David Gozalvez

Application Layer FEC for Mobile TV Delivery in IP Datacast Over DVB-H Systems

In this paper we investigate the potential gain that can be obtained in DVB-H using application layer forward error correction (AL-FEC) to perform a multi-burst protection of the transmission for improving the reception of streaming services for mobile terminals. Compared to the conventional approach with link layer multi protocol encapsulation FEC (MPE-FEC), this technique allows to increase the robustness of the DVB-H transmission not only as a function of the capacity devoted for error repair (FEC overhead), but also as a function of the number of bursts jointly encoded. The main drawback of this approach is an increase of the network latency, that can be translated into a larger service access time, and, in the case of mobile TV, a larger zapping time between channels, which is currently seen as a crucial parameter for DVB-H usability. In this paper the performance of the proposed approach is evaluated using field measurements. We evaluate the gain compared to MPE-FEC in terms of reduced IP packet error rate of the streaming service as a function of the FEC overhead and the latency introduced. Moreover, simulations have been performed to quantify feasible link margin gains. We also discuss techniques to reduce and hide the zapping time from the perception of the users.

AL-FEC for Improved Mobile Reception of MPEG-2 DVB-T Transport Streams

We investigate the use of application layer FEC protection in DVB-T (Digital Video Broadcasting-Terrestrial) networks for the provision of mobile services. Mobile reception is characterized by variations of the received signal caused by fast fading and shadowing. DVB-T was originally designed for fixed and portable reception, and generally does not provide enough quality in mobile environments. The link layer protection mechanism MPE-FEC (Multi Protocol Encapsulation-Forward Error Correction) was standardized in DVB-H (Digital Video Broadcasting-Handheld) for the protection of mobile TV services. Although DVB-T itself does not incorporate any link or application layer protection mechanism, AL-FEC (Application layer Forward Error Correction) protection can be introduced in DVB-T in a backwards compatible way. By means of AL-FEC, it is possible to improve the robustness of DVB-T services for the provision of mobile TV. In this paper, we explain the concept of AL-FEC protection in DVB-T and evaluate its performance by means of laboratory measurements and dynamic simulations with shadowing. We study different configurations of AL-FEC and compare its performance with MPE-FEC. In this paper, we discuss some implementation aspects of AL-FEC in real scenarios and propose an implementation based on Raptor codes and hash sequences. We also present results obtained by a first AL-FEC prototype for DVB-T that demonstrates the feasibility of the approach.

MIMO for DVB-NGH, the next generation mobile TV broadcasting [Accepted From Open Call]

DVB-NGH (Digital Video Broadcasting - Next Generation Handheld) is the next generation technology for mobile TV broadcasting, which has been developed by the DVB project with the most advanced transmission technologies. DVB-NGH is the first broadcasting standard to incorporate multiple-input multiple-output (MIMO) as the key technology to overcome the Shannon limit of single antenna communications. MIMO techniques can be used to improve the robustness of the transmitted signal by exploiting the spatial diversity of the MIMO channel, but also to achieve increased data rates through spatial multiplexing. This article describes the benefits of MIMO that motivated its incorporation in DVB-NGH, reviews the MIMO schemes adopted, and discusses some aspects related to the deployment of MIMO networks in DVB-NGH. The article also provides a feature comparison with the multi-antenna techniques for 3GGPs LTE/LTE-Advanced for cellular networks. Finally, physical layer simulation results calibrated within the DVB-NGH standardization process are provided to illustrate the gain of MIMO for the next generation of mobile TV broadcasting.

Mobile reception of DVB-T services by means of AL-FEC protection

This paper proposes and investigates the use of Application Layer Forward Error Correction (AL-FEC) based on Raptor codes for digital television DVB-T (Digital Video Broadcasting - Terrestrial) services. By means of AL-FEC it is possible to increase the robustness of traditional DVB-T transmissions for the provision of mobile TV. The AL-FEC protection is introduced in a backwards compatible way with the legacy DVB-T standard and does not alter the originally transmitted multimedia data. In order to evaluate the performance of AL-FEC in mobile channel environments, we employ laboratory measurements along with dynamic shadowing simulations. The paper presents direct comparisons with the link layer protection mechanism of DVB-H - referred to as MPE-FEC (Multi Protocol Encapsulation - Forward Error Correction) - and illustrates the link margin gains that can be achieved in mobile DVB-T reception by means of AL-FEC.

Time Diversity in Mobile DVB-T2 Systems

DVB-T2 implements a very flexible time interleaving that allows multiple tradeoffs in terms of time diversity, latency and power saving. In this paper, we study in detail these tradeoffs in the context of mobile reception. Together with time diversity, we also investigate the impact of reduced time de-interleaving memory and Alamouti-based MISO in the mobile reception of DVB-T2 services. In addition, we propose the utilization of upper layer FEC protection in order to overcome the limitations of the DVB-T2 physical layer for the provision of long time interleaving, and enable fast zapping. The performance is evaluated by means of simulations in mobile channels that include the presence of fast fading and shadowing in the received signal.

