Dr. Arash Asadi - SEEMOO, TU Darmstadt
Max Engelhardt - TU Darmstadt
Dr. Arash Asadi in the Secure Mobile Networking Lab (SEEMOO) led this project, and Professor Matthias Hollick in the Computer Science Department of TU Darmstadt, Germany headed the project. SEEMOO researches mobile and wireless systems with a focus on performance, quality of service, robustness/resiliency, and security. Founded in 1877, TU Darmstadt is considered one of the top universities for computer science research in Germany.
Device-to-device (D2D) communication often refers to the technology that allows user equipment (UE) devices to communicate with each other with or without the involvement of network infrastructures such as an access point or base stations. D2D is promising as it is used to make ultra-low latency communication possible.
One of the recent hot topics in both academic and industry is autonomous driving where the D2D communication technology can be utilized. Although there is a long road to a complete autonomous driving solution, they have been looking at utilizing the cellular networks to communicate with vehicles. This new area is often referred to as C-V2X, where “X” is “everything,” such as another car (V2V), pedestrians (V2P), networks (V2N), and so on. D2D is a technology that can address the C-V2X communications.
Our system includes an eNodeB (eNB) and several pieces of user equipment (UE). We used USRP RIO for our hardware platform, which offers two TX and RX ports as well as a Xilinx Kintex-7 FPGA that we use to offload computationally expensive PHY operations. We built our demo on the LabVIEW Communications LTE Application Framework, which implements the Physical Downlink Control Channel (PDCCH), Physical Downlink Shared Channels (PDSCH), and Physical Uplink Shared Channel (PUSCH) for the eNB and the UE. However, as of version 2.0.1, the LTE Application Framework does not support multiple UE per eNB in OFDMA and uses the PUSCH for downlink feedback information only. We changed the LTE Application Framework to support in-band D2D communication.
Figure 1 shows the eNB software architecture. The blue blocks highlight modifications and extensions to the reference design to:
- Support multiple UE with one eNB, for which we optimize and extend the FPGA logic
- Enable transmission of D2D channel quality indicators (CQIs) along with downlink CQIs on the uplink channel
- Implement a lightweight scheduler for uplink/D2D resources, which takes the reported quality of both the cellular and the D2D link into account
- Implement the necessary signaling messages to control which link the UE should use for data transfers
In accordance with the 3GPP standard, we use uplink frequencies for D2D communication. Figure 2 shows the software architecture of the UE. Our modifications of the reference design consist of:
- Integrating an additional D2D receiver chain, for which we reuse the LTE Application Framework PUSCH implementation
- Extending the PUSCH transmitter to enable simultaneous transmission of uplink feedback and D2D payload data
- Implementing D2D signaling messages to allow for the eNB to control which data should be forwarded via the D2D link
We achieved synchronization to the eNB for timing and carrier frequency offset (CFO) estimation by processing the primary synchronization signal in the downlink receiver chain. Timing and CFO data are shared across chains to enable time alignment and CFO compensation in all chains.
This demo paves the path for researchers in academia to freely implement their D2D proposals in a software defined radio (SDR) testbed and observe the impact of real-world channel characteristics on the system’s performance. As a next step, we will extend this testbed to support dynamic D2D pairing with adaptive discovery mechanisms. We can extend the current implementation to support adaptive power control to enable underlay in-band D2D.
Dr. Arash Asadi
SEEMOO, TU Darmstadt
Tel: +49 6151 16-25480