Barker code
The transmission of a pre-arranged synchronising pattern of digits can enable a signal to be regenerated by a receiver with a low probability of error.
The longer the pattern the more accurately the data can be synchronised and errors due to distortion omitted.
During and after WWII digital technology became a key subject for research e.g. for radar, missile and gun fire control and encryption.
In the 1950s scientists were trying various methods around the world to reduce errors in transmissions using code and to synchronise the received data.
Shannon realised that “communication signals must be treated in isolation from the meaning of the messages that they transmit” and laid down the theoretical foundations for digital circuits.
[4] In 1953 RH Barker published a paper demonstrating how this problem to synchronise the data in transmissions could be overcome.
The Barker sequence process at the time produced great interest, particularly in the United States as his method solved the problem, initiating a huge leap forward in telecommunications.
The process has remained at the forefront of radar, data transmission and telemetry and is now a very well known industry standard, still being researched in many technology fields.
“In a pioneering examination of group synchronization of binary digital systems, Barker reasoned it would be desirable to start with an autocorrelation function having very low sidelobes.
[12]) Barker codes of length N equal to 11 and 13 are used in direct-sequence spread spectrum and pulse compression radar systems because of their low autocorrelation properties (the sidelobe level of amplitude of the Barker codes is 1/N that of the peak signal).
[15] A Barker code resembles a discrete version of a continuous chirp, another low-autocorrelation signal used in other pulse compression radars.
The positive and negative amplitudes of the pulses forming the Barker codes imply the use of biphase modulation or binary phase-shift keying; that is, the change of phase in the carrier wave is 180 degrees.
[16] Applications of Barker codes are found in radar,[17] mobile phone,[18] telemetry,[19] ultrasound imaging and testing,[20][21] GPS,[22] and Wi-Fi.
Some examples where Barker code is used are: pet and livestock tracking, bar code scanners, inventory management, vehicle, parcel, asset and equipment tracking, inventory control, cargo and supply chain logistics.
[25] It is also used extensively for Intelligent Transport Systems (ITS) i.e. for vehicle guidance[26] Barker's algorithm is an alternative to Metropolis–Hastings, which doesn't satisfy the detailed balance condition.
