1、會計學(xué)1無線系統(tǒng)的微波與射頻設(shè)計無線系統(tǒng)的微波與射頻設(shè)計controlling the radiated frequency spectrum.more efficient use of the allocated RF bandwidth.flexibility in accommodating different baseband signal formats.第1頁/共69頁( )cos()V tAtAM FM PMAnalog modulation (vary continuously)Digital modulation (change in discrete steps)第2頁/共

2、69頁In contrast to analog modulation, digital modulation has:第3頁/共69頁第4頁/共69頁PPM (Pulse Position Modulation) is used in UWB (ultra wideband) system.第5頁/共69頁m(t): bandlimited modulating waveformfM: the maximum frequency of m(t)( )cos20mmMm tf tffn0/2: two-sided power spectral density of Gaussian white

3、 noise. Contributed by the transmitter channel and noise generated by the input stages of the receiver.第6頁/共69頁ttyttxtntntAtvIFIFmIFisin)(cos)()()()cos()(1( )( )coscoscos(2)2211(1cos2)( )sin222iIFmIFmIFIFv tv ttAAttxty ttxttAtvm21cos2)(02coscoscoscos/2cos1cos2/2sin22sincos第7頁/共69頁2/2ASiOutput signal

4、 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 degrade the input SNR.0022iMMnNfn f000iMSSNn f第8頁/共69頁Double-sideband suppressed ca

5、rrier (DSB-SC)()cos(2)cos(2)(tntAtAtvmIFmIFiiiNSNS200第9頁/共69頁FSSB=2FDSBBut002 222imMnNfn f000iMSSNn fConclusion: The coherent SSB and DSB-SC demodulators have the same SNR performance.第10頁/共69頁Disadvantage: the carrier power increases the total input power but does not contain any modulation informa

6、tion. 第11頁/共69頁tmtmtnttmAtvmIFicos)()(cos)(1 )(2202200222iiiMSSSmmNNmn fmIF m1, DSB-LC DSB-SC02iMNn f m=1 implies a reduction in SNR of 4.8dB. 第12頁/共69頁noncoherent demodulation 第13頁/共69頁20ii202for large S /N2iiSSmNNm第14頁/共69頁第15頁/共69頁An FM waveform: )sincos()(ttAtvmIFWhere, modulating signal tmtmmco

7、s)(Modulation index: m: Maximum frequency deviation.( )( )cos()0nIFmnv tAJnt 第16頁/共69頁( )( )cos()0nIFmnv tAJnt Spectrum:sidebands are 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頁/共69頁Through differentiator and envelop

8、e detection, the output voltage: ttvmmcos)(02/2ASi22030002200/2,2332mmmiiiSnnNNASSNN 2(1)|92( 1,)|23FMDSB LC mSNRifSNRImproving factor: 232第18頁/共69頁 , S/N, B =4 SNRFM=72SNRDSB-LC (m=1) BFM=5BDSB第19頁/共69頁第20頁/共69頁第21頁/共69頁Return-to-Zero codeNon-Return-to-Zero codePolar NRZ code DC=0第22頁/共69頁ttmtv0cos

9、)()(where m(t) =0 or 1(a) ModulatorIdentical to theDSB-SC modulator第23頁/共69頁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頁/共69頁(c) Envelope de

10、tection0( )( )v tm t第25頁/共69頁0201ttvcos)(12,( )1,( )0m tm t第26頁/共69頁第27頁/共69頁(PLL detector, the control voltage of VCO in PLL)Envelope detector121012011for11for0第28頁/共69頁ttmtv0cos)()(m (t) =1 or -1 Due to the sharp transitions caused by phase reversal, the spectrum of the PSK waveform is relatively

11、wide in bandwidth, resulting that PSK is impractical for multichannel wireless systems.PSK modulator第29頁/共69頁第30頁/共69頁ASK: Non-constant envelope modulationCoherent demodulationNoncoherent demodulation(envelope detection)FSK: Constant envelope modulationCoherent demodulationNoncoherent demodulation(a

12、fter conversion)PSK: Constant envelope modulationCoherent demodulation第31頁/共69頁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, employing digital signal p

