JP4883635B2 - Measuring apparatus, measuring method, and program - Google Patents

Description

  The present invention relates to a measuring apparatus, a measuring method, and a computer suitable for receiving an OFDM signal transmitted from the same transmitting location by a plurality of transmitting stations (typically broadcast stations) and obtaining a delay profile with high resolution. The present invention relates to a program that realizes these by using.

Conventionally, terrestrial digital broadcasting has adopted OFDM (Orthogonal Frequency Division Multiplex) communication that is resistant to multiple propagation such as multipath, and various techniques related to this have been proposed. Such a technique is disclosed in the following document.
Japanese Patent No. 3598371 Japanese Patent No. 3605638

  Here, in [Patent Document 1], in signal processing of OFDM communication, a plurality of signal points of a signal space diagram obtained by demodulation and a plurality of signal points of a signal space diagram plotted by the relative phase difference of the demodulated signal Is used to extract fluctuations in the signal space diagram, classify multiple signal points, determine areas in the signal space diagram where there is a high probability of information errors, and the signals contained in those areas Techniques have been proposed for excluding points from statistical processing.

  On the other hand, in [Patent Document 2], the entire band is divided into a plurality of segments, and a plurality of pieces of information having different transmission qualities are distributed to some of the plurality of segments and transmitted simultaneously, thereby providing a digital modulation having a hierarchical structure. The signal is separated for each layer, the characteristics of the transmission line are extracted from the signal of at least one layer, the equalization control information is generated using the extracted characteristic, and the signal of each signal separated into the layer by using this is generated. Techniques for equalization have been proposed.

  And the area where terrestrial digital broadcasting is provided is gradually expanded from metropolitan areas to all over the country.

  Here, in order to receive the broadcast wave from the transmitting station, it is necessary to satisfy the required electric field strength at the receiving point. However, in building shadows, indoors, underground spaces, etc., radio waves from the transmitting station do not propagate efficiently. For this reason, when the antenna installation height is low, such as a mobile object or a portable terminal type receiver, the received electric field strength is lowered, and the required electric field strength may not be obtained.

  Also, if the delay time difference between the arriving waves propagating from multiple paths is slight, depending on the phase relationship of the arriving waves synthesized at the receiving point, the power in the band may be reduced. Even if it exists, the area | region where an electric field strength becomes low will be scattered.

  In order to improve reception quality, there is a gap filler system that relays radio waves at a transmitting station. However, in order not to cause interference, it is necessary to accurately grasp the reception status of incoming broadcast waves.

However, in the current digital broadcasting, the channel width of a signal transmitted from a digital broadcasting station constituting one transmitting station is approximately 6 MHz, and the occupied bandwidth of the OFDM carrier is approximately 5.6 MHz. Therefore, when the delay profile is obtained using the signal transmitted from one transmitter station and the propagation characteristics are analyzed, the delay time resolution is 1 / 5.6 MHz = 0.17857 × 10 ^-6 s, which is converted to a path difference. Then, 3.0 × 10 ⁸ m / s / 5.6 MHz = 53.57 m.

  The distance resolution as described above is insufficient for analyzing indoor-scale propagation paths. Therefore, a method for acquiring a delay profile with higher resolution performance is strongly desired.

  On the other hand, in the current digital broadcasting, since different signals are transmitted from a plurality of transmitting stations, it is desirable to take this into account and use it.

  The present invention has been made to solve the above-described problems, and is a measurement apparatus suitable for acquiring a high-resolution delay profile by receiving OFDM signals transmitted from the same transmission location by a plurality of transmission stations. It is an object of the present invention to provide a measurement method and a program that realizes these using a computer.

  In order to achieve the above object, the following invention is disclosed in accordance with the principle of the present invention.

  The measuring apparatus according to the first aspect of the present invention receives OFDM signals transmitted from the same transmission location by a plurality of transmission stations, acquires a delay profile between the transmission location and the reception location, and Each of the OFDM signals transmitted by a plurality of transmitting stations has a known symbol time length and a known subchannel frequency interval, occupies different bands, and receives a receiving unit, a frequency converting unit, a symbol synchronizing unit, and a Fourier transform. Unit, a frequency deviation acquisition unit, a frequency correction unit, an individual profile acquisition unit, a symbol timing correction unit, and a connection profile acquisition unit, which are configured as follows.

  Here, the reception unit receives an observation signal observed at the reception location.

  On the other hand, the frequency conversion unit converts, for each of the plurality of transmission stations, an observation signal received using a modulation frequency and a carrier frequency set for the transmission station to a predetermined baseband frequency.

  Further, the symbol synchronization unit performs discrete time sampling of the observation signal frequency-converted for each of the plurality of transmission stations at a sampling period obtained by dividing the reciprocal of the subchannel frequency interval of the transmission station by N, and The symbol data included in the set symbol interval is extracted.

  The Fourier transform unit then performs Fourier transform on the symbol data extracted for each of the plurality of transmission stations to obtain subchannel symbols.

  On the other hand, the frequency deviation acquisition unit obtains a transfer function from known symbols included in the subchannel symbols acquired for each of the plurality of transmitting stations, and obtains a frequency deviation from the passage of time of the transfer function.

