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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
tightly coupled multiprocessors a system with multiple processors in which communication between the processors takes place by sharing data in memory that is accessible to all processors in the system. tilt angle the angle by which a surface slants away from the viewer's frontal plane. time constant mathematically, the time required for the exponential component of a transient response (input as the step function) to decay to 37% (1/e) of its initial value, or rise to 63% (1 - 1/e) of its final value, where e is the mathematical constant 2.718281828 . . . . In electronic circuits, the time constant is often related directly to the circuit RC value (i.e., the product of the resistance in ohms and the capacitance in farads) or to its L/R value (i.e., the ratio of the inductance in henrys to its resistance in ohms). See also settling time. In a control system transfer function factor, T is the time constant and is equal to where f is the corner frequency in the bode plot. A closed-loop control system commonly has more than one time constant. time correlation function a function characterizing the similarity of a received signal with respect to a shift in time. See also correlation. time delay a time-current response characteristic, established by national standards, which means that a time-delay fuse is designed to carry five times rated current for 10 seconds before opening. See also envelope delay. time diversity a way to try to obtain uncorrelated received signals to improve the performance of the system by transmitting the signals in different time instants. Interleaving is one way to implement time diversity.
Overview of Cooperative Communications in Wireless Systems
Published in Emad S. Hassan, Security and Data Reliability in Cooperative Wireless Networks, 2018
Time Diversity. Using time diversity the same symbol is transmitted at different time instants provided that the time separation exceeds the coherence time (Tc ) of the channel. This implies that the different transmitted symbols will experience channel realizations that are highly uncorrelated and can be used to obtain diversity. The simplest way to achieve this type of diversity is using a repetition coding scheme. Also, in order to guarantee that the repeated symbols will be transmitted over uncorrelated channel realization, an appropriate interleaver is applied to the stream of symbols to be transmitted. From the diversity gain point of view, the time-diversity system with repetition coding achieves full diversity gain. Nevertheless, the use of repetition coding sacrifices the total bit rate.
Basics on the Theory of Fading Channels and Diversity
Published in Athanasios G. Kanatas, Konstantina S. Nikita, Panagiotis Mathiopoulos, New Directions in Wireless Communications Systems, 2017
Vasileios M. Kapinas, Georgia D. Ntouni, George K. Karagiannidis
Time diversity exploits the frequency-dispersive nature of time-varying wireless channels to provide more reliable communication. This can be easily accomplished by using multiple time slots separated by at least the coherence time, Tc, of the channel to transmit the same data symbols. Particularly, every symbol is repeated L times and then interleaved before being transmitted over the wireless channel, so that consecutive symbols experience independent fading conditions.* Obviously, this technique can be viewed as repetition coding of the information sequence, with the length L of the code defining the diversity order obtained. However, the achieved gain comes at the expense of spectral efficiency, since a single symbol requires transmission over several time intervals. Furthermore, a repetition code does not effectively exploit all the DoFs available in a fading channel.
Transdermal subcarrier L-PSK or DBPSK optical wireless links with time diversity, skin attenuation and spatial jitter
Published in Journal of Modern Optics, 2020
G. K. Varotsos, H. E. Nistazakis, K. Aidinis, F. Jaber, K. K. Mujeeb Rahman
Diversity which has been thoroughly investigated in the wider free space optical (FSO) area generally refers to the consideration of multiple copies of the propagated signals in an attempt to overcome a poor transmission media state [25–27]. Using spatial or wavelength diversity an OWC system incorporates multiple transmitter and/or receiver apertures, while in time diversity configurations the system needs only a single transmitter–receiver pair provided that the same signal copy is retransmitted at more than one, different time slots. Considering thus that the location within the body is another common challenge for IMDs [3], time diversity seems to outperform spatial and wavelength diversity in terms of compact equipment for installation, deployment and redeployment. Additionally, to the best of the authors’ knowledge only on–off keying (OOK) and more recently in [15], L symbol pulse position modulation (L-PPM) formats have been investigated in the existing TOW literature.