Application Notes

There are many factors to consider while building a unique communications architecture. We have put together a list of the most common features to help explain what they are. We have designed our radios to optimize for performance based on these criteria.

If you have a question and don’t see the answer below, please don’t hesitate to get in touch.

Mobile Mesh

Mobile Mesh is an advanced feature of the Smart Radio’s BII™ OS. It helps deploy self-forming and self-healing mobile ad-hoc networks (MANET). Mesh maximizes connectivity and communication performance in difficult mobile conditions. Mobile Mesh is useful to implement network redundancy and range extension. Smart Radios employ any-node to any-node capabilities to continuously and instantaneously route data via the best available traffic path for any number of nodes, all with extremely low overhead.

Mobile Mesh operates on ISO/OSI Layer 2 and routes/bridges Ethernet Frames. It emulates a virtual network switch of all participating nodes. Therefore all nodes appear to be link local, thus all higher operating protocols are not affected by any changes within the network. It is possible to run almost any protocol above Mobile Mesh.

Mobile Mesh is an important enabler for innovative IoT applications. Coupled with Doodle Labs’ BII technology, our customers are able to deploy scalable, mobile, multi-hop, wireless communication.

Range Extension with Mesh

As use cases for unmanned systems get more complex, users often utilize multiple flyers in concert with ground vehicles and scattered access points. In addition, real world deployments mean that direct line of sight can occasionally be impaired. An integrated self-healing and self-forming mobile mesh technology extends the operating range and supports Non-Line of Sight situations.

Dual Band Mesh for Multi-Hop Networks

In typical mesh networks, the throughput loss with each hop is 50%, which compounds over multiple hops. This is primarily due to the repeater node needing to toggle back and forth between Tx and Rx modes for each channel. A dual-band mesh solves this problem by creating separate channels for Tx and Rx so that switching isn’t required. The overall throughput will no longer degrade with each incremental node.

drone in mesh topology

URLLC (Ultra Reliable Low Latency Channel)

Using a single radio on a vehicle mitigates the complexity of managing multiple data links and minimizes hardware weight. However, that single radio must then handle multiple types of communication streams (e.g. Command & Control, LiDAR, video, etc).

The uplink transmission of C&C data to mobile units needs to be highly reliable with low latency to ensure the connection is never lost and the mobile unit responds to commands with minimal delay.

The URLLC, integrated into all Smart Radios, is an in-band channel that has been optimized for command and control data. Since command and control data typically requires just a small amount of data, the Smart Radio uses special radio settings to send C&C packets with the lowest latency and ensures the highest chances of successful signal transmission in a noisy environment.

Drone and antenna establishing video link with URLLC

High Resolution Video Transmission over Wireless

A popular use for autonomous vehicles is surveillance, which relies on streaming high-resolution video from the mobile unit to the control station, or multiple control stations (multicast). The downlink must carry large amounts of sensor data: 4K video requires about 20 Mbps throughput, while HD video requires about 5 Mbps.

drone in mesh topology

Multicast

In mission-critical applications, there are often several stakeholders that need to be involved and to collaborate in real time. Therefore, enabling group communication via multicast allows for broadcasting streams to several receiving parties.

Popular use cases are having a remote pilot sending C&C information and receiving low resolution video for navigation, while reviewers in a separate location are receiving higher throughput data streams (e.g. HD video, LiDAR). Additionally, for military applications, it enables several members of a unit to be able to receive streams from a single drone scout at the same time.

Drone Multicast to 3 user and a mobile command post

Optimizing the RF Link

There are many factors that affect the link performance of a communications system. To get the best performance, we have put together an application describing the parameters involved and optimizations that can be made.

Parameters affecting link performance:

    1. RF Power
    2. Antenna Gain and Directivity
    3. Channel Size: Rx Sensitivity & Required Data Throughput
    4. MIMO, Signal Polarization, Diversity
    5. Fresnel Zone
    6. Fade Margin

Read our full application note to learn more about optimizing your RF link

Link Distance

Unmanned systems have the capabilities to complete missions over many kilometers, so they require a communications link that can perform over the same distance (or more). Operating frequency and antenna gain are two major factors in determining range and throughput, as explained below.

