Mohamed Shalaby

System Design and Performance Analysis of LTE Cognitive Femtocells

Femtocells’ deployment can extend the LTE coverage to include indoor areas. Unfortunately, a mutual electromagnetic interference can occur among the macro cells and femtocells due to the co-channel deployment. Moreover, interference among the femtocells themselves can occur due to utilizing the same subcarriers. The two types of interference can degrade the system performance. Femtocells base station power control can reduce the interference, which affects the macro users at the expense of a drop in the femto users’ geometry and throughput. A cognitive radio is proposed, as a novel approach, to completely eliminate the mutual interference among the macrocells and femtocells. The system is designed, mathematically analyzed, and simulated considering that the femto users are secondary users for the macro users. Analytical and simulation results show that applying the cognitive radio, to improve the system performance, is better than applying power control algorithms. The interference, which occurs among the femtocells, can be eliminated by different techniques. These novel techniques, which can achieve a maximization of the femto users’ geometry, are proposed and illustrated in details.

Evaluation of Electromagnetic Interference in Wireless Broadband Systems

Nowadays, the electromagnetic compatibility in radio frequency communication systems attracts a great attention as the wireless spectrum becomes overcrowded. A lot of wireless systems operate in the same bands or in the adjacent frequency ones. This operation results in an electromagnetic interference (EMI) among these systems. This EMI can degrade the performance of the wireless systems. Moreover, critical medical equipment, which is near to an electromagnetic radiation field, may be malfunction. A lot of studies handled the EMI phenomenon in radio systems. These studies range from the definition and the causes of the phenomenon to the development of suitable simulation tools for evaluating the EMI value. This paper handles the effect of the EMI existence on the performance of a broadband communication system in a complex radio environment. Moreover, this performance is clarified in a form of bit error rate. In addition, the complex radio environment is modeled as a summation of noise, narrow band interference (NBI), and ultra wide band interference (UWBI). The complete analysis model of a broadband radio system, which is interfered by a NBI and an UWBI, is carried out. Furthermore, the total interfering power is derived in a novel closed form formula. Finally, the performance of the system is simulated.

Performance Enhancement of LTE Underlay Cognitive Femtocells System Based on Macro Users Localization

LTE overlay cognitive femtocells system can provide a satisfied throughput for the macro and the femto users. On the other hand, the femto users can assign only the vacated subcarriers from the macro users. This assignment results in a reduced throughput for the femto users. Moreover, their throughput can have a zero value when the macro users operate on all subcarriers. In this paper, an underlay cognitive femtocells operation is proposed. The femtocells can share the subcarriers with the existing macrocells in such a way that their transmission cannot affect the macro users’ performance. The macro users’ positions can be determined, during their uplink transmission, using the received signal strength at the femto users. Then, the femtocells adapt their emitted power to guarantee a satisfied macro users’ performance. The performance of the proposed LTE underlay cognitive femtocells system is mathematically analyzed, simulated, and compared with the previous one which applies overlay cognitive femtocells. It can be observed that, the femto users’ throughput is existent and has a high value in comparison with the previous LTE overlay cognitive femtocells system. Furthermore, the proposed system has a higher macro and femto users’ throughput.

An Arnold Cat Map-Based Chaotic Approach for Securing Voice Communication

We present four encryption approaches for voice communication systems by combining Arnold cat map with either Henon or modified Henon or Unified or Lorenz chaotic maps. These approaches depend on permuting and substituting voice samples using transform domains and secret keys in time. We use two levels of chaotic maps to increase the security of the encrypted signal. We first apply Arnold cat map to permute the voice samples, then we apply either Henon or modified Henon or Unified or Lorenz chaotic maps to generate the mask key and hence substitute the permuted samples. We also present a comparative study between these approaches. Experimental results show that modifying conventional chaotic approaches from one level chaotic map to two levels chaotic map increases the key space of the encryption system.

Sensing Performance of Advanced LTE Cognitive Femtocells

The deployment of femtocells in a LTE advanced system can extend the system coverage to include indoors. Unfortunately, an electromagnetic interference may occur among the femto users and the macro users in the case of co-channel deployment. A cognitive radio can be used to mitigate the interference among the femtocells and the macrocells. It is applied by allowing the femto users to be handled as secondary users of any other existing network. In this paper, the performance of the LTE advanced Femtocell is studied by using different detectors such as energy detector, cyclostationary detector, and matched filter detector, which is not clarified until now. Moreover, the analysis of these detectors is made. Comparisons among these detectors are carried out. Different wireless channel models, Additive White Gaussian Noise (AWGN) and fading channels, are implemented to verify the operation of the proposed LTE advanced Femtocell. Simulation results show that there is a tradeoff between a false alarm probability and the signal to noise ratio value of any detector to have a certain performance. Moreover, the performance of the cyclostationary detector and the matched filter detector is better than the energy detector especially at low signal to noise ratio values. Unfortunately, the cyclostationary detector performance is not satisfying when the fading channels are employed.