Cooperative Decode-and-forward Research Articles

Performance Analysis of Selective DF Cooperative NOMA in Presence of Practical Impairments

In this article, we investigate a selective decode-and-forward (DF)-aided cooperative nonorthogonal multiple access (NOMA) system performance in the presence of practical impairments using imperfect successive interference cancellation (SIC) and channel estimation error (CEE). The base station communicates directly and via a relay with the two NOMA users in two-time phases. In particular, the selective DF with synchronized direct and relay transmission relaying protocol is proposed for the considered downlink NOMA system to offer enhanced quality of service and improved data reliability compared with the conventional NOMA and DF NOMA systems. The closed-form of exact and asymptotic expressions of the average bit error rate (ABER) at both NOMA users are derived considering the impact of imperfect SIC and CEE. Furthermore, the outage probability is also obtained. Finally, the improvement in the system performance acquired by the proposed scheme over the existing methods is corroborated by Monte Carlo simulations.

Securing Multiuser Communications via an Energy Harvesting Node: Jammer or Relay?

In this paper, we study the secure communication problem of a wireless multiuser network consisting of a base station (BS), multiple users, and an energy harvesting (EH) node in the face of an eavesdropper. We focus on the question that which role the EH node plays, as a friendly jammer or as a cooperative decode-and-forward (DF) relay. Accordingly, we propose two EH node aided multiuser scheduling schemes to help the secure communications between BS and multiple users, i.e., the EH jammer aided transmission (EHJT) scheme where the EH node acts as a friendly jammer and the EH relay aided transmission (EHRT) scheme where the EH node acts as a cooperative DF relay. For comparison purposes, the direct transmission (DT) scheme is also presented. We analyze the security-reliability trade-off (SRT) performance of the proposed EHJT and EHRT schemes as well as the DT scheme in terms of deriving their exact and asymptotic expressions of outage and intercept probabilities. Additionally, we propose an iterative algorithm based on the golden search to determine the optimal time allocation factor (OTAF) for the sake of minimizing the sum of outage and intercept probabilities for the proposed EHJT and EHRT schemes. Numerical results show that the EH node can improve the SRT performance of the multiuser network more significantly as a friendly jammer than as a cooperative DF relay. It is also shown that the best SRT performance of the EHJT and EHRT schemes can be achieved by adjusting the signal-to-noise ratio (SNR) and time allocation factor.

Full Euclidean Distance Based Selection Combining for SSK DF Cooperative Diversity Systems

Space Shift Keying (SSK) is a multiple-input multiple-output technique that has drawn more attention in recent years because of its low complex transceiver design. In this paper, an investigation on the Symbol Error Probability (SEP) performance of SSK in a Decode-and-Forward (DF) cooperative relaying system is done. The DF cooperative relaying scenario considers an origin node, an intermediate node and an end node with a direct link between origin and end node, and an indirect link between origin to the intermediate node and intermediate to end node. The SSK modulation is considered at the origin and intermediate nodes with Full Euclidean Distance based Selection Combining (FED-SC) employed at the end node for SSK symbol detection. The SEP expression of the SSK FED-SC in the DF cooperative relaying scheme is derived using the Order Statistics Approach (OSA). Further, a closed-form SEP expression is obtained using a Combined Order Statistics Approach (COSA) considering the number of receive antennas at the intermediate node is equal to the number of receive antennas at the end node. In addition, the closed-form asymptotic SEP expression is presented to evaluate the diversity order of the system. The SEP expressions derived through OSA and COSA are verified using the Monte Carlo simulations. The simulation results revealed that the proposed SSK FED-SC outperforms all the existing SSK DF cooperative selection combining schemes.

Secrecy performance of an uplink-downlink cooperative PD-NOMA DF network in PLS

ABSTRACT In this paper, we investigate the secrecy performance of an uplink-downlink power domain non-orthogonal multiple access (PD-NOMA) system with imperfect successive interference cancellation (SIC) in physical layer security (PLS). In the proposed system, two source users (SUs) communicate with two destination users (DUs) with the help of a cluster of multi-relay nodes using the decode-and-forward (DF) protocol in the presence of multi-eavesdroppers. These eavesdroppers try to overhear the wireless signal around the DUs. In our system, the selected DF-relay node also works as a jammer to improve security and protect confidential information from multi-eavesdroppers. In this role, the DF-relay node generates a jamming signal, creating artificial interference to reduce the quality of the eavesdropping channels. To evaluate the secrecy performance of the system, we derived the analytical expressions of the secrecy outage probability (SOP) for both DUs using three relay selection strategies over Rayleigh fading channels and used Monte Carlo simulations to confirm the accuracy of our calculations. Furthermore, we examined the effects of system parameters such as the number of eavesdroppers and DF relaying nodes, the power allocation, SIC performance, the position of eavesdropper on the SOP of the two DUs. We compared the performance of our proposed NOMA system with those of conventional orthogonal multiple access (OMA) schemes.

