宽带偏振不灵敏张应变InGaAs半导体放大器光开关

研制了一种张应变准体InGaAs半导体放大器光开关.该结构具有显著的带填充效应,从而导致在80mA的注入电流下,器件的3dB光带宽大于85nm(1520～1609nm).该带宽几乎同时全部覆盖了C带(1525～1565nm)和L带(1570～1610nm).最为重要的是,在3dB光带范围内,光开关的偏振灵敏度小于0.7dB;光纤到光纤无损工作电流在70～90mA之间;消光比大于50dB.通过降低了载流子寿命,开关速度有所提高.在未来密集波分复用通信系统中,这种宽带偏振不灵敏半导体放大器光开关很有实用前景.     

Dynamic Bandwidth and Carrier Allocation for Video Broadcast/Multicast Over Multi-Cell Environments

Recently, broadcast/multicast over cellular networks has been actively discussed over commercial wireless mobile terminals. Compared to conventional terrestrial or satellite broadcasting systems, the quality-of-service (QoS) for edge users is an important issue due to inter-cell interference over multi-cell environments. In this paper, we introduce a dynamic bandwidth and carrier allocation (DBCA) technique by fully utilizing different visual importance of each layer in multi-layer video for broadcast/multicast services when the number of users is limited over macro/micro/femto cell environments. To ensure an acceptable video quality for edge users, the bandwidth and the loading ratio are dynamically controlled to enhance the utility through the radio resource control in accordance with the visual importance. The simulation results show that DBCA exhibits much better QoS by sending visually more important data with high priority in the cell border region.     

全光归零(RZ)到非归零(NRZ)码型转换技术研究进展

随着多媒体网络服务业务类型的不断出现,人们对因特网带宽需求日益增长,未来的超高速大容量光子网络很可能是波分复用与时分复用相结合的智能网络。全光归零(RZ)到非归零(NRZ)的码型转换技术,是构建这种网络的关键技术之一,它能避免电子学器件的速率瓶颈,将时分复用(OTDM)与波分复用(WDM)有机结合,在光域内实现不同调制格式的数据在网络的不同部分之间自由传输,已经引起了越来越多人们的兴趣。介绍了当前全光归零到非归零码型转换技术的最新研究进展,分析了其工作原理,优缺点及性能参数,指出了目前存在的技术难点问题,最后对其发展前景进行了展望。     

Dynamic Microwave Frequency Division Characteristics of Coplanar Transferred-Electron Devices in a Resistive Circuit (Letters)

It is shown that dynamic microwave frequency division (divide-by-K) can be achieved by employing a transferred-electron device (TED) in a resistive circuit. The absolute bandwidth over which the input signal will be divided by a particular integer K and the maximum output frequency is the device transit time frequency. The percentage bandwidth is 200/(2K - 1) percent. With two-terminal TED's, divide-by-K (K = 2, 3, 4, 5) was demonstrated with substantial bandwidth.     

Five-channel polymer waveguide wavelength division demultiplexerfor the near infrared

A five-channel wavelength division demultiplexer (WDDM) fabricated in polymer gelatin waveguides and operating over a 100-nm bandwidth centered at 770 nm in the near infrared is discussed. The device has a maximum diffraction efficiency of 80% at 730 nm, has a spectral bandwidth of 17±3 nm per channel, and effectively utilizes a portion of the large optical transparency bandwidth (~2400 nm) of the photo-lime gelatin polymer material at laser diode wavelengths. High-channel-density WDDM devices at longer infrared wavelengths should be possible     

New structure of tunable wavelength-selective filters with a liquid crystal for FDM systems

To decrease the bandwidth of liquid-crystal Fabry-Perot interferometers (LC-FPIs), LC-FPIs having a double-layer cavity were devised where the intracavity consists of the LC layer and a glass layer. This filter is shown to have a very narrow bandwidth (full width at half maximum <10 GHz), low loss (4 dB), and a large tunability (9 nm). It is also shown to have the potential to select over 50 channels for FDM (frequency division multiplexing) systems.<>     

