Benchmarking Practical RRM Algorithms for D2D Communications in LTE Advanced

Device-to-device (D2D) communication integrated into cellular networks is a means to take advantage of the proximity of devices and allow for reusing cellular resources and thereby to increase the user bitrates and the system capacity. However, when D2D (in the 3rd Generation Partnership Project also called Long Term Evolution (LTE) Direct) communication in cellular spectrum is supported, there is a need to revisit and modify the existing radio resource management (RRM) and power control (PC) techniques to realize the potential of the proximity and reuse gains and to limit the interference at the cellular layer. In this paper, we examine the performance of the flexible LTE PC tool box and benchmark it against a utility optimal iterative scheme. We find that the open loop PC scheme of LTE performs well for cellular users both in terms of the used transmit power levels and the achieved signal-to-interference-and-noise-ratio (SINR) distribution. However, the performance of the D2D users as well as the overall system throughput can be boosted by the utility optimal scheme, because the utility maximizing scheme takes better advantage of both the proximity and the reuse gains. Therefore, in this paper we propose a hybrid PC scheme, in which cellular users employ the open loop path compensation method of LTE, while D2D users use the utility optimizing distributed PC scheme. In order to protect the cellular layer, the hybrid scheme allows for limiting the interference caused by the D2D layer at the cost of having a small impact on the performance of the D2D layer. To ensure feasibility, we limit the number of iterations to a practically feasible level. We make the point that the hybrid scheme is not only near optimal, but it also allows for a distributed implementation for the D2D users, while preserving the LTE PC scheme for the cellular users.Comment: 30 pages, submitted for review April-2013. See also: G. Fodor, M. Johansson, D. P. Demia, B. Marco, and A. Abrardo, A joint power control and resource allocation algorithm for D2D communications, KTH, Automatic Control, Tech. Rep., 2012, qC 20120910, http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10205

Cross-layer optimization protocols in Ad-hoc networks: analysis and practical implementation of transport and network layers

Ad-hoc wireless networks use multi-hop transmissions to communicate, without exploiting any infrastructure. Logical links create unreliable connections between nodes: the capacity of the channel can unpredictably change due to the presence of obstructions, interferences between nodes and stochastic phenomena such as fading. Moreover the medium is multi-access and resources are contended by different users. It is possible to notice that adjusting the power at the physical layer affects the interference perceived, which in turn modifies the resources availability, alters the queue length at the network layer and eventually influences the source rates at the transport layer. To this end, a lot of works have shown that a better understanding of inherent coupling between different layers in the networking stack is worth. Specifically, network performances can be increased if the traditionally separated network layers are jointly optimized. Network utility maximization has emerged as a powerful framework for studying such cross-layer issues and optimizing performances overall the network. In particular, we focus on distributed cross-layer algorithms that achieve a global optimum recurring to local information only. Although the literature is vast in this field, most of works remain as theory. We aim at clarifying the practical feasibility of such theoretical dissertations and what considerations are needed in order to establish a bridge between theory and practice. After analyzing different crosslayer methods, we focus on the work of Papandriopoulos et al.. We first discuss its theoretical benefits in an interference limited system such as CDMA, without accounting physical constraints of the network. In order to validate the performances in a more realistic scenario, we implement the algorithm of Papandriopoulos et al. in the NS-2 network simulator without breaking up the hierarchy of the standard ISO/OSI stack. We focus on modeling physical, data link, network and transport layer, underlining issues and possible solutions from a practical perspective. For instance, we propose a novel approach to calculate the congestion prices of the network. After discussing benefits and drawbacks of the underlying theory, we propose several results under many simulation scenarios and eventually a comparison with the standard protocol for wireless networks IEEE/802.11

On the Convergence and Optimality of Reweighted Message Passing for Channel Assignment Problems

Many assignment problems, and channel allocation in OFDMA networks is a typical example, can be formulated as bipartite weighted b-matching (BWBM) problems. In this letter we provide a proof of the convergence and the optimality of the reweighted message passing (ReMP) algorithm when applied to solve BWBM problems in a distributed fashion. To this aim, we first show that the ReMP rule is a contraction mapping under a maximum mapping norm. Then, we show that the fixed convergence point is an optimal solution for the original assignment problem

Optimal radio resources and transmission formats assignment in OFDMA systems

The problem of assigning radio resources and transmission formats to users in the downlink of an OFDMA network is addressed. In particular, a single cell environment with a realistic interference model and a margin adaptive approach is considered, i.e., the aim is of minimizing the total transmission power while maintaining a certain given rate for each user. The computational complexity issues of the problem are discussed, and an approximation analysis is presented. Heuristic approaches, based on rounding techniques and graph models, are also proposed. Computational experiences show that, in a comparison with a commercial state-of-the-art optimization solver and with alternatives from the literature, the proposed algorithms are effective in terms of solution quality and CPU times

Message passing resource allocation for the uplink of multi-carrier multi-format systems