Performance Analysis for SWIPT Cooperative DF Communication Systems with Hybrid Receiver and Non-Linear Energy Harvesting Model.

In this paper, we study the outage and throughput performance for the simultaneous wireless information and power transfer (SWIPT) cooperative decode-and-forward (DF) communication systems. The hybrid receiver that uses both time switching (TS) and power splitting (PS) methods for energy harvesting (EH) and information decoding (ID), and the piece-wise linear EH model that captures the non-linear input-output characteristic of the EH circuit, are considered. We present exact analytical expressions of the outage probability (OP) and throughput, which are expressed as single definite integral on finite interval and can be easily evaluated, for the systems in Rayleigh fading channel. For further simplicity of calculation, we derive novel and closed-form approximate expressions of the OP and throughput. The impact of different system parameters on the system performance is investigated. Numerical results show the high accuracy of the proposed closed-form approximate expressions especially in the region of higher signal-to-noise ratio (SNR). It is also shown that the system performance is greatly overestimated when the ideal linear EH model is used instead of the practical non-linear EH model. A different result to the non-hybrid receiver with both linear EH model and non-linear EH model that there exists an optimal location to minimize the OP for the hybrid receiving relay node with non-linear EH model is also demonstrated.

Multivariate Correlated Rayleigh Fading With MRC and Applications to Wireless Secrecy

This letter studies physical layer security of an outdated channel-state-information (oCSI) decode-and-forward (DaF) opportunistic-relay (OR) network under equal-correlated (equ.c.) Rayleigh fading with maximal ratio combining (MRC) deployment. By assuming that relays operate under equ.c. Rayleigh fading and wiretapper-Destination operate under exponential-correlated (exp.c.) Rayleigh fading, this work (i) derives an MRC output (MRCO) distribution of multivariate equ.c. Rayleigh fading, (ii) derives an MRCO distribution of bivariate exp.c. Rayleigh fading under oCSI conditions, and (iii) expresses the secrecy outage probability (SOP) in closed form. By considering oCSI severity, channel correlation among cooperative DaF ORs, Destination, wiretapper, and MRC deployment, this work's practicality can be significantly improved. Detailed discussions are given, in which the impact of several important parameters on the SOP is discussed. Monte Carlo simulation is shown to match theoretical predictions.

Joint Noisy Network Coding and Decode-Forward Relaying for Non-Orthogonal Multiple Access

We consider a non-orthogonal multiple access channel in which multiple users communicate with a base-station through a dedicated relay. For this setup, we propose a novel joint-noisy network-coded (J-NNC)-decode-and-forward (DF) cooperation scheme that employs NNC relaying with opportunistic DF. The proposed scheme utilizes the DF cooperation when messages from all users are successfully decoded at the relay and the NNC when the relay is unable to decode any one of the users. In the scenario when the relay decodes only a subset of users, the proposed scheme utilizes joint DF and NNC encoding. We derive the information theoretic conditions required for successful message recovery and show that the J-NNC-DF has a strictly better outage performance than the conventional DF-only, NNC-only, or DF-or-NNC schemes. For the two-user case, we derive closed-form expressions for the outage performance under Rayleigh fading while assuming access only to the local channel state information at the relay. For these expressions, let us choose the NNC quantization parameter so as to attain optimum outage performance. The simulation results validate the theoretical findings and show that the J-NNC-DF achieves a performance gain of 0.75, 1.7, and 2.1 dB compared with the DF-or-NNC, DF-only and NNC-only strategies, respectively.

Joint Relay and Eavesdropper Selection Strategy Against Multiple Eavesdroppers over Nakagami-$m$ Fading Channels in Cooperative Decode-and-Forward Relay Networks

