Literature Review - University of Khartoum Repository

SOFTWARE DEFINED RADIO

By

MARWA MAMOUN ABDELGADIR ABDELRAHMAN

INDEX NO. 074083

Supervisor

Dr. Tahani Abdalla Attia

A REPORT SUBMITTED TO

University of Khartoum

In partial fulfillment of the requirements for the degree of

B.Sc. (HONS) Electrical and Electronics Engineering

(COMMUNICATION ENGINEERING)

Faculty of Engineering

Department of Electrical and Electronics Engineering

September 2012

II

DECLARATION OF ORIGINALITY

I declare that this report entitled “Software Defined Radio for Cubesat” is my own work except

as cited in the references. The report has not been accepted for any degree and is not being

submitted concurrently in candidature for any degree or other award.

Signature: _________________________

Name: ____________________________

Date: _____________________________

III

ACKNOWLEDGEMENTS

From the very beginning to the end, I thank Allah who provided me with health and strength and

through whom a number of relatives, friends and many others helped me throughout this project.

I would like to express my sincere appreciation and gratitude to my supervisor Dr.Tahani Abdallah

for her support, help and guidance throughout this project.

I would like to thank also Dr. Nadir Omer, whose vision and constructive criticism over the last year

have been my privilege.

Special gratitude to my project partner Nibras Sirag, for her support, hard work, team spirit and

patience.

I am as ever, indebted to my family, especially my mother for supporting me throughout my life.

IV

ABSTRACT

Software defined radio (SDR) has emerged from obscurity to be heralded in recent years as offering

a potential solution to our historical and continued inability to achieve common global

communication standards. Software defined radio offers a highly flexible system that can work with

different communication standards. Moreover, it allows new features to be added to the system

without requiring the underlying architecture to be changed.

This project aims to develop a simple software defined radio transceiver for University of Khartoum

educational ground station that provides users with basic capabilities of changing the filtering

parameters, tuning frequency and modulation/demodulation scheme. The system is based on

software in which most of the transceiver functions are implemented with as minimum hardware as

possible.

The system was developed and implemented successfully using a PC and an RF front end. The

software program was written using C++ to cope with real time processing requirement. The

software operation for baseband processing was tested. Transmission and reception of baseband

signals were performed successfully.

Although the results obtained from testing the system are satisfactory, a software improvement is

still required in order to increase the signal quality. System integration was not completed due to

time constraints.

V

.

RF .

C++ .

.

VI

TABLE OF CONTENTS

TITLE.................................................................................................................................................. I

DECLARATION OF ORIGINALITY …....................................................................................... II

ACKNOWLEDGMENT.................................................................................................................. III

ABSTRACT...................................................................................................................................... IV

…..…………………………………………………………………………….……………..V

TABLE OF CONTENTS................................................................................................................. VI

LIST OF FIGURES......................................................................................................................... IX

LIST OF TABLES........................................................................................................................... XI

LIST OF ABBREVIATIONS .........................................................................................................XII

1. Chapter One ................................................................................................................................ 1

1.1 Overview ............................................................................................................................... 1

1.2 Problem Statement ................................................................................................................. 1

Background and Motivation .................................................................................................. 2 1.3

Objectives .............................................................................................................................. 2 1.4

Methodology .......................................................................................................................... 3 1.5

Report Layout ........................................................................................................................ 3 1.6

2. Chapter Two ............................................................................................................................... 5

Overview ............................................................................................................................... 5 2.1

Ground Station Overview ...................................................................................................... 5 2.2

Software Defined Radio ........................................................................................................ 6 2.3

2.3.1 Software Defined Radio Ideal Architecture ....................................................................... 6

2.3.2 Ideal Transceiver Operation ............................................................................................... 8

Software Defined Radio Platforms ........................................................................................ 9 2.4

2.4.1 FPGA Based Software Defined Radio ............................................................................... 9

2.4.2 DSP Based Software Defined Radio .................................................................................. 9

2.4.3 PC Based Software Defined Radio .................................................................................. 11

VII

Software Defined Radio Projects Review ........................................................................... 13 2.5

3. Chapter Three .......................................................................................................................... 15

Introduction ......................................................................................................................... 15 3.1

Design Considerations ......................................................................................................... 15 3.2

Development Methodology ................................................................................................. 16 3.3

Project Scope ....................................................................................................................... 16 3.4

System Requirements .......................................................................................................... 17 3.5

System Design ..................................................................................................................... 18 3.6

3.6.1 PC Sound Card ................................................................................................................. 18

3.6.2 Hardware Design ............................................................................................................. 19

3.6.2.1 Receiver RF Front End ................................................................................................. 19

3.6.2.2 Transmitter RF Front End ............................................................................................ 22

3.6.3 Software Design ............................................................................................................... 23

3.6.3.1 Sound Card Access ....................................................................................................... 23

3.6.3.2 The Object-Oriented Programming (OOP) .................................................................. 24

3.6.3.3 C++ Programming Language ....................................................................................... 25

System Implementation ....................................................................................................... 25 3.7

3.7.1 Hardware .......................................................................................................................... 25

3.7.2 Software ........................................................................................................................... 25

3.7.2.1 Audio Class .................................................................................................................. 27

3.7.2.2 Modulation Class .......................................................................................................... 28

3.7.2.3 Demodulation Class ..................................................................................................... 29

3.7.2.4 Filter Class .................................................................................................................... 29

3.7.2.5 GUI Implementation .................................................................................................... 30

4. Chapter Four ............................................................................................................................ 33

Introduction ......................................................................................................................... 33 4.1

VIII

Software Modules Testing ................................................................................................... 33 4.2

4.2.1 Audio Class Testing ......................................................................................................... 33

4.2.2 Filter Class Testing .......................................................................................................... 36

4.2.3 Modulation Class ............................................................................................................. 37

4.2.3.1 AM ............................................................................................................................... 37

4.2.3.2 DSB .............................................................................................................................. 37

4.2.3.3 ASK .............................................................................................................................. 38

4.2.3.4 FM ................................................................................................................................ 39

4.2.3.5 BFSK ............................................................................................................................ 40

4.2.3.6 BPSK ............................................................................................................................ 40

4.2.4 Demodulation Class ......................................................................................................... 41

4.2.4.1 AM ............................................................................................................................... 41

4.2.4.2 DSB .............................................................................................................................. 41

4.2.4.3 ASK .............................................................................................................................. 42

4.2.4.4 FM ................................................................................................................................ 43

4.2.4.5 BFSK ............................................................................................................................ 44

4.2.4.6 BPSK ............................................................................................................................ 44

Hardware Testing ................................................................................................................ 45 4.3

5. Chapter Five ............................................................................................................................. 46

Project Preview .................................................................................................................... 46 5.1

Future Work ......................................................................................................................... 46 5.2

REFERENCES .......................................................................................................................... 48

APPENDIX A…………………….…..…...………………………………………………….A-1

APPENDIX B……………………...…………………………………………………….........B-1

APPENDIX C………………………………………………………………………………....C-1

IX

LIST OF FIGURES

Figure Page

Figure 2.1 Ideal transceiver architecture .............................................................................................. 8

