05-03-2013, 01:11 PM
CRUSH: Cognitive Radio Universal Software Hardware
CRUSH Cognitive.pdf (Size: 3.78 MB / Downloads: 49)
Abstract
The FPGA is an integral component of a software dened radio (SDR) that provides
the needed recongurability for dynamically adapting its transceiver and data
processing functions. Because of the desire to process data faster and with less latency,
researchers are looking at FPGA-based SDR. Our architecture, called CRUSH
(Cognitive Radio Universal Software Hardware), is composed of a Xilinx ML605 connected
to an Ettus USRP through a custom interface board, allowing
exible data
transfer between them. In addition, we provide a framework that supports ease of
use, independent programming on both devices, and integration with software running
on the host. To demonstrate our platform we implemented spectrum sensing,
a key step in determining channel availability before transmission in dynamic spectrum
access networks. Spectrum sensing is implemented on CRUSH using FFTs
for a 100x speedup; the complete sensing cycles is 10x faster than the same design
without CRUSH. By reducing the load on the host and allowing a powerful FPGA
extension for o-the-shelf devices, CRUSH enables advances in both protocol design
and recongurable hardware targeting radio applications.
Introduction
There is an increasing interest in using Software Dened Radios (SDRs) for realtime
processing and for more and more sophisticated algorithms. The Universal
Software Radio Peripheral (USRP) [1] is a widely proliferated SDR platform used
for implementing radio schemes. There is a wide variety of research using these
devices with both software and hardware implementations [2][3][4]. However, realtime
processing is not possible for software implementations with the USRP due to
the latency of transmitting data between the host and the USRP over Ethernet.
The solution is to accelerate algorithms in recongurable hardware that is connected
directly to the USRP platform.
Background
This chapter contains background information necessary for the understanding of
this thesis. Specically, we discuss state of the art hardware platforms for research
in Software Dened Radio (SDR) and Cognitive Radio (CR) followed by a short
introduction into the area of Cognitive Radio and how the work presented ts into
the larger picture. Finally, we discuss the specics of the spectrum sensing algorithm
implemented in this thesis.
Software Dened Radio Platforms
There are a number of SDR platforms currently on the market for use by researchers.
In this section we describe the most popular current SDR platforms and the features
that make them unique. Specically, we discuss the two most popular SDR platforms,
the Universal Software Radio Peripheral (USRP) by Ettus Research [1] and
the Wireless Open Access Research Platform (WARP) by Rice University [5]. There
are additional SDRs that have been used in research that we do not discuss such
as the Berkeley Emulation Engine (BEE) [6] line of products and Networking over
White Spaces (KNOWS) by Microsoft Research [7]. Additionally, there are several
commercial products that are advertised as capable of SDR such as FPGA boards
from Pentek, Lyratech, 4DSP, Acromag and Innovative Integration. However, these
do not include a framework supporting existing SDR research.
USRP
The USRP is a line of products from Ettus Research that is used to implement various
SDR schemes. The device has several dierent versions depending on the intended
usage. A picture of the USRP N210 is shown in Figure 2.1 and is representative of
the size and appearance of the whole line. The USRP N210 is the SDR used in our
research.
Other USRPs
The current Ettus Research product line includes two other USRPs, the E1x0 series
and the B1x0 series. The E1x0 series is one of the latest to be released by Ettus
Research and it combines an onboard embedded processor with the radio frequency
(RF) features and design of the standard USRP. It has slightly reduced bandwidth
capabilities but the advantage of this device is that no other computer is required to
perform radio functions. The B1x0 series devices are designed as a legacy support
product replacing the USRP 1. The distinguishing feature of the B1x0 series is the
USB2 host interface, which limits the bandwidth to 16 MHz. The original USRP 1
device was USB based with similar features and this product provides that legacy
capability and price point but with a modern FPGA and updated software support.
Conclusions
In this chapter we introduced the required background information for understanding
this thesis. Specically, we gave an overview of the existing SDR platforms including
the USRP N210 which is used in this project. Next, we introduced the concept of
Cognitive Radio and discussed how a CR can opportunistically utilize unoccupied
spectrum space. Finally, we introduced spectrum sensing, the application implemented
by the CRUSH platform to nd free spectrum space.