In
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
s, direct-sequence spread spectrum (DSSS) 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 dom ...
modulation technique primarily used to reduce overall signal
interference
Interference is the act of interfering, invading, or poaching. Interference may also refer to:
Communications
* Interference (communication), anything which alters, modifies, or disrupts a message
* Adjacent-channel interference, caused by extr ...
. The direct-sequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth.
After the despreading or removal of the direct-sequence modulation in the receiver, the information bandwidth is restored, while the unintentional and intentional interference is substantially reduced.
The first known scheme for this technique was introduced by a
Swiss inventor,
Gustav Guanella
Gustav Guanella (21 June 1909 – 12 January 1982) was a Swiss inventor who held numerous patents.
Life
Guanella was born in Chur, then educated in Lucerne, Switzerland. He finished high school in 1929, studied electrical engineering at the ...
.
With DSSS, the message bits are modulated by a
pseudorandom bit sequence known as a spreading sequence. Each spreading-sequence bit, which is known as a chip, has a much shorter duration (larger bandwidth) than the original message bits. The modulation of the message bits scrambles and spreads the pieces of data, and thereby results in a bandwidth size nearly identical to that of the spreading sequence. The smaller the chip duration, the larger the bandwidth of the resulting DSSS signal; more bandwidth multiplexed to the message signal results in better resistance against interference.
Some practical and effective uses of DSSS include the
code-division multiple access
Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...
(CDMA) method, the
IEEE 802.11b
IEEE 802.11b-1999 or 802.11b is an amendment to the IEEE 802.11 wireless networking specification that extends throughput up to 11 Mbit/s using the same 2.4 GHz band. A related amendment was incorporated into the IEEE 802.11-2007 standard. ...
specification used in
Wi-Fi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wav ...
networks, and the
Global Positioning System
The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
.
Features
# DSSS
phase-shifts a
sine wave pseudorandom
A pseudorandom sequence of numbers is one that appears to be statistically random, despite having been produced by a completely deterministic and repeatable process.
Background
The generation of random numbers has many uses, such as for rand ...
ly with a continuous
string of chips, each of which has a much shorter duration than an information
bit
The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
. That is, each information bit is modulated by a sequence of much faster chips. Therefore, the
chip rate
In digital communications, a chip is a pulse of a direct-sequence spread spectrum (DSSS) code, such as a pseudo-random noise (PN) code sequence used in direct-sequence code-division multiple access (CDMA) channel access techniques.
In a binary di ...
is much higher than the
information
Information is an abstract concept that refers to that which has the power to inform. At the most fundamental level information pertains to the interpretation of that which may be sensed. Any natural process that is not completely random ...
bit rate.
# DSSS uses a
signal
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...
structure in which the spreading sequence produced by the transmitter is already known by the receiver. The receiver can then use the same spreading sequence to counteract its effect on the received signal in order to reconstruct the information signal.
Transmission method
Direct-sequence spread-spectrum transmissions multiply the data being transmitted by a pseudorandom spreading sequence that has a much higher bit rate than the original data rate. The resulting transmitted signal resembles bandlimited
white noise
In signal processing, white noise is a random signal having equal intensity at different frequencies, giving it a constant power spectral density. The term is used, with this or similar meanings, in many scientific and technical disciplines ...
, like an audio recording of "static". However, this noise-like signal is used to exactly reconstruct the original data at the receiving end, by multiplying it by the same spreading sequence (because , and ). This process, known as despreading, is mathematically a
correlation of the transmitted spreading sequence with the spreading sequence that the receiver already knows the transmitter is using. After the despreading, the
signal-to-noise ratio is approximately increased by the spreading factor, which is the ratio of the spreading-sequence rate to the data rate.
While a transmitted DSSS signal occupies a much wider bandwidth than a simple modulation of the original signal would require, its frequency spectrum can be somewhat restricted for spectrum economy by a conventional analog bandpass filter to give a roughly bell-shaped envelope centered on the
carrier frequency
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a ...
. In contrast,
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 ...
pseudorandomly retunes the carrier and requires a uniform frequency response since any bandwidth shaping would cause amplitude modulation of the signal by the hopping code.
