Gustavo Wagner Oliveira Da Costa

5G small cell optimized radio design

The 5th generation (5G) of mobile radio access technologies is expected to become available for commercial launch around 2020. In this paper, we present our envisioned 5G system design optimized for small cell deployment taking a clean slate approach, i.e. removing most compatibility constraints with the previous generations of mobile radio access technologies. This paper mainly covers the physical layer aspects of the 5G concept design.

Autonomous Component Carrier Selection for 4G Femtocells — A Fresh Look at an Old Problem

This paper addresses the interference management problem in the context of LTE-Advanced femtocells. Due to the expected large number of user-deployed cells, centralized network planning becomes increasingly less viable. Consequently, we consider an architecture of autonomous decision makers. Our main contribution in this paper, denominated Generalized Autonomous Component Carrier Selection (G-ACCS), is a distributed carrier-based inter-cell interference coordination scheme that represents one step towards cognitive radio networks. The algorithm relies on expected rather than sensed interference levels. This approach facilitates scheduler-independent decisions, however, it can lead to overestimation of the interference coupling among cells when the resources are not fully utilized. Acknowledging this fact, G-ACCS leverages the power domain to circumvent the restrictive nature of expected interference coupling. This work focuses on the downlink and also provides an extensive characterization of the network performance as a function of the topology as well as the often overlooked temporal traits of traffic. We compare G-ACCS with other carrier-based solutions, including the simplest universal reuse strategy. The encouraging simulation results demonstrate that G-ACCS achieves an efficient and fair distribution of resources in all considered traffic and deployment conditions. More importantly, this is attained in a truly autonomous fashion, without any explicit parametrization.

A Scalable Spectrum-Sharing Mechanism for Local Area Network Deployment

Current wireless access networks are able to provide relatively low data rates when compared with wired access. To extend the access to high-data-rate services to wireless users, the International Telecommunication Union (ITU) established new requirements for future wireless communication technologies of up to 100 Mb/s under high-mobility conditions and 1 Gb/s in low mobility. The low mobility goal can only be achieved through the use of highly optimized local area access networks operating at low range and low transmission power. The efficient sharing of radio resources among local area cells will be very difficult to achieve with a traditional network planning/dimensioning approach due to their intrinsic uncoordinated deployment characteristic. Cognitive radio (CR)-based networking methodologies are considered as the most promising solutions for such radio-resource-sharing problems, also enabling unlicensed/open spectrum operations. In this paper, a game-theory-inspired scalable algorithm for intercell dynamic spectrum access (IC-DSA) is introduced to enable distributed resource allocation in CR environments. Here, the new CR-based cell is called ¿cognitive cell (C-cell),¿ and it is the minimal entity that allocates a resource set. The simulation results demonstrate the effectiveness of the proposed spectrum-sharing approach. This solution achieves a better overall performance in several load and interference scenarios in terms of both outage and average capacity when compared with fixed-frequency-reuse cases.

Spectrum sharing for next generation wireless communication networks

Future wireless services are expected to provide data-rates in the order of 1 Gbps in local area and 100 Mbps in wide area. A very wide bandwidth is required to support such high rates, in the order of 100 MHz: this wideband will not be available for each operator, thus a shared access to the spectrum among operators is needed. An holistic approach to spectrum sharing is adopted in this paper: not a single layer or component is optimized, but the system as a whole. Advanced physical layer (PHY) and radio resource management (RRM) solutions, utilizing some cognitive radio concepts, are discussed.

A fully distributed method for dynamic spectrum sharing in femtocells

The traffic in cellular networks has been growing at an accelerated rate. In order to meet the rising demand for large data volumes, shrinking the cell size may be the only viable option. In fact, locally deployed small cells, namely picocells and femtocells, will certainly play a major role in meeting the IMT-Advanced requirements for the next generation of cellular networks. Notwithstanding, several aspects of femtocell deployment are very challenging, especially in closed subscriber group femtocells: massive deployment, user definition of access point location and high density. When such characteristics are combined the traditional network planning and optimization of cellular networks fails to be cost effective. Therefore, a greater deal of automation is needed in femtocells. In particular, this paper proposes a novel method for autonomous selection of spectrum/ channels in femtocells. This method effectively mitigates cotier interference with no signaling at all across different femtocells. Still, the method has a remarkable simple implementation. The efficiency of the proposed method was evaluated by system level simulations. The results show large throughput gains for the cells with unfavorable geometry, up to nearly 300% when compared to the unmanaged situation (reuse 1).

Self-Organizing Coalitions for Conflict Evaluation and Resolution in Femtocells

The recent introduction of carrier aggregation in LTE-Advanced enables new possibilities in designing frequency domain interference reduction and management schemes. These methodologies are of extreme interest in the case of dense and uncoordinated deployments of femtocells. In such scenarios, dense deployment of cells coupled with the scarcity of frequency resources may lead to a potentially disruptive amount of interference, which severely affects the performance of the system. This contribution presents a novel method inspired by graph and coalitional game theories. The proposed algorithm consists of a set of distributed and scalable rules for building coalitions; these rules essentially resolve the conflicts among avid femtocells competing for a limited amount of resources. The proposed scheme has been designed by targeting localized reconfigurations, thus avoiding reconfiguration storms in the network. Furthermore, the rules governing the resource redistribution ensure overall system performance improvements while maintaining a certain degree of fairness among the competing nodes. Simulation results prove the effectiveness of the proposed method.

Dynamic Spectrum Sharing in Femtocells: A Comparison of Selfish versus Altruistic Strategies

Dynamic spectrum approaches are steadily gaining momentum, especially in the context of femtocells. Yet designing efficient, stable, fair and scalable distributed algorithms is no easy feat, specially if the cells in a wireless network tend to act selfish and independently. Game Theory is a powerful toolbox which models the interaction of autonomous agents. In this paper we present a game theoretic model for a dynamic spectrum sharing framework recently proposed for femtocells. Our analysis includes cases where femtocells compete for spectrum as well as cooperative cases towards a common goal. The system level simulation results show that strict adherence to the game-theoretic selfish behavior performs poorly compared to the non-adherent rules which balance altruism and rational egoism. The main conclusion is that practical solutions should be guided but not limited by purely theoretical assumptions.

Dynamic Channel Selection for Cognitive Femtocells

The ever-growing demand for mobile broadband is pushing towards the utilization of small cells, including metrocells, picocells and femtocells. In particular, the deployment of femtocells introduces significant challenges. First, the massive number of expected femtocells cannot be deployed using the traditional planning and optimization techniques. This leads to uncoordinated deployment by the end-user. Second, the high density of femtocells, including vertical reuse, leads to very different inter-cell interference patterns than the ones traditionally considered in cellular networks. And last, but not least, the possibility of having closed-subscriber-groups aggravates the inter-cell interference problems. In order to tackle these issues we consider the implementation of some aspects of cognitive radio technology into femtocells, leading to the concept of cognitive femtocells. This chapter focuses on state-of-art techniques to manage the radio resources in order to cope with inter-cell interference in cognitive femtocells. Different techniques are presented as examples of gradually increasing sophistication of the cognitive femtocells, allowing for dynamic channel allocation, dynamic reuse and negotiated reuse based on information exchanged with neighbor cells.