ABNT NBR 15601 is the technical standard published by ABNT, the Brazilian Association of Technical Standards (Associação Brasileira de Normas Técnicas), that is responsible for addressing the aspects regarding transmission on the Brazilian Digital Terrestrial Television Standards, also known as SBTVD or ISDB-T version B. The document covers a vast number of issues regarding detailed characteristics of transmitters and is essential to the proper understanding and manufacturing of equipment aimed at Digital TV market in Brazil. The writing and discussions on the technical standard was performed by the SBTVD Forum (Fórum SBTVD). The standard was written by telecommunications and television experts from many countries with their works coordinated by the SBTVD Forum and cover in detail all the aspects of video and audio coding that applies to SBTVD. The complete document can be found and downloaded freely in English, Spanish and Portuguese at ABNT's website. Introduction The transmission aspects of the Brazilian Digital Terrestrial Television Standards are described in the ABNT NBR 15601:2007 - Digital terrestrial television - Transmission system document published by ABNT, the Brazilian Association of Technical Standards (Associação Brasileira de Normas Técnicas). Digital terrestrial television broadcasting in Brazil should be introduced in the VHF/UHF bands and fit into existing 6 MHz channels originally intended for analogue television transmission. The Digital Terrestrial Television Broadcasting service will coexist with existing analogue television transmissions for a temporary period. It was desirable to support the simultaneous transmission of a hierarchy of nested quality levels, including high definition television (HDTV) and standard definition TV (SDTV) within a single channel. Document technical overview The ABNT NBR 15601:2007 - Digital terrestrial television - Transmission system document describes modulation and channel coding for the Brazilian system, which is identical to the Japanese ISDB-T system and ITU-R System C. The transmission system was selected after extensive comparative test and based on the methodology and results of ITU Report BT.2035. Similarly to the European and Japanese approaches it specifies the digitally modulated signal in order to allow compatibility of equipment developed by different manufactures. As a general description, the following processes shall be applied to the transport stream: error-correction coding, time-interleaving and carrier modulation. The channel coding is conducted in units of OFDM segments as in ISDB-T. A set of segments defines a hierarchical layer, where the above-mentioned parameters can be specified independently. Up to three hierarchical layers can be provided, which include the partial reception layer