Jihua Zhou

Seamless Dual-Link Handover Scheme in Broadband Wireless Communication Systems for High-Speed Rail

Due to frequent handovers in broadband wireless communications in high-speed rail, communication interruption during handover could seriously degrade the experiences of passengers on the train. Aiming to reduce the interruption time, this paper proposes a seamless handover scheme based on a dual-layer and dual-link system architecture, where a Train Relay Station is employed to execute handover for all users in a train and two antennas are mounted at the front and rear of a train. In the proposed scheme, the front antenna executes handover while the rear antenna is still communicating with BS, so that the communication can keep non-interruptive throughout the handover. Moreover, bi-casting is adopted to eliminate the data forwarding delay between the serving BS and target BS. A complete handover protocol is designed and the performance of the proposed scheme is analyzed. It can be seen from analytical results that the handover failure probability decreases as cell overlap increases and the communication interruption probability decreases with the decrease of train handover location and the increase of cell overlap. The simulation results show that in the proposed scheme, the communication interruption probability is smaller than 1% when the handover location is properly selected and the system throughput is not affected by handover. In conclusion, both theoretical and simulation results show that the proposed scheme can efficiently perform seamless handover for high-speed rail with low implementation overhead.

A novel handover scheme for seamless wireless connectivity in high-speed rail

It is a great challenge to design an efficient handover scheme of broadband wireless communication systems for high-speed rail to reduce the communication interruption time during handover. A seamless handover scheme based on the dual-layer and dual-link system architecture is proposed in this paper. In the scheme, two antennas are mounted at the front and rear of a train, and one of them executes handover while the other is still communicating with BS. Therefore, the communication will not be interrupted throughout the handover. Furthermore, bi-casting is adopted to eliminate the data forwarding delay between the serving BS and target BS. In order to reduce handover implementation overhead, a Train Relay Station is employed to represent all the users in a train to execute handover in the proposed scheme. The performance of the proposed scheme is analyzed in terms of handover probability, handover failure probability and communication interruption probability. Simulation and theoretical results show that the proposed scheme can efficiently support seamless handover for high-speed trains with low implementation overhead.

Extension of SCTP for Concurrent Multi-Path Transfer with Parallel Subflows

With its new features such as multi-homing and multi-streaming the Stream Control Transmission Protocol (SCTP) has become a promising candidate as a general-purpose transport layer protocol. Multi-homing in an SCTP association can make concurrent multi-path transfer an appealing candidate to satisfy the ever increasing user demands for bandwidth. Multiple streams provide an aggregation mechanism to accommodate heterogeneous objects, which belong to the same application but may require different QoS from the network. However, the current approach lacks an internal mechanism to support preferential treatment among its streams for concurrent multi-path transfer. In this paper, we introduce WM2-SCTP (Wireless Multi-path Multi-flow - Stream Control Transmission Protocol), a transport layer solution for concurrent multi-path transfer with parallel subflows. WM2-SCTP aims at exploiting SCTPs multi-homing and multi-streaming capability by grouping SCTP streams into subflows based on their required QoS and selecting best paths for each subflow to improve data transfer rates. The results show that under different scenarios WM2-SCTP, can effectively enhance transmission efficiency.

Joint Power and Rate Control in Ad Hoc Networks Using a Supermodular Game Approach

In ad hoc networks, reducing energy consumption and improving throughput are both important for high network performance. This paper presents a joint power and rate control adaptive algorithm to optimize the trade-off between power consumption and throughput in ad hoc networks. Each node chooses its own transmission power and rate based on limited environment information in order to achieve optimal transmission efficiency. In a fictitious game framework with strategy space transformation, our joint power and rate control adaptive algorithm can be viewed as a supermodular game. By interpreting the supermodular game using myopic best response updates, this algorithm can converge to the unique optimal transmission efficiency. Finally, the simulation results show that this supermodular game approach improves the average transmission efficiency by about 33%.

Contention region allocation optimization in ieee 802.16 ofdma systems

The random access scheme is used for initial and periodic ranging in the IEEE 802.16 protocol. The number of contention slots in the uplink subframe decides the system performance. However, how many contention slots should be allocated for ranging is not standardized in the protocol, so it is still necessary to determine the optimal number of contention slots. In this paper, the exact equations of the optimal numbers of initial ranging slots and periodic ranging slots are derived. An optimal dynamic allocator is also proposed to optimize the allocation of the initial and periodic ranging regions in the uplink subframe. The simulation results show that good system performance can be achieved with the optimal dynamic allocator.

