What is the development trend of key technologies of software radio?
In recent years, the development of software radio technology has made some progress, but it still faces many technical challenges, including high-speed A/D, DSP digital processing, radio frequency front-end, antenna technology and other issues. It can be said that these technologies determine the development and realization of software radio. Over the years, the efforts in this area have never stopped, these technologies are still developing continuously, and some new development trends have also appeared.
1. Antenna Technology
The antenna part of an ideal software radio system should be able to cover all wireless communication frequency bands, and it should be able to achieve barrier-free communication in a wide range of operating frequencies. At present, a multi-band combined antenna is used, that is, several antennas are used in the whole frequency band or even in each frequency band to form a broadband antenna. The broadband antenna is regarded as the best antenna scheme to realize the ideal software radio system, and it is also regarded as unrealizable under the current technical conditions. The RF MEMS MEMS developed in recent years is a highly miniaturized device that can be used as a small switch to replace the high-cost and bulky PIN diodes, ultra-wideband field effect transistors FETs and vacuum relays VTR in antennas. A breakthrough technique for broadband reconfigurable antenna design. Using MEMS, the operating frequency of a ring-shaped slotted antenna can be changed electronically. On a square slotted antenna, when the perimeter is approximately one wavelength, good performance can be obtained at a certain frequency. When the antenna is to be reconstructed for a new frequency band, the entrance and Export. Therefore, it is possible to perform frequency conversion in the 3-8GHz range. The MEMS switch realized by PIN diode switch also has the advantages of low loss, high isolation and small size. In addition, new antenna element technologies are emerging, enabling the design and production of broadband WB and ultra-wideband UWB antennas for SDR, including ultra-wideband "resistive" resistive antennas and "curve" antenna MLAs. The application of MEMS technology will reduce the volume and cost of WB and UWB antennas by several orders of magnitude. In addition, advances in modeling and simulation methods enable accurate simulation of these new antenna elements.
2. RF front-end technology
At present, the level of RF components can only support about 20% of the bandwidth, so the technical solution adopted in the existing software radio system is to use a set of RF modules to cover the entire frequency band. RF module replacement may also be required when supporting multiple standards. With the maturity of broadband synthesis technology and low-noise high-performance semiconductor process technology, very flexible RF modules appear. Highly miniaturized multi-band multi-mode MB MM RF chips have been in production since 2003, and superconducting RF technology helps achieve the performance required for commercial government multi-band multi-mode front ends. These two technologies are now becoming the mainstream technology of SDR, and they will be common in 2005. RF MEMS technology is a new device technology, which has the characteristics of low loss and small size, and can realize a high-performance device with high integration. And the cost is reduced by an order of magnitude, and the processing speed and processing capacity of the chip are improved, so that the digital signal processor can complete the modulation and demodulation function. In addition, the movable characteristics of MEMS devices can dynamically adjust the parameter values of components, thus greatly improving the performance and flexibility of many radio frequency devices, including low phase noise voltage controlled oscillators based on MEMS high-Q resonators, variable voltage controlled oscillators based on MEMS Broadband transformers and phase shifters for capacitor and switched capacitor networks, tunable filters based on MEMS variable reactance cells and switches. Programmable bandpass filters are critical in transmitters and receivers, ensuring efficient channel utilization and high sensitivity, while being the most expensive and least flexible device in the RF module group, which are required for software radios to Electronically constructed or superimposed to form a filter bank. At present, most software radio systems adopt the latter method, and it is reported that the filter based on high Q MEMS has been demonstrated. In addition, the use of superconducting technology is also considered. This technique enables the realization of tunable bandpass filters with overspeed roll-off characteristics. At present, a tuning filter with an intermediate frequency of 3.5 and a tuning range of 620MHz has been realized by using the superconducting Pu film process. The process is characterized by low loss, which enables the design and realization of multi-stage Pu film filters with low insertion loss and broadband capability.
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