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Radio frequency identification (RFID) is a promising and widespread wireless communication technology for entity identification or authentication. By the emerging Internet of Things phenomenon, the use of RFID is densely augmenting in various daily life applications. However, RFID systems suffer from security and privacy issues. Recently, many researchers propose RFID authentication protocols based on elliptic curve cryptography (ECC) to efficiently mitigate the aforementioned concerns. In this work, we extensively examine the state-of-the-art RFID authentication protocols based on ECC in terms of security and performance. Some of these works claim that their protocols provide all general security and privacy properties. We revisit Vaudenay’s formal privacy model and show that they do not provide forward and/or backward privacy under this model contrary to their claim. Then, we propose a secure, privacy-preserving and efficient ECC based RFID authentication protocol. We also present a security and performance analysis of our proposed protocol and compare it to the existing relevant schemes in detail. Furthermore, we implement our proposal in a real RFID system to demonstrate its practicability. To the best of our knowledge, our proposed scheme is the most efficient ECC based RFID authentication protocol realized in a real-world environment that satisfies all common security and privacy features including backward and forward privacy.

Spatial modulation (SM) is a simple multi-input multi-output (MIMO) communication technique in which a single transmit antenna is active for each symbol period. Quadrature spatial modulation (QSM), on the other hand, is a form of SM in which independent transmit antenna selection is made for the real and imaginary parts of the symbols. In these techniques, the spectral efficiency (SE) can be increased logarithmically by increasing the number of antennas used on the transmitter-side. Besides, in classical SM and QSM schemes, the number of antennas must be the power of two. In this paper, a flexible QSM scheme is proposed, which eliminates the necessity of antenna number and increases SE value linearly with the number of antennas for RF systems. This scheme, called hardware-aware quadrature spatial modulation (HAQSM), uses optimized constellations for the desired SE value. Optimal constellations are obtained using convex optimization under a constraint aimed at keeping the distance between neighboring symbols above the desired value. The bit error rate (BER) performances of the HAQSM scheme were obtained by Monte Carlo simulations and compared with the existing schemes in the literature.

Quadrature-spatial modulation (QSM) offers high spectral efficiency (SE) without interchannel interference for both radio frequency and visible light communication (VLC) systems. In this article, a new QSM scheme called flexible quadrature spatial pulse amplitude modulation (FQSPAM) is proposed for VLC systems. In space modulation techniques (SMTs), the data bit stream is divided into two groups as the index bits and the signal bits. These grouped bits are mapped independently to modulation symbols and indices of light-emitting diodes (LEDs). However, this mapping strategy puts a constraint on the number of LEDs and the size of the signal constellation. FQSPAM jointly designs the signal and spatial components of the constellation to overcome these limitations. This approach removes the constraint on the number of LEDs and the size of the signal constellation. The constellation design problem is formulated as a convex optimization problem to identify power-efficient constellations with different $M$ values. A dimming-controlled optimization algorithm has also been proposed to take into account both illumination and communication at the same time. Analytical and numerical results show the improved bit error rate performance of the proposed FQSPAM compared to spatial pulse amplitude modulation and channel adaptive bit mapping.

The effect of unknown mutual coupling in receiving array seriously degrades the performance of direction-of-arrival (DoA) estimation algorithms. In order to compensate this effect, this paper develops an auto-calibration method for the uniform linear array (ULA) based on Root-MUltiple SIgnal Classification (MUSIC) algorithm. The proposed method can estimate the DoAs of the received signal and mutual coupling coefficients using the subspace principle without using any calibration source. Moreover, it can reduce computational complexity due to analytically estimating DoA without any spectrum search. In this paper, Monte-Carlo simulation is used to elucidate the errors in DoA and coupling parameter estimation. Cramer-Rao lower bound (CRB) is also presented to support the estimation results. Simulation results illustrate that the proposed Friedlander & Weiss (F&W) Root-MUSIC method efficiently estimates the DoA and mutual coupling coefficients, and also the performance of F&W Root-MUSIC is better than F&W MUSIC algorithm's.

