RU2433568C2 - Radio communication method, base station and user terminal - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: in a radio communication system, each of user terminal together with transmitting a data signal to a base station using different data transmission band frequencies which are assigned by a base station, performs time-division multiplexing of a pilot signal with the data signal and transmits the resulting signal to the base station. A resource management unit of the base station determines pilot signal transmission bands for each user terminal so that the pilot signal transmission band covers the data transmission band for each user terminal with frequency offset, and instructs the user terminal to transmit pilot signals using the determined pilot signal transmission band frequencies. That way, the base station can estimate channel for each frequency of the data transmission band using the pilot signal.

EFFECT: increase in throughput via adaptive change of the modulation technique.

22 cl, 28 dwg

Description

Technical field

The present invention relates to a radio communication method, its base station and a user terminal, and in particular, to a radio communication method, its base station and a user terminal in a radio communication system in which each user terminal uses different base band frequencies assigned by the base station for transmitting data signals to this base station, multiplexes the pilot signals with data signals according to the time division multiplexing scheme and transmits the resulting signal the base station.

State of the art

In a radio communication system, such as a cellular system, the receiving party typically uses a known pilot signal to perform timing synchronization and estimate the propagation path (channel estimate), and based on each of these operations performs data demodulation. Moreover, in an adaptive modulation method that provides the ability to improve throughput by adaptively changing the modulation method or coding rate according to the quality of the channel, the receiving side also uses the pilot signal in channel estimation, for example, to estimate the Signal to Noise Ratio, SIR) to determine the optimal modulation method or optimal coding rate.

As a radio access method that is resistant to selective frequency fading due to the presence of multiple propagation channels for broadband radio communications, the Orthogonal Frequency Division Multiplexing (OFDM) method is used. Nevertheless, from the point of view of the terminal’s energy efficiency, there is a problem in that the Peak to Average Power Ratio (PAPR) of the transmission signal is of great importance, and, accordingly, OFDM is not suitable as a transmission method for uplink communication. Therefore, in next-generation cellular systems according to the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard, uplink transmission uses single-carrier transmission where the receiving side performs equalization frequency (see 3GPP document TR25814-700 Fig. 9.1.1-1). Single-carrier transmission means that the transmission data and pilot signals are multiplexed only on the time axis, and when compared with the OFDM method, according to which the data and pilot signals are multiplexed on the frequency axis, it is possible to significantly reduce the PARR.

Single Carrier Transmission

FIG. 23 is an example of a frame format for transmission on a single carrier, and FIG. 24 is a diagram illustrating frequency alignment. The frame contains DATA data and PILOT pilots, each of which contains N samples and which are time-multiplexed, moreover, according to the illustration in Fig. 23, two blocks of pilot signals are inserted into one frame. When performing frequency equalization, the data / pilot separation unit 1 separates the DATA data and the PILOT pilots, and the first Fast Fourier Transform (FFT) unit 2 performs FFT processing on N data samples to generate N frequency components, and enters the result into the channel compensation block 3. The second FFT unit 4 performs FFT processing on N pilot samples to generate N frequency components, and the channel estimator 5 uses these N frequency components of the known pilot to estimate channel characteristics for each frequency, and inputs a channel compensation signal to the block 3 channel compensation. A channel compensation unit 3 multiplies N frequency components that were output from the first FFT unit 2 with a channel compensation signal for each frequency to perform channel compensation, and an Inverse Fast Fourier Transform (IFFT) unit 6 performs IFFT processing N channel-compensated frequency components converts this signal into a temporary signal and outputs the result.

CAZAC sequence

When transmitting on a single carrier, when the receiving side performs frequency equalization in order to improve the accuracy of channel estimation in the frequency domain, it is desirable that the pilot signal has a constant amplitude in the frequency domain, i.e., autocorrelation after an arbitrary cyclic time shift is '0'. On the other hand, when considering the PAPR aspect, it is desirable that the pilot also has a constant amplitude in the time domain. The sequence that allows these features to be implemented is the Constant Amplitude Zero Auto Correlation (CAZAC) sequence, and the use of CAZAC sequences as uplink pilot signals is defined in the 3GPP LTE system. The CAZAC sequence has ideal autocorrelation properties, so that the pilot signals obtained by cyclically shifting one CAZAC sequence are orthogonal to each other. The 3GPP LTE system adopts a method of using CAZAC sequences with different cyclic shift values to multiplex pilot signals from different users or to multiplex pilot signals from the same user transmitted from different antennas, and this method is called Code Division Multiplexing Multiplexing, CDM).

The Zadoff-Chu sequence, which is a CAZAC type sequence, is expressed according to Equation (1) (see BM Popovic, "Generalized Chirp-Like Polyphase Sequences with Optimum Correlation Properties", IEEE Trans. Info. Theory, Vol. 38, pp. 1406 -1409, July 1992).

Here, k and L are primes and express the sequence number and sequence length, respectively. Moreover, n represents the character number, q is an arbitrary integer, and L% 2 is the remainder when divided by 2 and can be denoted as Lmod (2). If we take the following factorization of L into prime numbers

(g₁ является простым числом), то количество последовательностей CAZAC может быть задано следующим уравнением

(g ₁ is a prime number), then the number of CAZAC sequences can be given by the following equation

More specifically, in the case where L = 12, L = 12 = 2 ² × 3 ¹ , then g ₁ = 2, e ₁ = 2, g ₂ = 3 and e2 = 1, and according to Equation (3) the number of sequences ( CAZAC sequences) becomes 4. Therefore, the number of sequences increases as L increases and the number of simple coefficients decreases. In other words, in the case when L is a prime number, the number ϕ (L) of CAZAC sequences becomes (L-1).

ZC _k (nc), for which in the CAZAC sequence ZC _k (n) only c cyclically shifts, is expressed as follows:

As shown in Equation (5) below,

The correlation R (τ) between ZC _k (n) and ZC _k (nc) becomes equal to '0' at any point except for the point where τ = c, so the sequences that are obtained by applying different values of the cyclic shift to the main sequence ZC _k (n) become orthogonal with respect to each other.

When a base station receives a plurality of pilots that are multiplexed by CDM using a cyclic shift, by correlating with the main sequence, pilots can be separated based on the locations where the peaks are generated. The ability to withstand multiple channel shifts or receive clock shifts decreases as the cyclic shift interval narrows, so there is an upper limit to the number of pilot signals that can be multiplexed by the cyclic shift. When the number of pilot signals that are multiplexed by a cyclic shift is taken to be P, the cyclic shift value c _p that is assigned to the pth pilot signal can be determined, for example, by the equation below (see 3GPP R1-060374, " Text Proposal On Uplink Reference Signal Structure ", Texas Instruments).

(6)

(6)

As described above, in the 3GPP LTE uplink, the pilots and data are multiplexed in a time division multiplexed manner and transmitted in a Single Carrier-Frequency Division Multiple Access (SC-FDMA) manner. 25 is a diagram illustrating the structure of an SC-FDMA transmission block, where 7 'is a N _TX Discrete Fourier Transform (DFT) block, 8' is a subcarrier mapping block, 9 'is a Reverse Discrete block The Inverse Discrete Fourier Transform (IDFT) of dimension N _FFT , 10 is a Cyclic Prefix, CP insertion unit. In 3GPP LTE, to reduce the amount of processing, the N _FFT is an integer equal to some power of 2, and the IDFT, after subcarrier mapping, is replaced by IFFT.

The process of adding a cyclic shift c to the main sequence ZC _k (n) can be performed either before the DFT or after the IFFT. When this process is performed after IFFT, the cyclic shift may have a value of c x N _FFT / N _TX samples. Essentially, the process is the same, respectively, in the following, an example is described in which the cyclic shift process is performed before the DFT.

Problems with the Related Art

To reduce inter-cell interference, it is necessary to reuse CAZAC sequences with different numbers as pilot signals between cells. The reason for this is that as the number of repetitions increases, the distance between cells that use the same sequence increases, so that the likelihood of serious interference is reduced. Therefore, the need arises to support a large number of CAZAC sequences, and to provide good performance for CAZAC sequences, it is desirable to use the length L of the sequence, which is a large prime number. 26 is a diagram illustrating inter-cell interference, where in case (A), when the number of CAZAC sequences that can be used is 2, CAZAC sequences (ZC ₁ ) with the same sequence number are used in adjacent cells, so that between adjacent cells cause serious interference. Moreover, in case (B), when the number of CAZAC sequences used is 3, CAZAC sequences with the same sequence number are not used, however, the number of repetitions is 3, which is small, so that the distance between cells that use CAZAC sequences with the same sequence number, is of little importance, and there is a high likelihood of interference between adjacent cells. In case (C), when the number of CAZAC sequences is 7, the number of repetitions is 7, which is a lot, and, accordingly, the distance between cells that use CAZAC sequences with the same number becomes large, and the probability of interference is gradually reduced.

