Guidance and steering control systems that are now in widespread use by farmers for ploughing and cultivating the land with unprecedented accuracy, require centimetre-level position as well as attitude information accurate to a few degrees. Additionally, position and attitude update rate of no less than 10Hz is required for successful guidance in agricultural environments. Guidance and steering control systems rely particularly on heading and roll measurements to steer the tractor on parallel straight lines or curves known as plough lines.

The year 1978 saw the launch of the first Global Positioning System (GPS) satellite. Today, GPS, as the first and currently only operational global navigation satellite system (GNSS), is widely used and is a vital technology for many of society’s economic, scientific and social activities. Applications can be found everywhere, such as spacecraft navigation, geodesy, surveying and mapping, precision navigation, machine guidance, vehicle fleet management and “intelligent transport systems” (ITS), emergency services and “location based services” (LBS). Clearly the development of GPS has revolutionised what are now termed “positioning, navigation and timing” (PNT) activities.

The Galileo E5 signal employs a complex sub-carrier modulation known as AltBOC(15,10) modulation. The sub-carriers are specially chosen waveforms that result in a split spectrum and a constant envelope after the modulation. Four codes are combined with these specially chosen complex sub-carriers to obtain the modulating signal which then phase modulates the E5 carrier. Alternatively, the complete modulation can be…