JP2004215295A - Data transmission apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve throughput in data communications using multi-value modulation. <P>SOLUTION: In the case of resending, a switch 604 is changed over, and transmission data stored in a buffer 603 in the first transmission are inputted to a multi-value modulation part 605 after converting a bit stream in a bit stream conversion part 606. That is, the order of arranging the bit streams within one symbol is inverted from that in the first transmission. The bit stream converted symbol is multi-value-modulated in the multi-value modulation part 605 by using 16QAM. The modulated symbol is multiplexed with a transmission time notice signal indicating second transmission in a multiplexer 608, and then transmitted via an antenna 613. Thus, in the case of resending, the symbol is transmitted while exchanging bit positions to which each data is allocated in the first transmission within one symbol. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

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

  2. Description of the Related Art 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 equal to or less than a predetermined value on a receiver side). Among the modulation systems, there is a multi-level modulation system in which a plurality of bits are transmitted in one symbol which is a modulation unit. In the multi-level modulation scheme, since information of a plurality of bits is transmitted in one symbol which is a modulation unit, throughput can be increased.

  In the multi-level modulation method, QPSK (Quarterary Phase Shift Keying) transmitting two bits of information in one symbol, 16QAM (Quadrature Amplitude Modulation) transmitting four bits of information in one symbol, and six bits of information in one symbol Is transmitted, and under the same propagation environment, the throughput can be improved as the amount of information transmitted in one symbol increases.

  A technique has also been proposed in which the transmitter side adaptively changes the modulation scheme of data to be transmitted according to the propagation environment to increase the throughput of the entire system. Such a technique is called adaptive modulation.

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

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

  The data transmitting apparatus of the present invention changes the bit position to which each data is allocated in a symbol each time data retransmission occurs, allocates each data to each bit, performs multi-level modulation on the symbol, A configuration in which value-modulated symbols are transmitted by radio is adopted.

  According to this configuration, since the bit position to which each data in the symbol is allocated is changed and dispersed for each retransmission, each data in the symbol is less likely to be error-prone, and the quality of all data can reliably satisfy the desired quality. Become like As a result, the number of retransmissions can be reduced, and the throughput can be improved.

  As described above, according to the present invention, it is possible to improve throughput in data communication using multi-level modulation.

  As described above, in the multi-level modulation scheme, information of a plurality of bits is transmitted by one symbol. For example, in the case of 16QAM, 4-bit information is transmitted in one symbol. In 16QAM, 4-bit information can be transmitted with one symbol by arranging 16 signal points at different positions on the IQ plane. A signal space diagram is used to represent this signal point arrangement. Hereinafter, a signal space diagram of 16QAM will be described using 16QAM as an example of the multi-level modulation scheme. FIG. 1 is a signal section diagram showing a 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 each of the I axis and the Q axis. As a result, multi-leveling can be performed and 4-bit information can be transmitted with one symbol. When multi-leveling is performed in this manner, signal points are arranged so that only one bit differs from an adjacent symbol as shown in FIG. 1 in order to improve the 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 where the bit is allocated. That is, in the case of 16QAM, the third bit and the fourth bit have a higher probability of being erroneously determined than the first bit and the second bit. Hereinafter, this point will be described. Note that, as shown in FIG. 1, a case will be described in which the determination thresholds are set to +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 points 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 bits of each symbol are determined as follows.

That is, in FIG. 1, focusing on the most significant bit (the leftmost bit) b ₁ , the plus region (region on the right side across the Q axis) 101 on the I axis is 0, and the minus region (Q The area 102 on the left side of the axis) is 1. Therefore, on the receiver side, as shown in FIG. 2 (a), a b ₁ is determined as 0 if the received symbol is located in the positive area 101 of the I-axis, the received symbols to the negative area 102 of the I axis when located determines b ₁ 1 and. That is, the reception symbol is only determined whether the one of the regions of the two areas, it is possible to b ₁ to determine the 0 or 1. In other words, the b ₁ can be determined only by 0 or 1 negative decision value on the I axis.

In FIG. 1, focusing on the second most significant bit (the second bit from the left) b ₂ , the plus area (the area above the I axis) 103 on the Q axis is 0, and A minus area (area below the I axis) 104 is 1. Therefore, on the receiver side, as shown in FIG. 2 (b), the b ₂ determined to 0 if the received symbol is located in the positive area 103 of the Q axis, the received symbol is the negative region 104 of the Q-axis when located determines b ₂ 1 a. That is, the reception symbol is only determined whether the one of the regions of the two areas, it is possible to b ₂ to determine whether 0 or 1. In other words, the b ₂ can determine whether 0 or 1 only in the positive and negative decision values on the Q axis.