In this regard, it can be noted that according to the 3GPP LTE description trend, the number of subcarriers occupied by data is taken to be a multiple of 12, and the subcarrier interval for pilot signals is taken to be twice the data interval to increase transmission efficiency, as shown in case (A) with Fig.27. In this case, when the length L of the CAZAC sequence is 6, the number of sequences ϕ (L) becomes 2 (k = 1.2), and CAZAC sequences with the same number are used, so that interference occurs between adjacent cells due to pilot signals. Moreover, when the length L of the sequence is taken equal to 5, then ϕ (L) becomes 4 (k = 1,2,3,4), which is still small, however, as shown in (B) of FIG. 27, there are subcarriers that are not covered by the pilot, so that channel estimation accuracy is reduced.

Therefore, it is assumed that by increasing the transmission bandwidth for the pilot signals to a value that is larger than the transmission bandwidth for the data, and by performing the transmission, a sufficient length L of the sequence can be provided (see 3GPP R1-060925, R1-063183). Fig. 28 illustrates an example of a case where the number of multiplexed pilot signals is 2. If the length L of the sequence is taken to be 12, then according to equations (2) and (3), the number of CAZAC sequences is only 4, and the inter-cell interference becomes large (k = 4 ) Therefore, the length L of the sequence is chosen equal to a prime number 11. When L = 11, then ϕ (L) is 10 and 10 CAZAC sequences (k = 1 ~ 10) can be used, so it is possible to reduce intercell interference. The length L of the sequence cannot be 13 or more. The reason for this is that when the length L of the sequence is 13 or more, interference occurs between adjacent frequency ranges.

Pilot signals from different users are multiplexed by the CDM method by cyclic shift. In other words, the CAZAC sequence ZC _k (n), which has a length L = 11 and for which cyclic shift c ₁ was performed, is used as a pilot signal for user 1, and the CAZAC sequence ZC _k (n), for which there was performed cyclic shift c ₂ is used as a pilot signal for user 2.

However, when the CAZAC sequence ZC _k (n) with a length L = 11 is cyclically shifted and used for users 1, 2, then, as can be clearly seen in FIG. 28, the relationship between the transmission frequency band for pilot signals and the frequency the data bandwidth is different for user 1 and for user 2, so the accuracy of channel estimation is different. In other words, the sub-carriers 23, 24 of the transmission frequency band for user 2 are different from the transmission frequency band for pilot signals, and the channel estimation accuracy for these sub-carriers is reduced.

As shown in FIG. 28, according to current 3GPP LTE specifications, the pilot subcarrier interval is equal to twice the data subcarrier interval. However, the above problem arises even when the ratio of the subcarrier intervals changes.

In view of the above problems, it is an object of the present invention to provide an accurate estimate of a channel of data subcarriers that deviate from the pilot transmission frequency band.

Another objective of the present invention is the ability to accurately estimate the channel subcarriers assigned to each user, even when a given sequence (for example, the CAZAC sequence ZC _k (n)), for which a cyclic shift by different values was performed, is used as user pilot signals to be multiplexed.

Another objective of the present invention is to enable accurate channel estimation by separating pilot signals for each user, using a simple method, even when a given CAZAC sequence for which a cyclic shift by different values has been performed is used as user pilot signals that are required multiplex.

Another objective of the present invention is to increase the accuracy of the channel estimation of the user data subcarriers, even if the propagation path is poor for that user.

Disclosure of invention

The present invention is a radio communication method, a base station and a user terminal in a radio communication system in which each user terminal, together with transmitting a data signal to the base station, using different data band frequencies that are assigned by the base station, performs multiplexing of the pilot signal with the data signal according to the time division multiplexing scheme and transmits the resulting signal to the base station.

Radio communication method

The radio communication method of the present invention comprises: a step of determining a pilot transmission band for each user terminal so that the pilot transmission band covers the data band of this user terminal with a frequency offset; and the step of instructing each user terminal to transmit a pilot using the frequencies of said specific pilot transmission band.

The step of issuing the command comprises: a step of calculating the frequency offset value for each user terminal and the cyclic shift value for the CAZAC sequence corresponding to the number of multiplexed user terminals and the frequency offset value; and the step of instructing each user terminal to cyclic shift the CAZAC sequence used as the pilot signal by the calculated cyclic shift amount, and instructing the user terminal to frequency shift said pilot transmission band by the calculated frequency offset amount.

The radio communication method further comprises: a step of summing the frequency components of a portion of the pilot signals that do not overlap when the base station has received multiplexed pilot signals that have been transmitted from a plurality of user terminals; the step of multiplying the combination of the summation result and the received multiplexed pilot signals with a copy of the pilot signal in the frequency domain; and the step of converting the results of multiplying the copy into a time-domain signal and, further, separating a portion of the signal of a given user terminal from the time-domain signal and performing channel estimation.

The radio communication method of the present invention, furthermore, comprises: a step of obtaining a state of a distribution path of user terminals; and the step of assigning, as a matter of priority, the middle band from the entire data band as a data band for a user terminal with a poor state of the propagation path, and notifying the user terminals. Alternatively, the radio communication method of the present invention further comprises: performing stepwise control by periodically assigning a middle band and an end band of the entire data band as data bands for user terminals.

Base station

The base station of the present invention comprises a resource control unit that determines a pilot transmission band for each user terminal so that this pilot signal band covers the data band of this user terminal with a frequency offset, and instructs the user terminal to transmit the pilot using the frequencies of said specific pilot transmission band.

In the base station, the resource control unit comprises: a cyclic shift amount calculating unit that calculates a frequency offset value for each user terminal and a cyclic shift value for a CAZAC sequence that corresponds to the number of multiplexed user terminals and the frequency offset value; and a command issuing unit, which, together with issuing a command to each user terminal to perform a cyclic shift of said CAZAC sequence used as a pilot signal by the calculated amount of cyclic shift, instructs the user terminal to perform frequency offset of the pilot signal by the frequency offset value.

The base station further comprises a channel estimating unit that performs channel estimation for each user terminal, the channel estimating unit comprising: a receiving unit that receives multiplexed pilot signals that are transmitted from a plurality of user terminals; a summing unit that summarizes the frequency components of the pilot portion of the signals that do not overlap; a copy multiplier unit that multiplies a combination of the summation results and the received multiplexed pilot signals with a copy of the pilot signal in the frequency domain; a conversion unit that converts the result of multiplying the copy into a time-domain signal; a separation unit that separates a portion of the signal of each user terminal from the time domain signal; and an estimator that converts the separated time-domain signal to a frequency-domain signal to estimate the channel of each frequency.

The resource control unit obtains the distribution states of the user terminals and, as a matter of priority, designates the middle band of the entire data transmission band as the data band for the user terminal with a poor distribution path state, and notifies the user terminals. Alternatively, the resource control unit performs hopping by periodically assigning a middle band and an extreme band from the entire data band as data bands for user terminals.

User terminal

The user terminal of the present radio communication system comprises: a receiving unit that receives uplink resource information from the base station; and a pilot generation unit that generates a pilot according to a command in uplink resource information; wherein the pilot signal generating unit comprises: a CAZAC sequence generating unit, which, based on the resource information, generates a CAZAC sequence with a predetermined sequence length and sequence number as a pilot signal; a first conversion unit that converts the CAZAC sequence, which is a time-domain pilot, to a frequency-domain pilot; a subcarrier display unit that performs mapping of the pilot subcarrier components based on frequency offset information that is part of the resource information; a second conversion unit that converts the pilot with the mapped subcarriers into a time domain signal; and a cyclic shift unit that performs a cyclic shift of the CAZAC sequence based on the amount of cyclic shift that is part of the resource information, either before the first conversion or after the second conversion.