100 channel optical FDM technology and its applications to opticalFDM channel-based networks

Optical frequency division multiplexing (optical FDM) technology, which allows the use of an extremely broad lightwave bandwidth (10-200 THz and over) and can realize transport systems that could replace the current digital (time division multiplexing based) transport networks, is described. The future outlook for communication networks based on optical FDM technology is assessed. Based on the technical results obtained from a 100-channel optical FDM experiment, of an optical FDM channel concept is proposed and a viable architecture for optical FDM-channel-based networks is developed     

Polarization independent, linear-tuned interference filter with constant transmission characteristics over 1530-1570-nm tuning range

We present a polarization independent optical tunable filter (OTF) with nearly constant transmission characteristics over 1530-1570 nm. The tuning is achieved by horizontally sliding an interference filter, resulting in a very low polarization dependent loss (PDL)<0.1 dB and nearly constant characteristics over the tuning range. By cascading interference filters in double or triple stage, narrower bandwidth characteristics are obtained allowing for smaller channel spacing in wavelength division multiplexing (WDM) systems. Experimental results for PDL, loss, and bandwidth are presented and compared to those of angle-tuned filter. The proposed OTF has shown superior performance promising a practical solution for dense WDM applications.     

Robust Design of Virtual Topology for WDM Networks under Bandwidth Demand Uncertainties

In this paper, a novel method is proposed to address the problem of designing virtual topology over wavelength division multiplexing （WDM） networks under bandwidth demand uncertainties. And a bandwidth demand model under uncertainties is presented. The optimization goal of virtual topology design is defined as minimizing the maximum value amongp percentiles of the bandwidth demand distribution on all Hght-paths. Correspondingly, we propose a heuristic algorithm called an improved decreasing multi-hop logical topology design algorithm （ID-MLTDA） that involves with a degree of uncertainties to design virtual topology. The proposed algorithm yields better performance than previous algorithms. Additionally, the simplicity and efficiency of the proposed algorithm can be in favor of the feasibility for topology design of large networks.     

Dynamic bandwidth partition schemes for integrated voice,video, and data traffic in the IEEE 802.11e distributed wireless LANs

In mobile cellular networks, bandwidth is deterministic in terms of the number of channels by frequency division, time division, or code division. On the other hand, bandwidth partition schemes in the contention‐based medium access control (MAC) in distributed wireless LANs are extremely challenging due to the contention‐based nature, packet‐based network, and the most important aspect: only one channel available, competed by an unknown number of stations. In this paper, we study this challenging issue. We propose and study four different bandwidth partition schemes for integrated voice/video/data traffic in the IEEE 802.11e wireless LANs: a Static bandwidth Partition (SP) scheme, a Dynamic budget Partition (DP) scheme, a Dynamic bandwidth Partition with Finer‐Tune (DP‐FT) scheme, and a Dynamic bandwidth Partition with Reserved Region (DP‐RR). The proposed schemes are compared and evaluated via extensive simulations. Results show that the DP‐FT scheme is the best scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

121.9-Gb/s PDM-OFDM Transmission With 2-b/s/Hz Spectral Efficiency Over 1000 km of SSMF

We discuss optical multi-band orthogonal frequency division multiplexing (OFDM) and show that by using multiple parallel OFDM bands, the required bandwidth of the digital-to-analogue/ analogue-to-digital converters and the required cyclic prefix can significantly be reduced. With the help of four OFDM bands and polarization division multiplexing (PDM) we report continuously detectable transmission of 10$,times,$ 121.9-Gb/s (112.6-Gb/s without OFDM overhead) at 50-GHz channel spacing over 1,000-km standard single mode fiber (SSMF) without any inline dispersion compensation. In this experiment 8 QAM subcarrier modulation is used which confines the spectrum of the 121.9 Gb/s PDM-OFDM signal within a 22.8 GHz optical bandwidth. Moreover, we propose a digital signal processing method to reduce the matching requirements for the wideband transmitter IQ mixer structures required for PDM-OFDM.      

