JP4482347B2 - Data transmission device - Google Patents

Description

  The present invention relates to a data transmission apparatus used in a digital wireless communication system.

  In a digital wireless communication system such as a mobile communication system, data is transmitted by a modulation method that can obtain a desired communication quality (for example, an error rate of a predetermined value or less on the receiver side). Among the modulation schemes, there is a multilevel modulation scheme in which a plurality of bits are transmitted with one symbol as a modulation unit. In the multi-level modulation method, information of a plurality of bits is transmitted with one symbol as a modulation unit, so that throughput can be increased.

  Multi-level modulation schemes include QPSK (Quarterary Phase Shift Keying) that transmits 2 bits of information in 1 symbol, 16QAM (Quadrature Amplitude Modulation) that transmits 4 bits of information in 1 symbol, and 6 bits of information in 1 symbol 64QAM and the like are transmitted, and the throughput can be improved as the amount of information transmitted in one symbol increases under the same propagation environment.

  In addition, a technique for increasing the throughput of the entire system by adaptively changing the modulation scheme of data to be transmitted on the transmitter side according to the propagation environment has been proposed. Such a technique is called adaptive modulation.

  In recent years, there has been an increasing demand for receiving image data, music data provided from a music distribution service, and the like with a wireless communication terminal such as a mobile phone. In order to receive such a large amount of data in a short time, it is desired to further improve the downlink throughput.

  The present invention has been made in view of this point, and an object of the present invention is to provide a data transmission apparatus capable of improving throughput in data communication using multi-level modulation.

The data transmitting apparatus according to one aspect of the present invention changes the bit position to which each data is allocated in the symbol every time data retransmission occurs, assigns each data to each bit, A configuration is employed in which value modulation is performed and a multi-value modulated symbol is wirelessly transmitted.

  According to this configuration, since the bit position to which each data in the symbol is allocated is changed and distributed for each retransmission, each data in the symbol is almost equal and less likely to be erroneous, and the quality of all the data can surely satisfy the desired quality. It becomes like this. Thereby, the number of retransmissions can be reduced and the throughput can be improved.

  As described above, according to the present invention, throughput can be improved in data communication using multilevel modulation.

  As described above, in the multi-level modulation method, information of a plurality of bits is transmitted with one symbol. For example, in the case of 16QAM, 4-bit information is transmitted with one symbol. In 16QAM, by arranging 16 signal points at different positions on the IQ plane, 4-bit information can be transmitted in one symbol. A signal space diagram is an example of the signal point arrangement. Hereinafter, 16QAM is taken as an example of the multi-level modulation scheme, and a signal space diagram of 16QAM will be described. FIG. 1 is a signal section diagram showing signal point arrangement of 16QAM.

  As shown in FIG. 1, in 16QAM, 16 signal points are arranged at different positions on the IQ plane by performing quaternary amplitude modulation on the I axis and the Q axis. As a result, multi-value processing can be performed, and 4-bit information can be transmitted with one symbol. When multi-leveling is performed in this way, signal points are arranged so as to be different from adjacent symbols by only one bit, as shown in FIG. 1, in order to improve bit error rate characteristics. This is called Gray coding. In FIG. 1, the numbers in parentheses indicate bit assignments.

  When gray coding is performed, the error rate of each bit in one symbol differs depending on the portion to which the bit is assigned. That is, in the case of 16QAM, the third and fourth bits have a higher probability of being erroneously determined than the first and second bits. Hereinafter, this point will be described. As shown in FIG. 1, a case will be described in which the determination threshold values are +2, 0, and −2 for both the I channel and the Q channel.

  FIG. 2 is a diagram for explaining a determination method in 16QAM. Black dots in FIG. 2 are signal points shown in FIG. 1, and bit allocation in each symbol is the same as that shown in FIG. On the receiver side, the bit of each symbol is determined as follows.

That is, in FIG. 1, focusing on the most significant bit (leftmost bit) b ₁ , the positive region 101 on the I axis (the right region across the Q axis) 101 is 0, and the negative region on the I axis (Q 102 is 1 on the left side of the axis. Therefore, on the receiver side, as shown in FIG. 2A, when the received symbol is located in the positive region 101 of the I axis, b ₁ is determined to be 0, and the received symbol is in the negative region 102 of the I axis. when located determines b ₁ 1 and. That is, it is possible to determine whether b ₁ is 0 or 1 simply by determining which of the two regions the received symbol is in. In other words, for b ₁ , it can be determined whether it is 0 or 1 only by determining whether the value on the I axis is positive or negative.

In FIG. 1, paying attention to the second most significant bit (second bit from the left) b ₂ , the plus region (upper region across the I axis) 103 on the Q axis is 0, The minus area (lower area across the I axis) 104 is 1. Therefore, at the receiver side, as shown in FIG. 2B, when the received symbol is located in the positive region 103 of the Q axis, b ₂ is determined to be 0, and the received symbol is in the negative region 104 of the Q axis. If it is located, b ₂ is determined to be 1. That is, it is possible to determine whether b ₂ is 0 or 1 simply by determining which of the two regions the received symbol is in. In other words, b ₂ can be determined to be 0 or 1 only by determining whether the value on the Q axis is positive or negative.

In FIG. 1, focusing on the third most significant bit (third bit from the left) b ₃ , the region 105 of 0 or more and less than +2 and the region 106 of −2 or more and less than 0 on the I axis are 0. , The region 107 of +2 or more in the I axis and the region 108 of less than −2 are 1. Therefore, on the receiver side, as shown in FIG. 2 (c), b _{3 is set} to 0 when the received symbol is located in the region 105 of 0 or more and less than +2 or the region 106 of -2 or more and less than 0 on the I axis. determining that, if the received symbol is located in the +2 or more regions 107 or less than -2 region 108, in the I-axis determines b ₃ 1 and. That is, in order to determine whether b ₃ is 0 or 1, it is necessary to determine in which of the four areas the received symbol is located.

