KR100602890B1 - Orthogonal Frequency Division Multiplexing Receiving System Using Adaptive Array Antennas And Method Thereof - Google Patents

Abstract

The present invention relates to an OFDM receiving system using an adaptive array antenna, and an OFDM receiving system using the same, wherein the OFDM receiving system comprises: an adaptive array antenna unit for receiving a radio signal from the outside and outputting an array signal including a corresponding spatial phase; An optimum beam forming unit adapted to adaptively output an array signal output from the adaptive array antenna unit using a specific beamforming coefficient; An OFDM receiver for converting a signal output from the optimum beamformer into a signal in a frequency domain and processing a signal in the converted frequency domain to form a beamforming in a desired direction; A demultiplexer for receiving a signal output from the OFDM receiver and separating a data signal and a pilot signal; A channel estimator for estimating a phase of a signal according to a channel change using a pilot signal separated by the demultiplexer; An error signal generator for comparing the signal obtained by combining the pilot signal separated by the demultiplexer and the phase estimated by the channel estimator and a reference pilot symbol to output an error signal; And a beam forming unit configured to generate the specific beamforming signal to be output to the optimum beam forming unit using the array signal output from the adaptive array antenna unit and the phase estimated by the channel estimating unit to minimize the error signal output from the error signal generating unit, And a beam forming control unit for updating the coefficient. According to the present invention, significant inter-symbol interference and noise due to multi-path fading occurring when data is transmitted at high speed in a wireless channel environment are reduced, and the system is improved in performance. In addition, by placing the FFT transformer at the rear end of the array antenna, computational complexity and hardware complexity are greatly reduced.

Array antenna, channel estimator, convergence rate, beam coefficient optimization, mobile communication system, OFDM reception system, beamforming coefficient, pilot signal, phase estimation

Description

[0001] The present invention relates to an OFDM reception system using an adaptive array antenna and an OFDM reception system using the adaptive array antenna.

1 is a block diagram of an OFDM receiving system using an adaptive array antenna according to an embodiment of the present invention.

2 is a detailed block diagram of the OFDM receiving system of FIG.

3 is a detailed block diagram of the beamforming controller shown in FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to reception of a radio signal used in a high-speed mobile communication system, and more particularly, to an OFDM (Orthogonal Frequency Division Multiplexing) reception system using an adaptive array antenna and a method thereof.

With the advent of the multimedia age in recent years, there is a growing demand for high-speed data transmission for providing various services of high quality to users. However, when data is transmitted at a high speed in a wireless channel environment, serious intersymbol interference occurs due to multipath fading, which makes high-speed data transmission difficult.

In order to overcome this problem, a rake receiver based on a DS-CDMA (Digital Signal-Code Division Multiple Access) system is used in a mobile communication system. With this receiver, the hardware complexity increases rapidly as the inter-chip interference increases during high-speed data transmission.

In order to solve such a problem caused by high-speed data transmission, the transmission scheme proposed recently is the OFDM scheme.

Unlike the scheme having a single carrier, the OFDM scheme converts serial input data into a parallel form, modulates the parallel input data with mutually orthogonal subcarriers of the number of parallel data, and transmits the data .

In this way, when the modulation is performed on the multi-carrier, the overall data transmission rate is kept at the original high speed, and the symbol period in the subchannel including each sub-carrier is increased by the number of sub-carriers.

Therefore, since the transmission time due to the subcarrier becomes much longer than the delay spread due to multipath fading, the frequency selective fading channel is approximated to the frequency non-selective fading channel, and the transmitted data is easily compensated using a simple single tap equalizer at the receiver, can do. Also, the process of modulating / demodulating from a transceiver to a subcarrier can be implemented at a high speed by using IFFT (Inverse Fast Fourier Transform) / FFT.

Since the OFDM scheme has an advantage of overcoming the fading phenomenon by using orthogonal multicarrier, it is used as a transmission scheme in broadcasting fields such as DAB (Digital Audio Broadcasting) and DVB (Digital Video Broadcasting) , And higher-order modulation (64ary QAM, 16ary QAM) can be used to transmit the high-speed data (20Mbps). Therefore, the transmission method for the fourth generation mobile communication system has been actively studied.

