JP2003046473A - Multicarrier signal receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress inter-symbol interference without deteriorating transmission efficiency so as to enhance the transmission quality. SOLUTION: Switches SW1, SW2 are thrown to the position A, a received parallel information signal is fed to an 8-DFT 23 to convert a time region into a frequency region, an equalizer 24 uses a pilot signal to estimate a transmission line to apply equalization processing to each signal point, and a demapping circuit 26 arranges the signal points again. Then a 2-DFT 271 converts an equalization processing output of the pilot signal into a time region, adders and subtractors 272 to 275 obtain a difference with each signal of a signal block on a time base of the received parallel information signal to obtain a noise component added to the received signal by signal delay through multi- path. Then the switches SW1, SW2 are thrown to the position B, the difference is made to be included in the parallel information signal to correct the signal on the time base and to eliminate the interference component by the multipath.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicarrier signal receiving apparatus used in a multicarrier transmission system for transmitting information such as digital audio broadcasting, digital television broadcasting and wireless LAN.

[0002]

2. Description of the Related Art In recent years, as a digital transmission method used in, for example, a digital television broadcasting system, a multi-carrier transmission method, particularly an OFDM (Orthogonal Freq.
quencyDivision Multiplex) has attracted attention. The OFDM multi-carrier transmission system is a system in which transmission data is divided into a certain number of data into a block signal, and each block signal is allocated to a large number of orthogonal carrier waves (subcarriers) and transmitted. . This system has a feature that the data transmission rate per carrier can be slowed down, so that it is resistant to ghosts, and the influence of transmission distortion can be reduced, so that waveform equalization processing can be simplified.

Regarding OFDM, for example, Kenichi Matsuo "Digital Broadcasting Technology" pp.135-144 (Tokyo Denki University Press) and John G. Proakis "Digital Communications,"
Third edition "pp.689-692 (McGraw-Hill, Inc.).

By the way, in the multi-carrier transmission system using OFDM or the like, even if a plurality of transmitting stations broadcast on the same channel, the received signal can be processed as a kind of ghost, so that the single frequency relay network ( It is known that SFN) can be constructed. In this case, broadcast waves from a plurality of transmitting stations arrive at the receiving point, causing multi-symbol interference due to multipath. Therefore, in the conventional multicarrier transmission system, a guard interval having a length corresponding to the allowable value of the multipath delay time is set between symbols, and intersymbol interference can be suppressed for multipaths within the guard interval period. .

However, the above intersymbol interference suppression method has a problem that the guard interval length becomes long and the transmission efficiency deteriorates in consideration of a long multipath delay time. Further, if the multipath delay time is longer than the guard interval time, the influence of inter-symbol interference cannot be avoided.

[0006]

As described above, in the conventional multicarrier transmission system, in order to suppress intersymbol interference, a guard interval of a length corresponding to a predetermined value of the multipath delay time is set between the symbols. However, if the long multipath delay time is taken into consideration, the guard interval length becomes long and the transmission efficiency deteriorates. Further, if the multipath delay time is longer than the guard interval time, the influence of inter-symbol interference cannot be avoided.

The present invention has been made to solve the above-mentioned problems, and it is possible to add a guard interval without adding a guard interval.
Alternatively, it is possible to suppress intersymbol interference even for a multipath delay time longer than the guard interval length, thereby providing a multicarrier signal receiving apparatus capable of improving transmission quality without degrading transmission efficiency. The purpose is to

[0008]

In order to achieve the above object, the present invention provides a signal block composed of a plurality of signal points into which a specific signal determinable on the receiving side is inserted at a predetermined interval. In the multicarrier signal receiving apparatus for receiving the multicarrier signal generated and transmitted by converting the signal on the frequency axis to the signal on the time axis by performing the inverse orthogonal transform, the received multicarrier signal Orthogonal transformation means for orthogonally transforming a signal block on the time axis into a signal block on the frequency axis, and in the signal block output from this orthogonal transformation means, transmission is performed based on the relationship between the specific signal and its fixed value. A transmission path characteristic estimating means for estimating a path characteristic and an inverse orthogonal transform of a specific signal corrected by the transmission path characteristic estimating means to convert a signal on a frequency axis into a signal on a time axis. An interference removing means for removing an interference component due to multipath from the signal on the time axis based on a difference value between the signal after the conversion and each signal of the signal block on the time axis of the received multicarrier signal. It is characterized by having.

In the multicarrier signal receiving apparatus having the above-mentioned structure, the signal block on the time axis is taken in, and after being converted into the signal block on the frequency axis by the orthogonal transform means,
The transmission path characteristics are estimated using a specific signal that can be determined on the receiving side, and the specific signal corrected based on this estimation result is subjected to inverse orthogonal transformation to be converted to a signal on the time axis. A difference value between the received multicarrier signal and each signal of the signal block on the time axis is obtained. This difference value corresponds to a noise component added to the received signal due to signal delay due to multipath. Therefore, by correcting the signal on the time axis based on the difference value, the interference component due to multipath can be removed. In this case, there is an effect that inter-block interference can be suppressed without using the guard interval.

