Zengji Liu

Xidian University, Ch’ang-an, Shaanxi, China

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Publications (48)37.61 Total impact

  • Source
    JiangBo Si · Zan Li · LanJun Dang · ZengJi Liu
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    ABSTRACT: In cooperative wireless networks, it is often the case that multi-source and multi-relay cooperate to transmit their own data to the destination, namely, the access point. For the cooperative systems, the choice of relay and the allocation of power between the source and the relay are important design issues. In this paper, based on the optimal power allocation between one source and one relay under an outage constraint, the joint optimization of relay selection and power allocation is done efficiently by introducing a greedy and exchange algorithm (GAEA), which aims at minimizing the total transmission power in the multi-source and multi-relay wireless networks where one relay can only be allocated to one source. Simulation results and numerical analyses show that, the proposed algorithm, with low computational complexity, can achieve the similar performance as the exhaustive search algorithm and save transmission power significantly.
    Full-text · Conference Paper · Dec 2008
  • Source
    JiangBo Si · Zan Li · ZengJi Liu · XiaoFeng Lu
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    ABSTRACT: In this paper, we address the problem of joint optimization of route and power allocation in cooperative- multihop networks, where a source node wants to transmit a sequence of messages to a single destination node out of the range of direct transmission. We first study the optimal power allocation between the single source node and single relay with DF (decode and forward) protocol in multihop transmission. Then under the assumption that intermediate node can adaptively select transmission scheme between DT(direct transmission) and DF , a heuristic algorithm is proposed to find a good route and allocate power efficiently for the minimum outage probability with a given power budget. Finally, our simulation results show that cooperative-multihop transmission outperforms the non-cooperative-multihop transmission, and the proposed algorithm can achieve lower outage probability compared to the equal power allocation with shortest path.
    Full-text · Conference Paper · Jun 2008
  • Jiangong Zhao · Aijun Wen · Zengji Liu · Peng Yue
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    ABSTRACT: Self-imaging theory is widely accepted as a good method in designing 1×N multimode interference (MMI) couplers, but it is also true that self-imaging theory is not suitable for low-contrast structures. An improved self-imaging theory is proposed in this paper for the optimal design of low-contrast 1×N MMI couplers. The average effective width of MMI waveguide and the average effective propagation constant of MMI waveguide are used as the basis to modify the conventional self-imaging theory. A direct calculation of the average effective width of low-contrast MMIs is presented. We use this approach in the optimal design of a 1×4 silica MMI coupler, and the results show that the improved self-imaging theory is more accurate than conventional self-imaging theory for low-contrast structures, the results also show that if the material parameters and the width of an MMI waveguide are fixed, the average effective width of the MMI waveguide will increase with the decrease of the height of the core layer.
    No preview · Article · Mar 2008 · Optics Communications
  • Source
    Yang Su · Zhanqi Xu · Ruiqin Zhao · Zengji Liu
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    ABSTRACT: A layered network model for optical transport networks is proposed in this paper, which involves Internet Protocol (IP), Synchronous Digital Hierarchy (SDH) and Wavelength Division Multiplexing (WDM) layers. The strategy of Dynamic Joint Routing and Resource Allocation (DJRRA) and its algorithm description are also presented for the proposed layered network model. DJRRA optimizes the bandwidth usage of interface links between different layers and the logic links inside all layers. The simulation results show that DJRRA can reduce the blocking probability and increase network throughput effectively, which is in contrast to the classical separate sequential routing and resource allocation solutions.
    Full-text · Article · Jan 2008 · Journal of Electronics (China)
  • Huaxi Gu · Jie Zhang · Kun Wang · Zengji Liu · Guochang Kang
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    ABSTRACT: Fault rings can be used to guide messages bypass faulty nodes/links in a fault tolerant interconnection network. However, nodes on the fault ring become hot spots, thus causing uneven distribution of the traffic loads. To avoid such traffic congestion, a concept of the balanced ring is proposed in this paper. The proposed balanced ring, defined as concentric rings of a given fault ring, can be applied to the fault tolerant routing algorithms for mesh and torus topologies. By properly guiding messages to route on the balanced ring and the fault ring, more balanced link utilization and greatly reduced traffic congestion can be achieved on a fault tolerant network. Methods of applying the balanced ring concept to some published fault tolerant routing algorithms are discussed. Proof of deadlock and livelock freedom is also presented. The use of balanced ring does not need to add new virtual channels. The performance of two routing algorithms with and without the balanced ring is simulated and evaluated. The results indicate that routing algorithms with the balanced rings constantly yield larger throughput and smaller latency than those without.