In FIG. 1, focusing on the least significant bit (rightmost bit) b ₄ , the region 109 of 0 or more and less than +2 on the Q axis and the region 110 of −2 or more and less than 0 are 0, and +2 or more on the Q axis. Area 111 and area 112 less than -2 are 1. Therefore, on the receiver side, as shown in FIG. 2 (d), b _{4 is set} to 0 when the received symbol is located in an area 109 of 0 or more and less than +2 or an area 110 of -2 or more and less than 0 on the Q axis. When the received symbol is located in the region 111 of +2 or more on the Q axis or the region 112 of less than −2, b ₄ is determined to be 1. That is, in order to determine whether b ₄ is 0 or 1, it is necessary to determine in which of the four areas the received symbol is located.

Thus, for b ₁ and b ₂ , it suffices to determine in which of the two regions the received symbol is located, whereas for b ₃ and b _4, which region of the four received symbols is in the four regions It is necessary to determine whether or not Further, each of the determination areas 101 to 104 is wider than each of the determination areas 105 to 112. Therefore, the probability that b ₁ and b ₂ are erroneously determined is lower than the probability that b ₃ and b ₄ are erroneously determined.

  This is not limited to 16QAM. That is, the same thing can be said for a multi-level modulation system in which a plurality of bits are included in one symbol and the error rate of each bit is different, and the higher the bit, the less the error (however, in the case of 16QAM, etc. The error rate is the same for multiple bits).

  The present inventors pay attention to the fact that the error difficulty of each bit varies depending on the bit position in the multi-value modulated symbol, and each of the data included in one symbol (4 bit data if 16QAM) is used. The present inventors have found that the error rate of data (that is, the quality of data) can be adjusted by allocating to each bit based on the difficulty of error of each bit, and have come to the present invention.

  That is, the main point of the present invention is that when data is modulated by a multi-level modulation method, the data that is less likely to be error (that is, the data that is desired to have higher quality) is assigned to the upper bits in the symbol that is the modulation unit and transmitted. By doing so, the throughput is improved.

(Embodiment 1)
Conventionally, when a base station simultaneously transmits data to a plurality of communication terminals in a CDMA digital communication system, the data transmitted to each communication terminal is spread corresponding to each communication terminal as shown in FIG. It is spread with a code and transmitted. Hereinafter, a case where data is simultaneously transmitted to four communication terminals # 1 to # 4 using 16QAM as the multi-level modulation method will be described. FIG. 3 is a diagram illustrating a correspondence relationship among communication terminals, spreading codes, and bit assignments in a conventional multilevel modulation communication system. B ₁ is the most significant bit, b ₂ is the second most significant bit, b ₃ is the third most significant bit, and b ₄ is the least significant bit.

  Conventionally, as shown in FIG. 3, the data transmitted to the communication terminal # 1 is spread code # 1, the data transmitted to the communication terminal # 2 is spread code # 2, and the data transmitted to the communication terminal # 3 is Data transmitted to spreading code # 3 and communication terminal # 4 is spread with spreading code # 4 and transmitted. That is, conventionally, communication terminals and spreading codes correspond to each other.

Here, as described above, the probability that b ₁ and b ₂ are erroneously determined is lower than the probability that b ₃ and b ₄ are erroneously determined. That is, the data assigned to b ₁ and b ₂ is of higher quality than the data assigned to b ₃ and b ₄ .

However, conventionally, data transmitted to each of the communication terminals # 1 to # 4 is subjected to multilevel modulation for each communication terminal. That is, 4-bit data transmitted with one symbol to each communication terminal is similarly assigned to the most significant bit b ₁ to the least significant bit b ₄ and transmitted for each communication terminal. Therefore, when the average error rates of b _{1 to} b ₄ are compared between the communication terminals, the average error rates are equal if the conditions such as the propagation environment are the same. That is, the error rate characteristics of the average error rate in all communication terminals are the same as the characteristics indicated by 203 in FIG. FIG. 4 is a diagram showing error rate characteristics in a conventional multilevel modulation system. In this figure, 201 indicates the error rate characteristics of b ₁ and b ₂ , 202 indicates the error rate characteristics of b ₃ and b ₄ , and 203 indicates the average error rate characteristics of b _{1 to} b ₄ .

Here, for example, in a communication system in which adaptive modulation is performed, a modulation scheme corresponding to the propagation environment is selected on the base station side so that the average error rate satisfies the desired quality on the communication terminal side. However, when the data reception SIR deteriorates due to temporary deterioration of the propagation environment due to fading or the like, as shown in FIG. 4, the average error rate 203 of b _{1 to} b ₄ has the desired quality at all the communication terminals. It may become impossible to satisfy. In a communication system in which an automatic repeat request (ARQ: Automatic Repeat reQuest) is performed, in this case, data retransmission occurs for all communication terminals, and the throughput of the entire system is greatly reduced.

  Therefore, in the present embodiment, data transmitted to a communication terminal having a higher priority is assigned with higher bits in the symbol and transmitted, and the data for the communication terminal having a higher priority is surely satisfied. To. As a result, the throughput of the entire system is improved.

FIG. 5 is a diagram showing a correspondence relationship between a communication terminal, a spreading code, and bit allocation in the multilevel modulation communication system according to Embodiment 1 of the present invention. Conventionally, communication terminals correspond to spreading codes, but in the present embodiment, as shown in FIG. 5, communication terminals correspond to bit allocation positions of data. That is, data transmitted to the communication terminal with the highest priority (here, communication terminal # 1) is assigned to b ₁ and the communication terminal with the second highest priority (here, communication terminal # 1). the data to be transmitted to the 2) assigned to b _2, a high communication terminal priority third (here, data to be transmitted to the communication terminal # 3) is assigned to b ₃ is (here, communication terminal # 4) lowest priority communication terminal data to be transmitted to is assigned to b _4.

As described above, the data assigned to b ₁ and b ₂ is of higher quality than the data assigned to b ₃ and b ₄ . Therefore, by performing the bit allocation as shown in FIG. 5, the data transmitted to the communication terminal # 1 and the data transmitted to the communication terminal # 2 have higher quality than the case of the bit allocation shown in FIG. The data is improved and can always satisfy the desired quality.

  As a result, for the data transmitted to the communication terminal # 1 and the data transmitted to the communication terminal # 2, the desired quality is ensured even when the reception SIR of the data is deteriorated due to temporary deterioration of the propagation environment due to fading or the like. Can be met. That is, the data for the communication terminal having a high priority can surely satisfy the desired quality. For this reason, the higher the priority communication terminal, the quicker the data reception can be completed. Further, the number of data retransmissions can be reduced as a whole system, and the throughput of the whole system can be improved.

