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- - -- - - - -- - - NSARC - Quick Guide to Digital Modulation 1 07-Dec-2006 Digital Modulation Nick Massey VA7NRM

Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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Page 1: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 107-Dec-2006

Digital Modulation

Nick MasseyVA7NRM

Page 2: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 207-Dec-2006

Encoding

Page 3: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 307-Dec-2006

Modulation

■ What aspects of the RF carrier can we �modulate� to convey the information?

Page 4: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 407-Dec-2006

ASK, FSK & PSK

ASKAmplitude Shift Keying

FSKFrequency Shift Keying

PSKPhase Shift Keying

I

Q

I

Q

I

Q

Page 5: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 507-Dec-2006

m-ary Modulation

■ Conveys more than one bit of data per symbol

Page 6: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 607-Dec-2006

Complex Modulation

Page 7: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 707-Dec-2006

Noise and Interference

■ The signal that is received is usually �contaminated� by Noise and Interference

● Noise� Galactic Noise� Atmospheric Noise� Man-made Noise

● Interference� Other Users, Radars, ISM� �License Free� systems use ISM bands

I

Q

Page 8: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 807-Dec-2006

"Eye" Pattern

Good Signal /Noise

Poor(er) Signal /Noise

Page 9: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 907-Dec-2006

Distortion

■ The signal that is received is not very often the same as the signal that was transmitted!● Fading

� Narrowband - Multiple paths, signal cancels� Fading varies as paths change (radios or obstacles move)

● Frequency Shift and Frequency Spread (Doppler)� Mobile Applications

● Time Dispersion and Delay Spread� Multiple paths, signals arrive with different delays� Paths change

Page 10: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 1007-Dec-2006

MultipathInter-symbol Interference

Page 11: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 1107-Dec-2006

Parallel Modems(OFDM)

■ Combat Inter-Symbol Interference● Many parallel signals● Symbol > Multipath Spread

■ Combat Fading● Few sub-channels lost

■ Modulation● Usually m-QAM

■ Coding● FEC● Interleaving

Page 12: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 1207-Dec-2006

OFDM (16 sub-carriers)

Page 13: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 1307-Dec-2006

Spread Spectrum

■ Spread Spectrum● Signal Bandwidth is much greater than Information

Bandwidth● A code, other than the data (message) to be transmitted,

determines the actual on-air bandwidth

■ Advantages● LPI, Anti-DF and Anti-Jam in a Tactical Environment● Spectrum Sharing● Resilient against multipath● "Whitens" noise and interference

Page 14: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 1407-Dec-2006

Direct Sequence

● High-speed code spreads the signal

● �Near-Far� problem

● CDMA Cellular, GPS Navigation, Wi-Fi

● De-spreading spreads (weakens) other non-correlated signals

Page 15: Digital Modulation - NORTH SHORE AMATEUR RADIO CLUBarchive.nsarc.ca/hf/modulation.pdf · -Ł-Ł--Ł--ŁŁ Ł ŁŁŁ-Ł--ŁŁŁ-Ł ŁŁŁ Ł-Ł 07-Dec-2006 NSARC - Quick Guide to Digital

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NSARC - Quick Guide to Digital Modulation 1507-Dec-2006

Frequency Hopping

● Code controls instantaneous frequency of transmission

● �Graceful Degradation�

● GSM Cellular, Bluetooth

● Resilient against Fading● Bit-Rate Hopping resilient

against Inter-symbol Interference