  Further, the frequency correction unit corrects the modulation frequency and the carrier frequency set for the transmission station until the frequency deviation obtained for each of the plurality of transmission stations converges to a minimum, and observes again in the frequency conversion unit. The frequency of the signal is converted, the symbol synchronization unit extracts symbol data again, the Fourier transform unit acquires the subchannel symbol again, and the frequency deviation acquisition unit calculates the frequency deviation again.

  Then, the individual profile acquisition unit obtains a complex delay profile from the subchannel symbols acquired for each of the plurality of transmission stations after frequency correction is performed for each of the plurality of transmission stations.

On the other hand, the symbol timing correction unit uses the complex delay profile obtained for any one of the plurality of transmission stations as the reference profile (C ₁ (m, τ)) for the plurality of transmission stations. For each of the stations, the phase difference between the complex corrected by the frequency difference between the occupied band of the transmitting station (i-th station) and the occupied band of the reference station and the complex delay profile obtained for the transmitting station is The symbol interval set for the transmission station is moved until convergence with respect to the delay time, the symbol synchronization unit extracts symbol data again, the Fourier transform unit acquires the subchannel symbol again, and the frequency deviation acquisition unit The frequency deviation is calculated again, the frequency correction unit corrects the frequency again, the individual profile acquisition unit acquires the reference profile again, and the phase difference The resulting unit to be re-acquired the phase difference.

  Further, the concatenated profile acquisition unit calculates a transfer function obtained from the subchannel symbol for each of the acquired subchannel symbols by the convergence value of the phase difference obtained for the transmitting station for the subchannel symbol. After correcting and concatenating all the corrected transfer functions, a complex delay profile is obtained.

  Further, in the measurement apparatus of the present invention, the symbol timing correction unit can be configured to correct the symbol section with a unit length smaller than the N division that is the reciprocal of the channel frequency interval of the transmission station.

  In the measurement apparatus of the present invention, the concatenated profile acquisition unit concatenates the transfer functions for all the acquired channel symbols by correcting the transfer functions to a predetermined channel frequency interval and a predetermined symbol time length, and the correction is performed. A complex delay profile can be obtained from all concatenated transfer functions.

  A measurement method according to another aspect of the present invention is a measurement apparatus that receives OFDM signals transmitted from the same transmission location by a plurality of transmission stations and acquires a delay profile between the transmission location and the reception location. Each of the OFDM signals transmitted by the plurality of transmitting stations has a known symbol time length and a known subchannel frequency interval, occupies different bands, and the measurement apparatus includes a receiving unit, A frequency conversion unit, a symbol synchronization unit, a Fourier transform unit, a frequency deviation acquisition unit, a frequency correction unit, an individual profile acquisition unit, a symbol timing correction unit, a connection profile acquisition unit, the measurement method includes a reception step, a frequency conversion step, Symbol synchronization process, Fourier transform process, frequency deviation acquisition process, frequency correction process, individual profile acquisition process, symbol timing correction process , A connecting profile acquisition step, which are configured as follows.

  That is, in the reception process, the reception unit receives an observation signal observed at the reception location.

  On the other hand, in the frequency conversion step, the frequency conversion unit converts, for each of the plurality of transmission stations, the observation signal received using the modulation frequency and the carrier frequency set for the transmission station into a predetermined baseband frequency. To do.

  Further, in the symbol synchronization step, the symbol synchronization unit performs discrete time sampling of the observation signal frequency-converted for each of the plurality of transmission stations at a sampling period obtained by dividing the reciprocal of the subchannel frequency interval of the transmission station by N, Symbol data included in the symbol section set for the transmitting station is extracted.

  In the Fourier transform process, the Fourier transform unit performs Fourier transform on the symbol data extracted for each of the plurality of transmitting stations to obtain subchannel symbols.

  On the other hand, in the frequency deviation acquisition step, the frequency deviation acquisition unit obtains a transfer function from the known symbols included in the subchannel symbols acquired for each of the plurality of transmission stations, and calculates the frequency deviation from the passage of time of the transfer function. Ask.

  Further, in the frequency correction step, the frequency correction unit corrects the modulation frequency and the carrier frequency set for the transmission station until the frequency deviation obtained for each of the plurality of transmission stations converges to a minimum, The frequency of the observation signal is again converted by the conversion unit, the symbol data is extracted again by the symbol synchronization unit, the subchannel symbol is acquired again by the Fourier conversion unit, and the frequency deviation is obtained again by the frequency deviation acquisition unit.

  Then, in the individual profile acquisition step, the individual profile acquisition unit obtains a complex delay profile from the subchannel symbols acquired for each of the plurality of transmission stations after the frequency correction is performed for each of the plurality of transmission stations. .

Further, in the symbol timing correction step, the symbol timing correction unit uses the complex delay profile obtained for any one of the plurality of transmitting stations as the reference profile (C ₁ (m, τ)). For each of the plurality of transmission stations, a complex correction of the frequency difference between the occupied band of the transmitting station (i-th station) and the occupied band of the reference station, and a complex delay profile obtained for the transmitting station The symbol interval set for the transmitting station is moved until the phase difference between and converges with respect to the delay time, symbol data is extracted again by the symbol synchronization unit, and subchannel symbols are acquired again by the Fourier transform unit. The frequency deviation acquisition unit to obtain the frequency deviation again, the frequency correction unit to correct the frequency again, and the individual profile acquisition unit to To obtain a semi-profile, thereby obtaining again the phase difference to the phase difference acquiring portion.

