JP2011259108A - Radio communications system, transmitter and transmission method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate scheduling for a transmitter using DFT-S-OFDM.SOLUTION: A radio communications system comprises: a transmitter using DFT-S-OFDM; and a control unit that determines the number of subcarriers that the transmitter uses for transmission. The transmitter changes the method for generating signals to be transmitted in accordance with the number of the subcarriers determined by the control device.

Description

  The present invention relates to a wireless communication system, a transmission apparatus, and a transmission method.

  As the amount of data communication increases in recent years, there is an increasing need for a mobile communication system having higher frequency utilization efficiency, and various studies on a one-cell reuse cellular system that uses the same frequency band in all cells. It is being advanced. E-UTRA (Evolved Universal Terrestrial Radio Access): Highly functional wireless access system, which is being standardized mainly around 3GPP (3rd Generation Partnership Project) In the air interface system, an OFDMA (Orthogonal Frequency Division Multiple Access) system is being considered as a downlink transmission system candidate. Also, non-contiguous / continuous DFT-S-OFDM (Discrete Fourier Transform Spread OFDM; discrete Fourier transform spread OFDM, which supports non-continuous use of frequency and continuous use of frequency (link OFDM) method) It is being considered as a promising candidate for this transmission system.

The OFDMA scheme, which is a downlink candidate, is a scheme in which a user accesses a resource block (RB) unit divided by time and frequency using an OFDM signal having excellent resistance to multipath fading. However, since the OFDMA scheme has high PAPR (Peak-to-Average Power Ratio) ratio, it is not suitable as an uplink transmission scheme with severe transmission power limitation.
On the other hand, the DFT-S-OFDM scheme can maintain a good PAPR characteristic with respect to a multicarrier scheme such as OFDM by continuously using a frequency (RB) of a signal spread by DFT, and can secure a wide coverage. . In addition, the DFT-S-OFDM scheme can suppress degradation of PAPR characteristics to some extent while using frequencies flexibly by using frequencies discontinuously. In addition, in non-continuous / continuous DFT-S-OFDM, switching between non-continuous and continuous is considered based on transmission power (for example, refer to Patent Document 1, hereinafter referred to as a hybrid system). . If this hybrid method is used, the throughput for the terminal at the center of the cell can be improved while maintaining the cell coverage of the method using only contiguous DFT-S-OFDM, so that the throughput of the entire cell can be improved.

  On the other hand, a frequency clipping technique that does not transmit a part of the frequency spectrum of the contiguous DFT-S-OFDM scheme has been studied. FIG. 9 shows an example of the configuration of a terminal apparatus when Clipped DFT-S-OFDM (hereinafter referred to as Clipped DFT-S-OFDM) is used for uplink transmission. As shown in FIG. 9, first, the encoding unit 1000 performs error correction encoding of transmission data. Next, the modulation unit 1001 modulates transmission data. Next, the S / P converter 1002 performs serial / parallel conversion on the modulated transmission signal, and a DFT (Discrete Fourier Transform) unit 1003 performs discrete Fourier transform on the serial / parallel converted transmission signal. To convert it to a frequency domain signal.

  Next, the clipping unit 1004 clips a part of the output of the DFT unit 1003 based on the clipping information C output from the clipping control unit 1016, and outputs the remaining signal. Here, clipping means that there is no signal, and in this specification, the clipping ratio is defined as (1-clipping unit output / DFT unit input). However, when the clipping ratio is 0, it means a normal DFT-S-OFDM signal. The component of the signal to be clipped may be a component at a predetermined position, or a method of notifying from a control station such as a base station at every communication opportunity as in the mapping information shown below. Similarly, the clipping ratio may be a predetermined ratio or may be notified from a control station such as a base station at every communication opportunity.

  Subcarrier mapping section 1005 assigns the signal output from clipping section 1004 to subcarriers (resource blocks) used for transmission. Also, the subcarrier mapping unit 1005 performs this allocation based on the mapping information MI, and inserts zeros into subcarriers that are not used for transmission. This mapping information is transmitted from the control station, received by the reception antenna unit 1012, and demodulated by the reception unit 1015 via the radio unit 1013 and the A / D (analog signal-digital signal) conversion unit 1014. can get.

  There are two methods for allocating a transmission signal to subcarriers used for transmission: a method of using subcarriers continuously and a method of allocating discontinuously. When the subcarrier is continuously used with a clipping rate of 0, the generated signal is equivalent to a single carrier signal.

  An IFFT (Inverse Fast Fourier Transform) unit 1006 receives a transmission signal allocated on a subcarrier used for transmission, and performs an inverse Fourier transform on the input transmission signal, thereby performing frequency domain Convert signal to time domain signal. The converted signal is converted from a parallel signal into a serial signal via a P / S conversion unit 1007 and input to a CP (Cyclic Prefix) insertion unit 1008. CP insertion section 1008 inserts CP (a signal obtained by copying the symbol after IFFT) into the converted signal. Next, the D / A (analog signal-digital signal) conversion unit 1009 converts the signal with the CP inserted into an analog signal. Next, radio section 1010 up-converts the signal converted into the analog signal into a radio frequency band signal and transmits it from transmission antenna section 1011.

International Publication No. WO2008 / 081876

  When a signal is generated using the DFT-S-OFDM method, generally, as shown in FIG. 9, DFT (block 1003 in FIG. 9) is used. For this reason, DFT-S-OFDM is sometimes called DFT Pre-coded OFDM. The DFT has a large circuit scale unless the factor when the number of input signals (equal to the number of output signals) is subjected to prime factorization is limited. For example, the number of signals input to the DFT is limited to a number that does not include other than 2, 3, and 5 as prime factors. Since the number of signals input to the DFT is equal to the number of output signals, if the number of input signals is limited, the number of subcarriers to be used is limited.

