Fausto Vieira

How feasible is network coding in current satellite systems

The benefits of network coding in terms of throughput, security and robustness are well understood for a large class of networks, such as wireless mesh networks and peer-to-peer systems. We ask if similar performance enhancements can be attained in satellite based communications. Our feasibility study focuses on GEO satellite communication systems including regenerative payloads and multi spot-beam satellites. In addition, we consider LEO satellite constellations with multi-path scenarios. Our analysis reveals that several network coding techniques are worthy of consideration for new generation satellite systems with highly dynamic and unpredictable behavior.

Network Coding Multicast in Satellite Networks

The broadcast nature of satellite networks such as DVB-RCS based systems provides a highly effective medium for content distribution, especially in the case of geographically scattered clients. Non-real-time services typically rely on application level protocols that often use forward error correction (FEC) and carousel data cycling schemes in unidirectional links. The presence of a feedback channel in satellite networks is mostly unexploited in the context of reliable multicast services. We show that network coding protocols offer a native and transparent solution for reliable multicast over satellites. When employing a feedback channel, network coding can reach near real-time performance at an efficiency level close to known theoretical bounds for lossy satellite links.

Codes and balances: Multibeam satellite load balancing with coded packets

Aiming to exploit the capabilities of next generation terminals to receive and process several, partially overlapping beams of a multibeam satellite, we present a mathematical analysis and propose algorithms to provide enhanced and robust load-balancing to unequal load demands between beams. At the core of our mechanisms is a resource allocation problem that aims to minimize the time to deliver packets taking into account the load (traffic demands) per beam and channel conditions. Network coding is a key enabler of our mechanism, allowing a seamless and efficient exploitation of the multiple, available paths from satellite gateways to end-users and leading to a more efficient allocation of resources in each beam. Advantages over current state-of-the-art for load balancing for multibeam satellites include: i) cooperation amongst neighboring beams to improve system stable throughput, ii) use of random linear network coded packets to enhance reliability and simplify the allocation of packets to the different beams, and iii) adaptation to short-term dynamics of the traffic of each beam, instead of only long term traffic characteristics. We provide numerical results for the case of a multibeam satellite covering Europe with 70 beams showing that our technique can increase the stable throughput by 30% or higher with respect to current techniques.

A mobile sensing architecture for massive urban scanning

Mobile Sensor Networks based on connected vehicles and smart phones are poised to become key enablers in the development of sustainable and intelligent transportation systems in urban environments. By gathering and processing massive amounts of data in real-time, this form of information and communication infrastructure can be instrumental towards improving traffic flow, reducing carbon emissions and promoting multi-modal mobility and enhanced coordination among public transit systems. We propose a system architecture for a Massive Multi-Sensor Urban Scanner capable of acquiring large quantities of real-time information from a vast variety of sources and sending the data to a back-end data processing cloud using multiple communication interfaces. Requirements, technical challenges, design choices and first results are explained in detail based on a prototype that is currently being deployed in Porto, Portugal.

VNS: An integrated framework for vehicular networks simulation

Vehicular networks are becoming one of the most important emerging technologies to enable Intelligent Transportation Systems (ITS). A strong research effort has been made in the last few years in the design and development of new systems using vehicle-to-vehicle or vehicle-to-infrastructure communications. Therefore, a large-scale evaluation of these networks is of critical importance. However, due to the prohibitive costs of real test-beds, computer simulation is the only viable solution. Building upon previous work, we extend the state-of-the-art in the field of vehicular simulation by proposing an integrated framework for Vehicular Networks Simulation (VNS). The key point of this framework is the complete integration between the mobility and network components, given the fact not only the networking dynamics are greatly dependent on the mobility aspect, but also the network-enabled applications can influence the mobility patterns of ITS systems. Finally, to demonstrate the capabilities of this framework, we provide a large-scale analysis of 802.11p-based communications when used for the exchange of status advertisements between vehicles. We ran simulations for different scenarios including the urban scenario of the city of Porto with a realistic mobility pattern.

The See-Through System: From implementation to test-drive

Cooperative awareness in vehicular networks is probably the killer application for vehicle-to-vehicle (V2V) communications that cannot be matched by infrastructure-based alternatives even when disregarding communication costs. New and improved driver assistance systems can be introduced by extending their reach to sensors residing in neighboring vehicles, such as windshield-installed cameras. In previous work, we defined theoretical foundations for a driver assistance system that leverages on V2V communication and windshield-installed cameras to transform vision-obstructing vehicles into transparent tubular objects. We now present an implementation of the actual See-Through System (STS), where we combine the communication aspects with the control and augmented reality components of the system. We present a validation methodology and test the system with multiple vehicles on a closed road segment. This evaluation shows that the STS is able to increase the visibility of drivers intending to overtake, thus increasing the safety of such critical maneuvers. It also shows that Dedicated Short Range Communication (DSRC) provides the required latency for this delay-critical inter-vehicle communication, which could hardly be guaranteed with infrastructure-based communication technologies.

