WCA 102 Fundamentals of Digital Modulation Introduction Digital

WCA 102 Fundamentals of Digital Modulation – Introduction Digital Modulation in Wireless Communications 1

Agenda 4 Introductions 4 Who Cares? 4 What is Modulation 4 IQ Modulation Types 4 Filters and How Things Go Wrong 4 Measurements

Advantages of Digital Modulation 4 Spectral efficiency – use of a narrow bandwidth to send a large amount of data 0 Effective use of limited frequency resources 4 Good privacy and security features 0 Digital encryption techniques may be employed 4 Lower power consumption 4 Repeatable, more easily produced 4 Reduced device size

Modulation for Wireless 4 Media 0 Carrier V(t) = A cos(2πfc t + Φ) 4 The 3 essential parameters 0 Amplitude value 0 Frequency value 0 Phase value A(t) φ(t) ― Amplitude Modulation f(t) ― Frequency Modulation ― Phase Modulation

Analog Modulation 4 Amplitude Modulation 0 AM radio 4 Frequency Modulation 0 FM radio, TV audio signal 4 Phase Modulation 0 TV color image signal (including Amplitude Modulation)

Transmission of a Digital Message 4 Basically, it’s the same as Analog Modulation Methods 0 ASK: 0 FSK: 0 PSK: Amplitude shift keying V(t) = A(t) cos(2πfc t + Φ) Frequency shift keying V(t) = A(t) cos(2πf(t) t + Φ) Phase shift keying V(t) = A(t) cos(2πf(t) t + Φ(t)) 4 Digital modulation: Amplitude, frequency and/or Phase are used to represent a digital state

ASK 4 Amplitude shift keying 01’s or 0’s represented by different amplitudes 0 Could be accomplished with an AM system + =

ASK in IQ domain 4 ASK(OOK) 0 I: In phase component 0 Q: Quadrature component I Q 0 (0) I (1) Amplitude variation on I axis Q 0

FSK 4 Frequency shift keying 0 Select frequency based on each bit, 0 or 1 0 Could be done with simple FM system + =

FSK in IQ 4 Frequency change causes constant -rate phase change versus the reference carrier 4 Amplitude remains constant on the IQ circle 1 Symbol only turns π(ex) Q Phase π Time I 4 If the phase change is 90 degrees －π in one symbol period, the modulation type is called Minimum Shift Keying (remember this one) 1 Sp Pos offset 2 Sp 3 Sp Neg. Offset 4 Sp 5 Sp Pos. Offset

PSK 4 Phase shift keying 0 At the bit transitions invert the phase by 180° + =

Representation of PSK in IQ 4 PSK 0 Specifically, BPSK(Binary Phase Shift Keying) I Q (1) 0 I (0) Q Change Phase to 180° Relative to reference 0

Digital Modulation in Modern Wireless Systems 13

Digital Modulation Block Diagram Raw Data 110101 Compression, Error Correction, Encryption 01 00 011010100101 Low Pass Filter 11 Low Pass Filter Modulation Mapping I - Signal Q - Signal 01 10 10 10 01 01 I - Signal Q - Signal 10 Convert to Symbols Modulation, Upconversion RF Amplifier To IQ Modulator

Raw Data Conversion Raw Data 110101 Compression, Error Correction, Interleaving, Encryption 011010100101 Convert to Symbols 4 Raw data comes from the user 0 Digitized voice, keystrokes, jpegs… 4 Compression is employed for efficiency 4 Error correction is applied for transmission quality 4 Interleaving creates signal-dropout resistance 4 Encryption is applied for security

Data Bits, to Symbols Raw Data 110101 Compression, Error Correction, Encryption 011010100101 Convert to Symbols 01 10 10 10 01 01 4 Symbols are represented by the possible states of digital modulation 4 Higher order modulation allows more bits per symbol 4 What in the world does that mean? 0 Mapping symbols to I and Q

IQ Mapping 4 What is Mapping: 0 Translate a Symbol to a point in the IQ space 4 Example Q (01) 01 00 10 11 (11) I Modulation Mapping (00) (10)

Differential Modulation 4 QPSK(Quadrature PSK) 0 Assign the value to points in IQ Space 4 DQPSK(Differential QPSK) 0 The value is based on the transitions between 2 points Q Q (01) (11) (00) I I (11) (00) (10) 00= 0 01= +90 10= -90 11= +180

Higher Order Modulation 4 8 PSK(8 -PSK) 0 Assign the value to points in IQ Space 03 points per symbol 4 p/4 DQPSK 0 The value is based on the transitions between 2 points 0 Eliminates Zero Crossings Q (001) Q (110) (11) (00) (01) (111) I (100) (000) (101) (010) I (10) 00= -45 01= +135 10= -135 11= +45

More Higher Order Modulation 4 4 16 QAM(16 -Quadrature Amplitude Modulation) 0 Each IQ symbol location is represented by 4 data bits 64 QAM (64 -Quadrature Amplitude Modulation) 0 Each symbol is now worth 5 bits Q Q (000100) (001100) (010100) (111100)(101100) (100100) (000101) (001101) (010101) (111101)(101101) (100101) (000111) (001111) (010111) (111111)(101111) (100111) (000110) (001110) (010110) (111110)(101110) (100110) (000010) (001010) (010010) (111010)(101010) (100010) (000011) (001011) (010011) (111011)(101011) (100011) (000001) (001001) (010001) (111001)(101001) (100001) (000000) (001000) (010000) (111000) (100000) (0010) (0110) (1010) (0011) (0111) (1011) I (0001) (0101) (1001) (0000) (0100) (1000) I

