The well-known major drawbacks of the Orthogonal Frequency-Division Multiplexing (OFDM), namely, the transmitter versus receiver Carrier Frequency Offset (CFO), and the Peak-to-Average Power Ratio (PAPR) of the transmitted OFDM signal, may degrade the error performance, by causing Intercarrier Interference (ICI), as well as in-band distortion and adjacent channel interference, respectively. Moreover, in spite of the utmost care given to CFO estimation and compensation in OFDM wireless systems, such as wireless local networks or the mobile radio systems of the fourth generation, e.g., the Long-Term Evolution (LTE), still some residual CFO remains. With this regard, though so far the CFO and the PAPR have been treated independently, in this paper, we develop an Error Vector Magnitude (EVM) based analytical model for the CFO-induced constellation symbol phase distortion, which essentially reveals that the maximal CFO-caused squared phase deviation is linear with the instantaneous (per-OFDM-symbol) PAPR. This implies that any PAPR reduction technique, such as simple clipping or coding, indirectly suppresses the CFO-induced phase deviation, too. The analytically achieved results and conclusions are tested and successfully verified by conducted Monte Carlo simulations.

In mobile communication systems, the transmitted RF signal is subject to mutually independent deterministic path loss and stochastic multipath and shadow fading. As at each spatial location mostly the composite signal samples are measured, their components are distinguished by averaging out the multipath-caused signal level variations, while preserving just the ones due to shadowing. The prerequisite for this is the appropriateness of the local area averaging path length that enables obtaining the local mean (composed of mean path loss and shadow fading) and the multipath fading as difference between the composite signal sample and the local mean. However, the so far reported analytical approaches to estimation of the averaging path length are based on considering either the multipath or just the shadow fading, with applicability limited to only specific topologies and frequencies. Therefore, in this paper, the most widely used Lee analytical method is generalized and improved by considering multipath and shadowing concurrently, so providing the general closed-form elementary-function based estimation of the optimal averaging path length as a function of common multipath and shadow fading parameters characterizing particular propagation environment. The model enables recommendations for the optimal averaging length for all propagation conditions facing the mobile receiver.

Accurate estimation of RF signal spatial local mean is of crucial importance in wireless communication systems planning, design and operation, specifically in coverage planning tools, channel access and power control, handoff algorithms, etc. However, so far, no universally applicable and verified approach for calculation of relevant averaging parameters has been developed. In this paper, comprehensive overview of spatial averaging problem is presented, including available methods for solving it. With this regard, closed-form expressions for averaging parameters calculation are delivered based on the approaches that are considered most accurate. Finally, the validity domains of these expressions are tested, indicating their applicability areas under specific propagation conditions.

In this paper, we analyze the relationship between the achieved Quality of Experience (QoE) of the web browsing network service and in-service network parameters obtained by passive monitoring. With this regard, we conducted experiments where the user QoE and in-service parameters are measured simultaneously, where the latter are derived from traffic data captured by passive probe on the Gn interface of the mobile network, and correlated to detailed records of HTTP and TCP protocols. Unlike most studies conducted in order to examine the connection between QoE of the web browsing network service and in-service network parameters, experiment in this research was performed in a live mobile network while QoE is measured by the participants in the experiment. For the purposes of research, nineteen in-service parameters are defined using the applications of system for performance management with passive probes. The link between QoE and in-service parameters was tested by Spearman's rank-order correlation. Based on the subjective evaluations by the participants in the experiment about the web browsing service quality, it was evident that there was strong relationship between the QoE and specific network parameters such as e.g. Average Time to get first data and Average Time to connect. However, no such relationship was found between the Cancellation rate parameter and QoE, as the hypothesis that there was no relationship between these two parameters, could not be rejected.

In this paper, we propose an analytical model for estimating the irreducible bit error ratio BER in multipath channel with small-extent delay dispersion, such as indoor, where the signal-to-noise ratio is high, implying dominance of inter-symbol interference as error-generating mechanism. Both channel and overall orthogonal frequency-division multiplexing OFDM symbols are modeled stochastically, resulting with novel expression for the residual BER prediction that is shown to analytically distinguish power delay profiles with equal delay spreads but having different profile shapes. In addition, the model could simply accommodate insertion of cyclic prefix onto the OFDM symbol, providing a means for either testing adequacy of any applied standard cyclic prefix length or finding its optimal value as a compromise between the performance enhancement achieved by inserting cyclic prefix and the consequently added redundancy. Finally, the model was modified as to include the analysis of effects of subcarrier frequency inaccuracy or Doppler shift, by adding additional equivalent delay dispersion with equal effect on BER degradation, while considering the system virtually free of carrier frequency offset. All analytically achieved results and conclusions are tested and successfully verified by conducted extensive Monte Carlo simulations. Copyright © 2015John Wiley & Sons, Ltd.

