This work introduces a novel blind channel estimation (CE) scheme for intelligent reflecting surface (IRS)-assisted networks with heterogeneous communications and sensing devices. The proposed approach operates in two stages: the first stage is dedicated to transmitting the sensing data, and the second to transmitting communications data. By leveraging the fact that sensing information typically has less stringent quality of service (QoS) requirements compared to communication data, the sensing data transmission stage is leveraged for blind CE. The CE is performed using a specific frame structure, where the modulated sensing symbols collaborate to estimate the channel coefficients for all IRS elements blindly and jointly. The performance of sensing data transmission is evaluated in terms of average bit error rate (BER), with exact closed-form expressions derived for the considered modulation schemes. For the communications data, the BER is analyzed, and a tight lower bound is derived. Additionally, an accurate closed-form expression is derived for the mean-squared-error (MSE) of the proposed CE. The MSE results demonstrate that the proposed blind CE outperforms state-of-the-art schemes.

This article presents a physical layer security (PLS) technique for non-orthogonal multiple access (NOMA), which can provide joint secrecy, fairness, and bit error rate (BER) improvement. The approach employs power hopping (PH), where users’ power coefficients are dynamically varied according to the instantaneous channel conditions. By randomizing both the detection order and the effective power allocation, PH obscures the underlying NOMA structure from a passive eavesdropper (Eve), thereby severely degrading the data detection capability. To enable secure coordination, a precoding-based mechanism is developed for sharing the PH patterns among legitimate users, leveraging the random and independent nature of wireless channels. The BER and secrecy outage probability (SOP) of the proposed framework are analytically characterized and compared to conventional NOMA under various channel and eavesdropping configurations. The obtained analytical results, corroborated by Monte Carlo simulations, confirm the effectiveness of the proposed scheme, where the SOP of legitimate users is never compromised regardless of Eve’s channel conditions, while incurring only negligible additional complexity compared to conventional NOMA. Furthermore, the fairness and BER performance of stronger users are significantly improved through the combined use of PH and optimal power allocation.

By harnessing compressed-sensing principles, sparse vector coding (SVC) compresses and delivers data with ultra-low latency and near-instantaneous reliability, making it a vital enabler of next-generation ultra-reliable and low-latency communications (xURLLC) services in sixth generation (6G) wireless communication systems. A fundamental challenge in SVC systems is developing a generalized sparse mapping mechanism that does not rely on either an index table or constellation labels. To meet such a requirement, this work proposes a base conversion index modulation (IM) that uses a novel mapping strategy for sparse vector construction. The proposed design achieves higher resource efficiency, requiring fewer positional resources for bit representation than conventional combination-based IM. Building on this foundation, a generalized SVC (GSVC) scheme is developed to enable fully pipelined bit-stream mapping and demapping. A further extension, termed enhanced GSVC (EGSVC), adopts a pairwise-grouped constellation assignment to improve the transmission performance of GSVC. Simulation results confirm that GSVC achieves block error rate (BLER) performance comparable to conventional SVC in single-block coding modes, yet significantly improves BLER under high-coding-rate multi-block coding modes. By balancing the constellation label count and the sparse vector length, EGSVC delivers superior BLER compared to conventional SVC schemes while maintaining lower latency.

This paper presents a novel physical layer security (PLS) scheme for non-orthogonal multiple access (NOMA) systems that jointly enhances secrecy and bit error rate (BER). The proposed approach leverages power hopping (PH), wherein users’ power coefficients are dynamically allocated to obscure both the decoding order and actual power allocation from potential eavesdroppers. This uncertainty significantly reduces the feasibility of successful interception. Analytical expressions for the BER and secrecy outage probability (SOP) are derived under diverse channel conditions and eavesdropping scenarios. The theoretical findings, validated through Monte Carlo simulations, confirm that the proposed scheme robustly preserves the secrecy of legitimate users regardless of the eavesdropper’s channel quality. Moreover, the approach yields substantial improvements in both BER and SOP, particularly for the near user.

In the rapidly advancing field of wireless communication, Unmanned Aerial Vehicles (UAVs) have become indispensable due to their extensive coverage capabilities and ability to access remote locations. Whether deployed as mobile base stations (BSs) or relays, UAVs significantly enhance network throughput and reliability. Alongside UAVs, Intelligent Reflecting Surfaces (IRS) have emerged as a cost-effective solution for improving communication quality through passive modulation arrays. Despite these advancements, the potential misuse of UAVs poses serious security risks, particularly in the form of communication eavesdropping. To address these challenges, this paper introduces a novel communication framework that integrates a UAV equipped with an adaptive IRS. The primary aim is to boost communication secrecy between BSs and multiple users, even in the presence of several UAV eavesdroppers. This objective is formulated as an optimization problem focused on maximizing the secrecy rate while considering UAV mobility constraints. To solve this non-convex problem, we propose a hybrid strategy that combines Genetic Algorithms and Gradient Descent techniques. This innovative approach efficiently determines suboptimal reflection angles and UAV trajectories for IRS-equipped UAVs, thereby enhancing the security of the communication network. This method not only addresses the complexity of the optimization but also provides a practical pathway to secure communications in environments with high eavesdropping risks.

This work proposes an efficient two-stage jamming detection and channel estimation algorithm for orthogonal frequency division multiplexing (OFDM)-based unmanned aerial vehicles (UAVs) communications. The proposed scheme is designed based on the unique time and frequency domain statistical characteristics of OFDM signals. In the time domain (TD), a likelihood ratio test (LRT)-based decision rule is derived as a function of the inherent correlation between the cyclic prefix (CP) samples and their counterparts in the OFDM symbol. In addition, in the frequency domain (FD), a closed-form joint jamming detection and channel estimation scheme is derived using the maximum a posteriori probability (MAP) principle as a function of the statistics of the received pilots and virtual subcarriers (VSCs) signals, which is then re-expressed using the generalized MAP ratio test (GMAPRT). The system’s complexity is reduced by applying the two stages sequentially, where the possible implementation of the second stage is conditioned on the outcome of the first stage. The performance of the proposed algorithm is evaluated using Monte Carlo simulations, where the results demonstrate its effectiveness compared to the TD-only and FD-only approaches. The results confirm the superior performance of the proposed scheme compared to the cyclostationary feature (CF)-based technique under various operating scenarios.

This work presents a novel signal design based on time-domain interleaving (TDI) of orthogonal frequency division multiplexing (OFDM). Unlike conventional OFDM-TDI that introduces a one-dimensional frequency diversity, the proposed design introduces a two-dimensional frequency diversity leading to a superior symbol error rate (SER) performance for various channel conditions. The performance of the proposed signal design is evaluated using zero-forcing (ZF) and minimummean-square-error (MMSE) equalizers where the signal-to-noise ratio (SNR) and signal-to-interference-plus-noise ratio (SINR) are derived and used to evaluate the SER, outage probability (OP), and diversity order. The analytical SER results obtained, corroborated by Monte Carlo simulation, demonstrate that the proposed signal model with MMSE equalizer achieves ∼40 dB gain over OFDM and ∼7 dB over conventional TDI in Rayleigh fading channels, and it is only 2 dB from the Gaussian channel SER in Rician channels. The proposed scheme also outperforms other state-of-the-art techniques such as interleave frequency division multiplexing (IFDM) and orthogonal time frequency space (OTFS). The proposed system architecture generally follows the conventional OFDM system model, which emphasizes its compatibility and low complexity.

