JP2000183845A - Receiving device of orthogonal polarization multi-carrier modulation / demodulation system - Google Patents

Abstract

(57) [Problem] To provide a receiving device of an orthogonal polarization multicarrier modulation / demodulation system capable of obtaining frequency offset compensation with high accuracy and high tracking ability. SOLUTION: In a receiver of an orthogonal polarization multicarrier modulation / demodulation system in which one of adjacent sub-channels is transmitted with vertical polarization and the other is transmitted with horizontal polarization, a reception signal component r _V (t ) In the effective symbol section,
The average value R _avV of the autocorrelation function between the two signals having the time difference is calculated, and the effective symbol section of the received signal component r _H (t) due to the horizontal polarization has a time difference of １ ／. An autocorrelation function between the two signals is calculated, an average value R _avH of a value obtained by multiplying the auto-correlation function by an inverse sign is calculated, and an estimated value f ′ _{off of the argument} is calculated from these two average values R _avV and R _avH. Is calculated,
Estimated value f 'the carrier frequency offset of the transmit and receive waves with _off those to compensate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an orthogonally polarized multicarrier modulation / demodulation type receiving apparatus, and more particularly to a transmitting / receiving apparatus suitable for a high transmission rate digital wireless transmitting / receiving apparatus used in mobile radio equipment and broadcasting equipment. And an orthogonal polarization multi-carrier modulation / demodulation method having a carrier frequency offset compensation function.

[0002]

2. Description of the Related Art In order to make mobile radio equipment such as moving image transmission multimedia, high efficiency of mobile radio equipment is required.
The establishment of high bit rate transmission technology is indispensable. One type of technology for this purpose is OFDM (Orthogonal Frequency) that performs modulation and demodulation using a large number of orthogonal subcarriers.
Division Multiplexing) has attracted attention, and studies for its practical use are underway.

[0003] The OFDM system has a plurality of subcarriers (subchannels) of different frequencies and a guard interval can be set, thereby providing resistance to selective fading, but increasing the number of subcarriers. Since the adjacent subcarrier interval becomes narrower as a result, the local oscillation frequency shift between the transceiver and the frequency offset caused by the Doppler frequency shift when moving, etc.,
Inter-Channel Interferance (ICI)
And the transmission characteristics are degraded.

Here, it is conceivable to reduce the number of sub-channels in order to increase the resistance to frequency offset. In this case, although the resistance to frequency offset is increased, the frequency selective distortion generated by multipath and the like is increased. Is undesirable because of reduced resistance to

Therefore, some countermeasures are required for compensating for the frequency offset. As a countermeasure against the frequency offset in the OFDM system, the periodicity of the guard time slot of the OFDM is used, that is, the OFDM method is used.
A method for estimating and compensating for an offset amount by using the fact that the waveform of a guard section of a signal is the same as the waveform of the last part of an effective symbol section has been proposed by the following document 1.

<Reference 1> Seki, Taga and Ishikawa, "A Study on New Frequency Synchronization Method Using Guard Period in OFDM" Technical Report of the Institute of Television Engineers of Japan, Vol.19, No.38, pp.13
-18 (Aug. 1995)

However, according to this method, the guard interval length that can be used for estimating the frequency offset is as small as a fraction of one symbol length to several tens of tenths. Since integration processing over several symbols to several tens of symbols is required, there is a problem that high-speed followability to a frequency offset cannot be sufficiently obtained.

Further, if compensation is performed with a small number of symbols in order to obtain high-speed followability in this system, the compensation accuracy cannot be maintained sufficiently, and the transmission characteristics are degraded as compared with the case where compensation is not performed. There is also a disadvantage that there are cases.

Therefore, as a technique for reducing interference between adjacent channels due to this frequency offset, OPFDM (Ort
hogonaL Polarization Frequency Division Multiplexi
ng) system, that is, an orthogonal polarization multi-carrier modulation system has been proposed in the following literatures 2 and 3.

<Reference 2> Susumu, et al., "Countermeasures for Frequency Offset of Multi-Carrier Modulation System" Technical Report of the Institute of Telecommunications, vol.96, No.83, pp.119-124, Aug. 1996 <Reference 3> A. Sumasu, et al. “Orthgonal Polarization and Frequency Divisio
nMultiplexing (OPFDM) in a Fast and Frequen
cy-Selective Fading Channel "Proc. of MoMuc '97, pp205-209, Sept-Oct, 199
7.

The OPFDM system is a system in which modulation is performed using two types of radio waves having different polarization planes as adjacent subchannels, that is, vertical polarization and horizontal polarization. In this case, adjacent subchannels having the same polarization are used. Because the carrier interval doubles,
The overlap of the carrier main lobes is reduced, and the immunity to interference between adjacent channels caused by the frequency offset can be improved.

