Bongsoo Roh

Performance Analysis of Asymmetric RF/FSO Dual-Hop Relaying Systems for UAV Applications

In this paper, we analyze the performance of a dual-hop relaying system composed of asymmetric radio frequency (RF) and free-space optics (FSO) (RF/FSO) links. We consider an asymmetric amplify-and-forward (AF) relay which converts the received RF signal into an optical signal using the subcarrier intensity modulation (SIM) scheme. The RF and FSO channels are assumed to experience Rayleigh and Gamma-Gamma fading distributions, respectively. Particularly, we derive the average probability of error as well as ergodic capacity upper bound of the asymmetric RF/FSO dual-hop relaying system, in closed-forms. As a result, the asymmetric RF/FSO relaying system shows slightly worse performance in average probability of error and ergodic capacity upper bound than the RF/RF relaying system in the low SNR. Over the SNR of 20 dB, however, the asymmetric RF/FSO relaying system shows very similar performance in average probability of error and ergodic capacity upper bound to the RF/RF relaying system. The derived mathematical expressions are verified by exactly matching Monte-Carlo simulation results.

Cooperative RS Selection Schemes for IEEE 802.16j Networks

The specification of IEEE 802.16j defines the operation of multi-hop relay stations (RSs) with cooperative communication as an optional functionality to achieve space diversity gain. One of the key issues in cooperative communication using RSs is to determine which RSs should be used as cooperative nodes, i.e., cooperative relay selection. In this paper, we investigate the conditions that should be tested for RSs to operate as cooperative nodes based on the signal intensity data. We also propose two cooperative RS selection schemes for determining a group of cooperative RSs out of all candidate RSs: max-min-max cooperative RS selection and joint cooperative RS-path selection. The first scheme selects a group of RSs with the highest diversity gain, whereas the second scheme selects the cooperative RSs and paths simultaneously that could yield the highest system throughput. Simulation results are presented to evaluate and compare the performance of the two schemes.

Joint resource allocation, routing and CAC for uplink OFDMA networks with cooperative relaying

In this paper, we propose a joint resource allocation, routing, and connection admission control (CAC) scheme for uplink transmission in orthogonal frequency division multiple access (OFDMA) relay networks with cooperative relaying. For cooperative relaying, relay station can relay uplink data from mobile station (MS) to base station with cooperation of the MS using transmit diversity. Transmit diversity can be achieved by virtual MISO via distributed space–time coding. The proposed scheme jointly allocates OFDMA resources and selects path for each user with CAC to maximize the upink throughput of cooperative OFDMA relay networks. The basic OFDMA resource unit is considered as a resource element which is one subcarrier over one OFDMA symbol. An efficient multi-choice multi-dimensional knapsack (MMKP) algorithm is presented for the proposed scheme. The proposed MMKP algorithm provides a unified framework which is applicable to OFDMA networks with and without cooperative relaying. We evaluate the performance of the proposed scheme with and without cooperative relaying in a hilly terrain with heavy tree density by using OPNET-based simulation. We show that the cooperative relaying improve the uplink system throughput compared with non-cooperative relaying, and the proposed scheme outperforms the conventional link quality-based scheme in both cooperative and non-cooperative relay networks.

Bio-Inspired Routing Protocol Based on Pheromone Diffusion in Mobile Ad Hoc Networks

Bio-inspired routing protocols use the principle of swarm intelligence, which finds the optimal path to the destination in a distributed and autonomous way in dynamically changing environments; therefore, they can maximize the routing performance, reduce the control overhead, and recover a path failure quickly according to the change in the network topology. In this paper, we propose a bio-inspired routing protocol for mobile ad hoc networks. The proposed protocol uses a technique of overhearing for obtaining routing information without additional overhead. Through overhearing, a pheromone is diffused around the shortest path between the source and the destination. On the basis of this diffused pheromone, a probabilistic path exploration is executed and the useful alternative routes between the source and the destination are collected. Therefore, the proposed routing protocol can gather up-to-date effective routing information while reducing the control overhead. The simulation results show that the proposed routing protocol outperforms the typical ad hoc on-demand distance vector (AODV) and AntHocNet protocols in terms of the delivery ratio and the end-to-end delay and significantly decreases the routing overhead against AntHocNet.

