KR20070035935A - Transmitter and receiver of digital implemented carrier interferometry orthogonal frequency division multiplexing, method of transmitting and receiving thereof - Google Patents

Abstract

The present invention relates to a digitally implemented carrier interference type orthogonal frequency division multiplexing transmitter / receiver and a method for transmitting and receiving the same.

According to the present invention, a carrier interferometry (CI) orthogonal frequency division multiplexing (OFDM) transmitter includes a CI code spreader for performing CI code spreading and an IFFT unit for performing subcarrier modulation. Independently implemented and implemented digitally using IFFT method. The CI OFDM transmitter has a structure corresponding to the CI OFDM transmitter. The CI OFDM transmitter is divided into an FFT unit performing subcarrier demodulation and a CI code despreader performing CI code despreading.

Accordingly, by implementing a simple digital implementation method, while effectively reducing the conventional system complexity and computational complexity of the CI OFDM structure, while solving the high PAPR problem of the conventional OFDM structure, it is possible to provide efficient and stable data transmission.

CI spreading code, OFDM, IFFT, FFT

Description

Transmitter and receiver of digital implemented carrier interferometry orthogonal frequency division multiplexing, method of transmitting and receiving information}

1 is a block diagram of a transmitter of a conventional OFDM system causing high PAPR.

2 to 3 are transmitter block diagrams and receiver block diagrams of a conventional CI OFDM system having complex system structures and calculations.

4 is a block diagram of a transmitter in a CI OFDM system according to an embodiment of the present invention.

FIG. 5 is a detailed configuration diagram of the CI code diffuser of FIG. 4.

6 is a block diagram of a receiver of a CI OFDM system according to an embodiment of the present invention.

FIG. 7 is a detailed configuration diagram of the CI code despreader of FIG. 6.

8 is a diagram illustrating a transmission method of a CI OFDM system according to an embodiment of the present invention.

9 is a diagram illustrating a receiving method of a CI OFDM system according to an embodiment of the present invention.

10 is a graph illustrating a comparison of the spectrum of the output signal of the CI OFDM system and the CI OFDM transmitter of FIGS. 1 and 2 according to an embodiment of the present invention.

FIG. 11 is a graph illustrating comparison between PAPRs of a CI OFDM system according to an embodiment of the present invention and the CI OFDM systems of FIGS. 1 and 2.

12 is a graph illustrating bit error rate performance (BER) in the AWGN channel of the CI OFDM system and the CI OFDM system of FIGS. 1 and 2 according to an embodiment of the present invention.

FIG. 13 is a graph illustrating bit error rate performance (BER) in a frequency non-selective Rayleigh channel of a CI OFDM system and a CI OFDM system of FIGS. 1 and 2 according to an embodiment of the present invention.

FIG. 14 is a graph illustrating bit error rate performance (BER) in a frequency selective Rayleigh channel of a CI OFDM system and a CI OFDM system of FIGS. 1 and 2 according to an embodiment of the present invention.

The present invention relates to a digitally implemented carrier interferometry orthogonal frequency division multiplexing (hereinafter referred to as "CI-OFDM") transmitter and receiver and a method for transmitting and receiving the same.

Orthogonal frequency division multiplexing (hereinafter referred to as “OFDM”) communication is a method of dividing an entire transmission band into a plurality of narrowband orthogonal subchannels and simultaneously transmitting data to each subchannel. Is as shown in FIG.

1 is a block diagram of a transmitter in a conventional OFDM system.

According to FIG. 1, the input signal d is converted into parallel data by the number of subcarrier signals by a serial to parallel converter (hereinafter referred to as “S / P”) 101. After passing through the IFFT operation unit 103, a parallel to serial converter (hereinafter referred to as "P / S") 105 is converted into serial data and a high power amplifier (hereinafter referred to as "HPA"). 107).

However, the output signal before passing through the HPA 107 generates a high peak-to-average power ratio (hereinafter referred to as “PAPR”) due to the sum of all subcarrier signals.

Therefore, the conventional OFDM communication method causes nonlinear distortion in a high power amplifier (HPA) due to high PAPR and causes interference to adjacent channels as well as in-band interference signals, thereby greatly reducing the power efficiency of the high output amplifier. Let's do it.

Therefore, it is very important to reduce the high PAPR, which is generated when multiple, parallel input data are combined, to a low PAPR.

Accordingly, the following methods for reducing such PAPR in the OFDM communication scheme have been proposed.

