One of the key challenges of the cognitive radio

Cognitive radio

A cognitive radio is a kind of two-way radio that automatically changes its transmission or reception parameters, in a way where the entire wireless communication network -- of which it is a node -- communicates efficiently, while avoiding interference with licensed or licensed exempt users...

 based wireless network

Wireless network

Wireless network refers to any type of computer network that is not connected by cables of any kind. It is a method by which homes, telecommunications networks and enterprise installations avoid the costly process of introducing cables into a building, or as a connection between various equipment...

s, such as IEEE 802

IEEE 802

IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks.More specifically, the IEEE 802 standards are restricted to networks carrying variable-size packets. IEEE 802 refers to a family of IEEE standards dealing with local area networks and...

.22 wireless regional area networks (WRAN), is to address two apparently conflicting requirements: assuring Quality of Services (QoS) satisfaction for services provided by the cognitive radio networks, while providing reliable spectrum sensing for guaranteeing licensed user protection. To perform reliable sensing, in the basic operation mode on a single frequency band (the so called “listenbefore-talk” mode) one has to allocate Quiet Times, in which no data transmission

Data transmission

Data transmission, digital transmission, or digital communications is the physical transfer of data over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibres, wireless communication channels, and storage media...

 is permitted. Such periodic interruption of data transmission could impair the QoS of cognitive radio systems.

This issue is addressed by an alternative operation mode proposed in IEEE 802.22 called Dynamic Frequency Hopping

Frequency-hopping spread spectrum

Frequency-hopping spread spectrum is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver...

(DFH) where data transmission of the WRAN systems are performed in parallel with spectrum sensing without any interruption.