JP2003032222A - Equalizer for ofdm demodulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an equalizer for an OFDM demodulator which enables adequate equalization of a transmission line, when transmission line characteristics change within a single frame period, without deteriorating the transmission efficiency in one frame. SOLUTION: Regarding initial several symbols of a data signal, equalization is performs by a preamble signal, in a manner similar to the conventional. Regarding to the following signal, equalization of a transmission line is performed by the following manner. A soft decision part 5 performs soft decision, stores the result in a RAM 6 and inputs the result in an error correction part 7, in which received data S4, after error correction, are obtained. A coding part 8 performs re-encoding of the received data S4, and a mapping part 9 performs mapping. The signal is compared with a signal of the RAM 6 by a transmission line predicting part 10 by each frequency, and equalization coefficients are calculated. An estimation error eliminating part 11 eliminates error data of soft decision result, and an averaging part 12 averages several symbols. Setting is performed in an equalization coefficient setting part 4a, thereby conducting equalization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM (Orthogonal Frequency Division Multiplexing) OFDM used for demodulation of wireless transmission.
The present invention relates to a demodulator equalizer.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram of essential parts for explaining a conventional equalizer for an OFDM demodulator. Received signal S3 in the time domain after establishing synchronization with the internal clock
Is input to the FFT 206 and converted into a reception signal in the frequency domain. The transmission path estimation unit 2 estimates the transmission path and determines the equalization coefficient by comparing the preamble signal inserted at the beginning of the frame of the received signal with the correct preamble signal in the frequency domain stored in the ROM 3. . The determined equalization coefficient is set in the equalization coefficient setting section 74a of the equalization section 74, and the equalization section 74 multiplies the equalization coefficient by the data symbol in the frequency domain to compensate for the frequency transmission characteristic of the transmission path. For equalization of. The soft decision unit 75 compares the data on the mapping obtained by the equalization unit 74 with the reference data to make a soft decision, and inputs the soft decision to the error correction unit 77. The error correction unit 77 obtains the reception data S74 after error correction by, for example, Viterbi demodulation, corresponding to the type of error correction code of the reception signal S3. As described above, in the conventional equalizer for OFDM demodulator, the equalization is performed by estimating the transmission characteristic of the transmission line only from the preamble signal for synchronization which is the known signal inserted at the beginning of the frame of the transmitted signal. The coefficient was decided. Therefore, since this equalization coefficient is used for one frame period, appropriate equalization will not be performed if the transmission path characteristics change during one frame period, and the deterioration of communication quality will increase. There was a problem. This problem is caused by shortening the frame length or
This can be avoided by inserting many pilot signals in the frame, but this causes a problem that the data transmission efficiency in one frame is reduced.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is suitable for a transmission line even when the transmission line characteristic changes in one frame period without lowering the transmission efficiency in one frame. O which can perform the equalization of
An object is to provide an equalizer for an FDM demodulator.

[0004]

OFDM demodulation for ensuring transmission quality by equalizing frequency transmission characteristics of a transmission line when demodulating transmission data transmitted using an OFDM (Orthogonal Frequency Division Multiplexing) system In the dexterous equalizer,
Estimating the frequency transmission characteristic of the transmission line by comparing the signal level of the data symbol in the frequency domain of the transmitted data symbol and the signal level of the data symbol in the frequency domain of the previously transmitted data symbol to estimate the transmission characteristic A transmission line estimation unit that determines an equalization coefficient for equalizing the transmission line and an equalization unit that compensates and equalizes the transmission characteristics of the transmission line by the determined equalization coefficient are provided. Perform channel estimation.

An error correction unit for error-correcting and demodulating the transmitted data symbols, an encoding unit for re-encoding the error-corrected signal, and a mapping unit for mapping the encoded signal are provided. A data symbol obtained by mapping a signal after error correction is used as the transmitted data symbol.

A soft decision unit for comparing data on a mapping with a reference value to determine a data symbol and a RAM for storing the result of the soft decision are provided, and the soft decision result is compared with the previously transmitted data symbol. Use it as a data symbol.

When the equalization coefficient determined by the transmission path estimation section is larger than a predetermined value, an estimation error determination section for excluding the equalization coefficient is provided to exclude the equalization coefficient determined from a data symbol having a possibility of error. To do so.

