JP2012019409A - Radio communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio communication device which can reduce an estimated error of a channel characteristic.SOLUTION: A pilot carrier extraction and code reproduction unit 105 extracts a pilot carrier from a subcarrier and performs code reproduction. A delaying unit 106 delays the code reproduced pilot carrier. A pilot carrier level calculation unit 107 calculates electric power of the pilot carrier. A pilot carrier level determination unit 108 determines whether the electric power of the pilot carrier is at or below a threshold value. A pilot carrier level fluctuation detection unit 109 detects variation of the pilot carrier on the time axis. A pilot carrier replacement unit 110 replaces the pilot carrier with a pilot carrier made by combining a pilot carrier generated by performing interpolation and extrapolation of variation in the frequency axis direction and a pilot carrier generated by performing interpolation and extrapolation of variation in the time axis direction when the electric power of the pilot carrier is at or below the threshold value and the variation is larger than a threshold value.

Description

  The present invention relates to a reference signal (hereinafter referred to as a pilot carrier) included in subcarriers of an OFDM (Orthogonal Frequency Division Multiplexing) system, which has known amplitude and phase used when demodulating a modulated signal. And a wireless communication apparatus that estimates the channel state between transmission and reception (hereinafter referred to as channel characteristics), equalizes the received signal based on the estimated channel characteristic, and demodulates the equalized received signal, In particular, the present invention relates to a wireless communication apparatus that reduces an estimation error of channel characteristics.

  In a wireless communication apparatus, channel characteristics are estimated using linear interpolation between pilot carriers and a frequency interpolation filter. In such channel characteristic estimation, if the reception level of the pilot carrier decreases due to instantaneous fluctuations, the channel characteristic estimation error around the pilot carrier where the reception level has decreased increases, and the carrier for transmitting data (hereinafter referred to as data carrier). ) Signal quality deteriorates.

  FIG. 14 shows an OFDM frame configuration 10. The OFDM frame configuration 10 is configured with two dimensions of a carrier number and an OFDM symbol number. Carrier numbers 0, 1,... K indicate subcarrier numbers (channel numbers). OFDM symbol numbers 0, 1, ..., m-1, m, m + 1, ... indicate symbol numbers. In such an OFDM frame configuration, each subcarrier is divided into symbol strings, data is allocated to the divided subcarrier areas (hereinafter referred to as data carriers (k, m)), and the data is transmitted in parallel. To do. Further, pilot carriers whose amplitude and phase are known are arranged at predetermined positions (k, n−1), (k, n), (k, n + 1), etc., in the carrier of the frame configuration 10. Subcarrier channel estimation is performed using this pilot carrier.

  Next, FIG. 15 shows an example of a channel estimation result when the pilot carrier reception level is instantaneously lowered. The reception level of the pilot carrier is detected in the order of (1), (2), and (3) in FIG. 15, and the reception level of the pilot carrier in (2) is lowered to be equal to or less than the pilot carrier effective threshold. In the channel estimation in such a case, the channel estimation result is (A) with respect to the original channel transition (A). For this reason, when channel estimation and channel equalization are performed using a pilot carrier whose reception level has dropped instantaneously in this way, the estimation error of channel characteristics around the pilot carrier whose reception level has dropped (c) increases. When the received signal is equalized, the data carrier around the pilot carrier may deteriorate.

  As a conventional channel estimation technique using a pilot carrier, there is Patent Document 1 below.

JP2008-118390

  The apparatus of Patent Document 1 uses an all-carrier system as a transmission path characteristic estimation method and reduces the range of the low-pass filter to ½ that of the conventional one, so that unnecessary noise components can be reduced, and high-speed and high-accuracy transmission is performed. Road characteristic estimation can be performed. However, when the reception level of the pilot carrier decreases due to instantaneous fluctuations, no countermeasure has been taken for the problem of signal quality deterioration of the data carrier due to channel characteristic estimation error around the pilot carrier where the reception level has decreased instantaneously.

  The present invention has been made in view of such a situation, and an object thereof is to provide a wireless communication apparatus capable of solving the above-described problems.

