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Because of the broadcast nature of the wireless communication medium, their security issues are receiving extensive concern. In this paper, we propose a spectrum-sparse signal based on multi-carrier modulation for secure wireless communication. The proposed signal is a summation of multiple sub-band signals over several equally spaced carriers. The power spectrum density of the proposed signal can be reduced to a level even lower than the background noise, provided the number of sub-bands is sufficiently large. Thus, the proposed signal possesses a favorable low probability detection property similar to that of spread spectrum signals. At the intended receiver, an under-sampling method based on active aliasing is proposed. In this way, the intended receiver can coherently collect the transmitted signal power over all sub-bands and extract the information reliably. We also derive a closed-form expression for bit error rate performance of the proposed scheme in additive white Gaussian channel with binary phase shift keying modulation. Finally, numerical and simulation results to testify the effectiveness of the proposed scheme are generated for both binary phase shift keying and eight-phase shift keying modulations in additive white Gaussian channel. [ABSTRACT FROM AUTHOR]

Multicarrier code division multiple access (MC-CDMA) systems have arrested a lot of attention, owing to the simple implementation and powerful resistance to frequency-selective channels and the CDMA with the suitability for multiuser systems. Although MC-CDMA systems spread symbols using orthogonal codes to ensure orthogonality, orthogonality may be destroyed at the receiver due to frequency selective fading and then results in multiple access interference (MAI) and inter-carrier interference (ICI). The space-alternating generalized expectation-maximization (SAGE) algorithm is with high convergence speed and performs maximum-likelihood estimation/detection of the transmitted signals. For MC-CDMA systems, existing SAGE algorithm is used to cancel the ICI (Panayirci et al. in IEEE Trans Signal Process 58(8): 4225-4238, ), or to cancel the MAI (Panayirci et al. in 16th IST Mobile and Wireless Communications Summit, ). In this paper, the proposed interference cancellation scheme not only performs MAI cancellation but also performs ICI cancellation for the MC-CDMA systems. Some simulation examples are given to show the effectiveness and comparisons of the proposed receiver. [ABSTRACT FROM AUTHOR]

This paper presents a prototype filter design using the orthant optimization technique to assist a filter bank multicarrier (FBMC) modulation scheme of a NextG smart e-healthcare network framework. Low latency and very high reliability are one of the main requirements of a real-time e-healthcare system. In recent times, FBMC modulation has gotten more attention due to its spectral efficiency. The characteristics of a filter bank are determined by t's, prototype filter. A prototype filter cannot be designed to achieve an arbitrary time localization (for low latency) and frequency localization (spectral efficiency), as time and frequency spreading are conflicting goals. Hence, an optimum design needed to be achieved. In this paper, a constraint for perfect or nearly perfect reconstruction is formulated for prototype filter design and an orthant-based enriched sparse ℓ1-optimization method is applied to achieve the optimum performance in terms of higher availability of subcarrier spacing for the given requirement of signal-to-interference ratio. Larger subcarrier spacing ensures lower latency and better performance in real-time applications. The proposed FBMC system, based on an optimum design of the prototype filter, also supports a higher data rate as compared to traditional FBMC and OFDM systems, which is another requirement of real-time communication. In this paper, the solution for the different technical issues of physical layer design is provided. The presented modulation scheme through the proposed prototype filter-based FBMC can suppress the side lobe energy of the constituted filters up to large extent without compromising the recovery of the signal at the receiver end. The proposed system provides very high spectral efficiency; it can sacrifice large guard band frequencies to increase the subcarrier spacing to provide low-latency communication to support the real-time e-healthcare network., Competing Interests: Conflict of interestThe authors Dr. Abhinav Adarsh and Dr. Basant Kumar declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper titled; “Low Latency and High Reliability FBMC Modulation Scheme using Optimized Filter Design for enabling NextG Real Time Smart Healthcare Applications”., (© The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2022, Springer Nature or its licensor holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.)

