Motivation and Goals

The Software Defined Radio Forum

Allan Margulies

SDR Forum Operations Committee

From its early beginnings as the MMITS Forum, the Software Defined Radio Forum, or SDR Forum, has emerged as a driving force in shaping the emergence, commercialization, and standardization of SDR technology on a global basis. This chapter provides a chronology of its origins and development, highlighting its key achievements and contributions.¹

Several easily noted phases and distinct milestones mark the history of the SDR Forum – starting with the statement of the initial concept through the development of cooperative agreements among a group of organizations with similar interests and then to its evolution into the major international association for those interested in the technology that is likely to become the foundation for advanced telecommunications networks in the future.

3.1 Motivation and Goals

Many successful new ventures are often the result of a confluence of common interests. In a commercial venture, it is sometimes the concurrent emergence of a predicated solution that serendipitously finds a perceived market need. In the case of the SDR Forum, it was the nexus of similar and complementary military and commercial interests to create a mechanism to stimulate the development and deployment of software radios and the underlying technology that makes those radios possible.

3.1.1 The Military Motivation

The genesis of the SDR Forum was in the SPEAKeasy program sponsored by the US Department of Defense (DoD) and managed by the Air Force Research Laboratory, but

1See www.sdrforum.org for details about presentations from past meetings or for more information on current activities.

with all of the military services participating – see Chapter 2 by Wayne Bonser for details of this program.

After the successful culmination of activities in the first phase of this groundbreaking SDR program, in which the team led by Hazeltine (now part of BAE Systems) demonstrated reprogrammability and other significant radio functions, a follow-on activity was planned to begin in the early summer of 1995 to further refine the architecture and implementation. By then, many in the DoD were convinced of the benefits that could be derived from using SDRs, specifically with regard to reducing the acquisition cost of new radios and with mitigating problems associated with lack of interoperability among services and among coalition forces. Therefore, one of the goals for that second phase, in order to maximize the utility of the results to the DoD, was to make the outcome of the program widely available, even to those organizations not participating in the program. In fact, fostering non-military participation was seen as an opportunity to stimulate and encourage the devel-opment of commercial products that could be used by the military, thereby reducing the need for special research and development and bringing the military into conformance with commercial products.

To get that kind of information distribution meant that there had to be some vehicle for disseminating the results. In September 1994, during the preliminary planning for SPEAK-easy Phase II, several alternatives were proposed, including the creation of a Multiband, Multimode, Radio (MBMMR) Forum to use the SPEAKeasy results as a point of departure for setting guidelines for radios with an open system architecture. The objective was an agreed-upon architecture and internal hardware and software interface specifications for an industry standard multiband, multimode, programmable radio. With that kind of industry participation, components and production models of such a radio should then be available from third-party vendors.

One common method for developing technology for the US military services is for the service laboratories to issue a series of contracts to one or more industrial organizations.

Three separate teams of highly qualified industrial contractors had been identified for SPEAKeasy Phase II, and an open industry-wide consortium would serve both as a neutral ground for discussions between these teams and as a means for getting comments and suggestions from the rest of the communications community. In effect, the rest of industry not involved in the contractual efforts would get an opportunity to see the results of the contracted work and the service labs would get their opinions on the results while there was still time to shape the work.

Thus the concept of an industry association to focus on software radios took root. Around that time, the mid-1990s, several industry associations had sprung up as alliances of compa-nies that were interested in standardizing particular technologies for the purpose of guaran-teeing compatibility or interoperability among products. For example, the Asynchronous Transfer Mode (ATM) Forum is a collective effort of more than 600 companies and govern-ment organizations interested in asynchronous transfer mode products and services. The members meet at frequent intervals and collectively agree to support specific standards, thereby assuring that products from diverse manufacturers will work together.

The ATM Forum, as well as other industry fora, had established working groups or committees to focus on specific functions. Moreover, the membership of such fora comes from commercial and industrial groups as well as from military and public safety government groups. It was such a paradigm that was seen as the goal for the MBMMR Forum.

The proposed organization was not expected to define all characteristics of SDRs. Physical characteristics (form/fit envelope, weight, battery type, power, etc.), implementation deci-sions (software language, microprocessors versus field programmable gate arrays, antenna design, etc.), and other internal characteristics would be left up to the manufacturers. In addition, the individual manufacturers, for reasons of competitive distinction, were expected to add features that would enhance radio performance as long as they did not conflict with the basic radio standard.

The goal was to have interoperable radios, and hardware and software modules, available from multiple sources, conceivably even from third parties, thereby reducing non-recurring engineering costs and procurement costs due to competitive economic pressures. Several versions of a SDR could be based on a common hardware suite, which would translate into logistics savings because spares would be procured on a larger base of systems.

Another factor was the need to comply with the DoD’s newly established principle of having new systems comply with open system standards as much as possible. (The IBM PC and its clones could be seen as providing an excellent example of an open system.) The hope was that the Forum would be able to define those characteristics that would be necessary to establish an open system; that means having many suppliers, many customers or users, an architecture with a long life, and the ability to easily incorporate technology upgrades.

