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See detailData Predistortion for Multicarrier Satellite Channels Based on Direct Learning
Piazza, Roberto UL; Shankar, Bhavani UL; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2014), 62(22),

Satellite communication is facing the urgent need of improving data rate and efficiency to compete with the quality of service offered by terrestrial communication systems. An imminent gain, achievable ... [more ▼]

Satellite communication is facing the urgent need of improving data rate and efficiency to compete with the quality of service offered by terrestrial communication systems. An imminent gain, achievable without the need of upgrading current satellite technology, can be obtained by exploiting multicarrier operation at the transponder and using highly efficient modulation schemes. However, on-board multicarrier joint amplification of high order modulation schemes is a critical operation as it brings severe non-linear distortion effects. These distortions increase as the on-board High Power Amplifier (HPA) is operated to yield higher power efficiencies. In this work, we propose novel techniques to implement on ground predistortion that enable multicarrier transmission of highly efficient modulation schemes over satellite channels without impacting infrastructure on the downlink. [less ▲]

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See detailExploiting polarization for spectrum awareness in cognitive satellite communications
Sharma, S. K.; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Exploiting polarization for spectrum awareness in cognitive satellite communications (2014)

The continuously increasing demand of spectrum and current static spectrum allocation policies are rendering the available radio spectrum scarce. To address the problem of spectrum scarcity in the ... [more ▼]

The continuously increasing demand of spectrum and current static spectrum allocation policies are rendering the available radio spectrum scarce. To address the problem of spectrum scarcity in the satellite paradigm, cognitive satellite communications has been considered as a promising technique. In addition to the existing spectrum sharing dimensions such as frequency, time, and space, polarization can be exploited as an additional degree of freedom in order to explore the spectral gaps in the underutilized licensed spectrum. In this context, this chapter firstly provides an overview of the existing works in polarization-based spectrum sharing. Secondly, it presents the theoretical analysis of energy detection technique for dual polarized Additive White Gaussian Noise and Rayleigh fading channels considering the spectral coexistence scenarios of dual and hybrid satellite systems. Thirdly, it provides the comparison of different combining techniques in terms of the sensing performance. Finally, it provides interesting future research directions in this domain. © 2015 by IGI Global. All rights reserved. [less ▲]

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See detailWeighted Fair Multicast Multigroup Beamforming under Per-antenna Power Constraints
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Signal Processing, IEEE Transactions on (2014), 62(19), 5132-5142

A multi-antenna transmitter that conveys independent sets of common data to distinct groups of users is considered. This model is known as physical layer multicasting to multiple co-channel groups. In ... [more ▼]

A multi-antenna transmitter that conveys independent sets of common data to distinct groups of users is considered. This model is known as physical layer multicasting to multiple co-channel groups. In this context, the practical constraint of a maximum permitted power level radiated by each antenna is addressed. The per-antenna power constrained system is optimized in a maximum fairness sense with respect to predetermined quality of service weights. In other words, the worst scaled user is boosted by maximizing its weighted signal-to-interference plus noise ratio. A detailed solution to tackle the weighted max-min fair multigroup multicast problem under per-antenna power constraints is therefore derived. The implications of the novel constraints are investigated via prominent applications and paradigms. What is more, robust per-antenna constrained multigroup multicast beamforming solutions are proposed. Finally, an extensive performance evaluation quantifies the gains of the proposed algorithm over existing solutions and exhibits its accuracy over per-antenna power constrained systems. [less ▲]

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See detailFrame Based Precoding in Satellite Communications: A Multicast Approach
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in In Proc. of IEEE, Advanced Satellite Multimedia Systems Conference (2014, September)

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See detailImplementation Issues of Cognitive Radio Techniques for Ka-band (17.7-19.7 GHZ) SatComs
Sharma, Shree Krishna UL; Maleki, Sina UL; Chatzinotas, Symeon UL et al

in Proceedings of 7th ASMS/13th SPSC (2014, September)

The usable satellite spectrum has become scarce due to continuously increasing demand for broadband multimedia, broadcast and interactive services. In this context, investigating efficient spectrum ... [more ▼]

