Fundamentals_Wireless_Communication_chapter5

《Fundamentals_Wireless_Communication_chapter5》由会员上传分享，免费在线阅读，更多相关内容在行业资料-天天文库。

1、CHAPTER5CapacityofwirelesschannelsIntheprevioustwochapters,westudiedspecifictechniquesforcommuni-cationoverwirelesschannels.Inparticular,Chapter3iscenteredonthepoint-to-pointcommunicationscenarioandtherethefocusisondiversityasawaytomitigatetheadverseeffectoffad

2、ing.Chapter4looksatcellularwirelessnetworksasawholeandintroducesseveralmultipleaccessandinterferencemanagementtechniques.Thepresentchaptertakesamorefundamentallookattheproblemofcommunicationoverwirelessfadingchannels.Weask:whatistheoptimalperformanceachievableo

3、nagivenchannelandwhatarethetechniquestoachievesuchoptimalperformance?Wefocusonthepoint-to-pointscenariointhischapteranddeferthemultiusercaseuntilChapter6.Thematerialcoveredinthischapterlaysdownthetheoreticalbasisofthemoderndevelopmentinwirelesscommunicationtobe

4、coveredintherestofthebook.Theframeworkforstudyingperformancelimitsincommunicationisinfor-mationtheory.Thebasicmeasureofperformanceisthecapacityofachan-nel:themaximumrateofcommunicationforwhicharbitrarilysmallerrorprobabilitycanbeachieved.Section5.1startswiththe

5、importantexam-pleoftheAWGN(additivewhiteGaussiannoise)channelandintroducesthenotionofcapacitythroughaheuristicargument.TheAWGNchan-nelisthenusedasabuildingblocktostudythecapacityofwirelessfadingchannels.UnliketheAWGNchannel,thereisnosingledefinitionofcapacityfo

6、rfadingchannelsthatisapplicableinallscenarios.Sev-eralnotionsofcapacityaredeveloped,andtogethertheyformasystem-aticstudyofperformancelimitsoffadingchannels.Thevariouscapacitymeasuresallowustoseeclearlythedifferenttypesofresourcesavailableinfadingchannels:power,

7、diversityanddegreesoffreedom.WewillseehowthediversitytechniquesstudiedinChapter3fitintothisbigpic-ture.Moreimportantly,thecapacityresultssuggestanalternativetechnique,opportunisticcommunication,whichwillbeexploredfurtherinthelaterchapters.1661675.1AWGNchannelca

8、pacity5.1AWGNchannelcapacityInformationtheorywasinventedbyClaudeShannonin1948tocharacterizethelimitsofreliablecommunication.BeforeShannon,itwaswidelybelievedthattheonlywayto