Tugcan Aktas

A low-complexity graph-based LMMSE receiver designed for colored noise induced by FTN-signaling

We propose a low complexity graph-based linear minimum mean square error (LMMSE) equalizer which considers both the intersymbol interference (ISI) and the effect of non-white noise inherent in Faster-than-Nyquist (FTN) signaling. In order to incorporate the statistics of noise signal into the factor graph over which the LMMSE algorithm is implemented, we suggest a method that models it as an autoregressive (AR) process. Furthermore, we develop a new mechanism for exchange of information between the proposed equalizer and the channel decoder through turbo iterations. Based on these improvements, we show that the proposed low complexity receiver structure performs close to the optimal decoder operating in ISI-free ideal scenario without FTN signaling through simulations.

Practical Methods for Wireless Network Coding With Multiple Unicast Transmissions

We propose a simple yet effective wireless network coding and decoding technique for a multiple unicast network. It utilizes spatial diversity through cooperation between nodes which carry out distributed encoding operations dictated by generator matrices of linear block codes. In order to exemplify the technique, we make use of greedy codes over the binary field and show that the arbitrary diversity orders can be flexibly assigned to nodes. Furthermore, we present the optimal detection rule for the given model that accounts for intermediate node errors and suggest a low-complexity network decoder using the sum-product (SP) algorithm. The proposed SP detector exhibits near optimal performance. We also show asymptotic superiority of network coding over a method that utilizes the wireless channel in a repetitive manner without network coding (NC) and give related rate-diversity trade-off curves. Finally, we extend the given encoding method through selective encoding in order to obtain extra coding gains.

Generalizing the sampling property of the Q-function for Error Rate analysis of cooperative communication in fading channels

This paper extends some approximation methods that are used to identify closed form Bit Error Rate (BER) expressions which are frequently utilized in investigation and comparison of performance for wireless communication systems in the literature. By using this group of approximation methods, some expectation integrals, whose exact analyses are intractable and whose Monte Carlo simulation computations have high complexity, can be computed. For these integrals, by using the sampling property of the integrand functions of one or more arguments, reliable BER expressions revealing the diversity and coding gains are derived. Although the methods we present are valid for a larger class of integration problems, in this work we illustrate the method by showing the step by step derivation of the BER expressions for a canonical cooperative communication scenario as well as a network coded system scenario. The derived expressions agree with the simulation results for a very wide range of signal-to-noise ratio (SNR) values.

Practical wireless network coding and decoding methods for multiple unicast transmissions

We propose a simple yet effective wireless network coding (NC) and decoding technique. It utilizes spatial diversity through cooperation between nodes which carry out distributed encoding operations dictated by generator matrices of linear block codes. For this purpose, we make use of greedy codes over the binary field and show that desired diversity orders can be flexibly assigned to nodes in a multiple unicast network, contrary to the previous findings in the literature. Furthermore, we present the optimal detection rule for the given model that accounts for intermediate node errors and suggest a network decoder using the sum-product algorithm. The proposed sum-product detector exhibits near optimal performance.

A diversity and coding gain analysis for the cooperativewireless communication channel under fading using sampling property of the Q-function

This work presents approximation methods that are used to identify Bit Error Rate (BER) expressions which are frequently utilized in investigation and comparison of performance for wireless communication systems in the literature. In this group of approximation methods, some expectation integrals, which are complicated to analyze and time-consuming to evaluate through Monte Carlo simulations, are handled. For this group of integrals, by using the sampling property of the Q-function under mid- and high- Signal-to-Noise Power Ratio (SNR) assumptions, reliable BER functions revealing the diversity and coding gains are derived. Although the methods we proposed cover a larger class of integration problems, the results presented in this work show the step by step derivation of the BER expression for a canonical cooperative communication scenario starting from basic building blocks. The derived expression agrees with the simulation results even under relatively low SNR values.

Effect of Water-Filling Method on the PAPR for OFDM and MIMO Systems

In this paper, the peak-to-average power ratio (PAPR) problem for orthogonal frequency division multiplexing (OFDM) is investigated. The variations in the nature of the problem along with the utilization of water-filling technique are observed and the corresponding cumulative distribution function for PAPR is determined. In addition to OFDM analysis, another analysis is carried out for the comparison of water-filling technique and an equal power distribution algorithm in case of a multiple input multiple output (MIMO) system and the same PAPR problem is examined in the spatial diversity scenario as well.

ISI channel equalizers based on the factor graphs for M-QAM signalling

In this work, we consider two methods especially for high order modulation types, namely the sum-product (SP) and linear minimum mean square error (LMMSE) algorithms, which were previously utilized to equalize the inter-symbol interference (ISI) channel. Techniques for reducing the computational complexity are proposed for the SP-based method. In addition, a new technique for the calculation of the extrinsic information is proposed, which significantly improves the performance in the LMMSE equalizer. The comparison of these proposed techniques is made through simulations carried out under the fading channel assumption.

Analysis of the performance of network coding using the sampling property of Q-function

In the area of cooperative and network coded communication that naturally arises from cooperation, which become increasingly important in wireless communications, the expected end-to-end bit error rate (BER) values are frequently required to compare the proposed coding, relaying, and decoding techniques. Instead of obtaining these values through time consuming Monte Carlo simulations, deriving the closed form expressions via approximations is also crucial. In this work, we make use of the sampling property of the Q-function, which we commonly face while dealing with the related expectation integrals, in order to derive the end-to-end BER expressions for a network coded system. Furthermore, we show that the obtained expressions well agree with the simulation results.

Probability of full-diversity for simple coded and rotated multidimensional constellation systems

The case of rotation, in use together with coding in a channel with B fading blocks, is analyzed in terms of diversity properties of the coded systems with multi-dimensional rotated constellations (coded-rotated system) output. First closed-form expression obtained is related to the diversity performance of unrotated generic coding structures with given minimum distance, d, block length, and number of fading blocks. Afterwards, another closed-form expression is derived for distinguishing the effect of rotation applied on the given coding structures. This latter expression yields a strict lower bound on the probability of attaining full diversity for any coded-rotated system and gives us a tool to evaluate the improvement with respect to systems involving only coding and also systems with only rotation. The results shown summarize the benefits of utilizing rotation together with coding, even in the cases of very simple non-full-diversity rotations like DFT rotations.