RF Simulation Glossary

Introduction

Using RF Blockset you can model and simulate radar and wireless communications systems with different architectures and used in multiple applications. RF or Radio Frequency deals with signals that work at very high frequency. RF signals change very rapidly and the simulation of such signals require very small time steps and long simulation runs. This combination allows you to capture data in milliseconds or seconds. RF Blockset provides you with two kinds of simulation libraries:

Circuit Envelope
Equivalent Baseband

Terms and Definitions

Equivalent Baseband

Equivalent Baseband simulation approach is for 2-port single carrier cascaded networks. This is a discrete time simulation and support frame-based processing of superheterodyne systems You can model filters, S-parameters, and in-band spectral regrowth caused by odd order nonlinearity.

Circuit Envelope

Circuit Envelope simulation approach is for multicarrier simulation of arbitrary network topologies. You can model filters, S-parameters, and in-band spectral regrowth caused by odd order nonlinearity. You can also model interferers, spurs, arbitrary LO signals, DC offset and even order nonlinearity.

Modulation

The process of superimposing a low frequency signal on to a high frequency signal also known as carrier (ω_c). The modulation signal can be complex, and described in terms of in-phase (I) and quadrature-phase (Q) components. The modulation process is equivalent to the complex multiplication:

$M o d u l a t e d S i g n a l = (I (t) + j Q (t)) * e^{j 2 π ω_{c} t}$

Baseband Signals

Signals that are at or near DC frequencies. This is the original frequency range of the transmitted signal before it is modulated. Baseband signals are limited mainly to wired communications.

Passband Signals

Signals that are at a higher frequency range after modulation. Passband signals are used for wireless transmissions.

Linear Circuits

In linear circuits, amplitude of the output signal is proportional to the input signal amplitude. The basic assumption is that passive devices described by lumped elements such as resistor, capacitor, inductor, or distributed elements such as transmission lines are linear. S-parameter blocks are also linear.

Simulation Time Step

Simulation time step in RF Blockset determines the bandwidth of the envelope signals for both Equivalent Baseband (single carrier envelope) and Circuit Envelope (multicarrier envelope) signals. In order to avoid aliasing, it is recommended that you use the same time step used to define the signal inputs in Simulink.

Mixers

Mixers translate signals from one frequency range to another. They have two inputs and one output. One input is information signal and other is the timing signal also known as Local Oscillator frequency or LO frequency input. Mixers are used for up conversion and down conversion of signals from baseband to RF and vice versa.

Local Oscillators

Local oscillators (LO) generate the timing or reference signals for the mixers.