Universidad
Politécnica de Madrid

As on other occasions, this pilot has been possible thanks to the collaboration of all the members that make up the Chair's Advisory Committee on technological aspects: Cellnex Telecom, Dolby, Sapec and the Televés Corporation (Gsertel, TRedess and Televés), as well as Abacanto as a supporting entity. SONY collaborated in the capture of the signal, and SGO and Abacanto collaborated in the post-production of the signal.  The visualization of the signal was done by Samsung, who prepared a Samsung QLED 8K model adapted for the occasion.

Given the current circumstances marked by the situation of the COVID-19, and following the appropriate recommendations and security measures, an event was organized in which the attendees could follow the event remotely, thanks to the streaming signal provided by the Official Institute of RTVE.
The event took place at the Official Institute of RTVE. In order to make the event more dynamic and entertaining, the format chosen was that of a talk show, in which a moderator (played by Carlos Garrido, Director of Media Relations and Institutional Coordination of the RTVE Corporation) interviewed a small number of participants who explained the technical characteristics of the pilot broadcast.

The event was opened by Federico Montero, Corporate General Director of RTVE, who highlighted the importance of innovation for a company such as RTVE, which operates in a sector in constant evolution. He underlined the importance for RTVE of carrying out this type of pilot projects with other companies and universities, in an open manner, always with the aim of acquiring new experiences and knowledge, and enriching both RTVE and the audiovisual sector, in general. Additionally, being pioneers in 8K broadcast pilots, at a world level, the international projection of the corporation is increased, which is established as a reference in audiovisual innovation in Europe.

"For TVE it is an honor to participate with this RTVE Chair at UPM, and with the rest of the companies that participate in this broadcast in 8K. Public Television is and has to be at the forefront of these events. RTVE is always a pioneer in the development of new technologies," explained the director of Televisión Española, David Valcarce.

Adolfo Muñoz, Director of Broadcasting and Networks of RTVE presented, in a general way, the broadcast pilot, describing the signal capture process carried out by RTVE thanks to the collaboration with SONY, and the post-production carried out with the help of SGO. He highlighted the importance of this pilot which demonstrates something that has been questioned by some, namely the possibility of broadcasting via DVB-T2 a high quality 8K signal, and ended by pointing out the next signal transport pilots that the Catedra RTVE is working on at the UPM, making use of 5G networks.

José Manuel Menéndez, Full Professor of Telecommunications Engineerin. and Director of the RTVE Chair at the UPM, highlighted the importance, both from a teaching and a research point of view, of the pilot experiences that are dealt with in the Chair, due to their innovative and formative aspect for the participants in the Chair (professors, researchers and students in general) and for the dissemination of information for the entire audiovisual sector. He highlighted the advantages of the quality of the QoE experience, which implies enjoying an 8K signal and everything that it can bring, including HDR, WCG, HFR and improved audio structured in objects, always understood as a premium TV signal that boosts the immersivity experience.

The detailed technical description of the process followed until the end of the pilot was opened by Miguel Angel Doncel, CEO of SGO, who explained how the industry is adapting to this type of content, as well as the technological challenges involved in handling so much information in real time, and also how to do it in a way that is transparent to the user. He also stressed the importance of combining these technical challenges with the traditional operations of the sector in a way that is transparent to the user, maintaining workflows that are conceptually similar to the current ones, and managing specific complexities in a way that is transparent to the user - all of this to facilitate the adaptation of users to this technology.

Miguel Ángel Cristóbal, CEO of Sapec, commented on the challenge of transmitting an 8K signal by any means and especially in DTT, but explained how compression technology with HEVC and modulation technology with DVB-T2 have been able to solve them. In the area that has corresponded to Sapec, the codification in HEVC, the main complexities that have been faced have been

• Compressing the UHD-8K signal, which represents more than 33 Gbps of video, into less than 33 Mbps, while maintaining the video quality required by a signal of these characteristics. This data yields a superior compression ratio of 1000:1. This challenge has led SAPEC to perfectly adjust all the parameters that improve HEVC encoding and optimize them to achieve it.
• Handling the huge amount of bits that a UHD-8K (48 Gbps) signal generates, since UHD-8K generates 50 images of 32 Mpixels (that's 32 times more than the HD signal).
• The necessary computing capacity. It was estimated that this capacity would be higher than about 6 times the one needed to encode UHD-4K, so formulas have been sought to parallelize the processes.

Javier Foncillas, Vice-President Commercial Partnerships Europe of the company Dolby, highlighted that the use of the AC-4 audio codec provides improved audio quality, facilitates accessibility features and great ease of integration into current distribution media, thus taking advantage of the current plant of televisions available that already integrate this new standard.

Regarding the broadcast made via DVB-T2, Miguel Angel Bona San Vicente, Head of DTT and Satellite Platform Planning Unit of RTVE, commented on the viability of DTT to broadcast 8K content because it is still an innovative and flexible platform that is prepared for the challenges of the future. In his speech he highlighted that, currently, both the technology and the regulatory framework already allow DTT to have the capacity to continue evolving and to support this type of 8K broadcasts, provided that spectrum is available and the most efficient technologies are used with the spectrum -such as DVB-T2- and the most advanced video coding systems.