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

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

As described above, it is sufficient to determine in which of the two regions the received symbol is located for b ₁ and b ₂ , whereas in which of the four regions the received symbol is located for b ₃ and b ₄ Needs to be determined. Further, each of the determination regions 101 to 104 is wider than each of the determination regions 105 to 112. Therefore, the probability that b ₁ and b ₂ are incorrectly determined is lower than the probability that b ₃ and b ₄ are incorrectly determined.

  Note that this is not limited to 16QAM. That is, the same can be said for a multi-level modulation system in which a plurality of bits are included in one symbol and the error rates of the respective bits are different from each other. , The error rate is the same for a plurality of bits).

  The present inventors have focused on the fact that the error resistance of each bit in a multi-level modulated symbol differs depending on the bit position, and each of the data (4 bits of data in 16QAM) included in one symbol is considered. The present inventors have found that the data error rate (that is, the data quality) can be adjusted by assigning each bit based on the difficulty of each bit error, and the present invention has been made.

  That is, the gist of the present invention is that, when data is modulated by a multi-level modulation scheme, data that is less likely to be error-prone (that is, data that has higher quality) is assigned to a higher-order bit in a symbol that is a 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, data transmitted to each communication terminal is spread as shown in FIG. The code is spread and transmitted. Hereinafter, a case will be described in which data is simultaneously transmitted to four communication terminals # 1 to # 4 using 16QAM as a multi-level modulation scheme. FIG. 3 is a diagram showing a correspondence relationship among communication terminals, spreading codes, and bit assignments in a conventional multilevel modulation communication system. Incidentally, b ₁ is most significant bit of the second most significant bit, b ₂ is, b ₃ bits of the upper third, b ₄ indicates the least significant bit.

  Conventionally, as shown in FIG. 3, data transmitted to communication terminal # 1 is spreading code # 1, data transmitted to communication terminal # 2 is spreading code # 2, and data transmitted to communication terminal # 3 is data Data transmitted to the spreading code # 3 and the communication terminal # 4 is spread by the spreading code # 4 and transmitted. That is, conventionally, the communication terminal corresponds to the spreading code.

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 has 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 multi-level modulated for each of the communication terminals. That is, the data of 4 bits to be transmitted in one symbol to each communication terminal is transmitted likewise assigned to the uppermost bit b ₁ ~ least significant bit b ₄ to the each communication terminal. Therefore, when the average error rates of b _{1 to} b ₄ are compared between the communication terminals, if the conditions such as the propagation environment are the same, the average error rates are equal. That is, the error rate characteristics of the average error rate in all the 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 multi-level modulation system. Incidentally, 201 the error rate characteristic of b ₁ and b ₂ in this figure, 202 is an error rate characteristic of b ₃ and b _4, 203 denotes an average error rate characteristics b ₁ ~b _4.

Here, for example, in a communication system in which adaptive modulation is performed, a modulation scheme according 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 reception SIR of data is deteriorated 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 is lower than the desired quality in all communication terminals. You may not be able to meet it. In a communication system in which an automatic retransmission request (ARQ) is performed, in this case, retransmission of data occurs to all communication terminals, and the throughput of the entire system is greatly reduced.

  Therefore, in the present embodiment, data transmitted to a high-priority communication terminal is allocated to higher-order bits in a symbol and transmitted, and data for a high-priority communication terminal surely satisfies desired quality. To Thereby, the throughput of the entire system is improved.

FIG. 5 is a diagram showing a correspondence relationship among communication terminals, spreading codes, and bit assignments in the multi-level modulation communication system according to Embodiment 1 of the present invention. Conventionally, a communication terminal and a spreading code correspond to each other, but in the present embodiment, as shown in FIG. 5, a communication terminal and a bit allocation position of data correspond to each other. That is, the highest-priority communication terminal (here assumed to be communication terminal # 1) data to be transmitted to is assigned to b _1, a high communication terminal priority to the second (here, communication terminal # 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 communication terminal # 1 and the data transmitted to communication terminal # 2 have lower quality than the case of performing the bit allocation shown in FIG. The data can be improved and always satisfy the desired quality.

