Cognitive Radio (CR) is an unprecedented concept in wireless communication and it is a technical solution to perfect utilization of spectrum. CR sense the presence of licensed primary users through measuring parameters related to channel characteristics. The power spectrum gives vital information with regard to the presence of a user at every frequency. In this paper we analyzed different spectrum sensing techniques like energy detection, Fast Fourier Transform Averaging Ratio (FAR) whose performance is low in non-stationary environment. In this paper we proposed Hilbert Huang Transform detector (HHT) to detect presence of primary user. In practical scenario, non-stationary and nonlinear processes can be efficiently detected by this HHT. It is evident from the results that the HHT transform average ratio detector outperformed the FFT average ratio detection.

Mobile cellular communications revolutionized in communication system applications. The present mobile cellular communication networks normally often suffer from poor penetration and reception in certain areas, like indoor and apartments in turn decreasing quality of service. The main backbone of Long Term Evolution Advanced (LTE)- mobile network is internet. In order to reduced the traffic and enhance data rates, femtocell can be used to improve wireless coverage over a small area, especially in indoor and urban environment. Femtocell is a small cellular base station that connects to a broadband Internet connection. The major technical challenges of femtocells are cross-tier, Intra-tier and user equipment interference, quality of service, handover operation and spectral accuracy. The predominate issue is cross-tier interference constituting macro cell and femtocell networks constitutes the greater portion of interference in terms of adjacent channel interference. In this paper, Interference levels in reception of heterogeneous LTE Network by using two different path loss models are investigated. Signal to interference ratio and the throughput are estimated The trade-off between selections of Femto or Macro BS link by the User Equipment (UE) is examined by considering number of walls and penetration losses of Computer Block (7 floors, 10 walls), KL University, Vaddeswaram, Guntur, India. It is found that that model-2 is better in Interference mitigation and path loss estimation compared to model-1.