Linh Mai

A low complexity branch-and-bound-based decoder for V-BLAST systems with PSK signals

In this paper, a fast sphere decoder is proposed for the joint detection of phase-shift keying (PSK) signals in uncoded Vertical Bell Laboratories Layered Space Time (V-BLAST) systems. The proposed decoder consists of preprocessing stage and search stage. The preprocessing stage is based on the enhancement of the ordering mean square error decision feedback equalizer (MMSE-DFE). Its role is to generate a tree structure suitable for the search stage. The search stage relies on the depth-first brand-and-bound (BB) algorithm with best-first orders stored in lookup tables. Simulation results show that the proposed decoder is able to provide the system with the maximum likelihood (ML) performance at low complexity.

On the Construction of High-Rate Quasi-Orthogonal STBC for MIMO QR Demodulation

Orthogonal space-time block codes (STBCs) [1],[2] appear to be a very fascinating means of enhancing reception quality in quasi-static MIMO channels due to their full diversity, and especially their simple maximum-likelihood (ML) decoders. However, full-rate full-diversity orthogonal STBCs do not exist for more than two transmit antennas. Vertical layered space-time architecture (so-called the V-BLAST) [3] with a nulling- and cancelling-based detection algorithm, in contrast, has an ability of achieving high transmission rates at the cost of having very low diversity gain, an undesirable consequence caused by the interference nulling and cancelling processes. The uncoded V-BLAST system is able to reach its ML performance with the aid of the sphere decoder algorithm [4] at the expense of higher detection complexity. Undoubtedly, the tradeoff between transmission rates, diversity, and complexity is inherent in designing space-time codes. This paper investigates a method to increase the nulling diversity gains for a general high-rate space-time code and introduces a new design strategy for high-rate space-time codes detected based on interference nulling and cancelling processes, thanks to which high-rate quasi-orthogonal space-time codes for MIMO applications are proposed. We show that when nT transmit and nR = nT receive antennas are deployed, the first code offers a transmission rate of (nT - 1) with a minimum nulling diversity order of 3, whereas the second one offers a transmission rate of (nT - 2) with a minimum nulling diversity order of 5. Therefore, the proposed codes significantly outperform the V-BLAST as nR = nT. Simulation results and discussions on the performance of the proposed codes are provided.

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.