Femtocells operate on licensed spectrum and provide data and voice services to user terminals by connecting them to the core network through a broadband Internet connection such as digital subscriber line DSL or cable.
Quality of service and max-min-fair transmit beamforming to multiple co-channel multicast groups by Eleftherios Karipidis, Student Member, Nicholas D.
Signal Processing" Abstract—The problem of transmit beamforming to multiple cochannel multicast groups is considered, when the channel state is known at the transmitter and from two viewpoints: The core problem is a multicast generalization of the multiuser downlink beamforming problem; the difference is that each transmitted stream is directed to multiple receivers, each with its own channel.
Such generalization is relevant and timely, e. The joint problem also contains single-group multicast beamforming as a special case.
The latter and therefore also the former is NP-hard.
This motivates the pursuit of computationally efficient quasi-optimal solutions. For a significant fraction of problem instances, the solutions generated this way are exactly optimal. Extensive numerical results using both simulated and measured wireless channels are presented to corroborate our main findings.
Index Terms—Broadcasting, convex optimization, downlink beamforming, multicasting, semidefinite relaxation. Convex conic formulations of robust downlink precoder designs with quality of service constraints by Michael Botros Shenouda, Timothy N.
Topics Signal Processing" We consider the design of linear precoders beamformers for broadcast channels with Quality of Service QoS constraints for each user, in scenarios with uncertain channel state information CSI at the transmitter. We consider a deterministically-bounded model for the channel uncertainty of each u Since this problem is not known to be computationally Robust downlink power control in wireless, we will derive three conservative design approaches that yield convex and computationally-efficient restrictions of the original design problem.
The three approaches yield semidefinite program SDP formulations that offer different trade-offs between the degree of conservatism and the size of the SDP.
We will also show how these conservative approaches can be used to derive efficiently-solvable quasi-convex restrictions of some related design problems, including the robust counterpart to the problem of maximizing the minimum signal-to-interference-plus-noise-ratio SINR subject to a given power constraint.
Show Context Citation Context In the third experiment, we used the randomly generated realizations of the estimates of the channel environments from the first experiment, and fo QoS-based transmit beamforming in the presence of eavesdroppers: Signal Process" Abstract—Secure transmission techniques have been receiving growing attention in recent years, as a viable, powerful alternative to blocking eavesdropping attempts in an open wireless medium.
This paper proposes a secret transmit beamforming approach using a quality-of-service QoS -based perspectiv This paper proposes a secret transmit beamforming approach using a quality-of-service QoS -based perspective.
Specifically, we establish design formulations that: The proposed designs incorporate a relatively new idea called artificial noise ANwhere a suitable amount of AN is added in the transmitted signal to confuse the eavesdroppers.
Our designs advocate joint optimization of the transmit weights and AN spatial distribution in accordance with the channel state information CSI of the intended receiver and eavesdroppers. Our formulated design problems are shown to be NP-hard in general.
We deal with this difficulty by using semidefinite relaxation SDRan approximation technique based on convex optimization. Interestingly, we prove that SDR can exactly solve the design problems for a practically representative class of problem instances; e.
Extensions to the colluding-eaves-dropper scenario and the multi-intended-receiver scenario are also examined. Extensive simulation results illustrate that the proposed AN-aided designs can yield significant power savings or SINR enhancement compared to some other methods.
Index Terms—Artificial noise, physical-layer secure communica-tions, semidefinite relaxation, transmit beamforming.
Suppose that the Alice-to-Bob channel is random with mean and covariance. It will be assumed in the sequel that is known to Alice. Moreover, for the case where the instantaneous channel realization of Bob is known to Alice, we Areas Commun" Abstract — In this paper, we study the design of the transmitter in the downlink of a multiuser and multiantenna wireless communications system, considering the realistic scenario where only an imperfect estimate of the actual channel is available at both communication ends.
Precisely, the actual ch Precisely, the actual channel is assumed to be inside an uncertainty region around the channel estimate, which models the imperfections of the channel knowledge that may arise from, e. In this context, our objective is to design a robust power allocation among the information symbols that are to be sent to the users such that the total transmitted power is minimized, while maintaining the necessary quality of service to obtain reliable communication links between the base station and the users for any possible realization of the actual channel inside the uncertainty region.
This robust power allocation is obtained as the solution to a convex optimization problem, which, in general, can be numerically solved in a very efficient way, and even for a particular case of the uncertainty region, a quasi-closed form solution can be found. Finally, the goodness of the robust proposed transmission scheme is presented through numerical results.Power Control in Wireless Cellular Networks Mung Chiang, Prashanth Hande, Tian in the management of interference, energy, and connectivity.
Power control in both the uplink and downlink of a cellular network has been extensively studied, especially over the last 15 years, and some of the Robust Distributed Power Control This study considers the joint transmission precoding design for downlink multicell multiuser multiple-input single-output systems where imperfect channel variances are available at the base stations.
The authors aim to tackle the robust signal-to-interference-plus-noise ratio (SINR) balancing problem to maximise the minimum worst-case user rate.
outer loop power control algorithm, which adjusts the target signal quality, expressed by the bit-energy-to-noise-density ra-tio1, based on weights declared by the mobile users. Hence, the approach does not require changes to fast closed-loop power control, whose objective is to adjust the transmission power in order to achieve the target signal quality.
In this paper we con-sider the case of trafﬁc with ﬁxed rate . 1 In Proc. of 4th IEEE Int’l Conference on Mobile and Wireless Communications Networks, Stockholm, Sweden, Sep.
, Congestion Sensitive Downlink Power Control. The goal of the robust problem in the conventional downlink scenario is to minimize the total transmitted power under the worst-case quality-of-service (QoS) constraints for the receivers.
we propose an alternative approach to the robust downlink beamforming problem. We consider the fact that the mismatch in the CSI is a combination of. Power Control in Wireless Cellular Networks Mung Chiang energy, and connectivity.
Power control in both uplink and downlink of a cellular network has been extensively studied, especially over the last 15 years, and some of the turning to their robust versions and joint SIR and power optimization.