JP5236670B2 - OFDM-MIMO receiver - Google Patents

Description

  The present invention relates to an OFDM-MIMO receiver used in a multiple input multiple output (MIMO) wireless communication system using an OFDM (Orthogonal Frequency Division Multiplexing) signal, and more particularly to a receiver capable of improving the signal quality of the entire system. .

[Description of Prior Art]
In a MIMO wireless communication system, both the transmitting side and the receiving side have a plurality of antennas, the transmitting side transmits a plurality of data using a plurality of antennas, and the receiving side separates each transmission signal from the received signal. Retrieve received data.
Therefore, a reception signal of one reception system includes transmission signal components from a plurality of transmission sequences, and each transmission signal component is affected by power attenuation, phase rotation, and delay depending on the channel.

  In general, in a system using an OFDM signal including a MIMO system, an FFT (Fast Fourier Transform) calculation process is performed on a received signal on the time axis, thereby converting the signal into a frequency axis signal and performing processing such as equalization. To reproduce the transmission signal.

  When performing the FFT calculation process, the signal in the symbol including the guard interval signal added to the effective symbol is fetched by the number of FFT points set in advance, and the calculation is performed.

  For detection of the head of the symbol, autocorrelation using a guard interval, or cross-correlation obtained by adding a preamble signal on the transmission side and using the preamble signal on the reception side is used.

  In the conventional receiving apparatus, the peak value of the largest transmission signal component included in the received signal and the peak position are detected by the above correlation calculation, and the FFT window (which is subject to FFT processing) is used as a reference. (Data import section) was set.

[Related technologies]
As a technique related to the OFDM system, there is "Data transmission device" (Japanese Patent Application Laid-Open No. 2001-103033) (Applicant: Hitachi Electronics, Patent Document 1).
In Patent Document 1, a receiving apparatus analyzes a cross-correlation value sequence signal between a received signal and a predetermined synchronization symbol signal, detects an effective correlation peak that minimizes intersymbol interference, and receives the signal based on the peak. It describes that sampling clock synchronization processing and frame timing and symbol timing are controlled.

JP 2001-103033 A

  However, in the conventional OFDM-MIMO receiver, the FFT window is set based on the peak value and peak position of the maximum transmission signal component included in the reception signal, so that the transmission signal delayed or preceded by the maximum transmission signal component There is a problem that inter-symbol interference occurs in the components, and the signal quality may be deteriorated.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an OFDM-MIMO receiver capable of reducing deterioration due to intersymbol interference and improving the signal quality of the entire system.

  The present invention for solving the problems of the above conventional example is an OFDM-MIMO receiver used in an OFDM-MIMO communication system for receiving OFDM signals transmitted from a plurality of transmission systems in a plurality of reception systems, A different known signal is stored in advance for each of a plurality of transmission systems, and a received signal is input based on a cross-correlation operation unit that performs a cross-correlation operation with a known signal for each transmission system, and a set FFT window start position An FFT calculator that performs an FFT operation on the received signal, and a cross-correlation peak and its position are detected for each transmission system based on the cross-correlation result, and the first peak that exceeds the threshold earliest in time is detected. The inter-symbol interference power of the received signal for each of the plurality of transmission systems is calculated using the FFT window start position search range from the position to the position of the second peak that most recently exceeds the threshold. Then, the inter-symbol interference power for each of a plurality of transmission systems is summed to calculate the sum of the inter-symbol interference power, and the sum calculation processing is performed for storing as the sum of the inter-symbol interference power corresponding to the FFT window start position. The sum calculation processing is performed for all FFT window start positions in the search range while shifting the FFT window start position within the search range, and the sum is minimized among the inter-symbol interference power corresponding to the stored FFT window start position. An FFT window setting unit for setting an FFT window start position in the FFT calculator is provided.

  The present invention for solving the problems of the above conventional example is an OFDM-MIMO receiver used in an OFDM-MIMO communication system for receiving OFDM signals transmitted from a plurality of transmission systems in a plurality of reception systems, A known signal to be added for each of a plurality of transmission systems is stored in advance, and a received signal is based on a cross-correlation calculation unit that performs a cross-correlation calculation with a known signal for each transmission system, and a set FFT window start position An FFT calculator that performs an FFT operation on the input signal, a cross-correlation peak and its position are detected for each transmission system based on the cross-correlation result, and the first that exceeds the threshold earliest in time If the position difference between the peak and the second peak that most recently exceeds the threshold is within the guard interval length added to the transmission signal, the FFT window starts based on the first peak. If the position difference of the peak exceeds the guard interval length, the first window to the second peak are used as the FFT window start position search range for each transmission system. The inter-symbol interference power of the received signal is calculated, the inter-symbol interference power for each of the plurality of transmission systems is added up to calculate the sum of the inter-symbol interference power, and the inter-symbol interference power corresponding to the FFT window start position is calculated. Perform sum calculation processing stored as sum, perform sum calculation processing for all FFT window start positions in the search range while shifting the FFT window start position within the search range, and perform inter-symbol interference power corresponding to the stored FFT window start position The FFT window setting unit for setting the FFT window start position at which the sum is minimized in the FFT calculator is provided.

