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LIGHT SOURCES AND MODULATORS
Published in Glenn R. Elion, Herbert A. Elion, Fiber Optics in Communications Systems, 2020
Glenn R. Elion, Herbert A. Elion
Light source encoding alters the information transmission by various techniques to give more efficient transmission per channel. In digital systems minimizing the source bit rate can increase the energy available per transmitted symbol thus lowering the channel BER for a given level of available optical power. In analog transmission source encoding is not used and the signal is modulated by various techniques, including AM, FM, IM, PL and PM. IM analog transmission is the most compatible with existing light sources. Pulse position modulation (PPM) may be used for low bandwidth systems when low dispersion optical fibers are used with light sources capable of high peak power levels at high repetition rates.
Introduction to Data Communications and Networking
Published in Mário Marques da Silva, Cable and Wireless Networks, 2018
As can be seen from Figure 1.3, when the source (e.g., a computer) generates a digital stream of data and the transmission medium is analog, a MODEM (MOdulator and DEModulator) is employed to perform the required conversion. The modulator converts digital data into analog signals, whereas the demodulator (at the receiver) converts analog signals into digital data. An example of an analog transmission medium is radio transmission, whose signals consist of electromagnetic waves (present a continuous variation in time).
Basic Fundamentals, Definitions, and Key Terms
Published in Fred Huffman, Practical IP and Telecom for Broadcast Engineering and Operations, 2013
Analog content in analog transmission channels or baseband signals on wire are susceptible to myriad distortions and interference. Effects of distortion and interference tend to be incremental and linear. Digital content on the other hand is either resistant to, or immune from interference, or when it fails, it deteriorates rapidly giving rise to a characterization called the cliff effect.
Testbed Implementation of a Scalable ARIMA Model for Spectrum Estimation in Cognitive Radio-A Null Hypothesis Approach
Published in IETE Journal of Research, 2021
Debashis Chakraborty, Salil Kumar Sanyal
The basic WARPLAB node architecture is shown in Figure 4. For multiple WARP nodes, connections are accomplished using a host PC running MATLAB and connected to an Ethernet switch. The basic WARPLAB flow is as follows [23]: Matlab creates digital baseband samples to be transmitted wirelessly. The samples from the MATLAB workspace are transferred to transmit buffers located in the WARP nodes. From the MATLAB workspace by sending a trigger signal transmission is initiated between transmitter and receiver nodes. The received samples are initially stored in the sample buffer and then transferred to the host PC for further signal processing according to the algorithms.The role of the transmitter radios is to convert the digital signal into analog and then upconvert for analog transmission. Receiver radio boards perform exactly the reverse job of detection and down-conversion.The user collects the captured baseband samples from the receive buffers in the WARP nodes to the MATLAB workspace and then processed them further to determine the PSD.
Satellite Constellation Concept for a Novel 3D Image Reconstruction of Urban Areas
Published in IETE Journal of Research, 2021
Nissen Lazreg, Omar Ben Bahri, Salem Hassayoun, Abdullah Alhumaidi Alotaibi, Kamel Besbes
The SSTV protocol and AX.25 use an analog transmission with NBFM modulation and GFSK is a digital modulation. The digital protocol can improve the quality of the image compared to analog. However, since GFSK uses a large bandwidth for transmission, GFSK data can often miss analog transmission.