  Hereinafter, a radio transmission apparatus and a radio reception apparatus used in the multilevel modulation communication system according to the present embodiment will be described. FIG. 6 is a block diagram showing a configuration of the multi-level modulation communication system according to Embodiment 1 of the present invention. In the following description, it is assumed that the wireless transmission device is used by being mounted on a base station, and the wireless reception device is used by being mounted on a communication terminal. A case where data is simultaneously transmitted to four communication terminals will be described.

  In radio transmission apparatus 300, encoding sections 301-1 to 301-4 perform encoding processing on data sequences # 1 to # 4, respectively, and the encoded data is P / S (parallel / serial). The data is output to the conversion unit 302. Data series # 1 to # 4 are data series transmitted to communication terminals # 1 to # 4, respectively.

  P / S conversion section 302 converts data series # 1 to # 4 input in parallel to serial and outputs the result to multilevel modulation section 304. At this time, the P / S conversion unit 302 performs parallel-serial conversion so that a data sequence for a communication terminal with a higher priority is assigned to higher bits within one symbol in accordance with control from the assignment control unit 303 described later. . Detailed description of bit allocation will be described later.

  The multi-level modulation unit 304 performs multi-level modulation on the parallel-serial converted data. Here, since it is necessary to simultaneously transmit data to four communication terminals, 16QAM capable of transmitting 4-bit data with one symbol is used as the multi-level modulation method. Therefore, the multi-level modulation unit 304 arranges the parallel-serial converted data at any signal point shown in FIG. The symbol after multilevel modulation is output to an S / P (serial / parallel) conversion unit 305.

  S / P conversion section 305 converts symbols input in series from multi-level modulation section 304 in parallel, and outputs the converted symbols to multipliers 306-1 to 306-4. That is, the S / P conversion unit 305 distributes the symbols input in series from the multi-level modulation unit 304 to the multipliers 306-1 to 306-4 in the input order, and outputs them. Multipliers 306-1 to 306-4 multiply the symbols output in parallel from S / P converter 305 by spreading codes # 1 to # 4, respectively. The symbol after spreading processing is output to multiplexing section 309.

  The assignment control unit 303 instructs the P / S conversion unit 302 on the bits to which the data sequences # 1 to # 4 are assigned based on the priority of the communication terminal. That is, the allocation control unit 303 controls the P / S conversion unit 302 so that data for a communication terminal with a higher priority is allocated to higher bits within one symbol. Detailed description of bit allocation will be described later.

  Further, the allocation control unit 303 outputs an allocation notification signal indicating which data series is allocated to which bit to the modulation unit 307. The assignment notification signal is modulated by the modulation unit 307, multiplied by the spreading code #A by the multiplier 308, and then input to the multiplexing unit 309.

  Multiplexer 309 multiplexes all the signals output from multipliers 306-1 to 306-4 and multiplier 308 and outputs the result to radio transmitter 310. Radio transmitting section 310 performs predetermined radio processing such as up-conversion on the multiplexed signal, and then transmits the multiplexed signal to radio receiving apparatus 400 via antenna 311. In the following description, it is assumed that the wireless reception device 400 is mounted on the communication terminal # 1.

  The multiplexed signal received via the antenna 401 of the wireless reception device 400 is subjected to predetermined wireless processing such as down-conversion in the wireless reception unit 402 and then input to the distribution unit 403. Distribution section 403 distributes the multiplexed signal to multipliers 404-1 to 404-4 and multiplier 408 and outputs the result.

  Multipliers 404-1 to 404-4 multiply the multiplexed signals output from distribution section 403 by spreading codes # 1 to # 4, respectively. Thereby, each symbol spread by spreading codes # 1 to # 4 is extracted from the multiplexed signal. The symbol after the despreading process is input to the P / S converter 405.

  The P / S conversion unit 405 converts the symbols input in parallel to serial and outputs the converted symbols to the multilevel demodulation unit 406. Multilevel demodulation section 406 performs demodulation processing corresponding to the multilevel modulation performed by radio transmission apparatus 300 on the parallel-serial converted symbols, and outputs the result to S / P conversion section 407. That is, here, the multilevel demodulation unit 406 performs multilevel demodulation based on 16QAM.

  The S / P converter 407 converts the data series input in series from the multi-level demodulator 406 in parallel and outputs it to the selector 411. At this time, the S / P conversion unit 407 performs serial conversion opposite to the parallel-serial conversion performed by the P / S conversion unit 302 of the wireless transmission device 300 in accordance with control from the conversion control unit 410 described later.

  Multiplier 408 multiplies the multiplexed signal by spreading code #A. As a result, the assignment notification signal spread by the spreading code #A is extracted from the multiplexed signal. The assignment notification signal is demodulated by the demodulation unit 409 and then input to the conversion control unit 410.

  Based on the assignment notification signal, conversion control unit 410 controls S / P conversion unit 407 such that serial conversion opposite to parallel-serial conversion performed by P / S conversion unit 302 of wireless transmission device 300 is performed. . Further, based on the assignment notification signal, conversion control unit 410 selects which signal line of S / P conversion unit 407 outputs a data series addressed to the own terminal (here, communication terminal # 1). To instruct.

  The selection unit 411 selects a data series addressed to the own terminal according to an instruction from the conversion control unit 410 and outputs the data series to the decoding unit 412. The decoding unit 412 decodes the data series selected by the selection unit 411. As a result, a data series addressed to the own terminal (that is, data series # 1) is obtained.

Next, an operation in which data series # 1 to # 4 are assigned to each bit in a symbol and transmitted will be specifically described. FIG. 7 is a diagram schematically showing the operation of the radio transmission apparatus used in the multi-level modulation communication system according to Embodiment 1 of the present invention. In FIG. 7, data indicated by d _nm indicates the mth data transmitted to the communication terminal #n. Therefore, for example, d ₁₁ , d ₁₂ , d ₁₃ , and d ₁₄ correspond to the data sequence # 1 transmitted to the communication terminal # 1. The number in parentheses above the data d _nm indicates the content (0 or 1) of the data. S _l indicates the l-th symbol transmitted from the wireless transmission device 300.