  As a result, for the data transmitted to communication terminal # 1 and the data transmitted to communication terminal # 2, the desired quality can be ensured even if the reception SIR of data deteriorates due to temporary deterioration of the propagation environment due to fading or the like. Can be satisfied. That is, the data for the communication terminal having the higher priority can surely satisfy the desired quality. Therefore, the higher the priority of the communication terminal, the sooner the data reception can be completed. Also, the number of data retransmissions can be reduced for the entire system, and the throughput of the entire system can be improved.

  Hereinafter, a radio transmitting apparatus and a radio receiving apparatus used in the multi-level 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. The following description is based on the assumption that the wireless transmission device is mounted on a base station and used, and the wireless reception device is mounted on a communication terminal. Also, a case where data is transmitted to four communication terminals simultaneously will be described.

  In radio transmitting apparatus 300, coding sections 301-1 to 301-4 perform coding processing on data sequences # 1 to # 4, respectively, and process the coded data in P / S (parallel / serial). Output to conversion section 302. Note that data sequences # 1 to # 4 are data sequences 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 to multi-level modulation section 304. At this time, P / S conversion section 302 performs parallel-to-serial conversion in accordance with the control from allocation control section 303, which will be described later, so that a data sequence for a communication terminal with a higher priority is assigned to a higher bit in one symbol. . A detailed description of the bit assignment will be described later.

  Multi-level modulation section 304 performs multi-level modulation on the parallel-serial converted data. Here, since it is necessary to transmit data to four communication terminals at the same time, 16QAM that can transmit 4-bit data with one symbol is used as the multi-level modulation scheme. Therefore, multi-level modulation section 304 arranges the parallel-serial converted data at any of the signal points shown in FIG. The symbols after multi-level modulation are output to S / P (serial / parallel) conversion section 305.

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

  Allocation control section 303 instructs P / S conversion section 302 on the bits to which data sequences # 1 to # 4 are allocated based on the priority of the communication terminal. That is, allocation control section 303 controls P / S conversion section 302 such that data for a communication terminal with a higher priority is allocated to a higher-order bit within one symbol. A detailed description of the bit assignment will be described later.

  Further, allocation control section 303 outputs an allocation notification signal indicating which data sequence has been allocated to which bit to modulation section 307. The allocation notification signal is modulated by modulator 307, multiplied by spreading code #A by multiplier 308, and then input to multiplexer 309.

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

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

  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 the spreading codes # 1 to # 4 is extracted from the multiplexed signal. The symbols after the despreading process are input to P / S conversion section 405.

  P / S conversion section 405 converts the symbols input in parallel to serial and outputs to multi-level demodulation section 406. Multi-level demodulation section 406 performs demodulation processing corresponding to the multi-level modulation performed in radio transmitting apparatus 300 on the symbols subjected to parallel-serial conversion, and outputs the result to S / P conversion section 407. That is, here, the multi-level demodulation unit 406 performs multi-level demodulation based on 16QAM.

  The S / P conversion section 407 converts the data series input in series from the multi-level demodulation section 406 into parallel and outputs the data series to the selection section 411. At this time, the S / P conversion unit 407 performs a serial conversion reverse to the parallel-serial conversion performed by the P / S conversion unit 302 of the wireless transmission device 300 under the control of a conversion control unit 410 described later.

  Multiplier 408 multiplies the multiplexed signal by spreading code #A. As a result, the allocation notification signal spread with the spreading code #A is extracted from the multiplexed signal. After the assignment notification signal is demodulated by demodulation section 409, it is input to conversion control section 410.

  Conversion control section 410 controls S / P conversion section 407 based on the assignment notification signal so that serial conversion opposite to parallel / serial conversion performed by P / S conversion section 302 of wireless transmission apparatus 300 is performed. . Further, conversion control section 410 selects selection section 411 from which signal line of S / P conversion section 407 the data sequence addressed to its own terminal (here, communication terminal # 1) is output based on the assignment notification signal. To instruct.

  Selection section 411 selects a data sequence addressed to the terminal itself and outputs it to decoding section 412 according to an instruction from conversion control section 410. Decoding section 412 decodes the data sequence selected by selection section 411. As a result, a data sequence addressed to the own terminal (that is, data sequence # 1) is obtained.

Next, the operation in which data sequences # 1 to # 4 are allocated to each bit in a symbol and transmitted will be specifically described. FIG. 7 is a diagram schematically showing an operation of the radio transmitting 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 m-th data transmitted to 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 radio transmitting apparatus 300.