Joint on-board amplification of multiple carriers reduces hardware and weight, enabling cost-efficient satellite architectures. However, on-board power amplification is inherently a non-linear operation and the distortion effects drastically increase when the high-power amplifier (HPA) is operated in multiple-carrier mode due to the generated inter-modulation products. In order to achieve the desired on-board power efficiency and to reduce the non-linear distortion, specific countermeasures need to be put in place. Emerging multi-gateway satellite systems where, in the most general case, each carrier is uplinked independently from a different gateway, would gain further flexibility by adopting a multicarrier architecture. While advanced predistortion techniques are already available for the single-gateway scenario, no solution has been proposed for the multi-gateway multicarrier scenario. In this work, we propose novel distributed predistortion techniques to improve spectral and power efficiency in multi-gateway non-linear satellite channels. Further, we analyze the multiple-carrier predistortion parameter estimation error with respect to noise sensitivity, proposing a robust version of the indirect learning method. Distributed processing becomes sensitive to synchronization amongst the actors, and we present an evaluation of the sensitivity of proposed techniques to imperfections. [ABSTRACT FROM PUBLISHER]

With the proliferation of smart-phones and tablet PCs, the data rates of wireless communications have been soaring. Hence, the need for power-efficient communications relying on low-complexity multiple-stream detectors has become more pressing than ever. As a remedy, in this paper we design low-complexity soft-input soft-output quantum-assisted multi-user detectors (QMUD), which may be conveniently incorporated into state-of-the-art iterative receivers. Our design relies on extrinsic information transfer charts. Our QMUDs are then employed in multi-carrier interleave-division multiple-access (MC-IDMA) systems, which are investigated in the context of different channel code rate and spreading factor pairs, whilst fixing the total bandwidth requirement. One of our QMUDs is found to operate within 0.5 dB of the classical maximum a posteriori probability MUD after three iterations between the MUD and the decoders, while requiring only half its complexity, at a BER of 10^-5 in the uplink of a rank-deficient MC-IDMA system relying on realistic imperfect channel estimation at the receiver, while supporting 14 users transmitting QPSK symbols. [ABSTRACT FROM PUBLISHER]

The wireless medium offers many opportunities for broadcast communications. However, it also opens the possibility for attackers to eavesdrop the broadcast data or to pretend to be another node or device. These two attacks define the protection goals, namely, confidentiality and authenticity. Traditionally, both are solved by cryptographic approaches exploiting knowledge available in the surrounding infrastructure. The novel communication paradigms for the Internet of Things or cyber–physical systems do not scale with the standard cryptographic approach. Instead it is possible to exploit properties of the underlying physical channel to provide countermeasures against eavesdropping and impersonation attacks. Thereby, the random fading channel induces uncertainty which is detrimental but at the same time also helpful. In this paper, we review and describe a generalized model for physical-layer-based confidential data transmission and wireless authentication. A key role is played by the channel uncertainty and available design dimensions such as time, frequency, and space. We show that wireless authentication and secret-key generation can work in multicarrier and multiple-antenna systems and explain how even outdated channel state information can help to increase the available secure degrees of freedom. This survey focuses on the system design of wireless physical-layer confidentiality and authenticity under channel uncertainty. The insights could lead to a design of practical systems which are preparing the ground for confidentiality and authenticity already on the physical layer of the communication protocol stack. [ABSTRACT FROM AUTHOR]

This paper develops a novel analytical framework for asynchronous wireless networks deploying multicarrier transmission over flat-fading channels. Nodes in the network have different notions of timing; therefore, from the viewpoint of a typical receiver, the received signals from different transmitters are asynchronous, leading to a loss of orthogonality between subcarriers. We first develop a detailed link-level analysis based on OFDM, based on which we propose a tractable system-level signal-to-interference-plus-noise ratio (SINR) model for asynchronous OFDM networks. The proposed model is used to analytically characterize several important statistics in asynchronous networks with spatially distributed transmitters, including: (i) the number of decodable transmitters; (ii) the decoding probability of the nearest transmitter; and (iii) the system throughput. The system-level loss from lack of synchronization is quantified, and to mitigate the loss, we compare and discuss four possible solutions including extended cyclic prefix, advanced receiver timing, dynamic receiver timing positioning, and semi-static receiver timing positioning with multiple timing hypotheses. The model and results are general, and apply to ad hoc networks, cellular systems, and neighbor discovery in device-to-device (D2D) networks. [ABSTRACT FROM PUBLISHER]

