Sangman Moh

CD-MAC: Cooperative Diversity MAC for Robust Communication in Wireless Ad Hoc Networks

This paper proposes a medium access control (MAC) algorithm, called Cooperative Diversity MAC (CD-MAC), which exploits the cooperative communication capability to improve robustness in wireless ad hoc networks. In CD-MAC, each terminal proactively selects a relay for cooperation and lets it transmit simultaneously when it is beneficial in mitigating interference from nearby terminals and thus improving the network performance. For practicability, CD-MAC is designed based on the widely adopted IEEE 802.11 MAC. System-level simulation study shows that CD-MAC significantly outperforms the original IEEE 802.11 MAC in terms of packet delivery ratio.

A Cooperative Diversity-Based Robust MAC Protocol in Wireless Ad Hoc Networks

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.

Mapping strategies for switch-based cluster systems of irregular topology

Mapping virtual process topology to physical processor topology is one of the most important issues in parallel computing. The mapping problem for switch-based cluster systems of irregular topology is very complicated due to the connection irregularity and routing complexity. This paper proposes two mapping schemes for irregular cluster systems, which try to map the nearest neighbors in the process topology to physically adjacent processors. In addition, an application-oriented performance metric, weighted cardinality, is introduced to represent the quality of mapping. A simulation study shows that, for a virtual topology of a 16/spl times/16 mesh, the proposed mapping schemes result in better mapping quality and about 15/spl sim/20% shorter communication latency compared to random mapping. The proposed algorithms should also be beneficial when they are applied to metacomputing and cluster of cluster systems, where the communication costs are an order of magnitude different depending on the relative position of the processor nodes.

Four-ary tree-based barrier synchronization for 2D meshes without nonmember involvement

This paper proposes a Barrier Tree for Meshes (BTM) to minimize the barrier synchronization latency for two-dimensional (2D) meshes. The proposed BTM scheme has two distinguishing features. First, the synchronization tree is 4-ary. The synchronization latency of the BTM scheme is asymptotically Olog4nU, while that of the fastest scheme reported in the literature is bounded between Olog3nU andOOn 1=2 U, wheren is the number of member nodes. Second, nonmember nodes are neither involved in the construction of a BTM nor actively participate in the synchronization operations, which avoids interference among different process groups during synchronization. This not only results in low setup overhead, but also reduces the synchronization latency. The low setup overhead is particularly effective for the dynamic process model provided in MPI-2. Extensive simulation study shows that, for up to 64 64 meshes, the BTM scheme results in about 40 70 percent shorter synchronization latency and is more scalable than conventional schemes.

Linux/SimOS - a simulation environment for evaluating high-speed communication systems

This paper presents Linux/SimOS, a Linux operating system port to SimOS, which is a complete machine simulator from Stanford. The motivation for Linux/SimOS is to alleviate the limitations of SimOS, which only supports proprietary operating systems. The contributions made in this paper are two-fold: First, the major modifications that were necessary to run Linux on SimOS are described. Second, a detailed analysis of the UDP/IP protocol 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 of communication performance, including the effects of the kernel, device drivers, and network interface.

Energy efficient and robust multicast protocol for mobile ad hoc networks

This paper reevaluates the multicast protocols for MANETs in terms of energy efficiency and proposes a new robust multicast protocol, called two-tree multicast (TTM). Multicast protocols can be broadly categorized into two types, tree-based multicast and mesh-based multicast, based on the network structure along which multicast packets are delivered to multiple receivers. Mesh-based protocols are more robust to mobility and result in high packet delivery ratio. On the other hand, multicast trees are more energy efficient than multicast meshes. This is because mesh-based protocols depend on broadcast flooding within the mesh and therefore, mobile nodes in the mesh must receive all multicast packets during the multicast communication. The proposed TTM uses two trees, a primary and an alternative backup tree, to improve energy efficiency compared to the mesh-based protocols and to offer a better energy balance and packet delivery ratio than the free-based protocols. Performance evaluation study shows that the proposed TTM saves energy consumption by a factor of 1.9/spl sim/4.0 compared to the mesh-based multicast. In terms of combined performance metric, energy per delivered packet, TTM shows up to 80% and 40% improved performance than the mesh-based multicast and the conventional shared tree multicast, respectively.

