JP6132707B2 - Transmission device, reception device, communication system, transmission method, and reception method - Google Patents

Description

  The present invention relates to a transmission device, a reception device, a communication system, a transmission method, and a reception method.

  One communication method is called a spread spectrum method. This method has the advantage of high confidentiality and noise resistance, but on the other hand, the peak-to-average power ratio (PAPR) of the signal because the primary modulation signal is spread by the PN sequence. There is a problem that becomes large. PAPR means the ratio of the average power and peak power of a signal.

  In order to improve the operating efficiency of the power amplifier in the transmission apparatus, it is necessary to reduce the back-off at the power amplifier. In general, the backoff increases as the difference between the average power and the maximum power increases. Therefore, in order to reduce the back-off, it is desirable that the PAPR of the transmission signal is small.

  Patent Document 1 describes a method in which primary modulation is FSK (frequency shift keying) and a phase rotation sequence is used as a spreading sequence. Since both the FSK signal and the phase rotation series are signals having a constant amplitude, it is possible to generate a transmission signal having a small PAPR by using these signals. Also, after spreading, CP (Cyclic Prefix) is added to block the signal, so that frequency domain equalization (FDE) can be performed in the receiver, and waveform distortion of the signal in the propagation path, etc. To compensate.

  Non-Patent Document 1 describes a transmission method in which an FSK signal is spread, blocked, and transmitted. Non-Patent Document 1 calls this transmission method MFSK / DS block transmission and describes a method for realizing a plurality of transmission rates by this transmission method. In Non-Patent Document 1, the system band Nb is divided into a plurality of carrier waves, and an M-value FSK signal is generated using M (M is an integer of 2 or more) of them. If the carrier width is Nsc, the system band Nb is divided into Nb / Nsc carriers. By changing the value of Nsc at this time, different transmission rates can be realized. As Nsc increases, the transmission rate increases and the FSK symbol length decreases.

  For example, if Nsc is doubled, the transmission rate is doubled. That is, the FSK symbol length is halved, and the number of FSK symbols in one block is doubled. Note that if Nsc is larger than 1 / M of Nb, the number of carriers becomes less than M, and an M-value FSK signal cannot be generated. Therefore, the transmission rate cannot be increased as compared with the case where Nsc is 1 / M of Nb.

As described above, in the method of Non-Patent Document 1, when the carrier width Nsc is increased 2 ⁿ times (n is an integer equal to or greater than 1), the transmission rate is increased 2 ⁿ times and the symbol length is 1/2 ⁿ times. That is, the transmission rate can be controlled in units of powers of 2.

  However, in practice, it is desirable to be able to control the transmission rate in units smaller than the power of 2. For example, the transmission rate can be changed by changing the modulation multi-value number and the coding rate of the error correction code without changing the Nsc value. By using such a method, it is possible to control the transmission rate in units smaller than a power of 2. This method is not limited to the case of using FSK, and is described in Non-Patent Document 2, for example.

JP 2011-49950 A

Masatsugu Higashinaka, Keisuke Ozaki, Hiroshi Tomitsuka, Akihiro Okazaki, Fumio Ishizu, “A Study on System Capacity in MFSK / DS Block Transmission”, 2013 IEICE General Conference, B-5-94, Proceedings of Communication Lecture 1 p504 , March 2013 Q. Liu, S. Zhou, G. B. Giannakis, “Cross-Layer Combining of Adaptive Modulation and Coding With Truncated ARQ Over Wireless Links”, IEEE Transactions on Wireless Communications, vol. 3, No. 5, September 2004

  However, in the MFSK / DS block transmission described above, if the transmission rate is changed by changing the modulation multi-value number and the coding rate of the error correction code as described in Non-Patent Document 2, there are the following problems. .

  First, consider a case where the coding rate of the error correction code is changed. There are methods such as puncturing and repetition to change the coding rate. However, with FSK, soft decision likelihood for each bit cannot be easily obtained at the time of decoding as in a linear modulation method such as PSK (Phase Shift Keying), and it is necessary to obtain the likelihood in symbol units. Therefore, a trellis diagram is also constructed for each symbol. In this case, there is a problem that it is difficult to perform puncturing and repetition.

  Next, consider the case where the modulation multi-level number is changed. Since the number of bits per symbol is changed by changing the modulation multi-value number, different transmission rates can be realized. However, considering the construction of a trellis diagram in symbol units as described above, the number of bits in one symbol changes when the modulation multilevel number is changed. For this reason, it is necessary to construct a trellis diagram corresponding to each multi-value number. That is, there is a problem that the number of decoding circuits required is the same as the number of modulation multi-level numbers, and the circuit scale increases.

  Another method is to multiplex a plurality of FSK signals in the frequency domain. For example, when Nb = 16 and M = 4, if Nsc = 1, the system band Nb is divided into 16 carriers, and 12 of the 16 carriers are used to generate three 4-valued FSK signals. At the same time, three FSK symbols are transmitted. Therefore, it is possible to realize a transmission rate that is three times that of the case where four of the 16 carriers are used to generate one quaternary FSK signal. However, there is a problem that the PAPR increases because the transmission signal is a superposition of a plurality of sine waves.

  The present invention has been made in view of the above, and a transmission apparatus and a reception apparatus capable of realizing transmission at many types of transmission rates while suppressing an increase in circuit scale without increasing PAPR. An object is to obtain a communication system, a transmission method, and a reception method.

