Krzysztof Wesolowski

WHT/OFDM - an improved OFDM transmission method for selective fading channels

The application of the Walsh-Hadamard transformation is proposed as the means to combat the influence of selective fading on the OFDM system performance. Substantial improvement as compared with the OFDM system applying the adaptive equalizer at the receiver is shown by simulation.

Analysis and properties of the modified constant modulus algorithm for blind equalization

A modification of the Godard blind equalization criterion and algorithm is presented. The analysis of the proposed criterion is performed, showing that the corresponding cost function has four equivalent global minima. The original Godard algorithm and the proposed algorithm are compared by simulation of data transmission through telephone channels.

On the Performance and Convergence of the Adaptive Canceller of Intersymbol Interference in Data Transmission

The two-stage equalizer of A. Gersho and T. L. Lim is analyzed, and simulation results of its performance, as well as derivation of the lower bound of the probability of error at the output of the canceller, are presented. They indicate that the overall performance of the canceller critically depends on the performance of the first-stage equalizer. Thus, a decision-feedback equalizer is proposed as the first-stage equalizer.

Efficient algorithm for adjustment of adaptive predistorter in OFDM transmitter

Adaptive predistortion is a technique which is aimed at compensation of nonlinear distortion introduced by a high power amplifier (HPA). This paper presents a simple method of acceleration of the adaptive algorithm of the HPA predistorter. The values of the predistorter complex gain stored in RAM and depending on the input signal amplitude are efficiently modified nor only in the address indicated by the current signal amplitude but also in the whole range of locations around it. The simulation results of the predistorters adaptation show a visible improvement in the convergence rate as compared with the standard gradient algorithm.

Power backoff reduction techniques for generalized multicarrier waveforms

Amplification of generalized multicarrier (GMC) signals by high-power amplifiers (HPAs) before transmission can result in undesirable out-of-band spectral components, necessitating power backoff, and low HPA efficiency. We evaluate variations of several peak-to-average power ratio (PAPR) reduction and HPA linearization techniques which were previously proposed for OFDM signals. Our main emphasis is on their applicability to the more general class of GMC signals, including serial modulation and DFT-precoded OFDM. Required power backoff is shown to depend on the type of signal transmitted, the specific HPA nonlinearity characteristic, and the spectrum mask which is imposed to limit adjacent channel interference. PAPR reduction and HPA linearization techniques are shown to be very effective when combined.

An Efficient DFE a ML Suboptimum Receiver for Data Transmission Over Dispersive Channels Using Two-Dimensional Signal Constellations

The DFE & ML receiver is presented for data transmission systems using QAM modulation. A substantial improvement in performance results as compared to other one- or two-stage receiver structures at relatively low computational complexity.

Frequency-domain echo cancellation in digital multicarrier modulation systems

The data driven frequency-domain echo canceller (EC) for a multicarrier modulation system is considered. An EC in such a system has to deal with both the interchannel and intersymbol interference occurring in the echo signal. For this reason, the main disadvantage of the data driven EC structure is the large computational complexity. Here, the solution of the computational complexity problem is presented. It is based on assumption that in practice, interchannel interference has a limited range. The number of operations per symbol as a measure of the EC computational complexity is given. Simulation results present echo attenuation in the frequency-domain EC, operating in the orthogonally multiplexed quadrature amplitude-shift keying system. Modifications of the proposed EC structure and its computational complexity in the systems with pulse shaping are discussed.

Change the Channel

This article presents a new channel model proposed by the International Telecommunication Union- the Radiocommunication Sector (ITU-R) for the evaluation of the International Mobile Telecommunications (IMT)-Advanced radio-access technologies. The model description is based on the perspective of the development of the wide-band multiple-input-multiple output (MIMO) channel models investigated within the European Union (EU)-funded wireless world initiative new radio (WINNER) projects. This article focuses on a soft ware implementation of an IMT-Advanced channel C++ based simulator developed within the CELTIC/EUREKA WINNER+ project at Poznari University of Technology.

Simple coarse frequency offset estimation schemes for OFDM burst transmission

Simple methods of the estimation of that part of the frequency offset, which is a multiple of the subcarrier spacing in the OFDM (orthogonal frequency division multiplexing) systems have been proposed. Described methods are aimed at burst transmission systems and take use of only one preamble symbol also required for the timing offset estimation. The methods are based on the frequency domain search for the unused subcarriers in the received signal spectrum. The proposed algorithms are immune to a constant phase shift (e.g. caused by timing errors). The estimation range depends on the algorithm but in general can be made as large as desired (but less than a half of the signal bandwidth). Simulation results show that the proposed algorithms estimate an integer part of the frequency offset in the AWGN channel even in the presence of some amount of the intercarrier interference (ICI). Satisfactory performance has been obtained also for OFDM transmission on multipath channels.

Channel Coding for Ultra-Reliable Low-Latency Communication in 5G Systems

This paper investigates block error rate (BLER) performance and computational complexity of candidate channel coding schemes for ultra-reliable low latency communication (URLLC) in 5G. The considered candidates are the same as those identified in 3GPP: turbo, LDPC, polar, and convolutional codes. Details of code constructions and decoding algorithms are provided with computational complexity analysis. Code construction parameters, number of iterations, and list sizes are selected to provide a fair comparison among candidate coding schemes. Simulation results on BLER are shown for several code rates and small-to-moderate block sizes. The results reveal that polar and LDPC codes outperform turbo codes for short block sizes of 40 bits, while the opposite is true for medium block sizes of 200 bits. None of the schemes is a clear winner at all considered block sizes and coding rates. Other aspects like implementation complexity, latency, and flexibility will also be important when deciding the URLLC coding scheme.