JP2012114807A - Communication device and radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication device and a communication method that can adequately select a reference signal even if the reception signal level of a desired wave is low.SOLUTION: A reception level detection unit 11 measures the reception level of a desired wave. If the reception level of the desired wave is equal to or larger than a first threshold value, a reference signal selection unit 9 performs a correlation operation between a known signal included in a reception signal and multiple reference signal candidates, and based on the correlation value, selects a reference signal from the multiple reference signal candidates. If the reception level of the desired wave is less than the first threshold value, the reference signal selection unit 9 selects a reference signal which was selected in the past. An adaptive array reception processing unit 6 performs adaptive array reception processing of the reception signal using the selected reference signal.

Description

  The present invention relates to a communication apparatus and a communication method, and more particularly to a communication apparatus having an adaptive array reception function and a communication method of such a communication apparatus.

  In a communication system such as a TD-LTE (Time Division Duplex Long-Term Evolution) system, an SC-FDMA (Single Carrier Frequency Division Multiple Access) system is adopted for transmission of an uplink signal. Each SC-FDMA symbol is added with a repetitive signal called CP (Cyclic Prefix) for absorbing delay before the data signal and transmitted (for example, Japanese Patent Application Laid-Open No. 2010-136347). See).

  By adding the CP, the receiving side can perform FFT (Fast Fourier Transform) processing of the received signal without causing inter-carrier interference or inter-symbol interference at any timing within the CP interval.

JP 2010-136347 A

  By the way, the phase relationship of each subcarrier of the signal after the FFT processing changes depending on the timing of the FFT processing. Therefore, when adaptive array reception processing is performed using a signal after FFT processing, it is necessary to use a reference signal in which the phase relationship of each subcarrier is changed according to the FFT processing timing.

  As means for selecting such a reference signal, a plurality of reference signals obtained by rotating the phase of each subcarrier are prepared in advance, and a demodulation reference signal (Demodulation Reference Signal: included in the received signal after the FFT processing is prepared. DMRS) and a plurality of phase-rotated reference signals are calculated, a reference signal having the largest correlation value is selected from the plurality of reference signals, and adaptive array processing is performed using the selected reference signal. A method of performing is conceivable.

  However, when the level of the received signal of the desired wave is low due to fading, shadowing, or the like, that is, when the signal to noise interference ratio (SINR) is low, it is difficult to peak the correlation calculation result. In such a case, the reliability of the reference signal selected according to the result of the correlation calculation is lowered.

  Therefore, an object of the present invention is to provide a communication device and a communication method capable of appropriately selecting a reference signal even when the received signal level of a desired wave is low.

  In order to solve the above problems, a communication device of the present invention includes a measurement unit that measures a reception level of a desired wave, and a known signal included in the reception signal when the reception level of the desired wave is equal to or higher than a first threshold. A correlation operation with a plurality of reference signal candidates is performed, a reference signal is selected from the plurality of reference signal candidates based on the correlation value, and the reception signal of the desired wave is selected in the past when the reception level is less than the first threshold value A reference signal selection unit that selects a reference signal, and an adaptive array reception processing unit that performs adaptive array reception processing on a reception signal using the selected reference signal.

  According to the present invention, the reference signal can be appropriately selected even when the received signal level of the desired wave is low.

It is a figure showing the structure of the flame | frame transmitted with the radio | wireless communications system of embodiment of this invention. It is a figure showing the structure of a sub-frame. It is a figure showing the structure of a sub-frame. It is a figure showing the structure of an SC-FDMA symbol. It is a figure showing the structure of the wireless base station of embodiment of this invention. It is a figure for demonstrating the relationship between the reception level of a desired wave, and a correlation value. It is a flowchart showing the selection procedure of the reference signal by the wireless base station of embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
(flame)
FIG. 1 is a diagram showing the configuration of a frame transmitted in the wireless communication system according to the embodiment of the present invention.

  As shown in FIG. 1, one frame is transmitted in a time of 10 ms. One frame is divided into half frames. Each half frame includes a downlink subframe DL, a switching subframe S, two consecutive uplink subframes UL, and a downlink subframe DL in time order.

  Here, the switching subframe S includes a DwPTS (Downlink Pilot Timeslot), a GP (Guard Period), and an UpPTS (Uplink Pilot Timeslot). UpPTS is composed of two SC-FDMA symbols.

(Sub-frame)
2 and 3 are diagrams illustrating the configuration of the uplink subframe UL.

  Referring to FIG. 2, one subframe is composed of two slots. Each slot is composed of seven SC-FDMA symbols. When the number of resource blocks RB included in each SC-FDMA symbol is 6, for example, each resource block RB includes 12 subcarriers, so each SC-FDMA symbol includes 72 subcarriers. Including. DMRS is arranged in the fourth slot of each slot. Using this DMRS, the phase relationship of each subcarrier of the received signal is derived.

