NRF24L01跳频程序及方法

APPLICATIONNOTENordicSemiconductorASA-VestreRosten81,N-7075Tiller,Norway-Phone[phone]-Fax[phone]Revision:1.0Page1of22October2004FrequencyAgilityProtocolfornRF24XXnAN24-071.GeneralThisapplicationnotedescribesthelow-levelFrequencyAgilityProtocolfornRF24XX.ThisisaprotocolthatgivesprotectionagainstdisturbingtrafficfromfrequencystationarysystemslikeWLANandfrequencyhoppingdeviceslikeBluetooth.Theprotocolisgenericandcanbeusedinmanydifferentsystemsthatrequireresistanceagainstdisturbancefromothersystems.Byusingthisprotocol,asystemcanoperateincloseproximitywithsystemsusingdifferentWLANchannels,2,4GHzcordlessphones,2,4GHzremotecontrols,microwaveovens,Bluetoothdevicesandotherproprietary2,4GHzsystems.Basingitsfunctionalityonrecoverybyretransmissionoflostpackets,itwillbemuchmorereliablethanauni-directionalcommunicationprotocol.Thisdocumentdescribestheassumptionsthattheprotocolisbasedon,adescriptionofthefunctionality,implementationdescribedwithstatemachinediagrams,currentconsumptioncalculationsandC-codeexamples.A2.4GHz-mouse/keyboardapplicationisatypical2.4GHzapplicationthatwillbeusedinproximitywithWLANandBluetoothnodes.Thisdocumentwillforthatreasonusethewirelessmouse/keyboardapplicationwhendescribingtheFrequencyAgilityProtocolfornRF24XX.USBMCUnRF2401nRF24E1OpticalSensornRF24E1USBFigure1:Wireless2.4GHzmouse/keyboardapplicationAsseeninFigure1,awireless2.4GHzmouse/keyboardapplicationconsistsofawirelessmouse,awirelesskeyboardandareceiverunitforthePCside,referredtoasa“dongle”intherestofthisdocument.APPLICATIONNOTEFrequencyAgilityProtocolfornRF24XXNordicSemiconductorASA-VestreRosten81,N-7075Tiller,Norway-Phone[phone]-Fax[phone]Revision:1.0Page2of22October20042.AssumptionsThefrequencyagilityprotocolisbuiltonaseriesofassumptionsregardingmouse/keyboardapplicationsandthetrafficinthe2.4GHzband.Thetrafficinthe2.4GHzbandismainlyconsistentoffrequencystationarysystemslikeWLANandfrequency-hoppingsystemslikeBluetooth.Whilefrequencystationarysystemsoperateinaspecificpartoftheband,frequency-hoppingsystemswillgeneratetrafficinthewholeband.Alltrafficgeneratedbysystemsoperatinginthe2.4GHzbandispacketbased.Atagivenchannelinthe2.4GHzband,ifafrequencyhoppingsystemispresent,thelikelihoodofacollisionwithtrafficfromthatsystemisthesameineverychannel.Itisthereforenouseinchangingtheoperatingchannelifdisturbedbyafrequencyhoppingsystem.Ifthedisturbancecomesfromafrequencystationarysystem,itispossibletomoveinsuchmannerthatthelikelihoodforacollisionwiththesamesystemonthenewchannelisminimal.Amousewillrequireamuchhigherupdateratethanakeyboard.Itisassumedthatwhenamouseisused,itshouldbeupdatedevery8thmillisecond.Themousewillthereforehavepriorityinfrontofthekeyboardregardingupdates.ThedisturbancefromothersystemswillbestrongestclosetothePC,andthedongleattachedtothePCwillsufferthemost.3.Frequencyagilityprotocolfora2.4GHzmouse/keyboardapplicationBasedonthepreviousassumptionsthedefinitionofthefrequencyagilityprotocolemerges:“Aprotocolthatwillmoveowntraffictoanotherchannelinthe2.4GHzbandifastationarydisturbanceoccursatthecurrentlyusedfrequency.”Themainfunctionalityofthefrequencyagilityprotocolwillbeto:•Detectstationarydisturbance.•Moveinsuchmannerthatnewdisturbancefromthesamesourcewillnotoccur.•Donotmoveifdisturbedbyafrequencyhoppingsource.•Giveprioritytomousetraffic.Itisimportanttonoticethatthisprotocolwillonlyforceachangeinoperatingfrequencywhenastationarydisturbanceoccurs.Afterithaschangedtheoperatingfrequency,itwillbeonthenewchannelforarelativelongtime.Thefrequencyagilityprotocolfunctionalityisbasedonthecommunicationbetweenthemouseandthedongle.Whenthemouseisinuse,itwillsendapackettothedongleevery8thmillisecondandwaitforacknowledge.Themousewillre-sendapacketuptotwotimesifnoacknowledgementhasbeenreceived.Bluetoothwillstayupto650microsecondsononechannelbeforehopping.ThismeansthatifaBluetoothsystemisknockingoutthemouse’sfirstattempttosendapacket,thenexttwoshouldgettroughsinceeachpacket–APPLICATIONNOTEFrequencyAgilityProtocolfornRF24XXNordicSemiconductorASA-VestreRosten81,N-7075Tiller,Norway-Phone[phone]-Fax[phone]Revision:1.0Page3of22October2004acknowledgementcycletakesaboutonemillisecond.Itisthereforenotlikelythatafrequencyhoppingsystemwillcauseachangeinfrequency.Ifallthreeattemptstosendapacketfail,themouseanddonglewillchangechannelaccordingtoatable.Thetableisbuiltuptotakecareofthefunctionalitythatavoidsdisturbancefromthesamesourceatthenewchannel.Figure2showsatypicaltablewithchannelsusedbythefrequencyagilityprotocol.Thetableis“WLANweighted,”meaningitwillfindthenextchanneloutsideoftheassumedWLANchannelthatisdisturbingthecurrentlyusedchannel.IndexChannelFrequency[MHz]02240213224322702470352405435243556824686824087392439865246591124111041244111622462Figure2:ExampleofaWLANweightedchanneltableAsseenfromtheFigure3,theWLANtrafficcanbefoundinthreesub-bandsinthe2.4GHzband.LookingatFigure2andFigure3we’llseethatthetableinFigure2willtakecareofmovingthetrafficoutofadisturbingWLANchannel.2.480f(GHz)2.4052.4002.4152.4102.4252.4202.4352.4302.4452.4402.4552.