Sangdeok Kim

Two-Dimensional ESPRIT-Like Shift-Invariant TOA Estimation Algorithm Using Multi-Band Chirp Signals Robust to Carrier Frequency Offset

In this paper, a two-dimensional (2-D) ESPRIT-like shift-invariant time-of-arrival (TOA) estimation (ELSITE) algorithm for multi-band chirp signals in the presence of a carrier frequency offset (CFO) is presented. For the shift invariant TOA estimation, the received signals must be transformed into a sinusoidal form. When the received signals are perturbed by a CFO, the frequency of the transformed sinusoids is also shifted such that the TOA estimation results are biased. The TOA-induced phase shift of the multi-band chirp signals is determined according to the parameters of the signal, while the CFO-induced phase shift is only proportional to the elapsed time. Based on this property, the proposed ELSITE algorithm achieves robust TOA estimation against CFO from the signal subspace of the stacked matrix. The root mean square error of the proposed algorithm was analyzed and verified in both an AWGN channel and a multipath channel with CFO via Monte-Carlo simulations.

An efficient non-line-of-sight error mitigation method for TOA measurement in indoor environments

In this paper, we propose an efficient non-line-of-sight (NLOS) error mitigation method for TOA measurement in indoor environments. In order to meet era of ubiquitous computing, there is a developing need for an accurate real-time locating system (RTLS). In the presence of a NLOS error, the location estimation performance is likely to be degraded. For effective location estimation, NLOS errors should be recognized and mitigated before measurements are used in conventional location estimation method such as non-linear least squares (NLS), linear least squares (LLS), weighted-linear least squares (WLS), and least median squares (LMS). For improve location estimation, we assumed that measured distances using weighing mitigation factor are exploited for location estimation. Through simulation results, theoretical analysis of the performance is demonstrated.

An efficient TDOA-Based localization algorithm without synchronization between base stations

An efficient localization algorithm is proposed by utilizing the time difference of arrival (TDOA) without synchronization between base stations. Generally, a TDOA-based localization algorithm requires synchronization between base stations in order to improve the accuracy of localization. Hence, correlations using wideband signals or wire connections between base stations have been used to synchronize the base stations; however, these approaches result in additional operating costs. Thus, the proposed algorithm does not require synchronization between base stations. The TDOA equations are derived by continuously varying the locations of the source and the location of a base station. The number of packets necessary for localization is also reduced. The localization performance of the proposed algorithm is verified with Monte-Carlo simulations.

Thermal aware clock tree optimization with balanced clock skew in 3D ICs

Thermal issues are a primary concern in the three-dimensional integrated circuit (3D IC) design. This paper addresses a clock tree synthesis problem under thermal variation for 3D IC designs. Our major contributions are the reduced and balanced skew with minimum wirelength under both nonuniform and uniform thermal conditions. Our proposed clock tree synthesis algorithms search the routing path to find the clock merging point at each level of the clock tree. Experimental results show that our methods significantly reduce and balance clock skew values with the minimum wirelength overhead.

Robust self-cancellation-based time-of-arrival estimation algorithm to carrier frequency offset for bi-directional chirp signals

This study presents a robust self-cancellation-based time-of-arrival (TOA) estimation algorithm against carrier frequency offset (CFO). The proposed algorithm is developed to exploit the up and down chirp of bi-directional chirp signals. Using the relationship between the phase shifts of the transformed signals of the up and down chirp symbols, the CFO-induced error of the TOA estimates can be cancelled without pre-estimation and compensation through the proposed method. The root mean squared error of the proposed algorithm is analysed and verified through simulations in an additive white Gaussian noise and multi-path channel in the presence of CFO.

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 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%.

A Novel TDOA-Based Localization Algorithm Using Asynchronous Base Stations

In this paper, a novel localization algorithm is proposed by utilizing the time difference of arrival (TDOA) with asynchronous base stations. Generally, a TDOA-based localization algorithm requires synchronization between base stations. Hence, correlations using wideband signals or wire connections between base stations have been used to synchronize the base stations; however, these approaches result in localization error by synchronization error between base stations. Thus, the proposed algorithm does not require synchronization between base stations. The TDOA equations of proposed algorithm are derived by continuously varying the locations of the mobile station and the location of a base station. Localization procedure is also reduced. The localization performance of the proposed algorithm is verified with Monte-Carlo simulations.

Chirp spread spectrum transceiver design and implementation for real time locating system

A chirp spread spectrum (CSS) transceiver architecture for IEEE 802.15.4a is proposed and implemented. In the transmitter, the size of the read-only memory that stores CSS signal samples for the chirp modulator is reduced by removing duplicate samples among subchirps. In the receiver, a matched filter is utilized to remove the other band noise caused by the band hopping property of CSS. A robust time synchronizer and chirp demodulator based on the matched filter are proposed. Low complexity architectures of the matched filter and biorthogonal decoder are also proposed. All of the proposed architectures are implemented in the field-programmable gate array chip and verified.

TOA Estimation Algorithm Based on Shift-Invariant Technique for Multi-band Signals

This paper proposes a new TOA estimation algorithm based on shift invariant structure for multi-band signals. The performance of the proposed method is compared with Cramer-Rao lower bound (CRLB) and the conventional algorithms such as MUSIC, matrix pencil, TLS-ESPRIT in additive white Gaussian noise (AWGN) and multipath channel.