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SCADA communication
Published in Mini S. Thomas, John D. McDonald, Power System SCADA and Smart Grids, 2017
Mini S. Thomas, John D. McDonald
The data flow between two devices can happen in two ways. In simplex flow, the data flow is only one way, and one device can transmit data to the other device, but the second device can only receive. In duplex flow, both devices can communicate over the link, which again can be done in two ways: half duplex and full duplex. In half duplex, both devices can communicate and receive, but not at the same time. A device can start communication using the whole channel, and the other device will receive and will start communication after the channel is free. In full duplex, both devices can transmit and receive at the same time. This can be done by having two dedicated channels between the devices, one for sending and another for receiving. Full duplex can also be achieved by dividing the channel capacity in two by suitable methods.
Bidirectional Transmission and an Extension of Network Utility Maximization Model
Published in Liansheng Tan, Resource Allocation and Performance Optimization in Communication Networks and the Internet, 2017
In a half-duplex system, both devices can transmit data between each other, but not simultaneously. There are still two clearly defined paths for bidirectional transmissions, i.e., from Device A to Device B and from Device B to Device A. Different from a full-duplex system, devices in a half-duplex system can either transmit or receive data at a time. A typical example of a half-duplex device is a handheld transceiver having bidirectional radio. The device, also called walkie-talkie, has a “push-to-talk” switch that starts transmission. When the local person wants to speak to the remote one, he pushes the switch. The device turns on the transmitter but turns off the receiver, so the person cannot hear the remote voice. To listen to the remote voice, the switch should be released, which turns on the receiver but turns off the transmitter.
A Brief History of Fiber Optics
Published in David R. Goff, Kimberly Hansen, Michelle K. Stull, Fiber Optic Video Transmission, 2013
David R. Goff, Kimberly Hansen, Michelle K. Stull
Three classes of communications systems exist. The first, simplex transmission, describes the fact that the information gets transmitted in only one direction, i.e., transmitter to receiver. The second, half-duplex transmission, describes a link that can transmit information in either direction, but only one channel at a time. A walkie-talkie is a good example of a half-duplex communication channel. In the third class, full-duplex transmission, both ends of the link contain a transmitter and a receiver, and information travels in both directions over two separate channels. A telephone represents a full-duplex communication channel. With the exception of teleconferencing and distance learning, most video transmission systems use simplex transmission.
Interference Cancellation in Wireless Communications: Past, Present, and Future
Published in IETE Journal of Education, 2022
S. M. Zafaruddin, Pranay Bhardwaj
A half-duplex system limits transmissions in one direction at one time, for example, the push-to-talk (PTT) communications. On the other hand, full-duplex systems with simultaneous transmission and reception of information signals are desirable in many applications. However, this creates self-interference between transmitted and received signals of the same user if uplink and downlink transmissions occur at the same time or frequency. Frequency division duplexing (FDD) uses two different bands for uplink and downlink. Time-division duplexing (TDD) uses different time slots to separate the uplink and downlink traffic. A critical difference between TDD and FDD is the requirement of channel state information (CSI). The CSI refers to the magnitude and phase of a communication channel. The CSI estimated at the receiver using training signals is required for signal detection and for adaptive transmissions. The FDD requires CSI to be estimated both for uplink and downlink due to transmission on two different frequencies whereas TDD needs to obtain the CSI during uplink transmission only and uses it for downlink provided the time difference is small to experience a significant change in thechannel.