  However, when the number of subcarriers to be used is limited, when the frequency to be used is allocated to a communication apparatus using the DFT-S-OFDM scheme (hereinafter referred to as scheduling), the number of subcarriers is not limited. Therefore, there is a problem that scheduling must be performed while considering the above, scheduling processing becomes complicated, and scheduling takes time.

  The present invention has been made in view of the above circumstances, and provides a radio communication system, a radio transmission apparatus, and a radio transmission method capable of facilitating scheduling for a transmission apparatus using the DFT-S-OFDM scheme. The purpose is that.

(1) The present invention has been made to solve the above-described problems, and the wireless communication system of the present invention generates a frequency axis signal by converting a time axis signal to a time frequency axis, and converts the frequency axis signal to A wireless communication system comprising a transmission device arranged and transmitted on subcarriers, and a control device that determines the number of subcarriers used by the transmission device for transmission, wherein the transmission device is determined by the control station device The method is characterized in that the method of generating a signal to be transmitted is changed according to the number of subcarriers.

(2) Moreover, the radio | wireless communications system of this invention is the above-mentioned radio | wireless communications system, Comprising: The said transmission apparatus differs from the said number of subcarriers, when the determined number of subcarriers is a predetermined value. The frequency axis signal is generated by converting the time axis signal into the time frequency axis in units of numbers.

(3) Moreover, the radio | wireless communications system of this invention is the above-mentioned radio | wireless communications system, Comprising: The said different number is a number larger than the determined said subcarrier number, The said transmission apparatus is the said determined subcarrier. When the number of carriers is the predetermined value, out of the generated frequency axis signals, the frequency axis signals of the determined number of subcarriers are arranged and transmitted on subcarriers.

(4) Moreover, the radio | wireless communications system of this invention is the above-mentioned radio | wireless communications system, Comprising: The said different number is a number smaller than the determined said subcarrier number, The said transmitter is the said determined subcarrier. When the number of carriers is the predetermined value, a signal obtained by adding a signal to the generated frequency axis signal and transmitting the determined number of subcarriers arranged in subcarriers It is characterized by that.

(5) Moreover, the radio | wireless communications system of this invention is the above-mentioned radio | wireless communications system, Comprising: The said signal to add is a part of the produced | generated frequency-axis signal, It is characterized by the above-mentioned.

(6) Moreover, the radio | wireless communications system of this invention is the above-mentioned radio | wireless communications system, Comprising: The said different number is characterized by the ratio of the determined number of subcarriers with respect to the said different number being larger than predetermined value. To do.

(7) Moreover, the radio | wireless communications system of this invention is one of the above-mentioned radio | wireless communications systems, Comprising: At least one part of the said predetermined value is prohibited as the number of input signals to the said time-frequency-axis conversion. Characterized by a number.

(8) Moreover, the radio | wireless communications system of this invention is the above-mentioned radio | wireless communications system, Comprising: At least 1 is the OFDM system among the generation methods of the said signal to transmit, It is characterized by the above-mentioned.

(9) Moreover, the transmission apparatus of the present invention is a transmission apparatus that generates a frequency axis signal by performing time-frequency-axis conversion on a time-axis signal, and transmits the frequency-axis signal arranged in a subcarrier. The transmitting apparatus is characterized in that a method of generating a signal to be transmitted is changed according to the number of subcarriers on which the frequency axis signal is arranged.

(10) In addition, the transmission method of the present invention includes a transmission apparatus that performs time-frequency-axis conversion on a time-axis signal, generates a frequency-axis signal, and transmits the frequency-axis signal on a subcarrier, and the transmission apparatus Is a transmission method in a wireless communication system comprising a control device for determining the number of subcarriers used for transmission, wherein the transmission device generates a signal to be transmitted according to the number of subcarriers determined by the control station device It has the process of determining a method.

  According to the present invention, scheduling for a transmission apparatus that uses the DFT-S-OFDM scheme can be facilitated.

It is a conceptual diagram which shows the structure of the radio | wireless communications system in the 1st Embodiment of this invention. It is a schematic block diagram which shows the structure of the terminal device 11a in the embodiment. An example of input / output signals of the spectrum deforming unit 104 in the same embodiment is shown. It is a schematic block diagram which shows the structure of the base station apparatus in the same embodiment. The mode of the input-output of the spectrum modification part 104 in the 2nd Embodiment of this invention is shown. It is a figure which shows the mode of the spectrum corresponding to FIG. 5 at the time of producing | generating and inserting another signal in the same embodiment. It is a schematic block diagram which shows the structure of the terminal device 21a in the 3rd Embodiment of this invention. It is a schematic block diagram which shows the structure of the terminal device 31 in the 4th Embodiment of this invention. It is a schematic block diagram which shows the structure of the transmission apparatus of the conventional DFT-S-OFDM system which performs clipping.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to such embodiment, A various change is possible within the range of the technical thought.
In each of the following embodiments, a base station apparatus includes a control apparatus that performs scheduling and a reception apparatus that receives a DFT-S-OFDM signal, and a terminal apparatus includes a transmission apparatus that transmits a DFT-S-OFDM signal. Although it is a radio communication system, the present invention is not limited to these configurations. For example, the base station device may include a control device and a transmission device, and the terminal device may include a reception device, or the control device, the transmission device, and the reception device may be separate devices. .

[First Embodiment]
FIG. 1 is a conceptual diagram showing a configuration of a wireless communication system according to the first embodiment of the present invention. The wireless communication system 10 in the present embodiment is a mobile communication system including terminal devices 11a, 11b,... 11c, and a base station device 12. Transmission from the terminal apparatuses 11a, 11b,... 11c to the base station apparatus 12 is basically a DFT-S-OFDM system. Transmission from the base station apparatus 12 to the terminal apparatuses 11a, 11b,... 11c is the OFDMA system, but other systems may be used. The terminal devices 11a, 11b,... 11c access the base station device 12 in units of RBs (resource blocks). Each RB is composed of 4 subcarriers, and the total number of RBs is 16. The number of subcarriers constituting the RB is an example, and other values may be used. However, it is desirable that the prime factors such as 12 and 24 do not include values other than the prime factors allowed by the DFT unit 103 in FIG.

