Wireless Technology Basics, Signals, Modulation Types, and Access Technologies by Lawrence Harte

Author:Lawrence Harte [Harte, Lawrence]
Language: eng
Format: azw3
Publisher: UNKNOWN
Published: 2017-03-22T04:00:00+00:00

Figure 1.14, Audio Signal Filtering

Digital Signal Processing

Digital signal processing is the manipulation of digital signals into other forms using computing circuits or systems. Digital signal processors use software programs to allow them to perform complex signal processing operations such as filtering, modulation, data compression, and shaping of the information (such as digital audio signal) that are represented by digital signals.

When analog signals are converted to digital format, the digital signals represent the original analog waveform. Just like analog signals that may be processed by filters, shaping circuits, combiners and amplifiers, digital signals can be processed to produce similar functions. To change a digital signal, a microprocessor is used to manipulate the incoming digital information via a program (stored instructions) that produces a new digital output. The program determines the functions that are performed in the digital signal.

Because radio signals can experience signal distortion that can result in the incorrect determination of a digital signal (whether a zero or one had been sent), digital systems typically include error detection and correction processing. Error detection processing involves the creation of additional bits that are sent with the original data. The check bits are created by using a formula calculation on the digital signal prior to sending the data signals. After the digital signal is received, the formula can be used again to create check bits from the received digital signal. If the check bits match, the original digital signal was received correctly. If the check bits of the received data signal do not match the calculated results, this indicates that some or the entire digital signal was received in error. This process is called error detection.

Some digital systems use sophisticated mathematical formulas to create the check bits so that the check bits can be used to make corrections (or predictions of the correct bits) to the received digital signal. This process is called error correction.

Early communication systems contained one or more microprocessors along with all other integrated circuits (such as memory and interface circuits) to perform digital signal processing. To reduce the number of components in a digital radio, digital signal processors (DSPs) and custom application specific integrated circuits (ASIC) are typically used. DSPs and ASICs are specialized integrated circuits that combine many electronic circuits and sometimes even contain the programs that process digital signals.

Figure 1.15 shows typical digital signal processor that is used in a digital communication system. This diagram shows that a DSP contains a signal input and output lines, a microprocessor assembly, interrupt lines from assemblies that may require processing, and software program instructions. This diagram shows that this DSP has 3 software programs, digital signal compression, channel coding, and modulation coding. The digital signal compression software analyzes the digital audio signal and compresses the information to a lower data transmission rate. The channel coding adds con

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