Repeater dalam dunia Telekomunikasi

Repeater 

Dalam dunia telekomunikasi, istilah repeater sudah tak asing lagi. Sesuai dengan namanya repeat atau mengulang maka repeater adalah perangkat elektronik yang menerima sinyal dan mengirim ulang itu pada tingkat yang lebih tinggi dan / atau kekuatan yang lebih tinggi, atau ke sisi lain dari suatu halangan, sehingga sinyal bisa menutupi jarak yang lebih jauh.

Berikut merupakan gambar dari repeater

 

di dalam sebuah repeater terdapat 2 buah colokan yang satu dari antena penangkap yang satunya untuk antena penguat. Selain itu repeater membutuhkan power supply yang dihubungkan dengan listrik dari PLN.

The "repeater" Istilah ini berasal dengan telegrafi dan dirujuk ke perangkat elektromekanis yang digunakan untuk meregenerasi sinyal telegraf. Penggunaan istilah terus dalam komunikasi telepon dan data.
Dalam telekomunikasi, repeater istilah memiliki arti standar berikut:
1. Perangkat analog yang menguatkan sinyal input terlepas dari alam (analog atau digital).
2. Perangkat digital yang menguatkan, membentuk ulang, retimes, atau melakukan kombinasi dari salah satu fungsi pada sinyal input digital untuk transmisi ulang.

Karena repeater bekerja dengan sinyal fisik yang sebenarnya, dan jangan mencoba untuk menginterpretasikan data yang dikirim, mereka beroperasi pada lapisan fisik, lapisan pertama dari model OSI.

Kegunaan
Repeater yang sering digunakan dalam kabel komunikasi trans-benua dan kapal selam, karena redaman (sinyal rugi) jarak tersebut akan diterima tanpa mereka. Repeater yang digunakan pada kedua kabel tembaga-kawat yang membawa sinyal-sinyal listrik, dan serat optik membawa cahaya. Repeater digunakan dalam layanan komunikasi radio. Radio repeater sering mengirim dan menerima pada frekuensi yang berbeda. Sebuah subkelompok khusus dari repeater adalah yang digunakan di radio amatir. Repeater juga digunakan secara ekstensif dalam penyiaran, di mana mereka dikenal sebagai penerjemah, penguat atau pemancar relay TV. Ketika memberikan link telekomunikasi point-to-point menggunakan radio di luar saling berhadapan, satu menggunakan repeater di relay radio microwave. Sebuah reflektor, sering di puncak gunung, bahwa relay sinyal tersebut sekitar kendala, disebut repeater pasif atau Passive Lendutan Radio Link. Sebuah repeater microwave dalam komunikasi satelit disebut transponder.
Dalam komunikasi optik repeater istilah digunakan untuk menggambarkan sebuah peralatan yang menerima sinyal optik, mengubah sinyal itu menjadi satu listrik, memperbaharui, dan kemudian mentransmisikan kembali sinyal optik. Karena alat tersebut mengubah sinyal optik menjadi satu listrik, dan kemudian kembali ke sinyal optik, mereka sering dikenal sebagai Optical-Listrik-Optik (OEO) repeater.
Sebelum penemuan elektronik amplifier, mikrofon karbon mekanik digabungkan digunakan sebagai amplifier dalam repeater telepon. Penemuan tabung audion dibuat benua praktis telepon. Pada 1930 repeater tabung vakum menggunakan kumparan hibrida menjadi biasa, memungkinkan penggunaan kawat tipis. Dalam perangkat keuntungan tahun 1950 impedansi negatif yang lebih populer, dan versi transistorized disebut repeater E6 adalah tipe utama akhir yang digunakan dalam Sistem Bell sebelum rendahnya biaya transmisi digital membuat semua repeater voiceband usang. repeater frogging Frekuensi yang biasa di frekuensi-division multiplexing sistem dari tengah untuk abad ke-20 akhir.

Simak

Baca secara fonetik

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Seven Segment

A seven-segment display, or seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays. Seven-segment displays are widely used in digital clocks, electronic meters, and other electronic devices for displaying numerical information.

Concept and visual structure

A seven segment display, as its name indicates, is composed of seven elements. Individually on or off, they can be combined to produce simplified representations of the arabic numerals. Often the seven segments are arranged in an oblique (slanted) arrangement, which aids readability. In most applications, the seven segments are of nearly uniform shape and size (usually elongated hexagons, though trapezoids and rectangles can also be used), though in the case of adding machines, the vertical segments are longer and more oddly shaped at the ends in an effort to further enhance readability.

Each of the numbers 0, 6, 7 and 9 may be represented by two or more different glyphs on seven-segment displays.

