This paper presents an analysis of the performance of a multi-hop multi-relay network where all nodes are battery-assisted (BA) energy harvesting (EH) devices, harvesting energy from a dedicated power beacon. In each hop, the relay with the largest energy is selected for relaying from the nodes that have successfully decoded the symbols in the previous hop. This selected node then augments the harvested energy with some battery energy to relay information. Note that such BA EH nodes can be readily implemented to extend battery lifetimes. In any hop, signalling stops if the direct link to the destination is successful. Using a practical nonlinear EH model, analytical expressions are presented for outage probability, throughput, average battery energy consumption, and battery energy efficiency (ηBEE). The results demonstrate that, despite the nonlinearity in EH, substantial enhancement in the system throughput and ηBEEis possible due to the presence of the direct link. Furthermore, an optimal combination of EH duration, hop count, and target information rate is demonstrated to maximize the overall ηBEEfor a desired throughput. Monte-Carlo simulations validate the accuracy of the derived expressions.

This paper considers a multi-user downlink non-orthogonal multiple access (NOMA) framework comprising of an access point (AP), a cluster of N near-users (NUs), and a cluster of F far-users (FUs). The AP shares direct links to both NUs and FUs. Using only a one-bit feedback from the selected users, the network switches between NOMA, cooperative NOMA, and orthogonal multiple access (OMA) modes. Considering channel-aware dynamic power allocation (DPA), closed-form expressions are derived for the outage probability, throughput, and EE for the first time in literature with novel power control, mode selection, and user selection. Further, it is demonstrated that the power allocation with very limited channel state information (CSI) results in a significant gain in throughput and also saves power at AP, thereby increasing EE. We show in that intelligent user selection and use of channel-aware techniques is the key to high spectral efficiency (SE) and energy efficiency (EE). It is shown how the minimum transmit power at the AP and the NU, as well as the best NOMA power-allocation can be determined based on limited channel knowledge to maximize SE and EE. The use of minimum power needed for all three modes further improve the EE of DPA by 16.43%. We also demonstrate that in contrast to the fixed power allocation (FPA) scheme, the DPA scheme increases the mode probability of NM, thereby increasing SE. Closed-form expressions are derived for the minimum average power consumption and power increments to switch to modes yielding larger throughput. We demonstrate that choosing the optimal target rate is essential to maximize the EE. Monte Carlo simulations validate the derived expressions.

The challenging issue of managing human eye irradiance from a light source poses a critical hurdle in uplink data transmission within visible light communication (VLC) systems. Eye irradiance and the data rate are influenced by the transmit power. Therefore, the transmit power must be optimized to achieve the maximum data rate while preventing the irradiance of the eye. To tackle this, multiple transmitters and receivers with partitioned intelligent reflecting surface (IRS) units cooperative VLC system is proposed in this work. Further, the formulation of an optimization problem is done in order to minimize the total transmit power requirements by putting constraints on achievable data rates. Furthermore, the optimization problem is addressed analytically and verified through simulations by employing the proposed evolutionary power minimization algorithm (EPMA). Our study shows that optimization and IRS make the system energy efficient. In addition, extensive numerical findings indicate that an IRS with optimization substantially reduces the transmit power requirements and improves the data rate.

This study analyzes the performance of a two-hop communication system that integrates free-space optical (FSO) transmission with intelligent reflecting surface (IRS)-aided radio frequency (RF) transmission. This analysis focuses on the transmission within a non-orthogonal multiple access (NOMA) system over heterogeneous channels: the source-to-relay FSO channel follows a Fisher-Snedecor$F$distribution, the relay-to-users RF channels are modeled as Rayleigh distributions, the relay-to-IRS and IRS-to-users RF channels are characterized by Rician distributions. A closed-form expression for the outage probability has been derived and approximated as a Gamma distribution using the moment-generating function under imperfect successive interference cancellation. Notably, the outage probability expressions and their approximation closely align with our simulation results, thus validating the accuracy of our findings. Additionally, an asymptotic expression for the outage probability has been derived, particularly in the FSO transmit SNR regime, and the corresponding diversity order is evaluated. The impact of various system parameters, such as turbulence, on the rate of decay of the outage probability is explained through the diversity order.

This work investigates a multihop multirelay network in which all nodes are of the battery-assisted (BA) energy harvesting (EH) type, and harvest energy from a power beacon. In each hop, the node with the most harvested energy is selected for relaying and augments the harvested energy with some battery energy. Note that such BA EH nodes are immediately realizable to prolong battery lifetimes. Considering nonlinear EH, analytical expressions are derived for outage probability, throughput, average battery energy consumption, and battery energy efficiency (BEE). It is first shown how the parameters can be chosen to maximize the network throughput. Since unsuccessful relaying that results in outage causes battery energy to be consumed, optimizing the network to minimize the average battery energy consumption or to maximize the node-level BEE is well motivated. We show that the judicious selection of the EH duration can minimize average battery energy consumption while achieving the target throughput requirement. Moreover, a joint optimal choice of EH duration, hop count, and target information rate is shown to maximize overall BEE. Monte Carlo simulations validate the accuracy of the derived expressions.

This paper investigates a cooperative Internet of Things (IoT) non-orthogonal multiple access (NOMA) network comprising of a multi-antenna base station (BS), a near IoT user (NU) with full-duplex capabilities, and multiple far IoT users (FU). The NU utilizes the power-splitting (PS) energy harvesting (EH) protocol and augments the harvested energy with a little energy from its battery to assist the FU. Considering the novel cooperative NOMA/non-cooperative (C-NM/NC) switching, the impact of successive interference cancellation (SIC), channel state information (CSI) errors, and nonlinear EH, closed-form expressions are derived for average blocklength error rates (BLER) of both users in finite blocklength regime. Utilizing the derived BLER expressions, the Goodput, Reliability, Latency, and battery power efficiency are expressed in closed form. We then demonstrate that the CSI errors severely degrades the performance of both the users. Monte Carlo simulations validate the accuracy of the derived analytical expressions. We also establish that a significantly better maximum performance is attained at the FU, given a target NU Goodput by the careful choice of NOMA and EH parameters. C-NM/NC switching offers a higher EE and better self-interference immunity. Results indicate that the choice of blocklength is crucial for efficient system performance.

In this work, we consider a cooperative communication network wherein a base station (BS) utilizes a simultaneous wireless power and information transfer (SWIPT) energized full duplex-decode and forward relay to communicate with a downlink user. The relay augments the harvested energy with a bit of energy from its battery. Assuming a practical nonlinear energy harvesting (EH) model, we derive approximated closed-form expressions for the end-to-end blocklength error rate (BLER) under the finite blocklength (FBL) regime for both power splitting (PS) and time switching (TS) protocols. We then derive a high-SNR approximated expression for end-to-end BLER to demonstrate the interplay of the battery energy, blocklength, and EH parameters on the system’s performance. We also analytically establish the convexity of the BLER with respect to the relay’s battery energy. Using the expression for the BLER, we derive expressions for the goodput and battery energy efficiency in approximated closed-form. Moreover, for a desired target BLER requirement, we show that, by carefully choosing the TS/PS parameter, the required relay’s battery energy can be minimized. The accuracy of the derived analytical expressions is validated using Monte Carlo simulations. Finally, we discuss the impact of key parameters such as transmit power, total available blocklength, nonlinear EH, TS, and PS parameters, and battery energy on the network’s performance.