In order to solve the above-described problems and achieve the object, the present invention generates a modulation symbol using a plurality of types of carriers having different carrier widths, and the modulation symbols generated using different types of carriers are constant. A modulation unit arranged so as to be mixed in time, and transmitting modulation symbols arranged by the modulation unit, the multi-value number of the modulation symbols is constant regardless of the type of carrier used for generation, the number of modulation symbols for each type of the carrier wave within a predetermined time is characterized Rukoto determined according to the transmission rate.

  According to the present invention, there is an effect that transmission at many types of transmission rates can be realized without increasing the PAPR and suppressing an increase in circuit scale.

FIG. 1 is a diagram illustrating a configuration example of a transmission apparatus according to the first embodiment. FIG. 2 is a diagram illustrating an example of CP addition. FIG. 3 is a diagram illustrating an example of a carrier wave according to the first embodiment. FIG. 4 is a diagram illustrating an example of a block in which Nsc = 2 symbols and Nsc = 4 symbols are mixed when M = 4 and Nb = 16. FIG. 5 is a diagram illustrating an example of a block in which Nsc = 4 symbols and Nsc = 8 symbols are mixed when Nb = 64 and M = 4. FIG. 6 is a diagram illustrating an example of a signal in which noise is superimposed on the signal illustrated in FIG. 3. FIG. 7 is a diagram illustrating an example of a table indicating correspondence between transmission rates and implementation methods. FIG. 8 is a diagram illustrating a configuration example of the receiving device according to the first embodiment. FIG. 9 is a diagram illustrating an example of the BER characteristic. FIG. 10 is a diagram illustrating an example of blocks mixed so that the power density is the same in the frequency domain. FIG. 11 is a diagram illustrating a state of a transmission signal when Nsc is changed. FIG. 12 is a diagram illustrating an example of a block in which Nsc = 2 symbols and Nsc = 4 symbols are mixed when Nb = 12. FIG. 13 is a diagram illustrating an example of blocks mixed so that the power density of the fourth embodiment is the same in the frequency domain.

  Hereinafter, embodiments of a transmission device, a reception device, a communication system, a transmission method, and a reception method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a transmission apparatus according to a first embodiment of the present invention. As shown in FIG. 1, the transmission apparatus according to the present embodiment includes an encoding unit 1, a transmission rate control unit 2, a modulation unit 3, a CP adding unit 4, a band limiting filter 5, a power amplifier 6, and an antenna 7.

  The encoding unit 1 performs error correction encoding processing on the input information bit sequence. After that, the encoding unit 1 performs interleaving as necessary, changes the order of transmission symbols, and outputs the result as a bit string. Interleaving is performed in symbol units, not in bit units. The transmission rate control unit 2 instructs the modulation unit 3 on the transmission rate of the transmission signal. The modulation unit 3 modulates the bit string output from the encoding unit 1 based on the transmission rate instructed from the transmission rate control unit 2 to generate an FSK signal. It is assumed that the modulation unit 3 is set in advance how to realize the transmission rate for each transmission rate (which Nsc value signal is generated and in what order). When spreading processing is necessary as the secondary modulation, the modulation unit 3 outputs the generated FSK signal after performing spreading processing. There is no particular limitation on the spreading sequence used by the modulation unit 3 during spreading processing.

  The CP adding unit 4 adds a CP to the FSK signal for one block output from the modulation unit 3 to form a block. FIG. 2 is a diagram illustrating an example of CP addition. In this way, the CP adding unit 4 copies a part of transmission data (in this case, an FSK signal for one block) and adds it as a CP. However, if it is not necessary to make a block, the CP adding unit 4 is not necessary.

  The band limiting filter 5 performs band limitation on the signal output from the CP adding unit 4. The power amplifier 6 amplifies the band-limited signal. The antenna 7 transmits the amplified signal.

  The present embodiment can be applied to modulation schemes such as FSK, MSK (Minimum Shift Keying), and GMSK (Gaussian filtered Minimum Shift Keying) that change the frequency of a signal according to a transmission signal. In the following description, it is assumed that FSK is used as a modulation method. However, any modulation method that changes the frequency of a signal according to a transmission signal may be used. The configuration and operation of this embodiment can be applied.

  First, an outline of a method for realizing a plurality of transmission rates in the present embodiment will be described. In the present embodiment, different transmission rates are realized by mixing symbols having different carrier widths. FIG. 3 is a diagram illustrating an example of a carrier wave according to the present embodiment. When the carrier width is Nsc and the system band is Nb, the system band is divided into Nb / Nsc carriers. By changing the value of Nsc at this time, different transmission rates can be realized in units of powers of 2. Here, the system bands Nb and Nsc are indicated by the number of unit bands having a predetermined frequency width.

FIG. 3 shows three cases (a), (b), and (c) where M = 4 and Nb = 16 (the system band Nb is composed of 16 unit bands). .
(A) Nsc = 1, the system band Nb is divided into 16 carriers, and a 4-level FSK signal is generated using 4 of them.
(B) Nsc = 2, the system band Nb is divided into eight carriers, and four of them are used to generate a quaternary FSK signal. The transmission rate is twice that of (a). Further, the symbol length and the power per symbol are ½ times (a).
(C) Nsc = 4, the system band Nb is divided into four carrier waves, and a quaternary FSK signal is generated using the four carrier waves. The transmission rate is four times that of (a). Further, the symbol length and the power per symbol are ¼ times (a).