1) May 1997 X. Li and LJ Cimini Jr. Vehicular Technology Conference , vol. Influence of the clipping technique on the performance of OFDM systems with transmit diversity, presented in Fig. 3, 2) in July 1995, by TA Wilkinson and AE Jones. of IEEE VTC'95, PAPR Minimization Technique in Multicarrier Transmission Systems Using Block Coding Method, published by Chicago, 3) October 1996 RW Bauml. RF Fischer and JB Huber published in IEE Electronic Letters, vol. 32, PAPR Reduction Techniques for Multi-Carrier Method Using Selective Mapping Method, February 1997. SH Muller and JB Huber published IEE Electronic Letters, vol. 33, a PAPR reduction technique in an OFDM system using a partial transmit sequences (PTS) method.

Here, the PTS (partial transmit sequences) method and the SLM (selective mapping) method have an advantage of reducing PAPR without distortion of a signal, but have limitations in the reduction. In addition, there are disadvantages such as transmission of side-information using a large amount of computation and additional channels.

And, since the clipping technique distorts the signal itself, it can provide a certain PAPR reduction effect as desired. However, since the clipped signal cannot be completely recovered at the receiver, the bit error rate of the system is “ BER ”) is very bad.

In the block coding method, a coding technique is added to the extra carrier so that the PAPR of the signal is lowered and transmitted. This technique can reduce PAPR without distortion, as well as error correction, but with very poor spectral efficiency and a large look-up table or generation matrix, which is very complex and computational. .

Meanwhile, another conventional OFDM communication method for reducing PAPR is CI OFDM.

Such a CI OFDM system is as shown in Figs.

That is, as shown in Figure 2, the CI OFDM transmitter 200 modulates the input data to all N carriers via the S / P converter 201. At this time, the CI code spreading unit 203 uses a special orthogonal spreading code called CI spreading code for the data located on the individual subcarriers. This is orthogonal in frequency and enables orthogonality among all N transmitted data.

In this case, the CI diffusion process P100 performed by the CI code diffusion unit 203 and the summer 205 may be expressed as follows.

은 전체 부반송파 수이고,

는 부반송파 간격이고,

는 k번 째 병렬데이터에 할당된 기저확산 위상 오프셋(base spreading phase offset)이다. 일반적인 표현을 위하여 k번 째 병렬데이터에 해당하는 CI 확산 시퀸스 계열을 다음과 같이 정의한다.

Is the total number of subcarriers,

Is the subcarrier spacing,

Is the base spreading phase offset assigned to the kth parallel data. For general expression, the CI spreading sequence series corresponding to the kth parallel data is defined as follows.

The transmission signal before passing through the HPA 207 is expressed as follows.

는 k번 째 병렬 브랜치에 있는 송신 데이터이고

는 중심 주파수이며 비트 주기는

이며 p(t)는 구형펄스라고 가정한다.

Is the transmission data in the kth parallel branch

Is the center frequency and the bit period is

And p (t) is assumed to be a spherical pulse.

Then, the received signal in the CI OFDM receiver 300 is as follows.

와

는 i번 째 캐리어의 페이드 파라미터(fade parameter)와 위상오프셋(phase offset)이고 n(t)는 전력스펙트럼밀도가

인 추가적인 백색 가우시안 잡음(AWGN: additive white Gaussian noise)이다.R (t) is the received signal

Wow

Is the fade parameter and phase offset of the ith carrier and n (t) is the power spectrum density.

Additive white Gaussian noise (AWGN).

That is, according to FIG. 3, the CI OFDM receiver 300 separates the received data into subcarrier signals based on the corresponding CI spreading code through the CI code despreading process P200 by the CI code despreading unit 301. do. This is converted in series by the P / S converter 303, and the determination unit 305 determines and outputs the final symbol estimate.

However, since the CI-OFDM scheme modulates each parallel channel and then adds a CI spreading code and transmits the sum signal, the increase in the number of parallel subchannels causes an increase in hardware complexity, which makes carrier expansion difficult. . In addition, a CI spreading code is added and a calculation is complicated when summing a modulated signal in each parallel channel.

Accordingly, the technical problem to be achieved by the present invention is to provide a CI OFDM system and method that can solve the PAPR problem and transmit high-performance and high-efficiency data while reducing the difficulty of carrier expansion, high system complexity and computational complexity.

