Characteristics of Noise Received by Software Defined Radio – Part 2
To study the characteristics of the noise received by Software defined radio (SDR) and the characteristics of signal transimtted from one SDR to the other SDR using Intermediate Frequency (IF) and Radio Frequency (RF).
Signal and its characteristics:
A baseband signal of frequency F Hz is generated and was upconverted to IF and transmitted via channel from one SDR to the other SDR.
Sine wave generation
In this model, we have generated a samples of sine wave for different frequencies with different sampling rates and was upsampled by 8 in the Matlab and pulse shaped using RRC filter and given to the SDR which upconverts the signal to IF for trasmission of the signal via channel from one SDR to the other SDR. The pots of the generated sine wave are shown in figure.
The Figure above shows the upsampled version of the baseband signal. We can see that there are zeros between any two samples this is because it is padded with zeros for upsampling.
The figure above shows the pulse shaped version of the previous figure. Pulse shaping was done using Raise Cosine filter with roll of factor 0.9.
2.3 Autocorrelation of received signal
The transmitted samples from the SDR was received by the other SDR. The received samples where analyzed using the autocorrelation function as given in equation (1.1) and by the Power Spectral Density (PSD) which is the DFT of the samples received by the SDR. The DFT is performed using Fast Fourier Transform (FFT) in Matlab. The received signal, its Power Spectral Density and its autocorrelation are shown in the following figure.
The above figure has three plots. The rst plot is the sine wave received from the channel which was transmitted by the SDR. The second plot is the PSD of the signal. The spikes we see here are because of the sine nature. Since its frequency is 120 kHz we can see two spikes at 120kHz.
The last part of plot is the autocorrelated version of the signal received by the SDR. This autocorrelation was done without taking the number of samples (N-k) in the equation (1.1). If that was taken we are expected to get a perfectly sine wave which was actually received by the SDR i.e., we are expected to get the first plot.
From the graphs above we can infer that the received samples were almost with zero noise and we recovered the samples transmitted by the SDR.
About the Author: Satyanarayana K is a Junior Graduate at Dept of Electrical Engineering,Indian Institute of Technology (IIT), Madras – India.