This paper proposes a pilot decoupling-based two-dimensional channel parameter estimation method for intelligent reflecting surface (IRS)-assisted networks. We exploit the combined effect of Terahertz sparse propagation and the geometrical structure of arrays deployed at the base station, the IRS, and the user equipment to develop a low-complexity channel parameter estimation method. By means of a new pilot design along the horizontal and vertical directions, the overall channel parameter estimation problem is decoupled into different domains. Furthermore, with this decoupling, it is possible to simultaneously sense/estimate the channel parameters and to communicate with the sensed node. Specifically, we formulate two estimators by decoupling the global problem into sub-problems and exploiting the built-in tensor structure of the sensing/estimation problem by means of multiple rank-one approximations for rank-one and low-rank channels. The Cramér-Rao lower bound is derived to assess the performance of the proposed estimators. We show that our two proposed methods yield accurate parameter estimates and outperform state-of-the-art methods in terms of complexity. The tradeoffs between performance and complexity offered by the proposed methods are discussed and numerically assessed.

We consider a constellation of low-earth-orbit (LEO) satellites connected to a handheld device on the ground. Due to the very large orbital speed, an effective handover strategy becomes of paramount importance. In particular, we study the benefits of soft handover in the uplink from the physical-layer point of view. We give a realistic model for both the ground-tosatellite and the inter-satellite links, following the 3GPP channel model for the former. We suppose that, during handover from a serving satellite to a target satellite, one of the two satellites forwards the received signal from the ground user to the other, thus acting as a relay. We quantify through simulations the loss of hard handover, compared to soft handover. For the latter, we test both amplify-and-forward (AF) and decode-and-forward (DF) relaying techniques and verify that, at least in the simulated conditions, DF does not repay, in terms of block error rate (BLER), the increase of complexity with respect to AF. Also, we study the effect of the LEO constellation size on the network BLER. Finally, we show that, with soft handover, the impact of misalignment on the inter-satellite link is severe, especially at optical frequencies.

Integrated access and backhaul (IAB) is one of the promising techniques for 5G networks and beyond (6G), in which the same node/hardware is used to provide both backhaul and cellular services in a multi-hop fashion. Due to the sensitivity of the backhaul links with high rate/reliability demands, proper network planning is needed to make the IAB network performing appropriately and as good as possible. In this paper, we study the effect of deployment optimization on the coverage of IAB networks. We concentrate on the cases where, due to either geographical or interference management limitations, unconstrained IAB node placement is not feasible in some areas. To that end, we propose various millimeter wave (mmWave) blocking-aware constrained deployment optimization approaches. Our results indicate that, even with limitations on deployment optimization, network planning boosts the coverage of IAB networks considerably.

In this work, a hybrid free-space optics (FSO)/ teraHertz (THz) based backhaul network is considered to provide high-data-rate reliable communication to the terrestrial mobile users (MUs) operating at millimeter-wave (mmWave) bands. The FSO link is affected by atmospheric turbulence and pointing error impairments. At the FSO receiver, both intensity-modulated direct detection and heterodyne detection techniques are considered. The multi-antenna THz link suffers from high path-loss, small-scale fading, and misalignment error. To minimize the effect of back-and-forth switching, soft switching method is introduced at the access point (AP) to select the signal coming through the hybrid FSO/THz link, and a comparison with hard switching method is presented. Selective decode-and-forward relaying is considered at the AP. In this context, we derive closed-form expressions of the individual link’s outage probability, end-to-end (E2E) outage probability, asymptotic outage probability, ergodic capacity, and generalized average bit-error-rate. Finally, we study the effect of different parameters such as atmospheric turbulence, pointing/misalignment errors, link distance, atmospheric attenuation/path-loss, fading parameters of the THz and access links, and number of antennas on the network performance. Our results indicate that, with a proper switching method, the joint implementation of FSO/THz links improves the rate/reliability of the backhaul links with limited switching overhead.

Intelligent reconfigurable surface IRS are becoming an attractive component of cellular networks due to their ability to shape the propagation environment and thereby improve coverage. While IRS nodes incorporate a great number of phase-shifting elements and a controller entity, the phase shifts are typically determined by the cellular base station (BS) due to its computational capability. Since controlling a large number of phase shifts may become prohibitive in practice, it is important to reduce the control overhead between the BS and the IRS controller. To this end, in this paper, we propose a low-rank modeling approach for the IRS phase shifts. The key idea is to represent the IRS phase shift vector using a low-rank tensor approximation model, where each rank-one component is modeled as the Kronecker product of a predefined number of factors of smaller sizes, obtained via tensor decomposition algorithms. We show that the proposed low-rank models drastically reduce the required feedback requirements associated with the BS-IRS control links. Our simulation results indicate that the proposed method is especially attractive in scenarios with a strong line of sight component, in which case nearly the same spectral efficiency is reached as in the cases with near-optimal phase shifts, but with significantly lower feedback overhead.

