KR100430524B1 - 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 and method using an adaptive array antenna, the OFDM receiving system includes an array antenna unit for receiving a radio signal from the outside and outputting an array signal including a corresponding spatial phase; An optimum beamformer configured to adaptively adjust and output an array signal output from the array antenna unit using a specific beamforming coefficient; An OFDM receiver for converting a signal output from the optimal beamforming unit into a signal in a frequency domain, and processing a signal in the frequency domain to form beamforming in a desired direction; A demultiplexer which receives a signal output from the OFDM receiver and separates a data signal and a pilot signal; A reference pilot symbol generator for generating a reference pilot symbol; Convert the pilot signal separated by the demultiplexer into a signal in the time domain, compare the converted pilot signal with the reference pilot symbol generated by the reference pilot symbol generator, and obtain an error signal. An error signal generator for outputting; And a beamforming controller for updating the specific beamforming coefficients outputted to the optimal beamforming unit so that the error signal outputted from the error signal generator is minimized using the array signal output from the array antenna unit. According to the present invention, severe inter-symbol interference and noise due to multipath fading are reduced, thereby improving performance of the system.

Description

OPDM reception system using adaptive array antenna and its method {Orthogonal Frequency Division Multiplexing Receiving System Using Adaptive Array Antennas And Method Thereof}

The present invention relates to wireless signal reception used in a high-speed mobile communication system, and more particularly, to an orthogonal frequency division multiplexing (OFDM) reception system using an adaptive array antenna and a method thereof.

Recently, with the advent of the multimedia era, the demand for high-speed data transmission for providing various services of high quality is increasing. However, when data is transmitted at high speed in a wireless channel environment, severe inter-symbol interference occurs due to multipath fading, which makes high-speed data transmission difficult.

In order to overcome this problem, a digital signal-code division multiple access (DS-CDMA) rake receiver is used in a mobile communication system. In the method using this receiver, hardware complexity increases rapidly as chip-to-chip interference increases during high-speed data transmission.

In order to solve such a problem that occurs during high-speed data transmission, a recently proposed transmission scheme is an OFDM scheme.

Unlike the method having a single carrier, the OFDM method converts serially input data into a parallel form, and then modulates the data into subcarriers with mutually orthogonal subcarriers corresponding to the number of data converted in parallel. .

In this way, when modulating multiple carriers, the symbol period in the subchannel including each subcarrier is increased by the number of subcarriers while maintaining the original high data rate.

Therefore, the transmission time due to the subcarrier is much longer than the delay spread due to the multipath fading, so the frequency selective fading channel is approximated to the frequency nonselective fading channel so that the transmitted data can be easily compensated and detected using a simple single tap equalizer at the receiver. can do. In addition, the process of demodulating a subcarrier in a transceiver may be implemented at high speed using an inverse fast fourier transform (IFFT) / FFT.

As such, the OFDM method is used as a transmission method in broadcasting fields such as DAB (Digital Audio Broadcasting) and DVB (Digital Video Broadcasting) because it has an advantage of overcoming fading by using an orthogonal multiple carrier. In addition, since high-order modulation (64ary QAM, 16ary QAM) technique can be used to transmit ultra-high speed data (20Mbps), it is being actively researched as a transmission method for 4G mobile communication systems.

In order to apply the OFDM method with various advantages to the mobile communication system, various techniques for improving the performance even in a poor wireless channel environment are being studied. The main contents studied up to now are wireless Channel equalization technique in the time-frequency domain for compensating channels.

Equalization techniques studied here include linear equalization techniques, crystal feedback equalization techniques, and blind equalization techniques in the frequency domain or in the time domain. Recently, research on equalization techniques in the time-frequency domain is underway.

In addition, in order to increase the capacity of the system without additional frequency spectrum allocation, an adaptive beamforming scheme has been proposed to be applied to an adaptive array antenna in a mobile communication system of DS / CDMA or time division multiple access (TDMA).

The beamforming scheme of the adaptive array antenna is a code filtering method using a signal received from the array antenna and the processing result without performing a separate position estimation, and the DMI ( There are a Direct Matrix Inversion (LMS) method, a Least Mean Square (LMS), a Recursive Least Square (RLS) method, and the like that form an optimal beam using a reference signal.