  The radio communication apparatus according to the present invention is a radio communication apparatus that estimates channel characteristics using a pilot carrier that is included in subcarriers of an orthogonal frequency division multiplexing scheme and whose amplitude and phase are known, and compares the pilot carrier power with a power threshold. Pilot carrier level determining means for determining, pilot carrier fluctuation detecting means for detecting instantaneous fluctuation of the pilot carrier in the time axis direction, and interpolation or extrapolation of the pilot carrier in at least one of the time axis and frequency axis directions Replacement pilot carrier generation means for generating a replacement pilot carrier, wherein the pilot carrier level determination means determines that the power of the pilot carrier is less than or equal to the power threshold value, and the pilot carrier fluctuation detection means determines the pilot key variation. When the instantaneous variation is detected in the rear, it is characterized by replacing the pilot carrier in the substituted pilot carrier.

  According to the present invention, when the reception level of the pilot carrier is instantaneously reduced, the pilot carrier is replaced with an interpolated / extrapolated pilot carrier to reduce the estimation error of the channel characteristics of the radio communication apparatus, and the data The signal quality of the carrier can be improved.

It is a figure which shows the structure of the receiving part in the radio | wireless communication apparatus which concerns on embodiment of this invention. It is a figure which shows the structure of the pilot carrier extraction and code reproduction | regeneration part which concerns on embodiment of this invention. It is a figure which shows the structure of the pilot carrier level determination device which concerns on embodiment of this invention. It is a figure which shows the structure of the pilot carrier fluctuation | variation detection part which concerns on embodiment of this invention. It is a figure which shows calculation of the variation | change_quantity of the pilot carrier which concerns on embodiment of this invention. It is a figure which shows the structure of the pilot carrier replacement part which concerns on embodiment of this invention. It is a figure which shows the example of a fluctuation | variation which needs replacement of the pilot carrier which concerns on embodiment of this invention. It is a figure which shows the example of a fluctuation | variation which does not require the replacement of the pilot carrier which concerns on embodiment of this invention. It is a figure which shows the structure of the replacement pilot carrier production | generation part which concerns on embodiment of this invention. It is a figure which shows the structure of the time-axis interpolation and external complement based on embodiment of this invention. It is a figure which shows the structure of the modification of the time-axis interpolation and a complement exterior which concerns on embodiment of this invention. It is a figure which shows the structure of the frequency-axis interpolation and extrapolation calculation part which concerns on embodiment of this invention. It is a figure which shows the channel estimation result when the reception level of the pilot carrier which concerns on embodiment of this invention falls instantaneously. It is a figure which shows the OFDM frame structure which concerns on the conventional Example. It is a figure which shows the channel estimation result when the reception level of the pilot carrier which concerns on the conventional Example falls instantaneously.

  Hereinafter, modes for carrying out the present invention (hereinafter referred to as “embodiments”) will be described with reference to the drawings. FIG. 1 shows the configuration of the receiving unit 100 in the wireless communication apparatus of the present invention. The OFDM frame configuration of the present invention is the same as the OFD frame configuration 10 according to the conventional example shown in FIG.

  A configuration of the receiving unit 100 in the wireless communication apparatus according to the embodiment of the present invention will be described. As shown in FIG. 1, the receiving unit 100 includes an A / D (Analog to Digital) converter 101, a synchronization detector 102, an FFT start position setting unit 103, an FFT computing unit 104, a pilot carrier extraction / code reproduction unit 105, a delay unit. 106, pilot carrier level calculator 107, pilot carrier level determination unit 108, pilot carrier level fluctuation detection unit 109, pilot carrier replacement unit 110, channel estimation unit 111, delay unit 112, channel equalization unit 113, and demodulation unit 114 It is configured.

  The A / D converter 101 converts the received signal (r) from an analog signal to a digital signal, and outputs it to the synchronization detector 102 and the FFT start position setting unit 103. The synchronization detector 102 detects the beginning of the OFDM symbol (hereinafter referred to as symbol) shown in FIG. 14 by correlation calculation of a predetermined synchronization word or CP (Cyclic Prefix) included in the received signal, and the detection result is an FFT start position setting device. To 103. The FFT start position setting unit 103 sets the FFT window start position based on the head of the symbol detected by the synchronization detector 102, and outputs the FFT window start position and the received signal to the FFT calculator 104. The FFT calculator 104 performs an FFT (Fast Fourier Transform) operation on the received signal based on the FFT window start position, and outputs a carrier signal (subcarrier) to the pilot carrier extraction / code reproduction unit 105 and the delay unit 112. .

