Journal of China Universities of Posts and Telecommunications最新文献

The reachability problem of synchronizing transitions bounded Petri net systems (BPNSs) is investigated in this paper by constructing a mathematical model for dynamics of BPNS. Using the semi-tensor product (STP) of matrices, the dynamics of BPNSs, which can be viewed as a combination of several small bounded subnets via synchronizing transitions, are described by an algebraic equation. When the algebraic form for its dynamics is established, we can present a necessary and sufficient condition for the reachability between any marking (or state) and initial marking. Also, we give a corresponding algorithm to calculate all of the transition paths between initial marking and any target marking. Finally, an example is shown to illustrate proposed results. The key advantage of our approach, in which the set of reachable markings of BPNSs can be expressed by the set of reachable markings of subnets such that the big reachability set of BPNSs do not need generate, is partly avoid the state explosion problem of Petri nets (PNs).

Opportunistic routing (OR) could adapt to dynamic wireless sensor networks (WSNs) because of its inherent broadcast nature. Most of the existing OR protocols focus on the variations of propagation environment which are caused by channel fading. However, a few works deal with the dynamic scenario with mobile nodes. In this paper, a mobile node (MN) aware OR (MN-OR) is proposed and applied to a WSN in the high-speed railway scenario where the destination node is deployed inside a high speed moving train, and the MN-OR not only considers the mobility of node but also utilizes the candidate waiting time induced by the timer-based coordination scheme. Specifically, to reduce the number of duplicate transmissions and mitigate the delay of information transmission, a new selection strategy of the candidate forwarders is presented. In addition, two priority assignment methods of the candidate forwarders are proposed for the general relay nodes (GRNs) and the rail-side nodes (RSNs) according to their different routing requirements. Extensive simulation results demonstrate that the proposed MN-OR protocol can achieve better network performances compared with some existing routing schemes such as the well-known Ad-hoc on-demand distance vector routing (AODV) and the extremely opportunistic routing (ExOR) protocols.

The output of each individual channel in multi-carrier system can be processed to detect moving targets by the approach used in tradition narrowband pulse Doppler (PD) radar and then using non-coherent integration to promote signal noise ratio (SNR). However, due to the difference of Doppler on sub-carriers, there occurs Doppler dispersion during non-coherent integration, which causes attenuation and extension on target's amplitude. Especially, it can deteriorate performance of target detection under wideband multicarrier system or fast-moving target scene. In this paper, a modified Fourier transform kernel is proposed to solve Doppler dispersion for multi-carrier chirp signal. It can achieve accumulation at the same frequency point for the target's Doppler of each subcarrier. The simulation results indicate that this method can effectively eliminate the integral loss caused by Doppler dispersion.

Aimed to enhance the supporting ability for diversified services, this paper proposes a hierarchy echo state network (HESE) based service-awareness (SA) (HESN-SA) mechanism in 10 Gbit/s Ethernet passive optical network (10G-EPON). In this HESN-SA, hierarchy architecture is adopted to realize echo state network (ESN) classification based SA. According to the network architecture of 10G-EPON, the parent-ESN (p-ESN) module works in the optical line terminal (OLT), while the sub-ESN (s-ESN) module is embedded in optical network units (ONUs). Thus, the p-ESN plays the main function of SA with a total view of this system, and s-ESN in each ONU conducts the SA function under the control of p-ESN. Thus, resources allocation and transport policy are both determined by the proposed mechanism through cooperation between OLT and ONUs. Simulation results show that the HESN-SA can improve the supporting ability for multiple services.

The maximum traffic intensity supported by a low earth orbit (LEO) mobile satellite system (MSS) (LEO-MSS) is important in practical application for providing satisfactory service. An analytical approach is proposed for determining the maximum traffic intensity of guaranteed handover (GH) scheme and channel complete sharing (CCS) scheme in LEO-MSS under quality of service (QoS) constraints. By evaluating performance of these two schemes, the relationship between the traffic intensity and the QoS constraints is established. The expressions of maximum traffic intensity of GH scheme and CCS scheme are deduced. Compared with the traditional method, the proposed analytical approach is more computationally efficient owing to the needlessness of the repeated iteration calculation. It also avoids the complex choice of the initial value of new call traffic intensity and its increment. Lastly, the accuracy and validity of the analysis approach have been verified by computer simulations.

Hybrid cloud peer to peer (P2P) system is widely used for content distribution by utilizing user's capabilities to relieve the cloud bandwidth pressure. However, as demands for large-size files grow rapidly, it is a challenge to support high speed downloading experience simultaneously in different swarms with limited cloud bandwidth resource in such system. Therefore, it requires an optimized cloud bandwidth allocation to improve overall downloading experience of users. In this paper, we propose a system performance model which characterizes the relationship between cloud uploading bandwidth and user download speed. Based on the model, we study the cloud uploading bandwidth allocation, with the goal of optimizing user's quality of experience (QoE) that mainly depends on downloading rate of desired contents. Furthermore, to decrease the computation complexity, we put forward a heuristic algorithm to approximate the optimized solution. Simulation results show that our heuristic algorithm can obtain higher user's QoE as compared with two typical bandwidth allocation algorithms.

A new variable step-size (VSS) affine projection algorithm (APA) (VSS-APA) was proposed for adaptive feedback cancellation suitable for hearing aids. So, a nonlinear function between step-size and estimation error is established and automatically adjusted according to the change of the estimation error, which leads to low misalignment and fast convergence speed. Analysis of the proposed algorithm offers large capacities in converging to the objective system. Simulation shows that the proposed algorithm achieves lower misalignment and faster convergence speed compared to fixed step-size APA and conventional adaptive algorithms.

An effective data hiding method based on pixel value differencing (PVD) and modulus function (MF) PVD (MF-PVD) was proposed. MF-PVD method was derived by Wang et al in which the MF was employed to adjust the remainder of two pixels for data embedding and extraction. In the proposed method, a new remainder function in a more general form is defined by selecting proper parameters, in which an indeterminate equation is constructed and an optimal solution is applied to revise the pixels. This strategy leads to a significant image distortion reduction compared with the original method. The experiment reveals that, by preserving the original embedding capacity, the method provides better embedding efficiency than both MF-PVD and PVD methods.

In contention-based satellite communication system, collisions between data packets may occur due to the randomly sending of the packets. A proper delay before each transmission can reduce the data collision rate. As classical random multiple access protocol, the slotted ALOHA (S-ALOHA) reduces the data collision rate through time slot allocation and synchronous measures. In order to improve the stability and throughput of satellite network, a backoff algorithm based on S-ALOHA will be effective. A new adaptive backoff algorithm based on S-ALOHA using grey system was proposed, which calculates the backoff time adaptively according to the network condition. And the network condition is estimated by each user terminal according to the prediction of the channel access success ratio using the model GM (1,1) in grey system. The proposed algorithm is compared to other known schemes such as the binary exponential backoff (BEB) and the multiple increase multiple decrease (MIMD) backoff. The performance of the proposed algorithm is simulated and analyzed. It is shown that throughput of the system based on the proposed algorithm is better than of system based on BEB and MIMD backoff. And there are also some improvements of the delay performance compared to using BEB. The proposed algorithm is especially effective for large number of user terminals in the satellite networks.

Wavelength division multiplexing (WDM) has been becoming a promising solution to meet the rapidly growing demands on bandwidth. Multicast in WDM networks by employing free wavelength is an efficient approach to saving bandwidth and cost. However, the free wavelength may not identical between different hops in a multicast light-path, particularly in heavy load optical WDM networks. In order to implement multicast applications efficiently, a network coding (NC) technique was introduced into all-optical WDM multicast networks to solve wavelength collision problem between the multicast request and the unicast request. Compared with the wavelength conversion based optical multicast, the network coding based optical multicast can achieve better multicast performance with paying lower cost.