无线系统的微波与射频设计学习教案

1、会计学1无线系统无线系统(xtng)的微波与射频设计的微波与射频设计第一页，共69页。controlling the radiated frequency spectrum.more efficient use of the allocated RF bandwidth.flexibility in accommodating different baseband signal formats.第1页/共69页第二页，共69页。( )cos()V tAtAM FM PMAnalog modulation (vary continuously)Digital modulation (change

2、 in discrete steps)第2页/共69页第三页，共69页。In contrast to analog modulation, digital modulation has:第3页/共69页第四页，共69页。第4页/共69页第五页，共69页。PPM (Pulse Position Modulation) is used in UWB (ultra wideband) system.第5页/共69页第六页，共69页。m(t): bandlimited modulating waveformfM: the maximum frequency of m(t)( )cos20mmMm tf

3、 tffn0/2: two-sided power spectral density of Gaussian white noise. Contributed by the transmitter channel and noise generated by the input stages of the receiver.第6页/共69页第七页，共69页。ttyttxtntntAtvIFIFmIFisin)(cos)()()()cos()(1( )( )coscoscos(2)2211(1cos2)( )sin222iIFmIFmIFIFv tv ttAAttxty ttxttAtvm21c

4、os2)(02coscoscoscos/2cos1cos2/2sin22sincos第7页/共69页第八页，共69页。2/2ASiOutput signal power: 48)2(21220iSAASxttAtvm21cos2)(0Input narrowband noise power: 2222211( )( )( )22( )( )iNE ntE xtE ytE xtE ytOutput noise power: 4)(41)(21220iNtxEtxENThe output SNR: iiNSNS00Conclusion: SSB demodulator does not degra

5、de the input SNR.0022iMMnNfn f000iMSSNn f第8页/共69页第九页，共69页。Double-sideband suppressed carrier (DSB-SC)()cos(2)cos(2)(tntAtAtvmIFmIFiiiNSNS200第9页/共69页第十页，共69页。FSSB=2FDSBBut002 222imMnNfn f000iMSSNn fConclusion: The coherent SSB and DSB-SC demodulators have the same SNR performance.第10页/共69页第十一页，共69页。D

6、isadvantage: the carrier power increases the total input power but does not contain any modulation information. 第11页/共69页第十二页，共69页。tmtmtnttmAtvmIFicos)()(cos)(1 )(2202200222iiiMSSSmmNNmn fmIF m1, DSB-LC DSB-SC02iMNn f m=1 implies a reduction in SNR of 4.8dB. 第12页/共69页第十三页，共69页。noncoherent demodulati

7、on 第13页/共69页第十四页，共69页。20ii202for large S /N2iiSSmNNm第14页/共69页第十五页，共69页。第15页/共69页第十六页，共69页。An FM waveform: )sincos()(ttAtvmIFWhere, modulating signal tmtmmcos)(Modulation index: m: Maximum frequency deviation.( )( )cos()0nIFmnv tAJnt 第16页/共69页第十七页，共69页。( )( )cos()0nIFmnv tAJnt Spectrum:sidebands are

8、spaced at fm on either side of the carrier at IF.amplitudes, given by AJn(), decrease for large n.)1 (2MfB , B IF bandwidth第17页/共69页第十八页，共69页。Through differentiator and envelope detection, the output voltage: ttvmmcos)(02/2ASi22030002200/2,2332mmmiiiSnnNNASSNN 2(1)|92( 1,)|23FMDSB LC mSNRifSNRImprov

9、ing factor: 232第18页/共69页第十九页，共69页。 , S/N, B =4 SNRFM=72SNRDSB-LC (m=1) BFM=5BDSB第19页/共69页第二十页，共69页。第20页/共69页第二十一页，共69页。第21页/共69页第二十二页，共69页。Return-to-Zero codeNon-Return-to-Zero codePolar NRZ code DC=0第22页/共69页第二十三页，共69页。ttmtv0cos)()(where m(t) =0 or 1(a) ModulatorIdentical to theDSB-SC modulator第23页

