JP3881919B2 - Radio transmission apparatus and radio transmission method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wireless transmission device and a wireless transmission method.
[0002]
[Prior art]
In wireless communication, in recent years, there has been an increasing demand for transmitting a large amount of data, and multicarrier transmission has attracted attention in order to satisfy this requirement. In multicarrier transmission, transmission data is distributed and transmitted to a plurality of subcarriers having different frequencies, so that transmission efficiency can be improved. A signal composed of a plurality of subcarriers having different frequencies is called a multicarrier signal.
[0003]
In wireless communication, particularly mobile communication, recently, a communication method in which the CDMA method is combined with the multicarrier transmission has been attracting attention. Of particular note is the MC-CDMA system in which transmission data is spread in the frequency axis direction and a multicarrier signal in which a plurality of chips after spreading are assigned to different subcarriers is transmitted. In the MC-CDMA system, transmission efficiency can be increased by multicarrier transmission, and diversity gain in the frequency axis direction can be obtained because spreading is performed in the frequency axis direction. That is, it is possible to improve reception quality while increasing transmission efficiency.
[0004]
Further, in wireless communication, there is a technique in which m-bit transmission data is converted into an M-bit fixed-length codeword (m <M) and transmitted in order to improve error rate characteristics. Since this fixed-length codeword is a so-called M-sequence codeword, the process of converting to such a fixed-length codeword is called M-ary processing. FIG. 4 is a table (M-ary table) used for M-ary processing. Here, it is assumed that 4-bit transmission data is converted into a 15-bit M-sequence fixed-length codeword. As shown in FIG. 4, 16 types of transmission data “0000” to “1111” are converted into corresponding 15-bit M-sequence codewords. The code word corresponding to '0000' has all bits of '1', and the code word corresponding to each of '0010' to '1111' circulates the code word corresponding to '0001' bit by bit. It has been shifted. These 16 types of codewords have very low cross-correlation.
[0005]
Here, considering the case where M-ary processing is applied to the MC-CDMA system, the transmission procedure is as follows. FIG. 5 is a diagram showing a conventional transmission procedure when M-ary processing is applied to the MC-CDMA system. Here, for convenience of explanation, an M-ary process for converting m = 3-bit transmission data into an M = 6-bit code word will be described as an example. Further, a case will be described in which two data, that is, transmission data # 1 to communication partner # 1 and transmission data # 2 to communication partner # 2 are code division multiplexed (code multiplexing).
[0006]
As shown in FIG. 5, transmission data # 1 and transmission data # 2 are each subjected to M-ary processing and converted into M-bit fixed-length codewords.
[0007]
These code words are spread in the frequency axis direction by a spreading code having a spreading factor N (N = 8 here). This spreading process is sequentially performed bit by bit with respect to 6 bits included in the code word. At this time, the spreading code used for the codeword corresponding to transmission data # 1 is different from the spreading code used for the codeword corresponding to transmission data # 2. That is, the spreading code used at this time is different for each communication partner. When attention is paid to a certain code word, the same spreading code is used for a plurality of bits included in the code word.
[0008]
The spread bits are code-multiplexed one bit at a time. The bits after code multiplexing are divided into the first to Nth chips of the spreading code for each chip, and the first to Nth chips are divided into N subcarriers f1 to f8 prepared for the spreading factor N. Assigned to each. Thereby, a multicarrier signal is generated. Specifically, at time t1, the first chip of the first bit that is code-multiplexed is assigned to subcarrier f1, and the eighth chip of the first bit that is code-division multiplexed is assigned to subcarrier f8. Also, at time t6, the 6th bit first chip code-multiplexed is assigned to the subcarrier f1, and the 6th bit 8th chip code-multiplexed is assigned to the subcarrier f8. Therefore, when the code length is M = 6, a total of 6 multicarrier signals are generated with the passage of time.
[0009]
[Problems to be solved by the invention]
Thus, when applying the M-ary processing to the MC-CDMA system, in the conventional proposed method, the code word after the M-ary processing is spread with a different spreading code for each communication partner. Different types of spreading codes are required. Therefore, the spreading factor increases as the number of communication partners increases, and as a result, the orthogonality between spreading codes is largely lost, and the mutual interference between spreading codes is increased. In other words, in the conventional proposed method, the reception quality deteriorates as the number of communication partners increases.
