Tag Archives: sdr

Wireless Radio Architecture

Wireless Radio Architecture

As we move forward towards the next generation of wireless protocols, the push for a better radio physical layer is ever increasing. Conventional radio architectures are limited to narrow operating regions and fails to adapt with changing technology. This is further strengthened with the advent of cognitive radio, which needs a more versatile and flexible framework that is programmable within the timing constraints of a protocol. In this research, we present an architecture for Software Defined Cognitive Radio that caters to the specific baseband processing requirements in a changing environment. We aim to provide more flexibility by deconstructing the radio pipeline into a framework of user controlled kernels that can be reconfigured at run-time. This architecture provides the barebones of a OFDM based radio physical layer that can adapt to perform a varied number of tasks in different radio networks. We also present a novel message based real-time reconfiguration method to transmit and receive a wide range of waveforms used in concurrent wireless protocols.


Cognitive Radio and Unmanned Aircraft

The Role of Cognitive Radio in Remote Operation of UAS

PIs: Timothy X Brown and Douglas Sicker

Unmanned Aircraft Systems (UAS) have the potential to play an important social, economic, and security role in the National Airspace System (NAS). The largest current barrier to the use of unmanned aircraft in the NAS is satisfaction of FAA regulations regarding safe flight operations and Air Traffic Control (ATC). In particular, the FAA requires all aircraft operating in the NAS to have detect, sense, and avoid capabilities; communication with ATC; as well as communication with a remote operator. Thus, one of the primary concerns in UAS deployment is the availability and allocation of bandwidth and spectrum for control, command, and communication (C3).

A significant C3 role can be filled by new radio technologies. One such technology is cognitive radio (CR). CRs enable fine-grained time, frequency, and location allocations of radio spectrum for communication. Current approaches allocate large swaths of spectrum over large regions for decades at a time. Finer grained allocations foster more efficient use of the spectrum with greater communication capacity to support future UAS growth and innovation. More importantly, CR can make such allocations automatically while still adhering to government policies. This automation provides government regulatory flexibility that is not currently present. However, such automated allocation has operational, security, and policy implications that are yet to be addressed for UAS.

This project investigates the possible operational models and infrastructure required to support CR-based spectrum allocation at different levels of granularity; and the security and policy models needed to support CR-based spectrum allocation. Information from this research will be relevant for the development of future requirements and standards for UAS and the NAS in general.


SMACK (SiMultaneous ACKnowledgment) and PAMAC (PHY-Aided MAC)

A Broadcast message followed by two SMACKs, using three prototype radio platforms

Network protocol designers, both at the physical and network level, have long considered interference and simultaneous transmission in wireless protocols as a problem to be avoided. This, coupled with a tendency to emulate wired network protocols in the wireless domain, has led to artificial limitations in wireless networks. In this paper, we argue that wireless protocols can exploit simultaneous transmission to reduce the cost of reliable multicast by orders of magnitude. With an appropriate application inter- face, simultaneous transmission can also greatly speed up common group communication primitives, such as anycast, broadcast, leader election and others.

In this research, we focus on using Orthogonal Frequency Division Modulation (OFDM) to provide distinct orthogonal signals. OFDM is a mechanism that splits the available spectrum into a number of orthogonal non-interfering subchannels. Being orthogonal, each of the subcarriers can be treated as an information carrying medium without significant interference with another subcarrier. In our protocol, since we only need to transmit a “yes” or “no” for an acknowledgment, we assign subcarriers to individual nodes. Using multicarrier modulation techniques, the AP receives ACKs from a greater number of clients in the shortest possible time, dramatically reducing the time to gather reliable acknowledgments for broadcasts.

Variation of Spectrum over Time, while transmitting SMACK

We exploit a programmable physical layer and SMACK to have clients signal whether they have packets to send. By detecting the high energy at the simultaneous transmission, the AP gets the following information: a) which stations have packets to send and b) whether the traffic load is high, medium or low. The AP schedules clients efficiently while wasting little of the spectrum on signaling overhead. The proposed protocol is a) fast, since no packet transmission is required for polling responses and all clients respond concurrently; b) reliable, as the poll response is contention free and c) scalable. We term this MAC protocol as PHY Aided MAC or PAMAC in short.


