Hefei Hu

Link stability based routing in mobile ad hoc networks

Node mobility is one of the dominant factors causing decreased performance in mobile ad hoc networks, thus stability of selected path is of prime importance. The proposed method uses link stability factor (LSF) and path stability factor (PSF) to select a stable path while minimizing number of hops. The nodes transmission range is divided into stable zone and caution zone. Rerouting is initiated when the distance between two neighboring communicating nodes exceeds the stable zone, before the old path actually breaks, thus realizing soft handoff and reducing the data packets ETE delay. The proposed LSB_AODV routing scheme is evaluated by simulation and results show that an improved packet delivery ratio and reduced ETE delay can be obtained.

An improved OFDM-MSK system for wireless communications

As a well attractive modulation scheme, Minimum-shift Keying (MSK) has a fast roll-off side-lobe spectrum. Because of this excellent property, we introduce MSK into the conventional OFDM to form an improved OFDM-MSK system. The new system can effectively overcome the carrier frequency offset (CFO), mitigate the interference among the sub-carriers. And two kinds of OFDM-MSK receiver are discussed in detail. At the same time, two FFT-based sampling modes (Mode A and Mode B) are also proposed and analyzed. And a practical OFDM-MSK structure design is given. Simulation results show that when SNR is high, the BER performance of OFDM-MSK systems outperforms that of OFDM-QPSK systems over AWGN and Rayleigh wireless fading channels.

A Novel OFDM-MSK Scheme for MB-OFDM UWB Based on Cognitive Radio

Minimum-shift Keying (MSK) has a fast roll-off sidelobe spectrum, which is an excellent property for multi-carrier modulation (MCM) systems. In this paper, we propose a novel OFDM-MSK modulation scheme and introduce it to MB-OFDM UWB systems based on Cognitive Radio (CR). Therefore, the new system has a better out-of-band attenuation property. In such situations, when incumbent radio services are detected, without additional measures, only by tuning off the sub-carriers on the corresponding interference frequency band, the requirements of MB-OFDM UWB systems based on CR can be satisfied, and the interference on incumbent users will be cancelled sufficiently.

Analysis of maximum traffic intensity under pre-set quality of service requirements in low earth orbit mobile satellite system for fix channel reservation with queueing handover scheme

Maximum traffic intensity supported by a low earth orbit mobile satellite system (LEO-MSS) is important in practical application for providing satisfactory service. Applying fix channel reservation with first in first out queueing handover scheme into LEO-MSS, a novel analytical approach is proposed for determining the maximum traffic intensity under pre-set quality of service (QoS) constraints on new call blocking probability and handover failure probability. The relationship between QoS constraints and maximum traffic intensity is established. The expression of maximum traffic intensity is then deduced. The optimal number of reserved channels is obtained. By comparing the results between the proposed approach and existing method, the correctness of the proposed approach is verified. The proposed approach greatly reduces the calculation complexity. Lastly, the accuracy of the analysis has been verified by computer simulations.

A servo design for slave clock in IEEE 1588 synchronization networks

Summary Clock synchronization is critical for a variety of applications in communication networks. In this paper, we design a clock servo named VI_PID-K, which consists of a variable integral PID controller and a Kalman filter. It is a pre-correction mechanism for the skew based on feedback principle to compensate for the poor stability of local clocks in IEEE 1588 networks. Our contribution is establishing discrete differential equation models, bringing in a variable integral PID controller to adjust the skew error and a Kalman filter to act as a skew estimator to predict the skew during one synchronization interval. Simulation results demonstrate that VI_PID-K provides a more stable disciplined clock, improves the speed of skew convergence, and reduces Allan variance in a large time scale when compared to PI method or Fixed_Integral method.VI_PID-K can improve the stability of slave clock and reduce the frequency that master clock sends Sync messages, so the network overhead for clock synchronization can be reduced. Copyright

MEED-WTR: An improved routing recomputation for intermediate nodes with two contacts

MEED has been introduced in Delay Tolerant Networks with per-contact routing recomputation in order to optimize the route with network topology variation. But it is not effectively for the network in which the nodes own several contacts and metrics make a large difference. In this paper, we propose an improved algorithm named MEED-WTR to deal with this particular network environment. By means of introducing metric proportion factor ρ and recomputation waiting factor σ, MEED-WTR can select better one between two contacts owned by one node. It is shown by the simulation that MEED-WTR can increase the delivery ratio and reduce the average transmission delay in DTNs.