Figure 2.2 FPGA based software defined radio ................................................................................. 10

Figure 2.3 Xilinix SpartanIIE FPGA kit ............................................................................................ 10

Figure 2.4 DSP based software defined radio .................................................................................... 11

Figure 2.5 Altera-Cyclone II DSP kit ................................................................................................. 11

Figure 2.6 PC Based Software Defined Radio ................................................................................... 12

Figure 3.1 Spiral model ...................................................................................................................... 16

Figure 3.2 Typical transceiver system ................................................................................................ 17

Figure 3.3 Receiver Subsystem .......................................................................................................... 18

Figure 3.4 Transmitter Subsystem ..................................................................................................... 18

Figure 3.5 Receiver RF front end block diagram ............................................................................... 19

Figure 3.6 Pre-selector filter ............................................................................................................... 20

Figure 3.7 Mixer ................................................................................................................................. 20

Figure 3.8 Phase transformer.............................................................................................................. 21

Figure 3.9 Transmitter RF front end block diagram .......................................................................... 22

Figure 3.10 Typical computer architecture ........................................................................................ 24

Figure 3.11 Receiver RF front end circuit schematic ......................................................................... 26

Figure 3.12 Transmitter RF front end circuit schematic .................................................................... 26

Figure 3.13 A photo of the system RF front end ................................................................................ 27

Figure 3.14 Audio stream flow .......................................................................................................... 28

Figure 3.15 GUI window ................................................................................................................... 30

Figure 3.16 Modulation mode operations .......................................................................................... 31

Figure 3.17 Demodulation mode operations ...................................................................................... 32

Figure 4.1 Sound card output at input of constant amplitude ........................................................... 35

Figure 4.2 Sound card output at input of constant frequency ............................................................ 35

Figure 4.3 Lowpass filter at 10KHz cutoff frequency Bode plot ....................................................... 36

Figure 4.4 AM modulated signal ........................................................................................................ 37

Figure 4.5 DSB modulated signal ...................................................................................................... 38

Figure 4.6 ASK modulated signal ...................................................................................................... 39

X

Figure 4.7 FM modulated signal ........................................................................................................ 39

Figure 4.8 BFSK modulated signal .................................................................................................... 40

Figure 4.9 BPSK modulated signal .................................................................................................... 41

Figure 4.10 AM demodulation ........................................................................................................... 42

Figure 4.11 DSB demodulation .......................................................................................................... 42

Figure 4.12 ASK demodulation ......................................................................................................... 43

Figure 4.13 FM demodulation ............................................................................................................ 43

Figure 4.14 BFSK demodulation ....................................................................................................... 44

Figure 4.15 BPSK demodulation ....................................................................................................... 44

Figure 4.16 Received signal using RF front end ................................................................................ 45

XI

LIST OF TABLES

Table Page

Table 4.1 Sound card output at 0.3Vp-p input ................................................................................... 34

Table 4.2 Sound card output at input of 12KHz ................................................................................ 34

Table 4.3 Lowpass filter of 10KHz cutoff frequency behavior ......................................................... 36

XII

LIST OF ABBREVIATIONS

A/D Analog To Digital Converter

AM Amplitude Modulation

API Application Programing Interface

ASK Amplitude Shift Keying

BFSK Binary Frequency Shift Keying

BPF Bandpass Filter

BPSK Binary Phase Shift Keying

BRF Bandreject Filter

BTS Base Transceiver Station

CR Cognitive Radio

D/A Digital To Analog Converter

DLL Dynamic Link Library

DSB Double Side Band

DSP Digital Signal Processer

FIR Finite Impulse Response

FM Frequency Modulation

FPGA Field Programmable Gate Array

GPL General Public License

GPP General Purpose Processor

GUI Graphical User Interface

HDL Hardware Description Language

HPF High Pass Filter

LPF Lowpass Filter

OOP Object Oriented Programming

OS Operating System

PC Personal Computer

RF Radio Frequency

SDR Software Defined Radio

SNR Signal To Noise Ratio

1

1. Chapter One

INTRODUCTION

1.1 Overview

Traditionally, radio communication systems required specialized hardware to implement

their functionality. In order to keep production costs low, these systems contained only

the hardware necessary to perform the tasks that they were designed for. Therefore these

hardware defined systems were often difficult to modify and upgrade.

Software based systems emerged offering a potential solution of higher flexibility and

comparatively lower cost. Software defined radio is defined as "Radio in which some or

the entire physical layer functions are software defined" [1]. Software defined radio

allows engineers to implement any number of different signal processing elements

without altering the underlying system hardware. This is done by simply upgrading

system software.

1.2 Problem Statement

2. The conventional hardware defined radios have little flexibility and mostly doesn't

support multiple wireless communication protocols because of the limitation of hardware.

Also, development of radio that involves new services is very difficult because it requires

hardware changes, which means more power consumption, long development time and

high production cost.

3. Performing the baseband signal processing in the software domain allows for much

greater re-configurability than traditional radios provide. In addition, the cost of a

software defined radio platforms are often lower than those of a more traditional

platforms because the software is reusable and often available at relatively low cost.

Introduction Chapter One

2

Background and Motivation 1.3

4. The costs incurred in evolving a communication system to a new standard, by means of

hardware replacement, is enormous. Therefore software defined radio must be employed.

Software defined radio decreases the cost dramatically because any system upgrade

requires only software update.

Moreover, software defined radio increases system flexibility. With software defined

radio, system becomes adaptable to the continuously changing requirements of

scrambling or encryption codes, modulation format, channel bandwidth, data rate, and

voice codec type. Therefore the system becomes able to operate with different equipment

standards.

Software defined radio evolved from pure academically concept to be implemented in the

defense sector in both U.S. and Europe [2]. The United States Military developed a

software defined radio system in the early 1990s that required four of the most powerful

digital signal processors (DSP) available and some FPGAs to glue them together. This

system, known as SpeakEasy, filled the back of a truck. By the time the engineers

finished writing the software for SpeakEasy, three years had passed and the hardware in

the system was already obsolete [3].

Then software defined radio broke out and revolutionized the communication world.

Nowadays most mobile handsets and base transceiver station (BTS) systems include

software defined radio system. Different manufacturing companies are developing

software defined radio systems for reception of RF signals such as FlexRadio and

SoftRock.

Software defined radio is future of radio, maximum flexibility a lot of possibility from

the same hardware, what was very hard to achieve with hardware realization now is very

easy by software.

Objectives 1.4

The main objective of this project is to develop a software defined radio of high

flexibility and minimum cost for University of Khartoum KNSAT educational ground


3

station. This is done with the aim of making the system available for usage and/or

modification by students, graduates and researchers.

Methodology 1.5

In order to implement a software defined radio consists of software that used for different

type of modulation and RF front end receiver, a small set of requirements is considered

and goes through each development phase for those set of requirements, design,

implementing and testing is done at each phase, based on that, functionality for additional

requirements is added in ever-increasing until the application is ready for integration,

installation and maintenance phase.