We propose two novel distributed resource allocation (RA) schemes for the uplink of a cellular multi-carrier multi-format system based on the message passing (MP) technique. In the proposed approaches each transmitter iteratively sends and receives information messages to/from the base station with the goal of achieving an optimal RA strategy. The exchanged messages are the solution of small distributed allocation problems. Hence, despite the NP-hardness of the original RA problem, they distribute the computational effort in the cell among all the transmitters and the base station. Specifically, the first algorithm combines MP with a dynamic programming formula solved at each step, while the second method initially solves to optimality a simplified single-format RA via MP, and eventually performs format allocation to satisfy the rate constraints. Compared to alternatives, numerical results assess the validity of MP-based schemes both in terms of efficiency and complexity

Message Passing Resource Allocation for the Uplink of Multi-Carrier Multi-Format Systems

We propose two novel distributed resource allocation (RA) schemes for the uplink of a cellular multi-carrier multi-format system based on the message passing (MP) technique. In the proposed approaches each transmitter iteratively sends and receives information messages to/from the base station with the goal of achieving an optimal RA strategy. The exchanged messages are the solution of small distributed allocation problems. Hence, despite the NP-hardness of the original RA problem, they distribute the computational effort in the cell among all the transmitters and the base station. Specifically, the first algorithm combines MP with a dynamic programming formula solved at each step, while the second method initially solves to optimality a simplified single-format RA via MP, and eventually performs format allocation to satisfy the rate constraints. Compared to alternatives, numerical results assess the validity of MP-based schemes both in terms of efficiency and complexity

A Joint Power Control and Resource Allocation Algorithm for D2D Communications

We consider the problem of joint power control, signal-to-noise-and-interference-ratio (SINR)target setting, mode selection and resource allocation for cellular network assisteddevice-to-device (D2D) communications.This problem is important for fourth generation systems, such as the release under study of the Long TermEvolution Advanced (LTE-A) system standardized by the Third Generation Partnership Project (3GPP).While previous works on radio resource management (RRM) algorithms for D2D communications dealt withmode selection and power control, the problem of resource allocation for the integrated cellular-D2Denvironment and in particularthe joint problem of mode selection, resource allocation and power allocation has not been addressed.We propose a utility function maximization approach that allows to take into account the inherenttrade off between maximizing spectrum efficiency and minimizing the required sum transmit power.We implement the proposed RRM algorithms in a realistic system simulator and report numericalresults that indicate large gains of D2D communications both in terms of spectrum- and energyefficiency.QC 20120910DORI

The Role of Social Worker of Social Service in Out-of-family Care of Children: Example of Ogre District

Aplūkojot Latvijas statistiskos datus par bērnu aizgādības tiesību pārtraukšanu vai atņemšanu, tiek secināts, ka vairumā gadījumu netiek sasniegts mērķis – atgriezt bērnu ģimenē. Autore, ņemot vērā to, ka sociālie darbinieki, strādājot ar ģimenēm un bērniem, palīdz risināt ģimenē esošās problēmas, kuru dēļ tiek pārtrauktas vai atņemtas aizgādības tiesības bērnu vecākiem, vēlējās noskaidrot, kāda loma ir sociālā dienestā strādājošam sociālajam darbiniekam, kad bērns atrodas ārpusģimenes aprūpē – bērnam esot sociālās aprūpes institūcijā, audžuģimenē vai pie aizbildņa, attiecībā pret bērnu un vai seko pēctecīgas darbības pret bērnu, kuram tiek nodrošināta ārpusģimenes aprūpe. Šī darba mērķis ir teorijas daļā aplūkot ārpusģimenes aprūpes formas, par pamatu pielietojot sistēmteoriju un ekoloģisko teoriju, bet pētījuma daļas mērķis ir pētīt kā piemēru Ogres novada Sociālā dienesta sociālo darbinieku praksi, atbilstoši maģistra tēmai. Mērķis ir noskaidrot sociālā darbinieka lomu bērnu ārpusģimeņu aprūpē bērna kontekstā. Uzdevumi – pētīt un analizēt sociālo darbinieku funkcijas attiecībā uz bērnu ārpusģimenes aprūpes kontekstā.Upon viewing Latvia's statistical data of interruption or removal of children's custody rights, it is concluded that the goal - to return the child to his/her family - is not achieved in majority of cases. Taking into account that social workers, whilst working with families with children, help to deal with problems that the families have, which result in interruption or removal of parents' custody rights over their children, the author wanted to find out what role is played by a social worker who works for the social service when a child is in out-of-family care - while the child is at a social care institution, lives with a foster family or with a custodian, in relation to the child and whether there are any subsequent actions towards he child who is provided with out-of-family care. The objective of this paper is to look at forms of out-of-family care in the theory part, based on system theory and ecological theory. In turn the objective of the research part is to study as an example the practice of social workers of the Ogre Region Social Service, in line with the theme of the Master Paper. The goal is to find what the role of a social worker is in the context of a child in out-of-family care. Tasks - to research and analyse functions of social workers in relation to a child in context of out-of-family care