The article introduces a novel concept of a PLC modem as a complement to the existing G3 and PRIME standards for communications using medium- or high-voltage overhead or cable lines. The proposed concept is based on the fact that the levels of impulse noise and frequency selectivity are lower on high-voltage lines than on low-voltage ones. Also, the demands for "cost-effective" circuitry design are not so crucial as in the case of modems for low-voltage level. In contract to these positive conditions, however, there is the need to overcome much longer distances and to take into account low SNR on the receiving side. With respect to the listed reasons, our concept makes use ofMCM, instead of OFDM. The assumption of low SNR is compensated through the use of an efficient channel coding based on a serially concatenated turbo code. In addition, MCM offers lower latency and PAPR compared to OFDM. Therefore, when using MCM, it is possible to excite the line with higher power. The proposed concept has been verified during experimental transmission of testing data over a real, 5 km long, 22 kV overhead line. [ABSTRACT FROM AUTHOR]

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We propose an optical multicarrier generation technique using silicon micro-ring modulator (MRM) and analyze the scheme. Numerical studies have been done for three types MRMs having different power coupling coefficients. The proposed scheme is found to generate four optical carriers having 12.5 GHz spacing. According to simulation, the maximum side-mode-suppression ratio (SMSR) of ~16.3 dB with flatness of ~0.2 dB is achieved by using this scheme. The minimum extinction ratio (ER) of the generated carriers is found to be more than 35 dB. We also propose modulator driver circuit to generate RF signal, which is needed to generate multicarrier using MRM. The effect of coupling coefficient on the SMSR of the generated carriers is also investigated. [ABSTRACT FROM AUTHOR]

Broadband Power Line Communications (PLC) have taken advantage of the research advances in multi-carrier modulations to mitigate frequency selective fading, and their adoption opens up a myriad of applications in the field of sensory and automation systems, multimedia connectivity or smart spaces. Nonetheless, the use of these multi-carrier modulations, such as Wavelet-OFDM, requires a highly accurate symbol timing estimation for reliably recovering of transmitted data. Furthermore, the PLC channel presents some particularities that prevent the direct use of previous synchronization algorithms proposed in wireless communication systems. Therefore more research effort should be involved in the design and implementation of novel and robust synchronization algorithms for PLC, thus enabling real-time synchronization. This paper proposes a symbol timing estimator for broadband PLC based on cross-correlation with multilevel complementary sequences or Zadoff-Chu sequences and its efficient implementation in a FPGA; the obtained results show a 90% of success rate in symbol timing estimation for a certain PLC channel model and a reduced resource consumption for its implementation in a Xilinx Kyntex FPGA. [ABSTRACT FROM AUTHOR]

This paper proposes filter bank multicarrier transmission technique (FBMC) as means to minimize adjacent band interference from long-term evolution (LTE) user equipment operating in the frequency band 792–862 MHz to short-range devices in the band 863–870 MHz. Main FBMC benefits are presented through comparison with reference case of orthogonal frequency-division multiplexing. The key advantage of FBMC modulation in reported electromagnetic compatibility studies is derived from its low out-of-band leakage, which guarantees minimum harmful interference level between stations using adjacent channels. The problem was evaluated in two aspects: first, theoretical analysis using minimum coupling loss method, complemented with statistical Monte-Carlo analysis (using SEAMCAT software tool) in order to verify results obtained in theoretical approach. [ABSTRACT FROM PUBLISHER]

