Ruey-Yi Wei

Noncoherent block-coded TAPSK

In this letter, we propose three noncoherent block coded twisted amplitude and phase shift keying (NBC-TAPSK) schemes which are derived from noncoherent block-coded MPSK. We also propose a new noncoherent detector and a corresponding noncoherent distance for nonconstant-energy signals over the additive white Gaussian noise (AWGN) channel. At high data rates, NBC-8TAPSK has the best bit error performance among all noncoherent schemes.

Differential Encoding by a Look-Up Table for Quadrature-Amplitude Modulation

In this paper, we propose a novel differential encoder for QAM (quadrature-amplitude modulation), by a look-up table instead of a rule. Using a table for differential encoding has the advantages of both low complexity and good error performance. We propose algorithms to construct the table for maximizing the minimum noncoherent distance and minimizing the number of different data bits between two codewords with small noncoherent distance. For 16QAM and 32QAM, we show that the differential encoders obtained by the proposed algorithms are optimal in terms of minimum noncoherent distance. Differential detectors for QAM, including a reduced-complexity two-symbol detector and multiple-symbol detectors, are proposed as well. Simulation results of 16QAM show that the proposed differential encoder provides significant gain over existent differential encoders as expected by distance analysis, and the proposed low-complexity multiple-symbol differential detector can further improve the error performance.

Further results on noncoherent block-coded MPSK [transactions papers]

A novel noncoherent block coding scheme, called noncoherent block-coded MPSK (NBC-MPSK), was proposed recently. In this paper, we present further research results on NBC-MPSK. We first focus on the rotational invariance (RI) of NBC-MPSK. Based on the RI property of NBC-MPSK with multistage decoding, a noncoherent near-optimal linear complexity multistage decoder for NBC-MPSK is proposed. Then we investigate a tree-search ML decoding algorithm for NBCMPSK. The derived algorithm is shown to have low complexity and excellent error performance. In this paper, we also utilize the idea of the NBC-MPSK to design noncoherent space-time block codes, called noncoherent space-time block-coded MPSK (NSTBC-MPSK). For two transmit antennas, we propose a signal set with set partitioning and derive the minimum noncohent distance of NSTBC-MPSK with this signal set. For the decoding of NSTBC-MPSK, we modify the ML decoding algorithm of NBC-MPSK and propose an iterative hard-decision decoding algorithm. Compared with training codes and unitary space-time modulation, NBC-MPSK and NSTBC-MPSK have larger minimum noncoherent distance and thus better error performance for the noncoherent ML decoder.

Noncoherent detection for trellis-coded MPSK

This letter shows several methods for improving the decoding of noncoherent trellis-coded M-ary phase-shift keying. We propose two new metrics for the basic decision-feedback algorithm. These metrics are derived based on the idea of reducing the effect of incorrect amplitude of the reference signal. We also propose a new decoding algorithm that uses a simple way to estimate the metric of the future sequence.

Differential phase detection using recursively generated phase references

We show that decision-feedback differential phase detection (DFDPD) is equivalent to a technique which generates a phase reference by averaging several primitive phase references. We then modify the DFDPD into a differential phase detection (DPD) technique which generates the phase reference using a simple recursive form. The proposed technique can be easily implemented and has satisfactory error performance.

Further Results on Differential Encoding by a Table

Recently we proposed a novel differential encoder by a look-up table. In this paper, we present further research results on this subject. We first propose a bit-assigning algorithm and construct some new tables for various constellations that maximize the minimum noncoherent distance. Then differential encoding for multiple-symbol differential detection is proposed. After that, we indicate that differential encoding by a table is equivalent to differential encoding by a trellis, so we propose a novel differential detector which uses the Viterbi algorithm on the trellis. A theorem about the sufficient number of states for various modulations is proposed. In addition, we further enhance the error performance of the proposed differential encoder by concatenating it with trellis coding. For this noncoherent trellis coding scheme, we propose augmented-state Viterbi decoding. Finally, we extend the proposed differential encoding and detection to differential space-time modulation (DSTM). We propose a new definition of DSTM by which the set of transmitted blocks is determined first. The differential encoding is implemented by a look-up table which can be optimized. The proposed DSTM has satisfactory error performance without constellation expansion.

Bandwidth-efficient noncoherent Trellis-coded MPSK

In this letter, we propose a novel bandwidth-efficient noncoherent trellis-coded MPSK scheme, in which a particularly designed differential encoder is added in front of the trellis encoder. With this differential encoder, trellis-coded MPSK proposed by Ungerboeck is no longer noncoherently catastrophic and thus achieves better error performance. Moreover, new trellis codes which, for the proposed scheme, have better bit error rates than Ungerboecks codes are found by computer searches.

Cross-sectional transmission electron microscopy of ultra-fine wires of AISI 316L stainless steel

Starting with 190 µm diameter wire of 316L stainless steel, ultra-thin wire just 8 µm in diameter has been made and characterized. There was no intermediate heat treatment used in the process of drawing, and the amount of true stain was about 6.3. A specimen preparation method for the cross-sectional transmission electron microscopy (TEM) of ultra-fine wires of 316L stainless steel has been developed. The ultra-fine wire was sandwiched between silicon chips and the bonded assembly then sliced to produce longitudinal and transverse sections of the wire in a form suitable for further processing into electron transparent samples. TEM reveals that the heavily deformed wire consists of nanoscale fine elongated structures along the drawing direction. The diffraction patterns indicate that a substantial amount of austenite has transformed into martensite. The TEM dark field images show nanosized patches of martensite distributed among the debris of austenite along the drawing direction. The evidence strongly suggests that severe deformation leads to mechanical stabilization of austenite against the growth of martensite.

Unitary space-time trellis codes

In this paper, a new noncoherent space-time coding scheme for the quasistatic flat fading channel is proposed. The proposed codes, called unitary space-time trellis codes, can be decoded by using the Viterbi algorithm without the knowledge of fading coefficients. The Viterbi decoder uses a sliding window for the observations where each observation covers several branches of the trellis. Appropriate decoding metrics for the observations are proposed also. We propose a systematic method for searching good unitary space-time trellis codes by computers. Simulation results indicate that the unitary space-time trellis codes are suitable for both the quasistatic and slow continuous flat fading channels.

A low-complexity noncoherent iterative space-time demodulator

Turbo coded unitary space-time modulation (USTM) can provide large coding gain as compared to uncoded USTM. Because the noncoherent space-time maximum a posteriori demodulator is very complicated, in this letter, we propose a new low-complexity noncoherent iterative space-time demodulator for the USTM constructed from pilot symbol-assisted modulation. The proposed demodulator utilizes both hard and soft decisions from the turbo decoder to simplify the computational task as well as produce reliable soft outputs. Several examples demonstrate that this demodulator has both low complexity and good error performance.