In fog radio access networks (F-RANs), caching popular content at edge fog access points (FAPs) helps alleviate the burden on base stations and backhaul links. To improve signal quality and connectivity, this work integrates cooperative communication and non-orthogonal multiple access (NOMA) into content-centric F-RANs with unreliable backhauls. Specifically, a NOMA-enabled joint transmission scheme is considered, where cache-enabled FAPs are coordinated into clusters to perform non-coherent joint transmission and NOMA, enabling multiplexing signals for multiple users. Under a hybrid caching policy and non-uniform Nakagami-mfading channels, the system performance is analyzed in terms of the successful content delivery probability and outage achievable rate. To optimize FAP coordination, the clustering problem is formulated as a coalitional game, and a low-complexity transfer-based clustering algorithm is designed. Furthermore, a hierarchical hybrid NOMA-based algorithm is developed to enhance multi-user access efficiency. Simulation results demonstrate that: 1) The NOMA-enabled joint transmission scheme allows the FAPs efficiently leverage the cached content to mitigate backhaul unreliability; 2) The NOMA-based design outperforms the orthogonal multiple access-based design by guaranteeing improved signal quality while maintaining the efficiency of multi-user access; 3) The coalitional game-based clustering algorithm effectively manages co-channel interference and improves spectrum utilization.

We propose an innovative physical layer authentication method, leveraging deep learning to robustly safeguard millimeter wave communications against pilot contamination and clone attacks. Unlike traditional upper-layer authentication mechanisms, our method capitalizes on the spatial-temporal characteristics of millimeter wave channels to extract unique fingerprints, thus establishing a lightweight channel-based authentication technique. Existing methods largely overlook pilot contamination attacks, which may severely degrade the performance of physical layer authentication. Furthermore, traditional threshold-based methods struggle to differentiate between multiple nodes, while supervised learning-based methods are practically constrained due to the unavailability of attackers’ instantaneous channel state information. Moreover, traditional real-valued deep neural networks are inefficient in utilizing the phase information of complex-valued channels, rendering them inadequate for designing practical physical layer authentication schemes. To address these challenges, we propose an autoencoder, empowered by an alternating direction method of multipliers, which can detect and mitigate pilot contamination attacks by exploiting the inherent sparsity of channels. Subsequently, we design a weighted loss function to optimize the proposed classifiable autoencoder to strike an effective balance between detecting clone attacks and authenticating multiple nodes. Finally, to further enhance feature extraction from complex-valued channels, we customize a complex-valued classifiable autoencoder incorporating an innovative complex-valued long short-term memory module. Our simulation results unveil that the proposed method significantly outperforms existing approaches in maintaining high authentication accuracy even under pilot contamination, achieving a desirable trade-off between false alarm and detection rates. Additionally, our proposed complex-valued neural networks further enhance the accuracy of clone attack detection and multiple legitimate nodes authentication.

This paper presents a novel resilient production problem in a multi-robot system (MRS) driven smart factory that suffers diverse degradation of accuracy among heterogeneous robots. The inevitable degradation in production robots’ accuracy undermines desirable productivity and efficiency. Although traditional maintenance and calibration strategies can be employed, they fail to support the continuity, flexibility and agility required in smart factories. Instead of pursuing accurate task execution relative to a consistent global reference, we formulate an innovative MRS coordination strategy, where a collaborative MRS autonomously pursues relative accuracy against accuracy degradation toward resilient operation. This new coordination strategy introduces challenges including adapting to time-dynamic production flows, difficulties in observing production robots’ accuracy, and the absence of a comprehensive architecture of resilient MRS in a smart factory. We propose a computational approach with social learning and AI to overcome these challenges. A cyber-physical MRS model is proposed, in which the physical domain represents the time-dynamic production flows, while the cyber domain forms a partially connected wireless network to automate the collection of data regarding production flows, accuracy degradation, and peer robot measurements. Social learning based on such data is employed to collaboratively estimate accuracy and AI decision-making, thereby enabling adaptive coordinated task execution against accuracy degradation. We further investigated a group decision-based predictive maintenance against point failures caused by accuracy degradation. Computational experiments demonstrate that the proposed approach improves the effective rate and mean-time-to-fail performances against accuracy degradation and point failures in a scalable manner. Note to Practitioners—The practical problem motivating our work revolves around resilient production, which is affected by diverse accuracy degradations among heterogeneous robots. This issue is particularly relevant for implementing smart factories with multi-robot systems (MRS), including production and transportation robots. We propose a cyber-physical multi-robot system (CPMRS) to comprehend the dynamics of MRS-driven smart factories, aiming to facilitate productivity, efficiency, and resilience through MRS coordination, as opposed to accurate production task execution achieved by frequent maintenance and calibration, which sacrifices the flexibility and agility of smart factories. CPMRS allows the autonomous collection and exchange of information about production flows, accuracy degradations, and peer robot measurements with limited wireless communications. CPMRS further enables computational solutions with social learning and reinforcement learning for robots as well as group-decision-based predictive maintenance. It facilitates autonomous coordinated task execution and resilient production. Computational experiments demonstrate a 124 percent improvement in the mean time to failure (MTTF) and a 317.27 percent improvement with predictive maintenance. As in our proposal to general manufacturing, further research may be adapted to specific manufacturing scenarios. This research can benefit broader applications, such as smart logistics, warehouses, and even smart cities, where similar collective actions among multiple robots or agents are required.

In this paper, we propose a safe motion planning protocol that integrates a distributed cyclic delay diversity (dCDD) system for indoor environments with static obstacles. In addition to collision avoidance, an additional goal of jointly minimizing energy consumption to control dynamic movements of an unmanned autonomous ground vehicle (AGV) and maximizing spectral efficiency (SE) achieved by a set of distributed remote radio heads is investigated in the framework of reinforcement learning (RL). There are several challenges, such as a lack of knowledge about the environment and nonexistent feasible mathematical analysis to utilize the distribution of the sum of the receive signal-to-noise ratios (SNRs) over the energy conscious motion planning. Thus, in this paper, we propose a model-free and off-policy soft actor critic (SAC) algorithm to learn and determine optimal actions for the AGV to reach its target with the following three objectives: i) achieving the safe motion planning that avoids collision with the static obstacles, ii) minimizing the control energy consumption, and iii) maximizing SE. Simulation results verify that these three objectives can be achieved efficiently and effectively by the proposed integrated SAC-based safe motion planning and dCDD system.

Semi-grant-free (SGF) transmission scheme enables grant-free (GF) users to utilize resource blocks allocated for grant-based (GB) users while maintaining the quality of service of GB users. This work investigates the secrecy performance of non-orthogonal multiple access (NOMA)-aided SGF systems. First, analytical expressions for the exact and asymptotic secrecy outage probability (SOP) of NOMA-aided SGF systems with a single GF user are derived. Then, the SGF systems with multiple GF users and the best-user scheduling scheme is considered. By utilizing order statistics theory, analytical expressions for the exact and asymptotic SOP are derived. Monte Carlo simulation results are provided and compared with two benchmark schemes. The effects of system parameters on the SOP of the considered system are demonstrated and the accuracy of the developed analytical results is verified. The results indicate that both the outage target rate for GB and the secure target rate for GF are the main factors of the secrecy performance of SGF systems.

System logs record rich information for system events. Practical anomaly detection from system logs should be able to address three challenges: 1) understanding complicated attributes in event logs; 2) extracting complex context relations among events; and 3) providing concrete explanations to human analysts. In this paper, we develop an attention-equipped encoder-decoder system to capture context from system logs for explainable anomaly detection. For each target event, we collect its nearby events in chronological order as its context events. Instead of using a recurrent neural network-based encoder like previous works, we adopt a Transformer-based encoder to extract complex relations among context events and their attributes. Then, a context vector is generated and passed to the decoder, where an attention matrix is learned and used to weigh the context events for detecting the anomalies. Evaluation on the large-scale real-world Los Alamos National Laboratory dataset shows that, compared with existing works, our methods can provide fine-grained one-to-one attention to help explain the importance of each attribute in the context events to the prediction, without sacrificing detection performance.

In the uplink cognitive radio-inspired nonorthogonal multiple access (CR-NOMA) systems, the successive interference cancellation (SIC), and power control (PC) schemes were designed to enhance the outage performance but they lack the capability of protecting signals from being eavesdropped. This work investigates the secrecy performance of uplink CR-NOMA systems with the hybrid SIC and PC (HSIC-PC) scheme in the presence of a passive eavesdropper. Furthermore, through transmitting artificial noise (AN), a new scheme is proposed to improve the security of the cognitive user with HSIC-PC without deteriorating the primary user’s quality of service. Specifically, the primary and secondary users transmit AN cooperatively to enhance the security of the secondary user. The secrecy performance of the proposed scheme is analyzed based on the relationship between the maximum interference power that the primary user can tolerate and the secondary user’s channel gain. The analytical expressions for the secrecy outage probability (SOP) are derived, and the effect of parameters on the SOP is discussed. We also derive the analytical expressions of the asymptotic SOP in the high-power region to obtain further insights. Monte Carlo simulation results are performed to verify the analytical results. The results demonstrate that the proposed scheme performs better than the benchmarks.

In this paper, a rate-splitting multiple access (RSMA) scheme is proposed to aid a mobile edge computing (MEC) system where multiple randomly deployed users offload their computation tasks to a MEC server. Considering that users are divided into the center and edge groups, a cognitive radio (CR)-inspired rate-splitting is designed to enable the paired users to simultaneously offload to MEC server. Under the CR principles, the rate-splitting parameters are jointly designed to attain the maximum achievable rate for the secondary user, meanwhile maintaining the primary user’s offloading performance same as in orthogonal multiple access. For the case of the paired users with fixed locations, we derive a closed-form expression for the successful computation probability (SCP) achieved by the RSMA-aided MEC (RSMA-MEC) scheme and formulate a SCP maximization problem to obtain the optimal offloading parameters. To reveal the impact of the user locations on the offloading performance of the RSMA-MEC system, various distance-based user pairing schemes are investigated by invoking stochastic geometry techniques. We provide closed-form expressions for the SCPs achieved by the user pairing schemes to characterize the offloading performance. Pros and cons of the user locations to maximize the SCP are highlighted. Simulation results verify the accuracy of the analytical results and clarify the superior offloading performance achieved by the RSMA-MEC scheme, which attains a higher SCP than the existing schemes.

In this paper, a cyclic-prefixed single-carrier (CPSC) transmission scheme with phase shift keying (PSK) signaling is presented for broadband wireless communications systems empowered by a reconfigurable intelligent surface (RIS). In the proposed CPSC-RIS, the RIS is configured according to the transmitted PSK symbols such that different cyclically delayed versions of the incident signal are created by the RIS to achieve multipath diversity. A practical and efficient channel estimator is developed for CPSC-RIS and the mean square error of the channel estimation is expressed in closed-form. We analyze the bit error rate (BER) performance of CPSC-RIS over frequency-selective Nakagami-$m$fading channels. An upper bound on the BER is derived by assuming maximum-likelihood detection. Furthermore, by applying the concept of index modulation (IM), we propose an extension of CPSC-RIS, termed CPSC-RIS-IM, which enhances the spectral efficiency. In addition to conventional constellation information of PSK symbols, CPSC-RIS-IM uses the full permutations of cyclic delays caused by the RIS to carry information. A sub-optimal receiver is designed for CPSC-RIS-IM to aim at low computational complexity. Our simulation results in terms of BER corroborate the performance analysis and the superiority of CPSC-RIS(-IM) over the conventional CPSC without an RIS and orthogonal frequency division multiplexing with an RIS.

