JP4181906B2 - Transmitter and receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention generally relates to a transmitter and a receiver in a communication system using a multi-carrier code division multiple access (MC-CDMA) system.
[0002]
[Prior art]
The MC-CDMA system is one of technologies that are being studied for application to next-generation broadband mobile communications, and has attracted particular attention in recent years. In addition to the advantages of MC or Orthogonal Frequency Division Multiplexing (OFDM), which enhances frequency selective fading resistance by using multiple subcarriers, it enables suppression of interference by code spreading. The frequency utilization efficiency is further enhanced while retaining the advantages of the CDMA system. The technology related to MC-CDMA is disclosed in Non-Patent Document 1, for example.
[0003]
FIG. 1 shows an outline of a transmitter used in an MC-CDMA communication system. As illustrated, the transmitter 100 includes an encoding unit 102, which encodes binary data using a technique such as convolutional encoding or turbo encoding. The transmitter 100 includes a modulation unit 104 connected to an encoding unit 102, which converts a data sequence encoded by the encoding unit 102 into signal points in a predetermined modulation scheme such as BPSK, QPSK, and 16QAM. A series of symbol sequences is output by sequentially mapping to (symbols). The transmitter 100 includes a serial / parallel converter 106, which converts a series of symbol sequences into, for example, M predetermined numbers of parallel signal sequences (streams). The transmitter 100 has a spreading unit 107, which code spreads the parallel signal sequence from the serial / parallel conversion unit 106. The spreading unit 107 includes a duplicating unit 108 provided for each stream. The duplicating unit 108 duplicates one stream into, for example, a predetermined number of SF streams, and outputs them as parallel signal sequences. The spreading unit 107 includes a multiplying unit 110 and a spreading code generating unit 112 for multiplying each stream by a spreading code. The length of the spread code is set according to the number of copies (SF) of the duplication unit 108. More specifically, the SF streams from the duplicating unit 108 are multiplied by a spreading code having a length SF.
[0004]
The transmitter 100 has a fast inverse Fourier transform unit 114 connected to the output of each multiplication unit 110. The fast inverse Fourier transform unit 114 has N = M × SF input points and output points corresponding to the number of subcarriers, and performs fast inverse Fourier transform on the input signal sequence. As a result, N = M × SF streams in the frequency domain are converted into N time domain signals. The transmitter 100 includes a serial / parallel converter 116, which converts N streams into one stream. The transmitter 100 includes a guard interval insertion unit 118, which creates a transmission data sequence by adding a guard interval for each symbol (for each OFDM effective symbol) to the output signal from the serial / parallel conversion unit 116. To do. The transmitter 100 includes, for example, Nt predetermined number of antenna elements 120, and each antenna element 120 includes a weight setting unit 122 that is multiplied by a complex weight coefficient. The antenna element 120 functions as an adaptive array antenna that can form a highly directional beam pattern.
[0005]
FIG. 2 shows an outline of a receiver used in the MC-CDMA communication system. As illustrated, the receiver 200 includes an antenna element 202 that receives a radio signal from the transmitter. The receiver 200 includes a guard interval removing unit 204, which removes the guard interval from the received series of symbol sequences. The receiver 200 includes a serial / parallel converter 206, which converts a series of symbol sequences into N = M × SF parallel symbol sequences (streams). The receiver 200 includes a fast Fourier transform unit 208, which outputs N frequency domain signals by performing a fast Fourier transform on the N time domain signals. The receiver 200 includes a despreading unit 209, which despreads the signal sequence for each subcarrier from the fast Fourier transform unit 208. The receiver 200 includes a multiplier 210 that multiplies each stream by a despread code, and a despread code generator 212 that generates a despread code. N streams from the fast Fourier transform unit 208 are divided into M streams, and each of the M streams is multiplied by a despreading code of length SF.
[0006]
On the other hand, the despreading unit 209 includes a channel estimation unit 214 connected to the output of the fast Fourier transform unit 208, which evaluates the influence of fading and the like by estimating a channel response for each subcarrier, and a multiplication unit. Compensate for each stream through H.216. The despreading unit 209 includes a combining unit 218. The combining unit 218 combines one or more SF streams to output one stream. As a result, M streams are output from the M combining units 218. The receiver 200 has a parallel-serial converter 220, which converts M parallel streams into serial streams. The receiver 200 has a data demodulator 222, which determines signal points that symbols represent the input stream according to a predetermined modulation scheme such as BPSK, QPSK, 16QAM. The receiver 200 has a decoding unit 224 connected to the data demodulation unit 222, which decodes a signal that has been encoded such as convolutional encoding. Thereafter, further subsequent processing (not shown) is performed.
