Chirps

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Frequency-hopping spread spectrum (FHSS)
direct-sequence spread spectrum (DSSS)
time-hopping spread spectrum (THSS)
chirp spread spectrum (CSS)

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  • 1. Chirp spread spectrum
  • 2. spectrum • "spectrum" is a general term used to encompass the spatial and temporal properties of any medium, including fiber optic cable, coaxial cable, and ambient air.
  • 3. spread-spectrum • spread-spectrum techniques are methods by which a signal (e.g. an electrical, electromagnetic, or acoustic signal) generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. • These techniques are used for a variety of reasons, including a)the establishment of secure communications, b) increasing resistance to natural interference, noise c) jamming, to prevent detection, and d) to limit power flux density (e.g. in satellite downlinks).
  • 4. • Frequency-hopping spread spectrum (FHSS) • direct-sequence spread spectrum (DSSS) • time-hopping spread spectrum (THSS) • chirp spread spectrum (CSS) and combinations of these techniques are forms of spread spectrum (more for examaple on http://en.wikipedia.org/wiki/Spread_spectrum)
  • 5. Chirp • A short, high-pitched sound, such as that made by a small bird or an insect. •The specificity of bird calls has been used extensively for species identification. •The calls of birds have been described using words or nonsense syllables or line diagrams. • Common terms in English include words such as quack, chirp The sound emitted by crickets is commonly referred to as chirping
  • 6. Chirp • A chirp is a signal in which the frequency increases ('up- chirp') or decreases ('down-chirp') with time. • In some sources, the term chirp is used interchangeably with sweep signal. • It is commonly used in sonar and radar, but has other applications, such as in spread spectrum communications. • In spread spectrum usage, SAW devices such as RACs are often used to generate and demodulate the chirped signals. • In optics, ultrashort laser pulses also exhibit chirp, which, in optical transmission systems interacts with the dispersion properties of the materials, increasing or decreasing total pulse dispersion as the signal propagates.
  • 7. Chirp modulation • Chirp modulation, or linear frequency modulation for digital communication was patented by Sidney Darlington in 1954 with significant later work performed by Winkler in 1962. • This type of modulation employs sinusoidal waveforms whose instantaneous frequency increases or decreases linearly over time. These waveforms are commonly referred to as linear chirps or simply chirps. • Hence the rate at which their frequency changes is called the chirp rate. • In binary chirp modulation, binary data is transmitted by mapping the bits into chirps of opposite chirp rates. For instance, over one bit period "1" is assigned a chirp with positive rate a and "0" a chirp with negative rate −a. Chirps have been heavily used in radar applications and as a result advanced sources for transmission and matched filters for reception of linear chirps are available
  • 8. Chirplet transform • having the three parameters a (scale), b (translation), and c (chirpiness). The projective chirp is ideally suited to image processing, and forms the basis for the projective chirplet transform.
  • 9. 2.4 GHz Frequency Band Channelization
  • 10. Magnetic Bunch Compression σz0 ∆Ε/Ε z σz under- compression V = V0sin(ωτ) RF AcceleratingRF Accelerating VoltageVoltage RF AcceleratingRF Accelerating VoltageVoltage ∆z = R56∆Ε/Ε Path Length-EnergyPath Length-Energy Dependent BeamlineDependent Beamline Path Length-EnergyPath Length-Energy Dependent BeamlineDependent Beamline …or over- compression ∆∆Ε/ΕΕ/Ε zz σE/E ∆Ε/Ε z ‘chirp’
  • 11. System Design OverviewSystem Design Overview Time Sender Receiver Chirp Request Message Record Timestamp Receive Chirp Request Begin Radio Sync Radio packet transmission Begin Chirp Begin Listening T1 Listen Chirp T2 T3 Detect T3 Result is (T3 - T2) * VS Critical synchronization Radio transmission Acoustic transmission
  • 12. SynchronizationSynchronization Sender Receiver T1 Listen Chirp T2 T3 Radio packet transmission Sync timestamp with start of listen Kernel module catches radio interrupt and saves a timestamp; radio interrupt assigned maximum priority Chirp begins immediately after radio controller accepts packet. Hopefully delay inside controller is fixed To achieve 1 cm resolution, maximum timing variance is 30 µs
  • 13. The End