Integrated access and backhaul (IAB) is envisioned as a possible solution to address the need for network densification in situations where fiber connection is not viable. In Release 18, 3rd generation partnership project (3GPP) will take another step on extending IAB capabilities. With mobile IAB (mIAB), IAB nodes can be deployed within vehicles, e.g., buses. As in every new technology, performance assessment and evaluation of the impact of interference is of interest for industry and academia. In this paper, we present contributions on those topics. First, we evaluate the performance of mIAB compared to fiber-connected deployments. Moreover, we study the impact of interference on the performance of mIAB networks and propose a solution based on inserting silent slots on the time division duplex (TDD) frame pattern. According to our simulation results, mIAB is capable of improving performance of onboard user equipments (UEs) without harming too much the quality of service (QoS) of surrounding UEs. Furthermore, we show that the TDD frame pattern should be carefully designed to account for scenarios with different levels of interference.

In this paper, we propose a rank-one tensor modeling approach that yields a compact representation of the optimum intelligent reconfigurable surface (IRS) phase-shift vector for reducing the feedback overhead. The main idea consists of factorizing the IRS phase-shift vector as a Kronecker product of smaller vectors, namely factors. The proposed phase-shift model allows the network to trade-off between achievable data rate and feedback reduction by controling the factorization parameters. Our simulations show that the proposed phase-shift factorization drastically reduces the feedback overhead, while improving the data rate in some scenarios, compared to the state-of-the-art schemes.

In this paper, we study the performance of cooperative millimeter wave (mmWave) networks with hybrid precoding architectures. Considering joint transmissions and BS silence strategy, we propose hybrid precoding algorithms which minimize the sum power consumption of the base stations (BSs), for both fully- and partially-connected hybrid precoding (FHP and PHP, respectively) schemes, for single-carrier and orthogonal frequency-division multiplexing systems. We reformulate the analog precoding part as an equal-gain transmission problem, which only depends on the channel information, and the digital precoding part as a relaxed convex semidefinite program subject to per-user quality-of-service constraints that gives the optimal sum power consumption in terms of the BS silence strategy. In order to reduce the complexity of the hybrid precoding algorithm with optimal BS silence strategy, we propose a sub-optimal hybrid precoding algorithm that iteratively put BSs with small power into the silent mode. The simulation results show that, depending on the parameter settings, the power consumption of the PHP may be dominated by the RF transmit power and it may result in a larger power consumption than the FHP. For the cases with 2 BSs and 4 users, implementation of the FHP and the PHP in cooperative networks reduces the required RF transmit power, compared to the case in a non-cooperative network, by 71% and 56%, respectively.

In a wirelessly-powered communication network (WPCN), an energy access point (E-AP) supplies the energy needs of the network nodes through radio frequency wave transmission, and the nodes store their received energy in their batteries for possible data transmission. In this paper, we propose an online control policy for energy transfer from the E-AP to the wireless nodes and for data transfer among the nodes. With our proposed control policy, all data queues of the nodes are stable, while the average energy consumption of the network is shown to be within a bounded gap of the minimum energy required for stabilizing the network. Our proposed policy is designed using a quadratic Lyapunov function to capture the limitations on the energy consumption of the nodes imposed by their battery levels. We show that under the proposed control policy, the backlog level in the data queues and the stored energy level in the batteries fluctuate in small intervals around some constant levels. Consequently, by imposing a negligible average data drop rate, the data buffer size and the battery capacity of the nodes can be significantly reduced.

Massive multiple-input multiple-output (M-MIMO) is recognized as a promising technology for the next generation of wireless networks because of its potential to increase the spectral efficiency. In initial studies of M-MIMO, the system has been considered to be perfectly synchronized throughout the entire cells. However, perfect synchronization may be hard to attain in practice. Therefore, we study a M-MIMO system whose cells are not synchronous to each other, while transmissions in a cell are still synchronous. We analyze an asynchronous downlink M-MIMO system in terms of the coverage probability and the ergodic rate by means of the stochastic geometry tool. For comparison, we also obtain results for the corresponding synchronous system. In addition, we investigate the effect of the uplink power control and the number of pilot symbols on the downlink ergodic rate, and we observe that there is an optimal value for the number of pilot symbols maximizing the downlink ergodic rate of a cell. Our results also indicate that, compared to the synchronous system, the downlink ergodic rate is more sensitive to the uplink power control in the asynchronous mode.

5G is finally here. Initial deployments are already operational in several major cities and first 5G-capable devices are being released. Though it is not limited only to millimeter wave deployments, the main promise of 5G lies in the utilization of the high bandwidth available at high frequencies. However, high-frequency deployments are coverage-limited and require denser placement of base stations, which can increase the cost significantly. One of the main contributing factors to the cost is fiber deployment. Integrated access backhauling (IAB), where part of the wireless spectrum is used for the backhaul connection of base stations instead of fiber, is an attractive solution that could make dense deployments economically viable. With this main objective, 3GPP is in the process of standardizing multi-hop IAB networks. This paper provides an overview of the main features of the multi-hop IAB 3GPP rel-16 standard and the rationale behind the design choices.

This paper studies the sum throughput of the multi-user multiple-input-single-output networks in the cases with a large-but-finite number of transmit antennas and users. Considering continuous and bursty communication scenarios with different users' data request probabilities, we derive quasi-closed-form expressions for the maximum achievable throughput of the networks using optimal schedulers. The results are obtained in various cases with different levels of interference cancellation. Also, we develop an efficient scheduling scheme using genetic algorithms (GAs) and evaluate the effect of different parameters, such as channel/precoding models, number of antennas/users, scheduling costs, and power amplifiers' efficiency, on the system performance. Finally, we use the recent results on the achievable rates of finite block-length codes to analyze the system performance in the cases with short packets. As demonstrated, the proposed GA-based scheduler reaches (almost) the same throughput as in the exhaustive search-based optimal scheduler, with substantially less implementation complexity. Moreover, the power amplifiers' inefficiency and the scheduling delay affect the performance of the scheduling-based systems significantly.

