This paper investigates the effects of co-channel interference (CCI) on a non-orthogonal multiple access (NOMA)-assisted integrated sensing and communication (ISAC) system. Considering the presence of CCI at both the communication users and sensing receiver as well as imperfect successive interference cancellation (SIC), it presents accurate expressions for the communication performance in terms of the outage probability and ergodic communication rate, and the sensing performance in terms of the probabilities of false alarm and detection. The accuracy of the newly derived expressions is then verified by Monte-Carlo simulations. The results highlight the undesirable effects of error propagation from SIC imperfections, sensing interference (SI), and CCI in NOMA-ISAC communications systems. It is also demonstrated that in the high signal-to-noise regime, the sum communication rate reaches a limit due to inter-user interference, imperfect SIC, and SI.

This paper is concerned with the performance of integrated sensing and backscatter communication system in the presence of arbitrary co-channel interference (CCI). New accurate expressions are derived for the communication ergodic rates that account for the mutual correlation between sensing and communication channels. The accuracy of the newly derived expressions is validated through Monte Carlo simulations. Numerical results reveal the adverse influence of CCI on both communication and sensing rate performance. It is also demonstrated that these adverse effects can be mitigated through an increase in the number of transmit antennas.

Ahstract-This paper considers an intelligent reflecting surface (IRS)-assisted multi-user non-orthogonal multiple access (NOMA) system operating in the terahertz band. It aims to assess the impacts of pointing errors on the system performance under two practical IRS phase shifting schemes: partitioned IRS with discrete phase shifts under quantization errors, and IRS with random phase shifts. By taking into account the joint effects of pointing errors and phase shift quantization errors, accurate analytical expressions for the ergodic rate and outage probability are derived, which are validated via numerical and simulation results. The results demonstrate that the pointing errors have a more pronounced effect on the system performance than random phase shifts and phase shift quantization errors. Furthermore, the results reveal that although the random phase shifting scheme achieves a lower performance in contrast to the partitioned IRS, it remains a promising candidate for multi-user NOMA. This is attributed to its ability to circumvent the costly channel estimation and computational complexity that are proportional to the numbers of IRS reflecting elements and users.

This paper considers a downlink non-orthogonal multiple access (NOMA) communication system over general fading channels. Specifically, a new unified analytical expression is derived for the bit error rate (BER) evaluation of NOMA systems having an arbitrary number of users with an arbitrary order of M-ary quadrature amplitude modulation (MQAM) scheme. The preciseness of the newly derived expression for different number of users, modulation orders and fading channels is then validated through numerical and Monte-Carlo simulation results.

In this paper, a new approach has been proposed and investigated with the help of variational auto-encoder (VAE) as a probabilistic model to reconstruct the transmitted symbol without sending the data bits out of the transmitter. The novelty of the proposed End-to-end (E2E) wireless system is in representing the symbol as a image hot vector (IHV) that contains the features of the shape such as spikes, closed squared frame, pixels index location and pixels grey-scale colours. The previously mentioned features are inferred by latent random variables (LRVs). The LRVs are used for fronthaul and backhaul data representation. The LRVs parameters have only been transmitted through the physical wireless channel instead of the original bits as in the classical modulations or the hot vectors in the Auto-encoders (AE) E2E systems. The new proposed VAE architecture achieved the reconstruction of the symbol from the received LRV. The results show that the VAE with a simple classifier can provide a better symbol error rate (SER) than both AE baseline and classical Hamming code with hard decision decoding, especially at high$E_{b}/N_{o}$.

Effective massive machine-type communication (mMTC) with short packet transmissions is essential to realize a fully connected Internet of Things (IoT). On the other hand, sparse vector coding (SVC) techniques have recently been proposed to support short packet communication (SPC) systems. The principle of SVC is to transmit the information as a sparse vector and then use a sparse recovery algorithm for signal decoding. This paper applies two new sparse recovery algorithms to SVC-SPC; namely, Compressive Sampling Matching Pursuit (CoSaMP) and Stagewise Orthogonal Matching Pursuit (St-OMP) and compares their performance with two of the previously proposed recovery algorithms for SVC-SPC including the Multipath Matching Pursuit (MMP) and Orthogonal Matching Pursuit (OMP) algorithms. Simulation and numerical results of the recovery errors, recovery times, covariance and block error rates are presented for the different recovery algorithms. We show the MMP to be the more effective algorithm in SPC with low recovery error, while CoSaMP and OMP consume less operational time.

This paper considers an intelligent reflecting surface (IRS)-assisted multi-tag ambient backscatter communication system over Nakagami-m fading channels. Assuming that the RF source-tags and tags-reader direct links are blocked, however, they are supported by two IRSs. Taking into account the IRSs phase errors, the outage and bit error rate performance of the system are assessed based on the selection combining (SC) diversity scheme through two different methods, Laguerre series and Gaussian approximation. Numerical and simulation results validate the superiority and accuracy of the Laguerre series method compared to that of the Gaussian approximation, in particular, for a small number of tags and IRS elements, and higher levels of phase errors. The results also indicate that the IRS phase errors significantly impact the system performance.

In this paper, intelligent reflecting surfaces (IRS) have been novelized as a mobile entity in the 26 GHz mm-wave band to offload the data in mobile networks for the nonline-of sight (NLOS) scenario. This new proposed mobile entity security has been enhanced by adding a federated learning (FL) scheme that utilizes a 2 GHz UHF band in order to enable cooperative communications with different network elements to propagate the desired signal between the transmitter and the receiver through the best set of available mobile IRSs (MIRSs). The numerical results of the proposed system show two improvements: increasing the reliability of V2V links by decreasing the symbol error rate (SER) and improving the link capacity by improving the SNR value. This leads to considering MIRS as a new type of mobile network resource, where increasing both the number of the elements per MIRS and the set of available MIRSs improves the V2V link capacity and decreases the SER, respectively.

In this paper, we consider an intelligent reflecting surface (IRS)-assisted backscatter communication system, where the direct link between the reader (R) and tag (T) is assumed to be unavailable. Taking into account the IRS phase shift dependent (PSD) amplitude response and hardware imperfections (HWI), accurate expressions for outage probability, average symbol error rate, and ergodic capacity are derived. The expressions are then validated through numerical and simulation results. The results reveal that non-ideal IRS PSD amplitude response and HWI severely impact the system performance. It is also shown that HWI introduce a capacity ceiling in the high-power and large number of IRS reflecting elements regimes, which is independent of fading levels and IRS PSD amplitude response.

Deep learning (DL) is playing an increasingly important role in the design of next-generation communication systems. In this paper, we apply DL algorithms to enhance signal detection and performance of multiple-input-multiple-output (MIMO) based orthogonal frequency-division multiplexing (OFDM) systems with index modulation (IM). The proposed detector termed DLIM is used as fully connected layers of a deep neural network (DNN) and adopted to achieve minimum bit error rates in IM-MIMO-OFDM over Rayleigh wireless channels. To show the enhancement of the proposed algorithm, the DL model is trained initially offline using data generated from simulation based on common statistical wireless channel models. DLIM is then adopted to recover the online transmitted data. Simulation results confirm that the proposed DLIM can detect the transmitted symbols with a performance comparable to near-optimal BER in a shorter runtime than required by the existing classical detectors.

In this paper, we are re-modelling the intelligent reflecting surfaces (IRS) assisted communication systems using the auto-encoder (AE) deep learning (DL) technique to represent the classical IRS system as an end-to-end communication system. The cascaded channels from source to sink through the IRS have been transformed to a deep neural network (DNN) that learns how to reduce the wireless environment impairments effect by optimizing the representation of transmitted symbols. The proposed system design shows superior symbol error rate (SER) performance under the AWGN channel compared to both classical IRS and conventional AE end - to-end systems. The relation between improvement of performance and the capability of the proposed AE to learn optimized presentation for transmitted symbols is being explained through observing and comparing the baseline AE constellations learning with the ones that the proposed model learned.

The diversity of users' applications based on content delivery in indoor environments dramatically increased such that the conventional RF wireless networks might not be enough to support applications such as 4K video streaming and virtual reality. Visible light communication (VLC) has emerged recently as a complementary unlicensed media. In this paper, we propose a hybrid WiFi-VLC system consist of one WiFi access point (AP) and multiple VLC APs. Based on the requested data rate, users can be assigned to WiFi or VLC AP in downlink such as to maximize the fairness among all connected users. We propose a reinforcement learning algorithm that can be implemented at the WiFi AP and help with assigning the users to a specific AP based on their requested data rate. We propose a new reward function that improves the satisfaction of all connected users. Numerical simulation results show that the proposed method improved the user satisfaction based on Jain's fairness index.

This article proposes a downlink/uplink decoupled (DUDe) access scheme for cellular-enabled unmanned aerial vehicle (UAV) communication systems. To minimize interference, the proposed scheme separates the control and data links of UAVs, as well as the uplinks (ULs) and downlinks (DLs) of ground users (GUEs), onto different serving base stations and operating frequencies. Since power availability is a major constraint in UAV communications, two power allocation schemes based on$Q$-learning (QL) and deep$Q$-learning (DQL) are proposed to optimize the communication energy efficiency (EE) of this DUDe network. To quantify the improvements achieved, the proposed schemes are compared with the fractional power control (FPC) scheme used in 4G and 5G networks, as well as a convex optimization-based optimal power allocation scheme. The results demonstrate that the proposed DUDe scheme can achieve up to several times higher sum rates and EE in the UL direction than its coupled counterparts. Moreover, it is shown that the EE performance of the QL and DQL power allocation schemes approach the optimal performance and surpass the conventional FPC scheme by 80%–100% in the UHF band, and by 160%–170% in the mmWave band.

The number of mobile devices in indoor environment has dramatically increased and the capacity of conventional RF wireless networks may not be enough to support the indoor traffic demand. Recently, Visible Light Communication (VLC) systems have emerged as a complementary unlicensed media. In this paper, we proposed a hybrid WiFi-VLC system where multiple VLC access points (AP) coexist with a WiFi AP. A number of indoor users share the hybrid WiFi-VLC system. All users employ WiFi for uplink whereas one access point (WiFi or VLC) is assigned for each user to maximize the overall capacity of the network. We propose a new reinforcement learning algorithm which can be implemented at the WiFi AP and results in the selection of an access point such that the total throughput is maximized. Numerical simulation results show that the proposed method improves the total system throughput significantly. Furthermore, the throughput achieved by the worst user in the proposed Q-Learning algorithm becomes higher than what would be received by the average user who used the conventional hybrid systems based on best connection.

In this paper, a new technique called Embedded Variational Auto Encoder (EVAE) is proposed for Vehicle-to-Everything (V2X) up-link scenario. An innovative method has been proposed for the accurate prediction of the interference at the receiving end of each user which leads to the enhancement of the end-to-end performance of the V2X. The new algorithm infers noise and fading probabilistic models effect using decentralized Probabilistic Neural Networks (PNNs), while a second centralized PNN has been embedded inside the first group of the PNNs. This single PNN will be used to infer the interference effect on each V2X receiver. The performance of EVAE is compared with the recently proposed neural networks (NN) algorithms based on conventional auto-encoders (AE). Numerical and simulation results for the achievable symbol error rates (SER) have shown a significant improvement particularly in the high SINR regime, compared with the classical systems based on maximum likeli-hood detection.

This study analyses the performance of downlink non‐orthogonal multiple‐access (NOMA) networks over independent but not necessarily identically distributed Rayleigh fading channels by deriving closed‐form expressions for the average signal‐to‐interference‐plus‐noise ratio (SINR), average achievable rate, and outage probability of all network users. Moreover, SINR‐based power allocation strategies are studied. Specifically, the optimisation problems of max–min SINR, multi‐objective SINR, sum‐SINR and proportional‐fairness‐SINR maximisation under minimum SINR constraints are formulated and shown to be non‐convex. Additionally, the problems of total power and sum‐SINR minimisation are also formulated. Particularly, the formulated problems take the form of linear‐fractional programming problems. By applying intelligent reformulation techniques, these problems have been reformulated into convex optimisation problems, and thus efficiently solved. Numerical evaluations are presented to validate the derived closed‐form expressions for the different performance metrics, which are found to be in agreement with the network simulation results. More importantly, it has been demonstrated that the user with the best channel conditions achieves full diversity order, whereas all the other users achieve diversity orders equivalent to their ordered channel conditions. Finally, the reformulated power allocation strategies are evaluated, and shown to coincide with the original problem formulations.

In this study, the problem of joint relay selection and power allocation (J‐RS‐PA) for NOMA‐based multicast cognitive radio networks is considered. In particular, the aim is to simultaneously maximise the end‐to‐end SINR/SNR of the primary and secondary transmitter–receiver (TR) pairs, subject to quality‐of‐service (QoS) constraints. Communication between the primary and secondary TR pairs is performed over two‐phases, namely, the broadcasting phase, and the cooperation phase. In the broadcasting phase, the primary and secondary transmitters broadcast their data symbols; while in the cooperation phase, the selected relay forwards the decoded symbols to their intended receivers. However, the formulated J‐RS‐PA problem happens to be non‐convex, resulting in computationally‐prohibitive complexity. Consequently, an optimal low‐complexity two‐stage relay selection and power allocation (TS‐RS‐PA) algorithm is devised, which is based on the solution of linear programming problem reformulations. Simulation results are presented to validate the proposed TS‐RS‐PA algorithm, which is shown to yield the optimal SINR/SNR values in comparison to the J‐RS‐PA scheme, but with lower computational complexity, while satisfying QoS constraints.

In this paper, the problem of joint subcarrier assignment and weighted-sum energy-efficient power allocation (J-SA-WSEE-PA) in multi-carrier uplink NOMA relay networks is considered. Specifically, the aim is to assign subcarriers to network users, while maximizing the weighted-sum energy-efficiency, subject to quality-of-service (QoS) constraints. The J-SA-WSEE-PA problem is shown to be non-convex, and thus is computationally-intensive. In turn, it is split into two subproblems: (1) WSEE maximizing power allocation per subcarrier, and (2) matching-theoretic subcarrier assignment. For the first sub-problem, a low-complexity iterative solution procedure is devised to optimally solve the WSEE-maximizing power allocation problem per subcarrier. As for the second sub-problem, a linear time-complexity stable matching algorithm based on the hospitals-residents matching problem is proposed to assign subcarriers to network users. Simulation results are presented to validate the devised solution procedure and the proposed stable matching algorithm, where it has been shown they yield comparable network sum energy-efficiency to the J-SA-WSEE-PA scheme, while satisfying QoS constraints.

In this paper, the problem of joint relay selection and power allocation (J-RS-PA) for NOMA-based multicast cognitive radio networks is considered. In particular, the aim is to simultaneously maximize the SINR/SNR of the primary and secondary transmitter-receiver (TR) pairs, subject to quality-of-service (QoS) constraints. Communication between the primary and secondary TR pairs is performed over two-phases, namely, the broadcasting phase, and the cooperation phase. In the broadcasting phase, the primary and secondary transmitters broadcast their data symbols to the intermediate relays; while in the cooperation phase, the selected relay forwards the decoded symbols to their intended receivers. However, the J-RS-PA problem happens to be non-convex (i.e. computationally-prohibitive). Alternatively, an optimal low-complexity two-stage relay selection and power allocation (TS-RS-PA) algorithm is devised, which is based on the solution of intelligent linear programming problem formulations. Simulation results are presented to validate the proposed TS-RS-PA algorithm, which has been shown to yield the optimal SINRlSNR values for the primary and secondary TR pairs in comparison to the J-RS-PA scheme, but with lower computational complexity, while satisfying QoS constraints.