Planning the Reassignment of Frequencies in Fiber-Wireless Access Networks

FiWi architectures have been proposed as efficient solutions to provide high bandwidth and ubiquity at access network areas. In multi-radio and multi-channel FiWi scenarios an effective frequency assignment should be done to radios so that higher throughput and low delay can be obtained and the best of such architectures is achieved. However, traffic conditions change over time meaning that radio channel reconfigurations can be done to improve network performance. In this article a methodology for FiWi frequency reassignment planning is proposed, together with two algorithms, that avoids service disruption and attempts to increase throughput, reduce delay and increase the overall QoS perceived by users. Results show that the RBR algorithm is the one able to better exploit channel reconfigurations, increasing parallel transmissions and reducing time division required by nodes at the transmission area of each other.     

Two-stage bandwidth-allocated algorithm for multi-subsystem-based VPON in metro-access optical network

In the metro-access optical network, a two-stage bandwidth-allocated algorithm is proposed for the multi-subsystem-based virtual passive optical network (VPON) that can achieve the syncretism of multiple systems such as time division multiplexing-PON, wavelength division multiplexing-PON and orthogonal frequency division multiplexing-PON. In this paper, the bandwidth is allocated in two stages. The first-stage allocation is designed to improve the admission probability of new VPONs by allocating bandwidth to all new VPONs followed by original VPONs. Meanwhile, to avoid the bandwidth being monopolized by the new VPONs, the bandwidth allocated to each VPON is no more than its guaranteed bandwidth. Therefore, the whole fairness can be guaranteed. The second-stage allocation is used to promote the bandwidth-utilized ratio by assigning the remaining bandwidth to VPONs whose demand is not fully met in the first stage. With the two-stage allocation, not only the admission probability can be improved, but also the bandwidth-utilized ratio can be promoted. MATLAB is used to evaluate the performance of proposed algorithm according to admission probability of new VPONs and bandwidth-utilized ratio.     

Bandwidth Sharing Schemes for Multimedia Traffic in the IEEE 802.11e Contention-Based WLANs

Bandwidth allocation schemes have been well studied for mobile cellular networks. However, there is no study about this aspect reported for IEEE 802.11 contention-based distributed wireless LANs. In cellular networks, bandwidth is deterministic in terms of the number of channels by frequency division, time division, or code division. On the contrary, bandwidth allocation in contention- based distributed wireless LANs is extremely challenging due to its contention-based nature, packet-based network, and the most important aspect: only one channel is available, competed for by an unknown number of stations. As a consequence, guaranteeing bandwidth and allocating bandwidth are both challenging issues. In this paper, we address these difficult issues. We propose and study nine bandwidth allocation schemes, called sharing schemes, with guaranteed Quality of Service (QoS) for integrated voice/video/data traffic in IEEE 802.11e contention-based distributed wireless LANs. A guard period is proposed to prevent bandwidth allocation from overprovisioning and is for best-effort data traffic. Our study and analysis show that the guard period is a key concept for QoS guarantees in a contention-based channel. The proposed schemes are compared and evaluated via extensive simulations.     

Split-Tee Power Divider

A new type of power divider is described which provides two in-phase isolated outputs with a constant arbitrary power division over a wide bandwidth. The derivation of the formulas from which the unit may be deisgned and its performance predicted are given. The bandwidth characteristics of a two-third, one-third power divider are given along with experimental verification.     

