Salwa Elramly

FPGA implementation of a reconfigurable Viterbi decoder for WiMAX receiver

Field Programmable Gate Array technology (FPGA) is a highly configurable option for implementing many sophisticated signal processing tasks in Software Defined Radios (SDRs). Those types of radios are realized using highly configurable hardware platforms. Convolutional codes are used in every robust digital communication system and Viterbi algorithm is employed in wireless communications to decode the convolutional codes. Such decoders are complex and dissipate large amount of power. In this paper, a low power-reconfigurable Viterbi decoder for WiMAX receiver is described using a VHDL code for FPGA implementation. The proposed design is implemented on Xilinx Virtex-II Pro, XC2vpx30 FPGA using the FPGA Advantage Pro package provided by Mentor Graphics and ISE 10.1 by Xilinx.

Dynamic generation of s-boxes in block cipher systems

Block cipher systems are widely used in cryptographic applications. The main problem in implementing any block cipher system is the fixed structure of s-boxes elements. In this paper we present a new method to build up dynamic look-up tables (s-boxes) changing with every change of the secret key in addition to an evaluation criterion of block ciphers. This new approach leads to more secure block cipher systems and consequently solves the problem of the fixed structure block ciphers.

A feature and appearance based method for eye detection on gray intensity face images

This paper presents a robust and precise eye detection algorithm on gray intensity face images. Our method combines the strength of two existing methods which are a feature based method and an appearance based method to detect and locate a precise pupil center. It includes the following three steps. First, the feature based method is used. The method uses a projection function to detect all possible regions of each left and right eye. Second, the appearance based method is used to filter out all non eye regions, and keep only one region for each left and right eye. All possible regions will go through a principal component analysis (PCA). Third, a modified hybrid projection function is used to locate the pupil center for both eyes. The experimental results show that the proposed method has an efficient performance with the accuracy of more than 90.52%.

FPGA implementation of a configurable viterbi decoder for software radio receiver

Convolutional codes are one of the Forward Error Correction (FEC) codes that are used in every robust digital communication system. Viterbi algorithm is employed in wireless communications to decode the convolutional codes. Such decoders are complex and dissipate large amount of power. Software Defined Radio (SDR) is realized using highly configurable hardware platforms. Field Programmable Gate Array technology (FPGA) is a highly configurable option for implementing many sophisticated signal processing tasks in SDR. In this paper, a generic, configurable and low power Viterbi decoder for software defined radio is described using a VHDL code for FPGA implementation. The proposed design of the Viterbi decoder is considered to be generic so that it facilitates the prototyping of the decoder with different specifications. The proposed design is implemented on Xilinx Virtex-II Pro, XC2vp30 FPGA using the FPGA Advantage Pro package provided by Mentor Graphics and ISE 10.1 by Xilinx.

Neural networks used for speech recognition

Neural networks are applied to the recognition of Arabic phonemes. Time delay neural networks (TDNN) have been chosen for the problem of Arabic speech recognition because of their ability to represent relationships between acoustic events. Two Arabic categories have been chosen, nasals and voiced stops, to evaluate the performance of TDNN in Arabic speech recognition. The effect of several factors on the recognition rate have been studied: (i) the length of the analysis frame (10 ms and 20 ms); (ii) truncating or zero padding the signal versus re-sampling the signal to obtain a signal of fixed length; (iii) using a single neural network versus a separate neural network for each phoneme category; and (iv) the size of the TDNN. The length of the 20 ms analysis frame obtained higher recognition rates than the 10 ms frames. Truncating or zero padding the signal to obtain a fixed length signal gave higher recognition rates than re-sampling the signal. A 9% increase for nasals and 2.4% increase for stops, were obtained when using a separate TDNN for each phoneme category. It was also found that the size of the network depends on the complexity of the recognition problem.

