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<h1>gr_ofdm_frame_acquisition Class Reference<br/>
<small>
[<a class="el" href="group__demodulation__blk.html">Signal Demodulation</a>, <a class="el" href="group__ofdm__blk.html">OFDM Blocks</a>]</small>
</h1><!-- doxytag: class="gr_ofdm_frame_acquisition" --><!-- doxytag: inherits="gr_block" -->
<p>take a vector of complex constellation points in from an FFT and performs a correlation and equalization.This block takes the output of an FFT of a received OFDM symbol and finds the start of a frame based on two known symbols. It also looks at the surrounding bins in the FFT output for the correlation in case there is a large frequency shift in the data. This block assumes that the fine frequency shift has already been corrected and that the samples fall in the middle of one FFT bin.
<a href="#_details">More...</a></p>
<p><code>#include <<a class="el" href="gr__ofdm__frame__acquisition_8h_source.html">gr_ofdm_frame_acquisition.h</a>></code></p>
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Inheritance diagram for gr_ofdm_frame_acquisition:</div>
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<div class="center"><img src="classgr__ofdm__frame__acquisition__inherit__graph.png" border="0" usemap="#gr__ofdm__frame__acquisition_inherit__map" alt="Inheritance graph"/></div>
<map name="gr__ofdm__frame__acquisition_inherit__map" id="gr__ofdm__frame__acquisition_inherit__map">
<area shape="rect" id="node2" href="classgr__block.html" title="The abstract base class for all 'terminal' processing blocks.A signal processing..." alt="" coords="60,237,129,267"/><area shape="rect" id="node4" href="classgr__basic__block.html" title="The abstract base class for all signal processing blocks.Basic blocks are the bare..." alt="" coords="40,160,149,189"/><area shape="rect" id="node6" href="classgr__msg__accepter.html" title="Accepts messages and inserts them into a message queue, then notifies subclass gr_basic_block..." alt="" coords="33,83,156,112"/><area shape="rect" id="node8" href="classgruel_1_1msg__accepter.html" title="Virtual base class that accepts messages." alt="" coords="25,5,164,35"/></map>
<center><span class="legend">[<a target="top" href="graph_legend.html">legend</a>]</span></center></div>
<p><a href="classgr__ofdm__frame__acquisition-members.html">List of all members.</a></p>
<table border="0" cellpadding="0" cellspacing="0">
<tr><td colspan="2"><h2>Public Member Functions</h2></td></tr>
<tr><td class="memItemLeft" align="right" valign="top">float </td><td class="memItemRight" valign="bottom"><a class="el" href="classgr__ofdm__frame__acquisition.html#a50418e0fba566a0c8fdb24bdba52688e">snr</a> ()</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Return an estimate of the SNR of the channel. <a href="#a50418e0fba566a0c8fdb24bdba52688e"></a><br/></td></tr>
<tr><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classgr__ofdm__frame__acquisition.html#ab46c54b18587dcbcd43803a0cc8c5cef">~gr_ofdm_frame_acquisition</a> (void)</td></tr>
<tr><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="classgr__ofdm__frame__acquisition.html#ac9e7650efc73d2febe2e90a5e1a9fd3f">general_work</a> (int noutput_items, <a class="el" href="classstd_1_1vector.html">gr_vector_int</a> &ninput_items, <a class="el" href="classstd_1_1vector.html">gr_vector_const_void_star</a> &input_items, <a class="el" href="classstd_1_1vector.html">gr_vector_void_star</a> &output_items)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">compute output items from input items <a href="#ac9e7650efc73d2febe2e90a5e1a9fd3f"></a><br/></td></tr>
<tr><td colspan="2"><h2>Protected Member Functions</h2></td></tr>
<tr><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classgr__ofdm__frame__acquisition.html#a1b7330d70565b77df6304d73a247fcfc">gr_ofdm_frame_acquisition</a> (unsigned int occupied_carriers, unsigned int fft_length, unsigned int cplen, const <a class="el" href="classstd_1_1vector.html">std::vector</a>< <a class="el" href="gr__complex_8h.html#aec4bfe41433369afae9327f1b0bc9109">gr_complex</a> > &known_symbol, unsigned int max_fft_shift_len)</td></tr>
<tr><td colspan="2"><h2>Friends</h2></td></tr>