  Each solid line in FIGS. 3A, 3B, and 3C indicates four carriers used for transmission of the quaternary FSK signal, and a dotted line indicates a carrier that is not used for transmission of the quaternary FSK signal. In the present embodiment, the power density in the time domain is constant, but since the symbol lengths are different, the powers in FIGS. 3A, 3B, and 3C (power in the frequency domain) are It depends on the carrier width.

  In the present embodiment, in the example of FIG. 3 described above, for example, an FSK symbol (when Nsc = 2) (a symbol when Nsc = 2) and an FSK symbol when (c) Nsc = 4 are used. A transmission signal is generated so as to mix symbols (Nsc = 4 symbols). FIG. 4 is a diagram illustrating an example of a block in which Nsc = 2 symbols and Nsc = 4 symbols are mixed when M = 4 and Nb = 16. The FSK symbol # 1 is a symbol with Nsc = 2, and the FSK symbols # 2 and # 3 are symbols with Nsc = 4. The transmission signal generated in this way transmits three FSK symbols in one block, and in the case of FIG. 3B in which two FSK symbols are transmitted in one block and four FSK symbols in one block. A transmission rate intermediate to that in the case of FIG. 3C to be transmitted can be realized.

  FIG. 5 shows a block in which Nsc = 4 (4 FSK symbols per block) and Nsc = 8 (8 FSK symbols per block) symbols are mixed when Nb = 64 and M = 4. It is a figure which shows an example. Many transmission rates can be realized by changing the ratio of mixing two types (two types of carrier widths) of symbols. FIGS. 5A and 5B show an example in which Nsc = 4 symbols and Nsc = 8 symbols are mixed at a power ratio of 1: 1, with Nsc = 4 and Nsc = 8. Can be achieved at an intermediate transmission rate (6 FSK symbols per block). The power ratio is 1: 1, but the symbol length in the case of Nsc = 8 is ½ times the symbol length in the case of Nsc = 4, so the ratio of the number of symbols is 1: 2. FIG. 5C shows a case in which the power ratio is 3: 1, and there are five FSK symbols per block, and a transmission rate smaller than that in FIGS. 5A and 5B can be realized.

  In the examples of FIGS. 4 and 5A to 5C, different types of FSK symbols are mixed in one block period. However, the period when mixing is not limited to one block, and may be a period of two or more blocks. For example, FIGS. 5D and 5E show examples in which two types of symbols are mixed in a cycle of 2 blocks. In the example of FIG. 5D, the power ratio of Nsc = 4 symbols and Nsc = 8 symbols is 3: 5, the number of symbols in two blocks is 13, and the number of symbols per block is 6. There will be five. In the example of FIG. 5 (e), the power ratio of the Nsc = 4 symbol and the Nsc = 8 symbol is 1: 1, and the transmission rate is the same as in FIGS. 5 (a) and 5 (b).

  Next, items to be considered when symbols having different carrier widths are mixed will be described. FIG. 6 is a diagram illustrating an example of a signal in which noise is superimposed on the signal illustrated in FIG. 3. A symbol with a larger Nsc, that is, a larger carrier width, has a lower carrier power density in the frequency domain. Therefore, symbols with a larger carrier width are more susceptible to noise and have a lower error rate characteristic. Therefore, it is desirable to reduce the influence of noise by performing error correction coding processing. In order to reduce the influence of noise, symbols with poor error rate characteristics are prevented from being transmitted as continuously as possible. For example, FIGS. 5A, 5B, and 5E have the same transmission rate, but two symbols with a large carrier width are continuous in (a), four in (b), ( In e), eight are transmitted continuously. For this reason, it is considered that among FIGS. 5A, 5B, and 5E, the case of FIG. 5E is most susceptible to noise.

  However, when the encoding unit 1 of the transmission apparatus performs interleaving on the transmission bit string after error correction encoding, the difference in how symbols are mixed ((a), (b), ( It is considered that there is no difference in susceptibility to noise due to the difference in c), and this is not a problem. On the other hand, when interleaving such as voice communication cannot be performed, there may be a difference in susceptibility to noise due to a difference in the way symbols are mixed. In such a case, it is desirable to mix symbols so that symbols having a large carrier width do not continue as much as possible. That is, when interleaving cannot be performed, for example, when transmitting at the transmission rates of FIGS. 5A, 5B, and 5E, the method of (a) in which symbols having a large carrier width are least consecutive is selected. Is desirable.

  As described above, the FSK signal decoding process is performed in symbol units. For this reason, interleaving is performed not on a bit basis but on a symbol basis.

  The example in which symbols of two types of carrier widths are mixed has been described above. However, it is possible to mix symbols having three or more types of carrier widths. Further, in the examples so far, the M-value FSK signal is generated using M adjacent carriers out of Nb / Nsc carriers, but it is not always necessary to use M adjacent Nb / Nsc. Any M of the carrier waves can be used. However, the receiving apparatus needs to know which M number is used. For this reason, a method is conceivable in which this information is transmitted from the transmitting device to the receiving device in advance, or both the transmitting device and the receiving device hold this information in advance.