The usable satellite spectrum has become scarce due to continuously increasing demand for broadband multimedia, broadcast and interactive services. In this context, investigating efficient spectrum coexistence techniques is a crucial challenge in order to enhance the spectral efficiency of future satellite systems. Herein, we study a satellite-terrestrial coexistence scenario where a Fixed Satellite Service (FSS) downlink coexists with the Fixed Service (FS) point to point microwave links in the Ka-band (17.7-19.7 GHz). First, we identify various practical challenges and provide possible solutions in order to allow this coexistence. Then we propose four different sensing and avoidance schemes in order to protect FSS satellite terminals from the harmful FS interference. Further, we evaluate the performance of one of the proposed solutions in the considered scenario with the help of theoretical and numerical analysis. More specifically, we focus on harmful FS detection problem in order to guarantee the sufficient protection of FSS terminals. It is shown that the FS harmful interference can be reliably detected with the help of an additional dipole antenna and this solution further overcomes the noise uncertainty problem encountered while sensing with the satellite dish. [less ▲]

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See detailCPU-Based Real-Time Surface and Solid Voxelization for Incomplete Point Cloud
Garcia Becerro, Frederic UL; Ottersten, Björn UL

in 22nd International Conference on Pattern Recognition (2014, August 27)

This paper presents a surface and solid voxelization approach for incomplete point cloud datasets. Voxelization stands for a discrete approximation of 3-D objects into a volumetric representation, a ... [more ▼]

This paper presents a surface and solid voxelization approach for incomplete point cloud datasets. Voxelization stands for a discrete approximation of 3-D objects into a volumetric representation, a process which is commonly employed in computer graphics and increasingly being used in computer vision. In contrast to surface voxelization, solid voxelization not only set those voxels related to the object surface but also those voxels considered to be inside the object. To that end, we first approximate the given point set, usually describing the external object surface, to an axis-aligned voxel grid. Then, we slice-wise construct a shell containing all surface voxels along each grid-axis pair. Finally, voxels inside the constructed shell are set. Solid voxelization results from the combination of all slices, resulting in a watertight and gap-free representation of the object. The experimental results show a high performance when voxelizing point cloud datasets, independently of the object’s complexity, robust to noise, and handling large portions of data missing. [less ▲]

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See detailJoint Channel Estimation and Pilot Allocation in Underlay Cognitive MISO Networks
Alodeh, Maha UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE International Wireless Communications and Mobile Computing Conference (2014, August)

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See detailNew Generation Cooperative and Cognitive Dual Satellite Systems: Performance Evaluation
Sharma, Shree Krishna UL; Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL et al

in Proceedings of 32nd AIAA ICSSC (2014, August)

Investigating innovative satellite architectures with enhanced system through- put is one of the most important challenges towards realizing the next generation of satellite communication systems. In this ... [more ▼]

Investigating innovative satellite architectures with enhanced system through- put is one of the most important challenges towards realizing the next generation of satellite communication systems. In this context, we study two advanced architectures, namely cooperative and cognitive satellite systems. These designs allow the spectral coexistence of two multibeam satellites over a common coverage area with the overlapping beam patterns. In the cooperative dual satellite system, we consider coordination between two coexisting transmitters in order to reduce the intersatellite interference. This is achieved by employing adequate user scheduling, based on the channel state information of each user. To this end, a semi-orthogonal interference aware scheduling algorithm is applied. Further, in the cognitive dual satellite system, we employ a cognitive beamhopping technique assuming that the secondary gateway is aware of the primary's beamhopping pattern. Moreover, we compare the performances of these schemes with those of the conventional multi- beam and overlapping dual satellite systems in terms of spectral efficiency, power efficiency and user fairness. Finally, we provide several insights on the performance of these schemes and provide interesting future works in these domains. [less ▲]

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See detailInline Interference Mitigation Techniques for Spectral Coexistence of GEO and NGEO Satellites
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in International Journal of Satellite Communications and Networking (2014)

The interest towards the deployment of Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) satellite systems in several frequency bands is increasing due to the requirement of low latency for real-time systems ... [more ▼]

The interest towards the deployment of Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) satellite systems in several frequency bands is increasing due to the requirement of low latency for real-time systems and high demand of broadband data. When the number of usable Non-Geostationary (NGEO) satellites, that is, LEO/MEO in space, increases, the frequency coexistence between the NGEO satellite systems with the already existing geostationary (GEO) satellite networks becomes a requisite. In this context, it is crucial to explore interference mitigation techniques between GEO and NGEO systems in order to allow their spectral coexistence. More specifically, in the coexistence scenario of GEO and NGEO satellite networks, in-line interference may be a serious problem, especially in the equatorial region. In this paper, we provide several frequency sharing studies in the context of the coexistence of an NGEO satellite link with another NGEO/GEO satellite link. Furthermore, we carry out interference analysis between GEO and MEO satellite systems considering the case of the O3b satellite system and propose an adaptive power control technique for both the uplink and downlink scenarios in order to mitigate the in-line interference. Moreover, we suggest several cognitive solutions for mitigating the in-line interference and provide future research issues. [less ▲]