Coordinated multipoint (CoMP) transmission and reception is a technique to reduce intercell interference and increase the cell edge throughput. In order to get maximum CoMP gain the networks and terminals involved in CoMP communication should be robust against time and frequency offset due to asynchronism between terminals and base stations. However, the modulation techniques proposed in LTE-Advanced standard (SC-FDMA and OFDMA) are quite sensitive to frequency offset because of DFT/IDFT used in the modulation systems, which brings difficulties for commercial implementation of CoMP technique based on LTE-Advanced. To relax the synchronization requirement in CoMP system, in this paper we introduce a CoMP technique based on a new multicarrier modulation scheme-multicarrier time division multiple access (MC-TDMA). In comparison with SC-FDMA and OFDMA, the MC-TDMA modulation can significantly improve the CoMP performance in case of carrier frequency offset. Simulation shows that at 20% of carrier frequency offset the CoMP system with MC-TDMA modulation can also keep high performance, while the system with SC-FDMA and OFDMA is totally lost in work. [ABSTRACT FROM AUTHOR]

This paper presents a multicarrier 60 GHz transmitter for distance measurement (ranging) in an indoor wireless localization system, achieving mm-precision with high update rate. The architecture comprises a baseband subcarrier generator, an upconverter, and a power amplifier. There are three key innovations, all stemming from careful hardware-algorithm co-design: 1) efficient frequency planning of the 6 GHz-wide band; 2) power-efficient multicarrier signal generation by means of digital frequency divisions exploiting the phase-based time-of-arrival ranging algorithm; and 3) PAPR reduction to enable efficient operation of the power amplifier. By implementing these key techniques, 0.7–2.7 mm precision is achieved over 5 m measured distance with 5.4 \mus symbol duration. During operation, the core digital subcarrier generator generates 16 non-equidistant subcarriers from a 3 GHz input clock, while consuming an average power of 1.8 mW out of 0.9V supply. The upconverter and the power amplifier altogether consume around 127 mW. The total area of the transmitter is 1.1 mm^2. The chip is fabricated in a 40nm general purpose CMOS process. [ABSTRACT FROM AUTHOR]

The ambition to achieve covering of secret messages into another file is implemented in many steganographic solutions, but usually the message is covered only into one file. In this paper the mechanism based on the method of steganography, with use of many cover files, is described. Proposal of the algorithm, based on Last Significant Bit method of steganography, is also described. The main contribution of this work is in the proposal of multi-carrier steganographic solution along with its implementation in the software application. [ABSTRACT FROM AUTHOR]

Non contiguous orthogonal frequency division multiplexing (NC-OFDM) is an efficient and adaptable multicarrier modulation scheme to be used in cognitive radio communications. However like OFDM, NC-OFDM also suffers from the main drawback of high peak to average power ratio (PAPR). In this paper PAPR has been reduced by employing three different trigonometric transforms. Discrete cosine transform (DCT), discrete sine transform (DST) and fractional fourier transform (FRFT) has been combined with conventional selected level mapping (SLM) technique to reduce the PAPR of both OFDM and NC-OFDM based systems. The method combines all the transforms with SLM in different ways. Transforms DCT, DST and FRFT have been applied before the SLM block or inside the SLM block before IFFT. Simulation results show the comparative analysis of all the transforms using SLM in case of both OFDM and NC-OFDM based systems. [ABSTRACT FROM AUTHOR]

Device coordination in open spectrum systems is a challenging problem, particularly since users experience varying spectrum availability over time and in different locations. In this paper, we propose a game-theoretic approach that allows cognitive radio (CR) pairs, namely the primary user (PU) and the secondary user (SU), to update their transmission power and frequencies simultaneously. Specifically, we address a Stackelberg game model in which individual users attempt to hierarchically access to the wireless spectrum while maximizing their energy efficiency. A thorough analysis of the existence, uniqueness, and characterization of the Stackelberg equilibrium (SE) is conducted. In particular, we show that a spectrum coordination naturally occurs when both actors in the system decide sequentially about their power and their transmitting carriers. As a result, spectrum sensing in such a situation turns out to be a simple detection of the presence/absence of a transmission on each subband. We also show that when users experience very different channel gains on their two carriers, they may choose to transmit on the same carrier at the SE as this contributes enough energy efficiency to outweigh the interference degradation caused by the mutual transmission. Then, we provide an algorithmic analysis on how the PU and the SU can reach such a spectrum coordination using an appropriate learning process. We validate our results through extensive simulations and compare the proposed algorithm to some typical scenarios, including the non-cooperative case in the work of Meshkati et al. and the throughput-based-utility systems. Typically, it is shown that the proposed Stackelberg decision approach optimizes the energy efficiency while still maximizing the throughput at the equilibrium. [ABSTRACT FROM PUBLISHER]