Load-aware soft-handovers for multibeam satellites: A network coding perspective

Driven by the increasing demand of Internet anywhere and anytime, mobile broadband services are set to represent an important share of the satellite traffic due to the availability advantages of satellite networks. These services require a robust and flexible mobility support mechanism, which includes efficient soft-handovers between beams. The latter poses important practical challenges at a physical and network level in order to provide two simultaneous connections to a mobile terminal via two different beams. From a network perspective, typical soft-handover algorithms require the system to transmit repetitions of the packets over both connections. Our approach breaks with this concept by considering soft-handovers as a resource allocation problem driven by the uncertainty of terminal mobility and the time-varying nature of loads in a multibeam satellite system. We propose a set of techniques and algorithms that provide load-aware soft-handovers for multibeam satellites that exploit the ability of advanced terminals to receive and process several overlapping beams. To provide a flexible resource allocation mechanism that exploits multiple routes, we rely on packet-level coding techniques, such as network coding, in order to increase robustness and relax the allocation problem. An advantageous collateral effect of our algorithms is the provision of load balancing between beams in satellites with conventional payloads. We provide simulation results for the case of a multi-beam satellite covering Europe with 70 beams serving fixed and mobile terminals that illustrate that our techniques can increase overall throughput by (i) reducing the resources allocated to each terminal for roaming support when compared to state-of-the-art soft-handover mechanisms, and (ii) spreading the load to beams with light traffic requirements.

Link layer FEC for quality-of-service provision for Mobile Internet Services over DVB-S2

This paper presents the performance that can be achieved when applying forward error correction (FEC) at the link layer (LL) level for Digital Video Broadcasting (DVB)-S2-based transmission to attain reliable reception in mobile environments. Our scenario of interest is the interactive railway scenario with two different channel assumptions: Line-of-Sight together with the effect of railway Power Archers (LOS+PA) and non-Line-of-Sight (nLOS). We analyze the performance and compatibility of the different LL-FEC schemes already available in the DVB family of standards: Multiple Protocol Encapsulation-FEC (MPE-FEC) and MPE Inter-Burst FEC (MPE-IFEC). We compare their performance when adopting Reed-Solomon (RS) or Raptor FEC Codes. Both theoretical and simulation analysis reveal that LL-FEC can overcome the fade in the railway scenario by selecting appropriate FEC codes. The solution finally adopted by the DVB-RCS+M standard is discussed and two cross-layer transmission architectures are presented that allow adaptive Quality-of-Service provision over generic LL encapsulation. Copyright

Network coding delay: A brute-force analysis

Understanding the delay behavior of network coding with a fixed number of receivers, small field sizes and a limited number of encoded symbols is a key step towards its applicability in real-time communication systems with stringent delay constraints. Previous results are typically asymptotic in nature and focus mainly on the average delay performance. Seeking to characterize the complete delay distribution of random linear network coding, we present a brute-force methodology that is feasible for up to four receivers, limited field and generation sizes. The key idea is to fix the pattern of packet erasures and to try out all possible encodings for various system and channel parameters. Our findings, which are valid for both decoding delay and ordered-delivery delay, can be used to optimize network coding protocols with respect not only to their average but also to their worst-case performance.

A non-intrusive multi-sensor system for characterizing driver behavior

Understanding driver behavior is critical towards ensuring superior levels of safety and environmental sustainability in intelligent transportation systems. Existing solutions for vital sign extraction are generally intrusive in that they affect the comfort of the driver and may consequently lead to biased observations. Moreover, low-complexity devices such as GPS receivers and the multitude of sensors present in the vehicle are yet to be exploited to the full extent of their capabilities. We present a real-life system that combines wearable non-intrusive heart wave monitors with a wireless enabled computing platform capable of gathering and processing the data streams of multiple in-vehicle sources. Observed variables include electrocardiogram, vehicle location, speed, acceleration, fuel consumption, and pedal position, among others. Preliminary results show that the proposed system is well suited not only for characterizing driver behavior but also for identifying and mapping potentially dangerous road segments and intersections.