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Research on ICI Cancellation Algorithms in High Frequency OFDM System

Author: XuXingHui
Tutor: HeChen
School: Shanghai Jiaotong University
Course: Communication and Information System
Keywords: Orthogonal Frequency Division Multiplexing Inter-carrier interference Linear time-varying channel Channel frequency domain response matrix Frequency domain linear equalization MMSE Singular Value Decomposition Pretreatment Channel segmentation cascade Radio channel factors
CLC: TN919.3
Type: Master's thesis
Year: 2010
Downloads: 135
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Abstract

Orthogonal Frequency Division Multiplexing (Orthogonal Frequeney Division Multiplexing, OFDM) technology as a multi-carrier modulation (Multi-Carrier Modulation, MCM) technology, widely applied in many fields, the most important advantages compared to the traditional frequency division multiplexing has higher spectrum efficiency. Thanks to the use of the orthogonality between the subcarriers, so that the overlapping of the different sub-carrier signals in the spectrum, but not affect their respective reception. However, this advantage also to the OFDM technology planted a hidden ICI (Inter-Carrier Interference ICI). With the continuous improvement of the communication requirements OFDM system gradually to the number of sub-carriers more, the development of the carrier frequency is higher, moving faster direction. This will result in a sub-carrier spacing narrower, the more serious the degree of ICI. Orthogonality of OFDM system has become very fragile, ICI impact will not be ignored. In this paper under the OFDM system as an object in the high-frequency wireless communication environment, the performance limitations of the hardware complexity of a high-frequency system, around the ICI cancellation algorithm research. Proposed for OFDM systems in doubly selective channel conditions before the channel average order equalizer to suppress the ICI is the most simple, low-complexity equalization algorithms. The algorithm response to the averaging of the various times of the channel within the OFDM symbol, is used to approximate the response of the entire channel, the channel is equivalent to time-invariant channel. The algorithm ignores the time-varying characteristics of the channel, it is not very effective to suppress the ICI. The conventional frequency domain equalization such as FDLE, LS, MMSE algorithm, use of the channel frequency response matrix for all channel information at the receiving end to compensate, could well inhibit ICI, but the complexity. Especially for the large number of subcarriers N, the concrete realization of the hardware requirements will be very high. Using ICI adjacent carrier distribution characteristic of the low complexity of the MMSE algorithm, in doing equilibrium with the ribbon structure to approximate the channel frequency response matrix, to be able to some extent to reduce system complexity. The algorithm by adjusting the width of the ribbon structure factor to achieve a compromise between performance and complexity, the partial channel information is discarded due to the approximation of the channel, and therefore must sacrifice some performance. The derived mathematical modeling based on the basic framework of the OFDM system and formula, proposed a frequency domain linear equalization algorithm based on pretreatment OFDM low complexity. The algorithm first of all based on OFDM symbol inclusive time channel response of the SVD decomposition results, carried out when the variable factor extract, in the receiver by using the variable factor one dimension domain filtering for linear time-variable channel under the entire symbol each time the channel response pretreatment; then extract time-varying factors of time-varying channel with a banded structure to approximate frequency domain response matrix, low complexity frequency domain linear equalizer at the receiving end. And linear time-varying characteristics of the channel, a channel segmentation the cascade (Channel Segmentation-cascade, CSC) lower complexity ICI cancellation algorithm. The algorithm uses the channel segmentation method equivalent linear time-varying channel approximation cascade varying channel too the same channel with no time delay when the receiving end of a one-dimensional domain equalization and frequency domain equalization to suppress the ICI, which avoid the frequency domain channel response matrix calculation and subsequent inversion process, further significant reduction in the complexity of the system. With Matlab tool for simulation of these algorithms, and compare these algorithms output SINR performance. In addition, the simulation results and performance analysis to discuss the band structure width, multipath channel, the correlation coefficient of the channel, the channel power delay spectrum-20dB width and other factors eliminate the ability of the system performance and algorithm ICI. In the last article, prospect research work on next.

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