本标准描述了有线频道专用的数字多业务电视分配系统的帧结构、频道编码和频道调制。由于许多电缆系统直接从卫星链路馈电，因此该系统可以通过卫星信道透明地使用。该规范涵盖64和256 QAM。两种调制方案的大多数特征是相同的。如果存在差异，则将介绍每个调制方案的具体细节。 调制、交织和编码的设计基于北美电缆系统的测试和特性。 调制是正交幅度调制，具有64点信号星座（64-QAM）和256点信号星座（256-QAM），发射机可选。前向纠错（FEC）基于级联编码方法，在中等复杂度和开销下产生高编码增益。级联编码以相似的总体复杂度提供了比分组码更好的性能。系统FEC优化为准无错误操作，阈值输出错误事件率为每15分钟一个错误事件。 调制和编码输入的数据格式假定为MPEG- 2.交通。然而，用于MPEG同步的方法与FEC同步是解耦的。例如，这使系统能够轻松携带异步传输模式（ATM）数据包，而不会干扰ATM同步。事实上，ATM同步可以通过定义的ATM同步机制来执行。 支持两种模式:模式1的符号速率为5.057 Msps，模式2的符号速率为5.361 Msps。通常，模式1将用于64-QAM，模式2将用于256-QAM。该系统将与采用高阶QAM扩展的更高数据速率方案的未来实现兼容。

This standard describes the framing structure, channel coding, and channel modulation for a digital multi-service television distribution system that is specific to a cable channel. The system can be used transparently with the distribution from a satellite channel, as many cable systems are fed directly from satellite links. The specification covers both 64 and 256 QAM. Most features of both modulation schemes are the same. Where there are differences, the specific details for each modulation scheme is covered. The design of the modulation, interleaving and coding is based upon testing and characterization of cable systems in North America. The modulation is Quadrature Amplitude Modulation with a 64 point signal constellation (64-QAM) and with a 256 point signal constellation (256-QAM), transmitter selectable. The forward error correction (FEC) is based on a concatenated coding approach that produces high coding gain at moderate complexity and overhead. Concatenated coding offers improved performance over a block code, at a similar overall complexity. The system FEC is optimized for quasi error free operation at a threshold output error event rate of one error event per 15 minutes. The data format input to the modulation and coding is assumed to be MPEG-2 transport. However, the method used for MPEG synchronization is decoupled from FEC synchronization. For example, this enables the system to carry Asynchronous Transfer Mode (ATM) packets easily without interfering with ATM synchronization. In fact, ATM synchronization may be performed by defined ATM synchronization mechanisms. There are two modes supported: Mode 1 has a symbol rate of 5.057 Msps and Mode 2 has a symbol rate of 5.361 Msps. Typically, Mode 1 will be used for 64-QAM and Mode 2 will be used for 256-QAM. The system will be compatible with future implementations of higher data rate schemes employing higher order QAM extensions.