  A pilot carrier extraction / code recovery unit 105 extracts a pilot carrier from a received signal converted into a carrier signal (subcarrier), performs code recovery, and outputs the code recovered pilot carrier to a delay unit 106 and a pilot carrier level calculator 107. To do. Details of pilot carrier extraction / code reproduction section 105 will be described later. The delay unit 106 delays the code-regenerated pilot carrier by a processing time required by the pilot carrier level calculator 107, the pilot carrier level determination unit 108, and the pilot carrier level fluctuation detection unit 109, and the code-regenerated pilot carrier is piloted. The data is output to the carrier replacement unit 110.

Pilot carrier level calculator 107 calculates pilot carrier power and outputs the calculated pilot carrier power to pilot carrier level determiner 108 and pilot carrier level fluctuation detector 109. In OFDM frame structure 10 as shown in FIG. 14, n-th pilot carriers (k, n) of the k th sub-carrier power _{P k} of the amplitude of the pilot carriers (k, n) A (k , n) Then, it can be calculated as Equation 1.

ここで、real（Ａ（ｋ、ｎ））はＡ（ｋ、ｎ）の実部、imag（Ａ（ｋ、ｎ））はＡ（ｋ、ｎ）の虚部である。

Here, real (A (k, n)) is the real part of A (k, n), and imag (A (k, n)) is the imaginary part of A (k, n).

  Pilot carrier level determiner 108 determines whether the power of the pilot carrier is equal to or lower than a threshold value, and outputs the threshold determination result to pilot carrier replacement section 110. Details of pilot carrier level determination unit 108 will be described later. Pilot carrier level fluctuation detection section 109 detects the power fluctuation of pilot carrier (k, n) and outputs the detected power fluctuation to pilot carrier replacement section 110. Pilot carrier replacement section 110 determines whether or not it is necessary to replace the pilot carrier based on the threshold determination result of pilot carrier level determination section 108 and the power fluctuation detected by pilot carrier level fluctuation detection section 109. . When it is necessary to replace the pilot carrier, pilot carrier replacement section 110 replaces the pilot carrier and outputs the replaced pilot carrier to channel estimation section 111. When it is not necessary to replace the pilot carrier, pilot carrier replacement section 110 outputs the pilot carrier input from delay unit 106 to channel estimation section 111. Details of pilot carrier replacement section 110 will be described later.

  Channel estimation section 111 estimates the channel characteristics using the pilot carrier and outputs signal H (j), which is the channel characteristics estimation result, to channel equalization section 113. Channel characteristics are estimated using, for example, a method such as linear interpolation between pilot carriers or a frequency interpolation filter. The delay unit 112 equalizes the signal X (j) obtained by delaying the carrier signal of the received signal by a processing time required for the channel estimation unit 111 to calculate the signal H (j) from the pilot carrier extraction / code reproduction unit 105. Output to the unit 113. Channel equalization section 113 calculates equalized signal Y (j) from signal X (j) and signal H (j), and outputs the calculated signal Y (j) to demodulation section 114. For the signal Y (j), the signal X (j) and the signal H (j) can be calculated by, for example, the calculation of Equation 2.

  The demodulator 114 performs demapping, error correction, and the like from the equalized received signal, and outputs the result to the subsequent data processor.

  Next, the configuration of pilot carrier extraction / code reproduction section 105 is shown in FIG. The pilot carrier extraction / code regeneration unit 105 includes a pilot carrier arrangement position information storage memory 201, a pilot extractor 202, a pilot code pattern storage memory 203, and a pilot code regenerator 204. The pilot carrier arrangement position information storage memory 201 outputs information indicating the carrier on which the pilot carrier is arranged, or enable “valid” to the pilot extractor 202. The pilot extractor 202 receives the carrier arrangement position information from the pilot carrier arrangement position information storage memory 201, passes the carrier corresponding to the pilot carrier, replaces the other carriers with 0, and outputs it to the pilot code regenerator 204. When enable “valid” is output at the time of a pilot carrier, the corresponding carrier is passed and other carriers are replaced with 0 and output to pilot code regenerator 204. Pilot code pattern storage memory 203 stores a pilot carrier code pattern on the transmission side, and outputs this code pattern to pilot code regenerator 204. Pilot code regenerator 204 receives a code pattern from pilot code pattern storage memory 203, performs code recovery of the pilot carrier using this code pattern, and outputs the code carrier to delay unit 106 and pilot carrier level calculator 107.

