Cognitive radio is a paradigm for wireless communication in which a wireless node (or a network) can change its transmission and reception parameters according to the user needs and the wireless environment. A cognitive radio transceiver is able to sense, learn, decide and react adaptively to avoid interference with licensed or unlicensed users and to achieve greater spectrum efficiency compared to existing systems. Cognitive radio opens a new era in digital communications involving numerous topics, such as spectrum sensing and dynamic spectrum management. CogWave is a free and open-source software platform aiming at developing cognitive radio waveforms. The CogWave application allows the exchange of video, audio and text between two USRPs through a graphical user interface (GUI) developed in Qt4 and cognitive radio waveforms developed in IT++. The USRP hardware driver (UHD) C++ application programming interface (API) allows to receive and transmit IQ samples. Combining CogWave with USRP gives a rapid prototyping platform for physical layer design and algorithm validation through a real-time video, audio and text transmission.
The cognitive blind OFDM waveform is an orthogonal frequency division multiplexing (OFDM)-based waveform divided into multiple sub-channels with a spectrum sensing block based on energy detection to determine the best sub-channel for transmission. Multiple users are handled by orthogonal frequency division multiple access (OFDMA) and full-duplex is enabled either by time division duplexing (TDD) or frequency division duplexing (FDD). A complete OFDM blind receiver which does not require the use of pilot symbols is used for time, frequency, phase offset and channel estimation. Cyclic redundancy check (CRC) and forward error correction (FEC) are used to detect and correct errors within a frame's preamble and postamble.
The next figure shows the demonstrator setup of 2 host PCs connected to 2 USRPs and exchanging data with the proposed waveform in TDD mode. The band of interest is divided into 4 sub-channels and the waveform automatically selects the best sub-channel according to the measured noise. The sampling rates and carrier frequencies in Tx and Rx for both USRPs are 2 Msps and 433.92MHz respectively, the OFDM has 512 sub-carriers and 128 samples for the cyclic prefix. The third computer and USRP is used as a jammer sweeping the whole bandwidth.
The next figure shows the spectrogram of the cognitive radio waveform in demonstration. The jammer in red sweeps the whole bandwidth and the cognitive waveform in yellow automatically changes its sub-channel whenever the jammer perturbs the transmission.
The next figure shows the application's GUI of the two computers exchanging data. The implemented services are video, audio and text. Data can still be exchanged in the presence of a jammer or other radio networks.