In digital communications, chirp spread spectrum (CSS) is a

spread spectrum In telecommunications, especially radio communication, spread spectrum are techniques by which a signal (electrical engineering), signal (e.g., an electrical, electromagnetic, or acoustic) generated with a particular Bandwidth (signal processi ...

technique that uses wideband linear frequency modulated

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 applied to sonar, radar, and laser syste ...

pulses to encode information. A

is a

sinusoidal A sine wave, sinusoidal wave, or sinusoid (symbol: ∿) is a periodic wave whose waveform (shape) is the trigonometric sine function. In mechanics, as a linear motion over time, this is '' simple harmonic motion''; as rotation, it correspond ...

signal whose frequency increases or decreases over time (often with a

polynomial In mathematics, a polynomial is a Expression (mathematics), mathematical expression consisting of indeterminate (variable), indeterminates (also called variable (mathematics), variables) and coefficients, that involves only the operations of addit ...

expression for the relationship between time and frequency).

Overview

As with other

methods, chirp spread spectrum uses its entire allocated bandwidth to broadcast a signal, making it robust to channel noise. Further, because the chirps utilize a broad band of the spectrum, chirp spread spectrum is also resistant to multi-path fading even when operating at very low power. However, it is unlike

direct-sequence spread spectrum In telecommunications, direct-sequence spread spectrum (DSSS) is a spread-spectrum modulation technique primarily used to reduce overall signal interference. The direct-sequence modulation makes the transmitted signal wider in bandwidth tha ...

(DSSS) or

frequency-hopping spread spectrum Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly changing the carrier frequency among many frequencies occupying a large spectral band. The changes are controlled by a code known to both transmitter ...

(FHSS) in that it does not add any pseudo-random elements to the signal to help distinguish it from noise on the channel, instead relying on the linear nature of the chirp pulse. Additionally, chirp spread spectrum is resistant to the

Doppler effect The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described ...

, which is typical in mobile radio applications.

Uses

Chirp spread spectrum was originally designed to compete with

ultra-wideband Ultra-wideband (UWB, ultra wideband, ultra-wide band and ultraband) is a radio technology that can use a very low energy level for short-range, high-bandwidth communications over a large portion of the radio spectrum. UWB has traditional applicat ...

for precision ranging and low-rate wireless networks in the 2.45 GHz band. However, since the release of IEEE 802.15.4a (also known as IEEE 802.15.4a-2007), it is no longer actively being considered by the IEEE for standardization in the area of precision ranging. Chirp spread spectrum is ideal for applications requiring low power usage and needing relatively low data rates (1 Mbit/s or less). In particular, IEEE 802.15.4a specifies CSS as a technique for use in low-rate wireless personal area networks (LR-WPAN). However, whereas IEEE 802.15.4-2006 standard specifies that WPANs encompass an area of 10 m or less, IEEE 802.15.4a-2007, specifies CSS as a physical layer to be used when longer ranges and devices moving at high speeds are part of your network. Nanotron's CSS implementation was actually seen to work at a range of 570 meters between devices. Further, Nanotron's implementation can work at data rates of up to 2 Mbit/s - higher than specified in 802.15.4a. Finally, the IEEE 802.15.4a PHY standard actually mixes CSS encoding techniques with differential phase shift keying

modulation Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message ...

(DPSK) to achieve better data rates. Chirp spread spectrum may also be used in the future for military applications as it is very difficult to detect and intercept when operating at low power. Very similar frequency swept waveforms are used in frequency modulated continuous wave radars to measure range (distance); an unmodulated continuous wave

Doppler radar A Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the fre ...

can only measure range-rate (relative velocity along the line of sight). FM-CW radars are very widely used as radio altimeters in aircraft. One application of chirp spread spectrum is

LoRa LoRa (from "long range", sometimes abbreviated as "LR") is a physical proprietary radio communication technique. It is based on spread spectrum modulation techniques derived from chirp spread spectrum (CSS) technology. It was developed by Cycleo ...

References

External links

Download the 802.15 standards from IEEE

* ttps://web.archive.org/web/20070107041810/http://www.nanotron.com/EN/SU_FAQ.php Nanotron Technologies Frequently asked Questions page
Nanotron Chirp Spread Spectrum page

Nanotron nanoNET Chirp Based Wireless Networks

About coexistence of IEEE 802.15.4aCSS with IEEE 802.11b/g (2.45 GHz WLAN)
{{cdma Multiplexing Radio modulation modes Wireless locating Digital signal processing

Overview

Uses

See also

References

External links