SDR (Software DefiniTIon Radio), "Software DefiniTIon Radio" is a radio broadcast communication technology, which is based on a software-defined wireless communication protocol instead of hardwired implementation. In other words, frequency bands, air interface protocols and functions can be upgraded through software downloads and updates without completely replacing hardware. SDR provides effective and safe solutions to the problem of constructing multi-mode, multi-frequency and multi-function wireless communication devices.
SDR can be reprogrammed or reconfigured, so that different waveforms and protocol operations can be used by dynamically loading new waveforms and protocols. These waveforms and protocols contain a variety of different parts, including modulation techniques, safety and performance characteristics defined as part of the waveform itself in the software.
With the development of mobile communications, starting from the early 1990s, the concept of Software Radio (Software Radio) has become popular. Due to the coexistence of multiple digital wireless communication standards, such as GSM, CDMA-IS95, etc., each standard has different requirements for its mobile phones, and mobile phones of different standards cannot be interconnected. In order to solve this problem, the software radio program proposes to collect all the air signals from 2MHz to 2000MHz for sampling, quantization, and conversion into digital signals for software processing. In other words, all the wireless communication signals that may exist in the air are received for digital processing, so as to communicate with the base station of any wireless communication standard. In theory, mobile phones using software radio technology are compatible with any wireless communication standard. Although software radio has good application prospects in theory, it requires extremely high-speed software and hardware processing capabilities in practical applications. Due to the limitation of the hardware technology level, until today, the pure software radio concept has not been widely used in actual products. However, a software-defined radio technology based on the concept of software-defined radio has attracted more and more attention. At the ITU-8F meeting held in October 2001, software-defined radio was recommended as the most likely direction for the development of wireless communications in the future. Software-defined radio is a system and architecture. It must have the ability to be reprogrammable and reconfigurable, so that the equipment can be used in multiple standards, multiple frequency bands and achieve multiple functions. It will not only use programmable devices to achieve Baseband digital signal processing will also program and reconstruct the analog circuits of radio frequency and intermediate frequency. The current requirements for software-defined radio functions include: the ability to reprogram and reset, the ability to provide and change services, and the ability to support multiple Standard capabilities and intelligent spectrum utilization capabilities and so on. It should be noted that SDR is not an isolated technology, but a common platform that can be used for all technologies.
The most important difference between software-defined radio and software-defined radio is that the former does not require all airborne wireless signals in the full frequency band (2MHz～2000MHz) to be received, but through manual configuration/automatic search, one frequency band is one frequency band. Find out the most suitable frequency band and system for communication in the current air. As we all know, due to various reasons, the IMT2000 or 3G standard did not form a global unified standard as its original intention envisaged, but formed WCDMA in Europe, cdma2000 in North America and TD-SCDMA in China as representatives. Series of standards. One of the problems brought about by multiple different standards is the roaming and compatibility issues of mobile phones between different standard standards. In addition, considering the smooth transition of the 3G standard from the existing 2G standard, 3G mobile phones should also support both GSM and CDMA-IS95 protocols. If software-defined radio technology is used, a general software platform is used, and the manual configuration/automatic search method is used to work in the possible working frequency band and standard mode in turn, and the received digital signal is processed by a targeted software processing scheme. Selecting and jumping to the most suitable working frequency band and standard for communication can achieve full compatibility with various modes, and its advantages will be self-evident. Of course, to achieve the goal of SDR, people still need to face huge challenges, including architecture, broadband programmable, configurable radio frequency and intermediate frequency technology and so on. When using software-defined radio schemes to implement different wireless communication standards, the TD-SCDMA standard is easier to combine with software-defined radio schemes due to its characteristics. Because TD-SCDMA is the only standard that explicitly designs smart antennas and high-speed digital modulation technology in the standard, and clearly uses software radio technology to implement it. At the same time, TD-SCDMA technology is relatively convenient to implement with SDR. First of all, the bandwidth of each frequency band in the TD-SCDMA standard is relatively narrow, and the amount of signal processing is not very large. It is easy to implement using a software platform instead of a hardware platform that requires a very high processing speed. Therefore, it is very easy to transplant to a software-defined radio solution. , No need to consider how to switch from a hardware platform to a software platform. Secondly, in the TD-SCDMA standard, both uplink and downlink signals use synchronous transmission, so coherent demodulation schemes with relatively simple implementation schemes can be used during demodulation, instead of complex incoherent demodulation, which also makes software programming processing capacity Down, easy to achieve
Open Source Software Radio
Open Source Software Defined Radio (Gnuradio) or Open Source Software Defined Radio is a free software toolkit for learning, building and deploying software defined radio systems. Initiated in 2001, Gnuradio is now one of the official projects of GNU. Philanthropist John Gilmore initiated and donated $320,000.00 (US) to Eric Blossom for code construction and maintenance.
Gnuradio is a radio signal processing program, which is distributed under the terms of the GNU GPL. Its purpose is to provide ordinary software programmers with opportunities to explore electromagnetic waves and to stimulate their smart use of radio frequency waves.
As with the definition of all software-defined radio systems, reconfigurability is its most important function. No longer need to buy a lot of transmitting and receiving equipment, as long as one can be loaded with signal processing software (here: Gnuradio) general equipment. Although it only defines a few limited radio functions at present, as long as you understand the mechanism (algorithm) of the wireless transmission system, you can accept it in any configuration.
Gnuradio originated from the branch of Pspectra code developed by the SpectrumWare project team of the Massachusetts Institute of Technology in the United States. It was completely rewritten in 2004. So today's Gnuradio does not contain any code of the original Pspectra. It is also worth mentioning that Pspectra has been used to create the commercial Vanu Software Radio.
Gnuradio has developed the Universal Software Radio Peripheral (USRP), which is a 12-bit ADC with 4 64 MS/s, 4 14-bit DACs at 128 MS/s, and other support lines including a high-speed USB 2.0 interface. The USRP can handle signal frequencies up to 16 MHz wide. Some plug-in daughter boards for transmitters and receivers can cover the 0 to 5.9 MHz frequency band. It was developed by Ettus.
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