Brief Description of the Drawings

1 is a diagram illustrating a first principle of the present invention;

2 is a diagram illustrating a second principle of the present invention;

3 is a diagram illustrating a third principle of the present invention;

4 is a diagram illustrating a process for generating a pilot signal at a transmitting side, which enables frequency offset d of subcarriers and cyclic shift (c ₂ -s (k, d, L));

5 is a diagram illustrating an offset performed by a subcarrier mapping unit;

6 is a diagram illustrating a channel estimation process at a receiving side;

7 is a diagram illustrating a second pilot signal generation process;

8 is a diagram illustrating a copy method in a transmitter;

9 is a diagram illustrating a second channel estimation process at a receiving side;

10 is a diagram illustrating a frame configuration;

11 is a diagram illustrating a method of separating a pilot signal;

12 is a diagram illustrating a third channel estimation process at a receiving side;

13 is a diagram of a structure of a mobile station;

Fig - structural diagram of the block generating the pilot signal;

15 is a diagram of a structure of a base station;

Fig. 16 is a structural diagram of a channel estimator;

17 is a structural diagram of a pilot signal generating unit and a channel estimating unit that performs a second pilot signal generating process and a channel estimating process;

Fig. 18 is a structural diagram of a pilot signal generating unit and a channel estimating unit that performs a third pilot signal generating process and a channel estimating process;

19 is a diagram illustrating frequency assignment when the number of multiplexed pilot signals is 4;

20 is a diagram illustrating hopping in which transmission bands that are assigned to users are switched after each frame, and also illustrating an assignment for an odd frame;

21 is a diagram illustrating hopping in which transmission bands that are assigned to users are switched after each frame, and also illustrating an assignment for an even frame;

Fig. 22 is a structural diagram of a pilot signal generating unit when performing jump control;

23 is an example of a frame format for transmission on a single carrier;

24 is a diagram for describing frequency equalization;

25 is a structural diagram of an SC-FDMA transmission block;

Fig. 26 is a diagram illustrating intercell interference;

27 is a first diagram illustrating a conventional data transmission band and a pilot transmission band;

28 is a second diagram illustrating a conventional data transmission band and a pilot transmission band.

The best embodiment of the invention

(A) Principles of the invention

As shown in part (A) of FIG. 1, when the CAZAC sequence ZC _k (n) to which cyclic shift c ₁ was applied is used as a pilot for user 1, and the CAZAC sequence ZC _k (n) to which cyclic shift c ₂ was applied is used as a pilot signal for user 2, then, as described with reference to FIG. 28, sub-carriers 23, 24 of the transmission frequency band for user 2 data are different from the transmission frequency band for pilot -signal, and the accuracy of channel estimation for this subcarrier decreases. 1, DFT {ZC _k (nc ₁ )} and DFT {ZC _k (nc ₂ )} are pilot signals that are obtained by performing cyclic shifts c ₁ , c _{2 of the} CAZAC sequence ZC _k (n) s length L = 11, after which DFT processing of the sequences ZC _k (nc ₁ ) and ZC _k (nc ₂ ) is performed.

Therefore, as shown in part (B) of FIG. 1, as a result of applying a frequency offset to the pilot signals of each user to ensure matching the transmission band and further multiplexing the pilot signals, the bandwidth for these pilots will always cover the transmission band for these data. In the example shown in part (B) of FIG. 1, the DFT pilot {ZC _k (nc ₂ )} for user 2 may be offset by one subcarrier.

However, when the DFT pilot {ZC _k (nc ₂ )} is shifted, on the receiving side, the correlation between the received pilot and the copy ZCk (n) of the known pilot does not reach a peak at τ = c ₂ , and the peak location shifted, as a result of which it will be impossible to correctly restore this pilot signal and obtain a channel estimate. The reason why the location of the correlation peak is shifted is described below.

The relationship between the frequency shift and the cyclic shift in the time domain.

First, the relationship between the frequency offset and the cyclic shift in the time domain will be considered. If we denote the result of the DFT transform of the CAZAC sequence ZCk (n) as F (m), then F (m) can be expressed as follows:

Using Equations (7) and (4), the expression can be reduced to the following form:

(8)

(8)

where d (mod L) means that after dividing kc and d by L, we get the same remainder.

You can also notice expressions (8) that, in the time domain, applying a cyclic shift c to a CAZAC sequence is equivalent to applying a cyclic shift with d subcarriers and phase rotation Q _{k, c} in the frequency domain. Here k and L are primes relative to each other, so c (<L) is uniquely determined according to k and d. To facilitate the understanding that c is determined according to k, d and L, the new value of c is taken to be c = s (k, d, L). Table 1 shows the values of c that correspond to different combinations of s (k, d, L) and k for the case when L = 11. For example, when k = 1, d = 1, L = 11 and c = 1; and when k = 2, d = 1, L = 11 and c = 6.

Table 1
s (k, d, L) when L = 11 k s (k, 1,11) s (k, 2.11) s (k, 3.11) one one 2 3 2 6 one 7 3 four 8 one four 3 6 9 5 9 7 5 6 2 four 6 7 8 5 2 8 7 3 10 9 5 10 four 10 10 9 8

Thus, applying a frequency offset of one subcarrier to pilot 2, as shown in part (A) of FIG. 2, corresponds to the movement of component P ₁₁ from subcarrier 1 to subcarrier 12 after adding a cyclic shift of one subcarrier in the frequency domain, as shown in part (B) of FIG. 2. As a result, according to Equation (8), the location of the correlation peak (see Equation (5)) of pilot signal 2 shifts only s (k, d, L) (τ = c ₂ + s (k, d, L)). The position of the correlation peak of pilot 1 (τ = c ₁ ) does not shift, so that the correlation peak of pilot 2 and pilot 1 changes, respectively, only s (k, d = 1, L = 11), and on the receiving it will be impossible for the party to correctly restore the pilot signal, as a result of which it becomes impossible to perform channel estimation.

To obtain the location of the normal correlation peak, the cyclic shift value can be changed from c ₂ to (c ₂ -s (k, d, L). In other words, as shown in part (A) of Figure 3, as a result of applying as a frequency offset value d of subcarriers (d = 1 in this figure) and of cyclic shift (c ₂ -s (k, d, L), the ratio between pilot signal 1 and pilot signal 2 becomes as shown in part (B) Figure 3. As a result of the described operations, the locations of the correlation peaks of the pilot signal 1 and the pilot signal 2 are not shifted, and on the receiving side, it is possible to correctly reconstruct to establish these pilot signals, as a result of which the accuracy of channel estimation can be improved, that is, it is possible to separate pilot signal 1 and pilot signal 2 using the locations (τ = c ₁ , τ = c ₂ ) of the correlation peaks, as in the case when frequency offset is not applicable.

(a) The first pilot signal generation process and the channel estimation process

FIG. 4 is a diagram for explaining the process of generating a pilot signal at the transmitting side, which allows frequency offset by d subcarriers and cyclic shift (c ₂ -s (k, d, L), which have been described with reference to FIG. 3 .

The CAZAC sequence generating unit 11 generates the CAZAC sequence ZC _k (n) as a pilot signal with L = 11, and the cyclic shift unit 12 cyclically shifts the CAZAC sequence ZCk (n) by the amount c ₂ -s (k, d, L) to generate ZC _k (nc ₂ + s (k, d, L)), and enters the result into block 13 of the DFT. Block 11 DFT with dimension N _TX (N _TX = L = 11) performs the DFT calculation process for ZC _k (nc ₂ + s (k, d, L)) to generate a DFT pilot signal {ZC _k (nc ₂ + s (k, d, L))}. The subcarrier display unit 14 biases the 11 components of the frequency domain pilot signal P ₁ ~ P ₁₁ by the value d of the subcarriers (d = 1 in this figure), and inputs the result into the IFFT block 15.

5 is a diagram illustrating an offset performed by a subcarrier display unit 14, where (A) illustrates a case where there is no offset (d = 0), and the subcarrier display unit 14 inputs ₁₁ pilot components P ₁ ~ P ₁₁ into the frequency terminals f _i , f _{i + 1} , f _{i + 2} , ..., f _{i + 10} of IFFT block 15 and enters 0 into other terminals. In this figure, part (B) illustrates the case where there is some bias (d = 1), and the subcarrier display unit 14 inputs ₁₁ pilot components P ₁ ~ P ₁₁ into the frequency terminals f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 11} and enters 0 into other terminals. An N _FFT IFFT block 15 (e.g., N _FFT = 128) performs IFFT calculation processing for the input subcarrier components to convert the signal to a time domain signal, and the CP insert block 16 adds a cyclic prefix to prevent interference and outputs the result. 5, part (C) illustrates another example of a case where an offset is present (d = 1). In this case, the cyclic shift unit 12 cyclically shifts the CAZAC sequence ZC _k (n) only by c ₂ to generate ZC _k (nc ₂ ), and enters the result into the DFT unit 13. DFT unit 13 performs DFT calculation processing for ZC _k (nc ₂ ) to generate a DFT pilot {ZC _k (nc ₂ )}. The subcarrier display unit 14 inputs the pilot components P ₂ ~ P ₁₁ to the terminals f _i , f _{i + 1} , f _{i + 2} , ..., f _{i + 10} of the IFFT block 15 and inputs the pilot component P ₁ to the terminal f _{i + 11} block 15 IFFT.

6 is a diagram illustrating a channel estimation process at a receiving side.

