Cristian Anghel

• Ph. D.
• Universitatea Națională de Știință și Tehnologie Politehnica București

Stereophonic acoustic echo cancellation (SAEC) requires the identification of four unknown impulse responses corresponding to four loudspeaker-to-microphone pairs. Recent developments in the field of adaptive filters for SAEC setups have allowed for the handling of a single complex-valued adaptive impulse response, instead of the four classical rea...

The recently proposed tensor-based recursive least-squares dichotomous coordinate descent algorithm, namely RLS-DCD-T, was designed for the identification of multilinear forms. In this context, a high-dimensional system identification problem can be efficiently addressed (gaining in terms of both performance and complexity), based on tensor decompo...

Modern solutions for system identification problems employ multilinear forms, which are based on multiple-order tensor decomposition (of rank one). Recently, such a solution was introduced based on the recursive least-squares (RLS) algorithm. Despite their potential for adaptive systems, the classical RLS methods require a prohibitive amount of ari...

The recursive least-squares (RLS) adaptive filter is an appealing choice in many system identification problems. The main reason behind its popularity is its fast convergence rate. However, this algorithm is computationally very complex, which may make it useless for the identification of long length impulse responses, like in echo cancellation. Co...

Due to its fast convergence rate, the recursive least-squares (RLS) algorithm is very popular in many applications of adaptive filtering, including system identification scenarios. However, the computational complexity of this algorithm represents a major limitation in applications that involve long filters. Moreover, when the parameter space becom...

The Sixteenth International Conference on Networks (ICN 2017), held between April 23-27, 2017 in Venice, Italy, continued a series of events targeting general networking and services aspects in multi-technologies environments. The conference covered fundamentals on networking and services, and highlighted new challenging industrial and research top...

This paper describes the implementation on field programmable gate array (FPGA) of a turbo decoder for 3GPP Long-Term Evolution standard. Considering the high data rates required by this standard, parallel decoding architecture is used. The parallel decoding latency is reduced N times compared with the serial decoding latency, N being the paralleli...

This paper describes a novel architecture for parallel turbo decoding used in Long Term Evolution (LTE) systems. The decoding scheme contains only one Quadratic Permutation Polynomial (QPP) interleaver, independently on the parallelization factor. Also, we propose an efficient implementation for the QPP interleaver. The arithmetic properties of the...

The regularization of the recursive least-squares (RLS) adaptive algorithm is a subject rarely approached in literature. The classical regularization method is implemented in the initial stages of the algorithm and has a time-limited effect on the corresponding correlation matrix. This paper proposes a new regularization technique for the RLS - dic...

The recently proposed joint-optimized normalized least-mean-square (JO-NLMS) adaptive algorithm employs a variable step-size parameter to achieve both high convergence and low misadjustment. In this paper, an efficient hardware implementation design is proposed, which exploits the key numerical properties of the JO-NLMS algorithm to reduce the hard...

This paper is dedicated to the memory of Steven L. Grant for his exceptional contributions to the echo cancellation problem. The regularization is mandatory in all ill-posed problems, especially in the presence of additive noise. In this paper, we consider the regularized recursive least-squares (RLS) algorithm and present a method to find its regu...

This paper describes an efficient hardware implementation for the address generation block used in the interleaving procedure associated with the channel turbo coding/decoding modules in the long term evolution (LTE) standard. The solution exploits key arithmetic properties of the corresponding equation to perform the address computation in a recur...

The overall performance of the affine projection algorithm (APA) is highly influenced by two important parameters, i.e., the step-size and regularization terms. In this paper, we follow a joint-optimization problem on both these parameters, in the context of a state variable model, which fits very well for acoustic echo cancellation (AEC). Thus, th...

This paper presents the main methods used for sorting when parallel decoding architecture is used for Long Term Evolution (LTE) systems turbo codes. Usually, the parallelization factor N represents the number of required interleavers. We propose a decoding architecture with only one Quadratic Permutation Polynomial (QPP) interleaver. All the interl...

The design of two channel Quadrature Mirror Filter (QMF) banks is considered with constraints on the peaks of the reconstruction error and that of the subband filter ripple sizes. In this paper a design method of the optimum quadrature mirror filters (QMF), by using grouped B-spline functions in each transition band, is presented. It was shown that...

This paper describes an efficient Field programmable gate array (FPGA) implementation of a convolutional turbo code (CTC) decoder for long term evolution (LTE) standard, release 8, using maximum logarithmic - maximum a posteriori probability (Max Log MAP) algorithm. The considered coding rate is 1/3 (the native coding rate), the puncturing procedur...