  According to the present invention, an OFDM-MIMO receiver used in an OFDM-MIMO communication system that receives OFDM signals transmitted from a plurality of transmission systems through a plurality of reception systems, the known signal being different for each of the plurality of transmission systems. Are stored in advance, and a cross-correlation operation unit that performs a cross-correlation operation with a known signal for each transmission system on the received signal, and an FFT that performs an FFT operation on the input signal based on the set FFT window start position Based on the calculation result and the cross-correlation calculation result, the cross-correlation peak and its position are detected for each transmission system, and the threshold is set the latest from the position of the first peak that exceeds the threshold earliest in time. The inter-symbol interference power of the received signal for each of the plurality of transmission systems is calculated using the search range of the FFT window start position up to the position of the second peak that exceeds, and The inter-symbol interference power is summed to calculate the sum of the inter-symbol interference power, and the sum calculation processing is performed to store the sum of the inter-symbol interference power corresponding to the FFT window start position. The sum calculation process is performed for all FFT window start positions in the search range while shifting, and the FFT window start position at which the sum is the minimum among the inter-symbol interference power corresponding to the stored FFT window start position is calculated by the FFT calculation. Since the OFDM-MIMO receiving apparatus includes an FFT window setting unit that is set in the receiver, the FFT window start position where the intersymbol interference power is minimized is set to minimize signal degradation due to intersymbol interference, and the system There is an effect that the overall signal quality can be improved.

  According to the present invention, there is provided an OFDM-MIMO receiver used in an OFDM-MIMO communication system that receives OFDM signals transmitted from a plurality of transmission systems through a plurality of reception systems, and is added to each of the plurality of transmission systems. A known signal is stored in advance, and the received signal is subjected to a cross-correlation calculation unit that performs a cross-correlation calculation with the known signal for each transmission system, and an FFT calculation of a signal input based on the set FFT window start position. The cross-correlation peak and its position are detected for each transmission system based on the FFT operation unit to be performed and the cross-correlation calculation result, and the first peak that exceeds the threshold earliest in time, and the latest threshold value are determined. If the position difference of the second peak that exceeds is within the guard interval length added to the transmission signal, the FFT window start position is set in the FFT calculator based on the first peak, If the peak position difference exceeds the guard interval length, the inter-symbol interference power of the received signal for each of the plurality of transmission systems is calculated using the FFT window start position search range from the first peak to the second peak. Calculating the sum of the intersymbol interference power for each transmission system, calculating the sum of the intersymbol interference power, and storing the sum as the sum of the intersymbol interference power corresponding to the FFT window start position. The sum calculation processing is performed for all FFT window start positions in the search range while shifting the FFT window start position within the search range, and the sum is the smallest among the inter-symbol interference power corresponding to the stored FFT window start position. Since the OFDM-MIMO receiver includes an FFT window setting unit that sets the FFT window start position in the FFT calculator, a delay difference due to the transmission system is large. Even if already there to set the FFT window starting position intersymbol interference power is minimized, minimizing the signal deterioration due to intersymbol interference, there is an effect that it is possible to improve the signal quality of the entire system.

It is explanatory drawing which shows the structural example of the OFDM-MIMO radio | wireless communications system with which the OFDM-MIMO receiver which concerns on embodiment of this invention is used. It is a block diagram which shows the structure of the reception baseband part 107 of this receiver. 3 is a block diagram illustrating a configuration of a cross-correlation calculation unit 302. FIG. FIG. 6 is a block diagram showing the configuration of an FFT window setting unit 303. It is explanatory drawing which shows the relationship between cross correlation power and a received signal. It is explanatory drawing which shows a cross correlation power when a path | route with high electric power is behind in time, and a received signal. It is explanatory drawing which shows the setting method of a FFT window start position in case a peak space | interval is less than guard interval length. It is explanatory drawing which shows the example in case a peak space | interval exceeds guard interval length. It is explanatory drawing which shows the example in case a peak space | interval exceeds guard interval length. It is explanatory drawing which shows the example in case a peak space | interval exceeds guard interval length. It is a schematic explanatory drawing which shows calculation of the interference power between symbols in this receiver. It is a schematic explanatory drawing which shows calculation of the interference power between symbols in this receiver. It is a schematic explanatory drawing which shows calculation of the interference power between symbols in this receiver. It is explanatory drawing of the cross correlation peak electric power in case a transmission system is M system | strain. 6 is a flowchart showing a schematic process of an FFT window position setting unit 502. It is a flowchart which shows the FFT window start position search process shown to the process 108 of FIG. 17 is a flowchart showing calculation processing of intersymbol interference power for each transmission system shown in processing 204 of FIG.

[Outline of the embodiment]
Embodiments of the present invention will be described with reference to the drawings.
The OFDM-MIMO receiver according to the embodiment of the present invention performs cross-correlation calculation with a known signal for each of a plurality of received transmission signals, finds a cross-correlation peak position and peak power, and temporally If the interval between the earliest peak position and the latest peak position is less than or equal to the guard interval length, the FFT window is set based on the earliest peak position in time, and if the guard interval length is exceeded, all transmissions Search for the position of the FFT window where the total amount of inter-symbol interference power in the signal component of the system is minimum, and set the FFT window at that position. By setting the FFT window at the optimum position, inter-symbol interference And the signal quality of the entire system can be improved.

