Van-Su Pham

Low-complexity maximum-likelihood decoder for four-transmit-antenna quasi-orthogonal space-time block code

This letter proposes a very low-complexity maximum-likelihood (ML) detection algorithm based on QR decomposition for the quasi-orthogonal space-time block code (QSTBC) with four transmit antennas, called the LC-ML decoder. The proposed algorithm enables the QSTBC to achieve ML performance with significant reduction in computational load for any high-level modulation scheme.

Design and Fabrication of ZnO-Based FBAR Microwave Devices for Mobile WiMAX Applications

In this letter, we present the design and fabrication of a novel ZnO-based film bulk acoustic wave resonator (FBAR) microwave devices. The novel FBAR devices employ a new-type of Bragg reflector with very thin chromium (Cr) layer formed between SiO2 and W films. The Cr layer seems to enhance the adhesion between SiO2 and W layers. The novel FBAR devices show good return losses (S11) and high Q-factors at the frequency range of 2.7-3.0 GHz. This approach will be very helpful for mobile worldwide interoperability for microwave access applications.

Low complexity MMSE-QRD-based ML decoder for quasi-orthogonal STBC scheme in MIMO wireless communications systems with four-transmit antennas

This work proposes a MMSE-QR decomposition-based (MMSE-QRD) low-complexity maximum-likelihood (ML) decoders for quasi-orthogonal space-time block code (QOSTBC) with 4 transmit antennas, denoted as MMSE-QRD LCML decoder. By stacking received symbols from different received symbol period together and applying QR decomposition on extended channel matrix (D. Wubben et al., 2001) resulting special format of matrix R, the proposed decoders is able to reduce complexity by decouple decoding as H. Jafarkhani (2001). In addition, by using the same principle of Minh-Tuan Le et al. (2005) to jointly detect signals, the MMSE-QRD LCML decoder is able to not only significantly reduce the computational load but also obtain ML performance

Efficient Algorithm for Blind Detection of Orthogonal Space-Time Block Codes

This letter proposes an efficient decoder for signal detection in orthogonal space-time block coded systems employing phase-shift keying modulation without channel state information at the receiver. The proposed decoder consists of a sphere decoder and a QRD-based decoder. Simulation results show that the proposed decoder enables the system to trade off performance improvement against complexity

Low Complexity Maximum-likelihood Decoder for VBLAST-STBC scheme in MIMO Wireless Communication Systems

In this work, we propose a low-complexity maximum-likelihood decoding approach based on QR decomposition (QRD) for signal detection in VBLAST-STBC systems, which employ less receive antennas than transmit antennas. With the example illustration of (6,3) system using rate 3/4 STBC for three transmit antennas, computer simulations are implemented to verify the performance and complexity of the proposed decoder

ZnO-Based Film Bulk Acoustic Resonator Devices Feasible for Worldwide Interoperability for Microwave Access Applications

In this paper, we describe a novel fabrication technique of ZnO-based film bulk acoustic resonator (FBAR) devices using a new type of multilayered Bragg reflector with very thin chromium (Cr) layers additionally formed between SiO2 and W layers. Each Cr layer is considered to enhance the adhesion between the SiO2 and W layers. The fabricated FBAR devices are shown to operate at the frequency range of 2.7 – 3.0 GHz, along with good return loss as well as high Q-factors. Furthermore, the effects of bottom electrode thickness on the FBAR device performance are also investigated and compared. This feasibility study indicates that the novel fabrication technique can be useful for future broadband mobile worldwide interoperability for microwave access (WiMAX) applications. [DOI: 10.1143/JJAP.47.6383]

Very-Low-Complexity Maximum-Likelihood Decoders for Four-Transmit-Antenna Quasi-Orthogonal Space-Time Code

This letter proposes two very-low-complexity maximum-likelihood (ML) detection algorithms based on QR decomposition for the quasi-orthogonal space-time code (QSTBC) with four transmit antennas [3]-[5], called VLCMLDec1 and VLCMLDec2 decoders. The first decoder, VLCMLDecl, can be used to detect transmitted symbols being extracted from finite-size constellations such as phase-shift keying (PSK) or quadrature amplitude modulation (QAM). The second decoder, VL-CMLDec2, is an enhanced version of the VLCMLDecl, developed mainly for QAM constellations. Simulation results show that both of the proposed decoders enable the QSTBC to achieve ML performance with significant reduction in computational load.

Second-order resonant ZnO-based film bulk acoustic resonator devices and thermal techniques to improve their resonant characteristics

In this article, the authors describe a novel fabrication technique of ZnO-based film bulk acoustic resonator (FBAR) devices using a new type of multilayered Bragg reflector with very thin chromium (Cr) layers additionally formed between silicon dioxide (SiO2) and tungsten (W) layers. Each Cr layer is considered to enhance the adhesion between the SiO2 and W layers. The fabricated FBAR devices are shown to operate at the frequency range of 2.7–3.0 GHz, along with good return loss as well as high Q factors. Furthermore, various thermal treatments are performed to further improve the resonant characteristics of the FBAR devices, and also their effects on the device characteristics are investigated. At the second-order resonant frequency, excellent resonant characteristics are observed in terms of high return loss and good figure of merit. This feasibility study indicates that the novel fabrication technique can be useful for future broadband mobile worldwide interoperability for microwave access applications.

A new fabrication technique for 2.75 GHz ZnO-based FBAR devices

We for the first time present a new fabrication technique of ZnO-based FBAR devices using a multi-layered Bragg reflector. To improve the resonance performance, 0.03?m-thick chromium (Cr)-adhesion layers were inserted into the Bragg reflector and also thermal treatments were made to the devices. At operating frequency of about 2.75 GHz, very high return loss values and quality factor (Q) were observed under an optimum thermal annealing condition.

Parameter-Optimized Extended MMSE-DFE based Detection for V-BLAST

In this work, the optimal value of parameter for complexity reduction of an Extended MMSE-DFE based Detection for V-BLAST system is considered. The detection, which is based on the fast sphere decoder for Phase-Shift Keying (PSK) signals in uncoded V-BLAST systems, namely PSD, generalizes the parameter beta in the extended channel matrix. It is shown that for M-ary PSK (M-PSK) signal, the PSD is always an optimal decoder irrespective of beta. In addition, with appropriately set the value of beta the PSD can operate at optimal low, i.e. minimum, computational load. In this work, from computer simulation, the trend of impact of beta on the complexity of the detection is presented.