Emerging systems such as Internet-of-things (IoT) and machine-to-machine (M2M) communications have strict requirements on the power consumption of used equipments and associated complexity in the transceiver design. As a result, multiple-input multiple-output (MIMO) solutions might not be directly suitable for these system due to their high complexity, inter-antenna synchronization (IAS) requirement, and high inter-antenna interference (IAI) problems. In order to overcome these problems, we propose two novel index modulation (IM) schemes, namely pulse index modulation (PIM) and generalized PIM (GPIM) for single-input single-output (SISO) schemes. The proposed models use well-localized and orthogonal Hermite-Gaussian pulses for data transmission and provide high spectral efficiency owing to the Hermite-Gaussian pulse indices. Besides, it has been shown via analytical derivations and computer simulations that the proposed PIM and GPIM systems have better error performance and considerable signal-to-noise ratio (SNR) gain compared to existing spatial modulation (SM), quadrature SM (QSM), and traditional M-ary systems., Comment: 5 pages, submitted for publication

In this paper, multi-input multi-ouuput (MIMO) with K users system model is considered where interference between users try to minimize by using minimum mean square error (MMSE) based interference alignmnet (IA) that is a linear technique. Each user in the considered system uses the channel state information (CSI) among all transmitters and receivers to generate own precoding and suppressing matrices. Since these matrices are generated according to the CSI between all transmitter-receiver pairs in the system, it is necessary to transmit this information to all transmitters via a feedback channel after estimating CSI at the receiver. However, the estimated CSI by each receiver is required to share with all transmitters including its own transmitter. In this study, it is investigated the effect of number of bits used to quantization of the CSI, the transmission of the CSI over noisy feedback channels, and outdated CSI on the IA performance. According to the results, impairment on the CSI significantly reduces GH performance.

In this paper, we analyze the impact of the small cell user density on the power consumption and the number of served users by the macro cell and small cells. It is assumed that users are distributed uniformly in all coverage area with different density and small cell user density is related linearly with macro cell user density. In the simulations, three different mean values are chosen, where the power consumption and the number of served users by the macro cell and small cells are investigated according to these values. The simulation results show that small cells with low mean value enable to save more power. When user density of macro cell is and mean value of small cell user density equals to 15, saved power by using the small cells sleeping technique is 695 Watts. When this saved power decreases to 372 Watts. Similarly, as the mean value of the small cell user density increases, the power gain obtained by the algorithm decreases.

Security and privacy concerns have been growing with the increased utilisation of RFID technology in our daily lives. To mitigate these issues, numerous privacy-friendly authentication protocols have been published in the last decade. Random number generators (RNGs) are necessarily used in RFID tags to provide security and privacy. However, low-end RNGs can be the weakest point in a protocol scheme and using them might undesirably cause severe security and privacy problems. On the other hand, having a secure RNG with large entropy might be a trade-off between security and cost for low-cost RFID tags. Furthermore, RNGs used in low-cost RFID tags might not work properly in time. Therefore, we claim that the vulnerability of using an RNG deeply influences the security and privacy level of the RFID system. To the best of our knowledge, this concern has not been considered in the RFID literature. Motivated by this need, in this study, we first revisit Vaudenay’s privacy model which combines the early models and presents a new mature privacy model with different adversary classes. Then, we extend the model by introducing RANDOMEYE privacy, which allows analyzing the security of RNGs in RFID protocols. We further apply our extended model to two existing RFID schemes.