[0010]
Focusing on one communication partner, the same spreading code is used for a plurality of bits included in the code word after the M-ary processing. For this reason, when the code length is M, M multicarrier signals are required to transmit the codeword. Therefore, as the code length M increases, the error rate characteristics can be improved, but on the other hand, the transmission time increases, and as a result, the reception side has a large delay in data reception. In data transmission that requires real-time performance (for example, a videophone), a delay occurring in data reception becomes a serious problem.
[0011]
The present invention has been made in view of such points, and when applying M-ary processing to the MC-CDMA system, it is possible to accommodate a plurality of communication partners without changing the spreading factor, An object of the present invention is to provide a wireless transmission device and a wireless transmission method capable of reducing data transmission delay.
[0012]
[Means for Solving the Problems]
The wireless transmission device of the present invention is a wireless transmission device that transmits a multicarrier signal composed of a plurality of subcarriers having different frequencies, and converts transmission data into a fixed-length codeword composed of a plurality of bits. And converting means for spreading each of the plurality of bits included in the codeword corresponding to each of the plurality of bits, and spreading using a common spreading code for a plurality of communication partners Multiplex means for code division multiplexing the plurality of spread bits for each communication partner, division means for dividing the plurality of code division multiplexed bits for each chip, and each of the divided chips A configuration is provided that includes generation means for generating the multicarrier signal allocated to each subcarrier, and transmission means for transmitting the generated multicarrier signal.
[0013]
According to this configuration, since the spreading factor of the spreading code can be fixed, it is possible to prevent the orthogonality between spreading codes from being lost due to the spreading factor becoming higher. In addition, since a multi-bit codeword can be transmitted with one multicarrier signal, a data transmission delay can be reduced.
[0014]
The radio communication base station apparatus of the present invention adopts a configuration in which the radio transmission apparatus is mounted.
[0015]
According to this configuration, it is possible to provide a radio communication base station apparatus having the same operations and effects as described above.
[0016]
The radio transmission method of the present invention is a radio transmission method for transmitting a multicarrier signal composed of a plurality of subcarriers having different frequencies, and converts transmission data into a fixed-length codeword composed of a plurality of bits. And each of the plurality of bits included in the code word is different corresponding to each of the plurality of bits, and spread with a common spreading code for a plurality of communication partners, The bits are code division multiplexed for each communication partner, the plurality of code division multiplexed bits are divided for each chip, and the multicarrier signal in which each of the divided plurality of chips is assigned to each of the subcarriers is transmitted. I made it.
[0017]
According to this method, since the spreading factor of the spreading code can be fixed, it is possible to prevent the orthogonality between spreading codes from being broken due to the spreading factor becoming higher. In addition, since a multi-bit codeword can be transmitted with one multicarrier signal, a data transmission delay can be reduced.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The essence of the present invention is that each of a plurality of bits included in a codeword after M-ary processing is different in correspondence with each of the plurality of bits and is a common spreading code for a plurality of communication partners. Spreading and code-multiplexing the spread bits for each communication partner.
[0019]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a radio transmission apparatus according to an embodiment of the present invention. In the following description, a case will be described in which there are two communication partners of the wireless transmission device, communication partner # 1 and communication partner # 2.
[0020]
1 includes S / P units 11 and 21, M-ary encoding units 12 and 22, spreading units 13-1 to 13-M and 23-1 to 23-M, code multiplexing Units 14 and 24, IFFT unit 31, GI adding unit 32, transmission RF unit 33, and antenna 34.
[0021]
The S / P unit 11, the M-ary encoding unit 12, the spreading units 13-1 to 13 -M, and the code multiplexing unit 14 perform processing on the transmission data # 1 for the communication partner # 1. 1. In addition, the S / P unit 21, the M-ary encoding unit 22, the spreading units 23-1 to 23-M, and the code multiplexing unit 24 perform transmission on the transmission data # 2 to the communication partner # 2. System # 2. Since the processing content performed in the transmission system # 1 and the processing content performed in the transmission system # 2 are substantially the same, in the following description, only the transmission system # 1 will be described for the same part, and the transmission system # 2 will be described. Description is omitted.
[0022]
The S / P unit 11 converts m-bit transmission data # 1 serially input from the input end (that is, transmission data # 1 having a data length m) in parallel and inputs the parallel data to the M-ary encoding unit 12. .