  Then, in the concatenated profile acquisition step, the concatenated profile acquisition unit, for each of all the acquired subchannel symbols, only the convergence value of the phase difference obtained for the transmitting station for the subchannel symbol, The transfer function obtained from (1) is corrected, and all the corrected transfer functions are concatenated to obtain a complex delay profile.

  Further, in the measurement method of the present invention, the symbol timing correction step can be configured to correct the symbol section with a unit length smaller than the N division of the reciprocal of the channel frequency interval of the transmission station.

  In the measurement method of the present invention, in the connection profile acquisition step, transfer functions for all acquired channel symbols are connected by correcting them to a predetermined channel frequency interval and a predetermined symbol time length, and the correction is performed. A complex delay profile can be obtained from all concatenated transfer functions.

  A program according to another aspect of the present invention causes various types of computers, for example, software radios that function as various types of wireless devices corresponding to the software by downloading the software, to function as each unit of the measurement device. Constitute.

  In addition, an information recording medium in which the program of the present invention is recorded can be distributed and sold independently from the computer such as the software radio. In addition, the program of the present invention can be transmitted, distributed, and sold via a computer communication network such as the Internet.

  In particular, when a computer such as the software radio has a programmable electronic circuit such as a DSP (Digital Signal Processor) or FPGA (Field Programmable Gate Array), the program recorded on the information recording medium of the present invention is wirelessly provided. Then, the data is transmitted to the computer, and the DSP or FPGA in the computer can execute this, so that the measuring apparatus of the present invention can be obtained.

  According to the present invention, a measuring apparatus, a measuring method, and a computer that are suitable for receiving OFDM signals transmitted from the same transmitting location by a plurality of transmitting stations and acquiring a delay profile with high resolution are realized using a computer. A program can be provided.

  An embodiment of the present invention will be described below. In addition, embodiment described below is for description and does not limit the scope of the present invention. Therefore, those skilled in the art can employ embodiments in which each or all of these elements are replaced with equivalent ones, and these embodiments are also included in the scope of the present invention.

  First, items to be considered in this embodiment are examined.

  First, the influence of inter-carrier interference cannot be ignored when the frequency shift is large as in mobile reception. However, when the difference in carrier frequency is about 1 Hz, the influence of inter-carrier interference can be ignored.

  Next, when a plurality of transmitting stations transmit signals from the same antenna (one transmission tower), they can be regarded as the same transmission point. On the other hand, at Tokyo Tower, each channel is transmitted from a different antenna, but if the distance to the reception point is sufficiently long, it can be regarded as radiation from the same transmission point.

  At this time, if the propagation path does not have a frequency characteristic limited to a specific frequency band, the transfer function is constant regardless of the channel frequency.

  Therefore, even if the transfer functions are obtained from mutually independent channels transmitted from different transmitting stations, a high correlation is established between the transfer functions.

  Therefore, in this embodiment, the resolution of the delay time is improved by connecting a plurality of adjacent channels and effectively expanding the observation band.

  Since each transmitting station transmits signals asynchronously with each other, in this embodiment, the transfer function is analyzed for each channel (for each transmitting station) for the received signal of the asynchronous channel, and then considered as a continuous band on the frequency axis. Concatenate the transfer functions.

  Once the transfer functions can be connected, a delay profile with improved resolution of the delay time can be obtained by performing a Fourier analysis on them in a lump.

The matter to be examined here is that the following situations occur because each channel is asynchronous.
(1) The frame timing is different.
(2) Symbol synchronization timing is different.
(3) A frequency difference remains in the synchronous circuit.

  First, in the current digital broadcasting, one frame consists of 204 symbols. Therefore, if the frame timing is different, the frame length becomes 204 symbols and becomes asynchronous.

  For example, in the current digital broadcasting, the time length of one symbol is common to each transmitting station and is 1.008 ms. Therefore, the maximum amount of frame deviation is 204 × 1.008 ms × 1/2 = 102.816 ms, and 103 ms. It will be about.

  Next, when the symbol synchronization timing is different, the absolute phase of the complex delay profile is different. And, if the symbol positions that are different from each other in the specific position of the main wave are shifted, the initial phase values of the plurality of delayed paths are different, and therefore, if the bands are simply connected, the channel phase continuity is lost. turn into.

  Further, when the frequency difference remains in the synchronization circuit, the information of the transfer function is rotated in phase by the period of the difference if the difference is small. Note that this difference can be removed by an equalizer.

  The details will be discussed below. FIG. 1 is a schematic diagram showing a schematic configuration of a measuring apparatus according to the present embodiment.

  FIG. 2 is a flowchart showing a control flow of measurement processing executed in the measurement apparatus according to the present embodiment. Hereinafter, a description will be given with reference to FIG.

  A measuring apparatus 101 according to the present embodiment includes a receiving unit 102, a frequency converting unit 103, a symbol synchronizing unit 104, a Fourier transform unit 105, a frequency deviation acquiring unit 106, a frequency correcting unit 107, an individual profile acquiring unit 108, and a symbol timing correcting unit. 109 and a linked profile acquisition unit 110.

  When the receiving unit 102 receives signals from a plurality of transmitting stations transmitted from the same position (step S201), the frequency converting unit 103 performs frequency conversion for each transmitting station (step S202).