  The seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top, middle, and bottom. Additionally, the seventh segment bisects the rectangle horizontally. There are also fourteen-segment displays and sixteen-segment displays (for full alphanumerics); however, these have mostly been replaced by dot-matrix

displays.

The segments of a 7-segment display are referred to by the letters A to G, as shown to the right, where the optional DP decimal point (an "eighth segment") is used for the display of non-integer numbers.

The animation to the left cycles through the common glyphs of the ten decimal numerals and the six hexadecimal "letter digits" (A–F). It is an image sequence of a "LED" display, which is described technology-wise in the following section. Notice the variation between uppercase and lowercase letters for A–F; this is done to obtain a unique, unambiguous shape for each letter (otherwise, a capital D would look identical to an 0 (or less likely O) and a capital B would look identical to an 8).

Seven segments are, effectively, the fewest required to represent each of the ten Hindu-Arabic numerals with a distinct and recognizable glyph. Bloggers have experimented with six-segment and even five-segment displays with such novel shapes as curves, angular blocks and serifs for segments; however, these often require complicated and/or non-uniform shapes and sometimes create unrecognizable glyphs

 

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ADC and DAC

In electronics, a digital-to-analog converter (DAC or D-to-A) is a device that converts a digital (usually binary) code to an analog signal (current, voltage, or electric charge). An analog-to-digital converter (ADC) performs the reverse operation.

Basic ideal operation

A DAC converts an abstract finite-precision number (usually a fixed-point binary number) into a concrete physical quantity (e.g., a voltage or a pressure). In particular, DACs are often used to convert finite-precision time series data to a continually varying physical signal.
A typical DAC converts the abstract numbers into a concrete sequence of impulses that are then processed by a reconstruction filter using some form of interpolation to fill in data between the impulses. Other DAC methods (e.g., methods based on Delta-sigma modulation) produce a pulse-density modulated signal that can then be filtered in a similar way to produce a smoothly varying signal.
By the Nyquist–Shannon sampling theorem, sampled data can be reconstructed perfectly provided that its bandwidth meets certain requirements (e.g., a baseband signal with bandwidth less than the Nyquist frequency). However, even with an ideal reconstruction filter, digital sampling introduces quantization error that makes perfect reconstruction practically impossible. Increasing the digital resolution (i.e., increasing the number of bits used in each sample) or introducing sampling dither can reduce this error.
Depending on how the DAC is configured, the transfer can be unipolar (only positive output values) or bipolar (positive and negative values).

DAC Characteristics:
1. Resolution
2. Offset Error
3. Gain Error
4. Monotonicity
5. Relative Accuracy
Resolution is the number of distinct analog outputs (voltage or current) that can be produced by a DAC.

Resolution = 2ⁿ

Practical operation

Instead of impulses, usually the sequence of numbers update the analogue voltage at uniform sampling intervals.
These numbers are written to the DAC, typically with a clock signal that causes each number to be latched in sequence, at which time the DAC output voltage changes rapidly from the previous value to the value represented by the currently latched number. The effect of this is that the output voltage is held in time at the current value until the next input number is latched resulting in a piecewise constant or 'staircase' shaped output. This is equivalent to a zero-order hold operation and has an effect on the frequency response of the reconstructed signal.
The fact that practical DACs output a sequence of piecewise constant values or rectangular pulses would cause multiple harmonics above the Nyquist frequency. These are typically removed with a low pass filter acting as a reconstruction filter.
However, this filter means that there is an inherent effect of the zero-order hold on the effective frequency response of the DAC resulting in a mild roll-off of gain at the higher frequencies (often a 3.9224 dB loss at the Nyquist frequency) and depending on the filter, phase distortion. Not all DACs have a zero order response however. This high-frequency roll-off is the output characteristic of the DAC, and is not an inherent property of the sampled data.

Some vocabulary
DAC: Digital to Analog converter
D0, D1, D..: Data lines
Analog: Continuous electrical signals
Digital: Method of representing information using "1" and "0" (usually 5v and 0V)
LSB: Least significant bit.
MSB: Most significant bit.

 

 

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Orthogonal Frequency Division Multiplexing

OFDM is a transmission technique that uses several frequencies are mutually perpendicular (orthogonal). This technology is actually already been proposed in about 1950, and the preparation of the basic theories of OFDM has been completed around 1960. In 1966, OFDM has been patented in the U.S. Then in the 1970s, appeared several papers have proposed to apply the DFT (Discrete Fourier Transform) in OFDM, and since 1985, appeared several papers which think about the application of OFDM technology is in wireless communication.Lately this OFDM technology again be the talk of communications experts, this can not be separated from the rapid development of LSI technology. Because prior to LSI technology develops, although theoretically highly promising, but OFDM is considered less applicable because it is too complicated.