Next, the configuration of pilot carrier level determiner 108 is shown in FIG. The pilot carrier level determiner 108 includes a delay unit 301, an average power calculator 302, a threshold calculator 303, and a threshold determiner 304. Hereinafter, the carrier (k, n) will be described. The delay unit 301 receives the pilot carrier power P _k from the pilot carrier level calculator 107, generates a delay corresponding to the processing time required for the average power calculation in the average power calculator 302 and the threshold calculator 303, and delays the delay. Pilot carrier power P _DLY (k, n) is output to threshold value decision unit 304. Average power calculator 302 receives pilot carrier power P _k from pilot carrier level calculator 107, calculates the average power of one symbol of pilot carrier, and outputs it to threshold calculator 303. The average power can be calculated by, for example, the calculation of Equation 3.

The threshold calculator 303 calculates the threshold P _thr from the average power and outputs it to the threshold determiner 304. The threshold value P _thr can be calculated by, for example, the calculation of Expression 4.

ここで、μは０<μ<１の範囲の定数である。

Here, μ is a constant in the range of 0 <μ <1.

The threshold determination unit 304 compares the pilot carrier power P _DLY (k, n) with the threshold P _thr and outputs P _result as a comparison _result to the pilot carrier replacement unit 110. The threshold comparison result P _result can be calculated by, for example, Formula 5.

Next, the configuration of pilot carrier level fluctuation detecting section 109 is shown in FIG. FIG. 5 shows calculation of the pilot carrier fluctuation amount ΔP (k, n). As shown in FIG. 4, the pilot carrier level fluctuation detection unit 109 includes a one-symbol delay memory 401, a subtracter 402, an absolute value calculator 403, a threshold storage register 404, and a threshold determiner 405. The 1-symbol delay memory 401 receives from the pilot carrier level calculator 107 the power P _k (hereinafter referred to as power P (k, n)) of the pilot carrier with the carrier number k and the OFDM symbol number n shown in FIG. The signal is delayed by one symbol, and pilot carrier power P (k, n−1) is output to the subtractor 402. The subtractor 402 receives the pilot carrier power P (k, n−1) from the 1-symbol delay memory 401 and the pilot carrier power P (k, n) from the pilot carrier level calculator 107. As shown in FIG. 5, the subtractor 402 subtracts the pilot carrier power P (k, n−1) and pilot carrier power P (k, n) one symbol before, thereby changing the pilot carrier fluctuation amount ΔP (k, n). And the pilot carrier fluctuation amount ΔP (k, n) is output to the absolute value calculator 403. The absolute value calculator 403 takes the absolute value | ΔP (k, n) | of the pilot carrier fluctuation amount ΔP (k, n) input from the subtractor 402 and makes | ΔP (k, n) | Is output to the threshold determination unit 405. The threshold value storage register 404 stores a threshold value of a variation amount regarded as a large variation and outputs the threshold value to the threshold value determination unit 405. The threshold value determination unit 405 compares the pilot carrier fluctuation amount | ΔP (k, n) | input from the absolute value calculator 403 with the fluctuation amount threshold value input from the threshold value storage register 404, and compares the comparison result with the pilot carrier replacement unit. To 110. The comparison result DET _VARI can be calculated by Equation 6, for example. That, | ΔP (k, n) | is set to "1" to the comparison result DET _VARI greater than _{ΔP THR, | ΔP (k,} n) | "is the comparison result DET _VARI equal to or less than [Delta] P _THR 0 ”And the comparison result DET _VARI is output to the pilot carrier replacement unit 110.

Next, the configuration of pilot carrier replacement section 110 is shown in FIG. FIG. 7 shows a variation example that requires pilot carrier replacement, and FIG. 8 shows a variation example that does not require pilot carrier replacement. As shown in FIG. 6, the pilot carrier replacement unit 110 includes a delay unit 501, a replacement pilot carrier generation unit 502, a replacement determination unit 503, and a signal selector 504. When a delay carrier 501 inputs a pilot carrier (hereinafter referred to as pilot carrier P (k, n)) from delay device 106, pilot carrier (hereinafter referred to as a delayed pilot) delayed by a processing time required by replacement pilot carrier generation section 502. The carrier P _DLY (k, n)) is output to the signal selector 504. Replacement pilot carrier generation section 502, when receiving pilot carrier P (k, n) from delay unit 106, generates a replacement pilot carrier and generates the generated replacement pilot carrier (hereinafter referred to as replacement pilot carrier P ′ (k, n)). Is output to the signal selector 504. Details of replacement pilot carrier generation section 502 will be described later.