[0007]
In such an MC-CDMA communication system, a highly directional beam is used. For example, when one cell is divided into three sectors, a 120-degree sector area is further divided into 15 areas (clusters) (each beam has a beam width of 8 degrees). The radio base station appropriately selects a beam to be used depending on the arrival angle (DoA) of the radio wave. As a result, the radio base station can perform high-gain one-to-one communication with less interference with the subordinate mobile terminals. From this point of view, it is expected that if the transmission beam width is narrowed down and transmitted, it is possible to increase the gain and suppress the interference accordingly.
[0008]
By the way, in a mobile communication system, depending on the communication environment of a receiver, the spread of radio waves arriving at the receiver, that is, angular dispersion or angular spreading changes. Note that there is a relationship as shown in FIG. 3 among the angular dispersion α, the transmission beam width γ, and the arrival direction θ. In FIG. 3, d indicates a linear distance between the radio base station and the mobile terminal, and R indicates a distance between an object (for example, a building or an obstacle) that scatters radio waves and the mobile terminal. If the angular dispersion α is relatively small (if it is smaller than the transmission beam width γ), the radio base station can accurately follow the mobile terminal and transmit the beam, and the mobile terminal can transmit in a certain direction. It becomes possible to receive radio waves stably. Therefore, high gain communication with less interference as described above is possible. Note that a method for measuring angular dispersion is disclosed in Non-Patent Document 2, for example.
[0009]
[Non-Patent Document 1]
H. Atarashi, S .; Abeta, M .; Sawahashi, “Broadband packet wireless access approve for high-speed and high-capacity throughput”, IEEE VTC2001-Spring, pp. 556-570, May2001
[0010]
[Non-Patent Document 2]
J. et al. Jeong, K .; Sakaguchi, J. et al. Takada, and K.K. Arai, “Performance of MUSIC and ESPRIT for joint Estimate of DOA and Angular Spread in Slow Fading Environment”, IEICE TRANS. COMMUN. , VOL. E85, NO. 5, May2002
[0011]
[Problems to be solved by the invention]
However, the angle dispersion α may be increased depending on the communication environment. In such a case, radio waves arrive at the mobile terminal from various directions, and the radio wave propagation environment for the mobile terminal is likely to change greatly, making it difficult for the radio base station to accurately follow the mobile terminal. In addition, due to the large angular dispersion α, the mobile terminal is also more likely to receive signals related to other users affected by fading different from the transmission beam for itself, and the interference signal increases. Become. For this reason, even if the transmission beam width is narrowed and a signal is transmitted to the mobile terminal, the orthogonality between the spreading codes on the receiver side deteriorates, and the desired effect as described above may not be sufficiently obtained. Concerned.
[0012]
An object of the present application is to provide a transmitter and a receiver in an MC-CDMA communication system that performs one-to-one communication between a base station and a mobile terminal using a highly directional beam pattern, and a radio wave propagation environment with a large angular dispersion. Even if it is, it is providing the transmitter and receiver which can suppress the deterioration of the orthogonality between spreading codes.
[0013]
[Means for Solving the Problems]
According to the present invention,
A transmitter for transmitting a desired signal to a receiver,
Spreading means for outputting a plurality of spread signal sequences by performing code spreading in a certain spread format for each of the parallel signal sequences including the desired signal;
An inverse Fourier transform means for performing an inverse Fourier transform on the plurality of spread signal sequences;
A transmission means for transmitting the output signal from the inverse Fourier transform means in a predetermined beam pattern;
Angular dispersion detection means for obtaining angular dispersion of radio waves arriving at the receiver;
Control means for adjusting the diffusion type based on a comparison result between the angular dispersion and the transmission beam width
And the spreading means comprises one or more frequency domain spreading means and a plurality of time domain spreading means, each of the one or more frequency domain spreading means,
Duplicating means for duplicating a signal given from one signal sequence by a first duplication number determined in the spreading format;
First output means for outputting a plurality of signals obtained by multiplying each duplicated signal by a spreading code selected in accordance with the first number of duplicates as a parallel signal sequence
Each of the plurality of time domain spreading means comprises:
Duplicating means for duplicating a signal given from one signal sequence by a second duplication number determined in the spreading format;
Second output means for outputting a plurality of signals obtained by multiplying each copied signal by a spreading code selected in accordance with the second number of copies as a serial signal sequence
Transmitter characterized by having
Is provided.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 4 shows a block of a transmitter according to the present embodiment. As illustrated, the transmitter 400 includes an encoding unit 402 that encodes binary data using techniques such as convolutional encoding and turbo encoding. The transmitter 400 includes a modulation unit 404 connected to the encoding unit 402, which converts the data sequence encoded by the encoding unit 402 into signal points in a predetermined modulation scheme such as BPSK, QPSK, and 16QAM. A series of symbol sequences is output by sequentially mapping to (symbols). The transmitter 400 includes a serial-to-parallel converter 406, which converts a series of symbol sequences into an appropriate number of parallel signal sequences (streams).