  In addition, when searching for the optimum FFT window position, the present OFDM-MIMO receiving apparatus sets the range from the earliest peak to the latest peak as the FFT window start position search range, and sets the initial position within the range. Processing for setting an FFT window, calculating inter-symbol interference power for each transmission system, and summing the inter-symbol interference power of all systems to obtain the total amount of inter-symbol interference power corresponding to the FFT window start position When the processing for obtaining the total amount of inter-symbol interference power for all FFT window start positions within the range is completed by sequentially shifting the position of the FFT window and calculating the total amount of inter-symbol interference power, The FFT window start position where the total amount of inter-interference power is minimized is specified, and the FFT window start position is set in the FFT calculator to reduce inter-symbol interference. And it is able to improve the signal quality of the entire system.

[OFDM-MIMO wireless communication system: FIG. 1]
An OFDM-MIMOMO wireless communication system in which an OFDM-MIMO receiver according to an embodiment of the present invention is used will be described with reference to FIG. FIG. 1 is an explanatory diagram showing a configuration example of an OFDM-MIMO wireless communication system in which an OFDM-MIMO receiving apparatus according to an embodiment of the present invention is used.
FIG. 1 shows a configuration of a 2 × 2 OFDM-MIMO wireless communication system having two transmission units (transmission devices) and two reception units (reception devices).
The OFDM-MIMO receiver according to the present embodiment operates as a first system and second system receiver in the system. In addition, you may comprise as a radio | wireless communication apparatus provided with both the transmission part and the receiving part.

As shown in FIG. 1, the wireless communication system includes, on the transmission side, a MIMO transmission processing unit 101, a transmission baseband unit (“transmission BB” in the figure) 102 provided for each system, and a transmission RF (Radio Frequency). ) Section ("transmission RF" in the figure) 103 and a transmission antenna 104.
On the receiving side, a reception antenna 105 provided for each system, a reception RF unit (“reception RF” in the figure) 106 and a reception baseband unit (“reception BB” in the figure) 107, and a MIMO reception processing unit 108 are provided. And.

In FIG. 1, the number after “-(hyphen)” in each block indicates a system number. In the figure, h _yx indicates the transmission path characteristic from the x-th system transmission unit to the y-th system reception unit.

[Description of each part]
Each component will be described.
[Configuration of transmitter]
[MIMO processing unit 101]
The MIMO transmission processing unit 101 separates and encodes the input signal in accordance with the MIMO communication method, and outputs the input signal to the transmission baseband units 102-1 and 102-2 of the first system and the second system.
In the following description, the system number is omitted.

[Transmission baseband unit 102]
The transmission baseband unit 102 includes a mapping processing unit, a known signal addition processing unit, an IFFT (Inverse Fast Fourier Transform) computing unit, and a guard interval addition processing unit, and adds a mapping and preamble signal to the input signal. Then, conversion from a frequency axis signal to a time axis signal and a process of adding a guard interval are performed and output to the transmission RF unit 103.

The mapping processing unit maps the input signal to the data carrier in accordance with a predetermined modulation scheme (for example, 16QAM (Quadrature Amplitude Modulation) or 64QAM).
The known signal addition processing unit adds a known signal (known signal) preset on the receiving side. Here, the known signals are different signals in the first system and the second system.

The IFFT calculator performs an IFFT calculation on the input signal and converts the frequency axis signal into a time axis signal.
The guard interval addition processing unit adds a guard interval having a predetermined length (for example, 1/4 or 1/8 of the effective symbol length) to the input time axis signal, and outputs the guard interval to the transmission RF unit 103. To do.

Further, as another configuration of the transmission baseband unit 102, there is a configuration in which a preamble signal is added after IFFT conversion.
In such a case, the transmission baseband unit 102 includes a mapping processing unit, an IFFT calculator, a preamble signal addition processing unit, and a guard interval addition processing unit.
Then, the preamble signal addition processing unit adds a preamble signal to the time-axis signal that has been subjected to IFFT calculation. The operation of other parts is the same as in the above-described example.

[Transmission RF unit 103, transmission antenna 104]
The transmission RF unit 103 performs D / A conversion on the input signal, performs frequency conversion to a transmission frequency band, and outputs the signal to the transmission antenna 104 for each system.
The transmission antenna 104 transmits the signal input from the transmission RF unit 103.

[Receiver configuration]
[Receiving antenna 105, transmitting RF unit 106]
The reception antenna 105 receives the signals transmitted from the transmission antennas 104-1 and 104-2, and outputs the signals to the reception RF unit 106.
The reception RF unit 106 converts the frequency of the reception signal input from the reception antenna 105 of each system to the baseband, performs AGC (Auto Gain Control) processing, performs A / D conversion, and receives the reception baseband of each system. Output to the unit 107.