Adaptive multicast on mobile ad hoc networks using tree-based meshes with variable density of redundant paths

Multicasting has been extensively studied for mobile ad hoc networks (MANETs) because it is fundamental to many ad hoc network applications requiring close collaboration of multiple nodes in a group. A general approach is to construct an overlay structure such as multicast tree or mesh and to deliver a multicast packet to multiple receivers over the overlay structure. However, it either incurs a lot of overhead (multicast mesh) or performs poorly in terms of delivery ratio (multicast tree). This paper proposes an adaptive multicast scheme, called tree-based mesh with k-hop redundant paths (TBMk), which constructs a multicast tree and adds some additional links/nodes to the multicast structure as needed to support redundancy. It is designed to make a prudent tradeoff between the overhead and the delivery efficiency by adaptively controlling the path redundancy depending on network traffic and mobility. In other words, when the network is unstable with high traffic and high mobility, a large k is chosen to provide more robust delivery of multicast packets. On the other hand, when the network traffic and the mobility are low, a small k is chosen to reduce the overhead. It is observed via simulation that TBMk improves the packet delivery ratio as much as 35% compared to the multicast tree approach. On the other hand, it reduces control overhead by 23–87% depending on the value of k compared to the multicast mesh approach. In general, TBMk with the small value of k offers more robust delivery mechanism but demands less overhead than multicast trees and multicast meshes, respectively.

VLSI-Oriented Architecture for Two's Complement Serial-Parallel Multiplication without Speed Penalty

A serial-parallel multiplier computes a product by multiplying a parallel input and a serial (or online) input. Serial-parallel multipliers are frequently used in digital communication systems, digital signal processing, on-line computing applications, and embedded computing and communication systems. In this paper, a VLSI-oriented, size-efficient twos complement serial-parallel multiplication architecture is proposed. In addition to its smaller size, it is also suitable for VLSI implementation because it consists of modularized logic cells and locally interconnected signals. According to the analysis results for 2- to 32- bit multiplication, the proposed architecture requires up to 30 percent smaller size without speed penalty compared to the previous architecture.In wireless sensor networks (WSNs), mobilizing sink node for data collection can minimize communication and maximize network lifetime. Several mobility algorithms have been proposed to control sink nodes movement. However, they do not consider mobility for coverage area problem. Hilbert space-filling curves technique is modified to navigate mobile sink in traversing specfiic area of the sensor field. The algorithm is called optimized-Hilbert, which provides mobility pattern of a sink node in covering an ellipsoidal monitoring area during data collection for a specific mission by traversing the entire area from an entry point and finish at an exit point of square grids. The optimized-Hilbert requires less number of steps as compared to conventional Hilbert. Additionally, it is also compared with circular mobility, and result indicates the efficiency of optimized Hilbert.

Approaches to using a wireless mobile terminal to help severely hearing impaired people

In this paper, new technology-adaptive approaches to using a wireless mobile terminal are presented in order to help severely hearing impaired people, which are remote human translation, remote server translation, and mobile terminal translation. The three step-by-step approaches are to adapt the evolution and feasibility of advanced computer and communication technologies. The first approach can be easily implemented but requires the involvement of human interpreters. The second and third approaches require not only speaker-independent voice recognition but also hand-writing text and sign language recognition. In particular, for the mobile terminal translation scheme, a light-weight, low-power, high-performance, small-sized mobile terminal should be provided to process the computing-centric voice, hand-writing text and sign language recognition on real-time basis. Even though this work is currently at the startup phase, as technology evolves, it will be possible to provide severely hearing impaired people with the context-aware mobile terminals that interpret voice, hand-writing text and sign language on the real-time basis.

Is the Store-and-Forward Delivery Still the Best in Ad Hoc Networks?

In multihop routed ad hoc networks, the conventional store-and-forward delivery has been used. However, we may ask a question: Is the store-and-forward delivery still the best? This paper presents a pipeline-through MAC (PT-MAC) protocol for ad hoc networks, in which nodes have two 3-channel interfaces in order to use limited radio resources efficiently and improve network performance. The proposed protocol reduces end-to-end delay significantly in multihop routed transmission by exploiting a novel pipeline-through technique rather than using the conventional store-and-forward. This results in improved network performance without increasing control overhead. Our extensive performance study shows that the proposed PT-MAC shows 20-40 percent shorter end-to-end delay and 25-55 percent better goodput compared to the IEEE 802.11 DCF with two 3-channel interfaces.