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Improvement on Inter Carrier Interference (ICI) mitigation techniques for OFDM caused by Doppler effects through minimizing channel estimation error and decreasing channel time varying rate is investigated. The performance of pilot-aided channel estimation techniques depends on pilot placement and arrangement and also on the channel time varying ra...
Contexts in source publication
Context 1
... block diagram of an OFDM system based on pilot-aided channel estimation with Doppler compensation and frequency domain equalizer is given in Fig. 1. The binary information is first mapped into QPSK (quadrature phase shift keying) symbols. The S/P (serial-to-parallel) block will group the symbols and insert pilots with or without guard band into all sub-carriers and the IFFT block will convert them into time- domain OFDM symbols according to the following ...
Context 2
... output of serial-to-parallel process on input block x n with guard interval x g in Fig. 1, i.e., y n is converted by the DAC (digital-to-analog converter) block into continuous- time signal, y(t). The transmitted signal subsequently passes through the time varying Rayleigh faded channel h(t) and additive white Gaussian noise v(t). The received signal is given ...
Citations
... In this paper, an OFDM system with a comb-type pilot arrangement is considered. The reason is that the comb-type pilot arrangement system provides better resistance to fast fading channels, unlike the block-type pilot arrangements [31]. In other words, they satisfy the need for equalizing even as the channel changes from one OFDM block to another. ...
Most existing works on the deterministic pilot design for sparse Channel Estimation (CE) in Orthogonal Frequency Division Multiplexing (OFDM) system are based on the assumption that the pilot symbols are equally-powered. This assumption may not necessarily exhibit low coherence compressed CE. This, therefore, calls for the optimization of pilot symbols and their placement which in the literature is considered as a disjoint optimization problem. In this paper, the joint pilot placement and symbol design optimization problem for sparse CE in OFDM systems is considered based on minimizing the mutual coherence of the Fourier submatrix associated with the pilot subcarriers. In order to avoid the disjoint optimization of the pilot symbol values and their placements, a joint pilot placement and pilot symbol design scheme is proposed that optimizes over both the pilot symbol values and their placements as a single design optimization problem. Simulation results demonstrate that the proposed scheme is effective and offer a better CE performance — in terms of Mean Square Error (MSE) and Bit Error Rate (BER), when compared to former pilot placement schemes that assume the equally powered pilot symbols and other schemes that jointly design the pilot symbols and their placement. It was also observed that the proposed scheme can realize 18.75% improvement in bandwidth efficiency with the same CE performance compared with the least squares (LS) CE.
... In the first system, block-type arrangement of pilots is used with alternating polarity to suppress midpoint channel estimation error, so that the channel influence can be cancelled by the equalizer. The alternating polarity for pilots in block is used because the pilot's side lobe spectra will cancel each other so that the power leakage on other pilots' main lobe spectrum can be minimized and ICI distortion due to orthogonality loss will be reduced [8]. Selection combining is selected because when the equalizer fails to reduce ICI in one OFDM symbol, most of the symbols will be in error and should be replaced with the correct ones from the other branch. ...
In mobile cooperative orthogonal frequency division multiplexing (OFDM) systems with amplify-and-forward (AF) relays, in which the source and relay terminals are moving, Doppler frequency might become very large due to the formation of double-hop channels, possibly causing very large intercarrier interference (ICI). Therefore, ICI mitigation technique capable of reducing the impact of high Doppler frequency is required. This paper reports the study of ICI mitigation technique that uses frequency domain equalizer (FDE) with improvements in three aspects, namely, better channel estimation using cubic-spline approximation, use of selection combining to utilize cooperative diversity in order to suppress ICI, and simple error correcting code with double interleaving to suppress errors due to residual ICI. By using the proposed ICI mitigation technique, error rate performance of mobile cooperative OFDM systems can be improved significantly. Even at high Doppler frequencies, error floors due to residual ICI can be decreased by up to two decades.
Rain attenuation from rain condition in tropical maritime is intruder for high frequency transmission, then attenuation can lead to communication breakdown. Rain rates in tropical signal are very significance fluctuations, these situations should be able to adapt for mobile communication, and one solution is adaptation instrument for rain attenuation in domain spatial and domain temporal. This research is conducted by wireless channel models transmission of WiMAX (Worldwide Interoperability for Microwave Access) transmission. Channel transmission is classified spatially into rural and urban conditions. Data is obtained directly from measurement results raingauge. Accuracy prediction for the mobile adaptation of the cell, assuming rain rate is not stationary, rain can move to anywhere by wind to other cell caused by "heavy attenuation". The results are indexs cell correlation of 0.1315dB/km in urban and 0.1143dB/km in rural.
Abstract
—
Rain attenuation from rain condition in
tropical
maritime is intruder for high frequency transmission, then
attenuation can lead to communication breakdown. Rain rates in
tropical signal are very significance fluctuations, these situations
should be able to adapt for mobile communication, and
one
solution is adaptation instrument for rain attenuation in domain
spatial and domain temporal. This research is conducted by
wireless channel models transmission of WiMAX (Worldwide
Interoperability for Microwave Access) transmission. Channel
transmiss
ion is classified spatially into rural and urban conditions.
Data is obtained directly from measurement results raingauge.
Accuracy prediction for the mobile adaptation of the cell, assuming
rain rate is not stationary, rain can move to anywhere by wind
to
other cell caused by "heavy attenuation". The results are indexs
cell correlation of 0.1315dB/km in urban and 0.1143dB/km in
rural.
Keywords:
WiMAX, chann
e
l, fading.