  First, the P / S conversion section 302 performs parallel / serial conversion (P / S conversion) under the control of the allocation control section 303 such that a data sequence for a communication terminal with a higher priority is assigned to a higher bit in one symbol. )I do. Here, it is assumed that the priority is 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 of determining the priority order. That is, a communication terminal having a better propagation path environment has a higher priority. As a result, the quality of the data sequence having good quality is further improved due to the good propagation path environment, so that the data transmission to the communication terminal having the good propagation path environment can be more quickly and reliably completed.

  As another method, a communication terminal having a larger amount of untransmitted data has a higher priority. As a result, the data sequence for a communication terminal having a large amount of untransmitted data has higher quality, and the throughput can be increased for a communication terminal having a large amount of untransmitted data. As the throughput increases, the amount of untransmitted data decreases more rapidly, so the priority order 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 equal.

  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 sequence for a communication terminal used by a user who pays a higher fee increases as the quality of the data sequence increases. Therefore, it is possible to provide a communication service with a difference in user convenience according to the fee. .

  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. As a result, it is possible to compensate for the quality deterioration due to the poor propagation path environment and to improve the quality of the data sequence for the communication terminal having the poor propagation path environment to the desired quality. Since the quality of the data sequence for a communication terminal with a good propagation path environment satisfies the desired quality in the first place, the adoption of this method can increase the throughput of the entire system.

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

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

  That is, the data for the communication terminal # 1 having the highest priority is assigned to the most significant bit, the data for the communication terminal # 2 having the second highest priority is assigned to the second highest bit, and the third highest priority is assigned to the data. , The data for communication terminal # 3 with the highest priority is assigned to the third most significant bit, and the data for communication terminal # 4 with the lowest priority is assigned to the least significant bit. Therefore, the data sequence transmitted to a communication terminal with 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 communication terminal # 3 is the same as the quality of the data sequence for communication terminal # 2, and the quality of the data sequence for communication terminal # 4 is the same.

Next, the data subjected to the parallel-serial conversion is subjected to multi-level modulation by the multi-level modulation section 304 using 16QAM. Since the symbols S ₁ are 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 symbols are subjected to serial / parallel conversion (S / P conversion) in S / P conversion section 305. Then, symbols S _{1 to} S ₄ are spread by multipliers 306-1 to 306-4, respectively.

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, the multiplexed signal is transmitted to radio receiving apparatus 400.

  Next, the operation of radio receiving apparatus 400 will be described in detail. FIG. 9 is a diagram schematically showing an operation of the radio receiving 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 despread 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 converter 405 and multi-level demodulation by the multi-level demodulator 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 sequence in which data addressed to communication terminal # 1 is assigned to the most significant bit of each symbol is output.

Next, in S / P conversion section 407, the data series output in series from multi-level demodulation section 406 is converted in parallel under the control of conversion control section 410. Conversion control section 410 can know from the assignment notification signal which bit data to each terminal is assigned to. Here, conversion control section 410 assigns data d ₁₁ , d ₁₂ , d ₁₃ , and d ₁₄ addressed to communication terminal # 1 to the most significant bit, and data d ₂₁ , d ₂₂ , and d ₂₃ addressed to communication terminal # 2. , D ₂₄ are assigned to the second most significant bit, and data d ₃₁ , d ₃₂ , d ₃₃ , and 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, conversion control section 410 performs S / P conversion section 407 so that the data series serially output from multi-level demodulation section 406 is output from S / P conversion section 407 for each of data series # 1 to # 4. To control the serial-parallel conversion (S / P conversion). The serial / parallel conversion is performed according to this control, and the data sequences # 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, selection section 411 selects a data sequence addressed to the terminal itself. Selection section 411 is instructed by conversion control section 410 from which signal line of S / P conversion section 407 the data sequence addressed to the terminal is output. According to this instruction, the selection unit 411 selects a data sequence addressed to the own terminal. Here, since the own terminal is the communication terminal # 1, the selecting unit 411 selects a data sequence output from the uppermost signal line among the signal lines from the S / P converting unit 407. Thereby, data sequence # 1 (d ₁₁ , d ₁₂ , d ₁₃ , d ₁₄ ) destined for communication terminal # 1 is selected and output to decoding section 412.