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See detailSpatial DCT-Based Least Square Estimation in Multi-antenna Multi-cell Interference Channels
Alodeh, Maha UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE International Conference on Communications(ICC) (2014, June)

Detailed reference viewed: 246 (18 UL)
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See detailWeighted Fair Multicast Multigroup Beamforming Under Per-antenna Power Constraints
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Multicast multigroup beamforming under per-antenna power constraints (2014, June)

Linear precoding exploits the spatial degrees of freedom offered by multi-antenna transmitters to serve multiple users over the same frequency resources. The present work focuses on simultaneously serving ... [more ▼]

Linear precoding exploits the spatial degrees of freedom offered by multi-antenna transmitters to serve multiple users over the same frequency resources. The present work focuses on simultaneously serving multiple groups of users, each with its own channel, by transmitting a stream of common symbols to each group. This scenario is known as physical layer multicasting to multiple co-channel groups. Extending the current state of the art in multigroup multicasting, the practical constraint of a maximum permitted power level radiated by each antenna is tackled herein. The considered per antenna power constrained system is optimized in a maximum fairness sense. In other words, the optimization aims at favoring the worst user by maximizing the minimum rate. This Max-Min Fair criterion is imperative in multicast systems, where the performance of all the receivers listening to the same multicast is dictated by the worst rate in the group. An analytic framework to tackle the Max-Min Fair multigroup multicasting scenario under per antenna power constraints is therefore derived. Numerical results display the accuracy of the proposed solution and provide insights to the performance of a per antenna power constrained system. [less ▲]

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See detailMulticarrier LUT-based data predistortion for non-linear satellite channels
Piazza, Roberto UL; Shankar, Bhavani UL; Ottersten, Björn UL

in Communications (ICC), 2014 IEEE International Conference on (2014, June)

Current satellite communication architectures can be potentially improved by applying multicarrier power amplification. Joint on-board amplification of multiple carriers reduces hardware and weight ... [more ▼]

Current satellite communication architectures can be potentially improved by applying multicarrier power amplification. Joint on-board amplification of multiple carriers reduces hardware and weight, enabling cost-efficient satellite architectures. However, on board power amplification is inherently a non-linear operation, whose distortion effects drastically increase when the high power amplifier (HPA) is operated in multiple carrier mode due to the generated inter-modulation products. In order to achieve the desired on-board power efficiency and to reduce the non-linear distortion, specific countermeasures need to be put in place. In this work we provide a novel data predistortion technique for multiple carriers satellite channel based on look up table (LUT) for high throughput applications. In contrast to known single carrier LUT techniques, the entries of the table are obtained by pursuing an analytical approach exploiting channel model and implementing recursive least squares techniques (RLS). A novel method to reduce the number of LUT entries based on LUT partitioning is proposed. Considerable performance gains over standard polynomial based predistortion are realized by the proposed technique. [less ▲]

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See detailA Hybrid Cognitive Transceiver Architecture: Sensing-Throughput Tradeoff
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of 9th International Conference on Cognitive Radio Oriented Wireless Networks (2014, June)

Spectrum Sensing (SS) and underlay have been considered as two important techniques for enabling the spectral coexistence of the licensed and unlicensed wireless communication systems. The SS only ... [more ▼]

Spectrum Sensing (SS) and underlay have been considered as two important techniques for enabling the spectral coexistence of the licensed and unlicensed wireless communication systems. The SS only approach ignores the interference tolerance capability of the Primary Users (PUs) while assuming the bursty PU traffic whereas the possibility of having secondary transmission with full power is neglected in an underlay based approach. To address this, it’s crucial to investigate suitable hybrid spectrum awareness and transmission strategies which can overcome the aforementioned drawbacks and achieve higher secondary throughput while protecting the PUs. In this context, we propose a hybrid cognitive transceiver which combines the SS approach with the power control based underlay approach. Furthermore, we evaluate the performance of the proposed hybrid approach considering both periodic sensing and simultaneous sensing/transmission schemes. Moreover, sensing-throughput tradeoff for the proposed hybrid approach is investigated and the performance is compared with the conventional SS only approaches in terms of the achievable throughput. It is shown that the proposed scheme can achieve a significant improvement in the secondary throughput over the conventional approaches while respecting the interference constraints of the PUs. [less ▲]

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See detailCompressive Sparsity Order Estimation for Wideband Cognitive Radio Receiver
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of IEEE International Conference on Communications (ICC) (2014, June)

