Open Topics

Vol. 72, n° 11-12, November-December 2017
Content available on Springerlink

Improving spectrum efficiency in self-organized femtocells using learning automata and fractional frequency reuse

Maryam Nasr-Esfahani, Behrouz Shahgholi Ghahfarokhi
Department of Information Technology Engineering, Faculty of Computer Engineering, University of Isfahan, Isfahan, Iran

Abstract Deploying heterogeneous networks (HetNets) and especially femtocell technology improves indoor cell coverage and network capacity. However, since users install femtocells which usually reuse the same frequency band as macrocells, interference management is considered a main challenge. Recently, fractional frequency reuse (FFR) has been considered as a way to mitigate the interference in traditional as well as heterogeneous cellular networks. In conventional FFR methods, radio resources are allocated to macrocell/femtocell users only according to their region of presence ignoring the density of users in defined areas inside a cell. However, regarding the unpredictability of cellular traffic, especially on the femtocell level, smart methods are needed to allocate radio resources to the femtocells not only based on FFR rules, but also traffic load. In order to solve this problem, new distributed resource allocation methods are proposed which are based on learning automata (LA) and consider two levels of resource granularity (subband and mini-subband). Using the proposed methods, femto access points learn to choose appropriate subband and mini-subbands autonomously, regarding their resource requirements and the feedback of their users. The goal of the proposed methods is reduction of interference and improvement of spectral efficiency. Simulation results demonstrate higher spectral efficiency and lower outage probability compared to traditional methods in both fixed and dynamic network environments.

Keywords Resource allocation – Self-organized femtocell – FFR – Learning automata – Heterogeneous networks

Erasure correction-based CSMA/CA

Patrick Tortelier1, Didier Le Ruyet2
1 Orange Labs Networks, Châtillon, France
2 Le CNAM, Paris, France

Abstract It is well known that the performance of carrier sense multiple access with collision avoidance (CSMA/CA) is poor when the number of users increases, because of collisions. In this paper, we consider a modified version of CSMA/CA based on erasure codes at the packet level, which significantly reduces the complexity of the decoding and does not require any change in the underlying physical layer. In order to improve the performance, we use non-binary maximum distance separable (MDS) codes. We give analytical derivation of the global goodput and show that there is a trade-off between the code parameters and the length of the contention window in order to maximize the global goodput for a given number of users.

Keywords 802.11 – CSMA/CA – Packet loss – Erasure codes – Performance evaluation

Fronthaul-aware superposition coding for noncoherent transmission in C-RAN downlink

Seok-Hwan Park1, Changick Song2
1 Division of Electronic Engineering, Chonbuk National University, Jeonju, Korea
2 Department of Information and Communications Engineering, Korea National University of Transportation, Chungju, Korea

Abstract Cloud radio access network (C-RAN) has arisen as a promising architecture for the 5G wireless communication system. Among many advantages, C-RAN is known to enable large-scale interference management by migrating baseband processing functionalities from radio units (RUs) to a control unit (CU) with the aid of fronthaul links. Most of literatures prescribe that perfect synchronization is available among distributed RUs and fronthaul links are equipped with infinite capacities. Since these assumptions are far from practical situations, this work proposes a more practical noncoherent transmission strategy, in which synchronization is not needed among the RUs, by means of a novel superposition, or broadcast, coding. Under the proposed superposition coding scheme, the problem of maximizing the weighted sum of per-user achievable rates is tackled while satisfying per-RU transmit power and fronthaul capacity constraints. Some numerical results are provided to validate the effectiveness of the proposed scheme.

Keywords Cloud radio access network – Constrained fronthaul – Noncoherent transmission – Superposition coding

A new look at AF two-way relaying networks: energy harvesting architecture and impact of co-channel interference

Nguyen Thanh Luan, Dinh-Thuan Do
Wireless Communications Research Group, Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Vietnam

Abstract In this paper, the performance of dual-hop amplify-and-forward (AF) two-way relaying systems is considered, where the terminals and relay are interfered by a finite number of co-channel interferers. In addition, the derived expressions are evaluated in terms of outage probability and throughput in delay-limited transmission mode. To make the analysis mathematically tractable, the unique expressions of outage probability are adopted to deal with energy harvesting protocols related to time switching and power splitting coefficients and expression of the throughput is also calculated. Based on the analytic results, this paper investigates the impact of system parameters such as energy harvesting time/power fractions, number of interferers and signal-to-noise ratio (SNR) on throughput performance. Monte Carlo simulation results are presented to prove the tightness of the proposed energy harvesting two-way relaying system.