  First, the P / S converter 302 performs parallel-serial conversion (P / S conversion) such that a data sequence for a communication terminal with a higher priority is assigned to higher bits within one symbol according to control from the assignment controller 303. )I do. Here, the priority is assumed to be higher in the order of communication terminal # 1, communication terminal # 2, communication terminal # 3, and communication terminal # 4.

  Here, for example, the following can be considered as a method for determining the priority order. That is, a higher priority is assigned to a communication terminal having a better propagation path environment. Thereby, since the quality of the data series with good quality is further improved due to the good propagation path environment, data transmission to a communication terminal with a good propagation path environment can be completed more quickly and reliably.

  As another method, a communication terminal with a larger amount of untransmitted data has a higher priority. As a result, the quality of a data sequence for a communication terminal with a large amount of untransmitted data is improved, and the throughput of a communication terminal with a large amount of untransmitted data can be increased. As the throughput increases, the amount of unsent data decreases more quickly, so the priority changes with time. Therefore, according to this method, it is possible to increase the throughput of the entire system while keeping the throughput of all communication terminals substantially the same.

  As another method, a communication terminal used by a user who pays a higher fee has a higher priority. According to this method, the quality of a data series for a communication terminal used by a user who pays a high charge becomes better, so that it is possible to provide a communication service with a difference in user convenience according to the charge. .

  As another method, for example, in a communication system in which adaptive modulation is performed, a communication terminal having a worse propagation path environment has a higher priority. Accordingly, it is possible to compensate for quality degradation due to a poor propagation path environment and to improve the quality of a data sequence for a communication terminal having a poor propagation path environment to a desired quality. Since the quality of the data series for a communication terminal having a good propagation path environment satisfies the desired quality in the first place, the throughput of the entire system can be increased by adopting this method.

  Note that which of these determination methods is adopted depends on the service provided by the multi-level modulation communication system according to the present embodiment and the situation and environment in which the multi-level modulation communication system according to the present embodiment is installed. It may be determined appropriately according to the situation.

Since the priority is higher in the order of communication terminal # 1 → communication terminal # 2 → communication terminal # 3 → communication terminal # 4, the P / S conversion unit 302 has data d ₁₁ , d ₁₂ , The parallel conversion is performed by assigning d ₁₃ and d ₁₄ to the most significant bits of the symbols S _{1 to} S ₄ . Similarly, the P / S conversion unit 302 assigns the data d ₂₁ , d ₂₂ , d ₂₃ , and d ₂₄ to the second most significant bit, and the data d ₃₁ , d ₃₂ , d ₃₃ , and d ₃₄ to the third most significant bit. And data d ₄₁ , d ₄₂ , d ₄₃ , d ₄₄ are assigned to the least significant bit. As a result, each data series is associated with the position of each bit in the symbol.

  That is, data for communication terminal # 1 with the highest priority is assigned to the most significant bit, data for communication terminal # 2 with the second highest priority is assigned to the second highest bit, and priority is third. The data for communication terminal # 3 having the highest priority is assigned to the third most significant bit, and the data for communication terminal # 4 having the lowest priority is assigned to the least significant bit. Therefore, the data sequence transmitted to a communication terminal having a higher priority can lower the error rate and improve the quality. In 16QAM, the quality of the most significant bit is the same as the quality of the second most significant bit, and the quality of the third most significant bit is the same as the quality of the least significant bit. The quality of the data sequence for 1 and the quality of the data sequence for communication terminal # 2 are the same, and the quality of the data sequence for communication terminal # 3 and the quality of the data sequence for communication terminal # 4 are the same.

Next, the parallel-serial converted data is subjected to multilevel modulation using 16QAM in the multilevel modulation section 304. Since the symbol S ₁ is 0011, S ₂ is 1110, S ₃ is 1000, and S ₄ is 0101, each symbol is modulated so as to be arranged at a signal point indicated by a black circle in FIG. The modulated symbol is subjected to serial / parallel conversion (S / P conversion) by the S / P conversion section 305. Symbols S _{1 to} S ₄ are each subjected to spreading processing by multipliers 306-1 to 306-4.

The multiplexing unit 309, and assignment notification signal S _c after spreading processing a symbol S ₁ to S ₄ after spreading processing are multiplexed. Then, this multiplexed signal is transmitted to the wireless reception device 400.

  Next, the operation of the wireless reception device 400 will be described in detail. FIG. 9 is a diagram schematically showing the operation of the radio reception apparatus used in the multi-level modulation communication system according to Embodiment 1 of the present invention.

The multiplexed signal received by radio receiving apparatus 400 is subjected to despreading processing by multipliers 404-1 to 404-4 and multiplier 408. Thus, the symbol S ₁ to S ₄ and assignment notification signal S _c is taken from the multiplexed signal. The symbols S _{1 to} S ₄ are subjected to parallel / serial conversion (P / S conversion) by the P / S conversion unit 405 and multi-level demodulated by the multi-level demodulation unit 406 based on 16QAM. As a result, the data series d ₁₁ , d ₂₁ , d ₃₁ , d ₄₁ , d ₁₂ , d ₂₂ ,... As shown in FIG. That is, a data series in which data addressed to communication terminal # 1 is assigned to the most significant bit of each symbol is output.

Next, in the S / P conversion unit 407, the data series output in series from the multilevel demodulation unit 406 is converted in parallel according to the control from the conversion control unit 410. The conversion control unit 410 can know to which bit the data addressed to each terminal is assigned by the assignment notification signal. Here, the conversion control unit 410 assigns the data d ₁₁ , d ₁₂ , d ₁₃ , d ₁₄ addressed to the communication terminal # 1 to the most significant bit, and the data d ₂₁ , d ₂₂ , d ₂₃ addressed to the communication terminal # 2. , D ₂₄ are assigned to the second most significant bit, and data d ₃₁ , d ₃₂ , d ₃₃ , d ₃₄ addressed to communication terminal # 3 are assigned to the third most significant bit and data addressed to communication terminal # 4 It can be seen that d ₄₁ , d ₄₂ , d ₄₃ , and d ₄₄ are assigned to the least significant bit.

