When I run my model that has a finite frequency grid and aperiodic input signals, the resultant BER (Bit Error Rate) plot is wrong.
MATLAB: Do I receive artifacts, associated with finite frequency grid and aperiodic input signals, that lead to wrong answers in BER plots when using the RF Blockset 1.3.1 (R2006b)
RF Blockset
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There are a couple of reasons for the peak gain not being 21dB:
1) The power going into the amp pushes it into saturation, so the (large signal) gain seen at the output is less than the small signal S21 gain plotted from the data file. You can plot the power out versus power in curve of the block to see this effect, or you can reduce the signal in to the small signal region.
2) In RF Blockset we interpret the unitless Simulink signal as being the source voltage, Vs, of a source with output impedance Zs, whose value you set in the Input Port block. The default is 50 ohm. This leads to 6dB less signal at the output than if we interpreted the Simulink signal as the voltage available from the source Vavs, where Vavs = Vs/2. Insert a Gain of 2 if you want to interpret the Simulink signal as Vavs.
3) The default Spectrum Scope calibration isn’t the calibration that is needed in this case, so you have to add a Gain block to calibrate it as desired (see attached model).
The reason for the shape looking different at the band edges is that the input signal is aperiodic. This would require an infinitely small frequency resolution to model it. With the finite frequency resolution in the model (frequency resolution = 1 / (length of FIR modeling filter * sample time)), the impulse response that should be at infinite delay appears erroneously at t = t_s * length of FIR. A workaround is to add an artificial delay after the amplifier that delays the model time window and prevents the “wrap-around.”
Procedures for interfacing SimRF with Simulink, Communication Systems Toolbox, and the RF Toolbox are outlined below:
Interfacing SimRF with Simulink:
Most of the SimRF blocks cannot be directly connected to standard Simulink blocks, and special conversion blocks are required to interface the two domains with one another. The interfacing procedure is different for Equivalent Baseband and Circuit Envelope modeling:
- Simulink <-> Equivalent Baseband: use the Input and Output Port blocks from the SimRF->Equivalent Baseband library. For more information on the various options/features of these blocks, please see the following links:
When interfacing signals between Simulink and SimRF Equivalent Baseband, please be careful when interpreting the physical meaning of the signals. Remember that a 0 Hz Simulink signal maps to the carrier frequency in the SimRF domain, and frequencies above/below 0 Hz in Simulink map to frequencies above/below the passband carrier frequency in SimRF. For more information, please see the following link:
- Simulink <-> Circuit Envelope: use the Inport/Outport block from the SimRF->Circuit Envelope library. For more information about these blocks, please see the following links:
When interfacing signals between Simulink and SimRF Circuit Envelope, please be careful when interpreting the physical meaning of the signals. Complex Simulink signals map to the amplitude modulations of the in-phase/quadrature carrier components in the SimRF domain. For more information on the way that Simulink signals map to SimRF Circuit Envelope signals, please see the following link:
http://www.mathworks.com/help/releases/R2013a/simrf/gs/minimize-computations-for-rf-simulations.html
Interfacing SimRF with Communication System Toolbox:
The Communication System Toolbox signals all exist in the Simulink domain. As such, they cannot be directly connected to SimRF blocks. To interface the SimRF domain with the Communication Systems Toolbox, the first step is to interface the SimRF blocks with the Simulink domain using the procedure outlined above.
Please see the following links for some examples of using SimRF and the Communication System Toolbox together:
Interfacing SimRF with RF Toolbox:
SimRF is used in the Simulink environment, while the RF Toolbox consists of a set of MATLAB functions/classes that are used in the MATLAB programming context. Nevertheless, it is possible combine some of the functionality of RF Toolbox with SimRF.
In RF Toolbox, it is possible to create data objects to represent circuit elements including amplifiers, mixers, S-parameter networks, and other generalized circuit elements. In general, S-parameters and amplifier/mixer data can be represented as RFDATA objects, and generalized circuit networks such as RLC networks can be represented as RFCKT objects.
Some of the blocks in the Equivalent Baseband Library offer the ability to import these RF Toolbox objects to define the block parameters.
The “General Mixer” and “General Amplifier” blocks can use an RFDATA object to define their parameters. To do so, choose the RFDATA option in the “Data Source” pull down menu under the Main tab of the block parameters. Similarly, an RFCKT object can be used to specify the behavior of the “General Circuit Element” block, by specifying the name of the object in the “RFCKT object” field in the block dialog. For more information on these blocks, please see the following links:
For more information on the RF Toolbox objects, please see the following link:
In addition, many of the blocks in the SimRF library have the ability to import S-parameter files such as “.snp”. It is possible to generate export RF Toolbox models/objects as S-parameter files that can be imported into other contexts such as SimRF. For more information on the data export capabilities of RF Toolbox, please see the following link:
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