While privacy concerns entice connected and automated vehicles to incorporate on-board federated learning (FL) solutions, an integrated vehicle-to-everything communication with heterogeneous computation power aware learning platform is urgently necessary to make it a reality. Motivated by this, we propose a novel mobility, communication and computation aware online FL platform that uses on-road vehicles as learning agents. Thanks to the advanced features of modern vehicles, the on-board sensors can collect data as vehicles travel along their trajectories, while the on-board processors can train machine learning models using the collected data. To take the high mobility of vehicles into account, we consider the delay as a learning parameter and restrict it to be less than a tolerable threshold. To satisfy this threshold, the central server accepts partially trained models, the distributed roadside units (a) perform downlink multicast beamforming to minimize global model distribution delay and (b) allocate optimal uplink radio resources to minimize local model offloading delay, and the vehicle agents conduct heterogeneous local model training. Using real-world vehicle trace datasets, we validate our FL solutions. Simulation shows that the proposed integrated FL platform is robust and outperforms baseline models. With reasonable local training episodes, it can effectively satisfy all constraints and deliver near ground truth multi-horizon velocity and vehicle-specific power predictions.

In this paper, a multiple cluster-based transmission diversity scheme is proposed for asynchronous joint transmissions (JT) in private networks. The use of multiple clusters or small cells is adopted to reduce the transmission distance to users thereby increasing data-rates and reducing latency. To further increase the spectral efficiency and achieve flexible spatial degrees of freedom, we consider that a distributed remote radio unit system (dRRUS) is installed in each of the clusters. A key characteristic of deploying the dRRUS in private networks is the associated multipath-rich and asynchronous delay propagation environment. Therefore, we consider asynchronous multiple signal reception at the remote radio units and propose an intersymbol interference free distributed cyclic delay diversity (dCDD) scheme for JT to achieve the full transmit diversity gain without requiring full channel state information of the private network. The spectral efficiency of the proposed dCDD-based JT is analyzed by deriving a new closed-form expression, and then compared with link-level simulations for non-identically distributed frequency selective fading over the entire network. Due to its distributed structure, the dRRUS relies on backhaul communications between the private network server and cluster master (CM), which is the main backhaul connection, and between the CM to remote radio units, which are the secondary backhaul connections. Thus, it is important for us to investigate the impact of reliability of main and secondary backhaul connections on the system. Our results show that the resulting composite backhaul connections can be accurately modeled by our proposed product of independent Bernoulli processes.

This paper proposes an anomaly detection algorithm for a factory automation system, which jointly performs data pre-processing and time-delay autoencoder (TDAE) with a hybrid loss function. The source data are pre-processed by digital filters before feeding into a TDAE for anomaly detection. The digital filters extract analog signals from a variety of frequency bands to facilitate identifying anomalies. The pre-processed data then takes time-delay reform to explore temporal relationship of data signals. In addition, two anomaly diagnosis algorithms, a statistical based method and an autoencoder based method, are presented. Numerical results show that time-delay reform can improve the anomaly detection accuracy compared to the conventional autoencoder. Data pre-processing can further improve the anomaly detection accuracy. Moreover, we confirm that our anomaly diagnosis algorithms outperform traditional method that does not perform data pre-processing and time-delay reform.

In this paper, a multiple cluster-based transmission diversity scheme is proposed for asynchronous joint transmissions (JT) in private networks, in which the use of multiple clusters or small cells is preferable to increase transmission speeds, reduce latency, and bring transmissions closer to the users. To increase the spectral efficiency and coverage, and to achieve flexible spatial degrees of freedom, a distributed remote radio unit system (dRRUS) is installed in each of the clusters. When the dRRUS is disposed in the private environments, it will be associated with multipath-rich and asynchronous delay propagation. Taking into account of this unique environment of private networks, asynchronous multiple signal reception is considered in the development of operation at the remote radio units to make an intersymbol interference free distributed cyclic delay diversity (dCDD) scheme for JT to achieve a full transmit diversity gain without full channel state information. A spectral efficiency of the proposed dCDD-based JT is analyzed by deriving the closed- form expression, and then compared with link-level simulations for non-identically distributed frequency selective fading over the entire private network.

A novel multi-task federated learning (FL) framework is proposed in this paper to optimize the traffic prediction models without sharing the collected data among traffic stations. In particular, a divisive hierarchical clustering is first introduced to partition the collected traffic data at each station into different clusters. The FL is then implemented to collaboratively train the learning model for each cluster of local data distributed across the stations. Using the multi-task FL framework, the route planning is studied where the road map is modeled as a time-dependent graph and a modified A * algorithm is used to determine the route with the shortest traveling time. Simulation results showcase the prediction accuracy improvement of the proposed multi-task FL framework over two baseline schemes. The simulation results also show that, when using the multi-task FL framework in the route planning, an accurate traveling time can be estimated and an effective route can be selected.

In this paper, a new transmit diversity scheme is proposed for cooperative pseudo-non-orthogonal multiple access (Pseudo-NOMA) without assuming full channel state information at the transmitter (CSIT). To support two users under the near-far user pairing constraint, a distributed cyclic delay diversity (dCDD) scheme is adapted into NOMA by dividing a set of remote radio heads (RRHs) into two groups for multiple cyclic-prefixed single carrier transmissions. To maximize a far user's rate and two users' sum rate over independently but non-identically distributed frequency selective fading channels and under a near-far user pairing constraint, we first derive closed-form expressions for the rates of the two users with full CSIT. Considering that only partial CSIT is available, a new RRH assignment and power allocation scheme is proposed for dCDD-Pseudo-NOMA. For various simulation scenarios, the provided link-level simulations verify that higher rates can be achieved by dCDD-Pseudo-NOMA compared with the traditional orthogonal multiple access with dCDD and dCDD-Conventional-NOMA that uses the superimposed signals. Furthermore, the proposed RRH assignment and power allocation scheme makes dCDD-Pseudo-NOMA achieve almost the same rate as that of ideal dCDD-Pseudo-NOMA which requires full CSIT.

In this paper, two novel adaptive spatial scattering modulation (ASSM) algorithms, namely unequal transmission probability-based ASSM (UTP-ASSM) and equal transmission probability-based ASSM (ETP-ASSM), are proposed to pursue a better tradeoff between the computational complexity and spectral efficiency. According to available channel state information, the proposed ASSM algorithms are conducted to compute the optimal numbers of scatters and the optimal modulation orders constrained by the maximal tolerable symbol error probability (SEP). In addition, the minimal tolerate value of the minimal tolerant signal-to-noise ratio and SEP threshold are computed with a given data rate requirement by the bisection algorithm. At the receiver, a new type of optimal maximum likelihood detector is proposed to enhance the SEP performance. Furthermore, the union upper bound on the SEP is derived and analyzed. In addition, the computational complexity and system performance of the ASSM schemes are analyzed. Simulation results demonstrate that the proposed ASSM algorithms yield a lower SEP than the conventional spatial scattering modulation at the same value of average data rate.

For a multi-cluster-based transmit diversity scheme that supports joint transmissions (JT) in private networks, a distributed remote radio unit system (dRRUS) is deployed in each of the clusters to increase the spectral efficiency and coverage, and to achieve flexible spatial degrees of freedom. Due to its distributed structure, the dRRUS relies on backhaul communications between the private network server (PNS) and cluster master (CM), which is the main backhaul communication, and between the CM to remote radio units (RRUs), which is the secondary backhaul communication. Thus, this paper mainly investigates the reliability of main and secondary backhaul connections for cluster-based transmit diversity schemes in private networks. Employing a Bernoulli process to model each backhaul reliability, a composite backhaul connection is modeled by an independent product of Bernoulli processes. By employing the distributed cyclic delay diversity scheme over the dRRUS and precision time protocol for clock synchronization, the multicluster-based JT can be achieved without full channel state information of the private network environment at the PNS and CMs. Having developed necessary distributions for the signal-tonoise ratio realized at the receiver, the closed-form expressions for the outage probability and spectral efficiency are derived. To verify their accuracy, the analytical performances are compared with link-level simulations.

In this paper, a new transmit diversity scheme for cooperative non-orthogonal multiple access (NOMA) is proposed without perfect channel state information at the transmitter (CSIT). To support two users under a near-far user pairing constraint, a distributed cyclic delay diversity (dCDD) scheme is adjusted into NOMA by dividing a set of remote radio heads (RRHs) into two groups for multiple cyclic-prefixed single carrier transmissions. Using only a limited channel relevant information needed to make dCDD work, a new RRH assignment and power allocation mechanism is proposed. After then, closed-form expressions for the rates of two users achieved by the proposed RRH assignment and power allocation mechanism are derived. For various scenarios, link-level simulations verify that superior rates can be achieved by NOMA with dCDD over the traditional orthogonal multiple access with dCDD.

To improve the traffic flow in the interconnected intersections, the vehicles and infrastructure such as road side units (RSUs) need to collaboratively determine vehicle scheduling while exchanging information via vehicle-to-everything (V2X) communications. However, due to a large number of vehicles and their mobility, scheduling in the interconnected intersection is a challenging problem. Moreover, since low-latency information exchange and real-time decision making process are required, it becomes more challenging to design a holistic framework incorporating traffic control and V2X communications. In this paper, an edge computing framework is proposed to solve a travel time minimization problem at the interconnected intersections. The proposed framework enables each RSU to decide intersection scheduling while the vehicles individually determine travel trajectory by controlling their dynamics. To this end, a V2X communications protocol is designed to exchange information among vehicles and RSUs. Then, the road segments around intersection are partitioned into sequence, control, and crossing zones. In the sequence zone, optimal time is scheduled for vehicles to pass the intersection with a minimum delay. In the control zone, the location and velocity of each vehicle are controlled to arrive the crossing zone at the scheduled time by using a control algorithm designed to effectively increase driving comfort and reduce fuel consumption. Thus, the proposed framework enables the vehicles to safely pass the crossing zone without collision. Simulation results show that the proposed edge computing can successfully reduce the total travel time by up to 14.3% based on optimal scheduling for the interconnected intersections.

Motivated by an increasing interest in wireless networking in mission-critical applications, and a recent amendment of the time slotted channel hopping to IEEE 802.15.4, the multichannel delay sensitive scheduling is investigated in the many-to-one network, which is also known as the convergecast network. In such a network, each node has data to be transmitted to a gateway through multi-hop communications. As a realistic setting, packet release time at each node is not assumed to be uniform. Under this assumption, the goal of this work is to design a scheduling scheme that minimizes the schedule length and maximum end-to-end delay, in which the former is essential for repetitive data acquisition, whereas the later improves the freshness of the acquired data. To achieve the scheduling goal, the problem is formulated as a multi-objective integer programming. To obtain a feasible solution and gain an insight into the problem, a lower bound on the schedule length is derived. Based on that, a new scheduling scheme is designed to minimize the two objectives simultaneously. Link level simulations verify the performance improvement of the proposed scheme over the existing schemes.