The overwhelming demand for data by an ever-increasing number of users is a great challenge wireless cellular networks are faced with. One potential solution to this issue is deploying a massive number of small cells (SCs) in the existing macro network. As SC overlay has a big role in the future wireless networks that can overcome the data traffic upsurge at little power cost, heterogeneous network (HetNet) has been viewed as a promising technology for 5G networks that extends cell coverage, improves network capacity and offloads the network traffic from the macro cell (MC) to the SCs. However, the hyper-dense SCs and their uncorrelated operation raise an important question about the joint power consumption of the macro base station (MBS) and the small base stations (SBSs) in the HetNet since the aggregate power consumption of the dense SBSs cannot be ignored. Recently, the SC sleeping technique has become a hot topic for saving energy in HetNets. To minimize power consumption in HetNets, we propose three algorithms to dynamically adapt the operation of the SBSs to active/sleep (on/off) for non-uniform user distribution in the HetNet. We investigate the general optimal power minimization problem for HetNet that requires relatively high computational complexity. Taking into account the additional increase of the traffic load brought to the MBS, a key design principle of the proposed algorithms is to switch off the SBSs gradually based on their locations, user densities in their coverage areas or the highest power that can be saved by switching some of them off, respectively. Then, we enhance the mathematical framework to make the analysis more realistic by considering the offloading between the SCs and the MBS that occurs when the traffic load exceeds SCs’ capacity. In this paper, based on the fact that user densities of SCs and MC change with time, we model the traffic on the European traffic profile and portray the power consumption of the HetNet throughout the day. Simulation results show that by applying SC sleeping and our proposed algorithms, the HetNet can save about 20% power daily. The performances of our proposed algorithms are close to that of the optimal algorithm and their computational complexities are remarkably lower.

Çelik, Yasin ( Aksaray, Yazar), In this paper, generalized quadrature spatial modulation (QSM) techniques are proposed for multiple-input single-output (MISO) visible light communication (VLC) systems using quadrature spatial modulation subcarrier intensity modulation (QSM-SIM). Additionally, realistic channel condition including both line-of-sight (LOS) and non-LOS (NLOS) components up to the third reflection is also considered and channel coherence bandwidths are calculated for varying number of LEDs. Since the indoor MISO VLC channel has strong correlation between coefficients, particle swarm optimization (PSO) and approximated maximum minimum Euclidean distance (AMMD) based precoding on the transmitter side are studied to reduce the channel correlation under illumination constraints. As a performance metric, bit error rate (BER) performance of considered modulation techniques is analyzed for different MISO schemes. The upper bound BER performances are also derived analytically in order to validate the simulation results. According to the results, we reached three important conclusions. First one is that variable length generalized QSM (VGQSM) by having few LED arrays on the transmitter side performs the best BER results compared to other schemes that provide the same spectral efficiency (SE) and the second is that precoding is essential for indoor MISO VLC systems to reduce the channel correlation. Finally, an increase in the number of LED arrays results in a decrease in channel coherence bandwidth.

Radio resource management (RRM) in a heterogeneous network (HetNet) has gained significant attention in order to manage the radio resources efficiently. In this paper, an adaptive radio resource management (ARRM) strategy is presented to implement the fractional frequency reuse with three sectors and three layers (FFR-3SL) model more efficiently in a conventional long term evolution advanced (LTE-A) HetNet system. In the FFR-3SL model, the entire macro-cell coverage area is split into three sectors and three layers; while the total available bandwidth is fractioned into seven subbands. The radio resources (subbands) are assigned to femto-cells and macro-cells according to the user equipment (UE) demand in high-density areas. In order to examine the model, four different cases of user location distribution (ULD) such as central layer focused (CLF), middle layer focused (MLF), outer layer focused (OLF), and uniform distribution are considered. A Monte Carlo simulation is applied to assess and analyze the overall system performance in terms of throughput and efficiency. The simulation results show that the CLF achieves higher throughput and better efficiency under the given parameters when the ARRM strategy applied properly.

30th IEEE Annual International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2019 -- 8 September 2019 through 11 September 2019 -- -- 155054, In this paper, we consider a cognitive K-user multi-input multi-output interference network in the presence of an eavesdropper and a partial-band jammer, where an iterative interference alignment technique is adopted in the primary network to minimize the interference leakage. For the proposed scheme, we first obtain the statistical properties of the signal-to-jamming-noise ratio (SNJR) by considering the partial band jammer. Thereafter, in order to quantify the secrecy performance of the proposed system, we derive new closed-form expressions for the average secrecy capacity and probability of positive secrecy. Finally, the numerical results which are validated with the aid of simulations show that the secrecy performance of the primary network can be deteriorated due to the adverse affects of partial band jammer. © 2019 IEEE.