This paper investigates the performance of a partition-enabled intelligent reflecting surface (IRS)-assisted cooperative non-orthogonal multiple access (C-NOMA) framework. In this setup, the source communicates with wireless powered near user (NU) directly as well as via the IRS, and with the far user (FU) solely through the IRS. Since the harvested energy is typically small, use of the IRS is explored (for the first time in literature) in the second phase of C-NOMA transmission to boost the FU performance. The system opportunistically switches between NOMA and C-NOMA modes using a feedback-based strategy to enhance user fairness. When operating in C-NOMA mode, the NU harvests energy for relaying information to the FU, which ensures that the NU does not have to expend its own energy for relaying, and also improves the overall energy efficiency (EE) due to use of the IRS in the second phase of C-NOMA transmission. Closed-form expressions for NU and FU throughputs, as well as EE are derived for the first time while considering wireless power transfer (WPT), as well as IRS partitioning and mode switching. These expressions are validated through Monte Carlo simulations.

Due to explosion in the number of Internet of Things (IoTs), and the need to ensure that they are of small cost and form factor, it is expected that most of these will be self-sustaining in the near future, deriving energy by energy harvesting. In this paper we analyze the performance of a multihop network consisting solely of energy harvesting IoTs. Clusters of IoTs in the vicinity assist in communication to the destination. In any hop, if the direct link to the destination is successful, the signalling is halted. The relay with the largest energy is picked in each hop from those that successfully decode the symbols in the previous hop. Using a practical nonlinear EH model, expressions are derived for the throughput of the scheme. It is shown that despite the nonlinearity in EH, the presence of the direct link significantly improves the throughput. Monte-Carlo simulations validate the accuracy of the derived expressions.

This paper examines the performance of an underlay uplink non-orthogonal multiple access (NOMA) network over Nakagami-m fading channels. With the help of NOMA signalling notions, two users are serviced in the secondary network concurrently with the primary user's transmission. The transmit powers of secondary users are determined such that the cumulative interference at the primary receiver from the two secondary transmitting nodes is within the interference temperature limit (ITL). Since hardware impairments and channel estimation errors cause imperfect successive interference cancellation (SIC) in practical scenarios, imperfect SIC is considered in the analysis. Channel state information (CSI) based ITL apportioning is proposed for the first time in such scenarios taking into consideration both decoding orders. Our results demonstrate the supremacy of the suggested scheme over underlay orthogonal multiple access. We derive expressions for the outage probability and throughput of both users. Monte Carlo simulations validate the analytical expressions.

This paper investigates the delay performance of a battery-assisted (BA) multi-hop cluster-based network assuming that each hop consists of multiple relays. At each hop, all the nodes harvest energy from the power beacon utilizing the time-switching (TS) energy harvesting (EH) protocol, and augment it with limited energy from a battery in a battery-assisted EH framework. Note that such BA EH nodes are immediately realizable and can prolong battery lifetimes. For efficient relay's battery utilization, the relay with successful decoding status and the largest amount of the harvested energy is selected for forwarding the information in each hop. The symbols are retransmitted after energy harvesting if an acknowledgment is not received from at least one node in the next hop. Considering saturation-based nonlinear EH, an expression is derived for the average delay performance. We then demonstrate that the average delay can be minimized by optimal selection of the TS parameter. Our results also demonstrate that augmenting the harvested energy with a small amount of battery energy dramatically improves the average delay performance. In view of the explosion in number of machine-type devices (MTDs) in recent times, such analysis is of immense practical importance. Monte Carlo simulations validate accuracy of the derived expressions.

This paper analyzes the secrecy performance of a two-hop cooperative network with battery-assisted energy harvesting (EH) nodes. Both the source and the relay employ jamming to improve secrecy. A power beacon (PB) supplies energy to the nodes using the harvest-store-use (HSU) architecture. To counter the variation in harvested energy, some battery energy is added to it. Both nodes apportion this sum energy between the information and jamming symbols. We consider the maximal ratio combining (MRC) of the direct and relayed signals at the destination and the eavesdropper. We assume channel state information (CSI) of destination and eavesdropper links are not available at both the source and relay. We derive an approximate expression for secrecy outage probability assuming the selective decode-and-forward (SDF) protocol. We then derive the high-SNR approximation to it. We demonstrate improvement in secrecy performance with an increase in the transmit power of PB. Also, there exists an optimal power apportioning parameter different from equal power allocation that minimizes secrecy outage both at the source and at the relay. Extensive simulations corroborate the derived analytical results.

In this paper, we consider an ambient backscatter communication (AmBC) assisted massive machine type communication (mMTC) network comprising of an access point (AP), a cluster of backscatter devices (BDs), and a user. To achieve mMTC, non-orthogonal multiple access (NOMA) principles are used. When channel state information (CSI) knowledge is available at the AP, it is shown that the BDs can be scheduled intelligently, and the reflection coefficients of the BDs can be carefully chosen to improve the system throughput as well as energy efficiency (EE). For the first time in the literature, analytical closed-form expressions for the outage probability and throughput are derived for a NOMA signaling-based mMTC network considering Rayleigh faded channel coefficients. We confirm the accuracy of our analytical findings and showcase the advantages of the proposed scheme using Monte Carlo simulations.

This article presents an optimization strategy for an Industrial Internet of Things (IoT) configuration, with particular emphasis on the enhancement of spectrum efficiency (SE) and reliable connectivity. Our analysis delves into the intricacies of a communication model designed to facilitate the concurrent exchange of information between sensor-cum-actuator nodes and a controlling station through the shared spectrum of a licensed cellular network. Pairing between the controller and any sensor-cum-actuator node is facilitated by a simple opportunistic selection mechanism that does not involve additional channel overheads. To improve SE, all IoT nodes are equipped with full-duplex (FD) functionality, while reliability is improved by making the network adaptive. The transmit powers of IoT nodes are chosen by apportioning the interference temperature limit (ITL), in a manner that cumulative interference caused to the cellular network does not exceed the ITL. Under this constraint, the random transmit powers induce significant signal-to-noise ratio variations, which we exploit through adaptive network strategies involving careful choice of transmit powers and switching between FD and half-duplex (HD) modes, for optimal performance. We establish that adaptation is more effective when assisted by instantaneous channel knowledge, which leads to the evolution of the statistically optimum scheme (SOS), local channel aware scheme (LCAS), and the global channel aware scheme (GCAS) in this article. Analysis is presented for network throughput for each of the evolved schemes, and critical parameters responsible for adaptation are presented in closed-form. The accuracy of our analytical findings is verified through computer simulations.

This article investigates a cooperative nonorthogonal multiple access (Co-NM)-based network consisting of a multiantenna source, a full-duplex energy harvesting (EH) near user (NU) Internet of Things (IoT) node, and multiple distant user (DU) IoT nodes. The source shares a direct link to the NU, while the NU augments the harvested energy by a limited amount of its battery energy to relay the information to the selected DU. Considering time-switching (TS) or power-splitting (PS) protocol, practical nonlinear EH, successive interference cancellation error, and opportunistic Co-NM/orthogonal multiple access (OMA) (OM) switching, closed-form expressions are derived for the outage probability and throughput of both DU and NU. We demonstrate that the proposed opportunistic Co-NM/OM switching can ensure a performance similar to OM at the NU without loss in DU throughput. Also, a joint optimal choice of battery energy and PS/TS parameter helps in attaining a maximum energy efficiency (EE). Moreover, Co-NM/OM switching ensures higher EE as compared with Co-NM and OM.

