Yeong-Sam Kim

Hybrid RSS/TOA wireless positioning with a mobile anchor in wireless sensor networks

In this paper, we propose a novel hybrid RSS/TOA positioning algorithm with a mobile anchor, which follows a spiral trajectory to cover the whole region of the wireless sensor networks (WSN). The conventional time of arrival (TOA) positioning algorithms have two considerable accuracy problems. Firstly, as the distance between the reference node and the sensor increases, its accuracy is degraded gradually. Secondly, when an obstacle exists between the reference node and the sensor, its accuracy is degraded greatly. In our proposed algorithm, the mobile anchor, which plays the same role as the reference node, moves on a spiral trajectory and transmits its signal periodically. The received signal strength (RSS) is utilized by the sensor not only to compute whether it is closed enough to the mobile anchor or not but also to distinguish the obstacle. As a result, the measurement range of the TOA ranging process is restricted within the interval of two adjacent spiral curves. Under the circumstance that no obstacle exists between the mobile anchor and the sensor, the TOA ranging process and the proposed two-step positioning calculation are operated to estimate the position of the sensor accurately. Simulations are performed to compare the performance of the proposed hybrid RSS/TOA positioning algorithm with the performance of the conventional TOA least square estimating positioning algorithm (TOA_LSE). Simulation results show that the average positioning error is reduced by 48.2% and the standard deviation of the positioning errors is reduced by 71.3%.

Robust and Accurate Packet Detection and Frequency Offset Compensation for CSS System

In this paper, we propose a new robust packet detection and frequency offset compensation structure for IEEE 802.15.4a chirp spread spectrum (CSS) which is a standard for wireless personal area network (WPAN). The proposed structure takes benefits of both cross- and auto-correlation. Cross-correlation is useful to remove additional side band noise in the CSS system and to find sharp peaks among filtered output values. In addition, we use the auto-correlation in order to suppress the effect of frequency offset and the initial channel phase. Simulation results show that the proposed procedure is robust to the frequency offset, and can detect the presence of a signal in very low signal to noise ratio (SNR).

Dual-band automatic gain control algorithm for chirp spread spectrum over indoor fading channels

In this paper, we propose a novel automatic gain control (AGC) algorithm as a solution to improve the signal reception performance based on the IEEE 802.15.4a chirp spread spectrum (CSS) over indoor fading channels. The CSS signals are composed of low-band and high-band signals whose frequency characteristics are different because of multipath fading in indoor environment. It is not appropriate to apply only one conventional AGC which regardless of the different bands, where the received signals are contaminated by quantization noise or clipped. The proposed AGC algorithm is based on two AGCs which are designed to be matched well with low-band and high-band signals separately.

Two-step automatic gain control algorithm applicable to chirp spread spectrum device

In this paper, we propose a novel automatic gain control (AGC) algorithm, which is applicable to a commercially available chirp-spread-spectrum (CSS) device. Because of the property of long guard time in the CSS, it is difficult to make use of the conventional AGC algorithm which only uses one window size to estimate the power of signal. Due to using only one window size, there is a tradeoff between adaptation time and stability. The proposed AGC algorithm synthetically utilizes large window size and small window size, simultaneously improving the performance of adaptation time and stability.

A new filtering method for chirp spread spectrum

In this paper, we propose a new filtering method for performance enhancement of chirp spread spectrum (CSS) in the IEEE 802.15.4a standard. The CSS signals are composed of low- and high-band signals which are alternatively transmitted in time-domain. A new dual-band filtering method proposed in this paper is based on two filters which are designed to be suitable for alternatively received CSS signals and it excludes undesired neighboring band noise. Simulation result shows that the proposed method has better bit error rate (BER) performance than the conventional one.

Efficient implementation of hybrid automatic gain control algorithm for chirp spread spectrum

In this paper, we propose a novel hybrid automatic gain control (AGC) algorithm as a solution to improve the signal reception performance based on the IEEE 802.15.4a chirp spread spectrum (CSS). The CSS signals are composed of a number of full-chirps, which are separated by long guard time. A full-chirp is composed of two low-band sub-chirps and two high-band sub-chirps whose frequency characteristics are different because of multipath fading in indoor environment. Due to long guard time and wideband properties of the CSS, it is not appropriate to make use of conventional AGC algorithm which only uses one window size in order to estimate the power of signal and regardless of the different bands. The proposed hybrid AGC algorithm is made up of two steps: the first step is synthetically to utilize large window size and small window size, simultaneously improving performance of adaptation time and stability; the second step is based on two AGCs which are designed to be matched well with low-band and high-band signals separately.