[Reception baseband unit 107]
The reception baseband unit 107 performs autocorrelation and cross-correlation correlation calculations on the input signal to detect correlation peak power and peak position, and performs FFT calculation to convert the time axis signal to the frequency axis signal. Channel estimation is performed and output to the MIMO reception processing unit 108.
In this receiving apparatus, the processing in the receiving baseband unit 107 is different from the conventional one. The configuration of reception baseband unit 107 will be described later.

[MIMO reception processing unit 108]
The MIMO reception processing unit 108 performs signal separation processing of the received signal on the signal output from the reception baseband unit 107 of each system using the channel estimation result. In the signal separation process, separation / detection by, for example, MMSE (Minimum Mean Square Error) or MLD (Maximum Likelihood Detection) is performed.

[Configuration of Reception Baseband Unit 107: FIG. 2]
Next, the configuration of reception baseband section 107 shown in FIG. 1 will be described using FIG. FIG. 2 is a configuration block diagram showing the configuration of the reception baseband unit 107 of the reception apparatus.
As shown in FIG. 2, the reception baseband unit 107 includes an autocorrelation calculation unit (described as “autocorrelation” in the figure) 301, a crosscorrelation calculation unit (“crosscorrelation” in the figure) 302, and an FFT window setting unit. 303, an FFT calculator (“FFT” in the figure) 304, and a channel estimation unit (“channel estimation” in the figure) 305.

  The autocorrelation calculation unit 301 performs autocorrelation using a fixed period signal included in the preamble signal added on the transmission side, detects the head of the frame, and outputs it to the crosscorrelation calculation unit 302.

  Cross-correlation calculating section 302 takes a correlation between a known signal of each system included in the preamble signal added on the transmission side and a known signal stored in advance, and outputs the correlation value to FFT window setting section 303. . The cross correlation calculation unit 302 will be described later in detail.

  The FFT window setting unit 303 is a characteristic part of this receiving apparatus, determines the position of the FFT window based on the calculation result of the cross-correlation calculation unit 302, and outputs it to the FFT calculator 304. Details of the FFT window setting unit 303 will be described later.

  The channel estimation unit 305 estimates a channel from the frequency axis signal converted by the FFT calculator 304 based on a known pilot signal or preamble signal, and outputs the channel to the MIMO reception processing unit 108.

[Correlation calculation unit 302: FIG. 3]
Next, the configuration of the cross-correlation calculation unit 302 shown in FIG. 2 will be described with reference to FIG. FIG. 3 is a configuration block diagram of the cross-correlation calculation unit 302.
As shown in FIG. 3, the cross-correlation calculation unit 302 includes known signal storage memories 401-1 and 401-2, and correlation calculation units 402-1 and 402-2.

The known signal storage memory 401-1 is a memory that stores the first known signal (REF1) on the transmission side, and outputs the known signal to the correlation calculator 402-1. The known signal is added to the preamble and transmitted on the transmission side.
The known signal storage memory 401-2 is a memory storing the second-side known signal (REF2) on the transmission side, and outputs the known signal to the correlation calculator 402-2.

Correlation computing unit 402-1 and 402-2 performs a correlation operation with a known signal of a known signal or the second line of the received signal r _y and the first line, the operation result CC _y1, CC _y2 an FFT window setting unit 303 Output to.

[FFT window setting unit 303: FIG. 4]
Next, the configuration of the FFT window setting unit 303 shown in FIG. 2 will be described with reference to FIG. FIG. 4 is a configuration block diagram of the FFT window setting unit 303.
As shown in FIG. 4, the FFT window setting unit 303 includes peak position / peak power detectors 501-1 and 501-2, and an FFT window position setting unit 502. In FIG. 4, the main line path is omitted.

Peak position and the peak power detector 501-1 detects the maximum value of the cross correlation calculation result CC _y1 of the known signal of the received signal r _y and the first line (peak power) and its position (peak position), Output to FFT window position setting section 502.
Similarly, the peak position and the peak power detector 501-2 detects the position of the maximum value and the maximum value of the cross correlation calculation result CC _y2 between the received signal r _y and a known signal of the second system, FFT window position Output to the setting unit 502.

  The FFT window position setting unit 502 determines the FFT window start position based on the input peak position and peak power, and outputs the FFT window start position to the FFT calculator 304 in FIG. The processing in the FFT window start position setting unit 502 is a characteristic part of this receiving apparatus.

[Cross-correlation power and received signal: Fig. 5]
Before describing the FFT window start position setting method of this receiving apparatus, the relationship between the cross-correlation power and the received signal will be described with reference to FIG. FIG. 5 is an explanatory diagram showing the relationship between the cross-correlation power and the received signal.
FIG. 5 shows the sum of the cross-correlation powers of the signal r ₁ received by the first system receiver and an image of the received signal. The vertical axis is the correlation power, and the horizontal axis is the sample (time).

P _r11 indicates a cross-correlation peak power between r ₁ and a known signal (known signal added in the first transmission system) from the known signal storage memory 401-1, and P _r12 indicates r ₁ and the known signal. The cross-correlation peak power with the known signal (known signal added in the second transmission system) from the storage memory 401-2 is shown.