As a concrete method of the interference removing means, the specific signal corrected by the transmission path characteristic estimating means is subjected to the inverse orthogonal transform, and the inverse orthogonal transform output of this specific signal and the received multicarrier signal on the time axis. The difference between the signal block and the signal that has undergone cyclic convolution is calculated, and based on this difference result, the signal that has undergone acyclic convolution among the signal blocks on the time axis of the received multicarrier signal has undergone cyclic convolution. To correct.

In the above configuration, preferably, the specific signals that can be determined on the receiving side are arranged at intervals of 2 ^N (N is a positive integer). This makes it possible to reduce the scale of the inverse orthogonal transform means on the receiving side.

As the specific signal, for example, a pilot signal whose amplitude and phase are known on the receiving side, or a signal having a higher error tolerance than other signals can be used.

Further, the multi-carrier signal includes hierarchical transmission information composed of a high priority layer having a wide signal point interval and a low priority layer having a narrow signal point interval, a high priority layer having a large amplitude and a low priority layer having a small amplitude. Hierarchical transmission information, consisting of
When the layered transmission information is composed of a high priority layer coded with a strong error correction code and a low priority layer coded with a weak error correction code or not error-correction coded, a determinable specification can be made on the receiving side. As the signal, a signal obtained by rearranging the reproduction data of the high priority layer can be used.

In the above structure, it is possible to use a guard interval together. In this case, it is possible to reduce the amount of calculation because interference cancellation processing is unnecessary for interference within the guard interval from the received multi-carrier signal before the input to the inverse orthogonal transform means. .

The conversion means and the inverse conversion means have the same L
Since it can be dealt with by SI code conversion or the like, it can be shared by time division processing.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 and 2 are block diagrams showing configurations of a transmitter and a receiver of an OFDM transmission system having eight subcarriers, respectively, as an embodiment of a multicarrier transmission system according to the present invention. . 1 and 2, the state of the signal block number n = 0 is shown, and each data of the transmitted information signal is 64QAM (Qu
adrature Amplitude Modulation) constellation.

The transmitting apparatus shown in FIG. 1 makes a block signal in units of six 64QAM data strings of a transmitted information signal, and a mapping circuit (MAP) 11 in parallel.
To enter. MAP11 is data 6 input in parallel
6 routes (C to C ₇ ) out of 8 routes (C to C ₇ )
₁ , C ₂ , C ₃ , C ₅ , C ₆ , C ₇ ) are sequentially allocated and output. A pilot signal generated by a pilot signal generation circuit (Pilot Signal Generator: PSG) 12 is assigned to the remaining two paths (C ₀ , C ₄ ). The output of MAP11 and PSG12 assigned to 8 pathway (C ₀ ~C ₇₎
Is an 8-point Inverse Discrete Fourier Transform
rete Fourier Transform: 8-IDFT) 13 and transforms the signal from the frequency domain into the time domain signal.

[0019] Eight parallel information signal output from the _{8-IDFT11 (c 0 ~c 7} ) is parallel - serial converter (Pa
rallel-Serial converter (PS) 14 converts the base-band serial multi-carrier symbols into a digital-analog converter (PS).
A transmitter (Tr) consisting of DA), amplifier, frequency converter, etc.
An ansmitter (TRA) 15 becomes a transmission signal in a predetermined frequency band and is transmitted to the transmission path.

The receiver shown in FIG. 2 comprises a frequency converter, an amplifier, and an analog-digital converter (Analog-Digital c).
Onverter: AD) (Receiver: RE)
C) 21 is provided. The receiver 21 receives a transmission signal sent through a transmission line, and acquires a baseband serial multicarrier symbol from the reception signal. This serial multi-carrier symbol is a serial-to-parallel converter (Se
It is converted by a rial-Parallel converter (SP) 22 into a parallel signal block consisting of eight data (v _{0 to} v ₇ ).

Of the respective data (v _{0 to} v ₇ ) of the parallel signal block obtained in SP22, the lower two outputs (v ₀ , v)
₁ ) is selectively through the switches SW1 and SW2, and the remaining 6 outputs (v _{2 to} v ₇ ) are directly connected to an 8-point Discrete Fourier Transform (8-DF).
T) 23 is supplied as a signal block (the 8-DFT input is (y ₀ to y ₇ )) and converted from the time domain signal to the frequency domain signal.

The eight parallel information signals (Y _{0 to} Y ₇ ) output from the 8-DFT 23 are supplied to the equalizer 24. For example, when n = 0, the equalizer 24 subtracts two pilot signals (Y ₀ , Y ₄ ) out of eight parallel information signals (Y _{0 to} Y ₇ ) that are input. SU
B1 and SUB2, and the difference with the pilot signal (C ₀ , C ₄ ) from the pilot signal generation circuit (PSG) 25 on the receiving side is obtained through the equalization circuits EQ0 and EQ4, and based on the result, etc. The parameters (g ₀ , g ₄ ) of the digitization circuits EQ0 and EQ4 are controlled. Estimates the channel characteristics from the output, based on the estimated result, six other parallel information signals _{(Y 1, Y 2, Y} 3, Y 5, Y 6, Y 7) for equalizer EQ1, Waveform equalization processing by EQ2, EQ3, EQ5, EQ6, EQ7 (parameters of each equalization circuit are set to (1 / g ₁ , 1,
/ g ₂ , 1 / g ₃ , 1 / g ₅ , 1 / g ₆ , 1 / g ₇ ))) to compensate for transmission distortion. The six parallel information signals that have been subjected to waveform equalization are de-mapping circuits (DM).
AP) 26 returns the original array of 64QAM and outputs as a parallel reproduction data string.

