1. DSP for Software Radio Waveform Processing – Single Carrier Systems Dr. Jamil Ahmad

2. 2 Digital Modulation Techniques Contents System Review The Fundamentals Digital Modulation Waveforms Bandwidth and Power Efficient Waveforms

3. 3 System Review Source Encode Encryption Channel Encoder Channel Encoder Modulator Channel D/A Conversion Decryption Source Decoder Channel Decoder Channel Decoder Demodulator Analog Input signal Analog Output signal Digital Output Direct Digital Input DSP/RF Front-End DSP/RF Front-End A/D Conversion Multiple Access Multiplex Waveform Processing

4. 4 The Fundamentals Why Modulate? Antenna Length Multiple Access Shannon’s Capacity Theorem Bandwidth and Power

5. 5 The Fundamentals- Modulation Principles Almost all communication systems transmit data using a sinusoidal carrier waveform. Electromagnetic signals propagate well. Choice of carrier frequency allows placement of signal in arbitrary part of spectrum. Modulation is implemented in practice by: Processing digital information at baseband. Pulse shaping and filtering of digital waveform. Baseband signal is mixed with signal from oscillator to bring up to RF. Radio frequency (RF) signal is filtered amplified and coupled with antenna.

6. 6 What is Modulation? Modulation shifts the spectrum of a baseband signal to that it becomes a bandpass signal. A bandpass signal has non-negligible spectrum only about some carrier frequency f c >> 0 Note: the bandwidth of a bandpass signal is the range of positive frequencies for which the spectrum is non- negligible. Unless otherwise specified, the bandwidth of a bandpass signal is twice the bandwidth of the baseband signal used to create it. BW=B BW=2B

7. 7 Digital Modulation Techniques The Definition Bits into Symbols and waveform Basic Types Amplitude Modulation (ASK) Frequency Modulation (FSK) Phase Modulation (PSK) Amplitude Frequency Phase

8. 8 Digital Modulation

9. 9 Waveform Processing Generic Modulation Waveform Generator I/Q-Comp. Mapping Symbol Converter Differential /Grey Encoder Pulse Shaping Sampling Converter Input Bits Modulated Signal Bit Rate Symbol RateSampling Rate Minimum Rate ?

10. 10 Digital Modulation Classification Linear Modulation Techniques Non-Linear Modulation Techniques -Digital Phase Modulations (PSK) -Digital Amplitude and Phase Modulations (QAM) -Continuous Phase Modulations (CPM) - FSK - GMSK Other Classifications: -Constant/Non-Constant Envelope -Bandwidth/Power Efficient Types

11. 11 Linear Modulation I/Q Complex Mapping Two independent real baseband signals (I and Q, Inphase and quadrature) are transmitted by modulating them into cosine and sine waveforms of the carrier frequency- Increased bandwidth Efficiency. For I- and Q-components, Nyquist pulse shaping principle (Overlapping pulses with zero- intersymbol interference, 0-ISI) is utilized in order to achieve high spectral efficiency.

12. 12 Linear Modulation Signal Representation Digital ModulationNyquist PulsesCarrier FrequencyM-ary Symbol Alphabet M-ary SymbolsBinary Bit Stream

13. 13 Digital Modulation Complex I/Q Modulation Taking Real Part of s(t) Where In-phase Channel Quadrature-Phase Channel

14. 14 Digital I/Q Modulation Simplified Traditional Diagram  Nyquist Filter Nyquist Filter I(t) Re[] Im[]Q(t) a(n)a(n)  s(t)s(t) Constellation Mapping

15. 15 Digital Modulation Complex Symbol Constellation Diagram BPSK BPSK, M=2 Re Im Mapping Rule bit phase 0 -> 0 1 -> 

16. 16 Complex Constellation QPSK M=4 QPSK, M=4 Bandwidth Efficiency = log 2 M = 2 bits/s/Hz