This paper investigates the diversity gain of a distributed cyclic delay diversity (dCDD) scheme for cyclic-prefixed single carrier systems in non-identical fading channels. Non-identical small-scale fading is assumed in the environment, in which non-identical line-of-sight and non-line-of-sight fading coexist. A condition for dCDD resulting in intersymbol interference free reception at the receiver, is extended to this new channel environment. For an overpopulated system setup, a generalized performance analysis, is not available from existing works, is conducted after developing closed-form expressions for the distribution of the signal-to-noise ratio (SNR) realized at the receiver. Since the order statistics are involved in the statistical properties of the SNR, the corresponding spacing statistics are utilized to derive feasible closed-form expressions. The finalized closed-form expressions are shown to provide very reliable outage probability and spectral efficiency of dCDD for underpopulated and overpopulated systems. An asymptotic performance analysis verifies the maximum achievable diversity of the dCDD even in the overpopulated case within the considered channel environment. Link-level simulations are conducted and these verify the maximum achievable diversity gain.

A joint data and interference transmission scheme based on a new distributed asynchronous cyclic delay diversity (dACDD) technique is proposed for cooperative communication systems. Without any perfect channel state information from a legitimate user (LU) and an eavesdropping user (EU), joint remote radio head (RRH) selection for the data and jamming signal transmissions is proposed for dACDD to achieve the maximum diversity gain at the LU, while degrading the receive signal-to-interference-plus-noise ratio at the EU. The proposed dACDD is the extension of distributed cyclic delay diversity, which requires a tight synchronization among the central control unit and RRHs. Thus, processing at each RRH causing no intersymbol interference at the LU is developed. Then, the selection scheme for a data RRH is proposed, which selects a single RRH connected with the channel having the greatest channel magnitude as the data RRH to transmit a desired confidential message and controls the remaining RRHs to transmit an artificial interference sequence to the LU and EU. For the proposed distributed system, the marginal secrecy outage probability and marginal probability of non-zero achievable secrecy rate are analyzed by deriving closed-form expressions, whose correctness is verified via link-level simulations over non-identically distributed frequency selective fading channels.

In this work, we investigate the relationship between the reliability and security of a typical two-user downlink non-orthogonal multiple access (NOMA) communication system. The level of successive interference cancellation on NOMA user is considered. Firstly, the impact of various key parameters on transmit signal-to-noise ratio (SNR) of the NOMA users with the reliability outage probability (ROP) constraint is discussed. Taking the minimum of transmit SNR for ROP into account, the secrecy outage performance of the downlink NOMA systems is studied and the analytical expressions of the secrecy outage probability of the NOMA system are derived under two cases of eavesdropping capability. Furthermore, the sum effective secrecy throughput of the NOMA system under two scenarios with considering ROP constraint is derived. Monte Carlo simulations are provided to verify the accuracy of our analysis.

A novel generalized polarization-space modulation (GPSM) is proposed for polarized multiple-input multiple-output (MIMO) systems with a limit number of radio frequency (RF) chains. In the spatial domain, multiple dual-polarized (DP) transmit antennas are activated, and then combinations of those indices are used to convey information. While in the polarization domain, depending on the random input bits, only one polarization state is selected for each active DP transmit antenna to transmit information following the rule of the polarized shift keying. At the receiver, the maximum likelihood detector is employed as a benchmark to detect information bits being used to select the polarization state and activated DP antennas. In the detector, imperfect channel state information (CSI) is taken into account. Two less computationally complex detectors, i.e., a linear detector and a sphere decoding (SD) detector are proposed to relieve the computational burden. Sacrificing the average bit error probability (ABEP) performance, the proposed linear detector can reduce the computational complexity significantly. The proposed SD detector can achieve the optimum ABEP performance, while reducing computational complexity by reducing the search space. A closed-form union upper bound (UUB) on the ABEP of the GPSM system with imperfect CSI at the receiver is analytically derived and validated through simulations. From the UUB, a loose asymptotic bound on the ABEP, which sheds light on deriving the diversity gain and the coding gain, is derived. Numerical results show that the signal-to-noise ratio loss caused by increasing the number of transmit antennas is less than 3 dB while the spectral efficiency is increased by 7 b/z/Hz. Therefore, the GPSM can be a promising candidate of down link massive MIMO systems to achieve a high spectral efficiency with a limit number of RF chains.

In this paper, we investigate rate splitting (RS) for an uplink non-orthogonal multiple access (NOMA) system with a pair of near and far users adopting cyclic prefixed single carrier transmissions. Frequency-domain equalization is applied to assist successive interference cancellation at the base-station. Two kinds of RS schemes, namely, fixed RS (FRS) and cognitive RS (CRS) schemes, are proposed to realize RS for uplink NOMA with the aim of improving user fairness and outage performance in delay-limited transmissions. Corresponding to the split data streams, transmit power is allocated in either a fixed or cognitive manner for the FRS and CRS schemes, respectively. Based on achievable rate region analysis, the benefits of applying RS to uplink NOMA for enhancing the user fairness and outage performance are revealed. A modified Jain's index is proposed to measure the user fairness for the considered delay-limited transmissions. Closed-form expressions are derived for the outage probabilities of the paired users, respectively, whereas the preferred system parameters are chosen based on asymptotic outage probability expressions. The enhanced user fairness and superior outage performance of the proposed RS schemes are corroborated by Monte Carlo simulation results.

In this paper, a distributed cyclic delay diversity (dCDD) is proposed to the cooperative infrastructure-to-vehicle (I2V) system comprising one road side unit (RSU). At a particular time, to connect a RSU and a target vehicle outside each other's transmission range, a multiple number of vehicles located within the transmission ranges of both the RSU and the target vehicle are configured to operate as the dCDD based decode-and-forward (DF) cooperative relays. By using dCDD in the I2V system, the transmission range of the RSU is extended without the need of full channel state information of the vehicles at the RSU, and the transmit diversity gain can also be achieved. For this new preliminary setting of the I2V system, we conduct performance analysis. The simulations are conducted to verify the outage probability. The asymptotic outage diversity gain is also investigated and justified by the link level simulations.

A joint data and jamming transmission scheme based on a new distributed asynchronous cyclic delay diversity (dACDD) scheme is proposed for cooperative communication systems. Without any exact knowledge of channel state information (CSI) at the transmitting side, a joint remote radio head (RRH) selection scheme for the data and jamming signal transmissions is proposed for dACDD to achieve the maximum diversity gain at a legitimate user (LU), while degrading the receive signal-to-interference-plus-noise ratio at an eavesdropping user (EU). A single RRH connected with the channel having the greatest channel gain is selected as a data RRH that transmits a desired confidential signal, whereas the remaining RRHs are controlled by the central control unit to transmit an artificial noise sequence (ANS) to the LU and EU. Without assuming exact knowledge of CSI of the whole system, the secrecy outage probability of the distributed communication system is analyzed by deriving a closed-form expression, and through link-level simulations over non-identically distributed frequency selective fading channels over the entire system.

In this paper, we propose a coordinated direct and relay transmission scheme based on non-orthogonal multiple access (NOMA), where the relay and cell- center user operate in full-duplex mode to help enhance the quality of service of the cell-edge user as well as ensure the secure transmission. In the proposed system, the base station directly serves the cell-center user and relay while communicating with the cell-edge user through the relay and cell-center user. Taking advantage of NOMA, the cell-center user and relay are able to cancel the mutual interference between themselves. Moreover, they can also cooperatively apply the artificial noise scheme to interfere any potential eavesdropper without impairing the legitimate cell-edge user. Exact and closed-form expressions for the outage probability, achievable rate, and achievable secure rate are derived. Numerical results prove that the proposed system outperforms the existing counterpart in the low signal-to-noise ratio region, and ensures secure communications with appropriate power allocation.

In this paper, we propose a variational Bayesian inference approach for a low-complexity symbol detection for massive MIMO systems with symbol- dependent transmit-side impairments. This study is motivated by observations that realworld communication transceivers are often affected by the hardware impairments, such as non-linearities of power amplifiers, I/Q imbalance, phase drifts due to non-ideal oscillators, and carrier frequency offsets. Particularly, symbol-dependent perturbations are fully accounted into the designed hierarchical signal model as unknown model parameters. The developed variational Bayesian symbol detector is able to learn the unknown perturbations in an iterative fashion. Numerical evaluation confirms the effectiveness of the proposed approach.

In power distribution networks, microgrids utilize Phasor Measurement Units (PMUs), to assess the voltage stability at critical nodes in the network. PMUs rely on precise time-keeping sources, such as GPS, to obtain synchronization. However, GPS signals are vulnerable to external spoofing attacks due to their unencrypted signal structure and low received power. To detect the spoofing-induced timing anomaly, an innovative geographically Distributed Multiple Directional Antennas (DMDA) setup is proposed, which is triggered using a common clock. Utilizing the configuration of the proposed DMDA, a Belief-Propagation (BP)-based Extended Kalman Filter (EKF) algorithm is developed to estimate the timing errors caused by spoofing. The BP-EKF algorithm analyzes the single difference pseudorange residuals across each pair of antennas in a probabilistic graphical framework not only to detect the spoofed antennas in the DMDA setup but also to estimate the timing errors associated with the spoofed antennas. Based on the BP estimate of timing error at each antenna and the known baseline distances across antennas, the pseudoranges are corrected, and then adaptive EKF is employed to estimate the GPS timing. The performance of the BP-EKF algorithm is assessed by subjecting the simulated authentic GPS signals to a simulated meaconing attack, which induces a time delay of 60 μs. Both successful detection of meaconing, and also accurate estimation of GPS timing that complies with the IEEE-C37.118 standards, is validated using the experimental results. At a critical node in the simulated microgrid, as compared to scalar tracking, an increased voltage stability is demonstrated using the BP-EKF by assessing a metric, namely, voltage stability index.

In this paper, a cooperative single carrier system comprising multiple cooperating remote radio heads and a single interferer operating in the presence of co-existing line-of-sight and non-line-of-sight paths is investigated. Distributed cyclic delay diversity is employed as the transmit diversity scheme for cyclic-prefixed single carrier transmissions over independent but non-identically distributed frequency selective fading channels. The main focus of this paper is to investigate the achievable diversity gain in the interference-limited and noise-limited regions. In contrast to the outage probability in the noise-limited region, it is shown that the diversity gain is not achievable in the interference-limited region. To justify this finding, the outage probability is derived first, and then verified by link-level simulations.

As a state of the art coding technology, fountain codes are promising to drive the outage probability to zero in non-orthogonal multiple access (NOMA) system suffering from severely fading channels. In this paper, we study cross-layer design for a downlink fountain-coded NOMA system with a base station and two users. In order to achieve successful decoding for both users over block Rayleigh fading channels, an optimization problem, taking optimal allocation of redundancy between packet-level fountain coding and physical-layer channel coding into account, is formulated. The sum of the overall code rates is maximized subjected to a minimum physical-layer code rate constraint of the weak user for the single-input single-output scenario. Numerical analysis shows that it is vital to rapidly increase the overall code rate for the weaker user to maximize the sum of the overall code rates and very little redundancy is required for packet-level fountain coding at the weak user, when the total transmit power is large and the channel gain difference between two users becomes small.