[0015]
The transmitter 400 includes a spreading unit 407 connected to a serial-to-parallel converter 406, which outputs N parallel signal sequences that are code-spread. The transmitter 400 includes a fast inverse Fourier transform unit 414 connected to each output of the spreading unit 406. The fast inverse Fourier transform unit 414 has N input points and output points corresponding to the number of subcarriers, and performs fast inverse Fourier transform on the input signal sequence. As a result, N streams in the frequency domain are converted into N time domain signals. The transmitter 400 includes a serial / parallel converter 416, which converts N streams into one stream. The transmitter 400 has a guard interval insertion unit 418, which creates a transmission data sequence by adding a guard interval for each symbol (for each OFDM effective symbol) to the output signal from the serial / parallel conversion unit 116. To do. The transmitter 400 includes, for example, Nt predetermined number of antenna elements 420, and each antenna element 420 is used to distinguish a weight setting unit 422 multiplied by a complex weight coefficient, an up converter 424 that performs frequency conversion, and a transmission / reception signal. It has a duplexer 426. Each antenna element 420 functions as an adaptive array antenna that can form a highly directional beam pattern.
[0016]
The transmitter 400 has an angle dispersion detector 428 for obtaining the angle dispersion of the incoming wave to the receiver, which estimates the angular dispersion of the incoming wave with respect to the receiver based on the upstream signal from the receiver. The transmitter 400 includes a spreading format control unit 430, which determines how to code spread a transmission signal depending on the magnitude relationship between the angular dispersion α and the transmission beam width γ, as will be described later. . The transmitter 400 has a control channel information creation unit 432 and performs processing for transmitting the contents of the spread format (control channel information) as a control signal.
[0017]
FIG. 5 shows a block diagram of the angular dispersion detector 428 of the transmitter shown in FIG. The angular dispersion detection unit 428 has a frequency conversion unit 502 connected to the duplexer 426 of the antenna element 420, which down-converts a radio frequency reception signal. The angle dispersion detection unit 428 includes a detection unit 504, which detects the angle dispersion α by a known method such as MUSIC based on the down-converted received signal (for the detection method, for example, non-patent literature). 2). The angular dispersion detection unit 428 includes a comparison / determination unit 506, which compares the detected angular dispersion α with the transmission beam width γ and outputs a comparison result. The comparison result is notified to the diffusion format control unit 430.
[0018]
FIG. 6 shows a partial block diagram of the spreading section of the transmitter shown in FIG. In general, the spreading unit 407 includes one or more frequency domain spreading units 602 and a plurality of time domain spreading units 604. One frequency domain spreading unit 602 has a first replication number SF. _f Can be output to the inverse Fourier transform unit 414. One time domain spreading unit 604 can output one signal sequence and provide it to the inverse Fourier transform unit 414. In the example shown, SF _f One frequency domain spreading section 602 for outputting a single signal sequence, SF _f A number of time domain diffusion units 604 are depicted. Each of the outputs of the one or more frequency domain spreading units 602 and the plurality of time domain spreading units 604 is supplied to the inverse Fourier transform unit 414 depending on the spreading format. Therefore, all the inputs of the inverse Fourier transform unit 414 may be given from the frequency domain spreading unit 602, and all the inputs of the inverse Fourier transform unit 414 may be given from the time domain spreading unit 604. In some cases, a part of the input of the inverse Fourier transform unit 414 is given from the frequency domain spreading unit 602 and the other is given from the time domain spreading unit 604.
[0019]
The frequency domain spreading unit 602 converts a signal given from one signal sequence into a first replication number SF. _f Duplicate only, SF _f A duplicating unit 606 that creates a plurality of parallel signal sequences is provided. First replication number SF _f Is a parameter given from the diffusion format control unit 430. The frequency domain spreading unit 602 has a spreading code multiplication unit 608 connected to the duplication unit 606, and the spreading code multiplication unit 608 applies the first duplication number SF to each duplicated signal. _f Is multiplied by the spreading code selected for the first replica number SF _f A parallel code spread signal sequence is output.
[0020]
The time domain spreading unit 604 converts the signal given from one signal sequence into the second replication number SF. _t Duplicate only, SF _t It has a duplicating unit 610 that creates a number of parallel signal sequences. Second replication number SF _t Is a parameter given from the diffusion format control unit 430. The time domain spreading unit 604 includes a spreading code multiplication unit 612 connected to the duplication unit 610, and the spreading code multiplication unit 610 adds a second duplication number SF to each duplicated signal. _t Is multiplied by the spreading code selected for the second replica number SF _t A parallel code spread signal sequence is output. The time domain spreading unit 604 includes a parallel / serial conversion unit 614, and the parallel / serial conversion unit 614 receives the second replication number SF from the spreading code multiplication unit 612. _t The parallel signal sequences are converted into one serial signal sequence.