10、/共69页第二十四页，共69页。22cos1)(cos)()(001ttmttvtvAfter low-pass filtering )(21)(0tmtv(b) Synchronous demodulationNotice: LO has precisely the same phase and frequency as the incoming signal, or distortion may be introduced.第24页/共69页第二十五页，共69页。(c) Envelope detection0( )( )v tm t第25页/共69页第二十六页，共69页。0201ttvco

11、s)(12,( )1,( )0m tm t第26页/共69页第二十七页，共69页。第27页/共69页第二十八页，共69页。(PLL detector, the control voltage of VCO in PLL)Envelope detector121012011for11for0第28页/共69页第二十九页，共69页。ttmtv0cos)()(m (t) =1 or -1 Due to the sharp transitions caused by phase reversal, the spectrum of the PSK waveform is relatively wide

12、in bandwidth, resulting that PSK is impractical for multichannel wireless systems.PSK modulator第29页/共69页第三十页，共69页。第30页/共69页第三十一页，共69页。ASK: Non-constant envelope modulationCoherent demodulationNoncoherent demodulation(envelope detection)FSK: Constant envelope modulationCoherent demodulationNoncoheren

13、t demodulation(after conversion)PSK: Constant envelope modulationCoherent demodulation第31页/共69页第三十二页，共69页。Two ways to realize synchronization: transmit a pilot carrier, used to phase-lock the LO. use a carrier-recovery circuit. Use a phase-locked loop or by frequency multiplier and divider. In fact,

14、 employing digital signal processing (DSP) circuits to perform all function of signal conditioning, carrier recovery and synchronization demodulation, and signal formatting.第32页/共69页第三十三页，共69页。1. PCM Signal and Detectors2. Synchronous ASK3. Synchronous PSK4. Synchronous FSK5. Bit rate and Bandwidth

15、Efficient6. Comparison of ASK FSK and PSK Systems第33页/共69页第三十四页，共69页。Pulse coded modulation (PCM)第34页/共69页第三十五页，共69页。)()()()()(0000TnTsdttntsTvTtwhere00if ( )( )( )if ( )0if ( )0TtVTs tVs Ts t dtVTs tVs t 00( )TtnTn t dt第35页/共69页第三十六页，共69页。TtbTVdttsE022)(The output noise power2002TnN2The variance of

16、 the gaussian probability distribution function第36页/共69页第三十七页，共69页。第37页/共69页第三十八页，共69页。2200(0)00/20022 ( )( )2( )22enVTnVTPP s Tn TVTeP n TdnLet 02nx2(0)2 211()22 2TxTVexVPedxerfc02dndx001242 22 22 2bbEEVTTTVTn Tn02n T(0)01()24beEPerfcn01()24beEPerfcn(1)(0)eePP2002TnN第38页/共69页第三十九页，共69页。 If 20s(t)s

17、(t)= -V, s (T)-VTThreshold level: 0(0)000 ( )( )0( )ePP s Tn TP n TVTASK: VT/22200/20201()22nbnVTEednerfcnDue to symmetry of the PSK signal and the demodulator.(1)(0)eePP第39页/共69页第四十页，共69页。20s (t)s (t)-V and s (T)-VTThreshold: 0 the signal levels are similar to the PSK case.(t) n-(t) n (t)n 21222221

18、212En (t)E n (t)-n (t) En (t)n (t)2En1 and n2 are uncorrelated. Conclusion: The total noise power of the FSK demodulator is doubled relative to the synchronous ASK or PSK demodulator.第40页/共69页第四十一页，共69页。2200(0)e012/4020P S (T)n(T)0Pn (T)-n (T)VT1()224nbnVTeEdnerfcn(1)(0)ePeP第41页/共69页第四十二页，共69页。00bbE

19、Snn Rdimension of Eb : WSdimension of n0 : W/HzEb/n0 : dimensionlessthe bit rate of the binary message signaldimension of Rb : bps (bit per second)The signal power: bbSR E It means the error rate will increase with an increase in bit rate, for a fixed noise power spectrum density, and is independent

20、 of the receiver bandwidth.第42页/共69页第四十三页，共69页。fnnfN00)2/(20bbESfnN RRb: depend on the type of modulation f may range from one to several times the bit rate Rb.S/N before demodulation = S/N after demodulation. Reference to equation (9.2), (9.3), (9.4) and (9.64, (9.65).第43页/共69页第四十四页，共69页。bandwidth

