CRASH: Cognitive Radio Accelerated with Software and Hardware

Jonathon Pendlum Miriam Leeser Kaushik Chowdhury
pendlum.j@husky.neu.edu mel@coe.neu.edu krc@ece.neu.edu

Abstract

Two key algorithms in Cognitive Radio are spectrum sensing and the spectrum decision. Many spectrum sensing algorithms have inherent parallelism and map well to a Field Programmable Gate Array (FPGA). Conversely, spectrum decision algorithms tend to require more sequential processing and lean towards a software implementation. These processing requirements suggest implementation on a heterogeneous computing system that accelerates parallel algorithms by offloading them to the FPGA fabric while performing sequential processing on the CPU.

Recently, FPGA vendors have released System-on-Chip (SoC) devices that tightly couple programmable logic and a multicore ARM processor. Due to the low latency interconnect, these SoCs show promise as an effective heterogeneous computing system. We have developed CRASH (Cognitive Radio Accelerated with Software and Hardware), a new software and programmable logic framework for Xilinx's Zynq SoC, to explore their potential in accelerating Cognitive Radio. CRASH provides the framework and interfaces to facilitate splitting algorithms between the Zynq's ARM processor and FPGA fabric. We built CRASH on a Xilinx ZC706 Zynq development board and used an Ettus Research USRP N210 software defined radio as the RF hardware. We leveraged CRUSH's hardware to implement a high speed serial interface between the Z706 and the USRP. This provides CRASH to use the full bandwidth of the USRP's ADC and DAC (100 Megasamples per second) with minimal latency.

To demonstrate CRASH, we implemented the spectrum decision in software and offloaded spectrum sensing to the FPGA fabric using our framework. For comparison, we also created a version with both algorithms in software. We determined the performance of each configuration by measuring the latency in sensing unoccupied spectrum and then transmitting in the spectrum. Compared to the purely software implementation, CRASH's improved processing performance reduced total system latency (or turnaround time) by 50%.

CRASH creates a low latency, high performance cognitive radio platform that simplifies offloading algorithms to programmable logic. This research shows that heterogeneous computing systems, such as CRASH, can provide cognitive radios substantial processing gains without sacrificing programmability.

Figure 1: Block diagram of the CRASH Framework on Xilinx Zynq Figure 2: CRASH Hardware


CRASH Installation Instructions

Prerequisite Hardware and Software

Building CRASH
CRASH is built with OpenEmbedded (OE) -- a powerful toolkit for creating embedded Linux distributions. We use OE to build all the required files to boot the ZC706 development board: the Linux kernel, DAS U-Boot boot loader, root filesystem, and the BOOT.BIN file.

Download all necessary files (with Google's git-repo tool and a manifest file):

curl http://commondatastorage.googleapis.com/git-repo-downloads/repo > repo
chmod a+x repo
sudo mv repo /usr/local/bin/
git clone git://github.com/balister/oe-gnuradio-manifest.git -b stable
mkdir oe-repo
cd oe-repo
repo init -u git://github.com/jpendlum/crash-manifest.git
repo sync

Noteworthy directories: Run the OE initialization script and build:

cd oe-repo
TEMPLATECONF=`pwd`/meta-crash/conf source ./oe-core/oe-init-build-env ./build ./bitbake
bitbake gnuradio-dev-image

Note: Bitbake takes several hours and uses ~40 GB of hard drive space

The output files end up in oe-repo/build/tmp-eglibc/deploy/images/zc706-zynq7/. The directory will contain many files. The files we need are:

Copy Files to SD Card
The ZC706 development board can boot from a SD card. However, the SD card must be formatted with two partitions: one named BOOT, fat32, size 40MB, marked as bootable and another named rootfs, ext4, rest of the free space. Once formatted, copy the files:

cd oe-repo/build/tmp-eglibc/deploy/images/zc706-zynq7/
cp BOOT-zc706-zynq7.BIN /path-to-sd-card/BOOT/BOOT.BIN
cp uEnv-zc706-zynq7.txt /path-to-sd-card/BOOT/uEnv.txt
cp uImage /path-to-sd-card/BOOT/uImage
cp uImage-zc706-zynq7-crash.dtb /path-to-sd-card/BOOT/devicetree.dtb
sudo tar -C /path-to-sd-card/rootfs/ -xzpf gnuradio-dev-image-zc706-zynq7-crash.tar.gz

Files to add CRASH support for GNU Radio and useful utilities:

cp -r gr-crash /path-to-sd-card/rootfs/home/root/
cp -r crash/arm/utils /path-to-sd-card/rootfs/home/root/

Configure Hardware to Boot from the SD Card
The ZC706 development has a set of DIP switches to determine the boot mode. Out of the box, all the boards should be set to boot from the SD card.

Boot the Board
The root file system has SSH built in and will start the DHCP client on boot up. Since the root user does not have a password, it is advisable to not connect ethernet on the first boot up and set the root password through the USB serial port.

Program USRP with CRASH's modified firmware
The USRP must run a modified firmware image to support CRASH. The prebuilt files are located in crash-uhd/images and programming instructions for custom firmware can be found in the USRP N2x0 User Manual.

Modifying the CRASH FPGA design
The FPGA design files for CRASH are located in the crash directory. The source files are located in crash/fpga/src. The FPGA design makefile resides in crash/fpga/zc706.

Publications

Acknowledgements

We would like to thank: