JP2009071636A - Receiving device and receiving method - Google Patents

Abstract

The present invention achieves high reception performance by weighted synthesis processing for spread symbols without performing complicated calculations with increased power consumption.
In a receiving apparatus 1 in MB-OFDM wireless communication, transmission path characteristics used for estimation of transmission path characteristics in a frequency region of a subcarrier unit in an equalizer 10 after FFT calculation in a fast Fourier transform calculation unit 9. Based on the estimated value 11, a symbol synthesis unit 12 that performs weighting in the synthesis of a plurality of spread symbols derived from a common OFDM symbol is provided, and a complicated calculation of S / N regarding each spread symbol 20 a is required. Rather, high reception performance is realized by appropriately combining a plurality of spread symbols 20a.
[Selection] Figure 1

Description

  The present invention relates to a reception technique in a radio transmission system, and more particularly to a technique that is effective when applied to an OFDM radio communication system that transmits and receives transmitted symbols in the time domain.

  In a conventional radio communication system, a radio transmission apparatus using an OFDM (Orthogonal Frequency Division Multiplexing) scheme is known as a transmission scheme, and a subcarrier signal is demodulated using FFT (Fast Fourier Transform) at the time of reception. Is demodulating.

  Also, in the MB-OFDM (MultiBand OFDM) system, which is standardized for the use of WPAN (Wireless Personal Area Network), which hops an OFDM signal between a plurality of frequencies, a transmission symbol corresponding to the transmission rate A time-domain-spreading method that spreads and transmits the message on the time axis is used to improve communication reliability.

  Generally, FFT is used to receive a signal transmitted by the OFDM method, and demodulation is performed by performing an FFT operation in units of OFDM symbols. The received OFDM symbol is distorted due to fading caused by interference with the delayed wave generated in the multipath transmission path. After the FFT conversion, the estimated value of the transmission path characteristic is calculated by the equalizer, and the inverse characteristic is obtained. By giving the received symbol, transmission path distortion is corrected.

  In the MB-OFDM system, a diversity effect can be obtained by combining the spread OFDM symbols with respect to the corrected OFDM symbols, and high reception performance can be obtained.

  In general, synthesis between spread symbols is performed by calculating an S / N (signal-to-noise ratio) between symbols and assigning weights between symbols based on the S / N (for example, patents). Reference 1).

In the technique for synthesizing spread symbols in Patent Document 1, the S / N is calculated by calculating the error vector for each subcarrier of the OFDM symbol, but the calculation processing becomes complicated, and the circuit processing is complicated. There was a technical problem of increased power consumption.
JP 2005-269392 A

  An object of the present invention is to provide a reception technique of a wireless transmission system that can realize high reception performance by weighted synthesis processing for spread symbols without performing complicated calculations with increased power consumption.

According to a first aspect of the present invention, there is provided a receiving apparatus in a wireless communication system for transmitting a first symbol carrying transmission information by spreading the first symbol into a plurality of second symbols in the time domain,
An equalizer for correcting the received second symbol in a frequency domain;
A symbol synthesizer that synthesizes a plurality of the second symbols derived from the common first symbol based on the channel characteristic estimation value obtained by the equalizer;
A receiving device is provided.

According to a second aspect of the present invention, in the receiving device according to the first aspect,
The first symbol is an OFDM (Orthogonal Frequency Division Multiplex) symbol obtained by carrying the transmission information distributed over a plurality of subcarriers and performing inverse fast Fourier transform (IFFT),
The symbol combining unit, based on the transmission path characteristic estimation value, corresponds to each of the plurality of second symbols, and the OFDM symbol of the OFDM symbol corrected by the equalizer in the frequency domain after Fast Fourier Transform (FFT) Provided is a receiving apparatus that combines weighted sub-carrier complex symbols.

According to a third aspect of the present invention, in the receiving device according to the second aspect,
The symbol combining unit obtains an average value of the channel characteristic estimation values of the individual subcarriers in the OFDM symbol, and the OFDM symbol corresponding to each of the plurality of second symbols based on the average value. Provided is a receiving device that combines the complex symbols of the subcarriers with weights.

