JP2008277936A - Ofdm reception device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable an OFDM reception device which receives a signal of its channel having been subjected to error correction encoding and modulation by an OFDM modulation system to precisely perform error correction decoding even in case of adjacent channel interference. <P>SOLUTION: Reception means 1 to 6 receive signals, and interference information detection means 9 to 12 detect information regarding the level of adjacent channel interference based upon the received signals; and a carrier determination means 12 determines a carrier lowering a soft decision likelihood at a frequency band end of its channel based upon the detected information, and a demodulating means 7 demodulates the received signals. Then an error correcting means 8 lowers the determined soft decision likelihood of the carrier based upon the demodulation results to subject the signal of its channel to the error correction decoding. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an OFDM receiver that receives a signal modulated by an Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme, and in particular, performs error correction decoding with high accuracy even when adjacent channel interference occurs. The present invention relates to an OFDM receiving apparatus.

For example, as a modulation method suitable for application to mobile digital transmission and terrestrial digital television broadcasting, an OFDM modulation method characterized by resistance to multipath fading and ghost has been attracting attention.
The OFDM modulation scheme is a type of multi-carrier modulation scheme, and is a transmission scheme that performs digital modulation on n (n is several tens to several hundreds) carrier waves (carriers) orthogonal to each other.
As digital modulation methods for these carriers, multi-value modulation methods such as 16-value quadrature amplitude modulation (16QAM: 16 Quadri Amplitude Modulation) and 64QAM are often used.

JP 2005-175878 A JP 2000-307544 A

In recent years, frequency resources have become tight and transmission with high frequency efficiency is desired. For this reason, a plurality of adjacent channels may be used by a plurality of users. When mobile transmission is performed in such an operation, the reception power of the adjacent channel may be larger than the reception power of the own channel due to the influence of fading, shadowing, and the like.
In general, in operations using adjacent channels, the amount of interference with adjacent channels is reduced by defining a spectrum mask of a transmission signal and providing a frequency margin between channels called guard bands.

However, when the DU ratio (desired signal power to interference signal power ratio) is high and the interference exceeds the allowable amount, the leakage power from the adjacent channel is mixed into the own channel and adjacent channel interference occurs. May end up.
FIG. 8 shows an example of the state of adjacent channel interference. The horizontal axis represents frequency (f). The signal spectrum of the frequency band of the own channel signal and the signal spectrum of the frequency domain of the adjacent channel signal are shown.
In this example, a part of the spectrum of the adjacent channel signal (shaded portion in FIG. 8) interferes with the spectrum of the own channel signal.
Such an amount of interference becomes the largest at the band edge, and the code error rate at the band edge deteriorates.

As described above, in the conventional OFDM receiver, in the OFDM transmission using the adjacent channel, the reception power of the adjacent channel becomes larger than the reception power of the own channel, and the leakage power of the adjacent channel is mixed in the own channel, so There has been a problem that channel interference may occur. Further, such an interference amount is particularly remarkable at the end of the band.
The present invention has been made to solve such a conventional problem, and provides an OFDM receiver capable of performing error correction decoding with high accuracy even when adjacent channel interference occurs. Objective.

In order to achieve the above object, in the present invention, an OFDM receiving apparatus that receives a signal of its own channel that has been subjected to error correction coding and modulated by the OFDM modulation scheme has the following configuration.
That is, the receiving means receives a signal. Interference information detection means detects information on the level of adjacent channel interference based on the signal received by the reception means. Carrier determining means determines a carrier whose soft decision likelihood is lowered at the frequency band end of the own channel based on the information detected by the interference information detecting means. Demodulating means demodulates the signal received by the receiving means. The error correction means lowers the soft decision likelihood of the carrier determined by the carrier determination means based on the demodulation result by the demodulation means, and performs error correction decoding on the signal of the own channel.

  Therefore, a carrier whose soft decision likelihood is lowered at the frequency band end of the own channel is determined according to the situation of adjacent channel interference, and the soft decision likelihood of the decided carrier is lowered, and the signal of the own channel is error-correction decoded. Therefore, for example, even when adjacent channel interference occurs, error correction decoding can be performed with high accuracy by reducing the soft decision likelihood of a carrier whose reliability is low due to interference.