In order to apply the OFDM scheme with various advantages to the mobile communication system, various techniques for improving the performance in a poor wireless channel environment are being studied. Recently, an adaptive array antenna has been used to improve the performance of the system Many cases have been published. In case of adaptive array antenna, a signal processing algorithm for controlling the beamformer is needed. That is, techniques for adjusting the coefficients of the adaptive beamformer to form a beam in a desired direction are required. These techniques include a method using a reference signal and a method using a signal characteristic without a reference signal.

First, when the reference signal is transmitted together with the data at the transmitting end, the MSE (Mean Square Error) between the reference signal and the array antenna output signal is obtained. Then, the beamforming coefficient is repeated (Least Mean Square) method, a RSL (Recursive Least Square) method, and the like.

In the LMS method, the error of the reference signal and the received signal is calculated, and the coefficient of the beam former is updated so that the MSE of the error is minimized. The RLS method is a method for calculating the beam former coefficient to compensate for the slow convergence speed of the LMS. This method has a disadvantage in that the convergence speed is fast but the amount of computation and complexity increase greatly as the antenna element increases.

Meanwhile, the method using the characteristics of the signal without using the reference signal uses the characteristics of the transmitted signal without using a separate reference signal, so that the coefficient of the beam former is updated to restore the signal received distorted at the array antenna output to the original signal CMA method, code filtering method, and so on.

The CMA method is a method of restoring a signal using a characteristic having a constant envelope distribution even if the transmitted signal is fading due to fading or an interference signal. The code filtering method uses a signal received at the array antenna And using the processed results.

As an example of an OFDM system using such an array antenna, there is "Adaptive antenna arrays for orthogonal frequency division multiplexing systems with cochannel interference" disclosed in US Pat. No. 5,973,642 to Ye Li et al. A converter is provided for each element of each array antenna and is followed by a parameter estimator for updating the beamforming coefficients, the decoder and the beamforming coefficients. The technique for updating the beamforming coefficients includes a method of updating the received signal and the reference signal The minimum mean square error (MMSE) is used to update the coefficients so that the error is minimized, and the performance of the OFDM system is greatly improved by using DMI. However, Converter, the computational complexity and hardware complexity are greatly increased. There is a problem.

On the other hand, the conventional LMS method has a problem in that it is difficult to apply to a mobile communication system which changes in a simple calculation amount and structure but is relatively slow in convergence speed in which a beam forming coefficient is optimized.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an OFDM receiving system using an adaptive array antenna which is simple in structure and improved in convergence speed while using an LMS beam forming method and a receiving method thereof.

According to an aspect of the present invention, there is provided an OFDM receiving system including:

An adaptive array antenna unit for receiving a wireless signal from the outside and outputting the wireless signal as an array signal including a corresponding spatial phase; An optimum beam forming unit adapted to adaptively output an array signal output from the adaptive array antenna unit using a specific beamforming coefficient; An OFDM receiver for converting a signal output from the optimum beamformer into a signal in a frequency domain and processing a signal in the converted frequency domain to form a beamforming in a desired direction; A demultiplexer for receiving a signal output from the OFDM receiver and separating a data signal and a pilot signal; A channel estimator for estimating a phase of a signal according to a channel change using a pilot signal separated by the demultiplexer; An error signal generator for comparing the signal obtained by combining the pilot signal separated by the demultiplexer and the phase estimated by the channel estimator and a reference pilot symbol to output an error signal; And outputting the error signal to the adaptive array antenna unit and the phase estimated by the channel estimator to minimize the error signal output from the error signal generator, And a beam forming control unit for updating the forming coefficient.

The OFDM receiving system may further include a decoding unit decoding the data signal output from the demultiplexing unit to an original signal, wherein the channel estimating unit is output from the demultiplexing unit using the estimated phase and input to the decoding unit And the distortion of the data signal is compensated.

Further, an OFDM receiving method according to a feature of the present invention is characterized in that,

a) multiplying an array signal including a spatial phase received through the adaptive array antenna by a specific beamforming coefficient for beamforming and outputting the result; b) converting the signal output in step a) into a signal in the frequency domain, separating the signal into a data signal and a pilot signal, and outputting the signal; c) estimating a phase of a signal according to a channel change using the pilot signal separated and output in the step c); d) generating an error signal by comparing a signal obtained by combining the pilot signal separated and output in step b) and a phase estimated in step c) with a specific reference pilot symbol; And e) updating the specific beamforming coefficients used in step a) using an error signal generated in step d), a phase estimated in step c), and an array signal output from the adaptive array antenna .