The coordinated on-ramp merging is one of the most common but critical vehicular applications that require complex data transmission and low-latency communication in the Connected and Automated Vehicles (CAVs) environment. An effective way to address on-ramp merging is to leverage the edge computing to optimize the coordination among vehicles to achieve overall minimum vehicle travel time and energy consumption. In this study, we propose an Bi-level Optimal Edge Computing (BOEC) model for on-ramp merging in the CAVs environment to optimize both merge time and vehicle trajectory. The simulation results show that the proposed BOEC model achieves great benefits in vehicle mobility, energy saving and air pollutant emission reduction by providing an energy-efficient trajectory following the optimal merge time without compromising safety.

A wide-area time authentication algorithm is proposed to compute the Global Positioning System (GPS) timing that is resilient against spoofing attacks. The considered wide-area network consists of multiple GPS receiving systems, each comprising of the innovative distributed multiple directional antennas (DMDA) setup triggered via a common clock.Based on the communication infrastructure of the grid, the single-difference pseudorange residuals across the antennas are processed using the wide-area belief propagation-based extended Kalman filter (BP-EKF) algorithm in a distributed manner. To detect spoofing, a KL-divergence-based threshold is used to estimate the dissimilarity in the antenna-specific timing errors. Thereafter, the pseudoranges are corrected using the BP estimates of timing error and processed via adaptive EKF to compute the GPS timing, which is given to the phasor measurement units (PMUs). We have demonstrated the successfully detection and mitigation of the external timing attack, by subjecting one receiving system to a simulated meaconing attack that induces a 60 micro second time delay. Thereafter, by analyzing the voltage stability index of a critical node in the simulated grid, we have also validated the compliance of the proposed wide-area BP-EKF estimated timing with the IEEE-C37.118 standards.

Aerial base stations (ABS) provide promising solutions for wireless coverage in adverse scenarios. By jointly designing with cooperative transmission, the system performance can even be boosted. In this paper, we consider an ABS-assisted cooperative system, where multiple ABSs hover around the macro base station (MBS) and relay the downlink signals through non- coherent joint transmission (NC-JT) to the user equipment (UE). Interfering nodes are randomly distributed over the 2D plane. Non-uniform line-of- sight (LoS) channel model is assumed for the desired signal propagation, while the communication links between ground terminals follow a distance related probabilistic LoS and non-line-of-sight (NLoS) channel model. Based on stochastic geometry framework, we derived closed form success probability for the cooperative system. Numerical results verify the accuracy of our expressions and show that jointly transmitting signals from the sky can bring in significant enhancement for the coverage performance of the system.

This IEEE Journal on Selected Areas in Communications (JSAC) special issue (SI) aims to provide a comprehensive overview of the state-of-the-art advances and a view of emerging research challenges and opportunities forSpatial Modulation in Emerging Wireless Systems. This SI solicits high-quality original research papers regarding theoretical studies, and application-oriented contributions dealing with architectures, platforms, and multiple access schemes.

Spatial modulation (SM) is an innovative and promising digital modulation technology that strikes an appealing tradeoff between spectral efficiency and energy efficiency with a simple design philosophy. SM enjoys plenty of benefits and shows great potential to fulfill the requirements of future wireless communications. The key idea behind SM is to convey additional information typically through the ON/OFF states of transmit antennas and simultaneously save the implementation cost by reducing the number of radio-frequency chains. As a result, the SM concept can have widespread effects on diverse applications and can be applied in other signal domains, such as frequency/time/code/angle domain or even across multiple domains. This survey provides a comprehensive overview of the latest results and progresses in SM research. Specifically, the fundamental principles, variants of system design, and enhancements of SM are described in detail. Furthermore, the integration of the SM family with other promising techniques, applications to emerging communication systems, and extensions to new signal domains are also extensively studied.

In this paper, a distributed cognitive underlay single carrier system is investigated. A secondary users' network consists of a control unit (CU) and a group of secondary user remote radio heads (S-RRHs). To effectively access the radio spectrum licensed to the primary users, a distributed cyclic delay diversity (dCDD) scheme is employed between the CU and S-RRHs as the transmit diversity scheme. Multiple primary user transmitters (PTXs) are assumed to be located isotropically within the secondary users' network, so that a mixture of line-of-sight (LoS) and non-line-of-sight (nLoS) paths from the PTXs to the secondary user receiver is considered. In addition, a mixture of LoS and nLoS paths is considered in the secondary users' network. For a new transmit diversity scheme and channel model, the performance of the secondary users' network achieved by the dCDD in the presence of isotropically distributed multiple PTXs is investigated. The dCDD enables the CU to use multiple S-RRHs at the same time, so that determining the effects of a different number of S-RRHs in the presence of a new channel model is an open research issue. To this end, a new closed-form expression for the outage probability is derived, and then its accuracy is verified by link-level simulations.

In this paper, a cooperative single carrier system comprising multiple cooperating remote radio heads and spatially distributed interferers is investigated. Due to the random location of the interferers within the communication range, a mixture of line-of-sight (LoS) and non-line-of-sight (nLoS) paths is considered in the channel model. Under a frequency selective fading channel with a mixture of the LoS and nLoS paths, the distributed cyclic delay diversity is employed to achieve the maximum transmit diversity gain without the exact knowledge of the channel state information at the transmitter side. It is shown that the operating signal-to-noise regions are divided into two regions, i.e., noise-limited and interference-limited. In this paper, the main focus is on the interference-limited region, in which diversity gain is not achieved due to performance limits determined by the system and channel parameters. The existence of these limits on the performance metrics, such as the outage probability and ergodic capacity, is derived analytically and then verified by link-level simulations.

The use of aerial base stations (ABSs) is gaining attention due to its potentials to provide a flexible wireless coverage in adverse scenarios. Investigations on key performance metrics are desirable to ensure the feasibility of these ABS-assisted networks, especially when they are jointly designed with advanced transmission technologies, e.g., cooperative transmissions and non-orthogonal multiple access (NOMA). In this paper, we consider an ABS-assisted cooperative system with NOMA enabled to boost connectivity ability. It is assumed that multiple ABSs hover around a macro base station to relay downlink signals to user equipments, while interfering nodes are randomly distributed on the ground. We assume a more realistic channel model featured with a distance-related probabilistic line-of-sight and non-line-of-sight propagation, as well as non-identical small-scale fading. We derive the outage probability, and study the impacts of various parameters on the system performance. Numerical results unveil that: 1) The reliability of backhauls plays an important role in the system and determines the outage performance floor. 2) Joint transmissions from the sky can bring in a significant performance enhancement for the system. 3) The NOMA based transmission outperforms the traditional orthogonal multiple access with an improved outage performance, provided a properly selected NOMA power allocation coefficient.

In this paper, a cooperative spectrum sharing system is investigated. To effectively access the radio spectrum licensed to the primary users, the distributed cyclic delay diversity (dCDD) scheme is employed as the transmit diversity scheme for distributed cyclic-prefixed single carrier transmissions. As a setup for the secondary users' network, it is assumed that it comprises the control unit and a group of remote radio heads. In the secondary users' network, a single primary user transmitter is assumed to be located isotropically, so that a mixture of line-of-sight and non-line-of-sight paths over frequency selective fading channels is considered. One of the objectives of this paper is to investigate the effects of this new channel model on the outage probability probability promised by dCDD. A closed-form expression for the outage probability is derived first, and then its asymptotic expression is derived to characterize the maximum achievable diversity gain. Link-level simulations are also conducted to verify the performance analysis.

In this paper, we investigate a coordinated direct and relay transmission for uplink (CDRT-UL) of a cooperative non-orthogonal multiple access (NOMA) system, in which two users communicate with a base station (BS) with the aid of a decode-and-forward relay. By incorporating both relay links and non-negligible direct links from two users to BS, the CDRTUL scheme forms an orthogonal structure at the BS receiver side, so that the BS receiver applies only linear combinations to recover the desired signals without abusing successive interference cancellation. Outage probability of the paired two users is derived in closed-form under independent but not necessarily identically distributed Nakagami-m fading channels. Asymptotic analysis in the high signal-to-noise ratio regime is also introduced that provides closed-form expressions, which indicates that both two users achieve the same asymptotic outage performance. It is also shown that an improved outage performance and the higher target rate can be achieved by the CDRT-UL scheme over those of the DF relay without direct links. The enhanced system performance achieved by the CDRT-UL scheme is corroborated by Monte Carlo simulations.

In this paper, a cooperative cyclic-prefixed single carrier (CP-SC) system to improve physical layer security is investigated. By considering a distributed cyclic delay diversity (dCDD) scheme, a jamming method is proposed to maximize the signal-to-noise ratio (SNR) over the channels from the transmitters to the legitimate user, while degrading the signal-to-interference-plus-noise ratio (SINR) over the channels from the transmitters to the illegitimate user. A CDD transmitter among the set of CDD transmitters is selected as the sentinel transmitter, and it transmits a jamming signal to the illegitimate user. The sentinel transmitter is the transmitter that provides the best channel gain in order to maximize the SNR at the legitimate user and minimize the SINR at the non-legitimate users. This allow us to enhance the security of the CP-SC system. New closed form expressions for the SNR and SINR for the dCDD protocol are derived for frequency selective fading channels. Monte-Carlo simulations are conducted to verify the analytic derivations of the performance metrics for various simulation scenarios.

This paper investigates the diversity gain of a distributed cyclic delay diversity (CDD) scheme for cyclic-prefixed single carrier systems in non-identical frequency selective fading channels. Two conditions are used to obtain an equivalent channel matrix that is free of intersymbol interference. These conditions allows the system to achieve the maximum diversity order at a full rate in frequency selective fading channels. A given number of CDD transmitters is obtained from the set of cooperative transmitters in the system and is shown to be determined by the symbol block size and the maximum time dispersion of the channel. A new expression for the received signal-to-noise ratio (SNR) is derived by using order statistics. To estimate the achievable maximum diversity gain provided by the distributed CDD scheme, we employ asymptotic analysis in the high SNR regime. From the analytical framework, it is shown that the maximum diversity is achieved even for non-identical frequency selective fading channels. Link-level simulations are conducted to verify the maximum achievable diversity gain.

This paper investigates the secrecy performance of a finite-sized in-band selective relaying system with M transmitters connected via unreliable backhaul links, N decode-and-forward relays, and K collaborative eavesdroppers. To send the source message to the destination, a transmitter-relay pair that achieves the highest end-to-end signal-to-noise ratio is selected for transmissions, while the K eavesdroppers combine all the received signals from the selected transmitter and relay using maximal ratio combining. The proposed model introduces backhaul reliability and eavesdropping probability parameters to investigate practical constraints on the transmitter-relay cooperation and eavesdropper collaboration, respectively. Closed-form expressions are derived for the secrecy outage probability, probability of non-zero achievable secrecy rate, and ergodic secrecy rate for non-identical frequency-selective fading channels with robust cyclic-prefixed single carrier transmissions. These results show that the asymptotic secrecy outage probability and probability of non-zero achievable secrecy rate are exclusively determined by the number of transmitters M and their corresponding set of backhaul reliability levels. Under unreliable backhaul connections, it is found that the secrecy diversity gain is determined by M, N, and the number of multipath components in the frequency selective fading channels. Link-level simulations are conducted to verify the derived impacts of backhaul reliability and collaborative eavesdropping on the secrecy performance.

