interconnect system which transmits and receives RF signals across a chip using integrated antennas, receivers, and transmitters is proposed and demonstrated. The transmitter consists of a voltage-controlled oscillator, an output amplifier, and an antenna, while the receiver consists of an antenna, a low-noise amplifier, a frequency divider, and buffers. Using a 0.18-μm CMOS technology, each of these individual circuits is demonstrated at 15 GHz. Wireless interconnection for clock distribution is then demonstrated in two stages. First, a wireless transmitter with integrated antenna generates and broadcasts a 15-GHz global clock signal across a 5.6-mm test chip, and this signal is detected using receiving antennas. Second, a wireless clock receiver with an integrated antenna detects a 15-GHz global clock signal supplied to an on-chip transmitting antenna located 5.6 mm away from the receiver, and generates a 1.875-GHz local clock signal. This is the first known demonstration of an on-chip clock transmitter with an integrated antenna and the second demonstration of a clock receiver with an integrated antenna, where the receiver's frequency and interconnection distance have approximately been doubled over previous results     

The use of optically coherent detection techniques for true-timedelay phased array and systems

We analyze a true-time-delay, optically controlled phased array antenna system whereby beam forming is accomplished using a large number of antenna elements that can receive any of several different microwave true-time-delays via the use of coherent optical carriers transmitted through a single fiber. The transmitter and receiver architectures are described in detail. We present calculations for the signal-to-noise ratio (SNR), the signal-to-interchannel interference ratio (SIR) and dynamic range (DR) of one channel for various modulation-demodulation schemes (i.e., AM-heterodyne, FM, PM). We show for an example system that can accommodate 128 antenna elements and provide 128 different delays (7 bits), assuming AM modulation with a bandwidth of 1 MHz, a transmitter power of -5 dBm and a laser linewidth of 10 MHz, we can obtain DR≃50 dB for one channel using a channel separation twelve times of that of the microwave frequency (f_m). For the FM scheme, DR≃60 dB can be obtained for one channel with a laser linewidth of 1 MHz, a FM modulation index of one, and a channel spacing of about 13f_m. With a local oscillator laser tuning range of 100 Å, the system can provide seven-bit resolution for a 128 element antenna array. It is found that coherent optically controlled phased array antennas provide improved controllability over direct detection method, and can have the SNR, SIR and DR that meet the stringent requirements of modern high resolution microwave antenna systems     

Radio-Optical Dual-Mode Communication Modules Integrated With Planar Antennas

This paper presents new results on integrated devices for radio and free-space optical dual-mode communication. Two novel hybrid packaging schemes using two different microwave printed antenna designs are presented for the integration of radio-optical front-end circuits on a planar compact printed circuit board with shared electrical and structural components. Full-wave electromagnetic (EM) simulations are presented for antenna optimization to minimize EM interference between the radio and optical circuits. A hybrid radio-optical package design is developed, prototyped, and experimentally studied using a modified quasi-Yagi antenna with split directors to form pads for opto-electronic device integration. Dual-mode link connectivity is investigated in simulations and experiments. A data rate of 2.5 Gb/s is demonstrated for the optical channel despite 15–20-dB signal coupling between the optical and microwave circuits.      

基于射频信号2阶零功率的链路色散测量技术

为了适应高速率大色散光纤信道对链路色散的精确补偿要求,研究并提出了一种基于射频信号2阶零功率点的信道色散测量方案。采用信号两边带的位相差来测量光纤链路中的色散值,通过在发射端加载射频信号,可以得到接收端射频信号功率大小随链路色散值的周期性变化关系,从仿真光纤链路色散随射频信号频率的变化曲线获得接收端射频信号2阶零功率点位置。结果表明,基于射频信号2阶零功率的信号测量方案色散测量误差可控制在±10ps/nm范围内。相较于1阶零功率点,基于射频信号2阶零功率点信道色散测量方案可满足高速率、长距离大色散光纤信道对色散值的精确测量需求。     

一种微型飞行器时空调制OFDM通信与跟踪系统

为了解决微型飞行器在特殊环境下的通信跟踪和多模导航定位问题,该文提出了一种新型的微型飞行器通信跟踪与辅助导航定位综合方案,其核心思想是在发射端发射一种载有空间方位信息的OFDM时空调制信号,以解决通信与二维测向跟踪问题。系统发射端采用八天线阵列,两天线一组发射OFDM信号,每个OFDM信号子载波中包含数字通信信息和空间方位信息,微型飞行器通过简单的单天线接收信号和多值分辨算法,解算出二维空间信息,实现高精度测向定位。文中给出了天线阵的结构,时空调制OFDM信号的设计,仰角方位角粗测和精测算法。并仿真了高斯信道下的二维空间信息的测向性能。     

Optical Chaotic Communication Using Generalized and Complete Synchronization

We propose a secure optical communication system based on the principles of generalized and complete chaotic synchronization. A transmitter and a receiver both composed by two chaotic external-cavity semiconductor lasers are coupled in a master-slave configuration to provide generalized synchronization, while the master lasers in the transmitter and in the receiver are completely synchronized through the synchronization channel via an optical fiber. A message is added to the transmitter slave laser and sent to the receiver through the information channel to be compared with the output of the receiver slave laser. The system is robust to a small mismatch of the laser parameters or of the coupling between the master and slave lasers, unavoidable in a real system, and can even enable a good communication up to a 5 Gb/s transmission rate using the chaos masking encryption method, when the master laseres are coupled bidirectionally.      

