Xu Huimin

A new management strategy of service flow in IEEE 802.16 systems

IEEE 802.16 standards define different service flows to better support the quality of service (QoS), but donpsilat provide related management strategies. Based on this, we propose a new management strategy which mainly includes an admission control algorithm named QBAC (QoS Based Admission Control) and scheduling algorithm named QBMS (QoS Based Multi-Level Scheduling). QBAC and QBMS are provided to grant the QoS request of different service flows. At the same time, we try to satisfy the request of real-time service flows and improve the performance of non-real-time service flows through this new strategy. Simulation results show that the performance of real-time service flows is good and the fairness of non-real-time services gets improvement compared with current strategies.

The Probability Distribution Modeling and Parameter Estimation Method of ROD in Different Packet Loss Pattern for Heterogeneous Network

The packet loss differentiating mechanism of TCP for heterogeneous network has the important influence to the stability of wireless network, relative one-way delay (ROD) of loss pair is adopted as a differentiating parameter to distinguish the loss type in reference [1]. The accuracy of this algorithm depends on ROD membership function. In order to differentiate packet loss pattern more accurately, first the probability distribution of ROD is analyzed in different packet loss pattern, then the probability distribution model is built, finally the method of parameter estimation is proposed. From the results of simulation the effect of this method model is more ideal.

IQ Imbalance Compensation in OFDMA based WiMAX Digital Receivers

WiMAX is one of the most promising technologies for broadcast wireless communication and based on the IEEE 802.16 standards. The WiMAX networks support high speed transmission. But some hardware design, such as the IQ (inphase quadrature) imbalance due to direct conversion in RF front-end, limits their throughput. This problem is especially serious in high-order modulation. Most current papers of this field focus on OFDM based systems, such as wireless local area networks (WLAN). Little attention has been paid to OFDMA based WiMAX systems. So we propose some time-domain compensation strategies to work on this problem according to the preamble symbol. In order to test the performance of compensation, we carry out simulation experiments in AWGN and multi-path fading conditions respectively. Simulation results show that the proposed strategies offer good effect.

A Novel Approach of Channel Utilization Measurement in WLAN

A novel approach of channel utilization measurement in WLAN was proposed. Source sends probe packets whose time stamp options are being set. The current time is recorded in the packets hop by hop. Through the improved channel utilization statistical processing, the process delay, propagation delay, transmission delay and router clock skew can be eliminated, the queuing delay of each probe packet is obtained. Quantized and smoothed by the statistic window, the queuing delay finally transformed into channel utilization. The Channel Utilization Compensation Algorithm is designed to improve the measurement accuracy in environment of high packet loss rate. This measurement method is verified through simulation.

Performance analysis of multicast polling based bandwidth request in IEEE 802.16 networks

In IEEE 802.16 networks, subscriber station (SS) can request bandwidth based on multicast polling of the base station (BS). In this way, SSs of the same group contend for the transmission opportunities (TOs) allocated by BS using a binary exponential backoff (BEB) algorithm. Different system parameters, such as polling group number and backoff parameters influence the delay of bandwidth request based on multicast polling. However, little attention has been paid to this problem. In this paper, we propose a mathematical model and compare the related simulation to analyze the delay of bandwidth request based on multicast polling. Simulation results reveal that the delay decreases when the polling group number increases especially in large-size network. At the same time, it also depends on TO number and backoff parameters.

A policy based multi-dimension adaptation framework in the virtual home environment [3G systems]

The virtual home environment (VHE) is becoming more and more popular for service providing in 3G systems. But the service adaptation mechanism, as a key problem in VHE systems, is still lacking feasible solutions. In contrast to the current uni-dimensional adaptation mechanisms, where adaptation is provided at the various layers (data link layer, network layer, application layer etc) in isolation, multi-dimension adaptation mechanisms should be provided to meet the requirements of VHE. In this paper, we first briefly introduce an OSA/PARLEY based VHE system, and then analyse the requirements of service adaptation in the VHE system. Next, we present the policy based multi-dimension adaptation framework in this system in detail. The final analysis shows that it can meet the adaptation requirements of VHE in efficiency, extensibility and scalability.

A study of load balancing in distributed wireless communication system

The distributed processing network (DPN) layer in a distributed wireless communication system (DWCS) constructs a distributed parallel structure to manage the signal processing resources. Thus, the method of load balancing is utilized within resource management. Further, by dividing DPN into load balancing domains (LBD), a logical concept, the flat topology with peer-to-peer interconnections is rearranged in a hierarchical structure. The division of DPN into LBDs should follow some rules, e.g., in one LBD, the call loss probability of PNs is distributed in a wide range. The evaluation of load, the granularity and the policy of load balancing are discussed. By simulation of the distributed time-driven algorithm, the efficiency of load balancing and the division method are proved to be acceptable.

Some criterions of QoS routing for the Internet

We consider some routing criterions for connections with QoS requirements in the Internet, which support QoS guarantees for both the services and networks. First we investigate the path consumption, and give the definition of the path consumption function (PCF). Then we observe the path selections influence on the link residual bandwidth, we find that letting the narrowband connection choose those links with small residual bandwidth can increase the admission probability of the broadband ones. We define the bandwidth fragmentation function (BFF) for connections which reflects this influence. After that we give the definition of the network efficiency function (NEF) for the network performance measure. A QoS routing scheme and some simulation results are given. We conclude with a summary and with directions for future work.