This letter proposes a hybrid multicarrier pulse width modulation (H-MCPWM) technique to reduce leakage current in a transformerless cascaded multilevel inverter for photovoltaic (PV) systems. The transformerless PV inverter topology has the advantages of simple structure, low weight and provides higher efficiency. However, the topology makes a path for leakage current to flow through parasitic capacitance formed between the PV module and the ground. A modulation technique has significant impact to reduce the leakage current without adding any extra component. The proposed H-MCPWM technique ensures low leakage current in the transformerless PV inverter system with simplicity in implementation of the modulation technique using lesser number of carriers. Experimental prototype developed in the laboratory demonstrates the performance of the proposed modulation technique in reducing the leakage current. [ABSTRACT FROM AUTHOR]

The wavelet packets based multicarrier (MC) multicode (MCD) code-division multiple-access (CDMA) transceiver consists of the MCD part, which ensures the transmission for high speed and flexible data rate; the MC part contributing to robustness to frequency-selective fading and flexibility for handling multiple data rates; and wavelet packets (WPs) modulation technique, which contributes to the mitigation of the interference problems. As WPs have lower sidelobes compared with sinusoidal carriers, this system is very effective in reducing the problem of inter-carrier interference. Of course, like any CDMA system, the system can suppress a given amount of interference. This paper considers an interference suppression scheme which will enhance the performance of the system. The receiver employs suppression filters to mitigate the effect of narrow-band jammer interference. The framework for the system and the performance evaluation are presented in terms of the bit error rate and the outage probability over a Nakagami fading channel. Also, we investigate how the performance is influenced by various parameters, such as the number of taps of the suppression filter and the ratio of narrow-band interference bandwidth to the spread-spectrum bandwidth. Finally, the performance of the system is compared with the performance of sinusoidal based MC/MCD-CDMA system denoted Sin-MC/MCD-CDMA. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Tracking interference is an effective interference patterns for a shortwave multi-carrier frequency-hopping (FH) communication system. In this paper, the relationship between sub-channels interference and orthogonal frequency division multiplexing (OFDM) symbol error rate is analyzed, and the part time parameters of best tracking interference are obtained by simulation, the system bit error rate (BER) in partial band jamming and the multi-tone interference is derived under Gaussian channel according to the relationship between OFDM spectrum and interference spectral, and the BER performance of anti-tracking interference is analyzed. Simulations show that: the BER is related not only with the tracking interference time window, but also with the partial-band interference factor and signal to interference ratio; there is interference equivalent region between the partial-band interference and the part-time interference; when the factor of multi-tone jamming is greater, the effect of the time-window on system is greater, the BER is related not only with the tracking interference time window, but also with the multi-tone interference factor and signal to interference ratio, and the effect of multi-tone interference on OFDM symbol is more critical than that of partial band interference; by combining FH and OFDM, increasing the carrier FH rate and reducing the impact of tracking interference on OFDM symbols, multi-tone interference can be eliminated effectively. [ABSTRACT FROM AUTHOR]

Orthogonal frequency division multiplexing (OFDM) is a common technique in multi carrier communications. One of the major issues in developing OFDM is the high peak to average power ratio (PAPR). Golay sequences have been introduced to construct 64-quaternary amplitude modulation (QAM) code for the OFDM, reducing the peak-to-mean envelope power ratio. In this paper we have considered the use of coding to reduce the peak-to-mean envelope power ratio (PAPR) for OFDM systems. By using QPSK and BPSK Golay sequences, 64-QAM sequences with low PAPR are generated and analyzed. [ABSTRACT FROM AUTHOR]