The system is divided into modules, so that each module is independent from the others,

to be reused for other implementation where ever it needed. For the hardware part, the

components with low cost are selected. On the other hand, free and open source software

is implemented.

Report Layout 1.6

This report is organized as follows:

Chapter 2 (Literature Review): This chapter presents an overview to software

defined radio and its projects. It begins by describing the software defined radio

architecture and the various platforms that are used to implement it and their

capabilities.

Chapter 3 (Design and Implementation): This chapter details the project

requirements and scope. Also, it presents the design methodology, components

description, in addition to the methods, and tools used to implement the system.

Chapter 4 (Testing and Results): Presents a description of how the system was

tested followed by the results of tests and their discussion.

Chapter 5 (Conclusion): The project is reviewed in this chapter, discussing the

achieved objectives and not achieved ones; in addition to the further

developments that can be made to the resulting system.


4

Appendix A: represents the GNU License of PortAudio

Appendix B: describes the audio I/O code.

Appendix C: Presents the software modules used.

1

2. Chapter Two

LITERATURE REVIEW

Overview 2.1

This chapter aims to examine the possible architectures for a software defined radio. This

is done with the aim of providing guidance to certain design decisions that will be made

later throughout the project. This chapter begins a brief overview of ground stations

which is provided to show the importance of software defined radio. Following that, the

various tools and techniques that can be used for software-defined radio are introduced

and discussed. The chapter ends by presenting some of the software defined radio

existing implemented projects.

Ground Station Overview 2.2

A ground station is a terrestrial terminal station designed for

telecommunication with spacecraft, or reception of radio waves from an astronomical

radio source. Ground stations are located either on the surface of the Earth, or within the

atmosphere [4]. Earth stations communicate with spacecraft by transmitting and receiving

radio waves using transceivers. Both the transmitter and receiver of the transceiver must

be customized to the signaling format used such as encryption, modulation/demodulation

and frequency used by the spacecraft or the astronomical radio source. This places high

burden in the choice of ground station equipment. When ground station is to be used to

receive signals from different radio sources, the equipment purchased must match the

wide range of signaling format used by each source and to be able to differentiate

between sources too. Therefore more equipment is purchased to cope with all inquiries

which increase the cost dramatically.

http://en.wikipedia.org/wiki/Telecommunication

http://en.wikipedia.org/wiki/Spacecraft

http://en.wikipedia.org/wiki/Radio_waves

http://en.wikipedia.org/wiki/Astronomical_radio_source

http://en.wikipedia.org/wiki/Astronomical_radio_source

Literature Review Chapter Two

6

A potential solution is to use software defined radio transceivers to increase flexibility

and to decrease cost.

Software Defined Radio 2.3

A software defined radio is defined as a form of transceiver in which ideally all aspects of

its operation are determined using versatile, general-purpose hardware whose

configuration is under software control. This is often thought of in terms of base-band

digital signal processers (DSPs). The following section describes how software defined

radio can be implemented in a transceiver system.

2.3.1 Software Defined Radio Ideal Architecture

A software defined radio consists of, for the most part, the same basic functional blocks

as any digital communication system [5]. Software defined radio lays new demands on

many of these blocks in order to provide multiple bands, multiple service operation and

re-configurability needed for supporting various air interface standards. To achieve the

required flexibility, the boundary of digital processing should be moved as close as

possible to the antenna, and application specific integrated circuits, which are used for

baseband signal processing, should be replaced with programmable implementations [6].

An ideal software defined radio would have a very minimal analog front end as illustrated

by Figure 2.1 Ideal transceiver architecture, note that the A/D converter is assumed to

have a built-in anti-alias filter and that the D/A is assumed to have a built-in

reconstruction filter [7]. The system consists of the following:

Digital signal processor: the modulation scheme, channelization,

protocols, and equalization for transmit and receive are all determined in

software within the digital processing subsystem. This is shown containing

a DSP in Figure 2.1 Ideal transceiver architecture.

Circulator: is used to isolate the transmit and receive path signals to

allow using a single antenna for both transmitter and receiver.

Amplifier: two amplifiers are used. One of which is responsible for

including enough power in the signal for transmission after the D/A


7

conversion. The other one magnifies the incoming signal from the antenna

before passing it to A/D. The amplifier must have linear characteristics to

prevent signal distortion.

Anti-Aliasing and Reconstruction Filter: anti-aliasing filter is included

before the A/D converter to prevent generation of image signals. Because

once an aliased image is created in the sampling process, no amount of

further processing can distinguish between a true signal and an aliased

signal.

The filter must be a lowpass filter tuned to a frequency that is less or equal

half the sampling frequency of the A/D converter. The filter must have

also linear characteristics in order to protect signal properties.

For the same reason, the output of a D/A converter requires a lowpass

analog filter, called a reconstruction filter, as the output signal must be

band limited, to prevent aliasing (here meaning Fourier coefficients being

reconstructed as low frequency waves, not as higher frequency aliases).

Ideally, both filters should be brick wall filters, constant phase delay in the

passband with constant flat frequency response, and zero response from

the Nyquist frequency.

Antenna: it is used to radiate and receive signals.

A/D converter: it is used to convert the incoming analog signal into

digital in order to perform digital signal processing techniques to it. The

converter must have a sampling rate that is twice maximum incoming

signal frequency according to sampling theorem. A/D converters of high

sampling rate for high frequency signals are quiet expensive and are not

usually available in the local markets. A potential solution is to down

convert the incoming signal frequency into a suitable frequency range

using a mixer stage before the converter.

D/A converter: it is used to convert digital signal into analog in order to

transmit it by the antenna. This component is chosen depending on the

required frequency band of the output signals. Its sampling rate must also

follow the sampling theorem.


8

2.3.2 Ideal Transceiver Operation

The signal is received by the antenna through the circulator which is then amplified. This

is because received signals power is very low due to attenuation encountered in the

propagation path. The signal is passed to an anti-aliasing filter then to A/D converter. The

signal is then passed to the final stage which is digital signal processing.

When the signal is to be transmitted, the data generated by the processor are passed to

D/A converter. The signal is then amplified and radiated by the antenna through the

circulator to space. The reason behind amplification here is to include enough power in

the signal that helps it to propagate to the required destination and to be detected by the

receiver.

Transmit/Receive

Antenna

Power

Amplifier Circulator RF-output DAC

RF-input ADC

DSP

Digital

Processing

D/A

A/D

Figure 2.1 Ideal transceiver architecture


9

Software Defined Radio Platforms 2.4

There exist a large number of available platforms for software defined radio, each with its

own features and capabilities. The choice between them depends on the particular

application area, the cost and power consumption. In the following section, the potential

digital hardware platforms are viewed.

2.4.1 FPGA Based Software Defined Radio

A field-programmable gate array (FPGA) is an integrated circuit that contains an array of

programmable logic components called "logic blocks" which can be configured by a

customer or a designer after manufacturing hence the name "field-programmable".

