Nikola Vucic

Globally Optimal Resource Allocation for Achieving Maximum Weighted Sum Rate

We establish a general optimization framework for joint resource allocation and interference mitigation. By utilizing axiomatic interference functions, our problem formulation is very general and includes many problems as special cases. We consider the sum rate maximization problem, which is known to be NP hard. It is shown that due to the structural model of the interference function, the joint optimization of powers and adaptive receive strategies ends up with the optimization solely with respect to powers. This facilitates a reformulation of the problem under consideration as a problem of difference of convex functions (DC). Based on this DC representation, we employ a prismatic branch and bound algorithm to find a global optimum.

A simplified scattered pilot for FBMC/OQAM in highly frequency selective channels

Filterbank multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM) avoids the usage of the cyclic prefix (CP) by using more localized prototype filters. However, channel estimation in highly frequency selective channels is very challenging, especially for the scattered pilots due to the intrinsic interference leaked from the neighboring symbols. This paper presents a novel pilot design called Composite Pilot Pair (CPP), which exploits the localization property of the filters to enable a simple estimation procedure at the receiver. The proposed CPP design and corresponding receiving algorithm have been evaluated on an FBMC-based, Long Term Evolution (LTE) like mobile system. The evaluation shows that the proposed algorithm outperforms the conventional auxiliary pilot algorithms substantially, both in terms of power overhead and pilot mean square error (MSE), whereas the overall receive complexity is low. Moreover, the proposed method respects the frame design principles for the mobile downlink, and is applicable to both common and dedicated pilot symbols in the next generation mobile systems.

Wireless-Optical Network Convergence: Enabling the 5G Architecture to Support Operational and End-User Services

This article presents a converged 5G network infrastructure and an overarching architecture to jointly support operational network and end-user services, proposed by the EU 5G PPP project 5G-XHaul. The 5G-XHaul infrastructure adopts a common fronthaul/backhaul network solution, deploying a wealth of wireless technologies and a hybrid active/passive optical transport, supporting flexible fronthaul split options. This infrastructure is evaluated through a novel modeling. Numerical results indicate significant energy savings at the expense of increased end-user service delay.

Fixed point iteration for max-min sir balancing with general interference functions

This paper studies the convergence of a fixed point iteration algorithm for the problem of max-min signal-to-interference ratio (SIR) balancing. Differently from the existing work on the subject, the interference in the system is assumed to fall into the axiomatic framework of general interference functions. Monotonicity of the extremal SIR values during the iterations of the algorithm is shown. In the case of strictly monotonic interference functions, a novel sufficient condition for the convergence of the algorithm to an optimal solution is derived. The obtained condition is easily verifiable, and presents a generalization of a related requirement for the power method from matrix analysis. It is also shown how the results transfer to the power-constrained case and standard interference functions.

Equalization for MIMO Isi Systems Using Channel Inversion Under Causality, Stability and Robustness Constraints

The problem of linear equalization for frequency selective multiple-input multiple-output wireless channels, using channel inversion, is considered. While in the flat-fading case, the solution with minimal noise enhancement is readily found and is automatically optimal in terms of energy norm, the problem becomes intricate when intersymbol interference is present. In order to analyze this behavior, a framework, based on the semidefinite programming technique, is employed in the paper. Additionally, connections with possible analytical solutions based on the common system block matrix representation are established. The proposed framework is easily adopted for other linear equalization methods, pre-equalization, and can also be used for the feedforward filter construction in successive interference cancellation strategies

5G-XHaul: a converged optical and wireless solution for 5G transport networks

The common European Information and Communications Technology sector vision for 5G is that it should leverage on the strengths of both optical and wireless technologies. In the 5G context, a wide spectra of radio access technologies-such as millimetre wave transmission, massive multiple-input multiple-output and new waveforms-demand for high capacity, highly flexible and convergent transport networks. As the requirements imposed on future 5G networks rise, so do the challenges in the transport network. Hence, 5G-XHaul proposes a converged optical and wireless transport network solution with a unified control plane based on software defined networking. This solution is able to support the flexible backhaul and fronthaul-X-Haul-options required to tackle the future challenges imposed by 5G radio access technologies. 5G-XHaul studies the trade-offs involving fully or partially converged backhaul and fronthaul functions, with the aim of maximising the associated sharing benefits, improving efficiency in resource utilisation and providing measurable benefits in terms of overall cost, scalability and sustainability. Copyright

A Joint Scheduling and Resource Allocation Scheme for Millimeter Wave Heterogeneous Networks

Millimeter wave (mm-wave) frequencies provide orders of magnitude larger spectrum than current cellular allocations and allow usage of high dimensional antenna arrays for exploiting beamforming and spatial multiplexing. This paper addresses the problem of joint scheduling and radio resource allocation optimization in mm-wave heterogeneous networks where mm-wave small cells are densely deployed underlying the conventional homogeneous macro cells. Furthermore, mm-wave small cells operate in time division duplexing mode and share the same spectrum and air-interface for backhaul and access links. The scheme proposed in this paper can significantly enhance network throughput by exploiting space-division multiple access, i.e., allowing non-conflicting flows to be transmitted simultaneously. The optimization problem of maximizing network throughput is formulated as a mixed integer nonlinear programming problem. To find a practical solution, this is decomposed into three steps: concurrent transmission scheduling, time resource allocation, and power allocation. A maximum independent set based algorithm is developed for concurrent transmission scheduling to improve resource utilization efficiency with low computational complexity. Through extensive simulations, we demonstrate that the proposed algorithm achieves significant gain over benchmark schemes in terms of user throughput.

5G systems: The mmMAGIC project perspective on use cases and challenges between 6–100 GHz

mmMAGIC (Millimetre-Wave Based Mobile Radio Access Network for Fifth Generation Integrated Communications) is an EU funded 5G-PPP project, whose overall objective is to design and pre-develop a mobile radio access technology (RAT) operating in the 6–100 GHz range, capable of impacting standards and other relevant fora. The focus of the project is on extreme Mobile Broadband, which is expected to drive the 5G requirements for massive increase in capacity and data-rates. This paper elaborates on some 5G key research areas such as: identification of the most compelling use-cases and Key Performance Indicators (KPIs) for future 5G systems, advantages and challenges of millimeter-wave (mmWave) technologies, channel measurements and channel modeling, network architecture; and the design of a new mobile radio interface including multi-node and multi-antenna transceiver architecture.

SIR Balancing for strongly connected interference networks — Existence and uniqueness of a solution

In this paper we revisit the problem of SIR Balancing which was extensively studied in the wireless communication literature. We generalize existing results by showing conditions for the existence and uniqueness of a max-min optimizer. It is shown that a unique positive optimizer exists if the underlying asymptotic coupling matrix is irreducible and the interference functions are strictly monotonic on the dependency set. We also show how the solution can be extended to include power constraints.

Cooperative Cellular Networks: Overcoming the Effects of Real-World Impairments

The fifth generation (5G) of mobile communication systems will need to support new applications with a variety of requirements, including high data rates, low latency, improved reliability, and sup-port for a large number of devices. We believe that these demands can be satisfied by the combined use of additional spectrum at higher frequencies, small cells, a more advanced air interface, and spectrally efficient transmission using multiple antennas. Base station (BS) cooperation is an advanced multiantenna technique that has the potential to eliminate intercell interference and enhance spectral efficiency. But attaining effective BS cooperation is challenged by a number of real-world channel and synchronization impairments.