Modern teleconferencing systems have been developed in recent years to use multiple acoustic channels (stereo communication). This feature improves the quality of communication (e.g., in terms of spatial localization), but the classic problem of the acoustic echo cancellation becomes more complicated. In this context, the dichotomous coordinate des...

This paper proposes a low-complexity proportionate affine projection algorithm (PAPA) suitable for echo cancellation. It is known that proportionate-type algorithms exploit the sparseness character of the echo path in order to achieve faster convergence and tracking as compared to the conventional algorithms. The proposed algorithm results as a com...

This paper presents a field-programmable gate array (FPGA) implementation of a low-complexity proportionate affine projection algorithm (PAPA), in the context of echo cancellation. The proposed algorithm results as a combination between the recently developed "memory"-improved PAPA (MIPAPA) and a dichotomous coordinate descent (DCD) method. The MIP...

In this paper we will describe the procedure for primary synchronization in the Long Term Evolution (LTE) systems downlink and we will propose two enhanced algorithms that rely on the traditional methods described in other papers (based on cross-correlation properties of Zadoff-Chu sequences), but provide extra robustness through a validation proce...

This paper describes the way synchronization is achieved in the Long Term Evolution (LTE) standard. It focuses on the detection of the Secondary Synchronization Signal (SSS), which is a key signal, along with the Primary Synchronization Signal (PSS), used to obtain synchronization. In the description of the detection algorithm, three major steps mu...

This paper presents the results of a hybrid automatic request (H-ARQ) capable, convolutional turbo decoder implementation on field programmable gate array (FPGA). It emphasizes area, speed, and the decoding performances when using fixed point implementation. The convolutional turbo coding scheme is the one specified in the 802.16e-2005 standard. Th...

Lucrarea prezintă pe scurt interfaţa OBSAI RP3-01 existentă între unitatea radio externă şi modulul în banda de bază ale unei staţii de bază cu arhitectură distribuită. Este propusă o implementare bazată pe niveluri pentru o staţie de bază cu arhitectură distribuită cu capabilităţi MIMO. Sunt furnizate rezultate ale implementării realizate pe un ci...

This paper describes a Field Programmable Gate Array (FPGA) implementation of a Digital Front End (DFE) block for a Multi-Carrier Multi-Antenna (MCMA) system. The decimation/ interpolation filters used for obtaining the required channel bandwidth are split into several low order decimation/ interpolation stages, each of them being implemented as a...

Many interesting adaptive algorithms have been proposed for acoustic echo cancellation. Even if they exhibit good performance in ldquoinfiniterdquo precision, their capabilities could be seriously affected when using practical implementation platforms, e.g., digital signal processor (DSP) or field-programmable gate array (FPGA). In this context, se...

This paper represents an overview of the main sphere decoders used in MIMO (multiple input multiple output) spatial multiplexing communication systems. The family of sphere decoders addressed in this paper exhibits fixed throughput, regardless of the radio channel conditions. The algorithms are compared with respect to their complexity and performa...

This paper proposes a multi-antenna spatial multiplexing receiver exhibiting very good performances in the presence of fading and low signal-to-noise ratio. These result from the use of a soft-output sphere decoder with reduced complexity and a robust turbo channel decoder affected by log-likelihood ratio quantization and saturation. Fixed-point im...

The paper presents briefly the OBSAI RP3-01 interface existing between the remote radio unit (RRU) and the baseband module (BBM) of a base Station (BS) with a split architecture. It describes a layer based implementation model for BS split architecture with MIMO capabilities and it presents some implementation results obtained when targeting the XC...

This paper presents the headlines of a turbo decoder implementation on an FPGA. Optimization techniques and performances are detailed for the implementation of an 802.16e-2005 compliant turbo code. The decoder supported data rates are 1/2, 2/3 and 3/4, the data block sizes are from 6 up to 600 bytes and the maximum number of iterations is 8. The ma...

Transmit diversity is a very attractive solution for efficient communications through fading wireless channels. The paper presents some aspects concerning the synthesis of the coding matrix in a multiantenna configuration. Because no optimal (maximum coding advantage, maximum transmission rate, minimum delay) codes can be found for systems with mor...

This paper presents a field-programmable gate array (FPGA) implementation of a recently proposed variable step-size affine projection algorithm (VSS-APA), in the context of acoustic echo cancellation. The proposed hardware imple-mentation scheme takes advantage of the algorithm's specific features. Area and speed results are provided for the Xilinx...

In this paper we present an evaluation of the fast algorithms used for motion estimation and compensation. The presented algorithms are classified in two categories. The first category contains the algorithms with fixed number of iterations, i.e., Three Step Search (TSS), New Three Step Search (NTSS), and Four Step Search (FSS). The second category...