JP2007028289A - Mobile communication system and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile communication system and a communication method which use a multicarrier communication system and are capable of using frequency bands which are divided or kept discontinuous. <P>SOLUTION: The subcarriers of scrambling codes are successively assigned to the boundaries of a frame configuration. Each subcarrier is multiplied by a chip code which is previously determined from a long series of codes. Chips corresponding to the unused subcarriers are set up among channel chips so as to fill up a spectrum mask. Chips corresponding to the unused sub-carriers are set up because channels are used in a manner in which channels #1 and #2 are combined into one channel of a wider bandwidth in the operation of a system, and chips corresponding to all the sub-carriers are prepared taking it into consideration that the unused subcarriers between the channels #1 and #2 are used as subcarriers for transferring data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a mobile communication system using a multicarrier communication system, and more particularly to a spread code allocation technique and a cell search technique.

  Currently, the mainstream mobile communication system in practical use is the wideband direct sequence code division multiple access (W-CDMA) communication system. In the W-CDMA communication system, the chip speed is set to 3.84 MHz, and high-speed wireless communication can be performed by performing wideband spreading compared to the conventional technology. The W-CDMA communication system is a communication system that uses the same frequency band in each base station, which is called a 1-cell repetitive communication system.

  In the 1-cell repetitive communication method, since the same frequency band is used in all cells, interference occurs due to signals from adjacent cells near the cell edge. In the W-CDMA communication method described above, the signal is spread by cell-specific spreading. A technique for preventing interference by performing spreading processing with codes has been introduced. Furthermore, spreading by orthogonal codes is used to multiplex signals to a plurality of mobile stations in the same cell.

  In general, there are two types of spreading codes used for spreading, which are called a long code and a short code, respectively. The long code is also called a scrambling code and is used for identifying different mobile stations in the uplink and for identifying different cells in the downlink. The short code is also called a channelization code, and is a code for multiplexing a plurality of channels without mutual interference, and uses a different code for each channel. Thereby, a plurality of channels can be simultaneously used in the same frequency band. Used in uplink wireless communication (uplink) to identify multiple channels used by one mobile station. In downlink wireless communication (downlink), it differs for most channels except some channels. A sign is used.

  The above-mentioned scrambling code is used by cutting out 38400 chips from a very long code sequence in the W-CDMA communication system, so that a very large number of codes can be secured. It is possible to use a different code for each. Generally, 224 scrambling codes are used for the uplink and 512 scrambling codes for the downlink.

  Recently, with the demand for an increase in the amount of information and an increase in information rate, development of a broadband wireless access scheme whose bandwidth is close to 100 MHz in the downlink is underway. This method is a communication method (multicarrier communication method) for performing broadband and high-speed wireless communication by spreading a plurality of subcarriers (multicarrier). This multi-carrier communication system is capable of 1-cell repetitive communication similar to the above-described W-CDMA communication system, multiplying each subcarrier by a scramble code and a short code, and multiplexing a plurality of data channels in the same frequency band, A wireless communication system that suppresses interference from other cells is realized. In this method, one of a use method of a usable spreading code and a cell search method is proposed in Non-Patent Document 1 below. In this proposed scheme, two types of codes used for spreading are used for cell recognition and channel identification, respectively, as in the above-described W-CDMA communication scheme.

  In addition, regarding the cell search method using the code, a cell search pilot channel is set at the beginning and end of the frame, which is the minimum unit of wireless communication data, and the cross-correlation between them is used to determine the start position of the frame. Techniques for identifying and simultaneously determining scramble code groups are shown.

