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<div class="title">Simulation of a Multicode CDMA system on an AWGN channel </div>  </div>
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<div class="textblock"><p>In this example we will introduce the multi-code spreading class <code>Multicode_Spread_2d</code>. This is the most general spreading class availiable in it++. Different spreading codes may be assigned to the I and Q branches. The number of multiple spreading codes and the spreading factor is determined by the number of rows and collumns respectively that is used when calling the member function set_codes. In this example we will use four Hadamard sequenced of length four, and the same spreading sequences will be used for the I and Q brances.</p>
<div class="fragment"><pre class="fragment"><span class="preprocessor">#include &lt;<a class="code" href="itcomm_8h.html" title="Include file for the IT++ communications module.">itpp/itcomm.h</a>&gt;</span>

<span class="keyword">using namespace </span>itpp;

<span class="comment">//These lines are needed for use of cout and endl</span>
<span class="keyword">using</span> std::cout;
<span class="keyword">using</span> std::endl;

<span class="keywordtype">int</span> main()
{
  <span class="comment">//Scalars:</span>
  <span class="keywordtype">int</span> SF, Ncode, sc, i, j, NumOfBits, MaxIterations, MaxNrOfErrors, MinNrOfErrors;
  <span class="keywordtype">double</span> Eb;

  <span class="comment">//Vectors and matrixes:</span>
  vec EbN0dB, EbN0, N0, ber;
  smat all_codes, spread_codesI, spread_codesQ;
  bvec transmited_bits, received_bits;
  cvec transmited_symbols, received_symbols, transmited_chips, received_chips;

  <span class="comment">//Classes:</span>
  <a class="code" href="classitpp_1_1Multicode__Spread__2d.html" title="Multicode spreading of complex symbols to complex output.">Multicode_Spread_2d</a> mc_spread;
  <a class="code" href="classitpp_1_1AWGN__Channel.html" title="Ordinary AWGN Channel for cvec or vec inputs and outputs.">AWGN_Channel</a> channel;
  <a class="code" href="classitpp_1_1QPSK.html" title="QPSK modulator.">QPSK</a> qpsk;
  <a class="code" href="classitpp_1_1BERC.html" title="Bit Error Rate Counter (BERC) Class.">BERC</a> berc;

  <span class="comment">//Initialize the spreading:</span>
  SF = 4;                            <span class="comment">//The spreading factor is 4</span>
  Ncode = 4;                         <span class="comment">//Use all four codes in the multi-code spreader</span>
  all_codes = <a class="code" href="group__convertfunc.html#gaf713af60052f77c79cdb145311341e99" title="Converts a Mat&lt;T&gt; to smat.">to_smat</a>(<a class="code" href="group__specmat.html#ga10afe3456dd34b57639dee69e8f7d06f" title="Hadamard matrix.">hadamard</a>(SF)); <span class="comment">//Calculate the spreading codes</span>

  <span class="comment">//Set the spreading codes:</span>
  spread_codesI.set_size(Ncode, SF, <span class="keyword">false</span>);
  spread_codesQ.set_size(Ncode, SF, <span class="keyword">false</span>);
  <span class="keywordflow">for</span> (sc = 0; sc &lt; Ncode; sc++) {
    spread_codesI.set_row(sc, all_codes.get_row(sc));
    spread_codesQ.set_row(sc, all_codes.get_row(sc));
  }
  mc_spread.<a class="code" href="classitpp_1_1Multicode__Spread__2d.html#aa77a0c16beadaa6e31824140a15bebce" title="Set the spreading codes.">set_codes</a>(<a class="code" href="group__convertfunc.html#ga7d8813d98735a505d262763fa149dd2d" title="Converts a Mat&lt;T&gt; to mat.">to_mat</a>(spread_codesI), <a class="code" href="group__convertfunc.html#ga7d8813d98735a505d262763fa149dd2d" title="Converts a Mat&lt;T&gt; to mat.">to_mat</a>(spread_codesQ));

  <span class="comment">//Specify simulation specific variables:</span>
  EbN0dB = <a class="code" href="group__specmat.html#gae5632baa525e231b015f3d45f3503cac" title="Linspace (works in the same way as the matlab version)">linspace</a>(-2, 14, 17);
  EbN0 = <a class="code" href="group__logexpfunc.html#ga0c42d158b1f623f9b72c1ccde7e2fd09" title="Calculates x to the power of y (x^y)">pow</a>(10, EbN0dB / 10);
  Eb = 1.0;
  N0 = Eb * <a class="code" href="group__logexpfunc.html#ga0c42d158b1f623f9b72c1ccde7e2fd09" title="Calculates x to the power of y (x^y)">pow</a>(EbN0, -1.0);
  NumOfBits = 50000;
  MaxIterations = 10;
  MaxNrOfErrors = 200;
  MinNrOfErrors = 5;
  ber.set_size(EbN0dB.size(), <span class="keyword">false</span>);
  ber.clear();

