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Chirp spread spectrum

From Wikipedia, the free encyclopedia

Chirp spread spectrum (CSS) is a spreadspectrum technique that uses wideband linear

frequency modulated chirp pulses to encode

information.[1] A chirp is a sinusoidal signalwhose frequency increases or decreases over acertain amount of time. Below is an example of an upchirp - as you can see, the frequencyincreases linearly over time.

Overview

As with other spread spectrum methods, Chirp Spread Spectrum uses its entire allocated bandwidthto 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 whenoperating at very low power. However, it is unlike direct-sequence spread spectrum (DSSS) orfrequency-hopping spread spectrum (FHSS) in that it does not add any pseudo-random elements tothe signal to help distinguish it from noise on the channel, instead relying on the linear nature of thechirp pulse. Additionally, Chirp Spread Spectrum is resistant to the Doppler effect, which is typical

in mobile radio applications.[2]

Uses

Chirp Spread Spectrum was originally designed to compete with ultra-wideband for precisionranging and low-rate wireless networks in the 2.45 GHz band. However, since the release of IEEE802.15.4a (also known as IEEE 802.15.4a-2007), it is no longer actively being considered by theIEEE for standardization in the area of precision ranging. Currently, Nanotron Technologies, whichproduces real-time location devices and was the primary force behind getting CSS added to IEEE802.15.4a, is the only seller of wireless devices using CSS. In particular, their primary product, thenanoLOC TRX transceiver, uses CSS and is marketed as a network device with real-time location

and RFID abilities.[3] Some areas where this type of technology can be useful are medicalapplications, logistics (i.e. containers need to be tracked), and government/security applications.Nanotron even tested the TRX Transceiver for industrial monitoring and control in a steel mill and it

survived when the computer and display that were interfacing with it failed because of the heat.[4]

Chirp Spread Spectrum is ideal for applications requiring low power usage and needing relativelylow amounts of bandwidth (1 Mbit/s or less). In particular, IEEE 802.15.4a specifies CSS as atechnique for use in Low-Rate Wireless Personal Area Networks (LR-WPAN). However, whereasIEEE 802.15.4-2006 standard specifies that WPANs encompass an area of 10 m or less, IEEE

A linear frequency modulated upchirp in the time

domain

Contents

1 Overview 2 Uses 3 References 4 See also 5 External links

of 3Chirp spread spectrum - Wikipedia, the free encyclopedia

12/11/2009http://en.wikipedia.org/wiki/Chirp_spread_spectrum



802.15.4a-2007, specifies CSS as a physical layer to be used when longer ranges and devices movingat high speeds are part of your network. Nanotron's CSS implementation was actually seen to work

at a range of 570 meters between devices.[5] Further, Nanotron's implementation can work at data

rates of up to 2 Mbit/s - higher than specified in 802.15.4a.[6] Finally, the IEEE 802.15.4a PHYstandard actually mixes CSS encoding techniques with Differential Phase Shift Keying Modulation(DPSK) to achieve better data rates.

Chirp Spread Spectrum may also be used in the future formilitary applications as it is very difficult to detect and

intercept when operating at low power.[7]

References

1. ^ IEEE Computer Society, (August 31, 2007). IEEEStandard 802.15.4a-2007. New York, NY: IEEE.

2. ^ Berni, A. J., & Gregg, W. D. (June 1973). On theutility of chirp modulation for digital signaling, IEEE

Transactions on Communications. Volume COM-21,748-751.

3. ^ Nanotron's nanoLOC TRX Transceiver, Nanotron marketing4. ^

[www.autoid.org/SC31/wg5/06/WG5_200603_010_InfoCSS.ppt], Nanotron Steel Mill SensorTest: slide 20

5. ^ [www.autoid.org/SC31/wg5/06/WG5_200603_010_InfoCSS.ppt], Nanotron Mine Test:slide 22

6. ^ Nanotron Technologies, (2007). nanoNET chirp based wireless networks. Retrieved fromhttp://www.nanotron.com/EN/docs/WP/WP_CSS.pdf

7. ^ The Revenge of Chirp Spread Spectrum, Military applications

See also

Real time locating Zigbee Ultra-wideband

Modulation techniques

Analog modulation

AM · SSB · QAM · FM · PM · SM

Digital modulation

FSK · ASK · OOK · PSK · QAMMSK · CPM · PPM · TCM · OFDM

Spread spectrum

CSS · DSSS · FHSS · THSS

See also: Demodulation, modem

Multiplex

techniques

Circuit mode(constant bandwidth)

TDM · FDM · WDM

Polarization multiplexing

Spatial multiplexing (MIMO)

Statistical multiplexing(variable bandwidth)

Packet mode · Dynamic TDM

FHSS · DSSS · OFDMA

Related topics

Channel access methods

Media Access Control (MAC)


12/11/2009http://en.wikipedia.org/wiki/Chirp_spread_spectrum



Bluetooth Spectral efficiency comparison table IEEE 802.11 IEEE 802.15.4 IEEE 802.15.4a IEEE 802.16 IEEE 802.20 IEEE 802.22

External links

Download the 802.15 standards from IEEE IEEE 802.15 WPAN Low Rate Alternative PHY Task Group 4a (TG4a) 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)

Retrieved from "http://en.wikipedia.org/wiki/Chirp_spread_spectrum"Categories: Channel access methods | Multiplexing | Radio modulation modes | Wireless locating

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