This paper analyzes the performance of a spectrally-efficient non-orthogonal multiple access (NOMA) based signalling scheme in which two selected users are scheduled for uplink transmissions in an underlay multiuser network, taking successive interference cancellation (SIC) errors into account. The transmit powers of users are adjusted to maximize throughput while jointly satisfying the interference temperature limit (ITL) imposed by the primary receiver. The ITL is first assumed to be a statistically fixed quantity. Analytical expressions are derived for outage and throughput. Performance is then analyzed for the case of channel state information (CSI) dependent ITL. It is demonstrated that by indirectly exploiting primary channel knowledge, CSI dependent ITL ensures large throughput gains. Our results show the superiority of the proposed scheme using NOMA compared to conventional underlay orthogonal multiple access (OMA). Computer simulations confirm accuracy of the derived expressions.

This paper investigates an unconventional superposition scheme, i.e., rate-splitting multiple access (RSMA) to maximize the overall user fairness and high system performance gain for ultra-reliable low-latency communication (URLLC), enhanced mobile-broadband (eMBB) traffic coexistence in uplink scenarios. In particular, we focus on maximizing the worst-case performance of uplink eMBB and URLLC users when multiplexed in a given resource block using an effective rate-splitting approach among multiple sub-messages. Subsequently, a multi-objective optimization problem (MOOP) is formulated to jointly maximize the worst-case rate and minimize the worst-case packet-error probability (PEP) for eMBB and URLLC users, respectively, using effective power splitting and successive interference cancellation (SIC) decoding of the sub-messages. To solve the non-convexity of the formulated MOOP, we adopt a priori articulation scheme combined with the weighted product approach to transforming the MOOP into a single objective optimization problem (SOOP) and later, solve it using a low complex differential evolution (DE)-based meta-heuristic algorithm. We derive an optimal decoding strategy for sub-messages to ensure better user fairness among eMBB-URLLC traffic. Numerical simulations demonstrate the superiority of the considered RSMA-based superposition for hybrid eMBB-URLLC traffic over conventional slicing and superposition techniques. Moreover, the adopted weighted product method-based DE algorithm outperforms the state-of-art solutions.

In this study, we investigate the performance of a hybrid reconfigurable intelligent surface (RIS)-assisted non-orthogonal multiple access (NOMA) network, augmented with backscattering capabilities, designed to facilitate integrated sensing and communication (ISAC). Our primary objective is two-fold: first, to enhance the overall communication throughput, and second, to strengthen the sensing power for target detection. To achieve these goals, we introduce two novel dynamic user clustering algorithms namely composite distance and angle-based (CDA) and channel-oriented adaptive (COA) algorithm for grouping users into clusters with fixed base station and RIS positions, where the successive interference cancellation (SIC) is employed for effective communication within each pair. Moreover, we present a comprehensive optimization problem that jointly maximizes the sum rate and sensing power. This problem involves optimizing the transmit beamformer at the base station, the power allocation factors within each cluster, and the phase shifts at the RIS. This methodology not only adheres to strict power constraints and quality of service requirements at each receiving node but also ensures equitable resource allocation among the targets and enforces unit modulus phase shifts at each RIS element. To tackle the complex interdependencies and non-convex nature of the optimization problem, we introduce an advanced iterative algorithm based on alternative optimization (AO). This state-of-the-art technique employs successive convex approximation (SCA) to systematically address this multifaceted problem. Finally, the simulation results empirically validate the proposed algorithm’s effectiveness, considering the number of RIS elements, maximum power budget, number of targets, and imperfect channel state information (CSI) while showing the trade-off between communication and sensing performance.

As a revolutionary paradigm for green communication architecture for next-generation, reconfigurable intelligent surfaces (RISs) has been considered for simultaneous wireless information and power transfer (SWIPT). Nevertheless, the performance gain achieved by the conventional passive RISs is limited due to the multiplicative fading effect. In this paper, we investigate an unconventional framework of active reconfigurable intelligent surface (ARIS) aided multi-user (MU) multi-input multi-output (MIMO) system to captivate better performance for the SWIPT system. Particularly, we focus on the problem of power minimization via joint beamforming design at the base station (BS) and the ARIS for the considered SWIPT system under statistical channel estimation error (CEE) while guaranteeing the minimum rate requirement and the minimum energy-harvested constraints for information and energy receivers, respectively. Owing to the non-convex and NP-hard nature of the formulated problem, we first utilize a minimum mean square error (MMSE) approach to transform the problem into its simplified form, and later utilize an alternating optimization framework which solves the problems of beamforming design at the BS and the ARIS independently in an iterative manner using general approximations. Simulation results confirm that the ARIS can significantly reduce the required transmission power by 50-60% when compared to passive RIS while satisfying given QoS constraints for SWIPT system under the CEE model.

In this paper, we consider a multi-user downlink non-orthogonal multiple access (NOMA) network comprising of an access point (AP), multiple near-user (NU) nodes and multiple far-user (FU) nodes. The NUs and FUs exist in clusters of size$N$and F, respectively. Using limited channel state information (CSI) knowledge, intelligent NU and FU selection coupled with mode switching between NOMA and orthogonal multiple access (OMA) is applied to improve the system throughput and energy efficiency. Considering the case of fixed power allocation (FPA) and dynamic power allocation (DPA), closed-form throughput expressions are derived for the first time in literature with mode selection and user selection. It is seen that power allocation with very limited CSI provides huge gains in throughput and saves power at the AP, and thereby increases the energy efficiency. We validate the correctness of analytical results and the superiority of the considered scheme through Monte-Carlo simulations.

This paper investigates an unconventional framework of active reconfigurable intelligent surface (ARIS) aided multi-user (MU) multi-input multi-output (MIMO) system for simultaneous wireless information and power transfer (SWIPT) network under statistical channel estimation error (CEE). Particularly, we focus on the problem of power minimization via joint beamforming design at BS and ARIS for considered SWIPT system while guaranteeing the minimum rate requirement and the minimum energy-harvested constraints for information and energy receivers, respectively. Owing to the non-convex and NP-hard nature of the formulated problem, we first utilize a minimum mean square error (MMSE) approach to transform the problem into its simplified form, and later utilize an alternating optimization framework which solves the problems of beamforming design at BS and ARIS independently in an iterative manner using general approximations. Simulation results confirm that ARIS can significantly reduce the required transmission power by 50-60% when compared to passive RIS while satisfying given QoS constraints for SWIPT systems under the CEE model.

In order to support the need for higher spectral and energy efficiencies with a wider coverage area, simultaneous refracting/transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) and rate splitting multiple access (RSMA) have emerged as the potential technologies required for architectural advancement in the next-generation wireless communication networks. In this work, we propose a novel analytical framework of an RSMA-enhanced STAR-RIS-aided downlink multi-user communication system. First, we discuss the statistical characteristics of the different channels involved in the transmission and derive their probability density function (PDF). Using the derived PDF, we analyze the performance of the system and derive the analytical closed-form expressions of the outage probability at each reflecting and refracting downlink user for two different STAR-RIS operational protocols namely i) energy splitting (ES) and ii) mode switching (MS). Furthermore, we validate the accurateness of the all analytical expressions through Monte-Carlo (MC) simulations. We also highlight the impact of some important parameters of the system such as transmit power at the BS, elements in the STAR-RIS, imperfect channel state information (CSI) on the outage probability of each user. Finally, we demonstrate the dominance of RSMA over non-orthogonal multiple access (NOMA) on the system performance.

This paper investigates the performance of an uplink multiuser IoT network in which green self-sustaining IoT users utilize the energy harvested from the downlink signal for uplink signalling using NOMA principles. The uplink user with best link signal-to-noise (SNR) is first chosen. To increase spectral efficiency, another user is also picked for concurrent transmission using non-orthogonal multiple access (NOMA) principles. We demonstrate that the choice of the second user depends on the target rate and number of users, and is not always the user with the second-best SNR. The users are selected using a timer-based mechanism, and no feedback of channel estimates is involved. Considering the time-switching protocol for energy harvesting, we obtain expressions for outage probability and throughput of this scheme. Unlike in traditional uplink NOMA networks, the transmit powers here are random, and this makes the analysis and user selection mechanism interesting. Accuracy of the derived expressions is illustrated by computer simulations.

