Seungku Kim

Link-State-Estimation-Based Transmission Power Control in Wireless Body Area Networks

This paper presents a novel transmission power control protocol to extend the lifetime of sensor nodes and to increase the link reliability in wireless body area networks (WBANs). We first experimentally investigate the properties of the link states using the received signal strength indicator (RSSI). We then propose a practical transmission power control protocol based on both short- and long-term link-state estimations. Both the short- and long-term link-state estimations enable the transceiver to adapt the transmission power level and target the RSSI threshold range, respectively, to simultaneously satisfy the requirements of energy efficiency and link reliability. Finally, the performance of the proposed protocol is experimentally evaluated in two experimental scenarios-body posture change and dynamic body motion-and compared with the typical WBAN transmission power control protocols, a real-time reactive scheme, and a dynamic postural position inference mechanism. From the experimental results, it is found that the proposed protocol increases the lifetime of the sensor nodes by a maximum of 9.86% and enhances the link reliability by reducing the packet loss by a maximum of 3.02%.

RSSI/LQI-Based Transmission Power Control for Body Area Networks in Healthcare Environment

This paper presents a novel transmission power control protocol for body area networks. Conventional transmission power control protocols adjust the transmission power on the basis of the received signal strength indication (RSSI). However, in the case of presence of interference, the RSSI is not a correct indicator to determine the link state. We first present empirical evidence for this and then propose a practical protocol to discriminate between the signal attenuation and interference using the RSSI and link quality indication. This protocol controls the transmission power and avoids interference based on the link state. Finally, we discuss the implementation of the proposed protocol on Tmote Sky and evaluate the performance in the presence and absence of interference. The experimental results showed that the proposed protocol has high energy efficiency and reliability, even in the presence of interference.

A Beacon Interval Shifting Scheme for Interference Mitigation in Body Area Networks

This paper investigates the issue of interference avoidance in body area networks (BANs). IEEE 802.15 Task Group 6 presented several schemes to reduce such interference, but these schemes are still not proper solutions for BANs. We present a novel distributed TDMA-based beacon interval shifting scheme that reduces interference in the BANs. A design goal of the scheme is to avoid the wakeup period of each BAN coinciding with other networks by employing carrier sensing before a beacon transmission. We analyze the beacon interval shifting scheme and investigate the proper back-off length when the channel is busy. We compare the performance of the proposed scheme with the schemes presented in IEEE 802.15 Task Group 6 using an OMNeT++ simulation. The simulation results show that the proposed scheme has a lower packet loss, energy consumption, and delivery-latency than the schemes of IEEE 802.15 Task Group 6.

An Adaptive Beaconing MAC Protocol Providing Energy-Efficient Healthcare Service

We present an Adaptive Beaconing Medium Access Control (AB-MAC) protocol based on time division multiple access (TDMA) in order to provide healthcare services. The purpose of our protocol is to gain not only energy-efficiency but also provide low delivery latency when both periodic data and event-driven data are present. In order to satisfy these requirements, we propose standby slots that are deployed during each beacon interval. The standby slots are able to identify unscheduled data with low delivery latency. An adaptive beacon is then provided that quickly reschedules the time slots. Furthermore, the AB-MAC asymmetrically assigns energy consumption to a coordinator instead of the sensor nodes when possible in order to reduce sensor node energy waste. In this paper, we analyze the IEEE 802.15.4 and the AB-MAC, and evaluate their energy consumption and delivery latency. NS-2 simulations are used to validate the numerical analysis. The evaluation results indicate that the AB-MAC is a more suitable protocol than the IEEE 802.15.4 when used in WBANs.

Flexible beacon scheduling scheme for interference mitigation in body sensor networks

This paper investigates the issue of interference mitigation in body sensor networks (BSNs). IEEE 802.15 Task Group 6 presented several schemes to reduce interference, but these are still not proper solutions for BSNs. We present a novel distributed TDMA-based flexible beacon scheduling scheme that reduces interference among the BSNs. A design goal of the scheme is to avoid the wakeup period of each BSN coinciding with other networks by employing carrier sensing before a beacon transmission. We analyze the flexible beacon scheduling scheme and investigate the proper back-off length when the channel is busy. We compare the performance of the proposed scheme with the schemes of IEEE 802.15 Task Group 6 using an OMNeT++ simulation. The simulation results show that the proposed scheme has a lower packet loss, energy consumption, and delivery-latency than the schemes of IEEE 802.15 Task Group 6.

A robust and space-efficient stack management method for wireless sensor network OS with scarce hardware resources

Due to such requirements as low power consumption and low cost, sensor nodes commonly do not include advanced H/W features. The absence of the features such as the memory management unit enforces several tasks to share a memory address domain on a small data memory space (1~16 KB). It exposes each task to the stack overflow causing the corruption of other memory areas. In this paper, we propose a robust and efficient stack memory management method (RESM) that dynamically assigns and releases a preestimated amount of stack memory to each function call at runtime. RESM maintains the stack memory usage with the similar amount of the stack usage that the system actually requires, and the stack memory area of each task is individually protected from corruption by the stack overflow. RESM can also anticipate a saturated condition in data memory at runtime. When the memory state is unsafe from the saturated condition, it conditionally allows function calls to operate tasks without any memory fault by using the proposed function call deferring algorithm. From the analytical and experiment results, it is proven that the performance of RESM outperforms the other mechanisms and RESM can provide more robust stack operation environment.

Tiny module-linking for energy-efficient reprogramming in wireless sensor networks

The remote and automatic reprogramming is an indispensable part in the wireless sensor networks. Especially, the energy saving problem is an important challenge because of a limited energy characteristics. Many kinds of conventional researches about reprogramming have tried to solve the energy saving problem. But they do not consider the energy consumption model and still have inefficient memory access times. In this paper, we propose a tiny module-linking scheme. It performs module relocation to decrease program code shifts and connects the relocated module with a tiny module-linker to eliminate module caller changes. This proposed scheme reduces access times to Electrically Erasable Programmable Read-Only Memory (EEPROM) and program memory during the decoding procedure of the reprogramming. Experimental results show that our scheme outperforms the previous reprogramming schemes in terms of the energy consumption.

Distributed Transmission Power Control for Network Programming in Wireless Sensor Networks

In wireless sensor networks, the necessity of network programming becomes more and more important due to the inaccessibility of the sensor nodes. Because the network programming produces a large amount of data, it consumes a great deal of energy and causes the network to suffer from much interference. Many conventional studies regarding the network programming attempted to reduce the energy consumption and the interference effect. However, they overlook transmission power effect on the energy-efficiency and the interference problem. In this paper, we present a novel network programming protocol that controls the transmission power at each sender node in a distributed manner. The protocol deals not only with the energy consumption of individual sensor node but also the network load distribution. Moreover, it reduces the interference effect on the network by decreasing the average transmission power of the sensor nodes. We verify that our protocol extends the lifetime of the sensor network and decreases the packet losses through simulation results.

Dynamic transmission power control for wireless sensor network reprogramming

In wireless sensor networks, the necessity of reprogramming becomes more and more important due to the inaccessibility of the sensor nodes. Because reprogramming produces a large amount of data, it consumes a great deal of energy and causes frequent collisions. Many conventional studies regarding reprogramming attempt to reduce the energy consumption and collisions. However, they overlook transmission power control which is highly related to energy efficiency and the collision problem. In this paper, we present a novel reprogramming scheme that uses dynamic transmission power control. The protocol deals not only with the energy consumption of each sensor node but also the network load distribution. We prove that our protocol extends the lifetime of the sensor network through OMNeT++ simulation results.