The pilot signal 1 and pilot signal 2, which are respectively transmitted from user 1 and user 2 (see FIG. 3), are multiplexed to become components (P ₁ ~ P ₁₂ ) of the subcarrier for frequencies f _i , f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 11} , and are entered into the channel estimator. The subcarrier summing unit 52 summarizes the subcarrier components P ₁₂ and P ₁ that do not overlap and takes the summing result as a new subcarrier component P ₁ for the frequency f ₁ .

A copy copy signal multiplying section 53 multiplies a copy of the pilot signal q _i and a received pilot signal pi for each subcarrier, the IDFT block 54 performs IDFT calculation processing for the copy multiplication results and outputs a delay profile in the time domain. A copy of the pilot signal is obtained by performing DFT calculation processing of the known CAZAC sequence ZC _k (n) for a zero cyclic shift.

The time-domain delay profile has a length L of samples with correlation peaks at t = c1, t = c2, and the profile extraction unit 55 separates the correlation peaks by t = (c1 + c2) / 2 to generate profiles PRF1, PRF2 with length L / 2 samples for user 1 and user 2. The DFT unit 56a with dimension L inserts L / 4 zeros on both sides of the PRF1 profile of length L / 2 to obtain the length L, and performs DFT calculation. Thus, the channel estimation values h ₁ ~ h ₁₁ for user 1 are obtained from the DFT unit 56a at frequencies f _i , f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 10} subcarriers. Similarly, a DFT unit 56b with dimension L inserts L / 4 zeros on both sides of the PRF2 profile of length L / 2 to obtain the length L, and performs DFT calculation. Thus, the channel estimation values h ₂ ~ h ₁₂ for user 2 are obtained from the DFT unit 56b at the frequencies f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 11} subcarriers. However, since the subcarrier summing unit 52 sums P ₁ and P ₁₂ to obtain a subcarrier component f _i , the channel estimate of the frequency channel f _{i of the} subcarrier that is output from the DFT block 56b takes as the channel estimate h ₁₂ the frequency channel f _{i + 11} subcarriers.

Based on the foregoing, provided that the distortion due to the state of the propagation path is small, it is possible to separate the pilot signal 1 and pilot signal 2 in a completely orthogonal form in the delay profile of the time domain after the components that do not overlap each other friend on the receiving side, are summed and multiplied with a copy of the signal, as shown in Fig.6. When the distortion due to propagation states is of great importance, it is possible to skip the summation of the subcarriers and separate pilot signal 1 and pilot signal 2 in the time-domain delay profile after direct multiplication with copy.

(a) Second pilot signal generation process and channel estimation process

In the first channel estimation process described above, the subcarrier components P ₁₂ ~ P ₁ that do not overlap are summed, and the sum result is taken as a component of the subcarrier frequency f _i . However, when the subcarrier component for the received signal subcarrier frequency f _i is already obtained by summing P ₁₂ and P ₁ , then there is no need to sum the subcarriers on the receiving side.

7 is a diagram illustrating a second pilot signal generation process, wherein part (A) illustrates data subcarriers for user 1 and user 2.

As shown in part (B) of FIG. 7, the transmitting side (user 1) copies the component P _{1 of the} subcarrier frequency f _{i of the} pilot signal 1 so that it becomes a component of the subcarrier frequency f _{i + 11} and performs transmission, and, as shown in part (C) of FIG. 7, user 2 copies the component 12 of the subcarrier frequency f _{i + 11 of} pilot signal 2, so that it becomes a component of the subcarrier frequency f _i , and performs transmission. Thus, as shown in part (D) of FIG. 7, these pilots are multiplexed and received by the receiving side, and the subcarrier component f _i becomes the sum of P ₁ and P ₂ , so that there is no need to sum the subcarriers on the receiving side.

FIG. 8 is a diagram illustrating a copying method on a transmitting side, where part (A) illustrates a copying method for pilot 1 by user 1, and in this method, subcarrier mapper 14 inputs component P _{1 of} subcarrier frequency f _{i of} pilot 1 also to the frequency terminal f _{i + 11} of the IFFT block 15, so that it is also a component of the frequency subcarrier f _{i + 11} . In this figure, part (B) illustrates a method of reproduction, the user pilot 2 2, and in this manner, the block 14, subcarrier mapping introduces component P _12, the subcarrier frequency f _{i + 11} of pilot 12 also to the terminal of frequency f _i unit 15 IFFT so that it is also a component of the subcarrier frequency f _i . In this figure, part (C) is an example implementation of a copy method for pilot 2 by user 2, and it corresponds to part (C) of FIG. 5.

9 is a diagram illustrating a channel estimation process that is performed by a receiving side. Pilot 1 and pilot 2 (see (B) and (C) of FIG. 7), which are respectively transmitted from user 1 and user 2, are multiplexed to become components of the (P ₁ ~ P ₁₂ ) subcarrier for frequencies f _i , f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 11} , and are entered into the channel estimator (see (D) of FIG. 7).

Block 53 of the copy signal multiplication for user 1 multiplies copies of the pilot signals q _i (q ₁ ~ q ₁₁ ) with the received pilot signals P _i (P ₁ ~ P ₁₁ ) for each subcarrier, and then IDFT block 54, separation unit 55 the correlations and the DFT unit 56 perform the processing in the same manner as in the case of FIG. 6 in order to generate channel estimation values h ₁ ~ h ₁₁ for user 1.

On the other hand, the copy copy signal multiplying section 53 'for user 2 multiplies the copy q _i (q ₁ ~ q ₁₁ ) of the pilot signal with the received pilot signals P _i (P ₂ ~ P ₁₂ ) for each subcarrier, and then block 54 The 'IDFT, correlation separation unit 55' and the DFT unit 56 'perform the same processing as for user 1 to generate channel estimation values h ₂ ~ h ₁₂ for user 2.

(c) Third pilot generation process and channel estimation process

In the first channel estimation process described above, the correlation separation unit 55 separates the pilot components for user 1 and the pilot components for user 2, however, as shown in FIG. 10, when two pilot blocks are included single frames, for example, they can be separated according to the method described below. 11 is a diagram illustrating a method for separating a pilot signal, and part (A) illustrates data subcarriers for user 1 and user 2.

As shown in parts (B) and (C) of FIG. 11, each of the subcarrier components of the first pilot signal 1 (= DFT {ZC _k (nc ₁ )}) and pilot signal 2 (= DFT {ZC _k (nc ₂ + s (k, d, L))}) of user 1 and user 2 are multiplied by +1 and transmitted, as shown in parts (D) and (E), and each of the components of the next pilot signal 1 and pilot signal 2 are multiplied by +1 and -1, respectively, and transmitted.

Thus, the receiving side first receives the next multiplexed pilot signal

DFT {ZC _k (nc ₁ )} × (+1) + DFT {ZC _k (nc ₂ + s (k, d, L)} × (+1),

further, a multiplexed pilot signal is received

DFT {ZC _k (nc ₁ )} × (+1) + DFT {ZC _k (nc ₂ + s (k, d, L)} × (-1).

Therefore, in order for the receiving side to generate pilot signals for user 1, the next multiplexed pilot signal can be added to the first multiplexed pilot signal. In other words, the polarities of the pilot signals 2 are different, so that by summing the signals, the pilot signals 2 are discarded, and only the pilot signal 1 remains. Moreover, for the receiving side to generate the pilot signals for user 2, the next multiplexed pilot signal can be subtracted from the first multiplexed pilot. In other words, the polarities of the pilot signals 1 are the same, so that by subtracting the signals, the pilot signals 1 are discarded, and only the pilot signal 2 remains.

12 is a diagram illustrating a channel estimation process at a receiving side. Pilot 1 and pilot 2, which are respectively transmitted from user 1 and user 2 (see (B), (C), (D) and (E) of FIG. 11), are multiplexed to become components (P ₁ ~ P ₁₂ ) subcarrier for frequencies f _i , f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 11} , and are entered into the channel estimator.

The subcarrier summing unit 61 between the blocks receives and stores the first received pilot signal. Further, after receiving the second received pilot signal, when generating pilot signals for user 1, the subcarrier summing unit 61 between the blocks sums the first and second received pilot signals for each subcarrier to generate subcarrier components P ₁ ~ P ₁₁ for frequencies f _i , f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 10 of} pilot signal 1. Block 53 of the copy signal multiplication for user 1 multiplies copies of q _i (q ₁ ~ q ₁₁ ) pilot signals with received pilot signals P _i (P ₁ ~ P ₁₁₎ for each subcarrier, and after that block 54 IDFT, correlation separation unit 55 and DFT unit 56 perform Obra whence the same manner as in the case of Figure 6 to generate channel estimation values h ₁ ~ h 1 ₁₁ for the user.

