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.

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?

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.

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:

• 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.

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

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.

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.