According to a fourth aspect of the present invention, in the receiving device according to the second aspect,
The symbol synthesizer performs soft decision output data corresponding to each subcarrier after demodulation processing based on the modulation processing given to the complex symbol of each subcarrier of the OFDM symbol. Provided is a receiving device that performs weighting based on a transmission path characteristic estimation value and performs synthesis.

According to a fifth aspect of the present invention, in the receiving device according to the fourth aspect,
The symbol combining unit obtains an average value of the channel characteristic estimation values of the individual subcarriers in the OFDM symbol based on the transmission channel characteristic estimation value obtained by the equalizer, and obtains the average value. There is provided a receiving device for combining the soft decision output data corresponding to each of the subcarriers based on weighting.

A sixth aspect of the present invention is a reception method in a wireless communication system for transmitting a first symbol carrying transmission information by spreading the first symbol into a plurality of second symbols in the time domain,
A first step of correcting the received second symbol in the frequency domain by an equalizer;
A second step of combining a plurality of the second symbols derived from the common first symbol based on the channel characteristic estimation value obtained by the equalizer;
A receiving method including:

According to a seventh aspect of the present invention, in the reception method according to the sixth aspect,
The first symbol is an OFDM (Orthogonal Frequency Division Multiplex) symbol obtained by carrying the transmission information distributed over a plurality of subcarriers and performing inverse fast Fourier transform (IFFT),
In the second step, the OFDM symbol of the OFDM symbol corrected by the equalizer in the frequency domain after fast Fourier transform (FFT) corresponding to each of the plurality of second symbols based on the channel characteristic estimation value. Provided is a reception method for combining weighted sub-carrier complex symbols.

According to an eighth aspect of the present invention, in the reception method according to the seventh aspect,
In the second step, an average value of the channel characteristic estimation values of the individual subcarriers in the OFDM symbol is obtained, and the OFDM symbol corresponding to each of the plurality of second symbols is obtained based on the average value. Provided is a receiving method for combining the complex symbols of the subcarriers with weighting.

According to a ninth aspect of the present invention, in the reception method according to the seventh aspect,
In the second step, the soft decision output data corresponding to each subcarrier after demodulation processing based on the modulation processing given to the complex symbol of each subcarrier of the OFDM symbol, Provided is a receiving method in which weighting is performed based on a transmission path characteristic estimation value and synthesis is performed.

According to a tenth aspect of the present invention, in the reception method according to the ninth aspect,
In the second step, an average value of the channel characteristic estimation values of the individual subcarriers in the OFDM symbol is obtained based on the channel characteristic estimation value obtained by the equalizer, and the average value is obtained. And a receiving method for combining the soft decision output data corresponding to each of the subcarriers with weighting.

  Advantageous Effects of Invention According to the present invention, it is possible to provide a reception technique for a wireless transmission system that can achieve high reception performance by weighted combining processing on spread symbols without performing complicated calculations with increased power consumption.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram illustrating an example of a configuration of a receiving apparatus that implements a receiving method according to an embodiment of the present invention, and FIG. 2 illustrates an example of a configuration of a symbol synthesis unit in the receiving apparatus of the present embodiment. FIG. 3 is a conceptual diagram illustrating the operation of the present embodiment.

The receiving apparatus 1 of this Embodiment comprises the receiving system of the radio | wireless communication apparatus of a MB-OFDM (MultiBand OFDM) system, for example.
The receiver 1 includes an antenna 2, a low noise amplifier 3, a frequency mixer 4, a radio frequency transmitter 5, a low pass filter 6, an automatic gain controller 7, an A / D converter 8, a fast Fourier transform calculation unit 9, and the like. And a demapping unit 13, a deinterleaver 14, and an error correction processing unit 15.

In the case of this embodiment, a symbol synthesis unit 12 is provided between the equalizer 10 and the demapping unit 13.
On the transmitter side (not shown), transmission information is distributed and carried on a plurality of subcarriers, and an OFDM symbol 20b (first symbol) obtained by inverse fast Fourier transform (IFFT) is converted into a plurality of spreading symbols 20a in the time domain. It is spread as (second symbol) and transmitted as a radio wave 20.

