JP6190221B2 - Receiver - Google Patents

Description

The present invention, MIMO; relates to a receiving equipment having a MIMO channel quality monitoring function of monitoring the quality of the propagation path in (Multiple-Input Multiple-Output multiple input multiple output) system.

  A MIMO system that performs wireless communication using multiple antennas for transmission and reception can be used to increase transmission capacity and improve line quality using multiple propagation paths between transmission and reception antennas. Applications are progressing in the field of broadcasting. When performing large-capacity transmission in a mobile environment, the frequency selective fading becomes a problem, so the MIMO system is used as a MIMO-OFDM system combined with a multicarrier orthogonal frequency division multiplexing (OFDM) scheme. It is often done.

  In the MIMO system, if the number of antennas is increased, the corresponding effect cannot be obtained. If the propagation path responses between the plurality of transmitting antennas and the receiving antenna are not similar and the correlation is low, the MIMO effect can be obtained. Therefore, even in a propagation environment where there is no problem in a conventional SISO (Single-Input Single-Output) system, there may be a problem in a MIMO system (for example, see Non-Patent Document 1).

  In a conventional SISO system with one transmission and one reception, the received power, constellation, delay profile, MER (Modulation Error Rate) and its margin are individually displayed to monitor the quality of the propagation path. (For example, see Patent Document 1 and Non-Patent Document 2).

JP 2009-290580 A

Takayuki Nakagawa, Tetsuomi Ikeda, “Field Experiments of 2 × 2 STTC-MIMO-OFDM System”, Eiji Meiho Technical Report, Vol. 36, no. 30, BCT2012-62 (2012) "PF-531 Digital FPU device", catalog, Ikegami Tsushinki, November 2009

  In a MIMO system, the transmission characteristics deteriorate when the channel response between each transmitting antenna and each receiving antenna is similar. Therefore, the antenna arrangement based on the channel quality monitoring method in the conventional SISO system, etc. However, there is a problem that the transmission may fail even if it is determined, and the conventional method cannot be applied as it is.

An object of the present invention has been made in view of such circumstances is to provide a receiving equipment having a MIMO channel quality monitoring function to accurately monitor the quality of the channel in a MIMO system.

In order to solve the above problems, a receiving apparatus according to the present invention is a receiving apparatus having a MIMO channel quality monitoring function for monitoring a channel quality of a MIMO system, and an input signal for estimating a channel response of the MIMO system. Based on the processing unit, a rice factor calculation unit that calculates a rice factor from the propagation path response, a correlation coefficient calculation unit that calculates a correlation coefficient of the propagation path response, the rice factor and the correlation coefficient, A display processing unit for displaying quality information indicating the quality of the MIMO propagation path , wherein the display processing unit has the rice factor as one axis and the correlation coefficient of the propagation path response as the other axis. -On the correlation coefficient coordinates, the rice factor calculated by the rice factor calculation unit and the correlation coefficient calculated by the correlation coefficient calculation unit are plotted. And wherein the Rukoto to display the rough.

  Furthermore, in the receiving apparatus according to the present invention, the display processing unit displays, in the rice factor-correlation coefficient coordinates, an area having a small rice factor and a large correlation coefficient to be distinguished from other areas. And

  The receiving apparatus according to the present invention further includes a CNR calculating unit that calculates a CNR of a received signal, and the display processing unit is a required CNR that is determined in advance according to a value of a rice factor and a correlation coefficient of a channel response. And the difference between the CNR calculated by the CNR calculation unit and the margin are displayed as a margin.

  Furthermore, in the receiving apparatus according to the present invention, the display processing unit displays an isoline with the required CNR as a parameter on the Rice factor-correlation coefficient coordinates.

  The receiving apparatus according to the present invention further includes a display device that displays the quality information.

  In the present invention, since the rice factor and the correlation coefficient of the propagation path response, which are parameters that affect the transmission characteristics of the MIMO system, are displayed and monitored in association with each other, the quality of the propagation path in the MIMO system can be accurately monitored. Can do. Then, by correcting the type and arrangement of the antenna based on the quality information of the propagation path, more stable wireless transmission can be realized, which can be used for constructing a stable operation of the MIMO system.