  This data sequence # 1 is all data that is allocated to the most significant bit of the symbol and transmitted. Therefore, the quality of the data sequence # 1 can reliably satisfy the desired quality even when the reception SIR is deteriorated due to the 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 with a higher priority is assigned to the higher-order bit in a multi-level modulated symbol and transmitted, so that data quality for a communication terminal with a higher priority is lower. It is much higher than the desired quality. For this reason, the quality of data for a communication terminal having a high priority can reliably satisfy desired quality. As a result, the possibility of retransmission occurring for a communication terminal having a high priority is reduced. Further, even when the propagation environment is deteriorated, it is possible to prevent data quality from being unable to satisfy desired quality in all communication terminals. Therefore, the number of data retransmissions can be reduced in the entire system, and the throughput of the entire system can be improved.

  Further, the possibility of retransmission occurring to a communication terminal with a higher priority is reduced, so that a communication terminal with a higher priority can complete data transmission more quickly. By completing data transmission to a communication terminal with a higher priority, it becomes possible to allocate high-quality bits assigned to the communication terminal to data to be transmitted to a communication terminal with a lower priority. As a result, the number of retransmissions for data for a communication terminal with a low priority is reduced. Therefore, the throughput of the entire system can be further increased.

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

  In addition, when the multi-level modulation scheme applied to each communication terminal is the same (in this embodiment, 16QAM is applied to all communication terminals), conventionally, the data error rate characteristics of all communication terminals Will be the same. However, in the present embodiment, bits are allocated according to the priority. Therefore, even when the multi-level modulation schemes applied to the respective communication terminals are all the same, as shown in FIG. Error rate characteristics can be set for each terminal. That is, as in the present 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 communication terminal # 1 and the error rate characteristic 501 of communication terminal # 2 can be made better than the error rate characteristic of communication terminal # 3 and the error rate characteristic 502 of communication terminal # 4. . That is, according to the present embodiment, a plurality of error rate characteristics can be set by one multi-level modulation scheme. Thus, 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 a plurality of qualities with one multi-level modulation scheme, when selecting a modulation scheme in a communication system in which adaptive modulation is performed, it is also necessary to select bits to which transmission data is to be allocated. This makes it possible to perform finer quality control than the conventional adaptive modulation.

  When the radio transmitting apparatus 300 is mounted and used in a base station used in a mobile communication system, and the radio receiving apparatus 400 is mounted and used in a communication terminal used in a mobile communication system, The communication terminals in the wireless zone of the base station change every moment. That is, in the present embodiment, the communication terminals that are the communication terminals # 1 to # 4 change every moment. Therefore, when the present embodiment is applied to a mobile communication system, it is necessary to transmit an assignment notification signal to each communication terminal as described above.

  However, in a wireless communication system in which the communication terminals # 1 to # 4 do not change (for example, a wireless LAN system), there is no need to transmit an assignment notification signal because bit assignment is known in advance in each communication terminal. . Therefore, in such a wireless communication system, a device configuration for generating, transmitting, and receiving an assignment notification signal from the wireless transmitting device 300 and the wireless receiving device 400 can be omitted. Therefore, the device configuration is simplified.

  Also, for example, in the case of 16 QAM, data for a maximum of four communication terminals can be transmitted in one symbol, and in the case of 64 QAM, data for a maximum of six communication terminals can be transmitted in one symbol. Therefore, in the present embodiment, it is assumed that the multi-level 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 retransmission request (ARQ; Automatic Repeat reQuest) is performed, a symbol having the same content is retransmitted at the time of retransmission. That is, when performing multi-level modulation, the position of the bit to which each data is assigned in one symbol is the same at the time of initial transmission and at the time of retransmission.

Here, as described above, in the multi-level modulation scheme, the lower bits in one symbol have a higher probability of being erroneously determined. For example, in 16QAM, as described above, third bit b ₃ and fourth bit b _4, the probability is determined by mistake compared with the first bit b ₁ and second bit b ₂ becomes high. Therefore, lower bits third bit b ₃ and fourth bit b ₄ is is likely to be an error at the time of retransmission. Therefore, the average error rate of b ₁ ~b ₄ is also in the time of retransmission becomes unable to satisfy the required quality, it may further retransmission may occur.