    No preview · Article · Dec 2007 · Journal of Systems Architecture
  • Source
    Ruiqin Zhao · Aijun Wen · Zengji Liu · Peng Yue
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    ABSTRACT: Added delay strategy can be used to solve the broadcast storm problem of ordinary broadcast mechanism (OBM) and maximize network life-time. Available added delay strategies take into account the distance and/or the residual energy. In this paper, we propose a new added delay strategy—Maximum Life-time Localized Broadcast (ML2B). As the node’s number of neighbors that have not received the broadcast message (we call it coverage degree) can better describe the coverage rate, ML2B takes the coverage degree rather than the distance into account. ML2B also takes the residual energy into account as other strategies do. ML2B only need one-hop neighbor information to find the coverage degree, so ML2B is a distributed protocol and the overhead is small. Simulation results show that, as compared with OBM, ML2B can save at least 50% rebroadcast, its maximum end-to-end delay is lower, its reachability is the same, and its network life-time is two times longer.
    Preview · Conference Paper · Sep 2007
  • Yantao Guo · Aijun Wen · Zengji Liu · Zhiqing Zhang
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    ABSTRACT: A novel differentiated service hybrid (DSH) signaling protocol is proposed for optical burst switching (OBS) networks. In an OBS network, real-time (circuit) traffic and non-real-time (bursty data) traffic are dealt respectively by TAW and JET protocol according to their different QoS requirements. TAW signaling is modified to adapt to the transport of circuit emulation traffic. A call request of circuit traffic may be used to set up a virtual channel from a source to a destination before the traffic arrives, and the virtual channel would be held until the call ends. In this way, smaller end-to-end delay and lower loss probability of data bursts may be achieved for accepted calls. By computer simulations, the performance of DSH protocol is studied; its effects on wavelength utilization and blocking probability of OBS network are investigated.
    No preview · Conference Paper · Aug 2007
  • Ruiqin Zhaol · Aijun Wen · Zengji Liu · Jungang Yang
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    ABSTRACT: Directional antennas are used for mobile ad hoc networks (MANET) to improve network security, capacity and energy efficiency. In this paper, we propose an unaided directional neighbor discovery (UADND) algorithm for directional transmission and reception in MANET. With UADND, network nodes could independently find neighbors that can be reached only when both of transmission and reception are directional. Additional information provided by GPS or other methods, such as node position or synchronization information utilized by other neighbor discovery algorithms is not necessitated in UADND. The proposed algorithm uses the geometrical relationship between the communication range of DT (directional transmission only) mode and the communication range of DTR (directional transmission and reception) mode to discover DTR neighbors. Cross layer design is used in UADND to integrate directional neighbor discovery with MANET routing, and thus making UADND a scenario-adaptive neighbor discovery algorithm. Simulations show that UADND is efficient in overhead and energy saving.
    No preview · Article · Jan 2007
  • Source
    Zhanqi Xu · Kechu Yi · Zengji Liu
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    ABSTRACT: Derived from a proposed universal mathematical expression, this paper investigates a novel algorithm for parallel Cyclic Redundancy Check (CRC) computation, which is an iterative algorithm to update the check-bit sequence step by step and suits to various argument selections of CRC computation. The algorithm proposed is quite suitable for hardware implementation. The simulation implementation and performance analysis suggest that it could efficiently speed up the computation compared with the conventional ones. The algorithm is implemented in hardware at as high as 21Gbps, and its usefulness in high-speed CRC computations is implied, such as Asynchronous Transfer Mode (ATM) networks and 10G Ethernet.