On the other hand, the respective outputs of the equalization circuits EQ0 and EQ4 are supplied to the interference elimination processing circuit 27. In the interference removal processing circuit 27, the signals from the equalization circuits EQ0 and EQ4 are two-point inverse discrete Fourier transformer (2-IDFT) 2
After being converted from the frequency domain to the time domain by 71, the signals are supplied to subtractors 272 and 273, respectively. One of the subtractors 272 has a (v ₂ , v
₄ , v ₆ ) The addition result of the output is supplied, and the other subtractor 2
73 includes (v ₃ , v ₅ , v of SP22 by the adder 275.
₇ ) The output addition result is supplied. Each subtractor 272, 2
The output of 73 serves as the other selection signal for the switches SW1 and SW2.

The processing operation of the above configuration will be described below.

First, in the transmitter shown in FIG.
The IDFT 13 outputs the n-th signal block C (n) = [C ₀ (n) C ₁ (n) ... C ₇ (n)] ^T in the frequency domain, which is composed of eight parallel information signals, to the n-th signal block in the time domain. signal block _{c (n) = [c 0} (n) c 1 (n) ... c 7 (n)] into a ^T. One signal block in this time domain is called a symbol. Where c _m (n) = 8 ^-1/2 (C ₀ (n) + α ^-m C ₁ (n) + α ^-2m C ₂ (n) +… +
α ^−7m C ₇ (n)) m = 0, 1, 2, ..., 7 and α = e ^{−j2π / 8} . Also, [] ^T represents the transpose of the block [].

In the present embodiment, for the 8-IDFT 13, eight elements C ₀ (n) ... C in the input block C (n) are used.
Of ₇ (n), it is assumed that pilot signals are assigned to C _i and C _{i + 4} (where i = n mod 4) and transmitted information signals are assigned to the remaining 6 elements. Therefore, the position of the pilot signal is as follows: when n = 0, when C ₀ (0), C ₄ (0) n = 1, when C ₁ (1), C ₅ (1) n = 2 , C ₂ (2), C ₆ (2) When n = 3, C ₃ (3), C ₇ (3) When n = 4, C ₀ (4), C ₄ (4) Move to. This pilot signal is used on the receiving side for estimating the channel response and compensating for the transmission distortion, and is allocated for each K = 2 ^h (where h is a natural number). The above example is for K = 4 = 2 ² .

Here, in the state of n = 0 shown in FIG.
The transmission data arranged in the 4QAM constellation is assigned to C ₁ (0) to C ₃ (0) and C ₅ (0) to C ₇ (0) by the MAP 11, and the pilot signal generated by the PSG 12 is
It is assigned to C ₀ (0) and C ₄ (0). In the drawings, (n) indicating the order is omitted. The same applies to the following description.

Eight parallel information signals c ₀ (n) to c ₇ (n) converted from the frequency domain to the time domain by the 8-IDFT 13
Is converted into a baseband serial multi-carrier symbol by the PS 14, and converted into a transmission signal in a predetermined frequency band by the TRA 15 and transmitted to the transmission path.

If there are multiple paths in the transmission path, samples will overlap in the received signal, causing interference between blocks, in other words, between symbols. In other words, due to the delay, a phenomenon occurs in which the nth block overlaps with the preceding (n-1) th block. For example, the delay is 2
For samples, c ₀ (n) overlaps with c ₆ (n-1) and c ₁ (n) overlaps with c
₇ (n-1) overlap. In addition, it overlaps after c ₂ (n), but it is n
Th is the overlap of the block, for example, c ₂ (n) to c ₀ (n)
Overlap, and c ₁ (n) overlaps c ₃ (n).

Next, in the receiving apparatus shown in FIG. 2, the receiver 21 receives the transmission signal sent through the transmission path, and acquires the baseband serial multicarrier symbol from this reception signal. This serial multicarrier symbol is converted into a parallel signal block v (n) = [v ₀ (n) v ₁ (n) ... v ₇ (n)] ^T by the SP 22. The element is degraded by the multipath characteristics of the transmission system.

Parallel signal block v (n) obtained in SP22
Of the elements v ₀ (n) ... v ₇ (n) of v ₀ (n), v ₁ (n) are selectively switched through the switches SW1 and SW2 to v ₂ (n) ... v ₇ (n). ) Is directly supplied to the 8-DFT 23 as a signal block.

Here, the input block y (n) = [y ₀ (n) y ₁ (n) ... y ₇ (n)] ^T of the 8-DFT 23 is defined, and the output block Y (n) = [Y ₀ (n) Y ₁ (n)… Y ₇ (n)] ^T is similarly defined. However, Y _k (n) = 8 ^-1/2 (y ₀ (n) + α ^k y ₁ (n) + α ^2k y ₂ (n) +… + α
^7k y ₇ (n)) k = 0, 1, 2, ...