In this paper, the problem of joint relay selection and global energy-efficient power allocation in energy-harvesting cooperative non-orthogonal multiple-access (NOMA) networks is studied. In particular, a base-station communicates with multiple users via a selected energy-harvesting relay, such that network global energy-efficiency (GEE) is maximized, subject to quality-of-service (QoS) constraints. To that end, the problem of joint-relay selection and global energy-efficient power allocation (J-RS-GEE-PA) is formulated, which happens to be non-convex (i.e. computationally-expensive). In turn, the J-RS-GEE-PA problem is decoupled into two sub-problems: (1) relay selection, and (2) GEE power allocation. Different relay selection schemes are explored, and then a computationally-efficient algorithm is devised to optimally solve the GEE power allocation problem for the selected relay. In addition, a low-complexity solution procedure is proposed to solve the J-RS-GEE-PA problem, so as to achieve the global optimal solution. Simulation results are presented to evaluate the resulting network GEE for the different relay selection schemes, and the proposed solution procedure. More importantly, the proposed solution procedure is shown to yield the optimal network GEE when compared to the J-RS-GEE-PA, and superiority to the other relay selection schemes, while maintaining QoS.

This paper studies device-to-device (D2D) group association and channel assignment in uplink multi-cell non-orthogonal multiple-access (NOMA) networks. In particular, the goal is to assign D2D groups to cellular user channels at each base-station, while accounting for the interference caused by pairing users with D2D groups. To that end, a multi-objective signal-to-interference-plus-noise ratio (SINR)-maximizing power allocation solution procedure is proposed to determine the optimal power allocation for each (D2D group, user) pair, while meeting quality-of-service (QoS) requirements. After that, the joint D2D group association and channel assignment problem is modeled as a student-project allocation with preferences over (student, project) pairs matching problem. Then, a polynomial-time complexity stable matching algorithm is proposed to pair D2D groups with users, and associate them with base-stations. Simulation results are presented to evaluate the proposed matching algorithm, and compare it to a joint D2D group association, channel assignment and power allocation (J-GA-CA-PA) scheme. The proposed algorithm is shown to efficiently yield comparable SINR-per user and D2D receiver-to the J-GA-CA-PA scheme, while maintaining QoS requirements.

This paper studies joint device-to-device (D2D) group association and channel assignment in uplink multi-cell non-orthogonal multiple-access (NOMA) networks. Particularly, the goal is to assign D2D groups to cellular user channels at each base-station, while accounting for negative network externality due to the interference caused by pairing a user with a D2D group. To that end, a multi-objective signal-to-interference-plus-noise ratio (SINR)-maximizing power allocation solution procedure is proposed to determine the optimal power allocation for each (D2D group, user) pair, while meeting quality-of-service (QoS) requirements. After that, the joint D2D group association and channel assignment problem is modeled as a student-project allocation with preferences over (student, project) pairs matching problem. More specifically, two polynomial-time complexity stable matching algorithms are proposed to pair D2D groups with users, and associate them with base-stations. Simulation results are presented to evaluate the proposed matching algorithms when combined with the devised solution procedure, and compare them to a joint D2D group association, channel assignment and power allocation (J-GA-CA-PA) scheme. More importantly, the proposed algorithms are shown to efficiently yield comparable SINR-per user and D2D receiver-to the J-GA-CA-PA scheme, while maintaining QoS requirements.

This paper studies the performance of wireless power transfer in distributed antenna systems (DAS). In particular, the distributed remote radio heads (RRHs), which are conventionally distributed in the network to enhance the performance, are also used to increase the energy harvesting (EH) at the energy-constrained users. Based on this idea, the network area is divided into two zones, namely: 1) EH zone and 2) interference zone. The users in the EH zones are guaranteed to harvest sufficient energy from the closed RRH, while the users in the interference zones harvest energy from the surrounding RRHs. A harvest-then-transmit protocol is adopted, where in the power transfer phase the multiple antennas RRHs broadcast energy signals to the users. In the information transmission phase, the users utilize the harvested energy to transmit their signals to the RRHs. In addition, zero-forcing is applied at the RRHs receivers, to mitigate the interference. The system spectral efficiency is evaluated in two different scenarios based on the channel state information (CSI) namely: 1) CSI is unknown at the RRHs 2) CSI is perfectly known at the RRHs. In contrast to conventional EH-muliple-input multiple-output (MIMO) systems, performance analysis of EH DAS-MIMO is a challenging problem, because the channels are characterized by non-identical path-loss and EH effects which make the classical analytical methods non-tractable. In light of this, new analytical expressions of the ergodic spectral efficiency are derived and then Monte Carlo simulations are provided to verify the accuracy of our analysis. The effects of main system parameters on the EH-DAS performance are investigated. The results show that there is an optimal value of the EH time for each users locations that maximizes the system performance. In addition, size of the EH-zone area depends on the required harvested power at the users which is dependent essentially on the target spectral efficiency.

This paper analyzes the performance of downlink non-orthogonal multiple-access (NOMA) networks over independent but not necessarily identically distributed Rayleigh fading channels for arbitrary number of network users. Specifically, closed-form expressions for the average SNR, average achievable rate, and outage probability are derived, where it has been shown that network users achieve diversity orders equivalent to their ordered channel gains. Numerical evaluations are presented to validate the derived closed-form expressions for the different performance metrics, which are found to be in agreement with the network simulation results.

In this paper, a comprehensive design and analysis of multiple-input multiple-output (MIMO) full-duplex (FD) relaying systems in a multi-cell environment is investigated, where a multi-antenna amplify-and-forward FD relay station serves multiple half-duplex (HD) multi-antenna users. The pivotal obstacles of loopback self-interference (LI) and multiple co-channel interferers (CCI) at the relay and destination when employing FD relaying in cellular networks are addressed. In contrast to the HD relaying mode, the CCI in the FD relaying mode is predicted to double since the uplink and downlink communications are simultaneously scheduled via the same channel. In this paper, the optimal layout of transmit (receive) precoding (decoding) weight vectors which maximizes the overall signal-to-interference-plus-noise ratio is constructed by a suitable optimization problem, and then a closed-form sub-optimal formula based on null space projection is presented. The proposed hop-by-hop rank-1 zero-forcing (ZF) beamforming vectors are based on added ZF constraints used to suppress the LI and CCI channels at the relay and destination, i.e., the source and relay perform transmit ZF beamforming, while the relay and destination employ receive ZF combining. To this end, unified accurate expressions for the outage probability and ergodic capacity are derived in closed form. In addition, simpler tight lower bound formulas for the outage probability and ergodic capacity are presented. Moreover, the asymptotic approximations for outage probability are considered to gain insights into system behavior in terms of the diversity order and array gain. Numerical and simulation results show the accuracy of the presented exact analytical expressions and the tightness of the lower bound expressions. The case of hop-by-hop maximum-ratio transmission/maximal-ratio combining beamforming is included for comparison purposes. Furthermore, our results show that while multi-antenna terminals improve the system performance, the detrimental effect of CCI on FD relaying is clearly seen. Therefore, our findings unveil that MIMO FD relaying could significantly improve the system performance compared to its conventional MIMO HD relaying counterpart.

This paper investigates the spectral efficiency of Zero-Forcing (ZF) receiver in a multi-user multiple-input multiple-output (MU-MIMO) system, taking the user status, transmit antenna correlation, shadowing and co-channel interference (CCI) (i.e., multi-cell environment) into account. In particular, we propose the classical Rayleigh/log-normal distribution (RLN) to characterize the fading channel. New closed-form expressions are derived for the uplink spectral efficiency and a new accurate closed-form lower bound is determined to obtain useful insights into the implications of the model parameters on the system performance. The numerical results are sustained via Monte-Carlo simulations.

In this paper, we provide joint subcarrier assignment and power allocation schemes for quality- of-service (QoS)-constrained energy-efficiency (EE) optimization in the downlink of an orthogonal frequency division multiple access (OFDMA)-based two-tier heterogeneous cellular network (HCN). Considering underlay transmission, where spectrum- efficiency (SE) is fully exploited, the EE solution involves tackling a complex mixed-combinatorial and non-convex optimization problem. With appropriate decomposition of the original problem and leveraging on the quasi-concavity of the EE function, the problem can be efficiently solved. On the other hand, the inherent inter-tier interference from spectrum underlay access may degrade EE particularly under dense small-cell deployment and large bandwidth utilization. We therefore develop a novel resource allocation approach based on the concepts of spectrum overlay access and resource efficiency (RE) (normalized EE-SE trade-off). Specifically, the optimization procedure is separated where the macro- cell optimal RE and the corresponding bandwidth is first determined, then the EE of small-cells utilizing the remaining spectrum is maximized. Simulation results confirm the theoretical findings and demonstrate that the proposed resource allocation schemes can approach the optimal EE with each strategy being superior under certain system settings.

Relays are expected be an important factor in the implementation of millimeter wave (mmWave) based cellular networks due to the limited coverage of mmWave communications. Adding a single or multiple relays in the link between two nodes is an inevitable step towards high capacity wireless access and/or backhaul links. In this paper we suggest employing two-hop multiple relay networks as a solution to link two points using mmWave frequencies. Hybrid (Analog and Digital) precoding is used at the two terminal nodes with analog beamformers/combiners at the relays. The proposed design algorithm requires no channel information with relatively limited training overhead. The performance of the system is examined under different channel and system layouts. The results highlight the positive impact of employing relays in mmWave link as well as the effect of array size on the overall system performance.

One of the challenges for the wireless networks is meeting the high demand for cellular data. One approach is to utilize the wide bandwidth provided by the millimeter wave (mmWave) frequencies. In this work, we propose using multiple relays to link two points in the outdoor mmWave environments. We use hybrid (analog and digital) beamformers in the Amplify-and-Forward (AF) half duplex relays to overcome the propagation losses usually arise in such environments. The design is based on the widely known Orthogonal Match Pursuit (OMP) algorithm. Results show significant performance improvement for multiple relay links as compared to links with a single relay. The results also discuss the influence of the array size and the number of RF chains on the overall performance.

In this paper, we study the performance of a wireless communication system, where an arbitrary number of relays cooperate to enhance the signal between source and destination. The source and destination are hidden from each other, and there is no direct link between them. Optimal Relay Power Control (ORPC) is introduced as an effective scheme to achieve cooperative diversity, where there is a trade-off between complexity and system performance. This paper develops a new and more accurate model for the ORPC scheme and takes into account the effects of fading and thermal noise at both the relays and destination. This leads to the derivation of new analytical expressions for the overall spectral efficiency which can be used to estimate the throughput of the ORPC in Rayleigh and Nakagami-m fading channels, and to study the impact of different system parameters on efficiency. The accuracy of the new mathematical results is confirmed by Monte Carlo simulation. The results of this paper can be used to estimate the aggregate throughput of a dual-hop system employing the ORPC protocols.

In this paper, we investigate and analyse the performance of amplify and forward (AF) relay system connecting a group of independent sources to their destinations employing a random carrier sense multiple access (CSMA) protocol. The sources are isolated from their destination and the only means for them to communicate with their destination is through the common relay. Sources are arbitrarily distributed around the relay and experience Rayleigh fading channels. This paper develops a new and more accurate model for multiple access interference at both the relay and destination which takes into account random sources location and the effects of fading and thermal noise at both the relay and destination. Moreover, the effect of the hidden nodes on the system performance is considered as a randomly occurring factor. This leads to the derivation of new analytical expressions for the overall spectral efficiency (SE) which can be used to estimate the throughput of the CSMA-based relay in Rayleigh fading channels and to study the impact of the different system parameters on their efficiency. The accuracy of the new mathematical results is confirmed by Monte Carlo simulation.

Cooperative diversity is a promising technique for use in wireless networks because it can provide diversity gain without the need to install multiple antennas at the source or destination. This paper is concerned with the performance analysis of a dual-hop random access network employed adaptive power technique (APT) relay in cooperative diversity networks. The network considered uses amplify-and-forward relaying, and is the only mean to connect source to its destination. This scheme is compared with such popular schemes as the orthogonal scheme, best relay selection, maximal ratio transmission (MRT) and the optimum combining scheme. A new unified mathematical method is developed, which leads to the derivation of new analytical expressions for the overall spectral-efficiency of the dual-hop random access network over Rayleigh fading channels. Numerical results show that the APT can benefit from an increase in the number of relays and reduction of the noise power at the relay and destination. The results also show that the performance of the APT is comparable to the other cooperative schemes, except the MRT. Furthermore, the new mathematical results obtained for APT have been confirmed by Monte Carlo simulation.

In this paper, we study the performance of a wireless communication system, where an arbitrary number of amplify-and-forward relays cooperate to enhance the signal between source and destination. The source and destination are hidden from each other, and there is no direct link between them. Optimal relay power control (ORPC) is introduced as an effective scheme to achieve cooperative diversity. This paper develops a new and more accurate model for the ORPC scheme in multiple antenna relays scenario, and takes into account the effects of fading and thermal noise at both the relays and destination. This leads to the derivation of new analytical expressions for the overall spectral efficiency which can be used to estimate the throughput, and to study the impact of different system parameters on efficiency. The accuracy of the new mathematical results is confirmed by Monte Carlo simulation.

The pilot contamination problem is one of the major obstacles that limit the performance of time-division duplex (TDD) multicell massive multiple-input multiple-output (MIMO) systems. Pilot contamination results from the re-use of the same set of pilot sequences in the different cells of the system. In this paper, we propose an Adaptive Pilot Allocation (APA) algorithm for pilot contamination mitigation. The proposed algorithm divides the users in the system into two groups according to the inter-cell interference they cause to the other users in the system. To improve the system performance, the algorithm allocates orthogonal pilot sequences to the users that can cause high inter-cell interference. Simulation results show that the proposed algorithm outperforms the conventional (random) allocation method. Also it show that the proposed algorithm improves both the minimum and the mean achievable rates.

Massive multiple-input multiple-output (MIMO) systems are expected to achieve significant gains in both energy and spectral efficiency compared to conventional MIMO systems. However, these promising gains are limited by the impact of pilot contamination in TDD multicell massive MIMO which results from reusing the same set of pilot sequences in all the system's cells. In this paper, we propose an algorithm for pilot sequences allocation that aims to maximize the minimum achievable rate in a target cell by utilizing the availability of the large-scale fading information at the BSs. Our results show that the proposed algorithm can significantly improve both the spectral efficiency and the minimum achievable rate compared to the conventional pilot allocation scheme which assigns the pilot sequences randomly.

We consider the case where a reference full-duplex (FD) node (e.g., base station), equipped with arbitrary number of transmit/receive antennas, utilizes generalized linear beamformers to simultaneously communicate with multiple FD radios (e.g., user equipments). The fading coefficients for the residual self-interference (SI) channels are drawn from the complex Gaussian distribution with arbitrary mean and variance. Here, it is not possible to directly derive the distribution of the bidirectional channel power gain. As a result, we adopt the method of moments in order to provide a new Gamma approximation for the residual SI distribution over FD multi-user MIMO Rician fading channels. The proposed theorem holds under arbitrary linear precoder/decoder design, number of antennas and streams, and SI cancellation capability. The validity of the theoretical findings is confirmed via extensive simulations of the entire transmit/receive processing chain.

