Enrique Rodriguez-Colina

Distributed Control Using Cognitive Pilot Channels in a Centralized Cognitive Radio Network

In this paper, a cognitive radio network (CRN) model is presented. In this model, the control of the CRN is distributed among the frequency spectrum considered for transmission using cognitive pilot channels (CPCs). This control is performed by using frequency-division and time-division multiplexing techniques. Frequency-division is used to divide the spectrum into predetermined frequency slots in which cognitive radio users (CRUs) communicate. Then, the frequency slots are divided into sub-frequency slots, some of which are defined as CPC and used by the CRUs to communicate with a central cognitive base station (CCBS) and to determine availability in a frequency slot. Time-division is used to determine if a primary user (PU) has accessed the channel used by CRUs. Using this time-division approach, presence of PUs is detected. We have designed a CRN able to work with today’s available technologies and CRU devices that use different frequency bands of operation. Results of the performance of the network will be presented in terms of the number of CRU and the time these CRUs use the CPCs for control.

Congestion Control for a Fair Packet Delivery in WSN: From a Complex System Perspective

In this work, we propose that packets travelling across a wireless sensor network (WSN) can be seen as the active agents that make up a complex system, just like a bird flock or a fish school, for instance. From this perspective, the tools and models that have been developed to study this kind of systems have been applied. This is in order to create a distributed congestion control based on a set of simple rules programmed at the nodes of the WSN. Our results show that it is possible to adapt the carried traffic to the network capacity, even under stressing conditions. Also, the network performance shows a smooth degradation when the traffic goes beyond a threshold which is settled by the proposed self-organized control. In contrast, without any control, the network collapses before this threshold. The use of the proposed solution provides an effective strategy to address some of the common problems found in WSN deployment by providing a fair packet delivery. In addition, the network congestion is mitigated using adaptive traffic mechanisms based on a satisfaction parameter assessed by each packet which has impact on the global satisfaction of the traffic carried by the WSN.

Análisis de la Movilidad Espectral en Redes de Radio Cognitiva

A review of the spectrum mobility in cognitive radio networks, describing the spectrum Handoff, their classifications, current approaches, decision criteria and evaluation metrics according to the current literature is presented. The review was based on the analysis of recent mainstream publications with their respective citations, trying to provide a comprehensive reference framework of the current literature on the spectrum mobility in cognitive radio networks. The main results determine the importance of scalable and optimizing detection and targeting channel, taking into account the traffic load, the behavior of the user, the interference levels, and the characterization of the spectrum, the type of application and the need for multiple frequency channels. The study suggests that it is necessary to design adaptive algorithms to optimize the resources involved during the spectrum Handoff.

A bit error rate analysis for TCP traffic over parallel free space photonics

Inter-satellite links (ISL) are a useful technology to transmit data to space stations and to communicate between satellites. However, there are serious limitations due to long delays and poor channel performance, resulting in high bit error rates (BER). In this paper, parallel transmission and the scaling of the Transport Control Protocol (TCP) window in free space optics (FSO) communications are analyzed in order to overcome these disadvantages in optical inter-satellite links. Latency and BER are the dominant effects that determine link performance. Thus, a physical, link, network and transport cross-layer analysis for FSO over ISL is presented in this paper. This analysis shows the advantages and disadvantages of using optical parallel transmission and TCP window scaling for free space optical links between stations and satellite constellations. The key contribution of this work is to simulate the effects of the BER and to link the results to packet error rate (PER) to determine the goodput for TCP transmissions by using a cross-layering approach. The results give evidence that wavelength division multiplexing (WDM) can mitigate the effects of long delay and high BER for a FSO communication using TCP.

Cluster-Based Localisation Method for Dense WSN: A Distributed Balance between Accuracy and Complexity Fixed by Cluster Size

Localisation is a fundamental requirement for a monitoring and tracking system based on wireless sensor networks (WSN). In order to build an accurate set of measurements, sensor nodes must have information regarding their own position within a system of coordinates. When a considerable number of nodes are randomly scattered over a monitoring area, sensor nodes must be part of a self-organised system which provides a set of local position estimates. Nodes participate under very stringent conditions, for example, limited power supply and reduced computational capabilities. This work presents a GPS-free localisation method consisting of four stages that are executed only once during the network initialisation process. These stages are aimed to increase the overall system lifetime by reducing the signalling overhead commonly involved in distributed localisation procedures. The proposed localisation method turns the initial and complex node deployment to several smaller instances by dividing the network into clusters, which can be solved simultaneously based on local resources only. Simulation results show that this approach produces important savings in the involved overall complexity, which can translate into a trade-off between computational cost and localisation accuracy.

