An interference and latency aware uplink scheduling mechanism in IEEE 802.16j networks

IEEE 802.16j spreads out the coverage of WiMAX networks and strengthens wireless signal transmission using relay technology. To take advantage of relaying in IEEE 802.16j networks, an efficient scheduling schedule with quality of service (QoS) provision for multiple link transmissions is necessary, especially when link interference exists. In this paper, we propose an uplink scheduling mechanism in the transparent mode of IEEE 802.16j, which enables multiple devices to transmit without interference. The maximum latency of each connection has been considered in order to optimize the violation and transmission rate. An interference detection task is first carried out, and then a resource allocation algorithm and a dynamic frame adjustment method are developed. Two simulation experiments were conducted with different interference levels. The results demonstrate that under a fixed QoS type of connection, when the total number of connections goes up to 360 and 420 and the maximum latency violation rate approaches 20%, the average uplink transmission rate of the proposed mechanism can achieve 6.67 and 7.92 Mbps, which apparently outperform regular relay scheduling schemes with rate of 4 and 3.91 Mbps, respectively.     

An approximation analysis for safety messages transmission in vehicle-to-vehicle WAVE networks

Wireless Access in the Vehicular Environment (WAVE) specification defines the WAVE Short Message Protocol (WSMP) for delivering WAVE Short Messages (WSMs). In the multihop transmission, WSMs are first received and stored in queues and then forwarded to the next hop. Unfortunately, WSMP does not specify any mechanism to avoid the messages loss resulted from queueing overflow. In this paper, a dual threshold-based queueing management which adjusts the message accepting rate upon the current queue length is proposed. The multihop transmission can be modeled as a tandem queueing network, and a discrete time Markov chain (DTMC) can be applied to evaluate the proposed queueing management. Since the computational complexity increases with the number of hops, an approximation approach to resolve DTMC model is also presented. Simulation results demonstrate the accuracy of approximation and the effectiveness of the proposed queueing management.     

A beacon-based handover scanning mechanism with QoS support in WiMAX femtocell architecture

WiMAX femtocell architecture has gained a lot of attention because of its better indoor service provision through traffic sharing between WiMAX and femtocell. However, since the signal of a WiMAX base station (BS) is usually stronger than that of a femtocell base station (fBS), the handover procedure of mobile stations may not be triggered due to the stronger signal association. And, a huge number of fBSs deployed within a WiMAX BS coverage area will require extra power to scan all fBSs for a handover determination. In this article, we propose a beacon-based handover scanning mechanism with Quality of Service (QoS) support. Through the modified beacons and MOB_NBR-ADV messages, a neighbor cell list with QoS parameters is generated automatically at each mobile station. The decision criteria for handover triggering and an appropriate target cell selection are also presented. The QualNet simulation results demonstrate that along with increased fBSs, the proposed mechanism can improve the total system throughput from 37% to 51% and obtain higher bandwidth utilization in the case of increasing number of fBSs, as compared with Full Scan and Neighbor Cell Information Mechanisms.     

Agent-Based Infrastructure and an Application to Internet Information Gathering

Pragmatic applications and studies of agent-based software engineering have evolved over the last decade. In order to explore how an agent is organized and applied, in this paper an agent framework is presented and applied to Internet information gathering. Agent systems are classified as micro or macro perspectives and agent applications are characterized by the four feature dimensions: behavior (user), knowledge (task), safety (time), and cooperation (social). An agent itself can be modeled according to the information, behavior, and organization aspects of the agent’s functional modules as proposed in this paper. A three-tier multi-agent and JAVA-implemented system, which coordinates information-gathering activities using KQML for inter-agent communication, is developed on the basis of the proposed architectural modules. Finally, we explore possible areas for future study. Received 1 February 1999 / Revised 30 June 2000 / Accepted in revised form 5 November 2000     

Energy Saving Mechanism with a Route Prediction Based Intra-handover in LTE Networks

Long term evolution standard employs the discontinuous reception (DRX) technology to help user equipment (UE) in energy saving. After the UE received nothing from the base station for a predefined time span, it turns off the radio frequency module to enter sleep mode for energy saving. An UE may fail to handover or lost connection for late handover in case it enters sleep mode before handover and missed the optimal handover timing, therefore results in data loss. This paper proposes an energy saving mechanism with a prediction based intra-handover which predicts the next target handover base station and the optimal handover time according to the historical path data kept in a database. The UE would check whether the next sleep mode outlast the handover time point before entering sleep mode to reduce power consumption for handover failure caused by the long DRX cycle and base station reselection. Simulation results show that the DRX mechanism helps reduce power consumption of UE by 90–95 % over the conventional one more than 7 % handover failures. The energy saving mechanism combined with route prediction leads to 22 % more energy saving while cutting handover failures to 5 %.