The basic principle of OFDMOFDM is a transmission technique with much frequency (multicarrier), using the Discrete Fourier transformation (DFT). The way it works is as follows. Rows of information data to be transmitted is converted into parallel form, so that when the original bit rate is R, then the bit rate in each parallel path is R / M where M is the number of parallel lines (equal to the number of sub-carrier). After that, the modulation performed on each sub-carrier. This modulation may be BPSK, QPSK, QAM or another, but the three techniques are often used in OFDM. Then the signal has been modulated is applied to the Inverse Discrete Fourier Transform (IDFT), for the manufacture of OFDM symbols. Use of this IDFT allows the allocation of frequencies that are perpendicular (orthogonal), on this matter will be explained further. After the OFDM symbols are converted back into serial form, and then the signal sent.




Where Re (.) Is the real part of the equation, f (t) is the response of the filter transmission implus, T is the symbol period, vo is the frequency (carrier frequency) in radians, j is the phase (carrier phase), and bn is data that has been modulated information which becomes the input of the IDFT.




For simplicity, the discussion about the state of the signal when melewai communication line (channel) will be discussed in another section. While at the receiving station, performed the operation opposite to what is done at the sending station. Starting from the conversion from serial to parallel, then parallel signal conversion with Fast Fourier Transform (FFT), after the demodulation, parallel to serial conversion, and finally back into the form of information data....

What is the Orthogonal?The term orthogonal in Orthogonal Frequency Division Multiplexing (OFDM) implies a mathematical relationship between the frequencies being used. With mathematical equations may be expressed as follows, two sets of orthogonal signal when said,



The use of orthogonal frequency in OFDM allows overlap between the frequency without causing interference with each other. There is a set of orthogonal signals, one that quite often we use is the sine signal, as shown in




Excellence
a. Efficient in the use of frequenciesTo clarify the difference OFDM, both in basic operations and in terms of spectrum efficiency, with a single carrier system, and also with conventional multicarrier system, can be seen in picture 3 . From these images can be seen, that OFDM is a kind of multicarrier (FDM), but has a frequency usage efficiency is much better. In OFDM the frequency overlap between adjacent allowed, because each is mutually orthogonal, whereas the conventional multicarrier systems to prevent interference between adjacent frequencies need to tuck the frequency barrier (guard band), where it has the side effect of decreasing the transmission speed when compared to with a single carrier system with the same broad spectrum. So that one characteristic of OFDM is the high level of efficiency in the use of frequencies. In addition to the conventional multicarrier band pass filter is also needed as much as the frequency used, while in OFDM is to use FFT only




b. Facing strong frequency selective fadingAnother main character is robust in the face of OFDM frequency selective fading. By using OFDM technology, despite lines of communication that is used have characteristics frequencyselective fading (where the bandwidth of the channel is narrower than the bandwidth of the transmission so that the resulting weakening of the power received is not uniform at some particular frequency), but each sub-carrier of OFDM system is only experiencing flat fading (weakening the power received in a uniform). Attenuation caused by flat fading is more easily controlled, so that the performance of the system is easy to be upgraded.
OFDM technology can change the frequency selective fading into flat fading, because even though the overall system has a very high-speed transmission that has a wide bandwidth, due to transmission using the subcarriers (carrier frequency) with a number of very much, so the speed of transmission in each subcarrier is very low and bandwidth of each subcarrier is very narrow, narrower than the coherence bandwidth (width than the bandwidth that have relatively similar characteristics). The change of frequency selective fading into flat fading can be illustrated as






c. Not sensitive to signal delayAnother advantage is that, with the low speed of transmission in each subcarrier symbol means the period becomes longer sehinnga system sensitivity to delay spread (the spread of the signals that arrive late) to be relatively reduced.
WeaknessAs a Man-made systems, OFDM technology certainly did not escape from these shortcomings. Among them, a very prominent and has long been a topic of research is the frequency offset and nonlinear distortion (nonlinear distortion).a. Frequency OffsetThis system is very sensitive to carrier frequency offset caused by jitter on the carrier wave (carrier wave) and also to the Doppler effect caused by the movement either by the station sending and receiving stations.b. Nonlinear DistortionTechnology OFDM is a modulation system using multi-frequency and multi-amplitude, so that the system is easily contaminated by the nonlinear distortion that occurs in the transmission power amplifier.c. Signal SynchronizationAt the receiving station, determining the start point to begin operating the Fast Fourier Transform (FFT) when the OFDM signal arrives at the receiving station is a relatively difficult. Or in other words, a synchronization than the OFDM signal is difficult.

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