A digital transmission system refers to a mechanism that controls the transmitter's transmission capacity by using signals fed into the receiver via a propagation path. The receiver generates control signals, which optimize the system’s transmission capacity based on monitored information such as transmission quality or the receive C/N ratio. These control signals are then sent to both the transmitter and the decision-making circuitry.
The decision circuit compares the transmission capacity of each line. When the first primary line reaches its lowest transmission capacity, the decision circuit outputs a switching signal. Subsequently, the transmission switching device and the receiving switching device activate, routing the input signal from the first primary line through the backup line for output. Notably, the transmission capacity of the signal now matches that of the backup line.
System Components
A digital transmission method comprising the steps of: monitoring operational information for both the primary and backup lines used in a capacity-variable transmission system that adjusts its transmission capacity; when a switching signal is generated during the monitoring step, routing the input signal originally intended for transmission on the primary line to the backup line based on that signal; thereby transferring the input signal—originally meant to travel via the primary line—to the backup line, with the transmitted signal subsequently output as the primary line’s output.
Digital system model:
Source — Source Encoder — Channel Encoder — Baseband Pulse Generator — Digital Modulator
Channel — Digital Demodulator — Sampling Decision Device — Channel Decoder — Source Decoder — Destination
System Design Methodology
(1) Worst-Case Design Method
The worst-case design method involves using the most unfavorable values allowed for all parameters—such as optical power, spectral range, spectral width, receiver sensitivity, fiber attenuation coefficient, and insertion loss of connectors and active connectors—when determining the regeneration segment distance, regardless of their specific distributions.
(2) Statistical Design Method
Statistical design methods leverage the statistical properties of optical parameter distributions to more efficiently determine regeneration segment distances. Compared to the worst-case design approach, statistical methods can extend the regeneration segment distance—but at the cost of no longer maintaining lateral compatibility.
(3) Joint Design Method
In some cases, designing based on standard optical interface parameter values may not meet the actual regeneration segment distance requirements. Operators need to carefully evaluate the key aspects of the design that fail to comply with the optical interface specifications.
Pros and cons of the system
Digital Transmission System
Advantages: Cutting-edge technology, exceptional image quality, significantly elevates the system's overall sophistication, fully showcases the high performance of the display device, and ensures easy implementation in engineering projects.
Drawbacks: The transmission distance needs to be accurately estimated in advance, and the current system is slightly more expensive.
Application of the system
A method and apparatus for the headend of a digital transmission system, featuring input terminals designed to receive first and second program information from first and second program sources, as well as input terminals for receiving first and second control information from first and second control sources. The first and second program information are fed into a switching circuit, while a dedicated switching control unit manages this circuit to output a channel containing a combined signal that includes both the first and second program information intended for a user. Additionally, processing circuitry enables the selective delivery of the first and second control information—either directly or via the switching circuit—to the channel’s output terminal.
A head-end device comprising: a first input terminal for receiving program information from a first channel of a first program source; a second input terminal for receiving program information from a second channel of a second program source; a switching circuit onto which both the first and second channel program information are applied; and a switching control mechanism that manages the switching circuit to output a third channel containing a combination of program information originally assigned to the first and second channels.