  Next, a more general description is shown. Consider a case where symbols of K types (K is an integer of 2 or more) types of carrier widths are mixed. Nsc corresponding to each type is Nsc (0), Nsc (1),..., Nsc (K−1). The power ratio when mixing is assumed to be r (0): r (1):...: R (K-1). At this time, the ratio of the number of symbols is Nsc (0) r (0): Nsc (1) r (1):...: Nsc (K-1) r (K-1). If the block length excluding the CP is N, the symbol length when Nsc = Nsc (k) is N / Nsc (k) (0 ≦ k <K), so that K types of carriers are mixed. The number of symbols Nsym per block at that time is expressed by the following equation (1).

  Accordingly, when a transmission rate to be realized is given, the number of symbols Nsym per block corresponding to the transmission rate is obtained, and the values of K, Nsc (k), r (k) for realizing the symbol Nsym are obtained by the above formula. Calculate according to (1). The solution of K, Nsc (k), r (k) calculated based on Nsym is not necessarily one set. When there are a plurality of sets of solutions, one set is selected from the plurality of sets. Any selection criterion can be used as the selection criterion at this time. For example, selection criteria such as selecting a pair with the smallest K and selecting a pair with the smallest ratio between the maximum value and the minimum value of Nsym are conceivable.

  As described above, when K, Nsc (k), r (k) calculated (or selected by calculation) for each Nsym are transmitted by the transmitting apparatus to generate a transmission rate (an FSK symbol (modulation symbol)). Information indicating one or more types of carrier waves to be used (carrier width) and information specifying the arrangement of FSK symbols) can be stored, and an implementation method can be selected (determined) according to the transmission rate.

  For example, when Nb = 16 and M = 4, the modulation unit 3 may hold information storing the transmission rate and the implementation method. FIG. 7 is a diagram illustrating an example of a table indicating correspondence between transmission rates and implementation methods. When the modulation unit 3 holds the information shown in the table in FIG. 7, an implementation method corresponding to the transmission rate can be acquired. In the example of FIG. 7, four types of transmission rates can be realized. The transmission rates of indexes # 1, # 2, and # 4 in FIG. 7 are realized by configuring one block with symbols having a single carrier width, and for the transmission rate of index # 3, symbols having a plurality of carrier widths are realized. Realized by mixing. For example, when the modulation unit 3 is instructed by the transmission rate control unit 2 for the index value in FIG. 7, the modulation unit 3 generates an FSK signal based on the implementation method corresponding to the instructed index value. However, it is not always necessary to specify an index value from the transmission rate control unit 2, and a transmission rate value may be indicated. Alternatively, there is no problem even if the number of symbols in one block is designated.

  When generalized, it becomes as follows. Assume that the number of symbols in one block is Nsym, and the symbol length of the i-th (0 ≦ i <Nsym) symbol is L (i). When the block length excluding CP is N, N is expressed by the following equation (2). The modulation unit 3 generates Nsym symbols and multiplexes them in the time domain to generate a signal of length N.

  Next, the receiving apparatus of this Embodiment is demonstrated. FIG. 8 is a diagram illustrating a configuration example of the receiving apparatus according to the present embodiment. The receiving apparatus according to the present embodiment includes an antenna 11, a band limiting filter 12, a CP removing unit 13, an FFT (Fast Fourier Transform) unit 14, an FDE unit 15, an IFFT unit 16, a demodulating unit 17, a transmission rate control unit 18, and a decoding unit. The unit 19 is provided. The receiving apparatus according to the embodiment receives a signal transmitted from the transmitting apparatus according to the present embodiment described above, but can receive and process a signal transmitted from a transmitting apparatus other than the transmitting apparatus according to the present embodiment. You may comprise as follows. Hereinafter, the operation of the receiving apparatus when receiving a signal transmitted from the transmitting apparatus of the present embodiment will be described.

  A signal received by the antenna 11 of the receiving apparatus is input to the band limiting filter 12. The band limiting filter 12 performs band limitation on the received signal and extracts a signal having a necessary frequency. The CP removing unit 13 removes the CP from the reception signal output from the band limiting filter 12. However, when the blocking is unnecessary and the CP is not added in the transmitting apparatus, the CP removing unit 13 of the receiving apparatus is unnecessary. The FFT unit 14 converts the received signal after CP removal, which is a time domain signal, into a frequency domain signal. The FDE unit 15 performs frequency domain equalization processing on the frequency domain signal to compensate for signal distortion. Thereafter, the IFFT unit 16 converts the signal processed by the FDE unit 15 into a time domain signal. If there is no need to compensate for signal distortion and frequency domain equalization is not performed, the FFT unit 14, the FDE unit 15, and the IFFT unit 16 are unnecessary.

  The demodulator 17 performs a demodulation process on the FSK signal that is a time domain signal output from the IFFT unit 16. However, when performing spreading processing in the transmission device, the demodulator 17 first performs despreading, and then performs demodulation processing of the FSK signal.

  In the FSK signal demodulation process, specifically, the soft decision likelihood of each symbol is calculated, and the calculation result is output to the decoding unit 19. Here, the number of symbols in the block being processed is Nsym, and the symbol length of the i-th (0 ≦ i <Nsym) symbol is L (i). When the block length excluding CP is N, N is expressed by the above equation (2). In the demodulation process, first, the soft decision value of the first symbol (the symbol of the first length L (0)) is calculated. Next, the soft decision value of the second symbol (the symbol of the next length L (1)) is calculated. This process is performed in order to calculate soft decision values for Nsym symbols.