  Here, spreading the OFDM symbol 20b to a plurality of spread symbols 20a in the time domain specifically means that the same OFDM symbol 20b is transmitted as a plurality of spread symbols 20a at different frequencies over time (by frequency hopping). It means to do.

  A spread symbol 20a (OFDM symbol 20b) arriving at the antenna 2 of the receiving apparatus 1 as a radio wave 20 is amplified by the low noise amplifier 3, and then down-converted by the frequency mixer 4, the radio frequency transmitter 5, the low-pass filter 6 and the like. The signal is converted into a baseband signal by the converter, and the signal level variation is corrected by the automatic gain controller 7, and then converted into a digital signal by the A / D converter 8 and input to the fast Fourier transform calculation unit 9.

  After the FFT calculation in the fast Fourier transform calculation unit 9, the equalizer 10 estimates the channel characteristics in the frequency domain in units of subcarriers. Based on the channel characteristics estimate 11, the complex symbol of each subcarrier is estimated. Symbol correction is performed.

For example, the equalizer 10 compares a known symbol inserted in the preamble of the received packet with a reference symbol, and obtains a transmission path characteristic H (l) corresponding to each subcarrier (carrier number l). Ask.

  In MB-OFDM as in the present embodiment, a frequency hopping method is employed in which OFDM symbols 20b are hopped in three frequency bands to generate a plurality of spread symbols 20a. In the processing to obtain, three types of characteristics corresponding to the frequency bands through which the preamble symbols have passed are calculated.

  Thereafter, for each received symbol X (n, l) in the packet, the inverse characteristic H of the transmission path characteristic H (l) corresponding to the frequency band through which each symbol has passed, as in the following equation (1). By complex multiplication of '(l) = 1 / H (l), each symbol is corrected in units of subcarriers to obtain a corrected symbol X ′ (n, l).

However, in this Formula (1), n is a symbol number and 1 is a subcarrier number.
Here, as described above, in the reception method such as MB-OFDM, correction by the equalizer 10 is performed in order to correct the distortion of the received symbol. However, in the synthesis of the spread symbol 20a after correction, Patent Literature When combining by weighting by calculation of S / N among a plurality of spread symbols 20a as in 1, there is a technical problem that calculation processing becomes complicated and power consumption increases.

  Therefore, in the present embodiment, a plurality of spread symbols 20a derived from a common OFDM symbol 20b are weighted based on the transmission path characteristic estimation value 11 for each subcarrier calculated by the equalizer 10, and a plurality of spread symbols 20a are weighted. The spread symbols 20a are synthesized.

  That is, as illustrated in FIG. 3, the correction amount Δa of the subcarriers A and B constituting the reception symbol performed by the equalizer 10 based on the transmission path characteristic estimation value 11 is the S / of the symbol before correction. The S / N before reception is degraded as the correction amount Δa is larger.

  For this reason, in the present embodiment, as will be described later, weighting is performed in units of subcarriers of the spread symbol 20a in the symbol combining unit 12 based on the channel characteristic estimation value 11 obtained by the equalizer 10. Therefore, without adding a function of calculating S / N, the synthesis between the spread symbols 20a is performed with an optimum S / N ratio, thereby realizing a diversity effect.

In the present embodiment, a symbol synthesizer 12 is arranged at the subsequent stage of the equalizer 10, and the symbol synthesizer 12 synthesizes a spread symbol 20 a using the transmission path characteristic estimation value 11.
That is, as illustrated in FIG. 2, the symbol synthesis unit 12 of the present embodiment includes a synthesis symbol selection unit 12a, a multiplication unit 12b, a multiplication unit 12c, an addition unit 12d, a normalization unit 12g, and an absolute value calculation unit 12e. A weighting calculation unit 12f is provided.

  The composite symbol selection unit 12a selects a pair of spread symbols 20a derived from the common OFDM symbol 20b at the time of transmission from a plurality of spread symbols 20a which are the equalization-corrected symbols 21 output from the equalizer 10 (X described later). The operation of selecting '(a, l), X' (a + 1, l)) is performed.

