CN1490944A - Segmented Demodulation Algorithm for Effectively Reducing Inter-Carrier Interference (ICI) - Google Patents

Abstract

The segmentation demodulation method that efficiently lowers the interference between the subcarrier ( ICI ) belongs to OFDM modulation and demodulation technology field, the feature is: divides OFDM symbol time domain of a N point into several segment, every segment adds zero to N point and makes FFT transformation, then makes frequency domain equilibrium adding. It increases the frequency deviation and expending width of frequency in system tolerance.

Description

A Segmented Demodulation Algorithm for Efficiently Reducing Inter-Carrier Interference (ICI)

technical field

A segmented demodulation method for effectively reducing inter-subcarrier interference (ICI) belongs to the technical field of PFDM system modulation and demodulation.

Background technique

In the next generation of mobile communications, it is required to support higher data rates and faster mobile speeds. OFDM is an effective multi-carrier modulation and demodulation method that can improve spectrum utilization and obtain high-speed transmission rates. It uses an orthogonal multi-carrier transmission mode and regards baseband data as modulated data of each subcarrier in the frequency domain. The baseband data is transformed by IFFT at the sending end, transformed into a time-domain signal and then reaches the receiving end through a wireless transmission channel, and the received time-domain signal is transformed into the frequency domain by FFT to obtain the modulated data on each subcarrier. The transmission speed of the adjustment data on each sub-carrier is not very high, but the multi-carrier transmits data in parallel, which greatly improves the transmission rate of the system, and each sub-carrier is orthogonal, so IFFT and FFT can be simply used to complete the time-frequency conversion. Taken together, OFDM has the advantages of simple system, anti-multipath interference, and high spectrum utilization rate.

However, since OFDM is an orthogonal multi-carrier system, frequency synchronization and frequency stability will become key factors affecting system performance. Under the condition of high-speed mobile wireless transmission channel, the frequency shift and frequency spread are relatively large. For the OFDM multi-carrier modulation mode, inter-carrier interference (ICI) will have a great impact on system performance. In a mobile environment, frequency offset and spectrum broadening are generated due to the Doppler effect, which causes mutual interference between subcarriers. If in a quasi-static environment, the channel within an OFDM symbol remains unchanged, there will be no inter-subcarrier interference; however, in the fast moving channel of the OFDM modulation system, the channel will change rapidly, which will lead to frequency shift and frequency The broadening produces large interference among sub-carriers, resulting in system performance degradation.

For a long time, how to combat the inter-subcarrier interference of the OFDM system in the mobile environment has become a research focus. The simple frequency domain equalization algorithm considers the entire OFDM symbol, and the frequency shift and frequency broadening that can be tolerated are relatively small. When the terminal When the moving speed increases, the applicability of these algorithms will be greatly damaged, causing a large number of bit errors and symbol errors in the reception, and the system cannot work normally, which limits the improvement of the mobile speed of the wireless terminal. Especially when the number of subcarriers is relatively large, each subcarrier will be more affected by interference from other subcarriers, and the distortion of frequency domain equalization will also become larger.

Based on such background technology, this patent application proposes a solution to effectively reduce ICI and improve frequency shift and frequency broadening tolerance. It divides a relatively large number of subcarriers in one symbol of the OFDM system into several segments, each segment uses its own midpoint channel characteristic value to perform frequency domain equalization, and then adds the demodulation results of each segment to obtain the overall demodulation result. Experiments have proved that this segmented demodulation algorithm can resist larger frequency offset and frequency extension range under the condition of relatively low signal-to-noise ratio, and reduce inter-subcarrier interference more effectively.

Contents of the invention

The purpose of the present invention is to provide a segmented demodulation method that effectively reduces inter-subcarrier interference (ICI).

The present invention is characterized in that: an N-point OFDM symbol is divided into several sections, and the frequency-domain equalization and addition are carried out after performing N-point FFT transformation respectively. This split is an even split.

Simulation experiments show that it can effectively reduce the interference between system sub-carriers and improve system performance. Compared with the original system without segment demodulation, the frequency offset and frequency broadening that the system can tolerate are increased by a factor proportional to the number of segments.

Description of drawings

Figure 1 Segment demodulation algorithm flow chart

Figure 2 Zero padding operation details

Detailed ways

The overall block diagram of the segmented demodulation algorithm idea is shown in Figure 1. The algorithm can be divided into three parts: segmentation, FFT, and frequency domain equalization. The detailed process of each part is introduced below.

On the basis of obtaining synchronization, first cut an OFDM symbol in the time domain, and the following operations will be completed based on the OFDM symbol. Assume that the OFDM symbol is N points. For the OFDM symbol of this N point, the symbol is equally cut into M parts in the time domain, and the data length of each part is N/M, and the corresponding data point position in the original OFDM symbol is still maintained. , so that the segmentation operation is completed first.

After the time-domain data is segmented, each piece of data should be zero-padded to the total number of points N of the OFDM symbol in the time-domain (attachment 2). When performing zero-filling operations, pay attention to padding the first piece of data with zeros, and the second piece of data Fill zeros for 1~N/M, and zeros for 2*N/M~N, that is to say, don’t just pad the second data with zeros to N points, other data is similarly operated, that is to say, each N/ The position of M-length data in the original OFDM symbol remains unchanged, and other positions are filled with zeros, so that the length of each piece of data becomes N points. After the zero-padding operation is completed, the N-point FFT of each piece of data is transformed into the frequency domain, so that the frequency domain value of the segmented data can be obtained without changing the original data information.

After the data is transformed into the frequency domain, frequency domain equalization will be performed. This step utilizes the results of OFDM channel parameter estimation. After the data is segmented, we take the frequency domain channel estimate corresponding to the midpoint of each segment of data to perform frequency domain equalization of the data in this segment, that is to say, use the value after the FFT transformation of the segment of data to remove the value of the midpoint of the segment. The frequency domain channel estimation value is used to complete the frequency domain equalization, remove the influence of the channel, and restore the original transmission data information of each segment.

After completing the frequency domain equalization of each segment of data, add the frequency domain values of each N point. After this step, the segmented demodulated data can be obtained. This data can be proved to be the OFDM symbol data originally sent.

Using the M-segment segment demodulation method can increase the frequency offset and frequency broadening that the system can tolerate by approximately M times, reduce the interference between system sub-carriers, and effectively improve system performance.

Claims (2)

1. effectively reduce the segmentation demodulation scheme that disturbs (ICI) between subcarrier, it is characterized in that: the OFDM symbol that a N is ordered on average is divided into plurality of sections, carries out the balanced addition in the laggard line frequency of N point FFT conversion territory respectively.

2. disturb the segmentation demodulation method of (ICI) between reduction subcarrier according to claim 1, it is characterized in that: be average and cut apart described cutting apart.

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