The outline of the technique described in the above non-patent document will be described. As a frame configuration, a common pilot channel for one OFDM symbol is arranged at the beginning and end of the frame, channel identification is performed by direct coding, and cell recognition is performed by scrambling code. In the scrambling method, scrambling code = number of subcarriers, code phase shift of 1 symbol is performed at the frame boundary, and phase shift of 8 symbols is performed in other areas. In the first step, cell search is performed by performing symbol synchronization based on the correlation characteristics of a guard interval (hereinafter referred to as “GI”). In the second step, frame synchronization / CSSC group identification, that is, correlation detection is performed for the preceding and succeeding symbols by using CPICH with continuous frame boundaries and erasing the scrambled shift portion for a period of one frame or more. Do. More specifically, the pilot channel at the beginning of the frame and the pilot channel at the end of the frame are shifted by one chip and multiplied, and at this time, the complex conjugate of the pilot channel chip at the beginning of the frame is multiplied. At this time, since C _ki remains at the frame boundary, the correlation value becomes high. In the third step, CSSC identification is performed. That is, the maximum correlation value is obtained by using the fact that correlation with the CPICH is performed for all CSCCs in the CSCC group at the frame timing detected in the second step, and the correlation of the pilot channel is increased when there is a scramble code. A CSCC is provisionally determined and the detected CSCC is confirmed (verified).
IEICE technical report RCS2004-11 April 2004, “In-house experimental results of a three-stage cell search method using a common pilot channel in downlink VSF-OFCDM broadband wireless access”

  Currently, the above-mentioned high-speed wireless communication system with 100 MHz bandwidth has not started international standardization activities to determine the details of the communication system, and there are many undecided parts such as the frequency band used. In addition, there is a situation where the frequency band that can use the bandwidth of 100 MHz differs depending on the country, or the usable band cannot be secured at present.

  Therefore, in the high-speed wireless communication using the above-mentioned bandwidth of 100 MHz, in a region where the 100 MHz band cannot be secured, the frequency band used by other wireless systems can be used by the high-speed wireless communication method of the 100 MHz bandwidth. The frequency band of the system is moved step by step so that a new system is introduced step by step from the vacant frequency band, the system is operated with a bandwidth of 100 MHz or less, or a discontinuous band is set. Deployment of the system used is expected.

  However, in the cell search method proposed in the VSF-OFCDM communication method described above, a code sequence having the same number of chips as the number of subcarriers is used as a scramble code and is used as a code for identifying a cell. Therefore, it is difficult to deal with flexible bandwidth changes and securing a sufficient scramble code sequence when the number of subcarriers is small. That is, when the bandwidth becomes narrower, the number of scrambling code sequences that can be secured decreases as the number of scrambling code chips depending on the number of subcarriers decreases. There arises a problem that a scrambling code having similar characteristics is assigned to an adjacent cell.

  In addition, there is a case where it is necessary to consider the case where the bandwidth is divided and used, and further, no consideration is given regarding the case where a terminal that cannot use the entire frequency band (for example, a terminal of 5 MHz band) is used.

  An object of the present invention is to use a multi-carrier communication system so that a band can be used as a divided or discontinuous band. It is another object of the present invention to introduce a system step by step into a frequency band that uses the same frequency band as other communication systems. Furthermore, a spreading code assignment method, cell search method, signal transmission method, signal reception method, transmission in a mobile communication system that can flexibly establish synchronization with a base station even when the used frequency bandwidth is changed An object is to provide an apparatus and a receiving apparatus.

  The present invention is characterized by multiplying a pilot channel of each channel by a predetermined number of chip sequences equal to the number of subcarriers from a scramble code sequence. As a result, even in a mobile station that performs communication in a narrow band, it becomes possible to identify a scramble code used by a cell by the same procedure as that of a mobile station that can use a wide band.

  According to an aspect of the present invention, a base station includes a plurality of mobile stations, and the base station communicates with the mobile station using a plurality of frequency channels configured by a plurality of carriers for downlink radio communication. The base station is configured to transmit a pilot channel at the beginning and end of the communication frame in order to detect a boundary of the communication frame, and to transmit an arbitrary code sequence to the pilot channel. There is provided a mobile communication system comprising means for allocating a part and control information transmitting means for transmitting control information to the mobile station by the code sequence assigned to the pilot channel.

