Atef Abou El-Azm

Proposed relay selection scheme for physical layer security in cognitive radio networks

In this study, the physical layer security for cognitive radio network (CRN) will be investigated in which a secondary user transmitter (SU-Tx) sends confidential information to a SU receiver (SU-Rx) on the same frequency band of a primary user (PU) in the presence of an eavesdropper receiver. Moreover, relay selection scheme is proposed for the security constrained CRNs with single eavesdropper, multiple eavesdroppers and PUs. The proposed scheme selects a trusted decode and forward relay to assist the SU-Tx and maximise the achievable secrecy rate that is subjected to the interference power constraints at the PUs for the different number of eavesdroppers and PUs under available channel knowledge. The SU cooperates with relays only when a high secrecy rate is achieved. Secrecy rate and secrecy outage probability are the two performance metrics that are used to verify the effectiveness of the proposed scheme although asymptotic approximations of the secrecy outage probability are also derived. Simulation and analytical results demonstrate that the performance improvement of the proposed scheme reaches to the double relative to the conventional scheme for the secrecy capacity.

COMBINED INTERLEAVING AND COMPANDING FOR PAPR REDUCTION IN OFDM SYSTEMS

Peak to Average Power Ratio (PAPR) is one of the serious problems in any wireless communication systems using multicarrier modulation technique as OFDM, which reduces the efficiency of transmit high power amplifier. In this paper, proposed scheme will be introduced, which combines interleaving technique and companding technique to reduce PAPR. This scheme will be compared with the system that uses other technique for reduction which is the clipping technique. By using proposed scheme, the PAPRof OFDM signal can be reduced by 6.8 dB over the original system, i.e., without PAPR reduction. Also, SNRdecreases by more than 5 dB for Bit Error Rate (BER) of 10 −3 over the original system. Moreover, the proposed scheme gives improvement more than 4.5 dB for BERof 10 −3 over the system that uses clipping. All these systems will be evaluated in the presence of nonlinear power amplifier.

Three bits softened decision scheme in cooperative spectrum sensing among cognitive radio networks

Recently, cognitive radio (CR) access has received much attention to overcome spectrum scarcity problem. Spectrum sensing methods are often used for finding free channels to be used by CR. In this paper, one of spectrum sensing method will be investigated. This method is cooperative spectrum sensing which is based on energy detection in CR networks in order to overcome fading, noise and shadowing effects on individual CR user and increase the reliability and efficiency of spectrum sensing. The sensing information from CR users combines at the Fusion center (common receiver) by soft combination or conventional hard combination techniques. Soft combination has excellent performance but, it requires a lot of overhead for feedback observation. In contrast, the conventional hard combination scheme requires only one bit of overhead, but it has worst performance because of loss of information caused by local hard decisions. In this paper, the detection performance improves by increasing the levels of local observations by proposing three-bit softened decision scheme which is not clarified until now. Analytical Expressions of proposed three bits scheme will be derived. Design parameters are optimized to find the detection performance with a given false alarm probability. The simulation results show that, at 90% detection probability, the cooperative signal detection improves by 1.75 dB of signal to noise ratio over conventional hard combination (i.e., one bit scheme). Moreover, comparisons between proposed scheme, one bit and two bits schemes will be made.

Blind separation of audio signals using trigonometric transforms and wavelet denoising

This paper deals with the problem of blind separation of audio signals from noisy mixtures. It proposes the application of a blind separation algorithm on the discrete cosine transform (DCT) or the discrete sine transform (DST) of the mixed signals, instead of performing the separation on the mixtures in the time domain. Wavelet denoising of the noisy mixtures is recommended in this paper as a preprocessing step for noise reduction. Both the DCT and the DST have an energy compaction property, which concentrates most of the signal energy in a few coefficients in the transform domain, leaving most of the transform domain coefficients close to zero. As a result, the separation is performed on a few coefficients in the transform domain. Another advantage of signal separation in transform domains is that the effect of noise on the signals in the transform domains is smaller than that in the time domain due to the averaging effect of the transform equations, especially when the separation algorithm is preceded by a wavelet denoising step. The simulation results confirm the superiority of transform domain separation to time domain separation and the importance of the wavelet denoising step.

JPEG image transmission over mobile network with an efficient channel coding and interleaving

This article studies improving of coloured JPEG image transmission over mobile wireless personal area network through the Bluetooth networks. This article uses many types of enhanced data rate and asynchronous connectionless packets. It presents a proposed chaotic interleaving technique for improving a transmission of coloured images over burst error environment through merging it with error control scheme. The computational complexity of the used different error control schemes is considered. A comparison study between different scenarios of the image transmission is held in to choose an effective technique. The simulation experiments are carried over the correlated fading channel using the widely accepted Jakes’ model. Our experiments reveal that the proposed chaotic interleaving technique enhances quality of the received coloured image. Our simulation results show that the convolutional codes with longer constraint length are effective if its complexity is ignored. It reveals also that the standard error control scheme of old Bluetooth versions is ineffective in the case of coloured image transmission over mobile Bluetooth network. Finally, the proposed scenarios of the standard error control scheme with the chaotic interleaver perform better than the convolutional codes with reducing the complexity.

Proposed relay selection scheme for physical layer security in Cognitive Radio networks

Cognitive Radio (CR) technology is one of the strong candidate technologies to solve the spectrum scarcity problems. In this paper, we tackle the problem of secure data transmission between a secondary user transmitter and receiver through a relay in the presence of an eavesdropper in a cognitive radio network. The proposed scheme selects the best Decode-and-Forward relay among different relays to assist the transmitter, and to maximize the achievable secrecy rate without harming the primary user. Simulation results show that the secrecy capacity of the network using this scheme will almost be double the capacity when selecting the conventional scheme of relay selection.

Designing a concatenated coding system for reliable satellite and space communications

This paper presents a design methodology of a concatenated coding system. The system uses a rate 1/2 convolutional code and NASA standard RS (255, 223) code. The decoder for the convolutional code is the Viterbi decoder and is designed with different values of quantization levels. An interleaver and deinterleaver between the two codes with different depth are also included. Simulation results of the bit error rate (BER) for the concatenated system and for a certain depth of interleaver are given. The obtained results are compared with that of the NASA/ESA system and good agreement is shown.

Experimental comparison among Fast Block Matching Algorithms (FBMAs) for motion estimation and object tracking

In this paper two different Fast Block Matching Algorithms (FBMAs) are introduced and analyzed. They are One Point Pentagon Inner Search (OPPEN) and Predicted One Point Hexagon Inner Search (POPHEX) algorithms. The proposed algorithms are compared with other FBMAs like Diamond Search (DS), and Hexagonal based search (HEX) algorithms using MATLAB environment. The comparison is conducted for both motion estimation and object tracking using group of known test video sequences. The results showed that the proposed OPPEN algorithm has the best performance in terms of complexity and average cost function. Also it have the smallest tracking time consumption.

Pre-decorrelation in Turbo-coded DS-CDMA system using Space-Time Coding over fading channels

In this paper, we deal with the multiple access interference (MAI) suppression problem in turbo coded space-time block coded (STBC) direct sequence code-division multiple-access (DS-CDMA) systems. In the proposed system, we preprocess (decorrelate) the coded bits in the transmitter side instead of using a decorrelating detector in the receiver. Using this method, the base station can perform decorrelation before transmission, and the mobile unit uses the conventional receiver achieving approximately the performance of the decorrelating detector. Performance comparison is made between this method and existing decorrelating detector in fading channels. This paper also investigates the performance improvement due to channel coding. Performance comparison between turbo coded STBC DS-CDMA systems employing different interleaver sizes and soft-decision convolutional codes (SD-CC) is also provided.

Digital computer simulation of high rate convolutional coding systems

This paper presents digital simulation to provide a practical approach to system design and analysis. The simulation is used to design convolutional systems of rate 1/2 and of rate 3/4 with Viterbi decoding algorithm and QPSK modulator. The systems are differentially encoded and decoded. The signal waveforms at each node of the rate 1/2 system are shown. Simulation curves of the performance of the two systems are also presented. These curves are plotted in the soft-decision case with eight level quantization and are repeated for unquantizated soft-decision decoding over an AWGN channel. The simulation provides coding performance very near the theoretical for the optimal length K=7 rate 1/2 and 3/4 Viterbi decoder algorithm. Keywords- Convolutional codes, Bit error rate, Viterbi Algorithm, SimulationOften communications systems are too complicated to analyze completely by using only analytical techniques, or a complete analytical approach would be too costly in terms of personnel and time. In these cases, a digital computer simulation is used, as shown in this paper, to provide a practical approach to system design and analysis. This paper presents computer simulation to design convolutional systems of rate 1/2 and 3/4 with Viterbi decoding algorithm and QPSK modulator. The systems are differentially encoded and decoded and signal waveforms at each node of the rate 1/2 system are shown. Simulation curves of the performance of the two systems are also presented. These curves are plotted in the soft-decision case with eight level quantization and are repeated for unquantized soft-decision decoding over an AWGN channel. The simulation provides coding performance very near the theoretical limits for the optimal constraint length K=7 rate 1/2 and 3/4 Viterbi decoder algorithm.