  As described above, the soft decision likelihood is calculated in symbol units. In addition, the error rate characteristic becomes worse as the carrier wave width is larger (symbol having a larger Nsc). Therefore, the demodulator 17 may weight the soft decision likelihood according to the carrier width of each symbol and output it to the decoder 19. For example, if symbols of K types of carrier widths are mixed, the weight of the symbol of the kth (0 ≦ k <K) carrier width is set to w (k), and the soft decision likelihood is set to w (k). You may make it output to the decoding part 19 what multiplied. Note that weighting is not necessarily performed.

  The transmission rate control unit 18 instructs the demodulation unit 17 on the transmission rate, similarly to the transmission rate control unit 2 of the transmission apparatus. The transmission rate instructed by the transmission rate control unit 18 and the transmission rate instructed by the transmission device need to match. For this reason, for example, the transmission rate may be notified from the transmission device to the reception device, or the transmission rate indicated by the transmission rate control unit 2 of the transmission device by the operator or the like and the transmission rate control unit 18 of the reception device. The transmission rate indicated by may be set to be the same. The decoding unit 19 performs a decoding process using the soft decision likelihood input from the demodulation unit 17. When interleaving is performed in the encoding unit 1 of the transmission apparatus, the decoding unit 19 first performs deinterleaving and changes the order of received symbols. At this time, the decoding unit 19 performs processing in units of symbols, similarly to the interleaving in the encoding unit 1. Thereafter, the decoding unit 19 performs a decoding process using the soft decision likelihood and outputs the obtained bit string.

  Here, an example of a soft decision likelihood calculation method performed by the demodulator 17 will be described. Consider a case where an M-value FSK signal is transmitted using M carriers having frequencies of f (0) to f (M−1). The value of the real part of each carrier component at the time of FSK modulation in the transmission device is u (i) (0 ≦ i <M), and the value of the real part of each carrier component at the time of FSK demodulation in the reception device is r (i) ( 0 ≦ i <M). When the carrier wave f (j) is selected at the time of FSK modulation, the value of each u (i) is expressed by the following equation (3). However, in the signal value in the frequency domain of the selected carrier wave, it is assumed that the real part is A and the imaginary part is 0.

  When the value of the real part of the carrier wave f (i) of the receiving device is r (i), the posterior probability that the value of the real part of the carrier wave f (i) of the transmission signal is u (i) is obtained by Bayes' theorem. It can be represented by the following formula (4).

Therefore, when only additive white Gaussian noise (AWGN) with power σ ² is considered as a propagation path, a log likelihood ratio (LLR) is expressed by the following equation (5).

Assuming that fluctuations in noise power and signal level can be ignored in the section where error correction is performed, 2σ ² can be ignored. Furthermore, since the modulation multi-level number is constant, ln (M−1) can also be ignored. Therefore, the log likelihood ratio can be expressed as the following formula (6).

Furthermore, the coefficient 2 of the first term of L ′ and the second term A ² are constant values irrespective of i, and these can also be ignored. Therefore, the log likelihood ratio can be expressed as the following equation (7).

Therefore, this L ″ can be used as the soft decision likelihood. Here, as described above, the signal value in the frequency domain of the carrier wave selected by the modulation unit 3 of the transmission device has a real part as A and an imaginary part as 0. When Nsc is increased 2 ⁿ times (n is an integer equal to or greater than 1), the power density of the carrier wave is 2 ⁻ⁿ times, and A is reduced to √ (2 ⁻ⁿ ) = 2 ^{−n / 2} times. Therefore, A is a value different depending on the value of Nsc, that is, the carrier width, and is considered to play the role of the weight w (k) described above. For this reason, the value of L ″ can be output to the decoding unit 19 without being weighted.

  Note that although an example in which block transmission is performed has been described in this embodiment, when block transmission is not performed, symbols having different carrier widths may be mixed in a signal transmitted within a certain period.

  As described above, in the present embodiment, symbols having different carrier widths are mixed and transmitted. For this reason, a plurality of transmission rates can be realized without increasing the PAPR. In this embodiment, since the FSK multilevel number is constant and only one type of decoding circuit is required, the circuit scale is not greatly increased. In the present embodiment, a plurality of transmission rates can be realized by changing the mixing ratio when symbols of a plurality of types of carrier widths are mixed. As described above, in this embodiment, it is possible to realize transmission at many types of transmission rates without increasing the PAPR and suppressing an increase in circuit scale.

Embodiment 2. FIG.
Next, a transmitting apparatus and a receiving apparatus according to the second embodiment of the present invention will be described. The configurations of the transmission device and the reception device of the present embodiment are the same as those of the first embodiment. Hereinafter, the same operations as those in the first embodiment will be described by omitting overlapping descriptions and focusing on portions different from those in the first embodiment. The operations of this embodiment other than the operations of the modulation unit 3 of the transmission device and the demodulation unit 17 of the reception device are the same as those of the first embodiment.

  FIG. 9 is a diagram illustrating an example of a BER characteristic (error rate characteristic). FIG. 9 shows a BER characteristic when Nb = 4096, M = 16, and Nsc = 128 (referred to as a first BER characteristic), and a BER characteristic when Nb = 4096, M = 16, and Nsc = 256 (the first BER characteristic). 2), Nb = 4096, M = 16, and as described in the first embodiment, Nsc = 128 symbols and Nsc = 256 symbols are mixed to have a power ratio of 1: 1. In this case, the BER characteristic in this case (referred to as a third BER characteristic) is shown. As shown in FIG. 9, the first BER characteristic matches the second BER characteristic. On the other hand, the third BER characteristic is worse than the first BER characteristic and the second BER characteristic. This is considered due to the fact that symbols of a plurality of types of carrier widths are mixed and symbols of different error rates are mixed.

