Effect of Location Accuracy and Shadowing on the Probability of Non-Interfering Concurrent Transmissions in Cognitive Ad Hoc Networks

Cognitive radio ad hoc systems can coexist with a primary network in a scanning-free region, which can be dimensioned by location awareness. This coexistence of networks improves system throughput and increases the efficiency of radio spectrum utilization. However, the location accuracy of real positioning systems affects the right dimensioning of the concurrent transmission region. Moreover, an ad hoc connection may not be able to coexist with the primary link due to the shadowing effect. In this paper we investigate the impact of location accuracy on the concurrent transmission probability and analyze the reliability of concurrent transmissions when shadowing is taken into account. A new analytical model is proposed, which allows to estimate the resulting secure region when the localization uncertainty range is known. Computer simulations show the dependency between the location accuracy and the performance of the proposed topology, as well as the reliability of the resulting secure region

Algoritmos de rendezvous para redes Radio Cognitivas

Cognitive radio is a promising paradigm to address the scarcity of radio spectrum as well as for efficient usage. The rendezovus process allows two cognitive users to meet on the same channel and establish a communication link. This work focuses on the study and comparison of different rendezvous algorithms proposed in the literature. We present the major rendezvuos challenges in the context of cognitive networks as well as the main metrics used for evaluation. Through simulation, we evaluate the performance of a group of rendezvous algorithms in practical scenarios and the results are contrasted with the theoretical results given by the authors. The simulation results show that for most of the rendezvous algorithms proposed in the literature the theoretical results provided by the authors are far from the real results achieved by the algorithms. Additionally, in symmetric scenarios, the EJS algorithm has the better results in terms of ETTR and MTTR, while in asymmetric scenarios the FRCH and SSB algorithms outperform the others rendezvous strategies.La radio cognitiva constituye un paradigma prometedor para enfrentar la escasez de espectro radio eléctrico así como para realizar un uso eficiente del mismo. El proceso de rendezovus permite que dos usuarios de la red cognitiva coincidan en un mismo canal y establezcan un enlace de comunicación. Este trabajo se centra en el estudio y comparación de diferentes algoritmos de rendezvous propuestos en la literatura. Son presentados los principales retos del rendezvuos en el contexto de las redes radio cognitivas así como las principales métricas empleadas para su evaluación. Mediante simulación se evalúa el desempeño de un grupo de algoritmos de rendezvous en escenarios prácticos y los resultados obtenidos son contrastados con los resultados teóricos proporcionados por los autores. Los resultados de las simulaciones evidencian que para gran parte de los algoritmos de rendezvous propuestos en la literatura los resultados teóricos brindados por sus autores están distantes de los resultados reales alcanzados por los algoritmos. Adicionalmente, en escenarios simétricos el algoritmo EJS obtiene los mejores resultados tanto en términos de ETTR como de MTTR, mientras que en escenarios asimétricos los algoritmos FRCH y SSB superan al resto de las estrategias de rendezvous

Comparison between MACAW and T_Lohi protocols for underwater networks.

The development of underwater networks presents great challenges, most of which are related to the complexity of the communication channel. The main difficulties to face in the underwater channel are the restricted bandwidth and the low propagation speed. Due to these difficulties, it is necessary the development of new and more competent communication protocols in order to obtain higher performance and minimize the energy consumption. Therefore, this paper presents a comparative evaluation between two medium access controls (MAC): MACAW and T_Lohi. Both protocols are based on random access mechanism, the first uses request to send (RTS); clear to send (CTS) and acknowledgement (ACK) messages to regulate transmissions while the second uses short duration tones which can be detected instantaneously. Thus, this study focuses on the performance, collisions and efficiency of these protocols in order to reserve the communication channel, whereby it highlights the advantages and deficiencies of each protocol in the underwater communication networks

