Essay On Space Time Coding Techniques For MIMO-Ofdm

Now the channel response at all data subcarrier are estimated using pilot subcarriers and are denoted as H ̂_k k= (-N)/2,-,0,-,N/2-1 and the received data can then be equalized

MIMO antenna configuration is requires in spatial multiplexing. In spatial multiplexing the high rate signal is divide into low rate signals and each individual stream is transmitted from different transmit antenna which is having the same frequency channel. Spatial multiplexing is technique which is capable of increasing channel capacity at higher signal to noise

The equation for radiation resistance is given in (1). As can be seen, the greater the radiation resistance, the more energy is radiated or received by the antenna. When the radiation resistance of the antenna matches the resistance of the transmitter or receiver, the system is optimized. Antennas also have ohmic or loss resistance which decreases efficiency. It can be shown that an efficient antenna must be comparable to a wavelength in size.

Multicarrier modulation is a technique of transmitting data over several subchannels instead of transmitting the data over the whole bandwidth in single carrier systems. The data stream to be transmitted is divided into a number of lower data rate data streams. The subchannels have narrow bandwidth compared to wideband channel in single carrier systems and also the symbol period on each subchannel is increased.

Here the signal is broadcasted all over. When it detects the object signal is sent back to the antenna and this way the object is detected. It is same as the person speaks some words in well and echo comes back with the same words. This way signal come back with some information about the object.

Turbo codes being a capacity approach codes are very popular and these codes are also being used for peak to average power ratio reduction. Three turbo coded OFDM systems for peak to average power ratio reduction were proposed where first using m-sequences for peak to average power ratio reduction and short codes for side information, second uses interleaving and third is combination of first two schemes. A tail-biting turbo coded OFDM system is proposed to generate candidates in a selective mapping scheme, without need of side information protection.

ORTHOGONAL FREQUANCY DIVISION MULTIPLEXING techniques allow the transmission of high data rates over broadband radio channels subject to multipath fading without the need for powerful channel equalization. However it is very sensitive to nonlinear effects due to the high PEAK TO AVERAGE POWER RATIO owned by their transmitted signals. Slimane Ben Slimane (2007) proposed an efficient technique for reducing the PEAK TO AVERAGE POWER RATIO of ORTHOGONAL FREQUANCY DIVISION MULTIPLEXING signals. The proposed technique is data-independent that does not require new processing and optimization for each transmitted ORTHOGONAL FREQUANCY DIVISION MULTIPLEXING block. The reduction in PEAK TO AVERAGE POWER RATIO of the ORTHOGONAL FREQUANCY DIVISION

Chin-Liang Wang and Yuan Ouyang ( 2005) introduce a Selected mapping method .The Selected mapping method approach provides good performance for peak to average power ratio reduction reduction, but it requires a bank of Inverse Fast Fourier Transforms to generate a set of candidate transmission signals, and this requirement usually results in high computational complexity. The author suggests low-complexity conversions to replace the Inverse Fast Fourier Transform blocks in the conventional Selected mapping method method. Two novel Selected mapping method schemes were proposed with much lower complexity than the conventional one; the first method uses only one Inverse Fast Fourier Transform block to generate the set of candidate signals, while the second one uses two Inverse Fast Fourier Transform blocks. Computer simulation results show that, as compared to the conventional Selected mapping method scheme, the first proposed approach has slightly worse peak to average power ratio reduction reduction performance and the second proposed one reaches almost the same peak to average power ratio reduction reduction performance. Chin Liang wang continues his investigation by oversampling two times of the Ortogonal Frequancy Division Multiplexing signals by applying peak search and partial interpolation method. The proposed scheme with two times