On the other hand, when generating pilot signals for user 2, subcarrier summing unit 61 between blocks subtracts the first and second pilot signals for each subcarrier to generate subcarrier components P ₂ ~ P ₁₂ for frequencies f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 11} pilot signal 2. Block 53 'copy signal multiplication for user 2 multiplies copies q _i (q ₁ ~ q ₁₁ ) of the pilot signal with the received pilot signals P _i (P ₂ ~ P ₁₂₎ for each subcarrier, and after that block 54 'IDFT, block 55' and the correlation separation unit 56 'DFT perform the same processing as that for user 1, Thu would generate a value h ₂ ~ h ₁₂ channel estimates for user 2.

The case has been described above when the number of pilot blocks is two, however, this third pilot generation process and the channel estimation process can also be applied when there is an even number of pilot blocks. In this case, the base station instructs a specific user terminal to multiply the pilot signals of all blocks by +1, and also instructs other user terminals to multiply half the pilot signals by +1 and multiply the other half of the pilot signals by -1. In addition, when the base station receives the multiplexed pilot signals that have been transmitted from each user terminal, the base station performs the computation process of adding or subtracting the pilot signals for all blocks, so that only the pilot signal from the given user terminal (user terminal) remains 1 or 2), then multiplies the result of the calculation with a copy of the pilot signal, converts the result of multiplying the copy into a time-domain signal, after which it separates part of the signal by the user terminal from the time domain signal and performs channel estimation.

(B) Mobile station

13 is an illustration of a structure of a mobile station.

In the case where uplink transmission data is generated, the mobile station (user terminal) transmits a request for resource assignment to the base station, and according to this request, the base station allocates resources based on the state of the propagation path of the mobile station and notifies the mobile station of the resource assignment information . The radio communication unit 21 of the mobile station converts the radio signal that is received from the base station into an unmodulated signal and inputs this unmodulated signal to the unmodulated signal processing unit 22. The unmodulated signal processing unit 22 separates data and other control information from the received signal, as well as resource assignment information, and inputs the resource assignment information into the transmission resource control unit 23. In addition to the transmission frequency band, timing, modulation method, and the like, the resource assignment information includes the pilot transmission frequency band, sequence number k, and CAZAC sequence length L, which is used as the pilot signal, the cyclic amount the shift, the magnitude of the frequency shift d, etc.

The transmission resource control unit 23 inputs the information necessary for transmitting control information to the data processing unit 24 and enters the information necessary for generating and transmitting the pilot signal to the pilot signal generating unit 25. Based on the entered information, the data processing unit 24 performs data modulation and transmission processing on one carrier for data and control information, and outputs the result and according to the instructions from the transmission resource control unit 23, the pilot signal generation unit 25 performs processing such as CAZAC- generation sequences, a cyclic shift, a frequency offset, and the like, to generate a pilot signal, after which the frame generation unit 26, as shown, for example, in FIG. 10, performs time division multiplexing esti data blocks and two pilot blocks to generate a frame, and the radio unit 21 transmits that frame to the base station.

14 is a diagram illustrating the structure of the pilot generation unit 25, this figure shows a case where the pilot signals are generated according to the first pilot generation process described with reference to FIG. 3, wherein part (A) illustrates a case when the cyclic shift is performed before the DFT, and part (B) illustrates the case where the cyclic shift is performed after the IFFT.

In part (A) of FIG. 14, the transmission resource control unit 23 inputs parameters (CAZAC sequence number, sequence length, cyclic shift amount, and frequency offset) that are included in the resource assignment information received from the base station and which are necessary for generating and transmitting pilot signals to the respective blocks.

The CAZAC sequence generating unit 11 generates a CAZAC sequence ZC _k (n) with a predetermined sequence length L and sequence number k as a pilot signal, and the cyclic shift unit 12 rotates the CAZAC sequence ZC _k (n) by an amount c of samples according to the instructions and enters the resulting sequence ZC _k (nc) in block 13 of the DFT. For example, for pilot signal 1 shown in part (B) of FIG. 3, the cyclic shift unit 12 shifts ZC _k (n) exactly by a value of c ₁ to generate ZC _k (nc ₁ ), and for pilot signal 2 the cyclic shift unit 12 shifts ZC _k (n) exactly by the amount c ₂ -s (k, d, L) to generate ZC _k (nc ₂ + s (k, d, L)), and enters the results into the DFT block 13 . Block 13 DFT with dimension N _TX (N _TX = L) performs DFT processing on the input pilot signal ZC _k (nc) to generate a pilot signal DFT {ZC _k (nc)} in the frequency domain. Based on the frequency offset value according to the instruction, the subcarrier display unit 14 controls the display position of the pilot signal and performs frequency offset, and the IFFT unit 15 with the dimension N _FFT (N _FFT = 128) performs IFFT processing on the introduced subcarrier components and converts this signal into a time signal area, and enters it into the block 26 of the generation of the frame.

Part (B) Fig. 14 illustrates the structure of the pilot generation unit 25 for the case where the cyclic shift is performed after the IFFT, where the c x N _FFT / N _TX samples are cycled, in this case the cyclic shift block 12 provides the same result as in the case shown in part (A) of Fig. 14.

(C) Base station

15 is a diagram illustrating a structure of a base station.

When uplink transmission data is generated, the mobile station (user terminal) performs the procedure for establishing a communication link with the base station, and in this procedure transmits the state of the propagation path to the base station. In other words, the mobile station receives a common pilot signal that was transmitted from the base station and performs a radio measurement (SIR or SNR measurement), after which it transmits the results of this radio measurement to the base station as the state of the propagation path. For example, the base station divides the transmission band into multiple transmission frequency bands and transmits common pilot signals for each transmission frequency band, after which the mobile station performs radio measurements for each transmission frequency band and transmits the measurement result to the base station. After receiving the resource assignment request, together with receiving the state of the propagation path from the mobile station, the base station allocates resources based on the state of the propagation path from the mobile station and transmits resource assignment information to the mobile station.

The radio communication unit 21 converts the radio signal that was received from the mobile station into an unmodulated signal, and the separation unit 32 separates the data / control information and the pilot signals, after which it enters this data / control information into the data processing unit 33 and inputs the pilot signals in block 34 channel evaluation. The data processing unit 33 and the channel estimator 34 comprise a frequency equalization structure shown in FIG. 24.

The data processing unit 33 demodulates the propagation path state information that was transmitted from the mobile station at the time of establishing the communication line, and enters this information into the uplink resource control unit 35. The uplink resource control unit 35 assigns resources based on the state of the propagation path, creates resource assignment information, and inputs this information into the unmodulated downlink signal processing unit 36. In addition to the transmission frequency band, timing, modulation method, and the like, the resource assignment information includes the sequence number k and the CAZAC sequence length L, which is used as the pilot signal, the amount of cyclic shift, the amount of frequency offset d and etc. The downlink unmodulated signal processing unit 36 performs time division multiplexing for data, control information, and resource assignment information and transmits the resulting signal from the radio communication unit 31.

After receiving the resource assignment information, the mobile station performs processing as described with reference to FIGS. 13 and 14, and transmits a frame containing data and pilot signals.

The channel estimator 34 uses the pilot signals that have been separated and input by the separator 32 to carry out the first channel estimation process, as described with reference to FIG. 6, and then inputs the channel estimate values to the data processing unit 33. The data processing unit 33 performs channel compensation based on the channel estimation values and demodulates the data based on the channel compensation results. The uplink resource control unit 35 includes a cyclic shift amount calculating unit 35a and a line assignment information instruction generating unit 35b.

FIG. 16 is a diagram illustrating the structure of a channel estimator 34, where like reference numbers indicate like elements shown in FIG. 6.

The DFT unit 51 performs DFT processing of the pilot signal, which is input from the separation unit, and converts this signal into a pilot signal in the frequency domain (P ₁ ~ P ₁₂ subcarrier components). The subcarrier summing unit 52 summarizes the subcarrier components P ₁₂ and P ₁ that do not overlap and designates the summation as the new subcarrier component P ₁ for the frequency f ₁ .

The copy signal multiplying section 53 multiplies the copy q _{i of the} pilot signals with the received pilot signals P _i for each subcarrier, and the IDFT block 54 performs IDFT processing of the copy multiplication result to output the time domain pilot. The profile extracting unit 55 separates the output IDFT signal at the point t = (c1 + c2) / 2, and when this signal is a signal received from user 1, it selects the PRF1 profile (see FIG. 6), then the DFT unit 56 performs DFT -processing the PRF1 profile and displays the values of h ₁ ~ h ₁₁ channel estimates. On the other hand, when said signal is a signal received from user 2, the profile extracting unit 55 selects the PRF2 profile, then the DFT unit 56 performs DFT processing of the PRF2 profile and outputs the channel estimation values h ₂ ~ h ₁₂ .

