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Monday, January 10, 2011

Cognitive Radio: Knowledge Applications

Cognitive radio comes with multitudes of features. The majority of these attributes are “Awareness”, “Sensing”, “Learning”, and “Adaptation”. CR applications can be broadly categorized into those, which contribute to the full or partial improvement of system performance in the existing wireless communications; and into those, which can be beneficial in establishing new wireless communication. The figure below represents a high level classification of possible CR applications.

In this article I will focus on wireless resource optimizing and quality enhancing applications. Wireless resources are limited. This scarcity in resources demands careful consideration and planning in their usage. The conventional radio resources encompass spectrum, hardware/software, network infrastructure, and power. Cognitive intelligence adds another dimension to these namely “knowledge”. This article explores the Cognitive Radio knowledge applications.

“Knowledge” is a significant resource exploited by cognitive radio to improve wireless communication. Knowledge comprises of information on the individual entities within a communication link. Configuration and capability parameters of hardware/software, network infrastructure, power, and spectrum can represent knowledge. Measured and predicted values of channel related information such as link quality, Signal-to-noise Ratio (SNR), and channel fading parameters might also be considered as knowledge. Similarly, information about user habits, location, and bio-metric information such as thumb print, voice, and retina print can be considered as knowledge as well.

The traditional wireless systems exploited some of these items in the recent years through various adaptation techniques. But, cognitive concept has the potential to bring revolutionary changes in knowledge utilization. The major tasks to use knowledge can include cognitive awareness of various parameters, tracking their changes, and employing appropriate action. These parameters can be provided to the cognitive radio via look-up tables, through the download process from a central/semi-central database, and through a software upgrade process. Some parameters can be measured in real or non-real time as well. Knowledge utilization tasks can be better understood through some examples as below:

 Cognitive awareness of channel fading characteristics, channel noise and/or interference level, and error correction capability can allow appropriate selection of Forward Error Correction (FEC) scheme, interleaving length, modulation order, and type, etc. This in turn, can reduce the effect of interference, and/or improve signal quality, and/or provide high data rate transmission.
 Knowledge on selectivity in multi-dimensional channel space can lead to adjusting various parameters like channel equalizer taps (in frequency selectivity dimension) as illustrated in Figure below, or channel tracking memory (in time selectivity dimension), or multi-antenna loading parameters (in spatial selectivity dimension).

 Knowledge on transmitted information type such as voice, data, text, video, audio or images can help determine the most appropriate source coding technique.
 Network knowledge on available routes, available bridging nodes, and protocol status of nodes can result in reducing network delay; minimizing network usage, and providing uninterrupted communication over heterogeneous network components.
 Spectrum knowledge beyond the traditional concept of fixed spectrum can lead to transmission over variable spectrums and variable dimensions of channel space. This in turn can provide ubiquitous connectivity and higher achievable data rate as well.

Cognitive radio may also deduce more knowledge from the available information. One such case can involve deriving channel characteristics [3] from the available Global Positioning System (GPS) information. It can subsequently reduce transmission of channel related information while increasing data rate.

Technology is futile without its application. One of the major driving forces of a new technology is the combination of man’s endless thirst for knowledge, unequal intuitive mind, and limitless ambition to better his life. The other important factor consists of user demand, user necessity, and increasing user desire to have it all in one single device. Wireless communication involves accessing and utilizing air spectrum for communication purpose. More and more devices may fall under the umbrella of “wireless communication technology” in the near and distant future. For example, every personal computer may soon be connected to its keyboard and mouse via the radio medium. This in turn can eliminate hardware manufacturing cost, manual labor for connection, and hardware pollution of the discarded parts. Wireless technology thus opens up an endless market of wireless communication applications. “Cognitive Radio” (CR) in the wireless world is relatively new and comprises of two magical words that encompass everything! It is the radio with intelligence; capable of using its radio ability in the most optimum manner by interacting with surrounding environment, learning about the environment, and using the learned knowledge to improve communication.

The figure below illustrates a generic flow from cognitive concept to the final end user products.

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