Enis Kocan

BER performance of MIMO OFDM-CDMA system in ricean fading channel

In this paper, bit error rate (BER) performance of the MIMO OFDM-CDMA system, in case of Ricean frequency selective fading, is evaluated using originally developed computer simulation. The assumed system uses space-time block coding applied to two, three and four transmit antennas and has arbitrary number of receive antennas. Channel estimation is performed by implementing pilot sequences at each transmit antenna. The results are compared with BER results of the competitive OFDM-CDMA down link system with threshold detection combining (optimum TDC). The results show that the presented system provides lower BER, even when less subcarriers are used for transmitting single data symbol, than its competitive solution.

On the optimal subcarrier mapping scheme in OFDM decode-and-forward relay systems

BER performance of the DPSK (Differentially Phase Shift Keying) modulated dual-hop OFDM based DF (Decode and Forward) relay system, implementing subcarrier mapping (SCM) at the relay (R) station, is examined. Closed form BER expressions are derived for the two SCM schemes, denoted as BTB SCM (Best-to-Best Subcarrier Mapping) and BTW SCM (Best-to-Worst Subcarrier Mapping) in the scenario with Rayleigh fading on both hops. The accuracy of the obtained analytical results is verified through comparison with the simulation results. It is shown that BTB SCM scheme achieves the lowest BER results for all SNRs (Signal-to-Noise Ratios) of interest, which approves it to be the optimal SCM scheme in dual-hop OFDM DF relay systems, as it has already been known that the same SCM scheme maximizes the capacity.

BER performance of OFDM Amplify-and-Forward relaying system with subcarrier permutation

We perform error probability analysis of the uncoded OFDM fixed gain Amplify-and-Forward (AF) relaying system with subcarrier permutation (SCP). Two SCP schemes, named: the best-to-best SCP (BTB SCP) and the best-to-worst SCP(BTW SCP) are considered. Closed-form expressions for the bit error rate (BER) of the above SCP methods are derived. Numerical results manifest that these SCP schemes may outperform one another, depending on the average channel conditions of the links involved. That is, BTB SCP is better in the low signal-to-noise ratio (SNR), while BTW SCP prevails in the medium and high SNR regime. Thus, it could be concluded that OFDM AF relaying systems may switch from the BTB SCP to BTW SCP in order to achieve optimum BER performance.

On the ergodic capacity of dual-hop OFDM based DF relay system with subcarrier mapping

In this paper ergodic capacity analysis of the dual-hop OFDM decode-and-forward (DF) relay system implementing subcarrier mapping (SCM) at the relay station (R) has been conducted. A scenario with no direct communication between the source of information (S) and destination terminal (D), with Rayleigh fading statistics on both hops is considered. Closed form expression for the achievable ergodic capacity in the case of equal average signal-to-noise ratios (SNRs) on both hops is derived, while for the case of unequal average SNRs on hops a tight upper bound is obtained. Comparison with the simulation results has confirmed the accuracy of the undertaken analytical approach. The obtained results have shown that significant capacity enhancement is achieved through implementation of best-to-best SCM (BTB SCM) scheme, even in the case when the average SNRs on hops are significantly different. Having in mind that this SCM scheme also improves bit error rate (BER) performance of the considered system, then it can be recognized as a very interesting solution for 4G cellular systems.

Ergodic capacity of OFDM AF fixed gain relay system with subcarrier mapping

In this paper ergodic capacity of dual-hop OFDM amplify-and-forward (AF) fixed gain (FG) relay system, implementing capacity maximizing best-to-best subcarrier mapping (BTB SCM) scheme at the relay (R) station, is examined. Scenario without direct communication between the source of information (S) and destination terminal (D) is considered, with Rayleigh fading statistics on both hops. A closed form relation for the tight lower bound of the system ergodic capacity is derived. Comparisons of the obtained ergodic capacity results with the simulation results have confirmed the accuracy of the undertaken analytical approach. Thus, the derived analytical expression presents very useful and most accurate available tool for the performance assessment of the OFDM AF FG relay system with BTB SCM, considered to be interesting solution for the next generation of mobile cellular systems.

New solution for BER performance improvement of OFDM AF relay systems

Dual-hop OFDM amplify-and-forward (AF) variable gain (VG) relay systems may improve bit error rate (BER) performance if ordered subcarrier mapping (SCM) is applied at the relay station (R). In previous works we showed that in the region of small and medium values of average signal-to-noise ratios (SNRs) on hops best-to-best SCM (BTB SCM) scheme should be applied, while in the region of high values of average SNRs on hops very small BER performance improvement is achieved by implementing best-to-worst SCM (BTW SCM) scheme. In this paper we propose new solution, where in the assumed relay system with BTB SCM the subcarriers having the lowest SNR on each hop are omitted. Analytical and simulation result comparison, for the scenario with DPSK modulation implemented and Rayleigh fading statistics on both hops, have confirmed that the proposed solution achieves the best BER performance for all the SNR values.

