JP4415050B2 - Orthogonal frequency division multiplex modulation transmission signal receiver - Google Patents

Description

  The present invention receives an OFDM signal which is a transmission signal of an orthogonal frequency division multiplex modulation system (hereinafter referred to as an OFDM system) that transmits information codes using a plurality of carriers orthogonal to each other as a transmission system. The present invention relates to an OFDM transmission signal receiving apparatus.

  In recent years, in the field of wireless devices, the OFDM method has attracted attention as a modulation method that is strong against multipath fading, and many applied researches in the fields of next-generation television broadcasting, FPU, wireless LAN, etc. in countries such as Europe and Japan. Is underway. UHF band terrestrial digital broadcasting has also been developed (see, for example, Non-Patent Document 1).

  As schematically shown in FIG. 2, the OFDM scheme provides a plurality of, for example, about 1400 carriers that are orthogonal to each other within a certain transmission bandwidth W, and designates a designated carrier such as 64QAM by an information code. This is a method of modulating and transmitting with a modulation method. Further, as schematically shown in FIG. 3, the time waveform has a guard interval Tg formed by copying the rear part b of the signal in the effective symbol period Tu to the head part b '. Due to this signal structure, the OFDM system can obtain characteristics that are strong against multipath.

  However, even the OFDM system is not universal and further improvements are desired. On the other hand, a diversity reception system is used to improve the reception characteristics in a multiple radio wave propagation environment or a mobile reception environment in a mobile phone or a car phone. Then, examination of application to this OFDM system of this diversity reception system is advanced.

  By the way, the diversity method has been studied in detail with respect to a single carrier method in which one carrier wave is modulated and transmitted, and a combining method such as selective combining, equal gain combining, maximum ratio combining has already been proposed. Among them, the maximum ratio combining is expected to have a large improvement effect although the circuit scale becomes large, and the result of examining the method of applying this combining method to the OFDM scheme by simulation has already been reported (for example, (Refer nonpatent literature 2.).

  FIG. 4 is a circuit configuration diagram of this conventional diversity receiver. However, for the sake of space, a plurality of branch circuits 71,... Having the same circuit configuration are indicated by thick broken line frames, and only the h-th branch circuit 7h is shown as its internal circuit configuration.

In the h-th branch circuit 7h, the antenna signal z _rfh received by the antenna 1h is down-converted into a baseband signal by the high-frequency RF circuit unit 2h and the intermediate-frequency IF circuit unit 3h, and is then converted by the A / D conversion circuit 4h. Converted into a digital signal. The digital OFDM signal zh obtained by the conversion is input to the FFT circuit 5h, subjected to DFT (Discrete Fourier Transform), demodulated into a carrier signal sequence Zh, and output.

  In the following, it is assumed that a lowercase signal such as z is a time signal, and an uppercase signal such as Z is a frequency signal after DFT.

  The carrier signal sequence Zh of the h-th branch output from the FFT circuit 5h is branched into two. The first branch is input to the transmission line frequency response calculation circuit 6 h, and the second branch is input to the synthesis weight multiplication circuit 80.

  Among these, the transmission path frequency response calculation circuit 6h compares the built-in reference frequency spectrum with the pilot signal CP inserted at a constant pitch between the input carrier signal sequence Zh. Then, a transmission line frequency response characteristic (hereinafter referred to as transmission line characteristic) is calculated, and the obtained transmission line characteristic signal sequence Hh (k) is output. Here, k represents a carrier number, but in the following description, it is omitted unless particularly necessary. For the signals received by the antennas 11 of the other branches, the same signal processing is performed by a branch circuit having the same configuration as that of the h-th branch circuit 7h surrounded by a thick broken line.

The transmission path characteristic signal sequences H1,..., Hh,... Calculated by the transmission path frequency response calculation circuits 61,. Collected and input, the following formula Wh (k) = Hh (k) ^* / {Σh _{= 1} ^m | Hh (k) | ² } (Formula 1)
(Where m is the number of all branch circuits)
Thus, the combined weight value Wh (k) for the carrier signal of the k-th carrier in the h-th branch is calculated. A ^* represents a conjugate complex signal of the complex signal A.

  In order for the combined weight value Wh calculated by (Equation 1) to be the maximum ratio described by the maximum ratio combining method, the noise levels mixed in the carrier signal sequences Z1,..., Zh,. (For example, refer nonpatent literature 3).

The combined weight values W1,..., Wh,... Calculated by the combined weight calculation circuit 90 are carrier signal sequences Z1,..., Output from the FFT circuits 51,. Along with Zh,... Then, a new carrier signal Zcom (k) weighted and synthesized by the following equation is calculated.
Zcom (k) = Σh _{= 1} ^m Zh (k) × Wh (k) (Formula 2)
(Where m is the number of all branch circuits)
The carrier signal Zcom calculated by this equation is a carrier signal that has been subjected not only to the multiplication / addition of the synthesis weight for the maximum ratio synthesis of diversity, but also to the transmission line response characteristic correction.

  The weight-combined carrier signal Zcom is input to the decoding circuit 100, and the information code is decoded and output.

  Through the above signal processing, a carrier signal with a high S / N ratio obtained by combining a maximum ratio for each carrier signal can be obtained from a plurality of antenna signals received by a plurality of antennas. Since the S / N of the carrier signal obtained by this signal processing is higher than that of the carrier signal demodulated from which antenna signal, a good information code with few code errors can be demodulated.

“Journal of the Institute of Image Information Media” 1998, Vol. 52, no. 11 “Technical Report of the Institute of Information and Video Media” Vol. 25, no. 50, PP13-18 (2001.1.730) Okumura et al. “Basics of Mobile Communications” Corona, p166

By the way, if this simulation result is applied to an actual diversity receiver, for example, an FPU in a microwave band, the following problem occurs.
That is, in order for the combined weight value Wh calculated by (Equation 1) to be the maximum ratio described by the maximum ratio combining method, the noise level mixed in the carrier signal sequence Z1,..., Zh,. Are equal. However, in the case of a microwave band FPU, the noise levels mixed in the carrier signal sequences Z1,..., Zh,... Output from the FFT circuits 51,. Therefore, the combination weight values W1,..., Wh,... Calculated in the conventional example do not become the maximum ratio, and there arises a problem that the effect expected in the diversity reception apparatus of the maximum ratio combination method is not necessarily obtained.