  In the first embodiment, the example in which the power density of each symbol is the same in the time domain has been described. On the other hand, in this embodiment, in order to improve the BER characteristic, signal power adjustment is performed for each symbol so that the power density of each symbol becomes the same in the frequency domain. By doing so, the error rate becomes equal for each symbol, and the same BER characteristic as when symbols of different carrier widths are not mixed can be realized. However, since the power density in the time domain is different for each symbol, the PAPR of the transmission signal is larger than that in the first embodiment. However, the increase in PAPR is greater than the method of multiplexing a plurality of FSK signals in the frequency domain. Few.

  FIG. 10 is a diagram illustrating an example of blocks mixed so that the power density is the same in the frequency domain. In FIG. 10, (b) the symbol when Nsc = 2 in FIG. 3 and the symbol when (c) Nsc = 4 in FIG. 3 are mixed so that the power density of each symbol is the same in the frequency domain. An example is shown. When mixed according to the method of the first embodiment, it is as shown in FIG. 4, but in the example of FIG. 4, the power density is the same in the time domain, and in the frequency domain, the power density is smaller as the symbol has a larger carrier width. On the other hand, in the example of FIG. 10, the power density is the same in the frequency domain, and the power density is larger in the time domain as the symbol has a larger carrier width.

  The operation of modulation section 3 of the transmission apparatus according to this embodiment will be described. After generating the FSK symbol, the modulation unit 3 of the transmission apparatus performs power adjustment between the symbols so that the power density in the frequency domain of each symbol becomes equal. When symbols of K types of carrier widths are mixed, assuming that each type of Nsc is Nsc (0), Nsc (1),..., Nsc (K−1), each symbol before power adjustment in the frequency domain The ratio of the power density is the ratio of the reciprocal of Nsc, that is, 1 / Nsc (0): 1 / Nsc (1),...: 1 / Nsc (K−1). Therefore, if the power of the symbol of the kth (0 ≦ k <K) carrier width is multiplied by Nsc (k), the power density in the frequency domain of each symbol becomes equal. For this purpose, the complex signal of the symbol of the kth carrier width may be multiplied by √ (Nsc (k)). In this way, the modulation unit 3 generates FSK symbols after power adjustment for one block. Thereafter, the modulation unit 3 performs power adjustment to make the power between the blocks the same, and outputs the result. However, when spreading processing is performed, it is output after spreading.

  The operation of the demodulator 17 of the receiving apparatus according to this embodiment will be described. The demodulator 17 calculates the soft decision likelihood of each symbol and outputs it to the decoder 19 as in the first embodiment. However, when the spread processing is performed by the modulation unit 3 of the transmission apparatus, the demodulation unit 17 first performs despreading, and then performs demodulation processing of the FSK signal. As a soft decision likelihood calculation method, the same method as in the first embodiment can be used. However, since the power density in the frequency domain of each symbol is the same in the modulation unit 3 of the transmission apparatus in the present embodiment, the value of A at the time of calculation is the same regardless of the difference in the carrier width. Equal for symbols. Therefore, L ″ in Expression (7) may be used as the soft decision likelihood as in the first embodiment, but r (i) is simply output to the decoding unit 19 as the soft decision likelihood. Good.

  As described above, in the present embodiment, symbols having different carrier widths are mixed and transmitted as in the first embodiment. At this time, power adjustment is performed so that the power density of each symbol is the same in the frequency domain. To do. For this reason, the error rate characteristics can be improved compared to the first embodiment.

Embodiment 3 FIG.
Next, a transmitting apparatus and a receiving apparatus according to the third embodiment of the present invention will be described. The configurations of the transmission device and the reception device of the present embodiment are the same as those of the first embodiment. Hereinafter, the same operations as those in the first embodiment will be described by omitting overlapping descriptions and focusing on portions different from those in the first embodiment. The operations of the present embodiment other than the operations of the encoding unit 1 and modulation unit 3 of the transmission device and the demodulation unit 17 and decoding unit 19 of the reception device are the same as those of the first embodiment.

  In the first embodiment, an example in which a modulation method such as FSK, MSK, GMSK or the like that changes the frequency of a signal in accordance with a transmission signal has been described. In the present embodiment, different Nsc symbols are used in the linear modulation system represented by PSK (Phase Shift Keying), QAM (Quadrature Amplitude Modulation), and APSK (Amplitude and Phase Shift Keying) as in the first embodiment. A method for realizing a plurality of transmission rates will be described.