In this study, the ergodic secrecy capacity and the corresponding outage probability of two‐hop amplify‐and‐forward relaying system in the presence of a passive eavesdropper are analysed. In order to improve the security, in this study, zero‐forcing (ZF) scheme is implemented at different locations in the system. The effect of the ZF‐based scheme on the system security is considered for three different scenarios, based on where the ZF scheme is applied, namely, (i) ZF receivers at the relay and destination nodes, (ii) ZF precoders at the source and relay nodes, and (iii) ZF precoders/receivers at the relay nodes. For each scenario, explicit analytical expressions for the ergodic secrecy capacity and secrecy outage probability are derived. Monte Carlo simulations are also provided to validate the analysis. Results show that increasing the number of source, relay and/or destination nodes can be favourable or unfavourable to the system security and the significance of this enhancement/degradation depends on the particular scenario deployed. In addition, the system security improves with increasing the source and/or relay power.

We provide a theoretical framework for the study of massive multiple-input multiple-output (MIMO)-enabled full-duplex (FD) cellular networks in which the residual self-interference (SI) channels follow the Rician distribution and other channels are Rayleigh distributed. In order to facilitate bi-directional wireless functionality, we adopt: 1) in the downlink (DL), a linear zero-forcing (ZF) with SI-nulling precoding scheme at the FD base stations and 2) in the uplink (UL), an SI-aware fractional power control mechanism at the FD mobile terminals. Linear ZF receivers are further utilized for signal detection in the UL. The results indicate that the UL rate bottleneck in the FD baseline single-input single-output system can be overcome via exploiting massive MIMO. On the other hand, the findings may be viewed as a reality-check, since we show that, under state-of-the-art system parameters, the spectral efficiency gain of FD massive MIMO over its half-duplex counterpart is largely limited by the cross-mode interference between the DL and the UL. In point of fact, the anticipated twofold increase in SE is shown to be only achievable when the number of antennas tends to be infinitely large.

We present a new accurate analysis for the downlink spectral efficiency of linear zero- forcing (ZF) beamforming over multi-user multiple- input multiple-output (MIMO) channels, experiencing composite fading effects in a multi- cell environment. In particular, Rayleigh/log- normal distribution (RLN) is proposed to model the composite fading channel. New exact expressions are derived for the downlink spectral efficiency followed by new tight closed-form lower and upper bounds on the spectral efficiency. In contrast to the previous analysis for the spectral efficiency of multi-cell MIMO systems, we present an accurate model for the co-channel interference where the number of users in each cell is random. The new analytical results are validated by Monte-Carlo simulation and used to shed light into the effects of the system parameters e.g., random number of active users, co-channel interference, and shadow fading on the spectral efficiency.

In this paper, we study a wireless-powered communication network (WPCN) scenario, in which a multiple antenna amplify-and-forward (AF) two-way relay coordinates power transfer and information exchange to multiple pairs of users. A harvest-then- transmit protocol is assumed where the relay first transmits energy signals to the users in a power transfer phase. Multi-pair of users, which have rechargeable batteries, then use the harvested energy to exchange their independent signals through the relay in two phases, up-link (UL) and down-link (DL). In the UL phase, the users transmit their information signals to the relay and in the DL phase the relay amplifies and forwards the signals to the intended destinations. Furthermore, in order to cancel out the interference, zero-forcing reception and transmission (ZFR/ZFT) is implemented at the relay. In order to characterize the system performance, we consider ergodic spectral and energy efficiencies for two cases, based on the availability of the channel state information (CSI) at the relay during the power transfer, 1) unknown CSI 2) partially known CSI. In light of this, we derive new analytical expressions for the ergodic spectral and energy efficiencies for the two cases and Monte Carlo simulations are provided throughout our investigations to validate the mathematical analysis. The impacts of some system parameters such as EH time, EH efficiency, number of relay antennas and user-pairs, on the system performance are investigated.

This paper analyzes the performance of full-duplex (FD) relaying with multiple-antenna amplify-and-forward (AF) relay. The system performance due to practical wireless transmission impairments of spatial fading correlation, cross-correlation due to correlated links is investigated. To this end, new exact closed-form expressions for the ergodic capacity are derived in the case of arbitrary correlations for both, the spatial and cross correlations. At the relay, the loopback self-interference (LI) is mitigated by using receive zero-forcing (ZF) precoding scheme, then steering the signal to the destination by using the maximum-ratio transmission (MRT) technique. Numerical results sustained by Monte Carlo simulations show the exactness of the proposed closed-form analytical expressions. In addition, it is seen that the ergodic capacity performance of FD relaying systems outperforms that of half-duplex (HD) relaying systems. Furthermore, the system performance insights reveal the negative and positive impact of the spatial and cross correlation on the ergodic capacity performance, respectively. Surprisingly therefore, an improvement in the ergodic capacity is seen as the cross-correlation between the two links increases. As a result, the ergodic capacity is not maximized by independent links as fully correlated links with uncorrelated spatial correlation results in the maximum ergodic capacity.

This paper analyzes the performance of energy beamforming in multiple-input multiple-output (MIMO) relaying systems, where the source and destination nodes are equipped with multiple antennas and communicating via a dual-hop amplify-and-forward (AF) single antenna energy-constrained relay, and the destination is subject to co-channel interference (CCI). The wirelessly powered relay scavenge energy from the source information radio-frequency (RF) signal through energy beamforming, using the time-switching receiver, and uses the harvested energy to forward the source message to the destination. To this end, tight lower and upper bound expressions for the outage probability and ergodic capacity of the considered system are presented in closed-form, through which the throughput of the delay-constrained and delay-tolerant transmission is investigated, respectively. Numerical results sustained by Monte Carlo simulations show the tightness of the proposed analytical expressions. The impact of various parameters such as the energy harvesting time, source transmit power and the number of antennas on the system throughput is also considered. It is seen that the system throughput increases as the number of antenna and/or the source transmit power increases. In addition, energy beamforming increases the harvested energy and hence reduces the optimal energy harvesting ratio, as a result, more time is left for information transmission.

In this paper, ergodic secrecy capacity is analyzed in a cooperative communication network, for an independent but non-identically distributed (i.n.i.d) Rayleigh fading channel. By using multi-trusted decode and forward relays, the model assumes direct links between a sender (Alice) and receiver nodes (Bob and an eavesdropper); in addition both Alice and the relay have perfect knowledge about the eavesdropper's channel state information (CSI). The protocol employed herein selects the best relay with the highest signal-to-noise ratio (SNR) in relation to the destination (Bob), while maximum ratio combining (MRC) is employed at Bob and the eavesdropper's terminals. Finally, the theoretical analysis is validated through simulation, and the results show that performance is enhanced with an increasing number of relays, in the event of a direct link between the sender and the receiver's terminals.

We devise a framework using tools from stochastic geometry and queuing theory for the study of irregular cellular networks when user traffic varies randomly in time and space. We consider a typical wireless cell with a guard zone surrounded by an interference environment comprised of a dominant node at the guard-edge plus an outer-bound Poisson field of sources. A systematic approach is presented to characterize the flow rate in the presence of elastic data traffic with closed-form expressions of the intended signal power and bounded aggregate interference statistics over Nakagami-m fading channels accordingly derived. We then formulate and solve an optimization problem for the computation of the traffic capacity defined as the maximum elastic data flow intensity for which the system remains unsaturated.

In this paper, power allocation over time-varying multi-user multi-relay amplify-and-forward networks is studied. Specifically, stochastic network sum-rate and max-min rate power allocation problems are formulated. However, solving such stochastic problems relies on perfect global instantaneous channel state information (CSI), and thus entails complex computations and excessive communication overheads. To circumvent these issues, second-order statistics of the CSI (i.e. partial CSI) are utilized to transform the stochastic formulations into deterministic optimization problems in terms of ergodic capacity while satisfying quality-of-service constraints via target outage probability. The obtained optimal deterministic problems are non-convex and thus are computationally prohibitive. However, at high enough signal-to-noise ratio, such problems can be transformed into asymptotically convex ones, and thus solved efficiently. Simulation results illustrate that the proposed approximate deterministic power allocation reformulations coincide with their optimal exact deterministic and dynamic counterparts.

In this paper the cooperation of beam-forming and artificial noise (AN) in two-hop amplify-and- forward (AF) relaying system is proposed to enhance the security. we consider a half duplex AF relaying network with a multi-antenna source node and a destination in the presence of a passive eavesdropper.Since channel state information (CSI) of the eavesdropper is unknown, the AN transmitted by the source in the first phase and by the relays in the second phase is in all directions except the legitimate node one. As such two scenarios are considered here,: i) when all the relays amplify and forward the information source signal ii) when only the best relay is selected to amplify and forward the information source signal. The beam-former weights and the power allocation are obtained by solving an optimization problem. Results reveal that the proposed system can provide considerable improvements in terms of secrecy rate. It is also found that increasing the AN power, relative to the information signal power, will further improve the secrecy rate.

We present an analytical model for the design and analysis of dense cellular networks (DenseNets) where load-awareness is explicitly incorporated in the system performance. New bounded expressions of aggregate interference and average rate are developed considering spatially-correlated heterogeneous sources. Subsequently, an optimization problem for pinpointing the optimal network density which minimizes the total energy expenditure is formulated and tackled. The validity of our framework and its advantages over the existing fully-loaded and interference- thinning methods are depicted via Monte-Carlo simulations. Based on state-of-the-art system parameters, a homogeneous pico deployment is revealed to be the most energy-efficient solution in future dense urban environments.

We propose an analytical stochastic geometry-based model for multiple-input multiple-output (MIMO) heterogeneous cellular networks (HetNets) with zero-forcing (ZF) precoding at transmitting base stations (BSs) and partial zero-forcing (PZF) beamforming at receiving user equipments (UEs). The user and area spectral efficiencies are characterized using a non-direct moment- generating-function (MGF) methodology with closed- form expressions of the intended signal power and aggregate network interference statistics accordingly developed. The impact of different cellular network deployments, antenna configurations, and transmission schemes on achievable performance are examined through theoretical and simulation studies. The results confirm the promising potential of multi-antenna communications and small-cell solution in emerging wireless environments.

The application of stochastic geometry theory for the study of cellular networks has gained huge popularity recently. Most existing works however rely on unrealistic assumptions concerning the underlying user traffic model. This paper aims to make a step in this direction by devising a new model for the performance analysis and optimization of heterogeneous cellular networks (HetNets) with irregular BS deployment and flow- level traffic dynamics. We provide a unified methodology for the evaluation of the flow rate with closed-form expressions of the useful signal power and aggregate network interference over Nakagami-m fading channels. The problem of computing the optimal loading factors which result in the greatest sustainable traffic whilst the system remains stable is formulated and tackled.

This paper presents a new accurate mathematical analysis on the performance of distributed cooperative systems employing time-based relay selection protocols. A time-based distributed protocol relates the packets' transmission time to their signal strengths such that the best relay transmits firstly and all other relays abort their transmissions once they sense a busy channel. However, this protocol fails to select the best relay when relay nodes become hidden from each other resulting in self-interferences. In this paper, a new unified mathematical method is developed in order to derive a new exact expression for the average spectral efficiency of the distributed cooperative system in the presence of self-interferences. The developed method accounts for arbitrary fading scenarios and significantly simplifies the difficult task of obtaining the exact average spectral efficiency. Monte Carlo simulations are presented in order to validate the analytical result and to illustrate the impact of hidden nodes on the system performance.

With the increase interest in developing small cells architecture for wireless communication, providing backhaul to the basestations is a major challenge. This paper propose the use of Amplify-and-Forward (AF) full duplex (FD) relays in millimeter wave (mmWave) communication in wireless backhaul links between the cells. We are using hybrid (analog and digital) beamforming to overcome the propagation losses of outdoor mmWave environment. The proposed system performance was analyzed using channels with limited number of paths. Results show significant performance improvement for the full duplex links over half duplex links. The results also show how the antenna array size at the source and destination influences the system performance.

Millimeter waves is considered to be one of the solutions that will be used in the next generation communications to meet the increasing data demands due to the wide bandwidth provided. However, using these bands in the outdoors environment requires high directivity between the transmitter and the receiver to overcome the severe propagation losses. This paper presents the spectral efficiency analysis for the analog beamforming system as a solution to provide the required directivity. Under certain assumptions, an upper-bound and a closed form for the spectral efficiency is derived. The performance of three different search techniques is compared in the light of the proposed analysis. The simulation results confirm the derived analysis.

In this paper, we explore the multiple access capabilities of amplify and forward (AF) gateways employing zero forcing (ZF) beamforming techniques in a space division multiple access (SDMA) scenario. A random number of users are isolated from their destination, and the only mean to communicate with their destination(s) is through the AF gateway equipped with multiple antennas, and employing ZF beamforming technique. The channels experience both small and large-scale fading. New exact analytical expressions are derived for the overall spectral efficiency (SE) in the collaborative and non-collaborative scenarios, where in the first case ZF is applied at the sources and destinations, whereas in the latter case ZF is implemented at the gateway. The new results is used to investigate the impact of different system parameters into the overall efficiency of ZF gateways. The accuracy of the new results is confirmed through comparison with Monte Carlo simulations.

This paper investigates the issues of a satellite gateway employs a random Slotted-ALOHA protocol. The gateway is considered as wireless backhaul, and acts as a blind amplify and forward (AF) relay, to relaying the signal between the source and destination nodes. The source nodes are isolated, and the only way to communicate with their destination through the gateway. The wireless channels between the source, gateway, and destination experience two different channels fading, namely, Rayleigh and Nakagami-m fading channels. In this paper, we develop a new and more accurate mathematical analysis, which leads to derive a simple expressions of the overall spectral efficiency (SE). We study the effect of the interference, and the impact of the different system parameters on their efficiency, such as number of the users and interferences, and thermal noise at both the gateway and destinations. Numerical results reveal that, all the derived expressions are very tight, and are valid for evaluations of the SE in different types of fading channel. We confirm our new mathematical results through comparison with Monte Carlo simulations.

Distributed multiple-input multiple-output (D-MIMO) is a promising technique for next generation wireless networks, which offers a remarkable spectral efficiency gain over the conventional co-located MIMO (C-MIMO) systems. In contrast to C-MIMO, which can be regarded as a special case of D-MIMO, performance analysis of D-MIMO is a challenging problem. This is because radio channels between a user and the distributed radio ports (RPs) are characterized by non-identical path-loss and shadowing effects which render the classical analytical methods non-tractable. In this paper, we consider the uplink spectral efficiency of a single-cell distributed MIMO (D-MIMO) system with linear zero-forcing (ZF) receivers. Without taking shadow fading effects into account, new accurate expressions for the average spectral efficiency for D-MIMO and C-MIMO systems are given and compared. These expressions provide meaningful insights into the impact of SNR, RPs and user positions, and number of RPs antennas on the spectral efficiency of the system under practical environments. Finally, numerical results are validated by simulation to confirm our analysis.