Physical layer security (PLS) in the presence of multiple eavesdroppers over Nakagami-m fading channels for cooperative decode-and-forward (DF) relay network that consists of one source, one destination, and multiple relays is investigated. Different from the recent PLS system model that only considers one eavesdropper during eavesdropping attack, this paper extends the one-eavesdropper case to a multiple-eavesdropper scenario and investigates joint relay and eavesdropper selection (JRES) strategy against eavesdropping attack over Nakagami-m fading channels. In the proposed strategy, the best relay is selected via the maximum relay forward channel capacity. In addition, since eavesdroppers are noncooperative, the worst case is considered. Namely, the wiretap channel between the best relay and the chosen eavesdropper has the maximum capacity. Traditional direct transmission and opportunistic relay selection (ORS) scheme in the presence of one eavesdropper over Rayleigh channel are regarded as benchmarks. Moreover, a security-reliability tradeoff (SRT) performance is analyzed, where the reliability performance is expressed by outage probability (OP), while the security performance is measured by intercept probability (IP). Closed-form expressions of OP and IP are derived. The numerical results show that the proposed JRES scheme outperforms the traditional direct transmission and the ORS scheme in the presence of one eavesdropper over Rayleigh channel. The SRT performance is enhanced obviously with the increasing of relay numbers and Nakagami channel fading factor m for a given number of eavesdroppers, which extends the PLS and SRT performance analysis to a more general case in a cooperative DF relay network.

On the performance of wireless-powered cooperative DF relaying networks with imperfect CSI

This paper studies several performance metrics of a wireless-powered de-code-and-forward (DF) relay network with imperfect channel state information (CSI). In particular, based on the time switching (TS) protocol, the energy-constrained relay harvesting energy from a power beacon (PB), and uses that harvested energy to forward the source information to destination. The closed-form expression of the outage probability is firstly derived over Rayleigh fading channels. Then, the asymptotic analysis, throughput as well as the symbol error probability (SEP) are derived based on the expression of the outage probability. Next, both transmission power of the source and the power beacon are optimized through the throughput optimization. Finally, simulations are conducted to corroborate our theoretical analysis, and to reveal the impact of the transmission power of the source and PB as well as the imperfect CSI on the system performance.

Cooperative communication system with multiple relays for performance improvement in wireless communication system

In a wireless communication system, a cooperative communication technique is a communication method for improving performance. In the conventional scheme, when a destination user is located in the cell boundary, one base station communicates with a destination user. At a same time, a destination user communicates with other base stations which cooperate with base station. If a distance between a base station and a destination user is far, the quality of communication is degraded by the effect of channel attenuation. Therefore, this paper proposes an enhanced cooperative transmission scheme using the orthogonal frequency multiplexing in the wireless communication system. The proposed scheme uses extra relays between a base station and a destination user. When the channel state of a destination user is bad, other base stations are used. In order to obtain better performance than the conventional scheme, the cooperative decode and forward (DF), and space time cyclic delay diversity (STCDD) and cyclic delay diversity (CDD) are applied in the extra relays. In simulation results, the proposed scheme has higher error and throughput performances than the conventional scheme for obtaining diversity gain when the used modulation scheme is increased. Also, the proposed scheme which uses cooperative DF has slightly better error and throughput performances than the proposed scheme which uses cooperative STCDD and CDD due to less error propagations and resultant higher diversity gain.

Application of best relay selection approach to cooperative DF IDMA systems over Rayleigh/Weibull fading channels

SummaryThis paper analyzes the performance of cooperative decode‐and‐forward (DF) interleave‐division multiple‐access (IDMA) networks with best relay selection over Rayleigh/Weibull fading environments. In the analysis, approximate outage probability (OP) and bit error probability (BEP) expressions are derived for the considered system. Further, a 2‐hop DF IDMA system is also designed to compare with cooperative one. We propose OP and BEP expression for 2‐hop DF IDMA systems. Numerical results are obtained by changing the number of relays and the value of fading parameter in the proposed expressions. Also, simulations are provided to corroborate the exactness of the derived approximate OP and BEP expressions.

Simultaneous Wireless Power Transfer and Secure Multicasting in Cooperative Decode-and-Forward Relay Networks.

In this paper, we investigate simultaneous wireless power transfer and secure multicasting via cooperative decode-and-forward (DF) relays in the presence of multiple energy receivers and eavesdroppers. Two scenarios are considered under a total power budget: maximizing the minimum harvested energy among the energy receivers under a multicast secrecy rate constraint; and maximizing the multicast secrecy rate under a minimum harvested energy constraint. For both scenarios, we solve the transmit power allocation and relay beamformer design problems by using semidefinite relaxation and bisection technique. We present numerical results to analyze the energy harvesting and secure multicasting performances in cooperative DF relay networks.

