WO2009134060A2

WO2009134060A2 - Ofdm receiver without reordering of sub-carrier and method for processing ofdm signal

Info

Publication number: WO2009134060A2
Application number: PCT/KR2009/002229
Authority: WO
Inventors: 박탄중
Original assignee: (주)에프씨아이
Priority date: 2008-04-28
Filing date: 2009-04-28
Publication date: 2009-11-05
Also published as: KR100980498B1; KR20090113519A; WO2009134060A3

Abstract

This invention discloses an OFDM receiver that does not require reordering of a sub-carrier and a method for processing an OFDM signal. The OFDM receiver comprises an I/Q demodulator, an FFT processor, a block for correcting fractional frequency errors, a first multiplier, a block for correcting integral frequency errors, a first adder and a second adder. The method for processing an OFDM signal comprises steps of: demodulating a received OFDM signal to an I/Q signal, applying an offset to the I/Q signal, and generating a spectrum signal by quickly Fourier-transforming the I/Q signal to which the offset is applied.

Description

OFDM receiver and OFDM signal processing method that does not require reordering of subcarriers

The present invention relates to an OFDM receiver, and more particularly, to an OFDM receiver and an OFDM signal processing method that do not require reordering of subcarriers.

Orthogonal Frequency Division Multiplexing (OFDM) divides one information into several subcarriers and adds orthogonal to minimize the spacing between the divided subcarriers. Multi-carrier transmission technology to transmit by multiplex. OFDM is expected to be widely used for 4G communication because it can solve the fading problem, which is a problem in broadband communication, efficiently utilize frequency resources, and easily integrate with technologies such as Multiple Input Multiple Output (MIMO). do. OFDM has a merit that high-speed communication is possible even under adverse conditions such as multipath interference due to reflection of radio waves by a mountaintop or a building, which has been a problem in a single carrier environment.

In general, an OFDM transmitter converts a signal in a frequency domain that modulates a signal to be transmitted into a signal in a time domain and transmits the received signal in a frequency domain. Convert it back to a signal and process it. The signal in the time domain is transformed into a signal in the frequency domain by fast Fourier transform (FFT), and the signal in the frequency domain is converted into a signal in the time domain by Inverse Fast Fourier Transform.

1 shows the flow of signals transmitted and received in an OFDM transmitter and a receiver.

Referring to FIG. 1, the transmitter 110 first generates a modulation spectrum signal 111 in which a signal to be transmitted is modulated. At this time, the modulation of the signal is supported by Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (16-QAM), and 32-QAM. The modulation spectrum signal 111 includes a portion (hatched portion) without modulated information in addition to the portion 0 to (N-1) with modulated information. The modulation spectrum signal 111 is ordered by the array spectrum signal 112 and then transmitted by inverse fast Fourier transform (113). The array spectrum signal 112 rotates the internal spectrum signal by a certain amount so that the unmodulated portion (hatched portion) at the bottom of the modulation spectrum signal 111 is centered.

The receiver 120 performs fast Fourier transform of the received time domain signal into a signal of frequency domain (123). The converted signal 122 corresponds to the array spectrum signal 112 at the transmitter 110. In a subsequent processing step, the channel estimation and the channel compensation according to the channel estimation are performed using the converted signal 122. For this purpose, the converted signal 122 is a modulation spectrum signal of the transmitter 110. It should be rearranged to the same type of spectral signal as 111).

When the rearrangement is performed in the OFDM receiver 120, a method of storing the converted signal 122 in the memory and rearranging the converted signal 122 into the modulated signal 121 and recomputing a subcarrier index This can be used. However, the above-described method has a disadvantage in that the receiver 120 is complicated and resources are increased because additional memory for rearrangement and additional generation of circuits or control signals necessary for performing the rearrangement are required. have.

An object of the present invention is to provide an OFDM receiver that does not require reordering of subcarriers.

Another technical problem to be solved by the present invention is to provide an OFDM signal processing method that does not require reordering of subcarriers.

A receiver according to the present invention for achieving the above technical problem, an I / Q demodulator, an FFT processing apparatus, a multiple frequency error correction block, a first multiplier, an integer multiple frequency error correction block, a first adder and a second adder.