Álvaro Llorente, researcher of the Visual Telecommunications Application Group of the E.T.S. of Telecommunication Engineers of the UPM, and member of the Chair, stressed the need to always monitor the quality with which the signal is being emitted to avoid possible degradations, and described the equipment that had been used to monitor the emission, highlighting the equipment of the Televés Corporation, specifically of the company Gsertel, with a portable measuring instrument Hexylon and another one for RCS monitoring, specially configured and adapted for this pilot emission.

During the event, attendees were able to view the UHD signal in 8K. This resolution is characterized by images of 7680x4320 pixels, four times the resolution of UHD in 4K. The signal, besides having 8K resolution, includes new technologies such as:

• High Dynamic Range (HDR) with the HLG (Hybrid Log-Gamma) transfer function approved in the STD-B67 standard by the ARIB (Association of Radio Industries and Businesses)
• 50 frames per second refresh rate (HFR - High Frame Rate)
• Extended color gamut (WCG - Wider Color Gamut) following the ITU-R BT.2020 recommendation color space, 10-bit depth and 4:2:0 subsampling.
• Multichannel audio 5.1.4.

Given the amount of information contained in the signal, very efficient standards are needed to compress and transmit signals with these types of characteristics. Therefore, the HEVC standard (already in use by the manufacturers) has been used for video encoding, the Dolby AC4 standard as an audio encoding format to ensure maximum compression and quality, and the DVB-T2 standard for the transmission of the content.

Regarding the video signal, according to the first tests and using the HEVC standard, the encoding with 8K resolution requires more than twice the bit rate to maintain the same quality compared to 4K resolution video. The bit rate required to transmit live 8K resolution video, with optimal quality, would be between 60 and 80 Mbps. However, with a proper adjustment of the compression parameters, it has been possible to compress at an average bit rate of 30 Mbps of video preserving high viewing quality and, once multiplexed with the audio channels and DVB tables, to keep below 32 Mbps, which has allowed the transmission on the DVB-T2 channel with the specifications detailed below.

In relation to the broadcast of the content, the signal was radiated from the TV head-end of the UPM Telecommunications Engineering School, located in the University City of Madrid, on channel 44 of the UHF, temporarily assigned to the RTVE Chair at the UPM by the State Secretariat of Telecommunications and Digital Infrastructures - SETID - for its test broadcasts. The 8K signal was also broadcasted on the UHD channel broadcast by Cellnex Telecom from the broadcasting centers of Torrespaña and San Fernando de Henares in Madrid, on channel 36; Collserola and Baix Llobregat in Barcelona, on channel 43; Valencina in Seville, on channel 36; Mijas in Malaga, on channel 26; Monte Pedroso in Santiago de Compostela, on channel 33; and La Muela in Zaragoza, on channel 23.

From a technical point of view, the resulting bit rate of the audiovisual content was around 32 Mbps. The COFDM modulation parameters used for transmission via DVB-T2 from the UPM were: 32k extended, guard interval of 1/128 and PP7 pilot pattern. A single PLP configuration was used, with 64QAM modulation and 5/6 FEC. With this configuration, a maximum useful binary rate of around 36 Mbps was obtained, which was valid for transmitting the content without any problem and for correctly receiving the signal at the RTVE Institute. For the UHD channel broadcast by Cellnex Telecom, the modulation parameters used for DVB-T2 transmission were: 32K Ext. 256QAM 2/3 GI 1/8 PP2 SISO. This is also a valid configuration for supporting bit-rate requirements, while committed to maintaining larger scale coverage and service resilience.

The reception and visualization of the content was possible thanks to the participation of the manufacturer Samsung, which adapted one of its commercial models Samsung QLED 8K to be able to complete the transmission-reception chain, and thus visualize the emitted 8K signal. "Users want to enjoy an image with the highest possible resolution, as conceived by its creators. That is why we are working with the industry to implement this technology and create as much 8K resolution content as possible. Says Nacho Monge, TV & AV Marketing Manager of Samsung Electronics Iberia. "For this project we have adapted our television with QLED 8K technology, a television with premium image quality, to be able to appreciate a real 8K resolution with 100% of the color volume, and HDR technology".

For the continuous monitoring and supervision of the signal, a Hexylon laptop and an RCS-100 from the company Gsertel (Televés Corporation) have been used, so that all the relevant parameters of the digital channel are analyzed in real time, both from the point of view of radio frequency, as well as content characteristics.

In the days following the pilot, and until October 30th, 2020, any person who wishes to do so may watch in situ, in the hall of the Official Institute of RTVE (Carretera de la Dehesa de la Villa, nº 14, 28040 Madrid), the screens with the 8K signal emission. Visitors must provide their personal data to the staff at the entrance for security reasons.

This pilot project is part of the activities of the Cátedra RTVE at the Universidad Politécnica de Madrid, set up in January 2015, which has participated in the development of a wide range of experiences in the field of UHD signal production and broadcasting during the last few years.