In this paper, a new instantaneous channel state information-based dynamic time-switching (TS) energy harvesting (EH) protocol is proposed for a two-hop battery-assisted full-duplex (FD) relay network. To ensure reliable communication, a quantum of the battery energy augments the harvested energy. Assuming nonlinear EH, performance is evaluated in terms of throughput for static TS and dynamic TS protocols. In such networks, node-level energy considerations are clearly important but have not attracted research attention. It is demonstrated that by jointly optimizing the average battery energy consumption and the TS parameter, the throughput for both static and dynamic TS protocols can be maximized. It is also demonstrated that the proposed dynamic TS protocol provides substantial gains in throughput and average energy savings compared to the static TS protocol. The accuracy of the derived analytical expressions is verified through Monte Carlo simulations.

In this paper, we analyze (for the first time in literature) the secrecy performance of a two-hop cooperative network in which all the nodes are of the energy-harvesting self-sustaining type. Both source and relay harvest energy from a power beacon (PB) and employ the harvest-use (HU) architecture. We consider optimal combining of the direct and relayed signals at the destination and eavesdropper. We do not assume any channel state information (CSI) at the source. We derive an approximate closed-form expression for secrecy outage probability assuming selective decode-and-forward (SDF) protocol at the relay. We demonstrate that secrecy outage is a convex function of the transmit power of PB. Further, the security-reliability trade-off (SRT) is analyzed to highlight the trade-off between outage and intercept probability. Computer simulations validate the derived analytical expressions.

High spectral and energy efficiencies are vital for the implementation of smart cities. To this end, this article investigates the performance of an amplify-and-forward (AF) relay-aided coordinated direct and relay transmission (CDRT) protocol in a downlink nonorthogonal multiple access (NOMA)-based Internet of Things (IoT) network in which the source shares the direct as well as the relayed links to the IoT near-user (NU) and the far-user (FU). Different from the existing literature, we exploit incremental relaying (IR) along with combining at the NU (and not just at the FU) to achieve a 20% increase in FU throughput while ensuring the desired performance at NU. Considering practical imperfect successive interference cancelation (SIC), we analyze the throughput performance. Both NU and FU accrue large throughput gains, and doubling of the energy efficiency (EE) is achieved over the nonincremental AF CDRT NOMA scheme and its relayed orthogonal multiple access counterpart. We accomplish this by intelligently exploiting feedback bits in the second phase of signalling to avoid unwanted relaying, which saves energy and improves EE, which is very much required from the perspective of IoT-based energy-efficient smart cities. It is seen that the proper choice of the power allocation coefficient and the target information rate is crucial for maximizing the sum throughput and EE of the considered IoT Network. Finally, we validate the correctness of the theoretical analysis and the superiority of the proposed scheme through Monte Carlo simulations.

This paper investigates the performance of a time-switching (TS) based cooperative non-orthogonal multiple access (NOMA) network consisting of a base station (BS), a near user (NU), a distant user (DU), and a full-duplex (FD) relay. The BS shares a direct link to the NU, while communication to the DU is assisted by a battery-aided energy harvesting FD relay. We consider a static battery energy (SBE) scheme in which a fixed amount of battery energy augments the harvested energy and analyze the performance of both NU and DU. Also, a new dynamic battery energy (DBE) scheme, wherein the harvested energy is augmented with as little battery energy as possible in order to achieve desired quality of service, is proposed and is shown to ensure efficient battery utilization. Considering a threshold-based nonlinear EH model, closed-form expressions are derived for the throughput of NU and DU for both SBE and DBE schemes. Furthermore, for the DBE scheme, we also derive an exact closed-form expression for the average battery energy drawn per symbol interval. We then demonstrate that the choice of battery energy and TS parameter is crucial to attain a maximum DU throughput while simultaneously guaranteeing a target throughput at the NU.

In this paper, we demonstrate that due to large variations in link signal-to-noise-ratios, the key to good performance in underlay cooperative non-orthogonal multiple access (CNOMA) is intelligent adaptation. First adaptation involves switching between the cooperative mode (CM) and the non-cooperative mode (NCM). While a full-duplex near user (NU) assists the multiple-antenna base-station in communication to a far user (FU) in CM, allowing the NU to switch to NCM ensures that its performance is same as in a network without the FU. The second adaptation relates to transmit antenna selection. In the first scheme, the NOMA power allocation parameter (NPAP), and the interference temperature limit (ITL) apportioning parameter (ITLAP) depend on channel statistics. The third adaptation (presented for the first time in literature) used in two other proposed schemes involves selection of inter-dependent NPAP and ITLAP based on channel state information (CSI). The fourth adaptation used in the third proposed scheme relates to use of CSI-dependent ITL, which is shown to dramatically improve performance. Optimum choices of NPAP and ITLAP are expressed in closed-form for all three schemes, and performance with these is analyzed (and validated by computer simulations) assuming imperfect successive interference cancellation and residual self-interference cancellation at the NU.

In this article, a multiuser cooperative nonorthogonal multiple access (NOMA) network is considered. In order to improve their battery lifetime, the near-user (NU) Internet of Things (IoT) nodes relay information to the far-user (FU) IoT nodes using only the energy harvested from the ambience. The harvested energy at all the NU IoT nodes is stored in energy buffers. To improve the throughput performance, the best NU and best FU (BNBF) user selection scheme is employed. Moreover, unlike conventional orthogonal multiple access (OMA) networks, an adaptive NOMA network is considered in this article that switches between direct NOMA, NOMA with relaying, and OMA modes to maximize throughput. To improve accuracy and reduce the computational complexity, the energy buffer states at the NU IoT nodes are modeled using a continuous state-space Markov chain (CSMC) instead of discrete state-space Markov chain (DSMC). We derive the limiting distributions of the stored energy in energy buffers with either the best effort policy (BEP) or the on–off policy (OOP) applied for buffer energy management. Expressions for throughput are derived for both harvest-store-use (HSU) and harvest-use (HU) architectures. The Monte Carlo simulations are used to validate the derived analytical expressions.

This paper investigates the performance of a new framework for low-outage downlink non-orthogonal multiple access (NOMA) using a coordinated direct and relay transmission (CDRT) scheme with direct links to both the near-user (NU) and the far-user (FU). Both amplify-and-forward and decode-and-forward relays are considered. In this framework, the NU combines the signals from base-station and relay at each stage of the successive interference cancellation (SIC) to attain good outage performance. For both NU and FU, the expressions for outage probability and throughput are derived in closed form. We also derive the high-SNR expressions for the outage probability to demonstrate that with the proposed framework, both users harness a diversity of two without feedback bits (this is the only framework to achieve this). We demonstrate that the choice of power allocation coefficient and target symbol rates is crucial to maximizing the NU throughput while ensuring a desired target FU throughput. We demonstrate that CDRT with the proposed framework outperforms known schemes in terms of outage probability, sum throughput, and energy efficiency. Moreover, we also show that optimal rate selection is important to maximize the energy efficiency. Monte Carlo simulations validate the accuracy of the derived analytical expressions.

