Chung-Ju Chang

Design of a fuzzy traffic controller for ATM networks

This paper presents the design of a fuzzy traffic controller that simultaneously manages congestion control and call admission control for asynchronous transfer mode (ATM) networks. The fuzzy traffic controller is a fuzzy implementation of the two-threshold congestion control method and the equivalent capacity admission control method extensively studied in the literature. It is an improved, intelligent implementation that not only utilizes the mathematical formulation of classical control but also mimics the expert knowledge of traffic control. We appropriately choose input linguistic variables of the fuzzy traffic controller so that the controller is a closed-loop system with stable and robust operation. We extract knowledge of conventional control methods from numerous analytical data using a clustering technique and then use this knowledge to set parameters of the membership functions and fuzzy control rules via fuzzy set manipulation (linguistically stated but mathematically treated) with the aid of an optimization technique named genetic algorithm (GA). Simulation results show that the proposed fuzzy admission control improves system utilization by a significant 11%, while maintaining the quality of service (QoS) contract comparable with that of the conventional equivalent capacity method. The performance of the proposed fuzzy congestion control method is also 4% better than that of the conventional two-threshold congestion control method.

Analysis of a cutoff priority cellular radio system with finite queueing and reneging/dropping

Queueing of new or handoff calls can minimize blocking probabilities or increase total carried traffic. This paper investigates a new cutoff priority cellular radio system that allows finite queueing of both new and handoff calls. We consider the reneging from the system of queued new calls due to caller impatience and the dropping of queued handoff calls by the system as they move out of a handoff area before being accomplished successfully. We use signal-flow graphs and Masons formula to obtain the blocking probabilities of new and handoff calls and the average waiting times. Moreover, an optimal cutoff parameter and appropriate queue sizes for new and handoff calls are numerically determined so that a proposed overall blocking probability is minimized. >

Modeling and Analysis for Spectrum Handoffs in Cognitive Radio Networks

In this paper, we present an analytical framework to evaluate the latency performance of connection-based spectrum handoffs in cognitive radio (CR) networks. During the transmission period of a secondary connection, multiple interruptions from the primary users result in multiple spectrum handoffs and the need of predetermining a set of target channels for spectrum handoffs. To quantify the effects of channel obsolete issue on the target channel predetermination, we should consider the three key design features: 1) general service time distribution of the primary and secondary connections; 2) different operating channels in multiple handoffs; and 3) queuing delay due to channel contention from multiple secondary connections. To this end, we propose the preemptive resume priority (PRP) M/G/1 queuing network model to characterize the spectrum usage behaviors with all the three design features. This model aims to analyze the extended data delivery time of the secondary connections with proactively designed target channel sequences under various traffic arrival rates and service time distributions. These analytical results are applied to evaluate the latency performance of the connection-based spectrum handoff based on the target channel sequences mentioned in the IEEE 802.22 wireless regional area networks standard. Then, to reduce the extended data delivery time, a traffic-adaptive spectrum handoff is proposed, which changes the target channel sequence of spectrum handoffs based on traffic conditions. Compared to the existing target channel selection methods, this traffic-adaptive target channel selection approach can reduce the extended data transmission time by 35 percent, especially for the heavy traffic loads of the primary users.

Design of power control mechanisms with PCM realization for the uplink of a DS-CDMA cellular mobile radio system

Power control (PC) is an important issue in a direct sequence-code division multiple access (DS-CDMA) cellular mobile radio system. Higher link performance and greater system capacity cannot be achieved unless an appropriate PC mechanism is employed. In previous research, a delta-modulation (DM) realization of strength-based and SIR-based PC mechanisms for uplink communication has been studied by simulation. In order to obtain higher PC trackability, we study a pulse-code-modulation (PCM) realization of the above two PC mechanisms for the uplink of a DS-CDMA cellular mobile radio system. The simulation results presented indicate that the PC mechanisms with PCM realization for the uplink can achieve a lower outage probability and thus higher link performance than the PC mechanisms with DM realization. We also obtain optimal design parameters such as the stepsize and the control mode for the two PCM PC mechanisms. In addition, we compare the two PCM PC mechanisms in terms of their outage probability and stability and find that the strength-based mechanism has a higher outage probability but greater stability than the SIR-based mechanism.