It is a block diagram which shows the structural example of the receiver which concerns on one Embodiment of this invention. It is a block diagram which shows the structural example of the input signal process part in the receiver which concerns on one Embodiment of this invention. It is a block diagram which shows the structural example of the propagation path quality process part in the receiver which concerns on one Embodiment of this invention. It is a flowchart which shows the MIMO propagation path quality monitoring method by the receiver which concerns on one Embodiment of this invention. It is a graph which shows the 1st example of the quality information which the receiver which concerns on one Embodiment of this invention outputs. It is a graph which shows the 2nd example of the quality information which the receiver which concerns on one Embodiment of this invention outputs. It is a figure which shows a CNR vs. BER characteristic.

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

  First, characteristics regarding transmission characteristics of the MIMO system will be described. Factors that influence the transmission characteristics of the MIMO system include the power ratio between the received signal and noise within the transmission band, the degree of multipath, and the correlation of the propagation path response.

  Examples of the parameter indicating the power ratio between the received signal and noise in the transmission band include RSSI (Received Signal Strength Indicator) and CNR (Carrier to Noise power Ratio).

  The parameter indicating the degree of multipath includes a rice factor that is a ratio of the received power of the main wave received at the maximum power and the received power sum of the other incoming waves.

  Furthermore, examples of the parameter indicating the correlation of the propagation path response include a transmission correlation coefficient related to the propagation path response between the transmission signals and a reception correlation coefficient related to the propagation path response between the reception signals.

  For each parameter, the larger the RSSI, the greater the CNR, and the better the transmission characteristics. However, the receiver usually performs automatic gain control in order to obtain a wide input dynamic range, and when the RSSI is large, in order to attenuate and keep the signal level input to the baseband signal processing unit constant, Even if the RSSI is large, the CNR is a value clipped at the upper limit of 30 dB or the like.

  As the rice factor increases, the direct wave is dominant and the level fluctuation of the received signal is reduced, so that the transmission characteristics are improved. In general, the rice factor of the line-of-sight environment becomes large, such as 10 dB or more, and the rice factor of the non-line-of-sight environment becomes small, such as 0 dB or less.

  The smaller the transmission correlation coefficient and the reception correlation coefficient, the more effective the propagation path between the transmission / reception antennas provided, and the effect of increasing the transmission capacity and improving the line reliability can be enjoyed.

  FIG. 7A is a diagram showing CNR vs. BER (Bit Error Rate) characteristics when the Rice factor is infinite (that is, free space propagation) and the MIMO channel response is uncorrelated. This figure shows that, as a basic property of the wireless transmission system, when the received signal power becomes small, it becomes difficult to identify the signal point due to the noise, so that the transmission characteristics deteriorate.

  FIG. 7B is a diagram showing the CNR vs. BER characteristics when the rice factor is small or when the correlation of the propagation path is large. When multipath arrives and the rice factor decreases, frequency selective fading occurs, the BER curve slope decreases, and transmission characteristics deteriorate. On the other hand, even when the correlation coefficient of the MIMO propagation path response becomes large, a plurality of propagation paths cannot be used effectively, so the slope of the BER curve becomes small and the transmission characteristics deteriorate. In order to make pseudo error free by error correction in such an environment, a large CNR is required.

  FIG. 7C is a diagram showing CNR vs. BER characteristics when the rice factor is small and the correlation of the propagation path is large. Generally, in the line-of-sight environment, the rice factor increases and the correlation coefficient of the propagation path response also increases. In the environment outside the line-of-sight environment, the rice factor decreases and the correlation coefficient of the propagation path response tends to decrease. However, depending on the antenna conditions such as the antenna interval being not sufficiently separated, even if the rice factor is small in a non-line-of-sight environment, the correlation of the MIMO channel response becomes large, and the transmission characteristics further deteriorate. In such a case, a larger CNR is required, and in some cases, it may not be possible to make a pseudo error free by error correction.

  The present invention utilizes such a characteristic of the MIMO system, generates quality information based on the rice factor and the correlation coefficient of the propagation path, and monitors the quality of the MIMO propagation path. Hereinafter, an embodiment of the present invention will be described by taking a 2 × 2 MIMO system with two transmissions and two receptions as an example. However, the present invention is not limited to a 2 × 2 MIMO system, and for example, a 4 × 4 MIMO system or a 2 × 4 MIMO system. The present invention can be similarly applied even to a system.

  FIG. 1 is a block diagram showing a configuration example of a system using a receiving apparatus according to an embodiment of the present invention. In the example illustrated in FIG. 1, the reception device 1 has a MIMO propagation path quality monitoring function, and includes a reception antenna 11 (11-1, 11-2), and a frequency conversion unit 12 (12-1, 12-2). And a baseband signal processing unit 13. Here, the video decoder 2 and the display device 3 are illustrated outside the reception device 1, but the reception device 1 may include one or both of the video decoder 2 and the display device 3. FIG. 1 also shows the transmission antennas 41 (41-1, 41-2) of the transmission apparatus.

The transmission signals of the 2 × 2 MIMO system transmitted from the two transmission antennas 41 receive the propagation path responses h _{11 to} h _{22 and} are received as the reception RF signal 1 and the reception RF signal 2 by the two reception antennas 11. The The propagation path matrix H of 2 × 2 MIMO transmission can be expressed by Equation (1).

  The frequency converter 12-1 converts the frequency of the received RF signal 1 received by the receiving antenna 11-1 into the received IF signal 1, detects RSSI1 that is the received signal strength of the received RF signal 1, and receives the received IF signal 1. And RSSI1 are output to the baseband signal processing unit 13. Similarly, the frequency conversion unit 12-2 frequency-converts the reception RF signal 2 received by the reception antenna 11-2 to the reception IF signal 2, detects RSSI2 that is the reception signal strength of the reception RF signal 2, and receives the received signal. The IF signal 2 and RSSI 2 are output to the baseband signal processing unit 13.

  The baseband signal processing unit 13 includes an input signal processing unit 131, a propagation path quality processing unit 132, a MIMO demodulation processing unit 133, and an output signal processing unit 134.

The input signal processing unit 131 performs OFDM or single carrier demodulation processing on the reception IF signal input from the frequency conversion unit 12 to obtain the reception signal and channel information (estimated propagation path responses h _{11 to} h ₂₂ ). And output to the propagation path quality processing unit 132 and the MIMO demodulation processing unit 133. Details of the input signal processing unit 131 will be described later.

  The propagation path quality processing unit 132 receives the RSSI, the received signal, and the channel information of the two reception systems generated by the input signal processing unit 131, performs a calculation process of a parameter indicating the quality of the propagation path, and outputs the quality information. Generate and output to the display device 3. Details of the propagation path quality processing unit 132 will be described later.

  The MIMO demodulation processing unit 133 receives the reception signals and channel information of the two reception systems generated by the input signal processing unit 131, performs demodulation processing according to the MIMO scheme, generates a MIMO demodulation signal, and outputs an output signal The data is output to the processing unit 134.

  The output signal processing unit 134 performs a process reverse to the transmission side, such as a deinterleave process, a data frame synchronization process, and an error correction process, on the MIMO demodulated signal generated by the MIMO demodulation process unit 133 to generate a TS signal. And output to the video decoder 2.

  The video decoder 2 uses the MPEG-4 AVC / H. Decoding processing is performed by a predetermined method such as the H.264 method, and a decoded signal is output to the display device 3.

  The display device 3 displays the quality information generated by the propagation path quality processing unit 132. Also, the video information generated by the video decoder 2 is displayed. The display device 3 may display the quality information and the video information separately in the vertical and horizontal directions, or may overlay the quality information on the video information. Two display devices 3 may be provided and displayed individually. The quality information may be displayed on application software. A specific example of the quality information will be described later.

[Input signal processor]
Next, details of the input signal processing unit 131 will be described. FIG. 2 is a block diagram illustrating a configuration example of the input signal processing unit 131. FIG. 2A is a block diagram illustrating a configuration of the input signal processing unit 131 in the case of a transmission scheme in which a 2 × 2 MIMO system is applied to the OFDM scheme. In this example, the input signal processing unit 131 includes an ADC unit 1311, an orthogonal demodulation unit 1312, an AFC (Automatic Frequency Control) unit 1313, a symbol synchronization unit 1314, and an FFT (Fast Fourier Transform). A conversion unit 1315 and a channel estimation unit 1316.

  The ADC unit 1311 performs discretization and quantization on the reception IF signal generated by the frequency conversion unit 12 to convert the received IF signal into a digital IF signal, and outputs the digital IF signal to the orthogonal demodulation unit 1312.

  The quadrature demodulation unit 1312 performs quadrature demodulation on the digital IF signal generated by the ADC unit 1311, converts the digital IF signal into a baseband signal of a real part and an imaginary part, and outputs the baseband signal to the AFC unit 1313.

  The AFC unit 1313 corrects a transmission and reception frequency shift with respect to the baseband signal generated by the orthogonal demodulation unit 1312 and outputs the corrected signal to the symbol synchronization unit 1314.

  The symbol synchronization unit 1314 detects the leading position of the OFDM symbol by sliding correlation processing or the like using the fact that the OFDM guard period is a copy of the rear part of the effective symbol period.

  The FFT unit 1315 performs an FFT process on the effective symbol obtained by removing the guard period from the beginning of the OFDM symbol with respect to the frequency-corrected baseband signal to generate a reception signal of each subcarrier, and a channel estimation unit 1316, output to the propagation path quality processing unit 132 and the MIMO demodulation processing unit 133.

  Channel estimation section 1316 uses the pilot pattern of transmission signal 1 and transmission signal 2 (for example, transmission signal 1 and transmission for each symbol) for the pilot carrier of known information allocated for channel estimation among the reception signals of each subcarrier. The propagation path response of the MIMO system is estimated according to a pilot pattern in which the signal 2 is alternately transmitted, a transmission signal 1 as it is, and a transmission pattern in which the transmission signal 2 is transmitted with its phase inverted for each symbol. . Then, the channel response is output as channel information to channel quality processing section 132 and MIMO demodulation processing section 133.

  FIG. 2B is a block diagram illustrating a configuration example of the input signal processing unit 131 ′ in the case of a transmission scheme in which a 2 × 2 MIMO system is applied to a single carrier scheme. In this example, the input signal processing unit 131 ′ includes an ADC unit 1311, an orthogonal demodulation unit 1312, an AFC unit 1313, a channel estimation unit 1316, and a block synchronization unit 1317. The ADC unit 1311, the orthogonal demodulation unit 1312, the AFC unit 1313, and the channel estimation unit 1316 are the same as those in the OFDM scheme.

  The block synchronization unit 1317 detects the beginning of the block based on the synchronization signal inserted at the beginning of the single carrier block and generates a reception signal. The channel estimation unit 1316, the channel quality processing unit 132, and the MIMO The data is output to the demodulation processing unit 133.

[Channel quality processing section]
Next, details of the propagation path quality processing unit 132 will be described with reference to FIGS. 3 and 4. FIG. 3 is a block diagram illustrating a configuration example of the propagation path quality processing unit 132. In the example illustrated in FIG. 3, the propagation path quality processing unit 132 includes a CNR calculation unit 1321, a rice factor calculation unit 1322, a correlation coefficient calculation unit 1323, and a display processing unit 1324.

  FIG. 4 is a flowchart showing a quality monitoring method by the propagation path quality processing unit 132 of the receiving apparatus 1 having the MIMO propagation path quality monitoring function.

  The CNR calculator 1321 calculates the CNR of the received signal (Step S101). As the CNR of the received signal, CNR1 and CNR2 can be calculated based on the ratio between RSSI1 and RSSI2 detected by the frequency converter 12 and the noise power measured in advance. The noise power is obtained, for example, by measuring the power of the null carrier. The CNR calculation unit 1321 can calculate the CNR even when the frequency conversion unit 12 does not output RSSI. In this case, the signal power and the noise power are detected from the received signal, and the ratio is set as the CNR. However, the CNR is a value clipped at the upper limit.

  When the channel estimation unit 1316 performs frequency domain channel estimation, the rice factor calculation unit 1322 can obtain a delay profile by performing IFFT (Inverse Fast Fourier Transform) on the channel estimation result. Further, when the channel estimation unit 1316 estimates a time domain impulse response, the estimated impulse response can be used as a delay profile.

The rice factor calculation unit 1322 converts the delay profile into a power delay profile expressed by power, and is the ratio of the received power P _{0 of the} main wave received at the maximum power and the received power sum (ΣP _i ) of other incoming waves. The factor K is calculated for each of the propagation path responses h _{11 to} h ₂₂ by the equation (2), and an average rice factor that is an average value or a weighted average value is calculated (step S102).

The correlation coefficient calculation unit 1323 represents the conjugate transpose matrix of H as ^{H H} shown in Expression (3) with respect to the channel matrix H representing the channel information (estimated channel responses h _{11 to} h ₂₂ ) as a matrix. And a transmission correlation matrix <H ^H H> shown in Expression (4) and a reception correlation matrix <HH ^H > shown in Expression (5). Here, <> represents an ensemble average. Then, the correlation coefficient calculation unit 1323 converts the absolute value of the 1 × 2 element normalized by the square root of the product of the diagonal elements to the transmission correlation coefficient shown in Expression (6) and Expression (7) ) Is calculated as a reception correlation coefficient (step S103).

  The display processing unit 1324 displays quality information indicating the quality of the MIMO propagation path based on the average rice factor calculated by the rice factor calculation unit 1322 and the correlation coefficient calculated by the correlation coefficient calculation unit 1323. The quality information is displayed on the display device 3 (step S104). The CNR information calculated by the CNR calculation unit 1321 may be included in the quality information. Specific examples of quality information are shown below.

  FIG. 5 is a graph showing a first example of quality information, and shows a rice factor-correlation coefficient coordinate A with the rice factor as one axis and the correlation coefficient of the propagation path response as the other axis. . In this example, the rice factor is in the range of -5 dB to 20 dB.

The display processing unit 1324 displays a graph in which the average rice factor calculated by the rice factor calculation unit 1322 and the correlation coefficient calculated by the correlation coefficient calculation unit 1323 are plotted on the rice factor-correlation coefficient coordinate A. Let Plot P _A is a plot of the average Rice factor and transmission correlation coefficient. Plot P _B is a plot of average rice factor and reception correlation coefficient. Plot P _A and plot P _B, in order to distinguish between them, it is preferable to be displayed in different forms, such as different colors or different patterns.

  The display processing unit 1324 displays the quality information shown in FIG. 5A on the display device 3 so that the user can monitor the quality of the MIMO propagation path from the value of the correlation coefficient of the rice factor and the propagation path response. Can do. The user can improve the quality of the MIMO propagation path by adjusting the type, position, interval, etc. of the receiving antenna while monitoring the quality of the MIMO propagation path.

  As described with reference to FIG. 7, the transmission characteristics deteriorate when the rice factor is small and the correlation coefficient is large. Therefore, as shown in FIG. 5B, the display processing unit 1324 displays the region R having a small rice factor and a large correlation coefficient in the rice factor-correlation coefficient coordinates A so as to be distinguished from other regions. Also good.

  The display processing unit 1324 causes the display device 3 to display the quality information shown in FIG. 5B, so that when the plot is displayed in the region R, the quality of the MIMO propagation path is poor. It can be easily judged.

  The display processing unit 1324 acquires the required CNR determined in advance according to the value of the correlation coefficient of the rice factor and the propagation path response from the storage unit provided internally or externally, and causes the display device 3 to display the required CNR. May be. The required CNR differs depending on the MIMO system method, the number of modulation levels, the type of error correction, and the like.

FIG. 6 is a graph showing a second example of quality information, and is a graph in which an isoline with the required CNR as a parameter is further displayed on the rice factor-correlation coefficient coordinates A shown in FIG. is there. Here, the vertical axis represents the sum of the transmission correlation coefficient and the reception correlation coefficient. Plot P _C is a plot Mean Rice factor calculated by the Rice factor calculator 1322, and the sum of the received correlation coefficient has been a transmission correlation coefficients computed by the correlation coefficient calculation unit 1323. Note that the vertical axis may be the average of the transmission correlation coefficient and the reception correlation coefficient, and, like FIG. 5, represents the transmission correlation coefficient or the reception correlation coefficient, and may plot two points. .

The required CNR increases as transmission characteristics deteriorate (that is, the rice factor decreases and the correlation coefficient increases), and generally requires attention. The CNR value depends on the distance from the transmission device, the propagation environment, etc. Varies depending on Even if the rice factor is small and the correlation coefficient is large, the quality of the MIMO propagation path is maintained if the CNR exceeds the required CNR. Therefore, the propagation path quality processing unit 132 causes the display device 3 to display a difference between the average CNR that is the average value or the weighted average value of CNR1 and CNR2 calculated by the CNR calculation unit 1321 and the required CNR as a margin. Is preferred. For example, as shown in FIG. 6, if required CNR for the plot _{P C} is the average CNR is 30dB at 21 dB, and displays the 9dB the CNR margin.

  Since the display processing unit 1324 displays the graph as shown in FIG. 6 on the display device 3, the user can monitor the margin of the radio line and can know the required CNR more specifically. Highly reliable operation is possible.

  The display processing unit 1324 may display only the difference between the average CNR and the required CNR without displaying the isoline of the required CNR, or the difference between the CNR1 and the required CNR and the difference between the CNR2 and the required CNR. Each may be displayed. The propagation path quality processing unit 132 may further display an isoline with the required CNR as a parameter on the rice factor-correlation coefficient coordinates A shown in FIG.

  In addition, a computer can be used to realize the above-described MIMO propagation path quality monitoring function. Such a computer stores a program describing processing contents for realizing each function of the MIMO channel quality monitoring method in a storage unit of the computer, and reads and executes the program by the CPU of the computer. Can be realized. This program can be recorded on a computer-readable recording medium.

  Although the above embodiments have been described as representative examples, it will be apparent to those skilled in the art that many changes and substitutions can be made within the spirit and scope of the invention. Accordingly, the present invention should not be construed as being limited by the above-described embodiments, and various modifications and changes can be made without departing from the scope of the claims. For example, a plurality of constituent blocks described in the embodiments can be combined into one, or one constituent block can be divided.

  In the above-described embodiment, the 2 × 2 MIMO system has been described as an example. However, the present invention can be similarly applied to a MIMO system having a larger number of transmission antennas and reception antennas. In the embodiment described above, the propagation path quality processing unit 132 includes the CNR calculation unit 1321. However, when the CNR is not used for the quality information, the CNR calculation unit 1321 may not be included.

  The present invention is useful for any application that monitors the quality of a propagation path in a MIMO system.

DESCRIPTION OF SYMBOLS 1 Reception apparatus 2 Video decoder 3 Display apparatus 11 Reception antenna 12 Frequency conversion part 13 Baseband signal processing part 41 Transmission antenna 131 Input signal processing part 132 Channel quality processing part 133 MIMO demodulation processing part 134 Output signal processing part 1311 ADC part 1312 Orthogonal demodulation unit 1313 AFC unit 1314 Symbol synchronization unit 1315 FFT unit 1316 Channel estimation unit 1317 Block synchronization unit 1321 CNR calculation unit 1322 Rice factor calculation unit 1323 Correlation coefficient calculation unit 1324 Display processing unit

Claims (5)

A receiving apparatus having a MIMO channel quality monitoring function for monitoring a channel quality of a MIMO system,
An input signal processing unit for estimating a propagation path response of the MIMO system;
A rice factor calculation unit for calculating a rice factor from the propagation path response;
A correlation coefficient calculation unit for calculating a correlation coefficient of the channel response;
A display processing unit for displaying quality information indicating the quality of the MIMO propagation path based on the rice factor and the correlation coefficient;
Equipped with a,
The display processing unit has a rice factor calculated by the rice factor calculation unit on a rice factor-correlation coefficient coordinate having the rice factor as one axis and a correlation coefficient of a propagation path response as the other axis, and receiving apparatus according to claim Rukoto to display a graph of the correlation coefficient calculated by the correlation coefficient calculation unit. 2. The reception according to claim 1 , wherein the display processing unit displays an area having a small rice factor and a large correlation coefficient in the rice factor-correlation coefficient coordinates so as to be distinguished from other areas. apparatus. A CNR calculation unit for calculating the CNR of the received signal;
The display processing unit displays, as a margin, a difference between a required CNR determined in advance according to a value of a correlation factor between a rice factor and a propagation path response and a CNR calculated by the CNR calculation unit. The receiving device according to claim 1 or 2 . The receiving apparatus according to claim 3 , wherein the display processing unit displays an isoline with the required CNR as a parameter on the rice factor-correlation coefficient coordinates. The receiving device according to any one of claims 1 to 4 , further comprising a display device that displays the quality information.

Images