  Referring to FIG. 3, the resource block includes 12 subcarriers. One subframe includes six resource blocks RB0 to RB6. Resource block RB0 includes 0th subcarrier to 11th subcarrier. Resource block RB1 includes 12th to 23rd subcarriers. Resource block RB2 includes 24th to 35th subcarriers. Resource block RB3 includes 36th to 47th subcarriers. Resource block RB4 includes 48th to 59th subcarriers. Resource block RB5 includes 60th subcarrier to 71st subcarrier.

(symbol)
FIG. 4 is a diagram showing the configuration of the SC-FDMA symbol.

  As shown in FIG. 4, a CP which is a copy of the last part of the symbol is added to the head of the SC-FDMA symbol. The time length of the CP is Tcp, and the time length of the data portion is T.

(Configuration of radio base station)
FIG. 5 is a diagram illustrating the configuration of the radio base station according to the first embodiment.

  Referring to FIG. 5, this radio base station 1 includes antennas 2a and 2b, FE units 3a and 3b, CP removal units 4a and 4b, FFT units 5a and 5b, an adaptive array reception processing unit 6, A signal processing unit 7, a resource allocation unit 8, a reference signal selection unit 9, and a reception level detection unit 11 are provided.

  The FE units 3a and 3b perform frequency conversion, amplification, and A / D conversion of signals received by the antennas 2a and 2b.

  CP removing units 4a and 4b remove the CP time length Tcp from the beginning of the signals output from FE units 3a and 3b.

The FFT units 5a and 5b perform FFT on the signals output from the CP removal units 4a and 4b.
The adaptive array reception processing unit 6 uses the reference signal selected by the reference signal selection unit 9 to perform adaptive array reception processing of signals output from the FFT units 5a and 5b.

The signal processing unit 7 decodes and demodulates the signal subjected to adaptive array reception processing.
The resource allocation unit 8 allocates resource blocks for data communication with each wireless terminal (user).

The reception level detection unit 11 measures the reception level of the desired wave.
The reference signal selection unit 9 switches the method (reference signal selection processing) for obtaining the inter-subcarrier phase relationship according to the level of the received signal of the desired wave for each wireless terminal (user) of the communication partner. That is, when the reception level of the desired wave is lower than the predetermined level, the reference signal selection unit 9 does not perform the correlation calculation and applies the reference signal (phase relationship) derived in the latest frame of the same user in the past. To do. The reference signal selection unit 9 performs the correlation calculation because the level of the received signal of the desired wave is higher than the predetermined level, but when the correlation value is less than the predetermined threshold (when the peak is not sharp), the processing is performed. A moving average is performed between the phase of the reference signal (candidate) estimated in step 1 and the phase of the reference signal (phase relationship) derived in the latest frame of the same user in the past, and the result is applied. The reference signal selection unit 9 performs a correlation calculation because the level of the received signal of the desired wave is higher than a predetermined level. If the correlation value is equal to or greater than a predetermined threshold (when the peak is sharp), the correlation calculation is performed. The obtained reference signal (phase relationship) is applied.

  Specifically, the reference signal selection unit 9 includes a reference signal candidate storage unit 17, a correlation calculation unit 10, a reference signal candidate determination unit 12, a moving average unit 16, a past reference signal position storage memory 15, and a reference. A signal position determination unit 13 and a reference signal determination unit 14 are provided.

The reference signal candidate storage unit 17 holds in advance a plurality of reference signals ri, t whose phases are rotated in accordance with the FFT timing, as shown by the equation (1). Here, T is the time length of the data part of the SC-FDMA symbol shown in FIG. 4, Tcp is the time length of CP shown in FIG. 4, j is an imaginary unit, and i is a subcarrier number. t (0 to 8) represents the phase position shown in FIG. 5, and t is the FFT timing position. ri ^org represents the original reference signal of the subcarrier number i, that is, a reference signal whose phase rotation due to the FFT timing shift is “0”.

  When the level of the received signal of the desired wave is equal to or higher than the threshold value TH1, the correlation calculation unit 10 calculates the correlation value Ct (t = 0 to 8) between the reference signal ri, t and DRMS for each FFT timing according to the equation (2). calculate.

  Here, S represents the first subcarrier number of the resource block assigned to the user (or the resource block having the smallest number when a plurality of resource blocks are assigned), and E is assigned to the user. Represents the subcarrier number at the end of the resource block (the resource block having the highest number when a plurality of resource blocks are allocated). For example, when resource blocks RB0 and RB1 are assigned to a certain user, S is 0 and E is 23.

ai, 3 represents a received signal after FFT processing arranged at a location where the subcarrier number is i and the symbol number is 3. This received signal is DRMS. ri, t ^* is the complex conjugate of ri, t.

