The technique of embedding a digital signal into an audio recording or image using techniques that render the signal imperceptible has received significant attention. Embedding an imperceptible, cryptographically secure signal, or watermark, is seen as a potential mechanism that may be used to prove ownership or detect tampering. While there has been a considerable amount of attention devoted t...

In this paper, a constant total system’s allocated bandwidth hybrid direct-sequence/fast frequency hopping code-division multiple-access (DS/FFH-CDMA) cellular system, when operating in a Rayleigh fading environment, is examined. The described analysis leads to a novel-closed form expression for the probability density function (pdf) of the channel capacity per user, which relates the pdf of th...

Spectral shaping is one of the primary technical challenges in spectrally constrained multiple access applications. In this paper, we introduce an efficient orthogonal CDMA-based spectral shaping technique. In our approach, termed CodeHopping CDMA, users are allowed to hop between available spreading codes in an orthogonal fashion with different frequencies. We show that code hoping patterns ca...

In dynamically changing environments, the spectrum-sharing method is a promising method to address the spectrum underutilization problem for cognitive radio (CR) systems. This paper investigates the capacity of cognitive radio multiple-access channel (CR-MAC) over a dynamic fading environment. Multiple secondary users (SUs) transmit to the secondary base station under the transmit power (TP) an...

The spectral efficiency of a multicarrier direct-sequence code-division multiple-access (MC/DS-CDMA) cellular system operating in a mobile radio environment with Rayleigh fading, is investigated. In this work, spectral efficiency is evaluated in terms of channel capacity (in the Shannon sense) per user, estimated in an average sense. It is analytically shown that, under normalized conditions an...

The increase data size transmitted in digital communication systems necessitates the use of high-capacity channels for transmission these data. To channel capacity, MIMO are widely used. Antenna selection is very important efficient sources. Cognitive Radio generally aim to spectrum efficiency by using systems. Therefore, must find empty regions with detection methods. Spectrum performance rela...

This paper presents a new spread-spectrum watermarking algorithm for digital images in discrete wavelet transform (DWT) domain. The algorithm is applied for embedding watermarks like patient identification /source identification or doctors signature in binary image format into host digital radiological image for potential telemedicine applications. Performance of the algorithm is analysed by va...

The problem of communication among nodes in an extended network is considered, where radio power decay and interference are limiting factors. It has been shown previously that, with simple multi-hopping, the achievable total communication rate in such a network is at most Θ( √ N). In this work, we study the benefit of node cooperation in conjunction with multi-hopping on the network capacity. W...

The optimization between the processing gain and the theoretically achievable average channel capacity per user (in the Shannon sense) of a constant total system's allocated bandwidth hybrid direct sequence/fast frequency hopping codedivision multiple-access (DS/FFH-CDMA) cellular system, when operating in a Rayleigh fading environment, is presented. ... Pagination p 902-910 Subject Engineering...