[0021]
The operation will be described next. The operation of the transmitter 400 of FIG. 4 will be mainly described, but FIGS. 5 and 6 are referred to as necessary. First, based on the received signal (upstream signal) received by the antenna element 420, the angular dispersion detector 428 detects the angular dispersion α. In angular dispersion detector 428, angular dispersion α is detected by detector 594 based on the received signal down-converted by frequency converter 502 (FIG. 5). As a method for detecting angular dispersion, for example, a method known in the technical field such as MUSIC or ESPRIT can be used (for example, refer to Non-Patent Document 2). The detected angular dispersion α is compared by a comparison / determination unit 506 with a transmission beam width γ having a predetermined size such as 8 degrees. The comparison result is given to the diffusion format control unit 430.
[0022]
Based on the comparison result, the diffusion format control unit 430 sets a pair of parameters (SF) that are the first and second replication numbers. _f , SF _t ). These parameters are given to the diffusion unit 407. In the diffusion unit 407, the first and second replication numbers (SF _f , SF _t ) Code spreads the signal sequence. For convenience of explanation, it is assumed that the angular dispersion α is smaller than the transmission beam width γ. In this case, conventional MC-CDMA can function well. Therefore, the diffusion format control unit 430 sets the first copy number to 4 (SF _f = 4), second replication number is 1 (SF _t = 1) (or select a combination of such parameters). Further, it is assumed that the number N of input points of the inverse Fourier transform unit 414 is 64 (N = 64). In this case, M ′ = 16 symbols are input in parallel to the spreading unit 407 from the serial-to-parallel conversion unit 406, the frequency domain spreading unit 602 is connected to each symbol, and the 16 frequency domain spreading units 602 are connected. All outputs (4 × 16 = 64) are input to the inverse Fourier transform unit 414.
[0023]
For example, one symbol obtained from one output of the serial / parallel conversion unit 406 is input to the duplication unit 606, and SF _f = Replicated to 4 signal sequences. These four signal sequences are respectively multiplied by a spreading code having a length of 4 and input to the inverse Fourier transform unit 414 as four parallel signal sequences. Similar processing is performed for the other 15 frequency domain spreading sections 602. In the case of the current example, the output of any time domain spreading unit 604 is not connected to the inverse Fourier transform unit 414. Therefore, the transmitter 400 performs the same operation as the conventional transmitter 100.
[0024]
Next, it is assumed that the angular dispersion α detected by the angular dispersion detection unit 428 is larger than the transmission beam width γ. In this case, the radio wave received by the receiver comes from various directions, and can receive not only its own signal but also the signals of others. Since the other's signal is affected by fading different from that of its own signal, there is a concern that the orthogonality of the code in the frequency domain deteriorates and interference with other users increases. However, even if the communication environment in the frequency domain is not good, the communication environment on the time axis may be good. For example, the moving speed of the moving body is relatively low and the incoming wave is constant in time or the time fluctuation of the incoming wave is small. In such a case, it is more advantageous to introduce orthogonal codes between codes as a series of time-series data than to introduce spread codes as simultaneous parallel data into a transmission signal. Therefore, the diffusion format control unit 430 uses the first replication number SF. _f The second replication number SF _t Select a set of parameters with increased.
[0025]
As an extreme example for convenience of explanation, the diffusion format control unit 430 includes the first replication number SF. _f Is set to 1 (SF _f = 1), second replication number SF _t 4 (SF _t = 4). In this case, each of the 64 time-domain spreading units 604 receives one signal sequence from the serial / parallel conversion unit 406 and gives a signal of one signal sequence to the inverse Fourier transform unit 414. In the case of the current example, no frequency domain spreading unit 602 is used.
[0026]
One symbol obtained from one output of the serial-to-parallel converter 406 is input to the duplicator 610, and SF _t = Replicated to 4 signal sequences. Each of these four signal sequences is multiplied by a spreading code of length 4. Each code-spread signal is input to the parallel-serial conversion unit 614 and input to the fast inverse Fourier transform unit 414 as time-series data as one serial signal sequence. Such processing is also performed in the other 63 time domain spreading units. Note that the order of the spread code multiplying unit 612 and the parallel-serial converting unit 614 can be reversed. This is because the code-spread symbols need only be output from the time domain spreading unit 604 as a series of time-series data. Subsequent processing is transmitted to the receiving side through processing such as inverse Fourier transform, parallel-serial conversion, addition of guard intervals, and up-conversion, as in the conventional case.
[0027]
The signal multiplied by the spreading code (the output of the time domain spreading unit 604) is input to the inverse Fourier transform unit 414 as a series of time series data, and is modulated (inverse Fourier transformed). In this respect, the signal multiplied by the spreading code (the output of the frequency domain spreading unit 602) is greatly different from the conventional method in which the inverse Fourier transform unit 414 modulates the signal as simultaneous parallel data. If the fluctuation of the propagation environment on the time axis is small, code spreading using the time domain spreading unit 604 can maintain the orthogonality between codes. However, depending on the communication environment, the propagation environment may fluctuate greatly in both the frequency domain and the time domain (for example, a case where the angular dispersion is large and moves at high speed).