Compressive Sensing (CS) has been widely investigated in the Cognitive Radio (CR) literature in order to reduce the hardware cost of sensing wideband signals assuming prior knowledge of the sparsity ... [more ▼]

Compressive Sensing (CS) has been widely investigated in the Cognitive Radio (CR) literature in order to reduce the hardware cost of sensing wideband signals assuming prior knowledge of the sparsity pattern. However, the sparsity order of the channel occupancy is time-varying and the sampling rate of the CS receiver needs to be adjusted based on its value in order to fully exploit the potential of CS-based techniques. In this context, investigating blind Sparsity Order Estimation (SOE) techniques is an open research issue. To address this, we study an eigenvalue based compressive SOE technique using asymptotic Random Matrix Theory. We carry out detailed theoretical analysis for the signal plus noise case to derive the asymptotic eigenvalue probability distribution function (aepdf) of the measured signal’s covariance matrix for sparse signals. Subsequently, based on the derived aepdf expression, we present a technique to estimate the sparsity order of the wideband spectrum with compressive measurements using the maximum eigenvalue of the measured signal’s covariance matrix. The performance of the proposed technique is evaluated in terms of normalized SOE Error (SOEE). It is shown that the sparsity order of the wideband spectrum can be reliably estimated using the proposed technique. [less ▲]

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See detailTo AND or To OR: How Shall the Fusion Center Rule in Energy-Constrained Cognitive Radio Networks?
Maleki, Sina UL; Leus, Geert; Chatzinotas, Symeon UL et al

in IEEE International Conference on Communications (ICC), 10-14 June 2014, Sydney, Australia (2014, June)

Distributed spectrum sensing enhances the detection reliability of a cognitive radio network. However, this comes at the price of a higher energy consumption. To solve this problem, a combined censoring ... [more ▼]

Distributed spectrum sensing enhances the detection reliability of a cognitive radio network. However, this comes at the price of a higher energy consumption. To solve this problem, a combined censoring and sleeping scheme is considered where the cognitive radios switch off their sensing module with a specific sleeping rate in each sensing period. The awake cognitive radios send their local decisions to the fusion center only if it is deemed to be informative. The fusion center either employs the OR or the AND rule to make the final decision about the presence or absence of the primary user. This paper investigates which rule performs better in terms of energy efficiency under various conditions. The underlying sensing parameters are derived by minimizing the maximum average energy consumption per sensor subject to a constraint on the probabilities of false alarm and detection. This way, it can be ensured that the spectrum opportunities are utilized efficiently while the primary users are not interfered with. A case study based on IEEE 802.15.4/ZigBee is considered for performance evaluation. It is shown that significant energy savings can be obtained by employing combined censoring and sleeping. [less ▲]

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See detailEnhanced List-Based Group-Wise Overloaded Receiver with Application to Satellite Reception
Abu Shaban, Zohair UL; Shankar, Bhavani UL; Mehrpoyan, Hani et al

in Proceedings of IEEE ICC 2014 (2014, June)

The market trends towards the use of smaller dish antennas for TV satellite receivers, as well as the growing density of broadcasting satellites in orbit require the application of robust adjacent ... [more ▼]

The market trends towards the use of smaller dish antennas for TV satellite receivers, as well as the growing density of broadcasting satellites in orbit require the application of robust adjacent satellite interference (ASI) cancellation algorithms at the receivers. The wider beamwidth of a small size dish and the growing number of satellites in orbit impose an overloaded scenario, i.e., a scenario where the number of transmitting satellites exceeds the number of receiving antennas. For such a scenario, we present a two stage receiver to enhance signal detection from the satellite of interest, i.e., the satellite that the dish is pointing to, while reducing interference from neighboring satellites. Towards this objective, we propose an enhanced List-based Group-wise Search Detection (LGSD) receiver architecture that takes into account the spatially correlated additive noise and uses the signal-to-interference-plus-noise ratio (SINR) maximization criterion to improve detection performance. Simulations show that the proposed receiver structure enhances the performance of satellite systems in the presence of ASI when compared to existing methods. [less ▲]

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See detailMaximum Eigenvalue Detection for Spectrum Sensing Under Correlated Noise
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing 2014 (2014, May)

Herein, we consider the problem of detecting primary users’ signals in the presence of noise correlation, which may arise due to imperfections in filtering and oversampling operations in a Cognitive Radio ... [more ▼]

