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Byline: Sunho Lim, Chansu Yu, Chita R. Das Recent studies discovered that many of social, natural and biological networks are characterised by scale-free power-law connectivity distribution. We envision that wireless networks are directly deployed over such real-world networks to facilitate communication among participating entities. This paper proposes Clustered Mobility Model (CMM), in which nodes do not move randomly but are attracted more to more populated areas. Unlike most of prior mobility models, CMM is shown to exhibit scale-free connectivity distribution. Extensive simulation study has been conducted to highlight the difference between Random WayPoint (RWP) and CMM by measuring network capacities at the physical, link and network layers.

Byline: Sanchita Mal-Sarkar, Iftikhar U. Sikder, Chansu Yu, Vijay K. Konangi The characterisation of uncertainty and the management of Quality of Service are important issues in mobile communications. In a Wireless Sensor Network, there is a high probability of redundancy, correlation and noise in the sensor features since data is often collected from a large array of densely deployed neighbouring sensors. This article proposes a soft computing approach to manage uncertainty by reasoning over inconsistent, incomplete, and fragmentary information using classical rough set and dominance-based rough set theories. A methodological and computational basis is provided and is illustrated in a real world sensor network application of aquatic biodiversity mapping under uncertainty.

Being readily available in most of 802.11 radios, multirate capability appears to be useful as WiFi networks are getting more prevalent and crowded. More specifically, it would be helpful in high-density scenarios because internode distance is short enough to employ high data rates. However, communication at high data rates mandates a large number of hops for a given node pair in a multihop network and thus, can easily be depreciated as per-hop overhead at several layers of network protocol is aggregated over the increased number of hops. This paper presents a novel multihop, multirate adaptation mechanism, called multihop transmission opportunity (MTOP), that allows a frame to be forwarded a number of hops consecutively to minimize the MAC-layer overhead between hops. This seemingly collision-prone nonstop forwarding is proved to be safe via analysis and USRP/GNU Radio-based experiment in this paper. The idea of MTOP is in clear contrast to the conventional opportunistic transmission mechanism, known as TXOP, where a node transmits multiple frames back-to-back when it gets an opportunity in a single-hop WLAN. We conducted an extensive simulation study via OPNET, demonstrating the performance advantage of MTOP under a wide range of network scenarios. [ABSTRACT FROM PUBLISHER]

Abstract: Carrier sensing is widely adopted in wireless communication to protect data transfers from collisions. For example, distributed coordination function (DCF) in IEEE 802.11 standard renders a node to defer its communication if it senses the medium busy. For the duration of deferment, each frame carries, in its MAC header, a 16-bit number in microseconds during which any overhearing node must defer. However, even if the carrier signal is detected, both ongoing and a new communication can be simultaneously successful depending on their relative positions in the network or equivalently, their mutual interference level. Supporting multiple concurrent communications is important in multihop ad hoc networks in order to maximize the network performance. However, it is largely ignored in DCF of the 802.11 standards because it is primarily targeted at single-hop wireless LANs. In addition, in DCF, the time duration information mentioned above is not delivered to all potential interferers, particularly those in the distance. This paper proposes Collision-Aware DCF (CAD) that efficiently utilizes the available channel resource along with the spatial as well as time dimension. First, each node makes its deferment decision adaptively based on the feedback from the communication counterpart and the status of the medium rather than on a simple, fixed carrier sense threshold as DCF. Second, CAD embeds the spatial and time reservation requirements in the PHY header, which is transmitted at the lowest data rate, so that a larger group of neighbors become aware of the ongoing communication and thus avoid collisions. Extensive experiments based on ns-2 network simulator show that CAD consistently outperforms DCF regardless of node mobility, traffic intensity, and channel randomness. For practicality, this paper discusses the implementation of CAD based on the DCF specification. [Copyright &y& Elsevier]

Carrier-sense Medium Access Control (MAC) protocols such as the IEEE 802,11 Distributed Coordination Function (DCF) avoid collisions by holding up pending packet transmission requests when a carrier signal is observed above a certain threshold. However, this often results in unnecessarily conservative communication, thus making it difficult to maximize the utilization of the spatial spectral resource. This paper shows that a higher aggregate throughput can be achieved by allowing more concurrent communications and adjusting the communication distance on the fly, which needs provisions for the following two areas: On the one hand, carrier sense-based MAC protocols do not allow aggressive communication attempts when they are within the carrier senseable area. On the other hand, the communication distance is generally neither short nor adjustable because multihop routing protocols strive for providing minimum hop paths, This paper proposes a new MAC algorithm, called Multiple Access with Salvation Army (MASA), which adopts less sensitive carrier sensing to promote more concurrent communications and adjusts the communication distance adaptively via "packet salvaging* at the MAC layer. Extensive simulation based on the ns-2 has shown MASA to outperform the DCF, particularly in terms of packet delay. We also discuss the implementation of MASA based on the DCF specification. [ABSTRACT FROM AUTHOR]

This paper presents a performance study of UDP/IP, TCP/IP, and M‐VIA using Linux/SimOS. Linux/SimOS is a Linux operating system port to a complete machine simulator SimOS. A complete machine simulator includes all the system components, such as CPU, memory, I/O devices, etc., and models them in sufficient detail to run an operating system. Therefore, a real program execution environment can be set up on the simulator to perform detailed system evaluation in a non‐intrusive manner. The motivation for Linux/SimOS is to alleviate the limitations of SimOS (and its variants), which only support proprietary operating systems. Therefore, the availability of the popular Linux operating system for a complete machine simulator will make it an extremely effective and flexible simulation environment for studying all aspects of computer system performance, especially evaluating communication protocols and network interfaces. The contributions made in this paper are two‐fold: First, the major modifications that were necessary to run Linux on SimOS are described. These modifications are specific to SimOS I/O device models and thus any future operating system porting efforts to SimOS will experience similar challenges. Second, a detailed analysis of UDP/IP, TCP/IP, and M‐VIA is performed to demonstrate the capabilities of Linux/SimOS. The simulation study shows that Linux/SimOS is capable of capturing all aspects communication performance, including the effects of the kernel, device driver, and network interface. [ABSTRACT FROM AUTHOR]

In interference-rich and noisy environment, wireless communication is often hampered by unreliable communication links. Recently, there has been active research on cooperative communication that improves the communication reliability by having a collection of radio terminals transmit signals in a cooperative way. This paper proposes a medium access control (MAC) algorithm, called Cooperative Diversity MAC (CD-MAC), which exploits the cooperative communication capability of the physical (PHY) layer to improve robustness in wireless ad hoc networks. In CD-MAC, each terminal proactively selects a partner for cooperation and lets it transmit simultaneously so that this mitigates interference from nearby terminals, and thus, improves the network performance. For practicability, CD-MAC is designed based on the widely adopted IEEE 802.11 MAC. For accurate evaluation, this study presents and uses a realistic reception model by taking bit error rate (BER), derived from Intersil HFA3861B radio hardware, and the corresponding frame error rate (FER) into consideration. System-level simulation study shows that CD-MAC significantly outperforms the original IEEE 802.11 MAC in terms of packet delivery ratio and end-to-end delay. [ABSTRACT FROM AUTHOR]