Tom Vermeulen, PhD Researcher - KU Leuven
Sofie Pollin - KU Leuven
NI Products Used
- USRP RIO
- LabVIEW Communications System Design Suite
Decreasing Collisions, Increasing Throughput
The next generation of wireless devices will require high speed, low latency, and high reliability to power new applications such as virtual reality, 4K video, and car-to-car communication. The main challenge is to build ultra-efficient protocols that are compatible with billions of devices. Densifying wireless networks requires new techniques for devices to access the wireless spectrum. A team of researchers from KU Leuven have addressed this challenge. With a history of research in telecommunications and focusing on various topics such as electromagnetic theory and networked systems, the team is paving the way for the next generation of wireless devices.
Currently, wireless devices listen first to check if the spectrum is free and then transmit their data. This works great in normal situations with a few devices. However, this mechanism breaks down in crowded places like conferences and football stadiums. In dense networks the probability is high that two or more devices may decide at the same time that the spectrum is free and transmit over each other, essentially corrupting each other’s data. Current-generation wireless devices waste valuable resources because they cannot sense the presence of other devices during their own transmission and therefore keep transmitting corrupted data packets.
The team found a solution that relies on in-band full duplex, so it can sense while transmitting, which potentially eliminates all collision overheads in wireless networks. We do this by continuously sensing for neighboring transmitters and aborting the transmission if we detect one. This helps us create dense Internet of Things (IoT) deployments in an energy-efficient way. Moreover, simulations show that we can more than double throughput by using a wireless listen-and-transmit scheme, which uses the available spectrum more efficiently. This solution means the IoT devices can transmit more data on a single battery charge.
Prototyping Next-Generation IoT Communication
To sense while transmitting, we must execute new fast and flexible wireless protocols in real time. We can implement the algorithms on the FPGA of a USRP RIO, effectively using it as a software defined radio (SDR). SDRs allow the swift implementation of low-level functions. However, high-level functions such as joining an existing network in real time have not been shown on a SDR before. We overcame this obstacle by integrating the low- and high-level functions on the FPGAs of these SDRs. We deployed the new devices in a dense network to allow for efficient spectrum contention in real time.
For prototyping this new idea, we used a USRP RIO in conjunction with the LabVIEW Communications System Design Suite. The seamless integration between NI’s hardware and software eased the implementation, so our team could focus on developing new algorithms. For network-level experiments, it is crucial to build a prototype that can join the network and respond in real time. This is made possible by using many of the built-in functional blocks found in LabVIEW Communications and implementing them on the FPGA of the USRP device. To remain backward compatible with current IoT devices, we implemented the IEEE 802.15.4 standard protocol, which is often used for smart devices. We fully utilized the capabilities of the FPGA by instantiating two microprocessors on it in parallel. One enables the SDR to join existing networks in real time, while the other runs the control algorithms of the in-band full duplex circuit. Furthermore, we implemented the collision detection algorithm in FPGA fabric. Our prototype can detect nearby transmitters within 10 percent of the full transmission time, which saves a great amount of energy and avoids long wasted spectrum usage.
The team connected six of these prototypes in a wireless network for the first network of in-band full duplex enabled wireless devices. Already for this small network, the results were highly promising and matched the simulations. We saw for a network of six devices an increase of 25 percent in throughput, but without an increase in energy consumption. This shows the potential of bridging the gap on an SDR between physical innovations and software protocols to control the spectrum access efficiently. This implementation powers the cooperation of multiple SDRs in a network, controlled by a single local protocol.
This project also shows the flexibility of these enhanced SDRs in terms of implementing standardized network protocols. The IEEE 802.15.4 standard inspired this implementation, and it is fully backward compatible to that standard. As a result, the SDRs running the novel technology can perfectly form a network with legacy, off-the-shelve IEEE 802.15.4 devices. This is extremely powerful, as we can now upscale the density of a network cost-efficiently and, moreover, compare performance with legacy nodes in very realistic network topologies.
Our current experiments already show the benefit of sensing while transmitting. However, our team wants to scale these experiments up to a network that comprises more than 40 SDRs that can all run the novel technology for dense network testing. In addition, these 40 SDRs can cooperate jointly to form a Massive MIMO system—a system in which all SDRs work together to form one massive antenna. The potential for future work is huge: all system configurations can be compared, ranging from 40 nodes with local decisions to 40 nodes with tight central control.
KU Leuven boasts a rich tradition of education and research that dates back six centuries. KU Leuven is the largest university in Belgium in terms of research. Telecommunications research at KU Leuven includes approximately 45 people focused on electromagnetic theory, numerical techniques, microwave and millimeter wave circuits, electromagnetic wave propagation, and networked systems. Professor S. Pollin heads networked systems research and led this project. The vision and passion of the network systems team is the prototyping of advanced wireless systems and networking concepts.
Tom Vermeulen, PhD Researcher
Dept. elektrotechniek ESAT-TELEMIC, Kasteelpark Arenberg 10, bus 2444