  Also, the base station apparatus 12 determines the number of RBs (number of subcarriers) and the RB position used by the terminal apparatuses 11a, 11b,... 11c and notifies the terminal apparatuses 11a, 11b,. Note that the number of RBs (number of subcarriers) may not be explicitly notified, and the RB position to be used may be notified as information indicating the number of subcarriers. Further, in order to reduce the burden of the DFT operation of the DFT unit 103 in FIG. 2 to be described later (to prevent the circuit scale from becoming large), the number of input signals to the DFT unit 103 (the RB number control unit 120 in FIG. 2 to be described later). Is limited to a number that does not include numbers other than 2, 3, and 5 as prime factors. That is, it is prohibited that the number of input signals is a number that includes numbers other than 2, 3, and 5 as prime factors.

  FIG. 2 is a schematic block diagram illustrating the configuration of the terminal device 11a. Since the terminal devices 11b,... 11c have the same configuration as the terminal device 11a, the description thereof is omitted. The terminal device 11a includes a transmission device 130, a reception antenna unit 112, a radio unit 113, an A / D conversion unit 114, and a reception unit 115. Transmitting apparatus 130 includes coding section 100, modulation section 101, S / P conversion section 102, DFT section 103, spectrum modification section 104, subcarrier mapping section 105, IFFT section 106, P / S conversion section 107, and CP insertion section 108. , D / A conversion section 109, radio section 110, transmission antenna section 111, pilot signal generation section 116, and RB number control section 120.

The encoding unit 100 receives the transmission data TD1, performs error correction encoding on the input transmission data TD1, and outputs the transmission data subjected to error correction encoding to the modulation unit 101.
Modulation section 101 receives transmission data subjected to error correction coding, modulates transmission data subjected to error correction coding, and outputs the modulated transmission signal to S / P conversion section 102.
The S / P conversion unit 102 receives the modulated transmission signal, converts the modulated transmission signal from a serial signal to a parallel signal, and outputs the parallel signal to the DFT unit 103. Here, when converting from a serial signal to a parallel signal, serial / parallel conversion is performed with the number of subcarriers determined from the transmission RB number TN specified by the RB number control unit 120 as a unit. That is, the S / P converter 102 performs serial / parallel conversion in units of subcarriers obtained by multiplying the number of transmission RBs TN by the number of subcarriers (here, 4) constituting the resource block.

  A DFT (Discrete Fourier Transform) unit 103 performs time-frequency axis conversion, that is, discrete Fourier transform, on the parallel signal output from the S / P conversion unit 102 to convert the time-axis signal into a frequency-axis signal. Similar to the S / P conversion unit 102, the DFT unit 103 performs DFT processing in accordance with the transmission RB number TN specified by the RB number control unit 120. Hereinafter, the signal converted into the frequency axis signal is referred to as a first frequency signal.

  In the present embodiment, the spectrum modifying unit 104 performs clipping (missing) on the first frequency signal (spectrum) based on the allocated RB number SN output from the RB number control unit 120. That is, if the number of input signals of the spectrum modification unit 104 is M and the number of output signals of the spectrum modification unit 104 is N, M ≧ N. Hereinafter, the output of the spectrum transformation unit 104 is referred to as a second frequency signal. The spectrum modification unit 104 may output the input first frequency signal as it is as the second frequency signal without performing clipping. In the clipping operation, when some signals (spectrums) are deleted from the output of the DFT unit 103 based on a certain rule, for example, clipping may be performed from a high frequency band or from a low frequency. Further, clipping may be performed from both sides of the band. In addition, the frequency band (subcarrier) to be clipped by the base station apparatus 12 may be designated, but in order to reduce control information when communicating with the base station apparatus 12, it is based on a predetermined rule. Clipping can reduce system control information and improve system performance. Detailed control of the RB number control unit 120 will be described later.

Pilot signal generating section 116 generates a pilot signal that is a known signal sequence in base station apparatus 12 and outputs the pilot signal to subcarrier mapping section 105.
To the subcarrier mapping unit (subcarrier allocation unit) 105, the signal clipped by the spectrum modification unit 104, the mapping information MI demodulated by the reception unit 115, and the pilot signal are input. Subcarrier mapping section 105 assigns the clipped signal to subcarriers used for transmission based on mapping information MI. Subcarrier mapping section 105 also assigns pilot signals to predetermined subcarriers. Furthermore, subcarrier mapping section 105 inserts zeros into subcarriers that are not used for transmission. Further, the assigned subcarriers may be continuous or discontinuous.

  This mapping information is transmitted from the base station apparatus 12, received by the receiving antenna unit 112, and demodulated by the receiving unit 115 via the radio unit 113 and the A / D conversion unit 114. Then, receiving section 115 outputs demodulated mapping information MI to subcarrier mapping section 105. Similarly, the number of assigned RBs SN transmitted from the base station apparatus 12 is also output to the S / P conversion unit 102 and the DFT unit 103.

IFFT section 106 receives a transmission signal assigned by subcarrier mapping section 105 on the subcarrier used for transmission. The IFFT unit 106 performs inverse Fourier transform on the input transmission signal to convert the frequency domain signal into a time domain signal, and outputs the converted time domain signal to the P / S conversion unit 107.
A P / S (Parallel Serial) converter 107 receives the converted time domain signal, converts the converted time domain signal from a parallel signal to a serial signal, and inserts the converted signal into a CP. Output to the unit 108.
CP (Cyclic Prefix) insertion section 108 receives a signal converted into a serial signal, inserts CP (a signal obtained by copying the symbol after IFFT) into the signal converted into a serial signal, and inserts CP Is output to the D / A converter 109.