WDM在SDH传输网中应用的技术问题

波分复用技术 ( WDM)在中国电信同步数字体系 SDH光传输网中的广泛运用 ,必将极大地满足宽带长途传输和接入的需求。通过分析波分复用技术相对于时分复用技术( TDM)的优越性及其在 SDH传输网中的应用 ,讨论了 SDH网络中使用 WDM的关键技术 ,并探讨了 WDM与 SDH网络管理一体化的技术方案和优势     

TD-SCDMA系统中Iub接口配置的计算方法

在TD-SCDMA无线网络规划优化中,定量分析Iub接口的传输需求、合理计算Iub接口传输带宽是非常重要和必要的。首先分析Iub接口协议结构,然后根据Iub接口控制和业务数据流配置,考虑时隙配置、站型等各种具体情况,最后提出Iub接口传输带宽的定量计算方法,从而达到最优化利用传输资源、服务于网络规划和工程建设的目的。     

Optimal transmission methodology for QoS provision of multi-hop cellular network

In this paper, we present a framework of link capacity analysis for optimal transmission over uplink MCN (Multi-hop Cellular Network) environments. An overlaid architecture is employed as the network topology, i.e., single-hop transmission over the inner region and multi-hop transmission over the outer region. In particular, we analyzed the gain that accrued from grafting a relay method onto a conventional, SCN (Single-hop Cellular Network) and investigated the conditions for optimal performance through the numerical results. At high-user density, a MCN exhibits a much more reliable transmission than the SCN. For maximal link capacity, optimal region partitioning is approximately accomplished at the normalized cell radius of 0.6 in most of cases for region division. Finally, the link capacity can be improved 1.2–1.8 times better than the SCN when the number of relay hops is 1.6 and the half-duplex mechanism is used. In addition, the proposed MCN scheme demonstrates an effective reduction in transmission power relative to the SCN.     

Next generation hierarchical CWDM/TDM-PON network with scalable bandwidth deliverability to the premises

Long haul optical networks have been on focus for more than two decades. With the advent of dense wavelength division multiplexing technology, optical long haul fiber networks have been so successful in delivering an unprecedented amount of bandwidth that they outperformed the traffic deliverability from/to the access network by orders of magnitude. The reason was a cost-efficiency mismatch; long haul ultra-high bandwidth networks can take advantage of state of the art and costly technology, which cost-sensitive access networks cannot. The result was an unbalanced traffic flow from/to access points to the network if one compares the aggregate flow of the long haul network with that of the access. Nevertheless, over the last decade technology at the access advanced and new standards have been developed so that in the access layer of the overall communications network the focus has shifted onto fiber optic access again. Thus, in the optical regime, two proposals have prevailed. One uses a time division multiplexing (TDM) scheme over a single wavelength and a comprehensive timing protocol, and the other uses coarse wavelength division multiplexing (CWDM) technology. Each technology has advantages and disadvantages, and the one attempts to address the disadvantages of the other. In this paper we describe a hierarchical CWDM/TDM passive optical network (PON). Our access network architecture is scalable, it is flexible to accommodate one of several topologies simultaneously, and it delivers any type of payload, synchronous and asynchronous that spans from DS0 to Gbps. We discuss the bandwidth flexibility, versatility, resiliency and cost efficiency of the access network. We also demonstrate that our network can deliver payload to more than 16,000 end-users using simple and existing optical technology. Thus, if one considers cost per bandwidth or per user, the cost-efficiency outperforms any previous PON access network. Moreover, we provide simulation results to support the viability of our network architecture.     

Integrated Optimal Cell Site Selection and Frequency Allocation for Cellular Radio Networks

Two major planning problems are encountered when designing a cellular radio network. The initial question is where to locate the base transmitter stations such that full coverage is achieved at low interference. This is relevant for frequency division (FDMA) as well as code division multiple access (CDMA) technology. If the locations of base stations are given, then for an FDMA-system frequencies have to be assigned such that there is a sufficient number of channels per cell available at a low total interference level. Since cell site selection and frequency allocation have mutual influences on each other, the ultimate goal is to deal with both problems in a single design step. The main intention of this paper is to model the above planning issues as linear integer programs, and to discuss solution methods for the corresponding NP-hard problems. According to their increasing complexity we proceed from channel allocation via cell site selection to an integrated single setup.