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- Elec 301 projects fall 2015
- Implementation of digital
- Creating the transmitter
Step by step sequence of how the transmitter was created.
The following section describes, in sequence, how the image was transmitted over the channel.
Image to vector of bits
The transmitter loads the image from the computer and converts it into a vector of bits. This is done using Matlab commands that first convert an image into a matrix of integers between 0-255, and then converts the matrix of integers into bits.
Encoding the message
After creating a vector of bits, the transmitter encodes the bits using a 7-4 hamming encoding. This is done through the built in Matlab function that takes a string of bits and encodes the bits according to specified parameters.
Bpsk modulation
The coded bits are converted into an analog waveform using a BPSK modulation scheme. A 0 is represented by sin(2 Pi fc t) and a 1 is represented by -sin(2 Pi fc t). A sampling rate of 48 kHz was chosen to generate these sine waves. Matrix manipulations and multiplications are performed to generate the BPSK waveform to be transmitted. Each bit is represented in .01 seconds, giving the scheme a bit rate of 100 bits/second.
Sounding the channel
After testing for the frequency response of the channel, a modulation frequency of fc = 2250 Hz was chosen as the channel least attenuated the signal around that frequency.
Chirp signal
Finally, a chirp signal, generated through the Matlab chirp function, is appended to the beginning of the BPSK modulated signal. The receiver uses the chirp signal to determine where in time to start processing the received signal.
Playing the signal
The final analog waveform to be transmitted is played through the laptop speakers using Matlab’s soundsc function.
Source:
OpenStax, Elec 301 projects fall 2015. OpenStax CNX. Jan 04, 2016 Download for free at https://legacy.cnx.org/content/col11950/1.1
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