J. Morris Chang

Roadside-Aided Routing (RAR) in Vehicular Networks

Inter-Vehicle Communications (IVC) and Roadside-to-Vehicle Communications (RVC) in vehicular networks based on IEEE 802.11 are emerging technologies for future Intelligent Transportation Systems (ITS). This paper presents a new efficient routing approach, called RAR (Roadside-Aided Routing), that is the first one to exploit the unique characteristics of vehicular networks. A novel affiliation method is proposed to affiliate a vehicle to several Roadside Units based on road constraints. This scheme allows (a) agent advertisement to be broadcast in one hop (instead of multi-hop), (b) routing to be done in single phase, comparing to two phases, (c) to eliminate the use of hierarchical addressing which is commonly used in single-phase schemes. Simulation results of ns-2 show that RAR approach can provide a high packet delivery rate in vehicular networks with a low and constant overhead.

Block-based reversible data embedding

This paper proposes a block-based reversible data embedding method applied to grayscale cover images. The image is first divided into two areas: data embedding area and auxiliary information embedding area. The data embedding area is further partitioned into 3*3 blocks. According to two predefined thresholds, all the blocks are divided into three categories: smooth, normal or complex. The complex blocks do not embed any data. A smooth block will embed twice the data of a normal block. After predicting the edge direction in a smooth or normal block, Alattars difference expansion of a generalized integer transform method is exploited to embed data into each vector in the block. Then, the location map and other auxiliary information are embedded in the auxiliary information embedding area using a novel least significant bit (LSB) substitution method. Our method not only improves the embedded image quality but also provides a higher payload capacity compared to Alattars method. For some smoother images, the embedding capacity of the proposed method is higher than 1 bit/pixel in a single pass and also derives acceptable embedded image quality (PSNR>=30). To the best of our knowledge, the proposed method is the first to do this.

QoS-Aware Data Replication for Data-Intensive Applications in Cloud Computing Systems

Cloud computing provides scalable computing and storage resources. More and more data-intensive applications are developed in this computing environment. Different applications have different quality-of-service (QoS) requirements. To continuously support the QoS requirement of an application after data corruption, we propose two QoS-aware data replication (QADR) algorithms in cloud computing systems. The first algorithm adopts the intuitive idea of high-QoS first-replication (HQFR) to perform data replication. However, this greedy algorithm cannot minimize the data replication cost and the number of QoS-violated data replicas. To achieve these two minimum objectives, the second algorithm transforms the QADR problem into the well-known minimum-cost maximum-flow (MCMF) problem. By applying the existing MCMF algorithm to solve the QADR problem, the second algorithm can produce the optimal solution to the QADR problem in polynomial time, but it takes more computational time than the first algorithm. Moreover, it is known that a cloud computing system usually has a large number of nodes. We also propose node combination techniques to reduce the possibly large data replication time. Finally, simulation experiments are performed to demonstrate the effectiveness of the proposed algorithms in the data replication and recovery.

WiMAX or LTE: Who will Lead the Broadband Mobile Internet?

Two main technologies are competing for the International Mobile Telecommunications (IMT)-Advanced initiative: WiMAX and LTE. This comparison reviews their development and deployment and provides an outlook on their adoption as 4G technologies.

CONTI: constant-time contention resolution for WLAN access

Designing an efficient and fair access control protocol is a challenging task in the field of wireless networks. Often in the known schemes, one of the important performance metrics is enhanced at the expense of another. In this paper, we present a distributed access scheme that is based on the binary countdown mechanism. The proposed scheme has two main features: 1) the ability to resolve the contention in a constant number of time slots, hence the name constant-time (CONTI) and 2) a very low collision rate even at large network sizes. The simulation results show that CONTI outperforms the IEEE 802.11 DCF scheme in all the essential performance metrics: CONTI achieves a higher throughput by up to 55%, reduces the collision rate by up to 84%, renders the delay less variant and exhibits high fairness.

