Jung-Ryun Lee

Hybrid Power Saving Mechanism for VoIP Services with Silence Suppression in IEEE 802.16e Systems

Current power saving mechanisms in the IEEE 802.16e standard are not designed to take into account silent periods in VoIP traffic. Therefore, we propose a hybrid power saving mechanism (HPSM) suitable for VoIP services with silence suppression, which basically follows the power saving class (PSC) II during talk-spurt periods, but uses the mechanism of PSC I during silent periods. The analysis and simulation results show that the proposed HPSM reduces energy consumption during silent periods while satisfying constraints on the packet drop probability imposed by VoIP services

Performance Evaluation of Opportunistic Vertical Handover Considering On–Off Characteristics of VoIP Traffic

Vertical handover is one of the key technologies to support seamless connectivity across multiple wireless communication systems and guarantee quality of service (QoS) for the applications therein. This paper proposes an opportunistic vertical handover scheme for a voice over Internet Protocol (VoIP) connection that makes use of the on-off characteristics of voice traffic by aligning the mutual silence period of the two parties engaged in conversation with the service disruption time that occurs during the vertical handover procedure. From the six-state Brady model, we derive a simplified two-state Markov model in which the characteristics of both the talk-spurt period and the mutual silence period are obtained. We then analyze the performance of the proposed scheme with respect to the handover execution time and the packet loss time. The analysis and simulation results show that the proposed scheme significantly decreases the VoIP packet loss time, whereas the total time required for the vertical handover procedure increases but remains within a tolerable time limit.

Energy-Efficient Probabilistic Routing Algorithm for Internet of Things

In the future network with Internet of Things (IoT), each of the things communicates with the others and acquires information by itself. In distributed networks for IoT, the energy efficiency of the nodes is a key factor in the network performance. In this paper, we propose energy-efficient probabilistic routing (EEPR) algorithm, which controls the transmission of the routing request packets stochastically in order to increase the network lifetime and decrease the packet loss under the flooding algorithm. The proposed EEPR algorithm adopts energy-efficient probabilistic control by simultaneously using the residual energy of each node and ETX metric in the context of the typical AODV protocol. In the simulations, we verify that the proposed algorithm has longer network lifetime and consumes the residual energy of each node more evenly when compared with the typical AODV protocol.

An optimal power-saving class II for VoIP traffic and its performance evaluations in IEEE 802.16e

A power-saving mode (PSM) is a commonly used method for reserving the energy of a mobile station (MS) in wireless networks. Recently, a new attempt has been made to apply a PSM to real-time traffic such as Voice over IP (VoIP) traffic. This paper investigates the methodology on the use of PSM for a VoIP connection in the context of IEEE 802.16e standard. Based on the network delay model, we develop an algorithm for finding the most energy-efficient length of sleep interval while satisfying the given delay constraint of the end-to-end VoIP connection. The performance of the proposed algorithm is numerically evaluated with respect to the packet buffering delay in the base station (BS) and the energy consumption of an MS. The results provide a guideline for deciding the sleep interval length for VoIP connections and show the trade-off between the energy consumption of an MS and the packet buffering delay in the BS.

On the use of a power-saving mode for mobile VoIP devices and its performance evaluation

The widespread use of mobile devices in the IP network has lead to a new attempt to apply a power-saving mode (PSM) to real-time traffic such as Voice over IP (VoIP). This paper evaluates the performance of the PSM when the PSM is used for VoIP services of mobile devices. Taking the activity of each conversational party into account, we consider two different kinds of PSMs: one is employed during the talk-spurt periods and the other is employed during the mutual silence periods of two conversational parties. The performance of each PSM is analyzed with respect to buffering delay, the probability of packet drop, and power consumption of a mobile VoIP device. Thereafter, the maximum bound of sleep interval in each period is derived, which minimizes the power consumption of the mobile device without violating the quality-of-service (QoS) of VoIP. In the various network environments, the analysis and simulation results show that the proposed PSM for VoIP significantly decreases the power consumption while satisfying the end-to-end delay and packet drop probability constraints of a VoIP connection.