In the dynamic realm of wireless communication, Unmanned Aerial Vehicles (UAVs) have gained increasing prominence due to their exceptional capabilities, which include expensive coverage of large areas and access to challenging and hazardous locations. When employed as mobile base stations or relays, UAVs have shown remarkable enhancements in system throughput and reliability. In addition, Intelligent Reflecting Surfaces (IRS) present a very low cost solution that efficiently enhances wireless communication quality using passive modulation arrays. Nevertheless, the use of UAVs for malicious intents can also introduce heightened security challenges such as communication eavesdropping. In response to these challenges, we present in this paper, a communication framework that incorporates a UAV equipped with an adaptive IRS aiming to enhance the communication secrecy between the Base Station (BS) and Bob in the presence of several UAV eavesdroppers. We formulate the objective as an optimization problem that aims to maximize the secrecy rate while considering the mobility constraints. To address this complex non-convex problem, our innovative solution harnesses a hybrid approach that combines Genetic Algorithms and Gradient Descent techniques, resulting in an efficient computation of suboptimal reflection angles and UAV trajectories for IRS-equipped UAVs towards a more secure communication.

This paper investigates various receiver architectures for uplink non-orthogonal multiple access (NOMA)-based integrated sensing and communication (ISaC) systems. Specifi-cally, a novel signaling approach is considered whereby mutual interference between the radar and communication signals is canceled by alternately reversing the radar symbols and phase-rotating the transmitted data symbols in consecutive periods. While such a signaling approach eliminates both detection ambiguity and radar interference at the receiver, this requires the receiver to detect the targets and data over two symbol periods at a time. To this end, in this paper, we adapt various well-known receivers, such as the maximum ratio combining (MRC), zero forcing (ZF), successive interference cancellation (SIC) and max-imum likelihood (ML) receivers, and compare their performance under a variety of conditions. When evaluating the bit error rate (BER), the achievable sum rate (ASR), and the radar channel estimation (RCE) accuracy, it is found that the proposed ISaC system exhibits remarkable performance regardless of the radar signal's power compared to other ISaC signaling approaches. It is also found that the MRC receiver suffers from error floors when the system loading is relatively high, while ZF and ML provide comparable and superior performances regardless of the system load.

This article presents a novel framework for integrating low-earth orbit satellites (LEOSs) with terrestrial-wired networks to improve coverage, throughput, and transmission reliability of 6th generation (6G) Internet of things (IoT) networks. The proposed framework utilizes the synergy of non-orthogonal multiple access (NOMA), automatic repeat request (ARQ), and cooperative communications to maximize the data downloaded from a LEOS to multiple terrestrial users. More specifically, we propose a novel offline packets repair and recovery (PRR) technique to reduce the number of dropped packets, where the wired-terrestrial connection is used to enable efficient bidirectional cooperation, to improve the reliability of the received data by reducing the multiuser interference inherent to NOMA. Moreover, by exchanging the acknowledgment messages used with ARQ, efficient Chase combining (CC) is applied to improve the signal to noise ratio (SNR) of the received packets. Extensive Monte Carlo simulation experiments are used to evaluate and quantify the advantages of the proposed system. The results obtained show that the proposed system can repair a significant number of dropped packets, which reduces the packet drop rate and improves the network throughput. In several scenarios, the proposed PRR managed to repair and recover more than 90% of the dropped packets.

This paper proposes a multiple target localization scheme using a clustered wireless sensor network (WSN) for terrestrial and underwater environments. In the considered system, sensors measure the total energy emitted by the targets and transmit quantized versions of their measurements to a data central device (DCD) with the help of intermediate cluster-heads (CHDs), which employ decode-and-forward relaying (DFR). Upon data collection from sensors, the DCD performs the localization process, which involves estimating the number and positions of the targets. Data transmission from the sensors to CHDs takes place through an imperfect medium, which is characterized by a Rician fading model. The penalized maximum likelihood estimator (PMLE), also known as regularized maximum likelihood estimation (MLE), is applied at the DCD to provide optimal estimates of the number and locations of targets. Furthermore, a suboptimal estimator is derived from PMLE that offers comparable performance under certain operating conditions, but with significantly reduced computational complexity. Cramer-Rao lower bound (CRLB) is derived to serve as an asymptotic benchmark for the root mean square error (RMSE) of the estimators in addition to the centroid-based localization benchmark. Monte Carlo simulation is used to evaluate the performance of the proposed estimation techniques under various system conditions. The results show that PMLE can effectively estimate the number and locations of the targets. Furthermore, it is shown that the RMSE of the proposed estimators approaches the CRLB for a large number of sensors and a high signal-to-noise ratio.

Security is an issue in non-orthogonal multiple access (NOMA) and partial-NOMA because a user may decode the message of its paired-user with which it shares a resource element (RE). Three scenarios are studied where, of the paired-users, the eavesdropper is: 1) an actively malicious strong-user, 2) a passive strong-user, 3) an actively malicious weak-user. We define the event of secure-communication in each scenario and derive the corresponding secrecy probabilities for partial-NOMA and NOMA. Our results highlight that with careful selection of the RE’s overlap α, partial-NOMA can significantly outperform NOMA in terms of secrecy probability. Further, careless selection of α can cause partial-NOMA to perform worse than NOMA. We show the non-trivial impact of incorporating the impact of intercell interference on secrecy. Our results shed light on parameter-selection if knowledge of the eavesdropper type is available highlighting that security can be improved without traditional techniques such as jamming that increase power consumption and interference. While NOMA decoding uses successive-interference-cancellation (SIC), partial-NOMA decoding employs receive-filtering followed by flexible-SIC (FSIC). We show that not employing receive-filtering or using SIC instead of FSIC can have a drastic negative impact on secrecy, highlighting the role of the partial-NOMA decoding approach in enhancing secure-communication.

In this work, we evaluate the bit error rate (BER) and block error rate (BLER) performances of a downlink two-user non-orthogonal multiple access system considering the received energy per bit per noise spectral density (Eb/N0). A one-to-one mapping between the Eb/N0and transmit signal to noise ratio (SNR) is derived for the uncoded and coded systems. Furthermore, the channel coding gain is quantified for turbo product codes with various code rates and block lengths. In addition, the performance is evaluated for Mn-ary quadrature amplitude modulation of selected orders. It is shown that the BER and BLER performances reach the waterfall region with smaller Eb/N0values compared to transmit SNR, which reduces the simulation run time to capture the desired performance.

Non-orthogonal multiple access (NOMA) based on orthogonal frequency division multiplexing (OFDM) multicarrier modulation technique is a promising multiple access scheme for next-generation wireless communication systems. This paper analyzes the bit error rate (BER) performance of a downlink power domain NOMA-OFDM system with time-domain interleaving (TDI) over frequency selective Rayleigh channel. Theoretical BER expressions for a downlink power domain NOMA-OFDM system with TDI and using minimum mean squared error (MMSE) equalizer are developed for an arbitrary number of users. The Monte Carlo simulation results show that the proposed downlink power domain NOMA-OFDM system with TDI has better BER performance over frequency-selective fading multipath channels compared to the conventional NOMA-OFDM system without TDI.

This article studies the end-to-end uplink (UL) and downlink (DL)-outage probability (OP) of an Internet of Things (IoT) network with radio-frequency (RF) energy harvesting (EH) over Nakagami-m fading channels. Power-domain nonorthogonal multiple access (NOMA) is adopted to support both the UL and DL transmissions to increase the network spectral efficiency. The system end-to-end UL and DL outage probabilities are analyzed where exact closed-form expressions are derived. The system performance is explored for various system parameters, such as time allocation for EH, transmission power, fading conditions, number of IoT devices (IoDs), and data rate. The obtained analytical results are corroborated using Monte Carlo simulation for various operating scenarios. The obtained results show that the optimum harvesting time may broadly vary based on the adopted system parameters. Moreover, the results show that the system OP is highly sensitive to the harvesting time where OP may vary drastically if the harvesting time deviates from the optimum. The impact of the perfect successive interference cancelation (SIC) (PSIC) is also evaluated and compared with imperfect SIC (ISIC), and the obtained results show that the OP of the system can be significantly underestimated with the PSIC assumption. Therefore, the commonly used PSIC assumption may cause substantial deviation from the practical case where the detection process experiences ISIC.

