Installation guidelines

• Sensor setup requirements
• GNSS antenna requirements
  • Guidelines for antenna selection
  • Antenna powered by Vision Navigator
  • Antenna powered by external power supply
• Typical installation scenario
• Other considerations
• Maintenance procedure

Sensor setup requirements

For the proper functioning and optimal performance of the Vision Navigator, the user must fulfill the following setup requirements:

• Mount the Vision Navigator firmly/rigidly to the vehicle’s body.
• Minimize vibrations experienced by the sensor (e.g., engine, gravel).
• Use shielded cables only and avoid sources of electromagnetic interference near the antennas (e.g., LiDAR, USB3).
• Ensure that the GNSS antennas have an unoccluded view of the sky.
• Employ an external lighting source if working in dim scenarios.
• Reduce static obstructions (e.g., vehicle’s structure) and featureless scenes (e.g., sky, mud) in the camera view (see the figure below).

The hood covers almost a third of the frame, preventing feature acquisition.

GNSS antenna requirements

The following GNSS antenna setup requirements have to be fulfilled:

• Attach the GNSS antennas to the same rigid body as the Vision Navigator, their relative positions must remain unchanged. Please carefully follow the antenna manufacturer’s installation guidelines and comply with their requirements to minimize interference.
• Measure the sensor-to-antenna distances with millimeter accuracy (see the figure below). Note that the antenna reference point corresponds to its phase center, described in the corresponding antenna datasheet. The default extrinsic parameters correspond to the measurements of the starter kit.

Sensor-to-antenna distance example

• Ensure that the GNSS antennas have an unoccluded view of the sky.
• We recommend the selected base station to be less than 15km from the rover. The sensor might experience degraded performance if the selected RTK base station is slightly far away (> 15 km). The sensor will experience degraded performance and difficulties computing an RTK-fixed solution if the base station is excessively far away (> 25 km). In this case, please choose a different NTRIP mountpoint or re-connect to the VRS service.
• GNSS antenna placement with respect to the Vision Navigator sensor can have various impacts on performance. We recommend always placing the sensor at any point between the two GNSS antennas to avoid any lever arms effects or within an ellipse, as shown in the figure below. Ideally, the sensor should be placed on the line between the two antennas. However, due to design considerations or camera visibility this might not be an option. Therefore, mounting the XVN on an ellipse that spreads up to 5 cm from the antennas is acceptable. Hereby, the antennas can be placed at a higher level to accommodate mounting the XVN within the ellipse. The 5 cm distance is an approximate range between the antenna and the origin of the XVN's reference frame.
• A longer baseline between the two GNSS antennas results in a better heading estimation. Depending on the relative positioning of the sensor, this may also slightly decrease the absolute positioning accuracy. We recommend having a baseline in the 35 cm to 3 meters range, with a minimum supported baseline of about 22 cm.
• Placing the GNSS antennas in the front and back of the sensor allows for slightly better pitch estimation while placing them on the sides for better roll estimation.

GNSS antenna placement ellipse

Guidelines for antenna selection

For guidance on GNSS antenna selection, please refer to Appendix E. Additionally, a comprehensive evaluation of different GNSS antennas available on the market can be found here. These sources are recommended so that the user is able to make an informed decision on the most suitable antenna for their platform.

When selecting an appropriate antenna, the users should pay close attention to the antenna’s specifications, especially its input voltage and current requirements. The following guidelines can assist in making an informed decision:

1. Check the input voltage requirements: Ensure the antenna’s lower limit for the input voltage aligns with the power supply’s output. For instance, if an antenna’s lower limit is 3.3V and requires 50mA, this translates to a power consumption of 165mW. Given that our supply provides a maximum of 140mW at 2.8V, this antenna would be incompatible.
2. Evaluate the current requirements: Even if an antenna with a lower voltage limit of 3.3V requires only 40mA (equivalent to 132mW), it might still power up with our 2.8V supply. However, this scenario is borderline and should be considered out of specification.
3. Consult the antenna’s datasheet: Most antennas have a detailed datasheet that provides all necessary electrical specifications. Always refer to this document when evaluating compatibility.
4. Safety first: Avoid pushing the boundaries of what the power supply can handle. Operating an antenna at its limits can lead to reduced performance or potential damage.

Always ensure that the antenna’s power requirements are well within the limits of the Vision Navigator’s power supply to guarantee optimal performance and longevity.

