Danh H. Nguyen

SDC testbed: Software defined communications testbed for wireless radio and optical networking

This paper describes the development of a new Software Defined Communications (SDC) testbed architecture. SDC aims to generalize the area of software defined radio to include propagation media not exclusively limited to radio frequencies (optical, ultrasonic, etc.). This SDC platform leverages existing and custom hardware in combination with reference software applications in order to provide a complete research and development platform. This platform can be used to implement current and future standards that make use of highly demanding communications techniques, including ultrawideband (UWB) radio and free-space optical communications. This paper describes the commercial and custom hardware that is being integrated into the platform, including the baseband hardware and the modular transceiver frontends. Furthermore, the paper describes the software development currently in progress with this platform, including the integration of available open source designs into the platform, and the development of custom IP for scalable OFDM PHY implementations in radio and optical communications. We seek to create a complete research platform for the commercial and academic wireless communities, capable of delivering the highest possible performance and flexibility while providing the necessary development tools and reference designs in order to minimize system learning curve and development cost.

FPGA-based latency-insensitive OFDM pipeline for wireless research

This paper develops a programmable hardware implementation of the physical layer for cognitive wireless communication systems that use orthogonal frequency division multiplexing (OFDM) schemes. Data-flows within hardware implemented baseband architectures for all communication standards are quite regular in nature, thereby enabling the construction of fast, synchronized and optimized baseband systems on FPGAs. We designed an OFDM pipeline comprising codec, modulation, interleaving, piloting, channel estimation, and IFFT stages in which each stage can be configured at design time or at run time to accommodate different communication standards as well as different configuration settings for a single standard-a key feature necessary for dynamic spectrum sensing and utilization. This flexibility in hardware is achieved by designing each individual stage with room for scaling/modification and having the overall pipeline be insensitive to the latencies incurred by individual pipeline stages. This is done by using stallable stages with centralized control through cross communication between modules both directly and indirectly using code running on the MicroBlaze processor. The OFDM pipeline is implemented on a Xilinx Virtex-6 FPGA and its performance is characterized in terms of functional correctness and FPGA implementation area cost. Experimental results and preliminary simulations of our FPGA based design can run at flexible coding rates of 1/2 and 3/4 with modulation schemes of 4QAM and 16QAM respectively.

A real-time and protocol-aware reactive jamming framework built on software-defined radios

This paper develops a software-defined radio (SDR) framework for real-time reactive adversarial jamming in wireless networks. The system consists of detection and RF response infrastructure, implemented in the FPGA of a USRP N210 and designed to function with the open source GNU Radio SDR library. The framework can be used to implement a fast turnaround reactive jamming system capable of timely RF response within \textit{80ns} of signal detection. Our framework also allows for full control and feedback from the FPGA hardware to the GNU Radio-based cognitive radio backend, making it applicable to a wide range of preamble-based wireless communication schemes. This paper presents the capabilities, design, and experimental evaluation of this framework. Using this platform, we demonstrate real-time reactive jamming capabilities in both WiFi (802.11g) and mobile WiMAX (802.16e) networks and quantify jamming performances by measuring the network throughput using the iperf software tool. The results indicate that our system works reliably in real time as a reactive jammer and can be used for practical assessments of modern jamming and secure communication techniques.

Experimental evaluation of a reconfigurable antenna system for blind interference alignment

In recent years, several experimental studies have come out to validate the theoretical findings of interference alignment (IA), but only a handful of studies have focused on blind interference alignment. Unlike IA and other interference mitigation techniques, blind IA does not require channel state information at the transmitter (CSIT). The key insight is that the transmitter uses the knowledge of channel coherence intervals and receivers utilize reconfigurable antennas to create channel fluctuations exploited by the transmitter. In this work, we present a novel experimental evaluation of a reconfigurable antenna system for achieving blind IA. We present a blind IA technique based on reconfigurable antennas for a 2-user multiple-input single-output (MISO) broadcast channel implemented on a software defined radio platform where each of the receivers is equipped with a reconfigurable antenna. We further compare this blind IA implementation with traditional TDMA scheme for benchmarking purposes. We show that the achievable rates for blind IA can be realized in practice using measured channels under practical channel conditions. Additionally, the average error vector magnitude and bit error rate (BER) performances are evaluated.

