quadrature amplitude modulation.htm

这是一个关于完成QAM调制的Matlab示例程序

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                  <H4><B><FONT face="Arial Rounded MT Bold"><FONT 
                  color=#3333ff><FONT size=+3>Q A 
                  M</FONT></FONT></FONT></B></H4></CENTER>
                  <CENTER><B><SUB><FONT color=#ffffff>-</FONT></SUB><SUP>(<FONT 
                  face=Verdana>A.K.A., I &amp; Q 
                  Modulation</FONT>)&nbsp;</SUP></B></CENTER></TD></TR>
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                  alt="Single Sideband Modulation" 
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                  <CENTER><B><FONT face="Arial Rounded MT Bold"><FONT 
                  point-size="12"><U><SUB><FONT 
                  color=#ffffff>-</FONT></SUB><FONT 
                  color=#cc0000>Q</FONT></U><FONT color=#cc0000>uadrature 
                  <U>A</U>mplitude&nbsp; <U>M</U>odulation&nbsp; 
                  (QAM)</FONT><SUP><FONT 
                  color=#ffffff>-</FONT></SUP></FONT></FONT></B></CENTER></TD></TR>
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                      <TD><B><FONT face="Times New Roman,Times">Brief 
                        Discussion</FONT></B></TD></TR>
                    <TR>
                      <TD><FONT face="Times New Roman,Times">I &amp; Q 
                        modulation, A.K.A., QAM, is a method for sending two 
                        separate (and uniquely different) channels of 
                        information.&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">As you know, the 
                        carrier is shifted to create two carriers: sin and cos 
                        versions.&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">The two modulation 
                        inputs (analog or digital) are applied to two separate 
                        balanced modulators (BM) each of which are 
                        supplied&nbsp; with the sin or cos carriers, i.e., 
                        modulator #1 is supplied with the sin carrier and 
                        modulator #2 is supplied with the cos 
                        carrier.&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">The outputs of 
                        both modulators are algebraically summed; the result of 
                        which is now a single signal to be transmitted,&nbsp; 
                        containing the I &amp; Q information.&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">This signal is for 
                        all intents and purposes a 'Double Sideband Signal' 
                        (DSB) with or without a carrier (reduced).&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">In the case of 
                        color television chroma, the subcarrier is transmitted 
                        as a very short burst (8 to 9 alternations); the 
                        reconstituted&nbsp; carrier is derived from this burst 
                        at the receiver.&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">This method of 
                        modulation has the advantage of reducing or eliminating 
                        intermodulation interference caused by a 
                        continuous&nbsp; carrier near the modulation 
                        sidebands.&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">====&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">Upon reception, 
                        the composite signal ( I &amp; Q) is processed to 
                        extract a carrier replica which is again shifted in 
                        phase to create&nbsp; both sin and cos 
                        carriers.&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">These carriers are 
                        applied to two different demodulators; each demodulator 
                        outputs one of the two original signals applied in 
                        the&nbsp; modulation process (I &amp; Q) at the 
                        transmitter.&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">In the more recent 
                        incarnations of the QAM or I &amp; Q modulation 
                        techniques, an Analog to Digital Convertor (ADC) is used 
                        to&nbsp; first convert the analog input to a serialized 
                        digital bit stream and is applied to the QAM modulators; 
                        likewise at the receiver.&nbsp;</FONT> 
                        <P><FONT face="Times New Roman,Times">For more detailed 
                        info on QAM, check out Analog Devices, Inc.&nbsp;&nbsp; 
                        <A 
                        href="http://www.analog.com/">http://www.analog.com/</A></FONT> 
                        <BR>&nbsp;</P></TD></TR>
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                  <CENTER><B><FONT face=Arial,Helvetica><FONT color=#000000>See 
                  also:&nbsp;&nbsp; <A 
                  href="http://www.williamson-labs.com/480_am.htm">AM</A></FONT><FONT 
                  color=#ffffff>--- </FONT><FONT color=#000000><A 
                  href="http://www.williamson-labs.com/480_dsb.htm">DSB</A></FONT><FONT 
                  color=#ffffff>--- </FONT><FONT color=#000000><A 
                  href="http://www.williamson-labs.com/480_ssb.htm">SSB</A></FONT><FONT 
                  color=#ffffff>--- </FONT><FONT color=#000000><A 
                  href="http://www.williamson-labs.com/480_fm.htm">FM</A></FONT><FONT 
                  color=#ffffff>--- </FONT><FONT color=#000000><A 
                  href="http://www.williamson-labs.com/480_mod.htm">Mix &amp; 
                  Mod</A></FONT></FONT></B></CENTER></TD></TR></TBODY></TABLE></CENTER>
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