  Therefore, in the present embodiment, at the time of retransmission, the position of the bit to which each data is assigned within one symbol is replaced with that at the time of the first transmission. That is, at the time of retransmission, data assigned to higher bits at the time of initial transmission is assigned to lower bits, and data assigned to lower bits at the time of initial transmission is assigned to higher bits and transmitted. As a result, at the time of retransmission, data assigned to lower bits at the time of initial transmission has a lower probability of being erroneously determined.

  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 almost the same and is 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 the throughput can be improved.

  Hereinafter, a radio transmitting apparatus and a radio receiving apparatus used in the multi-level 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 transmitting apparatus 600, error detection code adding section 601 adds an error detection code such as a CRC (Cyclic Redundancy Check) bit to transmission data for each predetermined unit and outputs the result to error correction coding section 602. .

  The error correction coding unit 602 performs error correction coding on transmission data by, for example, convolution coding. The error-correction-coded 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 controlled by the control unit 609 to connect the buffer 603 and the multi-level modulation unit 605 during odd-numbered transmissions including the first transmission, and to connect the buffer 603 and the bit-string conversion unit 606 during even-numbered transmissions. I do.

  The bit sequence 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 assigned within one symbol each time data retransmission occurs. As a result, data assigned to upper bits during odd-numbered transmission is assigned to lower bits during even-numbered transmission, and data assigned to lower bits during odd-numbered transmission is assigned to even-numbered transmission. It will be assigned to the upper bits.

  The multi-level modulation section 605 performs multi-level modulation on the data directly input from the buffer 603 or the data in which the bit string is converted by the bit string conversion section 606. Here, 16QAM that can transmit 4-bit data with one symbol is used as the multi-level modulation scheme. Therefore, multi-level modulation section 605 arranges the input data at any of the signal points shown in FIG. The symbol after multi-level modulation is output to multiplier 607. Multiplier 607 multiplies the symbol after multi-level modulation by spreading code # 1 corresponding to communication partner # 1. The symbols after the spreading processing are output to multiplexer 608.

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

  Further, control section 609 counts the number of times the retransmission request signal has been received, and connects buffer 603 and multi-level modulation section 605 during odd-numbered transmissions including the first transmission, and buffers 603 and bit string conversion during even-numbered transmissions. The switch 604 is controlled so as to be connected to the unit 606.

  Further, control section 609 generates a transmission number notification signal indicating the number of times of transmission of the same data, and outputs the signal to modulation section 610. This transmission number notification signal is modulated by modulator 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. After performing predetermined radio processing such as up-conversion on the multiplexed signal, radio transmitting section 612 transmits the multiplexed signal to radio receiving apparatus 700 via antenna 613.

  Radio receiving 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 the retransmission request signal output from radio reception section 614 by spreading code #B. The retransmission request signal after the despreading process is demodulated by demodulation section 616 and input to control section 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 outputs the multiplexed signal to multipliers 703 and 711. I do.

  Multiplier 703 multiplies the multiplexed signal by spreading code # 1. As a result, the symbols spread with the spreading code # 1 are extracted from the multiplexed signal. The symbols after the despreading process are input to multi-level demodulation section 704.

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

  The switch 705 is controlled by the control unit 713 to connect the multi-level demodulation unit 704 and the combining unit 706 during odd-numbered transmissions including the first transmission, and to perform multi-level demodulation with the multi-level demodulation unit 704 during even-numbered transmissions. Unit 707 is connected.

  The bit sequence inversion unit 707 performs the reverse of the bit sequence rearrangement performed by the bit sequence conversion unit 606 of the wireless transmission device 600. That is, the bit string inversion section 707 returns the arrangement order of the bit strings within one symbol to the state before the bit string was converted by the bit string changing section 606. The rearranged demodulation result is 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 combining unit 706 adds the soft decision value for each data. Thus, each time retransmission occurs, a high-quality demodulation result and a low-quality demodulation result are alternately combined for each data. Therefore, the quality of the demodulation result of each data is increased to the same degree within one symbol, and the quality of all data can surely satisfy the desired quality. The combined demodulation result is input to error correction decoding section 709 and stored in storage section 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 error-corrected decoded data is input to the error detection unit 710. The error detection unit 710 performs error detection using a CRC or the like. The data for which no error is detected by the error detection unit 710 is the received data. When an error is detected by error detecting section 710, error detecting section 710 generates a retransmission request signal and outputs the signal to modulation section 714.

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

  Multiplier 711 multiplies the multiplexed signal by spreading code #A. As a result, the transmission number notification signal that has been spread with the spreading code #A is extracted from the multiplexed signal. The transmission number notification signal is input to the control unit 713 after being demodulated by the demodulation unit 712.