  Therefore, the conversion control unit 410 includes an S / P conversion unit 407 so that the data series output in series from the multilevel demodulation unit 406 is output from the S / P conversion unit 407 for each of the data series # 1 to # 4. The serial / parallel conversion (S / P conversion) is controlled. Serial-parallel conversion is performed according to this control, and the data series # 1 to # 4 for each of the communication terminals # 1 to # 4 are output in parallel from the S / P converter 407, as shown in FIG.

Next, the data series addressed to the terminal is selected by the selection unit 411. The selection unit 411 is instructed by the conversion control unit 410 from which signal line of the S / P conversion unit 407 the data series addressed to its own terminal is output. In accordance with this instruction, the selection unit 411 selects a data series addressed to the terminal itself. Here, since the own terminal is the communication terminal # 1, the selection unit 411 selects the data series output from the uppermost signal line among the signal lines from the S / P conversion unit 407. As a result, the data sequence # 1 (d ₁₁ , d ₁₂ , d ₁₃ , d ₁₄ ) addressed to the communication terminal # 1 is selected and output to the decoding unit 412.

  This data series # 1 is all data transmitted by being assigned to the most significant bit of the symbol. Therefore, the quality of the data sequence # 1 can reliably satisfy the desired quality even when the reception SIR is deteriorated due to temporary deterioration of the propagation environment due to fading or the like.

  As described above, according to the present embodiment, data for a communication terminal having a higher priority is transmitted by being assigned to higher bits in a multi-level modulated symbol, so that the data quality for the communication terminal having a higher priority is improved. It is sufficiently higher than the desired quality. For this reason, the quality of the data with respect to the communication terminal with a high priority can surely satisfy the desired quality. As a result, the possibility that retransmission will occur is reduced for communication terminals with high priority. Further, even when the propagation environment is deteriorated, it is possible to prevent the data quality from failing to satisfy the desired quality in all the communication terminals. Therefore, the number of data retransmissions is reduced as a whole system, and the throughput of the whole system can be improved.

  In addition, since the possibility that retransmission will occur for a communication terminal with a high priority is reduced, data transmission can be completed more quickly with a communication terminal with a higher priority. By completing data transmission to a communication terminal with a high priority, it is possible to assign high-quality bits assigned to that communication terminal to data transmitted to a communication terminal with a low priority. As a result, the number of retransmissions also decreases for data for communication terminals with low priority. Therefore, the throughput of the entire system can be further increased.

  When data transmission to a communication terminal with high priority is completed and high quality bits are allocated to data transmitted to a communication terminal with low priority, data for the same terminal is allocated to 2 bits or more of one symbol. You may make it transmit. Thereby, the throughput can be further improved.

  Further, when all of the multi-level modulation schemes applied to each communication terminal are the same (in this embodiment, 16QAM is applied to all communication terminals), conventionally, the error rate characteristics of data in all communication terminals Will be the same. However, in this embodiment, since bit allocation according to priority is performed, even if all the multi-level modulation schemes applied to each communication terminal are the same, as shown in FIG. Error rate characteristics can be set for each terminal. That is, as in this embodiment, the priority is higher in the order of communication terminal # 1 → communication terminal # 2 → communication terminal # 3 → communication terminal # 4, and 16QAM is applied to all communication terminals # 1 to # 4. In this case, the error rate characteristic of the communication terminal # 1 and the error rate characteristic 501 of the communication terminal # 2 can be improved than the error rate characteristic of the communication terminal # 3 and the error rate characteristic 502 of the communication terminal # 4. . That is, according to the present embodiment, a plurality of error rate characteristics can be set with one multi-level modulation method. As a result, even when the same multi-level modulation scheme is applied to a plurality of communication terminals, it is possible to perform quality control for each communication terminal using one multi-level modulation scheme.

  In addition, since it is possible to set multiple qualities with one multi-level modulation method, when selecting a modulation method in a communication system in which adaptive modulation is performed, it is also necessary to select a bit to which transmission data is assigned Thus, finer quality control than conventional adaptive modulation can be performed.

  In addition, when the wireless transmission device 300 is mounted and used in a base station used in a mobile communication system, and the wireless reception device 400 is mounted and used in a communication terminal used in a mobile communication system, The communication terminals in the radio zone of the base station change from moment to moment. That is, in the present embodiment, the communication terminals that are the communication terminals # 1 to # 4 change from moment to moment. Therefore, when this embodiment is applied to a mobile communication system, it is necessary to transmit an allocation notification signal to each communication terminal as described above.

  However, in a wireless communication system (for example, a wireless LAN system) in which the communication terminals # 1 to # 4 do not change, it is not necessary to transmit an assignment notification signal because the bit assignment is known in advance in each communication terminal. . Therefore, in such a wireless communication system, it is possible to omit an apparatus configuration for generating an assignment notification signal, transmitting / receiving, and the like from the wireless transmission device 300 and the wireless reception device 400. Therefore, the device configuration is simplified.

  In addition, for example, data of up to 4 communication terminals can be transmitted with one symbol in the case of 16 QAM, and data for up to 6 communication terminals can be transmitted in one symbol with 64 QAM. Therefore, in the present embodiment, it is assumed that the multilevel modulation scheme to be used is selected according to the number of communication terminals to which data is simultaneously transmitted.

(Embodiment 2)
Conventionally, in a communication system in which an automatic repeat request (ARQ) is performed, symbols having the same contents are retransmitted at the time of retransmission. That is, when multilevel modulation is performed, the position of the bit to which each data is assigned within one symbol is the same at the time of initial transmission and retransmission.

Here, as described above, in the multi-level modulation method, the lower the bit within one symbol, the higher the probability of erroneous determination. For example, in 16QAM, as described above, the third bit b ₃ and the fourth bit b ₄ are more likely to be erroneously determined than the first bit b ₁ and the second bit b ₂ . Therefore, the third bit b ₃ and the fourth bit b ₄ , which are the lower bits, are prone to error even during retransmission. For this reason, the average error rate of b _{1 to} b ₄ cannot satisfy the desired quality even during retransmission, and retransmission may occur.

  Therefore, in this embodiment, at the time of retransmission, the position of the bit to which each piece of data is assigned within one symbol is replaced with that at the first transmission. That is, at the time of retransmission, the data assigned to the upper bits at the first transmission is assigned to the lower bits, and the data assigned to the lower bits at the first transmission is assigned to the higher bits for transmission. Thereby, at the time of retransmission, the probability that the data assigned to the lower bits at the first transmission is erroneously determined becomes lower.