This work presents a novel nonorthogonal multiple access (NOMA) cognitive radio (CR) system where the base station (BS) opportunistically multiplexes the secondary user (SU) with the primary user (PU) using power-domain NOMA. As the PU has the priority to transmit and SU is satisfied on best-effort basis, four different transmission-modes (TMs) are produced at the BS, which are PU orthogonal multiple access (PU-OMA), SU-OMA, PU/SU-NOMA, and silent mode. Consequently, the considered protocol can be classified as a hybrid underlay-interweave CR-NOMA. The TM adaptation should be seamless for the PU where its detector configuration remains unchanged regardless of the active TM. In contrast, the SU has to identify the active TM blindly, i.e. without side information, to select the appropriate detector. The identification process is performed using a classifier that is designed based on the maximum likelihood criterion. The performance of the proposed system is analyzed in terms of throughput, packet error rate (PER), and classification error. The Binomial and Multinomial theorems are utilized to simplify and allow a tractable analysis. The derived closed-form expressions, corroborated by Monte-Carlo simulation results, show that the hybrid CR-NOMA can provide substantial throughput improvement over conventional NOMA, which is about a 100%.

In this paper, a downlink cooperative non-orthogonal multiple accesses (C-NOMA) system assisted with a decode and forward (DF) UAV-relay is developed, where the channel gains follow the $\kappa-\mu$ generalized fading model to evaluate its system performance. The study involves two scenarios in which the NOMA signal is propagated through the outdoor-to-indoor channel and the outdoor-to-outdoor channels, where the practical successive interference cancellation (SIC) is addressed. In particular, exact closed-form expressions are derived for the outage probability (OP) of indoor-outdoor NOMA users on $\kappa-\mu$ fading channels. To obtain more insight into how channel fading parameters affect OP performance, asymptotic expression is also evaluated. The results provide insight into the impact of key parameters, such as power allocation and channel fading parameters, on system performance. Ultimately, Monte Carlo simulations were used to validate the analytical expressions.

In this work, we derive new closed-form expressions for the throughput of non-orthogonal multiple access (NOMA) system with adaptive modulation orders. The system design considers a packet-based transmission where the base station adapts the modulation orders to satisfy the block error rate (BLER) requirement for each user and maximize the throughput by minimizing the maximum signal to noise ratio (SNR) requirements of the users. The optimization problem is formulated as a minmax problem to jointly optimize the modulation orders and SNR thresholds, where the original mixed-integer programming is simplified to integer programming by introducing an auxiliary variable. Compared to the grid search approach, the analytical and simulation results show that the min-max approach can improve the throughput with a significant reduction in the number of transmission modes, the throughput can be improved by up to 2.5 dB at moderate SNRs and by 1 bit/symbol at extremely high SNRs.

Nonorthogonal multiplexing (NOM) is a novel superposition coding scheme that has been recently proposed to improve the throughput of wireless systems. However, restricting the number of multiplexed packets to two limits the throughput improvement of nonorthogonal multiplexing (NOM) to 100% in best-case scenarios. Therefore, this work presents a generalized NOM (GNOM) design with an unlimited number of multiplexed packets. In the multiplexing process, new and retransmitted packets due to arq are combined while considering the impact of channel conditions on the power assigned per packet. The proposed GNOM employs an efficient heuristic algorithm to perform the power assignment and multiplexing decisions. Moreover, the complexity can be controlled by enforcing a limit on the maximum number of multiplexed packets per transmission, making it suitable for iot nodes with diverse computational capabilities and quality of service requirements. The obtained results demonstrate the effectiveness of the proposed scheme, which offers up to 200% throughput improvement at moderate signal to noise ratios (SNRs), and up to 700% at high SNRs. Furthermore, the new scheme can reduce the transmission power consumption by up to 6 dB in the high SNR region.

This paper presents the design and bit error rate (BER) analysis of a phase-independent non-orthogonal multiple access (NOMA) system. The proposed NOMA system can utilize amplitude-coherent detection (ACD) which requires only the channel amplitude for equalization purposes. In what follows, three different designs for realizing the detection of the proposed NOMA are investigated. One is based on the maximum likelihood (ML) principle, while the other two are based on successive interference cancellation (SIC). Closed-form expressions for the BER of all detectors are derived and compared with the BER of the coherent ML detector. The obtained results, which are corroborated by simulations, demonstrate that, in most scenarios, the BER is dominated by multiuser interference rather than the absence of the channel phase information. Consequently, the BER using ML and ACD are comparable for various cases of interest. The paper also shows that the SIC detector is just an alternative approach to realize the ML detector, and hence, both detectors provide the same BER performance.

Non-orthogonal multiple access (NOMA) is a promising candidate for future wireless networks due to its ability to improve the spectral-efficiency and network connectivity. Nevertheless, the error rate performance of NOMA depends significantly on the power assignment, which requires accurate knowledge of the channel state information at the transmitter (CSIT). However, providing accurate CSIT can be challenging. Therefore, this paper proposes a data-aware adaptive power assignment NOMA scheme called PANOMA which adaptively changes the signal power based on the transmitted data to maximize the constructive interference. To quantify its potential, closed-form bit error rate (BER) expressions are derived for two users over the broadcast Rayleigh fading channel. Based on these expressions, the power assignment that minimizes the system’s average BER is found. The results demonstrate that PANOMA provides a tangible BER performance gain over conventional power-domain NOMA when both schemes use optimal power and sub-optimal power assignments. Also, PANOMA provides robustness to imperfect power assignment which results from imperfect CSIT. The integrity of the analytical results is verified by Monte Carlo simulation.

Nonorthogonal multiple access (NOMA) is a promising candidate for future wireless networks due to its ability to improve the spectral efficiency and network connectivity. Nevertheless, the error rate performance of NOMA depends significantly on the power assignment for each user, which requires accurate knowledge of the channel state information (CSI) at the transmitter, which can be challenging for several applications, such as wireless sensor networks (WSNs) and Internet of Things (IoT). Therefore, this article proposes a power-tolerant NOMA by adaptively changing the signal power of each user to reduce the system sensitivity to inaccurate power assignment. The power adaptation in the power-adaptive NOMA (PANOMA) is performed based on the transmitted data, and it does not require accurate CSI. To quantify its potential, the bit error rate (BER) and the lower bound capacity performance, over Rayleigh fading channels, are derived in exact closed forms for two and three users scenarios. The results demonstrate that PANOMA provides a tangible BER performance improvement over conventional power-domain NOMA when both schemes use suboptimal power assignment, which is typically experienced in practical scenarios involving channel time variation and CSI estimation errors. Specifically, it will be shown that both schemes provide similar BERs using optimal assignment, but the PANOMA offers BER reduction by a factor of 10 for certain scenarios when suboptimal power values are assigned. The integrity of the analytical results is verified via matching extensive Monte Carlo simulation experiments.

This work presents the symbol error rate (SER) and outage probability analysis of multi-layer unmanned aerial vehicles (UAVs) wireless communications assisted by intelligent reflecting surfaces (IRS). In such systems, the UAVs may experience high jitter, making the estimation and compensation of the end-to-end phase for each propagation path prone to errors. Consequently, the imperfect phase knowledge at the IRS should be considered. The phase error is modeled using the von Mises distribution and the analysis is performed using the Sinusoidal Addition Theorem (SAT) to provide accurate results when the number of reflectors$L\leq 3$, and the Central Limit Theorem (CLT) when$L\geq 4$. The achieved results show that accurate phase estimation is critical for IRS based systems, particularly for a small number of reflecting elements. For example, the SER at 10−3degrades by about 5 dB when the von Mises concentration parameter$\kappa =2$and$L=30$, but the degradation for the same$\kappa $surges to 25 dB when$L=2$. The air-to-air (A2A) channel for each propagation path is modeled as a single dominant line-of-sight (LoS) component, and the results are compared to the Rician channel. The obtained results reveal that the considered A2A model can be used to accurately represent the A2A channel with Rician fading.

