Francisco Fraile

Analysis and Evaluation of Adaptive LDPC AL-FEC Codes for Content Download Services

This paper proposes the use of adaptive low density parity check (LDPC) application layer-forward error correction (AL-FEC) codes for content download services over erasure channels. In adaptive LDPC codes, clients inform the content download server of the losses they are experiencing. Using this information, the server makes forward error correction (FEC) parity symbols available to the client at an optimum code rate. This paper presents an analytical model of the proposed adaptive LDPC codes. The model is validated through measurements realized with an application prototype. In addition, results show the performance of these codes in different scenarios, compared to the performance of nonadaptive AL-FEC, optimum LDPC AL-FEC codes, and an almost ideal rateless code. Adaptive LDPC AL-FEC codes achieve download times similar to almost ideal rateless codes with less coding complexity, at the expense of an interaction channel between server and clients.

Evaluation of Background Push Content Download Services to Mobile Devices Over DVB Networks

This paper proposes a multicast content download service based on the use of residual network capacity to push multimedia content to available local storage in personal multimedia devices. The service under study is based on the FLUTE protocol. Specifically, FLUTE packets fill the spare capacity in the IP tunnels reserved for the primary streaming service (opportunistic insertion). The paper also evaluates the use of application layer-forward error correction (AL-FEC) parity to overcome transmission errors, object multiplexing to send the most popular multimedia contents more frequently and cache management policies that consider user preferences to keep in storage the most useful items. The service has been evaluated through simulations and measurements performed with an application prototype based on the DVB-H standards. The results show that AL-FEC enables the use of residual capacity for background content download services. In turn, AL-FEC, as well as object multiplexing, improves the relation between the number of content items and the overall access time. Moreover, results show that high percentages of requests can be served from the local cache of the service, provided that it is possible to estimate the popularity of content items and the user preferences.

Performance evaluation of AL-FEC LDPC codes for push content applications in wireless unidirectional environments

FEC (Forward Error Correction) mechanisms improve IP content transmission reliability through the recovery of packets lost in transmission. Opposite to ARQ (Automatic Repeat Request), FEC mechanisms are especially suited to unidirectional environments or to multicast environments where multiple receivers perceived different channel losses, thus making difficult the implementation of mechanisms based on feedback information. Among the different types of FEC codes, this paper presents a thorough performance evaluation of LDPC (Low Density Parity Check) codes, based on an implementation developed by the authors, according to the specifications defined by RFC 5170 for the usage of LDPC codes by push content applications based on the FLUTE protocol. LDPC codes provide a good trade-off between performance and complexity, hence, they are appropriate for mobile applications. Contributions of this paper include tests conducted with commercial mobile phones connected to the push content download server over a Wi-Fi network. The evaluation highlights the advantages of using packet level FEC encoding in file transmission over unidirectional networks and provides with a comparison between two kinds of LDPC structures: Staircase and Triangle. This is accomplished by calculating the inefficiency ratio of these LDPC structures in different environments. Results show that the implemented LDPC codes can provide inefficiency ratios close to one when the different coding parameters (as the code rate or the number of blocks) are configured to an optimal value that depends on the packet loss rate.

Efficient interactive multicast over DVB-T2 - Utilizing dynamic SFNs and PARPS

In the terrestrial digital TV systems DVB-T/H/T2, broadcasting is employed, meaning that all TV programs are sent over all transmitters, also where there are no viewers. This is inefficient utilization of spectrum and transmitter equipment. Applying interactive multicasting over DVB-T2 is a novel approach that would substantially reduce the spectrum required to deliver a certain amount of TV programs. Further gain would be achieved by Dynamic single-frequency network (DSFN) formations, which can be implemented using the concept of PARPS (Packet and Resource Plan Scheduling). A Zipf-law heterogeneous program selection model is suggested. For a system of four coordinated transmitters, and certain assumptions, IP multicasting over non-continuous transmission DSFN gives 1740% increase in multiuser system spectral efficiency (MSSE) in (users·bit/s)/Hz/site as compared to broadcasting over SFN.

