Salvador Luna-Ramírez

Optimization of a Fuzzy Logic Controller for Handover-Based Load Balancing

In Self-Organizing Networks (SON), load balancing has been recognized as an effective means to increase network performance. In cellular networks, cell load balancing can be achieved by tuning handover parameters, for which a Fuzzy Logic Controller (FLC) usually provides good performance and usability. Operator experience can be used to define the behavior of the FLCs. However, such a knowledge is not always available and hence optimization techniques must be applied in the controller design. In this work, a fuzzy

Automatic Replanning of Tracking Areas in Cellular Networks

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Traffic steering by self-tuning controllers in enterprise LTE femtocells

-Learning algorithm is proposed to find the optimal set of fuzzy rules in an FLC for traffic balancing in GSM-EDGE Radio Access Network (GERAN). Load balancing is performed by modifying handover margins. Simulation results show that the optimized FLC provides a significant reduction in call blocking.

Design of a Computationally Efficient Dynamic System-Level Simulator for Enterprise LTE Femtocell Scenarios

In future cellular networks, tracking areas (TAs) that are defined for location management purposes will be frequently updated to cope with changes in user trends. In this paper, an automatic method for defining when and how to change an existing TA plan to minimize network signaling is presented. The method first detects periods of similar user trends that could share the same TA plan. For this purpose, a series of graphs showing the evolution of user mobility and traffic is built from handover and paging statistics in the network management system (NMS). Then, a clustering algorithm is used to identify periods of similar user trends based on graph correlation. Thus, a TA replan is performed at the end of each period. To build the new TA plan, the TA replanning problem is formulated as a classical graph partitioning problem, which is then solved by a sophisticated graph partitioning algorithm combining multilevel and evolutionary techniques. Assessment is based on graphs taken from a live cellular network. Results show that the proposed method can significantly decrease the total number of location update (LU) and paging requests in the network by only changing the TA plan twice a week.

Analysis of Throughput Performance Statistics for Benchmarking LTE Networks

Femtocells have been suggested as a promising solution for the provision of indoor coverage and capacity. This article investigates the problem of re-distributing traffic demand between long-term evolution (LTE) femtocells with open access in an enterprise scenario. Several traffic sharing algorithms based on automatic tuning of femtocell parameters are considered. The proposed algorithms are implemented by fuzzy logic controllers. Performance assessment is carried out in a dynamic system-level simulator. Results show that localized congestion problems in these scenarios can be solved without impairing connection quality by jointly tuning handover margins and cell transmit power.

Adjustment of a Fuzzy Logic Controller for IS-HO parameters in a heterogeneous scenario

In the context of Long-Term Evolution (LTE), the next generation mobile telecommunication network, femtocells are low-power base stations that efficiently provide coverage and capacity indoors. This paper presents a computationally efficient dynamic system-level LTE simulator for enterprise femtocell scenarios. The simulator includes specific mobility and traffic and propagation models for indoor environments. A physical layer abstraction is performed to predict link-layer performance with low computational cost. At link layer, two important functions are included to increase network capacity: Link Adaptation and Dynamic Scheduling. At network layer, other Radio Resource Management functionalities, such as Admission Control and Mobility Management, are also included. The resulting tool can be used to test and validate optimization algorithms in the context of Self-Organizing Networks (SON).

Optimal Traffic Sharing in GERAN

In this letter, a comprehensive analysis of throughput performance statistics in a live LTE network is presented. The analysis shows the relationship between several widely accepted throughput performance indicators, i.e., the user throughput, the cell throughput, and the radio link throughput, and how these indicators are related to signal quality statistics. The analysis is performed on a per-cell and per-connection basis. For this purpose, throughput and signal quality statistics are collected from network performance counters and call traces in cells of a live LTE system. Results show that all throughput measures are strongly affected by chatty applications dominating current LTE networks due to the last transmission time interval transmissions and the outer loop link adaptation mechanism.

Self-tuning of Remote Electrical Tilts Based on Call Traces for Coverage and Capacity Optimization in LTE

In this paper, a fuzzy logic controller (FLC) is proposed to tune several inter-system handover (IS-HO) parameters in a heterogeneous scenario with changing traffic distribution. Performance assessment is carried out by implementing FLC and IS-HO algorithms in a dynamic network simulator including GSM and UMTS radio access technologies. Preliminary results show that, although the FLC is able to modify network parameters to re-distribute traffic between technologies, its speed of response is severely limited. A sensitivity analysis is then performed to quantify the effect of several internal parameters in the FLC on the speed of response. Experiments show that tuning ranges and steps for the controlled IS-HO parameters have a strong impact on performance. Results show that, by adjusting tuning ranges and steps, a significant reduction in blocked call rates (BCRs) can be obtained in some iterations when compared to the default settings.

Analysis of Limitations of Mobility Load Balancing in a Live LTE System

In a mobile communications network, the uneven spatial distribution of traffic demand can be dealt with by redefining cell service areas. When resizing cells, network operators often aim at equalizing call blocking rates throughout the network in the hope that this will maximize the total carried traffic in the network. In this paper, an analytical teletraffic model for the traffic sharing problem in GSM-EDGE radio access network (GERAN) is presented. From this model, a closed-form expression is derived for the optimal traffic sharing criterion between cells. Using this expression, it can be shown that balancing call blocking rate between adjacent cells is not the optimal strategy. Results show that using the optimal traffic sharing criterion instead of balancing blocking rates across the network can increase network capacity, even under restrictions in the cell resizing process.

Analysis of User Mobility Statistics for Cellular Network Re-Structuring

Adjusting antenna tilts is one of the most powerful techniques to solve coverage and capacity problems in cellular networks. In this paper, a novel self-tuning algorithm for adjusting antenna tilts in a Long-Term Evolution (LTE) system on a cell-by-cell basis is presented. The aim of the algorithm is to improve both network coverage and overall spectral efficiency, while eliminating cell overshooting problems. For this purpose, several new indicators are computed to detect insufficient cell coverage, cell overshooting, and abnormal cell overlapping from information available in connection traces. Algorithm assessment is carried out over a static system-level simulator implementing different real macrocellular scenarios. During the analysis, the proposed algorithm is compared with classical self-tuning algorithms that modify other base station parameters, such as transmission power or antenna tilt. Results show that the proposed algorithm can solve overshooting and overlapping problems more effectively than previous algorithms, regardless of the scenario.