IEEE-20180 ICCCNT’ϭϮ 26 th -28 th July 2012, Coimbatore, India Efficient Spectrum Sharing and Allocation Schemes for Throughput Enhancements in a Cognitive Radio Network Dr. V. Jayaraj #1 , J. Jegathesh Amalraj #2 School of Computer Science and Engineering, Bharathidasan University, Tiruchirappalli, Tamilnadu, India 1 jaya_v@yahoo.com 2 amal.jas@gmail.com Abstract —Cognitive Radio Ad Hoc Networks (CRAHNs) constitute a viable solution to solve the current problems of inefficiency in the spectrum allocation, and to deploy highly reconfigurable and self-organizing wireless networks. Cognitive Radio (CR) devices are envisaged to utilize the spectrum in an opportunistic way by dynamically accessing different licensed portions of the spectrum[1]. However the phenomena of channel fading and primary cum secondary interference in cognitive radio networks does not guarantee application demands to be achieved continuously over time. The limited available spectrum and the inadequacy in the spectrum usage necessitate a new communication standard to utilize the existing wireless spectrum opportunistically[2]. Here, we discuss the mechanisms that can be followed to provide better efficiency in utilizing an existing cognitive network. This methodology also ensures that the existing channel frequencies are not wasted and the frequencies that are in use are utilized to the maximum extent without the need for bothering about the effects of interference[3]. We concentrate on, automatically detecting and exploiting unused spectrum, automatically detecting and interoperating with varying network standards and improving performance of the existing network. Keywords- Cognitive Radio Networks, Optimal Power Allocation, Spectrum Sensing, Spectrum Sharing, Throughput Maximization I. INTRODUCTION An Adhoc Network is a collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. Each node is considered to be alike here. It is needed to introduce some intelligence to the adhoc networks in order to improve their throughput efficiency. The concept of Cognitive Radio (CR) has been employed to achieve this. CR enabled devices are 'clever' and can listen to the surrounding wireless environment and can select appropriate frequency band, modulation scheme or specific power level as per the requirement. In this way an ability of self decision making can be incorporated in the wireless adhoc networks. Fig. 1 shows an example of a CR network. Frequency spectrum is a limited resource for wireless communications and may become congested owing to a need to accommodate the diverse types of air interface used in next generation wireless networks. This spectrum if utilized in an efficient manner, can lead to better utilization of the network. Wireless technology has enabled the development of increasingly diverse applications and devices resulting in an exponential growth in usage and services. These advancements made the radio frequency spectrum a scarce resource, and consequently, its efficient use is of the ultimate importance. To cope with the growing demand, network design focused on increasing the spectral efficiency by making use of advancement in Cognitive Radio technology. Cognitive Radio can reduce the spectrum shortage problem by enabling unlicensed users equipped with Cognitive Radios to reuse and share the licensed spectrum bands. Using the fact that a Cognitive Radio is capable of sensing the environmental conditions and automatically adapting its operating parameters in order to enhance network performance. Our research mainly focuses on the development of efficient spectrum sensing and selection techniques, thereby providing valuable insights on how such CR networks may be designed. II. 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. This alteration of parameters is based on the active monitoring of several factors in the external and internal radio environment, such as radio frequency spectrum, user behaviour and network state.