  FIG. 11 is a diagram illustrating a state of a transmission signal when Nsc is changed. In FIG. 11, Nb = 16. In PSK, QAM, and APSK, one carrier is used regardless of the number of modulation levels. FIG. 11A shows a case where Nsc = 1, FIG. 11B shows a case where Nsc = 2, and FIG. 11C shows a case where Nsc = 4. In this embodiment, different transmission rates are realized by mixing different Nsc symbols. FIG. 12 is a diagram illustrating an example of a block in which Nsc = 2 symbols (FIG. 11B) and Nsc = 4 symbols (FIG. 11C) are mixed when Nb = 16. Symbol # 1 in FIG. 12 is a symbol with Nsc = 2, and symbols # 2 and # 3 in FIG. 12 are symbols with Nsc = 4. Thus, in the example of FIG. 12, three symbols are transmitted in one block, and in the case of FIG. 11 (b) in which two symbols are transmitted in one block and in FIG. 11 (4) in which four symbols are transmitted in one block. An intermediate transmission rate with respect to the case of c) is realized.

  The encoding unit 1 of the transmission apparatus performs error correction encoding processing on the input information bit sequence in the same manner as in the first embodiment. Thereafter, interleaving is performed as necessary. In the first embodiment, interleaving is performed in symbol units. This is because FSK cannot easily determine the soft decision likelihood for each bit, and it is necessary to determine the likelihood in symbol units, and the decoding process is also performed in symbol units. However, in linear modulation schemes such as PSK, QAM, and APSK, the soft decision likelihood for each bit can be obtained, so the decoding process is also performed for each bit. For this reason, the interleaving in the encoding unit 1 can also be performed in bit units. However, interleaving may be performed in symbol units.

  The modulation unit 3 modulates the bit string input from the encoding unit 1 based on the transmission rate instructed by the transmission rate control unit 2, and generates a modulation signal (PSK signal, QAM signal, APSK signal, etc.). The modulation unit 3 holds the transmission rate and the realization method (which Nsc value signal is generated and in what order) as in the first embodiment. In the present embodiment, unlike the first embodiment, one carrier is used regardless of the modulation multi-level number. The modulation unit 3 outputs the generated modulation signal. However, as in the first embodiment, when the spreading process is necessary as the secondary modulation, the signal is output after the spreading process is performed. There is no particular limitation on the spreading sequence used at that time. In the present embodiment, as in the first embodiment, the power density of each symbol is made to be the same in the time domain.

  The demodulator 17 of the receiving device performs demodulation processing on the received signal. However, when the spread processing is performed by the modulation unit 3 of the transmission apparatus, the demodulation unit 17 first performs despreading, and then performs demodulation processing.

  Specifically, the demodulation unit 17 calculates the soft decision likelihood of each bit in the demodulation process, and outputs the calculation result to the decoding unit 19. At this time, unlike the first embodiment, the soft decision likelihood is obtained not in symbol units but in bit units. As described in the first embodiment, a symbol with a larger carrier width has a worse error rate characteristic. Therefore, the soft decision likelihood may be weighted according to the carrier width. For example, if symbols of K types of carrier widths are mixed, the weight of the symbol of the kth (0 ≦ k <K) carrier width is set to w (k), and the demodulator 17 determines the soft decision likelihood. The product of w (k) multiplied by w may be output to the decoding unit 19. Note that weighting is not necessarily performed.

  The decoding unit 19 performs a decoding process using the soft decision likelihood input from the demodulation unit 17. When interleaving is performed in the encoding unit 1 of the transmission apparatus, the decoding unit 19 first performs deinterleaving and changes the order of received bits. After that, decoding processing is performed using the soft decision likelihood, and the obtained bit string is output. Both deinterleaving and decoding are performed in bit units. However, when interleaving is performed in symbol units in the encoding unit of the transmission apparatus, deinterleaving is also performed in symbol units.

  As described above, in this embodiment, when a linear modulation scheme is used, symbols of different carrier widths are mixed and transmitted as in the first embodiment. For this reason, even when the linear modulation method is used, the same effect as in the first embodiment can be obtained.

Embodiment 4 FIG.
In the third embodiment, when the linear modulation method is used, an example has been described in which symbols having different carrier widths are mixed and transmitted, as in the first embodiment. Even in the case of using the linear modulation method, the BER characteristic is deteriorated when symbols having a plurality of carrier widths are mixed, as compared with a case where symbols are not mixed (when Nsc is constant). The configurations of the transmission device and the reception device of the present embodiment are the same as those of the third embodiment. Hereinafter, the same operations as those in the third embodiment will be described by omitting overlapping descriptions and focusing on the differences from the third embodiment. The operations of the present embodiment other than the operation of the modulation unit 3 of the transmission apparatus are the same as those of the third embodiment.

  In the present embodiment, in order to reduce the deterioration of the BER characteristics, the power density of each symbol is set to be the same in the frequency domain as in the second embodiment. By doing so, the error rate becomes equal for each symbol, and the same BER characteristic as when symbols of different carrier widths are not mixed can be realized.

  FIG. 13 is a diagram illustrating an example of blocks mixed so that the power density is the same in the frequency domain. In FIG. 13, (b) the symbol when Nsc = 2 in FIG. 11 and the symbol when (c) Nsc = 4 in FIG. 3 are mixed so that the power density of each symbol is the same in the frequency domain. An example is shown. When mixed according to the method of Embodiment 3, the result is as shown in FIG. 12, but in the example of FIG. 12, the power density is the same in the time domain, and in the frequency domain, the power density is smaller for symbols with a larger carrier width. On the other hand, in the example of FIG. 13, the power density is the same in the frequency domain, and the power density is larger in the time domain as the symbol has a larger carrier width.

