Pulse Forming filter Simulation

The pulse filter uses a molded pulse, that is, digital 1, and a rectangular pulse to represent a raised cosine pulse or a Gaussian pulse. It is mainly used for baseband data processing.

In a digital communication system, a baseband signal is a Rectangular Pulse before it enters the modulation. The rising and falling sides of a mutation contain a wide array of high-frequency components and the signal spectrum is generally relatively wide. In essence, pulse forming is a filter. The signals of the digital communication system must all be in a certain frequency band, but the spectrum of the baseband pulse signal is an SA function, which is infinitely wide in the frequency band, the pulse of a single symbol will extend to the adjacent runner-up to generate crosstalk between codes, which will interfere with other signals, which is not allowed. To eliminate interference, Pulse Forming filtering is required before the signal is transmitted, and the frequency of the signal is limited in the band. Therefore, when the channel bandwidth is limited, to reduce the bit error rate and improve the channel bandwidth utilization, Pulse Forming must be performed before signal transmission to improve the spectrum characteristics, generates waveforms suitable for Channel Transmission. Symbol/second indicates the unit of Port (baud). The baud rate is the bit rate of the symbol information. Generally, the pulse forming process requires oversampling. Otherwise, it does not make sense, because the forming filter expands the bandwidth, and oversampling aims to reduce the spectral aliasing.

Commonly used Pulse Forming filters include RC (Raised Cosine) and Gaussian molding.

MATLAB, as a powerful simulation tool, is widely used in communication signal processing. In the new version of MATLAB (2014a), many APIs have been updated on the filter design. The following is based on the simulation and comparison of several molded filters.

Earlier versions of the firrcos function were used to design the function for the raised cosine filter and have now been changed to the rcosdesign function.

For example, a 16-order raised cosine filter is designed. The carrier frequency fc is 1 kHz, the rolling down coefficient is 0.25, and the sampling rate is 8 kHz.

N = 16;
Fc = 1000;
R = 0.25;
FS = 8000;
H = firrcos (n, FC, R, FS, 'roloff', 'normal ');
Figure (); plot (h)


It is the extraction coefficient of the filter. The order is 16 and there are 17 filters.

　　

　　　　

 

 

 

 

 

 

 

 

 

 

 

 

If you use the rcosdesign function to design this filter, use the following call method.

H1 = rcosdesign (R, N/(FS/FC/2), FS/FC/2, 'normal ');

H1 = h1/MAX (H1)/(FS/FC/2); % quantize the Coefficient

Figure; plot (H1)

The drawing results are the same as above.

　　

Pulse Forming filter Simulation