According to a feature of the invention for achieving the above problem,

CI OFDM transmitter,

CLAIMS 1. A transmitter in a CI Carrier Interferometry Orthogonal Frequency Division Multiplexing (CI OFDM) system, comprising: a CI code spreader for performing CI code spreading for spreading a plurality of parallel data by corresponding CI spreading code vectors; And a modulator configured to modulate the parallel data on which the CI code spreading is performed to corresponding sub-carriers using fast Fourier inverse transform (IFFT).

According to another feature of the invention,

CI OFDM receiver,

A receiver in a CI OFDM system, comprising: a demodulator for demodulating a received multicarrier signal for each corresponding subcarrier using fast Fourier transform (FFT); And a CI code despreading unit for performing the CI code despreading process of removing the phase offset and combining the demodulated subcarrier signals based on the corresponding CI spreading codes.

According to another feature of the invention,

The transmission method of the CI OFDM transmitter is

A method of transmitting a CI OFDM transmitter, comprising: (a) converting a plurality of serially input serial data into a plurality of first parallel data; (b) generating second parallel data by multiplying the first parallel data by a corresponding CI spreading code vector; (c) performing a fast Fourier inverse transform that modulates the second parallel data into corresponding subcarriers, respectively; And (d) transmitting a multicarrier signal obtained by serially converting the fast Fourier inverse transformed second parallel data.

According to another feature of the invention,

Receiving method of the CI OFDM receiver,

A reception method of a CI OFDM receiver, comprising: (a) performing a fast Fourier transform that separates a received multicarrier signal into subcarrier signals by corresponding CI spreading codes; (b) removing and combining phase offsets for each of the separated subcarrier signals; And (c) outputting the multicarrier signal estimated through the predetermined channel estimation process for the combined subcarrier signal.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification. In addition, when a part is said to "include" a certain component, this means that it may further include other components, except to exclude other components unless otherwise stated.

A digitally implemented CI OFDM transmitter and receiver according to an embodiment of the present invention and a method of transmitting and receiving the same will now be described in detail with reference to the accompanying drawings.

4 to 7 are block diagrams of a CI OFDM system according to an embodiment of the present invention.

As shown in the figure, a CI OFDM system according to an embodiment of the present invention is digitally implemented and a simplified structure of a transmitter and a receiver using fast Fourier inverse, transform (IFFT, FFT) technique.

First, FIG. 4 is a block diagram of a transmitter of a CI OFDM system according to an embodiment of the present invention.

That is, according to FIG. 4, the CI OFDM transmitter 400 includes an S / P converter 401, a CI code spreader 403, a modulator 405, a P / S converter 407, an HPA 409, and the like. An antenna 411 is included.

The S / P converter 401 converts serially input serial data into N first parallel data. Here, 'N' means the number of parallel subchannels.

The CI code spreading unit 403 spreads the first parallel data converted by the S / P converting unit 401 with each corresponding CI spreading code to generate second parallel data. In this case, the CI code spread may use an IFFT operation.

The modulator 405 IFFT-processes the second parallel data generated by the CI code spreader 403 to modulate the corresponding subcarriers.

The P / S converter 407 converts the IFFT processed subcarriers in series to generate and output a multicarrier signal.

The HPA 409 amplifies the multicarrier signal output from the P / S converter 407.

The antenna 411 transmits the multicarrier signal amplified by the HPA 409.

Next, FIG. 5 is a diagram illustrating CI code spreading by the CI code spreading unit 403 in detail.

That is, according to Figure 5, the process of spreading the CI code is as follows.

Here, S _i is newly defined by the following equation.

Then, the newly defined S _i is expanded as follows.

는 i번째 병렬 브랜치의 CI 확산 시퀀스 계열인

에 속하는 하나의 CI 확산 코드이다. 즉, 제1 병렬 데이터(

)는 대응하는 직교 CI 확산 코드 벡터([c_i])에 곱해져 새로운 제2 병렬 데이터(S_i=

)를 생성한다. 이 과정을 CI 코드 확산(CI code spreading)이라고 정의한다. 그리고, 제2 병렬 데이터(S_i)는 제CI 확산 코드 벡터를 각각 곱해서 합산부(404)에 의해 합산한 결과이다.here,

Is a sequence of CI spreading sequences of the i parallel branch.

One CI spreading code belonging to. That is, the first parallel data (

) Is multiplied by the corresponding orthogonal CI spreading code vector [c _i ] to obtain new second parallel data S _i =

) This process is called CI code spreading. And, a second parallel data (S _i) is the result of summing by the CI spreading code vector to adder 404 by multiplying respectively.

Here, the second parallel data (S _i) may maintain a first parallel data CI OFDM inherent frequency diversity properties because the composition a certain combination of a (d _k) in the conventional OFDM CI.

