Mario Garcia-Lozano

Optimization of Soft Frequency Reuse for Irregular LTE Macrocellular Networks

Interference management has been recognized by the industry as a key enabler for 4G systems. Emerging technologies include multicarrier systems such as LTE and WiMAX for which effective management of intercell interference is of utmost importance in order to improve the Quality of Service (QoS) at cell edges. Static Intercell Interference Coordination (ICIC) techniques such as Soft Frequency Reuse (SFR) are aimed at alleviating this problem; however the usage of baseline SFR designs (schemes without optimization) only offers tradeoffs between cell edge performance and spectral efficiency and performance is indeed far from optimal as results herein confirm. Thus, this paper presents a novel multiobjective algorithm in order to address this problem and achieve effective optimization of SFR implementations. Results show that the proposed algorithm succeeds in finding good-quality SFR configurations enhancing simultaneously network capacity and cell edge performance while reducing energy consumption with respect to baseline designs and previous proposals.

UMTS optimum cell load balancing for inhomogeneous traffic patterns

The paper addresses the problem of adjusting simultaneously the electrical downtilt of base station antennas and the transmitted power assigned to common pilot channel (CPICH) signals in the framework of a UTRA-FDD system. The proposed optimization procedure is not based on an isolated cell by cell analysis, but on a global scenario by means of simulated annealing. Results show the convergence of the algorithm towards configurations that imply optimal system performance. Interference levels are minimized, effective cell load is reduced and therefore capacity can be increased.

A novel multiobjective framework for cell switch-off in dense cellular networks

The green communications paradigm has been receiving much attention in wireless networks in recent years. More specifically, in the context of cellular communications, the concept of Cell Switch Off (CSO) has been recognized as a promising approach to reduce the energy consumption. The need is expected to be pressing especially in the next decade with the increasing small cell deployment. However, the cell switch on/off decisions compounded by the resource allocation task in CSO constitute a highly challenging optimization problem due to the fact that this problem can be viewed as a generalized version of the resource allocation (scheduling) problem in the conventional cellular networks without CSO, which itself is already difficult. This paper introduces a novel framework to CSO based on multiobjective evolutionary optimization. The main contribution of this paper is that the proposed multiobjective framework takes the traffic behaviour in both space and time (known by operators) into account in the optimal cell switch on/off decision making which is entangled with the corresponding resource allocation task. The exploitation of this statistical information is done in a number of ways, including through the introduction of a weighted network capacity metric. This indicator prioritizes cells which are expected to have traffic concentration resulting in on/off decisions that achieve substantial energy savings in scenarios where traffic is highly unbalanced, without compromising the QoS. The proposed framework distinguishes itself from the CSO papers in the literature in two ways: 1) The number of cell switch on/off transitions as well as handoffs are minimized. 2) The computationally-heavy part of the algorithm is executed offline, which makes the real-time implementation feasible.

On the need for dynamic downlink intercell interference coordination for realistic Long Term Evolution deployments

Intercell interference is the main issue limiting the capacity of modern orthogonal frequency-division multiple access based cellular networks. Recently, extensive research work has been carried out in this field, and intercell interference coordination techniques have been recognized as key enablers of current and future cellular technologies. In this article, i a comprehensive survey of the most representative contributions is provided together with ii a generic methodology to measure their actual merit. The performance of several interference avoidance strategies has been evaluated both from system and user point of view in the context of a Long Term Evolution LTE-based network considering not only synthetic cellular scenarios but also realistic deployments. Our literature review indicates that there is a need for adaptive/operator-customizable low-complex intercell interference coordination ICIC schemes suitable for realistic LTE deployments. Results obtained by means of a comprehensive set of simulations corroborate and support this premise. In this article, it is shown that simultaneous gains in terms of spectral/energy efficiency and fairness can be achieved through dynamic mechanisms with respect to both classic hard reuse schemes and static ICIC techniques. Besides numerical results, a novel merit assessment methodology based on several weighted performance metrics is proposed. Our findings show that dynamic schemes outperform static techniques by around 20-35% in realistic deployments. Copyright

Effects of downtilting on RRM parameters

UMTS radio network planning has to deal with many parameters that simultaneously influence network performance. Their adjustment is not always an easy task since coverage, capacity and quality of service must be jointly maximized. This paper addresses the problem of adjusting antenna downtilt and its impact on the system, particularly on RRM parameters. Detailed results, furthest than well known effects, have been obtained in different scenarios with different loads by means of static Monte Carlo simulations. Adaptive and remote electrical downtilting arises as an interesting option since results show the existence of optimal configurations in which capacity is maximized. Fixed downtilt angles will lead the system to poor performance whenever scenario conditions slightly change.