Non-orthogonal multiple access (NOMA) is a promising candidate for future mobile networks as it enables improved spectral-efficiency, massive connectivity and low latency. This paper derives exact and asymptotic bit error rate (BER) expressions under Rayleigh fading channels for NOMA systems with arbitrary number of users and arbitrary number of receiving antennas and modulation orders, including binary phase-shift keying and rectangular/square quadrature amplitude modulation. Furthermore, the power coefficients' bounds, which ensure users' fairness, and solve the constellation ambiguity problem, are derived for N=2 and 3 users cases with any modulation orders. In addition, this paper determines the optimal power assignment that minimizes the system's average BER. These results provide valuable insight into the system's BER performance and power assignment granularity. For instance, it is shown that the feasible power coefficients range becomes significantly small as the modulation order, or N, increases, where the BER performance degrades due to the increased inter-user interference. Hence, the derived expressions can be crucial for the system scheduler in allowing it to make accurate decisions of selecting appropriate N, modulation orders, and power coefficients to satisfy the users' requirements. The presented expressions are corroborated via Monte Carlo simulations.

This paper considers the deployment of intelligent reflecting surfaces (IRSs) technology for wireless multi-hop backhauling of multiple basestations (BSs) connected in a mesh topology. The performance of the proposed architecture is evaluated in terms of outage and symbol error probability in Rician fading channels, where closed-form expressions are derived and demonstrated to be accurate for several cases of interest. The analytical results corroborated by simulation, show that the IRS-mesh backhauling architecture has several desired features that can be exploited to overcome some of the backhauling challenges, particularly the severe attenuation at high frequencies. For example, using IRS with four elements, N=4, provides a symbol error rate of about 10-5at a signal-to-noise ratio of about 0 dB, even for a large number of hops. Moreover, the obtained analytical results corroborated by Monte Carlo simulation show that the gain obtained by increasing N decreases significantly for N > 5. For example, increasing N from 1 to 2 provides about 8dB of gain, while the increase from 3 to 4 provides about 4dB. Moreover, the degradation caused by the relaying process becomes negligible when the number of IRS elements N= 3.

Driver inattentiveness during driving is a major cause in road accidents. In general, the inattentiveness is due to external distractions that change driver's focus from driving to non-driving activities. Hence, it is of imperative importance to alert drivers of their inattentiveness behaviors to prevent any possible accident. This paper investigates the inattentiveness behaviors such as texting over the phone, talking on the phone, tuning the radio player, eating and drinking, turn behind, makeup, and talking to passengers. We consider a car system that has a camera installed such that the camera will be capable of capturing the driver's body movement. Convolutional neural network (CNN) is used to extract image features from the camera video stream and perform the classification. We present performance results of model development, model loaded into vehicle system, and model updated on custom cloud dataset. The cross-validation evaluation indicates that our proposed approach offers a simple, reliable, low-cost and high in-vehicle model accuracy (>92%) solution in detecting the driver's inattentiveness problem during driving.

This article presents a novel decision fusion algorithm for Internet-of-Things-based wireless sensor networks, where multiple sensors transmit their decisions about a certain phenomenon to a remote fusion center (FC) over a wide area network. The proposed algorithm denoted as the individual likelihood approximation (ILA) can significantly reduce the decision fusion error probability performance while maintaining the low computational complexity of other state-of-the-art fusion algorithms. The performance of the ILA rule is evaluated in terms of the global fusion probability of error, and an efficient analytical expression is derived in terms of a single integral. The analytical results corroborated by Monte Carlo simulation show that the ILA significantly outperforms all other considered rules, such as the Chair-Varshney (CV) and MaxLog rules. Moreover, the impact of the link from the cluster head to the FC, which is modeled as a binary symmetric channel with unknown transition probabilities, has been investigated. It is shown that the probability of error over such links should not exceed 10-3to avoid severe performance degradation. Furthermore, we derive a closed-form expression for the system fusion error probability of the CV rule for the most general system parameters.

Orthogonal frequency-division multiplexing (OFDM) is one of the most widely adopted modulation schemes because it offers several desirable features, such as spectral efficiency and low complexity implementation. Moreover, it is highly suitable for adaptive implementation. Nevertheless, OFDM does not have any special immunity against multipath fading as compared to single-carrier systems. Therefore, we propose in this article a new OFDM configuration, denoted as OFDM-smart (OFDM-S), where superposition modulation is used to introduce transmit diversity to reduce the bit error rate (BER) while maintaining the spectral efficiency and bit rate fixed. The proposed scheme is based on clustering specific subcarriers that can cooperate by sharing their transmission resources. The cooperation is performed such that all subcarriers transmit their data jointly using all the subcarriers within their cluster. The system performance is derived in terms of BER performance over Nakagami-m frequency-selective fading channels where efficient expressions are presented in terms of a single finite integral, and closed-form expressions are derived for the asymptotic BER. The obtained analytical results corroborated by simulation show that the OFDM-S can provide substantial BER improvement over conventional OFDM, due to the transmit diversity.

Non-orthogonal multiple access (NOMA)-based cognitive radio (CR) networks have recently emerged as a promising solution to enhance the spectral efficiency and massive connectivity problems. In this paper, we investigate the error rate performance of relay-assisted NOMA with partial relay selection in an underlay cognitive radio network. In this setup, K relays are used to assist in transmission between secondary NOMA users and a secondary base station (SBS), where the relay (R) with the strongest link with the SBS is selected to amplify-and-forward (AF) its received signals to the secondary receivers. We derive an accurate approximation for the pairwise error probability (PEP) of the secondary users with imperfect successive interference cancellation (SIC). Subsequently, the derived PEP expression is utilized to deduce a union bound, which is considered as an upper bound on the bit error rate (BER). We further formulate an optimization problem to calculate the optimum power coefficients that minimize the derived union bound. Numerical and Monte Carlo simulation results are presented to corroborate the derived analytical expressions and give some useful insights into the error rate performance of each user.

Amplitude-coherent (AC) detection is an efficient technique that can simplify the receiver design while providing reliable symbol error rate (SER). Therefore, this work considers AC detector design and SER analysis using M-ary amplitude shift keying (MASK) modulation with receiver diversity over Rician fading channels. More specifically, we derive the optimum, near-optimum and a suboptimum AC detectors and compare their SER with the coherent, phase-coherent, noncoherent and the heuristic AC detectors. Moreover, the analytical and asymptotic SER at high signal-to-noise ratios (SNRs) are derived for the heuristic detector using single and multiple receiving antennas. The obtained analytical and simulation results show that the SER of the AC and coherent MASK detectors are comparable, particularly for high values of the Rician K-factor, and small number of receiving antennas. In most of the considered scenarios, the heuristic AC detector outperforms the optimum noncoherent detector significantly, except for the binary ASK case at low SNRs. Moreover, the obtained results show that the heuristic AC detector is immune to phase noise, and thus, it outperforms the coherent detector in scenarios where the system is subject to considerable phase noise.

