Modulation... pulse width modulation

Faced in everyday life with new concepts, many try to find answers to their questions. For this it is necessary to describe any phenomenon. One of these is such a thing as modulation. About it and speech will go further.

General description

Modulation – is the process of varying one or a whole set of parameters of high frequency oscillations in accordance with the law of low-frequency information messages. The result is a spectrum shift control signal to the high-frequency range as the effective broadcasting in space requires that all two-way radio operated on different frequencies, not interrupting each other. Through this process, the information placed on carrier oscillations, a priori known. The control signal contains the transmitted information. High frequency oscillation assumes the role of carrier information, thereby acquires the status of the bearer. In the control signal of the mortgaged transmitted data. There are different types of modulation, depending on the shape of oscillations are used: rectangular, triangular, or any other. When a discrete signal is accepted to speak about manipulation. So, modulation-is a process involving variation and it can be frequency, amplitude, phase etc.

Varieties

It is Now possible to consider what types of this phenomenon exist. In fact, modulation – a process in which a low frequency wave high frequency is transferred. Often uses the following types: frequency, amplitude and phase. When the frequency modulation changes the frequency at the amplitude-amplitude and phase-phase. There are mixed types. Modulation and modification belong to specific types. In this case, the parameters of the high frequency oscillations change discretely.

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Amplitude modulation

In systems with this type of change is a change in the amplitude of the carrier wave with high frequency with the modulating wave. In the analysis of output frequencies are identified not only input frequency, but also their sum and difference. In this case, if modulation – is a complex wave, such as, for example, speech signals consist of multiple frequencies, then the sum and difference frequencies will require two bands, one below the carrier, and the second above. They are called the side: the top and bottom. First – this is a copy of the original audio signal is shifted to a specific frequency. Lower band-this is a copy of the original signal, the last inversion, that is, the original upper frequency – is the lower frequency in the lower side.

The bottom side is a mirror display of the upper side relative to the carrier frequency. A system using amplitude modulation, transmitting the carrier and both side, called two-lane. The carrier contains no useful information, so it can be removed, but in any case, the signal band will be twice the original. Narrowing the strip is achieved by the displacement of not only carrier, but one of the side, as they contain one information. This species is known as single sideband modulation with suppressed carrier.

Demodulation

This process requires you to mix the modulated signal with a carrier of the same frequency that is emitted by the modulator. Then it turns out the original signal in a separate frequency or frequency band, and then filtered from other signals. Sometimes generating carrier for demodulation occurs in place, however, it is not always the same as the carrier frequency for the modulator. Due to the small difference between the frequencies appear mismatched, which is typical for telephone circuits.

Modulation

In this case, a digital modulating signal, that is, it allows to encode more than one bit per baud by encoding a binary data signal into a signal with multiple levels. The bits of the binary signals are sometimes divided into pairs. For a couple of bits you can use four option combinations, each pair is represented by one of four levels of amplitude. This coded signal is characterized in that the modulation speed in bauds is half less than the original data signal, so it can be used for amplitude modulation in the usual way. Its application she found in the radio.

Frequency modulation

System with such a modulation assume that the carrier frequency will change accordingly with the shape of the modulating signal. This kind of amplitude is superior in terms of resistance to certain impacts on the existing telephone network, so it should be used at low speeds where there is no need to attract a large bandwidth.

Phase / amplitude modulation

To increase the number of bits per baud, it is possible to combine phase and amplitude modulation.

As one of the modern methods of amplitude-phase modulation can be called that, which relies on the transmission of multiple carriers. For example, in some application uses 48 carriers separated by a strip 45 Hz. By combiningamplitude and phase modulation for each carrier is allocated to 32 discrete States for each individual period of the pod, so you can carry 5 bits per baud. It turns out that all this set enables the transfer of 240 bits per baud. With a speed of 9600 bit/s modulation rate requires only 40 bps. Such a low figure is quite tolerant of amplitude and phase jumps inherent to the telephone network.

Pulse code modulation

This species is generally considered as a system to broadcast analog signals, for example, the voice in digital form. This technique of modulation used in modems. Here is the Gating of the analog signal at a rate twice the highest frequency component of the signal in the analog form. When using such systems on telephony networks, the Gating occurs 8000 times per second. Each count – the voltage level of the encoded samobytnymi code. To best represent spoken speech encoding is used on a logarithmic law. Seven bits together with the eighth, speaking about the presence of a signal form the octet.

To restore the message signal requires modulation and detection, that is to reverse the process. The signal is converted to a non-linear way. Nonlinear elements enrich the spectrum of the output signal spectrum of new components, and to isolate the low-frequency components filters are used. Modulation and detection can be carried out with the use of vacuum diodes, transistors, semiconductor diodes as nonlinear elements. Traditionally used dot semiconductor diodes, since planar input capacitance is considerably greater.

Modern

Digital modulation provides much greater information capacity and ensures compatibility with various digital data services. In addition with it increased information security, improved communications, and faster access to them.

There are a number of constraints faced by developers of any system: the capacity and width of the frequency band, given the level of noise of communication systems. Every day increases the number of users of communication systems and the growing demand for them, which requires an increase of the radio resource. Digital modulation analog markedly different from that which it conveys large amounts of information.

Complexity

The developers of the systems of digital radio is a main task – to find a compromise between the bandwidth of the broadcast data and the complexity of the system in technical terms. To do this, it is appropriate to use different modulation techniques to get the desired result. Radio communication can be organized when using the basic circuits of the transmitter and receiver, but this will be used when the frequency spectrum is proportional to the number of users. For more complex transmitters and receivers requires less bandwidth for broadcast of information to the same extent. For the transition to the spectral-effective methods of communication to complicate the equipment accordingly. This problem does not depend on the type of communication.

Alternatives

Pulse width modulation is characterized in that its carrier signal represents a sequence of pulses, wherein the pulse frequency is constant. The changes apply only to the duration of each pulse of the modulating signal, respectively.

Pulse width modulation differs from frequency phase. The latter involves the modulation signal in the form of a sine wave. It is characterized by constant amplitude and variable frequency or phase. Pulsed signals can also be modulated by frequency. Maybe the pulse duration is fixed, and the frequency is an average value, but their instantaneous value will change depending on the modulating signals.

Insights

You Can use simple modulation schemes, however, only one parameter will be changed accordingly to the modulating information. A combined modulation scheme that is used in modern equipment for the operation of communication is when there is a simultaneous change, and the amplitude and the phase of the carrier. In modern systems may use multiple carriers, each using a modulation of a certain type. In this case we are talking about the modulation schemes of the signals. Used this term for a complex multi-species when comprehensive information is required additional features description.

In today's communication systems are used in the most efficient modulation types, thereby minimizing the width of the strip to release the frequency space for other types of signals. The quality of communication will only benefit from this, however, the complexity of the equipment in this case is very high. In the end, the frequency modulation produces a result visible to the end user only in terms of the ease of use of technical means.