Jae Yeol Ha

An Enhanced CSMA-CA Algorithm for IEEE 802.15.4 LR-WPANs

Two mechanisms are proposed to enhance throughput and energy efficiency of IEEE 802.15.4 CSMA-CA. The first one is an enhanced collision resolution (ECR) mechanism that adjusts the backoff exponent (BE) based on both consecutive clear channel assessment (CCA) busy results and a packet transmission. The second one is an enhanced backoff (EB) mechanism that shifts the range of backoff counters by utilizing the CCA outcome. The simulation results demonstrate that the proposed mechanisms significantly enhance both throughput and energy efficiency of IEEE 802.15.4

EHRP: Enhanced hierarchical routing protocol for zigbee mesh networks ee

This letter proposes the enhanced hierarchical routing protocol (EHRP) for ZigBee mesh networks. The EHRP finds the shortest hierarchical path based on the ZigBee hierarchical addressing scheme. The EHRP provides efficient and reliable routing paths. In addition, the EHRP is completely compatible with ZigBee v.1.0 standard. Simulation results demonstrate that the EHRP reduces routing overhead and route discovery delay of ZigBee mesh networks significantly compared with the hierarchical routing protocol (HRP) defined in ZigBee v1.0.

DCA: Duty-Cycle Adaptation Algorithm for IEEE 802.15.4 Beacon-Enabled Networks

In this paper, a new duty-cycle adaptation algorithm is proposed for IEEE 802.15.4 beacon-enabled networks. We modify the reserved frame control field in the MAC layer header to deliver the end devices buffer occupancy and queueing delay. A MAC status index is proposed to represent the queue occupancy and queueing delay. Based on the proposed MAC status index, the coordinator estimates the number of packets in the end devices and control duty-cycle adaptively. Simulation results show that the proposed algorithm decreases the packet drop and increases energy efficiency

Improving Spectral and Temporal Efficiency of Collocated IEEE 802.15.4 LR-WPANs

The number of frequency channels specified for IEEE 802.15.4 low-rate wireless personal area networks (LR-WPANs) does not suffice to operate a variety of collocated WPAN applications that the standard is targeting. To overcome this limit, we introduce virtual channel, a novel concept to increase the number of available channels by efficiently managing given spectral and temporal resources. A virtual channel is created by scheduling a superframe and selecting a logical channel. This extends the notion of a channel from spectral domain to spectral and temporal domain. Specifically, we propose a superframe scheduler using throughput estimation (SUTE) of the IEEE 802.15.4 carrier sense multiple access with collision avoidance (CSMA/CA). In addition, nearest vacancy search (NEVS) is proposed, both of which are for temporal efficiency of the collocation. For both spectral and temporal efficiency, virtual channel selector (VCS) is proposed. The simulation results show that a remarkable improvement on the collocation efficiency of IEEE 802.15.4 can be achieved by our proposals. Moreover, this study also reveals the fundamental drawback of the current standard in terms of the collocation efficiency that the beacon interval and superframe duration are adjustable only by exponent parameters.

Virtual channel management for densely deployed IEEE 802.15.4 LR-WPANs

The number of channels specified for IEEE 802.15.4 low-rate wireless personal area networks (LR-WPANs) is too few to operate many applications of WPANs in the same area. To overcome this limit, we introduce virtual channel, a novel concept to increase the number of available channels when various WPAN applications coexist. A virtual channel is basically created via superframe scheduling within the inactive periods in a logical channel preoccupied by other WPANs. To maximize the coexistence capability of WPANs using virtual channels, we propose (1) least collision superframe scheduler (LC-scheduler), (2) less complex heuristics, and (3) virtual channel selector (VCS) to efficiently manage multiple available logical channels. In addition, a simple but practical synchronization method is developed to compensate different time drifts among coexisting WPANs. The simulation results demonstrate that a remarkable improvement on the coexistence capability of the 802.15.4 can be achieved through the proposed schemes

ECAP: A Bursty Traffic Adaptation Algorithm for IEEE 802.15.4 Beacon-Enabled Networks

In IEEE 802.15.4 beacon-enabled networks, the length of active periods should be configured appropriately in order to save energy and accommodate traffic. This paper proposes ECAP, a bursty traffic adaptation algorithm for IEEE 802.15.4 beacon-enabled networks. To accommodate bursty traffic, the proposed algorithm is designed to extend the active periods dynamically based on the requests from devices. The simulation results show the performance enhancement in terms of end-to-end delay and energy consumption per packet transmission

Design and Implementation of Convergence sub-layer for a Heterogeneous Home Network

In this paper, a heterogeneous home network is designed and implemented using power line communications and IEEE 802.15.4. This paper presents the need of the heterogeneous home network in which IEEE 802.15.4 compensates for limitations of PLC based home networks. The convergence sub-layer (Cs-layer) is designed and implemented to enable a heterogeneous home network on the power line communication modem with IEEE 802.15.4 communication module. The main functions of Cs-layer are medium information management and medium selection. We built a test-bed and conducted experiments. Implementation and experimental results validate the feasibility of the Cs-layer to extend the PLC based home network to the heterogeneous home network.

Near-ultrasound communication for TV's 2nd screen services

In this paper, we propose a near-ultrasound chirp signal-based communication for the TVs 2nd screen services. While near-ultrasound (with under 20 kHz frequency) communication has been developed for various applications recently, none of the previous work provides a perfect solution for 2nd screen services between TVs and smart devices. This is due mainly to the following real world challenges. The embedded signal in TV contents should be successfully received in a typical TV-watching environment by (i) delivering information at least at 15 bps with significantly low volume to avoid human perception, (ii) despite the presence of ambient noise, e.g., a tick, a snap, or a knock. To fulfill (i), we design chirp quaternary orthogonal keying (QOK) symbols. Especially, we aim to minimize inter-symbol interference (ISI) effects by symbol design in order to completely eliminate guard intervals. To resolve (ii), we propose the novel J-shape detection algorithms for both frame synchronization and carrier sensing. The proposed modem achieves almost zero frame error rate on a smartphone 2.7 m away from the TV even with minimal receive sound pressure level of 35 dBSPL, i.e., the noise level in a very quiet room. Moreover, throughout experiments and log analysis of 2nd screen service deployed in a nation-wide TV broadcasting system, J-shape detection algorithms are proven to achieve highly resilient performance for both frame synchronization and carrier sensing compared to previous schemes.

Design and Implementation of Monitoring Software for Heterogeneous Control Network

XCP (extended control protocol) is an information oriented protocol which delivers information with high reliability according to the predefined rule. XCP network system can be implemented on top of several physical layer such as power line, IEEE 802.15.4 and so on. In this paper, a monitoring software that evaluates the reliability and performance of the XCP network is designed and implemented. This paper presents the structure and method of the packet monitoring in the network through several interfaces such as RS-232, ethernet. The feasibility of the implemented software is verified through the experimental evaluation.

Throughput and optimal ATIM window of IEEE 802.11 distributed coordination function in power saving mode

This paper analyzes the throughput and the optimal announcement traffic indication message (ATIM) window of the IEEE 802.11 Distributed Coordination Function (DCF) in the power saving mode. An analytical model based on Markov chain model is proposed to express the throughput and the optimal ATIM window in a mathematical form; it is validated by the simulation. The optimal ATIM window size is obtained to maximize the throughput and minimize the power consumption while solving the fairness problem.