  The control unit 713 connects the multi-level demodulation unit 704 and the combining unit 706 during odd-numbered transmissions, including the first transmission, according to the number of transmissions of the same data indicated by the transmission-number notification signal, and performs multi-level transmission during even-numbered transmission. The switch 705 is switched and controlled so that the value demodulation unit 704 and the bit string inverse conversion unit 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 illustrating 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 ′ represent a symbol transmitted at the time of the first transmission and a symbol transmitted at the time of retransmission (at the time of the second transmission), respectively.

First, at the time of the first transmission, the switch 604 of the wireless transmission device 600 connects the buffer 603 and the multi-level modulation unit 605. Therefore, the transmission data is input to the multi-level modulation section 605 without converting the 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. Symbols including d _{1 to} d ₄ are multi-level modulated by multi-level modulation section 605 using 16QAM. Since this symbol S ₁ is 1101, is modulated to be disposed in the signal point S ₁ indicated by a black circle in the upper part of the IQ plane of Figure 12. The modulated symbol is multiplexed with a transmission count notification signal indicating the first transmission in multiplexer 608, and then transmitted to radio receiving apparatus 700.

At the time of the first transmission, in wireless receiving apparatus 700, switch 705 connects multi-level demodulation section 704 and synthesis section 706. Therefore, the demodulation result of each data output from multi-level demodulation section 704 is input to synthesis section 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. This demodulation result is stored in the storage unit 708.

At the time of retransmission (at the time of the second transmission), in the wireless transmission device 600, the switch 604 connects the buffer 603 and the bit string conversion unit 606. Therefore, the transmission data stored in the buffer 603 at the time of the first transmission is input to the multi-level modulation section 605 after the bit string conversion section 606 converts the bit string. That is, the order of arrangement of the bit strings in one symbol is reversed from that in 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. Symbols including d _{1 to} d ₄ are multi-level modulated by multi-level modulation section 605 using 16QAM. Since the bit string converted symbol S ₁ ′ 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 lower IQ plane in FIG. The modulated symbol is multiplexed with a transmission count notification signal indicating the second transmission in multiplexer 608, and then transmitted to radio receiving apparatus 700.

At the time of retransmission (at the time of second transmission), switch 705 in radio receiving apparatus 700 connects multilevel demodulation section 704 and bit string inverse conversion section 707. Therefore, the demodulation result of each data output from the multi-level demodulation unit 704 is input to the synthesizing unit 706 after rearranging the bit strings. That is, the reverse of the bit sequence performed by the bit sequence conversion unit 606 of the wireless transmission device 600 is performed, and the order of the bit sequence within one symbol is changed before the bit sequence is converted by the wireless transmission device 600. It is returned to the state. By this rearrangement, d ₁ is returned to the first bit, d ₂ is returned to the second bit, d ₃ is returned to the third bit, and d ₄ is returned 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 Quality. The demodulation result is combined with the demodulation result stored in the storage unit 708 for each data in the combining unit 706.

  As a result of combining the demodulation result at the time of the first transmission and the demodulation result at the time of retransmission (at the time of the second transmission) in this manner, as shown in FIG. It becomes high with. 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 wireless transmission apparatus replaces the position of the bit to which each data is assigned within one symbol with the time of the first transmission, and transmits the symbol. 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. Further, in the present embodiment, the data assigned to the higher-order bits during the odd-numbered transmission is assigned to the lower-order bits during the even-numbered transmission, and the data assigned to the lower-order bits during the odd-numbered transmission is smaller. At the time of even-numbered transmission, it is assigned to the upper bits. Therefore, each data in one symbol is almost equal to each other and hard to error, and the quality of all data can surely satisfy desired quality. As a result, the number of retransmissions can be reduced, and the throughput can be improved.

  In the present embodiment, in the radio receiving apparatus, the error correction decoding is performed using the demodulation result after the combination, but the demodulation result after the synthesis is hard-decided as it is without performing the error correction decoding. Is also good. In this case, it becomes unnecessary for the wireless transmission device to perform error correction coding on the transmission data.

  Further, in the present embodiment, the combining unit of the wireless receiving apparatus is configured to combine all the demodulation results within one symbol, but may be configured to combine only the demodulation results of data allocated to arbitrary bits. For example, a configuration may be adopted in which only high-quality demodulation results are combined.