  The reference signal candidate determination unit 12 specifies the phase position t at which the correlation value Ct (integer of t = 0 to 8) is maximum as the reference signal candidate position t0, and specifies the maximum value as the maximum correlation value MAXC.

  The past reference signal position storage memory stores the reference signal position ot of the most recent frame in the past.

  When the maximum correlation value MAXC obtained by the correlation calculation unit 10 is less than the threshold value TH2, the moving average unit 16 performs a weighted moving average between the reference signal candidate position t0 and the reference signal position ot of the past latest frame of the same user. The value mt is calculated. In this weighted moving average, the weight applied to the reference signal position ot of the past most recent frame is increased as the time interval between the current frame and the past most recent frame is shorter.

  When the level of the received signal of the desired wave is less than the threshold value TH1, the reference signal position determination unit 13 sets the reference signal position ot of the latest frame of the same user as the reference signal position nt of the current frame. The reference signal position determination unit 13 sets the reference signal candidate position t0 as the reference signal position nt of the current frame when the maximum correlation value MAXC obtained by the correlation calculation unit 10 is greater than or equal to the threshold value TH2. The reference signal position determination unit 13 sets the weighted moving average value mt as the reference signal position nt of the current frame when the maximum correlation value MAXC obtained by the correlation calculation unit 10 is less than the threshold value TH2.

  The reference signal determination unit 14 obtains a value nnt obtained by rounding off the reference signal position nt of the current frame, and outputs the reference signal ri, nnt (i = S to E) to the adaptive array reception processing unit 6.

(Reception level and correlation value)
FIG. 6 is a diagram for explaining the relationship between the reception level of the desired wave and the correlation value.

  FIG. 6A is a diagram illustrating correlation values calculated using a plurality of reference signal candidates when the reception level of the desired wave is relatively high.

  As shown in FIG. 6A, the correlation value calculated using the reference signal candidate at the position ta is the maximum value PA. This maximum value is a sharp peak value, and it is highly likely that the reference signal candidate at the position ta is appropriately used as the reference signal.

  FIG. 6B is a diagram showing correlation values calculated using a plurality of reference signal candidates when the reception level of the desired wave is relatively low.

  As shown in FIG. 6B, the correlation value calculated using the reference signal candidate at the position tb is the maximum value PB. This maximum value is a dull peak value, and it is not highly likely that the reference signal candidate at the position tb is appropriately used as the reference signal.

(Operation)
FIG. 7 is a flowchart showing a reference signal selection procedure by the radio base station according to the embodiment of the present invention.

  Referring to FIG. 7, reception level detector 11 measures the reception level of the desired wave (step S101).

  When the level of the received signal of the desired wave is equal to or higher than the threshold value TH1 (YES in step S102), the correlation calculation unit 10 calculates a correlation value Ct (t = 0 to 8) according to the equation (2). The reference signal candidate determination unit 12 specifies t having the maximum correlation value Ct (an integer of t = 0 to 8) as the reference signal candidate position t0, and specifies the maximum value as the maximum correlation value MAXC (step S104). .

  When the maximum correlation value MAXC is greater than or equal to the threshold value TH2 (YES in step S105), the reference signal position determination unit 13 sets the reference signal candidate position t0 as the reference signal position nt of the current frame (step S106).

  When the maximum correlation value MAXC is less than the threshold value TH2 (NO in step S105), the moving average unit 16 calculates a moving average between the reference signal candidate position t0 and the reference signal position ot of the latest frame of the same user in the past. . The reference signal position determination unit 13 sets the weighted moving average value mt as the reference signal position nt of the current frame (step S106).

  On the other hand, when the level of the received signal is less than the threshold value (NO in step S102), the reference signal position determination unit 13 sets the reference signal position ot of the most recent frame of the same user as the reference signal position nt of the current frame. (Step S103).

  The reference signal position determination unit 13 stores the reference signal position nt of the current frame obtained in steps S103, 106, and S107 in the past reference signal position storage memory 15 as the reference signal position ot of the most recent frame in the past (step S108). ).

  Next, the reference signal determination unit 14 obtains a value nnt obtained by rounding off the reference signal position nt of the current frame, and outputs the reference signal ri, nnt (i = S to E) to the adaptive array reception processing unit 6. The adaptive array reception processing unit 6 performs an adaptive array reception process using the reference signal ri, nnt (i = SE) (step S109).

  For the above thresholds TH1 and TH2, the results obtained in advance by simulation are used.

