Bo Ryu

Power control for directional antenna-based mobile ad hoc networks

A number of power control algorithms have been proposed for mobile ad hoc networks. However, most of them either assume omni-directional antennas or mixture of omni-directional and directional antennas. Besides, there lack work that study the impact of power control on purely directional antenna-based protocols. In this paper, we evaluate the impact of power control on a purely directional antenna-based MAC protocol, LiSL/D MAC. Simulation results show that the proposed power control algorithm improves the system performance by 30% to 80% in terms of energy consumption while preserving network throughput and end-to-end delay.

Impact of linear regression on time synchronization accuracy and energy consumption for Wireless Sensor Networks

Linear regression is used in a number of time synchronization protocols to establish a linear relationship between clocks at different sensor nodes to achieve energy-efficient time synchronization. These protocols are predictive in the sense that a node predicts a target clock based on collected time stamp data. However, the use of linear regression for sensor network time synchronization has not been thoroughly studied in the literature. This paper attempts to close the gap by analyzing the impacts of two parameters on the precision of linear regression based time synchronization protocols: (1) the frequency at which the time stamp data are collected; (2) the window size, i.e., the number of time stamps used for linear regression. Through theoretical analysis, experiments and simulations, we show a counter-intuitive result: given the prediction interval, if the clock relationship varies slowly over time, more frequent synchronization results in worse synchronization precision. This result suggests that a linear regression based time synchronization protocol can achieve both high precision and good energy efficiency when operating at a low synchronization frequency. We also show that increasing the window size improves the synchronization performance but the synchronization uncertainty is bounded away from zero.

HAIPE compliant TCP performance enhancing proxy for Bandwidth-on-Demand environment

IP layer encryption introduces substantial challenges for bandwidth on demand satellite communication. Our solution, namely broadband HAIPE-embeddable SATCOM terminal (BHeST), utilizes novel network performance enhancement algorithms for high latency geosynchronous bandwidth-on-demand satellite links protected in the presence of high assurance Internet protocol encryption (HAIPE). The problems experienced by TCP over geosynchronous satellites are well understood: while standard modems (on the BLACK side) employ TCP PEPpsilas which have been shown to work well, the HAIPE encryption of TCP headers renders the onboard modempsilas PEP useless. This is attributed to the fact that under the bandwidth-on-demand environment, PEP must use traditional TCP mechanisms such as Van Jacobson to probe for the bandwidth of the link (which eliminates the usefulness of the PEP) or use the bandwidth signaling that does not violate RED/BLACK boundary. Modem vendors typically recommend disabling the PEP when a HAIPE device is used. By moving the PEP into the secure network (RED) and exploiting the bypass mechanisms allowed by the latest HAIPE standard, we have been able to regain the PEPpsilas desired network enhancement that was lost due to HAIPE encryption. Our c BHeST solution employs direct video broadcast - return channel service (DVB-RCS), an open standard chosen for joint IP modem (JIPM) initiative by Defense Information System Agency, as a means of providing bandwidth-on-demand satellite links as a placeholder for future transformational satcom (TSAT) terminals. Another issue we address is the estimation of current satellite bandwidth allocated to a remote terminal which is not readily available in DVB-RCS.

Robust extreme energy efficient sensor networks

Despite much research on sensor networks in general and on event-response applications in particular, simultaneously achieving the desired timeliness of response, longevity, and wide-area coverage still remains a significant challenge. In this paper, we present a robust, flexible, and extremely energy efficient sensor networking system solution with the goal of enabling orders of magnitude improvements in sensor network lifetime for time-stringent event-response applications with wide area coverage requirement such as maritime domain awareness and environmental monitoring. We first present a cross-layer hierarchical energy adaption framework, a main departure from traditional approach of single-component adaptation and efficiency paradigm. The proposed solution consists of the following components: duty-cycle optimized radio, low-power adaptive multimodal MAC (LPA-MAC), and cross-layer adaptive reconfiguration (CARE). This paper focuses on the cross-layer design aspects of LPA-MAC and CARE. For LPAMAC, we conduct a thorough investigation on the relationship among duty cycle, synchronization mode and traffic load. Contrary to common belief, we find that there exists a range of energy-optimal duty cycles for a given traffic load. The resulting relationship provides us with critical guidelines on how to adaptively select near optimal operational mode so that only the least possible energy is consumed for given traffic loads. For CARE, a concept of adaptively reconfiguring a backbone structure is introduced and evaluated. Preliminary simulation results indicate more than two orders of magnitude in energy saving over an ldquoalways-onrdquo system with comparable timeliness.

