| Communications Blockset | |
Scopes
The Sinks library contains scopes for viewing three types of signal plots:
The following table lists the scope blocks and the plots they generate.
| Block Name |
Plots |
| Continuous-Time Eye and Scatter Diagrams |
Eye diagram, scatter plot, or signal trajectory of a continuous signal |
| Discrete-Time Eye Diagram Scope |
Eye diagram of a discrete signal |
| Discrete-Time Scatter Plot Scope |
Scatter plot of a discrete signal |
| Discrete-Time Signal Trajectory Scope |
Signal trajectory of a discrete signal |
Eye Diagrams
An eye diagram is a simple and convenient tool for studying the effects of intersymbol interference and other channel impairments in digital transmission. When this blockset constructs an eye diagram, it plots the received signal against time on a fixed-interval axis. At the end of the fixed interval, it wraps around to the beginning of the time axis. Thus the diagram consists of many overlapping curves. One way to use an eye diagram is to look for the place where the "eye" is most widely opened, and use that point as the decision point when demapping a demodulated signal to recover a digital message.
The following two blocks produce eye diagrams:
The first processes continuous-time signals, while the second processes discrete-time signals. The blocks also differ in the way you determine the decision timing: the Continuous-Time Eye and Scatter Diagrams block draws a vertical line to indicate a decision every time a trigger signal has a rising edge, whereas the Discrete-Time Eye Diagram Scope block draws a similar line periodically according to a mask parameter.
An example appears in Example: Viewing a Sinusoid.
Scatter Plots
A scatter plot of a signal plots the signal's value at its decision points. In the best case, the decision points should be at times when the eye of the signal's eye diagram is the most widely open.
The following two blocks produce scatter plots:
Both the Continuous-Time Eye and Scatter Diagrams block and the Discrete-Time Scatter Plot Scope block produce scatter plots. The first processes continuous-time signals, while the second processes discrete-time signals.
An example appears in Example: Viewing a Sinusoid.
Signal Trajectories
A signal trajectory is a continuous plot of a signal over time. A signal trajectory differs from a scatter plot in that the latter displays points on the signal trajectory at discrete intervals of time.
The following two blocks produce signal trajectories:
The Discrete-Time Scatter Plot Scope displays points on the trajectory at discrete time intervals, corresponding to the decision points, while the Discrete-Time Scatter Plot Scope displays a continuous picture of the signal's trajectory between decision points.
| | Error Statistics | Example: Viewing a Sinusoid | |