  The symbol synchronization unit 104 performs discrete sampling at the cut-out positions for symbol synchronization for each transmission station (step S203), and the Fourier transform unit 105 performs fast Fourier transform for each transmission station (step S204).

  Then, the frequency deviation acquisition unit 106 obtains frame synchronization for each transmitting station (step S205), extracts SP (Scattered Pilot) (step S206), and obtains a transfer function of each subcarrier (step S207). The frequency deviation is obtained from the elapsed time (step S208).

  If the frequency deviation does not converge for any of the transmission stations (step S209; No), the frequency correction unit 107 performs frequency correction for the transmission station (step S210), and the process returns to step S202.

  Here, in the processing after returning to step S202, the processing of step S202 to step S208 may be repeated only for the transmitting station that has performed frequency correction. Therefore, the processing of the frequency conversion unit 103, the symbol synchronization unit 104, the Fourier transform unit 105, the frequency deviation acquisition unit 106, and the frequency correction unit 107 is typically performed independently for each transmitting station. .

  On the other hand, if the frequency deviation has converged for all transmission stations (step S209; Yes), the individual profile acquisition unit 108 obtains a delay profile for each transmission station (step S211).

  If the phase difference of another delay profile with respect to the delay profile of a certain reference station does not converge to a constant value (step S212; No), the symbol timing correction unit 109 causes the phase difference of the delay profile to converge. The cut-out position for symbol synchronization is corrected (step S213), and the process returns to step S203.

  On the other hand, if the phase difference of each delay profile has converged (step S212; Yes), the concatenated profile acquisition unit 110 concatenates the transfer functions corrected by the convergence value of the phase difference to obtain a delay profile (step S214). ).

  Hereinafter, each signal will be described with reference to the theoretical background.

(Transmission signal)
First, consider one transmitting station, that is, one channel. The transmission signal Q (t) at time t can be expressed as follows.
Q (t) = Re [Σ _{m = -∞} ^∞ g (t-mτ _s ) ・ Σ _{n = 0} ^N-1 {d (m, n) ・ r ・ exp (j 2π nf ₀ (t-mτ _s ) ) ・ Exp (j 2π (f _c + Δf _T ) t)}]

Here, for the one transmitting station,
m is the symbol number
n is the subcarrier number
N is the total number of subcarriers,
d (m, n) is the transmitted symbol
τ _s is the reciprocal of the subcarrier frequency interval,
Σ _{m = -∞} ^∞ g (t-mτ _s )
r is the amplitude,
f ₀ is the subcarrier frequency interval,
f _c is the carrier frequency,
exp (j 2π nf ₀ (t-mτ _s )) is the carrier frequency component
exp (j 2π (f _c + Δf _T ) t) is
Δf _T is the frequency difference
Each corresponds.

(Received signal)
Assuming that the arrival delay time is τ, the reception signal R (t) in the reception unit 102 for the transmission signal Q (t) rewrites t appearing in Q (t) to t−τ and considers the influence of the propagation path. And can be expressed as:
R (t) = Σ _{m = -∞} ^∞ g (t-τ-mτ _s ) ・ Σ _{n = 0} ^N-1 {d (m, n) ・ r ・ exp (j 2π nf ₀ (t-τ-mτ _s )) ・ exp (j 2π (f _c + Δf _T ) (t-τ)) ・ exp (jβ)} + Σ _{n = 0} ^N-1 {(A _n + jB _n ) ・ exp (j 2π (nf ₀ + f _c ) t)}

here,
β is the initial phase,
A _n + jB _n is the noise component,
Each corresponds.

Organize this,
R (t) = Σ _{m = -∞} ^∞ g (t-τ-mτ _s ) ・ Σ _{n = 0} ^N-1 {d (m, n) ・ r ・ exp (jβ) ・ exp (j 2π nf ₀ ( t-mτ _s )) ・ exp (j 2π (f _c + Δf _T ) t) ・ exp (-j 2π (nf ₀ + f _c + Δf _T ) τ)} + Σ _{n = 0} ^N-1 {(A _n + jB _n ) · exp (j 2π (nf ₀ + f _c ) t)}

  The R (t) is a signal that reaches the antenna of the receiving device (measuring device 101) from the transmitting station.

The received signal R (t) is theoretically an analog signal, but is digitally sampled at an appropriate time interval Δt _sample and the time-series data is stored in a storage device such as a hard disk. In the subsequent processing, if the time t is an integer multiple of Δt _sample , the sampled result is set as R (t), and if the time t is not an integer multiple of Δt _sample , appropriate interpolation is performed. R (t) is obtained. Various correction techniques such as linear interpolation / extrapolation and spline interpolation / extrapolation can be used for the interpolation.

(Frequency conversion)
Now,
exp (-j 2π f ' _c t)
S (t) can be expressed as follows, where S (t) is the result of frequency conversion unit 103 frequency-converting received signal R (t) to the baseband frequency.
S (t) = R (t) ・ exp (-j 2π f ' _c t)
= Σ _{m = -∞} ^∞ g (t-τ-mτ _s ) ・ Σ _{n = 0} ^N-1 {d (m, n) ・ r ・ exp (jβ) ・ exp (j 2π nf ₀ (t-mτ _s )) ・ Exp (j 2π (f _c + Δf _T ) t) ・ exp (-j 2π (nf ₀ + f _c + Δf _T ) τ)} ・ exp (-j 2π f ' _c t) + Σ _{n = 0} ^N-1 {(A _n + jB _n ) ・ exp (j 2π (nf ₀ + f _c ) t)} ・ exp (-j 2π f ' _c t)

Here, f ′ _c is a carrier frequency assumed on the receiving side, and is ideally equal to f _c . However, as described above, since a difference occurs in the frequency, it is actually necessary to perform frequency correction unlike f _c and f ′ _c .