[0028]
On the other hand, it is necessary to notify the receiving side of the information about the spreading format determined by the spreading format control unit 430 on the transmitting side. For this reason, the control channel information creation unit 432 includes the first and second replication numbers SF. _f , SF _t Is generated as a control signal, and is given to the serial / parallel converter 406 so as to be added to the transmission signal. Further, the serial / parallel converter 406 adjusts the number M ′ of parallel signal sequences to be output in accordance with the spreading format determined by the spreading format controller 430. In the previous example, (SF _f , SF _t ) = (4,1), M ′ = 16 and (SF _f , SF _t ) = (1, 4), M ′ = 64.
[0029]
For simplicity, (SF _f , SF _t ) = (4,1), (1,4), but for example (SF _f , SF _t ) = (2, 2), these two parameters can be set to take values other than 1. More generally, the diffusion format control unit 430 can also select parameters from a list as shown in FIG. For example, when communication is performed using a set of parameters indicated by A, each parameter is set so that the value of the parameter indicated by B is adopted when the angular dispersion α is further increased. Is possible.
[0030]
FIG. 8 shows a block diagram of a receiver according to the present embodiment. As illustrated, the receiver 800 includes an antenna element 802 that receives a radio signal from a transmitter. The receiver 800 includes a guard interval removing unit 804, which removes the guard interval from the received series of symbol sequences. The receiver 800 includes a serial / parallel converter 806, which converts a series of symbol sequences into N parallel symbol sequences (streams). The receiver 800 includes a fast Fourier transform unit 808, which outputs N frequency domain signals by performing fast Fourier transform on the N time domain signals. The receiver 800 includes a despreading unit 809, which multiplies the stream from the fast Fourier transform unit 808 by a spreading code and outputs despread M ′ signal sequences.
[0031]
The receiver 800 has a parallel to serial converter 820, which converts M ′ parallel streams into serial streams. The receiver 800 includes a data demodulating unit 822, which determines signal points that symbols represent the input stream in accordance with a predetermined modulation scheme such as BPSK, QPSK, 16QAM. The receiver 800 includes a decoding unit 824 connected to the data demodulation unit 822, which decodes a signal that has been encoded such as convolutional encoding. Thereafter, further subsequent processing (not shown) is performed.
[0032]
Furthermore, the receiver 800 includes a control channel information extraction unit 826, which detects information about the spreading format (specifically, the first and second replication numbers SF) from the control signal included in the received signal. _f , SF _t ). The receiver 800 includes a spreading format control unit 828, and the spreading format control unit 828 gives an instruction to the despreading unit 809 to perform despreading in the spreading format determined by the information extracted by the control channel information extraction unit 826. .
[0033]
FIG. 9 shows a partial block diagram of despreading section 809 of the transmitter shown in FIG. The despreading unit 809 is generally formed so as to perform the reverse process of the spreading unit 407 of the transmitter 400. Accordingly, the despreading unit 809 also includes one or more frequency domain despreading units 902 and a plurality of time domain despreading units 904. One frequency domain spreading unit 902 includes a spreading code multiplication unit 906, which has a first replication number SF. _f And a first copy number SF. _f The signal of each signal sequence is despread using the spreading code selected according to the above. The receiver 902 includes a combining unit 908, which is an SF. _f One stream is output by synthesizing a plurality of streams or selecting one stream. As a result, for one frequency domain despreading unit 902, SF _f One stream is output from one input signal sequence.
[0034]
The time domain despreading unit 904 converts the signal given from one signal sequence into the second replication number SF. _t A serial-to-parallel converter 910 that converts the signal sequences into individual signal sequences is included. The time domain spreading unit 904 includes a spreading code multiplication unit 912 connected to the serial / parallel conversion unit 910, and the spreading code multiplication unit 912 adds a second replication number SF to each parallel signal. _t Is multiplied by the spreading code selected for the second replica number SF _t Output a number of parallel despread signal sequences. The time domain spreading unit 904 has a combining unit 914, which is SF _t One stream is output by synthesizing a plurality of streams or selecting one stream. As a result, one stream is output for one time-domain despreading unit 904.
[0035]
The operation will be described next. The operation of the receiver 800 of FIG. 8 will be mainly described, but FIG. 9 is also referred to when necessary. First, a signal sequence of a series of symbols is received by the antenna element 802, and a guard interval is removed from the signal sequence by a guard interval removal unit 804. This signal sequence is converted into N parallel signals by the serial / parallel conversion unit 806, and is converted to a signal for each subcarrier in the frequency domain by being fast Fourier transformed by the fast Fourier transform unit 808.
