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Cognitive Network*. Xin Lu, Xin Su Member IEEE, Jie Zeng, HaiJun Wang. Tsinghua National Laboratory for Information Science and Technology. Tsinghua ...
A Single FPGA Embedded Framework for Secondary User in Cognitive Network* Xin Lu, Xin Su Member IEEE, Jie Zeng, HaiJun Wang Tsinghua National Laboratory for Information Science and Technology Tsinghua University,Beijing, China 100084 lu-x08, [email protected],

[email protected], [email protected]

Ahstract- The cognitive radio technology is very helpful

to handle the heavy computational missions, while support­

in improving the use of spectrum resources and reacting its

ing partial reconfiguration at run-time, and secondary user

operating environment. This paper presents a novel embedded

must contain a hybrid of programmable and reconfigurable

framework for secondary user based a single FPGA in cognitive

components designed to provide performance and flexibility.

network. By analyzing the processing ability of FPGA and

Meantime secondary user needs a processor as a decision

evaluating the existed architecture, this framework based FPGA supplying more logic resources and stronger embedded CPU

center to handle control, intelligence and higher application.

can support spectrum sensing and the transmission of complex

Our proposed framework is designed for these requirements.

communication protocols. In a single FPGA, we refer that the

[1] [2].

hardware and software mapped framework can realize the function of cognition easily. Meantime the pre-exist library

II. EX ISTING FRAMEWORKS

and design tools can improve the efficiency of cognitive radio design. At last, we introduce the mechanism of this single

The existing platform related to secondary user can mainly

FPGA embedded framework and demonstrate this framework

be classified into these classes: pure software framework,

by a practical application. Results of the application show that this framework can flexibly switch between sensory mode and

hardware framework, and hybrid software and hardware

transmission mode, which can meet the demands of secondary

framework. GNU radio [3] and OSSIE [4] are software

user in the cognitive network.

frameworks. These pure software frameworks writing in C++ are simple to use, simulate, and evaluate the development of

Index Terms-Cognitive Network. FPGA. Embedded frame­

communication protocol. However, processing performance

work.

of speed and large form factor limit application the areas of this framework. WARP [5] is a hardware platform. This

I. INTRODUCTION

platform consists of some real hardware components and

As more and more wireless services emerge in the com­

also has enough resources to satisfy the demand of intensive

munication market, the already heavily crowded radio spec­

processing demand. But it is not suit for cognitive radio

trum becomes much scarcer. At the same time, the use of

because of being void of an adaptive run-time reconfiguration

radio spectrum resource is insufficiency. Cognitive radio is

system for cognition.

a promising technology to alleviate the increasing stress on

designed for flexible processing at both radio physical and

KUAR [6] and WINC2R

[7] are

the fixed and limited radio spectrum. In the cognitive radio

MAC/network layer. These platforms consist of software and

networks, the secondary (unlicensed) users can periodically

hardware architecture aiming at providing adequate flexibility

search and identify available channels in the spectrum. Based

and adaptability to the environment and traffic changes as

on the searched results, the secondary users dynamically

desired in cognitive radio scenarios. But the mechanism of

tune its transceivers to the identified available channel to

run-time system, high-level design tool, and the library of

communicate among themselves without disturbing the com­

radio component are still in the research prior period.

munications of the primary (licensed) users. So a cognitive

According to the shortage of the existing platforms ,

node should complete these functions: Multi-band operation,

such as processing performance, the mechanism run-time

fast spectrum scanning, frequency agility, the library of

system, power consumption, high-level design tool, and the

spectrum policy processing, and different MAC algorithms

library of component, we refer that a combination of software

switching.

frameworks with the performance and hardware frameworks

Our single FPGA embedded framework for secondary user

with simple design-flow is effective for secondary user in

meets these requirements above in cognitive network. A cog­

cognitive network. By analyzing the processing ability of a

nitive node must provide sufficient computational resources

single FPGA and the requirements of secondary user ,Our proposed framework can base on a single FPGA.

-This paper is supported by Important National Science and Technology Specific Projects-No.2009ZX03005-004

978-1-4244-6871-3/10/$26.00 ©2010 IEEE

881

III. THE FPGA-BASED E MBE DDE D SOFTWARE AND

in the FPGA fabric and managed through a Linux device.

