DESCRIPTION RECEPTION DEVICE, COMMUNICATION DEVICE, AND DEMODULATION METHOD Field [0001] The present invention relates to a reception device that receives a signal transmitted in block transmission, a communication device, and a demodulation method. Background [0002] In a digital communication system, multipath fading caused by a transmission signal reflected from buildings or the like or Doppler shift caused by movement of a terminal device causes frequency selective and time variability of a transmission path. In such a multipath environment, a received signal becomes a signal in which a transmitted symbol and a symbol that arrives after a lapse of a delay time interfere with each other. [0003] For the frequency-selective transmission path as described above, a Single Carrier (SC) block transmission system intended for obtaining optimum reception characteristics has been recently drawing attention (see, for example, Non-patent Literature 1). The SC block transmission system can reduce a peak electric power as compared to an Orthogonal Frequency Division Multiplexing (OFDM) transmission system that belongs to Multiple Carrier (MC) block transmission (see, for example, Non-patent Literature 2). [0004] For example, a transmitter that performs SC block transmission implements measures for multi fading by performing transmission in the manner as described below. First, a "Modulator" generates a Phase Shift Keying (PSK) signal or a Quadrature Amplitude Modulation (QAM) signal that is a digital modulation signal, and then a precoder and an Inverse Discrete Fourier Transform (IDFT) processing unit transform the digital modulation signal into a time-domain signal. Thereafter, a Cyclic Prefix (CP) insertion unit inserts a CP in the time-domain signal for the purpose of multipath fading compensation. The CP insertion unit copies a predetermined number of samples from a later part of the time-domain signal, and adds the copy to the beginning of a transmission signal. In general, a transmitter performing SC block transmission carries out Discrete Fourier Transform (DFT) processing in a precoder in order to minimize a transmission peak power. [0005] In Non-patent Literatures 1 and 2, the transmission peak power is minimized while the influence of multipath fading is reduced. However, in the SC block transmission, since the phase and amplitude between SC blocks are discontinuous, an out-of-band spectrum or an out-of-band leakage power is caused. The out-of-band spectrum causes interference with adjacent channels. It is thus necessary to suppress the out-of-band spectrum. In a general communication system, a spectral mask is determined, and the out-of-band spectrum needs to be reduced so as to satisfy the spectral mask. [0006] Non-patent Literature 3 proposes a technique to insert symbols consisting of a static sequence into both ends of a block to thereby suppress an out-of-band spectrum. A transmitter described in Non-patent Literature 3 generates a data symbol and a static-sequence symbol for each block, and multiplexes these symbols in a time domain. The data symbol is a symbol obtained in a modulation method such as PSK or QAM and is thus changed randomly. The transmitter transforms the multiplexed signal into a frequency-domain signal through the DFT processing, and then performs interpolation processing in a frequency domain, for example oversampling, on the frequency-domain signal to generate a time-domain signal through the IDFT processing. The number of inputs/outputs of a DFT unit is represented as ND. The number of inputs of an interpolation processing unit is represented as ND, while the number of outputs from the interpolation processing unit is represented as LN. The number of inputs/outputs of an IDFT unit is represented as LN. An oversampling rate for oversampling that is interpolation processing is represented as L. In the transmitter, when L=l, N-point IDFT processing is performed and N>ND holds. Where N-ND>0, the interpolation processing unit inserts a zero into an output of the DFT unit. For such a zero insertion method, for example, a method as described in Non-patent Literature 4 is used. [0007] An output of the IDFT unit is referred to as "sample". The static-sequence symbols described above are constructed of M symbols, while an identical sequence is inserted into each of the all blocks at the same position thereof. Since the same sequence is generated for the static sequence symbols, any retained static-sequence symbols may be read out from a memory. While any processing can be used for the oversampling processing, zero padding or the like is used in general. [0008] As described above, a block of ND symbols in which a data symbol and a static-sequence symbol have been multiplexed is inputted to the DFT unit. Because the number of static-sequence symbols is M, the number of data symbols is ND-M. In Non-patent Literature 3, M static-sequence symbols are divided into halves, and for arrangement of static-sequence symbols within the block, M/2 symbols that are the second half of the