JP4245305B2 - Synchronization method, transmitter and receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a synchronization method, a transmitter, and a receiver in mobile communication using multicarrier CDMA.
[0002]
[Prior art]
In high-speed mobile communication, a multicarrier transmission system is known as a transmission system for improving frequency selective fading. In the multicarrier transmission scheme, a plurality of narrowband subcarriers are arranged in parallel, and transmission data is divided and transmitted using each subcarrier. By preparing a plurality of narrow-band carriers in this way, a transmission system with strong fading resistance can be obtained even in a selective fading environment. As this multicarrier transmission system, an orthogonal frequency division multiplexing (OFDM) system is known. In this OFDM system, a plurality of subcarriers orthogonal to each other are used.
[0003]
In addition, a multi-carrier CDMA (MC-CDMA) system in which a code division multiple access (CDMA) is combined with a multi-carrier transmission system is known as a system that applies the multi-carrier transmission system. The MC-CDMA system is a system that assigns a spreading code chip to each subcarrier and spreads it on the frequency axis, a system that assigns a spreading code to consecutive symbols of one subcarrier and spreads it on the time axis, A method combining the above has been studied.
[0004]
[Problems to be solved by the invention]
By the way, in mobile communication, control information necessary for mobile station cell search, incoming call control, outgoing call control, handover, etc. is exchanged using a control channel, and voice and data communication between the mobile station and the base station is performed. This is done using a communication channel. When communication is performed between a mobile station and a base station, the mobile station obtains information on a base station or the like that is in the area from control data received through a control channel. Therefore, the mobile station establishes synchronization of the communication channel transmitted from the base station and communicates with the base station. That is, there is a problem that communication channel synchronization must be established at the start of communication, and communication cannot be performed until synchronization is established. In order to establish synchronization of the communication channel, a start bit is inserted at the head of the frame in the communication channel as shown in FIG. In the example shown in FIG. 5, an example in which the start bit is 3 bits and the short code length unique to the control channel and the communication channel is 5 is shown. Thus, when the start symbol S is inserted before the communication data symbol D, there is a problem that the transmission efficiency is lowered by the start symbol S.
[0005]
Therefore, an object of the present invention is to provide a synchronization method, a transmitter, and a receiver that do not require establishment of communication channel synchronization at the start of communication and that do not reduce transmission efficiency due to synchronization.
[0006]
[Means for Solving the Problems]
[0007]
In order to achieve the above object, the synchronization method of the present invention is a multi-channel communication system in which a plurality of control channel subcarriers used in a control channel and a plurality of communication channel subcarriers used in a communication channel are separated and set exclusively. A synchronization method in carrier CDMA, wherein the communication channel frame is transmitted at a timing offset from the control channel frame timing by a predetermined time, and the communication channel frame is offset. Transmitting the control channel including difference information indicating time and synchronization information for establishing synchronization, and synchronizing the control channel using the synchronization information included in the received control channel Frame timing of the control channel with which synchronization is established Information, using the frame timing information offset based on the difference information that is included in the received control channel, and to perform frame synchronization of the received the communication channel. Furthermore, in the synchronization method of the present invention, the frame of the control channel and the communication channel is configured to have a common multiple of the spreading length of the control channel and the spreading length of the communication channel, and the start timing of the frame May be the frame timing.
[0009]
Also, the transmitter of the present invention that can achieve the above-described object is configured to separate a plurality of control channel subcarriers used in the control channel and a plurality of communication channel subcarriers used in the communication channel. Communication channel means for synchronizing the frame of the communication channel and transmitting the communication channel at a timing offset from the frame timing of the control channel by a certain time, and the communication channel comprises: A transmission unit including control channel means for transmitting the control channel including difference information indicating the offset time and synchronization information for establishing synchronization is provided. Further, in the transmitter of the present invention, the frame of the control channel and the communication channel is configured to have a common multiple of the spreading length of the control channel and the spreading length of the communication channel, and the start timing of the frame May be the frame timing.
[0011]
Further, the receiver of the present invention capable of achieving the above object is configured by separating a plurality of control channel subcarriers used in the control channel and a plurality of communication channel subcarriers used in the communication channel. The multi-carrier CDMA receiver establishes synchronization of the control channel using synchronization information included in the received control channel, and determines the communication channel from the frame timing of the control channel. The control channel receives difference information indicating the time when the frame timing is offset, and notifies the communication channel of the frame timing information of the control channel with which synchronization is established by offsetting based on the difference information. Control channel means and before notified from the control channel means Based on the frame timing information, the receiving unit comprising a communication channel means for performing frame synchronization of the received the communication channel is provided.