In this paper, a cooperative cyclic-prefixed single carrier (CP-SC) system is studied and a scheme to improve its physical layer security is proposed. In particular, a distributed cyclic delay diversity (dCDD) scheme is employed and a deliberate interfering method is introduced, which degrades the signal-to-interference-plus-noise ratio (SINR) over the channels from a group of remote radio heads (RRHs) to an eavesdropper, while minimizing the signal-to-noise ratio loss over the channels from the RRHs to an intended user. This is obtained by selecting one RRH that acts as an interfering RRH and transmits an interfering artificial noise sequence to the eavesdropper. Through the use of the dCDD scheme, a channel that minimizes the receive SINR at the eavesdropper is selected for the interfering RRH. This choice enhances the secrecy rate of the CP-SC system. The system performance is evaluated by considering the secrecy outage probability and the probability of non-zero achievable secrecy rate, which are formulated in closed-form analytical expressions for the case of identically and non-identically distributed frequency selective fading channels. Based on the proposed analytical framework, the diversity order of the system is studied. Monte Carlo simulations are employed to verify the analytical derivations for numerous system scenarios.

This paper investigates a cooperative non-orthogonal multiple access system, in which a base station communicates with two far users with the aid of a decode-and-forward (DF) relay. Three cooperative relaying schemes, namely, the fixed relaying (FR), the selective DF with coordinated direct and relay transmission (SDF-CDRT), and the incremental-selective DF (ISDF) relaying are proposed to enhance the outage performance for the two far users by utilizing both the direct and relay links. Taking into account the received signal-to-noise ratio (SNR) events at the relay, the SDF-CDRT scheme adaptively forms an orthogonal transmission branch with respect to the direct link or keeps silent to reduce error propagation. Besides considering the relay detection results, the ISDF scheme further exploits the limited feedback of the received SNR events from two users, so that error propagation can be avoided and unnecessary relaying can be reduced. Analytical expressions for the outage probabilities and average throughputs of the paired users are derived in closed-form for the three cooperative relaying schemes. Asymptotic expressions for the outage probabilities are derived in the high SNR region. It is shown that the FR and SDF-CDRT schemes achieve a diversity order of one for both users, while the ISDF scheme achieves a diversity order of two for both users. The superior system performance achieved by the proposed schemes over those of the existing methods is verified by Monte Carlo simulations.

In millimeter wave (mmWave) communication, analog and hybrid beamforming systems are proposed to reduce the number of RF chains when a large antenna array is utilized to achieve a high beamforming gain. In this paper, a new transmission scheme is first proposed by leveraging the hardware architecture of analog and hybrid beamforming to improve the spectral efficiency. The new scheme is called spatial scattering modulation (SSM), since it exploits the spatial scattering dimension to modulate information bits. And then, an adaptive transmission strategy (ATS) which chooses the best transmission scheme under instantaneous channel state information, is proposed to improve the performance. Link-level simulation results demonstrate the superiority of the proposed ATS in all the simulated signal-to-noise (SNR) values.

We investigate non-coherent multi-antenna signal processing which requires no channel state information (CSI) at either transmitter or receiver ends. With non-coherent constellations over Grassmannian manifold, a receiver employing generalized likelihood ratio test (GLRT) algorithm offers the maximum-likelihood performance even without CSI. The conventional GLRT relies on the assumption that the wireless channel is time-invariant during a block. We propose an improved GLRT algorithm which employs a novel two-dimensional basis expansion model (2D-BEM) to cope with doubly-selective fading channels. The proposed method uses sequential GLRT for multi-symbol detection to keep high performance yet low complexity. Furthermore, we introduce Fourier-Legendre product basis to be robust against hardware impairments including carrier frequency and timing offsets. We demonstrate that the proposed scheme significantly improves performance in rapid fading channels, and realizes highly spectrum-efficient transmission up to 6 bps/Hz without any pilots.

In this paper, channel estimation in millimeter wave (mmWave) communication systems is considered. In contrast to prevailing mmWave channel estimation methods exploiting the sparsity nature of the channel, we move one step further by exploiting the joint AoD-AoA angular spread. By formulating the channel estimation as a block-sparse signal recovery with an underlying two-dimensional cluster feature, we propose a two-dimensional sparse Bayesian learning method without a priori knowledge of two-dimensional angular spread patterns. It essentially couples the channel path power at one angular direction with its two-dimensional AoD-AoA neighboring directions. Compared with existing sparse mmWave channel estimation methods, the proposed method is numerically verified to reduce the training overhead and channel estimation error.

Energy harvesting is an emerging technology for enabling green, sustainable, and autonomous wireless networks. In this paper, a large-scale wireless network with energy harvesting transmitters is considered, where a group of transmitters forms a cluster to cooperatively serve a desired receiver amid interference and noise. To characterize the link-level performance, closed-form expressions are derived for the transmission success probability at a receiver in terms of key parameters such as node densities, energy harvesting parameters, channel parameters, and cluster size, for a given cluster geometry. The analysis is further extended to characterize a network-level performance metric, capturing the tradeoff between link quality and the fraction of receivers served. Numerical simulations validate the accuracy of the analytical model. Several useful insights are provided. For example, while more cooperation helps improve the link-level performance, the network-level performance might degrade with the cluster size. Numerical results show that a small cluster size (typically 3 or smaller) optimizes the network-level performance. Furthermore, substantial performance can be extracted with a relatively small energy buffer. Moreover, the utility of having a large energy buffer increases with the energy harvesting rate as well as with the cluster size in sufficiently dense networks.

This paper investigates a distributed cyclic delay diversity (CDD) transmission scheme for cyclic-prefixed single carrier systems in non-identically and identically distributed frequency selective fading channels. The distinguishable feature of the proposed scheme lies in providing a transmit diversity gain while reducing the burden of estimating the channel state information, which is a challenging task in distributed and cooperative systems. To effectively use the distributed CDD scheme at the transmitters, two sufficient conditions are derived to eliminate the intersymbol interference at the receiver and leveraged to convert the multi-input single-output channel into a single-input single-output channel. These conditions allow the system to achieve the maximum diversity for frequency selective fading channels at a full rate. To achieve this maximum diversity, a fixed number of CDD transmitters are selected based on the channel conditions, symbol block size, and maximum time dispersion of the channel, and a new two-stage transmission mode is proposed. Based on the distributed CDD and the proposed selection schemes, a new expression for the signal-to-noise ratio at the receiver is obtained with the aid of order statistics, and then closed-form expressions for the outage probability and average symbol error rate (ASER) are derived. As far as the identically distributed frequency selective fading channel model is concerned, the achievable maximum diversity gain is proved, with the aid of asymptotic analysis, to be equal to the product of the total number of transmitters in the system and the number of multipath components. Link-level simulations are also conducted to validate the analytical expressions for outage probability, ASER, and maximum achievable diversity gain.

This study investigates relay control for simultaneous wireless information and power transfer in full-duplex relay networks under Nakagami-mfading channels. Unlike previous work, harvest-transmit (HT) and general harvest-transmit-store (HTS) models are respectively considered to maximize average throughput subject to quality of service (QoS) constraints. The end-to-end outage probability of the network in an HT model is presented in an exact integral-form. To prevent outage performance degradation in an HT model, time switching (TS) is designed to maximize average throughput subject to QoS constraints of minimizing outage probability and maintaining a target outage probability, respectively. The optimal TS factors subject to QoS constraints are presented for an HT model. In general, in an HTS model, energy scheduling is performed across different transmission blocks and TS is performed within each block. Compared with the block-based HTS model without TS, the proposed general HTS model can greatly improve outage performance via greedy search (GS). By modeling the relay's energy levels as a Markov chain with a two-stage state transition, the outage probability for the GS implementation of the general HTS model is derived. To demonstrate the practical significance of QoS-constrained relay control, numerical results are presented showing that the proposed relay control achieves substantial improvement of outage performance and successful rate.

In this paper, the secrecy outage probability of cooperative cyclic prefixed single carrier (CP-SC) systems with multiple transmitters and unreliable backhaul connections is derived. The transmitters communicate with the destination in the presence of an eavesdropper over two-hop relay channels with non-identical frequency-selective fading. The existence of asymptotic limits on the secrecy outage probability is verified for various backhaul scenarios. For a fixed eavesdropper signal-to-noise ratio (SNR), the limit is found to be exclusively determined by the backhaul reliability. This shows that the diversity gain promised by cooperative CP-SC systems cannot be achieved in the high SNR region. Simulations are presented to verify the derived impact of backhaul reliability on the secrecy performance.

We consider the problem of channel estimation for millimeter wave communications (mmWave). We formulate channel estimation as a structured sparse signal recovery problem, in which the signal structure is governed by a priori knowledge of the channel characteristics. We develop a Bayesian group sparse recovery algorithm which takes into account for several features unique to mmWave channels, such as spatial (angular) spreads of received signals and power profile of rays impinging on the receiver array. We validate the developed method via numerical simulations and demonstrate an improved estimation performance relative to the existing methods.

In this paper, the spatial modulation (SM) technique is employed at the source and relay nodes in a full-duplex two-way relay channel (FD-TWRC) to support spectral-efficient bi-directional communications while guaranteeing a low cost implementation. Maximum likelihood detectors are employed at each node that is subject to an intrinsic self-loop interference. We first propose a tight upper bound on the average bit error probability (ABEP). Then, based on the ABEP upper bound, an asymptotic ABEP expression is derived in the high signal-to-noise ratio (SNR) regime. Exploiting the asymptotic ABEP, an exact SNR threshold for the selection between FD-TWRC-SM and half-duplex (HD)-TWRC-SM is derived in a closed form, which sheds light on when it is beneficial to select the FD (or HD) mode. In addition, the power allocation (PA) among sources and relay is investigated, through which an optimal PA factor in terms of ABEP is obtained. All analytical results derived in this paper are verified by Monte Carlo simulations, from which some new insights are obtained on the performance of FD-TWRC-SM.

This paper presents a performance analysis of a finite-sized co-operative wireless system, where a group of transmitters with unreliable backhauls serve a desired receiver using noncoherent joint transmission. To facilitate analysis, an analytical expression for the distribution of the spatially averaged signal-to-interference-plus-noise ratio (SA-SINR) is derived in terms of key system and channel parameters. Leveraging the derived expression, the joint impact of node co-operation, backhaul reliability, interference, and communication range is investigated in the considered finite-sized co-operative system. Furthermore, based on the SA-SINR, closed form expressions for the average bit error rate (ABER) and average spectral efficiency (ASE) are derived. Further insights are established by analyzing the asymptotic performance in the high transmission power regime. From analytical derivations for the outage probability, ABER, and ASE and link-level simulations, it is verified that these asymptotic performance metrics are exclusively influenced by unreliable backhauls, so that the conventional diversity gains are not achievable.

