Binary Digital Transmission

The code can be binary, consisting of only zeroes and ones, as summarized by Fig. 19.6. In other words, 5 could be represented by two pulses separated by a space. If the pulses are only 4.99 volts high instead of 5.00 volts, it causes no error. In fact, they can be 4.1 volts or 5.9 volts, still without causing error. Also, it is unlikely that natural lightning, etc., would generate groups of pulses that looked like these. 

Digital electronics can be billions of times more accurate than analog. Therefore, billions of operations can be done with essentially no error. Also, various operations can be done with digital coding such as parity checks, which further reduce errors. The main advantage of digital technology is accuracy 

A disadvantage of digital technology is that it requires equipment of great complexity. A digital radio receiver can not be made with just a loose coil and a diode. In fact, it requires hundreds of transistors. 

Because of the almost perfect accuracy, enormous amounts of digitally modulated information can be stored in small spaces. This is not because it is more efficient than analog methods — it is actually less efficient, in that it requires more operations to store the same amount of music, text, etc. However, the combination of photonic (Chapter 22) and integrated circuit (Chapter 23) technologies has allowed the inexpensive use of complexity crammed into small spaces, so using many operations to store or transmit data is no longer expensive. Some of the triumphs of these developments are apparent in Table 19.2. 

Low Frequency Radio Freq. Very High Freq. Ultra-High F. 20 Hz to 20 kHz 54 to 216 MHz 

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Just a few years ago, the so-called C3 laser (cleaved-coupled-cavity) appeared, wherein the alignment of two conventional semiconductor lasers yields a beam of exceptional purity that enables communication systems to send signals at rates as great as billions of bits, or binary digits per second. Just as recently as the late 1980s, commercial lightwave systems were limited to somewhat less than 2 million bits per second, but nevertheless a rate that permits the transmission of 24,000 simultaneous telephone calls on a single pair of fibers. 

The alternative is a digital transmission scheme. An analogue signal is sampled, a process that changes a continuous signal into a discrete one. The magnitude of each sample is converted into a binary code—a series of ones and zeros— and transmitted down the line. It is possible to apply error-checking... 

Lender, A. 1966. Correlative level encoding for binary data transmission. IEEE Spectrum (Feb.) 104-115. Proakis, J. G. 2001. Digital Communications, 4th ed. McGraw-Hill, New York. 

The value of the dynamic variable is represented as some encoding of the binary levels. Information in a digitally encoded system can be transmitted through the control loop by two methods the parallel transmission mode and the serial transmission mode. In the former method a separate wire is required for each binary digit in the word, whereas in the latter method a time sequence of pulses over a single wire transmits the whole word. 

A 10-bit digital system uses the sequence 180, 90, 45, 22.5, etc., to transmit the azimuth value. What is the accuracy of the transmission Give the binary numbers for S-23-E by excess, default and nearest. 

The qualifications tests consists of checking the transmission of the one-bit binary information sent by the controller to the contactors, relays, electrovalves, pilot lights, and other digital outputs of the system. 

In the serial mode, the digital word (number) is sent to the computer one bit at a time. Now a binary counter provides a parallel output since each of the output bits has its own data output channel and the value of each output bit is simultaneously available. To use a serial transmission scheme, this parallel output must be put into serial form. One way to accomplish this is to use a Universal Asynchronous Receiver Transmitter (UART). The detailed operation of the UART will not be given here as it is not germane to the subject of this book. It is sufficient to say that the heart of the UART is a shift register and the shift register is strobed by a signal from the computer that displaces the binary number, bit by bit, sequentially from the register to the computer. 

Fig. 3. DISl feature extraction. (A) Unprocessed 8-bit image of a petri dish with colonies of Rhodobacter capsulatus imaged in a transmission mode. (B) Image after digital processing to yield a binary (black and white) image that can be extracted by an automated routine to yield 210 different features. A comparison of (A) and (B) shows that the operator has erased certain groups of colonies that are not separable into individual features. In other cases, colonies that were overlapping in the unprocessed image have been manually separated by a tool provided in the user interface.

Transmission of 8-bit data in wireless EIT (a) RF Tx/Rx module and (b) schematic of the binary adder circuit. (From Bera T. K. and Nagaraju J., Switching of a sixteen electrode array for wireless EIT system using a RF-based 8-bit digital data transmission technique, ObCom 2011, Part I, CCIS 269, pp. 202-211, 2012. With permission.)... 

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