A 60GHz Wireless Cooperative Communication System Based on Switching Beamforming

The challenge of penetrating obstacles along with impact from weak multipath effects makes 60GHz signal very difficult to be transmitted in non-line of sight (NLOS) channel. So 60GHz system is vulnerable to obstructions and thus likely results in link interruption. While the application of cooperative technology to solve link blockage problemin 60GHz system should consider the characteristic of directional transmission for 60GHz signal. Therefore in this paper a system is proposed to solve the link blockage problem in 60GHz NLOS communication environment based on the concept of cooperation and also the beamforming technology, which is the basis of directional transmission for 60GHz communication system. The process of anti-blockage solution with cooperative communication is presented in detail, and the fast switching and recovery schemes are well designed. The theoretical values of symbol error rate (SER) using decode and forward (DF) cooperation and amplify and forward (AF) cooperation are presented respectively when the common channel interference exists. Simulation results demonstrate that the performance based on DF cooperation is better than the performance based on AF cooperation when directional transmission is used.

A Joint Antenna and Path Selection Technique in Single-Relay-Based DF Cooperative MIMO Networks

In this paper, we consider a single-relay-based decode-and-forward (DF) cooperative multiple-input multiple-output (MIMO) system in which the source, the relay, and the destination are equipped with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{s}$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{r}$</tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{d}$</tex-math></inline-formula> antennas, respectively. We propose a joint antenna and path selection scheme, which jointly selects the single-transmit and single-receive antenna pairs, along with the selection of either a direct path that consists of source–destination channels or a cooperative path that consists of source–relay and relay–destination channels. The proposed selection scheme is based on the maximization of minimum of maximums (max-min-max) criterion of instantaneous signal-to-noise ratio (SNR). The analysis in this paper is based on the assumptions that all the channels follow independent Rayleigh fading. A closed-form expression of the symbol error rate (SER) for the proposed scheme in a cooperative MIMO system with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$</tex-math></inline-formula> -ary phase-shift keying is derived. We extract the analytical diversity order from the derived SER and show that the proposed selection scheme achieves the diversity order of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{s}N_{d}+N_{r}\mathrm{min}(N_{s},N_{d})$</tex-math></inline-formula> in the considered cooperative MIMO system. Closed-form expressions of bandwidth efficiency (BE) and ergodic capacity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(C_{t})$</tex-math></inline-formula> are derived for the proposed scheme. An optimized selection parameter from the specific set of values is numerically evaluated by maximizing a heuristic utility function <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(C_{t}\times \mbox{BE}/\mbox{SER})$</tex-math></inline-formula> . By using the already-gathered information about the maximum instantaneous SNR of every hop, a power adaptation scheme that maximizes the instantaneous SNR in the cooperative path is proposed and analyzed. The proposed power adaptation scheme, which is applied only in the event of selection of a cooperative path, outperforms the uniform-power-distribution-based DF cooperative MIMO system.

A Fair Relay Selection Based on Mapping Functions in the Dual Hop DF Cooperative Networks

We address the load balance, referred as “fairness” in our work, in the relay selection procedure of the dual hop decode-and-forward (DF) cooperative networks. Firstly, the unfairness caused by the known best-path relay selection (BRS) scheme is analyzed by the metric of blocking probability at the relays with equal relay channels. Secondly, aiming to improve the fairness while keeping a satisfied and comparable outage performance, we propose a fair relay selection algorithm based on mapping functions, including the signal to noise ratio (SNR) mapping functions and load mapping functions. It is worth mentioning that BRS scheme can be viewed as a special case of the proposed algorithm. Afterwards, the outage probability of the proposed algorithm is derived. During the derivation, the mixture Gamma distribution is used to model SNRs of wireless fading channels, so this kind of derivation is valid for different fading channels, e.g. Rayleigh, Nakagami-m etc.. Finally, taking the average load and outage probability as performance metrics, we simulated the proposed algorithm and compared it with the proportional fair cooperation (PFC) algorithm in the literature. As observed in the simulation results, the proposed algorithm guarantees fairness well among the relays, especially when the network is heavily burdened

End-to-End Optimum ML Detection for DF Cooperative Diversity Networks in the Presence of Interference

Unlike the existing detectors, which are developed for decode-and-forward (DF) networks in the ideal interference-free case, we consider a more practical scenario where arbitrary interference exists. We consider a DF cooperative network consisting of a source, multiple relays, a destination, and multiple interferers affecting both the relays and the destination. Each relay is equipped with multiple antennas and knows its local instantaneous channel state information (CSI). Assuming that the destination knows the instantaneous CSI of the source-relay, relay-destination, and source-destination channels, we develop, for the first time in the literature, the end-to-end optimum maximum-likelihood (ML) detectors in closed-form for DF systems employing either simultaneous or orthogonal transmissions in the presence of interference. Furthermore, theoretical analysis shows that the proposed detectors achieve full diversity gains in the presence of interference with finite interference-to-noise ratios. Numerical results demonstrate that the proposed optimum detectors substantially outperform the conventional schemes which simply ignore interference.