Also, the rectangle described in the upper part is an image of the received signal, and the shaded portion indicates the guard interval of each transmission signal component. The width of the rectangle shows the image of the power difference.
POS ₁ and POS ₂ are positions of P _r11 and P _r12 , respectively, and ΔPOS is a difference (positional difference, interval) between POS ₁ and POS ₂ .
In addition, x′1 and x′2 in the figure are a first-system transmission signal component and a second-system transmission signal component included in the received signal, and are affected by power attenuation, phase rotation, and delay, respectively, depending on the channel.

FIG. 5 shows a case where the maximum cross-correlation peak power appears earlier in time and the peak interval ΔPOS is shorter than the guard interval length (L _GI ). In such a case, in principle, intersymbol interference does not occur by appropriately providing an FFT window.
However, since it actually has a margin α (0 <α <L _GI ), the peak position difference at which no intersymbol interference occurs is within (L _GI −α).
Since the example of FIG. 5 is a peak interval ΔPOS is in the (L _GI -α), based on the position POS ₁ of the maximum cross-correlation peak power P _r11, was set FFT window starting position earlier timing by margin α In this case, no intersymbol interference occurs in the first transmission system and the second transmission system.

[When high power path is behind in time: Fig. 6]
Next, a case where a path with high power is behind in time will be described with reference to FIG. FIG. 6 is an explanatory diagram showing cross-correlation power and a received signal when a high-power path is behind in time.
As shown in FIG. 6, when the FFT window start position is provided with reference to _Pr12 having the largest cross-correlation power, the first transmission system covers the subsequent symbol, and intersymbol interference occurs.

[FFT window start position setting]
Next, a method for setting the FFT window start position will be described.
[When the peak interval is within the guard interval length: Fig. 7]
First, the case where the peak interval is within the guard interval length will be described with reference to FIG. FIG. 7 is an explanatory diagram showing a method for setting the FFT window start position when the peak interval is within the guard interval length.
When the peak interval is equal to or shorter than the guard interval length, it is possible to set the FFT window so that intersymbol interference does not occur regardless of the path power.
As shown in FIG. 7, the peak interval ΔPOS is equal to or smaller than the guard interval length L _GI, regardless of the size of the peak power, based on the position POS ₁ of the earliest correlation peak power temporally, POS ₁ The FFT window start position is set at the position.
Thereby, not only the earliest transmission system in time but also inter-symbol interference does not occur in other transmission systems.

The path of interest, the cross-correlation power of the most peak power is large path as P _max, the threshold THR _P provided for P _max, to target those beyond it. The threshold value THR _P is calculated by the following equation, for example.
THR _P = μP _max (0 <μ <1)
μ is determined by system specifications and the like.

  Specifically, the peak position / peak power detection unit 501 of the FFT window setting unit 303 shown in FIG. 4 detects the maximum value and position of the cross-correlation power for each of the first and second transmission systems, and performs FFT. When the window position setting unit 502 calculates the interval ΔPOS between the cross-correlation peak power of the earliest system and the latest cross-correlation peak power, and the peak interval is equal to or shorter than the guard interval length (each transmitted signal component that has arrived) When the delay difference is within the guard interval length), the FFT window start position is set based on the position of the cross-correlation peak power that is earliest in time.

As described above, when setting the FFT window start position with the margin α, it is determined whether or not the peak interval ΔPOS is equal to or less than the length obtained by subtracting the margin from the guard interval length (L _GI −α). and, may be provided (L _GI -α) provided that the following is, FFT window position of with respect to the position POS ₁ of the earliest correlation peak power temporally (POS ₁ -α) .

[When the peak interval exceeds the guard interval length: FIGS. 8, 9, and 10]
Next, the case where the peak interval exceeds the guard interval length will be described with reference to FIGS. 8, FIG. 9 and FIG. 10 are explanatory diagrams showing examples when the peak interval exceeds the guard interval length.

  First, as shown in FIG. 8, when the FFT window start position is set at a timing earlier by a margin α from the first cross-correlation peak power in time as in FIG. 7, the first transmission system is good. However, in the second transmission system, inter-symbol interference occurs because the previous symbol is picked up.

  FIG. 9 shows the FFT window start position later than that in FIG. Even in this case, intersymbol interference with the previous symbol occurs in the second transmission system.

In FIG. 10, the FFT window start position is set later than in the case of FIG. In this case, intersymbol interference does not occur in the second transmission system, but intersymbol interference with subsequent symbols occurs in the first transmission system.
Thus, when the peak interval exceeds the guard interval length, intersymbol interference occurs in any transmission system regardless of where the FFT window is set.

  Therefore, in this receiving apparatus, when the peak interval ΔPOS exceeds the guard interval length, an FFT window start position that minimizes the sum of inter-symbol interference power generated in all (two in this case) transmission systems is searched. The position is set as the FFT window start position.

  Specifically, after calculating the inter-symbol interference power generated in each transmission system in accordance with each FFT window start position, while sequentially setting the FFT window start position within the search range of the FFT window start position. The inter-symbol interference power of all transmission systems is added to calculate the sum of the inter-symbol interference powers, which is stored as the sum of the inter-symbol interference powers corresponding to the FFT window start position. The position where the sum is minimum is detected, and the position is set in the FFT calculator 304 as the FFT window start position.