Wireless@CU – Prototypes

GENI Cognitive Radio Platform

The GENI Cognitive Radio Platform is an active development project that involves ground-up design and deployment of a highly programmable, frequency agile, multi-FPGA, wideband cognitive radio which will be connected to the GENI testbed framework. The basic idea behind this initiative is to make the platform accessible to other researchers using internet to run cognitive radio experiments in a realistic network. CU has teamed up with Rutgers University and Radio Technology Systems in this initiative to build this next generation testbed of cognitive radios.

Following is a demonstration of the latest version of the radio, which can be tuned from 100MHz to 7.5GHz.

GENI Cognitive Radio Prototype- version 1

The earlier version of the radio had the following features:

  • Virtex5-LX50 FPGA – Acts as the motherboard for the baseband OFDM design and ADC/DAC and RF daughter cards.
  • 100Mbps Ethernet to send control and data packet to and from the radio board.
  • Tunable to 2.4GHz and 5GHz ISM band.
  • Complete design and implementation of the OFDM pipeline is done using a combination Xilinx System Generator and ISE tools.
  • Design capabilities include – Non-contiguous OFDM with fine grain control over modulation and bandwidth.
  • Full transmit receive path implemented for OFDM based 802.11a/g packets.
  • Backward compatible with standard off the shelf Wi-FI cards.

We will continue to work on improving the prototype and add new features to achieve the ultimate goal of being a part of a global network testbed.

Nallatech XtremeDSP/Fidelity Comtech SDR

SDR prototype using Nallatech/Fidelity Comtech front-end

Prior to the GENI initiative, wirelesss@CU had been involved in development of basic software defined radio capable of demonstrating frequency agile techniques. The basic SDR was built as a hybrid design with partitioning of DSP algorithms into software and hardware components providing high flexibility as required in SDRs and cognitive radio. The development was carried out using a Nallatech XtremeDSP-IV kit with high speed ADC/DAC chip allowing wideband designs along with a RF front-end box that operates in the 2.4GHz.

Since its deployment in 2007-08, the prototype has been used in various experiments and resulted in a number of publications in the field of  wireless networking, cognitive radio and radio architectures.  Please refer to the publication list under various projects within the wireless@CU research group for more details on the design and development of the SDR prototype.


Wireless Networking Research

Non-Contiguous OFDM

Spectrogram using Non-Contiguous OFDM

Wireless networks provide data networking for more people than any other network technology. At Colorado, we’re focused on technologies that allow software defined cognitive radios to enhance spectrum use. Our research focuses on prototypes, technical mechanisms and analysis. We’ve developed a series of prototype systems based on FPGA’s for signal processing. We have developed a sophisticated software stack that lets us easily manipulate an OFDM waveform for real-time, high-bandwidth application.Earlier systems used devies from Nallatech and Fidelity Comtech. We’ve also done substantial work towards investigating the efficacy of directional and phased-array antenna technology in optimizing wireless networks and adhoc unmanned aerial networks, have developed more robust and realistic simulation techniques, and have done some work towards investigating coverage mapping strategies for large area wireless networks.

Active Projects

Hardware & Systems

  • NallaTech/Fidelity Comtech Software Defined Radio
  • GENI Cognitive Radio
  • Directional Antenna Radio

Recent Publications

  • Eric Anderson, Caleb Phillips, Douglas Sicker, and Dirk Grunwald. Signal Quality Pricing: Decomposition for Spectrum Scheduling and System Configuration. IEEE Dynamic Spectrum Access Networks 2011 (DySPAN2011). Aachen, Germany. May 3-6, 2011.
  • Aveek Dutta, Dola Saha, Dirk Grunwald, Douglas Sicker, SMACK – A SMart ACKnowledgment Scheme for Broadcast Messages in Wireless Networks,  ACM SIGCOMM, Barcelona, Spain, August 2009
  • Eric Anderson, Caleb Phillips, Douglas Sicker, and Dirk Grunwald. Modeling Environmental Effects on Directionality. Mathematical and Computer Modeling Journal. Special Issue on Modeling and Simulation of Wireless Networks. June, 2010. Elsevier.
  • Caleb Phillips, Douglas Sicker, and Dirk Grunwald. Bounding the Practical Error of Path Loss Models in Urban Environments. IEEE Dynamic Spectrum Access Networks 2011 (DySPAN 2011). Aachen, Germany. May 3-6, 2011.