KR20010035801A - Equalizing system in OFDM - Google Patents

Abstract

PURPOSE: An equalization system of OFDM(Orthogonal Frequency Division Modulation) is provided to use a signal strong to a channel distortion as a training sequence, and to use equalizers in a time area and a frequency area, then to insert the training sequence into a protection section of a time area equalizer. Therefore, a capacity of a frequency area equalizer is supplemented by using linear equalizers every frame. CONSTITUTION: Training sequence-removed parallel signals are applied to an FFT(Fast Fourier Transform)(64) to be processed FFT, and applied to a divider(66). The divider(66) divides the parallel signals into an I(In-phase) signal and a Q(Quadrature) signal. The divided I signal and the Q signal are inputted in linear equalizers(68). The linear equalizers(68) are installed as many as the parallel signals. Each linear equalizer(68) comprises as follows. A training sequence generator(205) generates a training sequence. A subtracter(207) subtracts the training sequence and an output of an amplitude varying device(201). A controller(203) controls an amplitude of the amplitude varying device(201) according to an output of the subtracter(207). Each linear equalizer(68) is composed of the first filter and the second filter. The first filter is connected to an output of the divider(66) forward. The second filter is connected to an output of the first filter, reversely. Each signal passing the linear equalizers(68) is converted in serial via a P/S(Parallel to Serial) converter(72). A signal processor(74) processes the signals.

Description

Equalizing system in OFDM

As a method of transmitting signals in a parallel manner, a method of transmitting signals by dividing a frequency band of the entire signal into N sub-frequency channels that do not overlap each other has been used. However, this approach is inefficient in the use of frequency bands. In order to effectively use the frequency band, a newly proposed method is overlapping multicarrier modulation. In the overlapping multicarrier modulation method, orthogonality must be maintained between subcarriers in order to prevent interference between subcarriers. One of the most effective of these multicarrier transmission schemes is OFDM (orthogonal frequency division modulation).

The OFDM method divides data into multiple bit strings and modulates the bit strings using multiple carriers. In other words, the OFDM method converts a serial bit string into a parallel bit string and transmits information by using subcarriers having different frequencies, respectively. The longer the interval, the less the influence of the delay time of the channel, and the interference between successive signals can be reduced, which is strong for the multipath channel, the efficiency of the spectrum can be increased, and the high-speed transmission allows the bandwidth efficiency. Therefore, the OFDM scheme is hardly affected by the time delay of the multipath, thus eliminating the need for an equalizer in the time domain, and eliminating interference between signals by inserting a small guard interval.

In general, if there is no inter symbol interference or adjacent channel interference caused by the distortion of the transmission channel, the orthogonality of the subchannels is maintained in the OFDM scheme, and each subchannel is completely separated by the FFT at the receiving end.

However, in the actual situation, since the spectrum of the OFDM signal is not a limited band, the energy of each subchannel spreads to the adjacent channel due to linear distortion such as multipath, which causes adjacent signal interference. In order to solve this problem, there is a method of increasing the number of carriers or the signal period, but its implementation is difficult due to the stability of the carrier, the Doppler shift and the size of the FFT. For this purpose, a guard period is inserted into an OFDM signal. Each OFDM symbol consists of two parts: the actual signal part and the guard interval. In the case of a protective section, the last part of the signal is made by attaching it to the beginning of the signal.

In applying the OFDM scheme, a system according to the OFDM scheme has difficulty in accurately channel estimation for each user in the reverse link. In addition, the OFDM scheme can completely control the interference between symbols on the linear channel, but if there are non-ideal channel characteristics such as selective fading of frequency, the effect of noise is severe and the interference between symbols continues to exist. do. Therefore, when data is transmitted at high speed, signal distortion becomes more severe.

An object of the present invention is to use a signal that is stronger in channel distortion than a conventionally used training sequence as a training sequence and to use a nonlinear equalizer in a frequency domain which is widely used in an OFDM system. Instead, the equalizer is used in the time domain and the frequency domain to efficiently equalize the signal-to-noise ratio by inserting the training sequence into the guard interval in the time domain equalizer and using the linear equalizer every frame to equalize the frequency domain equalizer. The purpose is to supplement the performance of the.

Another object of the present invention is to improve the performance of an OFDM system by using a nonlinear equalizer instead of a conventional linear equalizer in order to improve convergence speed and reduce complexity.

1A and 1B are overall system block diagrams of the present invention.

This object is achieved by receiving means for receiving a signal, a nonlinear equalizer for equalizing the received signal, and a serial-to-parallel converter for parallelizing the nonlinearly equalized signal. An FFT processor, a divider for distributing each FFT processed signal into an in-phase signal and a cross signal, a linear equalizer for equalizing each divided signal, and a linear equalized each And a parallel-to-serial converter for converting the signals in parallel to serial, and a signal processing unit for processing the serially converted signals.

In the present invention, the non-linear equalizer includes a training sequence generator and a switching element stored therein, and when the first training sequence is input, the non-linear equalizer switches the switching element to the training sequence generator, so that the training sequence generator and the internal training sequence generator are first transmitted. And an amplitude variable that inputs the generated training sequence to the amplitude adjusting element so that the deviation between the first transmitted training sequence and the training sequence generated by the training sequence generator is zero.

