**System Multiple Input Multiple output
(MIMO)**

System Multiple Input Multiple Output (MIMO) is a system yangerdiri of a number of terminal (antenna) the sender and recipient . Not like system antenna conventionally are highly susceptible to multipath, MIMO systems actually work with very well on the components of multipath. The multipath component is exploited to increase bandwidth diversity and efficiency (bps / Hz).

**MIMO channel modeling **

Effect of character statistics multidimensional of channel fading MIMO ( matrix H) have the role that was very significant to the performance of the system. By because it is , the design mode channel MMO, be a matter that is important . MIMO channel modeling based on the state of the dawn environment , divided into two , namely the physical (Deterministic / geometric) model and the stochastic model.

Deterministic models, ie the model physically involve the parameters of physical knanal in a state of true of all the components of multipath, Seeperti DoA (Directions of Arrivel ) and DoD (Directions of Departure). This modeling applies to the picocell / microcell environment . The model is able to be used as a basis for modeling in stochastic. An example of this modeling is the Codit Model. Model secondly , stochastic means characterized by probability or random , provides modeling in statistics from property property spatial channels on the element element antenna. The model is usually used p there are areas of measurement are spacious . An example of this model is the Metra MIMO model on 3GPP.

Variations track takes the distinct difference between TX to RX as a function of time , location , and frequency (multipath fading) can be represented by the distribution statistics. To focus to the problem Fading this , models of geometric can be transferred to the model of the stochastic.

**MIMO technique**

System MIMO can take advantage of the presence of multipath to create a number of channels equivalent to that as if separated one each other , where the conditions of normal existence of multipath actually detrimental because menimbulkn fading. In the application there are two kinds of techniques MIMO which are used in the system of telecommunication wireless or wireless and mobile , namely :

**Spatial Multiplexing**

Spatial multiplexing techniques transmit different data in parallel and are coded in parallel also for each transmission antenna . Objectives The main use of the techniques of this is to achieve the capacity of the canal BESA r, to break up the flow of data berlaju itnffi into a number of streams in parallel in accordance with the number of antenna transmitters, each respectively with a rate that is much lower than the flow of the original . Stream flow of data is passed to the matrix specifically the function merge combine signals from all streams with a combination of certain of in transmitted through each antenna. This is a multiplex process that takes place in a spatial dimension because each combination of parallel data is shown to one of the transmitter antennas.

Spatial multiplexing can add spectrum efficiency that can add speed trransmisi the data to megestimasi response of the channel in the system is , applied to a channel Umpa behind information on the receiver antenna to the transmitter. With the bait behind this , the transmitter can determine the value of a matrix multiplex optimum to get the capacity of the canal which is the maximum .

**Spatial diversity**

In engineering this , each antenna shippers on the system MIMO transmit the data together in parallel by using cosing are different . The goal is to get the highest possible signal quality by utilizing diversity techniques in the transmitter and receiver.

Diversity is conventionally applied to the installation of the antenna array on the receiver, with Harapa that the quality of the signal that is received can be improved on the system of the antenna in the condition of channel fading with adalanya multipath. The receiver and transmit diversity can be overcome fading and are significant to add a link quality or in other words to increase the SNR.

Improvement of the quality of the signal can be based on the value of the parameter strengthening diversity (diversity gain), which costs more and increases with increasing magnitude of the level of diversity R, ie the number of antennas used on receive. The use of STC (Space Time Coding) at system MIMO with a T antenna transmitter and R antenna Receiver promising increase in the level of diversity into TXR as a picture , with a4 antenna on each individual transmitter and receiver, siste MIMO with STC is expected to able to provide a level of diversity that is equivalent to the conventional method uses 16 antennas on the receiver.

**Orthogonal Frequency Division
Multiplexing (OFDM) System**

OFDM on basically is a scheme of transmitting multi-carrier, which incorporates a technique of modulation by multiplexing. The concept dasara of OFDM is the distribution or dissemination of the transmission of the data via the signal OFDM can be said to consist of a set of narrowband carrier that is transmitted from a source that is equal to the frequency that is different .

Included in each subcarrier mutually orthogonal to one each other. Orthogonality is this which allows the overlapping spectral in between subcarriers, where N spectrum of each of each subcarrier other so not going to happen interference between subcarrier. This is what distinguishes the working principle of OFDM with FDM, where FDM canal distribution is only based on frequency , with given a certain distance between channels (Guard Interval) to prevent interference . From this aspect it is clear that OFDM is more efficient in bandwidth usage compared to FDM.

**Advantages and disadvantages of using
OFDM techniques , **

**K -miss technique OFDM: **

** Efficient in the use of frequency **,
OFDM is one of the types of multicarrier (FDM), but has the efficiency of use
of frequencies that is much more good at . OFDM overlap between the frequency
of the adjacent diperbplehkan , because each individual has been mutually
orthogonal, while the system of multicarrier conventional to prevent
interference between frequencies are contiguous need to tuck frekkuensi barrier
(guard band), in which case it has the effect side in the form of decrease in
the speed of the transmission when compared with the system single carrier with
the same spectrum width . So one Saatu characteristic of OFDM is the high level
of efficiency in the use of frequencies . Besides that the multicarrier
conventionally also necessary band pass filter as the frequency which is used ,
while at the OFDM enough using FFT alone .

** Strong face frequency selective fading,
**Character
principal that another of OFDM is kuata face frequency selective fading. By
using teknoligo OFDM, although the lines of communication are used have
karakteristi frequency selective 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 the same at some frequency specific ), but on a
subcarrier of the system OFDM only experience flat fading ( weakening of the
power received by the same ). Attenuation which is caused by flat fading is
more easily controlled , so that the performance of the system is to be
upgraded .

**Lack of OFDM technique : **

In addition to several advantages , there are some disadvantages of the OFDM system, namely in terms of frequency offset and linear distortion . OFDM systems are very sensitive to carrier frequency offset caused by filters on the carrier wave and also to the Doppler effect caused by movement by both the sending and receiving stations .

Besides that , because of technology OFDM meruopakan a system modulator that uses a multi- frequency and multi- amplitude , so the system is easily contaminated by distortion nonlinear which occurred in the amplifier of power transmission .

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