When each of the switches SW1 and SW2 is connected to the A side and all the outputs of the SP22 are input to the 8-DFT 23, y _m (n) = v _m (n), m = 0, 1, ..., 7 Then, the output of the 8-DFT 23 becomes Y _k (n) = V _k (n), k = 0, 1, ... Here, if the parallel signal block v (n) = [v ₀ (n) v ₁ (n) ... v ₇ (n)] ^T output from the SP 22 is an input block of the 8-DFT 23, the output block V (n ) ＝ [V ₀ (n) V ₁ (n)… V ₇ (n)] ^T is V _k (n) ＝ 8 ^−1/2 (v ₀ (n) ＋ α ^k v ₁ (n) ＋ α ^2k v ₂ (n) ＋… ＋ α
^7k v ₇ (n)) k = 0, 1, 2, ..., 7 where α = e ^{−j2π / 8} .

V _k (n) (where k ≠ i, k ≠ i + 4, i =
When n mod 4) is directly input to the 64QAM DMAP 26 to reproduce data, the reproduction quality of the reproduced data is deteriorated. The reason is that the reception signal delayed from the original reception signal is added as additional noise due to the multipath characteristics of the transmission path, and interference occurs between blocks, in other words, between symbols.

Conventionally, in order to avoid this problem, a symbol which is a guard interval is inserted between symbols to remove interference. Therefore, the deterioration of the transmission efficiency is sacrificed. For example, the signal block _{[c0 (n) c 1 (} n) ... c 7
For (n)], [c
₆ (n) c ₇ (n)] is added to the beginning of the block and [c ₆ (n) c ₇ (n) c0
(n) c ₁ (n) ... c ₇ (n)] was being transmitted.

As described above, when c ₆ (n) and c ₇ (n) are inserted between the (n−1) th and nth blocks, when the delay is 2 samples, c ₀ (n) is c ₆ (n) overlap, and c ₁ (n) overlaps c ₇ (n). That is, the overlap of samples due to delay is a cyclic overlap within a block, in other words, a circular convolution. Due to the property of the DFT operation that the cyclic convolution of the time axis sample block is the multiplication of the complex number coefficient of each sample after the DFT transformation of the block, the effect of the transmission multipath delay is compensated by the multiplication of the complex number coefficient for the DFT output sample. be able to. The coefficient value to be multiplied is obtained by estimating the transmission path characteristic by observing the received pilot signal value. Therefore, conventionally, the influence of transmission multipath has been removed at the expense of deterioration of transmission efficiency.

On the other hand, the present invention reduces the influence of multipath by adding the interference removal processing circuit 27 to the receiving device side without using the guard interval. The technique used in the present invention will be described in detail below.

In this embodiment, the following properties of DFT are used.

First, the inputs D ₀ of the M points y ₀ (n), y ₁ (n),
y ₂ (n),…, y _M-1 (n) and output Y ₀ (n), Y ₁ (n), Y ₂ (n),…, Y
The relationship of _M-1 (n) is Y _k (n) = M ^-1/2 (y ₀ (n) + α ^k y ₁ (n) + α ^2k y ₂ (n) + ... + α
^{(M-1) ky} _M-1 (n)) k = 0, 1, 2, ..., M-1, where α = e- ^{j2π / M.} Next, N = M / K point DFT input z ₀ (n), z
₁ (n), z ₂ (n),…, z _M-1 (n) and output Z ₀ (n), Z ₁ (n), Z ₂ (n),
…, Z _M-1 (n), Z _h (n) = N ^-1/2 (z ₀ (n) + β ^h z ₁ (n) + β ^2h z ₂ (n) + ... + β
^{(N-1) h} z _N-1 (n)) h = 0, 1, 2, ..., N-1, where β = e ^{−j2π / N} = α ^k . Then, y _m (n), y _{m + N} (n), y _{m + 2N} (n),…, y
After preprocessing _{m + (K-1) N} (n), the relation with z _m (n) is defined as follows. z _m (n) ＝ K ^-1/2 (α ^mi y _m (n) ＋ α ^{(m + N) i} y _{m + N} (n) + α
^{(m + 2N) i} y _{m + 2N} (n) ＋… ＋ α ^{{(m + (K-1) N} i} y _{m + (K-1) N} (n)) m = 0,1,2, ..., N-1 i = 0,1,2, ..., K-1 At this time, z ₀ (n), z ₁ ( n), z ₂ (n),…, z _M-1 (n) is input to the DFT of N points, and its output Z ₀ (n), Z ₁ (n), Z ₂ (n),
…, Z _M-1 (n) is Y _{i + hK} (n) = Z _h (n) = N ^-1/2 (z ₀ (n) + β ^h z ₁ (n) + β ^2h z
₂ (n) + ... + β ^{(N-1) h} z _N-1 (n)) h = 0, 1, 2, ..., N-1. That is, the DFT values Y ₁ (n), Y ₂ (n), at the M point are
…, Y = M / K specific values of Y _M-1 (n) Y _{i + K} (n), Y
_{i + 2K} (n), Y _{i + 3K} (n), ..., Y _{i + (N-1) K} (n) is the signal when the preprocessed signal is input to the N-point DFT. It is shown that it is derived from the output.

