Digital modulation technique
- 1. INSERT THE TITLE OF YOUR PRESENTATION HERE Digital Modulation Technique Insert LOGO ALLPPT.com _ Free PowerPoint Templates, Diagrams and Charts
- 2. What is digital Modulation Technique? • In digital modulation, an analog carrier sign al is modulated by a discrete signal. • Digital modulation methods can be consider ed as digital-to-analog conversion, and • the corresponding demodulation or detection as analog-to-digital conversion.
- 3. 3 II. Digital Modulation • Better performance and more cost effective than analog modu lation methods (AM, FM, etc.) • Used in modern cellular systems • Advancements in VLSI, DSP, etc. have made digital solutions practical and affordable
- 4. 4 Digital Modulation • Performance advantages: 1) Resistant to noise, fading, & interference 2) Can combine multiple information types (voice, data, & vide o) in a single transmission channel 3) Improved security (e.g., encryption) → deters phone cloning + eavesdropping 4) Error coding is used to detect/correct transmission errors 5) Signal conditioning can be used to combat hostile MRC envi ronment 6) Can implement mod/dem functions using DSP software (inst ead of hardware circuits).
- 5. 5 Digital Modulation • Choice of digital modulation scheme – Many types of digital modulation methods → subtle differences – Performance factors to consider 1) low Bit Error Rate (BER) at low S/N 2) resistance to interference (ACI & CCI) & multipa th fading 3) occupying a minimum amount of BW 4) easy and cheap to implement in mobile unit 5) efficient use of battery power in mobile unit
- 6. 6 Digital Modulation – No existing modulation scheme simultane ously satisfies all of these requirements well. – Each one is better in some areas with tradeoffs of being worse in others.
- 8. ASK • ASK On-off keying (Amplitude Shift Keying) – frequenc y is kept constant, amplitude has 2 levels (for bit 1 and for bit 0) The binary sequence 0010110010
- 10. FSK (Frequency shift keyring)
- 12. PSK (Phase shift keyring)
- 13. PSK (Phase shift keying)
- 16. What is Quadrature Phase Shift Keying (QPSK)? • Quadrature Phase Shift Keying (QPSK) is a form of Phase Shift Keying in which two bits are modulated at once, selecting one of four possible ca rrier phase shifts (0, 90, 180, or 270 degrees). QPSK allows the signal to carry twice as much information as or dinary PSK using the same bandwidth.
- 17. 1999 BG Mobasseri 17 QPSK Quadrature phase shift keying • This is a 4 level modulation. • Every two bits is combined and mapped to one of 4 phases of an RF signal • These phases are 45o,135o,225o,315o Symbol energy
- 18. QPSK -Quadrature Phase Shift Keying • In Quadrature Phase Shift Keying (QPSK) two sinusoids (sin and cos) are taken as basis functions for modulation. • Modulation is achieved by varying the phase of the basis functions depending on the message symbols. • n QPSK, modulation is symbol based,where one symbol contains 2 bits. The follow ing equation outlines QPSK modulation technique. si(t)=2EsT√cos(2πfct+(2n−1)π4),n=1,2,3,4 where n=1, the phase shift is 45 degrees. This is called pi/4 QPSK