We present a new accurate analysis of a multiple-input multiple-output (MIMO) system employing linear zero-forcing (ZF) receivers in a multi-cell environment. New exact expressions are derived for the spectral efficiency of the uplink channel taking into account both small and large-scale fading. In contrast to the previous performance analysis of multi-cell MIMO systems, we present an accurate model for the co-channel interference where the number of users in each cell is random. The new analytical results are validated by Monte-Carlo simulation and used to shed light into the effects of the model parameters such as random number of users and shadow fading on the uplink spectral efficiency.

This paper analyzes the performance of full-duplex relaying (FDR) with multiple-antenna amplify-and-forward (AF) relay. The system performance due to practical wireless transmission impairments of spatial fading correlation and imperfect channel state information (CSI) is investigated. To this end, new exact closed-form expressions for the outage probability are derived, where the case of arbitrary, exponential, and no correlations are considered. Meanwhile, for a better system performance insights, simpler outage probability lower-bounds are also included. At the relay, the loopback self-interference (LI) is mitigated by using receive zero-forcing (ZF) precoding scheme, then steering the signal to the destination by using the maximumratio transmission (MRT) technique. Numerical results sustained by Monte Carlo simulations show the exactness and tightness of the proposed exact closed-form and lower-bound expressions, respectively. In addition, it is seen that the outage probability performance of FD relaying outperforms that of HD relaying at low to medium signal-to-noise ratio (SNR). Furthermore, in the presence of channel estimation errors, an outage probability error floor is seen as SNR increases.

In this paper, we present a low-complexity version of the Antenna Subset Modulation (LC-ASM), to enhance the physical layer security. LC-ASM consists of a conventional phased-array transmitter followed by antennas with an on-off switching circuit. The proposed solution maintains the objective of scrambling the constellation points in both amplitude and phase in undesired directions, while preserving a clear constellation in the target direction. LC-ASM is different from the original ASM in the following ways: (1) LC-ASM is not restricted to the use of phase modulation, and can accept any modulation type including QAM, (2) it does not need to modulate the signal in the RF domain, where the conventional phasedarray transmitter circuits remain unchanged, (3) in the far-field, LC-ASM scrambles the signal constellation by randomly driving a subset of the transmitting antennas, (4) LC-ASM can easily integrated with the current infrastructure of phased-array transmitters, and (5) LC-ASM breaks up the correlation between the data rates and the switching speed. We analysed the LC-ASM performance and derived an exact expression of the bit error probability, and we derived the secrecy capacity in a closed form. The results show that LC-ASM is a simple and very efficient solution to improve the physical layer security of mm-wave communication.

In conventional space shift keying (SSK) and generalized SSK (GSSK), the symbols are transmitted only by the active antennas indices, while the inactive antennas remain unexploited; this limits the spectral efficiency. In order to combat this limitation, we propose a direct-code for SSK (DC-SSK) modulation technique. In DC-SSK, the transmitter is allowed to use 0,1,..., Ntantennas for each symbol, and groups of Ntbits are used to derive the transmitting antennas directly according to the bit value, active for `1' and inactive for `0'. DC-SSK improves the spectral efficiency by exploiting the indices of both the active and inactive antennas to convey the information. The analysis shows that the data rate of DC-SSK increases linearly with the number of transmitting antennas, while the data rate of conventional SSK increases as a base-2 logarithm. To keep the transmit side simple, we propose an on-off keying modulation, instead of generalized QAM. We analyze the performance of the proposed solution and validate the results by simulation. The results show that the DC-SSK is a promising solution for the next generation of wireless communications, as a response to the massive demand for increased data rates.

In this paper, secrecy outage probability is analyzed in a cooperative network for an independent but non-identically distributed (i.n.i.d) Rayleigh fading channel. By using multi-trusted decode and forward relays, the model assumes direct links between a sender (Alice) and receiver nodes (Bob and an eavesdropper). The protocol employed herein selects the best relay with the highest signal-to-noise ratio (SNR) in relation to the destination (Bob). The eavesdropper's channel state information (CSI) is neither available to the sender nor to the best relay, while maximum ratio combining (MRC) is employed at Bob and the eavesdropper. Finally, the theoretical analysis is validated through simulation, and the results show that performance is enhanced with an increasing number of relays in the event of a direct link between the sender and the receiver's terminals.

In this paper, power allocation over time-varying multiple-access interference channels is studied. Particularly, a stochastic network sum-rate maximizing power allocation problem is formulated, capturing the random nature of communication channels. Typically, a centralized controller must have perfect knowledge of global instantaneous channel state information (CSI) for dynamic optimal power allocation; however, this may not be possible, due to the computational complexity and communication overheads/delays involved. Based on the second-order statistics of the CSI, the stochastic problem formulation is transformed into an optimal deterministic representation in terms of ergodic capacity, while ensuring satisfactory quality of service via target outage probability. However, such deterministic reformulation happens to be non-convex and thus is computationally expensive. In turn, a sub-optimal reformulation is derived and solved via an iterative low-complexity algorithm. Simulation results demonstrate that the proposed deterministic sub-optimal power allocation reformulation coincides with its optimal deterministic counterpart, with the proposed algorithm converging in a finite number of iterations.

In this paper, we consider a wireless-powered communication networks (WPCNs), in which a multi-antenna two-way amplify-and-forward (AF) relay transfers power to multipair of single antenna users. A harvest-then-transmit protocol is adopted here, where the relay first broadcasts energy signals to all users during a power transfer phase. Multiple pairs of users, then use the harvested energy to exchange information signals through the relay over two phases, up-link (UL) and down-link (DL) phases. In the former phase, all the users simultaneously transmit their information signals to the relay, then in the latter phase the relay amplifies and forwards the received signals to their intended users. In addition, in order to mitigate the interference, zero-forcing reception and transmission is applied at the relay. In light of this, analytical expressions for the ergodic spectral and energy efficiencies are derived and Monte Carlo simulations are provided throughout to validate our analysis. The impacts of some important system parameters such as energy harvesting (EH) time, number of user-pairs and relay antennas, on the system performance are investigated. The results show that, good selection of the EH time is the key to achieve optimal system performance and increasing the number of relay antennas can reduce this factor.

In this study, power allocation over time‐varying multi‐user multi‐relay amplify‐and‐forward networks is studied. Specifically, stochastic network sum‐rate, max–min rate power allocation and total power minimisation problems are formulated. However, solving such stochastic problems relies on perfect global instantaneous channel state information (CSI), and thus entails complex computations and excessive communication overheads. To circumvent these issues, second‐order statistics of the CSI (i.e. partial CSI) are utilised to transform the stochastic formulations into deterministic optimisation problems in terms of ergodic capacity while satisfying quality‐of‐service constraints via target outage probability. The obtained optimal deterministic problems are non‐convex and thus are computationally prohibitive. However, at high enough signal‐to‐noise ratio, such problems can be transformed into asymptotically convex ones, and thus solved efficiently. Simulation results illustrate that the proposed approximate deterministic power allocation reformulations closely agree with their optimal exact deterministic and dynamic counterparts.

This paper analyzes the performance of energy-constrained dual-hop amplify-and-forward relaying systems with multi-antenna nodes in the presence of multiple co-channel interferers at the destination. To maximize the overall signal-to-interference-plus-noise ratio, as well as the harvested energy so as to mitigate the severe effects of fading and enable long-distance wireless power transfer, hop-by-hop information and energy beamforming is proposed where the transmitted signal is steered along the strongest eigenmode of each hop. The wirelessly powered relay scavenges energy from the source information radio frequency signal through energy beamforming, where both the time-switching receiver and power-splitting receiver are considered, and then uses the harvested energy to forward the source message to the destination. To this end, tight lower and upper bound expressions for the outage probability and ergodic capacity are presented in closed form. These are employed to investigate the throughput of the delay-constrained and delay-tolerant transmission modes. In addition, the asymptotic high signal-to-noise ratio outage probability and ergodic capacity approximations are derived, where the achievable diversity order is also presented. Numerical results sustained by Monte Carlo simulations show the tightness of the proposed analytical expressions. The impact of various parameters, such as energy harvesting time, power-splitting ratio, source transmit power, and the number of antennas on the system throughput, is also considered.

In this paper, we propose a new wireless communication transmission architecture called switched phased-array (SPA), to enhance physical layer security. SPA works as a platform for three different transmission techniques: 1) conventional phased-array transmission; 2) antenna subset transmission (AST) technique; and 3) silent antenna hopping (SAH) transmission technique. SPA consists of a conventional phased-array blacktransmitter followed by antennas with an on-off switching circuit. The proposed solution maintains the objective of scrambling the constellation points in both amplitude and phase in undesired directions, while preserving a clear constellation in the target direction. The proposed solution-SPA-is different from previously used methods in the following ways: 1) SPA is not restricted to the use of phase modulation, and can accept any modulation type including QAM; 2) it does not need to modulate the signal in the radio frequency (RF) domain, where the conventional phased-array transmitter circuits remain unchanged; 3) in the far field, SPA scrambles the signal constellation by randomly switching-off some of the transmitting antennas (AST), or only one of them (SAH); 4) SPA can be easily integrated with the current infrastructure of phased-array transmitters; 5) SPA breaks up the correlation between the data rates and the switching speed; and 6) SPA performs a variety of DM transmission techniques. We present the potential transmission techniques including PA, AST, and SAH. We analyze the performance for all cases and derive an exact expression of the bit error probability, and also we analyze the secrecy capacity. The results show that SPA, and its variants AST and SAH, are simple and very efficient solutions to improve the physical layer security of mm-wave communication.

In this paper, we investigate the achievable energy efficiency of cognitive radio networks where two main modes are of interest, namely, spectrum sharing (known as underlay paradigm) and spectrum sensing (or interweave paradigm). In order to improve the energy efficiency, we formulate a new multiobjective optimization problem that jointly maximizes the ergodic capacity and minimizes the average transmission power of the secondary user network while limiting the average interference power imposed on the primary user receiver. The multiobjective optimization will be solved by first transferring it into a single objective problem (SOP), namely, a power minimization problem, by using the ε-constraint method. The formulated SOP will be solved using two different methods. Specifically, the minimum power allocation at the secondary transmitter in a spectrum sharing fading environment are obtained using the iterative search-based solution and augmented Lagrangian approach for single and multiple secondary links, respectively. The significance of having extra side information and also imperfect side information of cross channels at the secondary transmitter are investigated. The minimum power allocations under perfect and imperfect sensing schemes in interweave cognitive radio networks are also found. Our numerical results provide guidelines for the design of future cognitive radio networks.

In this paper, we consider a wireless-powered communication network in which a multiple-antenna two-way AF relay transfers power to multi-pair of single antenna users. A harvest-then-transmit protocol is adopted where the relay first broadcasts wireless power to all the users during a power transfer phase. Multiple pairs of users then use the harvested energy to exchange information through the relay over two phases: up-link and down-link. In the up-link phase, all the users transmit their independent signals to the relay, whereas in the down-link phase, the relay amplifies and forwards the received signals to the intended users. In order to mitigate the interference, zero-forcing reception and transmission is applied at the relay. To characterize system performance, we consider ergodic spectral and energy efficiencies in three different cases based on the knowledge of the channel state information (CSI) at the relay in the power transfer phase, namely: 1) unknown CSI; 2) partially known CSI; and 3) perfectly known CSI. In light of this, new analytical expressions for the ergodic spectral and energy efficiencies are derived for the three cases and Monte Carlo simulations are provided throughout to validate our analysis. The impacts of some important system parameters, such as energy harvesting time, energy harvesting efficiency, number of user-pairs, and relay antennas, on the adopted performance metrics are investigated.

In this paper, we analyze the secrecy capacity of a half-duplex energy harvesting (EH)-based multi-antenna amplify-and-forward relay network in the presence of a passive eavesdropper. During the first phase, while the source is in the transmission mode, the legitimate destination transmits an auxiliary artificial noise (AN) signal which has two distinct purposes: 1) to transfer power to the relay and 2) to improve system security. Since the AN is known at the legitimate destination, it is easily cancelled at the intended destination, which is not the case at the eavesdropper. In this respect, we derive new exact analytical expressions for the ergodic secrecy capacity for various well-known EH relaying protocols, namely, time switching relaying (TSR), power splitting relaying (PSR), and ideal relaying receiver (IRR). Monte Carlo simulations are also provided throughout our investigations to validate the analysis. The impacts of some important system parameters, such as EH time, power splitting ratio, relay location, AN power, EH efficiency, and the number of relay antennas, on the system performance are investigated. The results reveal that the PSR protocol generally outperforms the TSR approach in terms of the secrecy capacity.

This paper presents a stochastic geometry-based framework for the design and analysis of downlink multi-user multiple-input multiple-output (MIMO) heterogeneous cellular networks with linear zero-forcing transmit precoding and receive combining, assuming Rayleigh fading channels and perfect channel state information. The generalized tiers of base stations may differ in terms of their Poisson point process spatial density, number of transmit antennas, transmit power, artificial-biasing weight, and number of user equipments served per resource block. The spectral efficiency of a typical user equipped with multiple receive antennas is characterized using a non-direct moment-generating-function-based methodology with closed-form expressions of the useful received signal and aggregate network interference statistics systematically derived. In addition, the area spectral efficiency is formulated under different space-division multiple-access and single-user beamforming transmission schemes. We examine the impact of different cellular network deployments, propagation conditions, antenna configurations, and MIMO setups on the achievable performance through theoretical and simulation studies. Based on the state-of-the-art system parameters, the results highlight the inherent limitations of baseline single-input single-output transmission and conventional sparse macro-cell deployment, as well as the promising potential of multi-antenna communications and small-cell solution in interference-limited cellular environments.

This paper is concerned with the performance of a gateway connecting a group of independent users to their destinations and employ the random slotted- Aloha type protocol. The users are isolated from their destinations and the only way to communicate with their destinations is through the common gateway which acts as a blind amplify and forward relay. Users are randomly distributed around the gateway and experience a Rayleigh or Nakagami-m fading channels. This paper develops a new accurate models for the multiple access interference at both the gateway and the destinations taking into account, in addition to the random number of the active users and their locations, the effects of fading and thermal noise at both the relay and the destinations. This leads to the derivation of new analytic expressions for the overall spectral efficiency which can be used to estimate the throughput of the aloha based gateways in Rayleigh and Nakagami-m fading channels and to study the impact of the different system parameters into their efficiency. The accuracy of the new mathematical results is confirmed by Monte Carlo simulation.