The newly defined _Si is modulated by the modulator 405 to the corresponding carrier.

Now, the CI OFDM receiver 500 implemented with the structure corresponding to the CI OFDM transmitter 400 will be described.

First, FIG. 6 is a block diagram of a receiver of a CI OFDM system according to an embodiment of the present invention.

That is, according to FIG. 6, the CI OFDM receiver 500 includes an antenna 501, an S / P converter 503, a demodulator 505, a CI code despreader 507, and a P / S converter 509. And a determination unit 511.

The antenna 501 receives a multicarrier signal transmitted by the CI OFDM transmitter 400 through a predetermined channel.

The S / P converter 503 converts a multicarrier signal received in series through the antenna 501 into a parallel carrier signal.

The demodulator 505 separates each carrier signal, which the S / P converter 503 converts in parallel, into N orthogonal subcarrier signals through an FFT operation.

After performing the channel compensation, the CI code despreader 507 removes the phase offsets in each of the separated subcarrier signals. The vectors obtained from the individual subcarriers are combined into a carrier signal based on a predetermined combining method. In this case, CI code despreading may be implemented by an FFT operation. That is, when the channel is an additive white Gaussian noise (AWGN) channel, an FFT operation is possible because EGC (equal gain combining) is possible in the combiner 508. In this case, the combiner 508 may identify the reception channel of the received multicarrier signal and combine the carrier signals from which the phase offset is removed using the combination technique selected accordingly. The combination technique may combine carrier signals using a technique including any one or more of an equal gain combining (EGC) technique or a minimum mean square error combining technique (MMSE).

The P / S converter 509 converts the combined parallel carrier signals in series and outputs them.

The determination unit 511 outputs an estimated value of the output serial carrier signal through a predetermined channel estimation process. That is, the CI OFDM transmitter 400 performs hard decision and soft decision of the received multicarrier signal with respect to the multicarrier signal. Accordingly, the final symbol estimate is exported.

Next, FIG. 7 is a diagram illustrating a CI code inverse conversion process by the CI code despreader 507 in detail.

That is, according to Figure 6, the signal received from the CI OFDM transmitter 400 can be expressed as follows.

는 도 4를 참조하여 설명한 CI OFDM 송신기(400)의 제2 병렬 데이터(S_i)를 나타낸다.here,

Represents the second parallel data (S _i) of the CI OFDM transmitter 400 is described with reference to FIG.

)을 제거하고 이를 다시 조합한다. 이를 통해 서브 캐리어 신호 사이의 직교성을 보존할 수 있고 주파수 다이버시티 이득을 최대화하며 간섭과 노이즈 영향을 최소화할 수 있다. 여기서, 조합의 방법으로는 수신 채널 환경에 따라 EGC(equal gain combining)기법 또는 MMSEC (minimum mean-square error combining)기법을 이용하여 다른 확산 코드 및 노이즈에 의하여 발생하는 ISI(inter-symbol-interference)를 최소화할 수 있다.This CI code despreading uses the FFT operation to phase-separate the separated subcarrier signals.

) And recombine them. This preserves orthogonality between subcarrier signals, maximizes frequency diversity gain, and minimizes interference and noise effects. Here, as a combination method, an inter-symbol-interference (ISI) generated by different spreading codes and noises using EGC (equal gain combining) or MMSEC (minimum mean-square error combining) according to a reception channel environment. Can be minimized.

As described above, the CI-OFDM transmitter 400 performs CI code spreading and modulation by one CI code spreader 403 and one modulator 405 independently of each other, and performs simple discrete IFFT. It is a digital implementation using arithmetic. The receiver 500 having a structure corresponding to the CI OFDM transmitter 400 has a separate structure independent of the demodulator 505 and the CI code despreader 507, and decodes and spreads the CI code by FFT operation. Perform

Thus, N ^N Times carrier modulation and N ^N The CI spreading code multiplication operation is replaced by the carrier modulation by N IFFT operations by independent continuous operation of the CI code spreading unit 403 and one IFFT unit 405. Thus, the structure of the CI OFDM transmitter is not only very simplified but also considerably reduces the computational complexity.

In addition, since one IFFT unit 405 allocates a carrier, the complexity of the system due to the hardware addition of the carrier allocator may be simplified. This, of course, facilitates carrier expansion.

When the optional CI code has a maximum power of any d _i , the remaining N-1 d _k powers have a minimum value, and thus output a signal with stable amplitude and averaged PAPR. .