BeamViewer: Visualization of dynamic antenna radiation patterns using Augmented Reality

Wireless research and education are often hindered by the fact that RF electromagnetic signals are invisible and therefore hard to visualize. Domain-specific software, such as those used for antenna radiation pattern measurements, has significantly enhanced the level of radiation visualization through interactive 3D plots. However, the intuition stops there and does not carry over into the real-word operational environment of antennas and radios. As a result, there exists a real disconnect in visualization between the available antenna radiation patterns and their effects on wireless network performance. In this demo1 we present BeamViewer, an augmented reality framework to help visualize and capture the dynamic radiation patterns of reconfigurable antennas in real time. BeamViewer takes inputs from the cognitive radios controlling beam-steerable antennas and annotates on a live-view mobile screen the active pre-measured radiation patterns. This capability adds an unprecedented level of instant visualization and provides valuable insights into the dynamics of a reconfigurable antenna-based cognitive radio network.

Wireless cybersecurity education via a software defined radio laboratory

Cybersecurity is one of the fastest growing concerns in the world today. Recent global events show the need for more strict measures to protect the public from cyber attacks, which has triggered an increased demand for cybersecurity professionals. Many academic institutions began offering courses covering current cybersecurity concepts to satisfy this need. Although these courses educate students with proper skills, they lack the connection to current advancements in academic research. A more encompassing curriculum is needed in this rapidly growing field. For the most up-to-date education, we developed a course that takes a student-centric hands-on approach supported with Software Defined Radios to study current cybersecurity research projects in wireless networks. Our course consists of short lectures followed by lab sessions, where students implement security algorithms described by standards or by recent peer-reviewed research articles. Our results indicate that students appreciate the mixture of textbook and research topics being covered in the course and they feel more prepared for any future task in the cybersecurity field. While deviating from the textbook applies additional strain to educators, our paper shows that including current research practices in curriculum development efforts is a good investment towards a better educational outcome.

Enabling synchronous directional channel access on SDRs for spectrum sharing applications

Ubiquitous wireless small-cell deployment requires a fundamental rethink of interference management within the cell, between cells, and with overlaying macrocells. One mean to increase spectral efficiency in these scenarios is through simultaneous directional transmissions and receptions, wherein the antenna directions can be selected such that the overall interference is minimized, or some other cost function is satisfied. To realistically evaluate the performance of these beamsteering techniques, network simulators or testbeds are often required. Nevertheless, a capable testbed that covers sufficient small-cell operational aspects and incorporates directional antennas has yet to be found in the literature. In this paper we present WARP-TDMAC, a software-defined radio framework to enable the prototyping of directionality-based spectrum sharing schemes for small cells. WARP-TDMAC integrates compact pattern-reconfigurable antennas with a high performance 802.11 physical layer and uses a time division multiple access (TDMA) based medium access control (MAC) scheme for antenna direction scheduling. We characterize the synchronization and temporal/spatial scheduling capabilities of this testbed through several example MAC schemes that would have been difficult to realize without our cross-layer framework. The empirical results show that appropriate use of directionality can result in higher network sum rates in dense small-cell deployments, but further investigation is required to find an effective solution for this highly complex operational environment.

Leveraging an Agile RF Transceiver for Rapid Prototyping of Small-Cell Systems

This paper describes a new software-defined radio (SDR) platform targeted for rapid prototyping of small-cell systems. The SDR hardware combines the signal processing power of Xilinx ML605 Virtex-6 FPGA board with the Nutaq Radio420X frequency-agile transceiver and reconfigurable antennas to form a highly versatile platform for spectrum sensing, spectrum access, and cooperative communications. We evaluate the platform with two example applications: an offline OFDM physical processing flow based on WARPLab, and a real-time online automatic gain control mechanism. The results show that our SDR platform can reliably handle both offline and online processing demands with the added benefit of frequency agility offered by a state-of-the-art radio transceiver.

Sub-Microsecond Network Synchronization for Distributed Wireless PHY Protocols

We present a hybrid wired-wireless time synchronization method targeting enterprise WLAN networks to enable future deployments of distributed wireless PHY protocols. Our method synchronizes all network APs on the Ethernet backhaul using the IEEE 1588 Precise Time Protocol, while all clients are synchronized to their home AP via reference broadcast synchronization. We implement this synchronization primitive on WARP software-defined radios and evaluate through a microbenchmark involving four network links. The results verify that our method achieves sub-microsecond synchronization accuracy among all network nodes and therefore serves as an effective building block for protocol development.

Enhancing indoor spatial reuse through adaptive antenna beamsteering: demo

Widespread deployment of indoor wireless LANs has brought about many advantages, but at the same time posed tremendous challenges for interference management and service scalability. One means to improve wireless capacity in dense deployments is through simultaneous directional transmissions and receptions, but there has yet to be a coordinated approach that can adapt well to fast-changing channel conditions. In this demonstration we present a distributed directional antenna system to enhance spatial reuse in indoor scenarios. Our system is a holistic approach combining smart antennas, synchronous channel access, and an adaptive antenna beamsteering mechanism. We implement this system on software-defined radios and demonstrate the feasibility of dense spatial packing to maximize the network sum rate.