This paper investigates simultaneous wireless information and power transfer (SWIPT) for a decode-and-forward (DF) full-duplex relay (FDR) network. A battery group consisting of two batteries is applied to utilize the relay-harvested energy for FDR transmission. The virtual harvest-use model and the harvest-use-store model are considered, respectively. By switching between two batteries for charging and discharging with the aid of power splitting (PS), concurrent source and relay transmissions can overcome spectral efficiency loss compared with half-duplex relay (HDR)-assisted PS-SWIPT. The outage probability for the virtual harvest-use model is presented in an exact integral form and the optimal PS (OPS) ratio that maximizes the end-to-end signal-to-interference-plus-noise ratio (e-SINR) is characterized in closed form via the cubic formula. The fundamental tradeoff between the e-SINR and recycled self-power is quantified. The OPS ratios and the corresponding outage probabilities in noise-limited and interference-limited environments are also derived. In the harvest-use-store model, a greedy switching (GS) policy is implemented with energy accumulation across transmission blocks. The OPS ratio of the GS policy is presented and the corresponding outage probability is derived by modeling the relay’s energy levels as a Markov chain with a two-stage state transition. Numerical results verify the performance improvement of the proposed scheme over HDR-assisted PS-SWIPT in terms of outage probability and average throughput.

Machine-to-machine (M2M) communications have been considered as an important application to connect a massively large number of different devices in networks. In particular for M2M wireless networks, low latency and high reliability are of great importance. To fulfill the requirements, a diversity technique exploiting limited resources is proposed in this paper for short-message transmissions. The proposed method uses multiple stages of fast unitary transforms and diagonal phase rotations to achieve full- diversity gain. A monomial phase rotation is also proposed to facilitate an optimization of the precoding matrix. It is verified that the proposed four-stage precoding provides universal diversity gain irrespective of channel selectivity in time and frequency, without changing monomial parameters. In addition, it is shown that the four-stage precoding based on the discrete Haar transform (DHT) achieves a full diversity while the computational complexity is significantly reduced from a log- linear order to a linear order compared to the other unitary transforms such as the discrete Fourier transform (DFT).

We propose an unsupervised, received signal strength (RSS)- based indoor localization method, which as an infrastructure uses commercial WiFi chipsets and does not require any changes in the existing hardware. The method relies on path loss model for measured RSS levels where path loss coefficient is treated as a discrete random variable which takes values from some finite alphabet. The unknown location and path loss coefficient corresponding to each access point are jointly estimated using the Expectation Maximization (EM) approach. The algorithm is experimentally tested in an office space area of dimensions 32-by-52 m (1600 m2) with only five access points and the achieved average localization error is below 4.5 m.

We analyze the secrecy outage probability of selective relaying wiretap channels with K decode- and-forward (DF) relays and N collaborative eavesdroppers. In the main channel, we consider a two-hop relay network where the best relay is selected to transmit and the relay link is combined with the direct source-to-destination link at the destination. In the eavesdropper channel, we consider that the eavesdroppers can collaborate to exchange the information obtained from the source and relays. Different from previous works, we introduce an eavesdropping probability measure to model different intercepting capabilities of the malicious nodes. For this network, we derive new closed-form expressions for the secrecy outage probability in Rayleigh fading channels. The impact of the number of eavesdroppers and the eavesdropping probabilities are accurately reflected in the array gain of the asymptotic secrecy outage probability.

A large wireless network with energy harvesting transmitters is considered, where a group of K transmitters form a cluster to cooperatively serve a desired user. Using stochastic geometry, simple closed-form expressions are derived to characterize the outage performance as a function of important parameters such as the energy harvesting rate, buffer size and cluster size for a given cluster geometry. The developed framework also allows the K in-cluster transmitters to have different energy harvesting capabilities. A comparison with simulation results reveals that the derived expressions closely model the signal-to-interference-and-noise ratio distribution at the receiver, particularly in the low-outage regime. Lastly, the developed framework is used to investigate the impact of different parameters such as cluster and buffer size on outage performance.

In this paper, we propose cyclic prefix single carrier (CP-SC) full-duplex transmission in cooperative spectrum sharing to achieve multipath diversity gain and full-duplex spectral efficiency. Integrating full-duplex transmission into cooperative spectrum sharing systems results in two intrinsic problems: 1) the peak interference power constraint at the PUs are concurrently inflicted on the transmit power at the secondary source (SS) and the secondary relays (SRs); and 2) the residual loop interference occurs between the transmit and the receive antennas at the secondary relays. Thus, examining the effects of residual loop interference under peak interference power constraint at the primary users and maximum transmit power constraints at the SS and the SRs is a particularly challenging problem in frequency selective fading channels. To do so, we derive and quantitatively evaluate the exact and the asymptotic outage probability for several relay selection policies in frequency selective fading channels. Our results manifest that a zero diversity gain is obtained with full-duplex.

In this paper, the impact of multiple active eavesdroppers on cooperative single carrier systems with multiple relays and multiple destinations is examined. To achieve the secrecy diversity gains in the form of opportunistic selection, a two-stage scheme is proposed for joint relay and destination selection, in which, after the selection of the relay with the minimum effective maximum signal-to-noise ratio (SNR) to a cluster of eavesdroppers, the destination that has the maximum SNR from the chosen relay is selected. To accurately assess the secrecy performance, exact and asymptotic expressions are obtained in closed form for several security metrics, including the secrecy outage probability, probability of nonzero secrecy rate, and ergodic secrecy rate in frequency selective fading. Based on the asymptotic analysis, key design parameters, such as secrecy diversity gain, secrecy array gain, secrecy multiplexing gain, and power cost, are characterized, from which new insights are drawn. In addition, it is concluded that secrecy performance limits occur when the average received power at the eavesdropper is proportional to the counterpart at the destination. In particular, for the secrecy outage probability, it is confirmed that the secrecy diversity gain collapses to zero with outage floor, whereas for the ergodic secrecy rate, it is confirmed that its slope collapses to zero with capacity ceiling.

In this paper, the impact of multiple eavesdroppers on cooperative single carrier systems with multiple relays and multiple destinations is examined. To achieve the secrecy diversity gains in the form of opportunistic selection, a two-stage scheme is proposed for joint relay and destination selection, in which, after the selection of the relay with the minimum effective maximum signal-to-noise ratio (SNR) to a cluster of eavesdroppers, the destination that has the maximum SNR from the chosen relay is selected. In order to accurately assess the secrecy performance, the exact and asymptotic expressions are obtained in closed-form for the ergodic secrecy rate in frequency selective fading. Based on the asymptotic analysis, key design parameters such as multiplexing gain, and power cost are characterized, from which new insights are drawn. Moreover, it is concluded that capacity ceiling occurs when the average received power at the eavesdropper is proportional to the counterpart at the destination.

We examine the impact of transmit antenna selection with receive generalized selection combining (TAS/GSC) for cognitive decode-and-forward (DF) relaying in Nakagami-m fading channels. We select a single transmit antenna at the secondary transmitter which maximizes the receive signal-to-noise ratio (SNR) and combine a subset of receive antennas with the largest SNRs at the secondary receiver. In an effort to assess the performance, we first derive the probability density function and cumulative distribution function of the end-to-end SNR using the moment generating function. We then derive new exact closed-form expression for the ergodic capacity. More importantly, by deriving the asymptotic expression for the high SNR approximation of the ergodic capacity, we gather deep insights into the high SNR slope and the power offset. Our results show that the high SNR slope is 1/2 under the proportional interference power constraint. Under the fixed interference power constraint, the high SNR slope is zero.

Probabilistic Data Association (PDA) algorithm has shown promising performance in symbol detection and interference cancellation in different communication schemes. This paper proposes new algorithms that build on PDA and introduce modifications in the way the symbol being detected is treated. While PDA models this symbol as a discrete sample from a constellation, PDA with symbol uncertainty (SU-PDA) views it as a sum of a deterministic symbol and random noise, while the Gaussian PDA (G-PDA) models it as a random variable with either a single Gaussian or Gaussian mixture distribution. The proposed algorithms are tested via computer simulations on both simulated and experimentally measured channels. The performance study reveals that the SU-PDA and G-PDA outperform the conventional PDA with the performance gain ranging from few dBs on measured channel with block fading up to and exceeding 10 dB on the simulated channel with fast fading.

Intra-vehicle wireless sensor network, which is also called networked control system (NCS) is a promising new research area. NCS can not only provide part cost, assembly, maintenance savings, and fuel efficiency through the elimination of the wires, but also enable new sensor technologies to be integrated into vehicles. Ultra wideband (UWB) communication is a competitive candidate for the intra-vehicle NCS. In this paper, the performance of cyclic prefixed single carrier with frequency domain equalization (SC-FDE) transmission is investigated over intra-vehicle NCS propagation environment. The error-rate performance and the implementation complexity are compared among impulse based single carrier UWB (SC-UWB), multicarrier UWB (MC-UWB) employing orthogonal frequency-division-multiplexing (OFDM), and CP-SC under the same transmitting data rate conditions. Simulation results demonstrate conclusive performance advantage of the SC-FDE scheme on the communication of two different intra-vehicle NCS scenarios, especially when minimum mean square error method is taken into account.

We1propose two methods for the detection of RF interference. The first one is for the detection of the interferences from microwave ovens, and the second one is for Wi-Fi and Bluetooth signals. The motivation of this work is to design a system for reliable wireless communication. Specifically, the systems equipped with interference detectors will be able to choose the appropriate time intervals to transmit signals in the presence of other interferences, therefore avoid unnecessary collisions and retransmissions.

In this paper, the impact of interference from multiple licensed transceivers on cognitive underlay single-carrier systems is examined. Specifically, the situation is considered in which the secondary network is limited by three key parameters: 1) maximum transmit power at the secondary transmitter, 2) peak interference power at the primary receivers, and 3) interference power from the primary transmitters. For this cognitive underlay single-carrier system, the signal-to-interference ratio (SIR) of the secondary network is obtained for transmission over frequency-selective fading channels. Based on this, a new closed-form expression for the cumulative distribution function of the SIR is evaluated, from which the outage probability and the ergodic capacity are derived. Further insights are established by analyzing the asymptotic outage probability and the asymptotic ergodic capacity in the high-transmission-power regime. In particular, it is corroborated that the asymptotic outage diversity gain is equal to the multipath gain of the frequency-selective channel in the secondary network. The asymptotic ergodic capacity also gives new insight into the additional power cost for different network parameters while maintaining a specified target ergodic capacity. Illustrative numerical examples are presented to validate the outage probability and ergodic capacity under different interference power profiles.

This paper tackles the important question of how to compensate the inherent spectrum efficiency loss in cognitive relay networks. Particularly, by considering two-way cognitive relaying, we seek to enhance the performance of the secondary network in terms of the reliability due to limited transmit power, and the spectral efficiency of the half-duplex dual-hop relay transmission. We derive new closed-form expressions for the outage probability of a cognitive relay network with two-way communications in the presence of multiple primary users. Our expressions accurately take into account the impact of the maximum allowable interference constraint at the primary users on the secondary network.

We examine the impact of clusters of primary transceivers in cognitive multiple-input multiple-output (MIMO) relay networks with underlay spectrum sharing. In such a network, we propose antenna selection as an interference-aware design to satisfy the power constraints in the primary and secondary networks. To demonstrate this, we consider transmit antenna selection with maximal ratio combining (TAS/MRC) in the primary and secondary networks. With this in mind, we derive new closed-form asymptotic expressions for the outage probability and the symbol error rate (SER) over independent Nakagami-m fading channels. Our results lead to several new fundamental insights. In particular, we highlight that TAS/MRC achieves a full diversity gain when the maximum transmit power in the secondary network is proportional to the peak interference temperature in the primary network.

