Optimal radio access technology selection on heterogeneous networks

Seamless mobility is an important and challenging issue to guarantee required Quality of Service (QoS) in Next Generation Wireless Network (NGWN). In this paper, we have proposed a technique to support seamless mobility in optimized time with best utilization of network resources in heterogeneous network of UMTS (Universal Mobile Telecommunication System) and WLAN. Vertical handoff is analyzed to provide adaptive handoff trigger time for vertical handoff decision algorithm. Since performance of a wireless network depends upon accurate trigger timing of handoff, the proposed technique reduces the network load by minimizing link failure and maximizes the resource utilization and subsequently improves the system performance.

Optimal and Near Optimal Control of a Two-Part-Type Stochastic Manufacturing System with Dynamic Setups

For the design of call admission control (CAC) policy in wireless networks, how to decrease the average system cost is a key issue. In this paper, we study the optimal admission policy for minimizing the system cost. By modeling the admission control problem into a Markov decision process (MDP) and analyzing the corresponding value function, we obtain some monotonicity properties of the optimal policy. These properties suggest that the optimal admission control policy for the bandwidth asymmetry wireless networks should have a threshold structure and the threshold specified for a class of calls may change with the system state. Due to the prohibitively high complexity for computing the thresholds in a system with large state space, we propose a heuristic CAC policy called call-rate- based dynamic threshold (CRDT) policy to approximate the theoretical optimal policy based on the insights we obtain from the modeling and the analytical study on the properties of the optimal policy. The CRDT policy is efficient and can be easily implemented. The numerical results show that the performance of average system cost of the proposed CRDT policy is close to that of the optimal policy from the MDP model and is better than that of some known existing CAC schemes, including those performing well in bandwidth asymmetry wireless networks.

The problem of off-line inspection is of both practical and theoretical interest. It has been the subject of research in somewhat simplistic scenarios. In this paper, the theoretical coverage of this problem is extended to include inspection errors. In particular, a process which is subject to random failures that sequentially produces a batch of units is investigated. After the batch is complete, off-line inspections are performed. In the proposed model it is these inspections that are subject to errors. The optimal inspection policy, i.e., which units should be inspected and the inspection order so as to minimize the expected number of inspections, is determined. The considered objective function is to find the point at which the machine fails with a given confidence level. The optimal policy is found by a dynamic programming algorithm and four different heuristic policies are investigated. An extensive computational study that examines the behavior of both the optimal and heuristic policies is presented. In particular, the effect of the model parameters on the behavior of the optimal policy is analyzed. The heuristic policies are computationally studied with the goal of comparing their quality to the optimal solution, and also to compare the heuristics themselves.

The wireless network environment in the future is going to include various heterogeneous wireless networks. In a heterogeneous wireless network environment, vertical handoff processes caused by the movement of users are inevitable. However, the research related to how to achieve seamless vertical handoff and improve QoS guarantees in today's heterogeneous wireless networks is still something to work on. Therefore, this paper proposed the Advanced Vertical Handoff Translation Center (Advanced VHTC) architecture for Wi-Fi/WiMAX heterogeneous wireless networks, aiming to improve the quality of services in heterogeneous wireless networks by means of packet formats translation between heterogeneous wireless networks and the MIH-based seamless vertical handoff mechanism, which cut down the time for vertical handoff and obtain high quality and persistent connection service. Lastly, with the brilliant results of a complete simulation, this paper will show the performance in terms of delay, jitter, packets loss and throughput to prove that the Advanced VHTC for next generation heterogeneous wireless networks can provide good QoS guarantees and obtain persistent transmission with high performance while performing seamless vertical handoff.

Ubiquitous Wireless Network will be the important infrastructure for ubiquitous information service in the future. Ubiquitous Wireless Network is objectively heterogeneous network, so vertical handoff is one of crucial topics. A vertical soft handoff scheme is proposed based on SIP using Wireless Access Gateway (RGW). RGW triggers and controls the handoff session to ensure same two-way delay of handoff and rate of zero-loss packet for real-time streaming media. Using M/M/1 queue model, delay of the scheme meets requirement of real-time streaming media.

In an offload-capable Long Term Evolution (LTE)Wireless Fidelity (WiFi) Heterogeneous Network (HetNet), we consider the problem of maximization of the total system throughput under voice user blocking probability constraint. The optimal policy is threshold in nature. However, computation of optimal policy requires the knowledge of the statistics of system dynamics, viz., arrival processes of voice and data users, which may be difficult to obtain in reality. Motivated by the Post-Decision State (PDS) framework to learn the optimal policy under unknown statistics of system dynamics, we propose, in this paper, an online Radio Access Technology (RAT) selection algorithm using Relative Value Iteration Algorithm (RVIA). However, the convergence speed of this algorithm can be further improved if the underlying threshold structure of the optimal policy can be exploited. To this end, we propose a novel structureaware online RAT selection algorithm which reduces the feasible policy space, thereby offering lesser storage and computational complexity and faster convergence. This algorithm provides a novel framework for designing online learning algorithms for other problems and hence is of independent interest. We prove that both the algorithms converge to the optimal policy. Simulation results demonstrate that the proposed algorithms converge faster than a traditional scheme. Also, the proposed schemes perform better than other benchmark algorithms under realistic network scenarios.

