Communications Blockset

Example Using the RF Impairments Library Blocks

The model shown in the following figure simulates RF impairments to a signal modulated by differential quaternary phase shift keying (DQPSK).

Overview of the Model

The model does the following:

• Modulates a random signal using DQPSK modulation.
• Applies impairments to the signal using the blocks from the RF Impairments library.
• Forks the signal into two paths, and processes one path with an automatic gain control (AGC) to compensate for the free space path loss and the I/Q imbalance.
• Displays the trajectory of the signal with AGC and the trajectory of the signal without AGC.
• Demodulates both signals and calculates their error rates.

You can see the effect of the automatic gain by comparing the trajectories of the signals with and without AGC, as shown in the following figure.

The trajectory of the signal with AGC more closely matches the undistorted trajectory for DQPSK, shown in the figure below, than does than the signal without AGC. Consequently, the error rate for the signal with AGC is much lower than the error rate for the signal without AGC.

In this example, the error rate for the demodulated signal without AGC is primarily caused by free space path loss and I/Q imbalance. The QPSK modulation minimizes the effects of the other impairments.

Scatter Plot Examples

Synchronization