Nakjung Choi

Optimal multi-sink positioning and energy-efficient routing in wireless sensor networks

In wireless sensor networks, the sensors collect data and deliver it to a sink node. Most of the existing proposals deal with the traffic flow problem to deliver data to the sink node in an energy-efficient manner. In this paper, we extend this problem into a multi-sink case. To maximize network lifetime and to ensure fairness, we propose (i) how to position multiple sink nodes in a sensor network and (ii) how to route traffic flow from all of the sensors to these multiple sink nodes. Both of the problems are formulated by the linear programming model to find optimal locations of the multiple sink nodes and the optimal traffic flow rate of routing paths in wireless sensor networks. The improved lifetime and fairness of our scheme are compared with those of the multi-sink aware minimum depth tree scheme.

In-network caching effect on optimal energy consumption in content-centric networking

In content-centric networking (CCN), the in-network caching feature provides several attractive advantages such as low dissemination latency and network transport load reduction. Thus, CCN requires less transport energy but additional energy to provide a caching capability at every content router. In this paper, we investigate the minimum energy consumption that CCN can achieve with optimal cache locations by considering different caching hardware technologies, number of downloads per hour, and content popularity. We first set up an energy consumption model for CCN and then formulate linear and nonlinear programming problems to minimize total energy consumption of CCN. Also, a genetic algorithm (GA) approach is proposed to find energy-efficient cache locations. Using reported energy efficiency of computational hardware and network equipment, we show CCN yield greater energy savings for very popular content and small-sized catalog, compared to conventional CDN. Our results also indicate that two aspects of the memory technology, energy-proportional caching and sufficient memory capacity, are critical to the overall energy efficiency gain of CCN.

Multi-channel MAC protocol for mobile ad hoc networks

This paper introduces a new MAC scheme operating on multiple channels that maximizes network performance and provides differentiated services in mobile ad hoc networks (MANETs). Specifically, the IEEE 802.11 in ad hoc mode, the most popular MAC protocol in mobile ad hoc networks, is extended from single channel to multiple channels operation. The current standard allows the practical use of three channels in 802.11b and eight in 802.11a, but multiple channel operation is not supported in ad hoc mode. The proposed protocol ensures maximum performance, low delay, reliability, efficiency and fairness, while allowing transmission priorities to be set on a per-channel basis. In addition, a solution is provided for the hidden multi-channel problem, which arises when only one network interface card is used. Basic considerations for mobility management in a multi-channel environment is also given. We show through simulation that the multi-channel MAC protocol greatly outperforms the original IEEE 802.11 MAC protocol.

Rate-adaptive multimedia multicasting over IEEE 802.11 wireless LANs

Multimedia services are a major application for IEEE 802.11 WLANs but the current standard does not utilize any rate adaptation technique for multicasting. SARM (SNR- based auto rate for multicast) is a new rate adaptation mechanism for multicasting multimedia content in IEEE 802.11 WLAN environments. Since there is no RTS/CTS or MAC ACK frame in multicast packet transmissions, SARM uses an auxiliary signaling method to obtain the channel quality for each mobile node. By adapting a transmission rate based on the SNR of the node experiencing the worst air-channel, SARM achieves the best quality of service for the prevailing conditions. This reduces the proportion of wireless channel resources assigned to multicasting, allowing more bandwidth for unicast flows.

A Solicitation-based IEEE 802.11p MAC Protocol for Roadside to Vehicular Networks

Recently, vehicular networks have begun to attract much attention in industry as well as academia. In particular, IEEE 802.11-based solutions for vehicular networks are also investigated by IEEE 802.11p. As the original IEEE 802.11 standard is designed only for little mobility, the IEEE 802.11p working group should address important issues such as frequent disconnection and handoff. We first introduce new challenges with which IEEE 802.11p is faced, and then propose a new solicitation-based operation mode for IEEE 802.11p, in which the transmissions of data frames are initiated only by users. Throughput analysis reveals that our proposal achieve the high and stable throughput, irrespectively of the number of contending and moving-away stations.