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) has been recently proposed to increase the spectral efficiency and improve the error performance of multicarrier communication systems. However, all the OFDM-IM systems assume that the perfect channel state information is available at the receiver. Nevertheless, channel estimation is a challenging problem in practical wireless communication systems for coherent detection at the receiver. In this paper, a novel method based on the pilot symbol-aided channel estimation technique is proposed and evaluated for OFDM-IM systems. Pilot symbols, which are placed equidistantly, allow the regeneration of the response of the channel so that pilot symbol spacing can fulfill the sampling theorem criterion. Our results shows that the low-pass interpolation and SPLINE techniques perform the best among all the channel estimation algorithms in terms of bit error rate and mean square error performance.

Recently, a dual-mode OFDM relying on index modulation (DM-OFDM-IM) has been introduced to increase the data rate of the conventional IM based OFDM techniques. However, such a mechanism has bit error rate performance loss due to the deep fading channels such as the practical Rayleigh channels. In this work, to improve the BER performance of the DM-OFDM-IM technique, a new technique, that is called as DM-OFDM-IM with generalized prefix (DM-OFDM-IM-GP) is proposed. The simulation results illustrate that the proposed DM-OFDM-IM with GP achieves about 10 dB SNR gain over the existing DM-OFDM-IM at the spectral efficiency of 4, 2.22 and 1.33 bits/s/Hz in Rayleigh fading channel. Keywords-Index Modulation; Generalized Prefix; Orthogonal Frequency Division Multiplexing; Dual-Mode, Index Modulation, Spatial Modulation.

27th Signal Processing and Communications Applications Conference, SIU 2019 -- 24 April 2019 through 26 April 2019 -- -- 151073, In this work, the adverse effects of a partial band jammer on a multi-user, multi-input multi-output cognitive radio networks are analyzed. In the proposed model, primary user transmits its information to the receiver with the aid of linear interference alignment method which uses a precoder and an interference suppression matrix. In this network, it is assumed that a partial band jammer adversely affects the transmission quality of the primary network. The analysis starts with the derivation of end-to-end signal to jammer noise ratio. Then, with the aid of probability density function and cumulative distribution functions, symbol error probability and outage probability are derived. © 2019 IEEE.

Channel delays and mobility cause the transmitted signal to propagate in both time and frequency regions, resulting in inter-symbol and inter-carrier interference, respectively. The filter structures used in the transmitter and receiver structures for impact shaping affect the size of the interference between these symbols and carriers. In this study, the composite effects of the wireless environment and the filters used were examined on the equalization of multi-carrier systems and the determination of the appropriate filter structure was studied. The number of effective taps of the composite channel effect was obtained as a function of the channel, the transmitter/receiver filters and the signal to noise ratio (SNR). For this purpose, the composite channel was modeled as an symbol-spaced finite impulse response (FIR) filter, then the AIC (Akaike Information Criterion) method was used to determine the number of taps. Subsequently, the transmitter/receiver filter types were determined which minimized the effective taps of the composite channel model by energy optimization in the equalization process.

Nowadays, variants of Spatial Modulation (SM) are studied by a lot of researchers in order to increase Spectral Efficiency (SE) more. One of the important variants of SM is known as Orthogonal Frequency Division Multiplexing Index Modulation (OFDM-IM). In OFDM-IM, selection of active subcarriers is based on the idea of the selection of active antennas in the SM. Then, to take OFDM-IM a step further in terms of SE, Dual Mode OFDM-IM (DM-OFDM-IM) has been proposed that activates entire subcarriers unlike that of OFDM-IM. However, in all these studies same assumption is made, i.e., channel is perfectly known at the receiver. However, this assumption is not accurate for practical applications. For this reason, the presented simulation results and theoretical analysis without channel estimation cannot represent the real system performance. In this study, a pilot symbol aided channel estimation for DM-OFDM-IM scheme is considered. We investigate the effect on Bit Error Rate (BER) performance of five different interpolation techniques. The simulation results illustrate that, interpolation techniques perform similiar BER performance for low and moderate Signal-to-Noise Ratio (SNR) range. However, at the high SNR values (SNR> 30 dB), Low-Pass and SPLINE interpolation techniques give the highest performance among all considered techniques.

