ofdm simulink

8/6/2019 OFDM simulink

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Matlab Simulink

The OFDM system will be applied according to the LTE parameters of the 5 MHz

bandwidth that have been studied on Matlab Simulink, generate random bits will be

generated first so a RANDOM INTEGER GENERATOR block is to be used, the M-

ary number will be according to the desired Modulation technique, in this example is 16

QAM, the sample time will be 1 divided by the number of data subcarriers in this case it

will be 1/301 and the number of samples per frame is the number of data subcarriers

After generating random bits now these signals will be modulated with 16 QAM

Modulation techniques so a RECTANGULAR 16 QAM MODULATOR block is to be

called from the library, the M-ary number is 16 and the constellation ordering is Gray.


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The next step is to take these values to the IFFT step but the number of samples is 301

and the IFFT only accepts radix 2 numbers ( 2 ^N numbers ) so zero padding (add zeros

the stream you have ) will take place to the 301 to make it reach the nearest radix 2

number which is 512 , the zeros added will be in between the 301 data subcarriers so the

data will be divided into 2 parts and fill the zeros in between so that will be done with a

SELECT ROWS block and the indices to output will be {1:150,151:301} , now 211

zeros will be added between 150 and 151 so the total will be 512, this process needs a

CONSTANT block and the constant value will be equal to

complex(0,0)*zeros(211,1) , these 2 outputs of the SELECT ROWS and the

CONSTANT block all 3 need to be connected so a MATRIX CONCATENATE block

is to be used in this case, the number of inputs in this block will be 3 inputs 1 input

represents the data from 1 to 150 and the second input is the zero padding ( 211 zeros )and the third input is the data from 151 to 301 , so the data now became radix 2

(512) and an IFFT block to used in the next step.


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Now that o/p will be taken connected to a IFFT (frequency to time domain) block and it

must be taken in consideration that the boxes of the Divide output by FFT length and

inherit FFT length from input dimensions are both marked .

The next block used is the SELECTOR block which will act like a cyclic prefix,

according to the LTE parameters the number of samples of the cyclic prefix in the short 5

MHz is 36 samples, this means that the last 36 samples will be taken from the 512 data

samples and then put it in the beginning of the data samples so that the total number of

the data samples becomes 512 + 36, so in the SELECTOR block the index vector will be

[477:512 1:512].

Now that successfully generating the OFDM signal, the signal will pass through a noisy

channel, in this example an Additive white Gaussian noise channel will be used, so an

AWGN CHANNEL block is to be added to the design and the adjustments of the block

is : the mode on the signal to noise ratio (SNR) and the SNR (dB) is 20 and the inputsignal power is 0.01 watts

To see the output after the noisy channel the output will be taken to a |FFT| block so that

the signal is completely in the positive part and then into VECTORSCOPE block to see

the output


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.

Now after the signal has been transmitted, the next step is to receive the signal so the

cyclic prefix should be removed from the signal, a SELECTOR block to be used again

and this time the main 512 points will be selected before adding the cyclic prefix, the first

36 points are the ones which has been added so in the SELECTOR block the index

vector will be [37:548].


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The next step is to pass on a FFT block

After passing on a FFT block, a FRAME STATUS CONVERSION block is to be used

to convert the data into frames.

Retrieval of the 301 data symbols that we have transmitted is the main step in the

receiver, so the 211 zeros that have been added in the zero padding step is to be

completely removed, so a SELECTOR block to be used to remove these zeros and the

index vector for this block will be from [1:150 362:512], the first 150 data symbols to be

selected and then skip the 211 zeros that has been added and then the last 151 datasymbols which are from 362 to 512 is to be taken also.

The output after the removal of the zero padding on the scope will be


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Now demodulating the signal with a RECTANGULAR 16 QAM DEMODULATOR

will take place and hence the OFDM system design is finished.

Calculating the bit error rate is the next step, it will be calculated between the transmitted

bits and relatively with the received bits so a DATA_TX block is to be placed after the

random integer generator and a DATA_RX block is to be placed after the Demodulator

and both of them will be inputs to an ERROR RATE CALCULATION block and the

output will be on a DISPLAY block which will show the packet loss, bit loss and the

total bits.


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ofdm simulink

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