  There are two causes for this problem.

  First, the first cause will be described in detail. In a normal FPU, an AGC circuit is incorporated in a circuit unit that amplifies a high-frequency RF signal received by an antenna and down-converts it to an intermediate-frequency IF signal so that the converted IF signal level becomes substantially constant. Controlled. In other words, the level of the added signal obtained by adding the received OFDM signal and noise components such as thermal noise generated in the RF circuit unit is controlled to be constant. Hereinafter, this noise component is referred to as “RF noise component”.

  For example, it is assumed that the reception level of the OFDM signal zrf received by the antenna is sufficiently high. In this case, the relationship between the pure OFDM signal sif contained in the IF signal and the level of the RF noise component is as shown in the upper and lower stages of the schematic diagram of FIG. The relationship between the level of the pure OFDM signal component and the level of the RF noise component included in the carrier signal sequence Zh obtained from the IF signal is as shown in the schematic diagram of FIG.

  On the other hand, when the level of the pure OFDM signal srf received by the antenna decreases to a reception level at which the RF noise level generated in the RF circuit unit cannot be ignored, the shortage for keeping the IF signal level constant is the RF noise component. The relationship between the pure OFDM signal sif included in the IF signal and the level of the RF noise component is as shown in the upper and lower stages of FIG. The relationship between the level of the pure OFDM signal component and the level of the RF noise component included in the carrier signal sequence Zh obtained from the IF signal is as shown in the schematic diagram of FIG.

  On the other hand, since the level of the OFDM signal received by the antenna of each branch naturally varies from branch to branch, the level of the RF noise component mixed in the IF signal of each branch, and therefore mixed in the carrier signal sequence Zh demodulated from this IF signal. The level of the RF noise component being changed also varies from branch to branch. For this reason, the combination weight value Wh calculated by (Equation 1) deviates from the maximum ratio, and the effect expected by the diversity receiver of the maximum ratio combination method cannot be obtained.

  Next, the second cause of this problem will be described in detail. Generally, in mobile communication, fading due to multiple reflection described below occurs. That is, the carrier frequency of the OFDM signal emitted from the mobile body in all directions is shifted under the influence of Doppler frequencies of various sizes determined by the emission direction and the mobile body speed. Fading is a phenomenon that occurs because OFDM signals emitted in all these directions and subjected to different frequency shifts are received simultaneously. When fading occurs, the reception level fluctuates dramatically from moment to moment. In the diversity receiver of a single carrier transmission device that modulates and transmits one carrier wave, the main objective is to minimize the reduction in C / N with respect to RF noise due to the reduction in reception level. Although the influence of the shift of the carrier frequency generated by fading is known as random FM noise, it is said that there is no need to emphasize it (for example, see Non-Patent Document 3).

  However, this carrier frequency shift cannot be ignored in the OFDM system. The reason is as follows. That is, as is well known, the separation between carrier signals in the OFDM scheme is orthogonality obtained when the carrier frequency (carrier frequency) of each carrier signal has a correct frequency as shown in FIG. Is compensated by. This orthogonality is represented by the fact that the sinc function representing the frequency distribution obtained when the 0th carrier in FIG. 7A is modulated becomes 0 at carrier positions other than the 0th carrier. However, if the carrier frequency shifts, the distribution of the sinc function shifts as shown in FIG. 7B and does not become 0 at other carrier positions, and the orthogonality between carriers is lost. As a result, inter-carrier interference noise occurs.

  In the OFDM method, since a large number of carriers such as 1400 are modulated and transmitted, even if the inter-carrier interference noise level from each carrier is low, a large amount of noise is generated when the interference components from all carriers are combined. Become a level. Moreover, if the reflection condition and the Doppler frequency are the same, the inter-carrier interference noise level is proportional to the level of the pure OFDM signal sh, and is generated at a constant C / N regardless of the reception level.

  On the other hand, even if the maximum Doppler frequency of the received OFDM signal is the same, the inter-carrier interference noise level changes because the state of interference between carriers changes if the multiple reflection situation is different.

  For example, an OFDM signal received from an antenna facing in a direction with a certain degree of line of sight becomes a sum signal of signals emitted in almost the same direction, so that it is a signal subjected to a shift concentrated around a certain Doppler frequency. Become. Therefore, this frequency shift is canceled by the synchronization control of the Lo frequency, and an OFDM signal having a low inter-carrier interference noise level is obtained.

  On the other hand, an OFDM signal received by an antenna facing in a direction with no line of sight becomes a sum signal of signals emitted and reflected in all directions, and thus a signal subjected to a wide spread frequency shift. Therefore, it cannot be canceled out by synchronization control of the Lo frequency, and the OFDM signal has a high inter-carrier interference noise level.

  Therefore, the inter-carrier interference noise level differs from branch to branch, and the combined weight value Wh calculated by (Equation 1) deviates from the maximum ratio, and the effect expected by the diversity receiver of the maximum ratio combining method cannot be obtained.

  An object of the present invention is to provide an orthogonal frequency division multiplex modulation transmission signal receiver capable of diversity reception having performance expected by the maximum ratio combining method even in an OFDM transmission signal receiver. .

  Further, in the diversity receiver of the present invention, the noise level detection circuit can be applied to a normal OFDM transmission signal receiver that does not receive diversity, and when applied, the transmission path state can be visually monitored.

  Accordingly, another object of the present invention is to provide an apparatus for receiving an orthogonal frequency division multiplex modulation transmission signal that allows visual observation of the noise level.