Lower frequencies have lower transmission losses and allow for longer-distance communication, which means that lower gain (i.e. smaller) antennas may be utilized.  Many unmanned system manufacturers utilize the unlicensed ISM band 902-928 MHz instead of WiFi frequencies for this reason.

On the other hand, higher frequencies have smaller antennas, which means that a high-gain antenna will not be very heavy. Hence, a careful balance of the required range, operating frequency, and antenna configuration must be made.

distance between antenna and drone

Choosing an Antenna

We are often asked for recommendations on the best antenna, but the ideal antenna varies by application. Factors to consider are: operating frequency, size and weight allowance, gain, and radiation pattern. Contact us and we can discuss about your particular requirements.

Fresnel Zone

An important factor to consider when establishing a link is potential obstruction of the Fresnel zone. Even with nearly perfect line of sight, link performance can be affected. Radio waves will follow slightly different paths before reaching a receiver, especially if there are obstructions within the Fresnel zone, an ellipsoidal region between the transmitter and receiver. The different path lengths will cause the waves to arrive at slightly different times and to be slightly out of phase, which causes interference.

When designing your link, Fresnel zone interference can be usually be overcome by having the antenna high enough off the ground, and in the case of drones, having the ground antenna pointing up towards the flyer.

We’ve included a reference chart below that would give you an idea of the size of the Fresnel Zone based on distance and frequency.

Calculating the size of the Fresnel zone between two nodes can help to predict whether obstructions or discontinuities along the path will cause significant interference. Both distance and frequency affect the size of the Fresnel zone, which can be determined using a Fresnel Zone Calculator, like the one linked here.

fresnel zone between antenna and drone

Link Budget Calculator

One of the most frequent questions we get is “how far can your radios go?” The expected distance can be estimated using a link budget calculator, which incorporates a number of different factors that impact the quality of the RF link.

Factors that most impact the quality of an RF link are:

  •  Tx power of the radio: higher the power, stronger the signal
  •  Receive sensitivity of the radio: better Rx sensitivity will allow
  •  Antenna type and gain
  •  Frequency band
  •  Attenuation from cables
  •  Free space loss
  •  Fade margin
Maintaining a sufficient fade margin will create a buffer to account for natural degradation of the signal strength during operation. A fade margin of 15 dBm is a conservative value to target.

Here is a link to a free online calculator.

Example:

Using the 900 MHz Xtreme Smart Radio (RM-915-2H-XS) to stream HD video (12 Mbps) from a UAV,  how far can the link go with low-gain antennas?

Using the free calculator above, enter the values below and adjust the Distance value to get a fade margin close to 15 dBm.

 Frequency: 915 MHz

 Distance: try values to optimize the fade margin

 TX Power: 29 dBm (MCS 3)

 TX Cable: 2 dBm

 TX Antenna: 3 dBi

 RX Sensitivity: -92 dBm (MCS 3 from datasheet)

 RX Cable: 2 dBm

 RX Antenna: 9 dBi

Answer: Link range would be 13 km with a conservative 15.1 dBm fade margin.

Remote ID

Remote ID is a real-time “digital license plate” for drones and ensures accountability of UAS and their Remote Pilot operators. Today, there is no common system for real-time identification of drones in flight. A standard is necessary to ensure compatibility between systems and to maximize adoption and effectiveness, especially as UAS adoption rapidly increases.

The general consensus in the UAS industry is that Remote ID is a must before drones can be regularly flown in interesting situations such as beyond visual line of site (BVLOS) operation, flying over people, and operation at night. Current regulations only allow enterprises with FAA waivers to perform these operations, and as one would expect, obtaining a waiver is a tedious and costly endeavor.

The push towards standardization is particularly important at this stage in Remote ID’s development. A federal ruling on Remote ID is expected in September 2019. At the same time, NASA continues to test UTM technologies and is working to transfer their UTM project to the FAA. Once the federal agencies finalize the regulatory standards and conclude testing, we will see the private sector gain more confidence in adopting specific standards and solutions.

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