[0012]

The above prior art is based on the OP
It cannot be said that consideration is given to the improvement of the frequency offset compensation accuracy in the FDM system, and there has been a problem that it is unsatisfactory to obtain frequency offset compensation with high accuracy and excellent followability.

That is, in the OPFDM system according to the prior art, the compensation accuracy superior to that of the OFDM system without frequency offset compensation can be obtained, but the compensation accuracy is lower than that of the OFDM system with frequency offset compensation. There was a problem.

Further, even if the frequency compensation technique of Reference 1 is extended and applied to the OPFDM method, the disadvantages of the compensation technique of Reference 1 such as low compensation accuracy and low followability to fluctuations are not solved.

SUMMARY OF THE INVENTION An object of the present invention is to solve various problems associated with measures against transmission characteristic deterioration due to a frequency offset between transmission and reception in a multicarrier modulation system suitable for high efficiency and high pit rate transmission even in a multipath environment. An object of the present invention is to provide a receiving device of an orthogonal polarization multi-carrier modulation / demodulation system capable of obtaining frequency offset compensation with high accuracy and high tracking ability.

[0016]

An object of the present invention is to provide an orthogonally polarized multi-carrier modulation / demodulation receiving apparatus for transmitting one of adjacent sub-channels with vertical polarization and transmitting the other with horizontal polarization. Means for calculating an average value of an autocorrelation function between two signals having a time difference of で in an effective symbol section of a received signal due to a horizontal wave; Means for calculating an autocorrelation function between two kinds of signals having a time difference of / 2, and calculating an average value of a value obtained by multiplying the autocorrelation function by an inverse sign; and calculating a declination from the two kinds of average values. This is achieved by using the argument to compensate for the carrier frequency offset between the transmitted and received waves.

That is, in the orthogonal polarization multi-carrier modulation (OPFDM) system, for example, when even-numbered subcarriers are assigned to vertical polarization and odd-numbered subcarriers are assigned to horizontal polarization, Has the same signal waveform in the first half and the second half of one symbol section, and the transmission signal in the horizontal polarization has the same signal waveform in which the first half and the second half of the one symbol section are inverted. It focuses on that.

By estimating and compensating the frequency offset component from the above, there is obtained no result that the frequency offset compensation with high accuracy and excellent followability can be obtained. The receiver of the orthogonal polarization multi-carrier modulation / demodulation system can be realized by employing the means of (1).

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of an orthogonally polarized multicarrier modulation / demodulation receiving apparatus according to the present invention. FIG. 1 shows an embodiment of the present invention, in which reference numerals 1 and 2 denote high frequency sections of an OPFDM receiver,
4 is an intermediate frequency unit including a frequency conversion unit, 5 is a local oscillator that generates a local signal for frequency conversion, 6 and 7 are quadrature demodulators, 8 is a voltage controlled oscillator that generates a local signal for quadrature demodulation, 9 and 10 are AD converters, 11 and 12 are ts / 2
Delay device, 13 is a sign inverter, 14, 15 are multipliers, 1
6, 17 are integrating discharge filters, 18 is an adder, 19 is an argument calculator, 20 is a loop filter and a DA converter,
21 and 22 are guard interval elimination circuits, 23 is a multiplexer, and 24 is a DFT calculator.

Here, the antenna A _V is for vertical polarization, and the antenna A _H is for horizontal polarization. Therefore, a signal transmitted as vertical polarization from the transmitting side is input to the high frequency unit 1. The signal transmitted as a horizontally polarized wave is input to the high frequency unit 2.

Next, the operation of the embodiment shown in FIG. 1 will be described. First, a vertically polarized signal received by the vertically polarized antenna A _V is processed by the high frequency unit 1, the intermediate frequency unit 3, and the quadrature demodulator 6, while the horizontally polarized signal received by the horizontally polarized antenna A _H is processed. The polarization signal is processed by the high frequency unit 2, the intermediate frequency unit 4, and the quadrature demodulator 7, whereby the signals are converted into baseband complex signals, respectively, and digitized by the AD converters 9, 10, respectively.

Thereafter, the baseband complex signal components are combined by the multiplexer 23 after the guard sections are removed by the guard section removing circuits 21 and 22, respectively.
Further, the signal is supplied to the DFT calculator 24, and thereafter demodulated in the same manner as in a normal orthogonal polarization multi-carrier modulation / demodulation receiving apparatus.