[0023]
The M-ary encoding unit 12 converts the m-bit transmission data # 1 into an M-sequence M-bit code word (m <M) in the same manner as in the prior art. That is, when m = 4, based on the M-ary table shown in FIG. 4, transmission data # 1 is converted into a corresponding M = 15-bit fixed-length codeword. A code word having a code length M is input to spreading sections 13-1 to 13-M in parallel in M bits.
[0024]
Spreading units 13-1 to 13-M are provided corresponding to each of the M bits included in the M-ary-processed code word, and each of the M bits included in the code word is a spreading code with a spreading factor N. Spread. Each of the spread bits is input to the code multiplexing unit 14.
[0025]
At this time, the spreading codes used in the spreading units 13-1 to 13-M are different from each other. That is, the spreading code used in spreading sections 13-1 to 13-M is different for each of the M bits included in the code word. For example, the spreading unit 13-1 spreads the first bit with the spreading code # 1, the spreading unit 13-2 spreads the second bit with the spreading code # 2, ..., and the spreading unit 13-M takes the Mth bit. Spread with spreading code #M. The same applies to the diffusion units 23-1 to 23-M.
[0026]
Further, the spreading code used in the spreading unit 13-1 and the spreading code used in the spreading unit 23-1 are the same. Similarly, the spreading code used in the spreading unit 13-2 and the spreading code used in the spreading unit 23-2 are the same, ..., the spreading code used in the spreading unit 13-M and the spreading code used in the spreading unit 23-M. The spreading code to be used is the same. That is, the transmission system # 1 and the transmission system # 2 use the same spreading code. In other words, a common spreading code is used for a plurality of communication partners.
[0027]
Since the bits input from the spreading units 13-1 to 13-M are spread with different spreading codes, the code multiplexing unit 14 code-multiplexes all the input M bits. Then, the code-multiplexed bits are divided into the first chip to the Nth chip of the spread code for each chip. By this division, the data in which the first chip of the 1st to Mth bits are all multiplexed, the data in which the second chip of the 1st to Mth bits is all multiplexed,..., The 1st to Mth bits Data in which all the Nth chips of the eye are multiplexed is generated, and N pieces of these data are input to the IFFT unit 31 in parallel. Similarly, the code division unit 24 also inputs N pieces of data divided for each chip to the IFFT unit 31 in parallel. That is, the IFFT unit 31 receives data that is code-multiplexed for each communication partner and then divided for each chip.
[0028]
The IFFT unit 31 performs IFFT (Inverse Fast Fourier Transform) processing on the input data for each chip (2 × N in total). As a result, a multicarrier signal is generated in which each piece of chip data input from the code multiplexing unit 14 and the code multiplexing unit 24 is assigned to each of a plurality of subcarriers having different frequencies. Therefore, the required number L of subcarriers is 2 × N. The generated multicarrier signal is input to the GI adding unit 32.
[0029]
Here, since the OFDM (Orthogonal Frequency Division Multiplexing) method is used as the multicarrier transmission method, IFFT processing is performed. The OFDM scheme is a type of multicarrier transmission scheme in which a plurality of subcarriers constituting a multicarrier signal (a multicarrier signal generated by the OFDM scheme is particularly referred to as an OFDM signal) are orthogonal to each other. As described above, since a plurality of subcarriers are orthogonal to each other in the OFDM scheme, the spectrum of each subcarrier can be overlapped by using the OFDM scheme. As a result, frequency use efficiency can be improved.
[0030]
The GI adding unit 32 adds a guard interval to the head of the multicarrier signal and inputs the same to the transmission RF unit 33. The guard interval is added to make the multicarrier signal less susceptible to delay waves.
[0031]
The transmission RF unit 33 performs predetermined radio processing (D / A conversion, up-conversion, etc.) on the multicarrier signal input from the GI addition unit 32, and then transmits the multicarrier signal via the antenna 34 in FIG. To the wireless receiver shown in FIG.
[0032]
FIG. 2 is a block diagram showing a configuration of a radio reception apparatus according to an embodiment of the present invention. In the following description, the radio receiver of communication partner # 1 will be described. Note that the wireless receiver of communication partner # 2 has the same configuration.