Further, in the receiver of the present invention, the frame of the control channel and the communication channel is configured to be a common multiple of the spreading length of the control channel and the spreading length of the communication channel, and the frame timing information is The start timing of the frame may be set.
[0012]
According to the present invention as described above, frame synchronization of the communication channel can be performed using the synchronization timing information of the control channel in which synchronization is established. This eliminates the need to establish communication channel synchronization at the start of communication. Further, since information for establishing synchronization such as a start bit can be made unnecessary in the communication channel, it is possible to prevent transmission efficiency from being lowered due to synchronization. Further, by offsetting the frame timing of the communication channel from the frame timing of the control channel, the frame of the communication channel can be transmitted at an arbitrary timing.
[0013]
In addition, the following effects can be obtained by separating and setting the subcarriers used in the control channel and the subcarriers used in the communication channel. In multicarrier CDMA, when a subcarrier used in a control channel and a subcarrier used in a communication channel are used in common, the control channel and the communication channel are determined by different long codes assigned to each base station. Diffused. Therefore, in order to establish synchronization in the control channel, it is necessary to identify the subcarrier used by the control channel and the long code. In order to search for this subcarrier and long code, it is necessary to perform signal processing on all subcarriers, and the signal processing becomes enormous. Therefore, if the subcarriers used in the control channel and the subcarriers used in the communication channel are separated and set as dedicated, it is not necessary to spread the control channel subcarriers with a long code. Therefore, it is possible to easily establish synchronization of the control channel by performing signal processing only on the subcarrier for the control channel.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the configuration of a transmitter according to an embodiment of the present invention to which the synchronization method of the present invention is applied.
In the transmitter 1 shown in FIG. 1, control data is input to the control channel unit 10, and a start bit is added at the start bit adding unit 11 in front of the control data for each frame period. The control data to which the start bit output from the start bit adding unit 11 is added in advance is modulated by the modulation unit 12 such as QPSK modulation, and the modulation symbol is an IFFT (Inverse Fast Fourier Transform) unit. 30. In the IFFT unit 30, the modulation symbol is subjected to inverse fast Fourier transform, and the signal on the frequency axis is converted into a signal on the time axis. That is, the modulation symbol is multiplied by a subcarrier dedicated to the control channel and added to a subcarrier for a communication channel described later. Note that the control channel unit 10 may directly spread the control data so as to be spread on the time axis by a short code unique to the control channel.
[0015]
Further, the communication data is input to the communication channel unit 20, and the modulation unit 21 performs modulation such as QPSK modulation on the communication data. Further, the serial / parallel converter (S / P) 22 performs parallel conversion every predetermined number of modulation symbols. Next, in the spreading unit 23, the modulation symbol output from the S / P 22 is spread with a short code specific to the communication channel and a long code specific to the base station. Thereafter, the timing control unit 24 synchronizes the frame in the spread symbol with the frame of the control channel in the control channel unit 10. The spread symbols for each subcarrier output from the timing control unit 24 are input to the IFFT 30 and subjected to inverse fast Fourier transform, whereby a signal on the frequency axis is converted into a signal on the time axis. That is, each chip for each subcarrier is multiplied by a subcarrier orthogonal to each other, and the subcarriers are added. However, the subcarrier multiplied by the parallel output output from the communication channel unit 20 is a subcarrier dedicated to the communication channel separated for the communication channel, and when added, the subcarrier dedicated to the control channel is also added. Will come to be. The output of the IFFT unit 30 is transmitted from the antenna 31. Thus, in the communication channel unit 20, the communication data is spread on the frequency axis by the short code.
[0016]
Here, FIG. 3 shows a configuration example of a control channel subcarrier and a communication channel subcarrier.
