DESIGN OF BEAM-WAVE INTERACTION BASED ON HIGH EFFICIENCY OF A HIGH-POWER BROADBAND KLYSTRON

The paper mainly presents the design of beam-wave interaction of a C-band high-peakpower high-efficiency broadband klystron.The beam-wave interaction section is designed based on considerations of efficiency and bandwidth synthetically.As a part of beam-wave interaction section,buncher section is simulated by Particle-In-Cell(PIC) code to observe the bunching process of electron beam to achieve high conversion efficiency of electron beam and RF field.When it comes to the other part,output circuit is designed as a three-section filter by an output cavity loaded with Chebyshev filter,and the cold test results are given.The beam-wave interaction is simulated by EGUN code and Arsenal-MSU code respectively.The simulated results indicated that,the existence of power dips in the operating bandwidth is verified by Arsenal-MSU code,comparing proper results by EGUN code.Then,the method that design parameters are not adjusted except parameters of buncher cavities to remove potential power dips is described.What is more,the simulated results of electron optics system are given by EGUN code and Arsenal-MSU code respectively.The further hot test results of klystron prove that the whole design of beam-wave interaction is effective.

D2D Multicast Retransmission Algorithm in Mobile Cloud Based on SINR Constraint

In cellular network, users with same demand and in proximity to each other form the mobile cloud, in which the short-range D2 D technology is employed by users to improve the data dissemination efficiency. In view of the fact that the D2 D links with the poor channel conditions are likely to be the bottleneck of resource utilization improvement, aiming at the differentiation of link quality, this paper proposes a intra-cloud D2 D multicast retransmission algorithm based on SINR constraint to meet the minimum requirement of D2 D retransmission for Qo S. In the proposed algorithm, the model of system link cost is built, the number of multicast retransmission times is restricted and each link quality matrix is traversed to reasonably select the multicast transmitter as well as its routing, which further reduces the link cost consumption, and in turn improves the bandwidth efficiency. Simulation results show that the proposed algorithm is more efficient to improve the bandwidth utilization when the ratio between normal user and non-normal user is small in mobile cloud.

Underwater acoustic communication and the general performance evaluation criteria

Driven by the huge demand to explore oceans, underwater wireless communications have been rapidly developed in the past few decades. Due to the complex physical characteristics of water, acoustic wave is the only media available for underwater wireless communication at any distance. As a result, underwater acoustic communication(UAC) is the major research field in underwater wireless communication. In this paper, characteristics of underwater acoustic channels are first introduced and compared with terrestrial communication to demonstrate the difficulties in UAC research. To give a general impression of the UAC, current important research areas are mentioned. Furthermore, different principal modulation-based schemes for short-and medium-range communications with high data rates are investigated and summarized. To evaluate the performance of UAC systems in general,three criteria are presented based on the research publications and our years of experience in high-rate short-to medium-range communications. These three criteria provide useful tools to generally guide the design and evaluate the performance of underwater acoustic communication systems.

Study on modulation techniques free of orthogonality restriction

The Nyquist rate is a limit of transmission for traditional modulation methods from orthogonality restriction. Nonorthogonal modulation techniques （NMT） is proposed, which removes the orthogonality restriction, and as a result, higher bandwidth ef- ficiency than the traditional methods can be achieved. First, the symbol error rate of NMT is introduced by using estimation theory. Then the relation between bandwidth efficiency and signal to noise ratio is discussed. Finally, a design instance of NMT is present and numerical experiment is made. This study explores for new modulation methods and points out a widened direction for modulation theory and applications.

Flood Avoidance Mechanisms for Bridged Resilient Packet Rings

Resilient Packet Ring （RPR）, or the Standard IEEE 802.17, is a new IP-based network technology proposed to replace SONET/SDH in metropolitan area networks. RPR is well-adapted to handle multimedia traffic and is efficient. However, when RPR networks are bridged, inter-ring packets, or packets with the destination on a remote RPR network other than on the source network, are flooded on the source and the destination networks, and also on the path of the intermediate networks between the source and the destination networks. This decreases the available bandwidth for other traffic in those networks and is inefficient. As a result, we propose two solutions based on topology discovery, global topology discovery （GTD） and enhanced topology discovery （ETD）, that prevent the flooding of inter-ring packets. GTD enables the bridges to determine the next-hop bridge for each destination. ETD enables the source node to determine a default ringlet, so that packets reach the next-hop bridge without flooding the source network. The proposed solutions were analyzed and the overhead bandwidth and stabilization time were shown to be bounded. Simulations performed showed that the proposed solutions successfully avoid flooding and achieve optimal efficiency in the intermediate and destination networks, and in the source networks with one bridge.