Keywords Energy harvesting – Co-channel interference (CCI) – Amplify-and-forward – Outage capacity – Two-way relaying

Femtocells in centralized systems: green operation and radio resource management techniques

Elias Yaacoub
Faculty of Computer Studies, Arab Open University, Beirut, Lebanon

Abstract In this paper, a system of femtocells controlled by a single controller is investigated. In such a scenario, femtocell access points (FAPs) are assumed connected via wired links to a central controller within a certain vicinity (e.g., building, compound, hotel, and campus.). Thus, radio resource management (RRM) and green network operation of LTE femtocell networks are investigated in an integrated wired/wireless system. Consequently, it becomes possible to perform RRM in a centralized and controlled way in order to enhance the quality of service (QoS) performance for the users in the network. Furthermore, energy-efficient operation consisting of switching off redundant FAPs can be implemented. A utility maximization framework is presented, and an RRM algorithm that can be used to maximize various utility functions is proposed. Another algorithm is presented for the scenario of FAP on/off switching to achieve green operation. It consists of selecting the best FAP to switch off, then moving the femto user equipments (FUEs) to other active FAPs without compromising their quality of service (QoS). Simulation results show that the proposed algorithms lead to significant performance gains.

Keywords Femtocell – Energy efficiency – Resource allocation – Interference mitigation – LTE

GA3: scalable, distributed address assignment for dynamic data center networks

Elisa Rojas1, Joaquin Alvarez-Horcajo2, Isaias Martinez-Yelmo2, Jose M. Arco2, Juan A. Carral2
1 Telcaria Ideas S.L., Madrid, Spain
University of Alcala, Alcala de Henares, Madrid, Spain

Abstract Deployment and maintenance of current data center networks is costly and prone to errors. In order to avoid manual configuration, many of them require centralized administrators which constitute a clear bottleneck, while distributed approaches do not guarantee sufficient flexibility or robustness. This paper describes and evaluates GA3 (Generalized Automatic Address Assignment), a discovery protocol that assigns multiple unique labels to all the switches in a hierarchical network, without any modification of hosts or the standard Ethernet frames. Labeling is distributed and uses probes. These labels can be leveraged for shortest path routing without tables, as in the case of the Torii protocol, but GA3 also allows other label-based routing protocols (such as PortLand or ALIAS). Additionally, GA3 can detect miswirings in the network. Furthermore, control traffic is only necessary upon network deployment rather than periodically. Simulation results showed a reduced convergence time of less than 2 s and 100 kB/s of bandwidth (to send the GA3 frames) in the worst case for popular data center topologies, which outperforms other similar protocols.

Keywords Data centers – Automatic address assignment – Misconfiguration detection – Shortest path bridges

Matrix differentiation for capacity region of Gaussian multiple access channels under weighted total power constraint

Zhao-Xu Yang1, Guang-She Zhao2, Guoqi Li3, Hai-Jun Rong1
1 State Key Laboratory for Strength and Vibration of Mechanical Structures, Shaanxi Key Laboratory of Environment and Control for Flight Vehicle, School of Aerospace, Xi’an Jiaotong University, Xi’an, China
School of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an, China
3 Center for Brain Inspired Computing Research, Department of Precision Instrument, Tsinghua University, Beijing, China

Abstract Maximization the capacity region of Gaussian multiple access channels with vector inputs and vector outputs has been extensively studied in existing schemes. Although these schemes are proven effective in various real-life applications, they are inapplicable to deal with channels with matrix variables subjected to certain constraints. In this work, we present a new framework to estimate the capacity region of Gaussian multiple access channels with matrix inputs and outputs under weighted total power constraints. We propose an optimization model to address this issue and prove its concavity. By introducing an I-chain rule for matrix differentiation, the gradient of the objective function involving matrix variables can be obtained. An algorithm, named normalized projected gradient method (NPGM) is developed to find the global optimal solution for the proposed model. The convergence of NPGM is established by utilizing projection and normalization operators. Simulation results provide an interesting insight that NPGM can manage the existent situations within an unified framework, and provide a novel universal technical solution to optimize the capacity region under weighted total power constraints.

Keywords Gaussian channels – Matrix differentiation – Weighted total power constraint

Leveraging node gatherings to save cellular resources

Salah-Eddine Belouanas, Mehdi Bezahaf, Kim-Loan Thai, Prométhée Spathis, Marcelo Dias de Amorim
LIP6/CNRS – UPMC Sorbonne Universités, Paris, France

Abstract Cellular resources are expensive and should be saved whenever possible. In this paper, we propose Scheduled Content Delivery (SCoD), a resource-saving strategy that draws on the mobility of users to reduce the number of cellular transmissions. The idea is to postpone a transmission in order to maximize its benefits in terms of users located in the same cell. We exploit the delay tolerance of certain types of content combined with the natural tendency of users to get together in the same locations. By relying on multicast communications, we can then reduce the number of transmissions required to satisfy all requesting users. SCoD relies on previous observations to determine, in an adaptive way, the number of users that should trigger a multicast transmission in a cell. We evaluate SCoD and compare it against other strategies by running trace-driven simulations based on real-world mobility datasets. We also compare SCoD with an Oracle, which gives the best case but is unfeasible as it relies on the knowledge of future displacements of nodes. The results show that SCoD covers 100% of the users while consuming almost as few resources as the Oracle.