In this paper, with the aid of new analytical method, we present a new closed-form expression for the ergodic capacity of full-duplex relaying (FDR) systems, with multiple antenna amplify-and-forward (AF) cooperative networks and imperfect channel state information (CSI). At the relay, the loopback self-interfernce (LI) is mitigated by using receive zero-forcing (ZF) precoding scheme, then steering the signal to the destination by using the maximum-ratio transmission (MRT) technique. To facilitate comparison, a closed-form expression for the ergodic capacity of half-duplex relaying (HDR) systems with multiple antenna AF cooperative networks is also addressed, when maximum-ratio combining (MRC)/MRT precoding schemes are performed at the relay input/output, respectively. Therefore, since perfect CSI is not available in practice, this paper investigates the impact of channel estimation errors on the performance of receive ZF/MRT and MRC/MRT schemes. These expressions are exact in the case of perfect CSI and form a very tight indistinguishable lower-bound in the case of imperfect CSI. Numerical results sustained by Monte-Carlo simulations show the exactness of the proposed analytical expressions in perfect CSI and the tightness of the lower-bounds in imperfect CSI. In addition, it is seen here that the FDR AF cooperative systems outperforms the HDR AF cooperative systems in terms of capacity. Furthermore, in contrast to perfect CSI, in the presence of imperfect CSI, an ergodic capacity ceiling is seen as SNR increases. Besides, it is seen that the ergodic capacity degradation due to imperfect CSI is higher in the FDR case because of the extra LI estimation errors.

We propose a new wireless communication transmission technique called Silent Antenna Hopping (SAH) transmission technique, to enhance physical layer security. SAH consists of a conventional phased-array transmitter followed by antennas with an on-off switching circuit. The proposed solution maintains the objective of scrambling the constellation points in both amplitude and phase in undesired directions, while preserving a clear constellation in the target direction. SAH is different from the previously- used work in the following ways: (1) SAH is not restricted to the use of phase modulation, and can accept any modulation type including QAM, (2) it does not need to modulate the signal in the RF domain, where the conventional phased-array transmitter circuits remain unchanged, (3) in the far-field, SAH scrambles the signal constellation by randomly switching-off only one of the transmitting antennas, (4) SAH can easily integrated with the current infrastructure of phased-array transmitters, and (5) SAH breaks up the correlation between the data rates and the switching speed. We analysed the SAH performance and derived an exact expression of the bit error probability, and we derived the secrecy capacity in a closed form. The results show that SAH is a simple and very efficient solution to improve the physical layer security of mm-wave communication.

This paper proposes an adaptive scheduling strategy to improve the energy efficiency of massive MIMO. The proposed technique combines a novel adaptive discontinuous transmission (ADTx) and antenna optimization that can optimize the number of active antennas and transmission period such that data can be delivered to users with the minimum power. The proposed ADTx utilizes a DTx principle and adaptive precoding technique selection. On the other hand, antennas optimization is used to relax the number of active antennas once the required period has been calculated. Although massive MIMO is initially designed to utilize the multiplexing users found in dense users scenario, this paper discusses the impact of the proposed technique to low density scenarios, in particular suburban scenario, because major parts of cellular coverage are low density. It will be shown that the proposed scheme provides significant energy efficiency (EE) and QoS improvement that can support green cellular network.

This paper addresses energy efficiency (EE) of large scale antenna systems (LSAS) or massive MIMO based cellular networks. We propose a joint technique that combines a novel successive discontinuous transmission (SDTx) scheme with antenna array optimization (AAO). The SDTx utilizes information regarding the users' requirements and properties to deliver data efficiently and without compromising the users' service. On the other hand, AAO further reduces power consumption through minimizing the number of active antenna elements. Users requirements include bit rate and latency requirement while the users properties include pathloss between users and macro base station (MBS) and users' movement. It will be shown that, relative to conventional LSAS, the proposed scheduling significantly improves the EE of LSAS network for various network load under practical users' requirement in dense urban environment making it a potential candidate for green cellular networks.

In this paper, we present accurate performance analysis of amplify-and-forward (AF) relaying systems by introducing the effect of multipath flat Rayleigh fading channels on the additive white Gaussian noise (AWGN). The second hop channel is seen by the transmitted signal as flat fading when the signal bandwidth is less than the coherence bandwidth. However, the second hop channel is frequency selective fading to the AWGN noise since the AWGN bandwidth is much higher than the coherence bandwidth of the channel. Therefore, taking into account accurate statistical model for the received AWGN noise, a new exact expressions for the moment generating function (MGF) and the complementary error function of the end-to-end signal-to-noise ratio (SNR) are derived, which led to a unified precise expressions for the average bit error rate (BER) analysis of multilevel quadrature amplitude modulation (MQAM) signaling and the ergodic capacity evaluations of AF relaying systems over multipath flat fading channels. Numerical results reveals that the AWGN noise is underestimated since there is a huge degradation in BER analysis when the noise frequency selectivity is taken into account. Further, it is also seen that the noise selectivity has a little effect on the ergodic capacity of AF relaying systems.

In this paper, we analyze the secrecy capacity of a multiple-input multiple-out (MIMO) half duplex amplify-and-forward (AF) relay network in the presence of one passive eavesdropper. Zero forcing (ZF) processing is utilized at various locations to improve the capacity when the eavesdropper is equipped with a single antenna. The impact of the proposed ZF-based technique on the secrecy capacity is investigated for three different scenarios depending on where the ZF is applied, namely, 1) ZF at the relay and destination, 2) ZF at the source and relay, 3) ZF at the relay. For these configurations, analytical expressions for the ergodic-secrecy capacity are derived, and simulation results are provided throughout the paper to validate our analysis. Results reveal that reducing the number of source and/or destination antennas will enhance the ergodic-secrecy capacity and the significance of this enhancement is dependent on the particular scenario adopted. Furthermore, it will be shown that, in general, secrecy capacity improves with increasing the relay power.

We provide new results on the signal-to-interference-plus-noise ratio (SINR) statistics considering a Poisson point process (PPP)-based heterogeneous interference field. In particular, closed-form expressions for the density functions of the reciprocal of the aggregate interference and signal-to-interference ratio (SIR) are developed. We prove that the effect of PPP-based interference on useful transmission is mathematically equivalent to the severe impact from a one-sided Gaussian fading channel. As an application example, the proposed approach is used to design and analyze the average SINR performance of a typical user in heterogeneous cellular networks (HetNets).

Heterogeneous network (HetNet) deployment is considered a de facto solution for meeting the ever increasing mobile traffic demand. However, excessive power usage in such networks is a critical issue, particularly for the mobile operators. Characterizing the fundamental energy efficiency (EE) performance of HetNets is therefore important for the design of green wireless systems. In this paper, we address the EE optimization problem for downlink two-tier HetNets comprised of a single macro-cell and multiple pico-cells. Considering a heterogeneous real-time and non-real-time traffic, transmit beamforming design and power allocation policies are jointly considered in order to optimize the system energy efficiency. The EE resource allocation problem under consideration is a mixed combinatorial and non-convex optimization problem, which is extremely difficult to solve. In order to reduce the computational complexity, we decompose the original problem with multiple inequality constraints into multiple optimization problems with single inequality constraint. For the latter problem, a two-layer resource allocation algorithm is proposed based on the quasiconcavity property of EE. Simulation results confirm the theoretical findings and demonstrate that the proposed resource allocation algorithm can efficiently approach the optimal EE.

The cooperative diversity technique, combined with distributed space-time coding (DSTC), can efficiently improve the secrecy capacity and transmission reliability of wireless communication systems. In this paper, a multicast cooperative relaying system, based on distributed Alamouti space-time coding, is proposed, as a method of preventing an eavesdropper from accessing source data. A maximum likelihood (ML) decoder at the destination was chosen to receive the data, however, the ML decoder was unable to receive data at the eavesdropper. An analysis was carried out to synchronize DSTC, a Rayleigh fading channel, a Rician fading channel, and a combination thereof. It was assumed that channel state information (CSI) for the relay-destination link was known, although this was unknown for the relay-eavesdropper link. The theoretical results for the secrecy outage probability for the proposed scheme are then compared with existing results.

There is a huge demand for data traffic caused by increased usage of data-hungry applications on smart mobile devices. This has resulted into cellular network expansion and upgrade that have increased energy costs and generated environmental concerns. Distributed antenna systems (DAS) are applied to enhance the coverage of the cell via geographically distributed antennas elements (DAEs) which are connected to the base station that is located at the centre of the cell. In this paper, DAS is proposed as a network solution to fulfill increasing capacity demands while addressing the energy efficiency (EE) and environmental concerns associated with cellular network operation. Maximum Ratio Transmission (MRT) and Fractional Frequency Reuse (FFR) are applied to calculate the downlink ergodic spectral efficiency (SE), EE and energy consumption ratio (ECR). Nakagami-m fading and log-normal shadowing are considered. Our results demonstrate that DAS using MRT and FFR increases the spectral and energy efficiency of the network compared to a basic cellular network system.

Femtocell technology is widely known for its ability to improve cellular services while reducing the capital and operation expenditure of cellular providers. However, this can lead to more interference and accessibility issues. There are three types of femtocell access schemes currently, which are open, closed and hybrid access. While open access improves the overall network performance, closed access is a much more preferred by the end-user since it guarantees access to the femtocell owner. For this reason, hybrid access is a compromise which releases the femtocell access to the visitor when there is surplus resource left by the owner. This paper proposes a comprehensive method to solve the femtocell access issue by designing a joint multilevel priority scheduling and femtocell access policy based on a Matrix of Conflict RRM. It will be shown through computer simulation that the proposed scheduling and access policy provide network flexibility, for the femtocell owner and cellular provider, which can be utilized to achieve more benefits for both.

Spectral efficiency (SE) and energy efficiency (EE) are the main performance metrics for designing green radio (GR) networks; however they are conflicting criteria. Consequently, instead of separately focusing on either SE or EE, characterizing the fundamental trade-off between EE and SE of MIMO broadcast channels (BC) is significant for the development of green wireless communications. This paper investigates the fundamental EE-SE relationship in a multiple-input multiple-output (MIMO) broadcast channel, which is important for facilitating a desirable balance between energy savings and spectrum utilization. Through our investigation, we prove that EE-SE relationship for MIMO-BC is a quasiconcave function. Furthermore, EE is proved to be either strictly decreasing with SE or first strictly increasing and then strictly decreasing with SE. Based on these findings, we propose a two-layer resource allocation algorithm in order to tackle the comprehensive EE-SE trade-offs problem. The key of the proposed method lies in the inner-layer algorithm which is solved by applying the principle of multiple access channel - broadcast channel (MAC-BC) duality. The algorithm in its dual form is solved using sub-gradient method and bisection searching scheme. Simulation results confirm the theoretical findings and demonstrate that the proposed resource allocation algorithm can efficiently approach the optimal EE-SE trade-off for MIMO-BC.

This paper focuses on the spectral efficiency (SE) problem in amplify-and-forward (AF) and decode-and-forward (DF) relaying cooperative systems with full-duplex (FD) operation. Previous works on FD relaying systems have focused on outage performance or relay selection schemes wherein for the max-min relay selection scheme residual loop-interference has been neglected. Therefore, the motivation of this paper is to figure out which one of the relaying methods, AF or DF, is spectrally efficient in terms of the single relay selection scheme. For this, we apply time-based distributed method for max-min relay selection scheme by considering the residual loop interferences. Moreover, to see the impact of overhead, we consider a non-ideal FD relaying cooperative system. Numerical and simulation results are provided to illustrate the effect of collisions on the SE and a comparison of SE between two relaying methods for the distributed method.

In this paper, the problem of signal-to-interference plus noise ratio estimation over flat fading channels in non-Gaussian noise is addressed. Most previously published estimators assume the additive noise to be Gaussian. These estimation algorithms performs significantly worse when the additive noise is non-Gaussian. The additive non-Gaussian noise is modeled by a mixture of Gaussians distribution. Both data aided (DA) and non data aided (NDA) estimators are studied. The second and forth order moment based (M2M4) estimator is derived. Besides, the expectation maximization (EM) algorithm is proposed to iteratively estimate the maximum likelihood (ML) signal to interference plus noise ratio (SINR) estimate for both DA and NDA cases. The performance of the proposed estimators are compared in terms of their mean square error (MSE). Simulation results show remarkable performance improvements of the DA and NDA EM based ML SINR estimator over the M2M4moment based estimator. Besides, it reveals the degradation in accuracy due to the impulsive noise components over Additive white Gaussian noise (AWGN).

This paper presents new framework for spectral efficiency expression, that include unified interference analysis for two-hop fixed-gain amplify-and-forward relay systems. Utilizing Jensen inequality, the novel spectral efficiency expression enable us to accurately model various interference distributions at the relay and at the destination, together with the effect of noise, in a single unified equation. The framework enable tractable analytical interference analyses, that either based on the non-random interferers location or based on the random distribution of interferers distributed according to Poisson point process; by using moment generating function of the interferers. This method simplify the analysis of AF relay system in upcoming cellular systems and in heterogeneous communication systems. Simulations and analytical results are provided.

We present a new unified model for the design and analysis of load-aware downlink heterogeneous networks (HetNets) where interferers are inherently spatially-correlated. A closed-form expression for the aggregate network interference statistics generated by correlated load-proportional tiers of base stations (BSs) over Nakagami-m fading interfering channels is developed. This approach allows for relaxation of several major limitations in the existing state-of-the-art models, in particular the always-on-BSs, uncorrelated interferers, and Rayleigh fading with no shadowing assumptions. The validity and advantages of the proposed load-aware framework over the heavily-adopted fully-loaded model and the more recent interference-thinning-based approximation are confirmed via extensive Monte-Carlo (MC) simulations. The results reveal several important trends and design guidelines for the practical deployment of HetNets.

Heterogeneous network (HetNet) deployment is considered a de facto solution for meeting the ever increasing mobile traffic demand. However, excessive power usage in such networks is a critical issue, particularly for mobile operators. Characterizing the fundamental energy efficiency (EE) performance of HetNets is therefore important for the design of green wireless systems. In this paper, we address the EE optimization problem for downlink two-tier HetNets comprised of a single macro-cell and multiple pico-cells. Considering a heterogeneous real-time and non-real-time traffic, transmit beamforming design and power allocation policies are jointly considered in order to optimize the system energy efficiency. The EE resource allocation problem under consideration is a mixed combinatorial and non-convex optimization problem, which is extremely difficult to solve. In order to reduce the computational complexity, we decompose the original problem with multiple inequality constraints into multiple optimization problems with single inequality constraint. For the latter problem, a two-layer resource allocation algorithm is proposed based on the quasiconcavity property of EE. Simulation results confirm the theoretical findings and demonstrate that the proposed resource allocation algorithm can efficiently approach the optimal EE.

Orthogonal frequency division multiplexing (OFDM) over wireless channels is sensitive to carrier frequency offset (CFO), which destroys orthogonality amongst sub-carriers, giving rise to inter-carrier interference (ICI). Different techniques are available for estimating and compensating for the CFO at the receiver. However, in practice, a residual CFO remains at the receiver after CFO estimation, where the estimation accuracy depends primarily on the fractions of time and power used by the estimator. In this paper, we propose to measure the efficiency of OFDM systems with CFO estimation errors in terms of the spectral efficiency, which accounts for both, the degradation in signal-to-interference plus noise ratio (SINR) due to the residual CFO, and the penalty of the extra power and spectral resources allocated to achieve the desired CFO estimation accuracy. New accurate expressions are derived for the spectral efficiency of wireless OFDM systems in the presence of residual CFO and frequency-selective multipath fading channel. These are used to compare between two common CFO estimation methods in wireless OFDM systems, namely, the cyclic prefix based and the training symbols based CFO estimation techniques for fixed and variable pilot power. These results are further extended to include OFDM systems with transmit diversity techniques. In addition, the impact of imperfect channel estimation on the overall spectral efficiency is also included. Numerical results reveal that the cyclic prefix based CFO technique is more efficient than the training symbols based CFO technique when perfect channel state information (CSI) is known blindly at the receiver. Furthermore, fixed pilot power results in a spectral efficiency ceiling as SNR increases, whereas spectral efficiency increases with SNR without bound in the equal pilot and signal powers case.

