and a data communication protocol (such as WiFi) the next. This flexibility comes from the fact that the radio’s behavior is determined by software. Furthermore, software control changes the pace of innovation. Making a change in the radio’s behavior in the traditional hardware world means waiting six months or more for new hardware. In the world of software, change comes as quickly as a programmer can compile and debug, or overnight.

 

Living in a World of software Radios What is different about a world where software radios are the typical radio? The most obvious is that a consumer no longer buys a wireless protocol when buying a device. The notion that a PDA manufacturer would advertise support for Bluetooth or WiFi makes no sense in a world of software radios, as “Bluetooth” and “WiFi” would be applets any PDA could run. The focus will be on the PDA’s radio processing power, expressed in digital signal processor (DSP) or field programmable gate array (FPGA) capabilities.

Recasting this observation as an illustrative scenario, suppose when people arrive in a foreign country their PDAs would automatically download and start running the right phone and data-communications protocols for that country. If the protocols change overnight, the PDA simply loads ( wirelessly) the new versions in the morning. If the people go inside and want to use a local wireless network, the PDA downloads the protocols from the local base station, using, perhaps, WiFi as a legacy protocol to download the new protocols. All these steps happen without requiring any action by the PDA’s user.

Another difference is available bandwidth. If an application needs more wireless bandwidth, it simply asks the radio for more. The software radio would then scan the wireless spectrum looking for unused frequencies and agree with its peer radio (such as the base station) to employ an unused frequency to provide the necessary bandwidth.

In this future world, software radios would offer consumers wireless communication not limited at time of purchase to a particular set of protocols and data-communications band-

they are
chameleons,
running a telephony
protocol
(such as CDma)
one moment
and a data
communication
protocol (such as
Wifi) the next.

width not limited to a small set of overused frequencies.

The path to this future requires both technical and regulatory innovation and, as I aim to show here, the two paths are interlinked.

 

types of software Radios

Having sketched the future software radios have to offer, we need to consider how manufacturers will build them. At the moment it appears there will be a range of choices for constructing software radios. It is simplest to view this range from the extreme ends, where radios are near opposites in terms of their trade-offs.

The first type of software radio is a collection of programmable components, mixing FPGAs, DSPs, and possibly an embedded processor. To program it, a software engineer writes or assembles a suite of software for the programmable components.

Observe that the mix of components varies widely. The central issue is how to provide enough processing power, often parallel processing power, to address streams of digital samples at the rates required for the frequency ranges covered by the radio’s antennas.

Designers differ over how to best mix FPGAs, DSPs, and embedded processors to achieve the right processing power. There are also larger system issues; for instance, consider the filters used to select frequencies; better filters yield cleaner signals, which require less processing, but filters are more expensive than DSPs and FPGAs, so some systems choose less-good filters and more processing power. While there is still plenty of room to innovate, particularly in hardware accelerators that coexist comfortably with DSPs and FPGAs, the radio-engineering community understands this design space, as evidenced by a 2010 software radio design4 that cited 43 references.

At the other end of this design space for software radios is a highly configurable chip or chipset. To program the radio, the software engineer would set configuration registers in the chip to determine what frequencies, coding, and media-access protocol features are used.

The conceptual difference between the two ends of the design space is stark. In the programmable radio, software