Non-orthogonal multiple access (NOMA) is currently considered as a promising technology for the next-generation wireless networks. In this paper, the error rate performance of NOMA systems is investigated over Nakagami-m fading channels, while considering imperfect successive interference cancellation. In particular, this paper focuses on the pairwise error probability (PEP) analysis, where exact PEP expressions are derived to characterize the performance of all users under different fading conditions. The obtained PEP expressions are then used to derive an exact union bound on the bit error rate (BER). Through the derived PEP expressions, the asymptotic PEP analysis is presented to investigate the maximum achievable diversity gain of NOMA users. Moreover, using the derived BER bound, the power allocation problem for all users in NOMA systems is considered under average power and users BER constraints, which allows realizing the full potential of NOMA. Monte Carlo simulation and numerical results are presented to corroborate the derived analytical expressions and give valuable insights into the error rate performance of each user and the achievable diversity gain.

This work introduces a novel blind channel estimation technique for orthogonal frequency division multiplexing (OFDM) systems over time- varying mobile channels. The proposed estimator exploits the channel correlation over consecutive OFDM symbols to estimate the channel parameters blindly. In the new estimator, particular subcarriers are modulated usingM-ary phase shift keying (MPSK), and subcarriers with the same indices in the consecutive OFDM symbol are modulated usingM-ary amplitude shift keying (MASK), replacing the pilots in pilot-aided systems. Consequently, all subcarriers are data-bearing, which leads to spectral efficiency improvement. The proposed estimator uses the feature that MPSK and MASK modulated symbols have sufficient channel state information (CSI) that enable them to cooperate in order to detect the MPSK symbols coherently and blindly. Then, the CSI at the corresponding MPSK symbols can be acquired in a decision-directed (DD) fashion. The performance of the proposed estimator is evaluated in terms of symbol error rate (SER) and mean-squared error (MSE), where an exact analytical formula is obtained for the SER of binary phase shift keying (BPSK) symbols in mobile radio channels with various time-varying rates. The obtained results show that the proposed estimator produces accurate channel estimates as compared to pilot-aided and state-of-the-art systems without additional complexity.

This paper presents an efficient blind channel estimation technique for orthogonal frequency division multiplexing (OFDM) systems over-time varying channels. New frame structure is proposed, where different modulation schemes are employed to estimate the time-varying channel coefficients. Amplitude shift keying (ASK) and phase shift keying (PSK) modulation schemes are utilized to modulate particular pair of subcarriers over consecutive OFDM symbols, where the ASK and PSK symbols cooperate to enable blind estimation of the channel coefficients. In particular, PSK modulated symbols are employed in the amplitude- coherent detector (ACD) to allow blind detection for the ASK symbols. After that, the detected ASK symbols, with interpolation, are used to estimate the channel coefficients for the full frame. Exact closed-form expression for the symbol error rate (SER) of the ASK symbols is derived and corroborated with Monte Carlo simulations to evaluate the performance of the proposed technique and compare it with the pilot based OFDM system. Analytical and simulation results show that the proposed estimator can provide estimation with accuracy and computational complexity that are comparable to pilot based estimators.

In this paper, a low-complexity discrete adaptive bit loading algorithm is proposed for multicarrier systems with uniform power allocation operating in fading environments under the discontinuous bit rates assumption. The algorithm objective is to maximize the overall throughput of the system while guaranteeing that the average bit error rate (BER) remains below a prescribed threshold. The algorithm uses a signal-to-noise ratio (SNR) threshold to group adjacent subcarriers into slots where it allocates the same number of bits for all subcarriers within the slot. The grouping mechanism reduces the complexity of the bit-loading process with negligible throughput degradation as compared to optimal and near-optimal algorithms. In particular scenarios, the achieved complexity reduction may exceed 70% with throughput penalty that is less than 1% as compared to other well established bit loading algorithms.

Unequal error protection (UEP) divides the data into different levels of importance in order to ensure that the most important parts of the source information have more protection than the less important parts. In this study, the authors investigate the application of UEP using polar codes and propose a technique that utilises the channel polarisation property of these codes to achieve UEP without any significant modification. They demonstrate the error bounds of the proposed technique particularly within the context of JPEG2000. In addition, they propose a joint source‐channel decoding method that is based on iterative decoding. This method takes the advantage of the error resilience tools that already exist in the JPEG2000 decoder. It will be shown that the proposed technique offers better performance than the conventional transmission with equal error protection.

This paper considers the problem of dynamic power allocation in the downlink of multi-cell networks, where each cell utilizes non-orthogonal multiple access (NOMA)-based resource allocation. Also, coordinated multi-point (CoMP) transmission is utilized among multiple cells to serve users experiencing severe inter-cell interference (ICI). Under this CoMP- NOMA framework, CoMP transmission is applied to a user experiencing less distinctive channel gain with multiple base stations (BSs)/cells (i.e., severe ICI-prone user) and non-CoMP transmission (i.e., transmission without any coordination among multiple BSs) is applied to a user experiencing dominating channel gain with only one BS/cell, while NOMA is utilized at each BS to schedule CoMP and non-CoMP users over the same transmission resources, i.e., time, spectrum and space. After discussing various CoMP- NOMA models for downlink power allocation in multi-cell networks, we focus on a joint transmission CoMP- NOMA (JT-CoMP-NOMA) model. For the JT-CoMP-NOMA model, an optimal joint power allocation problem is formulated and the solution is derived for each CoMP- set consisting of multiple cooperating BSs (i.e., CoMP BSs). To avoid the huge computational complexity of the joint power optimization approach, we propose a distributed power optimization approach at each cooperating BS whose optimal solution is independent of the solution of other coordinating BSs. The distributed solution for the joint power optimization problem is validated and numerical performance evaluation is carried out for the proposed CoMP- NOMA models including JT-CoMP-NOMA and coordinated scheduling CoMP- NOMA (CS-CoMP-NOMA). The obtained results reveal significant gains in spectral and energy efficiency in comparison with conventional CoMP- orthogonal multiple access (CoMP-OMA) systems.

In this paper, we derive the maximum likelihood detector (MLD) for precoded space-frequency block coded (SFBC) systems where orthogonal frequency division multiplexing (OFDM) is incorporated. The obtained results reveal that the precoding process can be exploited to construct low complexity MLD even when the channel frequency response is not equal across each SFBC block. The derived MLD structure is similar to the conventional Alamouti linear decoder except that the decoding matrix has to be selected from four possible matrices. However, the decoding matrix selection and symbols' detection can be performed jointly, which minimizes the additional computational complexity of the derived MLD as compared to the conventional Alamouti decoder. Monte Carlo simulation results show that the MLD outperforms the suboptimal detector reported in [1] by about 5 dB at bit error rate (BER) of 10-4under various channel conditions.

In the literature, the spectral efficiency is considered a key performance indicator that is used to classify various communications systems, algorithms, and techniques. However, the classification is typically performed while assuming that all systems have a static structure, and without considering the quality of service (QoS) requirements or the constraints imposed by the system design. Therefore, this work presents a new reliable and accurate approach to evaluate the spectral efficiency of communications systems while considering the system dynamics, QoS requirements and design constraints. To demonstrate its effectiveness, the proposed approach is used to evaluate the spectral efficiency of various blind and pilot-aided channel estimation and synchronization algorithms. The obtained results reveal that the spectral efficiency depends on several system variables such the signal-to-noise ratio (SNR), QoS requirements, system constraints, and the channel characteristics. Contrary to what is usually believed, the obtained results show that pilot-aided systems can be more spectrally efficient than blind systems for several cases of interest.

This paper presents a blind channel estimation (BCE) technique for orthogonal frequency division multiplexing communications systems. The proposed system is based on modulating particular pairs of subcarriers using amplitude shift keying and phase shift keying, which enables the realization of a decision-directed one-shot BCE (OSBCE), with complexity and accuracy that are comparable to pilot-based channel estimation techniques. The performance of the proposed estimator is evaluated in terms of the mean squared error (MSE), where an accurate analytical expression is derived and verified using Monte Carlo simulation under various channel conditions. The obtained results show that the MSE of the proposed OSBCE is comparable to pilot-based estimators, which confirms the efficiency of the proposed OSBCE.

