KR20070109563A - Frequency diversity apparatus and method in mobile communication system - Google Patents

Abstract

A frequency diversity device and a method in a mobile communication system are provided to improve reception performance by obtaining a frequency diversity gain in an OFDMA(Orthogonal Frequency Division Multiplexing Access) radio communication system and decreasing PAPR(Peak-to-Average Power Ratio) at the same time. In a transmitter of an OFDMA radio communication system, a frequency diversity device includes an I signal generator(212) generating and outputting an I(In-phase) signal by receiving input data; an interleaver(211) receiving and interleaving a copy of the input data and then outputting the interleaved data; a multiplier(213) dual-multiplying the output of the interleaver and outputting the dual multiplication result; a Q signal generator(214) generating and outputting a Q(Quadrature-phase) signal through the dual multiplication result; and a combiner(215) combining the I signal of the I signal generator and the Q signal of the Q signal generator and then outputting the combined signal.

Description

Frequency Diversity Device and Method in Wireless Communication System {FREQUENCY DIVERSITY APPARATUS AND METHOD IN MOBILE COMMUNICATION SYSTEM}

1 is a block diagram of a physical layer for transmission and reception in a typical OFDM system,

2 is a block diagram of a physical layer for transmission and reception in an OFDM system to which the present invention is applied;

3 is a flowchart illustrating an operation of a transmitter to which a frequency diversity method is applied in a wireless communication system according to an embodiment of the present invention;

4 is a flowchart illustrating an operation of a receiver to which a frequency diversity method is applied in a wireless communication system according to an embodiment of the present invention;

5 is a performance analysis diagram when the interleaved QPSK is applied without considering the PAPR and the conventional frequency diversity is applied;

6 is a diagram illustrating a method of applying a frequency diversity method in a wireless communication system according to an exemplary embodiment of the present invention and a performance analysis in the case of not doing so.

The present invention relates to a frequency diversity apparatus and method in a wireless communication system, and more particularly, to a frequency diversity apparatus and method in a wireless communication system of an orthogonal frequency multiple access method.

In general, a mobile communication system using a cellular communication method is a representative system of a wireless communication system. Such mobile communication systems use a multiple access scheme to simultaneously communicate with multiple users. As the multiple access scheme, time division multiple access (TDMA), code division multiple access (CDMA) and frequency division multiple access (FDMA) schemes are typically used. Among them, the code division multiple access system has been developed in a form capable of transmitting high-speed packet data in a system mainly providing voice communication according to the rapid development of technology.

Recently, orthogonal frequency division multiple access (hereinafter referred to as 'OFDMA') has emerged in order to overcome the limitation of the use of a resource code in the code division multiple access scheme.

The OFDMA scheme is configured based on an Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme, wherein the OFDM system transmits data using a multi-carrier, and is a symbol input in series. Multi Carrier Modulation (MCM), which modulates and transmits a plurality of sub-carriers, that is, a plurality of sub-carrier channels, each of which is mutually orthogonal, by converting columns in parallel. ) Is a kind of way.

The system applying the multicarrier modulation scheme was first applied to military HF radio in the late 1950s, and the OFDM scheme of superimposing a plurality of orthogonal subcarriers started to develop in the 1970s, but the implementation of orthogonal modulation between multicarriers was implemented. Since this was a difficult problem, there was a limit to the actual system application. However, in 1971, Weinstein et al. Announced that modulation and demodulation using the OFDM scheme can be efficiently processed using a Discrete Fourier Transform (DFT). In addition, the use of guard intervals and the introduction of cyclic prefix (CP) into guard intervals are known, further reducing the negative effects of the system on multipath and delay spread.

Thanks to these technological advances, OFDM technology is used for digital audio broadcasting (DAB), digital television, wireless local area network (WLAN), and wireless asynchronous transfer mode (WATM). It is widely applied to digital transmission technology. In other words, due to hardware complexity, it is not widely used, but recently, the Fast Fourier Transform (FFT) and the Inverse Fast Fourier Transform (IFFT) are referred to as "FFT". The development of various digital signal processing technologies, including IFFT " The OFDM scheme is similar to the conventional Frequency Division Multiplexing (FDM) scheme, but most of all, an optimal transmission efficiency can be obtained during high-speed data transmission by maintaining orthogonality among a plurality of subcarriers. Has characteristics. In addition, the OFDM method has a characteristic of good frequency usage efficiency and strong characteristics of multi-path fading, thereby obtaining an optimum transmission efficiency in high-speed data transmission. In addition, because the frequency spectrum is superimposed, frequency use is efficient, strong in frequency selective fading, strong in multipath fading, and inter-symbol interference (ISI) effects using guard intervals. It is possible to reduce the design, and to simply design the equalizer structure in terms of hardware, and has the advantage of being resistant to impulsive noise, which is being actively used in the communication system structure.

