Techniques to accelerate the transition to a new generation of terrestrial digital tv

Resumen

This thesis explores the problem of compatibility between generations in the field of Digital Television, and proposes solutions to this problem. Since its inception, the DTV has been under development without taking into account the ability to continue receiving broadcasts with legacy equipment when a new generation is introduced. Therefore, when it comes time to introduce a new technology, a simulcast solution is usually used. The study carried out in this thesis explains the reasons why a traditional simulcast is a problem. As a concrete study example, the case of the transition from SD MPEG-2 to HD H.264 broadcasts according to the DVB-T standard is analyzed. And how this problem unnecessarily extends the transition periods between generations. In this way it postulates that one way to promote the development of new generations of Digital Television is precisely to shorten transition times. In order to facilitate the transition to a new generation, different technical solutions have been studied and developed that provide a certain degree of compatibility between generations. The results obtained conclude that it is not only feasible, but also desirable, to incorporate inter-generational compatibility solutions in Digital Television standards. Using the techniques described in this thesis, and others listed as future work, it would be possible for new standards and generations to incorporate this necessary capability. The thesis est omnis divisa in partes tres: Part I, on an analysis of the problems generated by the migration between the different digital television generations; Part II, on a technical description of the different techniques developed to alleviate the difficulties during the transition period; And Part III, describes the future challenges of the inter-generational compatibility in digital television broadcasting, emphasizing different potential solutions to incorporate enhanced functionality to facilitate the path for future generations. This thesis arises from the realization that despite the success of digital television, insufficient specifications to support the migration to new generations has produced a slow adoption of the new standards. Therefore, some solutions are proposed to cover this gap between the different generations of standards. The main idea behind all the proposals is based on the concept of an advanced mixed simulcast instead of the classic full simulcast. This new model is based on mixing elements encoded with technologies from different generations at the same time. The first chapter presents a discussion of the advantages and drawbacks of the current model of development of digital television standards from the point of view of inter-generational compatibility. The conclusion reached is that with the current model it will be possible that the new standards will produce an implosion in digital television broadcasts. The reason is that the market is not evolving as fast as the industry can produce new equipment. Therefore, a different approach is needed for the transition from one generation to the next. The second chapter describes three different techniques on how to improve inter-generational compatibility. The three solutions focus on the transition from MPEG-2 Standard Definition services using DVB-T signals to H.264 High Definition services using the same DVB-T modulation. This is considered the first transition in terrestrial broadcasts using the DVB standard. All solutions have been published in international journals and have been evaluated in different tests. The first idea that emerged was the proposal of a scalable compression of the video using independent codecs. The basis of this is the already known scalable spatial compression, but with the unique feature of not sharing information between encoders. Therefore, the different codecs of each generation can be used without modification. The challenge of this approach is the lossy model used by the current video compression codecs in use in digital television. It is therefore not possible to use a direct differential scalable compression. The proposed solution is a technique to generate a sufficiently robust enhanced secondary stream carrying the enhanced layer of the video that can be encoded using the H.264 codec. Then, the MPEG-2 base layer in SD and the special H.264 enhanced layer are used in the decoder to reconstruct the original video in HD. The bandwidth required to carry the MPEG-2 SD service and the enhanced H.264 layer is then less than the bandwidth required for a full simulcast carrying one MPEG-2 SD service and one H.264 service in HD. All this without the need to modify the codecs in use. The second idea developed in this thesis is a technique for sharing audio tracks between different services. In a regular simulcast —at the technical level— each service is completely independent of the other. However, some parts can be shared. And audio tracks are good candidates. The problem is then how to ensure the correct synchronization of the different sub-streams in the joint digital television services. And therefore a method has been defined to produce MPTS streams with the correct integrity. The challenge in this case is to create these joint services without the need to modify the encoders. The exposed technique guarantees the correct operation and it has been proven that it does not generate problems with the standard decoders. It can therefore be considered completely transparent. Finally, a third idea has been proposed for evaluation. Since a digital TV service is composed of different sub-parts, e.g. video stream, audio tracks, signaling, teletext, subtitles, etc.; the proposed objective was to share all elements between a simulcast service. In this case, if the sum of all the above consumes less bandwidth than a full simulcast, then it will be possible to simulcast more services. After some studies, we have determined that we only need two versions of the video stream to broadcast a service simultaneously with two standards. This is true since all other data can in fact be shared. With the only requirement of keeping the same encapsulation and radio frequency modulation. The objective has then been to produce a joint simulcast employing the same bandwidth as with a single generation of standards. The results obtained have been materialized in the technology called "Aggressive Joint Compression". We demonstrated how to broadcast one MPTS using DVB-T signals including a duplication of the services in SD (MPEG-2) and HD (H.264) over the same space consumed by regular MPEG-2 SD broadcasts. With the particularity of adjusting over time the quality assigned to the SD or HD versions. In the third chapter, with the techniques developed throughout this thesis, different uses of these techniques to accelerate the adoption of new standards in digital television broadcasts are presented. In particular an in-depth study of how to apply them to conclude the transition from MPEG-SD signals in the Spanish DTT. But also to go beyond this and accelerate the next transition to DVB-T2 broadcasts and UHD services. In addition, future open research areas on how to improve the intergenerational compatibility of upcoming standards in the field of digital television are finally described. For example, innovative ideas are presented on how to implement and deploy scalable hybrid models with video encoded using the H.265 and HEVC codecs. Ideas on how to apply hybrid transmission models using mixed coding to deploy mixed DVB-T/T2 networks are presented as well. And arguments are also presented for improving the level of compression using advanced techniques using GPU-based encoders. All this indicates that there is still a long way to obtain a smoother transition between different generations of digital television. The list of the different papers completed during this thesis are listed here: - Soto, Daniel. "Digital Television Backward Compatibility Based on Mixed Simulcast using Independent Scalable Video Coding." SMPTE Motion Imaging Journal 125.9 (2016): 42-56. - Soto, Daniel. "Digital TV simulcast with shared audio streams." 2015 IEEE 5th International Conference on Consumer Electronics-Berlin (ICCE-Berlin). IEEE, 2015. - Soto, Daniel. "Aggressive joint compression for DTV simulcast." Journal of Digital Media & Policy 11.2 (2020): 151-174.