The OFDM receiver according to the present invention has the following configuration as an example configuration.
That is, when the error correction means lowers the soft decision likelihood of a plurality of carriers at the frequency band end of the own channel, the degree of lowering the soft decision likelihood of the carrier as it goes from the frequency band end to the frequency band is reduced. To do.

  Therefore, the soft decision likelihood of the carrier at the end of the frequency band of the own channel, which is considered to be most affected by the adjacent carrier interference, is lowered to the largest degree, and the soft decision likelihood of the carrier as it goes inside the frequency band from there. Error correction decoding can be performed effectively by reducing the degree of lowering.

Here, for example, in the OFDM transmission apparatus, data of a plurality of carriers is error-correction-encoded and transmitted by the OFDM modulation method, and the OFDM reception apparatus demodulates the received signal and performs error correction decoding. In this case, interleaving may be performed in the OFDM transmitter, and correspondingly, deinterleaving may be performed in the OFDM receiver.
In addition, as the OFDM transmitter and the OFDM receiver, for example, a wireless communication device that performs wireless communication is used.

Various types of information may be used as information regarding the level of adjacent channel interference. As specific examples, information on the power level of the signal of the adjacent channel, information on the magnitude relationship between the power level of the signal of the adjacent channel and the noise power level (or a value based thereon), and the power level of the signal of the own channel are adjacent. Information on the ratio to the power level of the channel signal can be used.
Also, for example, on the upper side (higher frequency side) and the lower side (lower frequency side) of the frequency band of the own channel, a carrier is determined according to the situation of adjacent channel interference, and the soft decision likelihood of the carrier is lowered. May be performed separately, or the carrier may be determined in consideration of both the upper side and the lower side. As an example, the soft decision likelihood can be lowered in the same manner (the number of carriers, the degree of lowering the soft decision likelihood, etc.) on the upper side and the lower side. It is also possible to lower the soft decision likelihood in different ways.

Various modes may be used as a mode for determining a carrier that lowers the soft decision likelihood at the frequency band end of the own channel. For example, from the carrier at the frequency band end (upper side and lower side) of the own channel. A mode is used in which the number of carriers is determined as to how many carriers the soft decision likelihood is lowered. Moreover, the aspect etc. which determine the degree to which the soft decision likelihood of each carrier is lowered can also be used.
Depending on the condition of adjacent channel interference, the soft decision likelihood may not be lowered for any carrier, or the soft decision likelihood of any carrier may be set to zero. Good.

  Various modes may be used to reduce the degree of lowering the soft decision likelihood from the carrier at the end of the frequency band of the own channel to the carrier in the frequency band. Different degrees may be used for a plurality of carriers to be lowered (in this case, only the upper side or only the lower side is considered), or two or more carriers having the same degree of lowering the soft decision likelihood There may be places where It is also possible to change the degree of lowering in the same manner (for example, vertically) for a plurality of carriers that lower the soft decision likelihood on the upper side and a plurality of carriers that lower the soft decision likelihood on the lower side. is there.

  As described above, according to the OFDM receiver according to the present invention, when performing error correction decoding after demodulating the received signal of the own channel, the frequency of the own channel receiving the adjacent channel interference according to the situation of the adjacent channel interference. Since the soft decision likelihood of the carrier at the end of the band is lowered, for example, even when adjacent channel interference occurs, error correction decoding can be performed with high accuracy.

  Embodiments according to the present invention will be described with reference to the drawings.

A first embodiment of the present invention will be described.
FIG. 1 shows a configuration example of an OFDM receiving apparatus provided in a digital transmission apparatus according to an embodiment of the present invention. The OFDM receiver of this example receives a data signal modulated by the OFDM modulation method.
The OFDM receiver of this example includes a receiving antenna 1, a channel filter 2, a down converter 3, an A / D (Analog to Digital) converter 4, an FFT (Fast Fourier Transform) unit 5, and an equalizing unit 6 A demodulating unit 7, an error correcting unit 8, a noise power detecting unit 9, an own channel power detecting unit 10, an adjacent channel power detecting unit 11, and an interference detecting unit 12.

FIG. 2 shows a configuration example of the noise power detection unit 9.
The noise power detection unit 9 includes an LPF (Low Pass Filter) 91, a delay unit 92, a subtracter 93, a square calculator 94, and an in-guard integrator 95.
FIG. 3 shows a configuration example of the own channel power detection unit 10. In this example, the adjacent channel power detection unit 11 has the same configuration as that of the own channel power detection unit 10 although the target channel is different, and performs the same operation.
The own channel power detection unit 10 (or the adjacent channel power detection unit 11) includes a square calculator 101 and two integrators 102 and 103.