1 is a block diagram of a physical layer for transmission and reception in a typical OFDM system.

The transmitter simultaneously transmits the same data to different frequencies in order to transmit the input data to be transmitted in the frequency diversity scheme. That is, the input data are simultaneously transmitted to different frequencies in the same form as the input data 101 and the input data copy 102 indicating a copy of the input data, as shown in FIG. 1. The frequency diversity is a method of radiating two or more different frequencies at the same time at the same transmission point. Therefore, the frequency diversity can reduce the influence of fading, and the frequency difference can be separated from each other only by several hundred KHz or more.

The input data 101 and the input data copy 102 described above are input to the serial / parallel converter 103. The serial / parallel converter 103 receives the input data 101 and the copy of the input data 102 and converts the serial bit stream data into a parallel bit stream. The conversion of the serial bit stream to the parallel bit stream in the serial / parallel converter 103 is for performing a fast inverse Fourier transform. Accordingly, the parallel bit stream output from the serial / parallel converter 103 is input to the fast inverse Fourier transformer 104. In this case, it is assumed that the parallel bit stream is N symbols. The reason why the N symbols are received as described above is because the fast inverse Fourier transformer 104 performs inverse Fourier transform on the input streams in N units.

Accordingly, the fast inverse Fourier transformer (IFFT) 104 receives N symbols received in parallel and converts the symbols in the frequency domain into symbols in the time domain by fast inverse Fourier transforming the symbols to be transmitted. The symbols converted into the time domain are input to the parallel / serial converter 105. The peak-to-average power ratio (PAPR) may be measured through the output of the fast inverse Fourier transducer 104. The parallel-to-serial converter 105 converts N time-domain symbols input in parallel into serial, sequential N bit streams, and outputs them. As described above, the N bit streams sequentially output are referred to as " OFDM symbols "

The OFDM symbol is input to a Cyclic Prefix Adder 106. The CP adder 106 copies a predetermined number of bits back from the last bit of the input OFDM symbol and inserts it before the first bit of the OFDM symbol. The reason for adding the cyclic prefix symbol is to remove the influence of the multipath channel. The OFDM symbol to which the CP is added is input to the digital-to-analog converter 107. Before input to the digital-to-analog converter 107, clipping may be performed in a clipper (not shown). The digital-analog converter 107 then converts the input digital symbols into analog symbols and sends them to the receiver.

The analog symbols transmitted as described above are input to the receiver via a predetermined channel 110 having multiple paths. Then, the configuration and operation of the receiver will be described.

The analog-to-digital converter 121 of the receiver converts the analog signal received through the channel 110 into a digital signal. As such, the signals converted into digital signals by the analog-to-digital converter 121 are input to the CP remover 122. The CP remover 122 removes cyclic prefixes, ie, cyclic prefix symbols, contaminated by the effects of multipath. The signal from which the CPs are removed in the CP remover 122 is a serial signal. Accordingly, the signal from which the cyclic prefix symbols are removed is input to the serial / parallel converter 123 for fast inverse Fourier transform. The serial / parallel converter 123 converts the serially input symbols into N units in parallel and outputs them.

As described above, the serially inputted symbols are output in parallel in N units because the Fourier transformation is performed in N units on the transmitting side. Accordingly, the fast Fourier transformer (FFT) 124 receives N units of parallel data and Fourier transforms the signals. That is, the Fourier transformer 124 converts symbols in the time domain into symbols in the frequency domain. The symbols converted into the frequency domain are input to an equalizer 125. The equalizer 125 cancels and outputs the influence of the channel 110 transmitted from the input symbols converted into the frequency domain. At this time, the equalizer 125 estimates a channel using Zero Forcing (ZF) or Minimum Mean-Squared Error (MMSE). The symbols output from the equalizer 125 convert the parallel input symbols back to serial symbols in the parallel / serial converter 126 and output them. Accordingly, the unit of symbols converted in series in the parallel / serial converter 126 is N symbols. The symbols serially converted into N units are input to the input data output unit 127 and the input data copy output unit 128, respectively. The input data output unit 127 outputs input data from the serialized symbols to the combiner 129, and the input data copy output unit 128 combines input data copies from the serialized symbols into the combiner 129. Will output The combiner 129 combines the input data and the copy of the input data and then outputs the signal to the detector 130.

