Trung Dung Nguyen

An expending ring search algorithm for Mobile Adhoc networks

Routing protocols are challenges in designing Mobile Ad-hoc networks with low energy consuming. This paper extends the expanding ring search (ERS) algorithm proposed in [3] to optimize the energy consuming caused by broadcasting redundance messages. Simulation results show that the required message packages for routing by using our algorithm is significantly reduced in comparison with that required by using the ERS method.

Routing dual criterion protocol

Routing protocol is an important issue in mobile adhoc network (MANET). One of the most popular protocols is AODV [5] routing protocol. There have been many proposed protocols based on it, for example ERS and EERS [1]. Most of them select the best path using hopcount parameter. In this paper, beside hopcount parameter, we also use energy parameter to select best path. It balances energy of nodes in the network. Therefore, it increases the lifetime and throughput of the network. Our protocol is called routing dual criterion (RDC). Simulation results show that the lifetime and throughput when using our algorithm are better than when using EERS protocol.

An Energy-Efficient Ring Search Routing Protocol Using Energy Parameters in Path Selection

Routing protocol is very important in Ad hoc network. From the EERS [3] protocol, we have improved AODV protocol to consume energy more efficiently. However, this method depends only on hop count number, but not energy. This leads to central nodes’ exhaustion of energy and influences the entire network lifetime. In this paper, we propose two new protocols from EERS, called Avoid Bad Route (ABR) and Routing Dual Criterion (RDC). In both protocols, we base on energy criteria. Therefore, the lifetime as well as the throughput of the whole network are improved.

The genesis of tool wear in machining

This paper presents a series of experimental and theoretical efforts that we have made in unraveling the tool wear mechanisms under steady state conditions in machining for the last few decades. Two primary modes of steady state tool wear considered in this paper are flank and crater wear. We preface this paper by stating that flank wear is explained as abrasive wear due to the hard phases in a work material while crater wear is a combination of abrasive wear and generalized dissolution wear which encompasses both dissolution wear as well as diffusion wear. However, the flank wear was not a function of the abrasive cementite content when turning low alloy steels with pearlitic microstructures. The machined surfaces of these alloys are examined to confirm the phase transformation (ferrite to austenite), which diminishes the effect of cementite content. In particular, the cementite phase present in low alloy steels dissociates and diffuses into the transformed austenitic phase during machining. Dissolution wear is claimed to describe the behavior of crater wear at high cutting speeds. The original dissolution mechanism explains the crater wear in the machining of ferrous materials and nickel alloys at high cutting speeds, but the generalization of the dissolution wear is necessary for titanium alloys. In machining titanium alloys, the original dissolution mechanism did not show a good correlation with experimental results; generally the diffusivity of the slowest diffusing tool constituent in titanium limits the wear rate. The phase transformation from alpha (HCP) to beta (BCC) phases can also take place in machining titanium alloys, which drastically increases the crater wear due to the few orders of magnitude increase in diffusivity. The most puzzling issue is however the presence of the scoring marks even though no hard inclusion is typically present in titanium alloys. This is finally explained by the heterogeneity in the microstructure due to the anisotropic hardness of alpha (HCP) phase (the hardness in c-direction is 50% higher than the hardness in other directions) and the presence of lamellar microstructure (alternating layers of alpha and beta). The lamellar microstructure has not only the in-plane anisotropic hardness but also a greater hardness than other phases. Even though we cannot claim to fully understand the physics behind tool wear, our combined approaches have unveiled some elementary wear mechanisms.Copyright

Optimized MAC and network cross layer protocol for OFDMA based ad-hoc networks

In this paper, a new MAC and Network cross layer protocol for OFDMA-based Multi-hop Ad-hoc Networks is proposed. In wireless network, when a route is established, the radio resource allocation problems at MAC layer may decrease the end to end performance proportionally with the length of each route. The contention at MAC layer may causes routing protocol to respond by finding new routes and routing table updates. The cross layer protocol allows layers to exchange state information in order to solve the problem and obtain higher performance. The proposed MAC and Network optimized cross layer protocol based the dynamic Sub-channel Assignment Algorithm in [4] to ensure the performance of ad-hoc and multi-hop networks is significantly improved.

Cross-layered OFDMA-based MAC and routing protocol for multihop adhoc networks

In this paper, a dynamic Sub-channel Assignment Algorithm (DSA) based on orthogonal frequency division multiple access (OFDMA) technology operating in the time division duplexing (TDD) and a new routing protocol are proposed. The proposed of dynamic Sub-channel Assignment Algorithm solves several drawbacks of existing radio resource allocation techniques in OFDM system used in ad-hoc and multi-hop networks, such as the hidden and exposed node problem, mobility, co-channels interference in frequency (CCI). An interference avoidance mechanism allows the system to reduce CCI and to operate with full frequency re-use. The proposed routing protocol is jointed with the MAC protocol based the algorithm to ensure the mobility and multi-hop, thus the quality of service in ad-hoc and multi-hop networks is significantly improved.

OFDMA-based MAC protocol for adhoc and multihop networks

In this paper, a novel medium access control (MAC) protocol based on orthogonal frequency division multiple access (OFDMA) technology operating in time division duplexing (TDD) called MAC-TO for adhoc and multihop networks is proposed in order to counteract mobility, co-channel interference (CCI), hidden terminals and exposed nodes problems. In this method, the channel is divided into multiple sub-channels in frequency, and OFDM modulation is then used in every subchannel. In addition, time selectivity of the channel is assigned into slots for data transmission between a transmitter and a receiver only if the corresponding channels of those sub-channels linking to this transmitter to potential receivers are in deep fade. Powerful transmitters in the network are responsible for the dynamic channel assignment, power optimization and modulation method selection for all receivers in every slot. Numerical results reveal that MAC-TO achieves the overall throughput (end-to-end bits through multiple hops per OFDM symbol) higher than those of the conventional methods in the given quality of service for any specific circumstances of adhoc and multihop network.