This paper investigates the performance of a new coordinated direct and relay transmission (CDRT) NOMA framework in which a base station (BS) communicates directly to a near user (NU), and through an amplify-and-forward (AF) relay to a far user (FU). In the first signaling phase, the BS transmits superposed symbols to both NU and relay (R), whereas in the second phase R amplifies and re-transmits the signal from the BS. In this framework, the NU optimally combines the signals from BS and R, which gives it a significant performance advantage, and allows it to harness a diversity of two. This serves as an incentive to NU to participate in NOMA signalling to assist the FU. We derive closed form expressions for the outage probability and throughput of NU and FU. We elaborate on how the power allocation and target rates can be optimally chosen so as to maximize the NU throughput while ensuring a desired FU throughput. Computer simulation results validate the improved energy efficiency of the scheme and accuracy of the derived expressions.

This paper investigates a cooperative non-orthogonal multiple access (C-NOMA) network consisting of a base station (BS), a far user (FU) and a full-duplex (FD) near user (NU). The NU does not use its own battery energy to relay to FU, and harvests energy using SWIPT principles from the BS. In this paper we consider a more practical nonlinear energy harvesting model for the first time in such a framework. We show that use of the idealized linear EH model leads to gross over-estimation of FU performance. Considering the time-splitting (TS) energy harvesting (EH) protocol, and modelling the self-interference at the FD NU, expressions are derived for the FU and NU outage probabilities in closed-form. Further, we show that by optimal selection of the TS parameter performance of FU can be further enhanced. Computer simulations confirm the accuracy of the derived analytical expressions.

Cooperative downlink non-orthogonal multiple access (NOMA) is a spectrally-efficient signalling technique that can enhance throughput to an Internet of Things (IoT) distant from the access point, termed the far-user (FU) IoT, while simultaneously serving a closer IoT node, termed the near-user (NU) IoT. However, it requires relaying by the NU IoT, which can drain its battery energy. In this paper, we consider an energy-buffer equipped NU IoT that uses only harvested energy to relay to the FU IoT. To further enhance performance with the energy buffer, and allow it to accumulate energy, we switch between NOMA, cooperative NOMA and orthogonal multiple access (OMA) signalling modes. This hybrid scheme results in better FU IoT throughput performance as compared to individual modes, while simultaneously enhancing NU IoT performance, without requiring the latter to expend its battery energy. The energy buffers are modelled precisely using a continuous-state space Markov chain. The best-effort policy (BEP) energy management policy is considered. The limiting distribution of BEP policy is provided for stable buffers, and then use this to derive expression for throughput. Simulation results confirm accuracy of the derived analytical expressions.

In this paper, a coordinated direct and relay transmission (CDRT) based cognitive underlay downlink nonorthogonal multiple access network is considered, in which the source serves the near user (NU) directly while a dedicated relay assists the communication to the far user (FU). To ensure good performance in a power-constrained underlay scenario, NU combines (along with successive interference cancellation) the signals from the source and the relay in this unique CDRT framework. The secondary transmitter transmits with controlled power to ensure that the interference is below the interference temperature limit of the primary user. NU and FU performance is analyzed in terms of their outage probability and throughput in closed-form. Furthermore, we investigate how the choice of target rates and power allocation parameters is crucial to attaining the best performance. Extensive computer simulations are provided to validate the accuracy of the derived results.

In this article, we analyze the performance of a two-hop communication link between an energy-buffer-equipped IoT-type self-sustaining source and a destination, aided by a data-buffer-equipped relay. The source harvests radio-frequency energy from the ambience and stores it in an energy buffer. Using a discrete-time continuous-state Markov chain to model the energy buffer and a discrete-state Markov chain to model the data buffer, we analyze outage and throughput performance of the link. In typical applications, feedback of channel state information and buffer state information is not feasible, so simple link selection schemes are evolved. In the first only buffer-status (OBS) scheme, link selection is based on the energy-buffer status alone. A modified OBS scheme is then suggested, and its performance is analyzed. The third scheme uses both energy-buffer status and first-hop channel knowledge for link selection. Expressions are derived for throughput and limiting distributions of stored energy with all the three schemes. We show how the continuous-state energy buffer and the discrete-state data buffer can both be balanced while maximizing the throughput by suitable choice of the source transmit power, relay transmit power, and target information rates at the source and the relay. We also analyze statistical properties of the energy-buffer size with these schemes. The derived analytical expressions are validated by the Monte Carlo simulations.

Non-orthogonal multiple access (NOMA) has drawn tremendous attention, being a potential candidate for the spectrum access technology for the fifth-generation (5G) and beyond 5G(B5G) wireless communications standards. Most research related to NOMA focuses on the system performance from Shannon's capacity perspective, which, although a critical system design criterion, fails to quantity the effect of delay constraints imposed by future wireless applications. In this paper, we analyze the performance of a single-input multiple-output (SIMO) two-user downlink NOMA system, in terms of the link-layer achievable rate, known as effective capacity (EC), which captures the performance of the system under a delay-limited quality-of-service (QoS) constraint. For signal combining at the receiver side, we use generalized selection combining (GSC), which bridges the performance gap between the two conventional diversity combining schemes, namely selection combining (SC) and maximal-ratio combining (MRC). We also derive two approximate expressions for the EC of NOMA-GSC which are accurate at low-SNR and at high-SNR, respectively. The analysis reveals a tradeoff between the number of implemented receiver radio-frequency (RF) chains and the achieved performance, and can be used to determine the appropriate number of paths to combine in a practical receiver design.

This paper investigates the performance of full-duplex (FD) communication between two power beacon-assisted energy harvesting (EH) nodes. The proposed system consists of a power beacon (PB) and two FD nodes. Assuming the time-switching (TS) protocol for EH, both nodes first harvest the energy from the PB and then use this energy for information transmission. Closed-form expressions are derived for the terminal outage probabilities and the sum throughput. Further, using an asymptotic expression for the terminal outage probability, we present a closed-form expression for the TS parameter that maximizes the sum throughput. Computer simulation results demonstrate accuracy of the derived expressions.

In this paper, we analyze the performance of a two-hop communication link between an energy-buffer equipped IoT-type self-sustaining source and a destination, aided by a data buffer equipped access point, which serves as a relay. The source harvests RF energy from the ambience and stores it in an energy buffer. Using a discrete-time continuous-state Markov chain model to model the energy buffer, and a discrete-state Markov chain to model the data buffer, we analyze performance of the link. We show how the continuous-state energy buffer and the discrete-state data buffer can both be balanced by suitable choice of the source transmit power, relay target data rate, and relay power. Since feedback of channel estimates and buffer status is not feasible in this scenario, link selection is based solely on energy-buffer status at the source. The derived analytical expressions are validated by Monte Carlo simulations.

In this paper, we analyze the performance of an underlay downlink non-orthogonal multiple access (NOMA) network with multiple near and far-users. Different from cognitive radio (CR) inspired CR-NOMA where cognitive principles are used to guarantee performance of one selected user, all nodes here are in the underlay mode, and re-use the spectrum of the primary network. Use of NOMA is counter-intuitive in an underlay network since the transmit powers are constrained to ensure that the interference temperature limit is met. We show in this paper that switching carefully between NOMA, NOMA with relaying, and orthogonal multiple access (OMA) allows good performance to be attained in such networks. We further propose a user selection scheme, and analyze its performance. We derive approximate closed-form expressions for the near and far-user throughput. Simulations are carried out to verify the derived results.

In this paper we analyze the outage and throughput performance of a semi-grant free uplink based on non-orthogonal multiple access. We assume that the grant based user is selected in an opportunistic manner. We use underlay cognitive radio principles to manage interference to the grant based user. Expressions are derived for throughput of the non-grant based user. We show how power should be allocated to the opportunistically selected non-grant based uplink users to optimize their throughput performance while ensuring that performance of the grant-based user is maintained at the desired level. Computer simulations demonstrate accuracy of the derived expressions.

