JP4539969B2 - Multi-carrier spread spectrum communication apparatus and multi-carrier spread spectrum communication method - Google Patents

Description

  The present invention relates to a multicarrier spread spectrum communication apparatus and a multicarrier spread spectrum communication method.

  In wireless communication, reflected waves from various obstacles or the like may overlap to form a multiplex transmission path (multipath). Due to the difference in propagation delay of each transmission path, frequency selective fading in which the frequency characteristics in the transmission band are distorted and intersymbol interference in which adjacent signals (symbols) on the time axis interfere with each other cause deterioration in communication quality. Invite. As a countermeasure against such deterioration, a multi-carrier spread spectrum communication system has attracted attention.

  In this multi-carrier spread spectrum communication system, information is divided into a plurality of low-rate carriers (subcarriers) and transmitted. That is, in multicarrier spread spectrum communication, by increasing the length of one symbol, the amount of delay is small compared to the symbol length, so that the influence of the above-described multipath interference can be reduced. In particular, the one selected so that the carriers are orthogonal to each other is called an orthogonal multicarrier modulation scheme, and there is orthogonal frequency division multiplexing (OFDM). Further, a radio access scheme such as “MC-CDMA (Multi-Carrier-CDMA)” has been proposed as a radio transmission scheme combining multicarrier spread spectrum communication and “CDMA (Code Division Multiple Access)”. This MC-CDMA is a system in which information symbols are spread using a spreading code, and the spread information symbols are mapped onto a plurality of subcarriers or OFDM symbols and transmitted in parallel (for example, Patent Document 1). reference.).

Here, the case where a signal is transmitted using the transmission apparatus 20 of the multicarrier spread spectrum communication system shown in FIG. 8 will be described. First, the transmission device 20 generates information symbols for the input transmission data using the information symbol generation unit 21. Then, the transmission device 20 executes an error correction encoding process for adding an error correction code for correcting an error in the data in the error correction encoding unit 22. Next, the data modulation unit 23 performs data modulation processing on the generated information symbol. The data modulation unit 23 has a QAM (Quadrature
Amplitude Modulation), QPSK (Quadrature Phase Shift Keying) modulation, etc. are executed.

  Next, the transmitter 20 performs two-dimensional spreading in the code spreading unit 24. Specifically, the code spreading unit 24 performs serial / parallel conversion on the information symbols on which the data modulation processing has been performed, and divides the information symbols into a plurality of information symbols. Then, the code spreading unit 24 duplicates a plurality of information symbols that have been serial-parallel converted and divided into a number equal to the spreading code period of the spreading code corresponding to the data channel that transmits the information symbols. The code spreading unit 24 generates a spreading code corresponding to each data channel assigned to each data channel. Then, the transmission device 20 multiplies the duplicated information symbol by a spreading code corresponding to the data channel for transmitting the information symbol to obtain an information signal. Then, an information signal is assigned to a plurality of subcarriers. Further, the transmitter 20 inserts a pilot signal into the information signal, combines the information signal of each data channel and the pilot signal, and performs code multiplexing.

Then, the transmission device 20 spreads the code-multiplexed information signal to a plurality of subcarriers having different frequencies for transmitting the information signal. Specifically, the transmission apparatus 20 includes the IFFT unit 2
5 performs frequency-time signal conversion of the information signal. Here, an inverse fast Fourier transform (IFFT) process is performed. Then, an information signal is allocated to a plurality of subcarriers having different frequencies to generate an OFDM symbol.

  Furthermore, the transmission apparatus 20 performs a guard interval insertion process, a symbol shaping process, a digital / analog conversion process, and an orthogonal transform process for each OFDM symbol in the DA conversion unit 26. Here, in the guard interval insertion processing, it is possible to reduce the influence of interference between OFDM symbols by delaying due to the influence of multipath propagation by inserting guard intervals between OFDM symbols. For example, a signal obtained by duplicating the latter half of the OFDM symbol is inserted at the beginning of the OFDM symbol. The length of the guard interval can be determined in consideration of the delay time.

  In the symbol shaping process, waveform shaping is performed in order to reduce signals that fall outside the band. In the orthogonal transform process, a baseband signal expressed as a complex number is converted into an intermediate frequency radio signal. Then, the transmission device 20 transmits the multicarrier CDMA signal to the reception device via the antenna.

