Hyungkeun Lee

RIX-MAC : An Energy-Efficient Receiver-Initiated Wakeup MAC Protocol for WSNs

This paper proposes RIX-MAC (Receiver-Initiated X-MAC), a new energy-efficient MAC protocol based on an asynchronous duty cycling. RIX-MAC improves energy efficiency through utilizing short preambles and adopting the receiver-initiated approach, where RIX-MAC minimizes sender nodes’ energy consumption by enabling transmitters to predict receiver nodes’ wake-up times. It also reduces receiver nodes’ energy consumption by decreasing the number of control frames. We use the network simulator to evaluate RIX-MAC’s performance. Compared to the prior asynchronous duty cycling approaches of X-MAC and PW-MAC, the proposed protocol shows a remarkable improvement in energy-efficiency and end-to-end delay.

Header Compression for Resource and Energy Efficient IP over Tactical Data Link

Link-16 is a tactical data link for providing information including tactical data link message necessary to a command and control unit. Even though current Link-16 transmits and receives only tactical data link message, there is a desire to send many kinds of IP applications over Link-16. However, too large size of IP header decreases the transmission efficiency of IP applications over Link-16. Thus, IP header compression algorithm suitable to Link-16 is needed without loss of performance. Conventional header compression algorithms such as RFC 2507, RFC 2508 and RFC 3095 are not suitable to Link-16 because it broadcasts information with low transmission data rate. In this paper, we propose a novel IP header compression algorithm for transmitting tactical data link messages and IP application data without modification of Link-16.

A packet-loss recovery scheme based on the gap statistics

Packet losses are bursty in nature since the dominant reason is temporary overload situations in the shared resources over networks. To increase the effectiveness of forward error correction (FEC) schemes, adaptive FEC schemes have been suggested, where the amount of redundancy is controlled according to current network status. In this paper, we propose a gap- based adaptive FEC scheme, which is motivated by the Markov gap model for packet losses, and show that the gap-based adaptive FEC scheme performs better than the adaptive FEC scheme based on the Gilbert model.

Modeling and anaysis of an energy-efficient MAC protocol for wireless sensor networks

Energy efficiency is a very important requirement in designing a MAC protocol for wireless sensor networks (WSNs) using battery-operated sensor nodes. We proposed a new energy-efficient MAC protocol, RIX-MAC, based on asynchronous duty cycling and receiver-initiated scheme. In this paper, we analyze the performance such as throughput, delay, and energy consumption of RIX-MAC with modeling and simulation. Our modeling is validated by comparing it with the simulation results in NS-2. As the result, we obtain average 95% confidence interval of the simulation results of this paper.

The Performance Analysis of Hybrid ARQ-II for Cooperative Communication over Wireless Channels

The cooperative communication over wireless channels has recently attracted considerable attention promising significant reliability and capacity gains due to a new form of spatial diversity. In this paper, we propose a new cooperative communication scheme where the spatial diversity of cooperative communication and the incremental error correction of Hybrid ARQ with RCPC codes are exploited. Simulation results show that the proposed system achieves lower BER performance than the legacy system and that the channel state of Source-Relay play a important role in the performance of the cooperative systems.

A Cross Layer Routing Metric to Recognize Traffic Interference in Wireless Mesh Networks

As an emerging technology, wireless mesh networks are making significant progress in the area of wireless networks in recent years. However, the nature of sharing transmission medium makes it challenging to fully exploit these networks. In an attempt to improve the radio resource utilization, several routing metrics have been specifically designed for wireless mesh networks. However none of these routing metrics efficiently tackles interference issues. In this paper, we propose a routing metric for wireless mesh networks, which takes account of the amount of interference by considering the traffic situation of adjacent nodes and selects less interfered path for transmission. The aim of this metric is to route the traffic through interference areas and balance the load amongst the network nodes. Simulation results show that the proposed routing metric reduces the end-to-end delay when compared to the MIC, ETT and hop-count routing metrics.

Packet Forwarding Based on Reachability Information for VANETs

In the VANET, where the duration of communication is extremely short, the large amount of control overheads associated with discovering and maintaining end-to-end path information may not be tolerable. This paper presents a new multi-hop forwarding protocol which does not use explicit path information, but instead, uses reachability information towards the destinations in determining next-hop nodes. The reachability information for a particular node merely indicates that the node is reachable. At each hop, one of the neighbor nodes which hold the reachability information towards the same destination is selected as the next-hop node by contention based on some priority values. The proposed protocol is designed to be integrated with the IEEE 802.11 MAC protocol in order to achieve higher efficiency and accuracy in its time-critical operations. It is shown through simulations that the proposed protocol outperforms the AODV in a realistic the VANET scenario in terms of both the end-to-end delay and packet delivery ratio.

Cross-Layer Enhancement of IEEE 802.11 MAC for Mobile Ad Hoc Networks

In mobile ad hoc networks, the large amount of control overheads associated with discovering and maintaining end-to-end routing path information may not be tolerable. In this paper, we present the design and simulation of a new approach for IEEE 802.11 MAC based on the multipath routing information for ad hoc networks. The routing information about multiple paths discovered in the network layer is exploited by the MAC layer in order to forward a frame over the best hop out of multiple hop choices. The performance of our approach is compared with the one of the IEEE 802.11 MAC protocol via simulation. The results show that our proposed scheme exhibits a remarkable performance improvement over the IEEE 802.11 MAC protocol in terms of packet overhead and end-to-end throughput.

An Adaptive MAC Protocol Based on Path-Diversity Routing in Ad hoc Networks

We present the design and simulation of an adaptive MAC protocol based on the path-diversity routing information for ad hoc networks. As a routing protocol, a multipath routing protocol based on SPAFAR is used, where a route discovery algorithm finds multiple paths significantly reduce the delay in finding an alternate path. The information about multiple paths discovered in the network layer is exploited by the MAC layer in order to forward a frame over the best hop out of multiple hop choices. The performance of our approach is compared with IEEE 802.11 MAC through the simulation. The results show that our scheme exhibits a significantly better performance rather than the IEEE 802.11 MAC protocol in terms of packet overhead and end-to-end throughput.

Software optimization for embedded communication system

This paper presents general software optimization techniques to improve software performance and energy consumption in embedded systems. Software optimization can be categorized into three levels: algorithmic, source code-level. Then these techniques are applied to optimize our tactical message processing software, which is a message encoder-decoder for tactical communication equipped on weapon systems. The optimized software achieved performance increase of about 12%, memory access decrease of 72% and memory usage decrease of 35% over the original software.