Distributed Transmit Power Control for Maximizing End-to-End Throughput in Wireless Multi-hop Networks

Wireless multi-hop networks have a solidarity property, in which each multi-hop link interferes mutually and so an increase in one link’s rate results in a decrease of the other links’ rate. In a multi-hop link, the end-to-end throughput between a source and destination is restricted by the lowest link rate, so the max-min fair allocation on the link rates is an optimal strategy to maximize the end-to-end throughput. In this paper, we verify that if the wireless links have a solidarity property, the max-min fair allocation has all link rates equal, so we propose a transmit power control (TPC) algorithm that decides the transmit power of multi-hop nodes to equalize all link rates. The proposed algorithm operates in a distributed manner, where each node averages the recognized link rates around itself, allocates its transmit power to achieve this average rate, and iterates this operation until all link rates become equal. Intensive simulation shows that the proposed TPC algorithm enables all link rates to converge on the same value, and thus maximizes the multi-hop end-to-end throughput while decreasing the power consumption of multi-hop nodes.

Analysis of Tradeoff Between Energy Consumption and Activation Delay in Power Management Mechanisms

Power management mechanisms (PMMs) inherently have a tradeoff between the energy consumption and delay. In this letter, we analyze an active-idle state transition mechanism for power-saving in mobile stations by considering the general traffic pattern of smartphones, which consists of uplink request packets and downlink bursty data. We derive closed-form solutions of both the energy consumption and activation delay, and characterize their tradeoff relationship. The results show that the tradeoff curve is linear and its slope is not affected by the PMMs operational parameters or the traffic arrival rate.

Dual power-saving modes for voice over IP traffic supporting voice activity detection

In the context of the IEEE 802.16e standard, a dual power-saving mode (DPSM) algorithm for voice over IP (VoIP) traffic whose voice codec supports voice activity detection is proposed. The proposed algorithm utilises the inactivity of the voice codec of each conversing party during mutual silence periods. Using the suggested method, the length of the sleep intervals varies during mutual silence periods, while during talk-spurt periods it is fixed according the VoIP packet generation ratio. The performance of the proposed DPSM algorithm for the average packet-buffering delay in the base station (BS) and the energy consumption of a mobile station (MS) is evaluated numerically and validated with the aid of computer simulation. The results show that when the proposed combined method is used, the energy consumption of an MS is considerably less when a PSM that only uses sleep intervals of a fixed length is operating. This improvement in performance comes at the cost of greater packet-buffering delay in the BS.

A Bioinspired Fair Resource-Allocation Algorithm for TDMA-Based Distributed Sensor Networks for IoT

Many studies on distributed resource-allocation algorithms have been conducted recently because of the increasing number of network nodes and the rapidly changing network environments in the Internet of Things (IoT). In this paper, we propose the multihop DESYNC algorithm, which is a bioinspired Time Division Multiple Access- (TDMA-) based distributed resource-allocation scheme for distributed sensor networks. We define a detailed frame structure for the proposed multihop DESYNC algorithm and a firing message, which acts as a reference for resource allocation. In addition, operating procedures for resource allocation and collision detection avoidance under multihop DESYNC are explained. Simulations show that multihop DESYNC effectively resolves the hidden-node problem and that it fairly shares resources among nearby nodes in multihop networks. Moreover, it achieves better performance than the CSMA/CA algorithm in terms of channel reuse gain and average throughput.

Performance Evaluation of Vehicle-mounted Mobile Relay in Next Generation Cellular Networks

Compared to nomadic and fixed relay stations, vehicle-mounted mobile relay stations show different characteristics caused by the time-variant topology, due to their mobility. Especially, a relay mounted in a vehicle is differentiated from nomadic or fixed relay by the restricted distance between the relay and associated mobile station and the variable density of relay deployment in a cell. In this paper, we identify the characteristics of vehicle-mounted mobile relay stations and provide some parameters that highly influence the performance of vehicle-mounted relay. Through simulation, we measure the effect of relay density, zone ratio, relay transmission power, and frame transmission mode on the performance of vehicle-mounted relay. The results show that the performance of vehicle-mounted relay is highly susceptible to the above vehicle-mounted relay-specific parameters.