_Assuming that the frequency correction value f _adj is obtained by the method described later, the result S ′ (t) obtained by performing further frequency correction on the S (t) is
S '(t) = S (t) ・ exp (-j 2π f _adj t)
Can be obtained as follows. The frequency correction is repeated until this difference is eliminated. After the correction is made, S ′ (t) is set as a new S (t) and used in the subsequent processing.

  As described above, if a slight frequency difference remains in the received signal after synchronous demodulation, the phase of the transfer function rotates by the amount of the frequency difference over time. Therefore, as will be described later, if the period variation of the transfer function is analyzed for each transmitting station and the reverse correction is performed as described above, the difference in frequency components can be matched for the asynchronous transfer function for each transmitting station. It is.

(Discrete time sampling)
When frequency conversion (frequency correction) is performed, the symbol synchronization unit 104 performs discrete time sampling. Discrete sampling is performed at time t = pτ _s + k / (N f ₀ ) −Δt. here,
p is the subcarrier number,
k is the sample point number of the data,
Δt is the correction value for the symbol cutout position.
Each corresponds.

  For Δt, an appropriate initial value is initially adopted, and the symbol timing is matched by updating to a more appropriate estimated value in the subsequent processing.

The result S (m, k) of the discrete sampling can be expressed as follows.
S (m, k) = Σ _{n = 0} ^N-1 d (m, n) ・ h '(m, k, n) + Σ _{n = 0} ^N-1 (A _n + jB _n ) ・ exp (j 2π nf ₀ (mτ _s + k / (N f ₀ ))

However,
h '(m, k, n) = r ・ exp (jβ) ・ exp (j 2π (nf ₀ + Δf) k / (f ₀ N)) ・ exp (j 2π (Δf m τ _s -nf ₀ + f _c + Δf _T ) t);
Δf = Δf _T -Δf _R
And
Δf _R is a component of frequency deviation on the receiving side.
Equivalent to.

  Although details will be described later, a method for simply correcting Δt will be described here. That is, any one of the plurality of transmission stations is set as a reference transmission station. Then, a precise complex delay profile is obtained from the transfer function of the reference transmitting station, and a method-like propagation path is obtained.

  Next, the frequency difference between the transmission station and the reference transmission station is corrected. If the channel bandwidth of each transmitting station is Bw and the difference between the transmitting station numbers (channel numbers) is ch, this frequency difference can be expressed as Bw · ch.

  Then, the corrected main path component and the complex delay profile phase component other than the reference transmission station are compared, and the symbol cutout position Δt is slid so that the variation in the phase difference is minimized. As a result, the relative phase difference between the transmitting stations is obtained.

  If these processes are repeated and the symbol cut-out position converges, this is the desired symbol timing.

  FIG. 3 is an explanatory diagram showing a range in which the symbol cutout position can be slid. Hereinafter, a description will be given with reference to FIG.

  As shown in the figure, a guard interval section (G) is arranged in front of an effective symbol section (Effect symbol) in the time direction, and the boundary between the two corresponds to k = 0. The ideal symbol period coincides with the effective symbol period, but the practical symbol period may slide to the guard inter buff period (G) by Δt. Δt is moved within the adjustable range of the symbol timing.

(Fast Fourier transform)
When discrete sampling is performed as described above, the Fourier transform unit 105 performs fast Fourier transform in order to convert the time-multiplexed symbol data S (m, k) into mapping data on the frequency axis. That is,
y (m, p) = (1 / N) Σ _{k = 0} ^N-1 S (m, k) ・ exp (-j 2π kp / N)

here,
p corresponds to a subcarrier number.

Now, if y (m, p) is expanded in detail,
y (m, p) = d (m, p) ・ h (m, p, p) + Σ _{n = 0, n ≠ m} ^N-1 d (m, n) ・ h (m, p, n) + N (m, l);
It becomes. here,
Σ _{n = 0, n ≠ m} ^N-1 d (m, n) · h (m, p, n) is the intersubcarrier interference term
N (m, p)
Each corresponds.

Because there are multiple propagations, assuming that there are P main path paths and i is the path path number,
h (m, p, n) = Σ _{i = 1} ^P w _i (p, n) ・ φ _i (p, n) ・ f (m)
Can be written as here,
w _i (p, n) is the amplitude fluctuation component of the i-th path,
φ _i (p, n) is the phase fluctuation component of the i-th path,
f (m) is the frequency vibration component,
Each is equivalent, and specifically, it can be written as follows.
w _i (p, n) = r _i · sin (πα _i (p, n)) / πα _i (p, n);
φ _i (p, n) = exp [(j π (np) f ₀ + Δf) / f ₀ ] ・ exp (jβ _i ) ・ exp [-j 2π (nf ₀ + f _c + Δf _T ) τ _i ] ;
f (m) = exp (j 2π Δf m τ _s );
α _i (p, n) = ((np) f ₀ -Δf] / f ₀

here,
β _i corresponds to the initial phase of the i-th path.