This work presents a new digital communications receiver that requires only partial knowledge of the channel state information (CSI). Generally speaking, the CSI is composed of real and imaginary components, which can be expressed as h = |h| ejθ, where |h| corresponds to the channel attenuation and θ is the phase shift. In the proposed receiver, only |h| is required to detect the transmitted symbols with low probability of error. The proposed receiver can be used to increase the spectral efficiency of most digital communications receivers and/or reduce their error probability.

We present a new multiple input multiple output (MIMO) technique, based on Walsh Hadamard Transform (WHT) precoding, to improve the robustness of space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) systems. The WHT is applied to the data symbols prior the Alamouti encoder at the transmitter and to the output of the Alamouti decoder at the receiver. The computational complexity of the proposed system is evaluated in terms of complex additions and multiplications where the numerical results show that the proposed system has a lower complexity as compared to other precoded OFDM systems. Moreover, the proposed system is highly robust to the channel time and frequency selectivity as compared to conventional SFBC, space time block coded (STBC) and other precoded OFDM systems.

This paper presents the detector design and symbol error rate (SER) analysis of M-ary amplitude shift keying over multipath fading channels using amplitude-coherent detection (ACD). The optimum detector is derived using the maximum likelihood criterion, and then it is used to derive two efficient low-complexity suboptimal detectors. The probability distribution function of the decision variables and the SER of the two suboptimal detectors are expressed using simple closed-form analytical formulas when single receiving antenna is used. The SER with receiver diversity is obtained using Monte Carlo simulation. The obtained analytical and simulation results reveal that ACD can provide reliable SER as compared with noncoherent detection. Moreover, we present an efficient blind channel estimation algorithm using ACD and hybrid modulation frame structures.

Abstract Wireless resource virtualization (WRV) is currently emerging as a key technology to overcome the major challenges facing the mobile network operators (MNOs) such as reducing the capital, minimizing the operating expenses, improving the quality of service, and satisfying the growing demand for mobile services. Achieving such conflicting objectives simultaneously requires a highly efficient utilization of the available resources including the network infrastructure and the reserved spectrum. In this paper, the most dominant WRV frameworks are discussed where different levels of network infrastructure and spectrum resources are shared between multiple MNOs. Moreover, we summarize the major benefits and most pressing business challenges of deploying WRV. We further highlight the technical challenges and requirements for abstraction and sharing of spectrum resources in next generation networks. In addition, we provide guidelines for implementing comprehensive solutions that are able to abstract and share the spectrum resources in next generation network. The paper also presents an efficient algorithm for base station virtualization in long‐term evolution (LTE) networks to share the wireless resources between MNOs who apply different scheduling polices. The proposed algorithm maintains a high‐level of isolation and offers throughput performance gain. Copyright © 2016 John Wiley & Sons, Ltd.

This paper presents a hybrid automatic repeat request (HARQ) system using a parity error checking (PEC) technique with low processing power requirements. The proposed technique is applied to extended turbo product codes (TPC) where the parity check bits used for extending the component codes of TPC, are exploited to replace the conventional cyclic redundancy check (CRC) error detection in HARQ systems. Consequently, the required processing power can be reduced substantially while the throughput is almost unchanged for long TPC codes, or increased for short TPC codes. The proposed PEC technique is also compared to the state-of-the-art syndrome error checking (SEC) as well as conventional CRC. Monte Carlo simulation results reveal that PEC- HARQ can provide equivalent throughput to SEC-HARQ and higher throughput than CR-HARQ systems. Moreover, numerical results show that the PEC technique has lower computational complexity than both SEC and CRC error detection. In particular cases, the complexity of the proposed system is reduced by more than 50% as compared to the state- of-the-art, and by more than 80% when compared to the CRC error detection.

This paper presents an adaptive power control scheme for hybrid automatic repeat request (HARQ) systems with no channel state information feedback. The power control process is developed by noting that the throughput of particular HARQ systems may exhibit a staircase behavior. In such scenarios, the throughput remains fixed for a wide range of signal-to-noise ratios (SNRs). Consequently, the transmit power can be reduced significantly while the throughput remains almost unchanged. The obtained results reveal that invoking power optimization algorithms can achieve a significant power saving of about 80% for particular scenarios. The system considered in this work is a truncated HARQ with turbo product codes (TPC). Chase combining is also used to combine the retransmitted packets with the original transmission. HARQ acknowledgment/negative acknowledgment (ACK/NACK) feedback is used to estimate the packet error rate from which the system throughput is computed.

The continuous increase of mobile data traffic has created a substantial demand for high data rate transmission over mobile networks. However, mobile devices are provided with small batteries that can be drained quickly by high data rate transmission. Motivated by the fundamental requirement of extending the battery utilization time per charge of mobile devices, this work presents two power-efficient schedulers for mixed streaming services in LTE uplink systems. Our objective is to minimize the total transmission power for all users. The proposed schedulers are subject to rate, delay, contiguous allocation, and maximum transmission power constraints. We first consider an optimal scheduler that uses binary integer programming (BIP). Then, we propose an iterative scheduler that performs a low-complexity greedy algorithm which solves the BIP problem. We compare the performance of the proposed schedulers to the state-of-the-art schedulers such as the energy-aware resource allocation (EARA) [1] and the proportional fair (PF) [2] in terms of rate, delay, average transmission power and complexity. Simulation results show that the proposed schedulers offer a remarkable transmission power reduction as compared to the PF and the EARA schedulers, and satisfy the QoS requirements.

Single Carrier Frequency Division Multiple Access (SC-FDMA) is used for uplink data transmission in Long Term Evolution (LTE) systems. SC-FDMA requires contiguous resource blocks (RBs) allocation for each user, which challenges the uplink resource allocation in LTE. The contiguity constraint turns the allocation problem into a non-convex optimization problem. The optimal solution is achieved by solving a binary integer programming (BIP) problem which is computationally-expensive. In this work, we propose a genetic algorithm that is able to solve the resource allocation problem in the LTE uplink. The proposed algorithm maintains all the system constraints and provides a solution with lower complexity compared with the optimal solution. The proposed GA is evaluated and compared with the optimal approach in terms of efficiency and time complexity.

This work considers the development of a realistic statistical model to represent the interference in heterogeneous wireless networks. The considered networks are comprised of one or more femtocells deployed in buildings with unknown internal structures and a preplanned cellular network. The proposed interference model is based on a novel random floor plan generator, which is used to construct a statistical rather than site-specific floor plans. The developed model is augmented with Nakagami fading to represent the femtocell interference signal in the outdoor environment. The model is then utilized to evaluate the performance of the macrocell users where closed-form formulae for the outage probability and signal-to-interference ratio at the receiver front-end are derived. The obtained results reveal that a femtocell signal propagating from an indoor transmitter to an outdoor receiver will experience a composite shadowing/fading process where the Nakagami distribution is adopted for the fading part while the shadowing is modeled by lognormal mixture distribution. Analytical and simulation results show that placing the femtocell base-station (FBS) close to the center of the house can significantly reduce the impact of the interference on the outdoor macrocell users as compared to a randomly placed FBS.

