Georgi Iliev

Improving cell edge throughput for LTE using combined uplink power control

Uplink power control is used in 3GPP Long Term Evolution (LTE) systems to maximize the power of the desired received signals while limiting the interference. This paper analyzes two power control mechanisms, Fractional Power Control (FPC) and Interference Based Power Control (IBPC). A way of combining them is proposed in order to find an efficient algorithm to control the transmitted Power Spectral Density (PSD) in order to compensate poor channel conditions and thus to obtain better performance in terms of cell edge throughput.

Hybrid system for robust recognition of noisy speech based on evolving fuzzy neural networks and adaptive filtering

Speech and signal processing technologies need new methods that deal with the problems of noise and adaptation in order for these technologies to become common tools for communication and information processing. This paper is concerned with a method and a system for adaptive speech recognition in a noisy environment (ASN). A system based on the described method can store words and phrases spoken by the user and subsequently recognize them when they are pronounced as connected words in a noisy environment. The method guarantees system robustness in respect to noise, regardless of its origin and level. New words, pronunciations, and languages can be introduced to the system in an incremental, adaptive mode. The method and system are based on novel techniques recently created by the authors, namely: adaptive noise suppression, and evolving connectionist systems. Potential applications are numerous, e.g. voice dialling in a noisy environment, voice command control, improved wireless communications, data entry into databases, helping disabled people, multimedia systems, improved human computer interaction. The method and system are illustrated on the recognition of English and Italian spoken digits in different noisy environments.

Public access defibrillation: Suppression of 16.7 Hz interference generated by the power supply of the railway systems

BackgroundA specific problem using the public access defibrillators (PADs) arises at the railway stations. Some countries as Germany, Austria, Switzerland, Norway and Sweden are using AC railroad net power-supply system with rated 16.7 Hz frequency modulated from 15.69 Hz to 17.36 Hz. The power supply frequency contaminates the electrocardiogram (ECG). It is difficult to be suppressed or eliminated due to the fact that it considerably overlaps the frequency spectra of the ECG. The interference impedes the automated decision of the PADs whether a patient should be (or should not be) shocked.The aim of this study is the suppression of the 16.7 Hz interference generated by the power supply of the railway systems.MethodsSoftware solution using adaptive filtering method was proposed for 16.7 Hz interference suppression. The optimal performance of the filter is achieved, embedding a reference channel in the PADs to record the interference. The method was tested with ECGs from AHA database.ResultsThe method was tested with patients of normal sinus rhythms, symptoms of tachycardia and ventricular fibrillation. Simulated interference with frequency modulation from 15.69 Hz to 17.36 Hz changing at a rate of 2% per second was added to the ECGs, and then processed by the suggested adaptive filtering. The method totally suppresses the noise with no visible distortions of the original signals.ConclusionThe proposed adaptive filter for noise suppression generated by the power supply of the railway systems has a simple structure requiring a low level of computational resources, but a good reference signal as well.

Noise Cancellation in OFDM Systems Using Adaptive Complex Narrowband IIR Filtering

In this paper a very low sensitivity fourth-order complex band-pass filter section with independent tuning of the central frequency and the bandwidth is developed. A narrowband adaptive filter structure is formed around this section, using LMS algorithm to adapt the central frequency. The developed filter structure is providing a low computational complexity and a very fast convergence. We use this adaptive complex filter for noise cancellation in an OFDM transmission scheme and show that under certain conditions SNR gain and better bit error rate (BER) performance can be achieved.

Performance comparison of NBI suppression methods for MIMO OSTBC-OFDM systems

In this paper a comparison of several narrowband interference (NBI) suppression methods for Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) digital wireless communication systems with Orthogonal Space-Time Block Coding (OSTBC) is done. Each of the methods is analyzed in respect of its computational complexity parameters and the performance of MIMO system. When an NBI suppression method is implemented, the trade-off between performance and computational complexity is analyzed by introducing a pricing coefficient.

Combined power and inter-cell interference control for LTE based on role game approach

In this paper the application of Role Game Theory to Power Control (PC) and Inter-Cell Interference Control (ICIC) for Long Term Evolution (LTE) is considered. The authors propose an approach based on defining different roles of the users within a cell of the LTE network. The main idea is to apply different methods and algorithms for PC and ICIC depending on the classified by role subscriber. Such an approach will give the possibility for flexible application and combination of different PC and ICIC methods for achieving better performance.

Reduced Computational Complexity Beamspace Beamforming Design for MIMO Multicast Systems

An algorithm with reduced computational complexity for solving the transmit beamforming problem in the case of multiple co-channel multicast groups is considered. A new degree of freedom, which allows a trade-off between the transmission power, the number of antenna array elements and the computational time, is added. The optimization problem is transformed to a lower-dimensional optimization problem, which allows an antenna array with higher number of elements to operate with significant decrease in transmission power, while the increase in computational time is minor. The trade-off between the delay and the transmit power appears to be a promising direction for a crosslayer optimization research.

Narrowband interference suppression for MIMO OFDM systems using adaptive filter banks

In this paper we propose a scheme for Narrowband Interference (NBI) suppression for MIMO OFDM system using adaptive narrowband filter banks. We compare this method with other schemes for suppression of complex NBI, such as Frequency Excision method, Complex NBI Identification and Cancellation algorithm and Orthogonal Space Time Block Coding (OSTBC). The study shows that the different schemes give different performance depending on the parameters of MIMO system, but an optimal solution is applying an adaptive narrowband filter bank that offers a trade-off between outstanding NBI suppression efficiency and computational complexity.

Adaptive blind noise suppression in some speech processing applications

In many applications of speech processing the noise reveals some specific features. Although the noise could be quite broadband, there are a limited number of dominant frequencies, which carry the most of its energy. This fact implies the usage of narrow-band notch filters that must be adaptive in order to track the changes in noise characteristics. A method and a system for noise suppression are developed. The method uses adaptive notch filters based on second-order Gray-Markel lattice structure. The main advantages of the proposed system are that it has very low computational complexity, is stable in the process of adaptation, and has a short time of adaptation. Under comparable SNR improvement, the proposed method adjusts only 3 coefficients against 250-450 for the conventional adaptive noise cancellation systems. A framework for a speech recognition system that uses the proposed method is suggested.

High accuracy Hilbert transformer realization for multicarrier communications

The basic motivation for this work is to investigate how Hilbert transformer (HT) design optimization can influence the Bit Error Ratio (BER) performance of a multicarrier wireless system. The implementation of a novel digital allpass based HT is proposed. The HT realization is based on worst-case phase-sensitivity minimization of each individual allpass section used. This design procedure allows to improve the accuracy of the HT phase deviation even in the cases of severe wordlength limitations and fixed point arithmetic applications. A multicarrier wireless system is simulated and it is experimentally demonstrated that the low sensitivity HT design procedure can improve the BER performance. AWGN and Rayleigh wireless channels are considered.