Sung-Guk Yoon

Opportunistic Routing for Smart Grid With Power Line Communication Access Networks

Power line communications (PLCs) have recently absorbed interest in the smart grid since they offer communication capability in an easy and simple deployment. The main role of PLC access network (PLC-AN), which is constructed with medium and low voltage distribution networks, is to exchange control signals between substations and end users or to provide the Internet access to homes. Since a transmission signal of narrowband PLC penetrates electronic devices, a use of opportunistic routing (OR) can be a viable option in PLC-AN design. In this paper, we investigate the feasibility of OR use in PLC-AN and propose a customized OR for it, named PLC-OR, which uses static geographical information. For doing this, we formulate a bit-meter per second maximization problem and solves it in a distributed manner. Through simulations, we confirm that our proposed PLC-OR successfully reduces packet transmission time compared to the traditional sequential routing while achieving the same level of reliability in packet delivery.

Adaptive TXOP Allocation Based on Channel Conditions and Traffic Requirements in IEEE 802.11e Networks

IEEE 802.11e has established a new access mechanism called the hybrid coordination function (HCF) as a step toward provisioning quality-of service (QoS) support. In this mechanism, a simple HCF scheduler is introduced to take the QoS requirements of admitted flows into account and allocate transmission opportunities (TXOPs), which is the time under which a station (STA) can send its burst of data packets, to STAs. Although many approaches have been taken to address the mechanisms inherent problems, unsubstantial effort has been afforded in tackling a channel-aware allocation mechanism. An STA can be in either the good or bad channel state in any feasible data rate, which can be modeled as a Markov chain of two states for each data rate. In view of this, we propose a mechanism of adaptive TXOP allocation that is applicable to existing scheduling algorithms. Our method works in accordance with channel and traffic conditions and complies with the link adaptation mechanism. Extensive simulation results verify that our method shows improved performance while ensuring long-term fairness among STAs and being adaptive to the channel conditions and underlying physical transmission rates.

Stackelberg-Game-Based Demand Response for At-Home Electric Vehicle Charging

Consumer electricity consumption can be controlled through electricity prices, which is called demand response. Under demand response, retailers determine their electricity prices, and customers respond accordingly with their electricity consumption levels. In particular, the demands of customers who own electric vehicles (EVs) are elastic with respect to price. The interaction between retailers and customers can be seen as a game because both attempt to maximize their own payoffs. This study models an at-home EV charging scenario as a Stackelberg game and proves that this game reaches an equilibrium point at which the EV charging requirements are satisfied, and retailer profits are maximized when customers use our proposed utility function. The equilibrium of our game can vary according to the weighting factor for the utility function of each customer, resulting in various strategic choices. Our numerical results confirm that the equilibrium of the proposed game lies somewhere between the minimum-generation-cost solution and the result of the equal-charging scheme.

Regrouping algorithm to alleviate the hidden node problem in 802.11ah networks

An IEEE 802.11ah network has been designed to service a wide range of sensor network applications where a single access point (AP) covers a transmission range of up to 1źkm and needs to support more than 8000 nodes. As a result, it has much more hidden node pairs compared to conventional 802.11a/b/g/n/ac networks. In addition, since nodes in power saving mode wake up simultaneously to send frames after receiving a beacon frame from the AP, the hidden node problem can become worse, resulting in frequent packet collisions and performance degradation. The 802.11ah standard proposes a group-based contention scheme to resolve the performance degradation problem, but it cannot resolve it appropriately.In this paper, we analyze the harmful impact of the hidden node problem on network performance and propose a new grouping algorithm to alleviate the performance degradation. Our proposed hidden matrix based regrouping (HMR) algorithm first finds hidden node pairs, and generates a hidden node matrix accordingly. Then it regroups hidden nodes to alleviate the hidden node problem using the hidden node matrix. Through extensive simulations, we show that our HMR algorithm eliminates most of hidden node pairs, thereby improving the performance of the 802.11ah network significantly in terms of the number of hidden node pairs and power-save poll (PS-Poll) transmission end time.

Multichannel CSMA/CA Protocol for OFDMA-Based Broadband Power-Line Communications

Channel response and noise in the in-home power-line channel are time varying, and show periodic patterns since electric devices, which are major noise sources, synchronously run with the ac-line cycle. Using the relatively stable channel characteristic of the power line, orthogonal frequency-division multiple access (OFDMA) schemes in power-line communications (PLCs) can achieve multiuser diversity gain even in random access. In this paper, we propose a carrier-sense multiple access with a collision-avoidance (CSMA/CA) protocol for OFDMA-based broadband PLC. To achieve the maximum diversity gain, we formulate a utility maximization problem for our considered framework. Then, we solve this problem by dividing it into two subproblems. The first one divides the whole bandwidth into a certain number of subchannels appropriately, and then the second one allocates a subchannel to each node according to the channel condition. To solve each subproblem, we first consider optimal algorithms and then heuristic algorithms to overcome the complexity. Through extensive simulations, we show that our proposal greatly improves the overall system utility compared to the single-channel CSMA/CA scheme. The performance improvement of our proposal over the single channel scheme is mainly achieved by lowering collision probability and exploiting multiuser diversity.