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an OFDM receiving system using an adaptive array antenna according to an embodiment of the present invention, and FIG. 2 is a detailed block diagram of the OFDM receiving system of FIG.

1 and 2, an OFDM receiving system using an adaptive array antenna according to an embodiment of the present invention includes an array antenna 100, an optimal beamformer 200, an OFDM receiver 300, a demultiplexer 400, A channel estimator 500, a decoder 600, a reference pilot symbol generator 700, an error signal generator 800, and a beamforming controller 900.

The array antenna 100 receives a signal transmitted from the OFDM transmission system and outputs a signal for performing beamforming to the optimum beamformer 200 and the beamforming controller 900.

2, an array antenna 100 receives a signal transmitted from an OFDM transmission system, and outputs a plurality of antennas, which output array signals (V ₀ , V ₁ , ..., V _n ) (100-1, 100-2, ..., 100-n).

The optimum beamformer 200 adaptively adjusts a signal output from the array antenna 100 according to a signal output from the beamforming controller 900 and outputs the adjusted signal to the OFDM receiver 300.

The optimal beam former 200 includes a plurality of antennas provided in the array antenna (100) (100-1, 100-2, ..., 100-n) arranged in the output signal _{(V 0, V 1, ...} , V n ) and a signal output from the beamforming controller 900, that beamforming coefficients _{(W 0, W 2 ...,} W s-1) a plurality of multipliers (200-1, 200-2, which is multiplied by the ..., 200-n) .

The OFDM receiver 300 receives a signal output from the optimal beamformer 200 and outputs a signal to the demultiplexer 400 to adaptively form beamforming in a desired direction.

The OFDM receiver 300 includes a summer 310 for summing and outputting signals output from a plurality of multipliers 200-1, 200-2, ..., 200-n provided in the optimal beamformer 200, A serial-to-parallel converter 320 for converting a signal output from the IFFT unit 310 into a parallel signal and outputting the parallel signal, an FFT 330 for converting a parallel signal output from the S / P converter 320 into a frequency domain signal, And a parallel-to-serial (S / P) converter 340 for converting the signal converted by the serializer 330 into a serial signal and outputting the serial signal to the demultiplexer 400.

The demultiplexer 400 demultiplexes the data signal and the pilot signal by receiving the signal output from the OFDM receiver 300, outputs the data signal to the decoder 600, and outputs the pilot signal to the channel estimator 500 do.

The channel estimator 500 generates a phase estimation value by estimating the phase of a signal caused by the channel change using the pilot signal output from the demultiplexer 400 and outputs the phase estimation value thus generated to the error signal generator 800 And outputs a signal for compensating for the distortion of the data signal transmitted from the demultiplexer 400 to the decoder 600.

The decoder 600 decodes the data signal output from the demultiplexer 400 into an original signal and outputs the decoded data signal.

The reference pilot symbol generator 700 generates a reference pilot symbol and outputs it to the error signal generator 800.

The error signal generator 800 receives a value generated through an operation between a pilot signal output from the demultiplexer 400 and a phase estimation value output from the channel estimator 500 and a reference value generated from a reference pie symbol generator 700, And outputs error signals generated by comparing the pilot symbols to the beamforming controller 900.

The error signal generator 800 includes a multiplier 810 for multiplying the pilot signal output from the demultiplexer 400 by a phase estimation value output from the channel estimator 500 and a multiplier 810 for multiplying a value output from the multiplier 810 by a reference And a comparator 820 for comparing a reference pilot symbol output from the pilot symbol generator 700 and outputting a signal corresponding to the error to the beamforming controller 900.

The beamforming controller 900 uses the array signals V ₀ , V ₁ , ..., V _n output from the array antenna 100 and the phase estimates output from the channel estimator 500 to generate error signals from the error signal generator 800 (W ₀ , W ₂ , ..., W _s-1 ) output to the optimum beam former 200 so that the error signal to be output is minimized.

The beam forming controller 900 will be described in more detail below.

3 is a detailed block diagram of the beamforming controller 900 shown in FIG.

As shown in FIG. 3, the beamforming controller 900 includes a serial-to-parallel converter 910, IFFTs 920 and 940, and a beamforming coefficient updater 930.

