Sang-Hun Yoon

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.

Packet Detection and Symbol Timing Synchronization Algorithm for Multi-Band OFDM UWB

In this letter, we propose a novel packet detection and symbol timing synchronization algorithm for MB-OFDM UWB system over multi-path channel. To find more reliable and exact symbol timing, we utilize the merits of the auto- and cross-correlation at the same time. The auto-correlator can gather the energy of the received signal which is distorted by multipath fading. And, the cross-correlator can estimate symbol timing to sample level precision. We define the detection and symbol timing metric as the moving sum of autocorrelation of the pre-computed cross-correlated signals over zero pad duration. Simulation results show that the proposed algorithm can detect the presence of a signal with less than -4 dB SNR and find DFT window with at most 0.1 dB SNR reduction upon the receipt of two symbols.

Differentially Coherent Detection of Differentially Bi-Orthogonal Code

In this letter, we design and analyze a novel differentially coherent decision feedback structure for differentially bi-orthogonal code (DBOC). Proposed detector using decision feedback and partially maximum likelihood sequence estimation (DF-PMSE) can be applied to the DBOC detector irrespective of bi-orthogonal code length. Simulation and analyzed results show that the PER performance of the proposed detector is almost the same as that of the coherent detector for the various case of bi-orthogonal code length.

New high speed dynamic D-type flip flop for prescaler

The authors propose a new dynamic D-type flip-flop (DFF) suitable for a high speed prescaler. A prescaler and VCO are the main blocks determining the operating speed of a PLL. The PLL is important for frequency synthesis in wireless systems. Recently, the wireless frequency band has increased; therefore, higher speed of PLLs is needed. In order to increase the speed of PLLs, the prescaler and VCO must be optimized for high speed. First of all, prescaler consists of DFFs. Previous DFFs had many MOS transistors, and the more transistors flip-flops have, the slower their operating speed because of clock loads and effective capacitance. Thus, the authors reduced the effective capacitance by reducing the number of transistors to obtain a higher speed. They implemented a DFF with only 6 MOS transistors. This proposed circuit is verified by HSpice, and is implemented with 0.8 /spl mu/m CMOS technology. The proposed DFF operates up to 6.4 GHz at 5 V.

A new packet detection algorithm for IEEE 802.15.4a DBO-CSS in AWGN channel

In this paper, we propose a new packet detection algorithm for differentially bi-orthogonal chirp-spread-spectrum (DBO-CSS) over multiple piconets. Because of the band hopping property of the DBO-CSS, the conventional packet detection algorithms based on auto-correlation cannot avoid side band noise. And the conventional algorithms employed in DBO-CSS systems are not performed well over simultaneously operating piconets (SOP) because they did not consider the waveforms of signal. First, the proposed detector includes matched filters to eliminate the side band noise and to make SNR at the end of matched filters maximal. Second, the proposed detector also includes auto-correlators in order to make outputs of matched filters inphase. Finally, the proposed detector gathers the energy of all sub-chirps and employs the Permutator in order to operate regardless of piconet. Simulation results show that we can detect packets by using the proposed algorithm compared with the conventional one in about -4 dB SNR with the same miss detection probability and the false alarm probability between them.

A new freqeuncy offset estimation algorithm for DBO-CSS in multipath channels

In this paper, we propose a new frequency offset estimation algorithm for differentially bi-orthogonal chirp- spread-spectrum (DBO-CSS) which is a standard for wireless personal area network (WPAN). Because of both the long time difference between the samples of differential relations and the high permissible frequency offset and the high permissible frequency offset of the crystal oscillators between the transmitter and the receiver, there can be several integer multiples of 2pi in the phase rotation caused by the frequency offset. The integer part of the phase rotation can not be determined by the usual estimation methods based on auto-correlation. In this paper, we propose an estimation algorithm by using the relationships of each sub-chirp signals to find the integer part without the phase ambiguity. The proposed method is based on the matched filter in order to maximize the received signal-to-noise ratio (SNR) before differential demodulation. As a result, we can estimate the frequency offset without the phase ambiguity and reduce the estimation error in above constant SNR compared with the methods based on the auto-correlation in multipath channels.

Efficient structures of packet/frame synchronization in MB-OFDM UWB

The paper presents two signal detectors of low hardware complexity in MB-OFDM UWB (multi-band orthogonal frequency division multiplexing ultra wide band) systems. Since MB-OFDM UWB has 4 piconets, which are each composed of different preamble sequences, correlators execute cross-correlation with inputs and each coefficient set; therefore, existing correlators have problems of high hardware complexity. To reduce hardware complexity, we present a structure which is composed of a coefficient bank and a transposed filter. In addition to this, because of the property of preamble sequences, we provide a hierarchical structure which has coefficients of only -1 or 1. The results of simulations show that the proposed structures are superior to existing ones.

FIR digital filter implementation using flattened coefficient

In this paper, we present a new method to reduce the number of adders and registers in FIR digital filters. Few efforts have been taken for reducing the number of registers in filters, while a lot of methods have been developed to decrease the number of adders in the past decade. This paper presents a novel method to cut down the number of registers without loss of critical path delay by mixing the direct-form filter with the transversal one. Two adder-sharing structures, one for small area and the other for high data rate, are proposed. For low power consumption, each adder is shared only one time in these structures. As a result, proposed area-efficient adder-sharing structure can reduce area (15%), and power consumption (44%). Also, a new throughput efficient structure can decrease area (3%), delay (24%), and power consumption (25%).

Robust Packet Detection Algorithm for DBO-CSS

In this paper, we propose a robust packet detection algorithm for the differentially bi-orthogonal chirp-spread-spectrum (DBO-CSS). The conventional packet detection algorithms based on auto-correlation cannot avoid side band noise because of the band hopping property of the DBO-CSS. If we, therefore, use the conventional packet detection algorithms in the DBO-CSS, the performance degradation of the packet detector will break out. First, the proposed detector includes matched filters to eliminate the side band noise. Second, the proposed detector also includes auto-correlators in order to make outputs of matched filters inphase. Finally, the proposed detector gathers the energy of all sub-chirps by the summation. When we use the Permutator, the proposed detector works regardless of piconet. Simulation results show that we can detect packets in -4 dB SNR in AWGN channel and also in 0 dB in multipath channel.

Design and Implementation of The High Speed VP (Variable Parameter)- Cubic Interpolator for The System of MB-OFDM UWB.

In this paper, we propose the structure of high throughput VP-cubic interpolator which can be applied to the system of MB-OFDM UWB (multi-band orthogonal frequency division multiplexing ultra wide band). In spite of the simpler implementation than Lagrange interpolator as in L. Erup et al., (1993), the performance of VP-cubic interpolator is approximately same as Lagrange interpolator as in H. Zhang, (1997). And it can be applied to the applicative techniques of OFDM which are sensitive to the attenuation of main lobe edge. However the throughput of the conventional VP-cubic interpolator is lower than the system of MB-OFDM UWB. The conventional structure can not be used directly for the system of MB-OFDM UWB. So, we propose an improved VP-cubic interpolator which has high speed structure by applying the pipelining method and the parallel processing method. The critical path of proposed interpolator is reduced by the one third of conventional one. Finally, we experiment the performance of the interpolator. And the performance of the interpolator shows that the proposed structure can be successively applied to the system of MB-OFDM UWB