13、rocessing (DSP) circuits to perform all function of signal conditioning, carrier recovery and synchronization demodulation, and signal formatting.第32頁/共69頁1. PCM Signal and Detectors2. Synchronous ASK3. Synchronous PSK4. Synchronous FSK5. Bit rate and Bandwidth Efficient6. Comparison of ASK FSK and

14、PSK Systems第33頁/共69頁Pulse coded modulation (PCM)第34頁/共69頁)()()()()(0000TnTsdttntsTvTtwhere00if ( )( )( )if ( )0if ( )0TtVTs tVs Ts t dtVTs tVs t 00( )TtnTn t dt第35頁/共69頁TtbTVdttsE022)(The output noise power2002TnN2The variance of the gaussian probability distribution function第36頁/共69頁第37頁/共69頁2200(0

15、)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頁/共69頁 If 20s(t)s (t)= -V, s (T)-VTThreshold level: 0(0)000 ( )( )0( )ePP s Tn TP n TVTASK: VT/22200/20201()22nbnVTEednerf

16、cnDue to symmetry of the PSK signal and the demodulator.(1)(0)eePP第39頁/共69頁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 21222221212En (t)E n (t)-n (t) En (t)n (t)2En1 and n2 are uncorrelated. Conclusion: The total noise power of the FSK demod

17、ulator is doubled relative to the synchronous ASK or PSK demodulator.第40頁/共69頁2200(0)e012/4020P S (T)n(T)0Pn (T)-n (T)VT1()224nbnVTeEdnerfcn(1)(0)ePeP第41頁/共69頁00bbESnn Rdimension of Eb : WSdimension of n0 : W/HzEb/n0 : dimensionlessthe bit rate of the binary message signaldimension of Rb : bps (bit

18、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 of the receiver bandwidth.第42頁/共69頁fnnfN00)2/(20bbESfnN RRb: depend on the type of modulation f may range from one to several times the

19、 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頁/共69頁bandwidth 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 R

20、F. 第44頁/共69頁第45頁/共69頁Coherent PSK: The lowest error rate, 9.6 dB for 10-5, high price for LO and wide signal bandwidth (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頁/共69頁Noncoherent FSK: 13.4

21、 dB for 10-5, widespread historical application in a wide variety of systems, such as date modems, teletype, 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: Tran

22、smitter and receiver are simple, 16.5 dB for 10-5, very poor in a fading environment, low data rates, short-range, low-cost, used in telemetry and RFID.第47頁/共69頁EXAMPLE 9.3, page 319. ASKFSKPSK4 Eb/n0 2 Eb/n0Eb/n015.6dB12.6dB9.6dBEb/n0 for Pe=10-5第48頁/共69頁PDF of a Rayleigh fading is 222/2)(rrerrfwhe

23、re 2is the rms value of the distribution of r(t).第49頁/共69頁22(0)00( )1(| )( )()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頁/共69頁20/

24、1(| )2br EnebPEreFor envelope detection of FSK21eP第51頁/共69頁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/b

25、En =第52頁/共69頁Eye diagram EXAMPLE 9.4, p. 323. 第53頁/共69頁 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頁/共69頁第55頁/共69頁+=The carrier of QPSK: 000( )cos()cos()sin(

26、)iiIQS tAtAtAt0000=45 , 135 ,-135 ,-45 i(21)i=0, 1, 2, 34iori第56頁/共69頁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

27、 the 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頁/共69頁Gray CodingAdvantage: When an error occurs, it is most likely that only one of the bits will be in e

28、rror, rather than both bits.S04501,1S113500,1S2-13500,0S3-4501,0第58頁/共69頁)2(210)()(nEerfcPPsQeIe(0)01BPSK()2beEPerfcnThe overall probability of error for a symbol is:( )( )()( )( )2( )01(1)(1)1 12() 2()2sIQeeeIIIseeePPPEPPPerfcn 第59頁/共69頁( )01()222esesbEPerfcEEn( )(0)01()2ebeeEPerfcPnfor BPSK第60頁/共69頁 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 sys