1 WCA102 Fundamentals of Digital Modulation Digital Modulation – Introduction Digital Modulation in Wireless Communications

Agenda  Introductions  Who Cares?  What is Modulation  IQ Modulation Types  Filters and How Things Go Wrong  Measurements

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

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)

Analog Modulation  Amplitude Modulation  AM radio  Frequency Modulation  FM radio, TV audio signal  Phase Modulation  TV color image signal (including Amplitude Modulation)

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))

ASK  Amplitude shift keying  1’s or 0’s represented by different amplitudes  Could be accomplished with an AM system = +

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)

FSK  Frequency shift keying  Select frequency based on each bit, 0 or 1  Could be done with simple FM system + =

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) 1Sp2Sp3Sp4Sp5Sp Time Phase π －π－π Pos offsetNeg. OffsetPos. Offset 1 Symbol only turns π(ex)

PSK  Phase shift keying  At the bit transitions invert the phase by 180° + =

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 Digital Modulation in Modern Wireless Systems

Digital Modulation Block Diagram Compression, Error Correction, Encryption Raw Data Convert to Symbols Modulation Mapping I - Signal Q - Signal Low Pass Filter To IQ Modulator I - Signal Q - Signal Modulation, Upconversion RF Amplifier

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 Convert to Symbols

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 Convert to Symbols

IQ Mapping  What is Mapping:  Translate a Symbol to a point in the IQ space  Example I Q (00) (11) (10) (01) Modulation Mapping

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) (11) (10) (00) 00= 0 01= = = +180

Higher Order Modulation  8PSK(8-PSK)  Assign the value to points in IQ Space  3 points per symbol   /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

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)

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)

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

Symbol Rate and Bit Rate  Modulation type determines number of bits per symbol  BPSK1 bit/symbol  DBPSK1 bit/symbol  QPSK2 bit/symbol  p/4 DQPSK2 bit/symbol  DQPSK2 bit/symbol  8PSK3 bit/symbol  16QAM4 bit/symbol  64QAM5 bit/symbol  256QAM6 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

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

Filters, For Spectrum Control Modulation Mapping I - Signal Q - Signal Low Pass Filter To IQ Modulator

Sources of Error Compression, Error Correction, Encryption Raw Data Convert to Symbols Modulation Mapping I - Signal Q - Signal Low Pass Filter To IQ Modulator I - Signal Q - Signal Modulation, Upconversion RF Amplifier

Sources of Error  IQ Quadrature modulation 90 Q I fc 90° sin(2πfct) cos(2πfct) LPF BPF

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 Q I fc 90° sin(2πfct) LPF BPF

29 Common Measurements

What data was sent?  Data Display  Time vs. Amplitude  Error Summary

Error Summary  Error Vector Magnitude  Magnitude and Phase Error  Freq. Error  IQ offset

Modulation Errors vs. Time  Amplitude errors correlated to EVM  WCA is especially good at this

What can a WCA do?  Modulation types  Symbol rates  Filter types  One button setups  Standards

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

Product Line Contact Information  Dedicated Regional Contacts  Kurt Krukenberg phone: Regional Product Manager Americas  Dean Miles phone: Regional Product Manager EMEA  Charles Wu phone: Product Line Representative Asia/PacRim  Worldwide Factory Contacts  Dave McDonald phone: TSC Primary Contact WCA200A and WCA300  Tommy Sakurada phone: Product Manager WCA200A & Wireless Apps  Jerry Harris phone: Product Manager WCA300 & Non-Wireless Apps

36 Slide Archive (extras)

Filters Alter The Signal Modulation Mapping I - Signal Q - Signal Low Pass Filter To IQ Modulator

Common Filter Types  Gaussian  Raised Cosine  Root Raised Cosine  Setting up the WCA requires knowledge of what filter is used

Effect of Roll-off  Usually α is between  α determines the bandwidth α=0.0α=1.0 BW = (1+α) *Symbol rate

Put IQ on the Carrier Wave  IQ Quadrature modulation 90 Q I fc 90° sin(2πfct) cos(2πfct) LPF BPF

Structure of Tx/Rx Scrambling Error correction encoding Interleaving 1stInterleaving 2nd Data stream IQ mappingIQ modulation Scrambling Error correction decoding De-interleaving 1st De-interleaving 2nd Data stream IQ de-mappingIQ demodulation Encode