On the other hand, the vertical component r _V (t) of the received signal output from the AD converter 9 is processed by a ts / 2 delay unit 11, a multiplier 14, and an integration discharge filter 16 for frequency offset compensation. Similarly, the horizontal component r _H (t) of the received signal output from the AD converter 10 is processed by the ts / 2 delay unit 12, the sign inverter 13, the multiplier 15, and the integrating discharge filter 17, whereby the vertical components are respectively processed. An estimate of the autocorrelation function of the polarization and the horizontal polarization is obtained.

These estimated values are added and averaged by an adder 18 and supplied to a declination calculator 19, where the declination is calculated.
A voltage signal representing (arg: argument) is calculated. Then, the voltage signal representing the argument is supplied to the loop filter and D
The frequency is supplied to the voltage control oscillator 8 via the A converter 20 and the frequency of the local signal for quadrature demodulation is controlled, so that feedback for frequency offset compensation works.

Here, in the above description, the frequency control of the quadrature demodulation local oscillation signal is performed by the feedback system, but the present invention may be implemented by the feed forward system. In the embodiment shown in FIG. 1, a circuit provided in a receiving apparatus of a normal orthogonal polarization multi-carrier modulation / demodulation system such as synchronization establishment and control is omitted, and a DFT calculator 2
The circuit units 4 and thereafter are omitted because they are the same as those of the ordinary orthogonally polarized multi-carrier modulation / demodulation receiving apparatus.

Next, the frequency offset compensating operation according to the embodiment of FIG. 1 will be described in more detail. First, FIG. 2 shows the OPFDM targeted by this embodiment.
FIG. 2 is a conceptual diagram showing the OFDM frequency spectrum arrangement of a signal in the system in comparison with the case of the OFDM system. As shown, when the symbol time is ts seconds, the OFDM system shown in FIG. While the main ropes of the subcarriers overlap at the frequency interval of ts Hz,
In the OPFDM system of (b), vertical and horizontal subcarriers are alternately arranged at a frequency interval of 1 / ts Hz.

[0027] Then, FIG. 2 an equivalent reduction general representation of the transmission signal the vertical component in the OPFDM method _{(b) u V (t)} ,
If u _H (t) is a general equivalent reduction of the horizontal component of the transmission signal, these are expressed by the following equations (1) and (2).

[0028]

(Equation 1)

[0029]

(Equation 2)

Here, c _{(2k) i} : 2 in the i-th section
Modulation symbol of k-th vertical polarization sub-channel (or horizontal polarization sub-channel) c _{(2k-1) i} : 2k-1-th horizontal polarization sub-channel (or vertical polarization sub-channel) in i-th section modulation symbol f _c (t): in the pulse waveform of each sub-channel signal (-Δ ≦ t ≦ ts), in the case of _{f c (t) = 1 (} t <-Δ, t> ts) is _{f c (t) = 0 Δ} : guard interval ts: observation interval Ts = Δ + ts: symbol period

Next, when these equations (1) and (2) are transformed,
The following equations (3) and (4) are obtained. Here, 0 ≦ t ≦ (ts /
2), and N / 2 is the size of the observation window.

[0032]

(Equation 3)

[0033]

(Equation 4)

Then, first, according to equation (3), OP
In the case of a vertically polarized transmission signal in the FDM system, FIG.
As shown in (a), the first half of the symbol section (0 to ts / 2)
It can be seen that the signal waveforms in the second half (ts / 2 to ts) have the same shape.

Next, from the equation (4), in the case of a transmission signal by horizontal polarization, as shown in FIG. 4B, the first half (0 to ts / 2) and the second half (ts / It can be seen that the signal waveforms obtained by inverting the positive and negative values of 2 to ts) have the same shape.

From this, by comparing and observing the phase fluctuations of the first half and the second half of the received signal waveform,
The frequency offset amount can be estimated. Therefore,
Next, the calculation of the frequency offset amount will be described.

Now, assuming that there is no interference between the vertical polarization and the horizontal polarization, the vertical polarization component r _V (t) of the OPFDM received signal can be expressed by the following equation (5). The horizontal polarization component r _H (t) of the received signal can be similarly expressed by the following equation (6).

[0038]

(Equation 5)

[0039]

(Equation 6)

Where S _V (t): vertical component of the transmission signal S _H (t): horizontal component of the transmission signal z _V (t): vertical component of noise z _H (t): horizontal component of noise

Then, next, the autocorrelation function R _V (t; ts / 2) of the vertically polarized wave component r _V (t) when 0 ≦ t ≦ (ts / 2) is obtained,
When the autocorrelation function R _H (t; ts / 2) of the horizontally polarized reception signal r _H (t) is obtained, the auto correlation function of each of the transmission signals S _V (t) and S _H (t) is 0 ≦ t. Since it is 1 in the section of ≤ (ts / 2) and 0 in other sections, the following equations (7) and (8) are obtained.

