A. El-Hennawy

On the Performance of FFT/DWT/DCT-based OFDM Systems with Chaotic Interleaving and Channel Estimation Algorithms

The efficiency of data transmission over fading channels in orthogonal frequency division multiplexing (OFDM) systems depends on the employed interleaving method. In this study, we propose an improved chaotic interleaving scheme which aims to improve the performance of OFDM system under fading channel. In the proposed scheme, the binary data is interleaved with chaotic Baker map prior to the modulation process. In the sequel, significant degree of encryption is being added during data transmission. The performance of the proposed approach is tested on the conventional fast Fourier transform OFDM, discrete wavelet transform OFDM, and discrete cosine transform OFDM with and without chaotic interleaving. Furthermore, an expectation–maximization (EM) algorithm is proposed for improving channel impulse response (CIR) estimation based on a maximum likelihood principle. The proposed scheme makes use of EM algorithm to update the channel estimates until convergence is reached. The simulation results show the efficiency of the proposed algorithms under Rayleigh fading environments where the symbol error rate essentially coincides with that of the perfect channel case after the fifth EM iteration.

Reducing the peak to average power ratio in MIMO OFDM systems

Multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems have been receiving a great attention, as one of the solutions for achieving high speed, efficient, and high quality of service for wireless communications. However MIMO OFDM suffers from high PAPR, this demands expensive linear amplifiers with wide dynamic range. In MIMO OFDM systems, a straightforward way for PAPR reduction is to apply existing techniques separately on each transmit antenna, then the overall PAPR reduction is obtained. A proposed technique based on modified partial transmit sequences (PTS) using circular shifting and phase rotation is employed to achieve more reduction in the overall PAPR in MIMO OFDM, it exploits the extra degree of freedom provided by MIMO to reduce the overall PAPR. Two sub-optimal solutions for modified PTS are suggested, to reduce the complexity and side information in MIMO OFDM, with slight loss of PAPR reduction performance.

Over-The-Air Programming of PSoC sensor interface in wireless sensor networks

Over-The-Air Programming (OTAP) technology was developed originally to enable device manufacturers and network operators to deliver updated firmware for mobile handset. The growing popularity and complexity of wireless sensor networks implies the importance of usage of such technology (OTAP) the same way it is used in mobile networks. The idea of this work is to enable firmware update of motes and sensor interfaces used in wireless sensor networks in their final locations from a central base station. This work also focuses on the development of PSoC based sensor interface board. The usage of PSoC in sensors interfaces allows for a broad range of sensors to be interfaced. Signal conditioning, filtering and amplification tasks are all preformed on the PSoC chip and can be modified and tuned by means of OTAP. A complete OTAP working flow is detailed to program the developed PSoC sensor interface board. The OTAP of this sensor board is implemented using a very low power CPLD device.

Improving security and efficiency of enterprise digital rights management

Recently, private enterprises, governmental and military institutions have been relied mainly on digitizing their work. Digital files containing sensitive information should be protected against external and internal malicious attacks. Enterprise digital rights management (E-DRM) schemes provides several approaches to protect and securely distribute digital contents while empowering the enterprises administration to monitor and control access to these contents. In this paper we propose a new secure and efficient E-DRM system based on the Information Dispersal Algorithm (IDA). We achieved an improvement in the overall storage requirements, and the computations complexity at each server in the system, as well as preserving the security of information and system robustness.

Architecture of a Fully Digital CDR for Plesiochronous Clocking Systems

This paper describes a design of a fully digital clock and data recovery (CDR) system with plesiochronous clocking. Besides the well known advantages of digital implementations over analog ones in terms of robustness against process and temperature variations, scalability, compactness and low cost, the system also enjoys many features. It can withstand an input data cycle-to-cycle jitter up to ±37.5% UI. Data are obtained through digital correlation with the incoming symbol instead of ordinary sampling at the middle of the eye pattern, which improves BER. Furthermore, it needs only, at worst, three preamble bits to get into lock. It is insensitive to long runs of transition-free data patterns. The extracted data clock is not shifted as long as input data jitter is small (typically less than ±12.5% UI), thus, minimizing jitter in the extracted data clock. Besides, the extracted clock has a 50% duty cycle.

