• "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.
• 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
a)the establishment of secure communications,
b) increasing resistance to natural interference,
c) jamming, to prevent detection, and
d) to limit power flux density (e.g. in satellite
• 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)
• 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
• 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.
• 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
• 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
• having the three parameters
The projective chirp is ideally suited to
image processing, and forms the basis for
the projective chirplet transform.
System Design OverviewSystem Design Overview
Chirp Request Message
Receive Chirp Request
Begin Radio Sync
Radio packet transmission
Result is (T3 - T2) * VS
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