Performance Improvement of Dual-Hop OFDM Decode-and-Forward Relay System

Ergodic capacity of dual-hop orthogonal frequency division multiplexing (OFDM) based decode-and-forward (DF) relay system may be significantly enhanced if ordered subcarrier mapping (SCM) is implemented at relay station (R). We proved earlier that this SCM scheme also brings certain bit error rate (BER) performance improvement to assumed system. However, the level of the achieved BER reduction is very small, with no reduction at all for the high signal-to-noise ratios (SNRs) on both hops. Therefore, in this paper we propose a modification of the SCM scheme where one or more subcarriers with the lowest SNRs from both hops are omitted before ordered SCM is performed at the relay station of an OFDM DF relay system. For the scenario with Rayleigh fading statistics on both hops, and no direct communication between the source of information (S) and destination (D), we derived a closed form BER relation of the assumed uncoded BPSK modulated relay system. The analytically obtained BER results, which are verified through simulations, show that the proposed modified SCM scheme brings significant BER performance improvements for all SNR values on both hops. Additionally, in order to provide analytical tool for the assessment of ergodic capacity enhancement achieved through ordered SCM, we derived ergodic capacity expression of the dual-hop OFDM DF relay system with ordered SCM.

A Novel Solution for OFDM Based Relay Systems

Abstract In this paper we propose a novel solution for performance enhancement of dual-hop orthogonal frequency division multiplexing (OFDM) based decode-and-forward (DF) relay system, which assumes that relay station uses more than one antenna for downlink communications and implements transmit antenna selection (TAS) on subcarrier basis jointly with ordered subcarrier mapping (SCM). Ordered SCM is technique where subcarriers from the first hop are mapped to corresponding subcarriers on the second hop in accordance to their instantaneous signal-to-noise ratios (SNRs). It is proven to be a mapping scheme that maximizes the achievable ergodic capacity in OFDM based relay systems, while enabling bit error rate (BER) improvement at the same time. In order to assess the level of BER performance improvement in the system proposed in this paper, we analytically derive closed form BER expression of binary phase shift keying modulated OFDM DF relay system with TAS and SCM, assuming a scenario with Rayleigh fading statistics on both hops. Additionally, for further BER reduction, we analyze the combination of TAS with a modified SCM scheme, in which the subcarriers having the lowest SNRs on both hops are omitted. All derived analytical results are completely verified through simulations, showing that significant BER performance improvements are achieved with the novel proposed OFDM relay system, compared to the systems implementing only SCM, or only TAS, which approves that it can be considered as an interesting solution for the next generation of mobile cellular systems.

Comparison of average global exposure of population induced by a macro 3G network in different geographical areas in France and Serbia.

This article is the first thorough study of average population exposure to third generation network (3G)-induced electromagnetic fields (EMFs), from both uplink and downlink radio emissions in different countries, geographical areas, and for different wireless device usages. Indeed, previous publications in the framework of exposure to EMFs generally focused on individual exposure coming from either personal devices or base stations. Results, derived from device usage statistics collected in France and Serbia, show a strong heterogeneity of exposure, both in time, that is, the traffic distribution over 24 h was found highly variable, and space, that is, the exposure to 3G networks in France was found to be roughly two times higher than in Serbia. Such heterogeneity is further explained based on real data and network architecture. Among those results, authors show that, contrary to popular belief, exposure to 3G EMFs is dominated by uplink radio emissions, resulting from voice and data traffic, and average population EMF exposure differs from one geographical area to another, as well as from one country to another, due to the different cellular network architectures and variability of mobile usage. Bioelectromagnetics. 37:382-390, 2016.

SER Performance of OFDM Polarization Diversity System in Ricean Fading Environment

This paper analyzes SER (symbol error rate) performance of OFDM (orthogonal frequency division multiplexing) system with polarization diversity. It is assumed that the system consists of dual polarized transmit and receive antennas. Propagation environment is characterized with Ricean fading and an original method for analytical determination of the system SER performance is used. Input data streams are mapped according to M-ary PSK (phase shift keying) modulation. Comparisons between analytical and simulation results for M=4 PSK mapping and MRC (maximal ratio combining) of the received diversity signals are performed. It is shown that polarization diversity can be considered as a solution for improving performance of the analyzed M-PSK OFDM system.