Traffic control in an ATM network using fuzzy set theory

Due to the demand for high-speed and multimedia services, ATM (asynchronous transfer mode) networks have increasingly received high attention. The multimedia services in ATM networks have diverse traffic characteristics and service requirements, appropriate traffic controls of call admission and congestion are needed so as to guarantee the required quality of service (QOS) for services. Previous studies on the traffic control were based on the results of queueing analyses. In the present paper, an alternative traffic control for admission in conjunction with congestion based on fuzzy set theory are proposed for an ATM network. The performance evaluation via simulation shows the effectiveness of the proposed method in comparison with the equivalent capacity in Guerin et al. (1991); link utilization is effectively improved by 8% while keeping the QOS contract.<<ETX>>

Optimal Relay Location in Multi-Hop Cellular Systems

Relay stations (RSs) are usually used to enhance the signal strength for the users close to the cell boundary. However, transmission through a relay station needs two transmission phases, i.e., one is from the base station to the relay station and the other is from relay station to mobile stations. Thus, relay may also decrease system capacity if two-phase transmission time is considered. As a result, whether or not data are transmitted by one-hop or two-hop transmission should be determined based on both signal strength and throughput. In this paper, we investigate the optimal relay location aiming to maximize system capacity. We consider two relay selection rules for determining whether a two-hop transmission is necessary: signal strength-oriented and throughput-oriented. We find that the signal strength-oriented two-hop transmission may yield even lower system capacity than the one-hop transmission. Based on the throughput-oriented rule, we find that the throughput in the two-hop transmission can be higher than that in the one-hop transmission at some locations. We also identify the optimal relay location that can achieve the highest system capacity.

A Cost-Effective Strategy for Road-Side Unit Placement in Vehicular Networks

In this paper, we study the Roadside Unit (RSU) placement problem in vehicular networks. We focus on the highway-like scenario in which there may be multiple lanes with exits or intersections along the road. In our model, each vehicle can access RSUs in two ways: 1) direct delivery, which occurs when the vehicle is in the transmission range of the RSUs, and 2) multi-hop relaying, which takes place when the vehicle is out of RSU transmission range. We account for both access patterns in our placement strategy and formulate this placement problem via an integer linear programming model such that the aggregate throughput in the network can be maximized. We also take into account the impact of wireless interference, vehicle population distribution, and vehicle speeds in the formulation. The performance of the proposed placement strategy is evaluated via ns-2 simulations together with VanetMobisim to generate vehicle mobility patterns. The results show that our strategy leads to the best performance as compared with the uniformly distributed placement and the hot spot placement. More importantly, our solution needs the least number of RSUs to achieve the maximal aggregate throughput in the network, indicating that our scheme is indeed a cost effective yet highly efficient placement strategy for vehicular networks.

Intelligent call admission control for wideband CDMA cellular systems

In this paper, we propose intelligent call admission control for wideband code-division multiple-access (CDMA) cellular systems to support differentiated quality-of-service (QoS) requirements, guarantee the forced termination probability of handoffs, and maximize the spectrum utilization. The intelligent call admission controller (ICAC) contains a fuzzy call admission processor to make admission decision for a call request by considering QoS measures such as the forced termination (drop call) probability of handoff, the outage probability of all service types, the predicted next-step existing-call interference, the link gain, and the estimated equivalent interference of the call request. The pipeline recurrent neural network (PRNN) is used to accurately predict the next-step existing-call interference, and the fuzzy logic theory is applied to estimate the new/handoff call interference based on knowledge of effective bandwidth method. Simulation results indicate that ICAC achieves system capacity higher than conventional CAC schemes by an amount of more than 10% in both low and high moving speed cases. Moreover, ICAC can cope with the unpredictable statistical fluctuation of wireless multimedia traffic; it always fulfill QoS requirements for all service types and keep the forced termination probability satisfied, while the CAC of multimedia calls (MCAC) and SIR-based CAC with intercell interference prediction (PSIR-CAC) fail to adapt to the variation of traffic conditions.

A power-spectrum based connection admission control for ATM networks

The power spectrum of the input process explicitly contains the correlation behavior of input traffic and has a great impact on the queueing behavior of an ATM network. In this paper, we propose a power-spectrum based connection admission control scheme for ATM networks. The DC component, the average power, and the half-power bandwidth are the key factors of the input power spectrum. Here, we use a method to approximate the QoS by the result obtained from the equivalent average power. Finally, we construct an admission control table which contains the performance measure for different loads and the equivalent average power. Whether a new call can be accepted or not is determined by table lookup. Simulation results show that our proposed power-spectrum based connection admission control is an efficient control method for ATM networks.

Utility and Game-Theory Based Network Selection Scheme in Heterogeneous Wireless Networks

The paper proposes a utility function and game theory (UGT) based network selection scheme to maximize accommodated number of calls, minimize handoff occurrence frequency, and fulfill quality of service (QoS) requirements in heterogeneous wireless networks. When a new call or a handoff call arrives, UGT would calculate the utility value and preference value for each candidate network based on the QoS satisfaction of the call request and the cooperative game computation. Finally, the network, which has the maximum result of linearly combined utility value and preference value, would be selected as the most suitable network for the call request. Simulation results show that UGT has good QoS satisfaction. It also allows system to accommodate more calls than iterative TOPSIS scheme. In addition, UGT can reduce the handoff occurrence frequency by about 30% as compared to iterative TOPSIS.