(Frame synchronization, SP extraction, transfer function)
If fast Fourier transform is performed and a received symbol y (m, p) in the time direction m and the frequency direction p is obtained, frame synchronization can be achieved.

  Each frame can be confirmed by reading a synchronization byte embedded in TMCC (Transmission Multiplexing Configuration Control), and the head position of the frame can be determined.

  Then, the position of the pilot signal arranged on each subcarrier in the transmitting station can be accurately extracted. In this embodiment, SP (Scattered Pilot) is adopted.

  FIG. 4 is an explanatory diagram showing how SPs are arranged. Hereinafter, a description will be given with reference to FIG.

  As shown in this figure, in addition to normal symbols (white circles in this figure), SPs (black circles in this figure) are dispersedly arranged in the time (Time; m) direction and frequency (Frequency; p) direction.

This SP value is known data d (m, p) at the time of transmission, and the transfer function at m, p where the SP is arranged can be calculated as follows.
g (m, p) = y (m, p) / d (m, p)

  For m and p in which SPs are arranged, the transfer function g (m) is obtained by performing one-dimensional interpolation in either the time axis direction or the frequency direction, or two-dimensional interpolation with respect to the two axis methods. , p).

(Frequency correction)
When g (m, p) is obtained for each transmitting station as described above, the frequency deviation for each transmitting station is obtained.

As described above, Fourier transform is performed using the obtained transfer function g (m, p). For the number of symbols L in the symbol interval, the result of Fourier transform is as follows.
G (m, n) = (1 / L) Σ _{k = 0} ^L-1 g (k, n) ・ exp (-j 2π kn / L)

When the peak of G (m, n) appears at a place other than n = 0, there is a frequency deviation. Therefore, in this case, using the value n _peak of n at this peak,
f _adj = n _peak / (τ _s L)
As shown, f _adj is calculated so as to cancel the frequency difference, and the frequency correction unit 107 corrects the frequency.
S (t) ← S (t) ・ exp (-j 2π f _adj t)
(← corresponds to a so-called substitution operation), and the processing after frequency conversion is performed again.

(Symbol timing correction)
Δt for each transmission station needs to be set so that the phase continuity of the delay profile of the adjacent transmission station is maintained.

  The transmitting station number (channel number) ch of each transmitting station is set as 0, 1, 2,..., S-1 in ascending order of frequency band to be used. Further, the transmission bandwidth (channel bandwidth) Bw of each transmission station is assumed to be constant.

  Then, the frequency difference of the transmission station of channel number ch with respect to the reference transmission station of channel number 0 is ch · Bw.

The complex delay profile of each transmitting station is represented by τ = 0, 1, ..., Nc-1, where Nc is the number of subcarriers of the transmitting station.
C (m, τ) = (1 / Nc) Σk _{= 0} ^Nc−1 g (m, k) · exp (−j 2π kτ / Nc);
Can be obtained as follows.

  The peak of this complex delay profile becomes the main path component.

In the following, it is assumed that the delay profile of the transmission station number ch is expressed as C _ch (m, τ).

The complex delay profile obtained by correcting the delay profile C ₀ (m, τ) of the reference station by the frequency difference at the time of connection to the transmitting station of the ch is
C ' ₀ (m, τ) = C ₀ (m, τ) ・ exp (-j 2π τ ch Bw / (f ₀ Nc)
Can be obtained as follows.

Therefore, the phase difference component of the chth transmitting station with respect to the 0th reference station is
θ _ch (τ) = angle [C ' ₀ (m, τ) * conj (C _ch (m, τ))]
It is required as follows. here,
angle (・) is an operation to calculate the argument of a complex number,
conj (・) is an operation to find a complex conjugate,
* Is a correlation calculation for m.

In general, for complex number z
| z | = | conj (z) | = (z conj (z)) ^1/2
For the complex numbers a (m, τ) and b (m, τ) with m and τ as parameters, the above correlation calculation is
a (m, τ) * b (m, τ) = | Σ _m a (m, τ) b (m, τ) | / [| Σ _m a (m, τ) | | Σ _m b (m, τ ) |];
a (m, τ) * b (m, τ) = | Σ _m a (m, τ) conj (b (m, τ)) | / [| Σ _m a (m, τ) | | Σ _m b ( m, τ) |]
Calculate as follows.

Assuming that τ _{ch at} which the complex delay profile peaks for the ch-th transmitting station is τ _ch , θ _ch (τ _ch ) is the phase difference component of the main path obtained for the transmitting station ch.

Therefore, each transmission station 1, 2 is set so that θ ₁ (τ ₁ ), θ ₂ (τ ₂ ), θ ₃ (τ ₃ ),..., Θ _S-1 (τ _S-1 ) converge to the same value. For each of, 3,..., The symbol cutout position is slid, the symbol timing is corrected, and redoing from symbol synchronization (discrete sampling). A calculation method such as a Newton method or a steepest descent method can be employed for sliding of the cutout position.

On the other hand, _once θ ₁ (τ ₁ ), θ ₂ (τ ₂ ), θ ₃ (τ ₃ ),..., Θ _S-1 (τ _S-1 ) converge to the same value, Correct only the phase difference.

