Efficient Resource Allocation In Cognitive Radio Networks

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Efficient resource allocation in cognitive radio networks considering time varying constraints
Wide spread acceptance of wireless technologies has given rise to increase in demand for bandwidth .cognitive radio was developed as a promising technique to overcome the scarcity of spectrum resources in wireless communication. The term cognitive radio is defined as an intelligent radio that can be programmed and configured dynamically. Particular portion of the spectrum can be used only by a specific user of communication systems i.e. licensed user (or) primary user (PU). The secondary user is cognitive user (CR). There are two main paradigms to implement CR in practical, namely interweave and underlay techniques. The main motive of
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In underlay transmission method the secondary users use the licensed band along with the active primary users but to keep the interference to the PU’s under a predefined threshold level the SU’s will control their power accordingly, where as in interweave transmission the SU’s use the licensed band when no active primary user is present [3].
Spectrum sensing in cognitive radio is performed to know the surrounding radio environment such as PU’s existence and usage of spectrum in geo graphical area and it determine the spectrum holes. Based on the spectrum sensing results, the process of identifying the best channel to meet the QOS to the user is known as spectrum management. It assigns that channel to the cognitive user. Scheduling coefficients, rate, power are the resources available for cognitive radio to adapt. In spectrum management by using some time varying constraints it identifies the best channel in the spectrum, but there are still few challenges in design faced by cognitive radio paradigm For controlling interference we need some extra constraints. The volatile nature of CR may cause outdated statistical channel state information. It is difficult to acquire instantaneous CSI of the PU.
For first design challenge, interference can inflicted by either through average (long term) transmit-power constraints or instantaneous (short term) constraints [4]. The instantaneous constraints have been focused as the second design challenge, handling these constraints
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