The D / A converter 109 converts the CP inserted signal from a digital signal to an analog signal,
The signal converted into the analog signal is output to the wireless unit 110.
Radio section 110 receives a signal converted into an analog signal, up-converts the signal converted into an analog signal into a radio frequency band signal, and transmits the signal up-converted into a radio frequency band signal from transmission antenna section 111. .

  Next, a control method of the RB number control unit 120 will be described. The number of RBs control unit 120 receives the number of assigned RBs SN notified from the base station apparatus 12 and demodulated by the reception unit 115. The RB number control unit 120 determines the transmission RB number TN to be output to the S / P conversion unit 102 and the DFT unit 103 based on this input information. Thereby, the RB number control unit 120 determines a method for generating a signal to be transmitted in the terminal device 11a. Note that the mapping information MI may be input to the RB number control unit 120, and the RB number control unit 120 may calculate the allocated RB number based on the mapping information MI.

  In the present embodiment, since the number of input signals that can be processed by the DFT unit 103 is a number that does not include numbers other than 2, 3, and 5 in the prime factor, the RB number control unit 120 includes 2, 3, and 5 in the prime factor. The number of transmission RBs TN is determined so as to be a number that does not include other numbers. The number-of-RBs control unit 120 determines the number of transmission RBs TN according to the association between the number of allocated RBs and the number of transmission RBs stored in advance (Table 1 shown below). This table 1 shows that when the assigned RB number SN specified by the base station apparatus 12 includes a number other than 2, 3, 5 in the prime factor, the assigned RB number SN does not fall below the assigned RB number SN, and the prime factor is 2, 3, 5 Among the numbers not including the number other than, the number closest to the allocated RB number SN is selected. That is, when the number of assigned subcarriers is a predetermined value, the terminal apparatuses 11a to 11c perform DFT using a number different from the assigned number of subcarriers as a unit. When the allocated RB number SN does not include numbers other than 2, 3, and 5 in the prime factors, the allocated RB number SN and the transmission RB number TN are the same value. Also, the value obtained by multiplying the number of transmitted RBs TN by 4 which is the number of subcarriers constituting the resource block is the number M of input signals of the spectrum modifying unit 104, and the value obtained by multiplying the allocated RB number SN similarly by 4 is the spectrum. The number of output signals of the deforming unit 104 is N. In Table 1, portions where the number of assigned RBs is different from the number of transmitted RBs are underlined.

  FIG. 3 shows an example of input / output signals of the spectrum deforming unit 104. The upper part of FIG. 3 is the case where the number of assigned RBs is 8, and the lower part is 7. The left side with the symbol Din1 represents the input signal, and the right side with the symbol Dout1 represents the output signal. Each of the chevron portions hatched with diagonal lines indicates that a signal is disposed, and each of the open chevron portions indicates that no signal is disposed. As can be seen from the difference in Table 1, the numbers of assigned RBs are 7 and 8. When the number of assigned RBs is 8, spectrum modifying section 104 outputs the input 32 signals as they are, and when the number of assigned RBs is 7, 28 of the input 32 signals. Output a signal. That is, when the number of assigned RBs matches the number of transmission RBs, clipping is not performed, and clipping is performed only when they do not match. In this way, by controlling the number of transmission RBs according to the number of allocated RBs on the transmission side, scheduling can be performed more easily without considering the number of allocated RBs even when there is a limitation due to the DFT calculation.

  Here, as a method of obtaining the number of transmission RBs, a correspondence between the number of assigned RBs stored in advance and the number of transmission RBs is stored in advance, and a method of using this is shown. However, when the number of RBs increases, The amount will increase. In that case, the number of transmission RBs may be obtained by replacing a prohibited prime number (in this embodiment, a prime number greater than 5, for example, 7, 11, 13, etc.) with a corresponding number. For example, if the result of prime factorization has a power of 7, it is replaced with a power of 8. If there is a power of 11, the power is replaced with a power of 12. According to such a method, there is an advantage that even when the number of RBs increases, a table to be stored is not necessary.

  Table 2 is another example of association between the number of assigned RBs and the number of transmission RBs stored in advance by the RB number control unit 120. In Table 2, clipping is used more actively in order to further improve the frequency utilization efficiency while considering the limitation due to the DFT operation as in Table 1. In Table 2, a portion where the number of assigned RBs differs from the number of transmitted RBs is underlined.

  In addition to the limitation of Table 1, Table 2 adds a limitation such that the clipping rate is as high as possible within a range where the clipping rate does not exceed 0.25. The clipping rate is (number of assigned RBs−number of transmitted RBs) / (number of assigned RBs). Further, in Table 2, even when the number of assigned RBs SN does not include a number other than 2, 3, and 5 in the prime factors, the clipping ratio is as high as possible within a range where the clipping ratio does not exceed 0.25. The number of transmission RBs is set.

  Even when the base station apparatus 12 receives a signal in which a part of the spectrum is clipped, the base station apparatus 12 uses a non-linear iterative equalization (for example, frequency domain SC / MMSE turbo equalization) to improve reception characteristics such as an error rate. The transmission data is reproduced without deterioration. Of course, it is possible to apply nonlinear iterative equalization even when it is not clipped, and although the amount of improvement in reception characteristics is reduced, this application improves reception performance.

  FIG. 4 is a schematic block diagram showing the configuration of the base station apparatus in the present embodiment. As illustrated in FIG. 10, the base station apparatus 12 according to the present embodiment includes a receiving apparatus 230, a control apparatus 240, a transmission unit 220, a D / A conversion unit 221, a radio unit 222, and a transmission antenna 223. The reception device 230 includes a reception antenna unit 200, a radio unit 201, an A / D conversion unit 202, a synchronization unit 203, a CP removal unit 204, an S / P conversion unit 205, an FFT unit 206, a subcarrier demapping unit 207, a first Zero insertion unit 208, cancellation unit 209, equalization unit 210, demodulation / error correction decoding unit 211, repetition control unit 212, determination unit 213, propagation path estimation unit 214, second zero insertion unit 215, propagation path multiplication unit 216, A DFT unit 217 and a replica generation unit 218 are provided. The control device 240 includes a scheduling unit 219.