  The modulation unit 3 of the transmission apparatus adjusts the power between symbols after generating a modulation signal (symbol) in the same manner as in the third embodiment, so that the power density in the frequency domain of each symbol becomes equal. The power adjustment method for equalizing the power density in the frequency domain of each symbol is the same as in the second embodiment.

  As described above, in this embodiment, when using the linear modulation scheme, symbols having different carrier widths are mixed and transmitted, and at this time, the power density of each symbol is the same in the frequency domain. Adjustment was made. For this reason, the error rate characteristics can be improved compared to the third embodiment.

  As described above, the transmission device, the reception device, the communication system, the transmission method, and the reception method according to the present invention are useful for a communication system that realizes transmission at a plurality of transmission rates, and particularly for communication systems that perform block transmission. Is suitable.

  DESCRIPTION OF SYMBOLS 1 Encoding part, 2,18 Transmission rate control part, 3 Modulation part, 4 CP addition part, 5,12 Band-limiting filter, 6 Power amplifier, 7,11 Antenna, 13 CP removal part, 14 FFT part, 15 FDE part , 16 IFFT unit, 17 demodulation unit.

Claims (16)

A modulation unit that generates modulation symbols using a plurality of types of carriers having different carrier widths, and arranges modulation symbols generated using different types of carriers in a fixed time,
With
Transmitting modulation symbols arranged by the modulation unit ;
Multi-level number of the modulation symbols is constant regardless of the type of carrier used for the generation, the number of modulation symbols for each type of said carrier within said predetermined time and said Rukoto is determined according to the transmission rate Transmitting device. A modulation unit that generates modulation symbols using a plurality of types of carriers having different carrier widths, and arranges modulation symbols generated using different types of carriers in a fixed time,
With
Transmitting modulation symbols arranged by the modulation unit;
The modulation unit, transmit device you characterized in that symbol generated using a large carrier carrier width to place the modulation symbols so that non-contiguous. A modulation unit that generates modulation symbols using a plurality of types of carriers having different carrier widths, and arranges modulation symbols generated using different types of carriers in a fixed time,
With
Transmitting modulation symbols arranged by the modulation unit;
The modulation unit, characterized a to that transmit apparatus to implement a power adjustment to the power density is equal in the frequency domain of the plurality of modulation symbols generated respectively based on the plurality of kinds of carriers having different carrier width . The modulation unit, according to claim 1, characterized in that the power density in the time domain of a plurality of modulation symbols generated respectively based on the plurality of kinds of carriers having different carrier widths implementing power adjusted to be constant transmitting apparatus according to. A transmission rate control unit that selects and indicates one of a plurality of transmission rates;
With
The modulation unit holds correspondence between information indicating one or more types of the carrier used for generating a transmission rate and a modulation symbol and information designating the arrangement of the modulation symbol, from the transmission rate control unit. based on the instruction and the response and, transmitting apparatus according to any one of claims 1 4, characterized in that to determine the placement of the carrier and the modulation symbols used to generate the modulation symbols. The modulation unit, when the type of the determined carrier is one, to generate a modulated symbol using one type of carrier, the generated modulation symbols to claim 5, characterized in that arranged within a predetermined time The transmitting device described.   The transmission apparatus according to claim 1, wherein the modulation unit generates a modulation symbol by a modulation scheme that changes a frequency.   The transmission apparatus according to claim 1, wherein the modulation unit generates a modulation symbol by a linear modulation method. A reception device that receives a signal transmitted from the transmission device according to any one of claims 1 to 3 ,
A demodulator that demodulates a received signal for each type of carrier using a plurality of carriers having different carrier widths used in the transmitter and an arrangement of modulation symbols generated using the carriers;
A receiving apparatus comprising: A receiving device that receives a signal transmitted from the transmitting device according to claim 7,
A demodulator that calculates a soft decision likelihood for each symbol using a plurality of carriers having different carrier widths used in the transmission device and an arrangement of modulation symbols generated using the carrier;
A receiving apparatus comprising:   The demodulator weights the soft decision likelihood according to a carrier width of a carrier used in a transmission apparatus when generating a symbol corresponding to the soft decision likelihood. The receiving device described in 1. A reception device that receives a signal transmitted from the transmission device according to claim 8,
A demodulator for obtaining a soft decision likelihood for each bit using a plurality of carriers having different carrier widths used in the transmission device and an arrangement of modulation symbols generated using the carriers;
A receiving apparatus comprising:   The demodulator weights the soft decision likelihood according to a carrier width of a carrier used in a transmission device when generating a symbol including a bit corresponding to the soft decision likelihood. The receiving device according to claim 12. A transmission device according to any one of claims 1 to 3 ,
A receiving device according to claim 9;
A communication system comprising: A first step of generating modulation symbols using a plurality of types of carriers having different carrier widths;
A second step of arranging and transmitting modulation symbols generated using different types of carrier waves so as to be mixed within a certain period of time;
Only including,
The multi-level number of the modulation symbols is constant regardless of the type of carrier used for generation, and the number of modulation symbols for each type of carrier within the predetermined time is determined according to a transmission rate. How to send. A first step of receiving a signal transmitted from a transmission device;
A second step asking you to soft decision likelihood of each symbol using the arrangement of generated modulation symbols using a plurality of carriers and the carriers having different carrier widths used at the transmitting device,
Only including,
A receiving method comprising weighting the soft decision likelihood according to a carrier width of a carrier used in a transmitting apparatus when generating a symbol corresponding to the soft decision likelihood .

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