Posts Tagged ‘Basic knowledge’

Multi-carrier Transmission

Multi-carrier transmission

Preview linear and nonlinear distortion. ATDE is very useful but not is perfect, if range of  IBPD (InBand Power Difference – the difference with max and min in power of bandwidth of signal) is too big to ATDE can support, channel is bad to transmitting signal.   FIX: Divide the stream into N streams (rather small), each flow one subcarrier modulation (sub carrier) -> W each small carrier -> the difference is not too large -> ATDE well compensated .   Features – Read more [...]

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ADSL - ADSL 2 - ADSL 2+

ADSL – a member of Digital subscriber line (xDSL) family

Digital subscriber line (xDSL) is a family of technologies that provide internet access by transmitting digital data over the wires based on telephone network. In Viet Nam, ADSL (Asymmetric Digital Subscriber Line) is the most popular technology in xDSL , beside we have many other technologies like VDSL (very-high-bit-rate digital subscriber line), RADSL (rate-adaptive digital subscriber line) .. Almost of them having DSL, however ISDN (Integrated Services Digital Network) is an exception. Now, Read more [...]

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constellation diagram in distortion

Linear and nonlinear distortion

Linear distortion Made by linear elements in a channel (linear elements are when input/output amplitude characteristic is linear). Generically, passive elements (except diode) are linear in low power. In high power and large range, all elements are nonlinear. Cause The filter circuits are imperfect By medium – Wired line: The higher the frequency of consumption growth as much, but not all that gliding strokes, bumpy. – Radio Environment: Fading. Solutions ATDE (Adaptive Time Read more [...]

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Effect of environment with signal

When the signal travels through a medium / environment (wired or wireless),  it will be impacted and be misleading. The main factors affecting to transmission are: Distortion Interference Attenuation On the main factors affecting the electromagnetic waves (used in mobile and copper), in other different systems for example for optical communication systems: Attenuation (most important) Dispersion (second important) Nonlinear phenomena (in high-speed systems and long, we need care) I Read more [...]

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Transmission code/ line code

Transmission code or line code (also called digital baseband modulation, digital baseband transmission). This type of encoding is used to for transmitting digital signal in channel, because: It can change spectrum of baseband signal to better spectrum to transmitting it farther To get clock rate at the receiver. One usually imposes a maximum run length constraint on the generated channel sequence, i.e., the maximum number of consecutive ones or zeros is bounded to a reasonable number. Because Read more [...]

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QPSK constellation diagram

Signal constellation diagram

Signal constellation diagram or constellation diagram  is the diagram used to representation of a signal modulated by a digital modulation (and so Signal Constellation diagrams are used only in digital signal/technical ). It is the diagram with two-dimensional (normal are amplitude and phase) to representation a signal in complex number (with real and image elements) . Constellation diagram can be used to recognize the type of modulation, type of interference effect to signal and distortion in Read more [...]

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Digital modulation with ASK, PSK, FSK

Digital modulation

The first, see compare digital and analog signal and why do we need to modulation. There are some fundamental digital modulation techniques:   ASK (Amplitude Shift Keying): is an amplitude modulation of signal (with a finite number of amplitudes are used) . ASK signal has waveform with a f frequency, each bit in characterized by  a different amplitude of other signals. For example: ASK signal has 100KHz frequency, the signal amplitude = 1 for bit 1 and bit signal amplitude = 0 for Read more [...]

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Frequency Modulation

FM (Frequency Modulation)

The first, you need to see this article to get base of modulation. Like Amplitude modulation, but  frequency modulation conveys information over a carrier wave by varying its instantaneous frequency and amplitude of carrier wave is not changed. It was already known for a long time but little attend, because that does not have any advantages stand out for amplitude modulation. Around 1940, frequency modulation technique is used widely because of detecting anti-interference advantages of it Read more [...]

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Amplitude modulation - AM

AM (Amplitude modulation)

The first, you need to see this article to get base of modulation.   AM is a basic modulation type. Signal after modulated = amplitude of signal + amplitude of a carrier ( a high-frequency wave) Signal add to carrier and make amplitude of carrier vary strength. In the receiver, receiver will get original signal by demodulation processing. This image will show more: The first line is signal, the second is carrier and the third is amplitude modulation signal. We can get Read more [...]

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AWGN (Additive White Gaussian Noise)

AWGN is a channel model used in mathematical and simulation. AWGN introduces a channel very good (in wired line) with only have thermal noise. Wireless line is simulate with other models (Rayleigh, Rice ..) + AWGN because wireless have themal noise, too. If a simulation have not AWGN, It is because AWGN is too small with other models). It have three properties: Additive + White + Gaussian.   Additive Now we consider a circuit of a constant signal source (direct current source Read more [...]

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