一种星载可配置输出频率的X波段载波源

针对国内星载数传发射机无法实现载波频率灵活可变的问题,提出了一种可配置输出频率的载波源方案。采用现场可编程门阵列(FPGA)和数模转换器(DAC)相结合,实现参考频率高精度可变且灵活配置锁相环(PLL)中鉴相器的鉴相频率,使载波源输出频率可程控配置。实测结果表明,载波源可实现任意配置X波段8.025~8.4 GHz的输出中心频点,相位噪声优于-66 dBc/Hz@100 Hz、-75 dBc/Hz@1 kHz、-80 dBc/Hz@10 kHz、-95 dBc/Hz@100 kHz、-120 dBc/Hz@1 MHz,杂散抑制度优于-74 dBc,频率分辨率小于10 Hz。相关电路替代专用直接数字频率合成(DDS)芯片的功能,能适应空间应用环境。

WDM-PON无色ONU实现方法研究

WDM-PON是一种容量大、易升级、网络安全性高的新一代光接入网技术。文章简要分析了固定波长和可调谐波长的ONU实现方法,指出了其不足;重点研究了采用宽光源技术和无光源技术实现ONU的方法,指出无色ONU是构建WDM-PON的一种较理想的解决方案。

Dynamic Subcarrier Assignment for OFDM-PON Network Based on RSOA for ACCORDANCE

In this paper, we overview the principle of Orthogonal Frequency Division Multiplexing Passive Optical Network （OFDM-PON） systems, with a particular focus on upstream architectures capable of achieving 10Gbit/s colorless upstream transmission using Reflective Semiconductor Optical Amplifier （RSOA）. We propose an architecture of RSOA based OFDM-PON which can achieve 10Gbit/s upstream transmission over a single wavelength. A novel Dynamic Subcarrier Assignment （DSA） algorithm is also proposed to support my architecture, namely Service based Polling in Pipeline （SPP） dynamic subcarrier algorithm. A simulation was conducted to study the performance of SPP algorithm. Compared with the traditional dynamic bandwidth allocation algorithms, service based polling meets the quality of in pipeline algorithm service requirements excellently, and adapts orthogonal frequency division multiplexing passive optical network better with higher bandwidth efficiency and lower algorithm complexity.

Ultrafast Phenomena in Solids Excited by Femtosecond Pulse

The pump-probe technique is an effective instrument for investigating ultrafast dynamics. It is widely used in fundamental research and application fields, such as Physics, Chemistry and Biology. First introduced is the effect process between femtosecond laser and matter. And set forth is the fundamental of ultrafast phenomena and theory foundation of data disposal. Then introduced is the demand of making samples in experiment, experiment equipment, and the theory of strain pulse. We detect transient reflectivity change on surface of GaAs at different delayed time using femtosecond transient reflection spectroscopy. The changing curve consists of three parts： original scattering process of 100 fs, carriers-lattice thermal equilibrium of l. 5 ps and recombination process of 500 los.

Joint subcarrier and power allocation with threshold in cooperative multiuser networks

In this paper, we investigate a resource allocation issue in OFDMA-based decode-and-forward cooperative multiuser networks and propose joint subcarrier and power allocation schemes. The optimal solution of this combinable allocation shows high computational complexity, so we allocate subcarriers and power separately. At firstly, we distribute subcarriers to relays and users under the assumption of equal power distribution. Here, we propose an equal capacity increment （ECI） allocation strategy to achieve tradeoff between total throughput and fairness. To further improve the system performance, we introduce threshold into ECI strategy, named ECI strategy with threshold （ECI-T）, where subcarriers with bad performance are prevented from transmitting. Subsequently, a water-filling method is adopted to distribute the power to cooperative links in order to fully utilize the limited power. Simulation results show that system performance of the proposed schemes is significantly enhanced compared with an existing resource allocation scheme. Besides, the resource allocation schemes with the water- filling method notably outperform schemes with equal power allocation.

Cost Effective Scheme for OLT in Next Generation Passive Optical Access Network Based on Noise Free Optical Multi Carrier

We propos e a cos t-effective multi-carrier generation technique which minimizes the passive optical access network(PON) costs. In this study replacement of laser array with multi-carrier source at optical line terminal(OLT) side in PON is addressed. With 25-GHz frequency spacing, the generated optical multi-carriers exhibit good tone to noise ratio(TNR) i. e. above 20 d B, and least amplitude difference i. e. 1.5d B. At the OLT, multi-carriers signal based multiplexed differential phase shift keying(DPSK) data from all the channels each having 10 Gbps for downlink is transmitted through 25 km single mode fiber. While the transmitted information is retrieved at optical network unit(ONU), part of the downlink signal is re-modulated using intensity modulated(IM) on-off keying(OOK) for upstream transmission at 10-Gbps. Simulation results are in good agreement with the theoretical analysis, showing error free transmission in downlink and uplink with 10 Gbps symmetric data rate at each channel. The receivedpower, both for uplink and downlink transmission, is adequate for all channels at BER of 10-9 with minimum power penalties. Power budget is calculated for different splitting ratios showing excellent system margins for any unseen losses. The proposed setup provides a cost-effective way minimizing transmission losses, and providing greater system's margin in PON architecture.

A delay-constrained energy-efficient component carrier adjusting scheme for LTE-Advanced systems

The energy efficiency and packet delay tradeoffs in long term evolution-advanced(LTE-A) systems are investigated.Analytical expressions are derived to explain the relation of energy efficiency to mean packet delay,arrival rate and component carrier(CC) configurations,from the theoretical respective which reveals that the energy efficiency of multiple CC systems is closely related to the frequency of CCs and the number of active CCs.Based on the theoretical analysis,a CC adjusting scheme for LTE-A systems is proposed to maximize energy efficiency subject to delay constraint by dynamically altering the on/off state of CCs according to traffic variations.Numerical and simulation results show that for CCs in different frequency bands with equal transmit power,the proposed scheme could significantly improve the energy efficiency of users in all aggregation levels within the constraint of mean packet delay.

Coordination of multiple grid-connected inverters for harmonic compensation

For multiple grid-connected inverters with active filter function,it makes sense to regulate every unit to output maximum active power from photovoltaic arrays,as well as eliminate the harmonic due to the non-linear loads connected to the electric networks.Naturally,a centralized control coordination strategy was proposed for the purpose of high facility utilization,good harmonic compensation ability and unwanted overcompensation condition.Based on a vector decoupling control scheme and generalized instantaneous reactive power theory,the solution was to allocate the harmonic eliminating task for every inverter according to the instantaneous power margin of each.The grid current always keeps sinusoidal in spite of non-linear load change and output active power change for any inverter.The simulation results validate the efficacy of the proposed coordination strategy.