As shown in FIG. 3, the subcarrier for the control channel and the subcarrier for the communication channel are subcarriers arranged orthogonally and set separately. When the total number of control channel subcarriers and communication channel subcarriers is M, the number of control channel subcarriers is N, and the remaining number of subcarriers S (= MN) is the communication channel subcarrier. It is considered as a subcarrier. Each subcarrier is a dedicated subcarrier for each channel, a subcarrier for the control channel is used only for the control channel, and a subcarrier for the communication channel is used only for the communication channel. The total number M of subcarriers is actually considered to be on the order of 1000 to 2000. In this case, the number N of subcarriers for the control channel is several tens, and the number of remaining subcarriers is the number for the communication channel. It is considered as a subcarrier.
[0017]
For example, as shown in FIG. 3, when four subcarriers f1, f2, f3, and f4 are subcarriers for the control channel, each substation of f1, f2, f3, and f4 is assigned to each base station in the mobile communication network. Each carrier is assigned. In this case, subcarriers having the same frequency are not assigned to at least adjacent base stations. Then, the assigned subcarrier is multiplied by the modulation symbol of the control channel in IFFT section 30. In addition, when the number of subcarriers fa, fb, fc, fd, fe,... Fk is 50, for example, and this subcarrier is a subcarrier for a communication channel, the spreading length in the spreading unit 23 is set. For example, if 5 is assumed, in S / P22, every 10 modulation symbols (10 modulation symbols × 5 chips = 50) are converted in parallel, and 50 chips are respectively multiplied by 50 subcarriers of fa to fk in IFFT section 30. It becomes like this. Then, the assigned subcarriers f1 to f4 and 50 subcarriers fa to fk are added in the IFFT unit 30 and transmitted from the antenna 31.
[0018]
In the transmitter 1, the spreading code chip is arranged on the frequency axis and spread on the frequency axis. Instead, the spreading code is arranged on the time axis and the time axis is arranged. It may be diffused upward. In the transmitter 1 described above, for the sake of convenience, the timing control unit 24 has described the case where the start timing of the frame of the communication channel is synchronized with the start timing of the frame of the control channel, but in the present invention, The communication channel frame start timing is synchronized with a predetermined time offset from the control channel frame start timing. As a result, the frame of the communication channel can be transmitted at an arbitrary timing. When the frame start timing of the communication channel is offset by a certain time, difference information corresponding to the offset time is transmitted in the control channel. Thus, and establishes synchronization by offsetting the synchronization timing in the present invention.
[0019]
Next, FIG. 2 shows the configuration of a receiver according to an embodiment of the present invention to which the synchronization method of the present invention is applied.
In the receiver 100 shown in FIG. 2, the received MC-CDMA signal is separated into control channel subcarriers and communication channel subcarriers by means such as a filter. The extracted control channel subcarriers are supplied to the control channel unit 50 and demodulated into control data by the control channel demodulation unit 51. Next, the frame synchronization unit 52 establishes frame synchronization by the start bit added to the control data. The start bit is, for example, a plurality of bits such as all “1”. The frame synchronization unit 52 outputs control data from which the start bit is removed. When the control data is spread with a short code specific to the control channel, the control channel unit 50 may despread with the short code specific to the control channel.
[0020]
Further, the subcarrier for the communication channel is supplied to the communication channel unit 60, and a fast Fourier transform is performed in an FFT (Fast Fourier Transform) unit 61 to convert a signal on the time axis into a signal on the frequency axis. That is, a parallel signal for each subcarrier component for the communication channel is output from the FFT unit 61, and this parallel signal is input to the despreading unit 62. The despreading unit 62 is notified of the start timing information of the frame that has been established from the frame synchronization unit 52 in the control channel unit 50. Therefore, the despreading unit 62 performs despreading of the parallel signals input by the parallel short code and long code based on the frame start timing information. The despread parallel symbols are converted into serial symbols by a parallel / serial converter (P / S) 63 and input to a demodulator 64. Then, demodulation such as QPSK demodulation is performed in the demodulation unit 64, and demodulated communication data is output.
[0021]
As described above, the receiver 100 decodes the communication channel in synchronization with the control channel frame. In this case, in the transmitter 1, when the frame start timing of the communication channel and the frame start timing of the control channel are the same, the frame start timing of the communication channel is matched with the frame start timing of the control channel. The communication channel is decoded. Also, in the transmitter 1, when the frame start timing of the communication channel is offset by a certain time with respect to the frame start timing of the control channel, the frame start timing of the control channel based on the difference information notified by the control channel The communication channel is decoded at the frame start timing of the communication channel that is offset by a certain time.
[0022]
Here, the frames of the control channel and the communication channel will be described with reference to FIG.