An example of the operation performed in the OFDM receiver of this example is shown.
A signal (desired wave) addressed to itself and a signal (interference wave) from an adjacent channel wirelessly transmitted by the OFDM method from a transmitting device (OFDM transmitting device) using the OFDM method arrives at the OFDM receiving device.
The receiving antenna 1 receives a desired wave or an interference wave from an adjacent channel and outputs a received signal to the channel filter 2.
The channel filter 2 filters only the desired wave from the received signal input from the receiving antenna 1, attenuates the adjacent channel interference wave, and outputs the filtered signal to the down converter 3.

The down converter 3 performs frequency conversion (down conversion) on the signal input from the channel filter 2 and outputs the frequency-converted signal to the A / D converter 4.
The A / D converter 4 has a function of converting an analog signal into a digital signal. The A / D converter 4 samples a signal input from the down converter 3 to obtain a received sampling sequence, and the received sampling sequence is converted into an FFT unit 5. And output to the noise power detector 9.

The FFT unit 5 provides a time window having an effective symbol period length on the received sampling sequence input from the A / D converter 4, performs fast Fourier transform (FFT) on the signal within this time window, The signal in the region is converted into the signal in the frequency region, and the resulting signal is output to the equalization unit 6, the own channel power detection unit 10, and the adjacent channel power detection unit 11.
The timing of the time window to be provided is not particularly limited and will not be described in detail in this example. However, for example, it is desirable to provide it at an appropriate position where no intersymbol interference occurs.

The equalization unit 6 equalizes the amplitude and phase of the signal input from the FFT unit 5, and outputs the resulting signal to the demodulation unit 7.
It should be noted that equalization processing is required when a modulation scheme that requires absolute amplitude and phase, such as 16QAM and 64QAM, is used, but the information code is one symbol before as in π / 4 shift QPSK. It is not necessary to perform equalization when using a modulation scheme assigned to a phase difference with the above signal.

  Here, various methods may be used as the equalization processing method. As an example, the channel characteristic of the data carrier is calculated by interpolating the pilot carrier, which is a known signal inserted every several carriers, to the frequency, and equalization processing is performed by complex division by the calculated channel characteristic There is a method. As another example, there is a method of calculating channel characteristics by providing a training signal that is a known signal discretely in the temporal direction and interpolating the training signal in the temporal direction.

The demodulator 7 determines and demodulates the signal input from the equalizer 6 and determines the plausibility (softness) of the determination result calculated based on the distance between the determination result code (hard determination result) and the ideal reception point. The determination likelihood) is output to the error correction unit 8.
The error correction unit 8 performs error correction decoding on the signal input from the demodulation unit 7.
The error correction unit 8 can perform efficient decoding by performing error correction based on the hard decision result from the demodulation unit 7 and its soft decision likelihood. Specifically, error correction is performed by assuming that a signal received at a distance close to the ideal reception point is a plausible code and that a signal received at a distance away from the ideal reception point is an unreliable code. In this example, the likelihood is controlled based on information from the interference detection unit 12.

The noise power detection unit 9 has a configuration as shown in FIG. 2, calculates the noise power at the band center without adjacent channel interference for the signal input from the A / D converter 4, and the result Is output to the interference detection unit 12.
Specifically, the LPF 91 filters the signal input from the A / D converter 4 and outputs the filtered signal to the delay terminal 92 and the + terminal of the subtractor 93.
Here, the LPF 91 is a low-pass filter having a band-centered K carrier (K is an integer) as a pass band. Various passbands K may be used. For example, the center of the band excluding both ends of the band where adjacent channel interference occurs is set.

The delay unit 92 performs a delay process of the effective symbol length on the signal input from the LPF 91, and outputs the delayed signal to the − terminal of the subtractor 93.
The subtractor 93 subtracts the delayed signal input from the delay unit 92 from the undelayed signal input from the LPF 91 and outputs the resultant signal to the square calculator 94.