  <span class="comment">//Randomize the random number generators:</span>
  <a class="code" href="group__randgen.html#gadf5dd6e879881b651896c213e6efd3ba" title="Set a random seed for the Global Random Number Generator.">RNG_randomize</a>();

  <span class="keywordflow">for</span> (i = 0; i &lt; EbN0dB.length(); i++) {

    cout &lt;&lt; endl &lt;&lt; <span class="stringliteral">&quot;Simulating point nr &quot;</span> &lt;&lt; i + 1 &lt;&lt; endl;
    berc.<a class="code" href="classitpp_1_1BERC.html#a3b575cfbe8dd194c2cd51a6aa52651e5" title="Clears the bit error counter.">clear</a>();
    channel.<a class="code" href="classitpp_1_1AWGN__Channel.html#aedf43a1a192a6c474ef915c297e9fcbb" title="Set noise variance (for complex-valued channels the sum of real and imaginary parts)">set_noise</a>(N0(i) / 2.0);

    <span class="keywordflow">for</span> (j = 0; j &lt; MaxIterations; j++) {

      transmited_bits = <a class="code" href="group__randgen.html#ga5aa06887cf1fd3301b040987924068f0" title="Generates a random bit (equally likely 0s and 1s)">randb</a>(NumOfBits);
      transmited_symbols  = qpsk.<a class="code" href="classitpp_1_1Modulator.html#a53826bf7e0ec83b99592235b0c2f6235" title="Modulation of bits.">modulate_bits</a>(transmited_bits);

      <span class="comment">//This is where we do the multi-code spreading:</span>
      transmited_chips =  mc_spread.<a class="code" href="classitpp_1_1Multicode__Spread__2d.html#a17bb74ea4c88fe0ffd565b9020dede28" title="Spreading of signal.">spread</a>(transmited_symbols);

      received_chips = channel(transmited_chips);

      <span class="comment">//The multi-code despreading:</span>
      <span class="comment">//The second argument tells the despreader that the offset is zero chips.</span>
      <span class="comment">//This offset is usefull on channels with delay.</span>
      received_symbols = mc_spread.<a class="code" href="classitpp_1_1Multicode__Spread__2d.html#ad191b52b55d0306fd7e591a299b4d94d" title="Despreading of signal. timing is the start position of the first symbol, given in number of samples...">despread</a>(received_chips, 0);

      received_bits = qpsk.<a class="code" href="classitpp_1_1PSK.html#aa3b14b2e7174454ddd1270915161bb4e" title="Hard demodulation of bits.">demodulate_bits</a>(received_symbols);

      berc.<a class="code" href="classitpp_1_1BERC.html#a539b0c989badff3027d97e4693fc9cd7" title="Cumulative error counter.">count</a>(transmited_bits, received_bits);
      ber(i) = berc.<a class="code" href="classitpp_1_1BERC.html#af17d5f534ba34558d3632a98f29f0519" title="Returns the estimated bit error rate.">get_errorrate</a>();

      cout &lt;&lt; <span class="stringliteral">&quot;   Itteration &quot;</span> &lt;&lt; j + 1 &lt;&lt; <span class="stringliteral">&quot;: ber = &quot;</span> &lt;&lt; berc.<a class="code" href="classitpp_1_1BERC.html#af17d5f534ba34558d3632a98f29f0519" title="Returns the estimated bit error rate.">get_errorrate</a>() &lt;&lt; endl;
      <span class="keywordflow">if</span> (berc.<a class="code" href="classitpp_1_1BERC.html#a02e757f28e87003404ad0d4aec1e44a6" title="Returns the counted number of bit errors.">get_errors</a>() &gt; MaxNrOfErrors) {
        cout &lt;&lt; <span class="stringliteral">&quot;Breaking on point &quot;</span> &lt;&lt; i + 1 &lt;&lt; <span class="stringliteral">&quot; with &quot;</span> &lt;&lt; berc.<a class="code" href="classitpp_1_1BERC.html#a02e757f28e87003404ad0d4aec1e44a6" title="Returns the counted number of bit errors.">get_errors</a>() &lt;&lt; <span class="stringliteral">&quot; errors.&quot;</span> &lt;&lt; endl;
        <span class="keywordflow">break</span>;
      }