When the comparison result P _result is input from the pilot carrier level determination unit 108 and the comparison result DET _VARI is input from the pilot carrier level fluctuation detection unit 109, the replacement determination unit 503 receives the comparison result P _result and the comparison result DET _VARI. It is determined whether or not it is necessary to replace the pilot carrier, and a replacement determination signal as a determination result is output to the signal selector 504. For example, as shown in FIG. 7, the pilot carrier P (k, n) is less than or equal to the threshold P _thr , and both the fluctuation amount ΔP (k, n) and fluctuation amount ΔP (k, n + 1) of the adjacent pilot carriers are When it is larger than the fluctuation amount threshold value ΔP _THR , replacement determination unit 503 determines that the reception level of P (k, n) is an instantaneous decrease. In such a case, replacement determination unit 503 determines that pilot carrier replacement is necessary, sets “valid” that requires pilot carrier replacement to the replacement determination signal, and outputs the signal to signal selector 504. . Further, for example, as shown in FIG. 8, the pilot carrier P (k, n) is equal to or less than the threshold value P _thr , but the fluctuation amount ΔP (k, n−1) and the fluctuation amount ΔP (k, n) of adjacent pilot carriers. ) Is larger than the fluctuation amount threshold value ΔP _THR , the replacement determination unit 503 determines that the reception level of P (k, n) is not an instantaneous decrease. In such a case, replacement determination unit 503 determines that pilot carrier replacement is not necessary, sets “invalid” that does not require pilot carrier replacement in the replacement determination signal, and outputs the result to signal selector 504.

The signal selector 504 selects the replacement pilot carrier P ′ (k, n) output from the replacement pilot carrier generation unit 502 when “valid” is set in the replacement determination signal. The signal selector 504 selects the delayed pilot carrier P _DLY (k, n) output from the delay unit 501 when “invalid” is set in the replacement determination signal. Next, the signal selector 504 outputs the selected pilot carrier (hereinafter referred to as a selected pilot carrier P′sc (k, n)) to the channel estimation unit 111.

Next, the configuration of replacement pilot carrier generation section 502 is shown in FIG. The replacement pilot carrier generation unit 502 includes a time axis interpolation / extrapolation calculation unit 601, a frequency axis interpolation / extrapolation calculation unit 602, a subtractor 603, a multiplier 604, a multiplier 605, and an adder 606. The time-axis interpolation / extrapolation calculation unit 601 uses the pilot carrier P (k, n−1) and pilot carrier P (k, n + 1) that move back and forth in the OFDM symbol shown in FIG. P ′ _t (k, n) is calculated, and the calculated replacement pilot carrier is output to multiplier 604. Details of the time axis interpolation / extrapolation calculation unit 601 will be described later. The frequency axis interpolation / extrapolation calculation unit 602 uses the pilot carrier P (k, n−1) and the pilot carrier P (k, n + 1) that fluctuate in frequency in the carrier shown in FIG. The calculated replacement pilot carrier P ′ _f (k, n) is output to the multiplier 605. Details of the frequency axis interpolation / extrapolation calculation unit 602 will be described later. The subtractor 603 subtracts the coefficients “1” and “μ _f ” and outputs the result to the multiplier 604. “Μ _f ” is a weighting coefficient for the replacement pilot carrier calculated by extrapolation / interpolation on the frequency axis, and is in the range of 0 ≦ μ _f ≦ 1. The multiplier 604 multiplies the replacement pilot carrier P ′ _t (k, n) output from the time axis interpolation / extrapolation calculation unit 601 by the coefficient “1-μ _f ” output from the subtractor 603, and adds an adder. To 606. Multiplier 605 multiplies substitution pilot carrier P ′ _f (k, n) output from frequency axis interpolation / extrapolation calculation unit 602 and coefficient “μ _f ”, and outputs the result to adder 606. The adder 606 multiplies the replacement pilot carrier P ′ _t (k, n) output from the multiplier 604 by the coefficient “1-μ _f ” and the replacement pilot carrier P ′ _f output from the multiplier 605. A replacement pilot carrier P ′ (k, n) obtained by adding (k, n) and a value obtained by multiplying the coefficient “μ _f ” is output to the signal selector 504.