That is, when the transfer function of the ch-th transmitting station is g (m, n),
θ _ch = (1 / Nc) Σ _{τ = 0} ^Nc angle [C ' ₀ (m, τ) * conj (C _ch (m, τ))];
And the corrected transfer function g ' _ch (m, n)
g ' _ch (m, n) = g _ch (m, n) exp (jθ _ch )
Get like.

(Band concatenation)
When correction is completed for each transmitting station, band concatenation is finally performed.

If Nw = Bw / f ₀ , Nw corresponds to the number of subcarriers. Also, in this embodiment, since it is assumed that the subcarriers of each transmitting station are adjacent, the transfer function after concatenation is
g _w (m, ch ・ Nw + n) = g _ch (m, n)
Can be written as

In essence, the value of g _w (·, ·) has a relationship like g _w (time, frequency), and the deviation is removed by symbol synchronization in the time direction and frequency synchronization in the frequency direction. From this, the transfer function g _w having a two-dimensional spread in an appropriate unit may be obtained. At this time, if the symbol length or subcarrier frequency interval is different, appropriate interpolation or extrapolation is performed.

Band-connected delay profiles with high resolution are for τ = 0, 1, ..., Nw · S-1.
C _w (m, τ) = (1 / (Nw ・ S)) Σ _{k = 0} ^{Nw ・ S-1} g _w (m, k) exp (-j 2π k τ / (Nw ・ S)
It can be calculated as follows.

  That is, the delay time resolution and distance resolution of the delay profile obtained from S transmitting stations are inversely proportional to the value S, and the resolution can be increased as the number of transmitting stations is increased.

As described above, once the signal is received via the antenna and the received data obtained by performing A / D conversion with a time length of 1 / (N · f ₀ ) or less is stored, the subsequent frequency conversion is performed. In addition, all the processes of the fast Fourier transform can be performed by known digital processing. Therefore, the measurement apparatus of the present invention can be realized by executing it with a digital signal processor or operating a program with a CPU.

  In the above embodiment, it is assumed that each transmitting station has the same subcarrier frequency interval, the number of subcarriers, and the symbol time length, and the transmission frequency bands of each transmitting station are adjacent to each other by the subcarrier frequency interval. In addition, if these conditions are not satisfied, after the transfer function for each transmitting station is obtained, the value at the required point is changed to appropriate interpolation or extrapolation (for example, linear interpolation / extrapolation or If it is obtained by spline interpolation / extrapolation), it is possible to connect to the same conditions.

  As described above, according to the present invention, a measurement apparatus, a measurement method, and a computer suitable for receiving an OFDM signal transmitted from the same transmission location by a plurality of transmission stations and acquiring a delay profile with high resolution. The program which implement | achieves these using can be provided.

It is a schematic diagram which shows schematic structure of the measuring apparatus which concerns on this embodiment. It is a flowchart which shows the flow of control of the measurement process performed in the measuring apparatus which concerns on this embodiment. It is explanatory drawing which shows the range which can slide a symbol cut-out position. It is explanatory drawing which shows a mode that SP is arrange | positioned.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Measuring apparatus 102 Receiving part 103 Frequency conversion part 104 Symbol synchronization part 105 Fourier transformation part 106 Frequency deviation acquisition part 107 Frequency correction part 108 Individual profile acquisition part 109 Symbol timing correction part 110 Connection profile acquisition part

Claims (7)

