Protocols for Low-Power Wide-Area Networks in White Spaces
Source of support: NSF (2019--2024)
SNOW Architecture with dual radio base station and subcarriers
As a key technology driving the Internet-of-Things (IoT), Low-Power Wide-Area Networks (LPWANs) are evolving to overcome the range limits and scalability challenges in traditional wireless sensor networks. With the support from NSF and through collaboration with Microsoft Research, we have developed a highly scalable LPWAN architecture – called SNOW (Sensor Network Over White Spaces)- by designing sensor networks to operate over the TV white spaces. White spaces refer to the allocated but locally unused TV channels, and can be used by unlicensed devices, according to the FCC in the US. Compared to the existing LPWAN technologies, SNOW offers much higher scalability and energy efficiency and takes the advantages of freely available TV white spaces.
SNOW is the first design of a highly scalable low power and long range wireless sensor network over the TV white spaces. At the heart of its design is a Distributed implementation of Orthogonal Frequency Division Multiplexing (OFDM), called D-OFDM. The base station splits the wide white space spectrum into narrowband orthogonal subcarriers allowing D-OFDM to carry parallel data streams to/from the distributed nodes from/to the base station. Each sensor uses only one narrow-band radio. The base station uses two wide-band radios, one for transmission and the other for reception, allowing transmission and reception in parallel. Each radio of the base station and a sensor is half-duplex and equipped with a single antenna. SNOW supports reliable, concurrent, and asynchronous receptions with one single-antenna radio and multiple concurrent data transmissions with the other single-antenna radio. This is achieved through a new physical layer design by adopting D-OFDM for multiple access in both directions and through a lightweight MAC protocol. While OFDM has been embraced for multiple access in various wireless broadband and cellular technologies recently, its adoption in low power, low data rate, narrowband, and sensor network design is novel. Taking the advantage of low data rate and short payloads, we adopt OFDM in SNOW through a much simpler and energy-efficient design.
In SNOW, a subcarrier bandwidth can be chosen as low as 100kHz, 200kHz, 400kHz depending on the packet size and expected bit rate. Using a subcarrier, a sensor node can have several kilometers of transmission range at 0dBm. Using a single base station, SNOW has the capability of supporting millions of devices. As an added advantage, it can use fragmented spectrum of white spaces. We implemented SNOW on two hardware platforms -- USRP using GNU radio and TI CC1310. CC1310 is a tiny, cheap (<$30), and commercially off-the-shelf (COTS) device with a programmable PHY. We implemented SNOW with CC1310 (using CC-ANTENNA-DK2 antenna) as a node and the BS is a USRP210 with a laptop. Experiments through deployments in multiple geographical areas as well as large-scale simulations demonstrated that SNOW drastically enhances the scalability of sensor network and outperforms existing techniques in terms of scalability, energy, and latency. Both analytical and experimental study hint that SNOW will be one of the most scalable and the key technologies to drive the IoT. The design of SNOW is available here.
This YouTube video shows a short demonstration of SNOW: https://youtu.be/y7Q932A24Zc
Currently we have a temporary SNOW testbed of 43 nodes for experimental purposes that co-locates with our permanent wireless sensor network (WSN) testbed at Wayne State University. Specifically, we have 43 SNOW nodes of which 34 are based on CC1310 and 9 are based on USRP which are co-located with our WSN testbed as shown in the following figure. Currently all SNOW nodes are powered through USB from Laptop and the laptops are connected with those of WSN testbed through department Ethernet. The entire testbed is located in Maccabees Building at Wayne state University.