Blind subspace-based channel estimation methods have received considerable attention for multicarrier communication systems with virtual carriers over white Gaussian noises. In this paper, orthogonal frequency division multiplexing (OFDM) system without any training symbols or any prior knowledge of the noise covariance matrix is considered under unknown noise fields. No single subspace feature extraction method outperforms others under all circumstances, but applying a dual-space feature extraction method can overcome the limits of single subspace. A robust dual-space feature extraction is put forward based on minor component analysis (MCA) and independent component analysis (ICA) to increase the channel estimate accuracy. Especially, the proposed feature extraction always starts the procedure as a pure-MCA and ends as a pure-ICA. Once the new noise basis vectors are obtained, which is as orthogonal as possible to the estimated noise basis vectors especially for highly correlated and impulse noises, the noise subspace can be reconstructed for the MCA-based estimator. Computer simulation is provided for illustrating the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we propose three adaptive blind algorithms for multiuser multicarrier code division multiple-access systems in multipath fading channels. The proposed adaptive blind receivers are based on the property of the discreteness of the input data symbol and are updated in every symbol interval. We also use the concept that the variance of the output signal approaches to the variance of the desired signal to get the cost function. The three proposed receiver structures are the traditional finite impulse response (FIR) structure, the despreading (DES) filter structure and the generalized sidelobe canceller (GSC) structure. The advantage of the FIR filter is that the length of the filter weights does not have to be the same length as the spreading code. For the DES filter, the combination of the adaptive weight and the despreading code has the simplest structure than the other two proposed receiver structures. The constrained GSC filter is superior to the other two proposed receiver structures in the environments dominated by multiple-access interference. By this constraint, the blind GSC filter can guarantee to converge to the desired solution. Simulation results are given to show the effectiveness and comparison of the proposed adaptive blind receivers. [ABSTRACT FROM AUTHOR]

This work is motivated by the needs in the doubly dispersive underwater acoustic (UWA) communication channels. We propose and develop the use of filterbank multicarrier (FBMC) technique for communications in the channels of interest. A novel cost function for optimization of the filterbank prototype filter, to achieve a robust performance in doubly dispersive channels, is proposed. A design algorithm that optimizes the proposed cost function is then developed. The developed FBMC technique is compared with the celebrated orthogonal frequency-division multiplexing (OFDM). Our study shows that in doubly dispersive channels, in terms of signal-to-interference-plus-noise ratio (SINR), FBMC outperforms OFDM by several decibels. The theoretical results are validated and confirmed to be applicable to UWA communications, by examining real data from an at-sea experiment (ACOMM10), off the coast of New Jersey in July 2010. [ABSTRACT FROM AUTHOR]

ABSTRACT Adaptive fuzzy logic step size least mean square algorithm (FLCLMS) tuning unit is designed to adjust the step size of the linear constrained constant modulus algorithm for blind multiuser detection (MUD) in multi-carrier code division multiple access (MC-CDMA) systems is presented. In wireless communications system, the conventional constant modulus algorithm for blind MUD has some disadvantages such as slow convergence speed and phase rotation. To overcome these shortages, a modified constant modulus algorithm was developed for blind multiuser detector. On the basis of the deterministic behavior of the FLCLMS algorithm, it has also proposed simplification over the cost function calculation, obtaining more efficient algorithm and creating new perspective for the MUD implementation. The proposed algorithm ensures the algorithm convergence to the desired user and suppresses the multiple access interference in this cost function. Thus, the performance of the system is improved. The computational experiments show that the proposed FLCLMS not only can find optimal or closed-to-optimal solutions but also can obtain the low computation complexity both better and more robust results than existing algorithm reported recently in the literature. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this tutorial, we integrate the concept of cognitive radio technology into game theory and supermarket game theory to address the problem of resource allocation in multiuser multicarrier cognitive radio networks. In addition, multiuser multicarrier transmission technique is chosen as a candidate to study the resource allocation problem via game and supermarket game theory. This tutorial also includes various definitions, scenarios and examples related to (i) game theory (including both non-cooperative and cooperative games), (ii) supermarket game theory (including pricing, auction theory and oligopoly markets), and (iii) resource allocation in multicarrier techniques. Thus, interested readers can better understand the main tools that allow them to model the resource allocation problem in multicarrier networks via game and supermarket game theory. In this tutorial article, we first review the most fundamental concepts and architectures of CRNs and subsequently introduce the concepts of game theory, supermarket game theory and common solution to game models such as the Nash equilibrium and the Nash bargaining solution. Finally, a list of related studies is highlighted and compared in this tutorial. [ABSTRACT FROM AUTHOR]