基于天线选择的低秩信道MIMO系统容量研究

最近的研究表明,在衰落信道多天线MIMO系统的容量随发射天线数线性增加.而对于低散射环境,即使信号经历独立的衰落,信道秩的降低也会严重影响系统容量的增加.对于这种低秩环境,选择天线发射或接收可以有效地降低系统的成本.本文研究了天线选择对低秩信道MIMO系统容量的影响.仿真结果表明,对不同的信道条件,适当选择天线发射不仅可以增加信道容量,而且可以降低系统的复杂度和射频成本.适当选择天线接收,在不严重降低系统容量的前提下,也达到了降低系统成本的目的.     

基于垂直分层空时编码的自由空间光通信

垂直分层空时编码(V-BLAST)是一种将空间复用和空间分集相结合的技术,它具有极高的频谱利用效率和传输速率,因此将垂直分层空时编码技术应用于自由空间光通信。在研究了大气信道的特性之后,提出了一种基于垂直分层空时编码的自由空间光通信系统的信道模型。介绍了垂直分层空时编码的编码原理,并分析了该系统的信道容量。利用仿真实验比较了采用垂直分层空时编码前后系统信道容量及误码性能的变化。结果表明,当接收天线数大于或等于发送天线数时,系统的信道容量与发送天线数成正比例增长,误码性能被有效改善。说明该系统具有垂直分层空时编码所提供的信道容量和良好的误码性能,且能有效克服大气湍流所产生的闪烁效应。     

Variable-phase-shift-based RF-baseband codesign for MIMO antenna selection

We introduce a novel soft antenna selection approach for multiple antenna systems through a joint design of both RF (radio frequency) and baseband signal processing. When only a limited number of frequency converters are available, conventional antenna selection schemes show severe performance degradation in most fading channels. To alleviate those degradations, we propose to adopt a transformation of the signals in the RF domain that requires only simple, variable phase shifters and combiners to reduce the number of RF chains. The constrained optimum design of these shifters, adapting to the channel state, is given in analytical form, which requires no search or iterations. The resulting system shows a significant performance advantage for both correlated and uncorrelated channels. The technique works for both transmitter and receiver design, which leads to the joint transceiver antenna selection. When only a single information stream is transmitted through the channel, the new design can achieve the same SNR gain as the full-complexity system while requiring, at most, two RF chains. With multiple information streams transmitted, it is demonstrated by computer experiments that the capacity performance is close to optimum.     

A novel scheme for reception using an active microstrip antenna

An unique aspect of the injection-locked active microstrip antenna incorporating a Gunn diode, i.e., the variation of the device current within the lock band, is exploited for the demodulation of an FM microwave signal. A simple experimental arrangement has been presented to demonstrate the demodulation performance of the receiver even in a multichannel environment. Using two such separate antennas as transmitter and receiver, a two-way short-range communication system has been demonstrated that may be suited for certain commercial and military applications     

Performance analysis of space-time transmitter diversity techniques for WCDMA using long range prediction

Transmitter diversity in the downlink of code-division multiple-access (CDMA) systems achieves similar performance gains to the mobile-station receiver diversity without the complexity of a mobile-station receiver antenna array. Pre-RAKE precoding at the transmitter can be employed to achieve the multipath diversity without the need of the RAKE receiver at the mobile station. We examine feasibility of several transmitter diversity techniques and precoding for the third-generation wideband CDMA (WCDMA) systems. In particular, selective transmit diversity, transmit adaptive array and space-time pre-RAKE (STPR) techniques are compared. It is demonstrated that the STPR method is the optimal method to combine antenna diversity and temporal precoding. This method achieves the gain of maximum ratio combining of all space and frequency diversity branches when perfect channel state information is available at the transmitter. We employ the long range fading prediction algorithm to enable transmitter diversity techniques for rapidly time varying multipath fading channels.     

Power Equations and Capacity Performance of Magnetic Induction Communication Systems

Although a number of studies have been done on the traditional Radio Frequency (RF)terrestrial communication system, the potential applications and the advantages of Near-Field magnetically coupled coils in wireless short range communications is just emerging and is yet to be explored. This paper investigates the impacts of magnetically coupled transceiver antenna coil on the received signal power and the communication link capacity. Based on the equivalent circuit model in free space, theoretical foundations are laid with observed simulation results. The simulation result benefits the antenna designers and the network planning engineers to estimate the power at the receiver and a near field magnetic communication system capacity for different antenna coil characteristics and different communication ranges.     

240Mbit/s直线运动型无线光通信系统研究

详细分析了直线轨道上运动通信的特点,设计和研制了一种具有双向收发功能的直线运动型无线光通信系统。该系统主要包括1 550 nm半导体激光器、高灵敏度PIN光探测器、球面单透镜式光发射天线和实心光锥耦合式光接收天线等关键部件。130 m运动工作距离的系统性能测试结果表明,在3.5 m/s最高运动速度、240Mbit/s通信传输速率下,运动中的数据丢帧率为零,以太网和视频指标均满足实际应用要求,系统适用于存在直线运动轨道的无线光通信场合。     

Free space adaptive optical interconnect at 1.25 Gb/s, with beam steering using a ferroelectric liquid-crystal SLM

A free space adaptive optical interconnect is reported, in which an optically modulated channel from a vertical-cavity surface-emitting laser at 1.25 Gb/s is steered using reconfigurable binary phase gratings displayed on a ferroelectric liquid crystal on silicon (LCOS) spatial light modulator (SLM), to correct for misalignment. The optical system, and addressing scheme to maintain a transparent optical path, is described. The measured optical losses total 13.6 dB, sufficient to give a bit error rate (BER) of 10/sup -12/ with current optical transmitter and receiver technology. This is, to our knowledge, the first demonstration of a high-speed data transmission through an adaptive optical interconnect using an "off-the-shelf" commercial ferroelectric display panel.