| 1. |
- Alodeh, M., et al.
(author)
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Symbol-level and multicast precoding for multiuser multiantenna downlink : A state-of-the-art, classification, and challenges
- 2018
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In: IEEE Communications Surveys and Tutorials. - : Institute of Electrical and Electronics Engineers (IEEE). - 1553-877X. ; 20:3, s. 1733-1757
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Journal article (peer-reviewed)abstract
- Precoding has been conventionally considered as an effective means of mitigating or exploiting the interference in the multiantenna downlink channel, where multiple users are simultaneously served with independent information over the same channel resources. The early works in this area were focused on transmitting an individual information stream to each user by constructing weighted linear combinations of symbol blocks (codewords). However, more recent works have moved beyond this traditional view by: 1) transmitting distinct data streams to groups of users and 2) applying precoding on a symbol-per-symbol basis. In this context, the current survey presents a unified view and classification of precoding techniques with respect to two main axes: 1) the switching rate of the precoding weights, leading to the classes of block-level and symbol-level precoding and 2) the number of users that each stream is addressed to, hence unicast, multicast, and broadcast precoding. Furthermore, the classified techniques are compared through representative numerical results to demonstrate their relative performance and uncover fundamental insights. Finally, a list of open theoretical problems and practical challenges are presented to inspire further research in this area1.1The concepts of precoding and beamforming are used interchangeably throughout this paper.
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| 2. |
- Arnau, J., et al.
(author)
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Performance of the multibeam satellite return link with correlated rain attenuation
- 2014
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In: IEEE Transactions on Wireless Communications. - : IEEE Press. - 1536-1276 .- 1558-2248. ; 13:11, s. 6286-6299
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Journal article (peer-reviewed)abstract
- Rain attenuation is among the major impairments for satellite systems operating in the K-band and above. In this paper, we investigate the impact of spatially correlated rain attenuation on the performance of a multibeam satellite return link. For a comprehensive assessment, an analytical model for the antenna pattern that generates the beams is also proposed. We focus on the outage capacity of the link and obtain analytical approximations at high and low signal-to-noise ratio. The derived approximations provide insights into the effect of key system parameters such as the interuser distance, the satellite beam radius, or the rain intensity, and simulation results show that it fits tightly with the Monte Carlo results. Additionally, the derived expressions can be easily particularized for the single-user case, providing some novel insights.
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| 3. |
- Christopoulos, D., et al.
(author)
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Linear precoding in multibeam SatComs : Practical constraints
- 2013
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In: 31st AIAA International Communications Satellite Systems Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102448
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Conference paper (peer-reviewed)abstract
- Multiuser precoding of the linear kind is one of the most promising candidate techniques required for managing inter-beam co-channel interference in aggressive frequency re-use multibeam High Throughput Satellite (HTS) systems. Although academic research on precoding schemes for broadband interactive satellite communication (SatCom) systems is intensifying, there are a number of practical constraints in current DVB-S2-based HTS systems that may inhibit the application of precoding. These have not been dealt with hitherto in the literature. The present article attempts to list the relevant issues, propose some possible ways forward and present some preliminary simulation results.
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| 4. |
- Christopoulos, D., et al.
(author)
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MMSE Performance Analysis of Generalized Multibeam Satellite Channels
- 2013
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In: IEEE Communications Letters. - 1089-7798 .- 1558-2558. ; 17:7, s. 1332-1335
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Journal article (peer-reviewed)abstract
- Aggressive frequency reuse in the return link (RL) of multibeam satellite communications (SatComs) is crucial towards the implementation of next generation, interactive satellite services. In this direction, multiuser detection has shown great potential in mitigating the increased intrasystem interferences, induced by a tight spectrum reuse. Herein we present an analytic framework to describe the linear Minimum Mean Square Error (MMSE) performance of multiuser channels that exhibit full receive correlation: an inherent attribute of the RL of multibeam SatComs. Analytic, tight approximations on the MMSE performance are proposed for cases where closed form solutions are not available in the existing literature. The proposed framework is generic, thus providing a generalized solution straightforwardly extendable to various fading models over channels that exhibit full receive correlation. Simulation results are provided to show the tightness of the proposed approximation with respect to the available transmit power.
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| 5. |
- Christopoulos, D., et al.
(author)
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Multicast multigroup beamforming under per-antenna power constraints
- 2014
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In: 2014 IEEE International Conference on Communications (ICC). - : IEEE conference proceedings. ; , s. 4704-4710
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Conference paper (peer-reviewed)abstract
- 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.