[0033]
2 includes an antenna 41, a reception RF unit 42, a GI removal unit 43, an FFT unit 44, a selection unit 45, despreading units 46-1 to 46-M, and M-ary. The decoding unit 47 and the P / S unit 48 are included.
[0034]
The reception RF unit 42 performs predetermined radio processing (down-conversion, A / D conversion, etc.) on the multicarrier signal received via the antenna 41.
[0035]
The GI removal unit 43 removes the guard interval added to the multicarrier signal input from the reception RF unit 42.
[0036]
The FFT unit 44 performs an FFT (Fast Fourier Transform) process on the multicarrier signal input from the GI removal unit 43. Thereby, a multicarrier signal is divided | segmented into several data for every subcarrier. That is, the data is divided into a total of L = 2 × N pieces of data for each chip. The data divided for each chip is input to the selection unit 45 in parallel.
[0037]
Half of the data for every 2 × N chips is data for communication partner # 1. Further, the communication partner # 1 knows to which subcarrier of the L subcarriers the data addressed to itself is assigned by a prior arrangement or notification from the wireless transmission device. Therefore, the selection unit 45 selects N pieces of data addressed to the communication partner # 1 among the data for each chip input from the FFT unit 44, and inputs the selected data to the despreading units 46-1 to 46-M.
[0038]
Despreading units 46-1 to 46-M are provided corresponding to each of the M bits included in the code word subjected to M-ary processing. Here, for example, the first bit of the code word is divided and included in data of the first chip to data of the Nth chip. Therefore, the despreading unit 46-1 combines the data for each of N chips input from the selection unit 45 and then the same spreading code as used in the spreading unit 13-1 of the wireless transmission device shown in FIG. Despreading with the spreading code. As a result, the first bit among the M bits included in the code word subjected to the M-ary processing is obtained. Similarly, the despreading unit 46-2 combines the data for each of N chips, and then despreads with the same spreading code as the spreading code used in the spreading unit 13-2. -M combines the data for each of N chips, and then despreads with the same spreading code as the spreading code used in the spreading unit 13-M. By these despreading processes, all bits (M = 15 bits) included in the M-ary processed codeword are obtained. The code word of code length M is input to the M-ary decoding unit 47 in parallel with M bits.
[0039]
The M-ary decoding unit 47 performs reverse conversion to the M-ary encoding unit 12 of the wireless transmission device shown in FIG. That is, based on the M-ary table shown in FIG. 4, the M-bit code word input from the despreading units 46-1 to 46-M is converted into m-bit data (m <M). The converted data (that is, data having a data length of m) is input to the P / S unit 48 in m bits in parallel.
[0040]
The P / S unit 48 converts m-bit data input in parallel from the M-ary decoding unit 47 into serial. As a result, the same reception data # 1 as the transmission data # 1 is obtained.
[0041]
Next, the operation of the wireless transmission apparatus having the above configuration will be described. FIG. 3 is a diagram illustrating a transmission procedure of the wireless transmission device according to the embodiment of the present invention. Here, for convenience of explanation, an M-ary process for converting m = 3-bit transmission data into an M = 6-bit code word will be described as an example. Also, a case will be described in which two data, that is, transmission data # 1 to communication partner # 1 and transmission data # 2 to communication partner # 2 are included in one multicarrier signal.
[0042]
As shown in FIG. 3, transmission data # 1 is subjected to M-ary processing in transmission system # 1, and transmission data # 2 is subjected to M-ary processing in transmission system # 2, and converted to a fixed-length codeword of M = 6 bits. .
[0043]
Next, in each transmission system, 6 bits included in the code word are spread in parallel in the frequency axis direction. At this time, the spreading codes used for each of the 6 bits included in the code word are different from each other. However, the spreading factor N = 8 is the same. Also, six spreading codes used in transmission system # 1 (that is, used for communication partner # 1) and 6 spreading codes used in transmission system # 2 (that is, used for communication partner # 2) 6 Each spreading code is the same spreading code. That is, these spreading codes are different corresponding to each of the plurality of bits included in the code word, and are common spreading codes to a plurality of communication partners.
[0044]
Next, the spread bits are code-multiplexed in each transmission system. That is, code multiplexing is performed for each communication partner. The code-multiplexed bits are divided for each chip into the first to Nth chips of the spreading code.