FIG. 4 shows an example of a timing chart of signals in the noise power detection unit 9.
4A shows an output signal from the LPF 91, FIG. 4B shows an output signal from the delay unit 92, and FIG. 4C shows an output signal from the subtractor 93. Is shown.
As shown in FIG. 4A, the OFDM signal has a valid symbol and a guard interval, and has a symbol configuration in which the second half of the valid symbol is copied to the first half of the valid symbol as a guard interval.
Therefore, as shown in FIGS. 4A and 4B, the undelayed OFDM signal and the OFDM signal delayed by the effective symbol length become the same signal in the guard interval period, and FIG. As shown in (), when they are subtracted, it is ideally 0. However, as shown in FIG. 4C, since the noise component superimposed on the signal is uncorrelated, the subtraction result is not zero.

The square calculator 94 squares the signal input from the subtractor 93 and outputs the resulting signal to the in-guard integrator 95. The power of noise is calculated by this square calculation.
The in-guard integrator 95 provides a time window in the guard interval period for the signal input from the square calculator 94, integrates the signal in this time window, and based on the time window length in which the integration result is provided. The noise power PN thus obtained is output to the interference detection unit 12.
In order to detect correct noise power PN, the timing of the time window to be provided needs to be a guard interval period and a period without multipath interference. In this example, such a time window timing calculation method is used. The detailed description is omitted.

The own channel power detection unit 10 has a configuration as shown in FIG. 3, and based on the signal input from the FFT unit 5, the signal of its own channel (own channel) on the upper and lower sides of the band. The powers PL and PU are detected, and the detection result is output to the interference detection unit 12.
FIG. 5 shows an example of an output signal from the FFT unit 5. The horizontal axis represents frequency (f). The signal spectrum of the frequency band of the own channel signal and the signal spectrum of the frequency domain of the adjacent channel signal are shown. In this example, the spectrum of the adjacent channel signal that causes adjacent channel interference exists with respect to the spectrum of the own channel signal.
In general, in FFT processing, there are many cases in which a high frequency and a low frequency are switched with respect to the center frequency, but here, for convenience of explanation, the same expression as a signal spectrum in space is used. I am doing.

In the own channel power detection unit 10, the square calculator 101 calculates the square of the absolute value of the signal input from the FFT unit 5, calculates the power of each carrier, and calculates the signal of the calculation result as two integrals. Output to the units 102 and 103.
In the own channel power detection unit 10, the integrator (lower integrator) 102 calculates the power in the frequency band on the lower side (lower frequency side) of the own channel based on the signal input from the square calculator 101. Integration is performed to calculate the power (lower power of the own channel) PL, and a signal of the calculation result is output to the interference detection unit 12. Here, as the frequency band below the own channel, for example, the own channel region L shown in FIG. 5 is used.

  Similarly, in the own channel power detection unit 10, the integrator (upper integrator) 103 is based on the signal input from the square calculator 101, and the power in the frequency band on the upper side (higher frequency side) of the own channel. Is integrated to calculate the power (upper power of own channel) PU, and a signal of the calculation result is output to the interference detection unit 12. Here, as the frequency band on the upper side of the own channel, for example, the own channel region U shown in FIG. 5 is used.

The adjacent channel power detection unit 11 has a configuration as shown in FIG. 3, and based on the signal input from the FFT unit 5, signals of adjacent channels (adjacent channels) on the upper and lower sides of the band. The power PNL and PNU are detected.
An operation example in the adjacent channel power detection unit 11 is shown. Here, for convenience of explanation, the same reference numerals as those shown in FIG. 3 are used for explanation.

In the adjacent channel power detection unit 11, the square calculator 101 calculates the square of the absolute value of the signal input from the FFT unit 5 to calculate the power of each carrier, and the signal of the calculation result is integrated into two integrals. Output to the units 102 and 103.
In the adjacent channel power detection unit 11, the integrator (lower integrator) 102, based on the signal input from the square calculator 101, the frequency band of the adjacent channel on the lower side (lower frequency side) of the own channel. The power (lower adjacent channel power) PNL is calculated, and a signal of the calculation result is output to the interference detection unit 12. Here, for example, the adjacent channel region NL shown in FIG. 5 is used as the frequency band of the adjacent channel below the own channel. The presence of the adjacent channel interference or the magnitude of the interference is detected by the lower adjacent channel power PNL.