  In the above system, the assigning means assigns different portions of the first code sequence to a plurality of pilot channels of different frequency channels on the same time axis, and determines which of the pilot channels at the beginning and end of the frame A second code sequence for transmitting the control information is assigned.

  In the above-described system, the mobile station transmits a complex conjugate of one of the consecutive pilot symbols and a multiplication result of the other symbol between the pilot symbols transmitted in the time direction transmitted from the base station, and the mobile station. And a means for detecting a radio frame boundary by taking a cross-correlation with a code sequence owned by and identifying a code sequence group.

  In the above system, the first code sequence is a code sequence different for each cell. Further, the second code sequence is a code sequence indicating a group obtained by dividing the first code sequence into several groups. The control information is a code group used by the base station.

  According to another aspect of the present invention, the mobile station includes a base station and a plurality of mobile stations, and the base station uses the plurality of frequency channels configured by a plurality of carriers for downlink radio communication with the mobile station. A mobile communication system for performing communication, wherein the base station has means for assigning the same first code sequence to each data channel of a different frequency channel is provided.

  The means for assigning a code sequence to the data channel assigns the first code sequence for each frequency channel from the first symbol of the data channel in the frequency direction and repeatedly uses the first code sequence for each frame or TTI (Transmission Time Interval). preferable.

  The first code sequence is preferably a cell-specific code sequence used in another communication method using the same frequency band. Further, the first code sequence is a pseudo-random sequence.

  It is preferable to use the same code sequence as the W-CDMA communication system as the first code sequence. The mobile communication system preferably uses a part of the divided frequency channels.

  In the above system, chips corresponding to subcarriers that are not used are set to satisfy the spectrum mask of each frequency channel between the chips that are used in the pilot channel of each frequency channel in the first and second code sequences. It is characterized by.

  According to another aspect of the present invention, the mobile station includes a base station and a plurality of mobile stations, and the base station uses a plurality of frequency channels configured by a plurality of carriers for downlink radio communication, A communication method for performing communication, wherein the base station forms a pilot channel at the beginning and end of the communication frame to detect a frame boundary, and a part of an arbitrary code sequence in the pilot channel And a step of transmitting control information to the mobile station using the code sequence assigned to the pilot channel.

  According to the present invention, it is possible to flexibly establish synchronization with a base station even when a used frequency bandwidth is changed in a mobile communication system. Therefore, it is possible to introduce the system step by step into a frequency band that uses the same frequency band as other communication methods and use a flexible frequency band.

Before specifically describing the embodiment of the present invention, a presupposed technique will be described. The communication system according to the present embodiment is a multicarrier communication system such as OFDM. The frame configuration has a configuration in which a plurality of frequency channels are provided in a frame having a certain time width on a two-dimensional plane defined by the time axis and the frequency axis. The spreading code includes a scramble code that is different for each cell so that cell identification can be performed and a short code that is used for data multiplexing and is common to each cell, and the data symbol is multiplied by the scramble code and the short code. The The pilot symbol is multiplied only by the scramble code. A spreading code is also assigned to unused subcarriers between channels. The frequency is one cell repetition, and in the following embodiment, an example in which the frequency is divided into four on the frequency axis is shown.
First, the communication technique according to the first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing an example of a downlink frame configuration used in the mobile communication system according to the first embodiment of the present invention. As shown in FIG. 1, the downlink frame 1 includes a pilot channel 3 and a data channel 5. In the data channel 5, the channel of the multiplexing number Cmux7 is multiplexed by the short code, and the pilot channel 3 is time-multiplexed before and after the frame. The data channel 5 is multiplied by two types of codes: a scramble code unique to each cell and a short code that differs depending on each data channel. However, when data channel multiplexing is not performed, it is not always necessary to multiply the short code.

  As described above, since the scramble code is a cell-specific code, even if the same short code is used in an adjacent cell, a one-cell repetitive radio communication system can be configured without interference. Also, the pilot channel for cell search is multiplied by only the scramble code and set before and after the frame. However, it is not always necessary to set the scramble code at the beginning and end, and by setting it at a predetermined position in the frame, it is possible to specify one frame period. It is also possible to multiplex other pilot estimation pilot symbols in the data channel.