The absolute value calculation unit 12e calculates the absolute value of the above-described transmission path characteristic estimation value 11 output from the equalizer 10.
The weighting calculator 12f calculates a weighting value (in this case, the inverse ratio of the absolute value of the transmission path characteristic estimated value 11) from the absolute value of the transmission path characteristic estimated value 11 obtained by the absolute value calculating section 12e, and a multiplication section. The operation of outputting to 12b and multiplier 12c is performed.

Then, the multiplying unit 12b, the multiplying unit 12c, and the adding unit 12d perform an operation of Equation (2) described later.
The normalizing unit 12g normalizes the amplitude level of the spread symbol 20a after synthesis.

  That is, in the symbol synthesizing unit 12 of this embodiment illustrated in FIG. 2, the spread derived from the common OFDM symbol 20b is applied to the symbol input (the equalized corrected symbol 21) corrected by the equalizer 10. The two spread symbols 20a taken out and the absolute value based on the absolute value of the complex vector of H ′ (l) as the transmission path characteristic estimation value 11 multiplied by the equalizer 10 for each spread symbol 20a The calculating unit 12e and the weighting calculating unit 12f calculate a combined weight value, the multiplying unit 12b and the multiplying unit 12c weight each symbol, and the adding unit 12d combines them. An example of weighting synthesis is shown below.

  The equalized spread symbols 20a are X ′ (a, l) and X ′ (a + 1, l), respectively, and the channel characteristic estimation values 11 applied to the symbols are H1 ′ (l) and H2 ′ (l ), Weighted synthesis is performed with the inverse ratio of the absolute values of the respective transmission path characteristic estimation values 11.

  The synthesized symbol X ′ (A, l) is expressed by the following equation (2).

As a result, it is possible to suppress and synthesize a symbol component having a large correction amount Δa in the equalizer 10 (a spread symbol 20a having a poor signal S / N).
The synthesized symbol X ′ (A, l) is normalized by the normalizing unit 12g to have an appropriate amplitude level according to the weighting value, and is used as the synthesized symbol 22 in the demapping unit 13 that demodulates data. Entered.

  The data demodulated by the demapping unit 13 is returned to the original position of the transmission bits rearranged on the transmission side by the deinterleaver 14, and the error correction processing unit 15 performs an error by a desired algorithm. Correction processing is performed and the original information signal 24 is output.

  Thus, in the case of the present embodiment, when the symbol combining unit 12 combines a plurality of spread symbols 20a derived from the common OFDM symbol 20b, the transmission path characteristic estimation value 11 obtained in the equalizer 10 is used. Since the weighting using synthesizes and synthesizes, there is no need for complicated processing such as S / N calculation of each spread symbol 20a, and the power consumption of the receiving apparatus 1 including the symbol synthesizer 12 can be reduced, and the circuit configuration Can be simplified.

In addition, high reception performance of the receiving apparatus 1 can be realized by appropriately combining the spread symbols 20a derived from the common OFDM symbol 20b.
In the above example, the weighting value is calculated and combined for each subcarrier unit, but the average of each transmission path characteristic estimation value 11 in the spread symbol is calculated to calculate the combined weighting value, You may weight uniformly with respect to a subcarrier.

  Further, in the configuration example of the receiving apparatus 1 illustrated in FIG. 1 and FIG. 2 described above, weighting synthesis is performed on the complex symbols of each subcarrier before demapping. The symbols may be demodulated by demapping and synthesized by the same weighting process on the information data that has been soft-decision output.

FIG. 4 is a block diagram of a receiving apparatus 1A that performs symbol synthesis after soft decision.
The receiving apparatus 1A illustrated in FIG. 4 is different from the above-described receiving apparatus 1 illustrated in FIG. 1 in that the symbol combining unit 12 is arranged at the subsequent stage of the demapping unit 13.

  In the case of this receiving apparatus 1A, as in the case of the above-described receiving apparatus 1, the received symbol is corrected for transmission path distortion by the equalizer 10, and is input to the demapping unit 13 to perform demapping processing in units of subcarriers. Is done. In demapping, the information data is demodulated in accordance with the modulation performed on the subcarrier on the transmitter side (for example, QPSK). At this time, demodulated data is soft-decided according to the accuracy of the data from the subcarrier complex symbols and output.