  The present invention is a receiving apparatus for receiving an OFDM signal, which is a transmission signal of an orthogonal frequency division multiplexing modulation scheme (OFDM scheme) that transmits an information code using a plurality of carriers orthogonal to each other. A digital OFDM signal obtained by converting into a digital signal by an A / D conversion circuit is subjected to DFT (Discrete Fourier Transform), demodulated into a carrier signal sequence, and output, and the digital OFDM signal or the carrier signal sequence is A noise level detection circuit that detects and outputs a noise level mixed in the digital OFDM signal or a noise level mixed in the carrier signal sequence, and the noise level output from the noise level detection circuit The noise level ratio is calculated by outputting the noise level ratio relative to the reference noise level. And a noise level identifying circuit for inputting the noise level ratio output from the noise level ratio calculating circuit and outputting a carrier signal obtained by multiplying the carrier signal sequence by the noise level ratio, and the noise level identifying circuit A plurality of branch circuits having a transmission line response characteristic calculation circuit that inputs the carrier signal sequence output from the digital signal and calculates and outputs a transmission line frequency response characteristic for the digital OFDM signal, A plurality of carrier signal sequences output from each branch noise level equalization circuit of a plurality of branch circuits and a transmission channel frequency response characteristic output from each transmission channel response characteristic calculation circuit are input, and each carrier signal sequence is constant. Diversity combining by multiplying the weight signal of the signal and performing diversity frequency response characteristics correction and outputting a diversity combining circuit It is a receiving apparatus of orthogonal frequency division multiplexing modulation scheme transmission signal, wherein.

  According to the present invention, in the reception apparatus for the orthogonal frequency division multiplex modulation transmission signal described above, the noise level detection circuit inputs the digital OFDM signal converted by the A / D conversion circuit, and the digital OFDM signal Calculates a correlation value between signal parts having the same waveform in time and outputs the correlation signal as a correlation signal, and inputs a correlation signal output from the G correlation calculation circuit. An OFDM signal power calculation circuit that outputs an integral value of a correlation signal as a power value of a pure digital OFDM signal obtained by removing a noise component from the digital OFDM signal, and the power value P output from the OFDM signal power calculation circuit The noise level that is input and calculated and output the square root of the difference from the target signal power value of the AGC circuit of the receiver or an approximate value thereof. A receiving apparatus of orthogonal frequency division multiplexing modulation scheme transmission signal, characterized in that it consists Le calculating circuit.

  The present invention is a receiving apparatus for receiving an OFDM signal which is a transmission signal of an orthogonal frequency division multiplexing modulation system (OFDM system) that transmits information codes using a plurality of carriers orthogonal to each other. This is an OFDM signal having a carrier structure having two or more carriers (NULL carriers) that do not have signals at carrier positions separated from each other in the band, and is received by an antenna and converted into a digital signal by an A / D conversion circuit. An FFT circuit that performs DFT (Discrete Fourier Transform) on the obtained digital OFDM signal, demodulates and outputs a carrier signal sequence, and inputs the carrier signal sequence, and a plurality of NULL carriers or a plurality of symbols in the same symbol Is the square root of the mean square of the absolute value of the carrier signal detected by a plurality of NULL carriers across Is a noise level detection circuit that calculates and outputs the approximate value, and inputs the noise level output from the noise level detection circuit, and calculates and outputs a noise level ratio with respect to a reference noise level A noise level identifying circuit that inputs the noise level ratio output from the calculation circuit, the noise level ratio calculating circuit, and outputs a carrier signal obtained by multiplying the carrier signal sequence by the noise level ratio; and the noise level equalization A plurality of branch circuits having a transmission line response characteristic calculation circuit that inputs the carrier signal sequence output from the circuit and calculates and outputs a transmission line frequency response characteristic for the digital OFDM signal in one branch circuit; The plurality of carrier signal sequences output from each branch noise level equalizing circuit of the plurality of branch circuits, and each transmission line response characteristic A diversity combining circuit that inputs a transmission line frequency response characteristic output from the output circuit, multiplies each carrier signal sequence by a constant weight signal, performs diversity combining and transmission line frequency response characteristic correction, and outputs the resultant signal. An orthogonal frequency division multiplex modulation transmission signal receiver characterized by the above.

  The present invention is a receiving apparatus for receiving an OFDM signal which is a transmission signal of an orthogonal frequency division multiplexing modulation system (OFDM system) that transmits information codes using a plurality of carriers orthogonal to each other. An OFDM signal having a carrier structure having a unidirectionally modulated carrier that is modulated only in one direction on the signal space, for example, a pilot signal, at carrier positions separated from each other within the band, and received by an antenna and A / D converted. A digital OFDM signal obtained by converting into a digital signal by a circuit is subjected to DFT (Discrete Fourier Transform), demodulated into a carrier signal string and output, and the carrier signal string is input and inserted into the same symbol Component signal in the direction perpendicular to the modulation direction of the unidirectional modulation carrier, or multiple unidirectional changes across multiple symbols A noise level detection circuit that calculates and outputs a square root value of an average value of the square of an absolute value of a component signal in a direction perpendicular to the carrier modulation direction or an approximate value thereof, and the noise level detection circuit that outputs the noise level detection circuit A noise level ratio calculating circuit that inputs a noise level and calculates and outputs a noise level ratio with respect to a reference noise level, and the noise level ratio output from the noise level ratio calculating circuit is input, and the carrier signal sequence A noise level equalization circuit that outputs a carrier signal obtained by multiplying the noise level by the noise level, and the carrier signal sequence output from the noise level equalization circuit are input, and a transmission channel frequency response characteristic for the digital OFDM signal is calculated. A plurality of branch circuits included in one branch circuit, and each branch circuit of the plurality of branch circuits. Input a plurality of carrier signal sequences output from the noise level equalization circuit and transmission channel frequency response characteristics output from each transmission channel response characteristic calculation circuit, and multiply each carrier signal sequence by a constant weight signal. An orthogonal frequency division multiplex modulation transmission signal receiving apparatus comprising a diversity combining circuit that performs diversity combining and transmission path frequency response characteristic correction and outputs the result.