    Full-text · Article · Jul 2006 · Journal of Electronics (China)
  • Tao Shang · ZengJi Liu · Peng Yue · JianPing Chen
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    ABSTRACT: Due to triangular photonic crystal fiber (PCF) high nonlinearity and low dispersion slope, using the condition that the different linear phase shift combination must satisfy the phase match, the expressions of gain and bandwidth for one-pump fiber-optic parametric amplifiers (1P-FOPA) based on PCF in the normal and abnormal dispersion regimes are derived respectively. Then, 1P-FOPAs performance comparison among PCF, dispersion-shifted fiber (DSF) and highly nonlinear fibers (HNLF) are carried out by numerical simulations. It is shown that the 1P-FOPA based on triangular PCF can provide higher peak gain over wider bandwidth. When the pump wavelength is at the zero-dispersion wavelength (ZDWL), about 108.7 nm single-pass gain bandwidth and 91.4 dB peak gain can be obtained; when in the normal dispersion regime and near zero-dispersion wavelength, not less than 46 nm single-pass gain bandwidth 77.1 nm away from pump can be achieved. Finally the influence of dispersion fluctuation is analyzed, and the result shows that the tolerance of the 1P-FOPA based on photonic crystal fiber is better.
    No preview · Article · Jun 2006 · Science in China Series F Information Sciences
  • Source
    Huaxi Gu · Jie Zhang · Zengji Liu · Xiaoxing Tu
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    ABSTRACT: In this letter, a new addressing scheme for hexagonal networks is proposed. Using the new addressing scheme, many routing algorithms designed for networks using square-based topologies such as mesh and torus can also be applied to hexagonal networks. Methods of applying the turn model to hexagonal networks are derived, with some new minimal and partial adaptive routing algorithms obtained. Simulations of the new routing algorithms under different working conditions are carried on hexagonal networks of various sizes. The results show that the proposed algorithms can offer lower packet delay and loss rate than the popular dimension order routing algorithm.
    Full-text · Article · May 2006 · IEICE Transactions on Information and Systems
  • Yang Su · Zhanqi Xu · Zengji Liu
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    ABSTRACT: An extended layered graph of MPLS over WDM mesh networks is proposed in this paper, in which the label switch path (LSP) with various wavelengths and the limitation of optical transceivers at a routing node are both involved. Label switch paths are classified into different priorities according to each quality of service. The corresponding routing algorithm, differentiating integrated routing algorithm (DIRA), is proposed and studied. The quality of service (QoS) of a label switch path and the optimization of network resources utilization are taken into account comprehensively in DIRA. A comparison of DIRA with the representative optical routing algorithms via simulation shows that it can reduce the blocking probability of delay-constraint LSP and improve the network throughput.
    No preview · Article · Nov 2005 · Proceedings of SPIE - The International Society for Optical Engineering
  • Huaxi GU · Zengji Liu · Bing Zhang · Guochang Kang · Zhimin Gu
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    ABSTRACT: More and more attention is focused on direct interconnection networks when designing the switching fabrics in the terabit routers. Various congestion control mechanisms are proposed for multi-computer systems, which also rely on direct interconnection networks between processors to support the messages passing mechanism. But it remains unknown whether they are suitable for fabrics in the terabit routers. Based on the requirements of terabit class routers, we made analysis and simulations on various congestion control mechanisms, such as U-channel, INC, self-tune and GRCC. The results show that congestion control mechanisms eliminate performance degradation for loads beyond saturation, keeping adequate levels of throughput at high loads. The local mechanisms can achieve similar performance with the global ones. However, as we pointed in the paper, they all have limitations when used in switching fabrics of the terabit routers.
    No preview · Conference Paper · Nov 2005
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    ABSTRACT: Direct interconnection network has been widely used in supercomputer systems. Recently, it is considered to be used to build terabit router by the industry. This paper presents a distributed and scalable switching fabric based on a new direct interconnection network. It is a scalable topology and can be expanded in two ways easily, thus minimizing the initial investment of service providers. Its distributed control can offer low hardware complexity. Virtual cut through switching is used to achieve high throughput and low latency. The quality of service is guaranteed by introducing virtual channels based on the concept of DiffServ. The fault tolerant and load-balanced routing algorithm can offer deadlock and livelock freedom. It helps the network continue to work even with faulty parts existed. Finally, the performance of the proposed switching fabric is evaluated under various conditions. The results show it can outperform its counterpart in latency and throughput. It achieves terabit throughput with average latency of 1 us or so.
