Multibeam Joint Precoding: frame based design

in Cooperative and Cognitive Satellite Systems (2015)

Constructive Multiuser Interference in Symbol Level Precoding for the MISO Downlink Channel

in IEEE Transactions on Signal Processing (2015)

This paper investigates the problem of interference among the simultaneous multiuser transmissions in the downlink of multiple-antenna systems. Using symbol-level precoding, a new approach to exploit the ... [more ▼]

This paper investigates the problem of interference among the simultaneous multiuser transmissions in the downlink of multiple-antenna systems. Using symbol-level precoding, a new approach to exploit the multiuser interference is discussed. The concept of exploiting the interference between spatial multiuser transmissions by jointly utilizing data information (DI) and channel state information (CSI), in order to design symbol-level precoders, is proposed. To this end, the interference between data streams is transformed under certain conditions into useful signal that can improve the signal to interference noise ratio (SINR) of the downlink transmissions. We propose a maximum ratio transmission (MRT) based algorithm that jointly exploits DI and CSI to glean the benefits from constructive multiuser interference. Subsequently, a relation between the constructive interference downlink transmission and physical layer multicasting is established. In this context, novel constructive interference precoding techniques that tackle the transmit power minimization (min-power) with individual SINR constraints at each user's receivers is proposed. Furthermore, fairness through maximizing the weighted minimum SINR (max-min SINR) of the users is addressed by finding the link between the min power and max min SINR problems. Moreover, heuristic precoding techniques are proposed to tackle the weighted sum rate problem. Finally, extensive numerical results show that the proposed schemes outperform other state of the art techniques. [less ▲]

Multicast multigroup beamforming for per-antenna power constrained large-scale arrays

in IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC (2015), 2015-August

Large in the number of transmit elements, multi-antenna arrays with per-element limitations are in the focus of the present work. In this context, physical layer multigroup multicasting under per-antenna ... [more ▼]

Large in the number of transmit elements, multi-antenna arrays with per-element limitations are in the focus of the present work. In this context, physical layer multigroup multicasting under per-antenna power constrains, is investigated herein. To address this complex optimization problem low-complexity alternatives to semi-definite relaxation are proposed. The goal is to optimize the per-antenna power constrained transmitter in a maximum fairness sense, which is formulated as a non-convex quadratically constrained quadratic problem. Therefore, the recently developed tool of feasible point pursuit and successive convex approximation is extended to account for practical per-antenna power constraints. Interestingly, the novel iterative method exhibits not only superior performance in terms of approaching the relaxed upper bound but also a significant complexity reduction, as the dimensions of the optimization variables increase. Consequently, multicast multigroup beamforming for large-scale array transmitters with per-antenna dedicated amplifiers is rendered computationally efficient and accurate. A preliminary performance evaluation in large-scale systems for which the semi-definite relaxation constantly yields non rank-1 solutions is presented. © 2015 IEEE. [less ▲]

Sensing-Throughput Tradeoff for Interweave Cognitive Radio System: A Deployment-Centric Viewpoint

in Wireless Communications, IEEE Transactions on (2015), PP(99), 14

Secondary access to the licensed spectrum is viable only if the interference is avoided at the primary system. In this regard, different paradigms have been conceptualized in the existing literature ... [more ▼]

Secondary access to the licensed spectrum is viable only if the interference is avoided at the primary system. In this regard, different paradigms have been conceptualized in the existing literature. Among these, interweave systems (ISs) that employ spectrum sensing have been widely investigated. Baseline models investigated in the literature characterize the performance of the IS in terms of a sensing-throughput tradeoff, however, this characterization assumes perfect knowledge of the involved channels at the secondary transmitter, which is unavailable in practice. Motivated by this fact, we establish a novel approach that incorporates channel estimation in the system model, and consequently investigate the impact of imperfect channel knowledge on the performance of the IS. More particularly, the variation induced in the detection probability affects the detector’s performance at the secondary transmitter, which may result in severe interference at the primary receivers. In this view, we propose to employ average and outage constraints on the detection probability, in order to capture the performance of the IS. Our analysis reveals that with an appropriate choice of the estimation time determined by the proposed approach, the performance degradation of the IS can be effectively controlled, and subsequently the achievable secondary throughput can be significantly enhanced. [less ▲]

Distributed Coordinated Beamforming for Multi-cell Multigroup Multicast Systems

in arXiv preprint arXiv:1511.03561 (2015)

This paper considers coordinated multicast beamforming in a multi-cell wireless network. Each multiantenna base station (BS) serves multiple groups of single antenna users by generating a single beam with ... [more ▼]

This paper considers coordinated multicast beamforming in a multi-cell wireless network. Each multiantenna base station (BS) serves multiple groups of single antenna users by generating a single beam with common data per group. The aim is to minimize the sum power of BSs while satisfying user-specific SINR targets. We propose centralized and distributed multicast beamforming algorithms for multi-cell multigroup systems. The NP-hard multicast problem is tackled by approximating it as a convex problem using the standard semidefinite relaxation method. The resulting semidefinite program (SDP) can be solved via centralized processing if global channel knowledge is available. To allow a distributed implementation, the primal decomposition method is used to turn the SDP into two optimization levels. The higher level is in charge of optimizing inter-cell interference while the lower level optimizes beamformers for given inter-cell interference constraints. The distributed algorithm requires local channel knowledge at each BS and scalar information exchange between BSs. If the solution has unit rank, it is optimal for the original problem. Otherwise, the Gaussian randomization method is used to find a feasible solution. The superiority of the proposed algorithms over conventional schemes is demonstrated via numerical evaluation. [less ▲]

Spectrum Awareness and Exploitation for Cognitive Satellite Communications

in European Conference on Networks and Communications (EuCNC), Paris, France, Jun 2015. (2015)

Sum Rate Maximizing Multigroup Multicast Beamforming under Per-antenna Power Constraints

in In Proc. of IEEE, Global Communications Conference, GLOBECOM (2014, December)

Weighted Fair Multicast Multigroup Beamforming under Per-antenna Power Constraints

in IEEE Transactions on Signal Processing (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 ▲]

Implementation Issues of Cognitive Radio Techniques for Ka-band (17.7-19.7 GHZ) SatComs

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 ▲]

Cognitive Radio for Ka Band Satellite Communications

in 32nd AIAA International Communications Satellite Systems Conference, August 2014 (2014, August)

The satellite communication data traffic is increasing dramatically over the coming years. High throughput multibeam satellite networks in Ka band are potentially able to accommodate the upcoming high ... [more ▼]

The satellite communication data traffic is increasing dramatically over the coming years. High throughput multibeam satellite networks in Ka band are potentially able to accommodate the upcoming high data rate demands. However, there is only 500 MHz of exclusive band for download and the same amount for upload. This spectrum shortage impose a barrier in order to satisfy the increasing demands. Cognitive satellite communication in Ka band is considered in this paper in order to potentially provide an additional 4.4 GHz bandwidth for downlink and uplink fixed-satellite-services. In this way, it is expected that the problem of spectrum scarcity for future generation of satellite networks is alleviated to a great extent. The underlying scenarios and enabling techniques are discussed in detail, and finally we investigate the implementation issues related to the considered techniques. [less ▲]