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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 communication channel. This allows several users to share a band of frequencies. To permit this without undue interference between the users, CDMA employs spread spectrum technology and a special coding scheme.
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 systems (GNSS) that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. Obstacles such as mountains and buildings can block the relatively weak GPS signals.
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 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.
In cryptography, pseudorandom noise is a signal similar to noise which satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, pseudorandom noise consists of a deterministic sequence of pulses that will repeat itself after its period.
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 transmitter and receiver. FHSS is used to avoid interference, to prevent eavesdropping, and to enable code-division multiple access (CDMA) communications.
In computing, a linear-feedback shift register (LFSR) is a shift register whose input bit is a linear function of its previous state.
DCF77 is a German longwave time signal and standard-frequency radio station. It started service as a standard-frequency station on 1 January 1959. In June 1973 date and time information was added. Its primary and backup transmitter are located at 50°0′56″N9°00′39″E in Mainflingen, about 25 km south-east of Frankfurt am Main, Germany. The transmitter generates a nominal power of 50 kW, of which about 30 to 35 kW can be radiated via a T-antenna.
A maximum length sequence (MLS) is a type of pseudorandom binary sequence.
A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows small electronic receivers to determine their location to high precision using time signals transmitted along a line of sight by radio from satellites. The system can be used for providing position, navigation or for tracking the position of something fitted with a receiver. The signals also allow the electronic receiver to calculate the current local time to high precision, which allows time synchronisation. These uses are collectively known as Positioning, Navigation and Timing (PNT). Satnav systems operate independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the positioning information generated.
A pseudorandom binary sequence (PRBS), pseudorandom binary code or pseudorandom bitstream is a binary sequence that, while generated with a deterministic algorithm, is difficult to predict and exhibits statistical behavior similar to a truly random sequence. PRBS generators are used in telecommunication, such as in analog-to-information conversion, but also in encryption, simulation, correlation technique and time-of-flight spectroscopy. The most common example is the maximum length sequence generated by a (maximal) linear feedback shift register (LFSR). Other examples are Gold sequences, Kasami sequences and JPL sequences, all based on LFSRs.
Real-time kinematic positioning (RTK) is the application of surveying to correct for common errors in current satellite navigation (GNSS) systems. It uses measurements of the phase of the signal's carrier wave in addition to the information content of the signal and relies on a single reference station or interpolated virtual station to provide real-time corrections, providing up to centimetre-level accuracy. With reference to GPS in particular, the system is commonly referred to as carrier-phase enhancement, or CPGPS. It has applications in land survey, hydrographic survey, and in unmanned aerial vehicle navigation.
In a digitally modulated signal or a line code, symbol rate or modulation rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in baud (Bd), baud rate or symbols per second. In the case of a line code, the symbol rate is the pulse rate in pulses per second. Each symbol can represent or convey one or several bits of data. The symbol rate is related to the gross bit rate expressed in bits per second.
In telecommunication technology, a Barker code, or Barker sequence, is a finite sequence of digital values with the ideal autocorrelation property. It is used as a synchronising pattern between sender and receiver.
In applied mathematics, complementary sequences (CS) are pairs of sequences with the useful property that their out-of-phase aperiodic autocorrelation coefficients sum to zero. Binary complementary sequences were first introduced by Marcel J. E. Golay in 1949. In 1961–1962 Golay gave several methods for constructing sequences of length 2N and gave examples of complementary sequences of lengths 10 and 26. In 1974 R. J. Turyn gave a method for constructing sequences of length mn from sequences of lengths m and n which allows the construction of sequences of any length of the form 2N10K26M.
Kasami sequences are binary sequences of length 2N-1 where N is an even integer. Kasami sequences have good cross-correlation values approaching the Welch lower bound. There are two classes of Kasami sequences—the small set and the large set.
GPS signals are broadcast by Global Positioning System satellites to enable satellite navigation. Receivers on or near the Earth's surface can determine location, time, and velocity using this information. The GPS satellite constellation is operated by the 2nd Space Operations Squadron (2SOPS) of Space Delta 8, United States Space Force.
Binary offset carrier modulation was developed by John Betz in order to allow interoperability of satellite navigation systems. It is currently used in the US GPS system, Indian IRNSS system and in Galileo and is a square sub-carrier modulation, where a signal is multiplied by a rectangular sub-carrier of frequency equal to or greater than the chip rate. Following this sub-carrier multiplication, the spectrum of the signal is divided into two parts, therefore BOC modulation is also known as a split-spectrum modulation. Their major advantages are, that one can shape the spectrum to allow inter-system-compatibility and better theoretically achievable tracking capabilities, due to higher frequencies if downmixed to the complex baseband. On the other hand, a huge variety of different implementations/instantiations was setup, making it difficult to get the whole picture. Care must be taken, since early publications dealing with that topic usually do not include matched filters for pulse shaping as well as the concept of complex gaussian noise - which is very often not treated correctly - to yield a mathematically consistent baseband description, that models the physics correctly. I.e. if these standards are not treated correctly, theoretical results are not reliable. This is independend of the media and the peer-review and the person, who published it.
In the mathematical field of combinatorics, a bent function is a special type of Boolean function which is maximally non-linear; it is as different as possible from the set of all linear and affine functions when measured by Hamming distance between truth tables. Concretely, this means the maximum correlation between the output of the function and a linear function is minimal. In addition, the derivatives of a bent function are a balanced Boolean functions, so for any change in the input variables there is a 50 percent chance that the output value will change.
A software GNSS receiver is a Global Navigation Satellite System (GNSS) receiver that has been designed and implemented using software-defined radio.
JPL sequences or JPL codes consist of two linear feedback shift registers (LFSRs) whose code sequence lengths La and Lb must be prime. In this case the code sequence length of the generated overall sequence Lc is equal to:
References
- ↑ George, Maria; Hamid, Mujtaba; Miller, Andy (2001-01-10). "Gold Code Generators in Virtex Devices" (PDF). Virtex Series, Virtex-II Series, and Spartan-II family (Application note). 1.1. Xilinx. XAPP217. Archived from the original (PDF) on 2008-07-05. (9 pages)
- ↑ "Transmitted GPS Signals". The GPS System. kowoma GPS. 2009-04-19. Archived from the original on 2012-08-04.
- ↑ "Robert Gold, BS, MS, Ph.D." Robert Gold Comm Systems. 2011.
- ↑ Gold, Robert (October 1967). "Optimal binary sequences for spread spectrum multiplexing". IEEE Transactions on Information Theory (Correspondence). IT-13 (4): 619–621. doi:10.1109/TIT.1967.1054048.
- ↑ Holmes, Jack K. (2007-06-30). Spread Spectrum Systems for GNSS and Wireless Communications. GNSS Technology and Applications Series. 45. Artech House. p. 100. ISBN 978-1-59693-083-4.