Keywords Cellular wireless network – Delay tolerant content – Transmission scheduling

Relay selection in two-way full-duplex relay networks over Nakagami-m fading channels

Asil Koç1, İbrahim Altunbaş1, Abbas Yongaçoğlu2
1 Department of Electronics and Communications Engineering, Istanbul Technical University, Istanbul, Turkey
School of Electrical Engineering & Computer Science, University of Ottawa, Ottawa, Ontario, Canada

Abstract We analyze the outage performance of relay selection in two-way full-duplex amplify-and-forward cooperative systems in the presence of residual loop-interference (LI) over Nakagami-m fading channels. In the proposed system, a relay node is selected according to max-min policy and the physical-layer-network-coding technique is applied for two-way transmission. By using end-to-end signal-to-interference-plus-noise-ratio, a new exact outage probability expression is derived in a single-integral form. The numerical and Monte-Carlo simulation results verify the analysis. Moreover, lower-bound and asymptotic expressions for the outage probability are obtained in closed-form. The numerical results reveal that the max-min selection policy provides a significant performance improvement for two-way full-duplex relaying. We observe that the outage performance can be enhanced as long as either the number of relay nodes, the transmit power, or the efficiency of the LI cancellation process increases.

Keywords Full-duplex – Two-way – Relay selection – Outage probability – Amplify-and-forward – Nakagami-m

Crowded spot estimator for urban cellular networks

Sahar Hoteit1, Stefano Secci2, Marco Premoli3
1 Ecole d’ingénieurs du numérique ISEP, Issy les Moulineaux, France
2 Sorbonne Universities, UPMC Univ. Paris 06, UMR 7606, LIP6, Paris, France
3 Università di Milano, Milan, Italy

Abstract The real-time detection of crowded spots in access networks is considered nowadays a necessary step in the evolution of mobile cellular networks as it can be of great benefit for many use-cases. On the one hand, a dynamic positioning of contents and computing resources in the most crowded regions can lower connection latency and data loss and can allow us to have a seamless service provided for the users, without performance degradation across the network. On the other hand, a dynamic resource allocation among access points taking into account their loads can enhance the user’s quality of service and indeed network performances. In this context, using real mobile data traces from a cellular network operator in France, provided us with a temporal and spatial analysis of user content consumption habits in different French Metropolitan areas (Paris, Lyon and Nice). Furthermore, we put to use a real-time crowded spot estimator computed using two user mobility metrics, using a linear regression approach. Evaluating our estimator against more than one million user databases from a major French network operator, it appears to be an excellent crowd detection solution of cellular and backhauling network management. We show that its error count definitely decreases with the cell load, and it becomes very small for reasonable crowded spot load reaching upper thresholds. We also show that our crowded spot estimator is time and city-independent as it shows a stable behavior for different times of the day and for different cities with different topographies. Furthermore, compared to another crowded spot estimator from the literature, we show that our proposed estimator offers more suitable and accurate results in terms of crowded spot estimation for the three selected areas.

Keywords Mobile data – Crowded spot estimation – Radius of gyration

Discrimination rate: an attribute-centric metric to measure privacy

Louis Philippe Sondeck1, Maryline Laurent2, Vincent Frey3
1 Orange Labs, Telecom SudParis, Cesson Sévigné, France
2 SAMOVAR, Telecom SudParis, CNRS, University Paris-Saclay, Evry, France
3 Orange Labs, Cesson Sévigné, France

Abstract As far as we know, there is no good privacy metric for quantifying how privacy-efficient an anonymity system is. This paper discusses first the features needed for defining such a metric and proposes a new metric based on information theory and named DR for Discrimination Rate. The DR is the first metric enabling some fine-grained measurements down to the attribute level to quantify the attribute identification capacity with a score scaling from 0 to 1 for any given anonymity system. The DR can be easily applied in practice, thanks to the algorithms provided in the paper. The DR measurement onto attributes enables to reflect the attacker’s capacity, and to evaluate how much the attribute is able to refine the anonymity set. The formalization brought by the DR permits to give more accurate definitions of identifiers and to introduce new notions like sketchy-identifiers, zero-identifiers, and partial-identifiers. Finally, the usefulness and practical dimensions of the DR are illustrated through evaluation and comparison of the k-anonymity and l-diversity mechanisms over a dataset.

Keywords Privacy measurement – Information theory – Discrimination Rate – LBS – K-anonymity