  According to the present invention, in the receiving device according to any one of the above, a plurality of combined weight signals each composed of a combined weight value of each branch circuit output from the combined weight calculation circuit or each carrier of each branch circuit An external output terminal for outputting a synthesized weight signal composed of values obtained by averaging the synthesized weight values of symbols to the outside of the apparatus is provided, or a display unit for displaying an antenna weight signal is provided. An orthogonal frequency division multiplex modulation transmission signal receiver.

  According to the present invention, in the receiving device according to any one of the above, an addition value of a combination weight value of each branch output from the combination weight calculation circuit is calculated, and the addition value or a time average value thereof is calculated for each branch. An orthogonal frequency division multiplex modulation transmission signal receiving apparatus is characterized by including an external output terminal that outputs the antenna weight signal to the outside of the apparatus or a display unit that displays the antenna weight signal.

  The present invention is a receiving apparatus for receiving an OFDM signal, which is a transmission signal of an orthogonal frequency division multiplexing modulation scheme (OFDM scheme) that transmits an information code using a plurality of carriers orthogonal to each other. A digital OFDM signal obtained by converting into a digital signal by an A / D conversion circuit is subjected to DFT (Discrete Fourier Transform), demodulated into a carrier signal sequence, and output, and the digital OFDM signal or the carrier signal sequence is A noise level detection circuit that detects and outputs a noise level mixed in the digital OFDM signal or a noise level mixed in the carrier signal sequence, and an external connected to the output of the noise level detection circuit An orthogonal frequency division multiplex modulation transmission signal receiver characterized by comprising an output terminal or a display unit It is.

  According to the present invention, in the reception apparatus for the orthogonal frequency division multiplex modulation transmission signal described above, the noise level detection circuit inputs the digital OFDM signal converted by the A / D conversion circuit, and the digital OFDM signal is A correlation calculation circuit for calculating a correlation value between signal portions having the same waveform in time and outputting the correlation value as a correlation signal; a correlation signal output from the correlation calculation circuit; An OFDM signal power calculation circuit that outputs an integral value of a signal as a power value of a pure digital OFDM signal obtained by removing a noise component from the digital OFDM signal, and the power value P output from the OFDM signal power calculation circuit is input. The noise level for calculating and outputting the square root of the difference from the target signal power value of the AGC circuit of the receiver or its approximate value is output. It consists of calculating circuit is a receiving apparatus of orthogonal frequency division multiplexing modulation scheme transmission signal, wherein.

  The present invention is a receiving apparatus for receiving an OFDM signal which is a transmission signal of an orthogonal frequency division multiplexing modulation system (OFDM system) that transmits information codes using a plurality of carriers orthogonal to each other. This is an OFDM signal having a carrier structure having two or more carriers (NULL carriers) that do not have signals at carrier positions separated from each other in the band, and is received by an antenna and converted into a digital signal by an A / D conversion circuit. An FFT circuit that performs DFT (Discrete Fourier Transform) on the obtained digital OFDM signal, demodulates and outputs a carrier signal sequence, and inputs the carrier signal sequence, and a plurality of NULL carriers or a plurality of symbols in the same symbol Is the square root of the mean square of the absolute value of the carrier signal detected by a plurality of NULL carriers across Comprises a noise level detection circuit that calculates and outputs an approximate value thereof, and an external output terminal or display unit connected to the output of the noise level detection circuit, and an orthogonal frequency division multiplexing modulation transmission signal The receiving device.

  The present invention is a receiving apparatus for receiving an OFDM signal which is a transmission signal of an orthogonal frequency division multiplexing modulation system (OFDM system) that transmits information codes using a plurality of carriers orthogonal to each other. An OFDM signal having a carrier structure having a unidirectionally modulated carrier that is modulated only in one direction on the signal space, for example, a pilot signal, at carrier positions separated from each other within the band, and received by an antenna and A / D converted. A digital OFDM signal obtained by converting into a digital signal by the circuit is subjected to DFT (Discrete Fourier Transform), demodulated into a carrier signal sequence, and the carrier signal sequence is input. Of the carrier signal detected by a plurality of NULL carriers or a plurality of NULL carriers straddling a plurality of symbols. A quadrature comprising a noise level detection circuit that calculates and outputs a square root value of an average value of power or an approximation thereof, and an external output terminal or a display unit connected to the output of the noise level detection circuit It is a receiver for a frequency division multiplex modulation transmission signal.

  According to the present invention, it is possible to obtain an orthogonal frequency division multiplex modulation transmission signal reception apparatus that enables diversity reception having the performance expected by the maximum ratio combining method even in an OFDM transmission signal reception apparatus. Further, according to the present invention, it is possible to obtain an orthogonal frequency division multiplex modulation transmission signal receiver capable of visually observing the noise level.

  FIG. 1 shows the configuration of the diversity receiver according to the first embodiment of the present invention. However, as in the conventional example of FIG. 4, a plurality of branch circuits 111,... Having the same circuit configuration are indicated by thick broken line frames, and only the h-th branch circuit 11h is shown as its internal circuit configuration. Note that the number of antennas may be arbitrary.

  The circuit configuration of FIG. 1 and the operation thereof are the same as those of FIG. 4 except that three circuits of a noise level detection circuit 12h with a dot pattern, a noise level ratio calculation circuit 13h, and a noise level equalization circuit 14h are newly provided. This is the same as the conventional circuit. Therefore, the operation and effect of the newly established circuit will be mainly described below.

  The OFDM signal zh obtained by converting into a digital signal by the A / D conversion circuit 4h in the same manner as in the conventional circuit is branched into two, one of which is input to the FFT circuit 5h as in the conventional case, and the other is newly added. The noise level detection circuit 12h is provided. The noise level detection circuit 12h is a circuit that detects the level nh of the RF noise component mixed in the OFDM signal zh.

