software defined radio (SDR)
A Software Defined Radio (SDR) is a radio system that operates independently of the carrier frequency of the RF signal and supports various protocols, whereby the word radio is to be interpreted as radio technology. In an SDR radio, functions that were previously implemented exclusively in hardware are implanted by software routines. Thus analog and digital broadcasting standards such as AM/ FM and DAB+DAB+/ DMB.
The basic concept of Software Defined Radio offers advantages for both the network operator and the user of mobile devices. The network operator can implement changes in mobile radio standards, whether UMTS, GSM, Code Division Multiple Access( CDMA) or others, as well as adapt to new standards such as WIMAX, High Speed Downlink Packet Access ( HSDPA) and Long Term Evolution( LTE) via the programmable hardware platform. This concept enables the end customer to flexibly adapt a mobile terminal to other radio standards and also to access WLANs.
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The SDR radio is characterized by the fact that the received radio signal is digitized as far as possible after the antenna or mixer and processed further as a digital signal. In this case, the RF part with its analoguemixers and other RF circuits is implemented in digital design. Only the RF power amplifier on the transmit side is still analog. On the receive side, the RF signal is passed through selective filters and a low- noise amplifier( LNA) is processed in analog before it is digitized in a high- resolution AD converter and processed as a digital signal in the intermediate frequency range. These function groups can be realized by universally applicable function units, the Universal Software Radio Peripherals( USRP). There is an interface between these function units and the processor unit. The processor unit can be a single- board computer or a notebook, which are connected to the function unit via the USB interface. The higher layers are implemented in the processor unit.
The SDR concept is also used in measurement technology for RF generators, where it ensures short setting times and high accuracy and linearity values.