The FPGA kits contain many features. The most important for the transceiver

architecture are A/D converter, D/A converter, power amplifier, RF input pins, and a

processor. Therefore the kit along with an antenna and a circulator can be used as a

transceiver as shown in Figure 2.2.

FPGA processor is programmed using a hardware description language (HDL) such as

VHDL and Verilog. The DSP program is written in one of these languages on PC

compiler and then loaded into the FPGA using a USB port.

Different kits of different processing capabilities and sampling frequencies are available

which can be used depending on application and cost. Usually, the FPGA processor is

capable of performing high speed calculations but its operation is limited by the small

memory contained in the FPGA kit. Therefore optimization between memory and certain

operations (for example making a filter program) is needed. Moreover FPGA size is large

compared to other platforms discussed below.

FPGA is used with applications that require high processing requirements at high

frequencies such as military communication systems.

2.4.2 DSP Based Software Defined Radio

A digital signal processor (DSP) is a microprocessor that has an architecture specialized

for fast operational needs of digital signal processing. They are best suited to the less

http://en.wikipedia.org/wiki/Integrated_circuit

http://en.wikipedia.org/wiki/Programmable_logic_device

http://en.wikipedia.org/wiki/Field-programmable

http://en.wikipedia.org/wiki/Hardware_description_language

http://en.wikipedia.org/wiki/Microprocessor


10

computationally intensive forms of signal processing, rather than very high-speed front-

end applications.

The DSP kit - like the FPGA kit- contains many features that can be utilized for the

transceiver, such as A/D and D/A converters, anti-aliasing and reconstruction filters, RF

inputs pins and the processor. Figure 2.4 DSP based software defined radio describes a

possible architecture for the transceiver.

Figure 2.3 Xilinx SpartanIIE FPGA kit

The DSP based software-defined radio contains features that ease the DSP operations

more than the FPGA based architecture, but still not as much as the PC based one.

FPGA Kit

Diplexer

Transmit/Receive

Antenna

Figure 2.2 FPGA based software defined radio


11

Moreover, DSP based architecture is built to perform DSP operations; any other

operation type is not applicable, therefore decreasing the system flexibility.

Different aspects must be considered for purchasing the DSP kit for software-defined

radio; most important are the memory, sampling rate and clock speed.

Figure 2.5 Altera-Cyclone II DSP kit

2.4.3 PC Based Software Defined Radio

The PC based software defined radio depends on the PC processor. Each PC utilizes a

general purpose processor (GPP) to perform its functions. GPP is not restricted to a

Diplexer

DSP Kit

Transmit/Receive

Antenna

Figure 2.4 DSP based software defined radio


12

specific language or software. GPP has high processing capabilities therefore it can be

used in different application by simply programming it by any high level language such

as C and Java.

Today PCs can contain more than one processor and very large memory. Consequently,

implementing DSP operations on PC is simple, efficient and cost effective. Therefore

there is no need to buy an FPGA or DSP kit. Anyone with sufficient knowledge can

create his own transceiver using his PC. Figure 2.6 PC Based Software Defined Radio

illustrates the PC based software defined radio. The signal is input to the processor using

any one of the external ports. A/D and D/A converters are required in the system

preceding the ports as shown in the figure (the figure assumes that all input signals are of

frequency below half the sampling rate). To eliminate the need for an external A/D and

D/A converters, the PC sound card can be utilized. This is by passing the incoming signal

through the microphone jack and then taking the output signal after processing from the

speakers jack. This method limits the signal frequency band that can be received

depending on the sound card sampling rate.

A/D

D/A

Transmit/Receive

Antenna

Diplexer

Figure 2.6 PC Based Software Defined Radio


13

Software Defined Radio Projects Review 2.5

Software defined radio was first termed 'software radio' which was first introduced in

1984 by a team at the Garland Texas Division of E-Systems Inc. (now Raytheon). A new

digital signal processing laboratory was developed in which sellable software radio

products were produced and popularized within various government agencies. This 1984

software radio was a digital baseband receiver that provided programmable interference

cancellation and demodulation for broadband signals, typically with thousands

of adaptive filter taps, using multiple array processors accessing shared memory [8].

Perhaps the first software defined radio transceiver was designed and implemented by

Peter Hoeher and Helmuth Lang at the German Aerospace Research Establishment

(DLR, formerly DFVLR) in Oberpfaffenhofen, Germany, in 1988 [9]. Both transmitter

and receiver of an adaptive digital satellite modem were implemented according to the

principles of software defined radio, and a flexible hardware periphery was proposed.

Latter, in 1991, term "Software Defined Radio" was introduced by Joseph Mitola, who

published the first paper on the topic in 1992, though the concept was first proposed in

1991[2].

In the defense sector, software-defined radios have been known since the late 1970s in

both the U.S. and Europe [3]. The first military application that used software-defined

radio was SpeakEasy program that was initiated by the U.S. military. The program aimed

to use programmable processing to emulate multiple existing radios and to be able easily

incorporate new coding and modulation standards in future so that military

communications can keep pace with advances in coding and modulation techniques [4].

Another program by the U.S. military is the Joint Tactical radio system (JTRS) which

produces a family of interoperable, modular, software-defined radios that operate as

nodes in a network that provides secure wireless communication and networking services

for mobile and fixed forces, consisting of U.S. Allies, joint and coalition partners, and in

time, disaster response personnel [10].

Software defined radio was then spread from military to a wide variety of applications

making the platform itself a commodity that is available in everyone hand. Software

defined radio is used extensively in mobile communication systems, both in the handset

http://en.wikipedia.org/wiki/E-Systems

http://en.wikipedia.org/wiki/Baseband

http://en.wikipedia.org/wiki/Adaptive_filter

http://en.wikipedia.org/wiki/Array_processor

http://en.wikipedia.org/wiki/Transceiver

http://en.wikipedia.org/wiki/German_Aerospace_Center

http://en.wikipedia.org/wiki/DFVLR


14

and the base transceiver station. Nowadays there is no mobile that does not use software

defined radio.

Moreover, there are several companies that develop the hardware and/or the software

products to be used for different applications such as FlexRadio systems. Open source

hardware and software are also available for software-defined radio. GNU Radio is a free

and open source software development toolkit that provides signal processing blocks to

implement software radios upon which several open source hardware can be used [11].

Universal software radio peripheral (USRP) is an open source hardware which is

designed and sold by Ettus Research, LLC and its parent company, National Instruments.

The USRP is commonly used with the GNU Radio software suite to create complex

software-defined radio systems. HPSDR (high performance software defined radio) is

open source hardware and software project intended for use by Radio Amateurs ("hams")

and Short Wave Listeners (SWLs) [12].