(effect)
As described above, according to the present embodiment, the reference signal selection method can be appropriately switched according to the reception level of the desired wave and the value of the correlation calculation result when the reference signal is selected.

(Modification)
The present invention is not limited to the above embodiment, and includes, for example, the following modifications.

(1) Correlation calculation In this embodiment, the correlation is calculated using DRMS arranged at a location where the symbol number is 3, but the present invention is not limited to this, and the symbol number is 10 as shown in Equation (3). The correlation may be calculated using DRMS arranged at the location.

  Here, ai, 10 represents DRMS arranged at a location where the subcarrier number is i and the symbol number is 3.

(2) Moving Average In the embodiment of the present invention, the moving average unit calculates the weighted moving average value, but the present invention is not limited to this. A simple moving average in which the weights of the reference signal candidate position t0 and the reference signal position ot of the past most recent frame are equal may be calculated.

(3) Past Frame In the embodiment of the present invention, the most recent frame in the past is used as the past frame. However, the present invention is not limited to this, and a frame before the most recent frame may be used.

(4) Normalization of correlation value In step S105 of the embodiment of the present invention, the maximum correlation value MAXC is compared with the threshold value TH2. However, the value obtained by dividing the maximum correlation value MAXC by the reception level or reception power and the threshold value are calculated. It is good also as comparing.

(5) Phase In the embodiment of the present invention, as shown in Expression (1), eight types of phases are used. However, the present invention is not limited to this, and there are M types of phases (M is a natural number of 2 or more). It is good.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 radio base station, 2a, 2b antenna, 3a, 3b FE unit, 4a, 4b CP removal unit, 5a, 5b FFT unit, 6 adaptive array reception processing unit, 7 signal processing unit, 8 resource allocation unit, 9 reference signal selection , 10 correlation calculation unit, 11 reception level detection unit, 12 reference signal candidate determination unit, 13 reference signal position determination unit, 14 reference signal determination unit, 15 past reference signal position storage memory, 16 moving average unit, 17 reference signal candidate Memory part.

Claims (8)

A measurement unit for measuring the reception level of the desired wave;
When the reception level of the desired wave is equal to or higher than the first threshold, the correlation calculation is performed between the known signal included in the received signal and the plurality of reference signal candidates, and the reference signal is derived from the plurality of reference signal candidates based on the correlation value. A reference signal selection unit that selects a reference signal selected in the past when the reception level of a desired wave is less than the first threshold;
A communication apparatus comprising: an adaptive array reception processing unit configured to perform adaptive array reception processing on the received signal using the selected reference signal.   When the reception level of the desired wave is equal to or higher than the first threshold and the maximum value of the correlation value is equal to or higher than the second threshold, the reference signal selection unit selects the correlation among the plurality of reference signal candidates. The communication apparatus according to claim 1, wherein a reference signal candidate having a maximum value is selected as a reference signal.   The reference signal selection unit, when the reception level of the desired wave is equal to or higher than the first threshold, and when the maximum correlation value is less than the second threshold, the phase of the reference signal selected in the past, The communication apparatus according to claim 1, wherein a moving average value with a phase of a reference signal candidate having a maximum correlation value is calculated, and a reference signal is selected from the plurality of reference signal candidates based on the moving average value.   The communication apparatus according to claim 3, wherein the reference signal selection unit calculates a weighted moving average value as the moving average value. The received signal is a signal transmitted by SC-FDMA system,
The plurality of reference signal candidates are ri, t represented by equation (1).

Where T is the time length of the SC-FDMA symbol, Tcp is the time length of CP (Cyclic Prefix), j is the imaginary unit, i is the subcarrier number, t is the phase position, and ri ^org is the subcarrier number. 2. A communication device according to claim 1, which represents i's original reference signal.   The communication apparatus according to claim 5, wherein the known signal included in the received signal is a demodulation reference signal (DMRS). The communication device
A CP removing unit that removes the time length Tcp from the beginning of the received signal;
A Fourier transform unit for Fourier transforming the signal output from the CP removal unit,
The reference signal selection unit performs the correlation calculation between a known signal included in a signal output from the Fourier transform unit and a plurality of reference signal candidates,
The communication apparatus according to claim 6, wherein the adaptive array reception processing unit performs adaptive array reception processing on a signal output from the Fourier transform unit. Measuring the reception level of the desired wave;
When the reception level of the desired wave is equal to or higher than the first threshold, the correlation calculation is performed between the known signal included in the received signal and the plurality of reference signal candidates, and the reference signal is derived from the plurality of reference signal candidates based on the correlation value. Selecting a reference signal selected in the past when the reception level of a desired wave is less than the first threshold;
An adaptive array reception process using the selected reference signal.

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