static-sequence symbols are arranged in the leading part of the block before the (ND-M) data symbols arranged at the center of the block, while M/2 symbols that are the first half of the static-sequence symbols are arranged in the trailing part of the block after the (ND-M) data symbols. For example, the static-sequence symbols can be represented as F_M/2, F_ M/2+1/ ' ' ', F_i, F0, Fi, • • •, FM/2-2, FM/2-i. When a transmitter generates a plurality of blocks, M/2 symbols F0, Fi, • • •, FM/2-2, FM/2-i that are a second half of the static-sequence symbols arranged in the leading part of the block continue from M/2 symbols F_M/2, F_M/2+i, • • •, F_i that are a first half of the static-sequence symbols arranged in the trailing part of the immediately-previous block. For example, where an m-th data symbol in a k-th block is represented as dkfm, arrangement of data symbols and static-sequence symbols before being inputted to the DFT unit can be represented as FOA ' t FM/2-i, dkfi, ■ ■ ■, dkfND-M, F_M/2, ■ ■ ', F_i (the subscript "ND" means "ND") in order from the leading end of the block. Any sequence may be used for the static-sequence symbols, and specifically a Zadoff-Chu sequence, zeros, or other sequences can be used therefor. [0009] In the manner as explained above, a block in which the static-sequence symbols described in Non-patent Literature 3 are arranged is inputted to the DFT unit, and thereby the phases are continued between the blocks in output of the IDFT unit so that the out-of-band spectrum can be suppressed. In the example described above, equal numbers of static-sequence symbols are arranged in the leading part and tailing part of a block, respectively. However, different numbers of static-sequence symbols may be arranged in the leading part and trailing part of a block. [0010] Description is given for the principle of why waveform continuity is maintained by insertion of the static-sequence symbols explained above. Aliasing occurs in a block due to a combination of DFT processing, interpolation processing, and IDFT processing. In the aliasing caused by the above-mentioned processing combination, the waveform of each symbol is folded back to the opposite side of a block at the trailing end of the block. By taking advantages of such characteristics, static symbols are used at the beginning and ending of each block, thereby making it possible to smoothly continue the phases between blocks. Citation List Non Patent Literatures [0011] Non-patent Literature 1: N. Benvenuto, R. Dinis, D. Falconer and S. Tomasin, "Single Carrier Modulation With Nonlinear Frequency Domain Equalization: An Idea Whose Time Has Come-Again", Proceeding of the IEEE, vol. 98, no. 1, Jan 2010, pp. 69-96. Non-patent Literature 2: J. A. C. Bingham, "Multicarrier Modulation for Data Transmission: An Idea Whose Time Has Come", IEEE Commun. Mag., vol. 28, no. 5, May 1990, pp. 5-14. Non-patent Literature 3: Hasegawa, et al., "Static Sequence Embedded DFT-s-OFDM", IEICE technical report, vol. 14, no. 490, RCS2014-326, pp. 147-152, March 2015. Non-patent Literature 4: B. Porat, "A Course in Digital Signal Processing", John Wiley and Sons Inc., 1997. Summary Technical Problem [0012] In the case of SC block transmission described in Non-patent Literature 3, a reception device is capable of estimating a transmission path using a static sequence inserted regularly in a received signal. However, in a multipath environment, there has been a problem in that the reception device receives a signal in which a data component is multiplexed with a static-sequence component, thereby leading to degradation of the accuracy in estimating a transmission path, which has been problematic. [0013] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a reception device that is capable of improving the accuracy in estimating a transmission path. Solution to Problem [0014] In order to solve the above-mentioned problems and achieve the object, the present invention provides a reception device to receive a block signal from a transmission device that generates and transmits the block signal that is a signal having a construction in which a sequence of static symbols is added to a leading part and a trailing part of a sequence of data symbols. The reception device comprises: a transmission-path estimation unit to calculate a transmission-path estimation value on the basis of static symbols included in the block signal; and a block signal demodulation unit to demodulate the block signal on the basis of the transmission-path estimation value calculated by the transmission-path estimation unit. The transmission-path estimation unit calculates an initial value of the transmission-path estimation value on the basis of static symbols included in a first block signal that is a block signal to be demodulated, and recalculates a transmission-path estimation value on the basis of a result obtained by the block signal demodulation unit demodulating data symbols included in the first block signal using the initial value and a result of demodulation of data symbols