Fundamentals_Wireless_Communication_chapter9

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1、CHAPTER9MIMOIII:diversity–multiplexingtradeoffanduniversalspace-timecodesInthepreviouschapter,weanalyzedtheperformancebenefitsofMIMOcommunicationanddiscussedarchitecturesthataredesignedtoreapthosebenefits.Thefocuswasonthefastfadingscenario.ThestoryonslowfadingMIMOchannelsismorecomplex.While

2、thecommunicationcapabilityofafastfadingchannelcanbedescribedbyasinglenumber,itscapacity,thatofaslowfadingchannelhastobedescribedbytheoutageprobabilitycurvepout
·asafunctionofthetargetrate.Thiscurveisinessenceatradeoffbetweenthedatarateanderrorprobability.Moreover,inadditiontothepowerandde

3、gree-of-freedomgainsinthefastfadingscenario,multipleantennasprovideadiversitygainintheslowfadingscenarioaswell.Aclearcharacterizationoftheperformancebenefitsofmultipleantennasinslowfadingchannelsandthedesignofgoodspace-timecodingschemesthatreapthosebenefitsarethesubjectsofthischapter.Theout

4、ageprobabilitycurvepout
·isthenaturalbenchmarkforevaluatingtheperformanceofspace-timecodes.However,itisdifficulttocharacterizeanalyticallytheoutageprobabilitycurvesforMIMOchannels.WedevelopanapproximationthatcapturesthedualbenefitsofMIMOcommunicationinthehighSNRregime:increaseddatarate(via

5、anincreaseinthespatialdegreesoffreedomor,equivalently,themultiplexinggain)andincreasedreliability(viaanincreaseinthediversitygain).Thedualbenefitsarecapturedasafundamentaltradeoffbetweenthesetwotypesofgains.1Weusetheoptimaldiversity–multiplexingtradeoffasabenchmarktocomparethevariousspace-t

6、imeschemesdiscussedpreviouslyinthebook.Thetradeoffcurvealsosuggestshowoptimalspace-timecodingschemesshouldlook.Apowerfulideaforthedesignoftradeoff-optimalschemesisuniversality,whichwediscussinthesecondpartofthechapter.Wehavestudiedanapproachtospace-timecodedesigninChapter3.Codesdesignedusin

7、gthatapproachhavesmallerrorprobabilities,averagedover1Thecarefulreaderwillnotethatwesawaninklingofthetensionbetweenthesetwotypesofgainsinourstudyofthe2×2MIMORayleighfadingchannelinChapter3.383384MIMOIII:diversity–multiplexingtradeoffanduniversalspace-tim