(D) Second pilot generation unit and channel estimation unit

Part (A) of FIG. 17 is a diagram illustrating the structure of a pilot signal generation unit that performs the second pilot signal generation process described above with reference to FIG. 7, wherein in this diagram, the same reference numbers denote the same elements shown in part (A) Fig. 14. This pilot generation unit is characterized in that two additional operations are performed: the subcarrier display unit 14, based on the frequency offset value d, performs the subcarrier mapping, and the pilot components of the specified subcarriers are copied; other operations are the same.

The CAZAC sequence generating unit 11 generates the CAZAC sequence ZC _k (n) with the sequence length L and sequence number k according to the instruction as a pilot signal, and the cyclic shift unit 12 rotates the CAZAC sequence ZC _k (n) by a predetermined amount in c samples and enters the resulting sequence ZC _k (nc) into block 13 of the DFT. For example, in the case of pilot signal 1 for user 1 shown in part (B) of FIG. 7, the cyclic shift unit 12 shifts ZC _k (n) by c ₁ to generate ZC _k (nc ₁ ), and in the case pilot 2 for user 2, the cyclic shift unit 12 shifts ZC _k (n) by c ₂ −s (k, d, L) to generate ZC _k (nc ₂ + s (k, d, L)), and enters the results into block 13 of the DFT. Block 13 DFT with dimension N _TX (N _TX = L) performs DFT processing of the pilot signal ZC _k (nc) to generate a pilot signal DFT {ZC _k (nc)} in the frequency domain.

Subcarrier display unit 14 performs subcarrier mapping based on copy information and frequency offset information that has been set from transmission resource control unit 23. For example, for pilot 1 of user 1 shown in part (B) of FIG. 7, subcarrier display unit 14 performs the subcarrier mapping process shown in part (A) of FIG. 8, and for pilot 2 of user 2 shown in part (C) of FIG. 7, the subcarrier display unit 14 performs the subcarrier mapping shown in part (B) of FIG. 8. An N _FFT IFFT block 15 (e.g., N _FFT = 128) performs IFFT processing of the subcarrier components that are input to convert the signal into a time domain pilot, and enters the result into the frame generation block 26.

Part (B) of FIG. 17 is a diagram illustrating the structure of a channel estimator 34 that performs the second channel estimation process described above with reference to FIG. 9, wherein in this diagram, like reference numbers indicate like elements shown in FIG. 16 . This channel estimator 34 is characterized in that the subcarrier summing unit 52 has been omitted and a predetermined multiplication process, which is performed by the signal copy multiplier 53, has been added.

In addition to the DFT processing of the pilot signal input from the separation unit 32, the DFT unit 51 converts this signal into a frequency domain pilot (P ₁ ~ P ₁₂ subcarrier components). In the case of pilot signal 1 from user 1, the signal copy multiplication unit 53 multiplies the components P ₁ ~ P _{11 of the} subcarriers f _i , f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 10} received the pilot signal, which is derived from the DFT unit 51, with copies of the signal q ₁ ~ q ₁₁ , and in the case of pilot signal 2 from the user 2, multiplies the components P ₂ ~ P ₁₂ subcarriers f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 11 of the} received pilot signal, which is output from the DFT unit 51 with copies of the signals.

After that, the block 54 IDFT performs IDFT processing of the result of the multiplication of the copy and displays the delay profile of the time domain. The profile extracting unit 55 separates the output IDFT signal at the point t = (c1 + c2) / 2, and when this signal is a signal received from user 1, selects the PRF1 profile (see FIG. 6), then the DFT unit 56 performs DFT- processing the PRF1 profile and displays the values of h ₁ ~ h ₁₁ channel estimates. On the other hand, when said received signal is a signal received from user 2, the profile extracting unit 55 selects the PRF2 profile, then the DFT unit 56 performs DFT processing of the PRF2 profile and outputs the channel estimation values h ₂ ~ h ₁₂ .

(E) Third pilot generation unit and channel estimation unit

Part (A) of FIG. 18 is a diagram illustrating the structure of a pilot signal generation unit that performs the third pilot signal generation process described above with reference to FIG. 11, wherein in this diagram, the same reference numbers denote the same elements shown in part (A) Fig. 14. This pilot generation unit differs only in that a polarity assignment unit 61 has been added; other operations are the same.

The CAZAC sequence generating unit 11 generates a CAZAC sequence ZC _k (n) with a predetermined sequence length L and sequence number k as a pilot signal, and the cyclic shift unit 12 rotates the CAZAC sequence ZC _k (n) by a predetermined value in c samples and enters the resulting sequence ZC _k (nc) into block 13 of the DFT. For example, in the case of pilot signal 1 for user 1 shown in part (B) and (D) of FIG. 11, the cyclic shift unit 12 shifts ZC _k (n) by a value of c ₁ to generate ZC _k (nc ₁ ) and in the case of pilot signal 2 for user 2, the cyclic shift unit 12 shifts ZC _k (n) by c ₂ -s (k, d, L) to generate ZC _k (nc ₂ + s (k, d, L )), and enters the result into block 13 of the DFT. An N _TX DFT unit 13 (N _TX = L) performs DFT processing of the input pilot signal ZC _k (nc) to generate a frequency domain pilot DFT {ZC _k (nc)}.

The subcarrier display unit 14 performs subcarrier mapping based on the frequency offset information that has been set from the transmission resource control unit 23. The polarity attachment unit 61 attaches the polarity specified from the transmission resource control unit 23 to the output from the subcarrier display unit 14 and outputs the result to the IFFT unit 15. For example, in the case of pilot signal 1 for user 1, a polarity of +1 is set for the first and second pilot blocks (see (B) and (D) of FIG. 11), and the polarity attachment unit 61 multiplies all subcarrier components, which are derived from the subcarrier display unit 14 by +1 and inputs the result into the IFFT unit 15. In addition, in the case of pilot signal 2 for user 2, polarity +1 is set for the first pilot block, and polarity -1 is set for the second pilot block (see (C) and (E) of FIG. 11) and the polarity attachment unit 61 multiplies all subcarrier components that are output from the subcarrier display unit 14 by +1 for the first pilot block and by -1 for the second pilot block and inputs the result into IFFT block 15.

An N _FFT IFFT block 15 (e.g., N _FFT = 128) performs IFFT processing of the introduced subcarrier components to convert the signal to a time domain pilot, and inputs the result to the frame generation block 26.

Part (B) of FIG. 18 is a diagram illustrating the structure of a channel estimator 34 that performs the third channel estimation process described above with reference to FIG. 12, wherein in this diagram, like reference numbers indicate like elements shown in FIG. 16 . This channel estimator is characterized in that instead of a subcarrier summing unit 52, a subcarrier summing unit 62 is provided between the blocks.

In addition to performing DFT processing of the first pilot block input from the separation unit 32, the DFT unit 51 converts the signal into a frequency domain pilot (P ₁ ~ P ₁₂ subcarrier components), and the subcarrier summing unit 62 between the blocks stores this pilot -signal (subcarrier components P ₁ ~ P ₁₂ ) in the internal memory. After that, in addition to performing DFT processing of the second block of pilot signals input from the separation unit 32, the DFT unit 51 converts the signal into a pilot signal in the frequency domain (sub-carrier components P ₁ ~ P ₁₂ ) and inputs this signal to the summing unit 62 subcarriers between blocks.

When pilot signal 1 is received from user 1, subcarrier summing unit 62 between blocks sums the pilot signal (components P ₁ ~ P ₁₂ ) of the subcarrier of the stored first block and the pilot signal (components P ₁ ~ P _{12 of} subcarrier) of the second block for each subcarrier . Thus, the multiplexed pilot components from another user (eg, user 2) are removed. Moreover, when pilot signal 2 is received from user 2, the subcarrier summing unit 62 between the blocks subtracts the pilot signal (P ₁ ~ P ₁₂ subcarrier components) of the second block from the pilot signal (P ₁ ~ P ₁₂ subcarrier components) of the stored first block for each subcarrier. Thus, the multiplexed pilot components from another user (eg, user 1) are removed.

When the pilot signal 1 is received from user 1, the signal copy multiplication unit 53 multiplies the components P ₁ ~ P _{11 of the} subcarriers f _i , f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 10 of the} received the pilot signal, which is derived from the subcarrier summing unit 62 between the blocks, with copies of the signal q ₁ ~ q ₁₁ , and when the pilot signal 2 is received from the user 2, the components P ₂ ~ P _{12 of the} subcarriers f _{i + 1} , f _{i + 2} , f _{i + 3} , ..., f _{i + 11 of the} received pilot signal, which is derived from subcarrier summing unit 62 between blocks, with copies of q ₁ ~ q ₁₁ signal.

