Unmanned Systems Technology 006 | ECA Inspector Mk2 USV | Antenna systems | Northwest UAV NW-44 | Unmanned ground vehicles | Navigation systems | Lunar X challenge

66 Focus | Navigation systems Multi-GNSS modules Using all the systems available has clear advantages in terms of accuracy thanks to the ability to compare multiple signals for correcting for atmospheric distortion, reliability through redundancy, avoidance of signal blocking and resistance to interference, including jamming. However, providing separate receivers and processors for each of them comes with obvious penalties of size, weight, cost and energy consumption, so increasingly industry is offering integrated modules featuring multi-GNSS processors. The chipsets are tiny, with chip-scale packages measuring around 3.0 x 3.4 x 0.6 mm now available and supporting several industry-standard interfaces including USB, Inter-Integrated Circuit (I2C), Serial Peripheral Interface (SPI) and Universal Asynchronous Receiver/ Transmitter (UART). The latest modules typically handle GPS and GLONASS and their augmentation systems, and are described as ready for Galileo, Compass and QZSS. This flexibility comes from the application of software-defined radio technologies that integrate radio frequency (RF) components with computer processors and memory that, in theory, enables them to handle any waveform that the antenna can feed them, given the correct software/firmware. Some of the latest systems also include inertial sensors, dead reckoning and the ability to process other radio frequency navigation sources such as cellular phone networks and wi-fi. A GNSS receiver takes signals from its antenna and feeds them into its RF front end, which typically includes a bandpass surface acoustic wave filter that eliminates any signals that might interfere with those the system needs, and a low-noise amplifier that boosts the low-power satellite signal to meet the RF downconverter threshold. The downconversion process needs a very stable frequency reference if the system is to have sufficient sensitivity, as well as a short TTFF and good stability; this is provided by a temperature-compensated crystal oscillator. A second reference in the form of a real-time clock connected directly to the processor maintains the module’s warm- and hot-start capabilities, which enable it to restart quickly from power- saving standby modes. RF shielding of the enclosure protects the module from external interference and prevents its own emissions from interfering with other systems in the vehicle. Integrating antennas Increasingly, industry is building ‘system- in-package’ GNSS receiver modules with integrated antennas to reduce the risks to unmanned vehicle programmes associated with the integration of antennas and receivers, as well as to make the whole package more compact. Such antennas can be installed on February/March 2016 | Unmanned Systems Technology A single OEM board containing a precision GNSS receiver and inertial sensor components (Courtesy of Applanix) Consumer-grade motion tracking already features system-on-chip packages integrating sensors and control circuits (Courtesy of Invensense)