In the above pretreatment, for example, when i = 0, z _m (n) = K ^-1/2 (y _m (n) + ym _{+ N} (n) + ym _{+ 2N} (n) + ... ＋ y
_{m + (K-1) N} (n)) m = 0, 1, 2, ..., N-1. The above processing is performed, for example, in Japanese Patent Laid-Open No. 10-2
No. 47889.

The features of the present invention will be described below.
The details will be described.

M = 8, N = 2, K = M / N = 4, i = 0
The case will be described. For the signal received through the transmission path, for the M = 8 DFT input block v (n) = [v ₀ (n) v ₁ (n) ... v ₇ (n)] ^T that has undergone SP processing, After the above pre-processing, u ₀ (n) = (v ₀ (n) + v ₂ (n) + v ₄ (n) + v ₆ (n)) / 2 u ₁ (n) = (v ₁ (n) Generates + v ₃ (n) + v ₅ (n) + v ₇ (n)) / 2. If N = 2 point DFT input block u (n) = [u ₀ (n) u ₁ (n)] ^T , the output block U (n) = [U ₀ (n) U ₁ (n)] ^T is , U _k (n) = 2 ^-1/2 (u ₀ (n) + β ^k u ₁ (n)), k = 0, 1 where β = e ^{-j2π / 2} , and U ₀ (n) = V ₀ (n) U ₁ (n) = V ₄ (n).

Here, for example, it is assumed that the maximum delay is two samples and v ₀ (n), v ₁ (n) are overlapped with the sample of the (n-1) th block. That is, v ₀ (n),
Suppose v ₁ (n) undergoes acyclic convolution and v ₂ (n),…, v ₇ (n) undergoes circular convolution. The procedure of this embodiment is
It is as follows.

(1) By connecting the switches SW1 and SW2 to the A side and observing the pilot signal of the DFT output of the block sequence, the transmission line estimated value g _k when the multipath of the transmission line is assumed to be circular convolution , k = 0, 1,…, 7 is calculated. Note that the actual transmission line response when the guard interval is not used is acyclic convolution, but the response estimated from the DFT output is an estimated value when circular convolution is assumed.

(2) C₀(n) and C_Four(n) is the pilot signal
Then V₀(n) and V_FourThe circular convolution on the (n) transmission path is
When set, the true value is V₀(n) ′ ＝ g₀C₀(n), V_Four(n) ′ ＝
g_FourC _Four(n).

(3) U ₀ (n) '= V ₀ (n)', U ₁ (n) '= V
₄ (n) ′ is subjected to two-point IDFT processing, and u ₀ ′ and u ₁ ′
To get Since v ₂ (n), ..., v ₇ (n) are originally circular convolutions, the following relation is obtained. u ₀ (n) '= (v ₀ (n)' + v ₂ (n) + v ₄ (n) + v ₆ (n)) / 2 u ₁ (n) '= (v ₁ (n)' + v ₃ (n ) ＋ v ₅ (n) ＋ v ₇ (n)) / 2 (4) Transforming the above equation, v ₀ (n) ′ ＝ 2 u ₀ (n) ′ − v ₂ (n) −v ₄ (n) − v ₆ (n) v ₁ (n) ′ = 2 u ₁ (n) ′ − v ₃ (n) −v ₅ (n) −v ₇ (n), and the first and Obtain a second sample.

The switches SW1 and SW2 are connected to the B side,
[v ₀ (n) ′, v ₁ (n) ′, v ₂ (n), v ₃ (n), v ₄ (n), v ₅ (n), v
₆ (n), v ₇ (n)] is input to the 8-point DFT and its output is V
Let _k (n) '(where k = 0, 1, ..., 7).

(5) V _k (n) '/ g _k (where k = 0, 1,
, 7) is input to the DAM of QAM to reproduce the data, the reproduction data is obtained in which the influence of multipath is removed. When i ≠ 0, generalized u _m (n) = 4 ^−1/2 (α ^mi v _m (n) + α ^{(m + 2) i} v _{m + 2} (n) + α is used as preprocessing.
^{(m + 4) i} v _{m + 4} (n) + α ^{(m + 6) i} v _{m + 6} (n)) m = 0,1 i = 0,1,2,3 is used.

As is clear from the above operation, the receiving apparatus of this embodiment can suppress the inter-symbol interference due to multipath by the interference canceling circuit 27 regardless of the guard interval, thereby lowering the transmission efficiency. It is possible to improve the signal quality without doing so.

In particular, in normal OFDM, IDFT and D
Although the FT is used only for generation and reception of a multicarrier signal, in the present embodiment, the IDFT and DFT are used not only for multicarrier processing but also for compensation of intersymbol interference due to multipath. As is well known, IDFT and DFT
Are realized by the same LSI and can be selected by software processing. Therefore, it can be shared by one chip, and the number of constituent parts can be slightly increased.

A detailed description will be given below with reference to FIGS. 3 to 5.

