DIFFERENTIALLY ENCODING AND DECODING

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DIFFERENTIALLY ENCODING AND DECODING
Encoder
1s are converted to 180o phase shifts, 0s are
unchanged
Decoder
1s are inserted for every transition, 0s if
no transition
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BALANCED MODULATORS
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BPSK MODULATION
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MQPSK / OQPSK / SQPSK

• Modified QPSK such that by shifting the I and Q
  clocks, no phase transition will occur larger
  than 900

QPSK
SQPSK

• 00 00
• 01 900
• 1800
• 2700

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MINIMUM SHIFT KEYING
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WHICH MODULATION WOULD YOU CHOOSE ?

• Depends upon
• Effects on synchronization
• Sidelobe energy / bandwidth
• Complexity of modulator / demodulator
• Effects of jamming in interference
• Impact on size, weight, power, and reliability

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BASIC FREQUENCY HOPPER ARCHITECTURE
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FREQUENCY HOPPER RECEIVER
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FREQUENCY HOPPING EXAMPLE
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FREQUENCY HOPPING EXAMPLE
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FAST HOPPING VS. SLOW HOPPING
(a) Fast Hopping Example 4 hops / bit
(b) Slow Hopping Example 3 bits / hop
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SIMPLE DIRECT FREQUENCY SYNTHESIZER
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BASIC ADD-AND-DIVIDE FREQUENCY SYNTHESIZER
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BASIC INDIRECT FREQUENCY SYNTHESIZER
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BASIC NUMERICALLY CONTROLLED OSCILLATOR
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DIRECT DIGITAL SYNTHESIZER