  The output data soft-determined by the demapping unit 13 (soft-decision data 23) is multiplied by the equalizer 10 in the symbol synthesizing unit 12 provided at the subsequent stage of the demapping unit 13 in the same manner as the synthesis method described above. Based on the estimated channel characteristic value 11, the absolute value calculating unit 12e and the weighting calculating unit 12f calculate the weighting value, and the multiplying unit 12b, the multiplying unit 12c, and the adding unit 12d correspond to each subcarrier between the spread symbols. The soft decision data 23 are synthesized. The synthesized soft decision data 23 is normalized in accordance with the weighting value in the normalization unit 12g, and is input to the error correction processing unit 15 via the subsequent deinterleaver 14 as the soft decision output 23a.

  Also in the case of the receiving apparatus 1A illustrated in FIG. 4, the symbol combining unit 12 provided at the subsequent stage of the demapping unit 13 uses the transmission path characteristic estimation value 11 obtained from the equalizer 10 to perform a common OFDM. Since each of the soft decision data 23 corresponding to each subcarrier between the spread symbols 20a derived from the symbol 20b is weighted and synthesized, complicated processing such as S / N calculation of each spread symbol 20a is not required. Thus, it is possible to reduce the power consumption of the receiving apparatus 1 including the symbol synthesis unit 12 and to simplify the circuit configuration.

  As described above, according to the embodiment of the present invention, in the OFDM radio using the time-domain-spreading scheme such as MB-OFDM, the channel characteristic estimation value 11 derived by the equalizer 10 is obtained. Based on the weighting coefficient of the synthesis in the symbol synthesis unit 12 based on this, the spread symbols 20a can be synthesized at an appropriate ratio according to the distortion amount of the spread symbols 20a.

  As a result, it is possible to provide a reception technique for a wireless transmission system capable of realizing high reception performance by weighted combining processing on spread symbols without performing complicated calculations with increased power consumption.

Needless to say, the present invention is not limited to the configuration exemplified in the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
(Appendix 1)
In a radio transmission system that spreads OFDM symbols to be transmitted into a plurality of symbols in the time domain, a radio unit that corrects the received symbols by an equalizer in the frequency domain after FFT conversion of the received OFDM symbols, and a transmission path of the equalizer A receiving apparatus, characterized in that, based on an estimated value, weighting is performed on a complex symbol of each subcarrier between a plurality of symbols and weighted.
(Appendix 2)
The receiving apparatus of the wireless transmission system according to attachment 1, wherein an average of the channel estimation values of each subcarrier in the OFDM symbol is obtained based on the channel estimation value of the equalizer, and a plurality of symbols are obtained based on the average value. A receiving apparatus comprising weighting and synthesizing a complex symbol of each subcarrier in between.
(Appendix 3)
In the reception apparatus of the wireless transmission system according to attachment 1, when the soft decision is performed after the demodulation processing based on the modulation scheme given to the complex symbol of each subcarrier of the OFDM symbol and the information signal is derived, A receiving apparatus characterized in that a soft decision signal between a plurality of symbols is weighted and combined based on a transmission path estimation value.
(Appendix 4)
The receiving apparatus of the wireless transmission system according to attachment 3, wherein an average of the channel estimation values of each subcarrier in the OFDM symbol is obtained based on the channel estimation value of the equalizer, and a plurality of symbols are obtained based on the average value. A receiving apparatus characterized in that a soft decision signal between them is weighted and combined.

It is a block diagram which shows an example of a structure of the receiver which implements the receiving method which is one embodiment of this invention. It is a conceptual diagram which shows the structural example of the symbol synthetic | combination part in the receiver which is one embodiment of this invention. It is a diagram explaining the effect | action which is one embodiment of this invention. It is a block diagram which shows the modification of a structure of the receiver which implements the receiving method which is one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Receiver 1A Receiver 2 Antenna 3 Low noise amplifier 4 Frequency mixer 5 Radio frequency transmitter 6 Low pass filter 7 Automatic gain controller 8 A / D converter 9 Fast Fourier transform operation unit 10 Equalizer 11 Transmission path characteristic estimated value 12 symbol synthesis unit 12a synthesis symbol selection unit 12b multiplication unit 12c multiplication unit 12d addition unit 12e absolute value calculation unit 12f weighting calculation unit 12g normalization unit 13 demapping unit 14 deinterleaver 15 error correction processing unit 20 radio wave 20a spreading symbol 20b OFDM symbol 21 Equalization corrected symbol 22 Composite symbol 23 Soft decision data 23a Soft decision output 24 Information signal