[0036]
On the other hand, the received signal includes a control signal including information related to the spreading format, and the information is extracted by the control channel information extracting unit 826 and given to the spreading format control unit 828. Based on this information, a set of two parameters (SF _f , SF _t ) Is determined. These parameters are given to the diffusion unit 809. In the diffusion unit 809, the first and second replication numbers (SF _f , SF _t ) Code spreads the signal sequence. For example, the first replication number is 4 (SF _f = 4), the second replication number is 1 (SF _t = 1). It is assumed that the number N of input / output points of the Fourier transform unit 808 is 64 (N = 64). In this case, N = 64 symbols are input in parallel to the despreading unit 809 from the fast Fourier transform unit 808, and these 64 symbols are sent to one frequency domain spreading unit 902 (FIG. 9) every four symbols. Given. That is, 64 symbols are given to 16 frequency domain spreading sections 902.
[0037]
In one frequency domain spreading unit 902, SF _f = 4 signal sequences are multiplied by a spreading code of length 4, respectively, and four despread parallel signal sequences are created and input to the synthesis unit 908. The synthesizer 908 synthesizes these four signal sequences that are substantially equal (or selects one), and provides the resulting signal to the parallel-serial converter 820. Similar processing is performed for the other 15 frequency domain spreading sections 902. In the case of the current example, the output of any time domain spreading unit 904 is not connected to the Fourier transform unit 808. Therefore, the transmitter 400 performs the same operation as the conventional transmitter 100.
[0038]
Next, the first replication number SF _f Is 1 (SF _f = 1), second replication number SF _t Is 4 (SF _t = 4). In this case, each of the 64 time-domain despreading units 904 receives one signal sequence from the fast Fourier transform unit 808 and gives a signal of one signal sequence to the parallel-serial conversion unit 820. In the case of the current example, no frequency domain spreading unit 602 is used.
[0039]
In one time domain spreading section 904, one symbol obtained from one output of the fast Fourier transform section 808 is input to the serial / parallel transform section 910, and SF _t = Converted to 4 signal sequences. Each of these four signal sequences is multiplied by a spreading code of length 4. Each signal thus despread is input to the combining unit 914, and one signal series is output. Such processing is also performed by the other 63 time domain despreading units 904. Note that the order of the spread code multiplication unit 912 and the parallel-serial conversion unit 910 can be reversed. Subsequent processing is performed in the same way as in the prior art, through further processing such as serial / parallel conversion, demodulation and decoding.
[0040]
The signal multiplied by the spreading code (input of the time domain despreading unit 904) is input to the serial / parallel conversion unit 910 as a series of time series data. In this respect, the signal multiplied by the spreading code (input of the frequency domain despreading unit 902) is greatly different from the conventional method which is input to the spreading code multiplication unit 906 as simultaneous parallel data. If the fluctuation of the propagation environment on the time axis is small, it is possible to maintain the orthogonality between codes by using the time domain spreading unit 904.
[0041]
Further, the parallel-serial conversion unit 820 adjusts the number of parallel signal sequences M ′ input in accordance with the spreading format determined by the spreading format control unit 828. In the previous example, (SF _f , SF _t ) = (4,1), M ′ = 16 and (SF _f , SF _t ) = (1, 4), M ′ = 64.
[0042]
For simplicity, (SF _f , SF _t ) = (4,1), (1,4), but for example (SF _f , SF _t ) = (2, 2), the two parameters can take values other than 1. It is possible to select parameters from the list as shown in FIG.
[0043]
As described above, according to the embodiment of the present invention, the code-spread signal input to the inverse Fourier transform unit 414 on the transmission side can be input as a simultaneous parallel signal as well as a series of time-series signals. Can also be entered. For this reason, according to the communication environment between transmitter / receiver, it becomes possible to select and use the spreading | diffusion format which maintains the orthogonality between codes | symbols suitably. For example, when the angular dispersion is larger than the transmission beam width and the time change of the communication environment between the transmitter and the receiver is relatively gradual, the signal after code spreading is subjected to inverse Fourier transform (modulation) as a time series signal. Therefore, it is possible to maintain good orthogonality between codes. Conversely, when the angular dispersion is smaller than the transmission beam width, the frequency diversity gain is increased as much as possible by inverse Fourier transforming the code-spread signal as a simultaneous parallel signal, and the original advantages of the MC-CDMA system are utilized. It becomes possible to do. Further, depending on the communication environment, the first and second replication numbers SF _f , SF _t By selecting a combination of parameters, it is possible to flexibly change an appropriate diffusion format.
[0044]
The means taught by the present invention will be enumerated below.