    No preview · Conference Paper · Oct 2005
  • Huaxi Gu · Zengji Liu · Zhiliang Qiu · Xiaoxing Tu
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    ABSTRACT: Research is carried on a novel switching fabric-XD (cross and direct) network, which is the core of the terabit router. XD networks have many advantages such as simple rectangular structure, scalability and so on. Attention is focused on designing the routing algorithm CFRA (Cycle free routing algorithm), which is partially adaptive, minimal, deadlock and livelock free. For XD mesh, no virtual channels are required and four virtual channels are needed if wraparound connections are used. Proof of deadlock freedom and livelock freedom is presented. Finally, the simulation is carried out on (8,8)-XD networks to evaluate the performance. The results show that XD network has potentially an attractive interconnection network topology and CFRA is of good performance.
    No preview · Article · Oct 2005
  • Source
    Zhen Chen · Zengji Liu · Zhiliang Qiu · Peng Chen · Xiaoming Tao
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    ABSTRACT: A methodology is proposed to handle problem that under equiproble address of packet traffic at the input port, Generalized Shuffle-Exchange Network (GSEN) routes traffic unevenly because of the unbalanced routing tags. The idea is to use routing tag according to probability, which can be evaluated by using Moore-Penrose inverse in matrix analysis. An instance is used to illustrate the idea, and the simulation is done to show the improvement in performance issues.
    Full-text · Article · Jun 2005 · Journal of Electronics (China)
  • Yan Shi · Zengji Liu · Zhiliang Qiu · Min Shen
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    ABSTRACT: Satisfying critical QoS requirements in next generation networks poses major challenges, due to its intrinsic complexity of network resource allocation. This paper considers the problem of load balance based bandwidth allocation for delay sensitive services. For satisfying deterministic end-to-end delay requirement, a simple and efficient algorithm for path level optimal bandwidth allocation, path level equal ratio allocation algorithm (P-ERA), is developed first. Based on P-ERA, another algorithm for network level optimized bandwidth allocation, network level equal ratio allocation algorithm (N-ERA), is also presented for much more complicated network circumstances. N-ERA algorithm features appropriate route selection and balanced bandwidth allocation, and can adaptively avoid, or at least delay, the emergence of network bottleneck when a network is heavily loaded. Extensive simulations indicate that N-ERA algorithm can make full use of network bandwidth and admit more services, even if they are delay critical, than other ones dealing with the same problem. And the less computation complexity of N-ERA algorithm makes it of great application value.
    No preview · Conference Paper · Apr 2005
  • Source
    Zhen Chen · Zengji Liu · Zhiliang Qiu · Xiaoming Tao
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    ABSTRACT: To design a Banyan network with an arbitrary even-sized port number, the PN2I network is proposed. The PN2I network can be divided into two classes: the complete and incomplete versions. A simple routing algorithm is given, but in the incomplete PN2I networks, this routing algorithm fails to make the traffic in links even, which deteriorates the performance badly. Thus a new routing algorithm is proposed, which makes the incomplete PN2I networks behave almost the same as the PN2I networks with respect to the performance issues.
    Full-text · Article · Apr 2005 · Journal of Electronics (China)
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    ABSTRACT: More and more attention is focused on direct interconnection networks when designing the switching fabrics in the terabit routers. Various switching mechanisms are proposed for multi-computer systems, which also rely on direct interconnection networks between processors to support the messages passing mechanism. But it remains unknown which one is more suitable for fabrics in the terabit routers. Based on the requirements of terabit class routers we made analysis and simulations on various switching mechanisms, such as store and forward, wormhole switching, virtual cut through switching and pipelined circuit switching. The results show that virtual cut through exhibits superior performance characteristics over other switching mechanisms under various conditions. Simulations of the performances of virtual cut through shows that larger buffer, longer flit and more virtual channels help to sustain higher throughput at the cost of increasing latency.
    No preview · Conference Paper · Apr 2005
  • Yang Su · Zhanqi Xu · Zengji Liu
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    ABSTRACT: This paper proposes a dynamic routing optimal model in IP/MPLS over WDM networks. A corresponding on-line integrated routing algorithm minimizing the cost of total lightpaths (MCTLP) is designed accordingly. MCTLP optimizes the network resource utilization by integrally assigning bandwidth allocations on both IP layer and wavelength links usage on WDM layer. The performance comparison of MCTLP with two representative routing algorithms used in IP/MPLS over WDM networks via simulation shows that MCTLP can use less links on IP layer and WDM layer to carry IP traffic flows, resulting in accepting more connection requests and reducing the traffic blocking probability efficiently.
    No preview · Conference Paper · Jan 2005