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Software Defined Radio Wireless Standards: No More Islands!

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VoicenData Bureau
New Update

If there can be ten forms of government in the world, how do you expect to

have a single global wireless standard, asked a few zealous market movers after

ITU dropped the "single standard" objective from its IMT 2000 agenda.

They may be right in their own way.

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With no supplier or regional standard lobby committed to the users’

interest, this is one compromise ITU had to make to at least, move ahead. But

let us not forget that this "compromise" in no way undermines the

noble objective with which ITU started–end users’ convenience.

And that was sacrificed for the time being. ITU was handicapped. Suppliers

lobby was not interested.

But when people wanted to come closer to each other, even the Berlin Wall

could not stop them. What is suppliers’ infighting?

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Today, there is a renewed hope. And it is known as Software Defined Radio (SDR)

or simply software radios.

What does SDR promises?

When in Rome, do as Romans do. Simply put, this old adage

will now hold true for your cellphone. You can carry your GSM phone from India

to the US, and it will still work with the IS-95 CDMA networks over there. SDR

enables the phone to change according to the environment, notwithstanding the

modulation techniques that the network uses. Not only that, it will work with

all the future standards, and even the non-cellular wireless standards, such as

802.11 and bluetooth.

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The top-level view is a

simple representation of an entire information transfer thread. The left

side interface is the air interface. The right side interface is the wire

side and user interface. The next level view identifies a fundamental

ordered functional flow of four significant and necessary functional areas–front-end

processing, information security, information processing, and control. It

is noted that diagrams and processes discussed within this document,

unless otherwise specified, are two-way devices (send and receive).

While users can look forward to the convenience of what many

compare with the "the change from a typewriter to a word processor",

the regulators and spectrum managers are excited, because they feel it will in

some way help them to manage



the imminent spectrum crisis of the future, as new 3G networks come in with
multiple standards and the wireless usage surges. The FCC of the US, the most

influential regulator certainly feels so. In September 2001, FCC adopted a rule

change



to facilitate the deployment of SDR technology. And already, many feel this
could be one of the major landmark decisions of FCC after Reed Hundt’s

decision to auction airwaves in 1996.

SDR Forum (www.sdrforum.org), an industry group formed with

an objective to promote the commercial usage of SDR, lists out the major

advantages of SDR. According to the forum, SDR allows:

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  • End-users to realize ‘true’ choices with ‘pay as

    you go’ features, device independence and a single piece of scalable

    hardware that is, at once, compatible at a global scale

  • Network operators to differentiate their service

    offerings without having to support a myriad number of handhelds and to move

    to adjacent markets as well as offer new, tiered services to increase their

    revenue mix

  • Infrastructure suppliers to reduce cost and insure

    themselves against price-erosions through concentrated efforts on a common

    hardware platform and reduced component counts

  • Application developers to enhance value, without concern

    to hardware types

  • Terminal providers to add features, patches and

    capabilities, to devices for broader market participation

What is SDR?

"The term Software Defined Radios (SDRs) is used to

describe radios that provide software control of a variety of modulation

techniques, wide-band or narrow-band operation, communications security

functions (such as hopping), and waveform requirements of current and evolving

standards over a broad frequency range. The frequency bands covered may still be

constrained at the front-end requiring a switch in the antenna system",

according to the SDR Forum.

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Simply put, many basic functions, including the generation of

the transmitted radio signal that has traditionally been carried out in hardware

moves to software, in SDRs. And software, by its very nature, is programmable.

This allows SDRs to



be programmed. That gives them the flexibility that everyone needs, badly.

SDR Architecture

The figure shows the SDRF open architecture of the seven independent subsystems interconnected by open interfaces.

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SDR architecture as outlined by the SDR Forum is based upon a

high-level generic model with specific functional blocks connected via open

interface standards recommendations. The SDR architecture supports three

specific domains–handheld, mobile, and base-station (or fixed site). The

software is implemented by controlling the characteristics of equipment or

device subsystems through hierarchical and peer-level modules that support

scaleability and flexible extensions of applications. Modularity is the key to

successful implementation of software applications, within open systems. Between

modules are defined interfaces that are subject to standardization. Within a

module the developer is free to implement functionality in the most effective

way.

The figure below illustrates a high-level hierarchical

functional model for SDR systems. Three views of increased complexity are

presented. The top-level view is a simple representation of an entire

information transfer thread. The left side interface is the air interface. The

right side interface is the wire side and user interface. The next level view

identifies a fundamental ordered functional flow of four significant and

necessary functional areas–front-end processing, information security,

information processing, and control. It is noted that diagrams and processes

discussed within this document, unless otherwise specified, are two-way devices

(send and receive). Note that the functional model as shown in this figure is

not intended to show data or signal flow.

Front-end processing is that functional area of the end-user

device that consists generically of the physical air (or propagation medium)

interface, the front-end radio frequency processing, and any frequency up and

down conversion that is necessary. Also, modulation or demodulation processing

is contained in this functional block area.

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Information security is employed for the purpose of providing

user privacy, authentication, and information protection. In the commercial

environment, this protection is specified by the underlying service standard

while in the defense environment, this protection is of a nature that must be

consistent with the various governmental doctrines and policies in effect.

Content or information processing is for the purpose of

decomposing or recovering the embedded information containing data, control, and

timing. Content processing and I/O functions, map into path selection (including

bridging, routing, and gateway), multiplexing, source coding (including vocoding,

and video compression/expansion), signaling protocol, and I/O functions.

The SDR architecture consists of functions connected through

open interfaces, and procedures for adding software-specific tasks to each of

the functional areas. The software necessary to operate is referred to as a

software application. The figure shows the SDRF open architecture of the seven

independent subsystems interconnected by open interfaces. In this view, the

generalized SDRF functional architecture has been particularized by equating a

subsystem definition to each functional area. In general, this is not the case;

subsystems will be determined by implementation considerations. Interfaces exist

for linking software application-specific modules into each subsystem. Each

subsystem contains hardware, firmware, operating system, and software modules

that may be common to more than one application. The application layer is

modular, flexible, and software-specific. The common software API layer,

inferred in the following figure, is standardized with common



functions having open and published interfaces. Peer-to-peer interfaces are
neither required nor proscribed by the SDRF.

The Obstacles

Industry observers feel there are a few obstacles that have to be removed

before SDR is widely deployed. First and the most important, since it directly

concerns the end user, is the increased power consumption. With most of the

functions moving to software, there is a need for faster processing, which

increases power requirements. This needs to be eliminated or minimized before

SDR is deployed.

Also, in tightly regulated markets, where the licensing is done on the basis

of frequency (most markets) and type of services (developing markets like

India), many regulators would not be very comfortable with a device that changes

frequencies–that too, in such a wide range. So regulatory approval may be a

roadblock in many countries.

Despite these obstacles, the advantages of SDRs far outweigh the

disadvantage. The SDR Forum forecasts commercial deployments in many markets in

the next two to three years. Analysts feel markets with multiple wireless

technologies may be the first ones to adopt. That makes American and a few Asian

markets, the potential areas for SDR deployment.

With the FCC approval, the regulators have woken up to the need of SDR. One

only hopes the Oftels and TRAIs would follow.

Prepared with major inputs from SDR Forum’s primer on SDR.

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