A measurement apparatus that receives OFDM (Orthogonal Frequency Division Multiplex) signals transmitted from the same transmission location by a plurality of transmission stations and obtains a delay profile between the transmission location and the reception location. Each of the OFDM signals transmitted by the transmitting station has a known symbol time length, a known subchannel frequency interval, occupies different bands,
A receiver for receiving an observation signal observed at the reception location;
For each of the plurality of transmission stations, a frequency conversion unit that converts the received observation signal into a predetermined baseband frequency using a modulation frequency and a carrier frequency set for the transmission station,
The frequency-converted observation signal for each of the plurality of transmitting stations is sampled in discrete time with a sampling period obtained by dividing the reciprocal of the subchannel frequency interval of the transmitting station by N, and a symbol interval set for the transmitting station A symbol synchronizer for extracting symbol data contained in
A Fourier transform unit that obtains subchannel symbols by Fourier transforming the extracted symbol data for each of the plurality of transmitting stations;
A frequency deviation acquisition unit that obtains a transfer function from a known symbol included in the acquired subchannel symbol for each of the plurality of transmission stations, and obtains a frequency deviation from the passage of time of the transfer function,
The modulation frequency and carrier frequency set for the transmitting station are corrected until the obtained frequency deviation converges to the minimum for each of the plurality of transmitting stations, and the frequency conversion unit converts the observation signal again. A frequency correction unit that causes the symbol synchronization unit to extract symbol data again, causes the Fourier transform unit to acquire subchannel symbols again, and causes the frequency deviation acquisition unit to obtain frequency deviation again,
After the frequency correction is performed for each of the plurality of transmission stations, an individual profile acquisition unit that obtains a complex delay profile from the subchannel symbols acquired for each of the plurality of transmission stations,
A complex delay profile obtained for any one of the plurality of transmitting stations (first station) is used as a reference profile, and for each of the plurality of transmitting stations, the occupied bandwidth of the transmitting station and the occupied bandwidth of the reference station The symbol interval set for the transmitting station is moved until the phase difference between the complex correction of the frequency difference between and the complex delay profile obtained for the transmitting station converges with respect to the delay time, The symbol synchronization unit extracts symbol data again, the Fourier transform unit acquires the subchannel symbol again, the frequency deviation acquisition unit obtains the frequency deviation again, the frequency correction unit corrects the frequency again, A thin profile that causes the individual profile acquisition unit to acquire the reference profile again and causes the phase difference acquisition unit to acquire the phase difference again. Le timing correction unit,
For each of the acquired subchannel symbols, the transfer function obtained from the subchannel symbol is corrected by the convergence value of the obtained phase difference with respect to the transmitting station for the subchannel symbol, and the correction is performed. And a connected profile acquisition unit that acquires a complex delay profile after connecting all the transfer functions. The measuring device according to claim 1,
The symbol timing correction unit corrects the symbol section with a unit length smaller than N division that is the reciprocal of the channel frequency interval of the transmission station. The measuring device according to claim 1 or 2,
The concatenated profile acquisition unit concatenates transfer functions for all the acquired channel symbols by correcting the transfer functions to a predetermined channel frequency interval and a predetermined symbol time length, and all the transfer functions connected after the correction. A measurement apparatus characterized by acquiring a complex delay profile from A measurement method executed by a measurement apparatus that receives an OFDM (Orthogonal Frequency Division Multiplex) signal transmitted from the same transmission location by a plurality of transmission stations and acquires a delay profile between the transmission location and the reception location The OFDM signals transmitted by the plurality of transmitting stations all have a known symbol time length and a known subchannel frequency interval, occupy different bands, and the measurement apparatus includes a receiving unit, A frequency conversion unit, a symbol synchronization unit, a Fourier transform unit, a frequency deviation acquisition unit, a frequency correction unit, an individual profile acquisition unit, a symbol timing correction unit, a linked profile acquisition unit,
A receiving step in which the receiving unit receives an observation signal observed at the receiving location;
A frequency conversion step in which the frequency conversion unit converts, for each of the plurality of transmission stations, the received observation signal into a predetermined baseband frequency using a modulation frequency and a carrier frequency set for the transmission station;
The symbol synchronization unit performs discrete-time sampling of the frequency-converted observation signal for each of the plurality of transmission stations at a sampling period obtained by dividing the reciprocal of the subchannel frequency interval of the transmission station by N, and A symbol synchronization process for extracting symbol data included in the symbol interval set in
A Fourier transform step in which the Fourier transform unit Fourier transforms the extracted symbol data for each of the plurality of transmitting stations to obtain subchannel symbols;
The frequency deviation acquisition unit obtains a transfer function from a known symbol included in the acquired subchannel symbol for each of the plurality of transmitting stations, and obtains a frequency deviation from the passage of time of the transfer function,
The frequency correction unit corrects the modulation frequency and the carrier wave frequency set for the transmission station until the obtained frequency deviation converges to a minimum for each of the plurality of transmission stations, and again returns to the frequency conversion unit. A frequency correction step of frequency conversion of the observation signal, causing the symbol synchronization unit to extract symbol data again, causing the Fourier transform unit to acquire subchannel symbols again, and causing the frequency deviation acquisition unit to obtain frequency deviation again;
After the frequency correction is performed for each of the plurality of transmission stations, the individual profile acquisition unit obtains a complex delay profile from the subchannel symbols acquired for each of the plurality of transmission stations,
The symbol timing correction unit uses a complex delay profile obtained for any one reference station (first station) of the plurality of transmission stations as a reference profile, and occupies the transmission station for each of the plurality of transmission stations. It is set for the transmitting station until the phase difference between the complex corrected by the frequency difference between the band and the occupied band of the reference station and the complex delay profile obtained for the transmitting station converges with respect to the delay time. The symbol interval is moved, the symbol synchronization unit extracts symbol data again, the Fourier transform unit acquires the subchannel symbol again, the frequency deviation acquisition unit calculates the frequency deviation again, and the frequency correction unit The frequency is corrected again, the individual profile acquisition unit is made to acquire the reference profile again, and the phase difference acquisition is performed. Symbol timing correction step of re-acquiring the phase difference section,
For each of all the acquired subchannel symbols, the concatenated profile acquisition unit obtains a transfer function obtained from the subchannel symbol by the convergence value of the obtained phase difference with respect to the transmitting station for the subchannel symbol. And a connected profile acquisition step of acquiring a complex delay profile after connecting all of the corrected transfer functions. The measurement method according to claim 4,
In the symbol timing correction step, the symbol section is corrected with a unit length smaller than N division which is the inverse of the channel frequency interval of the transmitting station. The measurement method according to claim 4 or 5, wherein
In the connection profile acquisition step, transfer functions for all the acquired channel symbols are connected to each other by correcting the transfer functions to a predetermined channel frequency interval and a predetermined symbol time length, and all the transfer functions connected after the correction are connected. A measurement method characterized by acquiring a complex delay profile from   A computer capable of receiving an OFDM (Orthogonal Frequency Division Multiplex) signal transmitted from the same transmission location by a plurality of transmission stations is caused to function as each part of the measurement apparatus according to any one of claims 1 to 3. Program to do.

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