Another SDR hardware that has recently become available in small numbers and which

has been bought by amateur radio enthusiasts around the world is the Fun Cube Dongle

or „FCD‟ [13]. FCD can be used with any of the software defined radio programs

available such as Rocky developed by Alex VE3NRA and WINRAD developed by

Alberto IPHD [14].

http://www.ettus.com/

http://www.nationalinstruments.com/

http://en.wikipedia.org/wiki/GNU_Radio

1

3. Chapter Three

DESIGN AND IMPLEMENTATION

Introduction 3.1

The project is designed based on a straightforward methodology using PC components, to

help use and development of the project. The aim of this chapter is to describe the tools

and designs that were employed to implement the project and achieve its objectives. The

chapter begins by listing some considerations that were taken into account while

designing the system. Then the development methodology, project scope and system

requirements are discussed. The chapter continues by discussing system design in details

for both hardware and software and ends by discussing system implementation.

Design Considerations 3.2

Low cost: the system is to be designed and implemented using available

components, while at the same time perform its functions with high efficiency.

Re-configurability: The system should be easily reconfigurable and flexible so

that it can be used to support any number modulation, demodulation, or other

signal processing schemes.

Extensibility: The system must be designed such that new capabilities can be

added to it without major changes to the underlying architecture.

Modularity: The components of the resulting system should be well defined and

independent which leads to better maintainability. The components could then be

implemented and tested in isolation before being integrated to form the system.

Open Source: such that the source code is available for modification or

customization. Also the hardware is designed using simple components of low

cost such that hardware becomes available in anyone‟s hands.

Design and Implementation Chapter Three

16

Compatibility: The project target is to design a software-defined radio

transceiver that is compatible and operable on any PC.

Convenience: the system is to be designed such that it is convenient to use by all

users of all levels.

Simplicity: the system is designed based on a simple approach to help system

development.

Development Methodology 3.3

The system was developed under spiral model approach, according to which the

development starts with a small set of requirements and goes through each development

phase for those set of requirements. Based on that, functionality for additional

requirements is added in ever-increasing "spirals" until the application is ready for the

Installation and Maintenance phase. With the spiral model no need for full understanding

of the requirements and their implementation from the beginning.

Figure 3.1 Spiral model

Project Scope 3.4

The scope of the project is to develop a software defined radio that can be used for

reception and transmission of radio signals. This is by implementing the RF front end

part and the digital modulation and demodulation part of the transceiver system shown in

Figure 3.2 Typical transceiver system. The system is designed to be an educational

transceiver targeting different users such as students, graduates and researchers.

Analysis Evaluation

Planning Development


17

Figure 3.2 Typical transceiver system

System Requirements 3.5

In order to fulfill the project objectives and design considerations, certain system

requirements arise. Figure 3.3 Receiver Subsystemand Figure 3.4 Transmitter Subsystem

illustrate the general structure of receiver and transmitter subsystems. The soundcard will

be used to perform the conversion operation from analog to digital and from digital to

analog, and all processing is carried out by PC. Consequently, the system must contain

and perform the following:

i. A RF front end must be included in order to perform all analog operations and to

generate an in-phase and quadrature projection of the received signal and passing

them to the microphone jack.

ii. Getting the signals directly from the sound card.

iii. Modulation or demodulation on the input signals.

iv. Delivering the modulated or demodulated signal to the sound card at which the signal

can be taken from speakers jack.

v. Giving the user the ability to change the settings of the software and specify the mode

of operation (modulation, demodulation, others …) and the type of each.


18

Figure 3.3 Receiver Subsystem

Figure 3.4 Transmitter Subsystem

System Design 3.6

The system design is divided into hardware and software design. Both designs require the

knowledge of PC sound card accessing. Therefore sound card is first discussed then

hardware and software designs are presented.

3.6.1 PC Sound Card

Nowadays every PC nowadays comes with a sound card; they vary immensely in sound

quality, features and input/output options. Most standard PC soundcards allow the

incoming signal to be sampled at rates up to 44.1 kHz per channel. High end professional

soundcards allow higher sampling rates, typically 96 kHz and above. Most common

soundcards operate using 16 bit A/D converters. High end soundcards use 24 bit A/D

converters allowing a greater range of output values. This is because sound card is

intended to process only audio signals. Sound cards also contain a built in anti-aliasing

and reconstruction filter for their A/D and D/A converters respectively.

The sound card inputs audio signals from the microphone jack and outputs it to the

speakers through its A/D and D/A converters.

Input From Antenna

Analog Radio Front

End

A/D converter

(Sound Card)

Digital Signal

Processing on GPP

Digital Signal

Processing on GPP

D/A Converter

(Sound Card)

RF Front End

Output to Antenna


19

3.6.2 Hardware Design

The hardware design consists of designing a RF front end for receiver and transmitter

subsystems. These are discussed in the following.

3.6.2.1 Receiver RF Front End

In this section all the analog operations are performed to get the signal ready for the next

section in which the signal is transformed into digital. The RF front end constitutes of the

following components:

i. Antenna

For reception of radio frequency an antenna is used.

ii. Pre-Selector Filter

A simple bandpass filter is used to select the frequency band required for reception of

radio signals. A tank circuit is used with a variable inductor along with a variable

capacitor to change the frequency range. The circuit designed is shown in Figure 3.6.

The center frequency of the circuit is determined by the following equation:

Antenna

Pre-selector

Filter

VFO

Phase

Transformer

I

Q

L

R

Figure 3.5 Receiver RF front end block diagram


20

(Eqn. 3.1)

Figure 3.6 Pre-selector filter

iii. Mixer

An external analog mixer is required to down convert the signal frequency into low

frequencies depending on the sound card sampling rate.

Simple double diode mixer is used as shown in Figure 3.7 Mixer. The mixer has two

inputs. One of which is taken from the RF input signal, the other is taken from a

variable frequency oscillator.

Figure 3.7 Mixer

The mixer produces two frequency components. One of which with frequency equals

the sum of the two input signals frequencies and the other is the difference. Only the

lower frequency signal will be passed through the anti-aliasing filter. This is what is

referred to as frequency down conversion. It is described by the following equations:

(Eqn. 3.2)

(Eqn. 3.3)

(Eqn. 3.4)

And after filtering:


21

(Eqn. 3.5)

iv. Variable Frequency Oscillator

The variable frequency oscillator used is the laboratory signal generator. The signal

generator can generate a signal from dc up to a frequency of 1GHz. It can also

generate a signal of different forms. That is square, triangular and sinusoidal wave.

The signal form used here is the sinusoidal.

v. Phase Transformer

To make the 90° phase shift, the circuit shown in

Figure 3.8 was used. The circuit must be tuned to a specific frequency in order to

give the required phase shift. Therefore a potentiometer is used. By varying the

potentiometer the phase shift is varied until phase shift required is obtained at a

particular frequency. The capacitor and potentiometer values depend on the following

equation.

(Eqn. 3.6)

where f is the VFO frequency.

Figure 3.8 Phase transformer

Q I


22

3.6.2.2 Transmitter RF Front End

The transmitter RF front end contains most of the components used for the receiver part.

The signal is taken from the speaker jack that consists of the left and right components.

The transmitter RF front end (shown in Figure 3.9 Transmitter RF front end block

diagram) consists of the following:

i. Mixer

Here the mixer is used to up convert the signal from baseband to higher frequencies

suitable for transmission as described by (Eqn. 3.2)

(Eqn. 3.3)

ii. Variable Frequency Oscillator

The variable frequency oscillator is also needed here to generate the carrier. The

device used here is the laboratory function generator.

iii. Antenna:

The same reception antenna is used for the transmitter.