If an undesired transmitter transmits on the same channel but with a different spreading sequence (or no sequence at all), the despreading process reduces the power of that signal. This effect is the basis for the
code-division multiple access
Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...
(CDMA) property of DSSS, which allows multiple transmitters to share the same channel within the limits of the
cross-correlation properties of their spreading sequences.
Benefits
* Resistance to unintended or intended
jamming
* Sharing of a single channel among multiple users
* Reduced signal/background-noise level hampers
interception
In ball-playing competitive team sports, an interception or pick is a move by a player involving a pass of the ball—whether by foot or hand, depending on the rules of the sport—in which the ball is intended for a player of the same team ...
* Determination of relative timing between transmitter and receiver
Uses
* The United States
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
, European
Galileo and Russian
GLONASS
GLONASS (russian: ГЛОНАСС, label=none, ; rus, links=no, Глобальная навигационная спутниковая система, r=Global'naya Navigatsionnaya Sputnikovaya Sistema, t=Global Navigation Satellite System) is ...
satellite navigation
A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location (longitude, latitude, and altitude/elevation) to high pr ...
systems; earlier GLONASS used DSSS with a single spreading sequence in conjunction with
FDMA
Frequency-division multiple access (FDMA) is a channel access method used in some multiple-access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividing ...
, while later GLONASS used DSSS to achieve
CDMA
Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...
with multiple spreading sequences.
* DS-CDMA (Direct-Sequence Code Division Multiple Access) is a
multiple access
In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity. Examples of shared physical med ...
scheme based on DSSS, by spreading the signals from/to different users with different codes. It is the most widely used type of
CDMA
Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...
.
*
Cordless phones operating in the 900 MHz, 2.4 GHz and 5.8 GHz
bands
*
IEEE 802.11b
IEEE 802.11b-1999 or 802.11b is an amendment to the IEEE 802.11 wireless networking specification that extends throughput up to 11 Mbit/s using the same 2.4 GHz band. A related amendment was incorporated into the IEEE 802.11-2007 standard. ...
2.4 GHz
Wi-Fi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wav ...
, and its predecessor
802.11-1999. (Their successor
802.11g uses both
OFDM
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission and a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital commu ...
and DSSS)
*
Automatic meter reading
*
IEEE 802.15.4
IEEE 802.15.4 is a technical standard which defines the operation of a low-rate wireless personal area network (LR-WPAN). It specifies the physical layer and media access control for LR-WPANs, and is maintained by the IEEE 802.15 working group, ...
(used, e.g., as PHY and MAC layer for
ZigBee
Zigbee is an IEEE 802.15.4-based specification for a suite of high-level communication protocols used to create personal area networks with small, low-power digital radios, such as for home automation, medical device data collection, and o ...
, or, as the physical layer for
WirelessHART
WirelessHART within telecommunications and computing, is a wireless sensor networking technology. It is based on the Highway Addressable Remote Transducer Protocol (HART). Developed as a multi-vendor, interoperable wireless standard, WirelessHA ...
)
*
Radio-controlled model
A radio-controlled model (or RC model) is a model that is steerable with the use of radio control. All types of model vehicles have had RC systems installed in them, including ground vehicles, boats, planes, helicopters and even submarines and ...
Automotive, Aeronautical and Marine vehicles
See also
*
Complementary code keying Complementary code keying (CCK) is a modulation scheme used with wireless networks (WLANs) that employ the IEEE 802.11b specification. In 1999, CCK was adopted to supplement the Barker code in wireless digital networks to achieve data rate higher ...
*
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 ...
*
Linear-feedback shift register
In computing, a linear-feedback shift register (LFSR) is a shift register whose input bit is a linear function of its previous state.
The most commonly used linear function of single bits is exclusive-or (XOR). Thus, an LFSR is most often a ...
*
Orthogonal frequency-division multiplexing
References
The Origins of Spread-Spectrum Communications*
*
NTIA Manual of Regulations and Procedures for Federal Radio Frequency Management
External links
Civil Spread Spectrum History
{{cdma
Quantized radio modulation modes
Wireless networking
IEEE 802.11
ja:スペクトラム拡散#直接拡散