An averaging unit for averaging equalization coefficients determined by the transmission path estimation unit over several symbols is provided, and the equalization coefficient averaged over several symbols is used by the equalization unit.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic block diagram of (A) transmitting side and (B) receiving side of a wireless communication device using OFDM (Orthogonal Frequency Division Multiplexing) according to the present invention. First, on the transmission side, the scramble unit 101 scrambles the transmission data S1, and then the encoding unit 102 encodes the convolutional code, for example. Fig. 5 shows a restraint length of 7
FIG. 3 is a block diagram of an encoding unit that generates a bit convolutional code. Input signal S51 from scrambler 101 to 1
The first signal S52 and the second signal S convolutionally coded by the bit shift register Tb and the adders 51 and 52.
You get 53. The convolutionally encoded first signal S52 and second signal S53 are arranged bit by bit as (signal S52, signal S53, signal S52, signal S53) to form 4-bit data. The 4-bit data is mapped by the mapping unit 103 by, for example, 16QAM. FIG. 6 is a conceptual diagram of mapping in 16QAM. In 16QAM mapping, for example, 4-bit data (0000) is set to -3 of Ich as shown in FIG.
v, -3v for Qch, (1111) for 3v for Ich,
It corresponds to 3v of Qch. Here, each voltage of Ich and Qch is processed by 8-bit data of 256 levels, for example. The IFFT unit 104 performs an inverse Fourier transform on the mapped data to form a signal in the time domain, and the DAC 105 forms an analog I / Q signal. The I / Q signal is quadrature-modulated by a quadrature function in the quadrature transform unit 106, and then RF
The modulator 108 outputs the RF modulated signal S2 to the antenna 108.
Send from

On the other hand, on the receiving side, the RF modulation signal S2 received by the antenna 201 is demodulated by the RF demodulation section 202 and further orthogonally demodulated by the orthogonal conversion section 203 to obtain I / Q signals.
After digitizing this I / Q signal by the ADC 204,
The synchronization unit 205 synchronizes with the internal clock and obtains the reception signal S3 in the synchronized time domain. FFT section 2
In 06, the received signal S3 is Fourier transformed into a received signal in the frequency domain, and then the equalizer 207 equalizes the transmission path characteristics. The soft-decision unit 208 divides the signal output through the equalized transmission characteristics into a plurality of pieces of reference data to obtain provisional reception data, and the error correction unit 209 makes an error by, for example, Viterbi demodulation. Make corrections,
The received data before descrambling is S4. After that, descrambling (not shown) descrambles the final received data.

FIG. 2 is a block diagram of essential parts for explaining an embodiment of an equalizer for an OFDM demodulator according to the present invention.
Further, FIG. 3 is a configuration diagram of one frame of the received signal.
The reception signal S3 includes a preamble signal S3a for synchronization of several tens of cycles, a symbol S3b indicating the communication speed and the data length, a number of data symbols S3c corresponding to the data length of the transmission data, and a TAIL signal indicating the end of the frame. It is a signal that forms one frame from S3d. For the first several symbols of the reception signal S3 of one frame, the transmission line characteristics are equalized as described below in the same manner as the conventional technique. The preamble signal in the frequency domain obtained by Fourier transforming the received signal S3 by the FFT unit 206 is input to the transmission path estimation unit 2 and compared with the correct preamble signal in the frequency domain written in the ROM in advance, and the amplitude ratio of each frequency is compared. The initial value of the equalization coefficient is determined from. Figure 4
FIG. 4 is a conceptual diagram showing (A) a received signal level for each frequency and (B) an equalization coefficient for each frequency of an equalizer for an OFDM demodulator. Here, the horizontal axis is frequency Xa and one scale is, for example, 2
It is 0/64 MHz. The signal level Ya is represented by ± 11 bits, for example. The equalization coefficient Yb is represented by the amplitude ratio for each frequency described above. As shown in FIG. 4, when the signal level Ya at the frequency Xa is large, the equalization coefficient Yb becomes small, and conversely, at the signal level Y at the frequency Xa.
The equalization coefficient Yb becomes large where a is large. The determined equalization coefficient is set in the equalization coefficient setting unit 4a of the equalization unit 4, and the equalization unit 4 multiplies the equalization coefficient by the data symbol in the frequency domain to compensate for the frequency transmission of the transmission path. Equalize the characteristics.

For the signals after the first few symbols of the data signal, the transmission lines are equalized as follows. The soft decision unit 5 makes a soft decision on the data on the mapping obtained by the equalization unit 4 as a value obtained by dividing the reference data into a plurality of values, stores the soft decision result in the RAM 6 and inputs it to the error correction unit 7. The error correction unit 7 obtains the error-corrected received data S4 by, for example, Viterbi demodulation, corresponding to the type of error correction code of the received signal S3. Received data S4
The coding unit 8 performs coding by the convolutional code described above, for example, in accordance with the type of error correction code of the received signal S3 (see the description of FIG. 5). The coded signal is matched with the transmitter in the mapping unit 9, for example, 16Q described above.
Mapping is performed by AM as shown in FIG. The transmission path estimation unit 1 receives the mapped signal and the signal stored in the RAM 6.
0 is compared for each frequency, and the equalization coefficient is calculated and set in the equalization coefficient setting unit 4a of the equalization unit 4 as shown in FIG. As a result, for signals after the first few symbols of the data signal, the equalization coefficient is determined by the previously transmitted data symbol.