In this paper, the authors consider an underlay multi‐hop cognitive radio network with energy harvesting secondary nodes, where there is a cluster of secondary decode‐and‐forward relays in each hop. The secondary nodes have no separate energy source available with them, but wake up from idle mode to harvest energy from the primary signal with the time‐switching protocol, and use it for transmitting/relaying using the peak interference constraint. In each cluster, a relay with maximum transmit power is selected except in the last one. In the last cluster, a relay which has a maximum signal‐to‐noise ratio (SNR) at the secondary destination is selected. Though the suggested scheme has low implementation complexity and requires very little channel estimation, its performance is close to that of a scheme in which the link with the best SNR is chosen in each hop (which requires a lot of channel estimation). Analytical expressions are derived for the end‐to‐end outage probability and throughput assuming Rayleigh faded channels. They show that it is important to optimise the time‐switching parameter (fraction of time devoted to energy harvesting) and the number of hops. Simulations confirm the accuracy of the derived expressions.

This paper investigates the performance of a two-hop decode-and- forward full duplex relaying (FDR) network with a battery-assisted energy harvesting (EH) relay. We consider a practical scenario where the EH relay uses a limited amount of battery energy along with the harvested energy to enhance communication between the source and destination terminals. Utilizing time splitting (TS) protocol for EH, we analyze the performance of a dual-hop FDR system in terms of outage probability and throughput. Further, with fixed battery energy availability, we present closed-form expressions for the TSR parameter that maximizes throughput. For a desired target throughput, we show how the battery energy drawn and the TSR parameter can be chosen so as to extend battery lifetime. Computer simulation results demonstrate accuracy of the derived expressions.

In this paper, we consider an energy harvesting (EH) decode-and- forward (DF) based two-hop cooperative network with a direct link. The energy-buffer equipped relay harvests energy from the ambience, and uses the harvest-store-use (HSU) architecture. Since it is known that using a discrete-state Markov chain to model the energy buffer is inaccurate even for moderate number of states, we assume use of a discrete-time continuous-state space Markov chain. We derive the limiting distribution of energy for the incremental best- effort policy (IBEP) and use that to obtain expressions for outage probability and throughput. We also compare performance with non- incremental best-effort policy (NIBEP) which is a special case of the analysis presented here, with harvest-use (HU) and direct transmission (DT). Simulation results are presented to validate the derived analytical expressions.

In this paper, we analyze the performance of a two-hop cooperative communication network in which both source and the relay are energy buffer-aided energy harvesting nodes. We consider fixed-rate signalling at both the nodes. The source and relay are assumed to harvest energy from ambient sources and store it in energy buffers. In this paper we use discrete-time continuous-state space Markov chain to model the energy stored in the buffers. We consider two different energy management policies at the source - best-effort policy (BEP) and on-off policy (OOP) while only OOP is considered at the relay. Using these policies, two different cooperative transmission schemes are pre- sented. We also compare performance with direct transmission schemes. Simulation results are presented to validate the derived analytical expressions and bring out useful insights.

In this paper, we consider a new scenario where an energy- harvesting full-duplex battery-powered legitimate monitor (LM) monitors communication between a suspicious transmitter (ST) and a suspicious receiver (SR). We assume that the LM uses energy harvesting to prolong its battery life. We analyze the average eavesdropping rate and the probability of the non- eavesdropping event. We first consider the case when the channel gain of the ST-SR link and that from the transmitting antenna of LM to SR can be estimated by the eavesdropper. In addition, we consider for the first time the more realistic case when these channels cannot be estimated by the eavesdropper. Computer simulations are presented to confirm accuracy of the analysis presented.

In this study, the authors consider a two‐way relaying (TWR) system with source terminals and and a relay terminal . They analyse the performance of a fixed‐gain amplify‐and‐forward‐based TWR system over Rayleigh fading channels with co‐channel interference at all the terminals. Expressions are derived for the outage probability of the system at a medium‐to‐high signal‐to‐interference‐plus‐noise ratio (SINR) range. They also obtain the expression for the value of outage floor and use this to optimise relay location and power allocation. Simulation results demonstrate accuracy of the derived expressions in different SINR ranges.

In this paper, we consider a two-hop cooperative network with a direct link based on an energy harvesting (EH) decode-and-forward relay. The energy-buffer equipped relay harvests energy from the ambience, and uses the harvest-store-use (HSU) architecture. Since it is known that using a discrete-state Markov chain to model the energy buffer is inaccurate even for moderate number of states, we use a discrete-time continuous-state space Markov chain instead. We derive the limiting distribution of energy for both the incremental on-off policy (IOFP) and the incremental best-effort policy (IBEP), and use them to obtain expressions for outage probability and throughput. The corresponding expressions for non-incremental signaling follow as a special case. We show that the stable buffers using IBEP harness a diversity of two as compared with those using IOFP, which attain a diversity of one. However, while buffers using IBEP are consequently more reliable than those with IOFP, their throughput performance is only marginally superior. The simulation results are presented to validate the derived analytical expressions.

Multi‐hop relaying is used to extend the reach of wireless communication systems whereas cooperative relaying is used to improve the performance gain by exploiting the spatial diversity. In this study, the authors combine these two techniques to improve the range as well as the performance gain of cognitive radio networks (CRNs). Selective decode‐and‐forward relays are considered and two relay selection schemes are used to study the performance of multi‐hop CRNs over Rayleigh fading channels. The exact outage probability and throughput of the considered system are derived for both the schemes by considering the effect of both peak‐power and peak‐interference constraints. By using the derived outage probability, the diversity gains for both considered schemes are determined. Numerical results show that the outage probability monotonically improves, whereas the throughput has concave behaviour with respect to increasing number of relaying hops.

In this paper, we investigate the performance of a two-way relaying (TWR) network with a battery-assisted energy harvesting (EH) relay. The relay uses limited battery energy to augment the harvested energy and aid communication between the two source terminals. Considering a time-switching relaying (TSR) protocol at the EH relay, we investigate the performance of the TWR system in terms of outage, throughput, and ergodic rate. Assuming that the source with a better channel to the relay transfers energy in the EH phase, we investigate statistical and instantaneous channel state information (CSI)-based optimization of the TSR parameter to maximize throughput for a fixed amount of relay battery energy usage. We observe that the instantaneous CSI-based optimization results in higher throughput with less battery energy usage. Furthermore, we investigate the problem of minimization of battery energy consumption for target throughput using the statistical and instantaneous CSI-based optimization of the TSR parameter. We show that battery energy consumption can be drastically reduced by availability of instantaneous CSI. The derived insights are crucial from a designer point of view. Simulation results are presented to confirm accuracy of the derived analytical expressions.

In this paper, we analyze sum throughput and (asymptotic) sum ergodic rate performance of two co-existing downlink multiuser underlay secondary networks employing either fixed-rate transmission (FRT) or (channel aware) adaptive rate transmission (ART). In the considered scenario in which two secondary sources may transmit simultaneously, intelligent apportioning the interference temperature limit (ITL) is vital. We consider cases when this ITL apportioning is based on statistical properties of the channels, or on full (or partial) knowledge of the channel gains. For these cases, proper network management (NM) strategies are evolved to maximize sum throughput or sum ergodic rate of the secondary networks. Each NM strategy determines whether both secondary sources should transmit concurrently or not, and also determines their transmit powers. We demonstrate that a channel aware NM strategy is superior to an optimal fixed NM strategy. With secondary sources employing non-opportunistic user selection, in case of FRT (ART), we demonstrate that there exists a critical target-rate (ITL) below which it is advantageous to operate both secondary networks concurrently. We present closed form expressions of critical parameters that influence sum throughput and sum ergodic rate. Computer simulations are presented to corroborate the derived expressions.