[0045]
Then, data for each of eight chips for communication partner # 1 is assigned to subcarriers f9 to f16, and data for each of eight chips for communication partner # 2 is assigned to subcarriers f1 to f8, respectively. Thereby, transmission data # 1 and transmission data # 2 can be included in one multicarrier signal and transmitted. That is, when the code length is M = 6, in the present embodiment, all of the data transmitted at times t1 to t6 in the conventional proposed method can be transmitted at time t1.
[0046]
As described above, according to the present embodiment, the type of spreading code required depends only on the code length of the codeword after the M-ary processing, and does not depend on the number of communication partners. Further, since the code length of the code word is fixed, the necessary type of spreading code can be fixed regardless of the number of communication partners. That is, it is not necessary to increase the types of spreading codes even if the number of communication partners increases. Further, in order to increase the number of types of spreading codes to be used, it is necessary to increase the spreading factor. However, in this embodiment, since the types of necessary spreading codes can be fixed, the spreading factor can be fixed. it can. For example, when the code length is 15 bits, the spreading factor can be fixed to 16. Therefore, it is possible to prevent the orthogonality between spreading codes from being lost due to an increase in spreading factor, and as a result, it is possible to prevent the reception quality from deteriorating when the number of communication partners increases.
[0047]
Also, according to the present embodiment, the spreading factor can be fixed regardless of the number of communication partners, so that the spreading factor with the best performance can be selected and transmitted according to the fading environment. Thereby, reception quality can be improved.
[0048]
In addition, the code length of the codeword after the M-ary processing is relatively long, usually 15 bits or more. However, according to the present embodiment, the transmission time does not depend on the code length, and a multi-bit codeword can be transmitted with one multicarrier signal. Therefore, the data transmission delay can be reduced regardless of the code length.
[0049]
The radio transmission apparatus according to the present invention is suitable for use in a radio communication base station apparatus used in a mobile communication system or the like. By mounting the radio transmission apparatus of the present invention on a radio communication base station apparatus, a radio communication base station apparatus having the same operations and effects as described above can be provided.
[0050]
【The invention's effect】
As described above, according to the present invention, when the M-ary processing is applied to the MC-CDMA system, it is possible to accommodate a plurality of communication partners without changing the spreading factor, and Transmission delay can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a radio transmission apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a radio reception apparatus according to an embodiment of the present invention. FIG. 4 is a diagram showing a transmission procedure of a radio transmission apparatus according to an embodiment of the present invention. FIG. 4 is a diagram showing a conventional transmission procedure when an M-ary process is applied to the MC-CDMA system. [Explanation of symbols]
11, 21 S / P unit 12, 22 M-ary encoding unit 13-1 to 13-M, 23-1 to 23-M spreading unit 14, 24 code multiplexing unit 31 IFFT unit 32 GI addition unit 33 transmission RF unit 34, 41 Antenna 42 Reception RF unit 43 GI removal unit 44 FFT unit 45 Selection unit 46-1 to 46-M Despreading unit 47 M-ary decoding unit 48 P / S unit

Claims (3)

A wireless transmission device that transmits a multicarrier signal composed of a plurality of subcarriers having different frequencies,
Conversion means for converting transmission data into a fixed-length codeword composed of a plurality of bits;
Spreading means for spreading each of the plurality of bits included in the codeword corresponding to each of the plurality of bits, and spreading with a common spreading code for a plurality of communication partners;
Multiplexing means for code division multiplexing the spread bits for each communication partner;
Dividing means for dividing the plurality of bits subjected to code division multiplexing for each chip;
Generating means for assigning each of a plurality of divided chips to each of the subcarriers to generate the multicarrier signal;
Transmitting means for transmitting the generated multi-carrier signal;
A wireless transmission device comprising: A radio communication base station apparatus, comprising the radio transmission apparatus according to claim 1. A wireless transmission method for transmitting a multicarrier signal composed of a plurality of subcarriers having different frequencies,
Convert transmission data into a fixed-length codeword consisting of multiple bits,
Each of the plurality of bits included in the codeword is different corresponding to each of the plurality of bits, and spreads with a common spreading code for a plurality of communication partners,
Code division multiplexing the spread plurality of bits for each communication partner,
Dividing the plurality of code-division multiplexed bits for each chip,
Transmitting the multicarrier signal in which each of the divided chips is assigned to each of the subcarriers;
And a wireless transmission method.

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