Claims (10)

A reception apparatus in a wireless communication system for transmitting a first symbol carrying transmission information by spreading it into a plurality of second symbols in the time domain,
An equalizer for correcting the received second symbol in a frequency domain;
A symbol synthesizer that synthesizes a plurality of the second symbols derived from the common first symbol based on the channel characteristic estimation value obtained by the equalizer;
A receiving apparatus comprising: The receiving device according to claim 1,
The first symbol is an OFDM (Orthogonal Frequency Division Multiplex) symbol obtained by carrying the transmission information distributed over a plurality of subcarriers and performing inverse fast Fourier transform (IFFT),
The symbol combining unit, based on the transmission path characteristic estimation value, corresponds to each of the plurality of second symbols, and the OFDM symbol of the OFDM symbol corrected by the equalizer in the frequency domain after Fast Fourier Transform (FFT) A receiving apparatus characterized by combining weighted sub-carrier complex symbols. The receiving device according to claim 2,
The symbol combining unit obtains an average value of the channel characteristic estimation values of the individual subcarriers in the OFDM symbol, and the OFDM symbol corresponding to each of the plurality of second symbols based on the average value. A receiving apparatus characterized by combining the complex symbols of the subcarriers with weights. The receiving device according to claim 2,
The symbol synthesizer performs soft decision output data corresponding to each subcarrier after demodulation processing based on the modulation processing given to the complex symbol of each subcarrier of the OFDM symbol. A receiving apparatus characterized in that weighting is performed on the basis of an estimated value of transmission path characteristics and combining. The receiving device according to claim 4,
The symbol combining unit obtains an average value of the channel characteristic estimation values of the individual subcarriers in the OFDM symbol based on the transmission channel characteristic estimation value obtained by the equalizer, and obtains the average value. A receiving apparatus characterized in that the soft decision output data corresponding to each subcarrier is weighted and combined based on the data. A reception method in a wireless communication system for transmitting a first symbol carrying transmission information by spreading it into a plurality of second symbols in the time domain,
A first step of correcting the received second symbol in the frequency domain by an equalizer;
A second step of combining a plurality of the second symbols derived from the common first symbol based on the channel characteristic estimation value obtained by the equalizer;
A receiving method comprising: The receiving method according to claim 6, wherein
The first symbol is an OFDM (Orthogonal Frequency Division Multiplex) symbol obtained by carrying the transmission information distributed over a plurality of subcarriers and performing inverse fast Fourier transform (IFFT),
In the second step, the OFDM symbol of the OFDM symbol corrected by the equalizer in the frequency domain after fast Fourier transform (FFT) corresponding to each of the plurality of second symbols based on the channel characteristic estimation value. A reception method comprising weighting and synthesizing complex symbols of subcarriers. The receiving method according to claim 7, wherein
In the second step, an average value of the channel characteristic estimation values of the individual subcarriers in the OFDM symbol is obtained, and the OFDM symbol corresponding to each of the plurality of second symbols is obtained based on the average value. A reception method comprising weighting and combining the complex symbols of the subcarriers. The receiving method according to claim 7, wherein
In the second step, the soft decision output data corresponding to each subcarrier after demodulation processing based on the modulation processing given to the complex symbol of each subcarrier of the OFDM symbol, A receiving method, characterized in that weighting is performed based on an estimated value of transmission path characteristics and combining. The receiving method according to claim 9, wherein
In the second step, an average value of the channel characteristic estimation values of the individual subcarriers in the OFDM symbol is obtained based on the channel characteristic estimation value obtained by the equalizer, and the average value is obtained. A receiving method comprising weighting and combining the soft decision output data corresponding to each of the subcarriers based on the data.

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