Radio section 201 receives a signal received by reception antenna section 200, converts the input signal to a frequency that can be A / D converted, and outputs the converted signal to A / D conversion section 202.
The A / D conversion unit 202 receives the converted signal, converts the input signal from an analog signal to a digital signal, and outputs the converted signal to the synchronization unit 203.
The synchronization unit 203 receives a signal converted into a digital signal, establishes symbol synchronization with respect to the input signal, and outputs the signal with established symbol synchronization to the CP removal unit 204.
The CP removal unit 204 receives a signal with established symbol synchronization, removes the CP for each symbol from the input signal with established symbol synchronization, and converts the signal from which the CP for each symbol has been removed to the S / P conversion unit 205. Output to.

The S / P converter 205 receives the signal from which the CP for each symbol has been removed, converts the input signal from which the CP for each symbol has been removed from a serial signal to a parallel signal, and converts the signal converted to a parallel signal into an FFT. The data is output to the unit 206.
The FFT unit 206 receives the signal converted into the parallel signal, performs fast Fourier transform on the input signal converted into the parallel signal, converts the signal in the time domain to the signal in the frequency domain, and converts the signal in the frequency domain. The signal converted into is output to the subcarrier demapping section 207.
The subcarrier demapping unit 207 separates the signal converted into the frequency domain signal into the signal for each user according to the scheduling determined by the scheduling unit 219 for the current transmission, and first separates the signal into the signal for each user. Output to the zero insertion unit 208. Further, the signal separated by the subcarrier demapping unit 207 is smaller than the number of output signals of the DFT unit 103 on the transmission side when clipping is performed on the transmission side. Further, subcarrier demapping section 207 extracts pilot signal P for propagation path estimation from the signal converted into the frequency domain signal, and outputs the extracted pilot signal P to transmission path estimation section 514. Subsequent signal processing is performed for each user's received signal.

  The first zero insertion unit 208 receives a signal separated into signals for each user, and a signal clipped by the spectrum modifying unit 104 on the transmission side with respect to the input signals separated for each user. Zeros are inserted into the same frequency component, and a signal with the zeros inserted is output to the cancel unit 209. The first zero insertion unit 208 stores the clipping rules in the spectrum modification unit 104 in advance. For example, when the spectrum modification unit 104 clips signals at both ends, the output signal of the subcarrier demapping unit 207 Add zeros to both ends of. As a result, the same number of frequency signals as the output of the DFT unit 103 used on the transmission side are output from the first zero insertion unit 208.

  Note that first zero insertion section 208 stores the association between the number of assigned RBs and the number of transmitted RBs (Tables 1 and 2), and from the number of signals input from subcarrier demapping section 207, assigns assigned RBs. The number is determined, and zeros are inserted so as to be the number of transmission RBs corresponding to the number of allocated RBs. Therefore, when clipping is not performed in the spectrum deforming unit 104, the first zero insertion unit 208 outputs the input signal as it is without performing zero insertion.

The propagation path estimation unit 214 receives a propagation path estimation pilot signal, calculates a propagation path estimation value using the input pilot signal, and outputs the calculated propagation path estimation value to the second zero insertion unit 215. .
The second zero insertion unit 215 receives the calculated propagation path estimation value, inserts zero at the position of the clipped spectrum with respect to the input propagation path estimation value, and inserts the propagation path estimation value CE with the zero inserted. Are output to the equalization unit 210 and the transmission path multiplication unit 216.
The transmission path multiplication unit 216 receives the channel estimation value CE with the zero inserted, and multiplies the input channel estimation value CE with the zero inserted by the frequency domain signal output by the DFT unit 217. And the multiplication result of the propagation path estimation value is output to the cancel unit 209.

  The cancel unit 209 receives the signal with zero inserted and the multiplication result of the propagation path estimation value, and the soft replica generated by the replica generation unit 218 based on the reliability of the own signal with respect to the input signal, Then, the multiplication result of the propagation path estimated value with zero inserted at the clipped spectrum position is subtracted. As described above, in the frequency domain SC / MMSE turbo equalization targeted in this embodiment, the replica of the desired signal is once canceled and the residual signal component is calculated.

  This is because an equalization unit 210 (to be described later) performs an inverse matrix operation. Therefore, if cancellation and equalization are repeated while leaving only the desired signal, it is necessary to perform the inverse matrix operation several times for the desired signal included in the block. For this reason, by inputting the canceled residual components to the equalization unit 210, the residuals can be handled in common in the block, and all weights can be calculated if the inverse matrix operation is performed once in the block. In other words, the amount of computation associated with the inverse matrix computation is reduced by separately inputting a replica to the equalization unit 210 and reconfiguring it. However, since the cancel unit 209 has not generated a signal replica in the first process, the cancel signal is not performed and the received signal is output to the equalization unit 210 as it is.

  The equalization unit 210 obtains the residual component that is the output of the cancellation unit 209, the channel estimation value CE of the desired signal that is the output of the second zero insertion unit 215, and the replica of the desired signal that is the output of the replica generation unit 218. Signal equalization. Specifically, the equalization unit 210 calculates optimal weights from residual components, propagation path estimation values, and signal replicas, and demodulates the final equalized time-axis signal multiplied by the optimal weights. Output to the error correction decoding unit 211. However, since the replica is not input in the first process, this is equivalent to the conventional MMSE (Minimum Mean Squared Error) equalization without cancellation. As described above, the base station apparatus 12 according to the present embodiment performs equalization by treating the spectrum clipped on the transmission side as if it has been lost due to a drop in the propagation path. By doing this, it is possible to correctly reproduce the signal that should be transmitted (the signal before clipping on the transmission side).

