IPSA Institute

Sarajevo, Bosnia and Herzegovina

IPSA Institute

Sarajevo, Bosnia and Herzegovina
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Ligata A.,IPSA Institute | Gacanin H.,Alcatel - Lucent | Javornik T.,Jozef Stefan Institute
IEICE Transactions on Communications | Year: 2014

Multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (OFDM/TDM) based on frequency domain equalization (FDE) has been proposed to reduce the high peak-to-average power ratio (PAPR) of OFDM and improve the bit error rate (BER) performance in comparison to the conventional OFDM. However, due to the nonlinearity of the highpower amplifier (HPA) at the transmitter and the fact that the PAPR problem is not completely eliminated, the nonlinear noise due to HPA saturation still degrades the BER performance. In this paper, we theoretically evaluate the effect of nonlinear HPA on the performance of MIMO-OFDM/TDM using a minimum-mean square-error frequency-domain equalizer (MMSEFDE). We determine the equalization weights while taking into account the negative effect of HPA saturation and then evaluate the system performance in terms of average BER and ergodic capacity by way of both, numerical and computer simulation. Our simulation results have shown that appropriate system design can make MIMO-OFDM/TDM more robust against nonlinear degradation due to HPA saturation in comparison to MIMO-OFDM while reducing required signal-to-noise ratio (SNR) for the given target BER. Copyright © 2014 The Institute of Electronics, Information and Communication Engineers.


Ligata A.,IPSA Institute | Gacanin H.,Motive | Gacanin H.,IPSA Institute | Javornik T.,Jozef Stefan Institute
17th Asia-Pacific Conference on Communications, APCC 2011 | Year: 2011

Recently, multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (OFDM/TDM) based on frequency domain equalization (FDE) has been proposed to improve the performance of conventional OFDM-based relaying in terms of high peak-to-average power ratio (PAPR) and the bit error rate (BER). The PAPR problem, however, is not completely eliminated and thus, the effect of peak-limited channel is not negligible. In this paper, we present the BER performance analysis of MIMO-OFDM/TDM in a peak-limited and frequency-selective channel. The theoretical equalization weights in a nonlinear channel for MIMO-OFDM/TDM are derived to capture the negative effect of peak-limitation. Performance analysis presented in this paper was confirmed by the computer simulation and it was shown that the achievable BER performance of MIMO-OFDM/TDM in a peak-limited and frequency-selective channel is a function of the OFDM/TDM design parameter. © 2011 IEEE.


Ligata A.,IPSA Institute | Smolnikar M.,Jozef Stefan Institute | Mohorcic M.,Jozef Stefan Institute | Gacanin H.,Tohoku University | And 2 more authors.
12th IEEE International Conference on Communication Systems 2010, ICCS 2010 | Year: 2010

Orthogonal frequency division multiplexing (OFDM) system with frequency domain equalization (FDE) requires reliable channel estimation (CE). OFDM has a problem of high peak-to-average power ratio (PAPR), which makes it very sensitive to nonlinear distortions, affecting the channel estimation accuracy. In this paper, we investigate the effect of the nonlinearity to the the OFDM system with pilot-assisted CE based on time or frequency division multiplexed (TDM/FDM) pilot. A closed-form bit error rate (BER) expressions for OFDM system are derived in a nonlinear and frequency-selective fading channel. The analysis is based on the Gaussian approximation of the nonlinear noise, which is also confirmed by computer simulation. Our results in terms of BER and mean square error (MSE) show, that FDM-pilot based CE is more sensitive to nonlinear distortions as compared to CE based on TDM-pilot. © 2010 IEEE.


