What is SDR?

SDR (Software Definition Radio), “Software Defined Radio” A radio broadcast communications technology that is based on software-defined wireless communications protocols rather than hard-wired implementations. In other words, frequency bands, air interface protocols, and functionality can be upgraded through software downloads and updates without completely replacing the hardware. SDR provides an effective and secure solution to the problem of building multi-mode, multi-frequency, and multi-function wireless communications devices. SDRs can be reprogrammed or reconfigured to operate with different waveforms and protocols by dynamically loading new waveforms and protocols. These waveforms and protocols consist of various different parts including modulation techniques, security and performance features defined in software as part of the waveform itself. With the development of mobile communications, the concept of software radio has become widely popular since the early 1990s. 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 solution proposes to collect all the air signals of 2MHz~2000MHz for sampling and quantization, and convert them into digital signals for software processing. In other words, all possible wireless communication signals in the air are collected and processed digitally, so as to communicate with base stations of any wireless communication standard. In theory, mobile phones using software radio technology are compatible with any wireless communication standard. Although software radio has a good application prospect in theory, it requires extremely high-speed software and hardware processing capabilities in actual application. Due to the limitation of hardware technology level, the pure software radio concept has not been widely used in actual products until today. However, a software-defined radio technology based on the concept of software radio has attracted more and more attention. At the ITU-8F meeting held in October 2001, software-defined radio was recommended as a very likely direction for the development of wireless communications in the future. Software-defined radio is a system and system. It must have the ability to be reprogrammed and reconfigured so that the equipment can be used in multiple standards, multiple frequency bands and realize multiple functions. It will not only use programmable devices to realize baseband digital signal processing, but also program and reconfigure the analog circuits of radio frequency and intermediate frequency. At present, people's requirements for the functions of software-defined radio include: the ability to reprogram and reset, the ability to provide and change services, the ability to support multiple standards, and the ability to intelligently utilize spectrum, etc. It should be noted that SDR is not an isolated technology, but a public platform that can be used by all technologies. The most important difference between software defined radio and software defined radio is that the former does not require receiving all wireless signals in the air within the full frequency band (2MHz~2000MHz), but finds the most suitable frequency band and standard for communication in the air one by one through manual configuration/automatic search. As we all know, due to various reasons, IMT2000 or 3G standard did not form a global unified standard as originally envisioned, but formed a series of standards represented by WCDMA in Europe, cdma2000 in North America and TD-SCDMA in China. One problem brought by multiple different standards is the roaming and compatibility of mobile phones between different standards. In addition, considering the problem of smooth transition of 3G standard from the existing 2G standard, 3G mobile phones are better to support GSM and CDMA-IS95 protocols at the same time. If software-defined radio technology is adopted, a general software platform is used, and the system works in possible working frequency bands and standard modes in turn through manual configuration/automatic search, and the received digital signals are processed by targeted software processing solutions, and the most suitable working frequency band and standard are selected and jumped to communicate, full compatibility with various modes can be achieved, 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 RF and intermediate frequency technology, etc. When using software-defined radio solutions to implement different wireless communication standards, the TD-SCDMA standard is easier to combine with the software-defined radio solution due to its characteristics. Because TD-SCDMA is the only standard that clearly designs smart antennas and high-speed digital modulation technology in the standard and clearly implements it with software radio technology. At the same time, it is relatively convenient to implement TD-SCDMA technology with SDR. First, the bandwidth of each frequency band in the TD-SCDMA standard is relatively narrow, and the signal processing volume is not large, so it is easy to implement using a software platform, rather than a hardware platform with very high processing speed requirements. Therefore, it is very easy to migrate to a software-defined radio solution, and there is no need to consider how to convert from a hardware platform to a software platform. Secondly, the uplink and downlink signals in the TD-SCDMA standard are both transmitted synchronously, so when demodulating, a coherent demodulation solution with a relatively simple implementation solution can be used, rather than a complex incoherent demodulation solution, which also reduces the software programming processing volume and is easy to implement. now. Open Source Software 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 an official GNU project. Philanthropist John Gilmore initiated and donated $320,000.00 (US) to Eric Blossom for building the code and maintenance. Gnuradio is a radio signal processing program distributed under the terms of the GNU General Public License. Its purpose is to give ordinary software programmers the opportunity to explore electromagnetic waves and stimulate their ability to use radio frequency waves in a smart way. As with all software-defined radio systems, reconfigurability is its most important feature. You no longer need to buy a lot of transmitting and receiving equipment, just a universal device that can load signal processing software (here: Gnuradio). Although it currently only defines a few limited radio functions, as long as you understand the mechanism (algorithm) of the wireless transmission system, you can configure it arbitrarily to receive it. Gnuradio originated as a fork of the Pspectra code developed by the SpectrumWare project team at MIT in the United States. It was completely rewritten in 2004. So today's Gnuradio no longer contains any of the original Pspectra code. It is also worth mentioning that Pspectra has been used to create the commercial Vanu Software Radio. Gnuradio developed the Universal Software Radio Peripheral (USRP), which is a 12-bit ADC with four 64 MS/s, four 14-bit DACs with 128 MS/s, and other supporting circuits including a high-speed USB 2.0 interface. The USRP is capable of handling signals up to 16 MHz wide. Several transmitter and receiver plug-in daughter boards are available, covering the 0 to 5.9MHz band. It was developed by Ettus.