As shown in FIG. 4, the control channel is spread by a short code unique to the control channel, and the spreading length is, for example, 3 (the number of short code chips is 3). The communication channel is spread by a short code unique to the communication channel, and the spread length is, for example, 5 (the number of short code chips is 5). In order to make the frame length of the control channel and the frame length of the communication channel the same, the length of one frame is a common multiple of the spreading length of the control channel and the spreading length of the communication channel. In the case shown in FIG. 4, the length of one frame is “15” (number of chips is 15). In the control channel, five control symbols are included in one frame, and in the communication channel, three communication symbols are included in one frame. Will be.
[0023]
In the control channel, the start bit is added as described above, but in the case shown in FIG. 4, the start bit added for each frame is 3 bits, and each is spread to the spreading length “3”. It becomes the start symbol S of 3 symbols. Following this start symbol, two control data symbols D spread to a spreading length of “3” follow. Further, in the communication channel, one frame is composed of communication data symbols after spreading having a spreading length of “5” of 3 symbols. In the transmitter 1, for example, as shown in FIG. 4, the timing control unit 24 performs timing control so that the start timing of each frame of the control channel matches the start timing of the frame of the communication channel, and the communication channel is transmitted. Will come to be. Further, in the receiver 100, the start timing information of each frame of the control channel with which synchronization is established is notified from the frame synchronization unit 52 to the despreading unit 62, so that the frame of the control channel is displayed as shown in FIG. The communication channel frames are synchronized.
[0024]
As described above, in the receiver according to the present invention, frame synchronization of the communication channel is performed using the synchronization timing information of the control channel in which synchronization is established. This eliminates the need to establish communication channel synchronization at the start of communication. Further, since information for establishing synchronization such as a start bit can be made unnecessary in the communication channel, it is possible to prevent transmission efficiency from being lowered due to synchronization. In addition, if the receiver is notified of the long code information spreading the communication channel by the control data, it is not necessary to search for the long code in the receiver, and the signal processing amount for that purpose is greatly reduced. be able to.
[0025]
Here, as shown in FIG. 3, the subcarrier for the control channel and the subcarrier for the communication channel are subcarriers that are orthogonally arranged and set separately, and each subcarrier is a respective one. It is a channel dedicated subcarrier. The reason will be described next.
In MC-CDMA, a plurality of communication channels are set, and each communication channel is spread with a unique short code. However, since the number of short codes in an orthogonal relationship is limited, by assigning a unique long code to each base station and spreading the short code and the assigned long code, the same short code can be transmitted to each base station. It can be used.
[0026]
Then, in MC-CDMA, when the subcarrier used in the control channel and the subcarrier used in the communication channel are set in common, the control channel and the communication channel are spread with the short code and the long code. become. Therefore, in order to establish synchronization in the control channel, it is necessary to identify the subcarriers used by the control channel and the spread long code. In order to search for this subcarrier and long code, it is necessary to perform signal processing for all subcarriers, and the amount of signal processing is enormous.
[0027]
Therefore, if the subcarrier used in the control channel and the subcarrier used in the communication channel are separated and set as dedicated subcarriers, only the subcarrier for the control channel in the received signal can be extracted. become. For this reason, it becomes possible to perform signal processing of only the subcarriers for the control channel, and synchronization of the control channel can be established with a small amount of signal processing. In this case, even if the control channel is spread with a short code specific to the control channel, the number of control channels is much smaller than the number of communication channels, so the amount of signal processing is very small. Thus, synchronization of the control channel can be easily established. For this reason, in the present invention, the subcarrier for the control channel and the subcarrier for the communication channel are separated and set exclusively.
[0028]
In the above description, the number of control channel subcarriers is four, f1 to f4. However, the present invention is not limited to this, and an arbitrary number of control channel subcarriers can be set exclusively. Further, although the spreading code length for the control channel is set to 3, the present invention is not limited to this, and any spreading code length can be used. Furthermore, when a plurality of control channels are required for each base station, a plurality of control channel subcarriers may be assigned to each base pole, and the control channels of the transmitter and receiver may be a plurality of channels. Furthermore, although the spreading code length for the communication channel is set to 5, the present invention is not limited to this and can be set to an arbitrary spreading code length. Here, when the spreading code length for the control channel and the spreading code length for the communication channel are changed, the frame length becomes a frame length that is a common multiple of the spreading code length for the control channel and the spreading code length for the communication channel. Change as follows.