OFD when there is a guard symbol in FIG.
The transmission processing content in the M multipath environment is shown, and FIG. 4 shows the transmission processing content in the OFDM multipath environment when there is no guard symbol. In FIG. 3 and FIG. 4, the positions of the pilot signals are X _{0, n} and X _{4, n} , but in practice they change for each block. The maximum delay of multipath is assumed to be T / 4. Here, T represents one block length in the time domain. In FIG. 3, y _{6, n} , y _{7, n} are copied to the head of the nth symbol to form a guard symbol. The guard symbol length is T / 4.

In the absence of the guard symbol, the multipath path causes an acyclic convolution of the passed signal. In FIG. 3, the elements y _{0, n} to y _{7, n} of the block in the time domain undergo circular convolution due to the insertion of the guard symbol. g _{0 to} g ₇ are channel estimation values in the Fourier transform domain acquired using pilot signals over multiple blocks. g _i (i = 0 to 7) is obtained by learning over multiple blocks such that g _i X _{i, n} → Y _{i, n} when X _{i, n} is a pilot signal.

As a property of the discrete Fourier transform (DFT)
And the circular convolution in the time domain is the complex coefficient in the DFT domain.
There is a point that can be done by multiplication. Therefore, each element of the time domain
y_{0, n}~ Y_{7, n} Is assumed to be circularly convolved,
g₀ ~ G₇ Is derived. y_{0, n}~ Y_{7, n} Circular convolution
Received DFT value Y_{0, n} ~ Y_{7, n} And the equalization process
1 / g in theory₀ ~ 1 / g₇ Playback received signal X obtained by multiplying by_{0, n}′ 〜
 X_{7, n}′ Is the transmitted signal X _{0, n} ~ X_{7, n} Can be equal to
it can. Ie X_{i, n}′ → X_{i, n} (I = 0 to 7)
It However, in FIG. 3, the position X of the pilot signal is_{0, n} , X
_{4, n} Is known. Where the guard symbol insertion
There is a problem that the input deteriorates the transmission efficiency.

In FIG. 4, among the block elements in the time domain, y _{0, n} , y _{1, n} undergo a non-cyclic convolution, and y _{2, n} , y _{7, n} undergo cyclic convolution. y _{0, n} , y _{1, n} have undergone acyclic convolution, so they are obtained by multiplying the DFT values Y _{0, n} ~ Y _{7, n} by 1 / g ₀ ~ 1 / g ₇ in the equalization process. Playback received signal X _{0, n} ′
˜X _{7, n} ′ cannot be equal to the transmitted signal X _{0, n} ˜X _{7, n} . That is, X _{i, n} ′ ≠ X _{i, n} (i = 0 to 7)
Becomes In the present embodiment, y _{0, n} , y _{1, n} are modified so that they undergo circular convolution, so that X _{i, n} ′ → X _{i, n}
(I = 0 to 7).

FIG. 5 is a diagram schematically showing the processing procedure in the n-th block received through the multipath transmission line in the above embodiment.

In FIG. 5, among the block elements in the time domain, y _{0, n} , y _{1, n} are acyclic convolutions, and y _{2, n to} y _{7, n.}
Is undergoing a circular convolution. It is assumed that there are pilot signals (the transmission values of which are known and X _{0, n} and X _{4, n respectively} ) at the positions of Y _{0, n} and Y _{4, n} . Estimated value of transmission line at position Y _{0, n} , Y _{4, n} g ₀ ,,
It is assumed that g ₄ is obtained by learning over many blocks.

Here, the discrete Fourier transform (DFT) has the following properties. That is, D of 8 points from y _{0, n} to y _{7, n}
Z _{0, n} = (y _{0, n} + y _{2, n} + y _{4, n} + y _{6, n} ) / 2 z _{1, n} = (y _{1, where} FT is Y _{0, n} to Y _{7, n If} the two-point DFT of _n + y _{3, n} + y _{5, n} + y _{7, n} ) / 2 is Z _{0, n} , Z _{1, n} , Z _{0, n} = Y _{0, n} Z _1, There is a relationship of _n = Y _{4, n} .

Of the 8-point DFT values of y _{0, n} to y _{7, n} assuming that all of y _{0, n} to y _{7, n} have undergone circular convolution, Y _{0, n} , Y _{4, n} are From the pilot signal and the channel estimation value, g ₀ · X _{0, n} and g ₄ · X _{4, n} respectively. In the present embodiment, the procedure for modifying y _{0, n} , y _{1, n} so as to have undergone the cyclic convolution is as in (1), (2), and (3) below.

(1) With Z _{0, n} = g ₀ · X _{0, n} Z _{1, n} = g ₄ · X _{4, n} , two-point IDFT is executed to obtain the following equation. z _{0, n} = (y _{0, n} ＋ y _{2, n} ＋ y _{4, n} ＋ y _{6, n} ) / 2 z _{1, n} ＝ (y _{1, n} ＋ y _{3, n} ＋ y _{5, n} ＋ y _{7, n} ) / 2 (2) Since y _{2, n} , ~, y _{7, n} are originally subjected to circular convolution, y _{0, n} = 2 z _{0, n} −y _{2, n} −y _{4, n} −y _{6, n} y _{1, n = 2 z 1,} n -y 3, n -y 5, n -y 7, obtained from _{n y 0, n, y 1} , n is a assumed correction value and receiving the circulation convolution.