SUMMARY This work is aimed at researching and analyzing the performance of carrier recovery (CR) with two transmit antennas on a multicarrier digital TV system operating in time-selective fading channel. It is shown in the paper that CR can correct the performance degradation caused by Doppler effect when the terminal is receiving high resolution digital TV signals in a fast moving environment. To have the ability to cover a large frequency range, the CR system should do a frequency sweep first. Then the coarse and fine frequency offset estimation is introduced. Both the theoretical and simulated results give valuable insight that the CR is able to perform well with a certain amount of channel fading. The phase and noise effect on the CR performance is also studied. The CR system and the working procedure concerning CR and timing recovery are also researched to give a full solution on synchronization. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper studies the problem of downlink pre-equalization in a multicarrier wireless network under utility and sum-rate maximization. The network utility depends on two main factors: 1) an efficiency mapping which is a function of the signal-to-interference-noise ratio (SINR), and 2) the power of the pre-equalization variables. Meanwhile, the sum-rate index is constructed by the summation of a logarithmic function of the SINRs of the active users. The network utility and sum-rate maximization problems are formulated here by assuming that the data estimation at the mobile units (MUs) is carried out by a simple matched filter. The optimal solutions are derived in this work for the pre-equalization factors by following a strategy that is distributed with respect to the channel state information (CSI) and data rates, but centralized with respect to the spreading sequences of all active users. The construction of these optimal solutions requires in each case a two step procedure. First, the optimal SINR is computed for the maximum utility and sum-rate solutions based on the efficiency mapping and on the bound of the transmission power, respectively. Then, exploiting the induced diversity by the multiple subcarriers, the pre-equalization algorithms cancel the multiple-access interference (MAI) and channel distortions, minimize the transmission power and achieve the optimal SINR after signal detection. A comprehensive numerical evaluation is presented at the end of the paper to validate the analytical derivations. Applications of the proposed pre-equalization schemes could be associated among others to cellular communication systems, and wireless networks of actuators. [ABSTRACT FROM AUTHOR]

In this work we study the channel capacity from the point of view of a secondary user that shares the bandwidth of the channel with a primary user using dynamic spectrum access in cognitive radio.The secondary user sees bandwidth fluctuations (i.e, at any given time the bandwidth can be available or not) that impact its channel capacity. We study the outage capacity for the secondary user considering two scenarios in which the secondary user uses either a single carrier modulation for the case in which bandwidth fluctuates over the complete transmission band, and a multicarrier modulation for the case in which bandwidth fluctuations are over various transmission subbands. We derive expressions for the outage capacity of the secondary user for both single carrier and multicarrier. Results show that: (1) The outage capacity for single carrier can be higher than for multicarrier, but with a higher outage probability for single carrier than for multicarrier. In fact, a low value of outage probability for single carrier requires a duty cycle for the secondary user close to one, but this has the problem that it leaves a very short duty cycle for the primary user. (2) Although for the secondary user the outage capacity for multicarrier is smaller than for single carrier, for multicarrier lower values of the outage probability can be achieved even for short values of the duty cycle of the secondary user, allowing larger duty cycle values of the primary user. (3) For multicarrier, the outage capacity is more sensitive to changes in the duty cycle than to changes in the outage probability. To obtain a larger outage capacity with low values of both the outage probability and the duty cycle, it requires the use of a large number of subbands. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a novel analysis of the sensitivity of an important class of filter bank multicarrier (FBMC) systems to time and frequency offsets. For the FBMC system under consideration the mapping for each sub-carrier uses offset quadrature amplitude modulation (OQAM) constellations. Assuming that the time offset (TO) and carrier frequency offset (CFO) are less than the symbol duration and sub-carrier frequency spacing, respectively, we derive exact analytical expressions of the interference power resulting from TO and CFO. Our theoretical results are confirmed by simulations for a large set of prototype filters. Furthermore, in the case of perfectly orthogonal prototype filters, we establish the link with a simple expression that up to now was left unused. [Copyright &y& Elsevier]