Detection with erasure for error‐propagation mitigation in decode‐and‐forward relaying with general pulse amplitude‐modulated/quadrature amplitude‐modulated signals

In the research of decode-and-forward (DF) cooperative communications, it is often supposed that the included relay only transmits correctly decoded signals. This simplifies the analysis of DF cooperation. However, in practical circumstances, erroneous messages may be forwarded which makes the decision at the destination even worst. In this study, the authors formulate a special detection way, named ‘detection with erasure’, to make certain that the relay-forwarded signals are mostly correct. Specifically, whenever the decoded result at the relay falls into some preset ‘erasure regions’, the relay will not process and transmit it anymore. This effectively prevents the forwarding of erroneous messages. With general pulse amplitude-modulated or squared quadrature amplitude-modulated signals, the authors demonstrate that these erasure regions can be adjusted to minimise the end-to-end symbol error rate (SER). This detection scheme can be extended to be used in the DF cooperation employing multiple relays as well. Simulations reveal that in terms of the end-to-end SER performance, the proposed detection with erasure can outperform some signal-to-noise ratio threshold-based relaying approaches, and can perform quite similarly as compared with those decoding/combining methods realised at the destination with the advantage of less channel state information exchange.

Resource allocation in MIMO‐OFDM‐based cooperative cognitive radio networks: optimal and suboptimal low complexity approaches

SummaryThe problem of resources allocation in multiple‐input multiple‐output‐orthogonal frequency division multiplexing based cooperative cognitive radio networks is considered, in this paper. The cooperation strategy between the secondary users is decode‐and‐forward (DF) strategy. In order to obtain an optimal subcarrier pairing, relay selection and power allocation in the system, the dual decomposition technique is recruited. The optimal resource allocation is realized under the individual power constraints in source and relays so that the sum rate is maximized while the interference induced to the primary system is kept below a pre‐specified interference temperature limit. Moreover, because of the high computational complexity of the optimal approach, a suboptimal algorithm is further proposed. The jointly allocation of the resources in suboptimal algorithm is carried out taking into account the channel qualities, the DF cooperation strategy, the interference induced to the primary system and the individual power budgets. The performance of the different approaches and the impact of the constraint values and deploying multiple antennas at users are discussed through the numerical simulation results. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Performance Analysis of DF Cooperative Diversity System With OSTBC Over Spatially Correlated Nakagami-$m$ Fading Channels

In this paper, we investigate the performance of a cooperative decode-and-forward (DF) multiple-input–multiple-output (MIMO) relaying system with orthogonal space–time block code (OSTBC) transmissions over spatially correlated Nakagami- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$m$</tex></formula> fading channels for integer values of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$m$</tex></formula> . We consider both the opportunistic maximal-ratio combining (O-MRC) and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lambda$</tex></formula> -MRC receivers at the destination. For the former MRC, we give the closed-form expression for the cumulative distribution function (cdf) of the instantaneous end-to-end signal-to-noise ratio (SNR); relying on this, the exact analytical and asymptotic expressions are also derived for outage probability (OP) and symbol error rate (SER), whereas for the latter MRC, the closed-form expressions are derived for the exact and asymptotic bit error rate (BER) of binary phase-shift keying (BPSK) signals. The optimal value of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lambda$</tex></formula> that minimizes the BER is also provided by using Newton's method. It is shown that O-MRC outperforms <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lambda$</tex></formula> -MRC since the former MRC takes the relay decoding results into account. For <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lambda$</tex></formula> -MRC, the optimal <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lambda$</tex></formula> decreases with the increase in the SNR and spatial correlation since increasing the SNR and spatial correlation could increase the confidence of the source–destination link and decrease the confidence of the source–relay link, respectively.

Optimal and sub‐optimal resource allocation in multiple‐input multiple‐output‐orthogonal frequency division multiplexing‐based multi‐relay cooperative cognitive radio networks

The authors consider the resource allocation issue in multiple-input multiple-output-orthogonal frequency division multiplexing-based cooperative cognitive radio networks with the decode-and-forward (DF) as the cooperation strategy. The dual decomposition technique is recruited to obtain an optimal subcarrier pairing, relay selection and power allocation. The optimal resource allocation is performed subject to the individual power constraints in source and relays so that the sum-rate is maximised while the interference induced to the primary system is kept below a pre-specified interference temperature limit. Moreover, because of the high computational complexity of the optimal approach, a sub-optimal algorithm is further proposed. In the sub-optimal scheme, the joint allocation of the resources is performed taking into account the channel qualities, the DF cooperation strategy, the interference induced to the primary system and the individual power budgets. The performance of different approaches and the impact of the constraint values and deploying multiple-antennas at users are explored through numerical simulations.