The signal detector 130 uses the output of the combiner 129 to estimate the transmission signal according to a predetermined threshold.

The OFDM system is widely applied to a wideband transmission method because the OFDM system can efficiently use a transmission band as compared to a single carrier modulation scheme.

In reception characteristics, an OFDM system exhibits stronger characteristics than a frequency selective multipath fading channel compared to a single carrier transmission scheme. The receiver's input signal characteristics become frequency-selective channels in a band occupied by a plurality of subcarriers, but in each subcarrier band, they become frequency nonselective channels, so channel compensation can be easily performed through a simple channel equalization process. Because. In particular, by transmitting a cyclic prefix for copying and transmitting the second half of the OFDM symbol in front of each OFDM symbol, it is possible to remove the intersymbol interference (ISI) from the previous symbol. Therefore, such a strong characteristic of the multipath fading channel makes the OFDM transmission scheme suitable for wideband high speed communication.

Despite these advantages, in the orthogonal frequency multiple access wireless communication system, autocorrletion of subcarriers simultaneously transmitted is increased when the frequency diversity scheme is used. The higher the autocorrelation, the higher the PAPR measurable in the above-mentioned IFFT 104.

Also, in general, when zero crossing occurs in a constellation on a radio frequency, the PAPR is increased.

High PAPR causes the transmission power to be reduced due to the nonlinear nature of the power amplifier of the transmit stage. In addition, high PAPR reduces the receiver's signal-to-noise ratio (SNR). In addition, a signal with a high PAPR degrades the efficiency of the linear amplifier. In the nonlinear amplifier, the operating point is located in the nonlinear region, resulting in nonlinear distortion, and intermodulation and spectral emission between carriers are generated. As a result, in the orthogonal frequency multiple access wireless communication system, the use of frequency diversity increases the PAPR and reduces the reception performance due to distortion of the transmission signal itself.

Accordingly, an object of the present invention is to provide a frequency diversity apparatus and method in a wireless communication system for reducing PAPR while obtaining a frequency diversity gain in a wireless communication system of an orthogonal frequency multiple access method.

Another object of the present invention is to provide a frequency diversity apparatus and method in a wireless communication system that improves reception performance by reducing the PAPR while simultaneously obtaining a frequency diversity gain in a wireless communication system using an orthogonal frequency multiple access method.

A frequency diversity apparatus in a wireless communication system according to an embodiment of the present invention is a frequency diversity apparatus in a transmitter in a wireless communication system of an orthogonal frequency multiple access method, and receives input data and generates and outputs an I signal. A signal generator, an interleaver for receiving and interleaving a copy of the input data which is a copy of the input data, a multiplier for multiplying the output of the interleaver, and outputting a multiplication result, and a Q signal through the multiplication result And a combiner for combining and outputting a Q signal generator for generating and outputting a Q signal, which is an output signal of the I signal generator, and a Q signal, which is an output signal of the Q signal generator.

A frequency diversity method in a wireless communication system according to an embodiment of the present invention is a frequency diversity method in a transmitter in a wireless communication system of an orthogonal frequency multiple access method, which receives input data and generates and outputs an I signal. And receiving and interleaving a copy of the input data, which is a copy of the input data, outputting the interleaved output, multiplying the interleaved output, and outputting a multiplication result, and Q (orthogonal) through the multiplication result. Generating and outputting a signal; and outputting a combination of the I and Q signals.

In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

2 is a block diagram of a physical layer for transmission and reception in an OFDM system to which the present invention is applied.

Hereinafter, since there are components similar to those of FIG. 1, only the configuration changed from FIG. 1 will be described.

At the transmitter, input data is input to the I signal generator 212, and a copy of the input data is input to the interleaver 211. At this time, in order to apply the frequency diversity scheme, the same data is simultaneously transmitted to different frequencies.

The I signal generator 212 receives the input data, generates an I signal, and outputs the I signal to the combiner 215.