In this paper, we derive a prediction model for the block error rate (BLER) of an AWGN channel as a function of (known) bit error rate (BER) for transmission over small-delay-dispersion channels, such as indoor, where cyclic prefix protection mechanism reliably prevents inter-symbol interference due to multipath. By adopting hypergeometric rather than common binomial distribution of erroneous bits within a data block, a novel BLER prediction formula is derived and validated first by model-specific MC simulations. Then, it is verified in LTE FDD downlink channel conditions, using an industry-standard software simulation tool. The achieved test results are shown to match the block error rate prediction coming out of the developed model, within expected limits.

It is a great pleasure welcoming all of you to the IEEE International Wireless Communications and Mobile Computing Conference (IEEE IWCMC 2015) in the beautiful Dubrovnik, Croatia! We are indeed delighted that this year's IEEE IWCMC lived up to its goal under the conference theme “Communications for the 21st Century,” and continues its tradition of providing the premier forum for presentation of research results and experience reporting on the cutting edge research in the general areas of wireless communications and mobile computing. This year, we received more than 700 submissions from 42 countries. Each paper received at least three peer technical reviews, comprised of more than 450 TPC members from academia, government laboratories, and industries. After carefully examining all review reports, the IEEE IWCMC 2015 TPC finally selected about 36% high-quality papers for presentation at the conference and publication in the IEEE IWCMC 2015 proceedings. The conference program starts on Monday August 24th with a full day of Tutorials that are free of charge to all our attendees. Then, each day starts with a keynote speaker chosen from renowned world-class leaders in the area-Dr. Giuseppe Bianchi from University of Roma Tor Vergata, Italy, Dr. Mario Gerla from UCLA, and Dr. Slim Alouini from KAUST, highlighting the latest research trends in the wireless communications, mobile computing, and networks. This year, the technical sessions reflect the continued and growing interests in a wide range of spectrum, including wireless communications and networks, cross-layer design and optimization, mobile computing, wireless sensor networks, network security, and use of wireless technologies in social emergency applications. There are two special sessions composed of invited papers from renowned experts from around the world. Outstanding papers will be selected for four Special Issues in well known international journals. Our objective in the future is to reduce the acceptance rate further.

We address the received signal strength (RSS) based target localization problem in large-scale cooperative wireless sensor networks (WSNs). Using the noisy RSS measurements, we formulate the localization problem based on the maximum likelihood (ML) criterion. Although ML-based solutions have asymptotically optimal performance, the derived localization problem is non-convex. To overcome this difficulty, we propose a convex relaxation leading to second-order cone programming (SOCP) estimator, which can be solved efficiently by interior-point algorithms. Moreover, we investigate the case where target nodes limit the number of cooperating nodes by selecting only those neighbors with the highest RSS. This simple procedure can reduce the energy consumption of an algorithm in both communication and computation phase. Our simulation results show that the proposed approach outperforms significantly the existing ones in terms of the estimation accuracy and convergence. Furthermore, the new approach does not suffer significant performance degradation when the number of cooperating nodes is reduced.

In this paper, the earlier developed error floor model for the peak performance estimation of OFDM transmission over multipath channel with small delay dispersion is enhanced by deriving a novel expression for estimating the optimal sampling delay in the power delay profile. The validity of the estimation is checked in the LTE FDD downlink environment by means of the industry-standard simulator that provided values close to the analytically predicted ones. Optimal sample time estimation can be used as a means to explore the ultimate error floor values, but the model can also be of practical use in adaptive sampling schemes.

We address the problem of constellation design for single-subcarrier intensity-modulated direct-detected optical systems. We seek to design constellations that minimize the average electrical power, average optical power and peak optical power for a given minimum Euclidean distance between constellation points. The constellation design is formulated as a nonconvex optimization problem with a convex cost function, nonconvex quadratic constraints and second-order cone constraints. It is shown that this problem can be approximated by a second-order cone programming (SOCP) problem. We propose an iterative procedure in which the SOCP approximation is refined in each iteration. The new constellations are compared to the state-of-the-art constellations in terms of power efficiency. Our 32- and 64-point constellations outperform the corresponding QAM-based and face-centered cubic lattice constellations.