For example, assuming that information symbols are spread over 16 chips, chips can be arranged in a plurality of forms in the time axis direction and the frequency axis direction. Here, the spreading factor (SF) is calculated by multiplying the time axis spreading factor (SFtime) and the frequency axis spreading factor (SFfreq). When diffusing in (16 × 1) with respect to the time axis direction and the frequency axis direction, the chips are sequentially arranged in the diffusion pattern 101 of FIG. Similarly, when spreading to (8x2), (4x4), (2x8), and (1x16) with respect to the time axis direction and the frequency axis direction, the chips are sequentially arranged in the diffusion patterns 102 to 105 in FIG. . With respect to the chips arranged in this way, digital symbols arranged on the time axis are assigned to different subcarriers to generate OFDM symbols. Thus, by spreading in the time axis direction and the frequency axis direction, the transmission characteristics can be made better than before.
Japanese Patent Laid-Open No. 2002-190788 (first page, FIG. 1)

  In such a multi-carrier spread spectrum communication system, the spreading factor should also be variable according to the traffic and radio resources. In the previous example, it was assumed that the spreading factor was 16, but this value can take various values such as 1, 2, 4, 16. Again, a high degree of freedom is required. Implementing such a two-dimensional spreading function using a variable spreading code while maintaining a high degree of freedom leads to a significant increase in circuit scale.

  Furthermore, when the number of chips increases, various arrangements can be considered. Essentially, when there are MxN resources in the time axis direction and the frequency axis direction, (MxN)! There will be an arrangement method of the pieces, and the degree of freedom is very high.

  The present invention has been made in view of the above-described problems, and in multi-carrier spread spectrum communication, two-dimensional spread using various patterns can be efficiently realized, flexibility is high, and transmission characteristics can be improved. An object of the present invention is to provide a multicarrier spread spectrum communication apparatus and a multicarrier spread spectrum communication method.

In order to solve the above problems, the present invention provides a communication device used in a multicarrier spread spectrum communication system using a plurality of subcarriers, wherein the communication device spreads information symbols with a variable spreading code; Based on the address of each chip spread by the spreading means, mapping means for converting the time axis address and the frequency axis address to be arranged on the subcarrier, and the time axis address and the frequency axis address arranged by the mapping means. The present invention includes a buffer means for storing the data, and a signal generating means for extracting data to be subjected to IFFT processing at the same time from the data recorded in the buffer means and generating an OFDM symbol. As a result, the spread processing for spectrum spreading and the two-dimensional processing for OFDM are performed separately, and the flexibility of each processing can be increased.

  The present invention is a communication device used for a multicarrier spread spectrum communication system using a plurality of subcarriers, wherein the communication device stores buffer means for storing information symbols, and spreads the data of the information symbols with a variable spreading code. Means, a signal generation means for generating an OFDM symbol by performing IFFT processing, and a mapping means for controlling these, wherein the mapping means sets a time axis address and a frequency axis address necessary for generating the OFDM symbol. The chip data address corresponding to the time axis address and the frequency axis address is specified, information symbols for generating the chip data address are extracted from the buffer means, and the diffusion process and the IFFT process are executed. This is the gist. As a result, the spread processing for spectrum spreading and the two-dimensional processing for OFDM are performed separately, and the flexibility of each processing can be increased. Furthermore, since the data before the diffusion process is accumulated in the buffer means and only necessary data is extracted and the diffusion process and the IFFT process are executed, the storage capacity of the buffer means can be reduced.

  The gist of the present invention is that the mapping means includes a search table in which a time axis address and a frequency axis address arranged on a subcarrier are associated with each chip address. Thereby, the two-dimensional processing can be executed efficiently.

  The gist of the present invention is that the mapping means further executes chip interleaving processing. Thus, errors can be reduced by using subcarriers as far apart as possible in transmission of adjacent bits after encoding.

  The present invention is a method for performing multi-carrier spread spectrum communication using a plurality of subcarriers using a communication device, wherein the communication device spreads information symbols with a variable spreading code and uses the spread address of each chip. Based on the time axis address and the frequency axis address to be arranged in the subcarrier, store the data arranged in the time axis address and the frequency axis address, extract the data to be subjected to IFFT processing at the same time, and OFDM The gist is to generate a symbol. As a result, the spread processing for spectrum spreading and the two-dimensional processing for OFDM are performed separately, and the flexibility of each processing can be increased.