A New Low-Cost Centralized MPPT Controller System for Multiply Distributed Photovoltaic Power Conditioning Modules

In this paper, an integrated maximum power point tracking (MPPT) controller system using a ZigBee wireless communication module is proposed for multimodal power converters as a concept of an intelligent photovoltaic (PV) module of PV power conditioning systems. The proposed scheme can integrate all information under a single host controller to realize low-cost manufacturing. It can also simplify the monitoring and supervision processes through machine-to-machine communications for the smart-grid. The voltage and current information for each module are periodically sampled and transferred to the central inverter (or another host server) through the ZigBee module. After the transmission process, the MPPT control algorithm derives each of the PV voltage reference parameters to return to each PV module accordingly. The technical benefits of the proposed approach is the configuration of a PV-controller system composed of a single digital-signal processor (DSP), low-cost analog controllers, and some mandatory communication peripherals used to monitor the distributed multimodules. Also, the method is quite desirable for supervision and monitoring of the overall system due to its centralized control structure. For the experimental validation of the proposed MPPT control, multiple ZigBee (XBee-PRO series) modules, as well as a DSP, dual-module solar simulators, and a couple of 50 W dc-dc power conversion hardware prototypes were utilized.

Adaptive Rate Control and Contention Window-Size Adjustment for Power-Line Communication

Even though the power line is a wired medium, its channel characteristics are very different from that of conventional wired media, such as telephone and Ethernet as it is not designed for communications. Some characteristics of the power-line channel are that of the wireless channel, so most power-line communication (PLC) schemes use the carrier-sense multiple access with collision-avoidance protocol, which is popular in wireless communications, for random access. In addition, the power-line channel has some characteristics that are absent in wired and wireless channels. In this paper, we design a new PLC media-access control (MAC) protocol considering two different types of power-line noise models: 1) impulsive noise (generated by on-off switching of electronic devices) and 2) background noise. When a transmission error occurs, the transmitter in our proposal adjusts its transmission rate according to the receivers feedback and determines the contention-window size appropriately according to the current loading. Through extensive simulations, we verify that our proposed MAC scheme improves network throughput under various scenarios.

Priority Inversion Prevention Scheme for PLC Vehicle-to-Grid Communications under the Hidden Station Problem

Power line communication (PLC) has been selected by ISO/IEC 15118 as standard technology for vehicle-to-grid communication. Communication traffic to charge an electric vehicle should have a higher priority than normal traffic in order to improve the reliability and delay performance. To this end, HomePlug Green PHY, which is a standard PLC defined in ISO/IEC 15118, provides such a priority resolution scheme. However, when there is a hidden station with respect to the high-priority station, the priority resolution scheme does not operate properly, resulting in a higher delay or losses of high-priority traffic. This paper briefly analyzes the priority inversion probability under the hidden station problem and proposes a priority inversion prevention scheme. The adverse effect of the priority inversion problem is demonstrated through a numerical analysis and extensive simulations. We also show that our proposed scheme not only solves the problem but also improves the performance of the other stations.

Energy-efficient opportunistic scheduling schemes in wireless networks

Exploiting the multiuser diversity in wireless networks has a fundamental tradeoff between throughput and energy saving. To balance the tradeoff, we reconsider the opportunistic scheduling in the aspect of energy saving, and propose a new energy-efficient opportunistic (EEFO) scheduling. Our goal is to maximize the performance of bits per energy unit under the constraint of fair resource allocation, and EEFO scheduling achieves it by controlling the number of users participating in the channel feedback. Through simulations, we show that EEFO scheduling is able to transmit significantly more amount of traffic compared to the competitive schemes under the given energy constraint.

Q-BT: Queue-Based Burst Transmission Over an Asynchronous Duty-Cycle MAC Protocol

In this letter, we tackle the channel contention and hidden terminal problems of asynchronous duty-cycle MAC protocols under heavy traffic scenario. To resolve the problems, we design a queue-based burst transmission MAC protocol (Q-BT), which couples burst (and fast) transmission and asynchronous duty-cycle features together by using queue length information. We evaluate its performance in a multihop testbed, which shows that our proposal improves packet reception ratio and duty-cycle performance by 70.2% and 59.1%, respectively, at a maximum compared to BoX-MAC (i.e., the default MAC in TinyOS).