The transmitter according to the present invention can be applied to a transmission unit of a base station in a mobile communication network, and the receiver according to the present invention can be applied to a mobile station in a mobile communication network.
[0029]
【The invention's effect】
As described above, according to the present invention, frame synchronization of a communication channel can be performed using synchronization timing information of a control channel in which synchronization is established. This eliminates the need to establish communication channel synchronization at the start of communication. Further, since information for establishing synchronization such as a start bit can be made unnecessary in the communication channel, it is possible to prevent transmission efficiency from being lowered due to synchronization.
In addition, by separating the subcarriers used in the control channel and the subcarriers used in the communication channel and setting them exclusively, signal processing can be performed by extracting only the subcarriers for the control channel. Control channel synchronization can be easily established.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a transmitter according to an embodiment of the present invention to which a synchronization method of the present invention is applied.
FIG. 2 is a diagram showing a configuration of a receiver according to an embodiment of the present invention to which the synchronization method of the present invention is applied.
FIG. 3 is a diagram illustrating a configuration example of a control channel subcarrier and a communication channel subcarrier in the transmitter and the receiver according to the embodiment of the present invention;
FIG. 4 is a diagram showing a relationship between frames in a control channel and a communication channel in the transmitter and the receiver according to the embodiment of the present invention.
FIG. 5 is a diagram illustrating a configuration example of a communication channel in a conventional MC-CDMA system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Transmitter, 10 Control channel part, 11 Start bit addition part, 12 Modulation part, 20 Communication channel part, 21 Modulation part, 22 Serial / parallel conversion part, 23 Spreading part, 24 Timing control part, 30 IFFT part, 31 Antenna , 50 control channel unit, 51 control channel demodulation unit, 52 frame synchronization unit, 60 communication channel unit, 61 FFT unit, 62 despreading unit, 63 parallel / serial conversion unit, 64 demodulation unit, 100 receiver

Claims (6)

  A synchronization method in multi-carrier CDMA in which a plurality of control channel subcarriers used in a control channel and a plurality of communication channel subcarriers used in a communication channel are separated and set exclusively, the frame of the control channel Synchronize the frame of the communication channel with the timing offset by a certain time from the timing to transmit the communication channel, and the difference information indicating the time when the frame of the communication channel is offset, and synchronization for establishing synchronization Transmitting the control channel including information, establishing synchronization of the control channel using the synchronization information included in the received control channel, and Frame timing information is included in the received control channel. Using said frame timing information offset based on the difference information, the synchronization method being characterized in that to perform the frame synchronization of the received the communication channel are. The frame of the control channel and the communication channel is configured to be a common multiple of the spreading length of the control channel and the spreading length of the communication channel, and the start timing of the frame is the frame timing. The synchronization method according to claim 1 , wherein: A transmitter in multi-carrier CDMA in which a plurality of control channel subcarriers used in a control channel and a plurality of communication channel subcarriers used in a communication channel are separated and set exclusively, the frame of the control channel Communication channel means for synchronizing the frame of the communication channel and transmitting the communication channel at a timing offset by a certain time from the timing; difference information indicating a time when the communication channel is offset; and for establishing synchronization A transmitter comprising: a control channel means for transmitting the control channel including synchronization information. The frame of the control channel and the communication channel is configured to be a common multiple of the spreading length of the control channel and the spreading length of the communication channel, and the start timing of the frame is the frame timing. The transmitter according to claim 3 . A receiver in multicarrier CDMA in which a plurality of control channel subcarriers used in a control channel and a plurality of communication channel subcarriers used in a communication channel are separated and set exclusively, and the received control The synchronization information included in the channel is used to establish the synchronization of the control channel, and difference information indicating the time when the frame timing of the communication channel is offset from the frame timing of the control channel is determined by the control channel. Control channel means that receives and offsets the frame timing information of the control channel with which synchronization is established based on the difference information, and the frame timing information notified from the control channel means Based on the received communication Receiver, characterized in that the communication channel means for performing frame synchronization Yaneru, receiving unit consisting of are provided. The frames of the control channel and the communication channel are configured to be a common multiple of the spreading length of the control channel and the spreading length of the communication channel, and the frame timing information is set as the start timing of the frame. The receiver according to claim 5 .

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