Module III Taub Ch.6 PSK QPSK M-ary PSK FSK M-ary FSK MSK. - презентация

1 Module III Taub Ch.6 PSK QPSK M-ary PSK FSK M-ary FSK MSK

2 Examples of Modulation Amplitude Shift Keying (ASK) or On/Off Keying (OOK): Frequency Shift Keying (FSK): Phase Shift Keying (PSK):

3 Description of binary ASK,PSK, and FSK schemes Bandpass binary data transmission system Modulator Channel H c (f) Demodulator (receiver) {b k } Binary data Input {bk}{bk} Transmit carrier Clock pulses Noise n(t) Clock pulses Local carrier Binary data output Z(t) + + V(t) ּ+ּ+

4 Binary information over bandpass channels

5 Digital modulation and channel

6 Digital Demodulator

7 Signal Regeneration

8 Bandwidth of signal Baseband versus bandpass: Baseband signal Bandpass signal Local oscillator

9 BPSK-Transmitter

10 Scheme to recover the baseband signal in BPSK

11 BPSK-Receiver

12 Cont..

13 Spectrum of BPSK

14 PSD of NRZ data b(t) & binary PSK

15 Geometrical Representation of BPSK Signals

16 Differential Phase-Shift Keying Merit – it eliminate the ambiguity about whether the demodulated data is or is not inverted. Avoids the need to provide the synchronous carrier required at the demodulator for detecting a BPSK signal. Arbitrarily assuming that in the first interval b(0)=0. In the demodulator, the data will be correctly determined regardless of our assumption concerning b(0) - Invariant feature of the system. i.e no change in b(t) occur whenever d(t)=0, and a change in b(t) occurs whenever d(t)=1. When d(t)=0 the phase of the carrier does not change at the beginning of the bit interval, while when d(t)=1 there is a phase change of magnitude.

17 Means of generating a DPSK signal

18 Logic waveforms to illustrate the response b(t) to an input d(t)

19 Method of recovering data from the DPSK signal

20 Cont.. The transmitted data d(t) can be readily determined from the product b(t)b(t-T b ). If d(t)=0 then there was no phase change and b(t)=b(t-T b ) both being +1V or both being -1V. In this case b(t)b(t-T b )=1. If however d(t)=1 then there was a phase change and either b(t)=1V with b(t-T b )= -1V or vice versa. In either case b(t)b(t-T b )= -1.

21 Type-D flip-flop

22 Quadrature Phase-Shift Keying (QPSK) BW for BPSK must be nominally 2f b. QPSK allows bits to be transmitted at half the BW. In a QPSK system the type D flip-flop is used as a one bit storage device.

23 An offset QPSK Transmitter

24 Waveforms for the QPSK Transmitter

25 OQPSK

26 Phasor diagram for sinusoids in QPSK Transmitter

27 A QPSK Receiver Carrier Recovery Circuit

28 Signal Space Representation

29 The four QPSK signal drawn in signal space 2 2

30 M-ary PSK

31 Geometrical representation of M-ary PSK signals

32 Cont..

33

34 M-ary PSK Transmitter

35 M-ary PSK receiver

36 BFSK

37 BFSK signal generator

38 Spectrum of BFSK

39 The PSD of individual terms

40 A BFSK Receiver

41 Geometrical Representation of Orthogonal BFSK

42 Signal space representation orthogonal / non-orthogonal

43 An M-ary Communication System

44 M-ary FSK

45 Power Spectral Density of M-ary FSK (four frequencies)

46 Geometrical Representation of orthogonal M-ary FSK (M=3) when the frequencies are selected to generate orthogonal signals

47 MSK