Antenna powered by Vision Navigator

The Vision Navigator can power active GNSS antennas. The power supply is strictly: 2.8V@50mA (max. 140mW)

The Vision Navigator actively monitors antenna power consumption. To ensure the safety of both the Vision Navigator and GNSS receivers, antenna power is turned off when a short circuit is detected. This detection mechanism functions by capping the current drawn by the antenna. Notably, some antennas may draw excessive current upon startup, inadvertently activating the short circuit detection. The antenna’s startup current should not exceed 100mA for durations less than 10ms. If the "Antenna state and power" indicator within the "Status -> GNSS" menu doesn’t display an "OK and ON" status, users are advised to immediately contact Movella for expert guidance on GNSS antenna configuration adjustments.

Antenna powered by external power supply

For antennas with distinct power requirements (in terms of voltage and current), an external power supply is recommended. Utilize an appropriate bias tee, like Minicircuit’s ZFBT-4R2G-FT+, in conjunction with a suitable external power source to power these antennas. It’s imperative that the chosen external power supply is stable and exhibits minimal noise. Note that when using this setup, the short circuit detection will not be active.

Steps to employ a typical bias tee for external power supply:

• Connect antenna: Connect the GNSS antenna to the RF output of the bias tee.
• Inject DC power: Connect your DC power source to the DC input of the bias tee. Ensure the voltage and current ratings are compatible with your GNSS antenna’s requirements.
• Connect Vision Navigator: Connect the RF input of the bias tee to the Vision Navigator's GNSS1 or GNSS2 connector.
• Supply power: Turn on the DC power source to inject power into the RF line and feed the GNSS antenna.

Additionally, the user must comply with the following recommendations:

• Ensure the DC voltage applied is within the specifications of the bias tee and the GNSS antenna.
• Avoid short circuits and ensure proper connections before powering the system.
• Consult the GNSS antenna’s datasheet to confirm its power requirements.
• If the user intends to deploy an antenna that falls outside the above mentioned specifications, please consult Movella for professional guidance.
• If the "Antenna state and power" indicator does not display an "OK and ON" status within the "Status -> GNSS" menu, the user should promptly reach out to Movella for professional advice on GNSS antenna setup adjustments.

Typical installation scenario

Typical installation scenario

• The power supply must deliver 10 W at a 5-36 V voltage. The absolute maximum ratings are -14 V to 40 V.
• Depending on which interfaces and baud rate are used for communication, as well as other factors such as noise sources or cable quality, a certain cable length must not be exceeded. Table 4.1 indicates cable lengths that should result in good transmission properties.

Maximum cable length

• If the I/O connector is used, the PWR_SHDN and pin 6 have to be pulled down for proper operation.
• A correct CAN network topology with proper termination is important to avoid CAN communication errors caused by signal reflection or disturbance.
• The system can use the +5V1 signal to power an external device. This signal can supply a maximum of 500mA.
• Since electromagnetic interference can degrade the GNSS signals, the entire carrier system must be carefully designed to be low-noise.
• Use shielded twisted-pair cables for UART communication for better signal quality.
• Generally, the platform should only employ shielded cables to reduce interference.
• The system must have an optimal ground concept to avoid interference.

Other considerations

• Employ high-quality coaxial cables with minimal signal attenuation and delay with a male SMA connector.
• Select antennas and a correction service that supports L1 and L2 bands for as many satellite constellations as possible (see Appendices).
• Wheelspeed measurements can improve performance in GNSS outages; however, excessive slippage may be detrimental. Assess whether incorporating this data benefits you.
• Consider the camera FOV data when integrating the sensor (see Appendices).
• The Vision Navigator’s performance is not affected by whether the sensor is facing backward or forward in the direction of movement.
• Under ideal conditions, the high-precision GNSS receivers employed by the Vision Navigator can deliver accuracy down to the centimeter level: 0.01 m + 1 ppm circular error probable (CEP) - measured using a 1 km baseline and patch antennas with good ground planes. Thus, if the sensor connects to a base station located 20 km away, the receiver can provide an accuracy of approximately 3 cm. It is worth noting that the degradation rate increases significantly for distances longer than 20 km.

Maintenance procedure

To ensure the long-lasting adequate performance of the sensor, the user must periodically perform the following steps:

• Clean the camera lens from any obstructions.
• Verify the integrity of all cables.
• Tighten all connections to the sensor.
• Ensure the sensor and the GNSS antennas are firmly attached to the structure and rigid with respect to each other.
• Secure all unused connectors with protective caps (see figure below).

Vision Navigator's connectors secured with protective caps