Cognitive Radio Basics Explained

In the early days of modem development, designers were creating modems based on specific applications and frequency bands as needed. This approach led to longer system deployment times and increased costs for various reasons. This early development was primarily hardware-based.

With the introduction of Software Defined Radio (SDR), the required RF transceiver hardware, baseband transmitter, and baseband receiver algorithms are configured using software.

Following the SDR concept, research has focused on cognitive radio, which incorporates intelligence to allow the radio to sense its environment in terms of the radio spectrum, track changes accordingly, and utilize unused RF spectrum.

As illustrated in the figure, there are three main components: the radio frequency (RF) part, the ADC/DAC, and the baseband processing part.

• Radio Frequency Part: Consists mainly of an RF transceiver, LNA (Low Noise Amplifier), PA (Power Amplifier), RF filters, LO (Local Oscillator), and AGC (Automatic Gain Control).
• ADC/DAC: Used to convert analog signals to digital signals and digital signals to analog signals, respectively.
• Baseband Processing Part: Converts IF (Intermediate Frequency) signals to baseband I/Q signals and vice versa. This baseband part varies based on wireless technologies such as WLAN, WiMAX, LTE, LTE-Advanced, DVB-T, IMT-A, etc.

In cognitive radio, the RF part, ADC/DAC clocks, and baseband part are configured dynamically. Let’s examine how cognitive radio configures RF hardware.

• RF Filter: Configured according to the required frequency band.
• LNA Gain: Configured based on the RF link budget and input signal strength to prevent overdriving the ADC.
• LO for RF Signal: The necessary RF signal generation required for mixing with the input modulated RF signal to produce a modulated IF signal. The LO for the RF signal is generated according to the band of operation.
• Channel Selection Filter: Tuned according to the selected channel and to reject undesired adjacent channel frequencies.
• AGC Circuit: Developed dynamically based on signal strength, ensuring that the signal at the input of the ADC always falls within the dynamic range of the ADC.
• Clock: The clock required is based on the data rate and baseband requirements.

The biggest challenge in using cognitive radio is designing an efficient spectrum sensing algorithm so that unutilized spectrum can be efficiently used by various wireless technologies. This is because the spectrum is a scarce resource. Efficient information sharing between cognitive radios can be achieved.