The present invention relates to buffer means for storing information symbols, spreading means for spreading the data of the information symbols by a variable spreading code, signal generating means for generating OFDM symbols by performing IFFT processing, and mapping means for controlling them A multi-carrier spread spectrum communication using a plurality of subcarriers using a communication device comprising: a mapping means for identifying a time axis address and a frequency axis address necessary for generating an OFDM symbol A chip data address corresponding to the time axis address and the frequency axis address is specified, an information symbol for generating the chip data address is extracted from the buffer means, and a diffusion process and an IFFT process are executed. Is the gist. As a result, the spread processing for spectrum spreading and the two-dimensional processing for OFDM are performed separately, and the flexibility of each processing can be increased. Furthermore, since the data before the diffusion process is accumulated in the buffer means and only necessary data is extracted and the diffusion process and the IFFT process are executed, the storage capacity of the buffer means can be reduced.

  According to the present invention, in multicarrier spread spectrum communication, a multicarrier spread spectrum communication apparatus capable of efficiently realizing two-dimensional spread using various patterns, having high flexibility, and improving transmission characteristics. And a multi-carrier spread spectrum communication method.

  Hereinafter, an embodiment of multicarrier CDMA transmission (MC-CDMA) embodying a multicarrier spread spectrum communication system and a multicarrier spread spectrum communication receiver according to the present invention will be described with reference to FIGS. In the present embodiment, description will be made using OFDM transmission as multicarrier spread spectrum communication.

  As shown in FIG. 1, in the multicarrier spread spectrum communication system in the present embodiment, a transmission device 20 and a reception device (not shown) as a multicarrier spread spectrum communication device are used.

  First, the transmission device 20 generates information symbols for the input transmission data using the information symbol generation unit 21. Then, the transmission device 20 executes an error correction encoding process for adding an error correction code for correcting an error in the data in the error correction encoding unit 22. Next, the data modulation unit 23 performs data modulation processing on the generated information symbol. The data modulation unit 23 performs QPSK modulation, QAM modulation, and the like.

  Next, transmitting apparatus 20 performs information symbol spreading processing in code spreading section 24 serving as spreading means. Here, only one-dimensional diffusion of information symbols is performed. The code spreading unit 24 generates a spreading code corresponding to each data channel assigned to each data channel. Furthermore, a variable code that changes the arrangement on the frequency axis and the time axis according to the transmission path state is used. As a result, it is possible to easily adapt to a transmission line that is affected by a frequency selective fading transmission line, a transmission line with a large time fluctuation, or the like. Then, the transmission apparatus 20 performs spreading by multiplying the information symbol by this spreading code.

  Next, the transmission apparatus 20 performs a two-dimensionalization process on the spread information symbols using the mapper 30 as a mapping unit. The mapper 30 includes a counter and counts the input symbol order and chip order. This counter value is converted into an address when writing to a buffer unit 32 described later. A specific mapping rule is used for this conversion.

  In the present embodiment, the mapper 30 includes a search table storage unit 31 and uses a search table 310 stored in the search table storage unit 31. The search table 310 will be described with reference to FIG. In the search table 310, an address in the frequency axis direction (maped freq addr: frequency axis address) and an address in the time axis direction (maped time addr: time) corresponding to the chip data address (addr (before map): chip address). Axis address) is recorded in association with each other. Then, the mapper 30 uses the search table 310 to form each chip data of the one-dimensional information symbol from the corresponding frequency axis address and time axis address into a two-dimensional map in consideration of the symbol order. Deploy.

Next, the mapped data is stored in the buffer unit 32 as buffer means. When IFFT processing is performed, in order to convert each chip into an OFDM symbol, N pieces of chip data of a two-dimensional map (M × N) are required at time t. On the other hand, the code spreading unit 24 and the mapper 30 generate chip data in the order of the input information symbols. Therefore, a buffer unit 32 is provided in the transmission device 20 in order to accumulate (MxN) chip data generated for performing the IFFT processing. The buffer unit 32 is realized by a normal random access memory (RAM), and stores chip data spread for each frequency axis address and time axis address.

  Then, using the chip data recorded in the buffer unit 32, the IFFT unit 25 of the transmission device 20 performs frequency-time signal conversion. Here, inverse fast Fourier transform is used. Then, an information signal is allocated to a plurality of subcarriers having different frequencies to generate an OFDM symbol.

  Further, the transmission apparatus 20 performs a guard interval insertion process, a symbol shaping process, a digital / analog conversion process, and an orthogonal transform process for each OFDM symbol in the DA conversion unit 26 as a signal generation unit. Then, the transmission device 20 transmits the multicarrier CDMA signal to the reception device via the antenna.