In this paper, we analyze the throughput performance of two co-existing downlink multiuser underlay secondary networks that use fixed-rate transmissions (FRT). We assume that the interference temperature limit (ITL) is apportioned to accommodate two concurrent transmissions using an apportioning parameter to ensure that the overall interference to the primary receiver does not exceed the ITL. Using the derived analytical expressions for throughput, when there is only one secondary user in each network, or when the secondary networks do not employ opportunistic user selection (use round robin scheduling for example), there exists a critical fixed-rate below which sum throughput with co-existing secondary networks transmitting concurrently is higher than the throughput achieved by a single secondary network. We derive an expression for this critical fixed-rate. Below this critical rate, we show that careful apportioning of the ITL is critical to maximize the sum throughput of the co-existing networks. We derive an expression for this apportioning parameter. Throughput is seen to increase with increase in number of users in each of the secondary networks employing opportunistic selection. Computer simulations demonstrate accuracy of the derived expressions.

In this paper, we investigate the performance of an analog network coding based two-way relay system with multiple-antenna source terminals and single-antenna energy harvesting (EH) relay. We consider time-switching relaying protocol to perform EH and information processing at the amplify and forward EH relay. Assuming that the multiple-antenna source with a better link beamforms energy to the relay, we derive expressions for the system outage, ergodic sum-rate, and sum symbol error rate. In the analysis, we take into account the sensitivity of the energy harvesting circuit. We investigate the problem of throughput maximization by optimizing the fraction α of time spent on EH, and derive closed-form expressions for optimum α in important special cases. We analyze the problem of relay location for fixed α, and show that the optimum location varies with source terminal antennas. We further show that joint optimization of relay location and α yields best throughput performance. We show through simulations that unlike throughput, the optimum α that maximizes the ergodic sum-rate does not show much variation with system parameters. Simulation results with practical parameter values demonstrate the accuracy of the derived analytical expressions.

In this paper, we study the performance of cluster based multi-hop underlay cognitive radio networks using an ad-hoc path selection mechanism. Both peak power and peak interference constraints are taken into account. The exact end-to-end outage probability of the considered system employing decode-and-forward relays is derived for Rayleigh fading channels. Also, an approximate expression of the outage probability at high signal-to-noise ratio is derived. For fixed-rate and fixed distance between the source and destination, an expression is derived for the number of hops that minimizes the outage probability. Simulation results are presented to validate the derived analytical expressions.

In this paper, we consider a two-way relay (TWR) system in which two multi-antenna source terminals communicate with the help of an energy harvesting (EH) single-antenna relay utilizing the time switching relaying (TSR) protocol. Assuming beamforming at the terminals and analog network coding (ANC) at the EH based TWR, we derive expressions for the outage probability of the system for Rayleigh fading channels. Using high SNR approximations, we demonstrate that the diversity attained equals minimum of the number of antennas at the source terminals, just as in conventional TWR systems. We further show how system throughput can be maximized by optimizing the fraction of the time allocated for EH, and derive closed-form expression for it in some special cases.

In this study, the authors propose a new cooperative multiplexing scheme for downlink transmission using dynamic spectrum access (DSA) principles. In this scheme, the base‐station (BS) transmits to its distant user using a selected relay node in two hops. In the second hop, while the relay forwards information to the distant user, the BS transmits information to another selected user in its vicinity using DSA principles. Assuming peak power and peak interference constraints, the authors derive outage and ergodic rate performance of the user served by DSA assuming various user selection schemes. The authors consider gain‐based selection, SINR based selection (SS), interference cancellation (IC), as well as a hybrid scheme that employs both SS and IC. The authors demonstrate that apportioning of time between the first and second hop of relaying can improve outage performance of the user served by DSA while ensuring certain guaranteed performance for the distant user. The presented analytical expressions are compared with computer simulation results.

Linear zero‐forcing (ZF) canceller does not perform well in the presence of alien crosstalk (AXT) while the receivers based on minimum‐mean‐square‐error (MMSE) criterion require perfect knowledge of the noise covariance matrices. In this study, the authors consider the use of a constrained linear minimum‐output energy (MOE) receiver in the presence of self‐crosstalk and AXT in upstream vectored very high‐speed digital subscriber line systems, that does not require knowledge of the noise correlation matrices and can be trained using the received signals without the use of training sequences. They derive bounds on the performance of the MOE receiver in the digital subscriber line environment and show that it reaches the MMSE performance for self‐crosstalk cancellation. They also show that the performance of the proposed receiver lies in between that of the ZF receiver and the non‐linear ZF generalised decision feedback equaliser receiver. An adaptation of the canceller coefficients using MOE algorithm shows comparable performance to that of the least mean squares algorithm. The effect of noise correlation on the capacity has also been highlighted via the Cramer‐Rao lower bound. Computer simulations are presented to verify the analytical results and demonstrate the performance of the proposed receiver.

We consider a two-hop primary network with a multi-antenna primary base-station (PBS) communicating to its distant primary receiver (PR) through a relay, and a secondary network with one of several energy harvesting secondary transmitters (STs) communicating to the secondary base-station (SBS). In this paper we propose a novel framework where the PBS utilizes its excess available power to charge a ST so as to enable it to share its spectrum. In this framework, the PBS employs beamforming to facilitate energy harvesting by a selected ST in the first hop while forwarding information to the relay. In the second hop, while the relay communicates to PR, the selected ST employs dynamic spectrum access (DSA) to communicate to its SBS. Such a framework can be expected to help the primary network earn revenue for both energy transfer and spectrum sharing. Assuming peak interference power constraints, we derive an expression for the outage probability of the secondary link. We also derive a simple expression for the outage floor. A simple intuitive user-selection scheme is suggested. It is shown that secondary user-selection can greatly enhance performance.

In this paper, we consider a cellular communication system with half-duplex regenerative relays, and propose a dynamic spectrum access (DSA)-based protocol for simultaneous uplink transmission in the same frequency band as the downlink transmission. The proposed protocol facilitates better frequency utilization. In this protocol, relay selection is employed for the downlink, while distributed beamforming is used in the uplink. Assuming peak interference constraints as well as peak power constraints for all uplink transmissions, we analyze the outage performance of the protocol. Expressions are also presented for the asymptotic outage probability. Computer simulations demonstrate that asymmetry in rates that is characteristic of cellular links makes it possible to achieve good outage performance for both uplink and downlink transmissions.

In this work, the authors consider an amplify‐and‐forward (AF)‐based three‐phase two‐way system with interference at the relay. An optimum scheme to minimise the outage probability is formulated, and a closed form expression for the ‘channel‐dependent’ combining coefficient ‘ α ’ at the relay is derived. A novel approach is presented to derive an expression for the overall outage probability of the proposed three‐phase outage‐optimal two‐way relaying (3P‐OTWR) system. The authors also perform finite signal‐to‐noise (SNR) diversity‐multiplexing tradeoff and throughput analysis of the system. Furthermore, the problem of outage‐optimum power allocation is investigated. Using the asymptotic expression for the outage probability, it is shown that there is loss of diversity owing to interference at the relay. The authors perform Monte Carlo simulations to demonstrate that the 3P‐OTWR system outperforms a conventional three‐phase two‐way scheme. With outage‐optimum power allocation, the proposed scheme achieves a gain of approximately 3 dB in the medium‐to‐high SNR regime over a conventional scheme with α = 0.5 and equal power at terminals. The proposed three‐phase scheme in presence of co‐channel interference can provide a better throughput for higher transmission rates as compared with a two‐phase scheme when operated in the high SNR regime. Numerical results demonstrate accuracy of the derived expressions.