The I / Q demodulator demodulates an I (In phase) signal and a Q (quadrature) signal having a phase difference of 90 ° from the I signal using an OFDM digital signal. The first multiplier multiplies the output of the I signal by the Q signal and the first adder. The FFT processor generates a spectral signal by performing a fast Fourier operation on the signal output from the first multiplier. The prime frequency frequency error correction block outputs a prime frequency error compensation value that cancels the frequency error of the prime multiples included in the signal output from the first multiplier. The integer frequency error correction block outputs an integer frequency error compensation value that cancels an integer frequency error included in a spectrum signal output from the FFT processing apparatus. The first adder adds the decimal frequency error compensation value and the output of the second adder. The second adder adds the integer frequency error compensation value and an offset value M to be added to the I signal and the Q signal.

The OFDM signal processing method according to the present invention for achieving the above another technical problem is an OFDM signal processing method for demodulating the received OFDM signal into an I / Q signal and then fast Fourier transform the received OFDM signal, I / Q signal Demodulating a signal, applying an offset to the I / Q signal, and generating a spectrum signal by performing Fast Fourier transform on the I / Q signal to which the offset is applied.

The receiver and the signal processing method according to the present invention have the advantage of simplifying the system and minimizing the resource since no reordering is performed after the FFT on the subcarriers when processing the received OFDM signal.

2 is a block diagram of an OFDM receiver that does not require reordering of subcarriers according to an embodiment of the present invention.

FIG. 3 defines the offset value M shown in FIG. 2.

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

Referring to FIG. 2, the OFDM receiver 200 includes an ADC 210, an I / Q demodulator 220, an FFT processor 230, a prime frequency error correction block 240, and a first multiplier M1. , Integer frequency error correction block 250, first adder A1, second adder A2, symbol delay unit 260, second multiplier M2, channel estimator 270, and equalizer 280. It is provided.

The ADC 210 generates the OFDM digital signal by converting an analog signal received through an OFDM multiple antenna. The I / Q demodulator 220 demodulates an I (In phase) signal and a Q (quadrature) signal having a phase difference of 90 ° from the I signal using an OFDM digital signal.

The first multiplier M1 multiplies the I signal, the Q signal, and the output of the first adder A1. The FFT processor 230 generates a spectral signal by performing a fast Fourier operation on the signal output from the first multiplier M1. The prime frequency error correction block 240 outputs a prime frequency error compensation value ER1 that cancels the prime frequency frequency error included in the signal output from the first multiplier M1. The integer frequency error correction block 250 outputs an integer frequency error compensation value ER2 that cancels the integer frequency error included in the spectrum signal output from the FFT processor 230. The first adder A1 adds the outputs of the decimal frequency error compensation value ER1 and the second adder A2. The second adder A2 adds the integer frequency error compensation value ER2 and an offset value M to be added to the I signal and the Q signal.

The symbol delay unit 260 delays the symbols constituting the spectrum signal output from the FFT processor 230. The channel estimator 270 estimates a channel by using the spectrum signal output from the FFT processor 230 and outputs a channel compensation signal. The second multiplier M2 multiplies the output signal of the symbol delay unit 260 and the output signal of the channel estimator 270. The equalizer 280 equalizes the output of the second multiplier M2.

FIG. 3 defines the offset value M shown in FIG. 2.

Referring to FIG. 3, the offset value M corresponds to the spectral signals 111 and 112 of FIG. 1 at the transmitter and includes a portion A of the portion with modulated information and a portion without modulated information. ) And the remaining portion (B) with the modulated information, the rotation of the spectral signal is generated by the sum of the portion (A) of the portion with the modulated information and the portion without the modulated information (hatched). Means the amount to make.

The operations of the other symbol delay unit 260, the channel estimator 270, and the equalizer 280 are generally known and will not be described in detail here.

Hereinafter, a mathematical reason for reordering performed after the FFT is no longer needed by compensating the offset of the I / Q signal in the receiver shown in FIG. 2 will be described.

An OFDM signal is formed by modulating an orthogonal carrier using a sequence of symbols generated by mapping an input bit stream into I / Q symbols, which are complex symbols. The OFDM signal obtained by reducing the bit stream through this process is shown in Equation 1.

Equation 1

Here, N is the number of subcarriers (sub-carriers), X [m] means the m-th symbol in the interval [0, N-1].

Assuming that the subcarriers shown in Equation 1 are shifted by M in the frequency domain, the shifted subcarriers can be expressed as Equation 2.