High data rate and energy-efficient design are of paramount importance for 5G systems. Massive MIMO can ensure both of these by extending the number of antennas at base station (BS) to a few hundreds and operating in time division duplex (TDD) mode to serve several tens of terminals. This study evaluates the impact of user location distribution (ULD) variation on the energy efficiency of a load-adaptive massive MIMO system. Then, it suggests a dynamic resource allocation strategy that exploits the advantage of ULD variations to attain a more energy-efficient design. Daily ULD variation is modeled by splitting the cell into a certain number of coverage areas and assigning different user densities to each one for each hour. This modeling yields different ULD variations, such as boundary focused (BF), middle focused (MF), uniform, and center focused (CF) ULD variations. For clarity, all cells are assumed identical in terms of BS configurations, cell loading and ULD variation. The simulation performed in this study benchmarks the proposed dynamic strategy with a fixed strategy dimensioned at maximum cell load and BF ULD model. The results show that the optimal number of antennas depends primarily on ULD model and secondarily on cell loading. Up to one third of the active antennas can be turned off on a daily basis, and this in turn conserves up to 36–50% of the consumed energy.

In this paper, new pilot insertion techniques that make use of index modulation (IM) idea for channel estimation (CE) are proposed for orthogonal frequency division multiplexing (OFDM) systems. These techniques not only perform CE but also convey additional bits. Simulation results show that the performance of the proposed schemes are very close to the performance of the classical pilot symbol-assisted (PSA) OFDM system, with the additional benefit that more bits can be transmitted. Despite a slight increase in the complexity of the receiver, higher spectral efficiency than conventional OFDM systems can be achieved. Especially, the proposed method-II transmits more bits than the proposed method-I owing to its subblock form.

DOI : 10.26650/electrica.2019.19017 In this paper, the performance of a secondary user (SU) in an underlay cognitive radio (CR) network over a generalized-gamma (GG) fading channel in terms of three performance metrics, namely, outage probability, ergodic capacity, and bit error rate (BER), is investigated. According to the underlay approach, the transmit power of the SU should be limited to avoid interference to primary users (PUs). The performance metrics of the SU in the underlay CR network are theoretically derived and also obtained with Monte Carlo simulations for a GG fading channel with different fading parameters. To demonstrate the effect of limited power on the performance metrics, three different maximum transmit power levels (Pmax), namely, 10, 20, and 30 dB, are used. The simulation results lead to three conclusions: First, when high values are chosen for the fading parameters (α, c), the fading channel gets less distorted and the performance metrics improve. The second conclusion is that the BER performance gets better as the limited power increases. The final conclusion is that the BER performance of SUs improves as the interference power that PUs can tolerate increases. Cite this article as : Aldirmaz Colak S. Performance Analysis of a Secondary User in Cognitive Radio over Generalized-Gamma Fading Channels. Electrica, 2019; 19(2): 166-172.

In this work, two new transmission schemes are proposed to increase the spectral efficiency of orthogonal frequency division multiplexing (OFDM). In practical OFDM systems, channel estimation is usually performed by employing pilot symbols which is based on inserting known symbols in the time-frequency domain. However, pilot symbol designing is one of the bottlenecks of OFDM systems limiting the increase of spectral efficiency. We apply new pilot design structures, which are use orthogonal Walsh-Hadamard codes. To increase the spectral efficiency of OFDM systems, we assign the extra bits to the index of the each orthogonal Walsh-Hadamard codes. Simulation and theoretical results show that proposed methods have better performance than conventional OFDM with higher spectral efficiency. Moreover, no more energy is spent for additional information carried in the indices compared to classical OFDM systems. As a result, proposed methods provide both spectral efficiency and energy efficiency.