Next, the configuration of the time axis interpolation / extrapolation calculation unit 601 is shown in FIG. The time axis interpolation / extrapolation calculation unit 601 includes a 1 symbol delay memory 701, a 1 symbol delay memory 702, a 1 symbol delay memory 703, a 1 symbol delay memory 704, and an average calculator 705. It is assumed that pilot carrier P (k, n) to pilot carrier P (k, n + 2) are input from delay device 106 to time axis interpolation / extrapolation calculation unit 601. The input pilot carrier P (k, n + 2) is output to the 1-symbol delay memory 701 and the average calculator 705. When the pilot carrier P (k, n + 2) is input, the one-symbol delay memory 701 averages the pilot carrier P (k, n + 1) obtained by delaying the pilot carrier P (k, n + 2) by one symbol with the one-symbol delay memory 702 Output to the calculator 705. The 1-symbol delay memory 702 outputs the pilot carrier P (k, n) obtained by delaying the pilot carrier P (k, n + 1) output from the 1-symbol delay memory 701 by 1 symbol to the 1-symbol delay memory 703. The 1-symbol delay memory 703 uses a pilot carrier P (k, n−1) obtained by delaying the pilot carrier P (k, n) output from the 1-symbol delay memory 702 by 1 symbol, and an average calculator 705 and a 1-symbol delay. Output to the memory 704. 1-symbol delay memory 704 outputs pilot carrier P (k, n−2) obtained by delaying pilot carrier P (k, n−1) output from 1-symbol delay memory 703 by one symbol to average calculator 705. To do. The average calculator 705 adds the average of the pilot carrier P (k, n + 2), the pilot carrier P (k, n + 1), the pilot carrier P (k, n−1), and the pilot carrier P (k, n−2) or A weighted average is calculated, and the calculated pilot carrier is output to the multiplier 604 as an average pilot carrier P ′ _t (k, n).

As a modification of the time axis interpolation / extrapolation calculation unit 601, the configuration of the time axis interpolation / extrapolation calculation unit 601a is shown in FIG. The time axis interpolation / extrapolation calculation unit 601a has a configuration used in the case of a wireless communication apparatus that cannot have a long delay. The time axis interpolation / extrapolation calculation unit 601a includes a 1-symbol delay memory 703, a 1-symbol delay memory 704, and an average calculator 705. In the time axis interpolation / extrapolation calculation unit 601a in FIG. 11, the pilot carrier P (k, n) is output from the delay unit 106. The 1-symbol delay memory 703 includes a 1-symbol delay memory 704 and an average calculator 705 for the pilot carrier P (k, n−1) obtained by delaying the pilot carrier P (k, n) output from the delay unit 106 by 1 symbol. Output to. 1-symbol delay memory 704 outputs pilot carrier P (k, n−2) obtained by delaying pilot carrier P (k, n−1) output from 1-symbol delay memory 703 by one symbol to average calculator 705. To do. The average calculator 705 performs an arithmetic operation of addition average or weighted average of the pilot carriers P (k, n−1) and pilot carriers P (k, n−2), and calculates the calculated pilot carriers as average pilot carriers P ′ _t. The result is output to the multiplier 604 as (k, n). By using such a time axis interpolation / extrapolation calculation unit 601a, it is possible to obtain an average only with past pilot carriers.