Additional economic benefits to manufacturers and to consumers were envisaged from this approach because incremental development of new radio models based on existing models, would reduce the development cycle.

3.1.2 The Commercial Motivation

At the same time that the SPEAKeasy II program office was considering how to promote the development and use of reconfigurable radios in a military environment, BellSouth Wireless (now part of Cingular Wireless) was exploring the state of the art in software radios that could be used in commercial wireless networks.

On December 15, 1995, BellSouth released its Software Defined Radio Industry Request for Information (RFI)²to ‘‘solicit information from suppliers of technology, hardware, soft-ware, network and operational support infrastructure and subscriber terminals within the emerging and broader wireless telecommunications industry to implement the concept of Software Defined Radio’’. This was a defining document in the history of SDRs because, even though it was not the first explication of SDRs, it was the first attempt to define practical terms of use. BellSouth’s specific interest was in determining the ability to create a multiple mode wireless communications capability with ‘Total System Flexibility’ through flexible subscri-ber sets, base stations, network architecture and service level features, and management interfaces.

BellSouth was concerned about its future investment strategy and the ability to deploy technology that would not become obsolete within a few years. Its statement of requirements echoed that of the military almost word for word when it said that the company was interested in multifunction, multimode, and multistandard flexibility.

The significance of the 70-page RFI, which was released to more than 80 component and technology suppliers, was emphasized by BellSouth’s stature in the mobile communications

2The far-sighted BellSouth RFI was authored by Stephen Blust, a chapter contributor to the companion volume [1].

industry. At that time, the company and its partners served almost 6 million cellular, mobile, and digital paging subscribers in 15 countries.

The RFI was predicated on two factors: it recognized that there is no single wireless standard for digital services, and it also recognized that the solutions to the problem might not be fully developed at that time. It even speculated about the possible use of incentives to encourage development of software radio technology by sponsoring industry forums, funding proof of concept studies, or placing advanced orders for equipment.

The RFI sought technology solutions for a fragmented market by posing 55 questions based on time scales of availability ranging from 0 to 3 years, 3 to 5 years, 5 to 10 years, to longer than 10 years. The questions, on topics ranging from market complexity to technologies, were grouped into categories relating to the market environment, standards environment, development drivers, service and capability issues, technology and depen-dencies, cost, and network issues, with the bulk of the questions focused on this last category.

The market environment section addressed the fragmentation of the consumer marketplace and the proliferation of services offered, the proliferation of standards implemented, and the effect of roaming and mobility (movement between home zones due to changing residences) as distinct from roaming. The services section looked at consumer expectations regarding quality and level of service, multicapability functionality (mixed mode operations, including voice, data, short message service, etc.), multimode operation (revisiting the multistandard issue), and multiband operation to permit cordless operation in the home as well as in personal communications systems (PCS) or cellular networks.

The technology section asked the respondents to consider topics related to handheld subscriber terminals as well as base stations; specifically, it was concerned with digital signal processing elements, batteries, antennas, and architectures. The cost – or, more accurately, the prediction for time-variant cost curves – was also a major factor.

By far, however, the most substantive part of the questionnaire concerned the impact of software radios on the wireless network. This is a particularly sensitive area because a subscriber handset capable of roaming across networks with dissimilar air interfaces imposes a requirement on the host system for interswitch communications and interworking facilities to translate between protocol formats. Alternatively, to accommodate multimode roaming, the base station can be equipped to support multiple air interfaces. The BellSouth approach anticipated a combination of both approaches and asked questions accordingly. In the case of the multimode handset, it envisioned a need for a software download in order to acquire configuration data for the host network, and in the case of an adaptive base station, it postulated a channel reconfiguration based on instructions from the mobile station controller.

The RFI was an attempt to move from the point solutions for wireless services, which had worked well in the past, to a more universal solution that could accommodate a shift to the emerging niche services and protocols while still recognizing the need to accommodate legacy systems. BellSouth had a vision of allowing the network operators to control infra-structure investment while at the same time increasing revenues by offering new services. It clearly recognized the need for continuing technical development and efforts to obtain industry acceptance and commonality.

3.1.3 Common Goals

Although the military and commercial market segment representatives approached the problem from different perspectives, they had common goals. Life cycle costs (non-recurring engineering, logistics, maintenance, and system management), technology independence, flexibility and adaptability, open interfaces, interoperability (in the form of the ability to operate with multiple air interfaces), and ease of operation for the user are all basic require-ments for both markets.

Moreover, BellSouth and the SPEAKeasy program recognized the need for a coordinating industry association to become both a champion of the software radio concept and a medium for discussion of details and implementation. Until this time, both of these activities had been proceeding independently, each without knowledge of the other. It was against this back-ground that the SDR Forum began to take shape.