included in a second block signal that is a block signal having been received immediately-previously to the first block signal, and when the transmission-path estimation unit recalculates a transmission-path estimation value, the block signal demodulation unit demodulates the first block signal again using the recalculated transmission-path estimation value. Advantageous Effects of Invention [0015] According to the present invention, there is an advantageous effect in that it is possible to improve the accuracy in estimating a transmission path. Brief Description of Drawings [0016] FIG. 1 is a diagram illustrating an example of a communication system configured to include a transmission device and a reception device according to a first embodiment. FIG. 2 is a diagram illustrating a configuration example of the transmission device according to the first embodiment. FIG. 3 is a diagram illustrating an example of a signal generated by a multiplexing unit of the transmission device according to the first embodiment. FIG. 4 is a diagram illustrating a configuration example of the reception device according to the first embodiment. FIG. 5 is a diagram illustrating a configuration o example of a transmission-path estimation unit of the reception device according to the first embodiment. FIG. 6 is a flowchart illustrating an example of an operation of the reception device according to the first embodiment. FIG. 7 is a flowchart illustrating another example of an operation of the reception device according to the first embodiment. FIG. 8 is a diagram illustrating an example of hardware that realizes constituent elements of the reception device according to the first embodiment. FIG. 9 is a diagram illustrating another example of hardware that realizes constituent elements of the reception device according to the first embodiment. FIG. 10 is a diagram illustrating a configuration example of a reception device according to a second embodiment. FIG. 11 is a diagram illustrating a configuration example of a transmission-path estimation unit of the reception device according to the second embodiment. FIG. 12 is a flowchart illustrating an example of an operation of the reception device according to the second embodiment. FIG. 13 is a flowchart illustrating another example of an operation of the reception device according to the second embodiment. FIG. 14 is a diagram illustrating a configuration example of a reception device according to a third embodiment. Description of Embodiments [0017] A reception device, a communication device, and a demodulation method according to embodiments of the present invention will be described in detail below with reference to the drawings. The present invention is not necessarily limited by these embodiments. [0018] First embodiment. FIG. 1 is a diagram illustrating an example of a communication system configured to include a reception device according to a first embodiment of the present invention. The communication system according to the present embodiment includes a transmission device 1 and a reception device 2, and performs SC block transmission from the transmission device 1 to the reception device 2. It is noted that the communication system performing SC block transmission may be configured to have two communication devices each of which includes the transmission device 1 and the reception device 2, in which the communication devices perform SC block transmission bidirectionally. [0019] FIG. 2 is a diagram illustrating a configuration example of the transmission device according to the first embodiment. The transmission device 1 according to the present embodiment includes a static sequence generation unit 11, a data symbol generation unit 12, a multiplexing unit 13, a Discrete Fourier Transform (DFT) unit 14, an interpolation processing unit 15, an Inverse Discrete Fourier Transform (IDFT) unit 16, and a transmission unit 17. The transmission device 1 constitutes a communication device on a transmission side that performs Single Carrier (SC) block transmission. FIG. 2 illustrates only a configuration necessary for explaining an operation of the present invention, in which configurations required for a general transmission device are partially omitted in illustration thereof. [0020] The static sequence generation unit 11 generates a sequence of static symbols whose signal values are preset. Hereinafter, the sequence generated by the static sequence generation unit 11 is referred to as "sequence of static symbols". The sequence of static symbols is a symbol sequence to be inserted into an SC block in order to suppress an out-of-band spectrum, and is a symbol sequence to be inserted as a common value between SC blocks. The static sequence generation unit 11 generates a sequence of static symbols on a block-by-block basis in SC block transmission, and outputs the generated sequence of static symbols to the multiplexing unit 13. [0021] The data symbol generation unit 12 generates a data symbol such as a Phase Shift Keying (PSK) symbol or a Quadrature Amplitude Modulation (QAM) symbol on the basis of information data to be transmitted to the reception device 2. The data symbol generation unit 12 generates a sequence of data symbols on a block-by-block basis in SC block transmission, and outputs the generated sequence of data symbols to the multiplexing unit 13. [0022] The multiplexing unit 13 adds the sequence of static symbols generated by the static sequence generation unit 11 to the sequence of data symbols generated by the data symbol generation unit 12 to generate a block signal that is an SC block having ends in each of which the sequence of static symbols is inserted. The transmission device 1 is configured to include the static sequence generation unit 11 and the multiplexing unit 13 and to generate an SC block having ends in each of which the sequence of static symbols is inserted, and thereby can suppress an out-of-band spectrum in SC block transmission. [0023] The DFT unit 14 is a time-to-frequency transform unit that performs DFT, that is, Fourier transform on the SC block generated by the multiplexing unit 13 so as to transform the SC block from a time-domain signal to a frequency-domain signal. [0024] The interpolation processing unit 15 performs interpolation processing on an input signal from the DFT unit 14, that is, a frequency-domain SC block. For example, the interpolation processing is oversampling. Where the number of input signals to the interpolation processing unit 15 is represented as N and the oversampling rate is represented as L, the number of output signals from the interpolation processing unit 15 is LN. In a case of performing oversampling as the interpolation processing, the interpolation processing unit 15 inserts a zero into an input signal from the DFT unit 14. In this case, the interpolation processing unit 15 inserts a zero into the input signal by using, for example, the method described in Non-patent Literature 4 described above. [0025] The IDFT unit 16 is a frequency-to-time transform unit that performs IDFT, that is, inverse Fourier transform on a frequency-domain SC block after having undergone the interpolation processing by the interpolation processing unit 15 so as to transform the frequency-domain SC block to a time-domain signal. In the following descriptions, a single piece of data that is outputted from the IDFT unit 16 is sometimes referred to as "sample". [0026] The transmission unit 17 performs at least transform processing on an SC block after having been transformed to the time-domain signal by the IDFT unit 16 so as to transform the SC block to a radio-frequency band signal, and then transmits this signal to the reception device 2 that serves as a counterpart device. [0027] Next, a configuration of an SC block is described. In a case of generating a single SC block in the transmission device 1, the static sequence generation unit 11 generates symbols F0, Fi, • • •, FM/2-2, FM/2-i, • • •, FM_! as a sequence of static symbols formed of M static symbols and outputs the sequence of static symbols to the multiplexing unit 13. Meanwhile, the data symbol generation unit 12 generates and outputs (ND-M) data symbols to the multiplexing unit 13. For the sake of simplicity of descriptions, M is assumed to be an even number. However, M may be an odd number. Any sequence may be used for a sequence of static symbols generated by the static sequence generation unit 11. It is possible to use a Zadoff-Chu sequence, a zero sequence, or other sequences as a sequence of static symbols. [0028] The multiplexing unit 13 divides the sequence of static symbols inputted from the static sequence generation unit 11 into two which are a first sequence on the leading side and a second sequence on the trailing side, and adds the first sequence to the leading end of the (ND-M) data symbols inputted from the data symbol generation unit 12, while adding the second sequence to the trailing end of the (ND-M) data symbols. Specifically, the multiplexing unit 13 divides the inputted sequence of static symbols into a first sequence and a second sequence, the first sequence being a first half of the M symbols, F0, Fi, • • •, FM/2-2, Fu/2-ir and the second sequence being a second half of the M symbols, FM/2-ir ' ' ' t FM-i. The multiplexing unit 13 then adds to the leading end of the (ND-M) data symbols, while adding the second sequence to the trailing end of the (ND-M) data symbols. An SC block outputted from the multiplexing unit 13 to the DFT unit 14 is a signal having a configuration illustrated in FIG. 3. [0029] Where M is an odd number, the multiplexing unit 13 divides the sequence of static symbols into one group of (M+l)/2 symbols and another group of (M-l)/2 symbols. In the above descriptions, the multiplexing unit 13 divides the sequence of static symbols into two groups having equal numbers of symbols, that is, M/2 symbols for each group. However, the multiplexing unit 13 may divide the sequence of static symbols into two groups having different numbers of symbols, for example, Mi symbols for one group and M2 symbols for another group (0