[0045]
(Supplementary note 1) A transmitter for transmitting a desired signal to a receiver,
Spreading means for outputting a plurality of spread signal sequences by performing code spreading in a certain spread format for each of the parallel signal sequences including the desired signal;
An inverse Fourier transform means for performing an inverse Fourier transform on the plurality of spread signal sequences;
A transmission means for transmitting the output signal from the inverse Fourier transform means in a predetermined beam pattern;
Angular dispersion detection means for obtaining angular dispersion of radio waves arriving at the receiver;
Control means for adjusting the diffusion type based on a comparison result between the angular dispersion and the transmission beam width
And the spreading means comprises one or more frequency domain spreading means and a plurality of time domain spreading means, each of the one or more frequency domain spreading means,
Duplicating means for duplicating a signal given from one signal sequence by a first duplication number determined in the spreading format;
First output means for outputting a plurality of signals obtained by multiplying each duplicated signal by a spreading code selected in accordance with the first number of duplicates as a parallel signal sequence
Each of the plurality of time domain spreading means comprises:
Duplicating means for duplicating a signal given from one signal sequence by a second duplication number determined in the spreading format;
Second output means for outputting a plurality of signals obtained by multiplying each copied signal by a spreading code selected in accordance with the second number of copies as a serial signal sequence
A transmitter characterized by comprising:
[0046]
(Supplementary Note 2) When the control means determines that the angular dispersion is larger than the transmission beam width, the control means is configured to decrease the first replication number and increase the second replication number. The transmitter according to appendix 1, wherein:
[0047]
(Supplementary Note 3) When the control means determines that the angular dispersion is smaller than the transmission beam width, the control means is configured to increase the first replica number and decrease the second replica number. The transmitter according to appendix 1, wherein:
[0048]
(Supplementary note 4) The transmitter according to supplementary note 1, wherein the number of parallel signal sequences input to the spreading means is adjusted by the control means depending on the spreading format.
[0049]
(Additional remark 5) Furthermore, it has the preparation means which produces the control channel containing the information regarding the said 1st and 2nd replication number so that the information regarding the said spreading | diffusion format may be notified to a receiver via a control channel, It is characterized by the above-mentioned. The transmitter according to appendix 1.
[0050]
(Supplementary Note 6) Each of the plurality of time domain diffusion means includes:
Duplicating means for duplicating a signal given from one signal sequence by a second duplication number determined in the spreading format;
Spreading code multiplication means for multiplying each duplicated signal by a spreading code selected according to the second number of copies;
Parallel-serial conversion means for converting parallel signal sequences from the spreading code multiplier into one signal sequence
The transmitter according to appendix 1, characterized by comprising:
[0051]
(Supplementary Note 7) Each of the plurality of time domain diffusion means includes:
Duplicating means for duplicating a signal given from one signal sequence by a second duplication number determined in the spreading format;
Parallel-serial conversion means for converting parallel signal sequences from the replicating means into one signal series;
Spreading code multiplying means for outputting one spread signal sequence by sequentially multiplying the one signal sequence by a spreading code selected in accordance with the second number of copies.
The transmitter according to appendix 1, characterized by comprising:
[0052]
(Appendix 8) A receiver for receiving a signal from a transmitter,
A Fourier transform unit that performs Fourier transform on a parallel signal sequence of received signals, and a plurality of despreads by performing despreading in a predetermined diffusion format on each of the parallel signal sequences from the Fourier transform unit Despreading means for outputting a signal sequence;
Control means for extracting control channel information contained in the received signal and discriminating first and second replica numbers defining the content of the predetermined spreading format
The despreading means includes one or more frequency domain despreading means and a plurality of time domain despreading means, and each of the one or more frequency domain despreading means includes:
First output means for despreading each signal provided from the signal sequence of the first number of replicas by multiplying the signal by a spreading code selected according to the first number of replicas and outputting one signal sequence
Each of the plurality of time domain spreading means comprises:
Serial-to-parallel conversion means for converting a signal given from one signal sequence to the second replica number of parallel signal sequences;
Second output means for despreading each signal of the parallel signal series by a spreading code selected in accordance with the second number of replicas and outputting one signal series
A receiver comprising:
[0053]
【The invention's effect】
As described above, according to the present invention, in an MC-CDMA communication system in which one-to-one communication is performed between a base station and a mobile terminal using a highly directional beam pattern, a radio wave propagation environment with a large angular dispersion is used. Even so, it is possible to suppress the deterioration of the orthogonality between the spreading codes.
[0054]
[Brief description of the drawings]
FIG. 1 shows a block diagram of a transmitter in an MC-CDMA communication system.
FIG. 2 shows a block diagram of a receiver in an MC-CDMA communication system.
FIG. 3 is a diagram showing the relationship between angular dispersion, angle of arrival and transmit beam width.
FIG. 4 shows a block of a transmitter according to an embodiment of the present application.
FIG. 5 shows a block diagram of an angular dispersion detector of the transmitter shown in FIG.
FIG. 6 shows a partial block diagram of a spreading unit of the transmitter shown in FIG. 4;
FIG. 7 is a conceptual diagram of a list for setting the first and second replication numbers.