Static inter-cell interference coordination techniques for LTE networks: a fair performance assessment

This paper focuses in the analysis of 100% static and distributed inter-cell interference coordination techniques in the context of LTE networks. Several methods have been modeled and studied with the aim of deriving practical radio planning rules based on the joint effect of operational parameters and thresholds. The investigation places special emphasis on the efficiency vs. fairness tradeoff through a set of metrics that allow not only to evaluate the measurements from different points of view, but also to look at the effectiveness in radio resources usage. Results show that similar levels of spectral efficiency can be achieved by means of a proper and accurate network tuning. Moreover, interesting second order differences appear due to inherent features of each approach. These can be exploited depending on the particular network operator needs.

Performance Evaluation of Downlink Interference Coordination Techniques in LTE Networks

This paper presents a joint study of several intercell interference coordination strategies considering both static and dynamic approaches, and with different adjustments in their basic parameters. A wide evaluation is presented with special emphasis on the efficiency vs. fairness tradeoff. Besides, additional performance metrics have been considered as enablers of a full understanding of the strengths and weaknesses of each method. Results show that, although spectral efficiency can achieve similar values with proper tuning, certain schemas outperform others in important parameters such as the effectiveness in the utilization of resources. Dynamic semi-centralized approaches appear as an attractive option with an acceptable level of adaptability, moderate complexity and good performance.

System level evaluation of LTE networks with semidistributed intercell interference coordination

3GPP LTE is the evolution of UMTS which will make possible to deliver high quality multimedia services with an improved user experience. Since Radio Resource Management (RRM) has been recognized as a key point to successfully accomplish this target, the performance evaluation of a multi-cell resource allocation scheme applied to LTE downlink (DL) is presented in this paper. A semi-distributed RRM framework is discussed and evaluated from a system level viewpoint. Detailed link level simulations have also been carried out to properly back up the results.

Improved component carrier selection considering MPR information for LTE-A uplink systems

Carrier Aggregation (CA) is one of the key features introduced in LTE Release 10 to achieve higher levels of throughput. Two or more component carriers (CCs) are aggregated and user equipments (UEs) simultaneously transmit in more than one. The use of non-contiguous resource allocation in the uplink (UL) implies higher peak to average power ratio, so power de-rating is essential to avoid inter-modulation distortion and adjacent channel leakage-power ratio. CC selection is a key radio resource management procedure by which the eNB assigns UEs to CCs. While most CC selection algorithms deal with downlink, existing literature lacks efforts on UL CA. Moreover the mechanism is determinant on the UL performance. Given the UE power limitation, different criteria must be used in each link. This work proposes a novel CC selection algorithm that distinguishes between power limited and non-power limited UEs. In particular it is proposed to introduce information on maximum power reduction in selection decisions. Besides, UEs are not directly rejected if they are power limited, an acceptance margin is defined. This contains information on throughput variations between the allocation in several or just one CCs. This novel approach is contrasted with other CC selection techniques. Results show cell edge throughput improvements and the benefit of allowing bandwidth aggregation in a subset of power limited users.

On the Role of Downlink Control Information in the Provision of QoS for NRT Services in LTE

The provision of Quality of Service (QoS) to users of LTE networks depends to a large degree on the choice of an appropriate scheduling algorithm able to meet the requirements of mobile operators. Dynamic packet scheduling has been recognized as a key approach to maximize the utility of OFDMA-based systems due to its inherent ability to exploit the frequency selectiveness of wideband channels both in time and frequency domain. However, one of the main issues associated to dynamic scheduling is the high amount of signaling overhead required to provide users with resource allocation information. While the impact of control channel limitations on LTE VoIP capacity has been widely studied yet, tradeoffs associated to control channel usage and the provision of QoS for Non-Real Time (NRT) services has been basically omitted in current literature. In this paper, such tradeoffs have been addressed from several perspectives. Results show that the relationship between scheduling policies, offered levels of QoS (expressed in terms of guaranteed bit rates) and control channels capacity is not trivial and requires careful planning.