This paper studies the performance of delay-constrained hybrid automatic repeat request (HARQ) protocols. Particularly, we propose a fast HARQ protocol where, to increase the end-to-end throughput, some HARQ feedback signals and successive message decodings are omitted. Considering quasi-static channels and a bursty communication model, we derive closed-form expressions for the message decoding probabilities as well as the throughput, the expected delay, and the error probability of the HARQ setups. The analysis is based on the recent results on the achievable rates of finite-length codes and shows the effect of the codeword length on the system performance. Moreover, we evaluate the effect of various parameters, such as imperfect channel estimation and hardware on the system performance. As demonstrated, the proposed fast HARQ protocol reduces the packet transmission delay considerably compared with the state-of-the-art HARQ schemes. For example, with typical message decoding delay profiles and a maximum of 2,..., 5 transmission rounds, the proposed fast HARQ protocol can improve the expected delay compared with standard HARQ by 27%, 42%, 52% and 60%, respectively, independently of the code rate/fading model.

We consider a bi-directional point-to-point links and study the data transmission efficiency of frequency division duplex (FDD) and TDD (T: time) schemes with a bursty communication model. We use the recent results on the achievable rates of finite-length codes to analyze the end-to-end throughput and the data payload for TDD and FDD in the cases with codewords of finite length including the impact of guard time for TDD and guard bands for FDD. Also, in case of TDD we study the impact of adaptive resource allocation on the link throughput. As we demonstrate, TDD-based adaptive resource allocation based on the data traffic improves the performance over non-adaptive TDD and FDD schemes significantly. For instance, consider the data rates 0.1 and 1 bit/symbol and data request probabilities 0.2 and 0.6 in the two different directions, respectively, and Rayleigh fading conditions. Then, for a broad range of codewords lengths and moderate/high signal-to-noise ratios, the implementation of adaptive TDD improves the link throughput, compared to the nonadaptive duplexing by more than 50%.

We study the sum throughput of multiple-input-multiple-output (MIMO) networks in the cases with large but finite number of transmit and receive data terminals. We develop an efficient scheduling scheme using genetic algorithms (GAs), and evaluate the effect of various parameters, such as channel/precoding models, number of antennas/users, scheduling costs and power amplifiers efficiency, on the system performance. Also, considering continuous and bursty communication scenarios with different users' data request probabilities, we derive closed-form expressions for the maximum achievable throughput of the MIMO networks using optimal schedulers. As we show, our proposed GA-based scheduler reaches (almost) the same throughput as in the exhaustive search-based optimal scheduler, with substantially less implementation complexity. Also, the power amplifiers inefficiency affect the network throughput significantly. For instance, consider a MIMO setup with a 40-antenna base station, 60 users, total consumed power of 26 dB, continuous communications and the typical parameter settings of the power amplifiers. Then, the network throughput decreases by 50% when the power amplifiers efficiency reduces from 75% to 25%.

This paper develops a stochastic geometry-based approach for the modeling and analysis of single- and multi-cluster wireless networks. We first define finite homogeneous Poisson point processes to model the number and locations of the transmitters in a confined region as a single-cluster wireless network. We study the coverage probability for a reference receiver for two strategies; closest-selection, where the receiver is served by the closest transmitter among all transmitters, and uniform-selection, where the serving transmitter is selected randomly with uniform distribution. Second, using Matern cluster processes, we extend our model and analysis to multi-cluster wireless networks. Here, two types of receivers are modeled, namely, closed- and open-access receivers. Closed-access receivers are distributed around the cluster centers of the transmitters according to a symmetric normal distribution and can be served only by the transmitters of their corresponding clusters. Open-access receivers, on the other hand, are placed independently of the transmitters and can be served by all transmitters. In all cases, the link distance distribution and the Laplace transform (LT) of the interference are derived. We also derive closed-form lower bounds on the LT of the interference for single-cluster wireless networks. The impact of different parameters on the performance is also investigated.

Initial access (IA) is identified as a key challenge for the upcoming 5G mobile communication system operating at high carrier frequencies, and several techniques are currently being proposed. In this paper, we extend our previously proposed efficient genetic algorithm‐ (GA‐) based beam refinement scheme to include beamforming at both the transmitter and the receiver and compare the performance with alternative approaches in the millimeter wave multiuser multiple‐input‐multiple‐output (MU‐MIMO) networks. Taking the millimeter wave communications characteristics and various metrics into account, we investigate the effect of different parameters such as the number of transmit antennas/users/per‐user receive antennas, beamforming resolutions, and hardware impairments on the system performance employing different beam refinement algorithms. As shown, our proposed GA‐based approach performs well in delay‐constrained networks with multiantenna users. Compared to the considered state‐of‐the‐art schemes, our method reaches the highest service outage‐constrained end‐to‐end throughput with considerably less implementation complexity. Moreover, taking the users’ mobility into account, our GA‐based approach can remarkably reduce the beam refinement delay at low/moderate speeds when the spatial correlation is taken into account. Finally, we compare the cases of collaborative users and noncollaborative users and evaluate their difference in system performance.