FIG. 8 shows an internal circuit configuration of the noise level detection circuit 12h.
The OFDM signal zh input to the noise level detection circuit 12h is input to the G correlation calculation circuit 200. This circuit includes a Tu delay circuit 200a and a complex multiplier circuit 200b that are delayed by an effective symbol period Tu, and an adder circuit 200c that adds the multiplication results of the guard interval period length Tg. This circuit uses the fact that the waveform of the part b ′ is the same, and calculates its correlation.

More specifically, the complex multiplication s (t) of signals at the same timing between the OFDM signal of FIG. 9A input to the noise level detection circuit 12h and the signal of FIG. 9B delayed by one effective symbol period. ) × s (t−Ts) ^* is obtained by adding the signal of FIG. 9C obtained in the range schematically shown in FIG. 9D having the same period width as the guard interval Σ {s (T) × s (t−Ts) ^* } is sequentially calculated. Here, s ^* represents a conjugate complex signal of the complex signal s. The waveform of the correlation signal calculated in this way is shown in FIG.

  As described above, the waveform of the correlation signal calculated by the G correlation calculation circuit 200 is a triangular waveform having a peak at the boundary position of the symbol. Therefore, in order to detect the boundary position of the symbol, the OFDM receiver receives the signal. This is a frequently used circuit.

  When the received OFDM signal is only the main wave, the waveform of the correlation signal shown in FIG. 10 is a triangular waveform whose base is twice as wide as the guard interval length Tg. The peak value is proportional to the power Ps of the pure OFDM signal sh obtained by removing noise from the OFDM signal zh. Therefore, when the value of the hatched portion of the correlation signal is integrated, a value proportional to the power Ps of the pure OFDM signal sh is obtained.

  As shown in FIG. 11 (a), the correlation signal waveform when two waves of the main wave and the delayed wave are received is 2 for the main wave and the delayed wave shown in FIG. 11 (b). This is a waveform obtained by adding two triangular waveforms. FIG. 11C shows a correlation waveform when the delayed wave is delayed by the maximum delay time Tg that can be demodulated. When the value of the shaded portion of the square of 3 × Tg of the base is integrated, A value proportional to the power of a pure OFDM signal sh consisting of a main wave and a delayed wave is also obtained. Although a detailed description is omitted, in general, the integral value of the correlation signal in this 3 × Tg period is proportional to the power of the signal component that can be demodulated by the OFDM method using differential detection such as DQPSK. Even when more delay waves are included, the integral value of the obtained correlation signal is a value proportional to the power of the pure OFDM signal sh.

The OFDM signal power calculation circuit 201 in FIG. 8 is a circuit that performs an integration operation of the correlation signal of 3 × Tg during this period, and the integration value is a power value Ps of the pure OFDM signal sh included in the input OFDM signal zh. Output as.
This power value Ps is input to the noise level calculation circuit 202. Then, the square root √ (P0−Ps) of the difference from the power value P0 expected when there is no noise, or its approximate value is calculated and output as the noise level nh of the h-th branch.

  The noise level nh output from the noise level detection circuit 12h in FIG. 1 is input to the noise level ratio calculation circuit 13h, and a noise level ratio Rnh = n0 / nh, which is a ratio with a predetermined noise level n0, is calculated. Output. However, if the reception level is sufficiently high, nh≈0 and the value of the ratio n0 / nh diverges infinitely. Therefore, when the ratio n0 / nh exceeds a certain upper limit value, for example, the value 1, the ratio n0 The value of / nh is replaced with this upper limit value 1, and output as the value of the noise level ratio Rnh.

  The noise level ratio Rnh output from the noise level ratio calculation circuit 13h is input to the noise level equalization circuit 14h together with the carrier signal sequence Zh output from the FFT circuit 5h. The noise level equalization circuit 14h is a multiplication circuit, and outputs a carrier signal Zh ′ = Zh × Rnh obtained by multiplying the carrier signal sequence Zh by a noise level ratio Rnh.

  By the way, the noise level nh is an RF noise level originally included in the OFDM signal zh of the h-th branch, and the carrier signal Zh has an RF level Nh = α · nh proportional to the noise level nh. Noise component is mixed. Therefore, the level of noise included in the carrier signal Zh ′ obtained by multiplying the carrier signal Zh by Rnh = n0 / nh is α · nh × n0 / nh = α · n0, which is proportional to the reference noise level n0 set in advance. It becomes a constant value. However, the AGC circuit of each branch is set so that the target signal levels are all the same.

  In the circuit of FIG. 1, the carrier signal Zh ′ having the same noise level is synthesized in the same manner as the conventional circuit of FIG.

  At this time, since the level of noise contained in the carrier signals Z1h ′,..., Zh ′,... Of all branches to be synthesized becomes a constant value α · n0, the carrier signals synthesized by the synthesis weight multiplication circuit 80. Zcom becomes a signal synthesized with the maximum ratio, and the performance expected by the diversity receiver of the maximum ratio synthesis method can be obtained.

  As described above, in the diversity receiver according to the present embodiment, the noise level included in the signals of the respective branches to be combined is the same, so that the OFDM scheme that can achieve the performance expected by the diversity receiver of the maximum ratio combining method is obtained. A transmission signal diversity receiver can be obtained.

  FIG. 12 shows the configuration of a diversity receiver according to the second embodiment of the present invention. In the present embodiment, not only the level of the RF noise component mixed in the OFDM signal zh but also the noise level of each branch considering inter-carrier interference noise is adjusted to the same level, and then the maximum ratio is obtained. Synthesize.

  Therefore, unlike the circuit of FIG. 1, the output signal of the FFT circuit 5h is input to the noise level detection circuit 16h, and a null carrier without a signal inserted between the carrier structures of the OFDM signal as shown in FIG. It is configured to detect the level of the total noise component consisting of the RF noise component of the carrier signal and the inter-carrier interference noise.

