Jad Nasreddine

How a layered rem architecture brings cognition to today's mobile networks

In this article, we present a layered radio environment map architecture along with its applications to the self-organizing network functionalities of heterogeneous LTE radio access networks comprising macrocells and femtocells. In this architecture, the functional blocks reappear with different spatial and temporal granularity at different architectural layers. Although the radio environment map is one of the key promising technologies to enable future cognitive radio networks, it can be already applied to provide limited cognitive capabilities to todays commercial networks too. We explain why, and show how, this architecture can support today¿s LTE self-organizing network functions like automatic neighbor relation and minimization of drive tests, and also allow the smooth introduction of new radio access technologies through refarming. We also demonstrate some of the quantitative benefits adopting radio environment map technologies can bring using the minimization of drive tests as an example.

Transmit Power Control for Secondary Use in Environments with Correlated Shadowing

In this paper we propose a general model to estimate the maximum allowed transmit power of a secondary node based on the measured signal from the primary transmitter that is willing to share its downlink spectrum. The transmit power should satisfy primary constraints related to the minimum required Signal to Interference and Noise Ratio (SINR) of its users. The model can be used by secondary nodes whether or not they have full knowledge about the correlation between the different path losses. Simulation results have shown the high impact of the level of correlation on the performance of both primary and secondary users.

Impact of primary user activity patterns on spatial spectrum reuse opportunities

Activity patterns of primary users have significant influence on the opportunities for secondary use of spectrum. In this paper we explore this impact in terms of spatial spectrum reuse opportunities. More specifically, we model the primary user activity as a Semi-Markov ON/OFF process with varying distributions of holding times of ON and OFF states. We have used realistic holding time distributions obtained from extensive measurement campaigns. These activity patterns are combined with a collection of primary user transmitter locations, based on a real deployed cellular network. Based on these, we study the impact of activity model parameters on opportunities of spatial spectrum reuse. The results indicate that for the scenarios studied here the overall duty cycle defined by the activity pattern plays the key role also in determining spatial spectrum opportunities. We also discuss applications of the obtained results, including development of lightweight models for occurrences of spectrum opportunities over both time and space.

Design of layered radio environment maps for RAN optimization in heterogeneous LTE systems

In this contribution a layered radio environment map (REM) architecture is designed and applied in the framework of radio-access network optimization for heterogeneous LTE systems that comprise both macrocells and femtocells. We define layer as the hierarchical representation of a geographical area. In each layer, different instances of the same architectural block will have different spatial/temporal granularities, associated with network functionalities. The effectiveness of the proposed architecture to support LTE functions like automatic neighbor relation (ANR) and minimization of drive tests (MDT) is discussed. In addition, we present the benefits of using such architecture in the implementation of these functions along with its potential to bring performance gains.

Experimental spectrum sensor testbed for constructing indoor Radio Environmental Maps

In this paper we describe an experimental testbed to empirically study the construction of Radio Environmental Maps (REMs) in indoor environments. The testbed allows investigating the characteristics and modeling of the radio environment for indoor scenarios. The deployed system is a network of over 80 heterogeneous wireless spectrum sensors with significantly different measurement capabilities in an office building consisting of multiple rooms. As application examples we consider two scenarios, one illustrating the indoor propagation conditions and another showing temporal aspects of primary node activities as observed by sensing devices. The observed phenomena strongly indicate that development of general radio environment map solutions for indoor use are extremely challenging, unless heterogeneity of spectrum sensors and non-linearity of propagation conditions is considered. Our measurement results advocate dynamic construction of REMs instead of static solutions. We strongly believe that the deployed testbed and obtained experimental data can further facilitate research in the area of REMs.

Demonstrating radio environment map construction from massive data sets

In this demonstration we show an approach for constructing radio environment maps from massive data sets. Unlike earlier approaches, the methods used in the demonstrator can scale to millions of measurement points, enabling coverage prediction and other spatial estimation problems to be solved at country-wide scales. The demonstrator GUI enables attendees to construct different types of simulated measurement data sets, and perform spatial estimation based on those. The framework also allows the attendees to study the accuracy of the obtained estimates, as well as the computational time required for data processing.

Femtocell downlink power control based on Radio Environment Maps

The paper investigates the use of Radio Environment Maps (REMs) as a tool for Interference Management (IM) in two-tier cellular networks comprising macro- and femto-cells. The REMs are databases that provide, through different instances distributed over network elements, a variety of network- and user-related context information for improving IM and Radio Resource Management (RRM) procedures. In this context, the focus in this paper is to present the benefit of using REM information on practical power control schemes for the Femtocell downlink transmission in co-channel two-tier deployment.

Location-Based Adaptive Detection Threshold for Dynamic Spectrum Access

In this paper we propose a heuristic algorithm that exploits additional information that can be in general known by a secondary network willing to opportunistically access the spectrum allocated to a primary network. The algorithm aims at finding the maximum allowed transmission power with which a secondary node can transmit while respecting primary constraints. It is designed to be used in the presence of multiple primary transmitters with known positions but without information about their activity patterns. The estimation of the allowed transmission power is derived using a semi-analytical model characterizing interference probability. The latter is defined as the probability that the interference generated by the secondary node to any of the users in a primary cell exceeds a fixed threshold. The main idea is to autonomously determine a detection threshold based on the relative position of the secondary node towards base stations. Simulation results in a simple scenario are analyzed in order to explain the behavior of the algorithm. In addition, more results are introduced to evaluate the performance of the algorithm in more realistic scenarios.

Performance of TD-CDMA systems during crossed slots

Many multimedia services of the next generation mobile telecommunication systems have an asymmetric traffic distribution between uplink and downlink. The combination of the time division duplexing (TDD) with the time division multiple access (TDMA) technique in the Universal Mobile Telecommunications System (UMTS) allows an asymmetric use of radio resources due to the flexible allocation of time slots. To conserve this flexibility, the uplink and downlink slot distribution is preferred to be different in cells due to the different rates of asymmetry. Hence, crossed slots where a set of cells are active in downlink and another set are active in uplink, must be allowed. In crossed slots, intermobile and inter-base station interferences appear. Intermobile interference is very difficult to measure and may induce very high outage probability when two close mobiles are active in opposite link directions during the same slot. In this paper, a simplified optimum power control is used to study the performance of a TD-CDMA system during a crossed slot. Simulation results has shown that the system performance may be better in crossed slots than in uplink slots for some mobile distributions.

Using cognitive radio principles for wireless resource management in home networking

The demand for higher data rates, capacity and better quality-of-service is constantly growing for home networks. Therefore, there is a pressing need for efficient use of wireless network resources. In this context, the application of cognitive radio principles that enable network nodes to characterize their environment and control their resources based on the acquired knowledge, is the prominent solution for next generation home networks. In this paper we present an architecture and a prototype implementation based on these principles. The proposed system is able to autonomously optimize the performance of network nodes in a dynamic environment according to the goals, restrictions and policy regulations formulated by network stakeholders. The obtained results show the momentous and suitability of the cognitive framework for home networking.