  On the receiver side, the demodulation result of the symbol transmitted at the time of initial transmission and the demodulation result of the symbol transmitted at the time of retransmission are combined. As a result, each data in one symbol is comparable and less likely to be erroneous, and the quality of all data can surely satisfy the desired quality. Therefore, the number of retransmissions can be reduced, and throughput can be improved.

  Hereinafter, a radio transmission apparatus and a radio reception apparatus used in the multilevel modulation communication system according to the present embodiment will be described. FIG. 11 is a block diagram showing a configuration of a multi-level modulation communication system according to Embodiment 2 of the present invention.

  In radio transmission apparatus 600, error detection code adding section 601 adds an error detection code such as a CRC (Cyclic Redundancy Check) bit for each predetermined unit to transmission data and outputs the transmission data to error correction encoding section 602. .

  The error correction encoding unit 602 performs error correction encoding on the transmission data by, for example, convolutional encoding. The error-corrected encoded data is output to the switch 604 via the buffer 603. At this time, the transmission data is stored in the buffer 603.

  The switch 604 is switch-controlled by the control unit 609, and connects the buffer 603 and the multi-level modulation unit 605 at the time of odd-number transmission including the first transmission, and connects the buffer 603 and the bit string conversion unit 606 at the time of even-number transmission. To do.

  The bit string conversion unit 606 reverses the order of bits in one symbol between the odd-numbered transmission and the even-numbered transmission. That is, the bit string conversion unit 606 changes the bit position to which each data is allocated within one symbol each time data is retransmitted. As a result, the data assigned to the upper bit at the odd-numbered transmission is assigned to the lower bit at the even-numbered transmission, and the data assigned to the lower bit at the odd-numbered transmission is assigned to the even-numbered transmission. It will be assigned to the upper bits.

  The multi-level modulation unit 605 performs multi-level modulation on the data directly input from the buffer 603 or the data whose bit sequence is converted by the bit sequence conversion unit 606. Here, 16QAM capable of transmitting 4-bit data with one symbol is used as the multi-level modulation method. Therefore, the multi-level modulation unit 605 arranges the input data at any signal point shown in FIG. The symbol after multilevel modulation is output to multiplier 607. Multiplier 607 multiplies the symbol after multilevel modulation by spreading code # 1 corresponding to communication partner # 1. The symbol after spreading processing is output to multiplexer 608.

  The control unit 609 instructs the data to be retransmitted to the buffer 603 in accordance with a retransmission request signal for requesting retransmission of data transmitted from the wireless reception device 700. The buffer 603 outputs data to be retransmitted to the switch 604 in accordance with this instruction.

  In addition, the control unit 609 counts the number of times the retransmission request signal is received, and the buffer 603 and the multi-level modulation unit 605 are connected at the odd-numbered transmission including the first transmission, and the buffer 603 and the bit string conversion are performed at the even-numbered transmission. The switch 604 is controlled to be connected to the unit 606.

  In addition, the control unit 609 generates a transmission count notification signal indicating how many times the same data is transmitted, and outputs the signal to the modulation unit 610. This transmission count notification signal is modulated by modulation section 610, multiplied by spreading code #A by multiplier 611, and then input to multiplexer 608.

  The multiplexer 608 multiplexes the signal output from the multiplier 607 and the signal output from the multiplier 611 and outputs the multiplexed signal to the wireless transmission unit 612. The wireless transmission unit 612 performs predetermined wireless processing such as up-conversion on the multiplexed signal, and then transmits the multiplexed signal to the wireless reception device 700 via the antenna 613.

  Radio reception section 614 performs predetermined radio processing such as down-conversion on the retransmission request signal received via antenna 613 and outputs the result to multiplier 615. Multiplier 615 multiplies retransmission request signal output from radio reception section 614 by spreading code #B. The retransmission request signal after the despreading process is demodulated by the demodulation unit 616 and input to the control unit 609.

  In radio receiving apparatus 700, radio receiving section 702 performs predetermined radio processing such as down-conversion on the multiplexed signal received via antenna 701, and then outputs the multiplexed signal to multiplier 703 and multiplier 711. To do.

  Multiplier 703 multiplies the multiplexed signal by spreading code # 1. As a result, the symbols spread by the spreading code # 1 are extracted from the multiplexed signal. The symbol after the despreading process is input to the multilevel demodulator 704.

  Multilevel demodulation section 704 performs demodulation processing corresponding to the multilevel modulation performed by radio transmitting apparatus 600 on the symbol after despreading processing, and outputs the demodulation result to switch 705. That is, here, the multilevel demodulator 704 performs multilevel demodulation based on 16QAM. The multi-level demodulation unit 704 outputs a soft decision value of each data included in one symbol as a demodulation result.

  The switch 705 is switch-controlled by the control unit 713, and connects the multi-level demodulation unit 704 and the synthesis unit 706 at the odd-number transmission including the first transmission, and reverses the bit sequence from the multi-level demodulation unit 704 at the even-number transmission. The unit 707 is connected.

  The bit string reverse conversion unit 707 performs reverse sorting to the bit string rearrangement performed by the bit string conversion unit 606 of the wireless transmission device 600. That is, the bit string reverse conversion unit 707 returns the arrangement order of the bit strings in one symbol to the state before the bit string conversion unit 606 converts the bit string. The rearranged demodulation results are output to combining section 706.

  The combining unit 706 combines the demodulation result directly input from the multi-level demodulation unit 704 or the demodulation result obtained by converting the bit string by the bit string inverse conversion unit 707 and the demodulation result stored in the storage unit 708. In other words, the synthesis unit 706 adds a soft decision value for each data. Thereby, every time retransmission occurs, a high-quality demodulation result and a low-quality demodulation result are alternately synthesized for each data. Therefore, the quality of the demodulation result of each data becomes high at the same level within one symbol, and the quality of all data can surely satisfy the desired quality. The combined demodulation result is input to the error correction decoding unit 709 and stored in the storage unit 708.

