What’s going to be the next big thing in wireless technology? The best bet is Software-Defined Radio, and thanks to a piece of hardware called the Universal Software Radio Peripheral, or USRP, we can get right to the bleeding edge today.
SOFTWARE-DEFINED RADIO (SDR)
Software-defined radio (SDR), sometimes shortened to software radio (SR), refers to a wireless communication in which the transmitter modulation is generated or defined by a computer, and the receiver uses a computer to recover the signal intelligence? To select the desired modulation type, the proper programs must be run by microcomputers that control the transmitter and receiver
Currently, adding an audio, video, or data stream to a radio signal so it can be broadcast—a process known as modulation—is nearly always done by dedicated electronics. The same is true with the reverse process—demodulation—required to receive a transmission. Radio waves can be modulated in any number of ways, and each way requires different circuitry. This is why a TV designed for the U.S. NTSC broadcast standard cannot be expected to work in Europe, which uses mostly the PAL standard.
Traditional radio chips are hard-wired to communicate using one specific protocol. For example, a typical cell phone has several different chips to handle a variety of radio communications: one to talk to cell phone towers, another to contact Wi-Fi base stations, a third to receive GPS signals, and a fourth to communicate with Bluetooth devices. In contrast, software-defined radio hardware works with raw electromagnetic signals, relying on software to implement specific applications.
This makes software-defined radio devices tremendously versatile. The idea behind software-defined radio is to do all that modulation and demodulation with software instead of with dedicated circuitry as shown in figure below. The most obvious benefit is that instead of having to build extra circuitry to handle different types of radio signals, you can just load an appropriate program. One moment your computer could be an AM radio, the next a wireless data transceiver—and then perhaps a TV set. Or you could leverage the flexibility of software to do things that are difficult, if not impossible, with traditional radio setups. Want to broadcast an emergency message on every FM band? Scan a dozen walkie-talkie channels at once? Or design and test a new wireless data protocol? No problem with the software radio. Software-defined radio hardware also enables rapid prototyping of new communications protocols.
Simply put Software Defined Radio is defined as:
“Radio in which some or all of the physical layer functions are software defined”
Software-defined radio will make it possible to use the electromagnetic spectrum in fundamentally new ways. Most radio standards today are designed to use a fixed, narrow frequency band. In contrast, software-defined radio devices can tune into many different frequencies simultaneously, making possible communications schemes that wouldn’t be feasible with conventional radio gear. Unlike adopt Application Specific Integrated Circuit (ASIC) to implement radio elements in the past, the technologies such as Field Programmable Gate Array (FPGA), Digital Signal Processor (DSP) and General-Purpose Processor (GPP) are used to build the software radio elements. These components have reconfigurable capability which making these components tend to generalization in order to implement a variety of different radio applications.
The most significant asset of SDR is versatility. Wireless systems employ protocols that vary from one service to another. Even in the same type of service, for example wireless fax, the protocol often differs from country to country. A single SDR set with an all-inclusive software repertoire can be used in any mode, anywhere in the world. Changing the service type, the mode, and/or the modulation protocol involves simply selecting and launching the requisite computer program, and making sure the batteries are adequately charged if portable operation is contemplated.
The ultimate goal of SDR engineers is to provide a single radio transceiver capable of playing the roles of cordless telephone, cell phone, wireless fax, wireless e-mail system, pager, wireless videoconferencing unit, wireless Web browser, Global Positioning System (GPS) unit, and other functions still in the realm of science fiction, operable from any location on the surface of the earth, and perhaps in space as well.
UNIVERSAL SOFTWARE RADIO PERIPHERAL (USRP)
The Universal Software Radio Peripheral (USRP) products are computer-hosted software radios. USRPs are commonly used with the GNU Radio software suite to create complex software-defined radio systems.
While Software Radio (SDR) is still very much a work in progress, but the future is with the USRP. The hardware works in concert with free software developed by the GNU Radio project, an international collaboration of programmers who donate their time and skills. It is developed by Ettus Research which builds a range of devices specifically designed for software-defined radio. The USRP product family is intended to be a comparatively inexpensive hardware platform for software radio, and is commonly used by research labs, universities, and hobbyists.
The USRP acts as an RF front end for a computer running the GNU Radio software, converting radio waves picked up by an antenna into digital copies that the computer software can handle or, conversely, converting a wave synthesized by the computer into a radio transmission. We tested GNU Radio and the USRP together on both Linux and Windows, but the GNU Radio software will also work with other RF front ends, and it can be used with prerecorded signal samples in the absence of any radio hardware. Likewise, the USRP can be used with proprietary software such as Matlab and LabView, or with home-brewed code.
One of the most interesting applications for the USRP has been for open source cell phone telephony. Users have configured USRPs to provide GSM cellular service, deploying them “in a number of places, from cities to small islands in the Pacific”. The hackability of the USRP makes it more versatile than traditional cellular gear, making it ideal for unusual environments.
Wireless security research is another key application for the USRP. For example, one research group used a USRP to discover security vulnerabilities in the wireless communications protocol of a commercially available pacemaker. “If we want to determine wireless security, we need to be able to send those devices interesting packets,” they said. “We need complete control of the packets we send, and we need to examine the received packets at a fundamental level.” Conventional wireless hardware can’t match the flexibility of software-defined radio hardware for this kind of application.
USRP and GNU Radio have immense potential, and the full range of possible applications is not yet foreseeable. For those who have the technical chops and want a sneak preview of things to come, the USRP and GNU Radio deserve attention. The USRP is clearly a labor of love for Matt Ettus, the man behind Ettus Research, and the details regarding USRP components, peripherals and functioning can be downloaded from the Ettus Research Web site at www.ettus.com.
Hope you have enjoyed reading this blog; we will get back to you with more blogs in future
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