The performance of cognitive spectrum sharing systems with opportunistic relay selection over Nakagami-m fading is analyzed in the presence of multiple primary users (PUs). In particular, we derive an exact closed-form expression for the outage probability (OP) of the considered cognitive relay systems under the joint impact of maximal transmit power Ptat secondary transmitter and peak interference power Ipat the primary user. Our general formulas cover several specific practical scenarios, e.g., where the maximal transmit power can be neglected compared to the peak interference power. In addition, a tractable expression for the asymptotic OP is also derived and reveals important insights into the system performance. We show that the number of PUs only affects the coding gain but not the diversity gain.

Multihop network has been considered as a breakthrough frontier to enhance the coverage of wireless network. Spectrum-sharing is an efficient technique to enhance the utilization of the limited radio frequency bandwidth. In this paper, we therefore consider the extension of multihop network to cognitive radio networks with the spectrum sharing approach. In particular, we investigate the cognitive multihop networks in the presence of multiple licensed transmitters and receivers. Under the stringent power constraint imposed by the licensed users, we derive the closed-form and asymptotic expressions for the outage probability over Nakagami-m fading channels. The tractable closed-form expressions reveal the impact of important network parameters such as the fading severity parameters of the unlicensed network, the number of licensed users, the peak interference power imposed by the licensed receivers, the interference power from licensed transmitters. A significant observation corroborated by our study shows that the cognitive multihop networks benefit both cognitive radio and multihop networks for improving the coverage extension and frequency spectrum utilization.

Machine-to-Machine (M2M) wireless communication requires the transmission of short blocks of data with high reliability over fading channels. We discuss the use of the probabilistic data association (PDA) detector in conjunction with precoding to design high-performance systems for these links. First, the performance of the traditional PDA algorithm with precoding over ideal Rayleigh fading links is analyzed, which provides insight into its performance, and evidence of an error floor at high SNRs. Then, a novel ordering mechanism is proposed that takes advantage of the precoder characteristics. It is shown by simulation that the proposed modified algorithm can achieve near-ML performance for block sizes as small as 32 symbols.

In this paper, maximal-ratio combining (MRC) and selection combining (SC) are proposed in spectrum sharing single-carrier networks with multiple primary user receivers (PU-Rxs). Taking into account the peak interference power at the PU-Rx's and the maximum transmit power at the secondary user (SU), the impact of multiple PU-Rx's on the secondary network is characterized when the secondary user receiver (SU-Rx) is equipped with multiple antennas. In doing so, exact and asymptotic expressions are derived for the cumulative distribution function, taking into account two realistic scenarios: non-identical frequency selective fading between the secondary user transmitter (SU-Tx) and the PUs, and frequency selective fading between the SU-Tx and the SU-Rx. Based on these, exact and asymptotic expressions for the outage probability and average bit error rate are derived. Furthermore, an exact closed-form expression for the ergodic capacity is derived. It is shown that the asymptotic diversity gain depends only on the number of receive antennas and the number of multipath channels. It is further shown that the number of PU-Rx's and fading severities between the SU-Tx and the PU-Rx's have no impact on the asymptotic diversity gain.

A cyclic prefixed single-carrier (CP-SC) relaying system is considered for cognitive radio networks under spectrum sharing condition. The outage probability of secondary users employing a two-hop amplify-and-forward (AF) relay protocol is investigated under an interference constraint inflicted by the secondary user-source and the secondary user-relay on a primary user (PU). Assuming channel-state-information (CSI) is available, the end-to-end signal-to-noise-ratio (e2e-SNR) is first derived, and then an analytical expression for the cumulative distribution function (CDF) of this e2e-SNR is derived. Based on this derived CDF, analytical expressions for the exact outage probability, the approximate symbol error rate (SER), and approximate achievable rate can be obtained. In addition, to reveal further insights into the impact of channel lengths on the diversity and coding gains, the asymptotic outage probability and SER are provided. It is important to note that the performance of cognitive radio networks is degraded due to the limited power constraint inflicted on the primary network. As such, the optimal power allocation (OPA) is also derived to achieve a better asymptotic outage probability.

For cyclic prefixed single-carrier (CP-SC) spectrum sharing relaying systems, a two-hop decode-and-forward (DF) relaying protocol with a direct link and selection combining are employed in the secondary user relay network. For this cooperative CP-SC spectrum sharing system, the end-to-end signal-to-noise ratio (e2e-SNR) is first derived, and then the outage probability performance of the secondary user relaying system is investigated. Having derived an asymptotic expression for the cumulative distribution function of the e2e-SNR, the asymptotic outage diversity is obtained under a limited maximum transmit power at the secondary source and relay while satisfying the maximum allowable interference at the primary user. Notably, when the maximum allowable interference is independent of a limited transmission power, an outage probability floor is observed. Moreover, under the assumption of an unlimited transmit power at the secondary nodes, the asymptotic outage diversity is derived as a function of the interference. It can be seen that the same outage diversity gain can be achieved as in the non-spectrum-sharing CP-SC relaying system. Analytically derived asymptotic outage diversity gains for limited and unlimited transmission power cases are verified by Monte Carlo simulations.

In this paper, we study the problem of devising distributed bilayer quasi-cyclic Low-Density Parity-Check (QC-LDPC) codes for cooperative relaying communications. One theorem in designing the bilayer QC-LDPC code without small stopping sets and small girth is proposed, which significantly simplifies the bilayer QC-LDPC codes design. Based on the proposed theorem and the two-hop decode-and-forward (DF) relaying protocol, in which the relay node is used to assist the source to transmit extra parity bits to the destination, a new design method for a distributed irregular bilayer QC-LDPC is developed. It is demonstrated that the overall performance can be improved by using the proposed approach in DF-based cooperative relaying communications. Finally, it is shown that the proposed construction method also leads bilayer QC-LDPC codes to have a bigger minimum distance.

The applications of ultra wideband (UWB) technologies in commercial vehicles wireless networked control systems (NCS) are attracting attention recently. The transmitted reference (TR) signaling, along with an autocorrelation receiver (AcR), is used for UWB intra-vehicle communication systems. In this paper, we analyze the performance of UWB intra-vehicle NCS with TR signaling under different time-bandwidth products and different numbers of transmitted pulses per symbol conditions. The bit-error probability (BEP) performance of this system is estimated based on the Gaussian approximation and the sampling expansion methods. Through Monte Carlo simulations, we investigate the limitation of the validity of the conventional Gaussian approximation and the sampling expansion methods for the intra-vehicle NCS.

The average symbol error rate (ASER) for the single-input multiple-output (SIMO) cyclically prefixed single-carrier (CP-SC) system with best terminal selection (BTS) is considered. Using derived closed-form expressions for the ASER and an upper bound on it, an asymptotic diversity gain is derived. Based on this result, it is shown that a QR decomposition (QRD)-based receiver and BTS are both needed to maintain the asymptotic diversity gain. Monte Carlo simulations verify the derived diversity gain analysis.

This paper introduces a new link adaptation (LA) approach called the adaptive modulation, coding, and spatial mode (AMCS) scheme for multiple-input multiple-output bit-interleaved coded orthogonal frequency division multiplexing (MIMO BIC-OFDM) systems. The AMCS technique can provide both minimal performance degradation and significant throughput gain by controlling the spatial streams. With this technique, we can derive a simple and accurate closed-form expression of an instantaneous bit error rate (I-BER). Based on the I-BER, the proposed AMCS scheme chooses an appropriate modulation, coding, and spatial mode (MCS) type that improves the system performance while satisfying the quality of service (QoS) requirement. A simplified MCS type search method is also proposed, which allows the receiver to effectively select a MCS type and then send it back to the transmitter by using only a small amount of information bits. The simulation results confirm the superiority of the proposed AMCS approach over conventional LA schemes in trading high-throughput for reduced complexity.

In this paper, several important performance metrics for the cyclic prefix-based single-carrier (CP-SC) cooperative diversity systems with best relay node selection, are presented and quantitatively compared with Monte-Carlo simulations. The statistical evaluation of the upper bound of the average end-to-end signal-to-noise-ratio (SNR) of a two-hop amplify-and-forward (AF) relaying CP-SC transmission is presented. By using this upper bound, closed-form bounds for the maximum achievable average rate, the outage probability and the average symbol error rate (SER), are derived. Further, asymptotic analysis on the outage probability and the average SER reveal that the diversity gain is determined by both the number of relay nodes in the system and the number of channel taps being supported by the CP length. Simulation results verify the derived closed-form analytical expressions and also the diversity gains. Asymptotic performance is also verified in practically high SNR region via Monte Carlo simulations.

To address the issues of high peak-to-average power ratio and high power backing-off in orthogonal frequency-division multiplexing (OFDM) relaying systems, a cyclic prefixed single-carrier (CP-SC) relaying system employing best terminal selection (BTS) is considered in this paper. Under a system power constraint, the problem of joint optimal power allocation to the source and relay is investigated. For a two-hop amplify-and-forward (AF) relaying protocol, the optimal power allocation is first obtained by maximizing the achievable spectral efficiency. After applying the obtained optimal power allocations to the source and relay, a destination terminal that has the best effective end-to-end signal-to-noise ratio is selected. With the help of the statistical properties of circulant channel matrices in the relay links, closed-form bounds for the maximum achievable spectral efficiency, outage probability, and average symbol error rate (ASER) are derived. Further, an asymptotic analysis of the outage probability and ASER is conducted and it is shown that both the number of terminals in the system and the number of channel taps being supported by the CP length play key roles in determining the overall diversity gain. Monte Carlo simulation results verify the derived closed-form analytical expressions.

A new precoder that reduces the feedback overhead in an OFDM-based relay network is proposed. A joint Singular Value Decomposition (SVD) and QR Decomposition is employed at the source-destination link and source-relay-destination link. Using the proposed precoder, only one precoding matrix needs to be fed back, independent of the total number of subcarriers. The link achievable rate using the reduced complexity precoder is evaluated via simulations and compared with that of full SVD precoders and for varying codebook size.

Due to higher peak-to-average power ratio and higher power backing-off in OFDM relaying systems, a cyclic prefixed single-carrier cooperative diversity system is considered in this paper. Under the transmission power constraint, the joint optimal power allocation to the source and relay node is investigated. For a two-hop decode-and-forward relaying protocol, the optimal power allocation is first obtained in the considered system, and then the opportunistic destination terminal selection is applied to improve the achievable average spectral efficiency (ASE). Based on the proposed QR decomposition (QRD)-based receiver in the destination terminal, closed-form expressions for the maximum achievable ASE are derived. Simulation results verify the derived closed-form analytical expressions.

In this paper, several performance analysis metrics for the cyclic prefix-based single-carrier (CP-SC) opportunistic cooperative diversity systems are presented. After the statistical evaluation of the end-to-end signal-to-noise-ratio of a two-hop relaying transmission, we derive tight upper bounds for the maximum achievable average rate and lower bounds for the outage probability in closed form. Further, asymptotic analysis on the outage probability reveals that the diversity gain is determined by both the number of relay nodes in the system and the number of channel taps being supported by the CP length. Simulation results verify the derived closed-form analytical expressions and also the diversity gains. Asymptotic performance is also verified via Monte Carlo simulations.