The serial-to-parallel converter 910 converts the error signal output from the error signal generator 800 into a parallel signal and outputs the parallel signal to the IFFT 920. The IFFT 920 converts the parallel signal output from the serial- Into a signal in the time domain and outputs the signal to the beamforming coefficient updater 930.

Another IFFT 940 converts the phase estimation value output from the channel estimator 500 into a time domain signal and outputs the signal to a beamforming coefficient updater 930.

The beamforming coefficient estimator 930 estimates the beamforming coefficients of the respective time-domain signals output from the IFFTs 920 and 940 and a plurality of antennas 100-1, 100-2, ..., 100-n included in the array antenna 100, (W ₀ , W ₂ , ..., W _s-1 ) used in the optimum beam forming in the optimum beam former 200 by combining the array signals output from the beam forming unit 200.

Hereinafter, the operation of the OFDM receiving system according to the embodiment of the present invention will be described in detail.

The antennas 100-1, 100-2, ..., 100-n provided in the array antenna 100 receive and output the array signals V ₀ , V ₁ , ..., V _n , (200-1, 200-2, ..., 200 -n) is arranged a signal _{(V 0, V 1, ...} , V n) outputted from the beam forming coefficient estimator 930, a beamforming controller 900 And the beam forming coefficients W ₀ , W ₂ , ..., W _s-1 .

The adder 310 of the OFDM receiver 300 sums the signals output from the multipliers 200-1, 200-2, ..., 200-n and outputs the resultant signals, Converter 320, the FFT 330, and the P / S converter 340 and is converted into a signal in the frequency domain.

The demultiplexer 400 demultiplexes the frequency-domain signal converted by the OFDM receiver 300 into a data signal and a pilot signal, and outputs the separated data signal as a compensation signal according to the phase estimated by the channel estimator 500. [ And is then restored to the signal by the decoder 600.

The multiplier 810 of the error signal generator 800 multiplies the pilot signal separated by the demultiplexer 400 by the phase estimated by the channel estimator 500, And the reference pilot symbols output from the reference pilot symbol generator 700 are compared by the comparator 820, and the comparison result is output as an error signal.

The error signal output from the error signal generator 800 is converted into a time-domain parallel signal through the serial-to-parallel converter 910 and the IFFT 920 of the beamforming controller 900, The output phase estimation value also passes through the IFFT 940 and is converted into a signal in the time domain to update the beamforming coefficient in the time domain.

The beamforming coefficient estimator 930 in the beamforming controller 900 receives the error signal, that is, the time domain parallel signal output from the IFFT 920 and the time domain signal output from the channel estimator 500, The adaptive algorithm is performed by the array signals V ₀ , V ₁ , ..., V _n including the spatial phase information output from the antennas 100-1, 100-2, ..., 100- (W ₀ , W ₂ , ..., W _s-1 ) input to the optimum beam former 200 are updated. Here, there are various adaptive algorithms for updating the beamforming coefficients (W ₀ , W ₂ , ..., W _s-1 ), and it is assumed that the multiplication operation is performed by updating in this embodiment. That is, the beamforming coefficient estimator 930 multiplies the parallel signal of the time domain and the channel phase value of the time domain by the array signals V ₀ , V ₁ , ..., V _n to calculate beamforming coefficients W ₀ , W ₂ , ..., W _s-1 ).

Thus beamforming coefficients (W _0, W _2, the phase of the reference pilot symbol output from the phase and the reference pilot symbol generator 700, estimated by the channel estimator 500, so that the in-phase ..., W _{s- 1} ), the convergence rate for optimizing the beam forming coefficient can be improved.

Although the present invention has been described with reference to the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

According to the present invention, by applying an adaptive array antenna and a channel estimator to an OFDM reception system and using a technique for improving a convergence speed for optimizing an adaptive beamforming coefficient for optimal beamforming, There is an effect of improving system performance by reducing severe inter-symbol interference and noise due to multipath fading that occurs in the case of the conventional system.

In addition, by placing the FFT transformer at the rear end of the array antenna, computational complexity and hardware complexity are greatly reduced.