WISE: energy-efficient interface selection on vertical handoff between 3G networks and WLANs

The integration of 3G networks and WLAN as complementary has begun to attract much attention in industry as well as academia. This topic is becoming a burning issue, and one of the key questions which it raises is how to support a seamless vertical handoff. This paper introduces a new interface selection algorithm for energy-efficient vertical handoff in tightly coupled systems capable of supporting seamless handoff. Our proposed scheme, Wise Interface Selection (WISE) switches the active network interface, after taking into consideration the characteristics of the network interface cards and the current level of data traffic, with the cooperation of the mobile terminals and network. Interface switching operates independently on both the downlink and the uplink for the purpose of energy conservation. We show through simulation that less energy is consumed with WISE than when only a 3G network or WLAN interface is used, resulting in a longer lifetime for the mobile terminals. In the case of TCP connections, additional throughput gain can also be obtained.

AMVS-NDN: Adaptive mobile video streaming and sharing in wireless named data networking

Recently, mobile traffic (especially video traffic) explosion becomes a serious concern for mobile network operators. While video streaming services become crucial for mobile users, their traffic may often exceed the bandwidth capacity of cellular networks. To address the video traffic problem, we consider a future Internet architecture: Named Data Networking (NDN). In this paper, we design and implement a framework of adaptive mobile video streaming and sharing in the NDN architecture (AMVS-NDN) considering that most of mobile stations have multiple wireless interfaces (e.g., 3G and WiFi). To demonstrate the benefit of NDN, AMVS-NDN has two key functionalities: (1) a mobile station (MS) seeks to use either 3G/4G or WiFi links opportunistically, and (2) MSs can share content directly by exploiting local WiFi connectivities. We implement AMVS-NDN over CCNx, and perform tests in a real testbed consisting of a WiMAX base station and Android phones. Testing with time-varying link conditions in mobile environments reveals that AMVS-NDN achieves the higher video quality and less cellular traffic than other solutions.

Leader-Based Rate Adaptive Multicasting for Wireless LANs

Multicasting is useful for various applications such as multimedia broadcasting. In current 802.11, multicast frames are sent as broadcast frames at a low transmission rate without any acknowledgement or binary exponential backoff. This naive multicasting mechanism degrades the performance of not only multicast flows but also unicast flows. In this paper, we propose a new multicasting mechanism based on the leader- based approach to improve the legacy multicast transmissions, maintaining coexistence with legacy 802.11 devices. Simulations show that our protocol achieves well-balanced performance in terms of reliability, latency, goodput, and transmission fairness in comprehensive environments.

IA-TCP: A rate based incast-avoidance algorithm for TCP in data center networks

In recent years, the data center networks commonly accommodate applications such as MapReduce and web search that inherently shows the incast communication pattern; multiple workers simultaneously transmit TCP data to a single aggregator. In this environment, the TCP performance is significantly degraded in terms of goodput and query completion time, as a result of the severe packet loss at Top of Rack (ToR) switches. The TCP senders aggressively transmit packets causing throughput collapse even though the network pipe size, i.e., bandwidth-delay product, is extremely small. In this paper, we introduce a novel end-to-end congestion control algorithm called IA-TCP that avoids the TCP incast congestion problem effectively. IA-TCP employs the rate-based algorithm at the aggregator node, which controls both the window size of workers and ACK delay. Through extensive NS-2 simulations, we validate that our algorithm is scalable in terms of the number of workers achieving enhanced goodput and zero timeouts.

Leader-Based Multicast Service in IEEE 802.11v Networks

With the advent of various multimedia streaming applications requiring reliability and high bandwidth, multicasting in wireless LANs has been gaining more attentions as the supported bit rate increases. However, according to the specification of the IEEE 802.11 standard, broadcast/multicast frames are transmitted at a fixed and low bit rate due to the absence of a feedback mechanism such as ACK. This simple broadcasting technique with no feedback signal raises some issues; reliability, efficiency and fairness. In this paper, hence, we propose a framework for multicasting termed Leader-Based Multicast Service (LBMS) to alleviate those limitations. LBMS consists of a leader-based transmission and feedback mechanism for multicasting by extending the IEEE 802.11v standard, which is the next-generation standard for network management. Also, we try to support legacy 802.11 stations can still participate in multicasting. Simulation exhibits that the gain of the proposed multicasting scheme increases as (i) more stations compete for the channel, and (ii) the wireless channel condition becomes poorer.