The FFT window start position search process that minimizes the sum of inter-symbol interference power is performed by the FFT window position setting unit 502 of the FFT window setting unit 303 at the time of setting before system operation.
Specifically, before operation, the transmission signal from the transmission unit is actually received by the reception device and stored in a register, and the FFT window position setting unit 502 of the FFT window setting unit 303 stores the stored data. The FFT window start position is sequentially shifted and set, and the sum of inter-symbol interference power is calculated to identify the optimum FFT window start position. The system is operated based on the specified FFT window position.

[Calculation of Intersymbol Interference Power: FIGS. 11, 12, and 13]
Next, a specific calculation method of inter-symbol interference power in this receiving apparatus will be described with reference to FIGS. 11, 12, and 13 are schematic explanatory diagrams illustrating calculation of intersymbol interference power in the receiving apparatus.
As shown in FIG. 11, each peak position is POS ₁ and POS ₂ (POS ₁ <POS ₂ ), and the FFT window start position is w (POS ₁ ≦ w ≦ POS ₂ ) as shown in the figure, and w is moved. Thus, the intersymbol interference power C (w) corresponding to each start position (w) is calculated.

In the case of FIG. 11, the FFT window start position w is the position of the cross-correlation peak power POS ₁ that is earlier in time, and no intersymbol interference occurs in the first transmission system. The power of intersymbol interference occurring in the second transmission system corresponds to the area of the portion indicated by the shaded vertical lines in the figure,
C (w) = {(POS ₂ −L _GI ) −POS ₁ } · P _r12
Is calculated by

As shown in FIG. 12, when the FFT window start position is set later than that in FIG. 11, intersymbol interference occurs in both the first transmission system and the second transmission system. In the figure, FFT_PTS indicates the number of FFT points.
Therefore, the intersymbol interference power corresponding to the FFT window start position is
C (W) = {(w ₁ + FFT_PTS) − (POS ₁ + FFT_PTS)} · P _r11
+ {(POS ₂ −L _GI ) −w ₁ } · P _r12
= (W ₁ −POS ₁ ) · P _r11 + {(POS ₂ −L _GI ) −w ₁ } · P _r12
Is calculated by

As shown in FIG. 13, when the FFT window start position is set to the position of the cross-correlation peak power POS ₂ , intersymbol interference occurs only in the first transmission system, and intersymbol interference occurs in the second transmission system. Does not occur.
The intersymbol interference power in this case is
C (w) = {(w + FFT_PTS) − (POS ₁ + FFT_PTS)} · P _r11
= (W-POS ₁ ) · P _r11
Is calculated by

[General Intersymbol Interference Power Calculation Method]
As described above, the intersymbol interference power corresponding to the FFT window start position is the sum of the intersymbol interference power generated in each transmission system when the FFT window position is set.
Therefore, the FFT window start position setting unit 502 first obtains the intersymbol interference power for each transmission system, and then adds up the intersymbol interference power in all the systems to intersymbol interference corresponding to the FFT window start position. Get the sum of power.

The calculation method of the intersymbol interference power of each system is classified into three types according to the relationship between the FFT window start position w, the cross-correlation peak power position POS _{x of the} system, and the guard interval length.
Here, the intersymbol interference power of each transmission signal component included in the received signal is C _x (w), and each peak power is P _yx . x is a transmission system number, and y is a reception system number.

C _x (w) = {(POS _x −L _GI ) −w} · P _yx (w <POS _x −L _GI ) (Formula 1)
C _x (w) = (w−POS _x ) · P _yx (w> POS _x ) (Formula 2)
C _x (w) = 0 (POS _x −L _GI ≦ w ≦ POS _x ) (Formula 3)

  Equation 1 is applied to the second transmission system of FIGS. 11 and 12, for example, Equation 2 is applied to the first transmission system of FIGS. 12 and 13, and Equation 3 is the first transmission system of FIG. This is applied to the second transmission system.

  Then, in this receiving apparatus, the inter-symbol interference power of each transmission system calculated using any one of the above formulas (1) to (3) is summed, and the value corresponds to the FFT window start position. The sum of intersymbol interference power. That is, the sum of the intersymbol interference power corresponding to each FFT window start position is

It is expressed.
In the case of FIGS. 11 to 13, M = 2, and based on the FFT window start position and the position of the cross-correlation peak power for each transmission system, any one of the above formulas (1) to (3) is applied, By summing up, the sum of the interference power between symbols is obtained.
Then, the FFT window setting unit 303 sets an FFT window start position in the FFT calculator 304 that minimizes the sum of inter-symbol interference power.

[M system: Fig. 14]
Next, a method for setting the FFT window start position when the transmission system is the M system will be described with reference to FIG. FIG. 14 is an explanatory diagram of the cross-correlation peak power when the transmission system is the M system.
In this receiving apparatus, the cross-correlation calculation unit 302 includes M memories that store known signals corresponding to M transmission units. Then, the cross-correlation calculation is performed for each system, and the correlation calculation result is output to the FFT window setting unit 303.