Modified PTS with circular shifting for PAPR reduction in MIMO OFDM systems

Multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) technology is one of the most attractive candidates for fourth generation (4G) mobile radio communications. It effectively combats the multipath fading channel and improves the bandwidth efficiency. At the same time, it also increases system capacity so as to provide a reliable transmission. However, the main drawback of MIMO OFDM systems is high peak to average power ratio (PAPR), which result in many restrictions for practical applications. In this paper, the low complexity partial transmit sequences (PTS) is adopted to be modified using circular shifting, it exploits the extra degree of freedom provided by MIMO, to improve PAPR reduction in MIMO OFDM systems. Merging the circular shifting with phase rotation in low complexity PTS is also proposed, to provide more PAPR reduction.

A Comparative Study of Localization Algorithms in WSNs

Wireless Sensor Networks (WSNs) are the type of networks that are currently used in many applications. Some of these applications are critical and their information is very sensitive e.g. battle field and health care monitoring. Any transferred data has to be known from where it comes. In other words, most of the WSNs applications depend mainly on the location of each node in the network. In fact, the location may affect the decision to be made. The importance of localization is not only due to location identification but also it provides the base for routing, density control, tracking, and number many of other communication network aspects. Therefore, it is very important that each node reports its location accurately. Unfortunately, GPS is not suitable for WSNs due to its cost in terms of nodes consumed energy as well as its availability. Many localization algorithms are proposed for WSNs; however, their accuracy is the main concern. This paper is designated to help the WSNs designers in selecting suitable localization algorithm for their applications. The paper presents as well as implements different localization algorithms and evaluate them.

Detection of Gold Codes Using Higher-Order Statistics

In this paper the higher-order statistics (HOS) specified in terms of triple correlation function (TCF) of Gold code which is commonly used in spread-spectrum systems is studied. A detection method of Gold sequence is presented and the proposed gold code receivers based on the peak feature of the TCF are analysed. These receivers take advantage of the TCF and use it for self-synchronization. We study two types of TCF receivers, one-stage receiver which is used with divisible by three code length and two-stage receiver which can be used with any code length. A comparison between the performances of both receivers in Additive White Gaussian Noise (AWGN) channel is performed to prove the immunity of the receivers against different noise levels.

Adaptive packet sizing for OTAP of PSoC based interface board in WSN

Adaptive packet sizing techniques are widely used in wireless communication to enhance the link reliability. Typically, shorter packets are less error prone than longer packets. Adaptive packet size technique is used in IEEE 802.11 wireless network to enhance link reliability and packet delivery ratio. In this work, we adopt this technique to work in IEEE 802.15.4 based networks, and specifically in wireless sensor networks. A special protocol is designed to implement adaptive packet size transmission in WSN. In WSN, different mote designs and implementations are relying on the use of programmable circuits in their sensor interface boards. Delivering new firmware to these circuits by means of OTAP (Over The Air Programming) requires a reliable link between base station and target mote. Such reliable link can be achieved using the proposed adaptive packet sizing protocol. A testbed based on such scenario is constructed and the proposed protocol was tested to send new firmware update data to the target mote in its distant location under different environmental conditions.

Analysis of Optical Code Division Multiple Access Passive Networks for Different Encoder Delay Elements

One of the most important core technologies in the development of optical code division multiple access (OCDMA) local area networks is the optical encoder/decoder embodiment technology which codes information to fixed patterns at the transmitting side and decodes information at the receiving side. The selection of optimized encoding method for network composition is necessary to accommodate a maximum number of subscribers that have simultaneous access over the local area network and the bandwidth of subscriber services available on it. When composing this encoder/decoder optically, passive elements are exclusively used, if possible, so as to make the composition method simple and economical. In this paper we present an analysis of OCDMA passive communication networks focusing on the modeling of optical encoder/decoder blocks for different types of delay elements. The main objective of the paper is to study the performance of these networks including the effect of the passive encoder/decoder parameters such as splitter and optical delay line losses. Different types of delay lines are proposed including optical fibers and fiber Bragg gratings (FBG) as delay elements for the selection of the optical delay line which achieves a better performance. A statistical model of an OCDMA network has been developed and used for this study, including the effect of different passive encoder/decoder parameters, multiple access interference and noise