  A receiving apparatus that receives a multicarrier CDMA signal executes signal processing in the same manner as in ordinary multicarrier spread spectrum communication. That is, the receiving apparatus establishes synchronization of OFDM symbol timing and removes the guard interval inserted in each OFDM symbol. Then, the receiving apparatus performs fast Fourier transform on the multicarrier CDMA signal, and separates the CDMA signal spread on a plurality of subcarriers having different frequencies for each subcarrier. Further, the receiving apparatus performs despreading by multiplying the CDMA signal by a spreading code corresponding to each data channel. Next, the receiving apparatus performs parallel-to-serial conversion processing on the information symbols synthesized and restored over the spreading code period, and performs data demodulation processing. Further, the receiving apparatus performs error correction decoding processing and acquires information symbols. Thereby, multicarrier spread spectrum communication combining the OFDM communication method and the CDMA communication method is realized.

According to the multicarrier spread spectrum communication of the above embodiment, the following effects can be obtained.
In the above embodiment, the transmission device 20 performs the spreading process in the code spreading unit 24. Here, only one-dimensional diffusion of information symbols is performed. Transmitting apparatus 20 then performs two-dimensional processing of the spread information symbols using mapper 30. Thus, by separately performing the diffusion process and the two-dimensional process, the spreader and the mapper can be realized with a simple circuit configuration, and the degree of freedom of each process can be increased. For example, there are various sequences such as Barker, M-Sequence, Gold, Hadamard-Walsh, etc. to generate the spreading code used in the spreading process, and the degree of freedom of selection can be increased, and the spreading factor can be easily changed. become.

  Furthermore, unlike the case where the chip data is arranged in order, each chip data can be freely arranged, and the distance of each chip data can be increased as necessary. For example, it is possible to use a pattern that always keeps the minimum Euclidean distance between chips belonging to the same symbol at a certain level or more. Thereby, high-quality communication with higher throughput can be provided.

In the above embodiment, the mapper 30 includes the search table storage unit 31, and the search table storage unit 31 stores the search table 310. In the search table 310, a frequency axis address and a time axis address are recorded in association with each other in correspondence with the chip address assigned to the information symbol. Thereby, the mapper 30 can efficiently two-dimensionalize the chip data.

  In the above embodiment, the transmission device 20 provides the buffer unit 32 between the mapper 30 and the IFFT unit 25. When performing IFFT processing, each chip is converted to an OFDM symbol, so that all chip data (N chip data in the two-dimensional map (MxN)) is required at any one time, but is recorded in the buffer unit 32. The IFFT unit 25 can perform frequency-time signal conversion of the information signal using the chip data thus obtained.

In addition, you may change the said embodiment as follows.
In the above embodiment, the mapper 30 performs a two-dimensional process using the search table 310 stored in the search table storage unit 31. Alternatively, the arrangement on the two-dimensional map can be realized by a circuit configuration. This will be described with reference to FIG. For example, the size (time, freq) = (64, 256) of the two-dimensional buffer is provided in the buffer unit 32. When (SFtime, SFfreq) = (8, 2), the spreading factor (SF) = 16 can be expressed by 4 bits, and SFtime, SFfreq can be expressed by 3 bits and 1 bit, respectively. When the number of symbols to be transmitted is 1024, this symbol can be expressed by 10 bits. Therefore, using a counter of 14 (= 10 + 4) bits, 4 bits from the least significant bit (LSB) are allocated to the spreader, and 10 bits from the most significant bit (Most Significant Bit: MSB) are allocated to the symbol buffer. Assign to read.

  Then, the 4 bits given to the spreader are further divided into MSB1 bits and LSB3 bits in correspondence with the frequency spreading factor SFfreq and the time spreading factor SFtime. The 10 bits used as the symbol buffer read address are divided into 7 MSB bits and 3 LSB bits. Thus, the 14-bit counter is divided from the MSB by 7 bits, 3 bits, 1 bit, and 3 bits. Of these, 7 bits of MSB and 1 bit corresponding to SFfreq are collectively 8 bits, which are used as addresses in the frequency direction of the two-dimensional chip buffer. Similarly, 6 bits including the remaining 3 bits and 3 bits are used as an address in the time direction. Thereby, each spread chip of each symbol can be arranged two-dimensionally. That is, 1024 symbols can be spread 16 times and arranged in 2 × 8, and then arranged in a 256 × 64 size buffer.

