Chirp spread spectrum
Encyclopedia
In digital communications, Chirp spread spectrum (CSS) is a spread spectrum
technique that uses wideband linear frequency modulated chirp
pulses to encode information. A chirp is a sinusoidal signal whose frequency increases or decreases over a certain amount of time. Below is an example of an upchirp—as you can see, the frequency increases linearly over time.
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
(DSSS) or frequency-hopping spread spectrum
(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
, which is typical in mobile radio applications.
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. Currently, Nanotron Technologies, which produces real-time location devices and was the primary force behind getting CSS added to IEEE 802.15.4a
, is the only seller of wireless devices using CSS. In particular, their primary product, the nanoLOC TRX transceiver, uses CSS and is marketed as a network device with real-time location and RFID abilities. Some areas where this type of technology can be useful are medical applications, 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.
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 Network
s (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 (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.
Spread spectrum
Spread-spectrum techniques are methods by which a signal generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth...
technique that uses wideband linear frequency modulated chirp
Chirp
A chirp is a signal in which the frequency increases or decreases 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...
pulses to encode information. A chirp is a sinusoidal signal whose frequency increases or decreases over a certain amount of time. Below is an example of an upchirp—as you can see, the frequency increases linearly over time.
Overview
As with other spread spectrumSpread spectrum
Spread-spectrum techniques are methods by which a signal generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth...
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
Direct-sequence spread spectrum
In telecommunications, direct-sequence spread spectrum is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that is being modulated. The name 'spread spectrum' comes from the fact that the carrier signals...
(DSSS) or frequency-hopping spread spectrum
Frequency-hopping spread spectrum
Frequency-hopping spread spectrum is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver...
(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
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
, which is typical in mobile radio applications.
Uses
Chirp Spread Spectrum was originally designed to compete with ultra-widebandUltra-wideband
Ultra-wideband is a radio technology that can be used at very low energy levels for short-range high-bandwidth communications by using a large portion of the radio spectrum. UWB has traditional applications in non-cooperative radar imaging...
for precision ranging and low-rate wireless networks in the 2.45 GHz band. However, since the release of IEEE 802.15.4a
IEEE 802.15.4a
IEEE 802.15.4a is an amendment to IEEE 802.15.4 specifying that additional physical layers be added to the original standard.-Overview:...
(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. Currently, Nanotron Technologies, which produces real-time location devices and was the primary force behind getting CSS added to IEEE 802.15.4a
IEEE 802.15.4a
IEEE 802.15.4a is an amendment to IEEE 802.15.4 specifying that additional physical layers be added to the original standard.-Overview:...
, is the only seller of wireless devices using CSS. In particular, their primary product, the nanoLOC TRX transceiver, uses CSS and is marketed as a network device with real-time location and RFID abilities. Some areas where this type of technology can be useful are medical applications, 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.
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 Network
Personal area network
A personal area network is a computer network used for communication among computer devices, including telephones and personal digital assistants, in proximity to an individual's body. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters...
s (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 (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.
See also
- Real time locating
- ZigbeeZigBeeZigBee is a specification for a suite of high level communication protocols using small, low-power digital radios based on an IEEE 802 standard for personal area networks. Applications include wireless light switches, electrical meters with in-home-displays, and other consumer and industrial...
- Ultra-widebandUltra-widebandUltra-wideband is a radio technology that can be used at very low energy levels for short-range high-bandwidth communications by using a large portion of the radio spectrum. UWB has traditional applications in non-cooperative radar imaging...
- BluetoothBluetoothBluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
- Spectral efficiency comparison table
- IEEE 802.11IEEE 802.11IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent...
- IEEE 802.15.4IEEE 802.15.4IEEE 802.15.4 is a standard which specifies the physical layer and media access control for low-rate wireless personal area networks . It is maintained by the IEEE 802.15 working group....
- IEEE 802.15.4aIEEE 802.15.4aIEEE 802.15.4a is an amendment to IEEE 802.15.4 specifying that additional physical layers be added to the original standard.-Overview:...
- IEEE 802.16IEEE 802.16IEEE 802.16 is a series of Wireless Broadband standards authored by the Institute of Electrical and Electronics Engineers . The IEEE Standards Board in established a working group in 1999 to develop standards for broadband Wireless Metropolitan Area Networks...
- IEEE 802.20IEEE 802.20IEEE 802.20 or Mobile Broadband Wireless Access was a specification by the standard association of the Institute of Electrical and Electronics Engineers for mobile wireless Internet access networks...
- IEEE 802.22IEEE 802.22IEEE 802.22 is a standard for Wireless Regional Area Network using white spaces in the TV frequency spectrum. The development of the IEEE 802.22 WRAN standard is aimed at using cognitive radio techniques to allow sharing of geographically unused spectrum allocated to the Television Broadcast...
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)