Fundamentals of Digital Modulation.ppt
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The document discusses digital modulation techniques used in wireless communications. It begins by outlining the advantages of digital modulation such as spectral efficiency and privacy. It then covers fundamental modulation types including ASK, FSK, and PSK. Higher order modulations like QAM are also introduced that allow more bits to be transmitted per symbol. The role of filters in controlling spectrum and sources of error during transmission and reception are explained. Finally, common measurements used to analyze modulation quality are briefly described.
Fundamentals of Digital Modulation.ppt
- 1. 1 WCA102 Fundamentals of Digital Modulation Digital Modulation – Introduction Digital Modulation in Wireless Communications
- 2. Agenda Introductions Who Cares? What is Modulation IQ Modulation Types Filters and How Things Go Wrong Measurements
- 3. Advantages of Digital Modulation Spectral efficiency – use of a narrow bandwidth to send a large amount of data Effective use of limited frequency resources Good privacy and security features Digital encryption techniques may be employed Lower power consumption Repeatable, more easily produced Reduced device size
- 4. Modulation for Wireless Media Carrier The 3 essential parameters Amplitude value A(t) ― Amplitude Modulation Frequency value f(t) ― Frequency Modulation Phase value φ(t) ― Phase Modulation V(t) = A cos(2πfc t + Φ)
- 5. Analog Modulation Amplitude Modulation AM radio Frequency Modulation FM radio, TV audio signal Phase Modulation TV color image signal (including Amplitude Modulation)
- 6. Transmission of a Digital Message Basically, it’s the same as Analog Modulation Methods ASK: Amplitude shift keying FSK: Frequency shift keying PSK: Phase shift keying Digital modulation: Amplitude, frequency and/or Phase are used to represent a digital state V(t) = A(t) cos(2πfc t + Φ) V(t) = A(t) cos(2πf(t) t + Φ) V(t) = A(t) cos(2πf(t) t + Φ(t))
- 7. ASK Amplitude shift keying 1’s or 0’s represented by different amplitudes Could be accomplished with an AM system = +
- 8. ASK in IQ domain ASK(OOK) I: In phase component Q: Quadrature component I Q 0 0 I Q Amplitude variation on I axis (0) (1)
- 9. FSK Frequency shift keying Select frequency based on each bit, 0 or 1 Could be done with simple FM system + =
- 10. FSK in IQ I Q Frequency change causes constant-rate phase change versus the reference carrier Amplitude remains constant on the IQ circle If the phase change is 90 degrees in one symbol period, the modulation type is called Minimum Shift Keying (remember this one) 1Sp 2Sp 3Sp 4Sp 5Sp Time Phase π －π Pos offset Neg. Offset Pos. Offset 1 Symbol only turns π(ex)
- 11. PSK Phase shift keying At the bit transitions invert the phase by 180° + =
- 12. Representation of PSK in IQ PSK Specifically, BPSK(Binary Phase Shift Keying) I Q 0 0 I Q Change Phase to 180° Relative to reference (1) (0)
- 13. 13 Digital Modulation in Modern Wireless Systems
- 14. Digital Modulation Block Diagram Compression, Error Correction, Encryption Raw Data 110101 011010100101 Convert to Symbols 01 10 10 10 01 01 00 01 10 11 Modulation Mapping I - Signal Q - Signal Low Pass Filter Low Pass Filter To IQ Modulator I - Signal Q - Signal Modulation, Upconversion RF Amplifier
- 15. Raw Data Conversion Raw data comes from the user Digitized voice, keystrokes, jpegs… Compression is employed for efficiency Error correction is applied for transmission quality Interleaving creates signal-dropout resistance Encryption is applied for security Compression, Error Correction, Interleaving, Encryption Raw Data 110101 011010100101 Convert to Symbols
- 16. Data Bits, to Symbols Symbols are represented by the possible states of digital modulation Higher order modulation allows more bits per symbol What in the world does that mean? Mapping symbols to I and Q Compression, Error Correction, Encryption Raw Data 110101 011010100101 Convert to Symbols 01 10 10 10 01 01
- 17. IQ Mapping What is Mapping: Translate a Symbol to a point in the IQ space Example I Q (00) (11) (10) (01) 00 01 10 11 Modulation Mapping
- 18. Differential Modulation QPSK(Quadrature PSK) Assign the value to points in IQ Space DQPSK(Differential QPSK) The value is based on the transitions between 2 points I Q I Q (00) (11) (10) (01) (01) (11) (10) (00) 00= 0 01= +90 10= -90 11= +180
- 19. Higher Order Modulation 8PSK(8-PSK) Assign the value to points in IQ Space 3 points per symbol p/4 DQPSK The value is based on the transitions between 2 points Eliminates Zero Crossings I Q (000) (011) (010) (001) (111) (101) (110) (100) I Q (00) (10) (01) (11) 00= -45 01= +135 10= -135 11= +45