Next, the configuration of the frequency axis interpolation / extrapolation calculation unit 602 is shown in FIG. The frequency axis interpolation / extrapolation calculation unit 602 includes a 1 pilot carrier interval delay memory 801, a 1 pilot carrier interval delay memory 802, a 1 pilot carrier interval delay memory 803, a 1 pilot carrier interval delay memory 804, and an average calculator 805. Has been. It is assumed that pilot carrier P (k, n) to pilot carrier P (k, n + 2) are input from delay device 106 to frequency axis interpolation / extrapolation calculation unit 602. The input pilot carrier P (k, n + 2) is output to the 1 pilot carrier interval delay memory 801 and the average calculator 805. When one pilot carrier interval delay memory 801 inputs pilot carrier P (k, n + 2), pilot carrier P (k, n + 1) obtained by delaying pilot carrier P (k, n + 2) by one pilot carrier interval is set to one pilot carrier. The data is output to the interval delay memory 802 and the average calculator 805. The 1 pilot carrier interval delay memory 802 sets the pilot carrier P (k, n) output from the 1 pilot carrier interval delay memory 801 by delaying the 1 pilot carrier interval by 1 pilot carrier interval. Output to the delay memory 803. One pilot carrier interval delay memory 803 averages pilot carriers P (k, n−1) obtained by delaying pilot carrier P (k, n) output from one pilot carrier interval delay memory 802 by one pilot carrier interval. Output to the delay unit 804 and the 1 pilot carrier interval delay memory 804. 1 pilot carrier interval delay memory 804 is pilot carrier P (k, n-2) obtained by delaying pilot carrier P (k, n-1) output from 1 pilot carrier interval delay memory 803 by 1 pilot carrier interval, The result is output to the average calculator 805. The average calculator 805 adds or averages the pilot carrier P (k, n + 2), pilot carrier P (k, n + 1), pilot carrier P (k, n-1), and pilot carrier P (k, n-2) The weighted average is calculated, and the calculated pilot carrier is output to the multiplier 605 as the average pilot carrier P ′ _f (k, n).

  Next, FIG. 13 shows pilot carrier replacement when the reception level of the pilot carrier according to the embodiment of the present invention decreases instantaneously. The reception level of the pilot carrier is detected in the order of (1), (2), and (3) in FIG. 13, and the pilot carrier reception level of the pilot carrier in (2) decreases instantaneously, and is below the pilot carrier effective threshold. It has become. However, in the present invention, since the pilot carrier of (2) whose reception level is instantaneously reduced is replaced with (2) ′, when channel estimation is performed using this replaced pilot carrier (2) ′, As shown in FIG. 13, channel estimation (A) is performed for the original channel (A). As a result, the estimation error (c) of the channel characteristics around the pilot carrier does not increase, so that it is possible to suppress the deterioration of the data carrier around the pilot carrier when the received signal is equalized.

  In this embodiment, the replacement pilot carrier is generated by synthesizing a pilot carrier generated from temporally preceding and following pilot carriers and a pilot carrier generated from pilot carriers whose frequency is in order of frequency on the frequency axis. However, it is not limited to this. That is, it is possible to replace the pilot carrier generated from the pilot carriers before and after in time or the pilot carrier generated from the pilot carriers before and after the frequency in order of frequency on the frequency axis. Further, in the present embodiment, the pilot carrier P (k, n) has been described. However, the reception level of the pilot carrier P (k-1, n) and the pilot carrier P (k + 1, n) also instantaneously decreased. In some cases, this pilot carrier can be replaced with an interpolated / extrapolated pilot carrier.

  According to the present invention, when the reception level of the pilot carrier is instantaneously reduced, the pilot carrier is replaced, so that the estimation error of the channel characteristic of the radio communication apparatus is reduced and the signal quality of the data carrier is improved. Can do.

  As mentioned above, although this invention was demonstrated by specific embodiment, it cannot be overemphasized that the said embodiment is an illustration of this invention and is not limited to this embodiment.

