As the evolution of new communication techniques the exchange of data has upgraded. Distinct transmission algorithms and mechanism had up scaled to bring efficient services in wireless communication domain. Today, the aim of researchers is to find and develop advance techniques for allocation of resources, encoding mechanism and design antenna to gain high data through puts with extremely minimal degradation in services. In addition, channel estimation is the major concern when deal with wireless communication. Although, work on channel estimation has done in past. This paper brief the description of efforts in past towards channel estimation by using kalman filtration. For purpose to track the channel the kalman filter acts as a feedback estimator so that the process of estimation is provide to get an estimate. In MIMO-OFDM channel estimation technique the kalman filter s are utilize for its uncomplicated coding and feedback performance.
Transmission based System:
Kalman filters were used as an optimum problem solution in terms of channel diversity estimation process. As mention above the kalman filters have been also efficiently used with Space time block code (STBC). STBC refers as to send multiple copies of a data stream beyond a series of antennas and to exploit the distinct received versions of the data to improve the accuracy of transferred data. For channel estimation a system is proposed that are based on multiple antenna structure i-e multiple input single output (MISO) and multiple input multiple output (MIMO) and the system was grown using a modulation techniques such as BPSK and QPSK in addition with time varying conditions 1. By using cyclic prefix (CP) signal in domain of time and frequency correlation information was proposed. In addition, expectation maximization (EM) under the use of CP based two variations in forward and backward estimation access was suggested. Blind channel estimation for STBC communication was developed and based on second order statistic (SOS) meanwhile the Eigen channel estimation is suggested for STBC coding based on previous coding approach made of rotation or permutation of transmit antennas 2. For OFDM the channel estimation was based on iterative channel estimation that used to enhance the channel estimation with the help of imaginary interface at receiver end.
Channel Designing and Analysis:
The working of channel estimator totally dependent upon the characteristics of channel impulse response estimation in MIMO-OFDM system. Channel impulse response estimation typically an interaction of transmitter or receiver antennas 3. A step towards concatenated wiener filters for the development of channel estimation by enhancing the channel characteristics in time and frequency domain. In distinct mobiles surrounding a wiener filter based approach with basis expansion model (BEM) is defined for cannel estimation in time varying conditions 4. A novel asymmetric extension method was suggested for OFDM system to reduce the Mean squared error (MSE), leakage power and noise of conventional Discreet Fourier Transform (DFT). The estimation of partial frequency response is orderly extended as well as reduced MSE and noise eliminated by applying less power loss 5. By subspace tracking algorithm a channel estimator calculate the long-term features by identifying the invariant space–time modes of the channel. On the other hand, LS techniques are widely used to track the fast-varying fading amplitudes also achieved parallel temporal of the fading process. In 6 a time-varying estimation of MIMO-OFDM channels was presented for high mobility communication systems by means of discrete evolutionary transform. The parametric channel model used, which allows us to obtain the channel and estimate its parameters from the spreading function and also observed that robust against large variations on the channel frequency response, that is, fast fading.
a) Time domain estimation:
In OFDM system in the absence of iterative interference an easy and hypothesize technique based on examination and determination on a low complexity channel estimation was conferred which is suitable for SISO/MISO DTMP system, and endorse the OFDM of time domain synchronization mechanism. The proposed method shows MSE and BER decreased 7.
b) Minimum Error Estimation:
For OFDM algorithm by using LMMSE (fast linear minimum mean square error) gives conveniently channel estimation. The suggested technique not require channel auto correlation matrix in frequency domain and avoids inverse operation using FFT (fast Fourier transform), so that supposed approach minimize computational complexity 8.
Learning Approach to Kalman Filter:
a) Training based Approach
Improvement in channel estimation having low complexity can also achieve for MIMO-OFDM system by using Kalman filters and jack training sequences methods for channel estimation9. A newly developed 1146 (PE) training method for MIMO channel estimation was presented. That supports frequency as well as time selective fading channel. For estimation of channel impulse response length PE widely used. As a consequence the channel variation and Doppler rate becomes scale down 10. Fast linear minimum mean square error is used for two-way relay OFDM networks to channel estimation. The SIC channel response is needed and in time domain coherent detection are estimated. And to reduce the MSE derived an optimal training and also reduced PAPR.