<tr><td class="memItemLeft" align="right" valign="top"><a class="el" href="classboost_1_1shared__ptr.html">gr_ofdm_frame_acquisition_sptr</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classgr__ofdm__frame__acquisition.html#a7ef32b562ebffaa6114381c03ae05c9b">gr_make_ofdm_frame_acquisition</a> (unsigned int occupied_carriers, unsigned int fft_length, unsigned int cplen, const <a class="el" href="classstd_1_1vector.html">std::vector</a>< <a class="el" href="gr__complex_8h.html#aec4bfe41433369afae9327f1b0bc9109">gr_complex</a> > &known_symbol, unsigned int max_fft_shift_len)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Build an OFDM correlator and equalizer. <a href="#a7ef32b562ebffaa6114381c03ae05c9b"></a><br/></td></tr>
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<hr/><a name="_details"></a><h2>Detailed Description</h2>
<p>take a vector of complex constellation points in from an FFT and performs a correlation and equalization.</p>
<p>This block takes the output of an FFT of a received OFDM symbol and finds the start of a frame based on two known symbols. It also looks at the surrounding bins in the FFT output for the correlation in case there is a large frequency shift in the data. This block assumes that the fine frequency shift has already been corrected and that the samples fall in the middle of one FFT bin. </p>
<p>It then uses one of those known symbols to estimate the channel response over all subcarriers and does a simple 1-tap equalization on all subcarriers. This corrects for the phase and amplitude distortion caused by the channel. </p>
<hr/><h2>Constructor & Destructor Documentation</h2>
<a class="anchor" id="a1b7330d70565b77df6304d73a247fcfc"></a><!-- doxytag: member="gr_ofdm_frame_acquisition::gr_ofdm_frame_acquisition" ref="a1b7330d70565b77df6304d73a247fcfc" args="(unsigned int occupied_carriers, unsigned int fft_length, unsigned int cplen, const std::vector< gr_complex > &known_symbol, unsigned int max_fft_shift_len)" -->
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<td class="memname">gr_ofdm_frame_acquisition::gr_ofdm_frame_acquisition </td>
<td>(</td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>occupied_carriers</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>fft_length</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>cplen</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">const <a class="el" href="classstd_1_1vector.html">std::vector</a>< <a class="el" href="gr__complex_8h.html#aec4bfe41433369afae9327f1b0bc9109">gr_complex</a> > & </td>
<td class="paramname"> <em>known_symbol</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>max_fft_shift_len</em></td><td> </td>
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<td></td>
<td>)</td>
<td></td><td></td><td><code> [protected]</code></td>
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<a class="anchor" id="ab46c54b18587dcbcd43803a0cc8c5cef"></a><!-- doxytag: member="gr_ofdm_frame_acquisition::~gr_ofdm_frame_acquisition" ref="ab46c54b18587dcbcd43803a0cc8c5cef" args="(void)" -->
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<td class="memname">gr_ofdm_frame_acquisition::~gr_ofdm_frame_acquisition </td>
<td>(</td>
<td class="paramtype">void </td>
<td class="paramname"></td>
<td> ) </td>
<td></td>
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<hr/><h2>Member Function Documentation</h2>
<a class="anchor" id="ac9e7650efc73d2febe2e90a5e1a9fd3f"></a><!-- doxytag: member="gr_ofdm_frame_acquisition::general_work" ref="ac9e7650efc73d2febe2e90a5e1a9fd3f" args="(int noutput_items, gr_vector_int &ninput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items)" -->
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<td class="memname">int gr_ofdm_frame_acquisition::general_work </td>
<td>(</td>
<td class="paramtype">int </td>
<td class="paramname"> <em>noutput_items</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype"><a class="el" href="classstd_1_1vector.html">gr_vector_int</a> & </td>
<td class="paramname"> <em>ninput_items</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype"><a class="el" href="classstd_1_1vector.html">gr_vector_const_void_star</a> & </td>
<td class="paramname"> <em>input_items</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype"><a class="el" href="classstd_1_1vector.html">gr_vector_void_star</a> & </td>
<td class="paramname"> <em>output_items</em></td><td> </td>
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<td>)</td>