The demodulation / error correction decoding unit 211 receives an equalized signal, performs demodulation and error correction on the input signal, and provides logarithmic likelihood of the sign bit with increased reliability for the demodulated and error-corrected signal. A ratio (LLR: Log likehood Ratio) is calculated, and the calculated LLR and the signal subjected to demodulation and error correction are repeatedly output to the control unit 212.
The repetition number control unit 212 receives the calculated LLR and the signal that has been demodulated and error-corrected, calculates the number of times to repeat the process based on the input LLR, and controls the repetition process based on the calculation result. When the processing is repeated, the repetition number control unit 212 outputs a signal obtained by performing LLR, demodulation, and error correction to the replica generation unit 218 in order to generate a soft replica of the signal. In addition, the repetition number control unit 212 repeats the processing a predetermined number of times, and then outputs a demodulated and error-corrected signal to the determination unit 213.

The replica generation unit 218 is a soft replica proportional to the reliability according to the LLR of the sign bit, and generates a replica of the desired signal. The replica generation unit 218 outputs the desired signal replica generated in this way to the DFT unit 517 in order to cancel the desired frequency signal once in the cancellation unit 209, and further outputs the desired signal during equalization. Output to equalization section 510 for reconfiguration.
In this way, by repeatedly performing the processes of the cancel unit 209 to the repetition control unit 212 and the transmission line multiplication unit 216 to the replica generation unit 218, it is possible to obtain code bits with gradually increasing reliability.
After repeating a predetermined number of times controlled by the repetition control unit 212, the determination unit 213 receives the demodulated and error-corrected signal that is the output of the iterative control unit 212, and converts the demodulated and error-corrected signal to the input signal. On the other hand, a hard decision is made and the decoded data is extracted. Then, the determination unit 213 outputs the extracted code data to the signal processing unit (not shown) of the base station apparatus 12 as reception data RD.

  Further, in the present embodiment, the configuration example of the base station apparatus 12 that sequentially selects the received signal of each user and serially processes the selected signal has been described. However, the first zero insertion unit 208, the cancellation unit 209, A configuration in which equalization section 210, demodulation / error correction decoding section 211, replica generation section 218, DFT section 217, propagation path multiplication section 216, propagation path estimation section 214, second zero insertion section 215, etc. are provided as many as the number of users. By doing so, it is also possible to perform processing for all users (terminal devices) simultaneously. Furthermore, the predetermined number of repetitions may be fixed, or adaptive control may be performed such that the LLR determination result is repeated until there is no error.

  In the advanced reception processing shown in the present embodiment, processing delay and power consumption may become problems due to repeated processing. Therefore, iterative processing may be performed only for the signal of the terminal device that performs clipping. Thereby, such a problem can be solved without deteriorating the characteristics.

  The scheduling unit 219 assigns RBs (ie, sub-bands) to the terminal devices 11a to 11c based on the channel estimation values of the terminal devices 11a to 11c and the base station device 12 estimated by the channel estimation unit 214. Number of carriers). At this time, the scheduling section 219 determines the RB to be allocated to the terminal apparatuses 11a to 11c without being restricted by the number of input signals in the DFT section 103 for the number of RBs to be allocated. For this reason, since RB with good propagation path characteristics can be assigned to each of the terminal devices 11a to 11c, scheduling with high frequency utilization efficiency can be performed. Further, since clipping is performed in the terminal apparatuses 11a to 11c according to the number of assigned RBs, the number of transmission RBs is larger than the number of assigned RBs, and the frequency use efficiency can be increased.

  The scheduling unit 219 outputs mapping information, which is information indicating the RB allocated to each of the terminal devices 11a to 11c, and the number of allocated RBs to the transmission unit 220. The transmission unit 220 generates a transmission signal by performing error correction coding, modulation, or the like on the transmission data TD2, the mapping information, and the number of assigned RBs to be transmitted to each of the terminal devices 11a to 11c, and generates a transmission signal. To 221. The D / A conversion unit 221 receives a transmission signal that is a digital signal, performs digital / analog conversion on the transmission signal, and outputs an analog signal as a conversion result to the radio unit 222. The radio unit 222 up-converts the analog signal to a radio frequency and transmits the analog signal to the terminal devices 11a to 11c via the transmission antenna 223.

As described above, by performing clipping (spectrum modification) in the terminal apparatuses 11a to 11c, scheduling that is RB allocation in the base station apparatus 12 is facilitated, and further, frequency utilization efficiency can be improved.
In addition, the reception device 230 of the base station device 12 can obtain a good reception characteristic by using non-linear iterative equalization even when receiving a signal in which a part of the spectrum is clipped. Each throughput can be improved.

[Second Embodiment]
In the first embodiment, in addition to facilitating scheduling, the frequency utilization efficiency is increased. In the second embodiment, in addition to facilitating scheduling, stable communication characteristics are obtained. We will show you how. The configuration of the wireless communication system and the configuration of the terminal device in this embodiment are the same as those shown in the first embodiment (FIGS. 1 and 2). However, the control of the RB number control unit 120 in the terminal devices 11a to 11c is different from that in the first embodiment. Note that, in order to receive a clipped signal as in the first embodiment, it is preferable to use a receiving device 230 that performs an iterative process as shown by the base station device 12 in FIG. The reception device 230 may not use the iterative process.

  Table 3 shows correspondence between the number of assigned RBs and the number of transmitted RBs stored in advance by the RB number control unit 120 in the present embodiment. In Table 3, as in Table 1, the number of input signals that can be processed by the DFT unit 103 is a number that does not include numbers other than 2, 3, and 5 as its prime factors. Table 3 shows that when the number of assigned RBs specified by the base station apparatus 12 includes a number other than 2, 3, and 5 as a prime factor, the number of assigned RBs does not exceed the number of assigned RBs, and the prime factor is 2, 3, In this example, the number closest to the number of assigned RBs is selected from numbers that do not include numbers other than 5. Also in Table 3, as in Table 1, portions where the number of assigned RBs and the number of transmitted RBs are different are clearly indicated by underlining.