- 20. More Higher Order Modulation 16QAM(16-Quadrature Amplitude Modulation) Each IQ symbol location is represented by 4 data bits 64QAM (64-Quadrature Amplitude Modulation) Each symbol is now worth 5 bits I Q (0000) (0100) (1100) (1000) (0001) (0101) (1101) (1001) (0011) (0111) (1111) (1011) (0010) (0110) (1110) (1010) I Q (011011) (010011) (110011) (111011) (011010) (010010) (110010) (111010) (011110) (010110) (110110) (111110) (011111) (010111) (110111) (111111) (000011) (001011) (000010) (001010) (000110) (001110) (000111) (001111) (101011) (100011) (101010) (100010) (101110) (100110) (101111) (100111) (011101) (010101) (110101) (111101) (011100) (010100) (110100) (111100) (000101) (001101) (000100) (001100) (101101) (100101) (101100) (100100) (011000) (010000) (110000) (111000) (011001) (010001) (110001) (111001) (000000) (001000) (000001) (001001) (101000) (100000) (101001) (100001)
- 21. Why Not Just Keep Going? Errors in IQ modulation create symbol errors in transmission Vector Errors are created (what’s that?) Noise in the transmission channel create symbol errors Inaccuracies in the receiver creates errors Signal-to-noise requirements increase with higher order modulations I Q (0000) (0100) (1100) (1000) (0001) (0101) (1101) (1001) (0011) (0111) (1111) (1011) (0010) (0110) (1110) (1010) I Q (00) (11) (10) (01)
- 22. The World’s Most Popular Modulation Gaussian Minimum Shift Keying Gaussian Filtered Form of FSK Sum of I and Q results in a constant amplitude circle
- 23. Symbol Rate and Bit Rate Modulation type determines number of bits per symbol BPSK 1 bit/symbol DBPSK 1 bit/symbol QPSK 2 bit/symbol p/4 DQPSK 2 bit/symbol DQPSK 2 bit/symbol 8PSK 3 bit/symbol 16QAM 4 bit/symbol 64QAM 5 bit/symbol 256QAM 6 bit/symbol For a fixed symbol rate, having more bits will provide a faster transfer rate Setting up a WCA requires you to know the modulation type and symbol rate, not the bit rate
- 24. Others (for evening reading….) 32QAM ADSL etc 256QAM Microwave Communication Some Cable Modem 1024QAM Still experimental OQPSK Offset QPSK Used to avoid zero crossings DQPSK HPSK Hybrid Phase Shift Keying Also known as Orthogonal Complex Quadrature Phase Shift Keying (OCQPSK) Used in CDMA2000 (1xRTT) reverse link VSB Vestigial Side Band 8VSB, 16VSB US Digital Broadcast TV
- 25. Filters, For Spectrum Control 00 01 10 11 Modulation Mapping I - Signal Q - Signal Low Pass Filter Low Pass Filter To IQ Modulator
- 26. Sources of Error Compression, Error Correction, Encryption Raw Data 110101 011010100101 Convert to Symbols 01 10 10 10 01 01 00 01 10 11 Modulation Mapping I - Signal Q - Signal Low Pass Filter Low Pass Filter To IQ Modulator I - Signal Q - Signal Modulation, Upconversion RF Amplifier
- 27. Sources of Error IQ Quadrature modulation 90 90 Q I fc 90° sin(2πfct) cos(2πfct) LPF LPF BPF
- 28. Errors Receiving the Signal IQ Quadrature demodulation This could be your customers receiver, or it could be a WCA vector spectrum analyzer cos(2πfct) 90 90 Q I fc 90° sin(2πfct) LPF LPF BPF
- 30. What data was sent? Data Display Time vs. Amplitude Error Summary
- 31. Error Summary Error Vector Magnitude Magnitude and Phase Error Freq. Error IQ offset
- 32. Modulation Errors vs. Time Amplitude errors correlated to EVM WCA is especially good at this
- 33. What can a WCA do? Modulation types Symbol rates Filter types One button setups Standards Tektronix Wireless Communication Analyzer WCA230A / WCA280A Modulation types BPSK, QPSK, Pai/4 Shift DQPSK, 8PSK, 16QAM, 64QAM, 256QAM, GMSK, GFSK Symbol rates to 12.8 Msps Filter types Measurement Filter: Root Cosine Reference Filter: Cosine, Gauss Filter Parameter: α/BT： 0.0001 to 1, 0.0001 step One button setups PDC, PHS, NADC, TETRA, GSM, CDPD, Bluetooth Standards W-CDMA Downlink(opt.22), W-CDMA Uplink(opt.23), GSM/EDGE(opt.24)
- 34. Summary Digital modulation is cheaper, faster, more accurate, more efficient, more secure Higher order modulation is used for greater transmission rates in the same spectrum occupancy Higher order modulation is more susceptible to noise Baseband filters are used to control spectrum Wireless Communications Analyzers are used to evaluate modulation quality WCA is particularly good at connecting effects in multiple domains
- 35. Product Line Contact Information Dedicated Regional Contacts Kurt Krukenberg phone: +1 503-627-5039 Regional Product Manager Americas Dean Miles phone: +44 1344-392249 Regional Product Manager EMEA Charles Wu phone: +852 258-56774 Product Line Representative Asia/PacRim Worldwide Factory Contacts Dave McDonald phone: +1 503-627-1279 TSC Primary Contact WCA200A and WCA300 Tommy Sakurada phone: +81 3-3448-3272 Product Manager WCA200A & Wireless Apps Jerry Harris phone: +1 503-627-4827 Product Manager WCA300 & Non-Wireless Apps
- 37. Filters Alter The Signal 00 01 10 11 Modulation Mapping I - Signal Q - Signal Low Pass Filter Low Pass Filter To IQ Modulator
- 38. Common Filter Types Gaussian Raised Cosine Root Raised Cosine Setting up the WCA requires knowledge of what filter is used
- 39. Effect of Roll-off Usually α is between 0.2 - 0.5 α determines the bandwidth α=0.0 α=1.0 BW = (1+α) *Symbol rate
- 40. Put IQ on the Carrier Wave IQ Quadrature modulation 90 90 Q I fc 90° sin(2πfct) cos(2πfct) LPF LPF BPF
- 41. Structure of Tx/Rx Scrambling Error correction encoding Interleaving 1st Interleaving 2nd Data stream IQ mapping IQ modulation Scrambling Error correction decoding De-interleaving 1st De-interleaving 2nd Data stream IQ de-mapping IQ demodulation Encode