The same applies to the CI OFDM receiver 500.

Then, the transmission method and the reception method by the CI OFDM transmitter 400 and the receiver 500 will be described respectively.

8 is a diagram illustrating a transmission method of a CI OFDM transmitter 400 according to an embodiment of the present invention.

That is, according to FIG. 8, first, serial data sequentially input (S101) is converted into a plurality of first parallel data (S103).

Then, the second parallel data is generated by performing the CI code spreading process using the CI spreading codes corresponding to the first parallel data (S105). In this case, the CI code spreading process may be implemented by an IFFT operation.

Then, IFFT is performed to modulate the second parallel data to the corresponding subcarrier (S107).

Then, the multicarrier signal obtained by serially converting the second parallel data modulated by the IFFT operation (S109) is transmitted (S111).

9 is a diagram illustrating a reception method of a CI OFDM receiver 500 according to an embodiment of the present invention.

That is, according to FIG. 9, first, a multicarrier signal transmitted by the CI OFDM transmitter 300 is received (S201) and converted into parallel using a predetermined channel agreed with the CI OFDM transmitter 400 (S203). In this case, the channel may include at least one of an additive white Gaussian noise channel (AWGN channel), a flat fading channel, and a frequency selective channel.

Then, an FFT operation is performed to separate the received multicarrier signals into subcarrier signals by corresponding CI spreading codes (S205).

Then, the phase offset is removed for each of the separated subcarrier signals and combined (S207). In this case, the combination may be performed as follows according to the reception channel.

That is, first, the reception channel of the multi-carrier signal in the step S201 is checked (S209).

In this case, when the reception channel is an additive white Gaussian noise channel (S211) or when it corresponds to a flat fading channel (S213), the phase offset of each subcarrier signal is removed and combined by an equal gain combining method (EGC). (S215).

In addition, when the reception channel corresponds to the frequency selective channel (S217), each subcarrier signal from which the phase offset is removed is combined by a minimum mean square error combining (MMSE) technique (S219).

Then, the multicarrier signal estimated through the predetermined channel estimation process is output with respect to the subcarrier signals combined in steps S207 to S219 (S221).

10 to 14 show simulation results of PAPR reduction due to an improved CI OFDM structure according to an embodiment of the present invention.

First, FIG. 10 is a graph illustrating a result of comparing a spectrum of an output signal of a CI OFDM system according to an embodiment of the present invention and a conventional OFDM system of FIG. 1.

That is, when the number of subcarriers (N) is 2048, the spectrum of transmission signals in the conventional OFDM transmitter 100 and the CI OFDM systems 400 and 500 according to the embodiment of the present invention are shown.

According to FIG. 10, out of band spectrum due to the use of a digitally implemented CI OFDM structure according to an embodiment of the present invention, with or without a solid state power amplifier (hereinafter referred to as "SSPA"). It can be seen that the regrowth is reduced compared to the conventional OFDM structure.

Next, FIG. 11 is a graph illustrating a comparison between PAPR of a CI OFDM system according to an embodiment of the present invention and the conventional OFDM of FIG. 1 and the conventional CI OFDM system of FIGS. 2 and 3.

That is, when the number of subcarriers (N) is 12, 64, and 2048, respectively, complementary cumulative distribution of PAPR generated in conventional OFDM, conventional CI OFDM, and CI-OFDM of a digital implementation according to an embodiment of the present invention. function).

According to FIG. 11, it can be seen that the digitally implemented CI OFDM structure according to the embodiment of the present invention significantly reduces the PAPR than the conventional OFDM.

In addition, unlike the conventional CI OFDM structure, which is difficult to expand the system, the digitally implemented CI-OFDM structure according to the embodiment of the present invention is easy to implement even when the number of subcarriers is greatly increased (eg, 2048). This avoids system and computational complexity issues.

12 is a graph illustrating bit error rate performance (BER) in the AWGN channel of the CI OFDM system and the OFDM system of FIG. 1 according to an embodiment of the present invention.

According to FIG. 12, when the SSPA amplifier is used, a digitally implemented CI OFDM structure according to an embodiment of the present invention shows better BER performance regardless of the number N of subcarriers.

FIG. 13 is a graph illustrating bit error rate performance (BER) in a frequency non-selective Rayleigh channel of a CI OFDM system and an OFDM system of FIG. 1 according to an embodiment of the present invention.