  In the transmission device, a NULL carrier is inserted by distributing a 64QAM-modulated data carrier with a transmission information code, a carrier TMCC modulated with a control signal, and a carrier AC modulated with an auxiliary code to a specified carrier position of an OFDM signal by a distribution circuit. This is done by inserting a null carrier with no signal in between. Alternatively, a null carrier without a signal may be created by making AC no signal. The signal output from the distribution circuit is then subjected to IDFT (inverse Fourier transform), a guard interval is inserted, and then D / A converted. Then, it is converted into a high-frequency transmission signal by the IF circuit and the RF circuit and transmitted from the antenna.

FIG. 14 shows an internal circuit configuration of the new noise level detection circuit 16h. The carrier signal Zh output from the FFT circuit 5h in FIG. 12 and input to the noise level detection circuit 16h is input to the NULL carrier selection circuit 203 in FIG. 14, and the NULL carrier in FIG. 13 is selected.

  As is clear from FIG. 13, the signal of this NULL carrier consists only of RF noise and intercarrier interference noise indicated by broken lines, and does not include a signal component. Therefore, by calculating the power sum of the signal of this NULL carrier, it is possible to detect an average level in which all types of noise mixed in the carrier signal Zh of the received signal are added.

The NULL power calculation circuit 204 in FIG. 14 is a circuit for calculating this power sum, and is the square root of the addition average value of the absolute values of the fixed number of selected null carrier signals Zh (knull) √ {(Σknull | Zh (knull) | ² ) / (Number of carriers to be added)}. Here, “knull” represents a carrier number of a NULL carrier. The calculated value is output as the total noise level Nh including inter-carrier interference noise.

  In order to calculate a noise level value with high accuracy, it is desirable that the NULL carriers to be used are distributed over a wide band range. Further, the accuracy of the value to be calculated can be increased as the number to be added is at least 2 or more. When the number of NULL carriers to be inserted in one symbol is small, it may be calculated by adding signals of a plurality of NULL carriers.

  The noise level Nh output from the noise level detection circuit 16h of FIG. 12 is input to the noise level ratio calculation circuit 17h, and the noise level ratio RNh = N0 / Nh is calculated in the same manner as the circuit of FIG. However, the noise level N0 is a noise level serving as a reference with respect to the noise level Nh, and may have the same circuit configuration as the noise level ratio calculation circuit 13h in FIG. 1 except that the reference noise level is changed from n0 to N0. .

  The noise level ratio RNh output from the noise level ratio calculation circuit 17h is input to the noise level equalization circuit 14h together with the carrier signal string Zh output from the FFT circuit 5h, and the carrier signal string Zh is multiplied by the noise level ratio RNh. Carrier signal Zh ′ = Zh × RNh is output.

  By the way, noise of level Nh is mixed in the carrier signal Zh of the h-th branch. Therefore, the level of noise included in the carrier signal Zh ′ obtained by multiplying the carrier signal Zh by RNh = N0 / Nh is Nh × N0 / Nh = N0, which is a constant value of the noise level N0 that is a preset reference.

  In the circuit of FIG. 12, the carrier signal Zh ′ having the same noise level is synthesized in the same manner as in the conventional circuit of FIG.

  At this time, since the total noise level including inter-carrier interference noise becomes a constant value N0 in the carrier signals Z1 ′,..., Zh ′,. The signal Zcom becomes a signal synthesized at the maximum ratio, and the performance expected by the diversity receiver of the maximum ratio synthesis method can be obtained.

  As described above, in the diversity receiver according to the present embodiment, the noise level included in the signal of each branch to be combined is the same including the inter-carrier interference noise, so that the maximum ratio combining method is also used in mobile communication. It is possible to obtain an OFDM transmission signal diversity receiver capable of obtaining the performance expected by the diversity receiver.

  FIG. 15 shows the configuration of a diversity receiver according to the third embodiment of the present invention. This diversity receiver implements the same noise level in the circuit of FIG. 12 of the second embodiment with a feedback circuit.

  Unlike the second embodiment, in this embodiment, a signal Zh 'obtained by multiplying the output signal Zh of the FFT circuit 5h by a fixed noise level 14h is input to the noise level detection circuit 16h. Similarly to the second embodiment, the noise level Nh is detected using a NULL carrier, and the noise level ratio calculation circuit 17h calculates the noise level ratio RNh = N0 / Nh.

  The calculated noise level ratio RNh is input to a newly provided level error calculation circuit 18h, and a deviation amount ΔRNh = 1 from a value “1” indicating that the noise level N0 set as a reference is equal to the calculated noise level Nh. -RNh is calculated and output.

  The deviation amount ΔRNh output from the level error calculation circuit 18h is input to the integration circuit 19h, multiplied by a coefficient β smaller than 1, and then added to the amplification factor Mh ′ stored therein to obtain a new amplification factor Mh. = Mh ′ + β × ΔRNh is calculated and output.

  The amplification factor Mh output from the integration circuit 19h is input to the noise level equalization circuit 14h together with the carrier signal string Zh output from the FFT circuit 5h. Then, a carrier signal Zh ′ = Zh × Mh obtained by multiplying the carrier signal sequence Zh by the amplification factor Mh is calculated and output.

  In this circuit, the noise level mixed in the carrier signal Zh ′ output from the noise level equalizing circuit 14h is detected, and when the level is higher than the noise level N0 set as a reference, the amplification factor Mh is lowered. On the contrary, when it is smaller than N0, the gain is controlled to be large. Therefore, the magnitude of the carrier signal Zh ′ output from the noise level equalization circuit 14h finally converges to a magnitude at which the noise level mixed therein becomes the noise level N0 set as a reference.

  As a result, the level of noise contained in the carrier signals Z1 ′,..., Zh ′,... Of all the branches to be combined becomes a constant value N0, so that the carrier signal Zcom combined by the diversity combining circuit 80 is the maximum. The signal is synthesized by the ratio, and the performance expected by the diversity receiver of the maximum ratio synthesis method can be obtained.

  As described above, in the diversity receiver according to the present embodiment, the noise level included in the signal of each branch to be combined is the same including the inter-carrier interference noise, so that the maximum ratio combining method is also used in mobile communication. It is possible to obtain an OFDM transmission signal diversity receiver capable of obtaining the performance expected by the diversity receiver.