Regional Route Maintenance Protocol Based on Local Pheromone Diffusion for Mobile Ad Hoc Networks

Route maintenance protocol has a tradeoff between the amount of control overhead and the provision of useful alternative paths. To break through this tradeoff, we consider a bio-inspired approach based on the natural phenomena of ant pheromone. The pheromone is accumulated on the shortest path between the nest and the food, and then diffused into its vicinity over time. Thus, the ants can find another route along this locally diffused pheromone when the shortest path in use is blocked. Based on this local pheromone diffusion and rerouting behavior, we propose a new route maintenance protocol for mobile ad hoc networks. First, pheromones (i.e., routing information) are locally diffused around the shortest path between the source and the destination (i) by overhearing at the one-hop neighbors from the shortest path and (ii) by sharing the overheard pheromone information among the one-hop neighbors. Thereafter, a probabilistic path exploration is executed within the one-hop region based on the locally diffused pheromone and so useful alternative paths around the shortest path are discovered. Through intensive simulations, we verify that the proposed regional route maintenance protocol outperforms the conventional routing protocols in terms of disruption frequency, delivery ratio, delay, and jitter, while reducing the control overhead.

Tactical MANET architecture for Unmanned Autonomous Maneuver Network

A MANET is a self-configuring ad hoc network that could be very useful for battlefield communication. Because of its versatility, Tactical Mobile Ad-hoc NETwork (MANET) is also widely used by modern military units especially for the autonomous maneuvering of unmanned vehicles and robots. But Quality of Service in Tactical-MANET is difficult because the network topology changes dynamically. The resource allocation scheme of MAC layer and load balancing of network layer can be critical factors in Tactical MANET. Without a QoS scheme, users might have difficulties in getting their service in Tactical MANET. In this paper we present the architecture of the MAC and Network layers of tactical MANET for Unmanned Autonomous Maneuver Network in order to provide better communication support in battlefield. It aimed to provide real-time streaming over a multi-hop ad hoc network with QoS support. The simulation results are presented to demonstrate the effectiveness of proposed scheme.

SMAT: Simulator Monitoring And Analysis Tool

Simulators can perform experiments in various scenarios and optimize its parameters by performing and comparing experiments repeatedly. Simulators are suitable for comparing each simulations result, but it shows only its results. It is limited to compare its results in various ways and analyze the interim process of protocol to figure out its drawbacks in the simulation run. To overcome these problems, some tools for visualizing and animating the simulation are utilized but those can show a limited information. We propose the Simulator Monitoring and Analysis Tool (SMAT) that analyzes the elements inside the protocol which are hard to see by using simulator, solves the problems of the protocol. We also propose a framework for analyzing the operational states of protocol and information inside simulator in various ways. We expect that SMAT can help developer to solve the problems of new protocol.

Enhanced DESYNC-TDMA algorithm for efficient packet delivery in distributed MANETs

In MANET environments, resource sharing among nodes will be one of the problems to be solved. To solve the problems, the desynchronization algorithm, called DESYNC-TDMA, has been proposed as a variation of firefly-inspired algorithm. However, it has still problems of slow convergence and resource wastes as the number of nodes increases. In this paper, we propose an enhanced DESYNC-TDMA not only to reduce the convergence time, but also to enhance the packet delivery efficiency. The effectiveness of the proposed method has been shown by implementing the method using OPNET simulator.

Efficient and adaptive resource allocation scheme for self-organizing DESYNC TDMA network

DESYNC TDMA, based on biologically inspired primitive[1], provides excellent total throughput with a low implementation complexity in the under high traffic loads without using the global clock synchronization and centralized coordination. However, DESYNC TDMA has the inefficient time resource scheduling because all participating nodes always fairly share the time resources for accessing the transmission medium in a self-organized and decentralized manner without considering whether a node has a transmission data or not. Therefore, this paper addresses an Efficient and Adaptive Resource Allocation Scheme for Self-Organizing DESYNC TDMA Network, called EA-DESYNC, which improve the inefficient time resource scheduling of DESYNC TDMA. EA-DESYNC uses the mini-time slot to distinguish between the actual use time slots and the unused time slot of DESYNCs transmission time slot. Also, this scheme proposes a method that can be shared with the transmission medium according to the residual amount of its mini-time slot and 1-hop neighbors. Simulation results show that EA-DESYNC could outperform the DESYNC in terms of throughput.

Traffic-aware adaptive routing metrics for tactical ad hoc networks

In tactical environment, MANET (Mobile Ad Hoc Network) has the network characteristics which make highly dynamic nodes, self-organized in fully-distributed style. Also, it has a harsh wireless channel environment compared to the commercial networks. In these channel environments, optimal path decision suited for Quality of Service (QoS) of transmitted tactical traffics must be performed by recognizing various environmental factors of wireless channels and the status of tactical mobile radio nodes autonomously to construct reliable communication links. In this paper, we newly define the required QoS features of tactical traffics and the characteristics of routing metrics in tactical network environment. We also propose a new ad hoc routing algorithm to ensure an efficient communication in tactical environment by calculating the optimal path using adaptive selection of routing metrics according to traffic characteristics. Simulation results show that the proposed algorithm outperforms existing ad hoc routing schemes, especially when tactical network has a high mobility and a high traffic load.