This paper presents a hybrid automatic repeat request (HARQ) system using turbo product codes (TPC). The inherent word-error detection capability of TPC is exploited to replace the conventional cyclic redundancy check (CRC) used for packet error detection in conventional HARQ systems. Therefore, TPC are used for joint bit error correction and packet error detection. Consequently, the HARQ system efficiency is improved by increasing the system throughput when short packets are transmitted or by reducing the computational complexity/delay when the packets transmitted are long. Monte Carlo simulation results reveal that the CRC-free TPC-HARQ system consistently provides equivalent or higher throughput than CRC-based HARQ systems. Moreover, numerical results show that TPC self-detection has lower computational complexity than CRC detection, particularly for TPCs with high code rates. In particular scenarios, the relative complexity of the self-detection approach with respect to popular CRC techniques is about 0.3%.

This work presents a power-efficient multi-user scheduler for mixed streaming services in multi-user LTE uplink systems. We propose an optimal and iterative formulation for the sum-power minimization subject to rate, delay, contiguous allocation, and maximum transmitted power constraints. The results are presented for the rate, delay, average transmitted power and complexity.

In this work, a new low complexity linear precoded orthogonal frequency division multiplexing (LP-OFDM) system, called Haar-OFDM (H-OFDM), is proposed. The proposed system employs a fast precoder, denoted as inverse D-precoder (IDP), which is derived by merging the operations of the fast Haar precoder (FHP) and inverse fast Fourier transform (IFFT) as one transform. Interestingly, the number of arithmetic operations required by the H-OFDM system are noticeably smaller than the conventional OFDM. Furthermore, extensive simulation results demonstrate that the H-OFDM system is robust against the frequency-selectivity of the channel.

This paper presents an efficient technique to jointly mitigate the severe bit error rate (BER) performance degradation caused by impulsive noise (IN) and multipath fading in broadband transmission systems. The proposed system is based on a low complexity interleaving process applied after the inverse fast Fourier transform (IFFT) in orthogonal frequency division multiplexing (OFDM) systems, hence it is denoted as time-domain interleaving (TDI). The proposed TDI introduces both time and frequency diversity, which can be used to effectively combat impairments such as IN and frequency-selective fading. In addition to its substantial BER reduction capability, the TDI does not degrade the spectral efficiency and has low computational complexity. In frequency-selective fading channels, the BER of the proposed system is mathematically equal to that of Walsh-Hadamard precoded OFDM systems [1]. In presence of IN, analytical and simulation results show that TDI can remarkably reduce the level of the error floors that are commonly observed. Specifically, TDI can achieve a BER of 10-5for less than 1 dB difference from the IN-free case.

This work considers the development of an indoor-to-outdoor signal propagation model, which can be used to analyze and reduce the interference in various wireless communication networks, particularly 4G networks with femtocells and macrocells. The developed model is based on generating a large number of floor plans with random, but realistic, designs and use signal attenuation models to analyze the statistical properties of the signal at a certain distance from the indoor transmitter after penetrating through several layers of construction materials such as wall, doors and windows. Further studies conducted using the developed model demonstrated that the walls and buildings could be exploited to act like a shield that reduces the mutual interference of indoor and outdoor transmitters as in the case of femtocells. As an application, the proposed model is used to investigate the effect of the placement of an indoor transmitter on the signal level outdoors. The obtained results demonstrated that optimizing the location of the indoor transmitter can reduce the power leakage to the outdoor environment by about 18.5 dB.

In this work, a new technique for mitigating the impulsive noise impact on the orthogonal frequency division multiplexing (OFDM) system is proposed, and its performance is compared with a previously published technique (referred to as time-domain interleaving (TDI) technique). In the TDI technique, the samples contaminated by impulsive noise are spread in timedomain over N OFDM symbols by using an interleaver after the inverse fast Fourier transform (IFFT) process. Accordingly, the effect of the impulsive noise burst will be averaged over N OFDM symbols, which reduces the impact on the bit error rate (BER) considerably. However, to achieve the same goal, the proposed system is using an additional orthogonal transform in form of an IFFT at the output of the interleaver. In general, the two techniques have shown a superior improvement in BER performance compared to that of the standard OFDM system, which suffers from error floors at high values of signal to noise ratio (SNR). However, for quadrature phase shift keying (QPSK) modulation with low signal to impulsive noise ratio (SIR), the proposed technique outperforms the TDI technique for different impulsive noise distributions. For high modulation order 16 and 64 quadrature amplitude modulation (QAM) in severe impulsive noise channels, the proposed technique demonstrates more robustness than the TDI, which suffers from error floors for the considered values of SIR and impulsive noise distributions.

Due to the nonlinear characteristics of the high power amplifier (HPA), the employment of orthogonal frequency division multiplexing (OFDM) based modulation schemes results in significant amplitude and phase signal distortion due to the high peak-to-average power ratio (PAPR) nature of the OFDM. To overcome this problem, PAPR reduction methods are commonly applied at the transmitter. Among the plenitude of methods available, partial transmit sequences (PTS) and selected mapping (SLM) are the most powerful schemes. The computational complexity for these schemes is considered as the main disadvantage. In this paper, we propose a low-complexity scheme based on iterative PTS (IPTS) that employs two inverse fast Fourier transforms (IFFT) and two circulant transform matrices. Numerical results demonstrate that the proposed scheme using a partition vector for IPTS with an odd number of ones can achieve both a reduction in PAPR of approximately 2 dB and an improvement of 1.4 dB in terms of signal-to-noise ratio (SNR) to achieve a bit error rate (BER) of 10-4. A further simplification can be achieved by omitting one of the circulant transform matrices in order to improve the computational complexity reduction ratio (CCRR) by 30% and reduce the number of side information bits by 1-bit compared with the IPTS, however, at the cost of a small reduction in PAPR and BER performance.

This work considers the bit error rate (BER) performance of orthogonal frequency division multiplexing (OFDM) frequency hopping (FH) systems in the presence of Multitone jamming (MTJ) and multipath fading. Analytical and simulation results confirmed that optimum jamming strategies require channel and signal power side information. Moreover, the common assumption that the jamming tones and subcarriers frequencies are identical can be quite inaccurate at low signal-to-jamming power ratios (SJR), particularly for small number of jamming tones.

In this work, an elegant interleaving process is used not only to mitigate the impact of bursty impulsive noise on the performance of orthogonal frequency division multiplexing (OFDM) systems but also to break bursty multipath fading channel errors. While, conventional OFDM systems implement the interleaving process in the frequency domain, the system proposed here uses a block interleaver of size N2samples in the time domain. As a result, time diversity has been exploited through the use of the interleaver by spreading the samples contaminated by impulsive noise over the impulse-free OFDM symbols and breaking the correlated behaviour of the multipath fading channel. Nevertheless, the results, given in this work, have shown that the performance of the proposed system depends on the kind of equalization process used. A serious degradation in the performance is noticed when zero forcing (ZF) equalizer is utilized. However, a simple and low complexity solution to improve the ZF equalizer performance is also proposed. On the other hand, utilizing a minimum mean square error (MMSE) equalizer demonstrates better performance than the ZF equalizer. The simulation results have confirmed the validity of the proposed system over different scenarios of the channels considered in this work.

This paper presents an efficient technique to eliminate the inter-layer interference (ILI) inherent in hierarchical modulation (HM) schemes operating over nonlinear satellite channels. The HM considered in this work is used in conjunction with an orthogonal frequency division multiplexing (OFDM) system. The proposed technique is based on an enhanced version of the selective mapping (SLM) scheme used for peak-to-average power ratio (PAPR) reduction. The enhanced SLM is constructed by using a new metric, which is more informative than the conventional PAPR metric. Simulation results confirmed that a noticeable bit error rate (BER) and interference reductions can be achieved by using the proposed technique.

The standard Alamouti space-frequency block code (SFBC) suffers from performance degradation when used over highly frequency-selective channels because the channel frequency response is not necessarily flat over the Alamouti block. In this paper, we present an enhanced Alamouti space frequency block decoding scheme for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems over highly frequency selective channels. The enhanced Alamouti scheme uses the channel frequency variations in consecutive subcarriers to adapt the Alamouti decoder. Simulation results of DVB-T2 system confirm that the proposed method has substantial performance improvement in terms of bit error rate when compared to standard Alamouti decoder mainly over highly frequency-selective channels such as single frequency networks (SFN).