Initial access (IA) is identified as a key challenge for the upcoming 5G mobile communication system operating at high carrier frequencies, and several techniques are currently being proposed. In this paper, we extend our previously proposed genetic algorithm (GA)-based beam refinement scheme to include beamforming at both the transmitter and the receiver, and compare the performance with alternative approaches in the millimeter wave multi-user multiple-input-multiple-output (MU-MIMO) networks. Taking the millimeter wave communications characteristics and various metrics into account, we investigate the effect of different parameters such as the number of transmit antennas/users/per-user receive antennas, beamforming resolution as well as hardware impairments on the system performance employing different beam refinement algorithms. As shown, our proposed GA-based approach performs well in delay-constrained networks with multi-antenna users. Compared to the considered state-of-the-art schemes, our method reaches the highest service outage-constrained end-to-end throughput with considerably less implementation complexity. Moreover, taking the users' mobility into account, GA-based approach can remarkably reduce the beam refinement delay at low/moderate speeds when the spatial correlation is taken into account.

We study the performance of multi-hop networks composed of millimeter wave (MMW)-based radio frequency (RF) and free-space optical (FSO) links. The results are obtained in the cases with and without hybrid automatic repeat request (HARQ). Taking the MMW characteristics of the RF links into account, we derive closed-form expressions for the network outage probability. We also evaluate the effect of various parameters such as power amplifiers efficiency, number of antennas as well as different coherence times of the RF and the FSO links on the system performance. Finally, we present mappings between the performance of RF- FSO multi-hop networks and the ones using only the RF- or the FSO-based communication, in the sense that with appropriate parameter settings the same outage probability is achieved in these setups. The results show the efficiency of the RF-FSO setups in different conditions. Moreover, the HARQ can effectively improve the outage probability#x002F;energy efficiency, and compensate the effect of hardware impairments in RF-FSO networks. For common parameter settings of the RF-FSO dual- hop networks, outage probability 10^{-4} and code rate 3 nats-per-channel-use, the implementation of HARQ with a maximum of 2 and 3 retransmissions reduces the required power, compared to the cases with no HARQ, by 13 and 17 dB, respectively.

Cellular networks operating at millimeter wave (mmWave) frequencies are able to achieve multi-gigabit-per-second data rates due to the large bandwidth available. However, the data transmission range will be shorter and significant signal power difference will be observed between line-of-sight (LOS) and non-line-of-sight (NLOS) links. This paper considers interference management and useful signal enhancement in the uplink transmission of small-cell mmWave networks. Taking blockages into account, we analyze the coverage performance of the partial-zero-forcing (PZF) receiver which utilizes a number of antennas to cancel out the strongest uplink interferers and uses the rest of the antennas for boosting the useful signal. Using stochastic geometry, we derive analytical expressions for the coverage probability of the PZF receiver under a LOS probability function based path loss model. For a broad range of parameter settings, the maximum coverage probability is achieved by using most antennas for array gain and only canceling a few strongest interferers. Particularly, compared to zero-forcing, the PZF scheme can improve the coverage probability significantly.

In this paper, we study the performance of initial access beamforming schemes in the cases with large but finite number of transmit antennas and users. Particularly, we develop an efficient beamforming scheme using genetic algorithms. Moreover, taking the millimeter wave communication characteristics and different metrics into account, we investigate the effect of various parameters such as number of antennas/receivers, beamforming resolution as well as hardware impairments on the system performance. As shown, our proposed algorithm is generic in the sense that it can be effectively applied with different channel models, metrics and beamforming methods. Also, our results indicate that the proposed scheme can reach (almost) the same end-to-end throughput as the exhaustive search-based optimal approach with considerably less implementation complexity.

This paper introduces a new metric, referred to as delay-sensitive area spectral efficiency (DASE), to analyze the performance of delay-constrained wireless networks. We study DASE in different point-to-point, spectrum sharing, interference, and Poisson-point process-based dense network configurations and with different levels of channel state information (CSI) at the transmitters. Also, we determine the optimal rates/powers optimizing DASE. Finally, we use some recent results on finite block-length codes to analyze the effect of the codewords length on the network DASE. As demonstrated, DASE is a useful metric for analyzing delay-sensitive green networks. Moreover, adaptive power allocation and partial CSI feedback are powerful tools for performance improvement in green networks.

This paper studies the performance of multi-hop and mesh networks composed of millimeter wave-based radio frequency (RF) and free-space optical (FSO) links. The results are obtained in cases with and without hybrid automatic repeat request (HARQ). Using the central limit theorem as well as other state-of-the-art approximation schemes, we derive closed-form expressions for the networks' outage probability and ergodic achievable rates. We also evaluate the effect of various parameters such as power amplifiers efficiency, number of antennas as well as different coherence times of the RF and the FSO links on the system performance. Finally, we determine the minimum number of the transmit antennas in the RF link such that the same rate is supported in the RF- and the FSO-based hops. The results show the efficiency of the RF-FSO setups in different conditions. Moreover, HARQ can effectively improve the outage probability/energy efficiency, and compensate for the effect of hardware impairments in RF-FSO networks. For common parameter settings of the RF-FSO dual-hop networks, outage probability of 10-4and code rate of 3 nats-per-channel-use, the implementation of HARQ with a maximum of 2 and 3 retransmissions reduces the required power, compared to cases with open-loop communication, by 13 and 17 dB, respectively.