SIP-Based Handoff Scheme in Next Generation Wireless Networks

Increasing demand for ubiquitous high speed data access has resulted in widespread deployment of heterogeneous wireless networking domains. Integration of heterogeneous networks presents some considerable challenges which include the demand for seamless handoff, continuity of data traffic & multimedia sessions and central authentication system, billing & security. In this paper the main concern is to achieve terminal mobility between heterogeneous networks and evaluating the performance during handoff. Two SIP handoff schemes are used and compared to evaluate the performance of Session Initiation Protocol (SIP) as a mobility management protocol between heterogeneous wireless networks, Soft SIP-based seamless handoff (S-SIP) and SIP-based Soft Handoff with B2BUA. After illustrating the signaling message flows in the two handoff schemes we propose a new technique, Host Agent-Based SIP Session set up, to reduce the SIP session re-setup delay in VoIP service environment. This new technique is applied with the two SIP handoff schemes, VoIP performance parameters are analyzed and compared using OPNET simulation tool.

Reducing the effect of finite wordlength on the performance of an LMS adaptive filter

The paper proposes a modification of the LMS algorithm that reduces the effect of finite wordlength on the adaptive filter performance. The proposed algorithm is based on repeatedly freezing the filter coefficients for a certain period of time and then updating them on the base of the average innovation term during the freezing period. Expressions are derived for the steady state mean square error and the convergence time of the proposed algorithm. It is found that the proposed algorithm poses a significantly higher resistance to roundoff errors than that of the conventional LMS algorithm. The derived expressions are found to be in an excellent agreement with computer simulation results.

Novel modified energy detection spectrum sensing technique for FM wireless microphone signals

Spectrum Sensing is an important functionality of Cognitive Radio (CR). Accuracy and speed of estimation are the key indicators to select the appropriate spectrum sensing technique. In this paper, we focus on spectrum sensing of narrowband wireless microphone (WM) signals using the modified periodogram and Welch method for different window types. It is well-known that the power of the WM signal is highly concentrated in the frequency domain, particularly under silence. Due to this property, spectrum sensing can be performed by what we call modified energy detection (MED) which applies of two techniques. First, a proposed window is used to reduce the height of the side-lobes or spectral leakage, which is called modified periodogram method. This increases the difference between the signal PSD peak and the noise level resulting in better detection. Second, Welchs method is used, which takes the average of the modified periodograms using overlapped windows that decreases the noise variance compared to single periodogram estimation. The performance of the proposed spectrum sensing technique is demonstrated by computer simulations.

Tracking performance of a quantized adaptive filter equipped with the sign algorithm

Abstract The paper is concerned with analyzing the effect of finite wordlength on the tracking performance of a sign algorithm when used in the adaptive identification of a time-varying plant. Rounding quantization is assumed. Expressions of the steady-state mean-square error, steady-state mean-square weight deviation, and the corresponding optimum step sizes are derived. It is found that the mean-square error, mean-square weight deviation, and the optimum step sizes increase as the filter weight wordlength decreases. The effect of filter weight wordlength is found to be equivalent to an increase of the degree of nonstationarity of the plant. Conditions at which the effect of finite wordlength dominates (or is dominated by) the effect of plant nonstationarity are derived. The theoretical results of the paper are validated by computer simulations.

IP–Multimedia Subsystem (IMS) performance evaluation and benchmarking

Evaluating the IP Multimedia Subsystem (IMS) Performance is very important due to the critical role it plays in the Next Generation Network (NGN) of the Fixed and Mobile Networks. This paper proposes three robust and scalable methods that can be used to evaluate the performance, the Compliance of the IMS controllers and benchmark their different vendors. These methods are, Performance Test, FUZZING Test and the test using Spectra 2|SE tool. These issues are studied experimentally, using Open SIP Express Router (OpenSER), a high performance open source SIP server and SIPp, the de-facto standard for SIP performance benchmarking. It also provides the test results for Open SIP Express Router (OpenSER).