HARDWARE FRAME WORK

As shown in Fig.2. the software framework consists of regular modular, configuration modular, library modular,

In order to meet the requirement of the secondary user,

middleware, control and management modular at run-time,

the framework should have the ability to combine the advan­

network and application modular. The software framework

tage of hardware's high processing speed, low time delay

can map to hardware framework suitably. Every software

and software's flexible control, easy-to-adequate new pro­

modular can be supported by a hardware subsystem.

tocol.Meantime this framework must support partial recon­ figuration dynamically. Considering the portable, powerful, and flexible requirement in the development framework for secondary user, we propose a reality embedded framework

DODD

DODD

based on a single FPGA. The key feature of this frame­

Regular

Configuration

work is that software and hardware have the relationship

modular(IP)

modular

of mapped to each other. This framework makes full use

DODD

of the advantage of the software and hardware. Considering the rapid development of FPGA, more logic resources can

I

soft-core microprocessor chip such as NiosII can support

I

8-8-88

cognitive requirement. The design tools supplied by the FPGA manufacture company can improve the efficiency of designers. The system designers will pay more attention to the communication system design without knowing low­

library

J

Middleware

(

support complex digital signal processing, stronger embedded

Memory

00 )

( r:�:��ol ) I

I

I

(ApplicatiO�

level technology details of hardware. The virtual hardware architecture is shown in Fig.I.

Fig. 2.

The single FPGA embedded framework of software.

The hardware architecture based on a single FPGA mainly consists of the regular processing subsystem, reconfiguration processing subsystem, memory subsystem, and embedded processing subsystem. The regular processing subsystem is used for intensive computation in PRY, such as FFT, viterbi decoding. Considering these computations frequently used

Hardware

and highly performance, the design of hardware IP core

component

is a helpful way to handle stringent time constraints. The

Secondary Platform

reconfiguration processing subsystem is responsible for re­

Software

component Cognitive resource

configured computation at run-time. This is a special part in our propose framework for the demand of CR in order to change the system flexible. This subsystem is implemented

Fig. 3.

Regular

Reconfiguration

On-chip

processing(IP)

processing

memory

The structure of the pre-exist library in our framework.

In order to improve the efficiency of system design and shorten the time of development, it is important for the pre­ existed library and high-level tools of system component under our proposed framework. By using the library and

(

(( Fig. 1.

On-chip

Nios

)

BUS

Interface

Extras

design tools, system designer has not had to worrying about

)

)

low-level software and hardware details and pays more

J

attention to improving the performance of the cognitive node while taking advantage of computational power of the FPGA and dynamic reconfiguration for real-time system. Fig.3. shows the structure of pre-exist library. Software and hardware components, configuration and chain component,

The single FPGA embedded framework of hardware.

and cognitive resources etc. are built up this library. To adapt

882

specific spectrum environments, the cognitive users need to make adj ustments on component and chain parameters. This pre-exist library can be saved on on-chip memory based on

1 1 1 1 1 1 1 1 1 1 1-

a single FPGA. Besides software description language C++ and hardware description language, we can use high-level design tool such as DSPBuilder, EDS and est. to complete the development of components and high level of signal processing chains.

Radio

Frontend

________

1

Set frequency

� Hardware component � Software component Fig. 5.

library

The practical application of framework based on single FPGA.

The sense modular consists of estimator component and detection component. These aim at detecting the center frequency of any transmissions by receiving and analyzing the radio front-end.The advice engine is responsible for the management of the pre-exist library. Due to the library of cognitive radio including many components, it is efficient for the advice engine using the sensing signal to help the decision

Processing chain

engine control and excuse the radio processing chain. The decision engine is the core part in this mechanism. It aims

Fig. 4.

at intelligent processing in cognitive radio. The decision

The realizing mechanism of the secondary user in this framework.

engine is used for controlling and excusing the cognitive and processing chains while not considering implementation details of the components. Meantime this part controls the

IV. T HE MECHANISM AND APPLICATION OF T HIS

reconfigured components partly for the run-time system.

FRAME WORK

The co-design engine is responsible for hardware and software co-design. By the co-design engine, hardware and

In this section, we will introduce the mechanism and application of this framework for secondary user in cognitive

software components can be combined in a singer chain.

network. A transmitter, implemented with the tradition design

To improve the flexible of design, interface design is key

at the licensed frequency. The secondary user enters sensing

part in this engine. The hardware and software components

mode using energy detection based spectrum to find the va­

should be wrapped for the decision engine disposing into a

cancy frequency to set up a connection. Once the connection

custom interface. All the hardware interfaces based on a FIFO

sets up, the secondary user reconfigures into the reception

which has already been designed can connect consecutive

mode and begins to demodulate the signal. If this mission

components to chains. Especially, to satisfy the requirement

fails, the secondary user changes back into sensing mode,

of decision engine, some hardware components should be wrapped in software components with identical interfaces.

and searches for the connection built up.