This paper investigates the outage probability and the throughput of relay networks with joint information and energy transfer where the relay harvests energy from transmitted radio-frequency (RF) signal of the source. Considering different power consumption models, we derive the outage probability of the systems for both adaptive and non-adaptive power allocations at the relay. With a total energy consumption constraint at the source, we provide closed-form expressions for the optimal time sharing and power allocation between the source energy and information transfer signals. The analytical and simulation results demonstrate the efficiency of joint energy and information transfer systems in different conditions.

This paper studies the performance of hybrid radio-frequency (RF) and free-space optical (FSO) links in the cases with and without hybrid automatic repeat request (HARQ). Considering millimeter wave (mmwave) characteristics in the RF link and pointing errors in the FSO link, we derive closed-form expressions for the message decoding probabilities as well as the throughput and the outage probability of the RF-FSO setups. We also evaluate the effect of various parameters such as power amplifiers efficiency, different transmission techniques in the FSO link, pointing errors in the FSO link as well as different coherence times/symbol rates of the RF and the FSO links on the throughput and outage probability. The results show the efficiency of the RF-FSO links in different conditions. Moreover, the HARQ can effectively improve the outage probability/energy efficiency, and compensate the effect of hardware impairments in RF-FSO links.

In this paper, we develop a green joint power and information transfer system. To guarantee reliable communication, we implement hybrid automatic repeat request (HARQ) feedback both in the power and information transmission phases. Moreover, with a limit on the packet transmission delay, we derive the optimal power allocation minimizing the energy-constrained outage probability. The simulation and analytical results indicate that the diversity gain of the joint power and information transfer system is the same as the diversity gain of the conventional non-green information transfer systems. Also, the implementation of HARQ improves the power efficiency significantly. For instance, consider a Rayleigh fading channel, outage probability 10-3, code rate 1 nats-per-channel-use and the case where the receiver requires to receive 0.1 Joule-per-channel-use energy per codeword length from the transmitter to process the information. Then, with a maximum of two retransmissions in the power and information transfer phases, the HARQ reduces the average required energy by 4 dB, compared to the open-loop communication setup.

Recently, substantial attention has been paid to analyse the performance of wireless networks in the cases where the positions of the base stations are modelled by stochastic geometry. In this study, the authors analyse the performance of Rayleigh‐fading Poisson‐point‐process (PPP)‐based networks. They derive the optimal transmission rate that maximises the per‐user throughput. Also, they determine sufficient conditions for positive diversity gain in PPP‐based networks, develop tight approximations for the effective density of the network and give a simplified expression to calculate the outage probability for the interference‐limited case. The analytical and the numerical results demonstrate considerable potential for efficient data transmission in PPP‐based networks.

This paper investigates the performance of the point-to-point multiple-input-multiple-output (MIMO) systems in the presence of a large but finite numbers of antennas at the transmitters and/or receivers. Considering the cases with and without hybrid automatic repeat request (HARQ) feedback, we determine the minimum numbers of the transmit/receive antennas, which are required to satisfy different outage probability constraints. Our results are obtained for different fading conditions and the effect of the power amplifiers efficiency/feedback error probability on the performance of the MIMO-HARQ systems is analyzed. Then, we use some recent results on the achievable rates of finite block-length codes, to analyze the effect of the codewords lengths on the system performance. Moreover, we derive closed-form expressions for the asymptotic performance of the MIMO-HARQ systems when the number of antennas increases. Our analytical and numerical results show that different outage requirements can be satisfied with relatively few transmit/receive antennas.

In this paper, we propose and analyze a wireless energy and information transfer system. To reduce the outage probability, compared with open-loop communication, we implement retransmission protocols both in the energy and in the information transmission phases. We use some recent results on finite block-length codes to analyze the effect of the energy and information signals lengths on the system outage probability/throughput. Finally, under a packet transmission delay constraint, we derive the optimal power allocation and time sharing between the energy and information signals, such that the energy-constrained outage probability is minimized. The simulation and analytical results demonstrate that the retransmission-based protocols are efficient techniques to reduce the energy-limited outage probability of wireless energy and information transmission systems.

This paper studies the performance of hybrid radio-frequency (RF) and free-space optical (FSO) links assuming perfect channel state information (CSI) at the receiver. Considering the cases with and without hybrid automatic repeat request (HARQ), we derive closed-form expressions for the message decoding probabilities as well as the throughput and the outage probability of the RF-FSO setups. We also evaluate the effect of adaptive power allocation and different channel conditions on the throughput and the outage probability. The results show the efficiency of the RF-FSO links in different conditions.

This paper studies the performance of the hybrid radio-frequency (RF) and free-space optical (FSO) links assuming perfect channel state information (CSI) at the receiver. Considering the cases with and without hybrid automatic repeat request (HARQ), we derive closed-form expressions for the message decoding probabilities as well as the throughput and the outage probability of the RF- FSO setups. We also evaluate the effect of different channel conditions on the throughput and the outage probability. The results show the efficiency of the RF-FSO links in different conditions.

This paper studies the sum throughput maximization of the return-link in multi-beam satellite systems. Considering bursty communication scenarios with different users' data request probabilities, we develop an efficient scheduling scheme using genetic algorithms (GAs). Moreover, we consider co-channel interference (CCI) and adjacent channel interference (ACI). We consider a receiver with and without interference cancelation. Using a simplified channel model, we evaluate the proposed scheduler in a multi-beam system. The proposed GA-based scheduler approaches the throughput of an optimal scheduler based on exhaustive search with substantially less implementation complexity.

This paper studies the throughput of spectrum sharing networks utilizing rate adaptation. We use some recent results on the achievable rates of finite block-length codes to analyze the secondary user (SU) throughput with a constraint on the primary user (PU) codeword drop probability. With codewords of finite length, we derive closed-form expressions for the SU activation probability and throughput. The results are obtained in different scenarios with no channel state information at the SU transmitter. As demonstrated numerically and analytically, using finite-length codewords there is considerable potential for the data transmission of unlicensed secondary users under different quality-of-service requirements of the licensed primary users.

Hybrid automatic repeat request (HARQ) plays an important role in improving the transmission efficiency and the robustness of wireless networks. Considering K-tier heterogeneous networks (HetNets) and modelling the locations of the base stations (BSs) as a homogeneous Poisson point process (PPP), this paper investigates the performance of HetNets implementing HARQ. We give closed- form expressions for the quality of service (QoS) coverage probability which is defined in terms of whether the received signal quality is above a predetermined threshold, and the per-user throughput with HARQ. We show that using HARQ can indeed improve the QoS coverage probability. However, depending on the channel conditions, the per-user throughput of the HetNets may decrease by the implementation of HARQ. Furthermore, we show that the small cell density has negligible effect on the QoS coverage probability and the per-user throughput, and the per-user throughput may increase with the small cell path loss.

This paper studies the problem of feedback resource allocation in multiple-input-single-output (MISO) channels utilizing partial channel state information (CSI) feedback. Considering low/moderate signal-to-noise ratios (SNRs), the optimal quantizers and the feedback bit allocation maximizing the throughput are obtained in the asymptotic case where the number of feedback bits increases. Moreover, the results are utilized to derive the optimal retransmission rates in the automatic repeat request (ARQ) protocols and joint CSI-ARQ schemes are proposed for the MISO setups. We show that uniform channel amplitude quantization is asymptotically optimal in terms of throughput. Also, the optimal retransmission rates of the incremental redundancy (INR) ARQ protocols follow an arithmetic progression in the exponential domain. Under certain conditions, a MISO system using quantized CSI can be mapped to a MISO or a SISO (S: single) setup using ARQ or joint CSI-ARQ feedback in the sense that they lead to the same throughput. Finally, to maximize the throughput, the optimal number of channel direction quantization bits should be (M-1) times the number of amplitude quantization bits, where M is the number of transmit antennas.

This paper studies the throughput of spectrum sharing networks utilizing rate adaptation. We use some recent results on the achievable rates of finite block-length codes to analyze the secondary user (SU) throughput with a constraint on the primary user (PU) codeword drop probability. With codewords of finite length, we derive closed-form expressions for the SU activation probability and throughput. The results are obtained in different scenarios with perfect or no channel state information at the SU transmitter. As demonstrated numerically and analytically, using finite-length codewords and rate adaptation, there is considerable potential for the data transmission of unlicensed secondary users under different quality-of-service requirements of the licensed primary users.

This paper studies the energy-limited performance of multi-relay networks. Taking the properties of the power amplifiers (PAs) into account, we derive closed-form expressions for the optimal power allocation, the outage probability and the throughput in the cases with a sum consumed energy constraint. Moreover, we analyze the diversity and the multiplexing gains of the PA-aware systems. Finally, we investigate the performance of large-scale multi-relay networks and develop efficient multi-relay systems with low cooperation overhead. The numerical and the analytical results show that the inefficiency of the PAs affects the outage probability and the throughput of the multi-relay systems substantially.

This paper studies the effect of optimal power allocation on the performance of communication systems utilizing automatic repeat request (ARQ). Considering Type-I ARQ, the problem is cast as the minimization of the outage probability subject to an average power constraint. The analysis is based on some recent results on the achievable rates of finite-length codes and we investigate the effect of codewords length on the performance of ARQ-based systems. We show that the performance of ARQ protocols is (almost) insensitive to the length of the codewords, for codewords of length ≥ 50 channel uses. Also, optimal power allocation improves the power efficiency of the ARQ-based systems substantially. For instance, consider a Rayleigh fading channel, codewords of rate 1 nats-per-channel-use and outage probability 10-3. Then, with a maximum of 2 and 3 transmissions, the implementation of power-adaptive ARQ reduces the average power, compared to the open-loop communication setup, by 17 and 23 dB, respectively, a result which is (almost) independent of the codewords length. Also, optimal power allocation increases the diversity gain of the ARQ protocols considerably.

Recently, substantial attention has been paid to improve the spectral efficiency of communication setups using different spectrum sharing techniques. This paper studies the throughput of spectrum sharing channels utilizing hybrid automatic repeat request (HARQ) protocols. Considering different HARQ schemes, the unlicensed user throughput is obtained under an outage probability constraint for the licensed user. The outage-limited throughput is obtained for both independent and spatially-correlated fading conditions, where there is spatial dependency between the fading coefficients. The results show that, using HARQ and adaptive power allocation, the maximum throughput is achieved by combination of simultaneous transmission and interference-avoiding spectrum sharing paradigms. The performance of the spectrum sharing networks is not sensitive to spatial correlation, within the practical range, and the throughput changes are negligible at low/moderate correlations. Finally, there is considerable potential for data transmission of the unlicensed user with limited performance degradation of the licensed user.