  A diversity receiving apparatus according to the fourth embodiment of the present invention will be described. The circuit configuration of this diversity receiver is basically the same as the circuit configuration of FIG. 12 of the second embodiment.

  The difference is that in the second embodiment, the noise level is detected using a NULL carrier inserted between the carrier structures of the OFDM signal, whereas in this embodiment, the carrier of the OFDM signal is detected. A unidirectional modulation carrier modulated only in one direction on the signal space inserted between the structures, for example, a pilot signal CP modulated only in the I-axis (real axis) direction of the signal space as shown in FIG. It is in the point to detect.

In this method, noise is isotropically mixed in the signal space, whereas the signal is modulated only in one direction such as the I-axis direction and has no signal component in the vertical direction. That is, the square root value √ {(Σ _kp | Q (kp) | ² / (number of added carriers)) of the absolute value of the absolute value of the signal Qh (kp) in the direction perpendicular to the modulation direction of the signal or its approximate value The noise level is detected by calculating (where kp is the carrier number of the unidirectional modulation carrier).

  As can be seen from this detection method, the modulation direction of the unidirectional modulation carrier is not limited to the I-axis direction, but may be the imaginary axis (Q-axis) direction or any other direction. Further, the modulation method may be any modulation method such as BPSK, DBPSK, etc., as long as the modulation method is performed only in one direction.

  Therefore, in the present embodiment, the internal circuit configuration of the noise level detection circuit 16h in FIG. 12 is changed from the circuit configuration in FIG. 14 to the circuit configuration in FIG. The circuit configuration of FIG. 17 includes a unidirectional modulation carrier selection circuit 205 in which the selected carrier is changed from a NULL carrier to a unidirectional modulation carrier, a newly provided vertical direction component calculation circuit 206, and a NULL component to vertical component power. The vertical component power calculation circuit 207 changed to

  Since the operation method of the circuit of FIG. 12 in this embodiment is the same, the description thereof is omitted.

  As described above, in the diversity receiver according to the present embodiment, the noise level included in the signals of the respective branches to be combined is the same including the inter-carrier interference noise, as in the second embodiment. It is possible to obtain an OFDM transmission signal diversity receiver capable of obtaining the performance expected from the maximum ratio combining diversity receiver even during mobile communication.

  It is obvious that the noise level detection circuit used in the present embodiment can also be applied to the circuit of FIG. 14 of the third embodiment.

  In any of the above embodiments, the value to be multiplied by the noise level equalization circuit 14h is changed in the boundary region between two consecutive symbol carrier signals so that the signal level does not change in one symbol in any case. It goes without saying that it is preferable to carry out the above.

  Further, in the circuits of FIGS. 1 and 14, it goes without saying that the same effect can be obtained even if the noise level equalizing circuit 14h is inserted before the FFT circuit 5h.

  Further, in the above embodiments, in any case, it has been described that weight synthesis is performed using the synthesis weight value Wh (k) of each branch calculated from the signal in one symbol. Each time, the average value of the combined weight values Wh (k) of a plurality of symbols is calculated to reduce noise, and then a new carrier signal Zcom () which is weighted and combined using the calculated average value instead of Wh (k). k) may be calculated.

  Further, only the evaluation using the correlation signal as the noise level detection circuit 12h in FIG. 1 has been described, but it is obvious that the calculation may be performed using a signal that can detect the distribution and level of the delayed wave component of the OFDM signal zh. is there. For example, it may be calculated using a delay profile signal calculated by a method such as frequency analysis of a pilot signal inserted in the OFDM signal. In this case, when the amplitude value of the delay profile is proportional to the power value of the OFDM signal component of each delay wave, the sum (area) of the waveform of the delay profile signal is used instead of the sum (area) of the waveform of the correlation signal. A similar calculation may be performed.

  Further, as illustrated in the lower right corner of FIG. 1, a composite weight signal calculation circuit 91 is connected to the composite weight calculation circuit 90, its output is connected to the external output terminal 92, and a display device 93 is connected to the external output terminal 92. To do.

  Here, the combined weight calculation circuit 90 outputs the combined weight value Wh (k) of each branch as a combined weight signal, or calculates the average value of combined weight values Wh (k) of a plurality of symbols for each carrier of each branch. If the circuit is calculated and output as a combined weight signal, the display device 93 can grasp the importance of each carrier signal in each branch while visually observing as shown in FIG. Thus, it is possible to obtain a diversity receiving apparatus that can be used in practice while confirming the effects of the above, and has good usability. In this case, it is desirable to incorporate a display device in the diversity receiver itself so that it can be easily observed.

  Further, if the synthesis weight calculation circuit 90 is a circuit that calculates the addition value ΣkWh (k) of the synthesis weight value Wh (k) of each branch and outputs the addition value or the time average value thereof, a synchroscope or the like By making the display device 93 visually observable as shown in the left or right diagram of FIG. 19, for example, it is possible to carry out actual operations such as grasping an antenna with low usage frequency and adjusting its direction. Thus, it is possible to obtain a diversity receiver that is easy to use. In this case, it is desirable to incorporate a display device in the diversity receiver itself so that it can be easily observed.

  Next, FIG. 20 shows the configuration of a receiving apparatus according to the fifth embodiment of the present invention. 1 has only a single branch circuit 11h and a decoding circuit 100. The single branch circuit 11h is composed of only an OFDM demodulator circuit unit including an FFT circuit 5h to an RF circuit for a single antenna 1h, and a noise level detection circuit 12h or 16h, and the noise level detection circuit 12h or The output of 16h is connected to the output terminal 92 and the display device 93.

  Here, the noise level detection circuit 12h has the same configuration as that shown in FIGS. The noise level detection circuit 16h may have the same configuration as that shown in FIGS. Moreover, the same structure as FIG. 12 and FIG. 17 may be sufficient.

  Since the receiving apparatus according to the present embodiment includes a noise level detection circuit, it is possible to obtain an OFDM transmission signal receiving apparatus that can visually check the state of the transmission path.