Antenna

VCO

L

R

Figure 3.9 Transmitter RF front end block diagram


23

3.6.3 Software Design

When talking about the software part of the system, there are three important issues to be

determined; how the software program will interact with the sound card for audio I/O, the

programming language and approach. Both are discussed in the following two sections.

3.6.3.1 Sound Card Access

To develop a real time audio application it is necessary to obtain the audio data directly

from the sound card using the operating system (OS). Since there are different types of

operating systems and much hardware each with their own driver, there are a wide

variety of possibilities to access the audio data. These access points are commonly called

application programming interface (API).The software access to the sound card is guided

by varies application programming interfaces (API), which differs within and from

platform to platform.

For a cross platform application, one that works on different platforms or OS, it is

necessary to be able to use all these different API‟s. In this case an additional API which

is a fully software orientated API is used to create one access point to interface a number

of different system API‟s such as: CLAM, OpenAL,pureData, STK and PortAudio. Most

of these APIs are licensed under the General Public License (GPL) (see Appendix A) so

they are free to use within these regulations.

The API used for software design is Port Audio Library because it causes the smallest

overhead for this application and is easy to use.

PortAudio is a free, audio I/O library, it is meant to have cross platform abilities

(including Windows, Macintosh (8, 9, X), Unix (OSS), SGI, and BeOS) and a very easy

to use API for recording and/or playing. It is a simple API and does not bring any

functions like mixing, filtering or analyzing.

PortAudio Library was chosen among other API's that are used for audio data because it

causes the smallest overhead for this application and is easy to use.


24

Figure 3.10 Typical computer architecture

3.6.3.2 The Object-Oriented Programming (OOP)

The fundamental idea behind object-oriented languages is to combine into a single unit

both data and the functions that operate on that data. Such a unit is called an object. OOP

is not primarily concerned with the details of program operation. Instead, it deals with the

overall organization of the

Next are the major elements of object-oriented that are important to this project:

Objects: When you approach a programming problem in an object-oriented

language, you no longer ask how the problem will be divided into functions, but

how it will be divided into objects. The match between programming objects and

real-world objects is the happy result of combining data and functions: The

resulting objects offer a revolution in program design. No such close match

between programming constructs and the items being modeled exists in a

procedural language.


25

Classes: In OOP we say that objects are members of classes. A class is thus a

description of a number of similar objects. An object is often called an “instance”

of a class.

Reusability: Once a class has been written, created, and debugged, it can be

distributed to other programmers for use in their own programs.

3.6.3.3 C++ Programming Language

C++ is derived from the C language. The most important elements added to C to create

C++ are classes and objects, therefore it has been chosen as the programming language.

For this project it is preferred over the C language. C++ is also chosen over java although

it is also OOP language, because of the need for fast processing since real time signal is

applied, and the virtual machine that is used by Java or C# and its.NET environment

could be speed waster.

System Implementation 3.7

After designing the system hardware and software to fulfill the project objectives, the

system was implemented.

3.7.1 Hardware

The receiver RF front end components described in section Receiver RF Front End3.6.2.1

were connected together. The complete circuit schematic is shown in Figure 3.11. Also,

the Transmitter RF front end components described in section 3.6.2.2 were also

connected. The complete circuit schematic is shown in Figure 3.12. Since the two

circuits have components in common, the two circuits were combined into one circuit

that can operate as a transmitter or receiver, depending on the user requirements. The

created circuit is shown in Figure 3.13.

3.7.2 Software

The system software could was divided into five modules, each module represent a C++

class that consist of its own data and functions, the functions operate on these data to


26

perform a specific task. These classes are Audio class, Modulation class, Demodulation

class, Filter class and GUI class. See Appendix C for description about the classes found

in the header files.

Figure 3.11 Receiver RF front end circuit schematic

Figure 3.12 Transmitter RF front end circuit schematic


27

Figure 3.13 A photo of the system RF front end

3.7.2.1 Audio Class

This class is responsible for Audio I/O operations using PortAudio library functions as

illustrated by Figure 3.14 Audio stream flow Using PortAudio is quiet easy; the software

comes as pure code, therefore it was compiled as a dynamic link library (DLL). After

this, the header was included and the DLL was linked to the project. The two channels

(stereo) function of the soundcard was used. The first recorded block is the right channel

the next one the left and so on. In order to run PortAudio, the following steps were taken:

i. PortAudio was initialized

ii. The stream was managed.

iii. The manipulation of the audio data was performed depending on the mode

that the user selects.

iv. The stream was then terminated terminate.


28

The main part of initialization is to set the basic parameters for the audio, like input

channels, output channels, data type, sample rate, frames per buffer then the callback

function performs the audio manipulation. However, PortAudio delivers the audio data

always in blocks of sizes which must be chosen as minimum as possible.

The actual signal processing is done in the manipulation part. The task that has to be

performed by callback function is to call the sub-routines that will do the desired

processing by the user.

Figure 3.14 Audio stream flow

3.7.2.2 Modulation Class

An instance of this class (object) is created when the user choose to start a modulation

process. Then the carrier frequency, modulation type and the sampling rate values are

collected from the GUI and sent to the constructor to be initialized. According to the

modulation type that is chosen by the user, one of the following modulation techniques is

applied: AM, DSB, ASK, FM,BFSK or BPSK. For each type there is a function that

implements operations that needed by specific modulation type. Since C++ is a high level

language, the represention of the operations which are just mathmetical equatuions are

streightforward.

One important issue that was taken into account, is phase incrementation control, such

that it does not exceed the float number range. Since π) is same as ,

whenever the angle becomes more than 2π, 2π is subtracted from the angle. This ensures

that the phase incrementation is always within float range.

Another thing that should be considered, is that the values of the samples are represented

by float values in the range from -1 to 1, hence whenever the output of the modulation is

expected to be more than 1 or less than -1, it should be normalized to 1.


29

3.7.2.3 Demodulation Class

An instance of this class (object) is created when the user choose to start a demodulation

process. Then the filter bandwidth, modulation type and the sampling rate values are

collected from the GUI, this is used to initialize the data of the created object. According

to the modulation type that is chosen by the user, one of the following demodulation

techniques is applied: AM, ASK, FM, BFSK or BPSK. For each type there is a function

that implements operations that needed by specific demodulation type. Since C++ is a

high level language, the represention of the operations which are just mathmetical

equatuions are striegt forward.

Using I/Q represenation of the modulated signal, any signal can be demodulated, for an

AM , ASK , and BPSK it is just . For FM and BFSK quadricorrelator method is

used.

For digital demodulation, multi levels decision is used to determine the received digital

data if it is 0 or 1.