The interleaver 211 receives the input data copy, interleaves the data, and outputs the data to the multiplier 213.

The multiplier 213 multiplies the output of the interleaver 211 and then outputs the multiplication result to the Q signal generator 214. The reason for multiplying the output of the interleaver 211 is to change the phase by distinguishing between the imaginary axis and the real axis, and to reduce the frequency of zero crossing in the constellation on the radio frequency. to be

The Q signal generator 214 generates a Q signal as a multiplication result of the multiplier 213 and outputs the Q signal to the combiner 215.

The combiner 215 combines the I signal of the I signal generator 212 and the Q signal of the Q signal generator 214 and then outputs the serial / parallel converter 103. Due to the combination of the I and Q signals in the combiner 215, quadrature phase shift keying (QPSK) is mapped to generate modulation. The modulated signal is randomly modulated with an I signal and a Q signal, and is an independent signal because it is orthogonal.

Thus, the autocorrelation is lowered and the PAPR measurable through the output of the IFFT 104 is reduced.

Before the input to the digital-to-analog converter 107, the clipping (clipping) can be performed in the clipper (clipper), when the 2dB or 4dB clipping with respect to the PAPR, has excellent reception performance of more than 3dB. Computer simulation results for this will be described again with reference to FIG. 6.

A transmitter including the serial / parallel converter 103, an IFFT 104, a parallel / serial converter 105, a CP adder 106, a digital-to-analog converter 107, an analog-to-digital converter 121, The receiver including the CP remover 122, the serial / parallel converter 123, the FFT 124, the equalizer 125, and the parallel / serial converter 126 is the same as the prior art.

The symbols serially converted into N units output from the parallel / serial converter 126 are input to the real detector 281 and the imaginary detector 283, respectively.

The real detector 281 detects a real component among the serialized symbols and outputs the real component to the combiner 287.

The imaginary detector 283 detects an imaginary component among the serialized symbols and outputs the imaginary component to the deinterleaver 285. The deinterleaver 285 deinterleaves the detected imaginary component and outputs the deinterleaver 287 to the combiner 287.

The combiner 287 combines the outputs of the real detector 283 and the deinterleaver 285 and outputs the combined signal to the signal detector 130. At this time, the combining method uses the equal gain combining (EGC) technique, but may use MRC (Maximum Rate Combining) according to circumstances.

The signal detector 130 uses the output of the combiner 287 to estimate the transmission signal according to a predetermined threshold.

A frequency diversity method in a wireless communication system according to an embodiment of the present invention will be described with reference to FIG. 3. 3 is a flowchart illustrating an operation of a transmitter to which a frequency diversity method is applied in a wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the transmitter receives input data in step 301. The input data is then input to the I signal generator 212 of the transmitter, and the input data copy, which is a copy of the input data, is input to the interleaver 212. Then, the interleaver 212 of the transmitter interleaves the input data received in step 303 and outputs the result to the multiplier 213. Then, the multiplier 213 multiplies the interleaved data in step 305 and outputs the result to the Q signal generator 214.

In operation 307, the Q signal generator 214 generates a Q signal through the multiplication result of the multiplier 213 and outputs the Q signal to the combiner 215.

Simultaneously with the interleaving operation of the interleaver 211, the I signal generator 212 generates an I signal through the input data in step 309 and then outputs it to the combiner 215.

The combiner 215 combines and outputs the I signal and the Q signal in step 311. QPSK modulation is performed by combining the I and Q signals of the combiner 215. The modulated signal is randomly modulated with an I signal and a Q signal, and is an independent signal because it is orthogonal.

Thus, the autocorrelation is lowered and the PAPR measurable through the output of the IFFT 104 is reduced.

A frequency diversity method in a wireless communication system according to an embodiment of the present invention will be described with reference to FIG. 4. 4 is a flowchart illustrating an operation of a receiver to which a frequency diversity method is applied in a wireless communication system according to an exemplary embodiment of the present invention.

The real detector 281 and the imaginary detector 283 receive N-serial converted symbols in N units output from the receiver's parallel / serial converter 126 in step 401.

The imaginary detector 283 detects an imaginary component among the serialized symbols in step 403 and outputs the imaginary component to the deinterleaver 285. The deinterleaver 285 deinterleaves the imaginary component detected by the hub detector 283 in step 407 and outputs the deinterleaver 287 to the combiner 287.