WLC27-2: Subcarrier Allocation for OFDMA Wireless Channels Using Lagrangian Relaxation Methods

In this paper, we propose a practically efficient Subcarrier Allocation scheme based on Lagrangian relaxation to solve the problem of subcarrier allocation in OFDMA wireless channels. The problem of subcarrier allocation is formulated into an Integer Programming (IP) problem, which is relaxed by replacing complicating constraints with Lagrange multipliers using Lagrangian Relaxation. A subgradient method is used to optimize the Lagrangian dual function and a heuristic is designed to obtain the feasible solution. Lagrangian Relaxation Subcarrier Allocation (LRSA) is proven to be of polynomial complexity and it provides bounds on the value of channel efficiency. Numerical results show that compared with other algorithms proposed in the literature, LRSA can result in a significant improvement in channel efficiency, while at the same time guaranteeing minimum data rates of users.

Location Prediction Model Based on Bayesian Network Theory

Location prediction is one of the key technologies of active mobility management in the next generation of mobile communication systems. Most of known location prediction models only take parts of predictive factors into account, which leads to a low prediction success ratio of these models. The motivation of this paper is to design a location prediction model considering multiple predictive factors to improve the prediction success ratio and improve the efficiency of the model. In this paper, a location prediction model based on Bayesian Network theory is proposed. The proposed model can effectively solve multi-factor location prediction. Firstly, the relative predictive factors are coded in the Bayesian Network node, and location prediction results can be calculated based on cell topology information integrated in the model structure. A factors distribution mechanism is designed to solve the problem when the nodes cannot obtain location prediction information directly. Subsequently, the method of calculating location prediction results for each cell is presented. The simulation results indicate that the proposed location prediction model is effective in improving accuracy of location prediction and the stability of the model is better than that in comparative schemes.

A Weighted Bipartite Graph Based Network Selection Scheme for Multi-Flows in Heterogeneous Wireless Network

Network selection is an important issue in the next generation of heterogeneous wireless network and well studied for individual flows. However, researches of network selection for multi-flows at network side are seldom touched upon but also important from the global view of optimizing usage of network resources. In this paper, a weighted bipartite graph based network selection scheme for multi-flows is proposed, which adopt secondary exponential smoothing method to perform network resource prediction and assign flows to networks based on Matching Degree(MD). The network selection scheme is modeled as weighted bipartite graph with objectives of maximizing Matching Degrees and access ratio as well as the constraint of guaranteeing no network overloaded. Weighted Bipartite Graph Algorithm (WBGA) is designed to achieve the goals. Simulation results show that WBGA demonstrates best performance compared to other schemes, with regard to average MD, access ratio and utilization ratio of network resources.

Improving the Transmission Efficiency by Considering Non-Cooperation in Ad Hoc Networks

In ad hoc networks, each node is required to forward packets for others. However, based on energy consumption considerations, a node may reject other nodes’ forwarding requests to save the limited battery power for its own data transmission. Therefore, a lot of incentive schemes have been proposed to promote the cooperation of the nodes. Most of the existing research work assumes that all the nodes in the network should provide full cooperation in order to optimize the transmission efficiency. However, this assumption is too strict because the activities of the nodes in ad hoc networks have some inherent uncertainty. In this paper, we propose a power control mechanism in ad hoc networks under a dynamic repeated game-theoretic framework. A notion of nodes’ evaluation levels for the future experiences is defined to take account of the non-cooperation due to the inherent uncertainty in the ad hoc network nodes’ activities. Our scheme does not require all the nodes in the ad hoc network to absolutely cooperate with each other. The simulation results show that, compared with the existing schemes, our power control mechanism considering non-cooperative packet forwarding improves the average transmission efficiency by ∼25% and has good scalability.

A Distributed QoS Provision Scheme in IEEE802.16 Mesh Networks with Directional Antennas

QoS provisioning in wireless mesh networks has been to known as a challenging issue. In a distributed scheduling based wireless mesh backhaul network, conventional connection-based QoS provision mechanism requires considerable amount of overhead for per-link QoS signaling, thus cannot support high speed real time traffic. In this paper,we propose a DiffServ-like QoS provision mechanism for IEEE 802.16 mesh networks with directional antennas to increase network capacity and enable real time traffic. We develop a distributed scheduling algorithm based on our proposed scheme. Simulation results demonstrate that directional antennas can achieve higher network capacity compared with omni-antennas, and our QoS scheme can effectively guarantee QoS requirements of real time traffic.