Topology Control for Wireless Ad hoc Networks: A Genetic Algorithm-based Approach

In an ad hoc wireless network, the topology control problem is to minimize the transmission power, or selecting the least number of neighbors, while preserving the network connectivity. Recently, there have been increasing interests in applying biologically inspired approaches, such as swarm intelligence and simulated annealing, to this NP-complete global optimization problem. In this paper, we propose schemes of applying genetic algorithm to this problem. Simulation results demonstrate the effectiveness of our approach.

TCP accelerator for DVB-RCS SATCOM dynamic bandwidth environment with HAIPE

A high assurance IP encryption (HAIPE) compliant protocol accelerator is proposed for military networks consisting of red (or classified) networks and black (or unclassified) networks. The boundary between red and black sides is assumed to be protected via a HAIPE device. However, the IP layer encryption introduces challenges for bandwidth on demand satellite communication. The problems experienced by transmission control protocol (TCP) over satellites are well understood: While standard modems (on the black side) employ TCP performance enhancing proxy (PEP) which has been shown to work well, the HAIPE encryption of TCP headers renders the onboard modems PEP ineffective. This is attributed to the fact that under the bandwidth-on-demand environment, PEP must use traditional TCP mechanisms such as slow start to probe for the available bandwidth of the link (which eliminates the usefulness of the PEP). Most implementations recommend disabling the PEP when a HAIPE device is used. In this paper, we propose a novel solution, namely broadband HAIPE-embeddable satellite communications terminal (BH-eST), which utilizes dynamic network performance enhancement algorithms for high latency bandwidth-on-demand satellite links protected by HAIPE. By moving the PEP into the red network and exploiting the explicit congestion notification bypass mechanism allowed by the latest HAIPE standard, we have been able to regain PEPs desired network enhancement that was lost due to HAIPE encryption (even though the idea of deploying PEP at the modem side is not new). Our BHeST solution employs direct video broadcast-return channel service (DVB-RCS), an open standard as a means of providing bandwidth-on-demand satellite links. Another issue we address is the estimation of current satellite bandwidth allocated to a remote terminal which is not available in DVB-RCS. Simulation results show that the improvement of our solution over FIX PEP is significant and could reach up to 100%. The improvement over the original TCP is even more (up to 500% for certain configurations).

Supporting reliable and secure transport services over DVB-RCS satellite systems using XCP

The DVB-RCS standard provides a framework for Multi-Frequency TDMA (MF-TDMA) and dynamic resource (frequencies and time slots) allocation over satellite links. Nevertheless, MF-TDMA and dynamic resource allocation alone are not sufficient to achieve satisfactory throughput for TCP, the dominant transport protocol in IP-based networks such as the Global Information Grid (GIG) system, due to the inherent large delay-bandwidth product of the satellite links. Various mechanisms called TCP Performance Enhancement Proxies (PEP) are proposed to improve the performance of TCP over large delay-bandwidth product networks. However, typical TCP PEPs do not support GIGpsilas layer-3 security standard HAIPE (High Assurance Internet Protocol Encryption). In this paper, we identify eXplicit Control Protocol (XCP) as a desired performance enhancement mechanism, and propose a novel system architecture that integrates DVB-RCS, XCP and HAIPE. We implement XCP in the network simulator QualNet and evaluate its performance against that of TCP. Our simulation results show that XCP achieves higher throughput and fairer bandwidth allocation among competing traffic flows in DVB-RCS systems than TCP.