Francisco J. Martin-Vega

Analytical Modeling of Interference Aware Power Control for the Uplink of Heterogeneous Cellular Networks

Inter-cell interference is one of the main limiting factors in current heterogeneous cellular networks. Uplink fractional power control (FPC) is a well-known method that aims to cope with such a limiting factor and to save the battery life of the mobile terminals (MTs). In order to do that, the transmit power of each MT is adjusted as a function of a set of parameters that usually depend only on the link between MTs and serving base station (BS), such as the desired received power at the serving BS or the path loss between the MT and its serving BS. Contrary to these classical FPC schemes, in this paper, we use stochastic geometry to analyze a power control mechanism that keeps the interference generated by each MT under a given threshold. We also consider a maximum transmitted power and a partial compensation of the path loss. Our analysis reveals that such an interference aware method can reduce the average power consumption and increase the average spectral efficiency at once. In addition, the variance of the interference is reduced, thus improving the performance of adaptive modulation and coding schemes, since the interference can be better estimated.

Link abstraction models for multicarrier systems: A logistic regression approach

Summary Evaluation of complex wireless systems through simulations is commonly tackled with an abstraction of physical link behavior. This procedure is performed in 2 phases: Firstly, training is performed at the link level, resulting in a mapping function from signal-to-interference-plus-noise ratio (SINR) to block error rate (BLER); and secondly, physical layer signal processing is replaced by the resulting link-level mapping function. Several methods have been proposed in the literature for link abstraction. The well-known exponential effective SINR mapping (EESM) is likely to be the most extensively used procedure for multicarrier transmission. In short, EESM estimates an effective SINR from the whole set of SINRs of useful subcarriers by means of a single parameter mapping function, which must be previously optimized through training. Later on, BLER is assumed as that of the effective SINR over an additive white Gaussian noise channel. In this paper, we propose a novel method for BLER prediction named as logistic regression-based link method (LRLM). Mean and standard deviation of the SINR set can accurately capture BLER behavior for wideband multicarrier systems through a simpler function, thus reducing the amount of information to be stored compared to EESM. Moreover, LRLM is very flexible and may include extra predictors to reduce the number of different models to be stored. Performance results show that LRLM is able to predict accurately the BLER for all modulation and coding schemes and transport block sizes defined for Long-Term Evolution technology.

Downlink power setting for energy efficient Heterogeneous Cellular Networks

Heterogeneous Cellular Networks (HCNs) are aimed to provide high data rates to an user population which is non uniform in space in an energy efficient manner. However inter cell interference is a limiting factor that is exacerbated with the irregular locations of Base Stations (BSs) and heterogeneous nature of transmitted powers. Conventional deployments only apply power control in the uplink (UL) whereas BSs transmit with fixed power in the downlink (DL) with independence of each BS location. In this paper two power setting techniques are proposed for the DL of HCNs. These techniques adjust transmit power at each BS aiming to provide a target desired power ρ0 at the cell edge. Hence these schemes account for the interference that each BS transmission cause to users associated with neighboring cells, reducing unnecessary powerful transmissions for close BSs. It is shown through simulation that proposed schemes greatly increase the average energy efficiency of the network as well as the average binary rate or the fairness in the system.

A System-Level Simulator for the Downlink of LTE-A: Case of Study—Cell-Offloading in HetNets

In this paper, we present a novel and efficient data-flow oriented simulation platform for the downlink of Long Term Evolution Advanced (LTE-A). This tool accounts for a wide set of configuration parameters from LTE-A physical and medium access control layers as well as different traffic sources. The simulator, which is implemented in C++, does not consider any link abstraction mechanism, leading to accurate and realistic results. As a case of study, we investigate the performance of cell-offloading for different deployments of small cell base stations that differ in the distance towards their nearest macro base station under File Transfer Protocol type traffic. Additionally, the impact of the spatial user distribution on the performance of cell-offloading is assessed. Results reveal that aggregated throughput is maximized when macro base stations are highly offloaded, which means that a high bias for cell association is advisable in terms of aggregated throughput. However, if the fairness among users is also taken into account, the selected bias for cell-offloading should be smaller.