According to FIG. 13, a digitally implemented CI OFDM structure according to an embodiment of the present invention provides better BER performance regardless of the number of subcarriers using SSPA or using a linear amplifier (or without HPA). see. Through this, it can be seen indirectly that a digitally implemented CI OFDM structure according to an embodiment of the present invention has better performance even in a Rayleigh channel environment.

14 is a graph illustrating bit error rate performance (BER) in a frequency selective Rayleigh channel of a CI OFDM system and an OFDM system of FIG. 1 according to an embodiment of the present invention.

According to FIG. 14, as can be seen indirectly from FIG. 13, the digitally implemented CI OFDM structure according to the embodiment of the present invention not only provides excellent bit error rate performance but also frequency diversity gain in frequency selective Rayleigh channel. It can be seen that it has.

The embodiments of the present invention described above are not implemented only through the apparatus and the method, but may be implemented through a program for realizing a function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded. Implementation may be easily implemented by those skilled in the art from the description of the above-described embodiments. The scope of the present invention is not limited to the above-described embodiments, but various modifications and improvements of those skilled in the art using the basic concept of the present invention as defined in the following claims are also within the scope of the present invention.

By the above-described configuration, it is possible to prevent the occurrence of high PAPR of the output signal and to have a stable amplitude, averaged PAPR, thereby improving the PAPR reduction performance.

In addition, while maintaining the frequency diversity characteristics of the conventional CI-OFDM system, it is possible to reduce the complexity of the system structure and computational complexity and to easily expand to a system having a large number of subcarriers.

Claims (12)

In the transmitter of a CI Carrier Interferometry Orthogonal Frequency Division Multiplexing (OFDM) system, A CI code spreading unit for performing CI code spreading for spreading a plurality of parallel data with corresponding CI spreading code vectors; And A modulator for modulating the parallel data received from the CI code spreader into corresponding sub-carriers using fast Fourier inverse transform (IFFT) Transmitter comprising a. According to claim 1, The CI code diffusion unit, And performing the CI code spreading using fast Fourier inverse transform (IFFT). The method according to claim 1 or 2, Transmitter for transmitting the multi-carrier signal output from the modulator and serially converted Transmitter further comprising. In the receiver of the CI OFDM system, A demodulator for demodulating the received multicarrier signal for each corresponding subcarrier using a Fast Fourier Transform (FFT); And A CI code despreading unit which performs a CI code despreading process of removing a phase offset and combining the demodulated subcarrier signals based on a corresponding CI spreading code Receiver comprising a. The method of claim 4, wherein The CI code despreading unit, And performing the CI code despreading process using a fast Fourier transform. The method according to claim 4 or 5, The CI code despreading unit, Combination unit for checking the reception channel of the multi-carrier signal and combining the carrier signal from which the phase offset is removed using the selected combination method Receiver comprising a. The method of claim 6, The combination part, And combining the carrier signal using a technique including at least one of equal gain combining (EGC) and minimum mean square error combining (MMSE). In the transmission method of the CI OFDM transmitter, (a) converting a plurality of serial data sequentially input into a plurality of first parallel data; (b) generating second parallel data by multiplying the first parallel data by a corresponding CI spreading code vector; (c) performing a fast Fourier inverse transform that modulates the second parallel data into corresponding subcarriers, respectively; And (d) transmitting a multicarrier signal obtained by serially converting the fast Fourier inverse transformed second parallel data; Transmission method comprising a. The method of claim 8, In step (b), And CI code spreading the first parallel data into the second parallel data by a fast Fourier inverse transform. In the reception method of a CI OFDM receiver, (a) performing a fast Fourier transform that separates the received multicarrier signals into subcarrier signals by corresponding CI spreading codes, respectively; (b) removing and combining phase offsets according to the separated subcarrier signals; And (c) outputting a multicarrier signal estimated through a predetermined channel estimation process for the combined subcarrier signal; Receiving method comprising a. The method of claim 10, Before step (a) above, Receiving the multicarrier signal using a channel comprising at least one of an additive white Gaussian noise channel (AWGN channel), a flat fading channel and a frequency selective channel Receiving method further comprising. The method of claim 11, In step (b), Determining a reception channel of the multicarrier signal; As a result of the determination, when the reception channel corresponds to the additional white Gaussian noise channel or the flat fading channel, combining received data separated by subcarriers from which the phase offset is removed by an equal gain combining method (EGC); And As a result of the determination, combining the subcarrier signal from which the phase offset is removed by a minimum mean square error combining (MMSE) technique when the reception channel is the frequency selective channel; Receiving method comprising a.

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