(3) y _{1, n} ,-, y in the above y _{0, n} , y _{1, n}
Y _{0, n} , ~, Y _{1, n} obtained by applying DFT to 8 points including _{7, n}
, The equalization coefficient 1 / g ₀ , ~, 1 / g ₇ determined from the channel estimation value
X _{0, n} ′, ~, X _{7, n} ′ obtained by multiplying by becomes the reproduction signal.

Also from the above description, the receiving apparatus of this embodiment can suppress inter-symbol interference due to multipath by the interference canceling circuit 27 regardless of the guard interval, and thereby the signal efficiency can be maintained without lowering the transmission efficiency. It is clear that quality can be improved.

The above correction is executed for each block.
The pilot position is (Y _{1, n} , Y _{3, n} ), (Y _{2, n} , Y _{6, n} ),
For a block of (Y _{3, n} , Y _{7, n} ), z _{0, n} , z _{1, n}
In addition to addition, the relation of y _{0, n to} y _{6, n} includes multiplication of a complex fixed coefficient.

By the way, in the above embodiment, the pilot signal is a signal whose signal value is fixed on the receiving side, but there is also a method of not using the pilot signal. For example, in hierarchical transmission of information, when information is divided into high-priority layer information and low-priority layer information for transmission, the high-priority layer information can be used.

That is, the high-priority layer always contains the most important information to be reproduced on the receiving side, and the low-priority layer has a low importance level, which is not necessarily reproduced on the receiving side. Contains information. For example, in video coding, high-priority information means synchronization information, control information, motion prediction information, and discrete cosine transform (DCT: Di).
It is a low frequency coefficient of screte Cosine Transform), and if this information is missing or mistaken, fatal problems such as undecodability may occur, so it is essential information for decoding. On the other hand, the low-priority information is a high-frequency coefficient of DCT or the like, and is information which is not incapable of decoding although the reproduction quality is somewhat deteriorated when information is lost during decoding.

As an example, the high-priority layer arranges the information data at a signal point of 4PSK (Phase Shift Keying), and the low-priority layer arranges the information data at 64QAM (Quadrature A).
mplitude Modulation) signal points are considered. At this time, as compared with 64QAM, 4PSK has a longer distance between signal points, so that even if the position of the received signal point is displaced due to noise or interference, the probability that information data can be correctly reproduced is high, but the transmission efficiency is poor. All information 4Q
Non-hierarchical transmission with PSK has the least transmission error, but the transmission efficiency is reduced. From this,
Hierarchical transmission can be said to be a method of increasing error tolerance of important data without significantly reducing transmission efficiency.

When this hierarchical transmission is applied to the present invention, the information of the low priority layer has a high probability of being able to correctly reproduce the data even in the presence of inter-symbol interference, so that the reproduced data is rearranged at the signal point of 4PSK. The generated signal can be used as a signal having a fixed signal value in the same manner as the pilot signal. In this case, the data whose reproduction quality is improved by the correction processing is the information of the high priority layer.

The above example is a case where the layers are arranged by the signal point arrangement, but the high priority layer increases the signal amplitude and the low priority layer decreases the signal amplitude. There is also a method to make it. Alternatively, the high-priority layer is coded with a strong error-correction code, and the low-priority layer is coded with a weak error-correction code. There is also a method of layering.

In the above embodiment, the guard interval is not inserted, but a predetermined guard interval is inserted for the purpose of suppressing inter-symbol interference caused by a signal arriving later than the guard interval length. It can also be used. In this case, a guard interval removing circuit is added to the front stage of the receiving circuit shown in FIG.

That is, in the conventional multicarrier transmission, in order to suppress intersymbol interference, a guard interval having a length corresponding to a predetermined value of the multipath delay time is set between symbols. Therefore, considering a long delay time, there is a problem that the guard interval length becomes long and the transmission efficiency deteriorates. On the other hand, in the present invention, since the interference removal processing is added, it is possible to improve the transmission quality without degrading the transmission efficiency for a multipath delay time longer than the guard interval length. Also,
In the interference elimination processing, since the discrete Fourier transformer originally provided in the receiving device is used as the discrete Fourier inverse transformer by the time division processing, there is also an advantage that the circuit scale does not need to be increased.

The present invention is not limited to OFDM, but can be applied to all multicarrier transmission systems. The transmission line may be wireless or wired, for example, ADSL.
(Asymmetric Digital Subscriber Line) can also be applied. Further, in addition to the discrete Fourier transformer and the inverse discrete Fourier transformer, other orthogonal transforming means such as DCT (Disc
This can be used in a circuit using rete cosine transform) or IDCT.

Further, the multi-carrier transmission system and the CDM
A (Code Division Multiple Access)
It is also considered to combine the transmission methods, but in this case, when the pilot signal is code-division-multiplexed and transmitted by the spread code, this can be used.

[0073]

As described above, according to the present invention, it is possible to suppress intersymbol interference without adding a guard interval or even for a multipath delay time longer than the guard interval length. It is possible to provide a multicarrier signal receiving apparatus that can improve transmission quality without degrading transmission efficiency.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a transmitter of a multicarrier transmission system to which the present invention is applied.

