Kalman Filter Based Approach of a signal by removing ICI for OFDM Channel
Abstract
This paper deals with the case of a high speed mobile receiver operating in an orthogonal-frequency division multiplexing (OFDM) communication system. The OFDM communication is very much inspired from the channel frequencies over the network. In such network some kind of orthogonal distortion occurs over the channel called Inter carrier Interference. Here we will improve the ICI using Kalman Filtering improved by using repetitive slot and correlated channel tap.
The proposed work of this paper is when data travel over some channel it suffers from the problem of interference. The interference results the high signal to noise ratio as well as high bit error rate.The proposed system will improved the signal by removing the different kind of impurities over the signal. These impurities include the ICI, PAPR and the noise over the signal. The signal will be more effective than standard OFDM. So we needn't many pilot symbols in practice, still can ensure the algorithm performance and reduce the time- delay and complexity of this algorithm.
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Introduction
ORTHOGONAL frequency division multiplexing (OFDM) is an effective technique for high bit-rate transmission. In mobile communications, high speeds of terminals cause Doppler effects that could seriously affect the performance. In such case, dynamic channel estimation is needed, because the radio channel is frequency selective and time-varying, even within one OFDM symbol. It is thus preferable to estimate channel by inserting pilot tones, called comb-type pilots, into each OFDM symbol. Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation MCM) technique which seems to be an attractive candidate for fourth generation (4G) wireless communication systems. OFDM offer high spectral efficiency, immune to the multipath delay, low inter-symbol interference (ISI), immunity to frequency selective fading and high power efficiency. However OFDM system suffers from serious problem of high PAPR. In OFDM system output is superposition of multiple sub-carriers. In this case some instantaneous power output might increase greatly and become far higher than the mean power of system. To transmit signals with such high PAPR, it requires power amplifiers with very high power scope. These kinds of amplifiers are very expensive and have low efficiency-cost. If the peak power is too high, it could be out of the scope of the linear power amplifier. This gives rise to non-linear distortion which changes the superposition of the signal spectrum resulting in performance degradation. If no measure is taken to reduce the high PAPR, MIMO-OFDM system could face serious restriction for practical applications. PAPR can be described by its complementary cumulative distribution function (CCDF). In this probabilistic approach certain schemes have been proposed by researchers. These include clipping, coding and signal scrambling techniques. Under the heading of signal scrambling techniques there are two schemes included.
OFDM represents a different system design approach. It can be thought of as a combination of modulation and multipleaccess schemes that segments a communications channel in such a way that many users can share it. Whereas TDMA segments are according to time and CDMA segments are according to spreading codes, OFDM segments are according to frequency. It is a technique that divides the spectrum into a number of equally spaced tones and carries a portion of a user's information on each tone. A tone can be thought of as a frequency, much in the same way that each key on a piano represents a unique frequency. By allowing the tones to overlap, the overall amount of spectrum required is reduced.
Conclusion
In this project, the performance of OFDM systems in the presence of frequency offset between the transmitter and the receiver has been studied in terms of the Carrier-to-Interference ratio (CIR) and the bit error rate (BER) performance. Intercarrier interference (ICI), which results from the frequency offset, degrades the performance of the OFDM system.
One method is explored in this project for mitigation of the ICI i.e. ICI self-cancellation (SC). By using this method the BER is improved in comparison to simple OFDM system.
In this project, the simulations were performed in an AWGN channel. This model can be easily adapted to a flat-fading channel with perfect channel estimation. Performing simulations to investigate the performance of this ICI cancellation schemes in multipath fading channels without perfect channel information at the receiver can do further work.