This paper investigates the performance of multiple-input-multiple-output (MIMO) systems in the presence of automatic repeat request (ARQ) feedback. We show that, for a large range of performance metrics, the data transmission efficiency of the ARQ schemes is determined by a set of parameters which are scheme-dependent and not metric-dependent. Then, the results are used to study different aspects of MIMO-ARQ such as the effect of nonlinear power amplifiers, large-scale MIMO-ARQ, adaptive power allocation and different data communication models. The results, which are valid for various forward and feedback channel models, show the efficiency of the MIMO-ARQ techniques in different conditions.

We study the power allocation problem for the downlink of a cooperative system with different node activeness, i.e., each receiving node requests for data transmission according to a certain probability. Data symbols of the active nodes are jointly transmitted from cooperative transmission points using zero-forcing precoding. The problem is cast in form of maximizing the ergodic achievable rate subject to per-transmit-point average total power constraints. The derived power allocation indicates that depending on the channel conditions and receiving nodes' activation probability, the optimal solution takes the form of either greedy power allocation or power sharing allocation.

This paper studies the problem of feedback subsampling in temporally-correlated wireless networks utilizing quantized channel state information (CSI). Under both peak and average power constraints, the system data transmission efficiency is studied in two scenarios. First, we focus on the case where the codewords span one fading block. In the second scenario, the throughput is determined for piecewise slowly-fading channels where the codewords are so long that a finite number of correlated gain realizations are experienced during each codeword transmission. Considering different temporal correlation conditions in both scenarios, substantial throughput increment is observed with feedback rates well below 1 bit per slot.

This paper addresses the problem of limited CSI feedback in coordinated multi-point (CoMP) networks. Specifically, the system throughput is obtained for block-fading CoMP channels with quantized CSI feedback, and the effect of feedback bit allocation on the system throughput is investigated for different user locations and fading distributions. The analytical and simulation results show that substantial throughput increment is achieved via CoMP joint transmission with very limited number of feedback bits per base station. The effect of optimal bit allocation becomes more important for the user that is located in the CoMP cluster edge areas. Also, the standard Zonal-sampling scheme provides the best bit allocation strategy in many cases, maximizing the system throughput.

This paper addresses the problem of optimal power allocation for hybrid automatic repeat request (HARQ) feedback over slowly-fading channels. We mainly focus on the repetition time diversity HARQ scheme where the results are obtained for both continuous and bursting communication models. Moreover, the effect of an outage probability constraint on the system data transmission efficiency is studied under different transmission power constraints. Simulation results show that 1) for Nakagami fading channels, the optimal HARQ-based (re)transmission powers maximizing the system throughput should be decreasing in every (re)transmission round, 2) higher rates are achieved in the continuous communication, when compared with the bursting model, and 3) HARQ feedback leads to considerable performance improvement even in outage-limited conditions.

This study proposes the performance of a scheduling scheme using two-step quantised channel state information (CSI) feedback. Considering fixed and random access networks, the results are obtained under both short- and long-term power constraints and for both single- and multi-layer transmission techniques. Further, the authors evaluate the asymptotic performance of the proposed scheme and show that, while the users scheduling is based on quantised CSI feedback in the first round, the second round of partial CSI feedback can be provided by either channel quantisation or hybrid automatic repeat request feedback, leading to the same forward channel average rate. In comparison with the case of no CSI feedback, the results indicate substantial average rate increment with limited number of feedback bits. Also, the average rate increases via successive partial CSI feedback when compared with one-step CSI feedback schemes.

Recently, substantial attention has been paid to increase the achievable rates of wireless networks using different kinds of limited channel quality information feedback. Hybrid automatic repeat request (ARQ) and quantized channel state information (CSI) feedback are two well-known approaches applied by experts to provide the limited channel quality information at the transmitter. Considering quasi-static fading channels, this paper aims to provide some comparisons between the performance of these methods from different points of view. The paper first investigates the power- and outage-limited performance of hybrid ARQ and quantized CSI schemes under short- and long-term power constraints. Then, 1) the feedback signaling load, 2) robustness and 3) the complexity of these schemes are compared under short-term transmission power constraint. Both INcremental Redundancy (INR) and Repetition Time Diversity (RTD) approaches are considered for hybrid ARQ feedback. Finally, approximate low-complexity solutions are presented for power allocation in the INR ARQ-based scheme under long-term transmission power constraint. Analytical and numerical results demonstrate the equivalency or the superiority of these approaches in different circumstances.

Spectrum sharing networks are communication setups in which unlicensed secondary users are permitted to work within the spectrum resources of primary licensees. Considering quasi-static fading environments, this paper studies the effect of hybrid automatic repeat request (HARQ) feedback on the average rate of unlicensed spectrum sharing channels. The results are obtained for different scenarios; Under both peak and average secondary user transmission power constraints, the channel average rate is determined under primary user limited received interference power conditions when there is perfect information about the interference available at the secondary user transmitter. An approximate solution for power allocation between incremental redundancy (INR) HARQ-based data retransmissions is proposed which can be applied in single-user networks as well. Then, we investigate the effect of imperfect secondary-primary channel state information on the interference-limited average rate of the secondary channel. Finally, we restudy all mentioned scenarios in the case where the data transmission is constrained to have limited outage probability. Substantial performance improvement is observed with even a single HARQ-based retransmission in all simulations.