A technique for such an OFDM system using an array antenna is "Adaptive antenna arrays for othorgonal frequency division multiplexing systems with cochannel interference" disclosed in U.S. Patent No. 5,973,642 to Ye Li et al., In which the FFT converter demodulates a received signal. Is for each element of the array antenna, and this converter is followed by a beam estimator, a decoder, and a parameter estimator for updating the beamforming coefficients. The technique of updating the beamforming coefficients is an error between the received signal and the reference signal. We used MMSE (Minimum Mean Square Error) to update the coefficients to get the best value and minimize the performance of OFDM system by using DMI. Since the structure has a large amount of computation and hardware complexity The problem is.

Accordingly, an object of the present invention is to solve the above-mentioned problems, and it is possible to improve performance by using an adaptive array antenna having a good performance improvement effect and using an adaptive beamforming technique and a channel equalization technique. It is to provide an OFDM receiving system using an adaptive array antenna that greatly reduces the.

1 is a block diagram of an OFDM reception 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.

FIG. 3 is a detailed block diagram of the beamforming controller shown in FIG. 1.

An OFDM receiving system according to a feature of the present invention for achieving the above object,

An array antenna unit for receiving a wireless signal from the outside and outputting an array signal including a corresponding spatial phase; An optimum beamformer configured to adaptively adjust and output an array signal output from the array antenna unit using a specific beamforming coefficient; An OFDM receiver for converting a signal output from the optimal beamforming unit into a signal in a frequency domain, and processing a signal in the frequency domain to form beamforming in a desired direction; A demultiplexer which receives a signal output from the OFDM receiver and separates a data signal and a pilot signal; A reference pilot symbol generator for generating a reference pilot symbol; Convert the pilot signal separated by the demultiplexer into a signal in the time domain, compare the converted pilot signal with the reference pilot symbol generated by the reference pilot symbol generator, and obtain an error signal. An error signal generator for outputting; And a beamforming controller for updating the specific beamforming coefficients outputted to the optimal beamforming unit so that the error signal outputted from the error signal generator is minimized using the array signal output from the array antenna unit.

In addition, the OFDM receiving system includes a channel equalizer for estimating a channel using a pilot signal separated by the demultiplexer, and compensating for distortion of a data signal output from the demultiplexer by a change in the estimated channel; And a decoder which decodes the data signal corrected by the channel equalizer after being separated by the demultiplexer into an original signal.

In addition, the OFDM reception method according to a feature of the present invention,

An OFDM reception method of a mobile communication system having an array antenna,

A first step of multiplying and outputting an array signal including a spatial phase received through the array antenna by a specific beamforming coefficient for beamforming; A second step of converting a signal output in the first step into a signal in a frequency domain, separating the signal into a data signal and a pilot signal and outputting the separated signal; A third step of generating an error signal by comparing the pilot signal separated and output in the second step with a specific reference pilot symbol; And a fourth step of updating a specific beamforming coefficient used in the first step by using the error signal generated in the third step and the array signal output from the array antenna.

The OFDM reception method may further include estimating a channel using a pilot signal separated in the second step; Compensating for the distortion of the data signal separated in the second step by the estimated change in the channel; And decoding the distortion-compensated data signal into an original signal.

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

1 is a block diagram of an OFDM receiving system using an adaptive array antenna according to an embodiment of the present invention, Figure 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 is an array antenna 100, an optimal beamformer 200, an OFDM receiver 300, a demultiplexer 400 , A channel equalizer 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 an OFDM transmission system and outputs a signal for performing beamforming to the optimal beamformer 200 and the beamforming controller 900. As shown in FIG. 2, the array antenna 100 receives a signal transmitted from an OFDM transmission system and outputs a plurality of array signals V ₀ , V ₁ ,..., And V _n including corresponding spatial phases. Antennas 100-1, 100-2, ..., 100-n.

The optimal beamformer 200 adaptively adjusts the signal output from the array antenna 100 by the signal output from the beamforming controller 900 and outputs the signal to the OFDM receiver 300. The optimal beamformer 200 is configured to output array signals V ₀ , V ₁ , ..., V _n output from the plurality of antennas 100-1, 100-2,..., 100-n of the array antenna 100. ) And a plurality of multipliers 200-1, 200-2,..., 200-n that multiply the signal output from the beamforming controller 900, that is, the beamforming coefficients W ₀ , W ₁ , ..., W _n . Include.