  Similarly, in the adjacent channel power detection unit 11, the integrator (upper integrator) 103 is based on the signal input from the square calculator 101, and the frequency of the adjacent channel on the upper side (high frequency side) of the own channel. The power of the band is integrated to calculate the power (upper adjacent channel power) PNU, and the calculation result signal is output to the interference detection unit 12. Here, for example, the adjacent channel region NU shown in FIG. 5 is used as the frequency band of the adjacent channel above the own channel. The presence of the adjacent channel interference or the magnitude of the interference is detected by the upper adjacent channel power PNU.

  By the way, when forming the OFDM spectrum on the transmission side, in order to make it easy to configure a band limiting filter, the number of carriers to be used is set to some extent with respect to the number of points of inverse fast Fourier transform (IFFT). It is often specified with a small margin. FIG. 5 shows a certain frequency margin between the number of FFT points and the number of carriers to be used, and the frequency adjacent to the own channel indicates an adjacent channel signal.

In the interference detection unit 12, the own channel powers PL and PU output from the own channel power detection unit 10 and the adjacent channel powers PNL and PNU output from the adjacent channel power detection unit 11 are input to one input terminal. The noise power PN output from the noise detector 9 is input to the other input terminal.
Based on these input signals, the interference detection unit 12 correctly recognizes white noise and adjacent channel interference, and the ratio RL between the band end power of the own channel and the adjacent channel power interfering with the band end carrier (below) Side ratio) and RU (upper ratio), and outputs the result to the error correction unit 8.

  Here, in this example, efficient error correction is performed by lowering the soft decision likelihood of a carrier in which adjacent channel interference occurs. However, in the absence of adjacent channel interference and in a simple Gaussian noise environment (under normal noise environment), it is desirable to calculate the soft decision likelihood based on the distance from the ideal reception point, etc., and the likelihood of a specific carrier It is better not to lower it selectively.

As a first step, discrimination between Gaussian noise and adjacent channel interference is performed in order to detect the presence or absence of adjacent channel interference.
Since the noise mixed in the received signal is wideband, it is mixed in and out of the band. Therefore, in an environment where the noise is large, even if there is no adjacent channel interference, the adjacent channel powers PNL and PNU both show large values, and the adjacent channel interference and noise cannot be distinguished. For this reason, the interference detection unit 12 compares the value obtained by multiplying the noise power PN by the predetermined coefficient α with the adjacent channel powers PNL and PNU.
As α, various values (positive numbers) may be used. For example, a value less than 1 determined by experiments or the like is used.

FIG. 6 shows an example of a procedure of processing performed by the interference detection unit 12.
First, for the adjacent channel interference on the lower side, the value of (α · PN) is compared with the value of PNL (step S1). As a result, if the value of (α · PN) is larger, it is considered that lower side adjacent channel interference has not occurred (step S3), and carrier-selective control of the soft decision likelihood is not performed. On the other hand, if the value of PNL exceeds the value of (α · N), it is determined that lower adjacent channel interference has occurred (step S2).

  Similarly, for the upper adjacent channel interference, the value of (α · PN) is compared with the value of PNU (step S4). As a result, if the value of (α · PN) is larger, it is considered that the upper adjacent channel interference has not occurred (step S6), and carrier-selective control of the soft decision likelihood is not performed. On the other hand, if the value of PNU exceeds the value of (α · N), it is determined that upper adjacent channel interference has occurred (step S5).

As a second step, when it is determined that the adjacent channel interference has occurred in the first step, the ratios RL and RU of the own channel band edge power PL and PU and the adjacent channel power PNL and PNU are calculated. (Step S7). These ratios RL and RU are expressed by (Formula 1).
If the values of these ratios RL and RU are large, the degree of interference is low, and if the ratios are small, the influence of interference is large.
Note that such ratios RL and RU may be calculated for both the lower side and the upper side, or when adjacent channel interference occurs only in one of the lower side and the upper side. This may be performed only on the side where adjacent channel interference occurs.

(Equation 1)
RL = PL / PNL
RU = PU / PNU
.. (Formula 1)

The determination result of the interference amount in the interference detection unit 12 is input to the error correction unit 8.
Based on the information input from the interference detection unit 12, the error correction unit 8 lowers the soft decision likelihood of M (M is an integer) carrier at the band edge where adjacent channel interference occurs, and then performs error correction decoding. Do.