Characterizing the fundamental energy efficiency (EE) performance of multiple-input–multiple-output interfering broadcast channels (MIMO-IFBC) is important for the design of green wireless system. In this paper, we propose a new network architecture proposition based on EE maximization for Multi-Cell MIMO-IFBC within the context of interference alignment (IA). Particularly, EE is maximized subject to maximum power and minimum throughput constraints. We propose two schemes to optimize EE for different signal-to-noise ratio (SNR) regions. For high-SNR operating regions, we employ a grouping-based IA scheme to jointly cancel intra- and inter-cell interferences and thus transform the MIMO-IFBC to a single-cell MIMO scenario. A gradient-based power adaptation scheme is proposed based on water-filling power adaptation and singular value decomposition to maximize EE for each cell. For moderate SNR cases, we propose an approach using dirty paper coding (DPC) with the principle of multiple access channel and broadcast channel duality to perform IA while maximizing EE in each cell. The algorithm in its dual form is solved using a subgradient method and a bisection searching scheme. Simulation results demonstrate the superior performance of the proposed schemes over several existing approaches. It also shows that interference-nulling-based IA approaches outperform hybrid DPC-IA approach in high-SNR region, and the opposite occurs in low-SNR region.

We derive new results for the higher order moments of signal-to-interference-plus-noise ratio (SINR) in the presence of an arbitrary Poisson point process (PPP)-based heterogeneous interference field. The analysis leverages on a moment-generating-function (MGF) methodology, which only requires the statistics of intended signal and aggregate interference, thus eliminating the need for the exact distribution of SINR. We extend the existing results on interference statistics by deriving a generalized closed-form expression of the interference MGF considering Nakagami-m fading channels with exclusion region. In certain special cases, explicit expressions for the averages of different functions of SINR are found, which also lead to closed-form solutions for the probability distributions of aggregate interference reciprocal and signal-to-interference ratio. We prove that in such cases the effect of total PPP-based interference power on useful transmission is mathematically equivalent to the severe fluctuations from a one-sided Gaussian fading channel. As an application example, the proposed methodology is used together with stochastic geometry theory to characterize the average SINR and rate in heterogeneous cellular networks. The validity of our analytical derivations is confirmed via Monte Carlo simulations for various system settings. We show that with cellular network densification there exists a tradeoff between the average SINR and rate performance.

In this paper, we propose several power allocation strategies in cognitive radio network in terms of spectrum sharing. In spectrum sharing, secondary users can simultaneously transmit with the primary users but must strictly control their transmit power to avoid harmful interference to primary users. In this paper, we first maximize the ergodic capacity of a secondary link with full channel side information at the secondary transmitter. Then, different levels of channel side information are separately reduced to discuss the significance of having each level at the secondary transmitter. In most cases, we derived closed-form results for evaluating the maximum capacity over Rayleigh fading channels.

Characterizing the fundamental metric of energy efficiency (EE) of multiple-input multiple-output interfering broadcast channels (MIMO-IFBC) is important for the development of green wireless communications. In this paper, we address the EE optimization problem for multi-cell MIMO-IFBC within the context of interference alignment (IA). We employ grouping-based IA scheme to cancel both inter-cell interference (ICI) and inter-user inference (IUI), and thus transform the MIMO-IFBC to a single cell single user MIMO scenario. A gradient-based optimal power adaptation scheme is proposed which utilizes water-filling approach and singular value decomposition (SVD) to maximize EE for each cell. Simulation results confirm the theoretical findings and demonstrate that the proposed resource allocation algorithm can efficiently approach the optimal EE.

This paper examines the efficiency of employing energy detectors in a multi-user network, whose nodes are spatially distributed in a geographic area and employ a CSMA MAC protocol to access the channel. It has been observed that explicit expressions for the analysis of imperfect physical carrier-sensing MAC protocols using energy detection are non-existent in the literature. We, therefore, present simple expressions to achieve this for two protocols. Firstly, the mandatory physical carrier-sensing protocol is examined under the distributed coordination function of the IEEE 802.11 standard. Thereafter, a protocol which includes an optional virtual carrier-sensing scheme is examined alongside the physical carrier-sensing protocol. In this manner, the effect of CSMA inhibition zones arising due to neighbour node deactivation by the protocol is investigated. System parameters such as the energy detector detection threshold, the node density and the radius of inhibition are also studied and the analytical expressions are validated with Monte Carlo simulations.

The single relay selection (SRS) scheme in two-way relay cooperative systems has been focus of attention. This is because it offers higher spectral efficiency (SE) compared to multi-relay scheme and one-way relay cooperative systems. The SRS problem for two-way relays is not much studied in compare to one-way relay networks, and only few researches have been carried out. In all proposed problems in SRS scheme, researchers have ignored collisions in SRS scheme, and only considered an ideal system. In this paper, we investigate SE of the SRS based on distributed method which has not adequately addressed for two-way relay. Moreover, we investigate the effects of collision on SE, by considering an amplifier and forward network in a two-way cooperative system. Our numerical and simulation results show that in a small two-way relay system, the time selection period is the main factor in the system performance. However, in a large system, the probability of collision is the main consideration in designing a two-way relay system with high spectral efficiency.

Most of the prior researches in the field of relay selection techniques under security constraints for cooperative networks have only concentrated on single destination, although the factual communication environment comprehends multiple transmitters and receivers. This paper proposes relay selection for multi-destinations in cooperative networks. The study is implemented under a security constraint whereby an eavesdropper tries to eavesdrop on information sent from the sender. Hence, we investigate an optimal relay selection technique, in order to improve the level of security in the network by securing information sent to multi-destinations and thereby confusing the eavesdropper. The performance of the proposed system scheme is analysed using average secrecy capacity and outage probability, which are confirmed by numerical results based on simulations.

This paper investigates the secrecy outage probability of multicast cooperative relay networking in the presence of multi-destination and multi-eavesdropper nodes. The study is carried out in a multicast relay communication scenario whereby multi-eavesdropper nodes attempt to overhear the source message. Most of the previous studies in the field of cooperative communications and relay selection have considered the presence of either a single eavesdropper or a single destination environment. However, in the actual multicast communication scenario, multi-destination and multi-eavesdropper are presented. We therefore consider an optimal relay selection scheme in order to increase secrecy capacity for multi-destinations and to decrease it for eavesdroppers. The performance of the system is analysed using secrecy outage probability in Rayleigh and Rician fading scenarios, and the results are confirmed through Monte Carlo simulations. The proposed model is compared with other cooperative communication scenarios.

Femtocells are capable of achieving high capacity and improving indoor coverage due to a shorter distance between the transmitter and receiver, while fractional frequency reuse (FFR) has been proposed to improve spectral efficiency in emerging OFDMA networks. Due to spectrum limitations, FFR macrocell and femtocells are likely to share the same licensed spectrum, thereby inadvertently creating a possible dead-spot problem due to huge two-tier co-channel interferences. Using outage probability analysis, we derive the femtocell exclusion region (FER) or the minimum distance required for the co-channel femtocell to be able to reuse the same channels as the FFR networks. We show that a minimum of one FER could exist in FFR and at different combination of channel parameters and power ratio, two FER could exist; one in the cell-centre region and the other in the cell-edge region. A new static femtocell resource allocation strategy to improve the system performance is proposed.

Fractional frequency reuse (FFR) and soft frequency reuse (SFR) are efficient interference avoidance techniques for emerging OFDMA cellular networks in improving system performance by regularly reusing the frequencies. In this paper, we evaluate the energy efficiency (EE) in bits/J and EE per channel per cell in bits/J/Hz/cell for both the static FFR and SFR systems, in Nakagami-m fading and path-loss. In addition, we analyze the effect of fixed and variable cell-edge power amplification factor, α, on the FFR and SFR systems EE, the area spectral efficiency and the capacity. Our simulation and analytical results show that the SFR EE is higher than the FFR EE at low and medium α, whereas at very high α, the opposite is true. The observation is valid in fully-loaded cells, however, in partially-loaded cells, even at high α, SFR EE outperforms FFR EE.

In this study we analyze the performance of a class of detectors for deterministic signals with unknown amplitudes. We derive the test statistic and evaluate the performance in AWGN and some fading channels. The results help to give a better insight into the effect of number of recieved samples for the detector and its general performance. We compare our results to the classic energy detector and validate with Monte Carlo simulations in both cases.

The degradation to the performance of detectors due to noise and interference uncertainty has already been investigated and brought to the fore in earlier publications. This study seeks to compare the performance of two types of detectors in the presence of multiple interference. The main focus is to present alternate expressions for the false-alarm and detection probabilities of an energy detector and matched filter detector in a form which presents the random SNR or SINR only in the exponent. This greatly facilitates computing the average of the random variables as a moment generating function (MGF). In general, the results can serve as a guideline in designing detectors in the presence of multiple interferers.

Fractional frequency reuse (FFR) and soft frequency reuse (SFR) systems are an efficient cellular interference management technique to reduce inter-cell interference in multi-cell OFDMA networks. In this paper, a new and unified analytical framework for performance evaluation for both systems over a composite fading environment is presented. Explicit expressions are obtained for the area spectral efficiency (ASE) with both FFR and SFR, under fully loaded and partially loaded systems for downlink and uplink, and in generalized frequency reuse factor. The presented numerical result provides useful system design guidelines between the two systems. It is demonstrated that SFR outperforms FFR in a partially loaded scenario while the opposite is true for fully loaded system. The mathematical model is then extended to include the analysis of elastic data traffic in FFR system.

We develop a unified framework for the performance analysis of arbitrary-loaded downlink heterogeneous networks (HetNets) in which interfering sources are inherently spatially-correlated. Considering a randomly-deployed multi-tier cellular network comprised of a diverse set of large-and small-cells, we incorporate the notion of load-awareness and spatial-correlations in characterizing the activities of base stations (BSs) using binary decision variables. A stochastic geometry-based approach is accordingly employed to systematically develop a bounded expression of ergodic rate with different cellular association and load-balancing strategies. Employing the proposed unified framework hence allows for relaxation of several major limitations in the existing state-of-the-art models, in particular the always-transmitting-BSs, uncorrelated interferers, and Rayleigh fading assumptions. We elaborate on the usefulness of adopting this methodology by providing detailed analysis of the aggregate network interference generated by interdependent load-proportional sources over Nakagami-m fading interfering channels. The analytical formulations are validated through Monte-Carlo (MC) simulations for various scenarios and system settings of interest. We observe that the heavily-adopted fully-loaded model as well as the more recent interference-thinning-based approximations are significantly limited in capturing the actual performance curve. The proposed bounded load-aware model and MC trials reveal several important trends and design guidelines for the practical deployment of HetNets.

Spectral efficiency (SE) and energy efficiency (EE) are the main metrics for designing wireless networks. Rather than focusing on either SE or EE separately, recent works have focused on the relationship between EE and SE and provided good insight into the joint EE-SE tradeoff. However, such works have assumed that the bandwidth was fully occupied regardless of the transmission requirements and therefore are only valid for this type of scenario. In this paper, we propose a new paradigm for EE-SE tradeoff, namely the resource efficiency (RE) for orthogonal frequency division multiple access (OFDMA) cellular network in which we take into consideration different transmission-bandwidth requirements. We analyse the properties of the proposed RE and prove that it is capable of exploiting the tradeoff between EE and SE by balancing consumption power and occupied bandwidth; hence simultaneously optimizing both EE and SE. We then formulate the generalized RE optimization problem with guaranteed quality of service (QoS) and provide a gradient based optimal power adaptation scheme to solve it. We also provide an upper bound near optimal method to jointly solve the optimization problem. Furthermore, a low-complexity suboptimal algorithm based on a uniform power allocation scheme is proposed to reduce the complexity. Numerical results confirm the analytical findings and demonstrate the effectiveness of the proposed resource allocation schemes for efficient resource usage.

This paper presents a theoretical investigation of the spectral efficiency of a shared wireless channel. A large number of narrow bandlimited users share a common wideband channel with no cooperation between them. We derive an exact expression for the spectral efficiency of the shared spectrum when each user treats the interference from other signals as an additive noise. These new expressions are used to investigate the effects of non-orthogonal channel spacing on the overall spectral and area-spectral efficiencies of shared wireless channels. As far as the spectral efficiency in bits per second per Hertz is concerned, our results reveal that there is actually no gain that can be achieved with the channelization of the shared wideband channel. In contrast, when raised-cosine spectra are used, it shown that channelization results in a more than 21% loss in the spectral efficiency, and that it is more efficient to let users transmit arbitrarily at the shared wideband channel without channelization.

Selective-relay cooperative systems have been proposed to save energy as well as improving bandwidth efficiency and reducing time delay in wireless systems. In this paper, energy consumption of two proposed Timer-based selection methods, opportunistic relay (OR) and selective cooperation (SC), are investigated for a decode and forward (DF) relay network. We consider the best modulation strategy, uncoded M-QAM, in terms of green in our system model. The motivation is to figure out which one of these two methods consume less energy by studying the green modulation. We also use Dinkel-bach's concave-covex algorithm to minimize the total energy consumption required to send a given number of bits by optimizing transmission power and transmission time. By the optimization, a large amount of energy saving is achievable. The simulation and numerical results show that SC and OR will consume same amount of energy if threshold channel gain of source-relay be larger than relay-destination. However, energy consumption of OR will be much lower than SC if threshold channel gain of source-relay be smaller than relay-destination.

We consider a wireless network with a large number of nodes (access points) randomly placed in the plane, employing Carrier Sense Multiple Access (CSMA) protocols to transmit over the same wireless channel in a realistic propagation environment. Focusing on asynchronous rather than synchronous access scheme, several nodes which are mutually hidden from each other may start their transmissions simultaneously. Thus, we model asynchronous CSMA network according to a 3-D Poisson point process which accounts for random distribution of active (transmitting) nodes in time and space. To accurately study the dynamics of the number of active nodes, a novel state-dependant Markovian model is also proposed wherein transition rates are explicitly dependent on the stochastic geometry of the active nodes. This facilitates the procedure to derive a closed form expression for the back-off probability. Finally, the proposed model is validated through simulations and by comparison with previously developed methods.

Cognitive Radio (CR) is an effective way to improve the utilization of spectrum resources. One of the most important challenges in CR networks is how to sense the existence of a signal transmission. Thus, detecting the existence of the primary users (PUs), which is called spectrum sensing, is a fundamental task in CRs. In a conventional single threshold energy detection scheme, the higher the probability of detection, the better the PUs are protected, however; it gives higher probability of false alarm which means less chances the channel can be reused when it is available. This paper is concerned with the analysis of the secondary users' (SUs) achievable throughput with joint optimal number of sensing rounds and sensing threshold in a Double-Threshold sensing scheme. An iterative algorithm is proposed to obtain the optimal values of the sensing time and second detection threshold. The results show that significant improvement in the throughput of the SUs is achieved when the parameters for the number of sensing rounds and the sensing threshold are jointly optimized.