After that, the IDFT block 54 performs IDFT processing of the copy multiplication result and outputs a time-domain pilot. The profile extracting unit 55 separates the output IDFT signal at the point t = (c1 + c2) / 2, and when this signal is a signal received from user 1, selects the PRF1 profile (see FIG. 6), then the DFT unit 56 performs DFT- processing the PRF1 profile and displays the values of h ₁ ~ h ₁₁ channel estimates. On the other hand, when said signal is a signal received from user 2, the profile extracting unit 55 selects the PRF2 profile, then the DFT unit 56 performs DFT processing of the PRF2 profile and outputs the channel estimation values h ₂ ~ h ₁₂ .

(F) Adaptive management

As described above, the uplink resource control unit 35 included in the base station (see FIG. 15) determines the transmission frequency bands for the pilot signals, CAZAC sequence number and length L, cyclic shift amount, frequency offset d, etc. P. based on the state of the propagation path of the mobile station and notifies the mobile station thereof. Moreover, the uplink resource control unit 35 of the base station also determines the amount of multiplexing in the transmission frequency band based on the state of the propagation path of each mobile station.

19 is a diagram illustrating frequency assignments when the multiplexing number is 4, with the first 12 subcarriers being assigned to user 1, the second 12 subcarriers being assigned to user 2, the third 12 subcarriers being assigned to user 3, and the last 12 subcarriers being assigned to user 4, with CAZAC- the sequence ZC _k (n) with a length L = 19 is used as a pilot signal for each user by changing the magnitude of the cyclic shift.

The frequency offset of the pilot signal is determined so that the data transmission band for each user is covered as much as possible by the pilot signal transmission band. The cyclic shift unit 35a (see FIG. 15) calculates the amount of cyclic shift for each user according to the following equation

Here, i and p denote the data band number and the user number, respectively. In addition, s (k, d, L) represents the amount of cyclic shift for sequence number k with length L and frequency offset d, the ratio of which is set according to the following equation

where c _p for the p-th user can be calculated, for example, according to the following equation:

where P expresses the number of pilot signals (number of users) that are multiplexed by a cyclic shift. In the case of Fig. 19, the values of cyclic shifts c ₁ ~ c ₄ for users 1 ~ 4 take the following values:

c ₁ = 0

c ₂ = [L / 4]

c ₃ = [2 · L / 4] -s (k, d, L)

c ₄ = [3 · L / 4] -s (k, d, L)

Thus, depending on the method of receiving the pilot signals, the channel estimation characteristics at both ends of the pilot transmission band may be poor, and the channel estimation characteristics for the middle portion may be good. In other words, in the bandwidth for subcarriers 1 ~ 12 and 37 ~ 48 of Fig. 19, the channel estimation accuracy may be low, and in the transmission band for subcarriers 13 ~ 24 and 25 ~ 36, the channel estimation accuracy may be high.

Therefore, the middle of the transmission band for subcarriers 13 ~ 24 and 25 ~ 36 is assigned to users with poor propagation path condition, and both ends of the transmission band for subcarriers 1 ~ 12 and 37 ~ 48 are assigned to users with good propagation path state. Thus, a situation is excluded when there are users for whom the accuracy of channel estimation will be extremely poor. 19 illustrates an example assignment to user 2 and user 3 of the middle transmission band.

Moreover, as shown in FIGS. 20 and 21, it is possible to perform control (hop control) so that the transmission band assigned to users changes for each frame. FIG. 20 is a diagram illustrating an assignment for an odd frame, and FIG. 21 is a diagram illustrating an assignment for an even frame.

As shown in FIG. 20, for an odd frame, subcarriers 1 ~ 12 and 37 ~ 48 at both ends are assigned to user 1 and user 4, and middle subcarriers 13 ~ 24 and 25 ~ 36 are assigned to user 2 and user 3. In addition, as shown in Fig. 21, for an even frame, the middle subcarriers 13 ~ 24 and 25 ~ 36 are assigned to user 4 and user 1, and subcarriers 1 ~ 12 and 37 ~ 48 at both ends are assigned to user 3 and user 2. Frequency offset is applied to the pilot signals of user 3 and user 4 for an odd frame, and the frequency offset is applied to the pilot User 1 and User 2 for even frame. Thus, a situation is excluded when there are users for whom the accuracy of channel estimation will be extremely poor.

Fig. 22 is a drawing illustrating the structure of the pilot generation unit when step control is performed, the same reference numbers in this figure denoting the same elements of the pilot generation unit shown in part (A) of Fig. 14. This pilot generation unit only differs in that a frequency offset switching control unit 71 has been added; other operations are the same.

The CAZAC sequence generating unit 11 generates a CAZAC sequence ZC _k (n) with a predetermined sequence length L and sequence number k as a pilot signal, and the cyclic shift unit 12 rotates the CAZAC sequence ZC _k (n) by a predetermined value in c samples and enters the resulting sequence ZC _k (nc) into block 13 of the DFT. An N _TX DFT unit 13 (N _TX = L) performs DFT processing of the input pilot signal ZC _k (nc) to generate a frequency domain pilot DFT {ZC _k (nc)}. The frequency bias switching control unit 71 determines whether it is necessary to perform the frequency bias based on the frequency bias value d and the hopping pattern specified from the transmission resource control unit 23. The subcarrier display unit 14 performs subcarrier mapping depending on whether a frequency offset is being performed. An N _FFT IFFT block 15 (e.g., N _FFT = 128) performs IFFT processing of the introduced subcarrier components to convert the signal to a time domain pilot, and inputs the result to the frame generation block 26.

The beneficial effect of the invention

By means of the invention described above, it is possible to estimate the data subcarrier channel, which is different from the pilot frequency band, with high accuracy.

In addition, by means of the present invention, it is possible to perform channel estimation of data transmission subcarriers that are assigned to users even when a cyclic shift of different magnitude is performed on a given sequence (e.g., the CAZAC sequence ZC _k (n)) used as a pilot for users, which will be multiplexed.

Moreover, by means of the present invention, it is possible to perform channel estimation by separating the pilot signals of each user in a simple manner, even when a different amount of cyclic shift is performed on a given sequence used as a pilot signal for users to be multiplexed.

Moreover, by means of the present invention, by assigning the middle part of the pilot signal transmission band to users with a poor propagation path condition, it is possible to improve the channel subcarrier channel estimation accuracy even with a poor propagation path of this user.

Also, by means of the present invention, by performing an abrupt change in the data transmission bands assigned to users between the middle part and the end parts of the pilot signal transmission band, it is possible to improve the channel estimation accuracy of the data subcarriers even in a poor state of the user propagation path.

Claims (22)