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 adds up and outputs signals output from the plurality of multipliers 200-1, 200-2,..., 200-n included in the optimal beamformer 200, and adds them. Serial / parallel converter 320 for converting the signal output from the device 310 into a parallel signal and outputting, FFT 330 for converting the parallel signal output from the serial / parallel converter 320 into a frequency domain signal, and an FFT And a parallel / serial converter 340 for converting the signal converted by 330 into a serial signal and outputting the serial signal to the demultiplexer 400.

The demultiplexer 400 receives a signal output from the OFDM receiver 300, separates the data signal from the pilot signal, outputs the data signal to the decoder 600, and outputs the pilot signal to the channel equalizer 500. Output

The channel equalizer 500 estimates a channel using a pilot signal output from the demultiplexer 400 and distorts the data signal transmitted from the demultiplexer 400 to the decoder 600 by the estimated channel change. Outputs a signal to compensate.

The decoder 600 decodes the data signal output from the demultiplexer 400 into an original signal and outputs the original 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 compares the pilot signal output from the demultiplexer 400 with the reference pilot symbol output from the reference pilot symbol generator 700 and outputs an error signal to the beamforming controller 900.

The beamforming controller 900 uses the array signals V ₀ , V ₁ ,..., V _n outputted from the array antenna 100 so that the error signal output from the error signal generator 800 is minimized. The beamforming coefficients W ₀ , W ₁ , ..., W _n outputted to 200 are updated.

Hereinafter, the beamforming controller 900 will be described in more detail.

3 is a detailed block diagram of the beamforming controller 900 shown in FIG. 1.

As shown in FIG. 3, the beamforming controller 900 includes a serial / parallel converter 910, an IFFT 920, and a beamforming coefficient updater 930.

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

The beamforming coefficient updater 930 is output from the time domain signal output from the IFFT 920 and the plurality of antennas 100-1, 100-2, ..., 100-n provided in the array antenna 100. By combining the array signals, the beamforming coefficients W ₀ , W ₁ ,..., W _n used in the optimal beamforming in the optimal beamformer 200 are updated.

Hereinafter, the operation of the OFDM reception system according to an 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 array signals V ₀ , V ₁ , ..., V _n , and a multiplier of an optimal beamformer. (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 The beamforming coefficients W ₀ , W ₁ , ..., W _n are multiplied and output respectively.

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

The demultiplexer 400 separates the signal in the frequency domain converted by the OFDM receiver 300 into a data signal and a pilot signal, and outputs the separated data signal according to the channel estimated by the channel equalizer 500. After being compensated, the decoder 600 recovers the original signal.

Meanwhile, the error signal generator 800 compares the pilot signal separated by the demultiplexer 400 with the reference pilot symbol output from the reference pilot symbol generator 700 and outputs the error signal.

The error signal output from the error signal generator 800 passes through the serial / parallel converter 910 and the IFFT 920 of the beamforming controller 900 and is converted into a parallel signal in the time domain so that the beamforming coefficient in the time domain is reduced. To be updated.

The beamforming coefficient updater 930 outputs an error signal, that is, a parallel signal in the time domain output from the IFFT 920 and the antennas 100-1, 100-2, ..., 100-n of the array antenna 100. an array that contains the spatial phase information signal _{(V 0, V 1, ...} , V n) beamforming coefficients (W _0, W _1, is carried out an adaptive algorithm to enter the optimal beam former 200 by ... , W _n ). Here, there are various adaptive algorithms for updating the beamforming coefficients W ₀ , W ₁ ,..., W _n . In this embodiment, it is assumed that the multiplication operation is performed by updating. That is, the beamforming coefficient updater 930 updates the beamforming coefficients W ₀ , W ₁ ,…, W _n by multiplying the parallel signals in the time domain and the array signals V ₀ , V ₁ ,…, V _n . do.

Although the present invention has been described with reference to the most practical and preferred embodiments, the present invention is not limited to the above disclosed embodiments, but also includes various modifications and equivalents within the scope of the following claims.