It is a circuit block diagram of the receiver of the OFDM system transmission signal of the 1st Embodiment of this invention. It is a figure explaining the carrier structure of an OFDM system transmission signal. It is a figure explaining the structure of an OFDM signal. It is a circuit block diagram of the diversity receiver of the conventional OFDM system transmission signal. It is a figure for making the 1st explanation regarding the problem of the conventional diversity receiver. It is a figure for making the 2nd description regarding the problem of the conventional diversity receiver. It is a figure for making the 3rd description regarding the problem of the conventional diversity receiver. It is a circuit block diagram of the noise level detection circuit of the receiver of the OFDM system transmission signal of the 1st Embodiment of this invention. FIG. 5 is a diagram for describing a first operation of the noise level detection circuit according to the first embodiment of the present invention. It is a figure for carrying out the 2nd description of operation | movement of the noise level detection circuit in the 1st Embodiment of this invention. It is a figure for demonstrating the 3rd operation | movement of the noise level detection circuit in the 1st Embodiment of this invention. It is a circuit block diagram of the receiver of the OFDM system transmission signal of the 2nd Embodiment of this invention. It is a figure which shows the structure of the OFDM signal used in the 2nd Embodiment of this invention. It is a circuit block diagram of the noise level detection circuit in the 2nd Embodiment of this invention. It is a circuit block diagram of the receiver of the OFDM system transmission signal of the 3rd Embodiment of this invention. It is a figure explaining the noise level detection method of the 4th Embodiment of this invention. It is a circuit block diagram of the noise level detection circuit of the 4th Embodiment of this invention. It is a figure which shows the example of a display of the weight value of each branch in each carrier. It is a figure which shows the example of a display of the weight value of each branch. It is a circuit block diagram of the receiver of the OFDM system transmission signal of the 5th Embodiment of this invention.

Explanation of symbols

  11, 1h: Antenna, 2h: RF circuit unit, 3h: IF circuit unit, 4h: A / D conversion circuit, 5h: FFT circuit, 6h: Transmission path frequency characteristic calculation circuit, 71, 7h, 111, 11h, 151 15h: branch circuit, 80: synthesis weight multiplication circuit, 90: synthesis weight calculation circuit, 91: synthesis weight signal calculation circuit, 92: external output terminal, 93: display device, 100: decoding circuit, 12h, 16h: noise level detection Circuit, 13h, 17h: noise level ratio calculation circuit, 14h: noise level equalization circuit, 18h: level error calculation circuit, 19h: integration circuit, 200: G correlation calculation circuit, 200a: Tu delay branch, 200b: complex multiplication circuit , 200c: addition circuit, 201: OFDM signal power calculation circuit, 202: noise level calculation circuit, 203: NULL carrier selection circuit, 204: N LL power calculation circuit, 205: one-way modulated carrier selection circuit, 206: vertical component calculating circuit, 207: vertical component power calculating circuit.

Claims (2)

A receiving apparatus that receives an OFDM signal that is a transmission signal of an orthogonal frequency division multiplexing modulation scheme (OFDM scheme) that transmits an information code using a plurality of carriers that are orthogonal to each other,
Each branch circuit
An FFT circuit that receives a digital OFDM signal that is received by an antenna and converted into a digital signal by an A / D conversion circuit, performs DFT (Discrete Fourier Transform), and demodulates and outputs the carrier signal sequence;
A noise level detection circuit that inputs the digital OFDM signal or the carrier signal sequence, detects and outputs a noise level mixed in the digital OFDM signal or a noise level mixed in the carrier signal sequence;
A noise level ratio calculation circuit that inputs the noise level output from the noise level detection circuit, calculates a noise level ratio with respect to a reference noise level, and outputs the noise level ratio;
A noise level equalization circuit that inputs the noise level ratio output from the noise level ratio calculation circuit and outputs a carrier signal obtained by multiplying the carrier signal sequence by the noise level ratio;
A plurality of branch circuits having a transmission line response characteristic calculation circuit that inputs the carrier signal sequence output from the noise level equalization circuit and calculates and outputs a transmission line frequency response characteristic for the digital OFDM signal;
A combined weight calculating circuit for inputting a transmission line frequency response characteristic output from each transmission line response characteristic calculating circuit of the plurality of branch circuits and calculating a combined weight value;
A combination weight value for each carrier signal output from the combination weight calculation circuit and a plurality of carrier signal sequences output from each branch noise level equalization circuit of the plurality of branch circuits are input, and each carrier signal sequence A synthesis weight multiplication circuit that multiplies the signal with a constant weight signal to perform diversity synthesis and transmission path frequency response correction, and outputs the result,
It is composed of a composite weight signal composed of the composite weight value of each branch circuit outputted from the composite weight calculation circuit or a value obtained by averaging the composite weight values of a plurality of symbols for each carrier of each branch circuit. Provide an external output terminal for outputting the combined weight signal, or the combined weight value of each branch circuit or the average value of the combined weight values of each branch circuit to the outside of the device, or the antenna weight signal A display unit to display;
An apparatus for receiving an orthogonal frequency division multiplex modulation transmission signal. The orthogonal frequency division multiplex modulation transmission signal receiver according to claim 1, wherein the noise level detection circuit comprises:
A G-correlation calculation circuit that inputs the digital OFDM signal converted by the A / D conversion circuit, calculates a correlation value between signal portions of the same waveform in time that the digital OFDM signal has, and outputs the correlation value as a correlation signal When,
An OFDM signal that receives a correlation signal output from the G correlation calculation circuit and outputs an integral value of the correlation signal for a predetermined period as a power value of a pure digital OFDM signal obtained by removing noise components from the digital OFDM signal. A power calculation circuit;
It is composed of a noise level calculation circuit that inputs the power value output from the OFDM signal power calculation circuit and calculates and outputs the square root of the difference from the target signal power value of the AGC circuit of the receiving apparatus or its approximate value. An apparatus for receiving an orthogonal frequency division multiplex modulation transmission signal.

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