21-05-2012, 12:22 PM
Real Time Implementation of Binary Phase Shift Keying Using DSP Processor
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INTRODUCTION
In the scenario of high bit rate digital communication systems the major impartment are higher capacity, security, error rate ,BPSK provides a solution for this it helps in transmitting higher data rates provides less room for errors and more secure.
Introduction
Binary Phase Shift Keying (BPSK) is a digital modulation technique and the simplest form of PSK . It uses two phases which are separated by 180° and so can also be termed 2-PSK. Because there are two possible wave phases, BPSK is sometimes called bi phase modulation. It is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave). Any digital modulation scheme uses a finite number of distinct signals to represent digital data. In the case of PSK, a finite number of phases are used. Each of these phases is assigned a unique pattern of binary bits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. The demodulator, which is designed specifically for the symbol-set used by the modulator, determines the phase of the received signal and maps it back to the symbol it represents, thus recovering the original data.
A convenient way to represent PSK schemes is using a constellation diagram. This shows the points in the Argand plane where, in this context, the real and imaginary axes are termed the in-phase and quadrature axes respectively due to their 90° separation. Such a representation on perpendicular axes lends itself to straightforward implementation. The amplitude of each point along the in-phase axis is used to modulate a cosine (or sine) wave and the amplitude along the quadrature axis to modulate a sine (or cosine) wave.
In PSK, the constellation points chosen are usually positioned with uniform angular spacing around a circle. This gives maximum phase-separation between adjacent points and thus the best immunity to corruption. They are positioned on a circle so that they can all be transmitted with the same energy. In this way, the moduli of the complex numbers they represent will be the same and thus so will the amplitudes needed for the cosine and sine waves.
Two common examples are binary phase-shift keying (BPSK) which uses two phases, and quadrature phase-shift keying (QPSK) which uses four phases, although any number of phases may be used. Since the data to be conveyed are usually binary, the PSK scheme is usually designed with the number of constellation points being a power of 2.
Quadature
Among the advantages of BPSK are superior noise and interference rejection, enhanced immunity to signal fading, and reduced susceptibility to nonlinearities in the transmission and receiving systems.
What is Analog And Digital
In analog technology, a wave is recorded or used in its original form. So, for example, in an analog tape recorder, a signal is taken straight from the microphone and laid onto tape. The wave from the microphone is an analog wave, and therefore the wave on the tape is analog as well. That wave on the tape can be read, amplified and sent to a speaker to produce the sound.
In digital technology, the analog wave is sampled at some interval, and then turned into numbers that are stored in the digital device. On a CD, the sampling rate is 44,000 samples per second. So on a CD, there are 44,000 numbers stored per second of music. To hear the music, the numbers are turned into a voltage wave that approximates the original wave.
Differences between Analog and Digital
Even though modern information technologies are based on digital representations of data, many natural forms of representing information are analog. Strictly speaking, the terms "analog" and "digital" fit more comfortably in the discourse of signal processing--the realm of communications technologies. Considering these concepts in the context of how information may be represented in general, however, is useful. Analog representations are continuous over some dimension, such as time. Sound provides a good example for how information may be represented in analog form. Sounds are rapid vibrations that are transmitted as variations in air pressure. If you were to measure the intensity of a pure tone, for instance, it would be plotted as a continuously undulating line or wave, like the one depicted in Figure 1.2 . Its amplitude or intensity would vary smoothly and continuously over time.