Effect of the FDT transmission frequency for an optimum content delivery using the FLUTE protocol

File Delivery over Unidirectional Transport (FLUTE) is the standard protocol used in unidirectional environments to provide reliability in the transmission of multimedia files. The key element of this protocol is the use of the File Delivery Table (FDT), which is the in-band mechanism used by FLUTE to inform clients about the files (and their characteristics) transmitted within a FLUTE session. Clients need to receive the FDT in order to start downloading files. Thus, the delivery of FDT packets and the proper configuration of their parameters have a great impact on the Quality of Experience perceived by the users of FLUTE content download services. This paper presents a complete analysis about how the FDT transmission frequency affects the download time of files. Moreover, results show which are the optimum values that minimize this download time. An appropriate configuration of the FDT transmission frequency as well as the use of AL-FEC mechanisms provides an optimum content delivery using the FLUTE protocol.

Hybrid FLUTE/DASH video delivery over mobile wireless networks

This paper describes how File Delivery over Unidirectional Transport FLUTE and Dynamic Adaptive Streaming over Hypertext Transfer Protocol DASH can be used to provide mobile video streaming services over broadcast wireless networks. FLUTE is a multicast protocol for multimedia file download. In this proposal, the protocol is adapted to provide video streaming services in crowded environments. Thus, video is delivered over a single connection to all viewers, reducing the traffic in the network. FLUTE incorporates an application-layer forward error correction AL-FEC mechanism in order to improve the reliability of the broadcast communication channel. For streaming applications, AL-FEC improves the relationship between the peak signal-to-noise ratio PSNR of the received video and the bandwidth allocated to the broadcast connection. The AL-FEC hereby presented applies simple unequal error protection schemes to favour the download of key frames. Furthermore, the proposal is based on the same video segmentation mechanism as DASH, and therefore, clients can connect to a DASH repository to repair errors in the segments. This paper shows that FLUTE and DASH can be seamlessly integrated into a hybrid broadcast/unicast streaming technology, providing flexibility to trade off PSNR and bandwidth depending on the conditions of the mobile network. Copyright

Simple models of the content duration and the popularity of television content

This paper presents parametric statistical models for the content duration (running length) and the popularity of TV programs. The parameters of the models are obtained by curve fitting data obtained from the Internet Movie DataBase (IMDB). Later, the accuracy of the models is numerically assessed, providing an estimation of the error, together with a use case example. The content duration model has been obtained exclusively from the actual duration of TV programs, which is intrinsic to the content, instead of the file size of encoded videos which is application dependent. It is also worth emphasizing that, unlike several previous studies, the model does not account for User Generated Content. The model can be used to obtain the file sizes of video items in video delivery services for different formats or resolutions, by applying their characteristic video encoding rates. On the other hand, this paper shows parametric popularity models adjusted to fit the distribution of user ratings in the IMDB database. The popularity models can be used to estimate the probability of access of programs in video on demand services. Therefore, the content duration and popularity models hereby presented are useful to evaluate the performance of video delivery services dealing specifically with TV content.

Evaluation of a background push download service for personal multimedia devices

This paper presents the evaluation of an IP-multicast push download service for personal multimedia devices. The service under study uses residual bandwidth in communication networks (in this case, terrestrial broadcast) to push multimedia content to storage capacity in personal multimedia devices. The service has been evaluated through an application prototype for mobile TV systems. Results show that the addition of AL-FEC mechanisms achieves constant effective transmission rates, independently of the size of the content sent.

On the reuse of DVB-T transmitter infrastructure for DVB-T2

The new DVB-T2 standard was specifically designed to allow the reuse of DVB-T infrastructure if required. This paper presents measurement results that verify the correct performance of a commercial DVB Power Amplifier with DVB-T2 waveforms. Furthermore, the paper includes configuration guidelines and performance evaluation of the Tone Reservation PAPR reduction algorithm included in the DVB-T2 standard. PAPR reduction is key technology when reusing DVB-T amplifiers for DVB-T2 transmissions without penalizing amplifier efficiency.

Evaluation of adaptive LDPC AL-FEC codes for content download services

This paper presents a performance analysis of adaptive LDPC AL-FEC codes for content download services over erasure channels. In adaptive LDPC codes, clients inform the content download server of the losses they are experiencing. Using this information, the server makes FEC parity symbols available to the client at an optimum code rate. Results show the performance of adaptive AL-FEC codes for different scenarios as compared to non-adaptive AL-FEC, to optimum LDPC AL-FEC codes and to an almost ideal rateless code. Adaptive LDPC AL-FEC codes achieves download times similar to almost ideal rateless codes with less coding complexity, at the expense of an interaction channel between server and clients1.