Advantages Of Cognitive Radio

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I. INTRODUCTION
In today’s world there is an increasing demand for wireless connectivity. But with the present technology there is an inefficient use of the available. A large part of the spectrum is underutilised as shown in Fig 1. Due to the inefficient use of spectrum by the current spectrum allocation methods there is a need for developing new methods which aids in efficient use of available spectrum.

One alternative solution to this is the use of alternate technology. Cognitive radio (CR) is an available option. Cognitive radio concept was introduced by Mitoala [2]. CR in general can be defined as the usage of licensed spectrum by an unlicensed user when the former is not using it. This is called as spectrum hole. CR uses these for transmission of data/voice [3]. CR as defined by Haykin is:
“Cognitive radio is an intelligent wireless communication system that is aware of its surrounding environment (i.e., outside world), and uses the methodology of understanding by- building to learn from the environment and adapt its internal states to statistical variations in the incoming RF stimuli by making corresponding changes in certain operating parameters (e.g., transmit-power, carrier-frequency, and modulation strategy) in real-time, with two primary objectives in mind: highly reliable communication whenever and wherever needed; efficient utilization of the radio spectrum.” [4]
To clearly understand the concept of CR systems a background on software defined radio (SDR). Traditional radio systems which is oriented around hardware limits cross functionality and physical intervention is needed for modification. This reduces the flexibility and increases the cost of implementation and operation. An alternative to this is softwar...

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...CR-BS environment.
5) PS-MS ↔ PS-BS: This link being bi-directional at all times is a connection between MS and BS which has to be done in one hop. PR-BS being the master has the function of communication coordination in its cell coverage area and also providing access to PR-MS to backbone network.
6) PS-MS ↔ CR-MS: This is needed for enabling interoperability between systems of different kind. Here CR-MS will become a part of PS by reconfiguring itself.
7) PS-MS ↔ CR-BS: This link also serves the same purpose as that between PS-MS↔CR-MS. Additionally if CR-BS has the capability of running the protocol of PS, access service to PR-MS can be provided through it.
8) PS-MS ↔ PS-MS: This link may be useful as ad-hoc network for wireless connection. This is present in PS. Here, if both the nodes are given CR capability, this link will mirror that of between CR-MS↔CR-MS.
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