无线系统的微波与射频设计学习教案.pptx

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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。Comparing with transmitting baseband signal directlyComparing with transmitting baseband signal directly,to transmit data by modulating a higher frequency to transmit data by modulating a higher frequencycarrier wave has the effect on:carrier wave has the e

2、ffect on: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。Amplitude Frequency PhaseAM FM PMAnalog modulation(vary continuously)Digital modulation(change in discrete steps)第2页/共

3、69页第三页，共69页。more efficient use of the radio spectrum.more efficient use of the radio spectrum.usually requires less power.CDMAusually requires less power.CDMAover a fading communications channel.over a fading communications channel.more compatible with the use of error correcting codes.more compatib

4、le with the use of error correcting codes.In contrast to analog modulation,digital modulation has:第3页/共69页第四页，共69页。9.1 Analog Modulation9.1 Analog Modulation9.2 Binary Digital 9.2 Binary Digital ModulationModulation9.3 Error Probabilities for Binary 9.3 Error Probabilities for Binary ModulationModul

5、ation9.4 Effect of Rayleigh Fading on Bit Error 9.4 Effect of Rayleigh Fading on Bit Error RatsRats9.5 M-ary Digital 9.5 M-ary Digital ModulationModulation第4页/共69页第五页，共69页。9.1 Analog ModulationBasic analog modulation:Basic analog modulation:AM(SSB,DSB),FM,PMAM(SSB,DSB),FM,PMPPM(Pulse Position Modula

6、tion)is used in UWB(ultra wideband)system.1.Signal-Sideband Modulation1.Signal-Sideband Modulation2.DSB-SC 2.DSB-SC ModulationModulation3.DSB-LC 3.DSB-LC ModulationModulation4.Envelope Detection of DSB-LC 4.Envelope Detection of DSB-LC ModulationModulation5.Frequency Modulation(5.Frequency Modulatio

7、n(FMFM)第5页/共69页第六页，共69页。1.Signal-Sideband Modulation1.Signal-Sideband Modulation m(t):bandlimited modulating waveformfM:the maximum frequency of m(t)n0/2:two-sided power spectral density of Gaussian white noise.Contributed by the transmitter channel and noise generated by the input stages of the rec

8、eiver.第6页/共69页第七页，共69页。The demodulator LO is identical in frequency and phaseThe demodulator LO is identical in frequency and phasewith the modulator LO-synchronous or coherent demodulator.with the modulator LO-synchronous or coherent demodulator.第7页/共69页第八页，共69页。Input signal power:Input signal powe

9、r:Output signal power:Input narrowband noise power:Output noise power:The output SNR:Conclusion:SSB demodulator does not degrade the input SNR.第8页/共69页第九页，共69页。2.DSB-SC Modulation2.DSB-SC ModulationDouble-sideband suppressed carrier(DSB-SC)第9页/共69页第十页，共69页。Conclusion:Conclusion:the DSB-SC demodulato

10、r improves the the DSB-SC demodulator improves the input signal-to-noise ratio by a factor of two.input signal-to-noise ratio by a factor of two.FSSB=2FDSBButConclusion: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。3.DSB-LC Modulation3.DSB-LC ModulationAdv

11、antage:Advantage:the the carrier carrier signal signal can can be be used used as as a a reference reference signal signal to to phase-look phase-look the the local local oscillator oscillator to to synchronization synchronization with with the the incoming signal.incoming signal.Double-Sideband Lar

12、ge-Carrier(DSB-LC)Double-Sideband Large-Carrier(DSB-LC)Disadvantage: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。m:modulation index m:modulation index IF m1,DSB-LC DSB-SC m=1 implies a reduction in SNR of 4.8dB.第12页/共69页第十三页，共69

13、页。4.Envelope Detection of 4.Envelope Detection of DSB-LC ModulationDSB-LC Modulation Advantage of DSB-LCAdvantage of DSB-LC:can be detected by using an envelope:can be detected by using an envelope detector,without a LO and mixer,results in a much simple detector,without a LO and mixer,results in a

14、much simple receiver circuit,such as broadcast AM radio.receiver circuit,such as broadcast AM radio.noncoherent demodulation 第13页/共69页第十四页，共69页。Serious distortion for small SSerious distortion for small Si i/N/Ni i SNR SNRIf|m|1 over modulation,it will not correctly If|m|1 over modulation,it will no

15、t correctly recover the modulating recover the modulating waveformwaveform.第14页/共69页第十五页，共69页。5.Frequency Modulation(FM)5.Frequency Modulation(FM)Application:Application:Broadcast radio,television sound,two-way voice radio,Broadcast radio,television sound,two-way voice radio,AMPS cellular telephone