[0042]

(Equation 7)

[0043]

(Equation 8)

Then, these autocorrelation functions R _V (t; ts /
From each of 2) and R _H (t; ts / 2), when the argument is obtained by the following equations (9) and (10), the respective frequency offsets f _offV and f _offV
offH can be estimated.

[0045]

(Equation 9)

[0046]

(Equation 10)

Here, FIG. 4 shows only a portion necessary for obtaining the frequency offset compensating function in the embodiment of FIG. 1, and FIG. The operation of calculating the value will be described.

First, for the vertically polarized signal, ts /
The calculation of the approximate value R ' _V (t) of the autocorrelation function of the vertical component r _V (t) by the following equation (11) is obtained by the two delay unit 11 and the multiplier 14. Is calculated by the ts / 2 delay unit 12, the sign inverter 13, and the multiplier 15 to calculate the approximate value R ′ _H (t) of the autocorrelation function of the horizontal component r _H (t) by the following equation (12). can get.

[0049]

[Equation 11]

[0050]

(Equation 12)

After that, the approximate value R ′ _V (t) of the autocorrelation function for the vertically polarized signal is processed by the integral discharge filter 16 to calculate the following equation (13). Approximate value R ′ _H (t) of autocorrelation function for signal component
_{Is also} calculated by the following equation (14) by processing in the integrating discharge filter 17 to obtain the average value R _{avV of the} autocorrelation function of the vertically polarized signal and the average value of the autocorrelation function of the horizontally polarized signal. _Obtain R _avH .

[0052]

(Equation 13)

[0053]

[Equation 14]

The vertical and horizontal average values R
_avV and R _avH are added by the adder 18 and the argument calculator 1
9 and the estimated value f ′ of the argument is calculated by the following equation (15).
You get _off .

[0055]

(Equation 15)

Therefore, the declination estimated value f ′ thus obtained is
_off is an estimated value of the frequency offset, which is supplied to the control input of the voltage-controlled oscillator 8 so that feedback control is performed via the local oscillator of the intermediate frequency unit described with reference to FIG.
Alternatively, as shown in FIG. 1, the frequency offset can be compensated by operating the feedforward control.

Next, in order to verify the frequency offset compensation performance according to the above embodiment, computer simulation was performed, and the following results were obtained. First, this simulation was based on the following specifications. • Number of subcarriers: 128 • Guard section length (Δ / Ts): 0.01 • Subchannel modulation method: QPSK method • Communication path: AWGN (Additive White Gaussian Nois)
e) Environment • Cross polarization discrimination (XPD): 6.0 dB • Symbol synchronization: perfect state

The simulation results are as shown in FIGS. 5 and 6. In the figure, “w / o Compensation” represents no compensation. First, FIG. 5 shows the bit error rate characteristics with respect to the signal-to-noise ratio Eb / No. As is clear from FIG. 5, the characteristics of the embodiment of the present invention are QPSK.
Characteristic close to the theoretical characteristic of
It can be seen that it is far superior to the characteristics of the DM system.

Next, FIG. 6 shows the normalized frequency offset (f
_off ts), from this figure,
It can be seen that the characteristics of the embodiment of the present invention show the best compensation accuracy among all the characteristics.

That is, first, in the region where the normalized frequency offset is small, the characteristics of the OFDM system with compensation characteristics are worse than the characteristics of the OFDM system without compensation, whereas in the embodiment of the present invention. The properties show consistently good properties.

[0061] Next, similar in characteristics of OFDM scheme with compensation, whereas compensation only to the extent of the normalized frequency offset f _off ts ≦ 0.5 is not clever, a characteristic of the embodiment of the present invention, It can also be seen that the compensation is sufficiently effective until this f _off ts approaches 1.0.

Therefore, according to this embodiment, as compared with the conventional OFDM system having frequency offset compensation, there is no characteristic deterioration when the frequency offset is minute, there is almost no compensation error, and the offset which can be compensated is further reduced. Range 2
And Eb / No at a bit error rate of 10 ^-3.
Is improved by as much as 1 dB.

In the case of the conventional OFDM system, since the guard section length of the OFDM signal is usually as short as one-tenth of the effective symbol length, the number of correlation operations is small. For this reason, it is necessary to perform an averaging operation for ensuring accuracy over several tens of symbols, and as a result, it cannot follow the fluctuation of the offset during that period.

