802.11ax: An Uplink MU-MIMO SDR Testbed
The proliferation of smartphones and growth of user-generated content has led to substantial increase in uplink traffic in use by mobile devices. Multi-input multi-output (MIMO) technology has been successfully adopted in past 802.11 standards, leading to high throughput and robust performance. Downlink MU-MIMO (DL MU-MIMO) was introduced in 802.11ac, where an access point (AP) with multiple transmit antennas is able to transmit multiple data streams to multiple spatially distributed stations (STAs) at the same time. To address the challenge of burgeoning uplink traffic is one of the primary objectives of the new IEEE 802.11ax. Uplink multi-user MIMO (UL MU-MIMO) can improve uplink capacity by enabling multiple spatially separated clients to access the channel at the same time and is especially useful in scenarios where the STAs have limited number of antennas (e.g. typical smartphones). The focus of this project is to build a software-defined radio (SDR) testbed for prototyping UL MU-MIMO and studying related design trade-offs. The project uses Wireless Institute’s Software Defined Radio (SDR) Lab, namely the National Instruments (NI) USRP RIOs, the LabVIEW Communications System Design Suite, and NI’s 802.11 Application Framework.
The project is anticipated to have several phases. As the first step, we have already implemented two algorithms for UL MU-MIMO: Carrier Frequency Offset (CFO) correction at STAs, and multiuser detection (MUD) of users at the AP. The prototyping setup includes two NI USRP RIOs associated with their host computers, where the AP is implemented in one USRP and two stations are implemented in the second USRP. In comparison with the SISO system, we are able to get doubled system throughput. In the next step, we plan to add transmit power control functionality to the current framework to study the UL performance for the situations in which distances of stations to the AP are not similar. In addition, we will study the effect of asynchronous UL MU transmissions on the system performance.
The 802.11ax project was started in 2015 and is sponsored by InterDigital and National Instruments via the BWAC I/UCRC, an NSF program. J. Nicholas Laneman is the PI for this project.
Fast Mobile Network Characterization (FMNC)
The proliferation of smart devices has placed considerable pressure on the data capacity of the cellular network. WiFi has emerged as the de facto technology for selectively augmenting capacity for the short term. Critically, though, while WiFi generally tends to a positive for the user experience, user performance on WiFi is not always an improvement. In particular, automated roaming to WiFi has a strong potential to reflect poorly on the network carrier, institution, or place of business. Roaming and dead spots in WiFi coverage coupled with the “hard” handoff necessary to roam back to cellular further compound challenges.
The primary challenge is how to effectively gauge the capacity and quality of the wireless link for a given mobile device at a given location. Traditional techniques for speed testing tend to be exceptionally heavyweight (ex. SpeedTest.net) moving potentially tens of megabits of traffic and taking on the order of seconds to complete. Lighter weight variants fare better with regards to cost but tend to suffer under packet aggregation optimizations introduced in more recent WiFi and cellular variants. For decisions such as roaming or more importantly, upstream decisions with regards to data routing, such information may only be of limited value by the time it is finally resolved. The focus of this work is to radically overhaul in-band characterization of network performance by delivering reasonable network characterization requiring two magnitudes less of data (< 100 KB) and doing so on the order of less than a quarter of a second (< 250 ms).
The FMNC project started in 2015 and is sponsored by InterDigital and Nokia via the BWAC I/UCRC, an NSF program. Aaron Striegel is the PI for this project.
Drone Sounder: Measuring Cellular Signals
There is a largely anticipated market for drones and applications of drones across many verticals. With thousands of drones roaming the skies, in many cases semi- or fully autonomously, there is an urgent need for robust, high bandwidth, and standardized technologies to enable drone-ground and drone-drone wireless communication. The purpose of the Drone Sounder project is to build a test platform for signal measurements and waveform prototyping over such links.
Each Drone Sounder will be comprised of a COTS drone, 1-2 mobile phones, a software-defined radio (SDR), and one or more radio antennas. Drone Sounder will enable the following signal measurements, in several frequency bands of interest:
Commercial or emulated cellular base stations on the ground to a drone
Drone to emulated cellular base stations on the ground
Drone interference to emulated mobile devices on the ground
Drone to drone communications
Detailed study of the measurement data will enable the project team to provide recommendations on the frequency bands to utilize for various aspects of drone communication (command and control, detect-and-avoid, navigation, and payload) for both drone-ground and drone-drone communication.
The Drone Sounder project started in January 2016 and is sponsored by InterDigital via the BWAC I/UCRC, an NSF program. Aaron Striegel, J. Nicholas Laneman, and Hai Lin are the PIs for this project.