The outage probability and the symbol error rate (SER) with outdated erroneous opportunistic scheduling over the cyclically prefixed single-carrier downlink transmission, are analyzed. In the user equipment, the QR decomposition-based time domain equalization is employed. Based on this proposed receiver, the effective signal-to-noise ratio (ESNR) and its maximum ESNR are derived. By using the statistical properties of these defined ESNRs, closed-form expressions for the outage probability and the upper bound SER, are derived. Monte Carlo simulations verified the analytical expressions and the outage diversity gain.

QR decomposition (QRD)-based precoded MIMO-OFDM systems with reduced feedback are proposed to convert the MIMO-OFDM channel into layered subchannels. QRD-M is further combined with either singular value (SVD) or geometric mean decomposition (GMD) of the time-domain channel impulse response matrix. As a result, the receiver in the proposed systems only needs to feed back information describing one precoding matrix for all carriers. Simulation results confirm the bit-error-rate (BER) and throughput performance superiority of the proposed systems compared to conventional SVD per-carrier precoding schemes.

Joint carrier frequency offset (CFO) and channel estimation for uplink MIMO-OFDMA systems over time-varying channels is investigated. To cope with the prohibitive computational complexity involved in estimating multiple CFOs and channels, pilot-assisted and semi-blind schemes comprised of parallel Schmidt Extended Kalman filters (SEKFs) and Schmidt-Kalman Approximate Particle Filters (SK-APF) are proposed. In the SK-APF, a Rao-Blackwellized particle filter (RBPF) is developed to first estimate the nonlinear state variable, i.e. the desired user's CFO, through the sampling-importance-resampling (SIRS) technique. The individual user channel responses are then updated via a bank of Kalman filters conditioned on the CFO sample trajectories. Simulation results indicate that the proposed schemes can achieve highly accurate CFO/channel estimates, and that the particle filtering approach in the SK-APF outperforms the more conventional Schmidt Extended Kalman Filter.

A new closed-loop preceding method has been proposed for MIMO-OFDM systems with limited feedback by using the QR decomposition to the time-domain channel impulse response matrix. In contrast to the other methods where the receiver has to feed back full precoder index of each subcarrier or reduced index for a group of subcarriers to the transmitter, the GMD-based scheme can substantially reduce the amount of feedback information by returning only one precoder index to the transmitter, regardless of the number of subcarriers and channels. With this approach, the amount of required feedback for the proposed scheme does not grow with the number of subcarriers. This paper considers imperfect channel state information in the transmitter due to a feedback delay in the system.

In this paper, a detection algorithm with parallel partial candidate-search algorithm is presented. Two fully independent partial search processes are simultaneously employed for two groups of transmit antennas based on QR and QL decompositions of the channel matrix. Proposed QRD- QLD detection algorithm is compared with well-known QRD-M scheme adopted for several emerging wireless standards. Latency of the QRD-QLD candidate search is about twice as small for similar error-rate performance and for identical hardware resources. Total detection latency of QRD-QLD algorithm that also includes computation of soft information for outer decoder is also substantially smaller.

A QRD-based preceded MIMO-OFDM system with reduced feedback is proposed. Unlike the conventional preceding schemes in which the receiver has to feed back information about the channel frequency response of each carrier to the transmitter, the proposed system converts the MIMO-OFDM channel into layered channels by effectively exploiting the QR decomposition of the time-domain channel impulse response matrix. As a result, the receiver in the proposed system only needs to feed back information about one preceding matrix, regardless of the total number of carriers. Furthermore, a computationally efficient implementation scheme is devised for the proposed system. Analytical and simulation results show that the proposed scheme can achieve impressive BER performance compared to the conventional schemes, yet with considerably reduced feedback.

Opportunistic scheduling and beamforming schemes with reduced feedback are proposed for MIMO-OFDMA downlink systems. Unlike the conventional beamforming schemes in which beamforming is implemented solely by the base station (BS) in a per-subcarrier fashion, the proposed schemes take advantages of a novel channel decomposition technique to perform beamforming jointly by the BS and the mobile terminal (MT). The resulting beamforming schemes allow the BS to employ only one beamforming matrix (BFM) to form beams for all subcarriers while each MT completes the beamforming task for each subcarrier locally. Consequently, for a MIMO-OFDMA system with Q subcarriers, the proposed opportunistic scheduling and beamforming schemes require only one BFM index and Q supportable throughputs to be returned from each MT to the BS, in contrast to Q BFM indices and Q supportable throughputs required by the conventional schemes. The advantage of the proposed schemes becomes more evident when a further feedback reduction is achieved by grouping adjacent subcarriers into exclusive clusters and returning only cluster information from each MT. Theoretical analysis and computer simulation confirm the effectiveness of the proposed reduced-feedback schemes.

We propose an iterative soft detection algorithm based on the QR decomposition and M-algorithm (soft-QRD- M) for MIMO-OFDM incorporating error correction coding. The soft-QRD-M step generates approximate a posteriori probabilities (APPs) with significant computational savings over the optimal sum-product algorithm. Simulation results show comparable performance of the soft-QRD-M detector and SPA in a Turbo- coded iterative MIMO-OFDM receiver.

Joint estimation of the carrier frequency offset (CFO) and channel response of each active user in the uplink of an OFDMA system over time-varying channels is investigated in this work. To cope with the enormous computational complexity involved in tracking the time variations of CFOs and channels, we propose to use the parallel Schmidt Kaiman Filter (PSKF) to break down the complicated optimization problem into multiple parallel but smaller optimization problems. This results in an estimation scheme whose complexity only grows linearly with the number of users. Simulations indicate that the proposed scheme can achieve high estimation accuracy.

In this paper, we propose a new statistical joint frequency offset and channel estimation for the blind MIMO-OFDM system, where a state and parameters of dynamic systems are unknown. To reduce a channel mismatch problem, we use the fixed structure interacting multiple model (FS-IMM) and the Rao-Blackwellized Gauss-Hermite filter to estimate a model-dependent channel and offset parameter, which enters an observation function in a nonlinear manner. The resulting structure consists of M parallel bank of Kalman filters driven by sampled nonlinear state variable sequences.

In this paper, we evaluate the performance of the receiver employing an iterative RLS-based data detection and channel estimation for the structured irregular LDPC coded MIMO-OFDM system. Using the EXIT chart analysis, the performance of the detector with various approximate decoding algorithms is analyzed.

In this paper, we propose a new statistical joint fre- quency synchronization and channel estimation for the MIMO- OFDM system. To estimate a channel and offset parameter which enters the observation function in a nonlinear manner, we propose a Gauss-Hermite filter which incorporates the parallel Kalman filters (KFs) conditioned on a chosen offset sample. To reduce its prohibitive complexity in the MIMO system, the Rao- Blackwellization is employed. In the proposed MIMO-OFDM system, the frequency synchronization and channel estimation are made iteratively using one training symbol in front of the packet.

In this paper, we focus on the frequency offset estimation for a MIMO system with OFDM transmission technique. In our system, we directly approximate the a posteriori distribution employing the Gauss-Hermite integration in the preamble interval. Using this proposed approach, a better frequency offset estimation can be achieved in relatively large frequency offsets compared to the extended Kalman filter based approach over a quasi-static channel environment.

In MIMO systems, where multiple antennas are used at both transmitter and receiver to achieve high spectral efficiency, channel impulse responses are often assumed to be constant over a block or packet. This assumption of block stationarity on channels is valid for most fixed wireless scenarios. However, for communications in a high mobility environment, the assumption will result in considerable performance degradation. In this paper, we focus on channel estimation for a MIMO system with OFDM transmission technique. In our system, pilots are placed on subcarriers for a novel channel estimation at the receiver with Kalman filters. With the channels estimated by a Kalman filter, we apply the OFDM MIMO soft data detector with a reasonable computational cost. The soft outputs of soft data detection are fed back to another soft Kalman filter for an improved channel estimation. By alternatively and iteratively using these two Kalman filters, a better overall performance can be obtained.

The use of multiple transmit/receive antennas forming a multiple-input multiple-output (MIMO) system can significantly enhance channel capacity. This paper considers a V-BLAST-type combination of orthogonal frequency-division multiplexing (OFDM) with MIMO (MIMO-OFDM) for enhanced spectral efficiency and multiuser downlink throughput. A new joint data detection and channel estimation algorithm for MIMO-OFDM is proposed which combines the QRD-M algorithm and Kalman filter. The individual channels between antenna elements are tracked using a Kalman filter, and the QRD-M algorithm uses a limited tree search to approximate the maximum-likelihood detector. A closed-form symbol-error rate, conditioned on a static channel realization, is presented for the M=1 case with QPSK modulation. An adaptive complexity QRD-M algorithm (AC-QRD-M) is also considered which assigns different values of M to each subcarrier according to its estimated received power. A rule for choosing M using subcarrier powers is obtained using a kernel density estimate combined with the Lloyd-Max algorithm.

This paper proposes a time-varying, Doppler channel estimation approach using multiple hypothesis channel modeling for OFDM-MIMO systems. A non-linear estimation structure is derived using this problem formulation which is composed of a parallel bank of extended Kalman filters whose individual outputs are weighted and summed to form channel estimates. By using this approach, we can reduce the model-mismatch errors associated with fixed-parameter channel models which can be a significant source of channel estimation error. For time-varying, Doppler channels, the channel models (e.g. ITU models) are characterized by a small set of parameters such as Doppler frequency and spectral shape.

The use of multiple antennas at both the transmitter and receiver can significantly increase the channel capacity. These systems are called the multiple-input multiple-output (MIMO) systems. By using orthogonal frequency division multiplexing (OFDM) transmission techniques, the MIMO-OFDM system can achieve high spectral efficiency, which makes it an attractive candidate for high-data-rate wireless applications. In this paper, we propose a convolutionally coded MIMO-OFDM system with EM-based channel estimation and a QRD-M data detection algorithm. In our systems, one training symbol is transmitted from each transmit antenna for the MIMO channel estimation at the receiver. With the channel estimates available, we apply the QRD-M algorithm on the estimated channel matrix for suboptimal data detection with reasonable computational cost. The bit error rate (BER) and packet error rate (PER) performance of the MIMO-OFDM systems are compared. In the simulations, the bit error rate performance of our systems is 9 (or 5) dB better than that of uncoded (or coded) BLAST systems.

We consider a quasi-synchronous code-division multiple access (QS-CDMA) cellular system, where the code delay uncertainty at the base station is limited to a small number of chips. For such QS-CDMA systems, the need for code acquisition is eliminated, however, the residual code tracking and channel estimation problems still have to be solved. An extended Kalman filter (EKF) is employed to track the user delays and channel coefficients. By separating data detection, based on the QR decomposition combined with the M-algorithm (QRD-M) from the delay/channel estimation process, the computational complexity can be significantly reduced as the number of users increases. Simulations show that the EKF channel estimator performance is improved when the QRD-M algorithm is used instead of the MMSE detector or decorrelator for data decisions.