Spectrum sharing networks are communication setups in which unlicensed secondary users (SUs) are permitted to work within the spectrum resources of licensed primary users (PUs). This paper aims to study the ergodic achievable rates of spectrum sharing networks with finite backlogged primary user and an interference indicator signal. Here, in contrast to the standard interference-avoiding schemes, the secondary user activity is not restricted within the primary user inactive periods. Considering both fading and nonfading channels, the unlicensed user ergodic achievable rate is obtained for different unlicensed user transmission power and licensed user received interference power or signal-to-interference-and-noise (SINR) constraints. In the case of fading channels, the results are obtained for both short- and long-term primary user quality-of-service requirements. Further, the results are generalized to the case of multiple interfering users. In terms of unlicensed user ergodic achievable rate, analytical results indicate that while the standard interference-avoiding approach is the optimal transmission scheme at low secondary user or high primary user transmission powers, higher rates can be achieved via simultaneous transmission at high secondary user SINRs. Moreover, numerical results show that, using an interference indicator signal, there is considerable potential for data transmission of unlicensed users under different licensed users quality-of-service requirements.

We present a new rate allocation scheme for multilevel coded modulation based on the minimization of the total block error rate (BLER). The proposed method uses affine code components and hard decision multistage decoding. Exhaustive search for the rate allocation which minimizes the total BLER justifies the near-optimum performance of the introduced method in moderate to high SNRs. Compared to previous approaches this new rate allocation scheme can improve the performance of the system by 1 dB at BLER = 10-6for 16-QAM with Ungerboeck set partitioning. Interestingly, our results indicate that the optimum rate allocation is a function of the SNR. Finally, the performance of some specific codes are evaluated by simulation and union bounds to verify the theoretical results.

Recently, substantial attention has been paid to increase the achievable rates of wireless networks using different kinds of limited channel state information (CSI) feedback. This paper aims to investigate the effect of limited noisy CSI feedback on the achievable rates of power-limited block fading channels constrained to have limited outage probability. Considering different power allocation strategies and various fading conditions, the results are obtained for different outage probabilities and are compared with the case where there is no outage limitation. Moreover, considering different outage probability constraints, the effect of feedback channel noise on the average rates of the forward channel is studied and compared with the ones obtained under noise-free feedback link assumption. Simulation results show that 1) although the outage probability constraint reduces the channel average rate, its influence diminishes as the channel state information feedback or the input power increases, 2) the effect of the outage probability constraint decreases as the forward channel fading severity or the feedback channel noise is reduced.

Recently, substantial attention has been paid to compress the channel quality information feedback while preserving most of its relevant information, as required for Adaptive Modulation and Coding (AMC). This paper compares the performance of some lossy feedback compression methods and, particularly, investigate the effect of bit allocation on their performance. Simulation results show that the Discrete Cosine Transform (DCT) approach, along with our proposed bit allocation method, leads to the best feedback compression performance.

Recently, substantial attention has been paid to increase the achievable rates of wireless networks using different kinds of limited channel state information (CSI) feedback. This paper aims to investigate the effect of limited CSI feedback on the achievable rates of power-limited block fading channels constrained to have limited outage probability. Considering different power allocation strategies and various fading conditions, the results are obtained for different outage probabilities and are compared with the case where there is no outage limitation. Simulation results show that 1) although the outage probability constraint reduces the channel average rate, its influence diminishes as the channel state information feedback or the input power increases, 2) the effect of the outage probability constraint decreases as the channel fading severity is reduced.

Nonlinear principal component analysis (NLPCA) is one of the most progressive computational tools developed during the last two decades. However, in spite of its proper performance in feature extraction and dimension reduction, it is considered as a blind processor which can not extract physical or meaningful factors from dataset. This paper presents a new distributed model of autoassociative neural network which increases meaningfulness degree of the extracted parameters. The model is implemented to perform voice conversion (VC) and, as it will be seen through comparisons, results in proper conversion quality.

In this paper, a new constructive auto-associative neural network performing nonlinear principal component analysis is presented. The developed constructive neural network maps the data nonlinearly into its principal components and preserves the order of principal components at the same time. The weights of the neural network are trained by a combination of Back Propagation (BP) and Genetic Algorithm (GA) which accelerates the training process by preventing local minima. The performance of the proposed method was evaluated by means of two different experiments that illustrated its efficiency.

By using a novel 2D genetic algorithm, the band gaps of two-dimensional (2D) photonic crystals are maximized. In this procedure the unit cell is divided into small grids. Each filling pattern of the grids is translated into a matrix of binary elements. A novel crossover and mutation operator is developed to obtain structures with maximum relative band gaps. By applying the proposed operator, the required number of generations is extremely reduced. In addition, a semi-analytical method is introduced for calculating the photonic crystal band structures. Because of this efficient method, the required computation time of the fitness function is significantly reduced. The paper presents two optimized photonic crystal structures with a relative band gap of 21%.