Analytical Modeling of Distributed Location Based Access for Vehicular Ad Hoc Networks

One of the key ingredients of Intelligent Transportation Systems (ITS) is delivery of broadcast status messages among vehicles for safety purposes. This requires an efficient Medium Access Control (MAC) that provides low average delay and high reliability. To this end, Carrier Sense Multiple Access (CSMA) has been commonly proposed for Vehicle Ad Hoc Networks (VANETs). Nevertheless, the hidden- node problem can jeopardize the reliability of CSMA, whereas the latency when accessing the channel can be unbounded. To overcome these limitations, resource allocation based on the geo-location of the vehicles can be applied in VANETs. For example, a distributed location based access (DLOC) algorithm has been proposed such that vehicles access orthogonal resource blocks based on their position, aiming at maximizing the distance of co-channel transmitters. In this paper we propose a stochastic geometry approach to analyze DLOC taking into account path loss and fading as well as the random location of transmitting vehicles. Analytical results include the average interference, average binary rate and capture probability, i.e. probability of successful message transmission. It is shown that increasing the number of RBs increases reliability but there is a trade off between reliability and average BR.

Performance evaluation of cooperation-based techniques for M2M traffic over LTE

Long Term Evolution (LTE) and its evolved version, LTE-Advanced (LTE-A), are the standards developed by 3GPP to avoid the limitations associated to 3G networks. Efforts have been put on the improvement of system performance in terms of data rates. Coordinated Multipoint (CoMP) and inter-cell interference avoidance techniques have been widely studied in order to do that. However, not only is the increase in data rate important, but also latency reduction is a crucial factor to be considered for some applications. For instance, Machine-to-Machine (M2M) communications are nowadays one of the most promising applications, which are very sensitive to delay. In this work, we evaluate one of the most promising CoMP techniques, i.e. non-precoded Joint Transmission (non-precoded JT) and one of the most widely studied Inter-Cell Interference (ICI) avoidance technique, i.e. Partial Frequency Reuse (PFR). The objective is to determine whether, in addition to increase the data rates, they also reduce the latency. Simulation results show that PFR presents a greater reduction in the mean packet delay than this associated to non-precoded JT.

Geolocation-Based Access for Vehicular Communications: Analysis and Optimization via Stochastic Geometry

LTE V2X is the response of the 3GPP standardization body to the high market expectations related to vehicular communications for safety and infotainment services. To fulfill the stringent requirements in terms of reliability associated with safety applications, geolocation-based access (GLOC) has been proposed for direct vehicle-to-vehicle (V2V) communication. Such a scheme aims at maximizing the distance of co-channel transmitters (i.e., transmitter that use the same resources) while preserving a low latency when accessing the resources and a low overhead. In this paper, we analyze, with the aid of stochastic geometry, the delivery of periodic and nonperiodic broadcast messages with GLOC, taking into account path loss and fading as well as the random locations of transmitting vehicles. Analytical results include the average interference, average binary rate, capture probability, i.e., the probability of successful message transmission, and energy efficiency (EE). Mathematical analysis reveals interesting insights about the system performance, which are validated through extensive Monte Carlo simulations. In particular, it is shown that the capture probability is an increasing function with exponential dependence with respect to the transmit power and it is demonstrated that an arbitrary high capture probability can be achieved, as long as the number of access resources is high enough. Finally, to facilitate the system-level design of GLOC, it is obtained the optimum transmit power, which fulfill a given minimum capture probability constraint while maximizing the EE of the system.

Interference-Aware Muting for the uplink of heterogeneous cellular networks: A stochastic geometry approach

In this work, it is studied the performance of a scheduling algorithm where the Mobile Terminals (MTs) may be turned off if they cause a level of interference greater than a given threshold. This approach, which is referred to as Interference Aware Muting (IAM), may be regarded as an interference-aware scheme that is aimed to reduce the level of interference. The performance of IAM is studied in terms of transmit power, coverage probability, Spectral Efficiency (SE), and Binary Rate (BR). Simplified expressions of SE and BR for adaptive modulation and coding schemes are proposed, which better characterize practical communication systems. Our analysis unveils that, compared with conventional power control schemes, IAM increases the BR and reduces the transmit power.