Jetyak Communication Options
The options are listed by their IEEE radio band designation, in order of decreasing frequency. Higher-frequency bands would be more useful for video applications, whereas lower-frequency bands would be more useful for more robust ground control station and inter-robot communication.
The C band spans the range from 4 to 8 GHz (7.5 to 3.75 cm). Signals in this band can achieve very high throughput at relatively low power, but they require line-of-sight.
5.8 GHz FPV
There are many first-person view video systems on the market made for hobbyist radio-controlled vehicles. However, their high frequency means that they must have line of sight. This would be an issue on rivers and lakes, especially because the times that a video feed would be most useful
802.11ac is a Wi-Fi standard that operates on the 5 GHz band. While it can reach gigabit speeds totaled across multiple clients, it is highly sensitive to line-of-sight, especially since the beamforming technology designed to combat this is made for flat walls, not brush. Even in open space, the range is only a few dozen meters for most implementations.
The S band spans the range from 2 to 4 GHz (15 to 7.5 cm). The 2.4 GHz ISM band has been heavily used for electronics at every level, most notably in the Wi-Fi and Bluetooth standards. Signals in this band require line-of-sight, but are not as sensitive to this requirement as C-band signals.
802.11n is a Wi-Fi standard that operated on the 2.4 GHz band. Decent implementations can reach hundreds of meters, and can achieve 300 Mbps with individual clients in good conditions. The Raspberry Pis on the boats can connect to 802.11n access points, and this is useful for pre-mission configuration and initialization, but many missions will require greater range for in-mission communication.
Bluetooth is a personal area network technology that also operates on the 2.4 GHz band. However, Bluetooth is designed for low-power, short-range communication, and as such is not suitable for applications like the boats.
Other 2.4 GHz solutions
2.4 GHz radios are very common, and communication on the band is not limited to Wi-Fi and Bluetooth. For example, the remote control for the boats uses 2.4 GHz radios. However, due to the ubiquity of devices that use the band, and the importance of the remote control for the boats, the 2.4 GHz band is not advisable for robust in-mission communication other than for the remote control.
LTE is a cell network data standard. It can use a number of frequencies, many of which are in the L band (1 to 2 GHz). Unlike the other options on this list, LTE is not directly client-to-client, but instead uses a cell network. As such, a subscription would be required from a provider like Verizon. Verizon offers a data-only plan that could potentially be good for the boats. The following formula describes the pricing structure of the various plans, which are contracts at 2-gigabyte per month intervals:
The upload data rate for LTE peaks at 75 Mbps, but it is typically considerably lower. LTE has the advantage that the ground control station need not be anywhere near the boats, as communication would occur over the internet. However, it will not work at all in areas where there is not LTE or 3G cell coverage.
The IEEE defines the UHF band as 300 MHz to 1 GHz (1 to 0.3 m). Signals in this band also propagate mainly by line-of-sight, but they are far less sensitive to obstructions such as brush than signals in the S or C bands. The lower frequency, however, means that the data rate at a given power is considerably lower, making this band more suitable for inter-robot and ground control station control and reporting connections, rather than high-data-rate applications like video.
The boats use 900 MHz radios to connect to the ground control station using MAVLink. This connection is relatively important for monitoring and reconfiguring missions, and any overhead that is present in the connections is being used to connect multiple boats to single GCS radios. As such, while the 900 MHz band could be very useful for additional reporting and inter-robot communication, it should remain dedicated to the GCS connection.
The 433 MHz band has the potential for multi-kilometer range at low power, even with some obstruction, and much longer range at higher power. As such, it would be a good choice for inter-robot communication and basic reporting and command from the ground control station. The data rates are low enough that non-scalar streaming would be difficult, but basic coordination could be made very reliable. One consideration with 433 MHz is that the receiver should be mounted far from the internal combustion engine, as the engine generates noise.
I would recommend low-power 433 MHz for inter-robot communication on rivers and lakes, high-power 433 MHz for inter-robot communication on large lakes or the ocean and basic GCS communication on long river or lake missions, and the continued use of 900 MHz for MAVLink GCS communication.
I would recommend an LTE plan if many long-distance river missions are planned, provided service is available along the planned routes. LTE is capable of handling several video streams from the boats. On large lakes or the ocean, I would recommend using rotating 802.11n directional dishes to enable a long-distance Wi-Fi network that could support video and other data streams.
Writing: Chris McKinney
Primary research: Timothy Howland and Chris McKinney
Additional research: Austin Adcock, Rukia Brooks, and Chris O’Rourke