  The error correction decoding unit 709 performs error correction decoding on the combined demodulation result output from the combining unit 706 based on, for example, the Viterbi algorithm. The data subjected to error correction decoding is input to the error detection unit 710. The error detection unit 710 performs error detection by CRC or the like. Data for which no error is detected by error detection section 710 is received data. Further, when an error is detected by error detection section 710, error detection section 710 generates a retransmission request signal and outputs it to modulation section 714.

  This retransmission request signal is modulated by modulation section 714, multiplied by spreading code #B by multiplier 715, and then input to radio transmission section 716. Radio transmission section 716 performs predetermined radio processing such as up-conversion on the retransmission request signal after spreading processing, and then transmits the retransmission request signal to radio transmission apparatus 600 via antenna 701.

  Multiplier 711 multiplies the multiplexed signal by spreading code #A. As a result, the transmission frequency notification signal spread by the spreading code #A is extracted from the multiplexed signal. The transmission frequency notification signal is demodulated by the demodulator 712 and then input to the controller 713.

  The control unit 713 connects the multi-level demodulating unit 704 and the combining unit 706 in the odd-number transmission including the first transmission according to the number of transmissions of the same data indicated by the transmission count notification signal, and in the even-number transmission in the multiple transmission. The switch 705 is controlled to be switched so that the value demodulator 704 and the bit string inverse converter 707 are connected.

Next, the operation of the multi-level modulation communication system having the above configuration will be specifically described. FIG. 12 is a diagram schematically showing the operation of the multi-level modulation communication system according to Embodiment 2 of the present invention. 12, data indicated by d _m indicates the m-th data. Also, the numbers shown in parentheses above the data d _m indicates the contents of the data (0 or 1). S ₁ and S ₁ ′ respectively indicate a symbol transmitted at the first transmission time and a symbol transmitted at the time of retransmission (second transmission time).

First, in the first transmission, in the wireless transmission device 600, the switch 604 connects the buffer 603 and the multi-level modulation unit 605. Therefore, the transmission data is input to the multilevel modulation unit 605 without being converted into a bit string. That is, in one symbol, d ₁ is assigned to the first bit, d ₂ is assigned to the second bit, d ₃ is assigned to the third bit, and d ₄ is assigned to the fourth bit. Therefore, at the time of initial transmission, d ₁ and d ₂ become higher quality as compared to d ₃ and d _4, d ₃ and d ₄ is a lower quality in comparison with d ₁ and d _2. The symbols including d _{1 to} d ₄ are subjected to multi-level modulation using 16QAM in the multi-level modulation section 605. Since this symbol S ₁ is 1101, it is modulated so as to be placed at the signal point S ₁ indicated by a black circle on the upper IQ plane in FIG. The modulated symbol is multiplexed with a transmission frequency notification signal indicating that it is the first transmission in the multiplexer 608 and then transmitted to the radio reception apparatus 700.

At the time of the first transmission, in the wireless reception device 700, the switch 705 connects the multi-level demodulation unit 704 and the synthesis unit 706. Therefore, the demodulation result of each data output from the multilevel demodulating unit 704 is input to the synthesizing unit 706 without rearranging the bit strings. That is, the time of the first transmission, in radio receiving apparatus 700 the demodulation results of d ₁ and d ₂ become higher quality than the demodulation results of d ₃ and d _4, the demodulation results of d ₃ and d ₄ are of d ₁ and d ₂ The quality is lower than the demodulation result. The demodulation result is stored in the storage unit 708.

At the time of retransmission (second transmission), in wireless transmission device 600, switch 604 connects buffer 603 and bit string conversion unit 606. Therefore, the transmission data stored in the buffer 603 at the time of initial transmission is input to the multi-level modulation unit 605 after the bit string conversion is performed by the bit string conversion unit 606. In other words, the order of bit strings in one symbol is reversed from that at the first transmission. Therefore, d ₄ is assigned to the first bit, d ₃ is assigned to the second bit, d ₂ is assigned to the third bit, and d ₁ is assigned to the fourth bit. Therefore, in the second transmission, d ₃ and d ₄ become higher quality as compared with d ₁ and d _2, d ₁ and d ₂ are a lower quality compared to d ₃ and d _4. The symbols including d _{1 to} d ₄ are subjected to multi-level modulation using 16QAM in the multi-level modulation section 605. Since the symbol S ₁ ′ subjected to the bit string conversion is 1011, the symbol S ₁ ′ is modulated so as to be arranged at a signal point S ₁ ′ indicated by a black circle on the IQ plane in the lower stage of FIG. The modulated symbol is multiplexed with a transmission frequency notification signal indicating that it is the second transmission in the multiplexer 608, and then transmitted to the radio reception apparatus 700.

At the time of retransmission (at the time of second transmission), in radio receiving apparatus 700, switch 705 connects multi-level demodulation section 704 and bit string inverse conversion section 707. Therefore, the demodulated result of each data output from the multi-level demodulating unit 704 is input to the synthesizing unit 706 after rearrangement of bit strings. That is, the reverse of the bit string rearrangement performed by the bit string conversion unit 606 of the wireless transmission device 600 is performed, and the bit string arrangement order within one symbol is the same as that before the bit string is converted by the wireless transmission device 600. It is returned to the state. This rearrangement returns d ₁ to the first bit, d ₂ to the second bit, d ₃ to the third bit, and d ₄ to the fourth bit. At this time, the demodulation results of d ₁ and d ₂ become lower quality than the demodulation results of d ₃ and d _4, the demodulation results of d ₃ and d ₄ are high compared to the demodulation results of d ₁ and d ₂ It becomes quality. The demodulated result is synthesized by the synthesizing unit 706 for each data with the demodulated result stored in the storage unit 708.

  As a result of combining the demodulation result at the time of first transmission and the demodulation result at the time of retransmission (during the second transmission) in this way, as shown in FIG. 13, the quality of the demodulation result of each data is comparable within one symbol. Get higher. Therefore, the quality of all data can reliably satisfy the desired quality by retransmission.