Heterogeneous networks consisting of small cells (e.g. femtocells) are capable of achieving high capacity and improving indoor cellular coverage area, while the fractional frequency reuse (FFR) scheme has been proposed for upcoming and future cellular systems to improve spectral efficiency in cellular OFDM networks. In two-tier networks of macrocells layered with femtocells, the resource allocation will most likely be sharing the same licensed spectrum. In this paper, we formulate a simple femtocells resource allocation strategies that allows a femtocells base station (FBS) to allocate more resources (co-channel) in high usage areas such as commercial FBS (cFBS) and orthogonal resource allocation for randomly deployed home user FBS (hFBS). We analyze our strategy in a multi-cell systems using area spectral efficiency (ASE) in composite fading consisting of Nakagami-m fading, path-loss and log-normal shadowing. Analytical and simulation results show that our simple resource allocation strategies are able to reduce inter-tier interferences and to offer an improvement in the overall spectral efficiency of the two-tier systems.

This paper examines a sensing framework for a multi-channel occupied by a licensed user (primary user) employing slow frequency hopping to access a channel. This method of access presents a challenge to a sensing cognitive radio node because a licensed user effectively spreads its signal over the entire wideband and the spectrum holes are rapidly changing. By adopting a sensing strategy of jointly detecting all subbands in the channel simultaneously, we study the achievable unlicensed user (secondary user) throughput vis-a-vis the allowable interference on the primary network. The investigation assumes no knowledge of the licensed user's hop pattern or hop duration. In such a scenario, the primary user and secondary user time frames are most likely misaligned, unsynchronised and of unequal durations, which provides for an interesting anlaysis.

In spectrum sharing channels, a secondary user can simultaneously transmit data with a primary user as long as the so called interference temperature limit is kept less than a certain permissible level. In this paper, we consider a spectrum sharing scenario over a Nakagami-m fading channel, and formulate a minimization problem for the average bit error rate (BER) that can be achieved by a secondary user while keeping the interference level introduced to the primary user below a given threshold. We derive new results for the minimum average BER under either average or peak interference power constraints at the primary receiver. This paper also investigates the significance of having extra side information on the status of different channels at the secondary transmitter. Finally, the impact of posing additional constraints on the transmit power at the secondary transmitter is discussed via numerical results.

Spectrum sensing is an important task of a cognitive radio. An effective spectrum sensing algorithm enables the cognitive radio to transmit without causing harmful interference to the licensed user. However, in a multi-user environment, the aggregate interference to the sensing node may adversely affect its sensing performance. In this paper, we investigate the performance of a sensing node in the presence of unlicensed user interference in a non-cooperating secondary network. New expressions were developed to calculate the false alarm and detection probabilities of an energy detection sensor and the results obtained were verified using Monte Carlo simulation techniques. The method employed in this paper significantly reduces the computational task of otherwise directly computing the random interferer variance and hence the results could be used to design more efficient sensors.

This paper is concerned with the design of optimal power allocation strategies in opportunistic spectrum-sharing wireless channels where secondary users are allowed to coexist with the primary users as long as the interference they caused to the primary user is less than a predefined threshold level. We formulate and solve several minimization problems for the average BER experienced by a secondary transmitter-receiver pair under different average and peak interference power constraints at the primary receiver. New closed-form results for the average minimum BERs are derived over Nakagami fading channels for most cases examined. The other contribution of this work lies in reducing extra channel side information at the secondary transmitter, which has very minimal impact on the BER of the secondary link.

This paper presents an analytic framework using area spectral efficiency (ASE) for evaluating the uplink performance of Frequency Reuse (FR) techniques. There are two main FR techniques which are the Fractional Frequency Reuse (FFR) and Soft Frequency Reuse (SFR). The analysis adopts moment generating function (MGF) approach in which composite fading are considered. The composite fading encompass not only path loss and log-normal shadowing but also Nakagami-m fading. This is invaluable for evaluating the performance of uplink in FFR and SFR and provides insight into the design guidelines that encompass much of the real world channel models.

In this paper, we design optimal power allocation in cognitive radio in terms of spectrum sharing where secondary users concurrently transmit with primary users over the same band subject to an interference threshold constraint at primary receivers. The average bit error rate (BER) of the secondary link is minimized under either average or peak interference power constraint of secondary users at the primary's receiver. We derive closed-form expression for evaluating the minimum average BER under Nakagami channels. Furthermore, by numerical results, we show that reducing extra channel side information (CSI) which can be provided at the secondary transmitter has a small impact on the bit error rate.

In this paper, we evaluate the total ergodic capacity of channels in an ad-hoc cognitive radio network under interference constraint at the primary users. It is assumed that all links associated with primary and secondary networks experience Rayleigh fading. First, interference from only primary transmitters is discussed. In such case, the optimum power allocation scheme and the ergodic capacity are derived under average interference power constraint. This paper is also extended to include the impact of interference from both primary transmitters and other secondary transmitters. Then, we propose the iterative algorithm to maximize the total capacity due to non-convexity of the objective function. The effect of different types of interference is investigated via numerical analysis.

Cognitive radio (CR), as the novel approach to improve the utilization of the available radio spectrum is introduced under the constraint that the current authorized users are sufficiently protected against any harmful interferences. However, there are many challenges associated with detection of the primary users (PUs) which need to be addressed carefully. One of the most important challenges in CR networks is how to sense the existence of a PU transmission. The secondary users (SUs) are required to sense the channels, and once the PUs are found, they are required to vacate the channel in a specific amount of time. In a single threshold energy detection scheme, the higher the probability of detection, the better the PUs are protected, however; it gives higher probability of false alarm which means less chances the channel can be reused when it is available. A double threshold detection scheme ensures the target probability of detection while keeping the probability of false alarm as low as required at the cost of increasing the sensing time. This paper is concerned with analysis of the designing the sensing duration and two thresholds difference value in a cooperative double threshold sensing scheme that maximizes the throughput of the SUs, subject to adequate protection to the PUs. Through this work, we formulate the sensing-throughput tradeoff problem mathematically, and prove that the formulated problem is indeed a unimodal function of both parameters and there is an optimal set of two sensing parameters which yields the highest throughput for the secondary network.

Spectrum sensing is arguably the most important task expected of a cognitive radio. An effective spectrum sensing algorithm enables the cognitive radio to transmit without causing harmful interference to the licensed user. However, in a multi-user environment, the aggregate interference to the sensing node may adversely affect its sensing performance. In this paper, we investigate the performance of a sensing node in the presence of unlicensed user interference in a non-cooperating secondary network. We model the interference as a Poisson point process in the two dimensional plane and characterize the effect of various factors such as the sensing time and density of interferers on the overall performance of the spectrum sensor. To this end, novel expressions have been developed to calculate the false alarm and detection probabilities of an energy detection sensor in an interference environment. The results obtained were verified using Monte Carlo simulation techniques.

Cognitive radios have been advanced as a solution to improve spectral efficiency through opportunistic access of the spectrum by unlicensed users. In order to achieve its objective, a cognitive radio is required to conduct periodic spectrum sensing to avoid interfering with the licensed user of the spectrum. In this paper, we examine a multi-channel occupied by a licensed user (primary user) employing slow frequency hopping to access the channel. This method of access presents a challenge to a sensing cognitive radio node since the primary user effectively spreads its signal over the entire wideband and the spectrum holes are rapidly changing. By adopting a sensing strategy of jointly detecting all subbands in the channel simultaneously, we study the achievable unlicensed user (secondary user) throughput vis-a-vis the allowable interference on the primary network. The investigation is conducted under two cases; when the hop duration of the primary user is either synchronized or unsynchronized to the secondary user's time frame to investigate the effect of time frame misalignment which presents a more realistic model.

This paper presents a new mathematical analysis for the performance of orthogonal frequency-division multiplexed (OFDM) signals over multipath Nakagami-m fading channels. In contrast to the previous research, this paper focuses on the effects of the nonuniform phase distribution on the error rate performance. A unified expression is derived for the moment generating function (MGF) of the frequency-domain channel gains on Nakagami-m channels with nonuniform phase distributions. Classical MGF methods can then be straightforwardly employed to obtain accurate error rates expressions for different modulation and diversity formats.

Carrier frequency offset destroys the orthogonality between different subcarriers in multicarrier code division multiple access (CDMA) giving rise to inter-carrier interference (ICI). Taking into account accurate statistical models for the ICI, this paper presents new analytical expression for spectral efficiency of mobile multicarrier CDMA communication system. The expression is then used to estimate the spectral efficiency degradation over Rayleigh fading channels.

This study presents a system-level theoretical analysis of two different types of multirate code division multiaccess (CDMA) wireless communication systems, which include both variable spreading gain (VSG) CDMA and multicode (MCD) CDMA systems. Based on the accurate interference models, the authors derive unified expressions of the cumulative density function of the signal-to-interference-plus-noise ratio in the cases of both binary and quaternary multirate CDMA schemes. This leads us to achieve new packet error rate expressions, which consider the impacts of bit-to-bit error dependence, optimal power transmissions and random users’ distributions, for multirate-slotted packet CDMA systems. The expressions are used to investigate the system-level performance of VSG and MCD-based multicellular CDMA networks over Rayleigh fading environment.

In this paper, an efficient analytical technique for bit error rate (BER) of variable spreading gain code division multiple access (VSG CDMA) in Nakagami fading is introduced. Based on the accurate improve Gaussian approximation (IGA) technique, a new BER expression is derived in a closed form. Validated by Monte Carlo simulation, the proposed expression is used to accurately investigate the impacts of channel's conditions, power allocation and random users' distributions on the BER performance.

Orthogonal frequency division multiplexing (OFDM) transmission over mobile communication channels is very sensitive to time variations due to Doppler spreading. Time variations within the transmission time of one OFDM block destroy the orthogonality among the subcarriers giving rise to interchannel interference (ICI) which degrades the performance of OFDM over fast fading channels. Error rate analysis of OFDM in the presence of ICI is not trivial due to the cross-correlation between the ICI and the useful signal components. Based on accurate statistical models of the ICI, this paper presents a new accurate non-direct analytical method which simplifies greatly performance evaluation of OFDM in the presence of ICI. This results in new unified expressions for bit and symbol error rates of multilevel quadrature amplitude modulation (MQAM) and M-ary phase shift keying (MPSK) based OFDM communication systems over fast Rayleigh multipath fading channels. These results are further extended to include error rate analysis of OFDM with transmit diversity techniques.

We consider a wireless communication model where a large number of transmitter-receiver pairs share a common Rayleigh fading channel without any coordination between them. The performance of a simple coexistence etiquette is analyzed in details, where packets are allowed to be transmitted from a given terminal only if the signal-to-interference-plus-noise ratio (SINR) at their intended receiver exceeds a given threshold, and transmission from that terminal is prohibited otherwise. Accurate interference models are developed assuming a large number of transmitter-receiver pairs that are randomly distributed according to a Poisson spatial point process. These are used to derive accurate expressions for packet error rates in the case of direct-sequence code division multiple access (CDMA) physical layer model and slotted packet transmission schemes. These results are then used to study the efficiency of this threshold-based coexistence etiquette and compare it with systems which are based on CDMA only.

This paper is concerned with the performance analysis of decode-and-forward cooperative diversity wireless communication systems over general fading channels. New exact expressions are derived for the average mutual information with multiple relay nodes and arbitrary power allocations. This facilitates evaluating the performance of several suboptimal power allocation schemes which distribute the total relay transmit power based on the mean path-gains. Numerical examples are given for a cooperative diversity system in Nakagami-m fading channel with multiple relays that are randomly distributed in a given geographical area around the destination node.

This paper presents a new accurate error rate analysis of orthogonal frequency-division multiplexing signals in the presence multipath frequency-selective Nakagami-m fading. In contrast to previous research, we focus on the effects of the nonuniform phase distribution on the error rate performance. A new closed-form expression is derived for the moment generating function (MGF) of the frequency-domain channel gain. Classical MGF methods can then be straightforwardly employed to obtain accurate error rates for different modulation and diversity formats.

This paper presents a simple new expression for the exact evaluation of averages of the form E [ln (1+x1+...xN/y1+...+yM+1)], where x1,..., xN, y1..., yMare arbitrary non-negative random variables, in terms of the joint moment generating functions of these random variables. Application examples are given for the ergodic capacity evaluation of some multiuser wireless communication systems which are difficult to solve by the known classical methods.

Transform techniques based on moment generating functions (MGFs) and characteristic functions (CHFs) have recently provided efficient analytical tools for the performance evaluation of digital communication systems over fading channels. More recently, the convolution theorem of the Fourier transform has been employed to obtain unified expressions for the average error probabilities of equal gain combining (EGC) diversity reception in terms of the CHFs of the branches' amplitude gains. In this paper, we prove that these expressions include redundant terms. Furthermore, simpler analytical expressions for the average error rates of EGC diversity reception can be obtained when the convolutional theorem of the sine and cosine transforms are used instead of the conventional Fourier transform.

This paper presents a new unified analytical technique for accurate interference analysis of noncoherent M-ary frequency shift keying (MFSK) wireless communication systems in the presence of additive white Gaussian noise (AWGN) and multiple arbitrary interfering signals. New exact bit error rate expressions are derived for nonorthogonal noncoherent binary FSK in the presence of an arbitrary number of interfering signals having arbitrary spectral shapes at arbitrary frequency offsets. Furthermore, tight upper bounds for the symbol and bit error rates are given for noncoherent MFSK with arbitrary tone spacings. These results are extended to include MFSK signals experiencing Rayleigh, Nakagami-m or Rician fading. Some specific interference scenarios are analyzed in details, including jammers with a given Doppler-spread, direct sequence spread spectrum and orthogonal frequency division multiplexing signals, and a Poisson field of arbitrary interferers.

This paper presents a unified mathematical performance analysis of the physical layer in orthogonal frequency division multiple access (OFDMA) wireless ad hoc networks, where several independent transmitter-receiver pairs share a common wideband channel in a local area environment. Multiuser interference (MUI) occurs when the signals from different users arrive at a given receiver with arbitrary timing misalignments, leading to the destruction of the orthogonality between subcarriers. Precise interference analysis in white Gaussian noise and Rayleigh multipath fading is developed in a partially loaded OFDMA network. New exact expressions of symbol and bit error rates are given in the case of interleaved subcarrier assignment schemes. On the other hand, tight upper bounds and accurate improved Gaussian approximations are developed for arbitrary subcarrier assignment schemes. Furthermore, expressions of the cutoff rates are derived and employed to estimate the spectral efficiency in bits/sec./Hz. These are used to quantify the improvement in the spectral efficiency that can be achieved by a common MUI mitigating technique based on the extension of guard intervals and dynamic positioning of FFT windows.

This paper presents a new mathematical analysis for the evaluation of the average signal-to-interference plus noise ratio (SINR) of orthogonal frequency division multiplexing (OFDM) in the presence of carrier frequency offset (CFO). CFO destroys the orthogonality between different subcarriers giving rise to inter-carrier interference (ICI). The SINR of wireless OFDM in the presence of CFO and frequency-selective fading becomes a ratio of correlated random variables, and the exact evaluation of its average by using direct methods requires a huge computational effort. In this paper, we present an indirect method that leads to a new exact simpler expression for the average SINR over Rayleigh multipath fading channels.