Evaluación experimental del protocolo IEEE 802.15.4 TSCH en una red 6TiSCH

The Time-Slotted Channel Hopping (TSCH) mode for medium access control (MAC) included in the standard IEEE 802.15.4 has been designed as the multichannel MAC protocol for Low-power and lossy networks (LLNs), a key component of the Internet of Things (IoT). Its flexibility makes the TSCH mode a very promising candidate for the future of the MAC layer in LLNs. As such, its performance under different conditions must be assessed, so that accurate guidelines for its application can be drawn. In this paper, we present an experimental evaluation of the protocol based on simulations on ContikiOS Java Simulator (COOJA). The experimental setup is based on the 6TiSCH architecture for LLNs. Results show that TSCH performs better under conditions of medium traffic load than under low or high traffic loadEl modo Salto de Canal por Ranuras de Tiempo (TSCH1) para control de acceso al medio (MAC) en el estándar IEEE 802.15.4 ha sido designado como el protocolo MAC estándar para redes de baja potencia con pérdidas (LLN), un componente clave en la denominada Internet de las Cosas (IoT). Su flexibilidad hace del modo TSCH un candidato promisorio para el futuro de la capa MAC en LLN. Por tanto, es indispensable evaluar su desempeño bajo diferentes condiciones de carga de tráfico con el fin de trazar guías para su empleo y configuración en diferentes aplicaciones de IoT. En este artículo, se presenta una evaluación experimental del desempeño de TSCH basada en simulaciones en el simulador en Java de ContikiOS (COOJA). La evaluación se realiza utilizando diferentes valores de carga de tráfico en una configuración típica de LLN; y el desempeño del protocolo es evaluado en términos de razón de entrega de paquetes (PDR), demora extremo a extremo y consumo de energía. Los resultados muestran que TSCH se desempeña mejor en condiciones de tráfico medias que con baja y alta carga de tráfic

Estrategias de rendezvous en redes Radio Cognitiva multiusuario

Blind rendezvous strategies for dynamic spectrum access in ad-hoc networks have recently focused by many researches on reports. The works have focused mainly on the design of rendezvous strategies between two network devices that actively try to establish communication (rendezvous by pairs). In this paper, the analysis of pair-wise strategies to multiuser networks is extended and a strategy is proposed to implement the rendezvous process between multiple users. The maximum value and expected value of time to rendezvous in multiusers scenario are computationally derived for different network topologies by using different synchronization strategies. The results show that the numerical expressions provide good estimates of the time to rendezvous. Moreover, the proposed synchronization strategy ensures the time to rendezvous in a multi-user network does not exceed the maximum time to rendezvous of a rendezvous by pairs process, regardless of the total number of users and the network topology.Las estrategias de rendezvous ciego para el acceso dinámico al espectro en redes ad-hoc han atraído recientemente la atención de muchos investigadores. Los trabajos se han centrado principalmente en el diseño de estrategias de rendezvous entre dos dispositivos de red que intentan activamente establecer comunicación (rendezvous por pares). Este artículo amplía el análisis de los mecanismos de rendezvous por pares a redes multiusuario y propone una estrategia para implementar el proceso de encuentro entre múltiples usuarios. El valor máximo y el valor esperado del tiempo de rendezvous en escenarios multiusuario son derivados computacionalmente para distintas topologías de red empleando diferentes estrategias de sincronización. Los resultados muestran que las expresiones numéricas proveen una buena estimación de los tiempos de rendezvous. Además, la estrategia de sincronización propuesta garantiza que el tiempo de rendezvous en una red multiusuario no sobrepase el tiempo máximo de rendezvous de un proceso de rendezvous por pares independiente del número de usuarios y la topología de red

Channel hopping for blind rendezvous in cognitive radio networks: A review

International audienceCognitive radio networks enable unlicensed users to communicate using the licensed spectrum without causing interference to legitimate users. To establish a communication link, two or more cognitive users must simultaneously visit a common available channel and exchange the handshake information, such a process is referred to as rendezvous. The simplest solution to the rendezvous problem is to use a dedicated common control channel. However, it can suffer severe congestion or even be occupied by incumbent users, limiting the functioning of the cognitive network. Channel hopping (CH) techniques overcome these drawbacks and allow cognitive users to rendezvous on any common available channel. In this paper a classification framework is proposed based on relevant features for the design of CH rendezvous sequences. Using the proposed framework, an unprecedented number of CH sequences are reviewed and classified. Theoretical performance metrics of existing CH sequences are summarized. Finally, open issues and research directions for CH sequences design are discussed