  FIG. 5 shows an input / output state of the spectrum deforming unit 104. The upper part of FIG. 5 is the case where the number of assigned RBs is 8, and the lower part is 7. The left side with the symbol Din2 represents the input signal, and the right side with the symbol Dout2 represents the output signal. As can be seen from the difference in Table 3, the numbers of assigned RBs are 7 and 8. That is, when the number of assigned RBs matches the number of transmission RBs, the spectrum modifying unit 104 does not modify the spectrum, and performs the modification only when they do not match. In this embodiment, since the number of transmission RBs does not exceed the number of allocated RBs, when the number of allocated RBs and the number of transmission RBs do not match, a part of the spectrum is copied to the spectrum as a spectrum modification, so that the number of transmission RBs is increased. From the corresponding number of input signals, the number of output signals corresponding to the number of assigned RBs is generated.

  In the example of FIG. 5, the output spectrum with the assigned RB number of 7 is generated from the input signal with the transmission RB number of 6 by copying the four spectra located at the leftmost of the input to the right. This copying method is not limited to that shown in this embodiment, and can be realized by various methods.

  In the present embodiment, a method of obtaining stable communication characteristics by copying a spectrum has been shown. However, if RB allocation is performed so that the communication characteristics can be maintained, the frequency diversity effect may not be expected. Therefore, instead of copying, another signal may be generated and inserted. FIG. 6 is a diagram showing the state of the spectrum corresponding to FIG. 5 when another signal is generated and inserted. The upper part of FIG. 6 is the case where the number of assigned RBs is 8, and the lower part is 7. The left side with the symbol Din3 represents the input signal, and the right side with the symbol Dout3 represents the output signal. As another signal to be generated, there are a control signal, bits deleted (punctured) when generating error correction coding, a frequency signal for improving PAPR characteristics, and the like. Further, the signal format of the other signal may be the same as the signal format of the original signal (DFT-S-OFDM in the present embodiment) or may be different (for example, simply OFDM). .

  By controlling the number of transmission RBs according to the number of allocated RBs on the transmission side in this way, even when there is a limitation due to DFT calculation, it is not necessary to consider the number of allocated RBs, and scheduling can be performed more easily. . Further, since it is possible to obtain a frequency diversity effect with respect to the copied spectrum by the receiving device 230, it is possible to obtain stable communication characteristics.

[Third Embodiment]
In the present embodiment, clipping is performed by the spectrum transformation unit as in the first embodiment, but a method for reducing the influence of clipping will be described. The configuration of the wireless communication system in the present embodiment is the same as that shown in the first embodiment (FIG. 1). However, it replaces with terminal device 11a-11c, and is provided with terminal device 21a-21c.

  FIG. 7 is a schematic block diagram showing the configuration of the terminal device 21a according to the present invention. In the figure, the same numbers (100, 101, 103 to 116, 120) are assigned to blocks having the same functions as those in FIG. 2 differs from the configuration of the terminal device 11a shown in FIG. 2 in that a known data insertion unit 130 is added to the transmission device 131 instead of the transmission device 130, and that the S / P conversion unit 102 is replaced with the S / P. The conversion unit 141 is provided, and the S / P conversion unit 131 is input with the number of assigned RBs SN. The method of calculating the number of transmission RBs by the RB number control unit 120 is the same as that shown in Table 1. Moreover, since the structure of the terminal devices 21b-21c is the same as that of the terminal device 21a, description is abbreviate | omitted.

  The operation difference between the terminal device 21a and the terminal device 11a will be described. S / P changing section 141 inputs data from modulating section 101 according to the number of assigned RBs. When the value obtained by subtracting the number of assigned RBs from the number of transmitted RBs is 0, S / P conversion is performed as it is, and the result is output to the DFT unit 103. When the value obtained by subtracting the number of assigned RBs from the number of transmission RBs is not 0, data from the known data insertion unit 140 is input according to the number, and S / P conversion is performed according to the number of transmission RBs. The subsequent operation is the same as that of the terminal device 11a shown in the first embodiment.

  By inserting known data into a part of transmission data in this way, it is not possible to improve frequency utilization efficiency by clipping, but stable communication can be performed while maintaining the effect of facilitating scheduling. become.

[Fourth Embodiment]
In the first to third embodiments, the method of limiting the number of DFT input signals by setting the number of transmission RBs according to the number of allocated RBs has been described. However, in the present embodiment, according to the number of allocated RBs, A method of limiting the number of DFT input signals by switching between DFT-S-OFDM and other communication methods will be described. The configuration of the wireless communication system in the present embodiment is the same as that shown in the first embodiment (FIG. 1). However, terminal devices 31a to 31c are provided instead of the terminal devices 11a to 11c.

  FIG. 8 is a schematic block diagram showing the configuration of the terminal device 31 in the present embodiment. In the figure, the same numbers (100 to 102, 105 to 116) are assigned to blocks having the same functions as those in FIG. 2 differs from the configuration of the terminal device 11a shown in FIG. 2 in that the DFT unit 103 is changed to the ON / OFF control DFT unit 150 in the transmission device 132 instead of the transmission device 130, and the spectrum modification unit 104 and the number of RBs are controlled. The part 120 is not provided. The receiving unit 115 outputs the allocated RB number SN to the S / P conversion unit 102 and the ON / OFF control DFT unit 150, and the S / P conversion unit 102 configures a resource block in the allocated RB number SN. Serial / parallel conversion is performed in units of the number of subcarriers multiplied by the number of subcarriers to be multiplied (here, 4).

  The ON / OFF control DFT unit 150 has the same function as the DFT unit 103 of FIG. 2 when ON, and passes through the input data as it is when OFF. The signal generated when the signal is ON is a DFT-S-OFDM signal, as in the first to third embodiments. When the signal is OFF, the signal is an OFDM signal. The ON / OFF control DFT unit 150 stores the correspondence between the number of assigned RBs and ON or OFF as shown in Table 4, and determines ON or OFF according to the notified number of assigned RBs. That is, the ON / OFF control DFT unit 150 changes the method of generating a signal to be transmitted according to the number of assigned RBs. The ON / OFF control DFT unit 150 turns OFF when the number of assigned RBs SN does not satisfy the restriction on the number of input signals of the DFT operation (when the prime factor includes a number other than 2, 3, and 5), and inputs the DFT operation. When the restriction on the number of signals is satisfied (when the prime factor does not include a number other than 2, 3, 5), it is set to ON.