This paper presents a generalized analysis of Multiband OFDM (MB-OFDM) Ultra Wideband (UWB) communication in the presence of generic or non-specific interference sources. The interference sources are assumed to be distributed in a two-dimensional space according to a homogeneous Poisson field. An aggregate interference is formed by the asynchronous operation of these sources. To provide a generalized analysis, the conventional Gaussian approximation is replaced by a method involving the moment generating function (MGF) of the signal-to-interference-plus-noise ratio (SINR) and Laplace transform to derive the exact expression for the probability density function (pdf) of the interference power. From this, overall expression for the bit error rate, BER, is derived based on the cases where band limited interference is present and otherwise. This resulting expression is valid equally for the first and next generation devices.

This paper presents a unified analytical method for efficient computation of first and second order statistics of the signal-to-interference-plus-noise-ratio (SINR) in wireless communication systems. New exact expressions are derived for the moments of SINR and its autocorrelation function that are valid for arbitrary interfering signals. These are used to examine the accuracy of the commonly used approximations for the average SINR and to investigate effects of fast fading and interfering signals' temporal behavior on the autocorrelation properties of SINR.

Wideband code-division multiaccess (WCDMA) downlink transmission is prone to self interference caused by the loss of orthogonality between the spreading codes due to multipath fading. The degree of loss of orthogonality in downlink WCDMA is usually measured in terms of the orthogonality factor (OF) which is directly related to the level of intra-cell interference. This paper presents accurate theoretical analysis of the OF over generalized fading channels. New exact expressions of the average OF are derived for full and partial RAKE receivers over arbitrarily correlated multipath fading channels.

This paper presents a unified framework for interference characterizations and analysis in the unlicensed frequency bands and the like, where many narrowband heterogeneous terminals coexist and share a common wideband channel using less-restrictive transmission etiquettes. Here, each transmitter/receiver pair makes his own decision regarding when to access the channel without any direct coordination with the other users. This is usually based on the local channel conditions at the receiver or/and the transmitter. Due to the nature of the wireless channel, communication in such environments is usually prone to arbitrary partial-band interference which can be generated anywhere in the space and frequency domains. In this paper, a new spatial-spectral interference model is introduced, where interferers can be of any power spectral density and are distributed according to a Poisson process in space and frequency domains. This basic model is extended to include the effects of channelization, where users are allowed only to transmit at a preassigned set of discrete frequencies. This is further extended to include also the effects of spectral-spatial guard zones, where the interferers can not exist in a given band nearby the victim receiver. Based on this multidimensional spatial-spectral Poisson model and the accurate conditional Gaussian analysis, explicit expressions are derived for average error rates of different communication systems.

This paper presents a new unified analytical method for efficient computation of first and second order statistics of the signal-to-interference-plus-noise-ratio (SINR) in wireless communication systems. New exact expressions are derived for the moments of SINR and its autocovariance function that are valid for arbitrary interfering signals. These are used to examine the accuracy of the commonly used approximations for the average SINR and to investigate effects of fast fading and interfering signals' temporal behavior on the autocorrelation properties of SINR.

A new exact explicit expression is derived for the ergodic capacity of maximal ratio combining (MRC) schemes over arbitrarily correlated Rician fading channels. This is used to study the effects of channel correlation on the ergodic capacity. Numerical results reveal that both the phase and the magnitude of correlation have an impact on the ergodic capacity of Rician fading channels. This is in contrast to correlated Rayleigh fading, where the phase of the correlation has no effect on the ergodic capacity. It is also observed that negatively correlated branches in Rician fading may lead to an increase in ergodic capacity beyond that obtained by uncorrelated branches.

A new accurate mathematical analysis is presented for the efficient computation of the spectral efficiency of CDMA downlink wireless communication systems in the presence of multipath Rayleigh fading and log-normal shadowing. A new explicit expression is derived for the spectral efficiency, which is based on an accurate interference model that accounts for both intra-cell and inter-cell interferences. This is used to investigate the performance of downlink CDMA in different multipath delay profiles. The numerical results has shown that the loss of orthogonality deteriorates the spectral efficiency significantly at high signal-to-noise ratios (SNR) levels. On the other hand, the diversity gain will compensate the loss of orthogonality at low SNR levels.

This paper presents new mathematical analysis of orthogonal frequency division multiplexing (OFDM) in the presence of carrier frequency offset (CFO) and frequency selective Rician fading, which leads to new exact expression for the average capacity with and without channel state information (CSI) at transmitter. As far as the effect of CFO on the average capacity of OFDM in frequency selective fading is concerned, our numerical results indicate that correlations among subcarriers have little affect on the average capacity.

This paper is concerned with the transmission of multiple description coded (MDC) messages over frequency hopping multiple access wireless networks. We address the problem of optimal allocation of the MDC representations within transmitted packets in an interference limited environment. Taking into account the correlation between the interference experienced by the two representations of a Double-Description Coded (DDC) message, we develop a new mathematical analysis for computing the average distortion. It is shown that when a packet is subjected to a number of random interfering packets, then the quality of reception depends on the relative location of the representations within the transmitted packet. Furthermore, the average distortion is minimized when the representations are allocated at the opposite edges of the packet, resulting in a relative improvement in the required signal to noise ratio (SNR) that, depending on the number of interfering packets, exceeds 4 dB.

This letter presents a new efficient technique to solve a throughput maximization problem on the uplink of a variable spreading gain code division multiple access (VSG-CDMA) system operated in an independent Rayleigh fading environment. A new linear set of constrains is found that enables a linear-programming solution to the problem of maximizing the overall average throughput in a multiclass system while maintaining the QoS constraints for all users

We present new packet-error rate (PER) analysis for both slotted and unslotted direct-sequence spread-spectrum packet communication systems in a slow Rayleigh fading environment. Based on the accurate improved Gaussian approximation, we derive closed-form expressions for the cumulative probability distribution function of the signal-to-interference-plus-noise ratio in binary phase-shift keying (PSK), quadratic PSK, and differential PSK-based code-division multiple-access (CDMA) systems having different types of chip waveforms including bandwidth-efficient waveforms. This leads to new accurate unified expressions for the PERs that account for bit-to-bit error dependence, which are valid for packets with unequal power levels. These new results facilitate accurate computation of the throughput performance of CDMA-based ALOHA local radio networks

This paper presents a unified analytical method for computing the average E[g(x/(Sigmak=1Kyk+ b))] of some arbitrary function g(.) when x is a gamma random variable and independent of the arbitrary random variables y1, y2, ..., yk. This leads to new explicit expressions for the averages of some specific functions including, erfc(radicz), exp(-z), zn, and In(1 + z), in terms of the moment generating functions of y1, y2, ..., yK.

This paper presents a new analytical performance analysis of slow frequency-hopped synchronous spread-spectrum multiple-access (FHSS-MA) networks employing nonorthogonal binary frequency-shift keying (BFSK) and having arbitrary spacing between the hopping carriers. Taking into account the crosstalk due to the nonorthogonality of both hopping carriers and BFSK tones, and based on an accurate interference analysis, we derive new expressions for the average probability of error of a reference signal subjected to a number of similar signals in the additive white Gaussian noise Rayleigh-faded channel. These are used to investigate the effect of carrier and tone spacing on the spectral efficiency of an FHSS-MA network. It is shown that the spectral efficiency depends primarily on the shape of the employed pulses, in addition to both carrier and tone spacing. Numerical results show that rectangular pulses give higher spectral efficiency as compared with the half-sine pulses. Furthermore, orthogonal tone spacing is shown to be more efficient in the case of rectangular pulses, whereas half-sine pulses become more efficient with the nonorthogonal signaling.

This paper presents new analytical expressions for the spectral efficiency of variable spreading gain code division multiple access (VSG CDMA) networks in a Nakagami and Rician fading environments. These are used to gain insight into the impact of fading and background noise on the optimal transmit powers. Numerical results for a dual class and 5-class system, reveal that the spectral efficiency is optimized at higher signal-to-noise ratio levels when each user is retaining the same bit energy. However, at lower levels of the signal-to-noise-ratio, the spectral efficiency would be optimized when a larger amount of energy is allocated to the classes of higher data rate, as compared to the lower rate classes

This paper presents a theoretical performance analysis of downlink (base-to-mobile) OFDM (Orthogonal frequency-division multiplexing) micro-cellular radio communication systems. The model developed in this analysis determines accurate interference analysis which takes into consideration frequency and timing synchronization errors between cochannel cells in a Nakagami/Rayleigh fading scenario. This leads to new, accurate and computationally efficient expressions for average bit error rates and cutoff rates of MQAM-OFDM in a micro-cellular environment. Results obtained are applicable in the investigation of the effect of synchronization errors on the spectral efficiency of OFDM based micro-cellular systems. Whilst the system is more robust against timing jitters resulting from separation distances from the victim receiver, frequency synchronization errors above 10-1have the potential to create a loss in spectral efficiency of up to 7.5% for 16 QAM.

An investigation carried out for a generalized Nakagami fading channel in this paper, concerns the performance degradation introduced by a field of interferers surrounding a victim receiver in a shared wireless channel. A new mathematical model adopted assumes interferers are distributed according to a Poisson process in space and frequency. Based on this model, an expression derived for average bit error probability and employed to determine spectral efficiency of the shared wireless channel which emerges is not only exact but explicit. Numerical results obtained suggests that pulse waveshaping is vital to the overall performance of the wireless system. It is found that root raised cosine filters offer improved performance compared with Gaussian filters. For example, the enhancement is as much as 16.7% spectral efficiency when compared with Gaussian filter of time-bandwidth product of 0.3. Furthermore, single tone interference are less harmful than interference that has a waveshape that is identical to the useful signal.

We present new accurate packet error rate analysis of unslotted direct sequence spread spectrum packet communication systems in slow Rayleigh fading environments. Based on the accurate Improved Gaussian Approximation, we introduce a new technique that leads to accurate and efficiently computable expressions for packet error rates that account for bit-to-bit error dependence. These new results facilitate accurate computation of the throughput performance of CDMA-based Unslotted ALOHA local radio networks.

In this paper we consider the capacity of a Rayliegh faded wireless channel that is shared by K independent transmitter-receiver pairs. No cooperation is assumed between the different pairs. We examine the possible gain in the sum rate capacity when a binary side information is passed by each receiver to its corresponding transmitter on whether the instantaneous local signal-to-interference-plus-noise-ratio (SINR) is greater or less than a given threshold, and transmitters adapt their transmission power accordingly. It is shown that a substantial improvement in the channel capacity can be achieved by using this "opportunistic" transmission strategy. Our numerical results reveal that the total sum capacity increases linearly with the logarithm of the number of users sharing the channels.

This paper presents new accurate packet error rate analysis of ALOHA type networks that employ BPSK or QPSK modulation in a Rayleigh fading environment. Relying on a precise interference model, we derive new accurate expressions for the packet success probabilities that account for bit to bit error dependence, and are valid for unequal power levels. The accuracy of the new expressions is validated by simulation. These results are used to investigate the throughput performance of Aloha type networks in different local area environments

This paper is concerned with packet error rate analysis for a multirate VSG CDMA wireless packet communication system. Based on the improved Gaussian approximation (IGA), we derive new expressions for the packet error probability that account for the different classes of users' rates in a Rayleigh fading environment. This is used to select the optimum users' power levels that maximise the overall average throughput of a network with dual classes. Our numerical results show that the optimum power of an m-rate user is not always m times greater than the power of the basic rate, as commonly assumed in the previous literature. In contrast, the optimum power, in addition to the rates of the different classes, also depends on the spreading gain and the number of instantaneous packets.

A new mathematical model is presented for the analysis of interference in wireless systems sharing a common frequency band. It is applied to a random access environment, whereby a random number of users transmitting BPSK narrowband signals share a common wideband wireless channel, and the carrier frequency of each signal is randomly selected over the common frequency band. Based on this model, a new bit error rate analysis is derived and used to investigate the spectral efficiency of shared wireless channels. It is shown that the shape of the baseband pulse plays an important role. Specifically, numerical results suggest that the spectral efficiency of the shared wireless channel is increased when a rectangular waveshape is used instead of half-sine or raised-cosine.

This paper presents a theoretical performance analysis of frequency hopped multiple-access communication systems with spectrally overlapping hopping channels. Taking into account cochannel as well as the adjacent-channel interference, we develop an accurate interference analysis for the noncoherent detection of a FH/BFSK signal in the presence of other interfering signals. A new closed form expression for the corresponding bit error rate is derived in an AWGN Rayleigh faded channel. This result provides an accurate design approach for the selection of the channel spacing in frequency hopping multiple-access systems It is shown that the spectral efficiency depends on the form of the waveshaping pulses and the separation between adjacent hopping channels. When compared with the performance of systems with nonoverlapping channels, numerical results suggest that an improvement of about 100% is possible.

This letter is concerned with the interference analysis in time-unslotted frequency-hopping code-division multiple-access packet networks with error control coding. We derive, under the conditional independence assumption, a new exact closed-form expression for the packet error probability of a reference packet in the presence of other K interfering packets. In contrast to the previously known results, the computational complexity of the new result is independent of K. We also develop a new tight upper bound on packet error probability relying on mapping the unslotted system into an equivalent slotted one experiencing the same level of short-term average interference. The accuracy of the proposed approximation is demonstrated by some numerical examples and is shown to be tighter than the previously used results.

This correspondence is concerned with the statistical dependence of hits due to multiple-access interference in the time-unslotted frequency-hopping (FH) packet networks. Relying on the technique of joint probability generating functions (PGFs), we give a formal proof that if the ratio of the number of interfering packets to the number of frequency slots K/q is held constant, hits due to multiple-access interference are asymptotically independent as q/spl rarr//spl infin/. We also derive expressions for the correlation coefficients of hits in the packet.

We investigate the occupancy statistics of a wireless channel shared by a large number of terminals randomly distributed in the plane and employing the listen- before-talk coexistence etiquette. Relying on a realistic propagation model that accounts for the path loss with distance and log-normal shadowing, we present a new semi-analytical performance analysis. A state-dependent model is introduced that accurately tackles the spatial characteristics of signal propagation and the effect of hidden terminals. This is used to give a lower bound on the blocking probability of the shared wireless link.

We derive a new expression for the exact bit-error probability for the detection of a coherent binary phase-shift keying signal experiencing a number of asynchronous interferers having unequal power levels in Rayleigh fading channels. The new expression is readily computed in terms of the coefficients of a Hermite polynomial.

This paper presents an analytical framework for interference analysis in unslotted packet radio networks employing BPSK modulation. An accurate mathematical model that tracks the joint variations of the multiple access interference appearing at the postdetection filter over all bits of a test packet is formulated. The performance of the unslotted system is quantified by considering an equivalent slotted system that experiences the same amount of effective interference, where the latter is computed from the short term average interference experienced by all bits of the packet. Closed form expressions for the corresponding packet error probabilities are.

We derive the exact closed form expression for symbol error probabilities in slow frequency hopping multiple-access spread spectrum communications employing MFSK modulation schemes. The new expression is easy to compute and permits signal levels to be unequal or randomly distributed. However, it is exact only in the case of synchronous hopping and the Rayleigh fading channel.