Herein, we consider the problem of detecting primary users’ signals in the presence of noise correlation, which may arise due to imperfections in filtering and oversampling operations in a Cognitive Radio (CR) receiver. In this context, we study a Maximum Eigenvalue (ME) detection technique using recent results from Random Matrix Theory (RMT) for characterizing the distribution of the maximum eigenvalue of a class of sample covariance matrices. Subsequently, we derive a theoretical expression for a sensing threshold as a function of the probability of false alarm and evaluate the sensing performance in terms of probability of correct decision. It is shown that the proposed approach significantly improves the sensing performance of the ME detector in correlated noise scenarios. [less ▲]

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See detailPower Allocation for Energy-Constrained Cognitive Radios in the Presence of an Eavesdropper
Maleki, Sina UL; Kalantari, Ashkan UL; Chatzinotas, Symeon UL et al

in 2014 IEEE International Conference on Acoustics Speech and Signal Processing (ICASSP) (2014, May)

Reliable and agile spectrum sensing as well as secure communication are key requirements of a cognitive radio system. In this paper, secrecy throughput of a cognitive radio is maximized in order to ... [more ▼]

Reliable and agile spectrum sensing as well as secure communication are key requirements of a cognitive radio system. In this paper, secrecy throughput of a cognitive radio is maximized in order to determine the sensing threshold, the sensing time, and the transmission power. Constraints of the problem are defined as a lower-bound on the detection probability, an upper-bound on the average energy consumption per time-frame, and the maximum transmission power of the cognitive radio. We show that the problem can be solved by an on-off strategy where the cognitive radio only performs sensing and transmits data if the cognitive channel gain is greater than the average eavesdropper channel gain. The problem is then solved by a line-search over sensing time. Eventually, the secrecy throughput of the cognitive radio is evaluated employing the IEEE 802.15.4/ZigBee standard. [less ▲]

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See detailCarrier Rate Optimization on the Return Link of Interactive Mobile Satellite Networks
Piazza, Roberto UL; Shankar, Bhavani UL; Ottersten, Björn UL

in European Wireless 2014; 20th European Wireless Conference; Proceedings of (2014, May)

Emerging interactive satellite applications demand highly efficient transmission schemes. Narrow-band satellite return channels for mobile users have peculiar characteristics that make the optimal user ... [more ▼]

Emerging interactive satellite applications demand highly efficient transmission schemes. Narrow-band satellite return channels for mobile users have peculiar characteristics that make the optimal user-rate determination a hard problem. Carrier rate enhancement can only be enabled by increasing the user bandwidth and by the application of highly efficient coding schemes. However, with the system bandwidth held constant, gains from increased user bandwidth can be offset by interference from an adjacent user channels. Additional interference is caused by spurious emissions from adjacent channels; these arise from the spectral regrowth caused by the user terminal power amplifier when operated in high-efficiency region. On the other hand, efficient amplification is mandatory to achieve the required signal to noise ratio at the receiver. In this work we propose a combination of transmitter and receiver techniques to improve the user-rate while controlling the user power efficiency. [less ▲]

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See detailBeamforming for MISO Interference Channels with QoS and RF Energy Transfer
Timotheou, S.; Krikidis, I.; Zheng, Gan et al

in Wireless Communications, IEEE Transactions on (2014), 13(5), 2646-2658

We consider a multiuser multiple-input single-output interference channel where the receivers are characterized by both quality-of-service (QoS) and radio-frequency (RF) energy harvesting (EH) constraints ... [more ▼]

We consider a multiuser multiple-input single-output interference channel where the receivers are characterized by both quality-of-service (QoS) and radio-frequency (RF) energy harvesting (EH) constraints. We consider the power splitting RF-EH technique where each receiver divides the received signal into two parts a) for information decoding and b) for battery charging. The minimum required power that supports both the QoS and the RF-EH constraints is formulated as an optimization problem that incorporates the transmitted power and the beamforming design at each transmitter as well as the power splitting ratio at each receiver. We consider both the cases of fixed beamforming and when the beamforming design is incorporated into the optimization problem. For fixed beamforming we study three standard beamforming schemes, the zero-forcing (ZF), the regularized zero-forcing (RZF) and the maximum ratio transmission (MRT); a hybrid scheme, MRT-ZF, comprised of a linear combination of MRT and ZF beamforming is also examined. The optimal solution for ZF beamforming is derived in closed-form, while optimization algorithms based on second-order cone programming are developed for MRT, RZF and MRT-ZF beamforming to solve the problem. In addition, the joint-optimization of beamforming and power allocation is studied using semidefinite programming (SDP) with the aid of rank relaxation. [less ▲]

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