  Here, as the number M of carriers for lowering the soft decision likelihood, for example, a predetermined value set in advance may be used, or based on the values of the own channel power to interference wave power ratios RL and RU. It can also be set to be variable. Specifically, when the own channel power to interference wave power ratios RL and RU are large, it can be determined that the number of carriers causing interference is large, and the value of M can be set to a large value. Thus, the value of M can be adaptively controlled according to the amount of interference. Note that the value of M is set for each of RL and RU, for example.

Further, as the degree of lowering the soft decision likelihood, for example, the likelihood may be lowered for all of the M carriers, or the band edge is more affected by interference, The degree to which the likelihood is lowered can be maximized, and the degree to which the likelihood is lowered as it falls within the band can be reduced.
Note that the likelihood value may be 0.
In addition, in these error corrections, more efficient error correction decoding can be performed by combining with interleaving.

Thus, in this example, the signal powers PL and PU of the own channel calculated by the own channel power detection unit 10, the signal powers PNL and PNU of the adjacent channel calculated by the adjacent channel power detection unit 11, and the noise power detection unit 9 is compared by the interference detection unit 12 to determine whether or not interference has occurred in the upper adjacent channel or the lower adjacent channel. Lowers the soft decision likelihood of a carrier in which
As a result, the presence or absence of adjacent channel interference is detected, and when interference occurs, the soft decision likelihood of the carrier at the band edge where the interference occurs is lowered, thereby improving the efficiency of error correction decoding and the code error rate. Can be improved (improved).

Here, in this example, in FIG. 5, the lower adjacent channel region NL uses the outer region below the own channel frequency band, and the upper adjacent channel region NU uses the own channel frequency. An outer region above the band is used, and the lower self channel region L is a region closer to the lower end in the frequency band of the own channel, and the upper self channel region U is used. Is used in the frequency band of its own channel, the region located at the upper end.
In this example, as the M carriers that lower the soft decision likelihood, for example, M carriers from the lower end of the frequency band of the own channel (for example, carriers in the lower own channel region L) Alternatively, M carriers (for example, carriers in the upper self channel region U) are used from the upper end of the frequency region of the own channel.

Further, in this example, for example, error correction coding (for example, convolutional coding) is performed on the OFDM modulated signal to be communicated in the OFDM transmission apparatus, and error correction decoding (for example, in the OFDM correction apparatus 8) Viterbi decoding) is performed.
As a specific example, when considering the arrangement of symbols on the vertical axis (time arrangement) and the arrangement of carriers on the horizontal axis (frequency arrangement), error correction codes for each set in the horizontal axis direction (multiple carrier sets) And decoding. In this case, it is preferable to perform frequency interleaving at the time of convolution because data of a plurality of carriers are mixed. In this example, the accuracy of error correction is improved by lowering the soft decision likelihood of some carriers that receive adjacent channel interference. Data modulation and demodulation are performed for each carrier, and error correction is performed after data demodulation.

  As described above, the OFDM receiver of this example receives a signal modulated by the OFDM modulation method, detects the presence or absence of adjacent channel interference or the degree of adjacent channel interference based on the received signal, and detects adjacent channel interference. In such a case, the soft decision likelihood for error correction of the carrier causing interference is selectively lowered, and error correction is performed based on the subsequent soft decision likelihood.

  Further, in the OFDM receiving apparatus of this example, as processing for detecting the presence or absence of adjacent channel interference or the degree of adjacent channel interference, the signal power of the adjacent channel is calculated, the noise power at the center of the band is calculated, and the signal of the adjacent channel is calculated. The presence / absence of adjacent channel interference or the degree of adjacent channel interference is detected by comparing the power with the result obtained by multiplying the noise power at the center of the band by a predetermined coefficient α (α is a positive integer as an example).

  Further, in the OFDM receiver of this example, as processing for calculating the noise power at the center of the band, the low-frequency component is filtered with respect to the received sampling sequence, the filtered signal is delayed by the effective symbol period length, and the delay Calculate the noise power at the center of the band by calculating the difference between the signal and the undelayed signal, providing a temporal window in the guard interval period of this differential signal, and calculating the power within this time window To do.

  Therefore, in the OFDM receiver of this example, even in an environment where adjacent channel interference exists, the presence or absence of adjacent channel interference is automatically detected, and if it is determined that adjacent channel interference has occurred, the interference is not detected. By performing error correction by lowering the soft decision likelihood of the generated carrier at the band edge, efficient error correction decoding becomes possible, and improvement (improvement) of the code error rate can be realized.