Muhasilovic M.,CiM Program of the German International Cooperation Agency | Muhasilovic M.,IPSA Institute | Vela I.,German Federal Institute for Material Research and Testing | Trobok Z.,Center Importanne Sarajevo | And 3 more authors.
ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers | Year: 2012

Especially in the societies, where some technical and scientific (in world - most common) approaches are not yet a vivid part of the organised economy and mechanism for scientific high-education, a CFD-based research on phenomena in (both gaseous and liquid) fluid-flow is one of the essential tools to be applied in causes of research and development. An interesting position has Bosnia and Herzegovina, whose scientists during the 1960ties have set some fundamental stones into the area of the Computational Fluid Dynamics while constructing this fine engineering and scientific tool for all of us in today's CFD-community. Presumed as "already developed" and in possible attempt to demonstrate the power of once made mathematical kits on the sophisticated scientific way, a certain approach in turbulence treatment within the modern CFD-tool is engaged. During this numerical research in mode of prospective engineering, a direct application is seen for the CFD-based exploring in the first two minutes of an accidental thermal load in a road-tunnel close to the city of Sarajevo. Performing the turbulence-treatment with the k-epsilon mathematical and numerical mechanism in mentioned CFD-toolkit, the case for forced longitudinal ventilation of the gaseous consequences done by the established simulated tunnel-fire was explored as well. For the CFDoriented research, that certainly varies in it's approaches and characteristics according to the nature of the explored large-scale domains, this CFD-based research-paper presents one further step towards the "best practice" in application of prospective engineering.


Ligata A.,IPSA Institute | Gacanin H.,Motive | Gacanin H.,IPSA Institute | Adachi F.,Tohoku University
17th Asia-Pacific Conference on Communications, APCC 2011 | Year: 2011

Future wireless Internet services require a broadband frequency spectrum with high data rates. Cognitive radio (CR) concept is a novel approach to improve the spectrum efficiency. The CR is based on the opportunistic usage of frequency spectrum, which is not occupied by the primary users. Conventional multi-user access in bi-directional CR network may be done by using either time division multiple access (TDMA), frequency division multiple access (FDMA) or code division multiple access (CDMA). Without adaptive or dynamic frequency reuse, TDMA and FDMA have lower spectrum efficiency in comparison with CDMA. However, the problem of CDMA in a multipath channel is a multi-user interference (MUI). In this paper, we present a bi-directional CR network with wireless network coding (WNC) in a multipath channel. Unlike the conventional multi-user bi-directional CR network, where the users access the spectrum holes in different time-slot or frequency, the proposed method allows secondary users (SUs) to access the spectrum holes simultaneously. The performance of bi-directional CR network with WNC is theoretically analyzed in terms of spectrum efficiency and the maximum number of SUs. The numerical results show that the spectrum efficiency and the maximum number of SUs of the proposed method increases in comparison with conventional CR network. © 2011 IEEE.


Ligata A.,IPSA Institute | Gacanin H.,Motive | Gacanin H.,IPSA Institute | Adachi F.,Tohoku University
17th Asia-Pacific Conference on Communications, APCC 2011 | Year: 2011

Cooperative transmission, where spatially distributed users form a multi-antenna system and assist in forwarding the information from source to destination node, achieves the diversity gain of a multiple-input multiple-output (MIMO) system. Cooperative network based on OFDM has been proposed to cope with the channel frequency-selectivity but due to high peak-to-average power ratio (PAPR) of OFDM, expensive power amplifier are required. In this paper, we present cooperative network based on OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency-domain equalization (MMSE-FDE) in a frequency-selective fading channel. We theoretically analyze the network performance with respect to the bit error rate (BER). The conditional signal-to-interference plus noise ratio (SINR) expressions are derived based on Gaussian approximation of the residual inter-slot interference (ISI) after MMSE-FDE for the given set of channel gains. The average BER performance for OFDM/TDM is evaluated by Monte-Carlo numerical computation method using the derived theoretical expressions and confirmed by computer simulation. The results show that the lower BER is achieved with cooperative OFDM/TDM in comparison with OFDM based cooperative network because OFDM/TDM exploits both cooperative and frequency diversity gains. © 2011 IEEE.


Gacanin H.,Motive | Ligata A.,IPSA Institute
ISPLC 2013 - 2013 IEEE 17th International Symposium on Power Line Communications and Its Applications, Proceedings | Year: 2013

In this paper, we theoretically analyze the achievable physical layer performance of multiple-domain diversity mechanism in wireline home networks, where the content is either kept within the same domain or distributed over different domains. We theoretically evaluate the symbol error rate (SER) performance and outage probability of multiple-domain PLC network based on minimum mean square-error (MMSE) combining while taking into consideration the impact of different noise impairments in powerline channel. It has been shown that required signal-to-noise ratio can be reduced while achieving the target performance if the system is properly designed. © 2013 IEEE.