This paper presents a robust timing recovery scheme for orthogonal space-time block coding (OSTBC) multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with constant modulus constellation. In the proposed system, the symbol timing is achieved either by minimizing the power difference between adjacent subcarriers in one STC block or between subcarriers with similar indices in consecutive STC blocks. The proposed technique is totally blind because it does not require any prior information about the channel state or the transmitted data. The early-late gate (ELG) configuration is utilized to realize the proposed timing recovery scheme efficiently. Monte Carlo simulations are used to assess the performance of the two realizations of the proposed system over fading channels with different frequency-selectivity conditions. Simulation results demonstrated the superiority of the proposed technique to provide accurate symbol timing even in severe frequency-selective fading channels which remarkably outperforms other timing metrics.

In this work, we propose a new decoding algorithm to correct closed-chains error patterns in hard-input hard-output (HIHO) turbo product codes (TPCs). The proposed technique is based on correlating the horizontal and vertical component codes to estimate the location of the erroneous bits in the closed-chain of errors, then erasure decoding is used to correct the identified bit errors. Simulation results demonstrated that, for particular codes, a noticeable coding gain improvement of about 1.5 dB can be achieved when compared to the standard sequential HIHO decoding and about 0.8 dB when compared to the non-sequential HIHO decoding. The computational complexity of the proposed decoder can be substantially reduced at moderate and high signal-to-noise ratios by stopping the iterative process when it is not more beneficial to perform further iterations.

In this work, an efficient interleaving process is proposed for orthogonal frequency division multiplexing (OFDM) systems over impulsive noise channels. Unlike the conventional OFDM systems where the interleaving process is implemented before the inverse discrete Fourier transform (IDFT), the proposed scheme is based on performing the interleaving process post the IDFT. The aim of this process is to average the effect of the impulsive noise burst over a large number of OFDM symbols, which can reduce its impact on the bit error rate (BER) significantly. For the system and channel models considered in the work, simulation results have confirmed that the proposed system can effectively reduce the BER degradation due to the impulsive noise to about 1 dB as compared to the impulsive noise-free case.

This paper presents a new blind symbol timing offset (STO) estimation scheme for wireless orthogonal frequency division multiplexing (OFDM) systems with constant modulus constellation. In the proposed scheme, the STO estimation is performed by minimizing the power difference between either adjacent or consecutive subcarriers, which basically depends on the assumptions made on the channel conditions. Monte Carlo simulation is used to assess the two realizations of the proposed system. The system performance is evaluated by means of mean squared error (MSE) over additive white Gaussian noise (AWGN) and frequency selective mobile radio channels. The simulation results demonstrate that the MSE of the proposed system is well below the MSE of other well-established estimators reported in the literature.

This study presents an iterative carrier frequency offset estimator for orthogonal frequency division multiplexing (OFDM) systems. The proposed estimator is based on the efficient Viterbi-and-Viterbi (VAV) algorithm. The proposed estimator is blind and can be used with non-constant modulus subcarrier modulations such as quadrature amplitude modulation (QAM). The performance of the proposed estimator is assessed theoretically and via Monte Carlo simulations over various channel models and compared to the performance of other well established blind techniques in addition to the Cramèr–Rao lower bound. The comparison results demonstrate that the proposed estimator outperforms other well-established blind estimators by more than 12 dB at moderate and high signal-to-noise ratios (SNRs).

This study presents a new blind carrier frequency offset (CFO) estimation technique for multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems employing space–time coding (STC). CFO estimation is crucial for OFDM systems to avoid the performance degradation because of the inter-carrier interference that results when the CFO is not estimated and compensated accurately. Based on the assumptions that the data symbols are selected from a constant modulus constellation and the channel is varying slowly over time, a new blind CFO estimator is proposed by minimising the power difference between all subcarriers in two consecutive STC blocks. Therefore the proposed system exploits all subcarriers in time and frequency domain, which provides a remarkable performance improvement over other techniques reported in the literature. The complexity of the proposed estimator is substantially reduced by approximating the cost function by a sinusoid that can be minimised using direct closed-form computations within one OFDM symbol period. Monte Carlo simulations are used to assess the performance of the proposed system by means of mean squared error (MSE) in both static and time-varying frequency-selective fading channels. The simulation results demonstrate that the proposed estimator can eliminate the MSE error floors that usually appear at moderate and high signal-to-noise ratios for the estimators that work only in frequency domain.

We propose a novel iterative decoder for block turbo codes (BTCs). The proposed decoder combines soft-input/softoutput (SISO) and hard-input/hard-output (HIHO) constituent decoders in order to obtain better error performance and reduce the computational complexity compared to classical BTC decoders. We show that the new decoder, called 'hybrid decoder', offers a better complexity/performance tradeoff than a classical BTC decoder.

In this letter, we propose a new decoding algorithm to improve the bit error rate performance of the hard-input hard-output (HIHO) turbo product codes (TPC) with hard iterative decoding. The proposed algorithm iteratively, but not sequentially, decodes the received TPC blocks based on the reliability of the constituent codes. Simulation results confirm a noticeable coding gain improvement using the proposed decoding process with respect to standard HIHO TPC decoding. An efficient implementation of the new technique offers a negligible additional complexity when the channel-bit error probability is less than 10-2.

This work presents a new technique for blind and joint estimation of symbol timing and carrier frequency offset in wireless orthogonal frequency division multiplexing (OFDM) systems. The joint estimation is achieved by sensing the interference introduced at the fast Fourier transform (FFT) output when a carrier frequency or timing offsets exist. The synchronization parameters are selected such that the interference is minimized. The proposed joint estimator is highly efficient because it does not require any overhead or channel state information. Simulation results show that the system is effective and robust even at low signal-to-noise ratios.

A new highly efficient non-data-aided technique to recover symbol timing of orthogonal frequency-division multiplexing systems is proposed. The algorithm in the proposed work exploits the interference that results due to the loss of orthogonality between subcarriers, where the second-order statistics of the resulting interference is proportional to the offset from the optimum sampling point. The presented technique does not require prior fine carrier synchronization, and it is capable of extracting symbol timing at low E/sub s//N/sub 0/ values with large carrier frequency offsets (CFOs). The system performance was investigated in multipath fading channels with large CFOs and additive white Gaussian noise.

A new technique to recover the carrier frequency offset of OFDM systems is proposed. The proposed technique does not require cyclic prefix, pilot signals, training symbols, or any other supplementary data, this will significantly improve the system power and bandwidth efficiency. The proposed algorithm exploits the interference that results due the loss of orthogonality between subcarriers where the variance of the resulted interference is proportional to the carrier frequency offset. The proposed technique does not require prior fine symbol synchronization and it is capable of estimating the carrier offset at E/sub b//N/sub o/ as low as -3 dB with symbol timing offset that is less than or equal to 10% of the symbol duration.

A noncoherent, bandwidth-efficient modulation scheme is proposed for frequency-hopping multiple-access (FH-MA) networks. The proposed scheme is a combination of noncoherent M-ary amplitude-shift keying (NMASK) and orthogonal frequency-division multiplexing (OFDM). Using this scheme minimizes the required data bandwidth. The number of frequency slots available to the users increases significantly for a fixed spread-spectrum bandwidth (BW/sub SS/). The effect of the multiple-access interference is reduced. Simple and accurate bit error rate expressions have been derived for FH-OFDM-MASK in additive white Gaussian noise channels and for FH-OFDM-ASK in Rayleigh fading channels.