On the other hand, in the embodiment of the present invention, as described above, since the correlation operation can be performed in a 1/2 symbol section,
The averaging operation can be performed within a few symbols, and as a result, an effect is obtained that the following speed with respect to the time variation of the frequency offset can be greatly improved.

In the above embodiment, the intermediate frequency is subjected to feedback control or feedforward control to perform frequency offset compensation. However, the main carrier frequency is subjected to feedback control or feedforward control to perform frequency offset compensation. You may do so.

[0066]

According to the present invention, as compared with the prior art, there is no characteristic degradation at the time of a small offset, there is almost no compensation error, and the compensable offset range can be widened.
Further, various excellent effects can be obtained, such as improvement of Eb / No at the same bit error rate. Further, according to the present invention, there is an effect that the following speed of the frequency offset compensation can be significantly improved as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an orthogonal polarization multi-carrier modulation / demodulation receiving apparatus according to the present invention.

FIG. 2 is an explanatory diagram of a frequency spectrum arrangement of an OFDM system and an OPFDM system.

FIG. 3 is an explanatory diagram of a modulation signal waveform due to vertical polarization and horizontal polarization.

FIG. 4 is a block diagram conceptually showing a frequency offset compensation part according to an embodiment of the present invention.

FIG. 5 is a characteristic diagram illustrating an example of Eb / No versus bit error rate characteristics.

FIG. 6 is a characteristic diagram showing an example of a normalized frequency offset versus bit error rate characteristic.

[Explanation of symbols]

 1, 2 High frequency section of OPDDM receiver 3, 4 Intermediate frequency section 5 Local oscillator for forming intermediate frequency section 6, 7 Quadrature demodulator 8 Voltage controlled oscillator 9, 10 AD converter 11, 12 ts / 2 delay 13 Sign Inverter 14, 15 Multiplier 16, 17 Integral Discharge Filter 18 Adder 19 Declination Calculator 20 Loop Filter and DA Converter 21, 22 Guard Section Elimination Circuit 23 Multiplexer 24 DFT Calculator

 ──────────────────────────────────────────────────続 き Continuation of front page (71) Applicant 000187725 Matsushita Communication Industrial Co., Ltd. 4-3-1 Tsunashimahigashi, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture (71) Applicant 000000295 Oki Electric Industry Co., Ltd. 1-chome Toranomon, Minato-ku, Tokyo No. 7-12 (72) Inventor Masaaki Ota 2-31-19 Shiba 2-chome, Minato-ku, Tokyo Inside (72) Inventor Hiroshi Takegaki 31-19-19 Shiba 2-chome, Minato-ku Tokyo (72) Inventor Satoshi Miyazawa 2-31-19, Shiba 2-chome, Minato-ku, Tokyo Inside the communication and broadcasting organization (72) Inventor Hiroshi Sakakibara 31-19-19 Shiba 2-chome, Minato-ku, Tokyo Inside the communication and broadcasting organization (72) Person Yasuo Murazumi 2-31-19 Shiba, Minato-ku, Tokyo Inside the Communications and Broadcasting System (72) Inventor Shozo Komaki 2-31-19 Shiba, Minato-ku, Tokyo Inside the Communications and Broadcasting System (72) Inventor Okada Shiba, Minato-ku, Tokyo Eye No. 31, No. 19 communication and broadcasting mechanism in (72) inventor 須増 Atsushi Shiba, Minato-ku, Tokyo chome No. 31, No. 19 communications and broadcasting mechanism in the F-term (reference) 5K022 DD01 DD03 DD13 DD19 DD33 DD43

Claims (2)

[Claims] 1. An orthogonal polarization multi-carrier modulation / demodulation system for transmitting one of adjacent subcarriers with a vertical polarization and transmitting the other with a horizontal polarization, wherein an effective symbol section of a reception signal by the vertical polarization is provided. And 1
Means for calculating an average value of an autocorrelation function between two signals having a time difference of / 2, and 1 in an effective symbol section of the received signal due to the horizontal polarization.
Means for calculating an autocorrelation function between two signals having a time difference of / 2, and calculating an average value of a value obtained by multiplying the autocorrelation function by an inverse sign; calculating an argument from the two average values; An orthogonal polarization multi-carrier modulation / demodulation receiving apparatus, wherein a carrier frequency offset between transmission and reception waves is compensated for using an argument. 2. The invention according to claim 1, wherein the offset compensation operation of the carrier frequency controls the local oscillation frequency for intermediate frequency conversion or the local oscillation frequency for main carrier frequency conversion in accordance with the argument. ,
A receiving device of an orthogonal polarization multi-carrier modulation / demodulation system, characterized in that the receiving device is configured to be provided.