<td></td><td></td><td><code> [virtual]</code></td>
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<p>compute output items from input items </p>
<dl><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>noutput_items</em> </td><td>number of output items to write on each output stream </td></tr>
<tr><td valign="top"></td><td valign="top"><em>ninput_items</em> </td><td>number of input items available on each input stream </td></tr>
<tr><td valign="top"></td><td valign="top"><em>input_items</em> </td><td>vector of pointers to the input items, one entry per input stream </td></tr>
<tr><td valign="top"></td><td valign="top"><em>output_items</em> </td><td>vector of pointers to the output items, one entry per output stream</td></tr>
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</dd>
</dl>
<dl class="return"><dt><b>Returns:</b></dt><dd>number of items actually written to each output stream, or -1 on EOF. It is OK to return a value less than noutput_items. -1 <= return value <= noutput_items</dd></dl>
<p>general_work must call consume or consume_each to indicate how many items were consumed on each input stream. </p>
<p>Implements <a class="el" href="classgr__block.html#a137b93d87dc83bbdb6369d33f4ea8197">gr_block</a>.</p>
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<a class="anchor" id="a50418e0fba566a0c8fdb24bdba52688e"></a><!-- doxytag: member="gr_ofdm_frame_acquisition::snr" ref="a50418e0fba566a0c8fdb24bdba52688e" args="()" -->
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<td class="memname">float gr_ofdm_frame_acquisition::snr </td>
<td>(</td>
<td class="paramname"></td>
<td> ) </td>
<td><code> [inline]</code></td>
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<p>Return an estimate of the SNR of the channel. </p>
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<hr/><h2>Friends And Related Function Documentation</h2>
<a class="anchor" id="a7ef32b562ebffaa6114381c03ae05c9b"></a><!-- doxytag: member="gr_ofdm_frame_acquisition::gr_make_ofdm_frame_acquisition" ref="a7ef32b562ebffaa6114381c03ae05c9b" args="(unsigned int occupied_carriers, unsigned int fft_length, unsigned int cplen, const std::vector< gr_complex > &known_symbol, unsigned int max_fft_shift_len)" -->
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<td class="memname"><a class="el" href="classboost_1_1shared__ptr.html">gr_ofdm_frame_acquisition_sptr</a> gr_make_ofdm_frame_acquisition </td>
<td>(</td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>occupied_carriers</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>fft_length</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>cplen</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">const <a class="el" href="classstd_1_1vector.html">std::vector</a>< <a class="el" href="gr__complex_8h.html#aec4bfe41433369afae9327f1b0bc9109">gr_complex</a> > & </td>
<td class="paramname"> <em>known_symbol</em>, </td>
</tr>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">unsigned int </td>
<td class="paramname"> <em>max_fft_shift_len</em></td><td> </td>
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<td>)</td>
<td></td><td></td><td><code> [friend]</code></td>
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<p>Build an OFDM correlator and equalizer. </p>
<dl><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>occupied_carriers</em> </td><td>The number of subcarriers with data in the received symbol </td></tr>
<tr><td valign="top"></td><td valign="top"><em>fft_length</em> </td><td>The size of the FFT vector (occupied_carriers + unused carriers) </td></tr>
<tr><td valign="top"></td><td valign="top"><em>cplen</em> </td><td>The length of the cycle prefix </td></tr>
<tr><td valign="top"></td><td valign="top"><em>known_symbol</em> </td><td>A vector of complex numbers representing a known symbol at the start of a frame (usually a BPSK PN sequence) </td></tr>
<tr><td valign="top"></td><td valign="top"><em>max_fft_shift_len</em> </td><td>Set's the maximum distance you can look between bins for correlation </td></tr>
</table>
</dd>
</dl>
</div>
</div>
<hr/>The documentation for this class was generated from the following file:<ul>
<li><a class="el" href="gr__ofdm__frame__acquisition_8h_source.html">gr_ofdm_frame_acquisition.h</a></li>
</ul>
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