The chain module connects all the components which are

Under this background of communication, the data and control flows of this application are shown in FigA. The

selected from the pre-exist library and excuses reconfigured

sensory modular with environment interaction sends out the

components at real-time for cognitive demands.

trigger. The trigger transfers to the advice engine. After

We realize this mechanism by a practical application

searching the pre-exist library, the advice engine will give the

simply. Considering LTE femtocells might be deployed in

signal to decision engine. The decision engine controls the

GSM spectrum in order to increase frequency utilization,

whole processing chain and realizes the run-time system. The

an LTE femtocell need to detect the signal activity if this

co-design plane is used for hardware and software component

frequency is already occupied. Spectrum sensing can be

wrapper and interface of the chain. After wrapper of co­

used to solve this problem. Our framework is based on this

design plane, the chain modular builds up the processing

practical background. So a real platform using this framework

chain and excuses partly reconfiguration function. The mech­

supports switching between sensing and transmission mode.

anism of this framework consists of the cognitive chains in

It is effective to use the same hardware resources for those

the bottom and the processing chains in the below.

operations without wasting hardware resources and power,

883

thus using a single FPGA.

signal. Once it has found the space channel, it switches into transmission node and start transmitting the streaming video. The receiver tries to receive the transmission, once a

Primary user

transmission has been found, the receiver will demodulate

---l:I I J

.. \ ......

· , , · ·

- --�

Secondary user

the signal. Fig.5. show this application. On our platform

:\

-' -- -� . -=- --....---'

.

,it is used a Altera EP2C70 to complete mainly processing

.

. . .

component and chain.Nios processor only uses about

.....

1810

LEs and IDE can be used for design. A 2-1-7 viterbi decoder uses about

1425 LEs. A 256-point FFT IPcore uses about

3658 LEs.A time-averaged power spectral density is used for Secondary user

.................!r.�!'���..........................

. ... .t

signal detection. The basic outline of detector contains two

f

units: the FFT and an averaging memory. The realization of the switch between sensory and transmission mode illustrates in Fig.7. V. CONCLUSION AND FUTURE WORK

"

�........... Reception .... . . . ..... .. .... .

. . . . . . ...

. " .................. .

f

In this paper, we introduce embedded framework for secondary user in cognitive network based on single FPGA

Fig. 6.

from three aspects: the mapped architecture of hardware and

The demonstration of this practical application.

software, the pre-exist library and tools, and the mechanism of framework. We realize this mechanism by a practical demonstration . With the improvement of processing abil­ ity, this proposed framework can meet the requirement of

Switch Between Sensory And Transmission Mode

intelligent wireless communication. Our future works aim at speeding up the development of this framework based already existed work. This includes that improving the ability of decision engine and advice engine, developing components of new communication protocol and function, and the high level of design tool for hardware reconfiguration. REFERENCES [I] Mitola J III, Cognitive radio: an intergrated agent architecture for software radio. PhD thesis, Royal Insititute of Technology [2] M. J. Marcus, "Unlicensed Cognitive Sharing of TV Spectrum: The controversy at the Federal Communications Commission," IEEE Com­

Transmission Mode

munications Magazine, vol. 43,pp.24-25, May 2005 Fig. 7.

[3] D. Cabric, S. M. Mishra, and R. W. Brodersen, "Implementation issues

The switch between sensory and transmission mode.

in spectrum sensing for cognitive radios,"

Signals, Systems, and Computers,

[4] GNU

Radio,

"Thd

in Proc. Asilomar Con!

Nov.7-1O, 2004, vol. 1, pp.772-776.

GNU

Software

Radio

Project."

http://www.gnu.org!software!gunuradio! [5] M. Robert, S. Sayed , C. Aguayo, et al. "OSSIE: Open source SCA for

The demonstration as shown in Fig.6 consists of three radio

researchers;' SDR Forum Technical Conference and Product Exposition,

nodes; the primary node, the secondary transmission and

Phoenix, Arizona, USA, Nov. 2004. [6] K. Amiri, Yang Sun, P. Murphy, et al. "WARP, a Unified Wireless

reception node. The first node is implemented on a PC

Network Test bed for Education and Research " IEEE International

and radio frontend which is SDR platform. This node is

Conference on Microelectronic Systems Education, San Diego, CA,

used to broadcast the presence of a femtocell's LTE-like

USA, 3-4 Jun. 2007 [7] G. J. Minden, J. B. Evans, L. Searl, et al.. "KUAR: A Flexible Software­

signal and acts the interfering node. The transmission and

Defined Radio Development Platform" In Symposium on New Frontiers

reception node are implemented on New Generation Unified

in Dynamic Spectrum Access Networks, Dublin, Ireland, 17-22 Apr.

platform for Wireless Communication developed in our lab.

2007. [8] Z. Miljanic, I. Seskar, K. Le, D. Raychaudhuri "The WINLAB Net­

The transmission node detect the space spectrum, then begin

work Centric Cognitive Radio Hardware Platform-WiNC2R" Mobile

to transmit streaming video. The reception node attempts to

Networks and Applications, vol. 13, no. 5, pp. 533-541, Oct. 2008

receive the transmission and decodes the video.

[9] Erich Stuntebeck, Timothy O'She, Joseph Hecker, T. Charles Clancy "Architecture for an open-source cognitive radio" SDR Forum Technical

The interfering node broadcasts the signal as the environs

Conference, Orlando, Florida, USA, Nov 13- 17 2006

of a femtocell. The transmitter node begins in sensory mode to find the space channel without interfere with LTE-like

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