Yao-Liang Chung

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.

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

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 Analysis of Two Multichannel Fast Retransmission Schemes for Delay-Sensitive Flows

This paper presents a Multiradio multichannel Fast Automatic-Repeat-reQuest (MF ARQ) scheme and an MF Hybrid ARQ (MF HARQ) scheme intended for transporting delay-sensitive flows in a multichannel environment. The proposed schemes are designed to allow the retransmission(s) only once using one or multiple channels simultaneously, unlike other ARQ/HARQ schemes where the retransmission(s) of a link packet can only be in one channel and continue until it is successfully received. By using the application throughput as the objective, the optimal retransmission policy can be determined based on the estimated channel quality and the size of the application-layer protocol data unit. For these two schemes, we show their improvement of the link packet delay and derive formulas of the application throughput, which are then validated via simulations. In addition, a cost analysis for systems adopting the proposed schemes is included. Next, the optimized MF ARQ/HARQ schemes are shown to be able to achieve better effective throughput (goodput) than similar multichannel ARQ/HARQ schemes in various Nakagami-m fading environments. Analytical and simulation results show, when optimized, that the MF HARQ scheme has much better throughput performance than the MF ARQ scheme in highly unreliable environments. We thus conclude that both the MF ARQ scheme and the MF HARQ scheme are excellent ARQ candidates for real-time multimedia transport in the multiradio multichannel environment.

Modeling and Analysis of Dynamic Spectrum Allocation of Two Wireless Communication Systems

Dynamic spectrum allocation can improve spectrum efficiency by exploiting the traffic loads variations of multiple wireless network systems, when they share neighboring band. In this study, we use a centralized approach in which a spectrum manager periodically re-allocates spectrum among two networks in a single cell. We propose a two levels model (a spectrum level model and a call level model) to characterize the dynamic spectrum allocation. We have further validated the approximated numerical results by simulations. Numerical and simulation results show that the performances of networks with the dynamic spectrum allocation are better than those with fixed allocation and complete its performance analysis via approximation and iterative approach. Hence, we conclude that our model and scheme can improve quality of service (QoS) of wireless networks when spectrum is limited

A study of dynamic network selection for HSPA dual-network users

Due to the fact that existing 3.5G network cards usually select networks with the highest data rate as their priority choices, the radio resources may not be efficiently and equally utilized in a multiple network environment, even when the network with the highest rate is already congested. In this paper, we propose two dynamic resource allocation algorithms to resolve such issues assuming an HSPA dual-network architecture, which is common in many existing 3.5G networks. The presented algorithms include two major versions: 1) maximum utility algorithm and 2) enhanced maximum utility algorithm. Performance metrics such as the overall system utility (i.e. the satisfaction index), the blocking probability, and the system utilization are employed in the investigation of these two algorithms. Simulations show that the presented algorithms have significant improvements in the overall system performance than that of the existing algorithm. The system performance can be further improved if the concentration ratio can be dynamically adjusted.

Cooperative Diversity with Fast HARQ for Delay-Sensitive Flows

This work addresses the problem of a fast hybrid automatic-repeat-request (HARQ) scheme intended for transporting delay-sensitive flows in a cooperative diversity (CD) environment. This CD with fast HARQ scheme allows the retransmission for only one time via the cooperating user (i.e. partner) or via both the sender and the partner simultaneously. A complementary link packet is used for retransmissions. The retransmission policy can be adjusted based on the qualities of channels among the sender, the partner, and the receiver and the application layer protocol data unit size by using the application throughput as the objective. For this presented scheme, we completely derive the application throughput formulas, which are then validated via simulations. Next, the CD with optimized fast HARQ scheme is shown able to achieve better throughput than effective throughput of other CD with ARQ schemes in various Nakagami-m slow-fading environments. As a result, the fast HARQ scheme should be an excellent ARQ mechanism for the real-time multimedia transport in CD environments.

Quota-based dynamic network selection for HSPA/UMTS multi-network users

In this paper, we present a quota-based dynamic network selection algorithm for accommodating access requests in a multi-network (HSPA+, HSDPA and UMTS) co-location environment, which is common for todays 3G operators. In most commercial networks, the accesses of individual users are often charged at a flat rate. In such a charging scheme, a few extremely heavy users may degrade the performance and the fairness of the whole network. Therefore, we propose an algorithm called Quota-based Utilization Balance Algorithm (QUBA), designed to settle such a problem and also maximize the overall utility of all users. The design philosophy of QUBA is to let the system utilization in the 2 fastest networks, HSPA+ and HSDPA, be statistically balanced and sufficiently utilized. Performance metrics in terms of the overall system utility (i.e., the satisfaction index) and the blocking probability are investigated. From simulation results, it is shown that the QUBA algorithm has significant improvements in the aspect of the overall system performance than that of existing approaches.

Introduction to the Retransmission Scheme Under Cooperative Diversity in Wireless Networks

As implied by the word “Cooperative Diversity (CD),” mobile users in a multi-user environment can share their antennas in a manner that creates a virtual Multiple-Input Multiple-Output (MIMO) system, which can be conceptually viewed as a multichannel transmission environment in the network layer, to achieve individual or common purposes of those users. By employing CD for transmissions, the quality and reliability of users’ data in wireless networks can thus be improved, mainly owning to the reason that the effect of wireless channel fading can be reduced. In this chapter, we aim to introduce existing representative retransmission schemes under various environments and further present a novel packet retransmission scheme for Quality-of-Service (QoS)-constrained applications in a general CD environment.