In summary, the present invention has the following characteristics.
(1) A radio communication apparatus according to the present invention is a radio communication apparatus that estimates channel characteristics from a pilot carrier that is included in subcarriers of an orthogonal frequency division multiplexing system and whose amplitude and phase are known. Pilot carrier level determining means for comparing and determining, pilot carrier fluctuation detecting means for detecting instantaneous fluctuation of the pilot carrier in the time axis direction, and interpolating the pilot carrier in at least one of the time axis and the frequency axis Or replacement pilot carrier generation means for generating a replacement pilot carrier by extrapolation, wherein the pilot carrier level determination means determines that the power of the pilot carrier is less than or equal to the power threshold, and the pilot carrier fluctuation detection means The pilot When the instantaneous variation is detected in the carrier, it is characterized by replacing the pilot carrier in the substituted pilot carrier.
(2) The radio communication device of the present invention of (1) includes pilot carrier average power calculation means for calculating average power of a plurality of pilot carriers arranged in the frequency axis direction, and the power threshold value of the pilot carrier It is calculated from the average power.
(3) The pilot fluctuation detecting means of the wireless communication apparatus according to the present invention of (1) or (2) calculates a fluctuation amount with the pilot carrier adjacent in the time axis, and the fluctuation amount of the pilot carrier is calculated. It is characterized in that it is determined that an instantaneous fluctuation is detected in the pilot carrier when the fluctuation amount threshold value is larger.
(4) The replacement pilot carrier generation means of the radio communication apparatus according to any one of (1) to (3), wherein the replacement pilot carrier is extracted from the pilot carrier that is in a temporal relationship with respect to the time axis. It is characterized by generating.
(5) The replacement pilot carrier generation means of the wireless communication apparatus according to any one of (1) to (3), wherein the replacement pilot carrier is extracted from the pilot carrier whose frequency is in order of frequency on the frequency axis. It is characterized by generating.
(6) The replacement pilot carrier generation means of the wireless communication apparatus according to any one of (1) to (3) includes a time axis replacement pilot carrier generated from the pilot carriers before and after the time axis. The replacement pilot carrier is generated by synthesizing with a frequency axis replacement pilot carrier generated from the pilot carrier in which the order of frequency in the frequency axis has a front-rear relationship.
(7) A pilot carrier replacement method for a radio communication apparatus according to the present invention is a radio communication apparatus that estimates channel characteristics using a pilot carrier that is included in subcarriers of an orthogonal frequency division multiplexing system and whose amplitude and phase are known. A pilot carrier level determination step for comparing and determining the power of the pilot carrier and a power threshold, a pilot carrier variation detection step for detecting instantaneous variation of the pilot carrier in the time axis direction, and at least one of the time axis and the frequency axis for the pilot carrier A replacement pilot carrier generation step of generating a replacement pilot carrier by interpolation or extrapolation in any direction, wherein the pilot carrier level determination step determines that the power of the pilot carrier is less than or equal to the power threshold, and the pilot Career change When the instantaneous variation is detected in the pilot carrier by detection step it is characterized by replacing the pilot carrier in the substituted pilot carrier.

  The present invention is suitable for a wireless communication apparatus, but can be applied to general devices that perform channel estimation.

DESCRIPTION OF SYMBOLS 10 ... OFDM frame structure 100 ... Reception part 101 ... A / D converter 102 ... Synchronization detector 103 ... FFT start position setting device 104- · · · · FFT computing unit 105 ----- pilot carrier extraction and symbol recovery unit 106 ----- delayer 107 ----- pilot carrier level calculator 108 ----- pilot carrier level determiner 109: Pilot carrier level fluctuation detection unit 110: Pilot carrier replacement unit 111: Channel estimation unit 112: Delay device 113: Channel equalization unit 114 ... Demodulator 201... Pilot carrier arrangement position information storage memory 202... Pilot extractor 203. Pattern storage memory 204... Pilot code regenerator 301... Delay unit 302... Average power calculator 303. ... 1 symbol delay memory 402 ... Subtractor 403 ... Absolute value calculator 404 ... Threshold storage register 405 ... Threshold decision unit 501 ... Delay unit 502... Replacement pilot carrier generation unit 503. Replacement determination unit 504... Signal selector 601... Time axis interpolation / extrapolation calculation unit 601 a.・ Time axis interpolation / extrapolation calculation unit 602... Frequency axis interpolation / extrapolation calculation unit 603... Subtractor 604 ..Multiplier 605. ... Adder 701 ... 1 symbol Total memory 702 ... 1 symbol delay memory 703 ... 1 symbol delay memory 704 ... 1 symbol delay memory 705 ... Average calculator 801 ... 1 pilot carrier Interval delay memory 802... 1 pilot carrier interval delay memory 803... 1 pilot carrier interval delay memory 804... 1 pilot carrier interval delay memory 805.

Claims (1)

In a radio communication apparatus that estimates channel characteristics using pilot carriers that are included in subcarriers of an orthogonal frequency division multiplexing scheme and whose amplitude and phase are known,
Pilot carrier level determination means for comparing and determining the power of the pilot carrier and a power threshold;
Pilot carrier fluctuation detecting means for detecting instantaneous fluctuation of the pilot carrier in the time axis direction;
Replacement pilot carrier generation means for generating a replacement pilot carrier by interpolating or extrapolating the pilot carrier in at least one of the time axis and frequency axis directions;
When the pilot carrier level determining means determines that the pilot carrier power is less than or equal to the power threshold, and the pilot carrier fluctuation detecting means detects an instantaneous fluctuation in the pilot carrier, the pilot carrier is A wireless communication apparatus that is replaced with a replacement pilot carrier.

Images