In this work, we examine the interference alignment (IA) performance of a multi-input multi-output (MIMO) multi-hop cognitive radio (CR) network in the presence of multiple primary users. In the proposed architecture, it is assumed that linear IA is adopted at the secondary network to alleviate the interference between primary and secondary networks. By doing so, the secondary source can communicate with the secondary destination via multiple relays without causing any interference to the primary network. Even though linear IA can suppress the interference in CR networks considerably, interference leakages may occur due to a fast fading channel. To this end, we focus on the performance of the secondary network for two different cases: (i) the interference is perfectly aligned, (ii) the impact of interference leakages. For both cases, closed-form expressions of outage probability and ergodic capacity are derived. The results, which are validated by Monte Carlo simulations, show that interference leakages can deteriorate both system performance and the diversity gains considerably.

With the integration of the index modulation concept, the popular OFDM has gained an appealing new dimension. However, OFDM with index modulation (OFDM-IM) causes a decrease in data rate for higher order modulations due to its unused subcarriers. Recently, dual-mode OFDM with index modulation (DM-OFDM-IM) has been proposed to prevent this decrease in data rate. The spectral efficiency (SE) of both techniques depends on the selection of different parameters, such as modulation types and number of active subcarriers. However, the quality of the wireless channel has not been taken into account yet to increase the data rate. In this paper, we propose a new adaptive DM-OFDM-IM (A-DM-OFDM-IM) system to enhance the bit error probability (BER) performance considering the channel conditions and obtain a substantial increase in SE. Unlike the previous DM-OFDM-IM and the classical OFDM-IM schemes, our proposed system enables the use of different types of modulations for different subblocks in one OFDM signal. We demonstrate that the SE of the proposed system is comparable with that of its OFDM-IM and DM-OFDM-IM counterpart under frequency selective Rayleigh channels. Moreover, computer simulations corroborate that the derived theoretical results are considerably accurate for the SE of A-DM-OFDM-IM systems. (C) 2018 Elsevier B.V. All rights reserved.

The large scale (massive) MIMO system is one of the candidate technologies for use in 5G due to its high energy efficiency (EE) and offered high data rate. In this paper, energy efficiency and proposed data rate of the large scale MIMO system in downlink mode are investigated according to the traffic load in the cellular network. In addition, three different user distribution models have been proposed for understanding the effect of users' position within the cell on EE. Under equal traffic load in all cells, simulations show that BS requires fewer antennas if most of the users are close to the cell center. As a result of simulations, it has been shown that the energy efficiency can be increased by changing the number of antennas that BS will use depending on the traffic load on the cell and user locations.

In this paper, the problem of selecting the best relay using the Amplify-and-Forward method for interference forwarding is investigated in heterogeneous cellular networks. A macrocell user is modeled as a victim exposed to the interference due to the Femtocell network, and 3 macrocell users close to the victim are used as a relay to provide interference forwarding. The links between stations-users and users-users are designed as an unrelated Rayleigh channel model. The best relay selection is made based on distance and small scale channel fading. Computer simulations show success rate against the targeted spectral efficiency.

The purpose of this study is to design DSP (Digital Signal Processor) based IFF (Identification of Friend and Foe) signal simulator. Design of hardware based signal generation scheme that corresponds to range, azimuth and altitude data which is defined for interrogation of platform and reply codes and user interface for scenario definition is suggested. Fundamental information of IFF system signals and platform-signal relationship are defined in this scope. Moreover; DSP resource assignments for such a signal generation and key parameters of application algorithm are given. Besides generated signal waves and characteristics are observed. Finally, general comparison with available systems is performed and success of developed solution is discussed.

Due to copyright restrictions, the access to the full text of this article is only available via subscription. In this paper, we consider a DC-biased optical-orthogonal frequency division multiplexing (DCO-OFDM) visible light communication system and investigate its error rate performance under illumination constraints. First, we find the optimum signal power for a given DC bias level assuming a fixed number of LEDs. Then, for a desired lighting requirement, we determine the optimum combination of DC bias, signal power and the number of LEDs which gives the best bit error rate (BER) performance. Numerical results are presented to demonstrate the BER under different settings under consideration. Qatar National Research Fund