Equation 2

Referring to Equation 2, it can be seen that a subcarrier shifted by M in the frequency domain may be implemented by multiplying a sine wave having an M / N frequency in the time domain. In the OFDM receiver that does not require reordering of subcarriers according to the present invention, referring to FIG. 2, the rotation of the spectrum signal is achieved by applying an offset M to the I and Q signals.

In a conventional OFDM receiver, only a constant frequency error is considered for an I / Q signal, and then FFT is performed, and a process of reordering the FFT signal is performed. However, referring to FIG. 2, in the present invention, as shown in FIG. 2, at least the reordering is not performed at the time of performing the FFT or performed as necessary by applying an offset to the signal of the step before performing the FFT. Only a reordering block of is required.

In the above, only the apparatus called a receiver has been described, but a process performed by the receiver can be inferred as follows. That is, the OFDM signal processing method performed by the receiver is an OFDM signal processing method for demodulating a received OFDM signal into an I / Q signal and then performing fast Fourier transform, and demodulating the received OFDM signal into an I / Q signal. And applying an offset to the I / Q signal and generating a spectrum signal by performing fast Fourier transform on the I / Q signal to which the offset is applied.

In the above description, the technical idea of the present invention has been described with the accompanying drawings, which illustrate exemplary embodiments of the present invention by way of example and do not limit the present invention. In addition, it is apparent that any person having ordinary knowledge in the technical field to which the present invention belongs may make various modifications and imitations without departing from the scope of the technical idea of the present invention.

OFDM is expected to be widely used in 4G communication because it can solve the fading problem that is a problem in broadband communication, efficiently utilize frequency resources, and easily integrate with technologies such as MIMO (Multiple Input Multiple Output). do. OFDM may be widely used in the future by enabling high-speed communication even under bad conditions such as reflection of radio waves by mountain tops or buildings, which have been a problem in a single carrier environment, causing multipath interference.

Claims

An I / Q demodulator 220 for demodulating an I (In phase) signal and a Q (quadrature) signal having a phase difference of 90 ° from the I signal using an OFDM digital signal;

A first multiplier (M1) that multiplies the output of the I signal by the Q signal and a first adder;

An FFT processor 230 generating a spectral signal by performing a fast Fourier operation on the signal output from the first multiplier;

A multiples frequency error correction block 240 for outputting a multiples frequency error compensation value ER1 that cancels the multiples frequency error included in the signal output from the first multiplier M1;

An integer frequency error correction block 250 for outputting an integer frequency error compensation value ER2 that cancels an integer frequency error included in the spectrum signal;

A first adder (A1) for adding outputs of the fractional frequency error compensation value (ER1) and a second adder (A2); And

And a second adder (A2) for adding the integer frequency error compensation value (ER2) and an offset value (M) to be added to the I signal and the Q signal. .
The method of claim 1,

And an ADC (210) for converting an analog signal received through an OFDM multiple antenna to generate the OFDM digital signal.
The method of claim 1,

A symbol delay unit (260) for delaying symbols constituting the spectrum signal;

A channel estimator 270 for estimating a channel using the spectrum signal and outputting a channel compensation signal;

A second multiplier (M2) for multiplying an output signal of the symbol delay unit and an output signal of the channel estimator; And

And an equalizer (280) for equalizing the output of the second multiplier (M2).
The method of claim 1,

The offset value (M) is,

When the spectral signal at the transmitter corresponding to the spectral signal is arranged in the order of a part of the part with modulated information, a part without modulated information and the remaining part with modulated information,

And reordering of subcarriers, wherein the spectral signal is rotated by a sum of a portion of the portion with modulated information and a portion without the modulated information.
An OFDM signal processing method for demodulating a received OFDM signal into an I / Q signal and then performing fast Fourier transform on the received OFDM signal,

Demodulating the received OFDM signal into an I / Q signal;

Applying an offset to the I / Q signal; And

And a fast Fourier transforming the I / Q signal to which the offset is applied to generate a spectral signal.
The method of claim 5,

The offset is,

When the spectral signal at the transmitter corresponding to the spectral signal is arranged in the order of a part of the part with modulated information, a part without modulated information and the remaining part with modulated information,

OFDM signal processing method, characterized in that the rotation of the spectrum signal by the sum of the portion of the portion with the modulated information and the portion without the modulated information.