    }

    <span class="keywordflow">if</span> (berc.<a class="code" href="classitpp_1_1BERC.html#a02e757f28e87003404ad0d4aec1e44a6" title="Returns the counted number of bit errors.">get_errors</a>() &lt; MinNrOfErrors) {
      cout &lt;&lt; <span class="stringliteral">&quot;Exiting Simulation on point &quot;</span> &lt;&lt; i + 1 &lt;&lt; endl;
      <span class="keywordflow">break</span>;
    }

  }

  <span class="comment">//Print results:</span>
  cout &lt;&lt; endl;
  cout &lt;&lt; <span class="stringliteral">&quot;EbN0dB = &quot;</span> &lt;&lt; EbN0dB &lt;&lt; endl;
  cout &lt;&lt; <span class="stringliteral">&quot;ber = &quot;</span> &lt;&lt; ber &lt;&lt; endl;

  <span class="comment">//Exit program:</span>
  <span class="keywordflow">return</span> 0;

}

</pre></div><p>A typical run of this program will look like this:</p>
<div class="fragment"><pre class="fragment">
Simulating point nr 1
   Itteration 1: ber = 0.13016
Breaking on point 1 with 6508 errors.

Simulating point nr 2
   Itteration 1: ber = 0.103
Breaking on point 2 with 5150 errors.

Simulating point nr 3
   Itteration 1: ber = 0.07886
Breaking on point 3 with 3943 errors.

Simulating point nr 4
   Itteration 1: ber = 0.05534
Breaking on point 4 with 2767 errors.

Simulating point nr 5
   Itteration 1: ber = 0.03822
Breaking on point 5 with 1911 errors.

Simulating point nr 6
   Itteration 1: ber = 0.02388
Breaking on point 6 with 1194 errors.

Simulating point nr 7
   Itteration 1: ber = 0.01316
Breaking on point 7 with 658 errors.

Simulating point nr 8
   Itteration 1: ber = 0.00586
Breaking on point 8 with 293 errors.

Simulating point nr 9
   Itteration 1: ber = 0.0027
   Itteration 2: ber = 0.00247
Breaking on point 9 with 247 errors.

Simulating point nr 10
   Itteration 1: ber = 0.00094
   Itteration 2: ber = 0.00086
   Itteration 3: ber = 0.00076
   Itteration 4: ber = 0.00077
   Itteration 5: ber = 0.0008
   Itteration 6: ber = 0.000796667
Breaking on point 10 with 239 errors.

Simulating point nr 11
   Itteration 1: ber = 0.00016
   Itteration 2: ber = 0.00016
   Itteration 3: ber = 0.000186667
   Itteration 4: ber = 0.000175
   Itteration 5: ber = 0.000172
   Itteration 6: ber = 0.000173333
   Itteration 7: ber = 0.000162857
   Itteration 8: ber = 0.00017
   Itteration 9: ber = 0.000166667
   Itteration 10: ber = 0.000172

Simulating point nr 12
   Itteration 1: ber = 4e-05
   Itteration 2: ber = 2e-05
   Itteration 3: ber = 2.66667e-05
   Itteration 4: ber = 2.5e-05
   Itteration 5: ber = 2e-05
   Itteration 6: ber = 2e-05
   Itteration 7: ber = 3.14286e-05
   Itteration 8: ber = 2.75e-05
   Itteration 9: ber = 2.44444e-05
   Itteration 10: ber = 2.6e-05

Simulating point nr 13
   Itteration 1: ber = 0
   Itteration 2: ber = 0
   Itteration 3: ber = 0
   Itteration 4: ber = 0
   Itteration 5: ber = 0
   Itteration 6: ber = 0
   Itteration 7: ber = 0
   Itteration 8: ber = 2.5e-06
   Itteration 9: ber = 2.22222e-06
   Itteration 10: ber = 2e-06
Exiting Simulation on point 13

EbN0dB = [-2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14]
ber = [0.13016 0.103 0.07886 0.05534 0.03822 0.02388 0.01316 0.00586 0.00247 0.000796667 0.000172 2.6e-05 2e-06 0 0 0 0]
</pre></div><p>Use copy-and-paste to insert the variables <code>EbN0dB</code> and <code>ber</code> into Matlab and plot the result. </p>
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libitpp-doc 4.2-4 / usr / share / doc / libitpp-dev / html / spread.html