The real detector 281 detects a real component among the serialized symbols in step 405 and outputs the real component to the combiner 287.

The combiner 287 combines the outputs of the real detector 283 and the deinterleaver 285 and outputs them to the signal detector 130 in step 409. At this time, the combining method uses the equal gain combining (EGC) technique, but may use MRC (Maximum Rate Combining) according to circumstances.

The signal detector 130 estimates a transmission signal according to a predetermined threshold value using the output of the combiner 287 in step 411.

5 is a performance analysis diagram when the interleaved QPSK is applied without considering the PAPR and when the conventional frequency diversity is applied.

Referring to FIG. 5, when BPSK is applied through computer simulation (510), when QPSK is applied (520), when general frequency diversity QPSK is applied (530), when interleaved QPSK is applied without considering PAPR (540). ).

It can be seen from FIG. 5 that the performance of the case of applying BPSK (510) and the case of applying QPSK (520) is the same. In addition, it can be seen that the performance of the conventional frequency diversity QPSK 530 and the interleaved QPSK 540 without considering PAPR are almost the same.

6 is a diagram illustrating a method of applying a frequency diversity method in a wireless communication system according to an exemplary embodiment of the present invention and a performance analysis when the method is not. In a wireless communication system according to an embodiment of the present invention, the frequency diversity method is a case in which the interleaved QPSK is considered and the interleaved QPSK is applied unlike the case in which the interleaved QPSK is applied without considering the PAPR shown in FIG. 5.

6, the reception performance is the same in the case of not applying clipping and applying interleaved inter QPSK Org (610) to clipping and not having frequency diversity QPSK Org (640). It can be seen.

6, in the case of applying frequency diversity according to an embodiment of the present invention, that is, in the case of interleaved QPSK P2 620 and in the case of interleaved QPSK P4 630, that is, in case of applying the conventional frequency diversity, that is, frequency It can be seen that reception performance is higher than that of the diversity QPSK P2 650 and the frequency diversity QPSK P4 660. At this time, P2 indicates that the PAPR level is 2dB, and P4 indicates that the PAPR level is 4dB.

In addition, it can be seen from FIG. 6 that 2dB or 4dB clipping for the PAPR has an excellent reception performance of 3dB or more.

In the present invention operating as described in detail above, the effects obtained by the representative ones of the disclosed inventions will be briefly described as follows.

The present invention can reduce the PAPR while obtaining a frequency diversity gain in a wireless communication system of an orthogonal frequency multiple access method.

In addition, the present invention can improve the reception performance by reducing the PAPR while at the same time gaining the frequency diversity gain in the orthogonal frequency multiple access wireless communication system.

Claims (6)

A transmitter in a wireless communication system of an orthogonal frequency multiple access method, An I signal generator that receives input data and generates and outputs an in-phase signal; An interleaver that receives the copy of the input data and interleaves the output; A multiplier for multiplying the output of the interleaver and outputting a multiplication result; A Q signal generator for generating and outputting a quadrature-phase signal through the multiplication result; And a combiner for combining and outputting the I signal, which is an output signal of the I signal generator, and the Q signal, which is an output signal of the Q signal generator. The method of claim 1, The combiner, Frequency modulation apparatus characterized in that the modulation is generated by the Quadrature Phase Shift Keying (QPSK) mapping due to the combination of the I signal and the Q signal. The method of claim 2, And said modulated signal has orthogonality. A receiver in a wireless communication system of an orthogonal frequency multiple access method, A real number detector for detecting real components among serially converted symbols, An imaginary detector which detects a imaginary component among the serially converted symbols while detecting a real component in the real detector; A deinterleaver for deinterleaving the detected imaginary component; And a combiner for combining and outputting the output of the deinterleaver and the output of the real detector. A frequency diversity method in a transmitter in a wireless communication system of an orthogonal frequency multiple access method, Receiving input data and generating and outputting an I (in-phase) signal; Receiving a copy of the input data and interleaving the output data; Multiplying the interleaved output and outputting a multiplication result; A process of generating and outputting a quadrature-phase (Q) signal through the multiplication result; And combining and outputting the I signal and the Q signal. A frequency diversity method in a receiver in a wireless communication system of an orthogonal frequency multiple access method, Detecting a real component and an imaginary component of the serialized symbols, Deinterleaving the detected imaginary component; And combining and outputting the output of the deinterleaver and the detected real component.

Images