Why Not Just Keep Going? 4 4 4 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 Q (01) Q (0010) (0110) (1010) (0011) (0111) (1011) (0001) (0101) (1001) (0000) (0100) (1000) (11) I (00) (10) I

The World’s Most Popular Modulation 4 Gaussian Minimum Shift Keying 4 Gaussian Filtered Form of FSK 4 Sum of I and Q results in a constant amplitude circle

Symbol Rate and Bit Rate 4 Modulation type determines number of bits per symbol 0 BPSK 1 bit/symbol 0 DBPSK 1 bit/symbol 0 QPSK 2 bit/symbol 0 p/4 DQPSK 2 bit/symbol 08 PSK 3 bit/symbol 016 QAM 4 bit/symbol 064 QAM 5 bit/symbol 0256 QAM 6 bit/symbol 4 For a fixed symbol rate, having more bits will provide a faster transfer rate 4 Setting up a WCA requires you to know the modulation type and symbol rate, not the bit rate

Others (for evening reading…. ) 4 32 QAM 0 ADSL etc 4 256 QAM 0 Microwave Communication 0 Some Cable Modem 4 1024 QAM 0 Still experimental 4 OQPSK 0 Offset QPSK 0 Used to avoid zero crossings 4 DQPSK 4 HPSK 0 Hybrid Phase Shift Keying 0 Also known as Orthogonal Complex Quadrature Phase Shift Keying (OCQPSK) 0 Used in CDMA 2000 (1 x. RTT) reverse link 4 VSB 0 Vestigial Side Band 08 VSB, 16 VSB 0 US Digital Broadcast TV

Filters, For Spectrum Control 01 00 I - Signal Low Pass Filter Q - Signal 10 11 Modulation Mapping Low Pass Filter To IQ Modulator

Sources of Error Raw Data 110101 Compression, Error Correction, Encryption 01 00 011010100101 Low Pass Filter 11 Low Pass Filter Modulation Mapping I - Signal Q - Signal 01 10 10 10 01 01 I - Signal Q - Signal 10 Convert to Symbols Modulation, Upconversion RF Amplifier To IQ Modulator

Sources of Error 4 IQ Quadrature modulation cos(2πfct) I LPF fc BPF 90 90° 90 Q LPF sin(2πfct)

Errors Receiving the Signal 4 IQ Quadrature demodulation cos(2πfct) LPF I LPF Q fc BPF 90 90 90° sin(2πfct) 4 This could be your customers receiver, or it could be a WCA vector spectrum analyzer

Common Measurements 29

What data was sent? 4 Data Display 4 Time vs. Amplitude 4 Error Summary

Error Summary 4 Error Vector Magnitude 4 Magnitude and Phase Error 4 Freq. Error 4 IQ offset

Modulation Errors vs. Time 4 Amplitude errors correlated to EVM 4 WCA is especially good at this

What can a WCA do? 4 Modulation types 4 Symbol rates 4 Filter types 4 One button setups 4 Standards

Summary 4 Digital modulation is cheaper, faster, more accurate, more efficient, more secure 4 Higher order modulation is used for greater transmission rates in the same spectrum occupancy 4 Higher order modulation is more susceptible to noise 4 Baseband filters are used to control spectrum 4 Wireless Communications Analyzers are used to evaluate modulation quality 0 WCA is particularly good at connecting effects in multiple domains

Product Line Contact Information 4 Dedicated Regional Contacts 0 Kurt Krukenberg phone: +1 503 -627 -5039 Regional Product Manager Americas 0 Dean Miles phone: +44 1344 -392249 Regional Product Manager EMEA 0 Charles Wu phone: +852 258 -56774 Product Line Representative Asia/Pac. Rim 4 Worldwide Factory Contacts 0 Dave Mc. Donald phone: +1 503 -627 -1279 TSC Primary Contact WCA 200 A and WCA 300 0 Tommy Sakurada phone: +81 3 -3448 -3272 Product Manager WCA 200 A & Wireless Apps 0 Jerry Harris phone: +1 503 -627 -4827 Product Manager WCA 300 & Non-Wireless Apps

Slide Archive (extras) 36

Filters Alter The Signal 01 00 I - Signal Low Pass Filter Q - Signal 10 11 Modulation Mapping Low Pass Filter To IQ Modulator

Common Filter Types 4 Gaussian 4 Raised Cosine 4 Root Raised Cosine 4 Setting up the WCA requires knowledge of what filter is used

Effect of Roll-off 4 Usually α is between 0. 2 - 0. 5 4 α determines the bandwidth BW = (1+α) *Symbol rate α=0. 0 α=1. 0

Put IQ on the Carrier Wave 4 IQ Quadrature modulation cos(2πfct) I LPF fc BPF 90 90° 90 Q LPF sin(2πfct)

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