Huy-Dung Han

A blind channel shortening criterion based on high-order cumulants

In this work, we propose a new criterion for blind channel shortening based on high order statistical information. This method overcomes the weakness of two existing channel shortening criteria derived from only second order output statistics of the unknown channel. It is applicable to both single-input-single-output and single-input-multiple-output frequency selective channels. The optimization criterion can be achieved through either a stochastic gradient descent algorithm or a batch algorithm. Simulation results demonstrate successful shortening of wireless channels that the existing criteria fail to shorten.

A low cost mobile ECG monitoring device using two active dry electrodes

Mobile electrocardiograph (ECG) monitoring provides crucial information about the cardiac rhythm and system anomaly helping doctors to efficiently diagnose heart diseases. This paper presents the development of a low cost mobile ECG monitoring device, which early warms abnormalities throughout long-term ECG observation. For user convenience, two active dry electrodes are used as touch sensors. A buffer circuit is applied to remove the over-sensitivity effect of the electrodes. Experimental results indicated that ECG quality when using active dry electrodes is equivalent to that of wet Ag/AgCl electrodes application.

Joint transmission using global codeword and codebook design for coordinated multipoint processing (CoMP)

In this paper we propose a joint transmission scheme for LTE-CoMP using a single codeword to transmit from multiple transmission points to a single UE. Transmission with a single codeword makes the signal better aligned with the dominant eigenmode of the channel and achieves higher capacity. A design methodology of the global codebook for joint transmission from two transmission points is developed. A codebook is created using K-mean clustering algorithm from a large number of channel samples generated through simulation. Simulation results show that this approach can outperform traditional local precoding approach where two separate codewords from the existing LTE-A MIMO codebook are used from two transmission points.

On Steepest Descent Adaptation: A Novel Batch Implementation of Blind Equalization Algorithms

Blind equalization typically achieves parameter optimization through cost minimization using stochastic gradient descent in both batch and adaptive algorithms. In general, stochastic descent algorithms typically require large number of iterations or long data samples to converge. The batch approach is generally based on data reuse (recycling) and re-filtering to recompute the cost gradient after each iterative parameter update, thereby causing long processing delays. In this work, we present a novel steepest descent batch algorithm that does not require data recycling. We consider the popular Constant Modulus Algorithm and the Minimum Entropy Deconvolution for normalized cumulant maximization. Both algorithms utilize 4-th order cumulants. The proposed steepest descent batch implementation of both algorithms converge rapidly in a few iterations and deliver superior performance without the delay due to data recycling and refiltering

A Convex Relaxation Approach to Higher-Order Statistical Approaches to Signal Recovery

In this paper, we investigate an efficient numerical approach for solving higher order statistical methods for blind and semiblind signal recovery from nonideal channels. We develop numerical algorithms based on convex optimization relaxation for the minimization of higher order statistical cost functions. The new formulation through convex relaxation overcomes the local convergence problem of existing gradient-descent-based algorithms and applies to several well-known cost functions for effective blind signal recovery, including blind equalization and blind source separation in both single-input–single-output (SISO) and multiple-input–multiple-output (MIMO) systems. We also propose a fourth-order pilot-based cost function that benefits from this approach. The simulation results demonstrate that our approach is suitable for short-length packet data transmission using only a few pilot symbols.

Cross-Layer Chase Combining With Selective Retransmission, Analysis, and Throughput Optimization for OFDM Systems

In this paper, we present a bandwidth efficient retransmission method employing selective retransmission approach at a modulation layer under orthogonal frequency division multiplexing (OFDM) signaling. The proposed cross-layer design embeds a selective retransmission sub-layer in physical layer (PHY) that targets the retransmission of information symbols transmitted over poor quality OFDM sub-carriers. Most of the times, a few errors in decoded bit stream result in packet failure at medium access control (MAC) layer. The unnecessary retransmission of good quality information symbols of a failed packet has detrimental effect on the overall throughput of transceiver. We propose a cross-layer Chase combining with selective retransmission (CCSR) method by blending Chase combining approach at MAC layer and selective retransmission in PHY. The selective retransmission in PHY targets the poor quality information symbols prior to decoding, which results in lower hybrid automatic repeat reQuest retransmissions at MAC layer. We also present bit-error rate upper bound and throughput lower bound for the CCSR method. In order to maximize the throughput, we formulate optimization problem with respect to the amount of information to be retransmitted in selective retransmission. We also present an impact of selective retransmission on latency. The proposed CCSR method achieves a significant throughput gain as compared with the conventional Chase combining method.

Steepest descent algorithm implementation for multichannel blind signal recovery

In the literature, there exists a number of blind signal recovery algorithms that are implemented as stochastic gradient descent (SGD)-based adaptive schemes. SGD typically has low complexity at the expense of slower convergence. On the other hand, packet-based data transmission in many practical digital communication systems makes it attractive to develop steepest descent (SD) implementation in order to speed-up convergence. This work aims at developing SD implementation of several well-known blind signal recovery algorithms for multi-channel equalisation and source separation. The authors SD formulation is more amenable to additional parametric and signal subspace constraint for faster convergence and superior performance.

A bandwidth efficient design of IM/DD optical OFDM

We present a new optical OFDM design that achieves significantly improved bandwidth efficiency. We introduce an optimum DC bias to the modulated signal prior to clipping and present an iterative receiver to combat nonlinear distortions.

A Convex Optimization Approach to Blind Channel Shortening in Multicarrier Modulations

We study the problem of channel shortening in multicarrier modulation systems without training. We reformulate two existing methods, the sum-squared and the sum-absolute autocorrelation minimization algorithms (SAM and SAAM), into semidefinite programming to overcome their shortcoming of local convergence. We present the original SAM and SAAM cost functions into as a batch optimization problem before relaxing the original problem into globally convergent semidefinite programming algorithms. Our batch processor is superior to the original stochastic gradient algorithms in terms of achievable bit rate and signal to interference and noise ratio (SINR).

Pilot decontamination for multi-cell massive MIMO systems using asynchronous pilot design and data-aided channel estimation

Abstract In this work, we investigate the pilot contamination problem in multi-cell massive multi-input multi-output (MIMO) systems. The conventional approaches to address pilot contamination for multi-cell MIMO systems impose orthogonal pilots constraint across multiple users and cells, which leads to bandwidth inefficiency under large number of active users. We propose an uplink (UL) transmission protocol in which the pilot segments of users partially overlap across cells and even overlap with data from other cells, which provides more freedom in system designing. We also apply semi-blind algorithms at base station (BS) in order to separate the data streams of each user. Our analysis shows that semi-blind receiver removes pilot contamination effectively under large UL data length. The simulation results demonstrate that the performance of the proposed protocol with semi-blind receiver employing Constant Modulus Algorithm (CMA) is superior as compared to the existing schemes.