Wireless networks are becoming a combination of more and more diverse and complicated networks. Handoff is a process to maintain data session continuity where mobile node changes from one base station coverage area to another base station area. Mobile maintains its existing connections via vertical handoff. In wireless environment single node mobility is known as host mobility and group of nodes moving together as single network is known as Network Mobility (NEMO). NEMO is extension of MIPv6, invented for reducing number of individual handoffs. To influence smooth mobility between these heterogeneous wireless access networks, expeditious and dependable vertical handoff (VHO) schemes are required. While taking VHO decision several parameters has to consider like received signal strength (RSS), addressable bandwidth, power intake, monetary cost, security, user predilection and etc. In this paper various handoff decision techniques based on different parameters for host mobility, and vertical handoff technique for Network mobility (NEMO) are discussed. Finally gave research issues and future research directions to NEMO.

Despite recent interests in developing vertical handoff decision algorithms, an essential component of the architecture of the next generation heterogeneous wireless networks, very few studies have so far reported any meaningful comparative performance analysis. This paper attempts to fill this gap in the literature by presenting a comprehensive study on the performance of three vertical handoff decision algorithms, namely, SAW (Simple Additive Weighting), TOPSIS (Technique for Order Preference by Similarity to Ideal Solution), and MDP (Markov Decision Process). We have used both analytical and simulation tools (ns-2.29) to evaluate and compare expected total QoS offerings in the mean duration of a service under different state transition probability distributions, user perception models on the importance of QoS parameters, and network switching costs. To our surprise, we have observed TOPSIS achieving the best performance despite MDP’s using the optimal policy. We suspect that the user satisfiability model used in MDP to estimate link rewards might have contradicted the underlying user perception model used to estimate normalised weight of each QoS parameter, which will be investigated in future.

This study considers a periodic‐review joint pricing and inventory control problem for a single product, where production incurs a fixed cost plus a convex or concave variable cost. Our objective is to maximize the expected discounted profit over the entire planning horizon. We fully characterize the optimal policy for the single‐period problem. As the optimal policy for the multi‐period problem is too complicated to be implemented in practice, we develop well‐structured heuristic policies, and establish worst‐case performance bounds on the profit gap between the heuristic policies and the optimal policies. Numerical studies show that our heuristic policies perform extremely well. To further reveal the structural properties of the optimal policies, we also introduce two new concepts named κ‐convexity and sym‐ κ‐convexity, provide the associated preservation results, and then characterize the optimal policies.

Heterogeneous networks are consisted of the networks with different Radio Access Technologies (RAT).Vertical handoffs would be triggered while mobile users moving across two cells implemented different RATs during the session.Thus, some serious problems will be caused due to characteristics of different RATs.Numerous solutions have been proposed to solve these problems.However, most of existing solutions only take into account single traffic, e.g.vertical handoffs (VHO).In this paper, an analytical model is proposed, with which VHO is taken into account, but also new services (NS).Simulation results illustrate that the performance could be significantly improved with the algorithms in the proposed model.Compared with existing strategies, i.e.Signal to Interference and Noise (SINR) and Vertical Handoff Management (VHOM), for NS, the blocking probability could be improved by 33% and 40%, respectively; for VHO, the blocking probability could be improved by 17% and 19%, respectively; and the resource utilization could be improved by approximately 8% and 11%, respectively.

The integration of WLAN and cellular network is the development trend of the next generation mobile communications. With the movement of mobile devices, in order to keep the best quality of service, mobile devices are required to carry seamlessly handoff. The vertical handoff is a key point to solve the seamlessly handoff of heterogeneous networks. A vague based algorithm for vertical handoff in heterogeneous networks is proposed. The algorithm maps parameters to area vague sets, and a new score function on vague set is given, which improves the intelligence of vertical handoff. Our simulation results have proved that the algorithm reduces unnecessary handoff frequencies, and improves the efficiency of vertical handoff.

Multi-product Dynamic Pricing with Limited Inventories under Cascade Click Model

Maximizing the throughput (or revenue generation) rate has become one of die most important criteria in die design and management of Flexible Manufacturing Systems (FMSs). This paper develops dynamic part-allocation policies for FMSs having finite storage capacity at each work station. Maximizing the throughput rate means that the resulting queueing network model has a state-dependent arrival process; therefore, product-form solutions do not hold. Consequently, several alternative modeling approaches are described and formulated for deriving die optimal part-routing policies. One of these optimal policies is based on a new initiated-suspension part-routing strategy. This strategy results in a reduced load on the material handling system while increasing die expected throughput (or revenue generation) rates of the manufacturing work stations. We also propose several efficient closed-loop heuristic policies that exploit die response structure of die optimal policies. These heuristic policies are of...

Biosensors are tiny wireless medical devices which are attached or implanted into the body of a human being or animal to monitor and control biological processes. They are distinguished from conventional sensors by their biologically derived sensing elements. Biosensors generate heat when they transmit their measurements and their temperature rises when recharged by electromagnetic energy. These phenomena translate to a temperature increase in the tissues surrounding the biosensors. If the temperature increase exceeds a certain threshold, the tissues might be damaged. In this paper, we discuss the problem of finding an optimal operating policy for a rechargable biosensor under a strict maximum temperature increase constraint. This problem can be formulated as a Markov decision process with an average reward criterion. The solution is an optimal policy that maximizes the average number of samples which can be generated by the biosensor while observing the constraint on the maximum safe temperature level. Due to the exponential nature of the problem, a heuristic policy is proposed. The performance of the policies is studied through simulation. A greedy policy is used as a baseline for comparison.