Claims (10)

An adaptive array antenna unit for receiving a wireless signal from the outside and outputting the wireless signal as an array signal including a corresponding spatial phase; An optimum beam forming unit adapted to adaptively output an array signal output from the adaptive array antenna unit using a specific beamforming coefficient; An OFDM (Orthogonal Frequency Division Multiplexing) apparatus that performs a Fast Fourier Transform (FFT) on signals output from the optimum beam forming unit to convert the signals into frequency-domain signals, processes signals in the frequency- Division Multiplexing) receiver; A channel estimator for estimating a phase of a signal according to a channel change using a pilot signal among signals output from the OFDM receiver; An error signal generator for combining the pilot signal and the phase estimated by the channel estimator among the signals output from the OFDM receiver and comparing the combined signal with a reference pilot symbol to output an error signal; And And an error signal generator for generating an error signal by using the array signal output from the adaptive array antenna unit and the phase estimated by the channel estimator to minimize the error signal output from the error signal generator, And a beam forming control section for updating the beam forming control section, A serial / parallel converter for converting an error signal output from the error signal generator into a parallel signal; A first IFFT (Inverse Fast Fourier Transform) for converting a parallel signal output from the S / P converter into a time domain signal; A second FFT for converting a phase estimated by the channel estimation unit into a signal in a time domain; And A beamforming coefficient updater for outputting the specific beamforming coefficient generated by multiplying the time-domain signal output from the first IFFT and the second IFFT by the array signal output from the adaptive array antenna unit, ≪ / RTI > / RTI > The method according to claim 1, Wherein the adaptive array antenna unit includes a plurality of antennas for receiving radio signals from outside and outputting a plurality of array signals, Wherein the beam forming controller outputs a specific beam forming coefficient corresponding to a plurality of array signals output from the plurality of antennas, Wherein the optimal beam forming unit includes a plurality of multipliers for multiplying a plurality of array signals output from the adaptive array antenna unit and a plurality of specific beamforming coefficients output from the beamforming control unit and outputting the multiplied signals to the OFDM receiver, And an OFDM receiver. The method according to claim 1, The OFDM receiver An adder for summing and outputting signals output from the optimum beam forming unit; A serial-to-parallel converter for converting a signal output from the summer into a parallel signal; An FFT (Fast Fourier Transform) for converting a parallel signal converted by the serial-to-parallel converter into a frequency domain signal; And A parallel-to-serial (S / P) converter for converting a frequency-domain signal converted by the FFT into a serial signal and outputting the serial signal to the demultiplexer; / RTI > The method according to claim 1, The error signal generator A multiplier for multiplying a pilot signal among signals output from the OFDM receiver by a phase estimated by the channel estimator and outputting the multiplied signal; And A comparator for comparing the signal outputted by the multiplier with the specific reference pilot symbol and outputting an error signal; / RTI > delete The method according to claim 1, And a decoder for decoding the data signal among the signals output from the OFDM receiver into an original signal, Wherein the channel estimator compensates distortion of a data signal output from the OFDM receiver using the estimated phase and input to the decoder. And an OFDM receiver. In an OFDM reception method of a mobile communication system having an adaptive array antenna, a) multiplying an array signal including a spatial phase received through the adaptive array antenna by a specific beamforming coefficient for beamforming and outputting the result; b) summing the signals output in the step a), performing an FFT (Fast Fourier Transform) process to convert the signals into frequency-domain signals, separating the signals into data signals and pilot signals, and outputting the signals; c) estimating a phase of a signal according to a channel change using the pilot signal separated and output in the step c); d) combining the pilot signal separated and output in step b) with the phase estimated in step c), and generating an error signal by comparing the combined signal with a specific reference pilot symbol; And e) updating a specific beamforming coefficient used in step a) using an error signal generated in step d), a phase estimated in step c), and an array signal output from the adaptive array antenna, Wherein the step of updating the beamforming coefficients comprises: Converting the error signal generated in step d) into a parallel signal; Converting the converted parallel signal into a time domain signal; And Multiplying an array signal received from the adaptive array antenna by a signal of the transformed time domain and outputting the multiplied signal with the specific beamforming coefficient ≪ / RTI > / RTI > 8. The method of claim 7, The step b) Summing and outputting the signals output in the step a); Converting the summed output signal into a parallel signal; Converting the converted parallel signal into a frequency domain signal; Converting the converted frequency domain signal into a serial signal; And Separating the data signal and the pilot signal from the converted serial signal / RTI > delete 8. The method of claim 7, Estimating a channel using the pilot signal separated in step b); Compensating a distortion of the data signal separated in the step b) by the estimated channel variation; And A step of decoding the distortion compensated data signal into an original signal / RTI >

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