Ligata A.,IPSA Institute | Gacanin H.,Motive | Adachi F.,Tohoku University
Eurasip Journal on Wireless Communications and Networking | Year: 2013

In this paper, we analyze the impact of nonlinear high-power amplifier (HPA) on the performance of cooperative network based on orthogonal frequency division multiplexing combined with time-division multiplexing (OFDM/TDM) using minimum mean-square-error frequency-domain combining (MMSE-FDC) in a frequency-selective fading channel. We design a novel MMSE-FDC weights while taking into account the nonlinearity of HPA at source and relay. Closed-form symbol error rate and outage probability expressions are derived while approximating the residual inter-slot interference after the MMSE-FDC as a random Gaussian variable. We discuss and address the nonlinear OFDM/TDM system design issues in cooperative network using the obtained simulation and theoretical results. We show that the OFDM/TDM with MMSE-FDC can be used to reduce the impact of nonlinear HPA on overall performance of cooperative network in comparison to OFDM while providing the target quality-of-service for reduced required signal-to-noise ratio. This is because OFDM/TDM with MMSE-FDC achieves frequency diversity in addition to cooperative diversity, while reduced peak-to-average power ratio makes it more robust on nonlinear degradation due to HPA saturation in comparison to conventional OFDM. © 2013 Liao et al.; licensee Springer.


Ligata A.,IPSA Institute | Gacanin H.,Motive | Adachi F.,Tohoku University
Eurasip Journal on Wireless Communications and Networking | Year: 2013

Recently, a variant of network coding at the physical layer named wireless network coding (WNC) has gained much attention due to it's simplicity and capacity improvement of a bi-directional link. In this paper, we design and analyze a bi-directional cognitive radio (CR) system with multiple pairs based on WNC while taking into account the imperfect spectrum sensing and interference from/to the CR system. In addition, we design a resource allocation framework consisting of a subcarrier allocation strategy with different priority assignments and optimal power allocation algorithm. We show that the quality of service within the CR system highly depends on a proper design of the spectrum sensing process to minimize the probability of missed detection, while the spectrum efficiency of the CR system increases with the number of pairs within the system to which we assign priorities. © 2013 Stolojescu-Crisan and Isar; licensee Springer.


Ligata A.,IPSA Institute | Gacanin H.,Motive | Adachi F.,Tohoku University
Eurasip Journal on Wireless Communications and Networking | Year: 2013

Analog network coding (ANC) as a simple implementation of physical layer network coding based on orthogonal frequency division multiplexing (OFDM) has been proposed to increase the network capacity and reliability of bi-directional link between a pair of users. In ANC protocol, an information between a pair of users is exchanged through two orthogonal time phases (i.e., multiple-access and broadcast phases). On the other hand, the phase noise (PN) introduces phase offset and inter carrier interference (ICI) to the useful signal. Thus, in ANC scheme PN will affect the useful signal during both multiple-access and broadcast phases. In this article, we present a performance analysis of ANC scheme using OFDM in the presence of PN in frequency-selective fading channel. We derive the total composite variance of ANC scheme in the presence of PN to obtain the signal-to-interference-plus-noise ratio (SINR) expression. Then, we evaluate the system's performance in terms of bit error rate (BER), SINR degradation, and ergodic capacity through both numerical and computer simulations. Computer simulated average BER has been consistent with the numerical results, validating the presented analysis. Our results have shown that the ANC scheme is more sensitive to the PN introduced during the broadcast phase (i.e., at destination) than during the multiple-access phase (i.e., at relay). This is because of the higher ICI to the useful signal and enhanced noise due to the imperfect self-information removal at the destination. In addition, the performance degradation of ANC scheme based on OFDM in the presence of PN is highly expressed for the PN linewidth values up to 20 Hz. © 2013 Ligata et al.; licensee Springer.

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