3.7.2.4 Filter Class

An instance of this class (object) is created when the user choose to start a filtering

process. Then the filter bandwidth, filter type and the sampling rate values are collected

from the GUI, which is used to initialize the data of the created object. According to the

filter type LPF, HPF, BPF or BRF will be performed for the samples. The filter chosen to

be implemented is FIR with Blackman window. Blackman filters are excruciatingly slow,

because they must use convolution but they have high selectivity.

When using filter in a real-time environment there is one problem occurring. The

resulting signal is going to contain a periodic clipping noise. This is because of the nature

of the filters and their tendency to settlement. To avoid this problem, the values of the

delay lines after every filtering are saved, so they can be used as the filter initialization of

the next block. With this, a smooth crossover from one to the next block is guaranteed

and the settlement takes only place during the first initialization of the filter, which is

negligible.


30

3.7.2.5 GUI Implementation

Through the GUI the user is able to select different modulation, demodulation and filter

types in addition to setting other parameters. Moreover, the GUI allows user to save and

play back signals to or from file, and display these signals as in oscilloscopes. User

Interface window made is shown in Figure 3.15.

The Two Important modes for the program are modulation and demodulation. When the

user checks the button Mod Enable on the window enters the requested values and then

presses the Start button, the program will run on the modulation mode. This process is

described by the flow chart shown Figure 3.16. On the other hand, when user checks

Demod Enable, the program will run on the demodulation mode as described by the flow

chart will in Figure 3.17.

Figure 3.15 GUI window


31

Figure 3.16 Modulation mode operations


32

Figure 3.17 Demodulation mode operations

1

4. Chapter Four

TESTING AND RESULTS

Introduction 4.1

As a consequence of using the spiral model for the system development, the design

procedure is carried out for each module separately. Then the modules were

implemented, tested, debugged and improved by adding more features. Any PC running

windows 98 SE or better has Microsoft Visual C++ 2008 Express with PortAudio V 19

audio library installed in it can be used. Since the software has not been integrated yet, a

special test code for each module was written. The hardware was also tested separately

for performing its function.

Software Modules Testing 4.2

The testing was performed by passing a sine wave signal from the function generator to

the microphone jack. The signal parameters were changed depending on the test

performed.

4.2.1 Audio Class Testing

The main purpose of this test is to examine the sound card behavior with signals. This

was done by varying the signal frequency at constant amplitude then varying the

amplitude at constant frequency. The results obtained are shown in Table 4.1 Table 4.2.

It was realized that, and during varying the frequency at constant input voltage, the signal

starts to exhibit distortion at frequency of 15 KHz. This is due to the built in anti-aliasing

filter in the sound card. On the other hand, when the input voltage was varied at constant

frequency, it was realized that signal exhibits clipping at voltages greater than 0.3Vp-p

such that the output voltage stays constant at 2.5Vp-p. This is because the sound card has

Testing and Results Chapter Four

34

the limitation that maximum input voltage that can be applied to it is 0.3Vp-p and

maximum output voltage is 3Vp-p. It worth noting here that the results were taken at

speakers volume of 100%, that‟s why the output results are amplified by almost ten times

the input voltage.

Table 4.1 Sound card output at 0.3Vp-p input

Frequency (kHz) Output voltage (Vp-p)

1 1.3

5 2.2

10 3

15 2.8

20 2.4

25 1

30 0

Table 4.2 Sound card output at input of 12 KHz

Input voltage (Vp-p) Output voltage (Vp-p)

0 0.02

0.1 2.2

0.15 2.5

0.2 2.58

0.3 3

0.4 2.5

0.5 2.5

2.5 2.5


35

Figure 4.1 Sound card output at input of constant amplitude

Figure 4.2 Sound card output at input of constant frequency

0

0.5

1

1.5

2

2.5

3

3.5

1 5 10 15 20 25 30

Output (Vp-p)

Frequency (KHz)

0

0.5

1

1.5

2

2.5

3

3.5

0 0.1 0.15 0.2 0.3 0.4 0.5 2.5 3 4

Output (Vp-p)

Input (Vp-p)


36

4.2.2 Filter Class Testing

This test is used to examine the low pass filter designed. Table describes a filter of 10

KHz cutoff frequency behavior at different input signal frequencies.

Table 4.3 Lowpass filter of 10 KHz cutoff frequency behavior

Frequency (kHz) Amplitude (Vp-p)

0.5 3

1 3

2 3

4 3

5 3

6 3

10 3

10.5 2

10.8 0.5

11 0.1

11.5 0

15 0

20 0

Figure 4.3 Lowpass filter at 10 KHz cutoff frequency Bode plot

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.5 1 2 4 5 6 10 10.5 10.8 11 11.5 15 20

Amplitude (Vp-p)

Frequency (KHz)


37

4.2.3 Modulation Class

Here all modulation types implemented are tested. Note that the speakers output volume

was 100% and the function generator signal frequency was 1.9 KHz.

4.2.3.1 AM

Here the program modulates the incoming signal through the microphone jack and

outputs the result through the speakers jack. The message signal voltage used was 0.3Vp-

p. Then signal from the speakers jack was measured using an oscilloscope. The signal is

shown in Figure 4.4.

Figure 4.4 AM modulated signal

As shown in Figure 4.4, the AM modulation is perfect. And the message and AM signal

are in phase.

4.2.3.2 DSB

For DSB modulation, the program modulates the incoming signal through the

microphone jack and outputs the result through the speakers jack. The program also asks

for the modulation index required. This option is limited by the maximum output voltage

that the sound card can deliver, for example if the speakers volume is 100% and the

maximum modulated signal amplitude is greater than 0.3 the output signal will suffer


38

from clipping. Therefore it is important to carefully calculate the modulation index and to

put under consideration the speakers volume. By performing a DSB modulation on the

message signal, the output was displayed on the oscilloscope and it is shown in Figure

4.5.

Figure 4.5 DSB modulated signal

Figure 4.5 illustrates DSB modulation with a modulation index of 40%. The results were

taken at speakers volume of 100% and carrier amplitude=0.5Vp-p.

4.2.3.3 ASK

For ASK modulation, the ASK option must be chosen. The program modulates the

incoming signal through the microphone jack, which was 0.2Vp-p, and outputs the result

through the speakers jack. The signal from the Speakers jack was is displayed on an

oscilloscope. The signal is shown in Figure 4.6.

As shown in Figure 4.6, we realize that the ASK signal in not smooth. This is because the

sound card D/A converter cannot represent a smooth square signal, because the sound

card has a limited bandwidth, while a perfect square wave would require infinite (or at

least very large) bandwidth.


39

Figure 4.6 ASK modulated signal

4.2.3.4 FM

Here the incoming signal is FM modulated. The results is then taken from the speakers

jack and displayed on the oscilloscope. The results are shown in Figure 4.7.

Figure 4.7 FM modulated signal


40

From Figure 4.7, the FM modulated signal is perfect; having the frequency of the carrier

varies in accordance with the message signal amplitude. The results were taken with

input signal voltage of 0.2Vp-p.

4.2.3.5 BFSK

Here then program will BFSK modulate the incoming signal. The results were pictured as

they were displayed on its screen. The results are shown in Figure 4.8.

