Software Defined Radio (SDR)

1. Generality

Several definitions of a software defined radio can be found in the literature or on the web. The idea is to design a radio with an analog to digital converter as close as possible to the antenna to switch into the software world as soon as possible in the receiving chain.
In the transmitting chain, the idea is similar except that it is the digital to analog converter which is place as close as possible as the antenna.

In practice, it is not (yet at least) possible the sample the RF signal since the Shannon condition is quite hard to satisfy. To circumvent this issue, the software part is done on the baseband samples, which are the input of a RF block that is in charge to modulate these symbols and do the transmission.

2. What is software ?

By software, all peoples do not understand the same thing. For people doing signal processing for digital communications, the software is done on a computer that entirely perform the baseband processing, and communicate thought one of its port with a SDR device which is in a charge of modulate these symbols.
For people doing numerical electronics, the software part can be done on a FPGA for example.

3. Opportunist radio and cognitive radio

An important aspect of the SDR concept is that it is the enabler or opportunist radio and cognitive radio concept. The idea first raised by Mitola is the following one: Giving a radio which can be entirely reconfigured by software, the next step is to make it able to reconfigure itself according to its radio surrounding. This idea has given two new concepts: opportunist radio and cognitive radio

3.1. Opportunist radio

An opportunist radio is a radio that is able to sense the spectrum, detect the unused band, and switch its transmitting chain to use, in an opportunistic way, this band. More information is available here.

3.2. Cognitive radio

A cognitive radio is a radio that is able to analyze the state of the different networks in its surrounding, and to connect to the most adapted one to its needs. More information is available here.

4. Products, Research activities,…

On this website, you may found much information about the software defined radio concept: products, a list of conferences where papers are published about this topic, the coming standards based on this technology...

5. External links

• The SDR Forum
• The Wikipedia page