A Comprehensive Analysis of Bandwidth Request Mechanisms in IEEE 802.16 Networks

The IEEE 802.16 standard is considered to be one of the most promising technologies. Bandwidth reservation is employed to provide quality of service (QoS)-guaranteeing services. A request/grant scheme is defined in the IEEE 802.16 standard. There are two types of bandwidth request (BR) mechanisms, i.e., unicast polling and contention resolution, which are defined in the standard. As specified, connections belonging to scheduling classes of extended real-time polling service, non-real-time polling service, and best effort have options to make BRs via both mechanisms, depending on the scheduling decision made by the base station (BS). However, most research assumes that only one of them is available and do not take both of them into account. A comprehensive study of both mechanisms is critical for the BS to make an appropriate decision for those connections to achieve better system performance. To the best of our knowledge, this is the first attempt to analyze this issue. There are two major contributions presented in this paper. First, a comprehensive study of both BR mechanisms in terms of bandwidth utilization and delay is provided. Additionally, we propose two practical performance objectives: When the expected delay or target bandwidth utilization is given, how does the BS make a scheduling decision such that the performance of the other metric (either delay or bandwidth utilization) is optimized? As our second contribution, we proposed two scheduling algorithms to find the combination of both mechanisms to meet our objectives. The simulation results show that our scheduling algorithms can always help the BS make a scheduling decision to reach better system performance.

A layered approach to cognitive radio network security

Cognitive radios have been identified as a solution to the crowded spectrum issue. With the realization of cognitive radio networks came the recognition that both new and old security threats are relevant. The cognitive radio network is still vulnerable to many of the denial of service, wormhole, routing, and jamming attacks that plague other wireless technologies. In addition, the cognitive radio network is vulnerable to new attacks based on cognitive radio innovations, such as spectrum sharing, spectrum sensing, cognitive capability, and radio reconfigurability. The scope of this survey is to present an overview of security threats and challenges to the cognitive radio network, especially focusing on new solutions from 2012 and the first half of 2013. Included are prior mitigation techniques that are adaptive to the new technology, as well as new mitigation techniques specifically targeted at new cognitive radio vulnerabilities. The threats provided are organized according to the protocol layer at which the attack is targeted.

Quality of service support in IEEE 802.11 wireless ad hoc networks

Abstract Supporting Quality of Service (QoS) in wireless networks is a challenging problem. The IEEE 802.11 LAN standard was developed primarily for elastic data applications. In order to support the transmission of real-time data, a polling-based scheme called the point coordination function (PCF) was introduced in IEEE 802.11. However, PCF was not able to meet the desired and practical service differentiation requirements to fulfill the need of real-time data. Therefore, Task Group E of the IEEE 802.11 working group released several IEEE 802.11e drafts, whose main task is to support QoS in IEEE 802.11 LANs. The polling scheme of PCF is extended in IEEE 802.11e into the more complex hybrid coordination function (HCF). We found that HCF has several performance issues that may affect its anticipated performance. In this paper, we address these issues and propose a QoS enhancement over PCF, called enhanced PCF (EPCF) that enables Wireless LAN to send a combination of voice, data and isochronous data packets using the current IEEE 802.11 PCF. First, we compare the performance of the proposed model (EPCF) with the HCF function of the IEEE 802.11e through simulation. Second, we extend the proposed model (EPCF) to work in a multihop wireless ad hoc mode and present the advantages and limitations in this case. Simulation results demonstrate an enhanced performance of our scheme over the legacy PCF and a comparable performance to the IEEE 802.11e HCF in terms of the average delay and system throughput. However, EPCF is much simpler than HCF, provides flow differentiation, and is easy to implement in the current IEEE 802.11 standard.

Hot Topics in Cloud Computing

Cloud computing is no longer just hype. Its quickly evolving and gradually realizing its business value, as the articles in this special issue show. Its now attracting more and more researchers and practitioners, who are creating innovations around its core enabling technologies and architectural building blocks.

DMMX: dynamic memory management extensions

Dynamic memory management allows programmers to be more productive and increases system reliability and functionality. However, software algorithms for memory management are slow and non-deterministic. It is well known that object-oriented applications tend to be dynamic memory intensive. This has led programmers to eschew dynamic memory allocation for many real-time and embedded systems. Instead, programmers using Java or C++ as a development language frequently decide to allocate memory statically instead of dynamically. In this paper, we present the design of a bitmap-based memory allocator implemented primarily in combinational logic to allocate memory in a small, predictable amount of time. It works in conjunction with an application-specific instruction-set extension called the dynamic memory management extension (DMMX). Allocation is done through a complete binary tree of combinational logic, which allows constant-time object creation. The garbage collection algorithm is mark sweep, where the sweeping phase can be accomplished in constant time. This hardware scheme can greatly improve the speed and predictability of dynamic memory management. The proposed DMMX is an add-on approach, which allows easy integration into any CPU, hardware-implemented Java virtual machine, or processor in memory.