Zsehong Tsai

Message delay analysis of multiclass priority TDMA, FDMA, and discrete-time queueing systems

A multiplexing communications channel is considered. The network stations share the channel on a time-division multiple-access (TDMA) basis or by using a slotted frequency-division multiple-access (FDMA) scheme. Messages are categorized by their differing priorities. Two service disciplines are considered: nonpreemptive and preemptive-resume. A discrete-time priority queuing system is introduced and investigated. Message-delay distributions are obtained for priority and ordinary messages in a two-class system model, under each service discipline. Next, delay analysis for a p-class model is carried out. The results are then applied to general, slotted, priority FDMA and TDMA schemes. >

An efficient downlink packet scheduling algorithm in LTE-Advanced systems with Carrier Aggregation

Carrier Aggregation (CA) is one of the promising features to support the much wider bandwidth for packet transmissions in Long Term Evolution-Advanced (LTE-A) systems. To the best of our knowledge, works regarding the packet scheduling algorithm in LTE-A systems with the CA mechanism have not thoroughly been investigated yet till now. In this paper, we therefore aim to design an efficient packet scheduling algorithm based on the proportional fair criterion in such environment. We focus on downlink transmissions supporting both Real-Time (RT) and non-RT traffics simultaneously. Simulation results show that performance measures in terms of the system throughput, the mean delay, and the fairness are much better than those of a system in which component carriers are not aggregated but used independently.

A Spectral Efficient and Fair User-Centric Spectrum Allocation Approach for Downlink Transmissions

Traditional spectrum allocation approaches assume that the intended users of BSs are treated equally, without consideration of their distances. Consequently, the efficiency of spectrum usage for downlink transmissions may suffer, because a BS may interfere with other BS transmissions; this would not happen if a proper transmission power is used. In this paper, we propose a user-centric spectrum allocation algorithm based on a physical interference model for downlink transmissions. In our approach, BSs set the power of an allocated spectrum band to ensure an effective transmission range for covering a group of intended users. A spectrum band is allocated to a BS if it can satisfy a group of users with the least amount of power possible (relative to other spectrum bands). Thus, after spectrum bands and transmission ranges are assigned, each BS owns several spectrum bands that can cover a group of users within varying transmission ranges. This approach leads to a higher rate of spectral reuse and improves system performance. In addition, the approach properly considers fairness issues among both users and BSs. Overall, simulation results show that our approach not only outperforms traditional BS-centric approaches by offering a 26% higher throughput in dense networks, but also provides fairer spectrum allocation.

Performance analysis of two echo control designs in ATM networks

An ATM call interworking with the public switched telephone network may experience echo problems due to impedance mismatch. The authors propose two echo control designs to assure the quality of voice services by reducing round-trip echo delay. Performance of these two echo control designs is then analyzed. >

Introduction to Packet Scheduling Algorithms for Communication Networks

As implied by the word “packet scheduling”, the shared transmission resource should be intentionally assigned to some users at a given time. The process of assigning users’ packets to appropriate shared resource to achieve some performance guarantee is so-called packet scheduling. It is anticipated that packetized transmissions over links via proper packet scheduling algorithms will possibly make higher resource utilization through statistical multiplexing of packets compared to conventional circuit-based communications. A packet-switched and integrated service environment is therefore prevalent in most practical systems nowadays. However, it will possibly lead to crucial problems when multiple packets associated to different kinds of Quality of Service (QoS) (e.g. required throughput, tolerated delay, jitter, etc) or packet lengths competing for the finite common transmission resource. That is, when the traffic load is relatively heavy, the first-come-first-serve discipline may no longer be an efficient way to utilize the available transmission resource to satisfy the QoS requirements of each user. In such case, appropriate packet-level scheduling algorithms, which are designed to schedule the order of packet transmission under the consideration of different QoS requirements of individual users or other criteria, such as fairness, can alter the service performance and increase the system capacity . As a result, packet scheduling algorithms have been one of the most crucial functions in many practical wired and wireless communication network systems. In this chapter, we will focus on such topic direction for complete investigation. Till now, many packet scheduling algorithms for wired and wireless communication network systems have been successfully presented. Generally speaking, in the most parts of researches, the main goal of packet scheduling algorithms is to maximize the system capacity while satisfying the QoS of users and achieving certain level of fairness. To be more specific, most of packet scheduling algorithm proposed are intended to achieve the following desired properties: 1. Efficiency: The basic function of packet scheduling algorithms is scheduling the transmission order of packets queued in the system based on the available shared resource in a way that satisfies the set of QoS requirements of each user. A packet scheduling algorithm is generally said to

On the Femtocell-Based MVNO Model: A Game Theoretic Approach for Optimal Power Setting

Both the femtocell technology and the concept of mobile virtual network operators (MVNO) are believed to be key directions for future mobile network evolutions. This paper proposes a detailed model for the femtocell-based MVNO and analyzes the dynamics between the femto base station transmit power and its absorbing effect on the macrocell users via game theoretic techniques. The results show that the power settings given by the Nash equilibrium maintain the required QoS level without causing excessive interferences. Such numerical results should help the feasibility of large-scale deployment of femtocell-based MVNOs.

A differentially coherent delay-locked loop for spread-spectrum tracking receivers

A novel differentially coherent delay-locked loop (DCDLL) for accurate code tracking is proposed for direct sequence spread-spectrum systems. Due to the use of the differential decoder and exactly one correlator, the proposed scheme avoids the problems of gain imbalance. The tracking error variance is derived by linear analysis. When the proposed DCDLL scheme is applied in ranging with additive white Gaussian noise (AWGN) channel, the performance of the proposed DCDLL scheme is about 1.4 dB better than that of one-correlator tau-dither loop (TDL), and near that of the noncoherent DLL.

Performance evaluation of dynamic spectrum sharing for two wireless communication networks

Dynamic spectrum sharing has become an important approach to improve spectrum efficiency by exploiting traffic loads variations of multiple wireless networks when a radio band is shared. In this study, the authors present an effective centralised decision approach to deal with the problem regarding how a spectrum manager should periodically re-allocate the spectrum between two networks in a single cell, while maintaining both the call blocking and dropping probabilities in their acceptable levels, and improving the spectrum efficiency simultaneously. In the decision algorithm, a two-level model (a spectrum level model and a call level model) is used to characterise the dynamic spectrum sharing mechanism and network resource usage within the two networks. Performance analysis begins with an approximated Markov Chain analysis and an iterative approach. The authors then further validate the approximated numerical results with simulations. These numerical results demonstrate that the call blocking and dropping probabilities of each network employing dynamic spectrum sharing are much better maintained than those using a fixed allocation under heavy traffic load. The authors thus conclude that the dynamic spectrum sharing algorithm can maintain the quality of service (QoS) of each network while the effective spectrum utilisation is improved under a fluctuation traffic environment when the available spectrum is limited.

Performance of ATM switches with age priority packet discarding under the on-off source model

In the current ATM AAL5 implementation, even a single cell loss event can lead to the corruption of one whole packet. Hence, it has been observed that the throughput of the upper layer protocol may easily collapse on a congested ATM network. We propose a buffer management method called age priority packet discarding (APPD) scheme to be used along with two other schemes: the early packet discarding (EPD) and the partial packet discarding (PPD) schemes. After describing the operations and the pseudo code of the proposed APPD scheme and how it operates with the EPD/PPD schemes, the packet level QoS of APPD and its extended versions are derived analytically under homogeneous on-off source model. Numerical results obtained via, analytical approach suggest that the proposed APPD scheme can more effectively and fairly reduce the packet loss probability than other schemes.

Bid-Proportional Auction for Resource Allocation in Capacity-Constrained Clouds

Currently most commercialized cloud providers mainly offer cloud computing resources by the fixed price approach. However, this may not be efficient for cloud resource usage especially when the total computing capacity is limited. Since the auction mechanism is already shown to be an approach to many resource-limited problems, how to apply such a mechanism to the cloud computing environment for improving revenues and resource utilization of providers is worth investigations. In this paper, we have used a bid-proportional auction model which is capable of adaptively adjusting resource price. We also study the decision of the optimal bid among all users in this environment. Finally, we conduct two simulations to validate the operation of the proposed model in dynamic and stochastic demand environments. Furthermore, several remarkable observations of the relationships between users and providers regarding price dynamic are elaborated.