17. 17 Complex Constellation 16-QAM M=16 1.0 3.0 -3.0 Bandwidth Efficiency = log 2 M = 4 bits/s/Hz

18. 18 QPSK Modulation Phase Maping in QPSK Grey Encoding Differential Encoding Bits Phase (Grey) 00 01 10 11 -3  /4 3  /4 -  /4  /4 Phase (Diff. Change) 0  /2  /2  11 10 01 00 01 10 11

19. 19 QPSK Digital Modulator Architecture Symbol Converter Differential /Grey Encoder Digital Modulator Pulse Shaping Sampling Converter Input Bits Modulated Signal Baseband Processor 00 0 01 1 10 2 11 3 Binary- M-ary 01230123 -3  /4 3  /4 -  /4  /4 b(n)

20. 20 QPSK Modulator Differential Encoder 01230123 0  /2  /2  b(n) T

21. 21 Pulse Shaping T(n+1)TnT

22. 22 Digital Modulation Techniques Role of Pulse Shaping Issues with QPSK Design Example Input Bit Rate = 1Mbps Pulse Shaping  = 0.3 B = ?

23. 23 Digital Modulations OQPSK Same Signal Constellation as QPSK Phase Variations Restricted to Only 90 o Less Co-Channel Interference

24. 24 Digital Modulations OQPSK Symbol Converter Grey Encoder QPSK Modulator Sampling Convert Input Bits Modulated Signal Insert T/2 Delay

25. 25 Digital Modulations MSK Continuous Phase Frequency Modulation Technique Carrier Symbol Period Input Symbols Continuous Phase

26. 26 Digital Modulation MSK Phase Modulation Where

27. 27 Digital Modulations Comparison 1001000011 I(t) for QPSK/OQPSK Q(t) for QPSK Q(t) for OQPSK I(t) for MSK Q(t) for MSK

28. 28 Digital Modulation Spectrum Comparison QPSK/OQPSK BPSK MSK

29. 29 Digital Modulations GMSK Gaussian Filtered MSK Used in GSM and DECT More Compact Spectrum than MSK Some ISI Member of CPM Schemes

30. 30 Digital Modulations GMSK Where For GMSK

31. 31 Digital Modulations GMSK Filter Impulse Response Gaussian LPF FM Modulator h=0.5  (t) s(t)

32. 32 Digital Modulations  /4-QPSK Better Bandwidth Efficiency than GMSK Better Spectral Efficiency than QPSK/OQPSK Both Absolute and Differential Phase Encoding Used in IS-54 and PHS

33. 33 Digital Modulations  /4-QPSK Gray Encoding 01230123 -3  /4 3  /4 -  /4  /4 b(n)  /4 Gray Encoder t=2nT t=(2n+1) T  /4-QPSK Modulator In Bits Modulated Signal

34. 34  /4-QPSK Differential Encoding 01230123  /4 3  /4 -  /4 -3  /4 b(n)  /4 Differential Encoder t=2nT t=(2n+1)T  /4-QPSK Modulator T 0 1 2 3

35. 35 Digital Modulations M-PSK M=8 M=16

36. 36 Digital Modulation Techniques Issues with MPSK Less Amplitude fluctuations Allows Differential Encoding Frequency/Phase Sync Problems with Higher Order MPSK Degraded BER Performance for higher Order as Non-Optimal Euclidean Distance Between Constellation Points.

37. 37 Digital Modulation Techniques M-QAM Better BER Performance for higher M than equivalent M-PSK Bandwidth Efficient - Allows Power- Bandwidth Tradeoffs Requires Linear/Linearised PAs Generally not Suitable for Wireless Applications Used in DVB ETSI Standard

38. 38 Digital Modulation Techniques M-QAM M=16 Square Constellation Requires Absolute GrayEncoding

39. 39 Digital Modulation Techniques M-QAM for Wireless Application Star Constellation Non-Optimal ED Allows Differential Encoding Viewed as 2 8-PSK Signals