Browsing by Author "Said, Karim A."
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- Physical-Layer Security in Power-Domain NOMA Based on Different Chaotic MapsAbu Al-Atta, Mariam; Said, Karim A.; Mohamed, Mohamed A.; Raslan, Walid (MDPI, 2023-01-10)Nonorthogonal multiple access (NOMA) is a relevant technology for realizing the primary goals of next-generation wireless networks, such as high connectivity and stability. Because a rising number of users are becoming connected, user data security has become a critical issue. Many chaotic communication systems have been established to address this important issue via exhibition of affordable physical-layer-security solutions. In this study, we propose a chaotic downlink NOMA (C-DL-NOMA) system over the additive white Gaussian noise and Rayleigh-fading channels to enhance the security of the DL-NOMA system. The proposed algorithm is based on a coherent analog modulation technique that combines various chaotic maps for chaotic masking of encrypted data. On the transmitter, chaotic encryption was used for transmitted data with fixed power-allocation-level control, whereas on the receiver, successive interference-cancellation demodulation was utilized to detect multiple users, after which chaotic decryption was performed. Simulation results were evaluated based on security analyses, such as statistical analysis (histogram and correlation analyses and information entropy), bit-error-rate performance, and achievable-data-rate performance. According to these security analyses and numerical results, the proposed C-DL-NOMA system outperformed traditional unencrypted NOMA systems.
- PicoRF: A PC-based SDR Platform using a High Performance PCIe Plug-in Card ExtensionSaid, Karim A. (Virginia Tech, 2012-06-22)Wireless communication serves as the foundation for a wide range of services that have become an integral part of human life in this day and age. Driven by the desire to have a single piece of hardware that can provide multiple wireless services, attention has been directed to SDRs due to their programmable nature and the flexibility they can offer in operating over multiple standards. In addition, they can provide effective solutions to current challenges in wireless communication, such as spectrum overcrowding and inter-standard operability, as well as future challenges to come due to their upgradeability. Although SDRs have been around in the research community for over a decade, they have not reached the point of transitioning to the mass consumer market, size being one of the major obstacles. Numerous SDR hardware platforms have been developed demonstrating successful functionality, yet to this day most of them remain trapped in desktop/benchtop form factors which are not suited for mobility. A main factor contributing to the size of SDR units is the RF front end. Using current technology, wide-band operation of SDR RF front-ends is achieved by aggregating multiple dedicated components, each covering a portion of the frequency range. Recent technology advances have enabled the integration of wide frequency functionality inside a single integrated package. One example is a prototype RFIC transceiver chip from Motorola Research Labs which contains a complete direct conversion RF transceiver in a single chip, with a frequency coverage range of 100MHz-2.4GHz. RFIC5, the latest version of the chip, has additionally integrated high speed ADC and DAC units, leading to a significant reduction in the component count and the overall size of the SDR hardware. This thesis describes the implementation of a highly compact, SDR PC plug-in card, known as PicoRF. PicoRF is based on the Motorola's RFIC chip for the RF front-end functionality, while the combined computational power of a V5 FPGA and a PC host is used for waveform signal processing. An overlay gird consisting of an interconnection of PR slots is reserved on the FPGA to host the components of a signal processing pipeline which can be modified during run-time. Through a high speed PCIe connection, partial bitstreams can be downloaded from the host PC to the FPGA at a very high speed making it possible for the radio to modify its function in very short time intervals and greatly reducing the service interruption time. Control software running on the PC host manages the overall system operation including the RFIC which is controlled through a custom developed API. The combination of the laptop host and the plug-in card form a small form factor, mobile SDR node that is one step towards satisfying both the performance and ergonomics demand of the consumer market.
- Prolate Spheroidal Sequence Based Transceivers for Time-Frequency Dispersive ChannelsSaid, Karim A. (Virginia Tech, 2017-07-12)Most existing transceivers are Fourier-centric where complex sinusoids play a central role in the internals of the core building blocks. From the channel perspective, complex sinusoids constitute the fundamental effects in the wireless baseband equivalent channel model; exemplified by the time-invariant and time-varying transfer functions in static and time-varying channel conditions respectively. In addition, complex sinusoids are used as signaling waveforms for data transmission through the channel. The dominant mode of transmission in modern communications is in the form of finite time duration blocks having approximately finite bandwidth. As a result, the time-frequency space becomes projected to a time-frequency subspace having essentially limited support where complex sinusoids suffer from leakage effects due to the finite time extent of a block. In addition, Kronecker delta signals (duals of complex sinusoids) suffer from the same vulnerability due to the finite extent bandwidth. Gabor signaling bases using non-rectangular pulse shapes can attain good confinement in the time-frequency space, however, at the expense of completeness which reduces the utilization efficiency of the time-frequency signaling resources. Over a signaling block period, a doubly dispersive (DD) channel is projected onto an essentially limited time-frequency subspace. In this subspace, the Discrete Prolate Spheroidal (DPS) basis matched to the channel parameters is known to be optimally compact in representing the channel using a basis expansion decomposition. Unlike the Discrete Fourier Transform (DFT) basis which lacks compactness due to the leakage effect. Leakage in the expansion coefficients of a particular channel using the DFT basis has a direct correspondence with the Inter-Symbol Interference (ISI) between the DFT signaling components when transmitted through the same channel. For the DPS basis, however, the correspondence is not as obvious. Nevertheless, DPS when used for signaling results in ISI compactness in the form of an exponential decay of distant ISI components. The efficacy of DPS signaling in DD channels in addition to its efficiency in modeling DD channels motivates the investigation of a new transceiver baseband architecture where DFT is supplanted by DPS.