In the present invention, the linear equalizer is composed of an amplitude variable and a training sequence generator for generating a training sequence, a subtractor for subtracting the output of the training sequence and the amplitude variable, and a controller for controlling the amplitude of the amplitude variable according to the output of the subtractor. A first filter connected forward to the output and a second filter configured in a reverse direction to the output of the first filter in the same configuration as the first filter.

When the OFDM system used in the present invention transmits to remove distortion caused by the channel at the receiving side, the Gold code string is inserted into the guard interval to equalize every frame at the receiving side. To this end, the present invention has a gold code heat generator therein.

Preferred Embodiment

In the signal according to the present invention, a training sequence is transmitted prior to the first transmission of a frame, and then a training sequence is inserted between each frame and the frame. The training sequence transmitted first of the signal input to the antenna 52 of the receiver 5 is corrected by the frequency offset corrector 54 and applied to the nonlinear equalizer 56.

The nonlinear equalizer 56 includes a plurality of delay elements 101a, 101b, 101c,... 101n connected in series, and a plurality of amplitude variable elements 121a, 121b, 121c, connected in parallel for each delay element, respectively. ... 121n), a summer 131 that sums the output of the amplitude variable, and an amplitude adjusting element 141 for adjusting the amplitude of each of the amplitude variable 121a, 121b, 121c,... 121n. And a training sequence generator 141.

When the first transmitted training sequence is input, the nonlinear equalizer 56 switches the switching element 151 to the training sequence generator 161 so that the first transmitted training sequence and the training sequence generated by the training sequence generator 161 are transmitted. Are inputted to the amplitude adjusting element 141, so that the amplitude variable 121a, 121b, 121c,... So that the deviation between the firstly transmitted and applied training sequence and the training sequence generated by the training sequence generator 161 becomes zero. , 121n). Ideally, if the delay element and the amplitude variable is infinite, the deviation can be zero, but in practice, the range of the deviation can be within a certain limit even if not zero by appropriately adjusting the number of delay elements and the amplitude variable.

After reception of the training sequence, the switching element 151 is switched towards the serial-to-parallel converter such that the output of the nonlinear equalizer 56 is applied to the serial-to-parallel converter 58, and the signal thereafter is converted by the training sequence. Equalized in conditioned nonlinear equalizer 56 and then input to serial-to-parallel converter 58.

The serially input signal is converted into a parallel signal across the serial-to-parallel converter 58, and then input to the training sequence remover 62 to become a parallel signal from which the training sequence has been removed.

The parallel signal from which the training sequence is removed is applied to the FFT 64, FFT processed, and then applied to the divider 66. Each parallel signal is again distributed to divider 66 as an in-phase component signal and a cross component signal. Accordingly, the n parallel signals become 2n parallel signals across the divider 66 and are input to the linear equalizer 68, respectively.

The linear equalizer 68 is installed as much as the parallel signal output from the divider 66. The linear equalizer 68 is a training sequence generator 205 for generating an amplitude variable 201 and a training sequence, and a training sequence and amplitude. A subtractor 207 for subtracting the output of the variable 201 and a controller 203 for controlling the amplitude of the amplitude variable 201 in accordance with the output of the subtractor 207 and having a first forward connection to the output of the distributor. The filter and the 2nd filter comprised in the reverse direction to the output of a 1st filter by the same structure as a 1st filter are comprised.

Each signal across the linear equalizer is converted in series across the parallel-to-serial converter 72 and then processed by the signal processor 74.

In the OFDM system, the equalization is faster and more efficient from channel distortion in the OFDM system, and the equalization is efficiently performed in the signal-to-noise ratio, and the training sequence is protected in the time domain equalizer by using the equalizer in the time domain and the frequency domain. The performance of the frequency domain equalizer can be compensated by inserting and equalizing the linear equalizer every frame. In addition, in the case of the frequency domain, a nonlinear equalizer may be used instead of a conventional linear equalizer to improve convergence speed and reduce complexity.

Claims (2)

A receiving means for receiving a signal, a nonlinear equalizer for equalizing the received signal, a series-parallel converter for parallelizing the non-linear equalized signal, and an FFT processor for FFT processing each signal processed in parallel; A divider for distributing each FFT processed signal into an in-phase signal and a cross signal, a linear equalizer for equalizing each divided signal, and a linear equalized signal Equalization system of OFDM including a parallel-to-serial converter for parallel-to-serial conversion and a signal processor for processing the serially converted signal The method of claim 1, The non-linear equalizer includes a training sequence generator, an amplitude variable, and a switching element stored therein, and when the first training sequence is input, the switching element is switched to a training sequence generator so that the first transmitted training sequence and the internal training sequence are transmitted. The equalization system of OFDM which inputs the training sequence generated in the generator to the amplitude variable so that the deviation between the firstly transmitted training sequence and the training sequence generated in the training sequence generator is zero.