Figure 4.8 BFSK modulated signal

From Figure 4.8, we can realize that the frequency is high during the logic one and low

during the logic zero.

4.2.3.6 BPSK

For BPSK, the program performs the modulation. Figure 4.9 describes the BPSK

modulation. The signal is inverted at inversion points from positive to negative and from

positive to negative. The results were for a message signal of 0.2Vp-p and speakers

output volume of 100%.


41

Figure 4.9 BPSK modulated signal

4.2.4 Demodulation Class

The testing was performed by passing the earlier generated modulated signals to the

microphone jack of another PC with the program installed in it. The demodulated signal

was measured from the new PC speakers jack. The signal parameters were changed

depending on the test performed.

4.2.4.1 AM

For AM demodulation option, any AM signal that is passed to the microphone jack is

demodulated and the message signal is extracted from it. Figure 4.10 shows the AM

demodulation performed on the AM modulated signal that was previously generated in

section 4.2.3.1.

4.2.4.2 DSB

As in section 4.2.4.1, the DSB demodulation will take the generated DSB modulated

signal and demodulate it. Figure 4.11 shows the results of the demodulation operation

that is performed on the DSB modulated signal generated previously.


42

4.2.4.3 ASK

Here the demodulation is also performed on the ASK signal that was generated

previously to have the output results are shown in Figure 4.6. We can realize that the

generated signal is not smooth. This is for the same reason mentioned in section 4.2.3.3.

Figure 4.10 AM demodulation

Figure 4.11 DSB demodulation


43

4.2.4.4 FM

FM demodulation was performed on the generated FM signal that was generated in

section 4.2.3.4; the generated output is shown in Figure 4.13.

Figure 4.12 ASK demodulation

Figure 4.13 FM demodulation


44

4.2.4.5 BFSK

Here too the BFSK demodulation was tested on the BFSK signal generated previously in

section 4.2.3.5. The generated output is shown in Figure 4.14.

Figure 4.14 BFSK demodulation

4.2.4.6 BPSK

As done previously, the BPSK demodulation is performed on the signal generated in

section 4.2.3.6 is used to test the demodulator. The results are shown in Figure 4.15.

Figure 4.15 BPSK demodulation


45

Hardware Testing 4.3

The RF front end circuit (shown in Figure 3.13) operation was tested for reception. HF

dipole antenna and the function generator. A free licensed program that performs

spectrum analyzing was used. The function generator frequency was changed until a

radio signal was received at 0.95475MHz. The variable resistors, capacitor and inductor

were varied for maximum signal reception. The results obtained from the program are

shown in Figure 4.16.

Figure 4.16 Received signal using RF front end

1

5. Chapter Five

CONCLUSION

Project Preview 5.1

The project has met its deign considerations and requirements and has successfully

implemented many of the software defined radio features. These features include the

ability to change the filtering parameter, tuning frequency and modulation/demodulation

scheme.

On the other hand, further research and developments for the software implementation of

the radio functionality and the RF frond end is still required. For the current

implementation, further work is needed software modules integration and testing the

overall system behavior.

Future Work 5.2

For future work many features can be added to the system. These features include:

Matched filter must be implemented in order to increase the SNR.

Reading and writing the signal to and from the file feature should be added.

The software defined radio needs to be migrated to other platforms. At present the

software is only available for Windows platform.

Making it multi terminal, so it could read the signal from USB or serial port other

than sound card.

Control the RF front end using the software. This is also a major area where work

is to be done, i.e. adding software modules that responsible for controlling the

hardware and designing the hardware in order to make that possible.

Including more blocks of the digital transmitter and receiver, that shown in Figure

2.1, like encryption and decryption, to be implemented on software,

Conclusion Chapter Five

47

A web based software defined radio.

Some other modern techniques that to be applied to software defined radio, such

as Artificial Neural Networks which will provide a number of fascinating features

such as automatic modulation recognition.

Looking even beyond software defined radio, software defined radio technology

is an enabler for Cognitive Radio (CR). Whereas software defined radio

represents the implementation of a radio in software, cognitive radio represents a

model-based representation for a radio, one which allows a radio to further

configure itself to meet application needs and demands which utilizes the artificial

intelligence algorithms.

It is important to note here almost all of these feature are to be performed in software,

therefore higher flexibility and lower cost are always achievable.

1

6. REFERENCES

[1] “What is Software Defined Radio” The Wireless Innovation Forum and IEEE

p1900.1 Group [online]. Available:

http://www.wirelessinnovation.org/introduction_to_sdr, accessed in Jan 14, 2012.

[2] “Software Defined Radio” Wikipedia [online].

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[3] RJ Lackey and DW Upmal, "Speakeasy: The Military Software Radio," IEEE

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[4] "Earth station" , Federal Standard 1037C, General Services Administration, 1996

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Research and Development Challenges”, The 8th International Conference on

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[7] Peter B. Kenington, RF Baseband Techniques for Software Defined Radio.

London: Artech House, 2005.

[8] P. Johnson, "New Research Lab Leads to Unique Radio Receiver," by space

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[11] “GNU Radio” [online]. Available:

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http://en.wikipedia.org/wiki/General_Services_Administration

http://chordite.com/team.pdf

http://jpeojtrs.mil/Pages/about.aspx

http://gnuradio.org/redmine/projects/gnuradio/wiki.%20Accessed

http://openhpsdr.org/

49

[13] “Fun Cube Dongle” [online]. Available:

http://www.funcubedongle.com/?page_id=2.Accessed in Mar 29,2012

[14] “SoftRock” [online]. Available: http://softrocksdr.wikispaces.com/Software.

Accessed in Mar 30, 2012.

http://www.funcubedongle.com/?page_id=2.Accessed

http://softrocksdr.wikispaces.com/Software

A-1

A. APPENDIX A: GNU License

PortAudio is free to use software where even the source code is free and users are

allowed to change the code. To ensure that it is used in the way the primary developer

wanted it, it is published under the “The GNU General Public License (GNU GPL or

simply GPL) is a widely used free software license, originally written by Richard

Stallman for the GNU project. It is the license used by the Linux kernel. The GPL is the

most popular and well-known example of the type of strong copy left license that requires

derived works to be available under the same copy left. Under this philosophy, the GPL

is said to grant the recipients of a computer program the rights of the free software

definition and uses copy left to ensure the freedoms are preserved, even when the work is

changed or added to. This is in distinction to permissive free software licensees, of which

the BSD licenses are the standard examples.

The GNU Lesser General Public License (LGPL) is a modified, more permissive, version

of the GPL, intended for some software libraries. There is also a GNU Free

Documentation License, which was originally intended for use with documentation for

GNU software, but has also been adopted for other uses, such as the Wikipedia project.”

[http://en.wikipedia.org/wiki/GNU_General_Public_License]

B-1

B. APPENDIX B: Audio.cpp

C-1

C. APPENDIX C: Software Modules

C.1 Audio.h

C-3

C.2 Modulation.h

C-4

C.3 Demodulation.h

C-5

C.4 Filter.h

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