‘‘If I have seen farther, it is by standing on the shoulders of giants.’’ is very truly coated by Sir Isaac Newton. Ideas gave way to idea. When Marconi invented wireless communication 100 years ago, we had no idea that one day life will seem to be impossible without it. It has penetrated each and every aspect of human life and has resulted into endless demands on bandwidth and spectrum. And by standing on the shoulders of giants, Teletarand Foschinigave the technique of MIMO system which would increase the spectral efficiency of the wireless system to its maximum compared to all the current technologies. Multiple antennas are used for transmission and reception to increases the capacity of the wireless channel.Capacity is expressed as the

In this technique of MIMO system, the signals processing occurs at the transmitter only as the signal processing is restricted at the transmitter therefore it is more beneficial for downlink scenario, because no signals is required at the mobile station. In case of downlink system there is N number of antennas at the receiver with having N number of data stream and each of it is multiplexed and output. There were three techniques used by the MIMO system with antenna processing at the transmitter and having a simple receive structure which is the transient zero forcing scheme, Filter bank method and transmit MMSE. All the interference has been cut by the transmit zero forcing technique whereas the filter bank method is used to minimise the signal to interference ratio in all sub-channels.

The MIMO antenna for wireless communications is required to have a multiple bandwidth to cover the GSM, and ISM bands. On the other hand, it is said that about 70% of the user demands and mobile flow for high-speed data services occur in indoor environments [2-3]. In modern antenna design multiple-input multiple-output are employed so that the multipath effects is taken as advantage to transmit multiple data stream. Designing MIMO antennas have their own challenges such as mutual coupling because of electromagnetic interaction between antenna elements [4-5].

A decade ago, Communication systems haven’t been able to properly exploit the spatial component of mobile radio channel. Communication systems has been facing two main problems. One is using very small amount of energy and second is interference problem i.e., mixing of main signal with signal from other communication links. Here, the solution is eliminating interference and collecting total radiated energy. It may sound simple, but yes it is the solution. The system which can able to do these two works is smart antenna system.

The high-definition TV program is modulated by the time domain OFDM (TDS-OFDM), and then transmitted in the hybrid system to evaluate its performance. We use the mode (64QAM, Multi-carrier, PN420, FEC 0.6, TI 720) [30] for the first-step demo. The system bandwidth is 8 MHz located from 2 MHz to 10 MHz. The point to point system (with one LED lamp on) can still work well with the visible light path

In a single carrier system, single fade causes the whole data stream and undergo distortion i.e frequency selective fading. The Single carrier systems also suffer with heavy Inter Symbol Interference . In telecommunication Inter Symbol Interference was a form of distortion of signal in which one symbol interferes with the subsequent symbol. Thus it causes an unwanted phenomena as the previous symbols have similar effect as noise thus making communication less reliable . ISI occurs when the signal bandwidth is less than the coherence bandwidth or when the delay spread is greater than symbol duration. To combat the problem multicarrier techniques have been proposed for high data rate transmission. Multicarrier techniques divide the whole bandwidth into large number of narrow band orthogonal subcarriers [1, 2]. Thus the signal bandwidth becomes very less compared with coherence bandwidth ensuring no ISI in time domain and flat fading in frequency domain. Multicarrier systems such as Orthogonal Frequency Division Multiplexing (OFDM) and Multi Carrier Code Division Multiple Access (MC-CDMA) were considered to be the best technologies for 4G wireless communication [1, 2]. Fig. explains the spectrum of multicarrier and single carrier systems. In the single carrier system the information symbols are loaded into one of

Antennas – antennas serve as interfaces between transmitted/received signals and transmitters/receivers. Depending on the type, shape, and size of the transmitter antenna, the transmitted signal will have directionality and polarization properties. A receiver antenna is designed to match this directionality and polarization so that the transmitted signal can be received. Earth-facing antennas are usually designed to provide a coverage region with a particular contour shape. Typically, horn antennas and parabolic reflector antennas are used for this purpose. In some satellites, multiple transmit antennas (lens antennas and antenna arrays) are used to generate multiple “spot beams” for higher signal directionality and gain. The coverage region and the spot beams may be fixed or dynamically formed depending on the application. Some advanced experimental