According to the present invention, by applying an adaptive array antenna and a channel equalizer to an OFDM receiving system and using an adaptive beamforming method and a channel equalization method for optimal beamforming, multipath fading generated when data is transmitted at high speed in a wireless channel environment By reducing the severe intersymbol interference and noise caused by the system has an excellent effect on improving the performance of the system.

In addition, by placing the FFT converter behind the array antenna, the computational complexity and hardware complexity is greatly reduced.

Claims (9)

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 beamformer configured to adaptively adjust and output an array signal output from the adaptive array antenna unit using a specific beamforming coefficient; An orthogonal frequency division multiplexing (OFDM) receiver for converting a signal output from the optimal beamforming unit into a signal in a frequency domain and processing the converted frequency domain signal to form beamforming in a desired direction; A demultiplexer which receives a signal output from the OFDM receiver and separates a data signal and a pilot signal; An error signal generator for outputting an error signal by comparing a pilot signal separated by the demultiplexer with a specific reference pilot symbol; And A beamforming control unit for updating the specific beamforming coefficients outputted to the optimum beamforming unit such that the error signals outputted from the error signal generator are minimized using the arrayed signals output from the adaptive array antenna unit, wherein the beamforming unit The control unit, A serial / parallel converter for converting the error signal output from the error signal generator into a parallel signal; An Inverse Fast Fourier Transform (IFFT) for converting a parallel signal output from the serial / parallel converter into a signal in a time domain; And A beamforming coefficient updater for outputting the specific beamforming coefficient to the optimum beamforming unit by multiplying the time domain signal output from the IFFT and the array signal output from the adaptive array antenna unit; Contains OFDM receiving system comprising a. The method of claim 1, The adaptive array antenna unit includes a plurality of antennas for receiving a radio signal from the outside to output a plurality of array signals, The beamforming controller outputs specific beamforming coefficients corresponding to a plurality of array signals output from the plurality of antennas, The optimal beamforming 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 multiplier to the OFDM receiver. OFDM receiving system, characterized in that. The method of claim 1, The OFDM receiver A summer for summing and outputting signals output from the optimum beamforming unit; A serial / parallel converter for converting the signal output from the summer into a parallel signal; Fast Fourier Transform (FFT) for converting the parallel signal converted by the serial / parallel converter into a signal in the frequency domain; And A parallel / serial converter converting the signal in the frequency domain converted by the FFT into a serial signal and outputting the serial signal to the demultiplexer OFDM receiving system comprising a. delete The method of claim 1, A channel equalizer for estimating a channel using a pilot signal separated by the demultiplexer and compensating for distortion of a data signal output from the demultiplexer by a change in the estimated channel; And A decoder which decodes the data signal corrected by the channel equalizer after being separated by the demultiplexer into an original signal OFDM receiving system further comprising. In the OFDM reception method of a mobile communication system having an adaptive array antenna, A first step of multiplying and outputting an array signal including a spatial phase received through the adaptive array antenna by a specific beamforming coefficient for beamforming; A second step of converting a signal output in the first step into a signal in a frequency domain, separating the signal into a data signal and a pilot signal and outputting the separated signal; A third step of generating an error signal by comparing the pilot signal separated and output in the second step with a specific reference pilot symbol; And A fourth step of updating the specific beamforming coefficients used in the first step by using the error signal generated in the third step and the array signal output from the adaptive array antenna, wherein the fourth step, Converting the error signal generated in the third step into a parallel signal; Converting the parallel signal converted in the step into a signal in a time domain; And Multiplying an array signal received from the adaptive array antenna by a signal in the time domain converted in the step and outputting the specific beamforming coefficient; Contains OFDM receiving method comprising a. The method of claim 6, The second stage Summing and outputting the signals output in the first step; Converting the summed and output signals into parallel signals; Converting the parallel signal converted in the step into a signal in a frequency domain; Converting the signal in the frequency domain converted in the step into a serial signal; And Separating the data signal and the pilot signal from the serial signal converted in the step OFDM receiving method comprising a. delete The method of claim 6, Estimating a channel using the pilot signal separated in the second step; Compensating for the distortion of the data signal separated in the second step by the estimated change in the channel; And Decoding the distortion-compensated data signal into an original signal OFDM receiving method further comprising.