  Further, in the present embodiment, the case where 16QAM is used as the multi-level modulation scheme has been described, so that the quality that can be set in a symbol is two levels of high and low. For this reason, each time retransmission occurs, retransmission data is alternately assigned to high-quality bits and low-quality bits in a symbol. However, for example, when 64QAM is used as a multi-level modulation scheme, the quality that can be set in a symbol is three levels of high, medium, and low. Therefore, when 64QAM is used, the retransmission data may be 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.

  Further, in the present embodiment, the number of transmissions is notified from the wireless transmission device to the wireless reception device. However, the number of receptions may be counted by the wireless reception device without notifying the number of transmissions. .

  Further, in the present embodiment, there is no particular limitation on the retransmission method. Therefore, a SAW (Stop-And-Wait) method, a GBN (Go-Back-N) method, an SR (Selective-Repeat) method, a hybrid ARQ method, or the like can be used as the retransmission method.

  Also, in Embodiments 1 and 2, it is desirable that the multi-level modulation scheme be changed with time in the wireless transmission apparatus according to the propagation path environment. That is, it is desirable to use Embodiments 1 and 2 in combination with adaptive modulation.

  Further, 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-valued number has 16 values (that is, the case where one symbol is 4 bits) has been described as an example, but the first and second embodiments have A multi-level modulation scheme in which a plurality of bits are included in one symbol and the error rates of the bits are different from each other can be similarly implemented.

  Further, the multi-level modulation communication system 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.

  ADVANTAGE OF THE INVENTION Since the data transmission apparatus which concerns on this invention changes and distributes the bit position which allocates each data in a symbol for every retransmission, it has the effect of reducing the number of retransmissions and improving throughput in data communication using multi-level modulation. However, the present invention can be applied to applications such as base stations and communication terminals used in digital wireless communication systems.

Signal section diagram showing signal point arrangement of 16QAM Diagram for explaining a determination method in 16QAM FIG. 4 is a diagram showing a correspondence relationship among communication terminals, spreading codes, and bit allocation in a conventional multi-level modulation communication system. Diagram showing error rate characteristics in conventional multi-level modulation system FIG. 6 is a diagram showing a correspondence relationship among communication terminals, spreading codes, and bit assignments in the multi-level modulation communication system according to Embodiment 1 of the present invention. FIG. 1 is a block diagram showing a configuration of a multilevel modulation communication system according to Embodiment 1 of the present invention. FIG. 4 is a diagram schematically showing an operation of a radio transmitting apparatus used in the multi-level modulation communication system according to Embodiment 1 of the present invention. FIG. 4 is a diagram showing a signal point arrangement in a radio transmitting apparatus used in the multi-level modulation communication system according to Embodiment 1 of the present invention. FIG. 3 is a diagram schematically showing an operation of a radio receiving apparatus used in the multilevel modulation communication system according to Embodiment 1 of the present invention. FIG. 4 is a diagram illustrating error rate characteristics of each communication terminal in the multilevel modulation communication system according to Embodiment 1 of the present invention. FIG. 4 is a block diagram showing a configuration of a multi-level modulation communication system according to Embodiment 2 of the present invention. FIG. 5 is a diagram schematically showing an operation of the multi-level modulation communication system according to Embodiment 2 of the present invention. FIG. 9 is a diagram schematically showing the quality of each data in the multi-level modulation communication system according to Embodiment 2 of the present invention.

Explanation of reference numerals

Reference Signs List 300 wireless transmission apparatus 302 P / S conversion section 303 assignment control section 304 multi-level modulation section 305 S / P conversion section 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 Multilevel demodulator 407 S / P converter 408 Multiplier 410 Conversion controller 411 Selector 600 Radio transmitter 601 Error detection code adding section 603 Buffer 604 Switch 605 Multi-level modulation section 606 Bit string conversion section 607 Multiplier 608 Multiplexer 609 Control section 611 Multiplier 615 Multiplier 700 Wireless receiver 703 Multiplier 704 Multi-level demodulation section 705 Switch 706 Synthesis Unit 707 bit string inversion unit 708 storage unit 710 error detection unit 715 multiplier

Claims (1)

  Each time data retransmission occurs, the bit position for allocating each data in a symbol is changed, and each data is allocated to each bit, multi-level modulation is performed on the symbol, and a multi-level modulated symbol is wirelessly transmitted. A data transmission device, comprising:

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