The FFT window setting unit 303 detects the cross-correlation peak power and its position for each system, and the FFT window position setting unit 502 sets the FFT window start position based on it.
As shown in FIG. 14, in the case of M systems, M cross-correlation power peaks are obtained. Further, x ′ ₁ , x ′ ₂ ,... X ′ _M−1 , x ′ _M are transmission signal components from the first transmission system to the Mth transmission system, and are affected by power attenuation, phase rotation, and delay. .

The FFT window position setting unit 502 includes the earliest temporal peak position (first leading position) POS _first and the temporally latest peak position (last position) among all peak positions POS _{1 to} POS _M. The POS _bottom is detected, and the position difference ΔPOS is detected.
In the example of FIG. 14, POS _first is POS ₁ and POS _M does not exceed the threshold value THR _P , so POS _bottom is POS _M−1 .

Then, as in the case of two systems, spacing ΔPOS the POS _first and POS _bottom is equal to or less than the guard interval L _GI, provided FFT window based on the earliest POS _first.
If ΔPOS exceeds the guard interval L _GI , the position of the FFT window where the sum of the inter-symbol interference power is minimized is searched using the above equations (1) to (3) and Equation 1. Then, the position is set in the FFT calculator 304 as the FFT window start position.
However, the search range of the FFT window start position (w) is POS _first <w <POS _bottom .
In this way, the FFT window start position in the case of the M system is set.

[Schematic Processing of FFT Window Position Setting Unit 502: FIG. 15]
Next, schematic processing of the FFT window position setting unit 502 will be described with reference to FIG. FIG. 15 is a flowchart showing a schematic process of the FFT window position setting unit 502.
As shown in FIG. 15, when the processing is started, the FFT window position setting unit 502, based on the cross-correlation peak power input for each system, the most advanced position (POS _first ) and the last position of the cross-correlation peak The position (POS _bottom ) is detected (100), and the position difference (ΔPOS) between POS _first and POS _bottom is detected.

Then, the FFT window position setting unit 502 determines whether ΔPOS is within the guard interval length (104). If ΔPOS is within the guard interval length (in the case of Yes), the first peak position, POS _first. Based on the above, an FFT window start position is set in the FFT calculator 304 (106).

In addition, when the POS exceeds the guard interval length in the process 104 (in the case of No), the FFT window position setting unit 502 makes the FFT window start position where the sum of the inter-symbol interference powers of all transmission systems is minimized. And the FFT window start position search process for setting the position as the FFT window start position in the FFT calculator 304 is performed (108). The FFT window start position search process will be described in detail with reference to FIG.
In this way, the rough process in the FFT window position setting unit 502 is performed.

[FFT window start position search processing: FIG. 16]
Next, the FFT window start position search process shown in the process 108 of FIG. 15 will be described with reference to FIG. FIG. 16 is a flowchart showing the FFT window start position search process shown in process 108 of FIG.
When ΔPOS exceeds the guard interval in the process 104 of FIG. 15, the FFT window position setting unit 502 searches for an FFT window start position that minimizes the sum of the inter-symbol interference powers of all transmission systems.
As shown in FIG. 16, the FFT window position setting unit 502 first sets the FFT window start position to the initial position (w = POS _first ) (200), and sets the transmission system number x to 1 (x = 1). ) (202).

Then, the FFT window position setting unit 502 calculates the intersymbol interference power C _x (w) in the received transmission signal of the x-th system (204). The calculation method is performed based on the above-described equations (1) to (3) and will be described later with reference to FIG.

After calculating C _x (w), the FFT window position setting unit 502 determines whether x has reached the number M of transmission systems (whether x ≧ M) (110).
If x has not reached the number M of transmission systems (in the case of No), the FFT window position setting unit 502 increments x (x = x + 1) (206), and returns to processing 204.

When x reaches the number M of transmission systems in the processing 110 (in the case of Yes), the FFT window position setting unit 502 sums up C _x (w) of x = 1 to M to calculate the FFT window. The sum of the intersymbol interference power C _x (w) at the position is calculated and stored (212). The processes 204 and 212 correspond to the inter-symbol interference power calculation process in the claims.

Then, the FFT window position setting unit 502 determines whether or not a search has been performed for the FFT window position search range (POS _first <w <POS _bottom ), that is, whether or not the FFT window position shift has ended (w ≧ POS _bottom ) ( 214) If it is not the end (in the case of No), the FFT window position is shifted (w = w + 1) (216), and the process proceeds to process 202 to calculate the sum of the inter-symbol interference power for the next FFT window position. .

In the process 214, when the shift of the FFT window position is completed, the sum of the inter-symbol interference powers among the sum of the inter-symbol interference powers stored corresponding to the FFT window start position within the search range. Is selected as the FFT window start position in the FFT calculator 304 (222), and the process ends.
In this way, the FFT window start position search process is performed.