  In the OFDM receiver of this example, the receiving antenna 1, the channel filter 2, the down converter 3, the A / D converter 4, the FFT unit 5, and the equalizing unit 6 receive signals and process the received signals. The reception means is configured, and the interference information detection means is configured by the function of the noise power detection unit 9, the own channel power detection unit 10, the adjacent channel power detection unit 11, and the interference detection unit 12 detecting information on adjacent channel interference. Then, the interference detection unit 12 (or the error correction unit 8) determines a carrier that lowers the soft decision likelihood according to the situation of adjacent channel interference (for example, the number of carriers and the degree of reduction may be determined). Carrier determining means is configured by the function, demodulating means is configured by the function of the demodulating unit 7, and error correcting means is configured by the function of the error correcting unit 8. It is.

A second embodiment of the present invention will be described.
FIG. 7 shows a configuration example of an OFDM receiver provided in a digital transmission apparatus according to an embodiment of the present invention.
The OFDM receiver of this example includes a reception antenna 1, a channel filter 2, a down converter 3, an A / D converter 4, an FFT unit 5, an equalization unit 6, a demodulation unit 7, and an error correction unit. 8, an adjacent channel power detection unit 11, a C / N detection unit 21, and an interference determination unit 22.

Here, the configuration and operation of the OFDM receiver of this example are compared with those shown in FIG. 1, the noise power detection unit 9, the own channel power detection unit 10, the adjacent channel power detection unit 11 shown in FIG. 1, The difference is that an adjacent channel power detection unit 11, a C / N detection unit 21, and an interference determination unit 22 are provided instead of the interference detection unit 12, and the others are the same, and are denoted by the same reference numerals. It is.
In this example, points different from those shown in FIG. 1 will be described in detail.

An output signal from the A / D converter 4 is output to the FFT unit 5.
The result of performing the FFT process on the received signal by the FFT unit 5 is output to the equalization unit 6 and the adjacent channel power detection unit 11.
Based on the input signal from the FFT unit 5, the adjacent channel power detection unit 11 calculates the adjacent channel power outside the band (in this example, the lower adjacent channel power PNL and the upper adjacent channel power PNU) to determine the interference. To the unit 22.

An output signal from the equalization unit 6 is output to the demodulation unit 7 and the C / N detection unit 21.
The C / N detection unit 21 calculates C / N or noise power for each carrier, or C / N or noise power for a plurality of carriers based on the signal input from the equalization unit 6, Is output to the interference determination unit 22.
Here, as a calculation method such as C / N, for example, an error between an ideal reception point and an (actual) reception point is considered as a noise component, and a ratio to the signal level calculated from the ideal power or the power of the noise component is calculated. The calculation method is used.

Further, since the noise component has disturbance, averaging may be performed in the time direction in order to remove the disturbance.
Further, average C / N and noise power may be calculated in units of G (G is an integer) carriers.
The C / N or noise power of the carrier unit or the plurality of carrier units detected by the C / N detection unit 21 in this way is input to the interference determination unit 22.

  The interference discriminator 22 receives the C / N or noise power from the C / N detector 21 at one input terminal, and the adjacent channel powers PNL and PNU from the adjacent channel power detector 11 at the other input terminal. Is entered. The interference discriminating unit 22 compares the C / N or noise power of the carrier unit or a plurality of carrier units input from the C / N detection unit 21 with the adjacent channel power PNL and PNU input from the adjacent channel power detection unit 11. And the presence / absence of adjacent channel interference is determined, and the determination result is output to the error correction unit 8.

Specifically, it is determined that there is adjacent channel interference when adjacent channel power PNL and PNU are larger than the noise power at the band center where no adjacent channel interference occurs. Alternatively, the adjacent channel powers NPL and NPU are large (for example, greater than or equal to a predetermined threshold or a predetermined value even though the C / N at the center of the band is good (for example, better than a predetermined threshold)). If it exceeds the threshold value, it is determined that there is adjacent channel interference.
In this example, it is determined that there is adjacent channel interference even when the noise power at the band edge is larger than the noise power at the center of the band.

  The error correction unit 8 inputs information such as the result of determining the presence or absence of interference by the interference determination unit 22, and based on this information, for example, as described with reference to FIG. Decrease decision likelihood. Thereby, efficient error correction decoding becomes possible, and improvement (improvement) of the code error rate can be realized.

