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

spread spectrum In telecommunication and radio communication, spread-spectrum techniques are methods by which a signal (e.g., an electrical, electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately spread in the frequency d ...

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 chirp is a

sinusoidal A sine wave, sinusoidal wave, or just sinusoid is a mathematical curve defined in terms of the '' sine'' trigonometric function, of which it is the graph. It is a type of continuous wave and also a smooth periodic function. It occurs often i ...

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

polynomial In mathematics, a polynomial is an expression consisting of indeterminates (also called variables) and coefficients, that involves only the operations of addition, subtraction, multiplication, and positive-integer powers of variables. An exampl ...

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 than ...

(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 distinct frequencies occupying a large spectral band. The changes are controlled by a code known to both tr ...

(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 or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who ...

, 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 applicati ...

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 Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at a ...

modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...

(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 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.

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 (2.45GHz WLAN)
{{cdma Multiplexing Radio modulation modes Wireless locating

Overview

Uses

See also

References

External links