21、efficiency (bps/Hz) of 1 bps/Hz. For a binary modulation method, transmitting one bit each bit period. means thatThis is for the baseband, not for the IF or RF. 第44页/共69页第四十五页，共69页。第45页/共69页第四十六页，共69页。Coherent PSK: The lowest error rate, 9.6 dB for 10-5, high price for LO and wide signal bandwidth (

22、2Rb4Rb). Best in fading environments. Used in space and satellite communications.Coherent FSK: Requires 34 dB more power than PSK. 12. 6 dB for 10-5. 第46页/共69页第四十七页，共69页。Noncoherent FSK: 13.4 dB for 10-5, widespread historical application in a wide variety of systems, such as date modems, teletype,

23、fax. Coherent ASK: Transmitter is simple. 15.6dB for 10-5, very poor in a fading environment, low data rates limited to short-range, low-lost, used in telemetry and RFID.Noncoherent ASK: Transmitter and receiver are simple, 16.5 dB for 10-5, very poor in a fading environment, low data rates, short-r

24、ange, low-cost, used in telemetry and RFID.第47页/共69页第四十八页，共69页。EXAMPLE 9.3, page 319. ASKFSKPSK4 Eb/n0 2 Eb/n0Eb/n015.6dB12.6dB9.6dBEb/n0 for Pe=10-5第48页/共69页第四十九页，共69页。PDF of a Rayleigh fading is 222/2)(rrerrfwhere 2is the rms value of the distribution of r(t).第49页/共69页第五十页，共69页。22(0)00( )1(| )( )(

25、)2bebS TVTr EPErP n TrVTerfcn (0)(0)01(| )( )121eebrrPPEr fr dr(0)000 ( )( )0( )ePP s Tn TP n TVT2bEV T022nEbis the average received bit energy-to-noise power spectral density ratio of the faded received signal.第50页/共69页第五十一页，共69页。20/1(| )2br EnebPEreFor envelope detection of FSK21eP第51页/共69页第五十二页，共

26、69页。Conclusion: Fading has the effect of dramatic increasing the required bit energy-to-noise ratio. Error-correcting codes can be used very effectively to improve the error rate for channel fading occurring in short bursts.Nonfaded case: 2021/bEn =第52页/共69页第五十三页，共69页。Eye diagram EXAMPLE 9.4, p. 323

27、. 第53页/共69页第五十四页，共69页。 The data can be divided into groups. Each group have n binary codes. One symbol in M=2n is transmitted in each signaling interval. Thus a bandwidth efficiency of n bps/Hz is achieved.第54页/共69页第五十五页，共69页。第55页/共69页第五十六页，共69页。+=The carrier of QPSK: 000( )cos()cos()sin()iiIQS tAtA

28、tAt0000=45 , 135 ,-135 ,-45 i(21)i=0, 1, 2, 34iori第56页/共69页第五十七页，共69页。Note: Each QPSK phase state can be used to represent two bits of data.The bandwidth of the QPSK spectrum is narrower than the spectrum of a BPSK signal, because of the average transition between phase states is 900.The output of t

29、he QPSK modulator is a double sideband suppressed carrier signal.The QPSK output is a constant envelope signal. The channel should be constant group delay.Block diagram of a QPSK modulator第57页/共69页第五十八页，共69页。Gray CodingAdvantage: When an error occurs, it is most likely that only one of the bits will

30、 be in error, rather than both bits.S04501,1S113500,1S2-13500,0S3-4501,0第58页/共69页第五十九页，共69页。)2(210)()(nEerfcPPsQeIe(0)01BPSK()2beEPerfcnThe overall probability of error for a symbol is:( )( )()( )( )2( )01(1)(1)1 12() 2()2sIQeeeIIIseeePPPEPPPerfcn 第59页/共69页第六十页，共69页。( )01()222esesbEPerfcEEn( )(0)01()2ebeeEPerfcPnfor BPSK第60页/共69页第六十一页，共69页。 Led to the extensive use of QPSK modulation in a wide variety of applications, such as CDMA-PCS telephone systems, The Iridium LEO satellite telephone system, and the DB