1. A radio communication method in a radio communication system in which each of the user terminals, together with the transmission of the data signal to the base station, using different data band frequencies that are assigned by the base station, performs time division multiplexing of the pilot signal with the data signal and transmits the resulting signal to a base station comprising: a step of determining a pilot transmission band for each user terminal so that the pilot transmission band spans the band n data transmission of the user terminal with a frequency offset; and the step of instructing each user terminal to transmit the pilot using the frequencies of said specific pilot transmission band. 2. The radio communication method according to claim 1, wherein the CAZAC sequence is used as said pilot signal. 3. The radio communication method according to claim 2, wherein the step of issuing the command comprises: the step of calculating the magnitude of said frequency offset for each user terminal and the magnitude of the cyclic shift of the CAZAC sequence corresponding to the number of multiplexed user terminals and the frequency offset; and the step of instructing each user terminal to cyclic shift said CAZAC sequence used as a pilot by the amount of cyclic shift, and to perform a frequency offset of said pilot transmission band by said frequency offset amount. 4. The radio communication method according to claim 1 or 3, comprising: the step of summing the frequency components of a portion of the pilot signals that do not overlap when the base station has received multiplexed pilot signals that have been transmitted from multiple user terminals; the step of multiplying the combination of the summation result and the received multiplexed pilot signals with a copy of the pilot signal in the frequency domain; and the step of converting the results of multiplying the copy in the frequency domain into a time-domain signal and, further, separating a portion of the signal of a given user terminal from the time-domain signal and performing channel estimation. 5. The radio communication method according to claim 2, wherein said step of issuing a command comprises: a step of calculating a magnitude of said frequency offset for each user terminal and a cyclic shift value of a CAZAC sequence corresponding to the number of multiplexed user terminals and the frequency offset value; and the step of instructing each user terminal to cyclic shift said CAZAC sequence used as a pilot by a cyclic shift, perform a frequency shift of the pilot transmission band by said frequency bias, and copy the frequency component of any extreme band on the opposite side pilot transmission bands to a strip where the entire data transmission band and the pilot transmission band of the user terminal do not overlap. 6. The radio communication method according to claim 5, comprising: the step of multiplying the received frequency components that correspond to the pilot signal transmission band of the user terminal with a copy of the pilot signal in the frequency domain when the base station received multiplexed pilot signals that were transmitted from a plurality of user terminals; and a step of converting the results of multiplying the copy into a time-domain signal, and then separating a portion of the user terminal signal from the time-domain signal and performing channel estimation. 7. The radio communication method according to claim 1, comprising: the step of issuing a command to a specific user terminal to multiply the pilot signals of all blocks by +1, and instructing other user terminals to multiply half the pilot blocks by +1 and multiply the remaining half of the pilot blocks -1 when an even number of pilot blocks are present in one frame;
a step of performing a computational operation of adding or subtracting for the pilot signals of all blocks, so that the pilot signal of a given user is stored when the base station has received multiplexed pilot signals that have been transmitted from multiple user terminals; the step of multiplying the calculation results with a copy of the pilot signal in the frequency domain; and a step of converting the results of multiplying the copy into a time-domain signal, and then separating a portion of the signal of said user terminal from the time-domain signal and performing channel estimation. 8. The radio communication method according to claim 1, comprising: the step of obtaining the state of the distribution path of user terminals; and the step of assigning, as a matter of priority, the middle band of the entire data band as a data band for a user terminal with a poor state of the distribution path and notification of the user terminal. 9. The radio communication method according to claim 1, comprising:
a step of performing stepwise control by periodically assigning a middle band and an end band of the entire data band as data bands for user terminals. 10. The base station in a radio communication system in which each of the user terminals, together with the transmission of the data signal to the base station, using different data band frequencies that are assigned by the base station, performs time division multiplexing of the pilot signal with the data signal and transmits the resulting signal to a base station, comprising: a resource control unit that determines a pilot transmission band for each user terminal so that this transmission band the Ilot signal covered the data terminal bandwidth of the user terminal with a frequency offset, and instructs the user terminal to transmit a pilot signal using the frequencies of said specific pilot signal band. 11. The base station of claim 10, in which the CAZAC sequence is used as said pilot signal. 12. The base station of claim 11, wherein said resource control unit comprises:
a cyclic shift amount calculating unit that calculates said frequency offset value for each user terminal and a cyclic shift value of a CAZAC sequence that corresponds to the number of multiplexed user terminals and the frequency offset value; and
a command issuing unit, which, together with issuing an instruction to each user terminal to perform a cyclic shift of said CAZAC sequence used as a pilot signal by the calculated amount of cyclic shift, instructs each user terminal to perform a frequency shift of the pilot signal transmission band by said value frequency offset. 13. The base station according to claim 11, in which said resource control unit comprises:
a cyclic shift amount calculating unit that calculates a cyclic shift amount of a CAZAC sequence for each user terminal according to the number of multiplexed user terminals and the frequency offset; and a command issuing unit, which, together with issuing a command to each user terminal to rotate said CAZAC sequence used as a pilot signal by a calculated amount of cyclic shift, instructs the user terminal to move the components of the pilot subcarrier that corresponds to said frequency offset to the adjacent band of the pilot transmission band on the opposite side. 14. The base station of claim 10 or 12, wherein said base station comprises a channel estimator that performs channel estimation for each user terminal; wherein said channel estimation unit comprises: a receiving unit that receives multiplexed pilot signals that are transmitted from a plurality of user terminals; a summing unit that summarizes the frequency components of the pilot portion of the signals that do not overlap; a copy multiplier unit that multiplies a combination of the summation result and the received multiplexed pilot signals with a copy of the pilot signal in the frequency domain; a conversion unit that converts the result of multiplying the copy into a time-domain signal; a separation unit that separates a portion of the signal of each user terminal from said time-domain signal; and an estimator that converts the separated time-domain signal to a frequency-domain signal to estimate the channel of each frequency. 15. The base station according to claim 11, wherein said resource control unit comprises: a cyclic shift calculation unit that calculates a magnitude of said frequency offset for each user terminal and a cyclic shift value of a CAZAC sequence that corresponds to the number of multiplexed user terminals and the frequency offset value; and a command issuing unit, which, together with issuing a command to each user terminal to perform a cyclic shift of said CAZAC sequence used as a pilot signal by the amount of cyclic shift, instructs each user terminal to perform a frequency shift of the pilot transmission band by said frequency offsets, and copy the frequency component of the extreme band on the opposite side of the pilot signal band to the band where the entire data band and the pilot signal transmission band of the user terminal does not overlap. 16. The base station of claim 11, wherein said resource control unit comprises: a cyclic shift amount calculation unit that calculates a cyclic shift amount of a CAZAC sequence for each user terminal according to the number of multiplexed user terminals and the frequency offset; and a command issuing unit, which, together with issuing an instruction to each user terminal to cyclically shift said CAZAC sequence used as a pilot signal by the calculated cyclic shift value, instructs the user terminal to copy the components of the pilot subcarrier that corresponds to said frequency offset to the adjacent band of the pilot transmission band on the opposite side. 17. The base station of claim 15, which comprises a channel estimator that performs channel estimation for each user terminal; and wherein said channel estimation block comprises:
a receiving unit that receives multiplexed pilot signals that are transmitted from a plurality of user terminals; a copy multiplier unit that multiplies the frequency components of the received multiplexed pilot signals, which correspond to the pilot signal transmission band of the user terminal, with a copy of the pilot signal in the frequency domain; a conversion unit that converts the result of multiplying the copy into a time-domain signal; a separation unit that separates a portion of a user terminal signal from a time domain signal; and an estimator that converts the separated time-domain signal to a frequency-domain signal to estimate the channel of each frequency. 18. The base station of claim 10, which contains a channel estimation unit that performs channel estimation for each user terminal; and wherein said channel estimation unit comprises: a receiving unit that receives multiplexed pilot signals that are transmitted from a plurality of user terminals;
an addition / subtraction unit which, when said resource control unit instructs a specific user terminal, multiply the pilot signals of all pilot blocks by +1 and instructs other user terminals to multiply the pilot signals of half the pilot blocks by +1 and multiply the pilot -signals of the remaining half of the blocks of pilot signals by -1, performs the computational process of adding or subtracting for pilot signals of all blocks of pilot signals so that the pilot signal of a given user saved;
a copy multiplying unit that multiplies a calculation result with a copy of the pilot signal in the frequency domain;
a conversion unit that converts the results of multiplying the copy into a time-domain signal;
a separation unit that separates a portion of a signal of a given user terminal from said time-domain signal; and
an estimator that converts the separated time-domain signal to a frequency-domain signal to estimate a channel of each frequency. 19. The base station of claim 10, wherein said resource control unit obtains distribution states of user terminals and, as a matter of priority, designates a middle band from the entire data transmission band as a data transmission band for a user terminal with a poor distribution path state, and notifies user terminals . 20. The base station of claim 10, in which the resource control unit performs hopping by periodically assigning the middle band and the last band of the entire data band as data bands for each user terminal. 21. A user terminal in a radio communication system in which each of the user terminals, together with transmitting a data signal to a base station, using different data band frequencies that are assigned by the base station, performs time division multiplexing of the pilot signal with the data signal and transmits the resulting signal to a base station, comprising: a receiving unit that receives uplink resource information from a base station; and a pilot signal generating unit that generates pilot signals according to instructions in the uplink resource information; wherein said pilot signal generating unit comprises: a CAZAC sequence generating unit which, based on the resource information, generates a CAZAC sequence with a predetermined sequence length and sequence number as a pilot signal;
a first conversion unit that converts the CAZAC sequence, which is a time-domain pilot, to a frequency-domain pilot; a subcarrier display unit that performs mapping of the pilot subcarrier components based on frequency offset information that is included in said resource information;
a second conversion unit that converts the pilot with the mapped subcarriers into a time domain signal; and
a cyclic shift unit that performs a cyclic shift on a CAZAC sequence based on a cyclic shift value that is included in said resource information, either before the first conversion or after said second conversion. 22. A radio communication method in a radio communication system in which data signals for the first and second users are respectively transmitted using the first and second groups of subcarriers, and pilot signals for the first and second users are multiplexed with data signals for these users, comprising the steps of: the pilot signal of the first user at frequencies other than the frequencies at which the pilot signal of the second user is located; and displaying the pilot subcarrier components such that one of the higher frequency subcarrier components corresponds to one of the lower frequency subcarrier components, the pilot signals being generated using the Zadoff-Chu sequence.

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