FIG. 2 is a block diagram showing the configuration of an embodiment of a multicarrier transmission / reception device according to the present invention.

FIG. 3 is a diagram showing the contents of transmission processing in an OFDM multipath environment when there is a guard symbol in the receiving apparatus shown in FIG.

FIG. 4 is a diagram showing the contents of transmission processing in an OFDM multipath environment when there is no guard symbol in the receiving apparatus shown in FIG.

FIG. 5 is a diagram schematically showing a processing procedure in an n-th block received through a multipath transmission line in the above embodiment.

[Explanation of symbols]

11 ... Mapping circuit (MAP) 12 ... Pilot signal generation circuit (PSG) 13 ... 8-point inverse discrete Fourier transformer (8-IDFT) 14 ... Parallel-serial converter (PS) 15 ... Transmitter (TRA) 21 ... Receiver (REC) 22 ... Series-parallel converter (SP) 23 ... 8-point discrete Fourier transformer (8-DFT) 24 ... Equalizer SUB1, SUB2 ... Subtractor EQ0 to EQ7 ... Equalization circuit 25 ... Pilot signal generation circuit (PSG) 26 ... Demapping circuit (DMAP) 27 ... Interference removal processing circuit 271 ... Two-point inverse discrete Fourier transformer (2-IDFT) 272, 273 ... Subtractor 274, 275 ... Adder SW1, SW2 ... Switch

Continued front page    F-term (reference) 5C021 PA66 PA67 PA73 PA83 SA11                       YA11 YC11                 5C063 AA01 AB03 AB05 AB15 AC01                       AC05 AC10 CA23 CA36 DA07                       DA13 DB10                 5K022 DD01 DD33                 5K067 AA03 CC10 HH21 HH22

Claims (10)

[Claims] 1. A signal block composed of a plurality of signal points into which a specific signal decidable on the receiving side is inserted at a predetermined interval is assigned to a plurality of carriers, and inverse orthogonal transformation is performed to obtain a time from a signal on a frequency axis. In a multi-carrier signal receiving apparatus for receiving a multi-carrier signal generated and transmitted by converting the signal on the axis, a signal on the frequency axis is obtained by orthogonally converting a signal block on the time axis of the received multi-carrier signal. Orthogonal transforming means for transforming into a block; transmission path characteristic estimating means for estimating a transmission path characteristic from the relationship between the specific signal and its determined value in a signal block output from the orthogonal transforming means; The specific signal corrected by the estimating means is subjected to inverse orthogonal transformation to convert the signal on the frequency axis to the signal on the time axis, and the converted signal and the received multicarrier signal A multicarrier signal receiving apparatus comprising: an interference removing unit that removes an interference component due to multipath from the signal on the time axis based on a difference value from each signal of the signal block on the time axis. 2. The interference removing means includes an inverse orthogonal transforming means for performing an inverse orthogonal transform on the specific signal corrected by the transmission path characteristic estimating means, a signal output from the inverse orthogonal transforming means, and the received multicarrier signal. Of the signal blocks on the time axis of the received multi-carrier signal based on the calculation result of the difference calculation means for calculating the difference between the signal block on the time axis of the The multicarrier signal receiving apparatus according to claim 1, further comprising a correction unit that corrects a signal that has undergone non-circular convolution as if it had undergone cyclic convolution. 3. The specific signal is 2 ^N (N is a positive integer)
The multicarrier signal receiving device according to claim 1, wherein the multicarrier signal receiving devices are arranged at intervals. 4. The multicarrier signal receiving apparatus according to claim 1, wherein the specific signal is a pilot signal whose amplitude and phase are known on the receiving side. 5. The multicarrier signal receiving apparatus according to claim 1, wherein the specific signal is a signal having a higher error resistance than other signals. 6. When the multi-carrier signal is hierarchical transmission information composed of a high priority layer having a wide signal point interval and a low priority layer having a narrow signal point interval, the specific signal decidable on the receiving side is: The multicarrier signal receiving apparatus according to claim 1, wherein the reproduced data of the high priority layer is a rearranged signal. 7. When the multi-carrier signal is hierarchical transmission information composed of a high-priority layer having a large amplitude and a low-priority layer having a small amplitude, the specific signal decidable at the receiving side is the high-priority signal. The multicarrier signal receiving apparatus according to claim 1, wherein the reproduction data of the layer is a rearranged signal. 8. The hierarchical transmission information, wherein the multi-carrier signal is composed of a high priority layer coded with a strong error correction code and a low priority layer coded with a weak error correction code or not error correction coded. The specific signal decidable at the receiving side is a signal obtained by rearranging the reproduction data of the high-priority layer at a certain time.
The multi-carrier signal receiving device described. 9. When a guard interval is set between signal blocks of the multicarrier signal, a guard interval removing means is provided for performing a guard interval removing process from the received multicarrier signal before inputting to the orthogonal transforming means. The multicarrier signal receiving device according to claim 1. 10. The multicarrier signal receiving apparatus according to claim 1, wherein the orthogonal transforming unit and the inverse orthogonal transforming unit are shared by time division processing.