  In the above embodiment, the mapper 30 includes the search table storage unit 31 and performs a two-dimensional process using the search table 310 stored in the search table storage unit 31. The arrangement method of the two-dimensional map is not limited to that sequentially arranged. For example, as the search table 310, a table in which adjacent chips are arranged in a distributed manner may be set. Thereby, chip interleaving can be realized. Also in this case, the arrangement on the two-dimensional map can be realized by a circuit configuration. This is shown in FIG. Here, the spreading code is shuffled. If errors are concentrated in one place or if there is periodicity in the place where the error occurred, the error correction capability may drop. In addition, in a wireless communication channel, for example, only a specific frequency (= subcarrier) receives interference with narrowband noise, and only an OFDM symbol at a specific time may deteriorate due to, for example, shadowing. Chip interleaving shuffles noise / interference generated on the wireless communication path to avoid concentrating errors in one place and corrects the error later in the error correction decoder (turbo decoder, Viterbi decoder, etc.) Can be prevented. Furthermore, as shown in FIG. 6, all bits of the counter may be shuffled, and then the frequency direction address and time direction address of the two-dimensional chip buffer may be generated.

In the above embodiment, the mapped data is stored in the buffer unit 32 of the transmission device 20. Instead, as shown in FIG. 7, the buffer unit 40 may be provided before the diffusion process is performed. As described above, when IFFT processing is performed, each chip is converted to an OFDM symbol, so that N pieces of all chip data of the two-dimensional map (M × N) are required at time t. Therefore, the mapper 30 reverses the arrangement positions of the N pieces of chip data necessary for performing the IFFT processing at time t using the search table 310 in which the search table storage unit 31 is stored. That is, the mapper 30 specifies chip data necessary for IFFT processing and information symbol data necessary for generating the chip data in the buffer unit 40 in the two-dimensional map.

  Then, the mapper 30 extracts information symbol data necessary for IFFT processing, and causes the code spreading unit 24 to execute spreading processing. Then, the IFFT unit 25 performs frequency time signal conversion of only necessary data. As a result, only the information symbols necessary for the OFDM frame need to be stored, and the storage capacity of the buffer unit can be reduced as compared with storing all chip data.

The block diagram of the transmission apparatus of the multicarrier spread spectrum communication of this invention. Explanatory drawing of the search table stored in the search table memory | storage part. Explanatory drawing of the mapping for two-dimensional spreading | diffusion. Explanatory drawing of chip interleaving. Explanatory drawing of the mapping for other two-dimensional spreading | diffusion. Explanatory drawing of the mapping for other two-dimensional spreading | diffusion. The block diagram of the transmission apparatus of other multicarrier spread spectrum communications. The block diagram of the transmission apparatus of the conventional multicarrier spread spectrum communication. The conceptual diagram of two-dimensional spreading | diffusion on a frequency axis and a time axis.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Transmission apparatus, 24 ... Code spreading part as spreading means, 30 ... Mapper as mapping means, 31 ... Search table storage part, 310 ... Search table, 32 ... Buffer part as buffer means, 25 ... IFFT part, 40 ... Buffer section as buffer means.

Claims (4)

A communication device used for a multi-carrier spread spectrum communication system using a plurality of subcarriers,
The communication device is
Buffer means for storing information symbols;
Spreading means for spreading the data of the information symbol by a variable spreading code;
Signal generating means for generating an OFDM symbol by performing IFFT processing;
Mapping means for controlling these,
The mapping means specifies a time axis address and a frequency axis address necessary for generating an OFDM symbol,
Specify the address of the chip data corresponding to the time axis address and the frequency axis address,
An information symbol for generating an address of the chip data is extracted from the buffer means, and spread processing and IFFT processing are executed. 2. The multicarrier spread spectrum communication apparatus according to claim 1, wherein the mapping unit includes a search table in which a time axis address and a frequency axis address arranged in subcarriers are associated with each chip address. . Wherein the mapping unit is a multi-carrier spread spectrum communication apparatus according to claim 1 or 2, characterized by further executing the chip interleaving processing. Buffer means for storing information symbols, spreading means for spreading data of the information symbols with a variable spreading code, signal generating means for generating an OFDM symbol by performing IFFT processing, and mapping means for controlling them A method for performing multicarrier spread spectrum communication using a plurality of subcarriers using a communication device,
The mapping means is
Specify the time axis address and frequency axis address necessary to generate the OFDM symbol,
Specify the address of the chip data corresponding to the time axis address and the frequency axis address,
An information symbol for generating an address of the chip data is extracted from the buffer means, and spread processing and IFFT processing are executed.

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