16、system.AMPS cellular telephone system.第15页/共69页第十六页，共69页。An FM waveform:Where,modulating signal Modulation index:Maximum frequency deviation.第16页/共69页第十七页，共69页。Spectrum:sidebands are spaced at fm on either side of the carrier at IF.amplitudes,given by AJn(),decrease for large n.Carsons rule ,B IF ba

17、ndwidth第17页/共69页第十八页，共69页。Through differentiator and envelope detection,the output voltage:For the equal transmit powerFor the equal transmit powerImproving factor:第18页/共69页第十九页，共69页。Conclusion:FM allows an improvement in SNR at the expense of FM allows an improvement in SNR at the expense of increa

18、sed bandwidth,while AM does not.increased bandwidth,while AM does not.,S/N,B=4 SNRFM=72SNRDSB-LC(m=1)BFM=5BDSB第19页/共69页第二十页，共69页。9.2 Binary Digital Modulation9.2 Binary Digital ModulationAmplitude shift keying(ASK)Frequency shift keying(FSK)Phase shift keying(PSK)第20页/共69页第二十一页，共69页。1.Binary Signals

19、1.Binary Signals2.Amplitude Shift 2.Amplitude Shift KeyingKeying3.Frequency Shift Keying(3.Frequency Shift Keying(FSKFSK)4.4.PSKPSK5.Carrier Synchroniza5.Carrier Synchronizationtion第21页/共69页第二十二页，共69页。1.Binary Signals1.Binary SignalsReturn-to-Zero codeNon-Return-to-Zero codePolar NRZ code DC=0第22页/共

20、69页第二十三页，共69页。2.Amplitude Shift Keying2.Amplitude Shift Keyingwhere m(t)=0 or 1(a)ModulatorIdentical to theDSB-SC modulator第23页/共69页第二十四页，共69页。Synchronous demodulation:After low-pass filtering(b)Synchronous demodulationNotice:LO has precisely the same phase and frequency as the incoming signal,or di

21、stortion may be introduced.第24页/共69页第二十五页，共69页。Envelope detectionnoncoherent,no LO(c)Envelope detection第25页/共69页第二十六页，共69页。3.Frequency Shift Keying(FSK)3.Frequency Shift Keying(FSK)-frequency deviation -frequency deviation第26页/共69页第二十七页，共69页。IF =IF =1 1,the up branch output:1/2,the up branch output:

22、1/2 The down branch output:0 The down branch output:0 IF =IF =2 2,the up branch output:0,the up branch output:0 The down branch output:1/2 reverse phase The down branch output:1/2 reverse phase It requires two coherent LO operating at It requires two coherent LO operating at1 1,and,and 2 2.第27页/共69页

23、第二十八页，共69页。(PLL detector,the control voltage of VCO in PLL)Envelope detector第28页/共69页第二十九页，共69页。4.PSK4.PSKThe phase of the carrier wave is“0The phase of the carrier wave is“0”or“180”or“180”.”.m(t)=1 or-1 Due to the sharp transitions caused by phase reversal,the spectrum of the PSK waveform is relati

24、vely wide 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 demodulationNon

25、coherent demodulation(after conversion)PSK:Constant envelope modulationCoherent demodulation第31页/共69页第三十二页，共69页。5.Carrier Synchronization5.Carrier Synchronization The effect of a phase error The effect of a phase error is that the output signal is is that the output signal is reduced in amplitude by

26、 cosreduced in amplitude by cos,while an error while an error in in frequency introduces a factor of cosfrequency introduces a factor of cost.t.The bit error rates of envelope detection are not as good as The bit error rates of envelope detection are not as good as those obtained with coherent detec

27、tion.those obtained with coherent detection.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 processing(DSP)circuits to perform all fun

28、ction 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。9.3 Error Probabilities for Binary Modulation The presence of noise in a communication channel introduces The presence of noise in a communication channel introduces the possibili

29、ty that errors will be made during the detection the possibility that errors will be made during the detection process.process.1.PCM Signal and Detectors2.Synchronous ASK3.Synchronous PSK4.Synchronous FSK5.Bit rate and Bandwidth Efficient6.Comparison of ASK FSK and PSK Systems第33页/共69页第三十四页，共69页。1.P

30、CM Signal and Detectors1.PCM Signal and DetectorsPulse coded modulation(PCM)第34页/共69页第三十五页，共69页。where第35页/共69页第三十六页，共69页。DefineDefine:bit energy:bit energyThe output noise powerThe variance of the gaussian probability distribution function第36页/共69页第三十七页，共69页。2.Synchronous ASK2.Synchronous ASKIdeal i