[Calculation processing of inter-symbol interference power C _x (w) for each transmission system: FIG. 17]
Next, the calculation process of the intersymbol interference power for each transmission system shown in the process 204 of FIG. 16 will be described with reference to FIG. FIG. 17 is a flowchart showing the calculation process of intersymbol interference power for each transmission system shown in process 204 of FIG.
As shown in FIG. 17, the FFT window position setting unit 502 first starts the FFT window start position (based on the cross-correlation peak power position (POS _x ) and guard interval length (L _GI ) of the transmission signal of the x-th system. It is determined whether w) is w <POS _x −L _GI (300). If w <POS _x −L _GI (in the case of T), the above-described formula (1) C _x (w) = C _x (w) is calculated according to {(POS _x −L _GI ) −w} · P _yx (302).

Further, in the processing 300, <(for F) if not a POS _x -L _GI, FFT window position setting section 502 further w> w determines whether the _{POS x (304), w>} POS x (T), C _x (w) is calculated according to the above-described formula (2) C _x (w) = (w−POS _x ) · P _yx (306).

If w> POS _x is not satisfied in processing 304 (in the case of F), the FFT window position setting unit 502 calculates the intersymbol interference power as 0 according to Expression (3) C _x (w) = 0 (308) ).
In this way, the calculation process of the intersymbol interference power for each transmission system shown in FIG. 16 is performed.

[Effect of the embodiment]
According to the OFDM-MIMO receiving apparatus according to the embodiment of the present invention, the cross-correlation calculating unit 302 stores in advance a known signal that is added to a plurality of transmission signals and is different for each system. The transmission signal is subjected to a cross-correlation operation with each stored known signal, and the FFT window setting unit 303 detects the cross-correlation peak and its position for each system, and the time among the cross-correlation peaks for each system If the position difference between the earliest peak and the latest peak is within the guard interval length, the FFT window 304 is set to the FFT calculator 304 based on the earliest peak position in time, and the position difference is guarded. When the interval length is exceeded, FFT window start position search processing for searching for the FFT window start position that minimizes the sum of inter-symbol interference power in all transmission systems Since the FFT calculator 304 is set to the specified position as the FFT window start position, there is an effect that the inter-symbol interference can be reduced and the signal quality of the entire system can be improved. When the peak position difference is within the guard interval, there is an effect that the processing can be reduced without performing the search processing.

  Further, according to the present OFDM-MIMO receiving apparatus, the FFT window position setting unit 502 of the FFT window setting unit 303 determines the range from the earliest peak to the latest peak in the FFT window start position search process. As the start position search range, inter-symbol interference power for each transmission system is calculated, and the inter-symbol interference power of all transmission systems is summed to calculate and store the total amount of inter-symbol interference power corresponding to the FFT window start position. Stored in the search range by calculating and storing the total amount of inter-symbol interference power for all FFT window start positions in the search range while setting the FFT window start position in the search range by shifting. The FFT window start position corresponding to the smallest of the total amount of inter-symbol interference power is selected, and the FFT window 304 is set in the FFT calculator 304. Even if there is a large delay difference due to the transmission system, it is possible to set an optimum FFT window start position that minimizes intersymbol interference, minimizing signal quality degradation, and There is an effect that the overall signal quality can be improved.

  Further, according to the present OFDM-MIMO receiver, the FFT window position setting unit 502 sets a threshold based on the maximum value of the cross-correlation peak, and detects a cross-correlation peak exceeding the threshold. As a result, the search range can be determined based only on substantially valid received signals, and there is an effect that wasteful processing can be avoided.

  The present invention is suitable for an OFDM-MIMO receiver that can improve the signal quality of the entire system.

  DESCRIPTION OF SYMBOLS 101 ... MIMO transmission processing part, 102 ... Transmission baseband part, 103 ... Transmission FR part, 104 ... Transmission antenna, 105 ... Reception antenna, 106 ... Reception RF part, 107 ... Reception baseband part, 108 ... MIMO reception processing part, DESCRIPTION OF SYMBOLS 301 ... Autocorrelation calculation part 302 ... Cross correlation calculation part 303 ... FFT window setting part 304 ... FFT operation unit 305 ... Channel estimation part 401 ... Known signal storage memory 402 ... Correlation calculation unit 501 ... Peak position・ Peak power detector 502: FFT window position setting unit

Claims (1)

An OFDM-MIMO receiver used in an OFDM-MIMO communication system that receives OFDM signals transmitted from a plurality of transmission systems in a plurality of reception systems,
A cross-correlation calculation unit that stores a known signal different for each of the plurality of transmission systems in advance and performs a cross-correlation calculation with the known signal for each transmission system,
An FFT calculator that performs an FFT calculation of an input signal based on the set FFT window start position;
Based on the cross-correlation calculation result, the cross-correlation peak and its position are detected for each transmission system, and the first peak position that exceeds the threshold value earliest in time is the first that exceeds the threshold value latest. The inter-symbol interference power of the received signals for each of the plurality of transmission systems is calculated up to the peak position of 2 as the search range of the FFT window start position, and the inter-symbol interference power for each of the plurality of transmission systems is added to obtain the symbol The sum of the inter-interference power is calculated and stored as the sum of the inter-symbol interference power corresponding to the FFT window start position, and the entire search range is shifted while shifting the FFT window start position within the search range. The FFT window start position where the sum is the smallest among the inter-symbol interference power corresponding to the stored FFT window start position. OFDM-MIMO receiver is characterized in that a FFT window setting unit for setting the FFT processor.

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