The long-time vision of Software Defined Radios (SDRs) has been to enable the flexible provisioning of fielded radios to multiple air interfaces, protocols, revisions, and subscriber service profiles. Additionally, SDR appears to be an appealing technology to achieve:

•  Economies of scale in manufacturing and Bill of Material(s) (BOM);

•  New voice, data, video, and multimedia services; flexible infrastructure provisioning and configuring;

•  International roaming, supporting legacy 2G, 2.5G, and multiple 3G air interface standards and emerging Wireless LAN (WLAN) and emerging WiMAX broadband wireless initiatives;

•  Graceful, cost-effective air interface transitions and evolutions

•  eventually with over-the-air provisioning of waveforms and protocols, and services

SDR extend concepts that have been utilized in wireless phones and terminals, wireline modems, and associated infrastructure for many years. Programmable Digital Signal Processors (DSPs) and microprocessors have been employed to provide flexible and more cost-effective implementations of the less-throughput-intensive, typically baseband, network, and related control functions in wireless modems. Configurable and custom Application Specific Integrated Circuits (ASICs) have been integrated, usually at the board level or more recently on SOC chips, to execute more throughput-intensive functions. These throughput-intensive functions have traditionally been implemented with ASICs (custom or FPGA) with less than desirable flexibility for multiple air interfaces. Even FPGAs which are programmable have utilized Hardware Description Languages (HDL) that has created a more complex and expensive development environment than programmable DSPs.

A generic wireless transceiver block diagram is presented in the following Figure. The trend as technology advances is to move the digitization closer to the antenna and to accomplish more functions using Digital Signal Processing (DSP) technologies. Although not explicitly depicted in the figure, the spread/de-spread functions for Direct Sequence Spread Spectrum for WCDMA, CDMA2000, TD-SCDMA, etc. and (FFT's) functions for OFDM are implicitly part of the modulation/de-modulation functions.

Generic Wireless Single Channel Transceiver Architecture
[Depicting three Data Acquisition Alternatives: RF Band, IF Channel, and Baseband]

As CMOS semiconductor technology evolves below current mainstream 0.13 micron technologies, SDRs appear feasible for cost-effective, low power, potentially “system-on-a-chip” (SOC), implementations. SDR and supporting CMOS semiconductor appears currently feasible of implementing these throughput-intensive functions with flexibility and programmability to support multiple air interfaces. At these nodes, mask costs for custom ASICs become prohibitive and make commodity base stations using flexible, higher volume ASSPs, FPGA's, co-processors, etc. that support flexible software waveform generation more cost effective than traditional non-flexible approaches. This also allows base station vendors to focus on their core competencies of system integration and network optimization and devote fewer resources to the expensive develop of ASIC IP and circuits. This is a more critical consideration today due to the recent poor, but improving, economic environment and fewer available resources. Much semiconductor IP and related product development is moving down the food chain from the Network Equipment vendors to the semiconductor vendors.

While the digital DSP, ASSP, Co-processor, and microprocessor technologies benefit from the rapid pace of Moore 's Law advances in circuit speed and density, the RF, analog, and data acquisition technologies advance at a slower pace. The long time military vision for SDR has been a common platform for RF bands from 2 MHz to 2.5 GHz. At a recent IEEE ISSCC session on SDR it was joked that if we digitize this entire band that the analog to digital (ADC) converter will consume a kilowatt. Thus, wireless data conversion technology and supporting up/down converters, frequency shift mixers and oscillators, filters, etc. have been evolving from single RF carrier bandwidths and supporting bit resolutions to service band bandwidths and supporting bit resolutions (e.g. Cellular band coverage with ADC of 14-16 bit resolution at 60 Msps or greater). It should also be noted that current Power Amplifier technologies are trending toward Multi-carrier Power Amplifiers (MCPA) that provide complete service band operations. However, the power transistors for implementation are tuned at manufacture for frequency band of operation.

While the suite of currently available digital, analog/RF, and data acquisition technologies may still fall short of cost effective technological performance to support the full vision of SDR, we believe few can question that we are on the path to achieve in the not-so distance future. In the near term, we are already observing SDR-like trends for commodising the various components and subsystems for commodity base stations. A first step is the development of common boxes (or cabinets) with standardized backplanes (e.g. RapidIO, etc.), power supplies, etc that can be personalized by populating with appropriate boards, subassemblies, or chips. Increasingly, Network Equipment vendors are stating that 50% or more of their staff are devoted to developing software.

Although common platforms for all standards, waveforms, and bands of operations do not currently seem cost effective for many commercial applications, many benefits of SDR seem achievable. The ability to develop waveforms for various standards that operate in multiple bands is achievable via software and reduces develop costs. An excellent example of this is the various cellular standards (e.g., GSM/EDGE, CDMA2000, WCDMA, etc.) that can be cost effectively provisioned via software for a targeted set of bands (e.g., cellular, PCS, and emerging 3G bands).

The rural United States market, which is often not an attractive market for the large US national carriers, provides a potential attractive market for SDR technologies. Often these rural markets do have sufficiently large POPs to support more than one or two operators. However, regional or local operators are often able to create very workable business models for these rural areas, often depending on significant roaming revenue. However, with the national carriers supporting multiple standards, an infrastructure supporting multiple standards can substantially improve their business model. Vanu, Inc of Cambridge , Massachusetts provides a leading example. Vanu conducted tests for Mid-Tex Cellular radio access network by installing a software radio GSM base station in DeLeon , Texas , in June 2003. Mid-Tex operates an IS-136 AMPS/TDMA system covering 8000 square miles in six counties, about two hours west of Dallas-Fort Worth metroplex.

The clear industry trend is commodisation where network equipment vendors purchase chips, modules, subassemblies, boards, and software from outside sources and integrated, internally developed value added hardware and software IP, and provide system engineering, system integration, installation, testing, and even post-commissioning operation and optimization services. And the clear benefit of SDR technology for commodity open base stations is achievable today by more cost effective and flexible software development of waveforms including throughput intensive functions.