Safety on the Roads: LTE Alternatives for Sending ITS Messages

This article discusses different alternatives for sending intelligent transportation systems (ITS) messages using long-term evolution (LTE) networks. Specifically, it compares the unicast and evolved Multimedia Broadcast Multicast Services (eMBMS) transmission modes by means of system-level simulations and a cost modeling analysis. The optimum configuration of the eMBMS carrier is studied for the case of ITS services. This article also includes some recommendations on the configuration of the ITS server in charge of distributing safety messages as well as on its interaction with the mobile network operator (MNO). The results show that eMBMS is significantly more efficient in terms of resource consumption than the unicast mode, implying an important reduction of the delivery costs.

Rotated Constellations for Improved Time and Frequency Diversity in DVB-NGH

In this paper, we investigate the potential gains that can be obtained with rotated constellations in DVB-NGH, the next-generation mobile broadcasting standard. Rotated constellations exploit the concept of signal-space diversity (SSD) to increase the diversity order of bit-interleaved coded modulation (BICM) at the expense of higher demodulation complexity without the need of additional transmission power or bandwidth. Two-dimensional rotated constellations (2DRC) were originally included in DVB-T2 (terrestrial second generation) to improve the reception robustness in fading channels. DVB-NGH inherits the same 2DRC from DVB-T2 and includes four-dimensional rotated constellations (4DRC) for certain configurations. Moreover, the standard has adopted a new component interleaver optimized for the utilization of rotated constellations with long time interleaving (TI) and time-frequency slicing (TFS). In this context, the additional robustness of rotated constellations is very interesting to counter the presence of signal outages in the time and frequency domains. To investigate the potential gains of 2DRC and 4DRC, we employ an information-theoretic approach based on mutual information, as well as physical layer simulations in DVB-NGH systems. The results reveal that rotated constellations are important to increase the diversity gains of long TI and TFS, and also to reduce the zapping time perceived by the users.

Combined Time, Frequency and Space Diversity in DVB-NGH

In this paper, we investigate the combined use of time, frequency, and space diversity in DVB-NGH, the next generation mobile broadcasting standard. Compared to current standards like DVB-H or DVB-SH, the largest improvement in next generation systems is expected to be achieved by means of better diversity in the time, frequency, and space domains. In this sense, DVB-NGH is the first broadcasting system to exploit the use of diversity in the three domains by incorporating at the physical layer long time interleaving (TI), time-frequency slicing (TFS), and multiple-input multiple-output (MIMO). This paper investigates the gains of using time, frequency, and space diversity in DVB-NGH, as well as the mutual influence between the different types of diversity. To this purpose, we employ an information-theoretic approach based on the outage capacity of the channel in addition to physical layer simulations.

AL-FEC for streaming services in LTE E-MBMS

Abstract3rd Generation Partnership Project specified Application Layer - Forward Error Correction (AL-FEC) to be used for Enhanced Multimedia Broadcast Multicast Services (E-MBMS) in Long Term Evolution (LTE) networks. Specifically, Raptor coding is applied to both streaming and file delivery services. This article focuses on streaming services and investigates the optimum configuration of the AL-FEC mechanism depending on the signal-to-interference plus noise power ratio conditions. These configurations are compared with a scenario without an application layer protection to obtain the potential gain that can be achieved by means of AL-FEC. This article also studies the multiplexing of services within the AL-FEC time interleaving. These analyses were performed using a proprietary system level simulator and assuming both pedestrian and vehicular users. Different quality criterions were used to ensure the completeness of the study. Results show the significant benefit of using AL-FEC in E-MBMS in terms of coverage and service quality.

Performance evaluation of the MPE-iFEC Sliding RS Encoding for DVB-H streaming services

This article studies the performance of the Sliding RS Encoding (SRSE) in the transmission of streaming services in DVB-H (Digital Video Broadcasting - Transmission System for Handheld Terminals) networks. The SRSE forms part of a set of specifications called MPE-iFEC which has been recently defined in the DVB-SH (Digital Video Broadcasting - Satellite Services to Handheld Devices) standard and is fully compatible with the link layer of DVB-H. MPE-iFEC is capable of encoding information related to different datagram bursts in a jointly manner in order to counteract the long signal blockages expected in satellite reception. This is what is usually referred to as Multi-Burst Encoding (MBE) and provides a protection that extends across several time sliced bursts. MBE can also improve the reception in terrestrial networks such as DVB-H, which relay in the use of MPE-FEC (Multi Protocol Encapsulation - Forward Error Correction) for link layer protection. The SRSE employs the same Reed Solomon (RS) algorithm used in MPE-FEC and a sliding encoding mechanism in order to perform MBE. This paper evaluates the improvements that the use of SRSE can achieve over the legacy MPE-FEC using vehicular urban field measurements in a DVB-H single frequency network. The effect of the different parameters that regulate the operation of the SRSE will be evaluated and the best configurations for its use in DVB-H will be highlighted.