The purpose of this paper is to compare the turbo-coded. Orthogonal Frequency Division Multiplexing (OFDM) and turbo-coded Single Carrier Frequency Domain Equalization (SC-FDE) systems under the effects of Carrier Frequency Offset (CFO), Symbol Timing Offset (STO) and phase noise in wide-band Vogler-Hoffmeyer HF channel model. In mobile communication systems multi-path propagation occurs. Therefore channel estimation and equalization is additionally necessary. Furthermore a non-ideal local oscillator generally is misaligned with the operating frequency at the receiver. This causes carrier frequency offset. Hence in coded SC-FDE and coded OFDM systems; a very efficient, low complex frequency domain channel estimation and equalization is implemented in this paper. Also Cyclic Prefix (CP) based synchronization synchronizes the clock and carrier frequency offset. The simulations show that non-ideal turbo-coded OFDM has better performance with greater diversity than non-ideal turbo-coded SC-FDE system in HF channel. [ABSTRACT FROM AUTHOR]

In this paper, Critically Sampling Inverse DiscreteMulti-Wavelet Transform (CSID-MWT) are proposed as a modulator technique instead of Inverse Fast Fourier Transform (IFFT) in the realization of the Multi-Carrier Code Division Multiple Access (MC-CDMA) system. The proposed structure improved the bandwidth efficiency through the elimination of the cyclic prefix (CP) due to the good orthogonality and time-frequency localization properties of the Multi-Wavelet transform. The proposed system was simulated using MATLAB to allow various parameters of the system to be varied and tested. Simulation results showed that the proposed system outperforms conventional MC-CDMA system, and its performance is superior to that of the conventional MC-CDMA with CP. [ABSTRACT FROM AUTHOR]

We present an evaluation method to estimate the spurious emission levels produced by a multicarrier system in the specially defined spurious domain due to the nonlinearity of its high-power amplifier (HPA). We compared the results from our proposed analytical model with the actual experimental results from the multicarrier system and found good agreement. The method is accurate enough to determine whether a system is compatible with International Telecommunication Union (ITU) recommendations without needing to conduct complex tests. [ABSTRACT FROM AUTHOR]

Abstract: The Daubechies, coiflet and symlet wavelets, with properties of orthogonal wavelets are suitable for multicarrier transmission over band-limited channels. It has been shown that similar wavelets can be constructed by Lagrange approximation interpolation. In this work and using established wavelet design algorithms, it is shown that ideal filters can be approximated to construct new orthogonal wavelets. These new wavelets, in terms of BER, behave slightly better than the wavelets mentioned above, and much better than biorthogonal wavelets, in multipath channels with additive white Gaussian noise (AWGN). It is shown that the construction, which uses a simple simultaneous solution to obtain the wavelet filters from the ideal filters based on established wavelet design algorithms, is simple and can easily be reproduced. The Cramer–Rao lower bound is applied to access the BER performance of the proposed wavelet. [Copyright &y& Elsevier]

This paper develops two spectrally efficient orthogonal frequency division multiplexing (OFDM)-based multicarrier transmission schemes: a scheme with message-driven idle subcarriers (MC-MDIS) and another with message-driven strengthened subcarriers (MC-MDSS). The basic idea in MC-MDIS is to carry part of the information, which is named carrier bits, through an idle subcarrier selection while regularly transmitting the ordinary bits on all the other subcarriers. When the number of subcarriers is much larger than the adopted constellation size, higher spectral and power efficiency can be achieved compared with OFDM. The reason is that each idle subcarrier carries more bits than a regular symbol, with no power consumption. Moreover, the existence of idle subcarriers can also decrease possible intercarrier interference between their neighboring subcarriers. In MC-MDSS, the idle subcarriers are replaced by strengthened subcarriers, which, unlike idle subcarriers, can carry both carrier bits and ordinary bits. Therefore, MC-MDSS achieves even higher spectral efficiency than MC-MDIS. Both theoretical analysis and numerical results are provided to demonstrate the performance of the proposed schemes. [ABSTRACT FROM AUTHOR]