  As described above, the OFDM receiver of this example equalizes the amplitude and phase of the signal after FFT processing, calculates the difference between the equalized signal and the ideal reception point, and based on this difference signal The noise power at the center of the band is calculated. Even in an environment where adjacent channel interference exists, the presence / absence of adjacent channel interference is automatically detected, and if it is determined that adjacent channel interference is occurring, the carrier at the band edge where the interference occurs is detected. By performing error correction while lowering the soft decision likelihood, efficient error correction decoding can be performed, and improvement (improvement) in the code error rate can be realized.

  In the OFDM receiver of this example, the receiving antenna 1, the channel filter 2, the down converter 3, the A / D converter 4, the FFT unit 5, and the equalizing unit 6 receive signals and process the received signals. The reception means is configured, and the interference information detection means is configured by the function of the adjacent channel power detection unit 11, the C / N detection unit 21, and the interference determination unit 22 detecting information related to adjacent channel interference, and the interference determination unit 22 (or the error correction unit 8) determines the carrier whose soft decision likelihood is lowered according to the situation of adjacent channel interference (for example, the number of carriers and the degree of reduction may be decided). The demodulating unit is configured by the function of the demodulating unit 7, and the error correcting unit is configured by the function of the error correcting unit 8.

Here, the configuration of the system and apparatus according to the present invention is not necessarily limited to the configuration described above, and various configurations may be used. The present invention can also be provided as, for example, a method or method for executing the processing according to the present invention, a program for realizing such a method or method, or a recording medium for recording the program. It is also possible to provide various systems and devices.
The application field of the present invention is not necessarily limited to the above-described fields, and the present invention can be applied to various fields.
In addition, as various processes performed in the system and apparatus according to the present invention, for example, the processor executes a control program stored in a ROM (Read Only Memory) in hardware resources including a processor and a memory. A controlled configuration may be used, and for example, each functional unit for executing the processing may be configured as an independent hardware circuit.
The present invention can also be understood as a computer-readable recording medium such as a floppy (registered trademark) disk or a CD (Compact Disc) -ROM storing the control program, and the program (itself). The processing according to the present invention can be performed by inputting the program from the recording medium to the computer and causing the processor to execute the program.

It is a figure which shows the structural example of the OFDM receiver which concerns on 1st Example of this invention. It is a figure which shows the structural example of a noise power detection part. It is a figure which shows the structural example of a self-channel power detection part and an adjacent channel power detection part. It is a figure which shows an example of the timing chart of the signal in a noise electric power detection part. It is a figure which shows an example of the output signal of an FFT part. It is a figure which shows an example of the procedure of the process performed by the interference detection part. It is a figure which shows the structural example of the OFDM receiver which concerns on 2nd Example of this invention. It is a figure which shows an example of adjacent channel interference.

Explanation of symbols

  1 ·· Receiving antenna 2 ·· Channel filter 3 ·· Down converter 4 ·· A / D converter 5 ·· FFT unit 6 ·· Equalizer 7 ·· Demodulator 8 ·· Error Correction unit, 9 ... Noise power detection unit, 10 ... Own channel power detection unit, 11 ... Adjacent channel power detection unit, 12 ... Interference detection unit, 21 ... C / N detection unit, 22 ... Interference discrimination 91, LPF, 92, delay unit, 93, subtractor, 94, 101, square calculator, 95, guard integrator, 102, 103, integrator

Claims (2)

In an OFDM receiver that receives a signal of its own channel that is error correction encoded and modulated by an OFDM modulation scheme,
Receiving means for receiving a signal;
Interference information detecting means for detecting information on the level of adjacent channel interference based on the signal received by the receiving means;
Carrier determining means for determining a carrier for lowering soft decision likelihood at the frequency band edge of the own channel based on information detected by the interference information detecting means;
Demodulating means for demodulating the signal received by the receiving means;
Error correction means for lowering the soft decision likelihood of the carrier determined by the carrier determination means based on the demodulation result by the demodulation means and performing error correction decoding on the signal of the own channel;
An OFDM receiving apparatus comprising: The OFDM receiver according to claim 1, wherein
When the error correction means lowers the soft decision likelihood of a plurality of carriers at the frequency band edge of the own channel, the error correction means decreases the degree of lowering the soft decision likelihood of the carrier from the frequency band edge to the frequency band;
An OFDM receiver characterized by that.

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