When the soft decision result by the soft decision unit 5 input to the RAM 6 and the mapping data of the mapping unit 9 are largely different, there is a high possibility that the soft decision result is incorrect. Therefore, the estimation error excluding unit 11 compares the equalization coefficient for each frequency with a predetermined value, determines that the result of the soft decision is erroneous when it is larger than the predetermined value, and excludes it. . Further, an averaging unit 12 that averages the equalization coefficients determined by the transmission path estimation unit 10 over several symbols is provided, and the equalization coefficients averaged over several symbols are used by the equalization unit. As a result, more accurate equalization of transmission line characteristics can be performed.

[0014]

As described above, comparing the data symbol in the frequency domain of the data symbol transmitted by the equalizer for the OFDM demodulator with the data symbol in the frequency domain of the previously transmitted data symbol. A transmission path estimation unit that estimates the frequency transmission characteristics of the transmission path by using to determine the equalization coefficient for equalizing the transmission characteristics, and equalizes the transmission characteristics of the transmission path by using the determined equalization coefficient. A transmission section is provided so that transmission channel estimation is performed using the transmitted data symbols, so that even if the transmission channel characteristics change during one frame period, transmission channel characteristics can be changed without reducing transmission efficiency. Can be equalized, and it can be applied to a field such as mobile communication in which transmission characteristics are likely to change.

[Brief description of drawings]

FIG. 1 OFDM (Orthogonal Frequency Division Multiplexing) according to the present invention
FIG. 3 is a schematic block diagram of (A) a transmitting side and (B) a receiving side of a wireless communication device using the.

FIG. 2 is a block diagram of essential parts for explaining one embodiment of an equalizer for an OFDM demodulator according to the present invention.

FIG. 3 is a configuration diagram of one frame of a received signal.

FIG. 4 is a conceptual diagram showing (A) a received signal level for each frequency and (B) an equalization coefficient for each frequency of an equalizer for an OFDM demodulator.

FIG. 5 is a block diagram of an encoding unit that generates a convolutional code having a constraint length of 7 bits.

FIG. 6 is a conceptual diagram of mapping in 16QAM.

FIG. 7 is a main block diagram for explaining a conventional equalizer for an OFDM demodulator.

[Explanation of symbols]

2 Channel estimation unit 4 Equalization section 4a Equalization coefficient setting section 5 Soft decision section 6 RAM 7 Error correction section 8 Encoding section 9 Mapping section 10 Transmission path estimation unit 11 Estimated error exclusion section 12 Averaging unit 74 Equalizer 74a Equalization coefficient setting unit 75 Soft decision section 77 Error correction section 101 scramble section 102 encoding unit 103 mapping unit 104 IFFT section 105 DAC 106 Orthogonal transformation unit 107 RF modulator 108 antenna 201 antenna 202 RF demodulator 203 Quadrature demodulator 204 ADC 205 synchronization unit 206 FFT section 207 equalizer 208 Soft decision section 209 Error correction unit S1 transmission data S2 RF modulation signal S3 received signal S4 received data

Claims (5)

[Claims] 1. An equalizer for an OFDM demodulator that secures transmission quality by equalizing frequency transmission characteristics of a transmission line when demodulating transmission data transmitted using an OFDM (Orthogonal Frequency Division Multiplexing) system. In order to estimate the frequency transmission characteristic of the transmission path by comparing the signal level of the data symbol in the frequency domain of the transmitted data symbol and the signal level of the data symbol in the frequency domain of the previously transmitted data symbol. A transmission path estimation unit that determines the equalization coefficient for equalizing the transmission characteristics, and an equalization unit that compensates and equalizes the transmission characteristics of the transmission path with the determined equalization coefficient are provided, and the transmitted data symbols are OFDM characterized by performing transmission path estimation using
Equalizer for demodulator. 2. An error correction unit for error-correcting and demodulating a transmitted data symbol, an encoding unit for re-encoding the error-corrected signal, and a mapping unit for mapping the encoded signal. The data symbol obtained by mapping a signal after error correction is used as the data symbol transmitted in advance.
An equalizer for an OFDM demodulator as described in 1. 3. A soft decision section for comparing a signal on a mapping with a reference value to decide a data symbol, and a RAM for storing a result of the soft decision, wherein the soft decision result is the previously transmitted data symbol. The equalizer for an OFDM demodulator according to claim 1, wherein the equalizer is used as a data symbol to be compared with. 4. An equalization coefficient determined from a data symbol having a possibility of error by providing an estimation error determination section that excludes the equalization coefficient determined by the transmission path estimation section when it is larger than a predetermined value. The equalizer for an OFDM demodulator according to claim 1 or 2, wherein is excluded. 5. An averaging unit for averaging equalization coefficients determined by the transmission path estimation unit over several symbols is provided, and the equalization coefficient averaged over several symbols is used in the equalization unit. The OF according to any one of claims 1 to 4, characterized in that
Equalizer for DM demodulator.