We consider a two-way relay system where multi-antenna sources employ beamforming to communicate bidirectionally via a single-antenna relay with analog network coding over Nakagami-m fading channels. We address the problem of both separate and joint optimization of power allocation and relay location in order to minimize the overall system outage probability. Our results demonstrate that separate optimization of relay location is more significant than that of power allocation to improve the overall system outage performance. We further emphasize that the joint optimization of power allocation and relay location can provide noticeable outage performance improvement over unbalanced per-hop fading conditions and/or nonidentical antenna configurations.

Alien noise in the vectored very-high-speed digital subscriber line (VDSL) system is part of the additive noise at the receiver and exhibits strong correlation among users. We present a per-tone co-operative alien noise cancellation (CoMAC) algorithm for the upstream (US) VDSL that can be applied subsequent to any self far-end-crosstalk (FEXT) mitigation strategy. CoMAC operates by predicting the noise seen by a given user based on the error samples from the remaining users. These errors are conveniently obtained after slicing the self-FEXT canceled signal of all the vectored users. We show that if the estimation of these errors is accurate, the proposed alien canceler achieves the Cramer-Rao lower bound (CRLB). In practice, the seamless rate adaptation (SRA) operation, which enables increased bit rate by increasing the bit-loading per-tone, can cause decision errors in any decision directed strategy. We also analyze the impact of these decision errors - an issue not addressed in the literature. We propose a strategy for bit-loading during the SRA operation by formulating a max-min optimization problem and demonstrate a possibility of a guaranteed (minimum) improvement in the per-user rate. Simulations indicate that performance of the algorithm can exceed the minimum value significantly in practical situations.

This paper evaluates the performance of an opportunistic scheduling scheme for a multiuser two-way relay network, wherein an analog network coding (ANC)-based relay assists the communication between multiple pairs of users. To ensure fairness for each user pair, we consider a scheduler based on maximizing the normalized minimum of the instantaneous signal-to-noise ratios (SNRs) at each user of the pair. Under a high SNR assumption, we derive upper and lower bound expressions for the outage probability and the average sum-rate in a Rayleigh fading environment and establish that a multiuser diversity of order equal to the number of user pairs is harnessed by the scheme. Numerical and simulation results are presented to confirm the performance gain of the proposed scheme.

In a distributed cooperative environment, synchronization is a major issue. Especially when OFDM is employed in the physical layer, frequency offset synchronization is of great significance. In addition, transmitter and receiver IQ imbalances are known to be important implementation issues in OFDM systems. In this paper, a novel precoding strategy is proposed that enables blind estimation of carrier frequency offsets (CFOs) of each transmitter (separately) in cooperative scenario when the SFBC OFDM is employed in the physical layer, even when the transmitter and receiver IQ imbalances are present, and the channel is frequency selective. This non-redundant precoding strategy involves multiplication of the symbols to be transmitted by a random phase precoding sequence, and results in no loss in rate or bandwidth. Computer simulations are presented to demonstrate the effectiveness of the algorithm.

In this paper a simple blind algorithm is presented for estimation of carrier frequency offset (CFO) in OFDM links with IQ imbalance distortion that exploits the finite alphabet nature of the transmitted symbols. Most algorithms proposed to date estimate the CFO using a specially designed preamble sequence, which makes them unsuitable for use in time-varying environments. Other algorithms based on the null carriers and the cyclic prefix either place restrictions on the CFO or the channel, or result in rate reduction. The proposed algorithm requires no pilot (no rate reduction), and instead just requires (assuming oversampling is used at the receiver), the symbol onanyonecarriertobeM-PSK. Performance of the proposed algorithm is evaluated by computer simulations to demonstrate its effectiveness.

We address the problem of blind multiuser detection in DS/CDMA systems that employ QPSK data modulation. We show that by suitable precoding (modification) of the phase of the QPSK data at the transmitter (before spectrum spreading), it is possible to detect the data of any user blindly using only the knowledge of the preceding sequence, regardless of the power of the interferes. The proposed method can be seen as an extension to our earlier preceding approach for BPSK signals in AKS Al Bayati et al. (2004). However, the phase preceding/decoding operation of QPSK signals is a more challenging problem, especially in its decoding procedure. The proposed detection scheme has a deterministic nature and is therefore shown to provide performance advantage in the medium-to-high SNR region.

A new approach for blind multiuser detection of binary phase-shift keying/direct-sequence code-division multiple-access signals is proposed, based on precoding the phase of the transmitted data uniquely for each user, over a block of data. This would enable separation and detection of a desired user's signal in an unknown multipath channel without channel estimation. The method does not involve any sacrifice in data rate or system bandwidth. The proposed method exhibits good performance, compared with some existing methods.

We propose a blind multiuser detector based on a new data precoding technique for direct-sequence code-division multiple-access signals. The modulus of all users' data is block encoded, using a sequence that is unique for each user. This precoding method, together with the analytical constant modulus algorithm for detection, enables a closed-form, one-shot detection of the desired user's signal in a multipath channel using one or more antennas. The detection process does not involve or require a channel estimation step. The proposed detector is shown to be extremely near-far resistant, and can operate properly in the presence of severe carrier frequency offset.

Constrained minimum variance (CMV) detection has been proposed for blind multiuser detection of DS/CDMA signals in multipath channels. We suggest a new approach for implementing the CMV detection when an antenna array is used at the receiver. A simple technique is used for restricting the domain of the CMV detector to a smaller subspace based on signals directions of arrivals (DOAs), in a beamformer-like formulation. The proposed technique requires prior knowledge of only the timing of the desired user's signal. It is seen that the proposed subspace restriction is useful for accurate path DOA estimation followed by efficient data detection in heavily loaded systems and over small block sizes of the input signal. This makes this method suitable for slowly time varying channels.

In this paper, blind algorithms based on a deterministic framework are proposed for equalization of finite-memory linear time-invariant (LTI) channels carrying OFDM signals. Unlike algorithms proposed to date, the channel memory is not restricted to be smaller than the cyclic prefix. It is shown that equalizers termed "synchronizer-equalizers" can be estimated blindly and always result in block-synchronized output, thus making separate synchronization unnecessary. These algorithms are based on a deterministic frame-work, and require short data records. Performance of the proposed algorithms is analyzed by computer simulations.

A simple method is proposed for blind identification of discrete-time nonlinear models consisting of two linear time invariant (LTI) subsystems separated by a polynomial-type zero memory nonlinearity (ZMNL) of order N (the LTI-ZMNL-LTI model). When the input to the model is a circularly symmetric Gaussian sequence, the linear subsystem of the model can be identified efficiently using slices of the N+1/sup th/ order polyspectrum of the output signal, even when the second linear subsystem is of non-minimum phase (NMP). The ZMNL coefficients need not be known. The order N of the nonlinearity can, in principle, be estimated from the received signal. The methods possess noise suppression characteristics. Computer simulations support the theory.

Identification of non-parametric linear systems with cyclostationary inputs has received considerable attention in recent years. However, identification of parametric linear models has received very little attention. In this paper, some methods are proposed for identification of moving average (MA) and autoregressive moving average (ARMA) linear models with fractionally spaced data input using only the output sequence. It is shown that q-length MA and MA part of ARMA can be identified using only q points of the cyclic autocorrelation provided it is nonzero at two or more incommensurate cycle frequencies. This can be ensured by using the sum of cycle frequency separated signals or by using signals with a low frequency pilot. Computer simulations are presented to support the methods.>