31、f s(t)=sIdeal if s(t)=s2 2(t)=0,s(t)=0,s0 0(T)=0(T)=0 if s(t)=s if s(t)=s1 1(t)=V,s(t)=V,s0 0(T)=VT(T)=VTPractical if sPractical if s0 0(T)+n(T)+n0 0(T)VT/2,m(t)=0 ok!(T)VT/2,m(t)=1 (T)VT/2,m(t)=1 第37页/共69页第三十八页，共69页。Let 第38页/共69页第三十九页，共69页。3.Synchronous PSK3.Synchronous PSK If Threshold level:0ASK:

32、VT/2 For For the the same same probability probability of of error,error,PSK PSK requires requires only only one-fourth one-fourth the the power power of of an an ASK ASK system.system.Since Since an an ASK ASK signal signal is is off off half half the the time,time,in in terms terms of of average a

33、verage transmit power,the PSK result is better by a factor of two(3 transmit power,the PSK result is better by a factor of two(3 dBdB).).Due to symmetry of the PSK signal and the demodulator.第39页/共69页第四十页，共69页。4.Synchronous FSK4.Synchronous FSKThreshold:0 the signal levels are similar to the PSK cas

34、e.For the noise voltages:For the noise voltages:n1 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。Conclusion:Conclusion:synchronous FSK requires 3 dB more signal power than equivalent s

35、ynchronous FSK requires 3 dB more signal power than equivalent PSK system for the same probability of error.PSK system for the same probability of error.synchronous FSK requires 3 dB less power than an ASK system on a synchronous FSK requires 3 dB less power than an ASK system on a peak power basis.

36、peak power basis.FSK and ASK have equal error rates when compared in FSK and ASK have equal error rates when compared in terms of average transmit terms of average transmit powerpower.第41页/共69页第四十二页，共69页。5.Bit Rate and Bandwidth Efficient5.Bit Rate and Bandwidth EfficientDefine RDefine Rb:b:dimensio

37、n 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: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页/

38、共69页第四十三页，共69页。IF bandwidth fIF bandwidth f RF bandwidthRb: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 efficiency(bps/Hz)of 1

39、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。6.Comparison of ASK FSK 6.Comparison of ASK FSK and PSK Systemsand PSK Systems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,

40、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 syst

41、ems,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:Transmitter and receiver are simple,16.5 dB for 10-5,very poor in a fading environment,l

42、ow data rates,short-range,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。9.4 Effect of Rayleigh Fading on Bit Error RatsPDF of a Rayleigh fading is where is the rms value of the distribut

43、ion of r(t).第49页/共69页第五十页，共69页。1.Effect of Rayleigh Fading 1.Effect of Rayleigh Fading on Coherent PSKon Coherent PSKWhereWhereis 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。2.Effect of Rayleigh Fading Effect of Rayleigh Fadi

44、ng on Noncoherent on Noncoherent FSKFSKFor envelope detection of FSK第51页/共69页第五十二页，共69页。3.Comparison of Faded and3.Comparison of Faded and Nonfaded Error Rates Nonfaded Error RatesConclusion:Fading has the effect of dramatic increasing the required bit energy-to-noise ratio.Error-correcting codes ca

45、n be used very effectively to improve the error rate for channel fading occurring in short bursts.Nonfaded case:第52页/共69页第五十三页，共69页。Eye diagram EXAMPLE 9.4,p.323.第53页/共69页第五十四页，共69页。9.5 M-ary Digital Modulation9.5 M-ary Digital Modulation Binary modulation methods(ASK,FSK and PSK)Binary modulation m

46、ethods(ASK,FSK and PSK)transmit one bit per signaling interval,with a transmit one bit per signaling interval,with a bandwidth efficiency of 1bps/Hz.bandwidth efficiency of 1bps/Hz.The data can be divided into groups.Each group have n binary codes.One symbol in M=2n is transmitted in each signaling

47、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。1.Quadrature Phase Shift Keying1.Quadrature Phase Shift Keying2.Probability of Error for 2.Probability of Error for QPSKQPSK3.M-ary Phase Shift 3.M-ary Phase Shift Keying4.Quadrature Amplitude Modulationtion (QAM)(QAM)5

48、.Channel 5.Channel CapacityCapacity第55页/共69页第五十六页，共69页。1.Quadrature Phase Shift Keying1.Quadrature Phase Shift Keyingn=2,M=4n=2,M=4+=The carrier of QPSK: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 sp

49、ectrum of a BPSK signal,because of the average transition between phase states is 900.The output of 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页/共69页第五十

50、八页，共69页。Gray CodingAdvantage:When an error occurs,it is most likely that only one of the bits will 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.Probability of Error for QPSK2.Probability of Error for QPSKThe overall probability of error for a symbol is: