26.software radio - copy

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Software

R adio

By

J.Dheeraj Kumar 3rd C.S.E

Email: [email protected]

Cell: 9866189502

D.Rajesh 3rd

C.S.E

E mail: [email protected]



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Alfa College of

Engineering and Technology

Allagadda

Abstract:

Software radio is one of the more important emerging

technologies for the future of wireless communication services.

By moving radio functionality into software that has previously

been implemented in hardware, software radio promises to

change the economics of deploying and operating wirelessnetwork services...

Introduction:

Wireless services are increasingly ubiquitous and essential

components in our global communications infrastructure. The

mobility, flexibility, and reconfigurability of wireless offer

compelling complements, or at times, substitutes for wired

infrastructure. They enable many new services and expand the

usability of old services, extending our ability to stay connectedanywhere and anytime we desire. The proliferation of new

wireless services being offered over satellites, over cellular

networks, and over wireless LANs (WLANs) is fueling concern

over how to

allocate (or reallocate) scarce radio frequency (RF) spectrum.

The research community and industry have responded to this

challenge by developing a host of new technologies to allow

spectrum to be used more flexibly and efficiently.

What is software radio?

Software radio is the art and science of building radios using

software. Given the constraints of today's technology, there is

still some RF hardware involved, but the idea is to get the



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They can talk and listen to multiple channels at the same. OK,

so what do I care? Imagine you're a cop, or a fire fighter, or an

ambulance driver. Today there are many and many places where

public safety people from one organization can't talk to another.

The locals can't talk to the emergency crew from the next town because they've got different kinds of radios. Software radio

solves this problem.

We can build new kinds of radios that have never before existed.

Smart radios or cognitive radios can look at the utilization of the

RF spectrum in their immediate neighborhood, and configure

themselves for best performance.

What's the story with free software radio?

First off, let's make sure we're on the same page with regard to

free software. Free software means the user has the freedom to

run, copy, distribute, study, change and improve the software.

Access to the source code of the program is a precondition for

this freedom. Without the source code there is no straight

forward path to study or improve a piece of code.

One of the first software radios was a U.S. military project

named Speakeasy. The primary goal of the Speakeasy project

was to use programmable processing to emulate more than 10

existing military radios, operating in frequency bands between 2

and 200 MHz. Further, another design goal was to be able to

easily incorporate new coding and modulation standards in the

future, so that military communications can keep pace with

advances in coding and modulation techniques.

Types of speak easy are:1. Speak easy1.

2. Speak easy2.

3. Joint tactical radio system (jtrs).

4. Armature software radios.



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5. Software defined radio & RFID technology.

The antenna:

Coupard recommends connecting an unshielded parallel cable to

your PC's parallel port connector and forming it into a coil,which you then loop around your radio's receiving antenna. You

can see what this looks like in this photo.

RTAI software radio transmission antenna and AM receiver

I cheated. I plugged a printer cable into my PC that had a female

DB25 on its other end, and inserted the bare end of a thin copper

wire into one of the data lines (pin 2 works) of the dangling end

of the cable. Then, I wrapped the wire tightly around my AM

radio's telescoping antenna. Anything along those lines ought to



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work, but you do need a good antenna or you won't hear anything. How it works?

First you need to know a bit about RTAI. Please bear with me,

for I'm about to attempt a highly simplified two-paragraph

explanation of RTAI. If you prefer all the gory details, read

some of the whitepapers referenced here.

Basically, RTAI is a tiny kernel that assumes ultimate control of

system resources and runs Linux as a low-priority task beneath

itself. Thereafter, RTAI has dominion over system Interrupts, a

situation which allows it to respond in a near-instantaneous

manner to certain real-world events when they occur. The term

"near-instantaneous" is, of course, relative. At the risk of settingmyself up for an email deluge, I'll oversimplify it like this:

Linux itself is capable of handling response times, depending on

who you ask, in the range of a few milliseconds to a few dozen

milliseconds. RTAI, according to Lineo's specs on Embedix

Real-Time, can respond to interrupts within approximately 15

microseconds -- making it around a thousand times as

responsive as the Linux kernel.

One further comment, before moving on, is that although RTAIcan obviously greatly improve a system's responsiveness to real-

world events in comparison to normal Linux that improvement

comes at a price -- which is that the techniques needed to take

advantage of RTAI fall outside the normal Linux programming

model. You can't, for instance, simply install RTAI and instantly

see improvements in applications such as streaming multimedia

-- unless they were designed to take advantage of RTAI.

In any case, it is this thousand-fold improvement in event

responsiveness provided by RTAI that forms the essence of the

software radio demo.

The ideal scheme would be to attach an analog to digital

converter to an antenna. A digital signal processor would read

the converter, and then software would transform the stream of

data from the converter to any other form.



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An ideal transmitter would be similar. A digital signal processor

would generate a stream of numbers. These would be sent to a

digital to analog converter connected to a radio antenna.

Software-defined radio infrastructure:

The flexibility of a software-defined radio system resides in its

capability to operate in multiservice environments without being

constrained to a particular standard. In theory, software-definedradio should be able to offer services for any already

standardized system or future ones on any radio frequency band.

The most attractive property of a software-defined radio system

is its ability to adapt itself according to environmental

conditions and traffic requirements, especially in the support of

multimedia traffic. For example, a mobile operator would have

the opportunity to configure the network to support the video,

data or voice traffic streams that will maximize its income.

Software-defined radio implies that the boundary between the

analog and digital world in base stations moves as much as

possible toward radio frequency, by adopting analog-to-digital

and digital-to-analog wideband conversion as close as possible

to the antenna; and the replacement of fixed-function dedicated

hardware with technologies that can support as many radio

functions as possible in software.

Scalability in software-defined radio systems defines the ability

to independently vary the number and size of resources(memory, processing and I/O bandwidth) that is used to support

the radio infrastructure. Scalable high performance is an

intrinsic characteristic of software-defined radio: the ability to

scale the architectural components to meet evolving standard,

traffic and service requirements, without the need to introduce



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new architectural components or changing the underlying

infrastructure.

A good software radio must operate at any symbol rate within a

wide range of rates, in order to be compatible with many

protocols, so this adaptive control is crucial. It can beimplemented either with a hardware linkage to the converter, or

in software.

The latest implementation of the ASP architecture, called Line

dancer, implements 4,000 processing units that can deliver in

excess of 100 Giga operations per second, and is operating at

266 MHz. The ASP's SIMD structure makes it suitable for

supporting processing for software-defined radio infrastructures,



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since the available processing resources can be used to process

either long filter sequences or long bit sequences of data

decoding for one or more users simultaneously. Indeed, ASP

implementations like the Line dancer device can deliver

processing power that is typically associated with ASICs and performance flexibility that is characteristic of microprocessors.

A single Line dancer device is capable of processing in true

software-programmable fashion tens of CDMA users

simultaneously.

Universal Software Radio Peripheral:



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Practical receivers:

Current (2003) digital electronics are too slow to receive typical

radio signals that range from 10 kHz to 2 GHz. An ideal

software radio would have to collect and process samples at



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twice the maximum frequency at which it is to operate. Real

software radios solve this problem by using a mixer and a

reference oscillator to heterodyne the radio signal to a lower

frequency.

The above mixer changes the frequency of the signal. The phaseinformation becomes more difficult to detect in it. Many digital

encoding systems depend on phase encoding. The classic

solution is to mix and digitize two channels, using a reference

oscillator that produces two signals that are the same frequency.

However, one of the frequency outputs lags the other by 90

degrees of a cycle. Thus, the two sets of samples provide the

needed phase information.

Another related problem is that the information about the bit-

timing is lost when the frequency changes. The phase

information helps recover that as well.

Phase information:

The sampling works best if it is at a simple multiple of the

protocol's symbol rate. Since the distant transmitter and the

receiver are linked only by the radio, this means that the

sampling speed should somehow adapt to the distant radio's

symbol rate. The phase information may therefore be used to

adjust the effective sampling rate, as well.

A good software radio must operate at any symbol rate within a

wide range of rates, in order to be compatible with many

protocols, so this adaptive control is crucial. It can be

implemented either with a hardware linkage to the converter, or

in software.

Any signals above the sampling frequency would "interfere"

with the sampling, causing spurious signals to appear in the data

stream at a frequency that's the difference between the signaland the sampling frequency. For this reason, a low-pass analog

electronic filter must precede the digital conversion step.

Real analog-to-digital converters lack the discrimination to pick

up sub-microvolt, nano watt radio signals. Therefore a low noise

amplifier must precede the conversion step. The amplifier



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introduces its own problems. If spurious signals are present

(which is typical), these compete with the desired signals for the

amplifier's power. They introduce distortion in the desired

signals, or may block them completely. The standard solution is

to put a filter between the antenna and the amplifier, but thisreduces the radio's flexibility- the whole point of a software

radio. Real software radios have two or three analog "channels"

that are switched in and out. These contained matched filters,

amplifiers and sometimes a mixer.

Software radio technology has gained momentum as engineers

everywhere are developing radio architectures that include

minimal hardwired analog components. The ability to program

intermediate frequency (IF), bandwidth, modulation, coding

schemes and other radio functions is the appeal for suchwidespread interest. Besides providing all these flexibilities,

software radio must improve on performance in terms of

sensitivity, dynamic range and adjacent-channel rejection.

Software radio is still a radio and must perform better than the

conventional radio it is replacing.

High-speed data transfer over Pn4 PMC user

I/O:

In some applications, it is more convenient for systemintegrators to move high-speed data over user-defined protocols

from COTS PMC modules, leaving the system bus free for other

functionalities. One such protocol that is commonly used is the

front-panel data port (FPDP) protocol, which is an American

National Standard Institute/VMEbus Industry Trade Association

(ANSI/VITA) standard. To ensure high-speed data movement,

ICS has implemented transmit and receive cores in the user

FPGA to support FPDP over the Pn4 user I/O connector of the

PMC module. Thus, system integrators will have a seamless

way of moving data in and out of ICS PMC modules over

FPDP. Other standard and proprietary data transfer protocols

may also be implemented in the user FPGA.

Using LVDS signaling over the Pn4 user I/O connector allows

high-speed data transfer between PMC modules or from PMC



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modules to motherboards. This is useful as larger bandwidth and

channel counts put an increasing demand on the data transfer

capability. It is undesirable for system engineers to be limited by

data transfer bottlenecks, preventing them from using the full

feature set of a board.Conclusions and future research:

Software radio is one of the key enabling technologies for the

wireless revolution. It enhances flexibility and lowers the costs

of constructing and operating wireless infrastructure. By

enabling digital conversion closer to the antenna, software radio

facilitates the exploitation of new techniques in wireless

communications ranging from smart antennas to adaptive power

management to advanced digital signal processing. Bysubstituting software for hardware, software radio increases

flexibility in the form of enhanced upgradeability,

customizability, and dynamic adaptability. This in turn

facilitates the replacement of dedicated hardware with general-

purpose hardware. This lowers entry barriers, facilitates system

unbundling, and increases scale and scope economies. The long-

term effect is likely to be increased competition all along the

wireless value chain, from semiconductors through to wireless

service provisioning. Consumers are likely to be the ultimate

long-term beneficiaries from the increased competition. They

will benefit from the expansion of the product space, reduced

provider lock-in, and lower prices. Of course, realization of

these benefits depends on the continued evolution of software

radio and the emergence of open-interface architecture. Whether

this will occur or not remains an open question, but in either

case, software radio is likely to be an important technology in

the years to come.

References:

Arnott, Robert, Seshaiah Ponnekanti, Carl Taylor, and Heinz

Chaloupka, "Advanced

Base Station Technology," IEEE Communications Magazine,

Vol. 36, Issue 2 (February



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1998) 96-102.

Baines, Rupert, "The DSP Bottleneck," IEEE Communications

Magazine, Vol. 33, Issue

5 (May 1995) 46-54.

Buracchini, Enrico, ³The Software Radio Concept´, IEEE

Communications Magazine,

Vol. 38, Issue 9 (September 2000) 138-143.

Bose, Vanu, Michael Ismert, Matt Welborn, and John Guttag,

"Virtual Radios," IEEE

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