Direction of Encounter (DoE): A Mobility-Based Location Method for Wireless Networks

Traditional location methods require specialized network infrastructure or add-on location hardware in order to estimate node positions. As an opposite approach, direction of encounter(DoE) uses standard wireless networking equipment and takes advantage of node mobility to establish static node locations. In DoE, as a mobile node enters and leaves a static nodes coverage area, it is able to discover the static nodes location with respect to its own trajectory. Mobile nodes are able to determine the position of a set of static nodes by collaborating in this discovery process. In this work, this set is called a constellation. This collaboration consists of exchanging constellation data in order to establish and improve the accuracy of the position estimates. Not only does DoE establish static node positions, but it also allows mobile users to be aware of the direction where static nodes can be found. DoE needs minimal user intervention, although fully automatic operation can be achieved if inertial sensors are available. This method can be used to develop both location-based applications and guiding procedures. By means of simulations and experiments, we carried out a performance evaluation of DoE under diverse conditions. The results show that the DoE algorithm indeed is able to estimate the static node positions without requiring additional functionality from static nodes. We believe this is an important requirement for a successful deployment of a location method.

Linear Algorithms for Radioelectric Spectrum Forecast

This paper presents the development and evaluation of two linear algorithms for forecasting reception power for different channels at an assigned spectrum band of global systems for mobile communications (GSM), in order to analyze the spatial opportunity for reuse of frequencies by secondary users (SUs) in a cognitive radio (CR) network. The algorithms employed correspond to seasonal autoregressive integrated moving average (SARIMA) and generalized autoregressive conditional heteroskedasticity (GARCH), which allow for a forecast of channel occupancy status. Results are evaluated using the following criteria: availability and occupancy time for channels, different types of mean absolute error, and observation time. The contributions of this work include a more integral forecast as the algorithm not only forecasts reception power but also the occupancy and availability time of a channel to determine its precision percentage during the use by primary users (PUs) and SUs within a CR system. Algorithm analyses demonstrate a better performance for SARIMA over GARCH algorithm in most of the evaluated variables.

Dynamic OFDM Transmission for a Cognitive Radio Device Based on a Neural Network and Multiresolution Analysis

Cognitive radio communications depend on methods for sensing the spectrum as well as adapting transmission parameters to available resources. In this context, this work proposes a novel system that makes use of prediction to dynamically allocate subcarriers to different transmissions in an orthogonal frequency division multiplexing (OFDM) system. To this end, the proposal is comprised of a predictive component which makes use of a neural network and multiresolution analysis and a second component, which uses wavelet analysis and cognitive radio functions to carry out a dynamic allocation of subcarriers in an OFDM system. The use of wavelets allows the system to split the data stream in blocks of information to be transmitted over multiple orthogonal subcarriers. This proposed system makes use of the decision-making functions of a cognitive radio device to select the number and position of the subcarriers used for communications without interference. Although there exist other OFDM systems using wavelets, they are not used in combination with the decision-making functions implemented in cognitive radio devices. In contrast, the proposed OFDM system operates using some of these functions, thus being able to better adapt its operational parameters. The use of wavelets combined with a neural network model improves the prediction of the bandwidth utilization as shown in this work. It is concluded that the proposed system improves spectral efficiency and data rate by using the decision-making functions of cognitive radios to select the appropriate OFDM subcarriers to be used during the data transmissions.

Performance Trade-Offs for Wavelength Striping Optical Switching Using a Novel Star Architecture

This work describes various performance trade-offs that arise from the use of a technique for optical switching under various network topologies. Such switching operation can be summarized as follows: (a) user data are divided into fixed-length fragments, (b) each fragment is assigned to a different wavelength, and (c) all wavelengths are simultaneously switched to the egress links. This concept of dividing user data into several wavelengths to be simultaneously switched is called wavelength striping and its purpose is to reduce latency and increase throughput for short distance interconnects. We depart from previous work where a building block implementing this basic switching function has been built around semiconductor optical amplifiers (SOAs). In this paper, we investigate diverse trade-offs that arise from the use of this switching approach in different network topologies. One of the main issues addressed in this paper is the relation between cascadability and bit error rate (BER). In this case, our results indicate that a switch fabric can cascade up to five stages without exceeding a BER of 10−9 and without incurring in power budget problems. We also show that the performance degradation, introduced by cascading SOAs, can be compensated with a star interconnect architecture that is introduced. Other issues addressed in this paper are the effect of scalability on cost and the effect of latency on TCP performance and reliability.

Energy-Efficient Model for Overlay Cognitive Communications

Current approaches regarding energy-efficient cognitive radio networks found in the literature aim to optimize the functionalities met by cognitive systems. This is done in order to improve the number of transmitted bits per energy unit and to increase the network lifetime of cognitive devices when they have limited power resources. However, many of these approaches may not fit together when designing a full cognitive radio system. For this reason, a five-layer network model for energy-efficient overlay-based cognitive radio is proposed in this paper. This model includes a set of functionalities necessary to achieve energy-efficiency. We show, by means of simulations, that these functionalities may reduce the number of secondary transmissions by improving the exploitation of primary channels. We also found that, under certain scenarios, the number of transmissions necessary to achieve successful communications can be reduced to the half when the primary network is loaded at 60% of its maximum capacity, when transmissions with low Eb/N0 are combined with adaptive bandwidth channels.