FIG. 8 shows a block diagram of a receiver according to an embodiment of the present application.
FIG. 9 shows a block diagram of a despreading section of the transmitter shown in FIG.
[Explanation of symbols]
100 transmitter
102 Encoding unit
104 Modulator
106 Serial-to-parallel converter
107 Diffusion part
108 Duplicator
110 Multiplier
112 Spreading code generator
114 Fast inverse Fourier transform
116 Parallel to serial converter
118 Guard interval insertion part
120 Antenna element
122 Weight setting section
200 receiver
202 Antenna element
204 Guard interval remover
206 Series-to-parallel converter
208 Fast Fourier Transform
210 Multiplier
212 Despread code generator
214 Channel Estimator
216 channel compensator
218 synthesis unit
220 Parallel to serial converter
222 Demodulator
224 decryption unit
400 transmitter
402 Encoding unit
404 Modulator
406 Series-parallel converter
407 Diffusion part
108 Duplicator
414 Fast inverse Fourier transform unit
416 Parallel to serial converter
418 Guard interval insertion part
420 Antenna element
422 Weight setting part
424 Frequency converter
426 Duplexer
428 Angular dispersion detector
430 Diffusion format control unit
432 Control channel information creation unit
502 Frequency converter
504 detector
506 Comparison judgment unit
602 Frequency domain spreader
604 Time domain diffusion
606 Duplicator
608 Spreading code multiplier
610 Duplicator
612 Spreading Code Multiplication Unit
614 Parallel-serial converter
800 receiver
802 Antenna element
804 Guard interval remover
806 Series-parallel converter
808 Fast Fourier Transform
809 Despreading part
820 Parallel to serial converter
822 Demodulator
824 decryption unit
826 Control channel information extraction unit
828 Diffusion format control unit
902 Frequency domain despreading unit
904 Time domain despreading section
906 Spreading code multiplier
908 synthesis unit
910 Series-parallel converter
912 Spreading code multiplier
914 synthesis unit

Claims (5)

A transmitter for transmitting a desired signal to a receiver,
Spreading means for outputting a plurality of spread signal sequences by performing code spreading in a certain spread format for each of the parallel signal sequences including the desired signal;
An inverse Fourier transform means for performing an inverse Fourier transform on the plurality of spread signal sequences;
A transmission means for transmitting the output signal from the inverse Fourier transform means in a predetermined beam pattern;
Angular dispersion detection means for obtaining angular dispersion of radio waves arriving at the receiver;
Control means for adjusting the spreading format based on the comparison result between the angular dispersion and the transmission beam width, and the spreading means has one or more frequency domain spreading means and a plurality of time domain spreading means. And each of the one or more frequency domain spreading means comprises:
Duplicating means for duplicating a signal given from one signal sequence by a first duplication number determined in the spreading format;
First output means for outputting a plurality of signals obtained by multiplying each copied signal by a spreading code selected in accordance with the first number of copies as a parallel signal sequence; Each of the time domain spreading means
Duplicating means for duplicating a signal given from one signal sequence by a second duplication number determined in the spreading format;
And a second output means for outputting a plurality of signals obtained by multiplying each duplicated signal by a spreading code selected in accordance with the second number of replicas as a serial signal sequence. Transmitter.   When the control means determines that the angular dispersion is greater than the transmit beam width, the control means is configured to decrease the first replica number and increase the second replica number. The transmitter according to claim 1.   When the control means determines that the angular dispersion is smaller than the transmission beam width, the control means is configured to increase the first replication number and decrease the second replication number. The transmitter according to claim 1.   2. The information processing apparatus according to claim 1, further comprising creation means for creating a control channel including information on the first and second replication numbers so that information on the spreading format is notified to a receiver through the control channel. Transmitter. A receiver for receiving a signal from a transmitter,
Fourier transform means for performing Fourier transform on a parallel signal sequence composed of received signals;
Despreading means for outputting a plurality of despread signal sequences by performing despreading in a predetermined spreading format for each of the parallel signal sequences from the Fourier transform means;
The included in the received signal, based on the angle variance estimates and the transmitted beam width as comparison information diffusion form the transmitter is adjusted according to of about the received signal, the first and determining the spreading format Control means for discriminating a second number of replicas, wherein the despreading means has one or more frequency domain despreading means and a plurality of time domain despreading means, and the one or more frequency domain despreading means Each of
First output means for despreading each signal given from the signal sequence of the first replica number by a spreading code selected according to the first replica number and outputting one signal sequence; have, each of the plurality of time-domain despreading means,
Serial-to-parallel conversion means for converting a signal given from one signal sequence to the second replica number of parallel signal sequences;
A second output means for despreading each signal of the parallel signal series by a spreading code selected in accordance with the second number of replicas and outputting a serial signal series; Receiving machine.

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