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| 6. |
- Christopoulos, D., et al.
(author)
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Multicast Multigroup Precoding and User Scheduling for Frame-Based Satellite Communications
- 2015
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In: IEEE Transactions on Wireless Communications. - 1536-1276 .- 1558-2248. ; 14:9, s. 4695-4707
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Journal article (peer-reviewed)abstract
- The present work focuses on the forward link of a broadband multibeam satellite system that aggressively reuses the user link frequency resources. Two fundamental practical challenges, namely the need to frame multiple users per transmission and the per-antenna transmit power limitations, are addressed. To this end, the so-called frame-based precoding problem is optimally solved using the principles of physical layer multicasting to multiple co-channel groups under per-antenna constraints. In this context, a novel optimization problem that aims at maximizing the system sum rate under individual power constraints is proposed. Added to that, the formulation is further extended to include availability constraints. As a result, the high gains of the sum rate optimal design are traded off to satisfy the stringent availability requirements of satellite systems. Moreover, the throughput maximization with a granular spectral efficiency versus SINR function, is formulated and solved. Finally, a multicast-aware user scheduling policy, based on the channel state information, is developed. Thus, substantial multiuser diversity gains are gleaned. Numerical results over a realistic simulation environment exhibit as much as 30% gains over conventional systems, even for 7 users per frame, without modifying the framing structure of legacy communication standards.
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| 7. |
- Christopoulos, D., et al.
(author)
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Sum rate maximizing multigroup multicast beamforming under per-antenna power constraints
- 2014
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In: 2014 IEEE Global Communications Conference. - : IEEE conference proceedings. ; , s. 3354-3359
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Conference paper (peer-reviewed)abstract
- A multi-antenna transmitter that conveys independent sets of common data to distinct groups of users is herein considered, a model known as physical layer multicasting to multiple co-channel groups. In the recently proposed context of per-antenna power constrained multigroup multicasting, the present work focuses on a novel system design that aims at maximizing the total achievable throughput. Towards increasing the system sum rate, the available power resources need to be allocated to well conditioned groups of users. A detailed solution to tackle the elaborate sum rate maximizing, multigroup multicast problem, under per-antenna power constraints is therefore derived. Numerical results are presented to quantify the gains of the proposed algorithm over heuristic solutions. The solution is applied to rayleigh as well as Vandermonde channels. The latter case is typically realised in uniform linear array transmitters operating in the far field, where line-of-sight conditions are realized. In this setting, a sensitivity analysis with respect to the angular separation of co-group users is included. Finally, a simple scenario providing important intuitions for the sum rate maximizing multigroup multicast solutions is elaborated.
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| 8. |
- Christopoulos, D., et al.
(author)
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User scheduling for coordinated dual satellite systems with linear precoding
- 2013
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In: 2013 IEEE International Conference on Communications (ICC). - 9781467331227 ; , s. 4498-4503
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Conference paper (peer-reviewed)abstract
- The constantly increasing demand for interactive broadband satellite communications is driving current research towards novel system architectures that reuse frequency in a more aggressive manner. To this end, the topic of dual satellite systems, in which satellites share spatial (i.e. same coverage area) and spectral (i.e. full frequency reuse) degrees of freedom is introduced. In each multibeam satellite, multiuser interferences are mitigated by employing zero forcing precoding with realistic per antenna power constraints. However, the two sets of users that the transmitters are separately serving, interfere. The present contribution, proposes the partial cooperation, herein referred to as coordination, between the two coexisting transmitters in order to reduce interferences and enhance the performance of the whole system, while maintaining moderate system complexity. In this direction, a heuristic, iterative, low complexity algorithm that allocates users in the two interfering sets is proposed. This novel algorithm, improves the performance of each satellite and of the overall system, simultaneously. The first is achieved by maximizing the orthogonality between users allocated in the same set, hence optimizing the zero forcing performance, whilst the second by minimizing the level of interferences between the two sets. Simulation results show that the proposed method, compared to conventional techniques, significantly increases spectral efficiency.
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| 9. |
- Christopoulos, D., et al.
(author)
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Weighted fair multicast multigroup beamforming under per-antenna power constraints
- 2014
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In: IEEE Transactions on Signal Processing. - : IEEE Press. - 1053-587X .- 1941-0476. ; 62:19, s. 5132-5142
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Journal article (peer-reviewed)abstract
- A multiantenna 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 cochannel 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.
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| 10. |
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