Channel estimation for OFDM systems based on comb-type pilot arrangement in frequency selective fading channels

Abstract

In this paper, the channel estimation methods for OFDM systems based on comb-type pilot sub-carrier arrangement are investigated. The channel estimation algorithm based on combtype pilots is divided into pilot signal estimation and channel interpolation. The pilot signal estimation based on LS or MMSE criteria, together with channel interpolation based on piecewise-linear interpolation or piecewise second-order polynomial interpolation is studied. Owing to the MMSE estimate of pilot signals, the inter-carrier interference and additive white Gaussian noise are reduced considerably. The computational complexity of pilot signal estimation based on MMSE criterion can be reduced by using a simplified LMMSE estimator with low-rank approximation using singular value decomposition. Phase compensators before and after interpolation are also presented to combat the phase changes of subchannel symbols arising from the frame synchronization errors. Comparing to the transform-domain processing based channel estimation algorithm, the MMSE estimate of pilot signals together with phase compensated linear interpolation algorithm provides better performance and requires less computations.

Frequency MMSE Equalization Combined with Kalman Channel Estimation in OFDM System

“…The BER and the estimated MSE of linear interpolation algorithm [4] and DFT interpolation method [5] are shown for comparison. Computer simulations are done over 50000 OFDM symbols.…”

OFDM Channel Estimation Enhancement using Null Subcarriers

“…As it has been stated, the cyclic prefix will remove the ISI and ICI, if the size of the CP part is longer than the channel impulse response. Then, the signal will be expressed as [5],…”

“…According to the aforementioned scenarios, OFDM signals may overlap with each other causing intersymbolinterference (ISI) and intercarrier-interference (ICI), therefore, guard interval can be used to mitigate this problem. This guard interval is implemented using cyclic prefix, which has to be longer than the order of the propagation channel as stated in [4][5][6]. Thus, the channel can be supposed to be invariant within the entire interval of the OFDM symbol, then, the orthogonality of the subchannels will be maintained [4].…”

Windowed DFT-Based OFDM Channel Estimation by Adding Virtual Channel Frequency Response

“…With the aid of pilot signals, a preestimated channel frequency response (CFR) can be obtained by the least-squared (LS) method. Based on the pre-estimated CFR, three approaches on channel estimation are proposed, interpolation-based [1,2], discrete Fourier transform (DFT) -based [3][4][5][6][7], and model-based [8,9]. The simplest approach is the interpolation-based method, where the estimated CFR is obtained from directly interpolating the pre-estimated CFR by classical interpolation methods such as piece-wise and cubic interpolations.…”