Rafael Asorey-Cacheda

A Survey on Cooperative Diversity for Wireless Networks

Diversity, i.e. transmitting multiple replicas of a signal, may mitigate fading in wireless networks. Among other diversity techniques, the space diversity of multi-antenna systems is particularly interesting since it can complement other forms of diversity. The recent cooperative diversity paradigm brings the advantages of multi-antenna space diversity to single antenna networked devices, which, through cooperation and antenna sharing, form virtual antenna arrays. However, cooperative diversity is a complex technique and research on this topic is still in its early stages. This paper aims at providing a general survey on the theoretical framework; and the physical and medium access control proposals in the literature.

On Maximizing the Lifetime of Wireless Sensor Networks by Optimally Assigning Energy Supplies

The extension of the network lifetime of Wireless Sensor Networks (WSN) is an important issue that has not been appropriately solved yet. This paper addresses this concern and proposes some techniques to plan an arbitrary WSN. To this end, we suggest a hierarchical network architecture, similar to realistic scenarios, where nodes with renewable energy sources (denoted as primary nodes) carry out most message delivery tasks, and nodes equipped with conventional chemical batteries (denoted as secondary nodes) are those with less communication demands. The key design issue of this network architecture is the development of a new optimization framework to calculate the optimal assignment of renewable energy supplies (primary node assignment) to maximize network lifetime, obtaining the minimum number of energy supplies and their node assignment. We also conduct a second optimization step to additionally minimize the number of packet hops between the source and the sink. In this work, we present an algorithm that approaches the results of the optimization framework, but with much faster execution speed, which is a good alternative for large-scale WSN networks. Finally, the network model, the optimization process and the designed algorithm are further evaluated and validated by means of computer simulation under realistic conditions. The results obtained are discussed comparatively.

A Review of Aeronautical Electronics and Its Parallelism With Automotive Electronics

Aeronautical electronics and communication technologies have evolved from the analog domain to the digital domain, and nowadays, planes are complex structures serviced by many standalone systems that communicate through data buses. Many of these systems have found applicability in other sectors. This paper reviews the most recent technologies in modern aircraft and identifies their application in the automotive sector. It also identifies automotive electronics as applied in planes.

WiMAX for smart grid last-mile communications: TOS traffic mapping and performance assessment

This paper addresses specific smart grid communication requirements. It considers a last-mile network based on an IEEE 802.16 cell deployed to cover a group of customers and serve their Energy Services Interfaces. Based on the communication requirements of smart grid last-mile applications and entities, we propose a traffic priority model and setup for the WiMAX air interface. Finally, we evaluate the proposal using a discrete-event simulator.

Measures and Countermeasures for Null Frequency Jamming of On-Demand Routing Protocols in Wireless Ad Hoc Networks

Distributed network protocols operate similar to periodic state machines, utilizing internal states and timers for network coordination, which creates opportunities for carefully engineered radio jamming to target the protocol operating periods and disrupt network communications. Such periodic attacks targeting specific protocol period/frequency of operation is referred to as Null Frequency Jamming (NFJ). Our hypothesis is that NFJ is a pervasive phenomenon in dynamic systems, including wireless ad-hoc networks. This paper aims to test the hypothesis by investigating NFJ targeted at the on-demand routing protocols for ad-hoc networks. Our mathematical analysis and simulation results show substantial degradation in end-to-end network throughput at certain null periods/frequencies, where the jamming periodicity self-synchronizes with the route-recovery cycle. We also study an effective countermeasure, randomized route-recovery periods, for eliminating the presence of predictable null frequencies and mitigating the impact of NFJ. Our analytical model and simulation results validate the effectiveness of randomized route recovery with appropriately chosen randomization ranges.

Maximizing α-Lifetime of wireless sensor networks with solar energy sources

In this paper, using linear programming, we formulate the problem of maximizing the a-lifetime of wireless sensor networks with solar energy sources. The a-lifetime of a sensor network is defined as the duration in which a percentage of sensor data can be collected by the base station. Our formulation takes account of varying solar energy recovery rate at different sensors and jointly optimizes the transmission power of the sensors and data routing for maximizing a-lifetime. We study the break point, which marks the level of solar energy supply above which the sensor network can operate perpetually. We also study the changes in a-lifetime with the solar energy supply rate, distribution of solar energy, and the values of a. Our study provides useful guidance in practical deployment of sensor networks with renewable energy sources.

A Survey and Perspective on NVoD Systems for Satellite Networks

In this paper, we review different architectures for near video-on-demand (NVoD) systems on satellite networks. In many scenarios, satellites are the only available option for content distribution. On the other hand, video-on-demand (VoD) has been a topic of intense research in the past. The main problem of VoD systems is that their bandwidth requirements do not scale well with user requests. For this reason, VoD is only feasible under some constraints. In general, NVoD systems are an approximation of VoD ones. In them, downloads do not necessarily start when the request arrives, but some time later. By doing so, it is possible to bound the total required bandwidth at the cost of introducing some delay in content download.

Real-time transcoding and video distribution in IEEE 802.11b multicast networks

In this paper, we propose a real-time transcoding system to generate contents for mobile networks. Video transcoding is widely used to change storage formats. However, as far as the authors know, it has not been proposed to generate real-time contents. We implement and evaluate an indoor video service that delivers transcoded contents to wireless pocket PCs via IEEE 802.11b multicast. We propose a generic methodology for mobile video planning.

A zero-overhead error-correcting nVoD schema

In this paper we present a novel multicast near-Video on Demand (nVoD) coding schema, which relies on the intrinsic redundancy of the underlying nVoD protocol to provide implicit error correction, by employing content segments as blocks for coding operations. As a result, this implicit error correction has zero overhead, unlike the direct application of error-correcting codes, which increase content bitrate in the same proportion as target error probability. The findings in this paper indicate that our proposal outperforms previous approaches with explicit error correction (error protection within content segments) in terms of transmission bandwidth for the same packet loss probability. We present an analytical approach that can be used to tune implicit error correction (coding matrix selection), which we validate with simulations. We also simulate the impact of the coding schema on two different nVoD protocols, fast broadcasting (FB) and recursive frequency splitting (RFS). Finally, we show the benefits of applying this schema to a real scenario with WiMax transport.

A packet snif.ng and synchronization technique to boost P2P satellite networks

In this paper we propose a collaborative technique called P2P-SatBoost to improve the performance of P2P protocols over satellite networks, and we evaluate it from the perspective of user satisfaction. Highly asymmetric satellite IP connections (satellite downlink and POTS uplink, for example) may be the only reasonably fast access possibility for users in remote regions, especially in the third world. Our technique exploits user ubiquitous access (within a given satellite footprint) and it relies on packet sniffing and any synchronization protocol between peers. We provide a brief description of the packet sniffing procedure and propose a synchronization protocol. The simulation results indicate that joint packet sniffing and synchronization can substantially speed up P2P downloads