  As described above, according to the present embodiment, at the time of retransmission, the radio transmission apparatus transmits symbols by replacing the positions of bits to which each data is assigned in one symbol with that at the time of initial transmission. The demodulation result of the symbol transmitted at the time of transmission and the demodulation result of the symbol transmitted at the time of retransmission are combined. In the present embodiment, the data assigned to the upper bits at the odd-numbered transmission is assigned to the lower bits at the even-numbered transmission, and the data assigned to the lower bits at the odd-numbered transmission. It is assigned to the upper bit at the even transmission. Therefore, each data in one symbol is comparable and less likely to be erroneous, and the quality of all data can surely satisfy the desired quality. Thereby, the number of retransmissions can be reduced and the throughput can be improved.

  In the present embodiment, the radio reception apparatus is configured to perform error correction decoding using the combined demodulation result, but is configured to make a hard decision on the combined demodulation result without performing error correction decoding. Also good. In this case, it is not necessary for the wireless transmission apparatus to perform error correction encoding on the transmission data.

  In this embodiment, the synthesis unit of the radio reception apparatus combines all demodulation results within one symbol. However, only the demodulation results of data assigned to arbitrary bits may be combined. For example, only high-quality demodulation results may be combined.

  Further, in the present embodiment, the case where 16QAM is used as the multi-level modulation method has been described, and therefore the quality that can be set in the symbol is high and low. For this reason, every time retransmission occurs, retransmission data is assigned alternately to high-quality bits and low-quality bits within a symbol. However, for example, when 64QAM is used as the multi-level modulation method, the quality that can be set in the symbol is three levels of high, medium, and low. Therefore, when 64QAM is used, a configuration may be adopted in which retransmission data is sequentially allocated to high-quality bits, medium-quality bits, and low-quality bits in a symbol every time retransmission occurs. The same applies to other multi-level modulation schemes such as 256QAM.

  In this embodiment, the wireless transmission device notifies the wireless reception device of the number of transmissions. However, the wireless reception device may count the number of receptions without notifying the number of transmissions. .

  In this embodiment, there is no particular limitation on the retransmission method. Therefore, SAW (Stop-And-Wait) method, GBN (Go-Back-N) method, SR (Selective-Repeat) method, hybrid ARQ method, etc. can be used as the retransmission method.

  In the first and second embodiments, it is desirable that the multilevel modulation scheme is temporally changed in the radio transmission apparatus according to the propagation path environment. That is, it is desirable to use Embodiments 1 and 2 in combination with adaptive modulation.

  The present invention is not limited to Embodiments 1 and 2 described above, and can be implemented with various modifications. For example, in the first and second embodiments, the case where the multi-value number is 16 values (that is, one symbol is 4 bits) has been described as an example. However, in the first and second embodiments, A multi-level modulation scheme in which a plurality of bits are included in one symbol and each bit has a different error rate can be similarly implemented.

Further, the multi-level modulation communication system according to one aspect of the present invention can be applied to a digital radio communication system such as a mobile communication system. That is, the wireless transmission device can be applied to a base station, and the wireless reception device can be applied to a communication terminal such as a mobile station.

A data transmitting apparatus according to one aspect of the present invention changes and distributes the bit position to which each data in a symbol is allocated for each retransmission, and thus reduces the number of retransmissions in data communication using multi-level modulation, thereby improving throughput. It has the effect of improving and can be applied to uses such as base stations and communication terminals used in digital radio communication systems.

Signal interval diagram showing 16QAM signal point arrangement The figure for demonstrating the determination method in 16QAM The figure which shows the correspondence of a communication terminal, a spreading code, and bit allocation in the conventional multi-level modulation communication system The figure which shows the error rate characteristic in the conventional multi-level modulation system The figure which shows the correspondence of a communication terminal, a spreading code, and bit allocation in the multi-value modulation communication system which concerns on Embodiment 1 of this invention. 1 is a block diagram showing a configuration of a multi-level modulation communication system according to Embodiment 1 of the present invention. The figure which showed typically operation | movement of the radio | wireless transmitter used with the multi-value modulation communication system which concerns on Embodiment 1 of this invention. The figure which shows the signal point arrangement | positioning in the radio | wireless transmission apparatus used with the multi-value modulation communication system which concerns on Embodiment 1 of this invention. The figure which showed typically operation | movement of the radio | wireless receiving apparatus used with the multi-value modulation communication system which concerns on Embodiment 1 of this invention. The figure which shows the error rate characteristic for each communication terminal in the multi-value modulation communication system which concerns on Embodiment 1 of this invention. FIG. 3 is a block diagram showing a configuration of a multi-level modulation communication system according to Embodiment 2 of the present invention. The figure which showed typically operation | movement of the multi-value modulation communication system which concerns on Embodiment 2 of this invention. The figure which shows typically the quality of each data in the multi-value modulation communication system which concerns on Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 300 Wireless transmission apparatus 302 P / S conversion part 303 Assignment control part 304 Multi-value modulation part 305 S / P conversion part 306-1 to 306-4 Multiplier 308 Multiplier
309 Multiplexer 400 Wireless receiver 403 Distributor 404-1 to 404-4 Multiplier 405 P / S converter 406 Multi-level demodulator 407 S / P converter 408 Multiplier 410 Conversion controller 411 Selector 600 Wireless transmitter 601 Error Detection Code Addition Unit 603 Buffer 604 Switch 605 Multilevel Modulation Unit 606 Bit String Conversion Unit 607 Multiplier 608 Multiplexer 609 Control Unit 611 Multiplier 615 Multiplier 700 Wireless Receiver 703 Multiplier 704 Multilevel Demodulator 705 Switch 706 Synthesis Unit 707 bit string inverse conversion unit 708 storage unit 710 error detection unit 715 multiplier

Claims (2)

Modulation means for modulating data into symbols for each of a plurality of bits;
Transmitting means for transmitting the symbol during the first transmission;
Changing means for changing the positions of the plurality of bits assigned to the symbols before the modulation at the time of retransmission,
The modulation means modulates the plurality of bits whose bit positions are changed into symbols at the time of retransmission,
The transmission means transmits the symbol whose bit position is changed at the time of retransmission.
A data transmitting apparatus characterized by that. Modulating data into symbols for each of a plurality of bits;
Transmitting the symbol during a first transmission;
Changing the position of the plurality of bits assigned to the symbol before modulation during retransmission; and
Modulating the plurality of bits whose bit positions have been changed into symbols at the time of retransmission; and
Transmitting the symbol with the bit position changed at the time of retransmission.
A data transmission method characterized by the above.

Images