Facebook Terragraph Radios

Preliminary Results with Facebook Terragraph Radios

Overview of AERPAW's Facebook Terragraph deployments and some preliminary results can be found in the following conference submission:

• Kairui Du, Omkar Mujumdar, Ozgur Ozdemir, Ender Ozturk, Ismail Guvenc, Mihail L. Sichitiu, Huaiyu Dai, Arupjyoti Bhuyan, "60 GHz Outdoor Propagation Measurements and Analysis Using Facebook Terragraph Radios", submitted to IEEE Radio Wireless Week, Las Vegas, NV, Jan. 2022.

Terragraph Use Cases

In below, we provide a list of example use cases that may be possible with Terragraph radios deployed in AERPAW. We intend to make Facebook Terragraph radios remotely accessible to AERPAW users by the end of our Phase-2 for supporting related experiments.

Transmitter/Receiver Beamforming Tracking for mmWaves

One of the toughest problems in mmWave systems is the initial discovering and subsequent tracking of mobile receivers from transmitters (e.g., a mobile phone from a cellular base station). Due to the limited range of mmWave systems if broadcast antennas are being used, beamforming is widely considered the best way to close high SNR links in mmWave. However, this immediately raises the question on how do the two ends of a link find the proper beamforming angles and subsequently track each other. There are literally already hundreds of papers looking at various solutions for this problem. References [1-21] are a small sample. We expect that many researchers would be interested in implementing their algorithms on our platform. For example, we can place a transmitter on a fixed node (e.g., a tower, rooftop, or light pole), and a receiver on a portable node (e.g., mounted on a UAV, a rover, a cart, or a shuttle). The researchers can test various tracking algorithms, but only if they can control exactly (and relatively fast) at what angles the two units transmit or receive. If all the researchers can do is scan a range of angles, none of these algorithms can be implemented.

mmWave as UAV Sensing Instruments

Consider two towers (e.g., two of the ones installed at Lake Wheeler Research Lab) equipped with TG units pointed at each other. If a single mmWave beam is correctly pointed from one to the other, it’s likely that a UAV can be sensed as it breaks the mmWave beam. However, this simple beam breaking can be extended to tracking of the UAV if instead of simply breaking the beam, the UAV is being used to reflect the beam (a form of radar where the receiver is not collocated with the transmitter). Even more interesting is the case with several transmitters and receivers (taking turns in quick sequence. Several researchers are looking into similar radar-communication systems [22-25]. In this case it is, again, paramount that the researchers have full control over the beam angles, duration of the transmission and the received signals to be able to distinguish the signature of an UAV.

mmWave for Vehicle Sensing on a Street

Conceivably, it is possible to use two TG units on opposite sides of a street to not only detect the presence of vehicles, but also possibly to classify the vehicles (using AI or classical data processing), as well as estimate their speed and direction of travel. If the units are low enough, possibly even pedestrians. For this application, researchers also need full access to the TG units to set the transmission parameters (angle, strength, duration) as well as the reception parameters. An example of an algorithm for estimating direction and speed of vehicles is as follows: maintain a strong link continuously and monitor the signal strength. As soon as the signal changes (due to an intervening vehicle), immediately check the angle above and below the current angle to see if the vehicle is coming from the left or from the right, and see when the vehicle appears at this new angle. Estimate the vehicle’s direction and speed (and check with the ground truth provided by a video camera). This type of experiment is not possible by using a traditional channel sounding application.

mmWave Channel Sounding

A main use case for the Terragraph radios will be channel sounding. Since there will be Terragraph radios deployed at multiple fixed nodes, it becomes possible to experiment with mmWave propagation in various different link distances and LOS/NLOS configurations (for different beam angles), to extract insightful information about mmWave signal coverage in urban environments [26-30]. Having spatial distribution of transmit/receive paths in different environments will help develop more effective MIMO and beam tracking techniques, and improve communication performance. One can collect long-term data to capture the environmental effects such as changes in foliage, movement of vehicles and people, among others, across different seasons and different days of the week. It can be possible to use a Terragraph radio on the ground to evaluate propagation effects at the access link, for different link distances and NLOS geometries, to study coverage. Use of mmWave reflectors and repeaters (see e.g. [27,28,30]), including passive or reconfigurable meta-surface reflectors, can be tested for evaluating the effectiveness of e.g. around-the-corner link coverage. One can study scattering, reflection, and penetration loss characteristics of different materials in the environment. Air-to-ground channel sounding with UAV platforms is also possible with the Terragraph radios [31, 32]. Optimum placement of reflectors and base stations can be studied using channel sounding data, and compared with ray tracing simulations [33]. The channel sounding data will be contributed to NIST’s channel model database.

Ideal API

Ideally, the API would let a researcher set and get the following parameters:

• Transmitter/Receiver mode

• Transmitter/Receiver beam angle

• Transmitter power

• Transmitter signal duration

• Receiver reception duration

• Transmitter/Receiver frequency/channel

• As much insight in the transmitter/receiver signal as possible

References:

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[2] H. Deng and A. Sayeed, “Mm-wave MIMO channel modeling and user localization using sparse beamspace signatures,”inInternational Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Toronto, ON, Canada, Jun 2014, pp. 130–134.

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[26] F. Erden, O. Ozdemir, I. Guvenc, and D. W. Matolak. "EMR: A New Metric to Assess the Resilience of Directional mmWave Channels to Blockages." arXiv preprint arXiv:2009.14724 (2020).

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