Comparison of RZ and NRZ Modulation Techniques by Varying Duty Cycle and Mach Zehnder Modulator

The aim of the research being undertaken is to examine the performance of advanced modulation formats such as RD and NRZ modulation schemes and their long-haul repeater-free fibre-traffic (SMF). Modular transmission of signals by SMF has been highly attracted by several benefits, such as high chromatic dispersion tolerance (CD), simplicity of deployment and higher spectrum efficiencies. These are the essential performance indicators of an optimal modulation technique for the creation of multiplexed (DWDM) transmission networks of the future generation of dense wavelengths. Based on a comparison of the two modulation approaches I give my findings. To mimic both modulation schemes, OptiSystem software is employed. Eye diagram with measurement of the Q factor and BER is generated. Keywords: Return to Zero, Non-Return to Zero, Eye Diagram, Bandwidth, BER, Q factor.

Study of Modulation Schemes over a Multipath Fading Channels

Communications systems concerted over wireless channels depend on the environment. Communications system can be more reliable and efficient by properly analyzing wireless channels. Today's most important features are a high data rate and reliable performance to exploiting viable networks during this new information age. The channel is not time-invariant in wireless communication, so the received signal exhibits amplitude, phase, and angle variations due to multipath fading. Increasing data rates and reducing bandwidth make Orthogonal Frequency Division Multiplexing (OFDM) an important component of wireless communication systems. The OFDM technique uses many carriers very efficiently. With this scheme, interference is robustly reduced, and fading scenarios are easily accommodated. Analyzing digital modulation schemes requires evaluating link performance with fading channels. The paper compares channel performance over varying fading environments using a variety of modulation schemes. We study the BER and SNR properties of the AWGN, Rician fading and Rayleigh fading channels modulated with BPSK, QPSK, and M-ary QAM.

M-ary quadrature amplitude modulation order optimization for terahertz wireless communications over dispersive channels

Highly accurate atmospheric models, based on molecular resonance information contained within the HITRAN database, were used to simulate the propagation of high capacity single-carrier quadrature amplitude modulated signals through the atmosphere for various modulation orders. For high-bandwidth signals such as those considered in this work, group velocity dispersion caused by atmospheric gases distorts the modulated waveform, which may produce bit errors. This leads to stricter Signal-To-Noise Ratio requirements for error-free operation, and this effect is more pronounced in high-order modulation schemes. At the same time, high-order modulation schemes are more spectrally efficient, which reduces the bandwidth required to maintain a given data rate, and thus reduces the total group velocity dispersion in the link, resulting in less distortion and better performance. Our work with M-ary quadrature amplitude modulated signals shows that optimal selection of modulation order can minimize these conflicting effects, resulting in decreased error rate, and reducing the performance requirements placed on any equalizers, other dispersion-compensating technologies, or signal processing hardware.

A Literature Survey on Algorithms and Hardware Architectures of Max-Log-MAP Demapping

Emergent wireless communication standards, which are employed in different transmission environments, support various modulation schemes. High-order constellations are targeted to achieve high bandwidth efficiency. However, the complexity of the symbol-by-symbol Maximum A Posteriori (MAP) algorithm increases dramatically for these high-order modulation schemes. In order to reduce the hardware complexity, the suboptimal Max-Log-MAP, which is the direct transformation of the MAP algorithm into logarithmic domain, is alternatively implemented. In the literature, a great deal of research effort has been invested into Max-Log-MAP demapping. Several simplifications are presented to meet with specific constellations. In addition, the hardware implementations dedicated for Max-Log-MAP demapping vary greatly in terms of design choices, supported flexibility and performance criteria, making them a challenge to compare. This paper explores the published Max-Log-MAP algorithm simplifications and existing hardware demapper designs and presents an extensive review of the current literature. In-depth comparisons are drawn amongst the designs and different key performance characteristics are described, namely, achieved throughput, hardware resource requirements and flexibility. This survey should facilitate fair comparisons of future designs, as well as opportunities for improving the design of Max-Log-MAP demappers.