  Thus, by selecting a communication method according to the number of assigned RBs on the transmission side, even if there is a limitation due to DFT calculation, it is not necessary to consider the number of assigned RBs, and scheduling can be performed more easily.

In each of the above embodiments, the unit of the frequency to be accessed is basically called RB, and the description has been made on the assumption that the RB is composed of four subcarriers. However, the RB is composed of one subcarrier. It can also be applied.
As shown in the first to fourth embodiments, when the signal generation method is changed according to the number of assigned subcarriers, the PAPR characteristic may change and deteriorate. Therefore, in a system in which DFT-S-OFDM with excellent PAPR characteristics and Clustered DFT-S-OFDM with degraded PAPR characteristics are used in a switched manner, when using Clustered DFT-S-OFDM, that is, good A method of applying a technique for changing a signal generation method as in the first to fourth embodiments is also conceivable only when a specific PAPR characteristic is not required.

    Further, a program for realizing part or all of the functions of the terminal device and the base station device in the above-described embodiment is recorded on a computer-readable recording medium, and the program recorded on the recording medium is stored in a computer system. The function may be realized by being read and executed. Here, the “computer system” includes an OS and hardware such as peripheral devices.

  The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case, and a program that holds a program for a certain period of time are also included. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  Moreover, you may implement | achieve part or all of the terminal device and base station apparatus in embodiment mentioned above as LSI which is typically an integrated circuit. Each functional block of the mobile station apparatus and the base station apparatus may be individually chipped, or a part or all of them may be integrated into a chip. Further, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. In addition, when an integrated circuit technology that replaces LSI appears due to progress in semiconductor technology, an integrated circuit based on the technology can also be used.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like within a scope not departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Wireless communication system 11a-11c, 21a-21c, 31a-31c ... Terminal device 12 ... Base station apparatus 100 ... Encoding part 101 ... Modulation part 102 ... S / P conversion part 103 ... DFT part 104 ... Spectrum modification part 105 ... Subcarrier mapping unit 106 ... IFFT unit 107 ... P / S conversion unit 108 ... CP insertion unit 109 ... D / A conversion unit 110 ... radio unit 111 ... transmission antenna 112 ... reception antenna 113 ... radio unit 114 ... A / D conversion unit DESCRIPTION OF SYMBOLS 115 ... Reception part 116 ... Pilot signal generation part 120 ... RB number control part 130, 131, 132 ... Transmission apparatus 140 ... Known data insertion part 141 ... S / P conversion part 150 ... ON / OFF control DFT part 200 ... Reception antenna 201 ... Wireless unit 202 ... A / D unit 203 ... Synchronizing unit 204 ... CP removing unit 205 ... A / P change Unit 206 ... FFT unit 207 ... subcarrier demapping unit 208 ... first zero insertion unit 209 ... cancellation unit 210 ... equalization unit 211 ... demodulation / error correction decoding unit 212 ... repetition control unit 213 ... determination unit 214 ... propagation path estimation Unit 215: second zero insertion unit 216: propagation path multiplication unit 217 ... DFT unit 218 ... replica generation unit 219 ... scheduling unit 220 ... transmission unit 221 ... D / A conversion unit 222 ... radio unit 223 ... transmission antenna 230 ... reception device 240 ... Control device

Claims (10)

A time-axis signal is converted to a time-frequency axis to generate a frequency-axis signal, and the frequency-axis signal is arranged on a subcarrier and transmitted, and control for determining the number of subcarriers used by the transmission device for transmission A wireless communication system comprising a device,
The transmission apparatus changes a generation method of a signal to be transmitted according to the number of subcarriers determined by the control station apparatus. When the determined number of subcarriers is a predetermined value, the transmission device generates a frequency axis signal by performing time-frequency axis conversion of the time axis signal in units different from the number of subcarriers. The wireless communication system according to claim 1, wherein: The different number is greater than the determined number of subcarriers;
When the determined number of subcarriers is the predetermined value, the transmitting device arranges the frequency axis signal of the determined number of subcarriers among the generated frequency axis signals in subcarriers. The wireless communication system according to claim 2, wherein The different number is smaller than the determined number of subcarriers;
When the determined number of subcarriers is the predetermined value, the transmission device is a signal obtained by adding a signal to the generated frequency axis signal, and the signal having the determined number of subcarriers The radio communication system according to claim 2, wherein the radio communication system is transmitted in a subcarrier.   The wireless communication system according to claim 4, wherein the signal to be added is a part of the generated frequency axis signal.   The wireless communication system according to claim 4, wherein the different number has a ratio of the determined number of subcarriers to the different number larger than a predetermined value.  The wireless communication system according to claim 1, wherein at least a part of the predetermined value is a number that is prohibited as the number of input signals to the time-frequency axis conversion. .   The radio communication system according to claim 1, wherein at least one of the generation methods of the signal to be transmitted is an OFDM system. A time-axis signal is time-frequency-axis converted to generate a frequency-axis signal, and the frequency-axis signal is arranged on a subcarrier and transmitted.
The transmission apparatus changes a generation method of a signal to be transmitted according to the number of subcarriers on which the frequency axis signal is arranged. A time-axis signal is converted to a time-frequency axis to generate a frequency-axis signal, and the frequency-axis signal is arranged on a subcarrier and transmitted, and control for determining the number of subcarriers used by the transmission device for transmission A transmission method in a wireless communication system comprising an apparatus,
The transmission method comprising: a step of determining a generation method of a signal to be transmitted according to the number of subcarriers determined by the control station device.

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