  In the mobile communication system according to the first embodiment of the present invention, the frequency band is divided into several parts, and as an example, a system that is divided into four channels will be described as an example. However, the number of band divisions is not particularly limited to four. It is also possible to perform a cell search using a non-continuous band among the divided bands.

  Next, a configuration example of the wireless communication apparatus according to the present embodiment will be described with reference to the drawings. FIG. 2 is a functional block diagram illustrating a configuration example of a transmission device included in a base station among the wireless communication devices according to the present embodiment. As shown in FIG. 2, transmission apparatus A according to the present embodiment includes transmission data generation section 11 that generates, encodes, and modulates transmission data, and a multiplex section that multiplexes the modulated transmission data with pilot symbols. 15, an S / P converter 17 that performs serial-parallel conversion of multiplexed transmission data, a code generator 37 that generates a code, a code multiplier 23 that performs code multiplication, and an IFFT (Inverse Fast Fourier) IFFT unit 25 for performing (Transform) processing, GI insertion unit 27 for inserting GI (Guard Interval) into the output signal of IFFT unit 25, and D / A conversion unit for converting the digital output signal of GI insertion unit 27 into an analog signal 31, a wireless transmission unit 33 that converts an output signal of the D / A conversion unit 31 into a high-frequency signal, and an antenna unit 35 that outputs wireless data. As shown in the figure, a plurality of transmission data generation units 11, multiplex units 15, and S / P conversion units 17 may be provided.

  FIG. 3 is a functional block diagram showing a configuration example of a receiving device included in a mobile station in the wireless communication device according to the present embodiment. As shown in FIG. 3, the receiving apparatus B according to the present embodiment includes an antenna unit 41 that receives radio data, a radio reception unit 43 that converts radio data from a high frequency signal to a low frequency signal, and an analog signal to a digital signal. A / D conversion unit 45 for converting, GI removing unit 47 for removing GI, symbol boundary detecting unit 51 for detecting symbol boundaries, FFT unit 53 for performing FFT (Fast Fourier Transform), received data and possession A correlation detector 55 that calculates a correlation value with data, a code multiplier 57 and a code generator 61 that perform encoding, a P / S converter 65 that performs parallel-serial conversion, and reception that demodulates received data And a data demodulator 67.

  FIG. 4 shows a pilot channel obtained by multiplying a frame boundary with respect to the time axis by a scramble code in the communication frame configuration in the multicarrier wireless communication system shown by a two-dimensional plane defined by two axes of frequency and time. It is the figure which showed a mode that it has arrange | positioned. FIG. 4 illustrates the case where the number of channels in the frequency axis direction is four. FIG. 5 is a diagram illustrating an example of a scrambling code.

  As shown in FIG. 5, the scrambling code 72 forms a code sequence configured as a set of a large number of chips continuing in the direction indicated by the arrow. Each subcarrier of the scrambling code 72 is sequentially assigned to the boundary of the frame configuration shown in FIG.

  For example, as shown in FIG. 4, as an example of a channel configuration in a frame, each symbol before and after one frame is set as a cell search pilot channel (PLCH) 73, 75, 77, 81, and the others. Are data channels 73a, 75a, 77a, 81a. The data channels 73a, 75a, 77a, 81a include user data, user individual control information, common information, and the like, and a plurality of channels can be multiplexed and used for wireless communication by the short code described above. In practice, it can be seen that the scrambling code sequences shown in FIG. 5 are sequentially allocated to the cell search pilot channels (PLCHs) 73, 75, 77 and 81. Data channel assignment will be described later with reference to FIG.

  Furthermore, a frame can be handled by being divided into shorter sections called TTI (Transmission Time Interval) when packet data is allocated.

  In FIG. 4, the arrows described in cell search pilot channel section 73 indicate the multiplication state of the scramble code multiplied by the pilot channel in the frame configuration described above. The pilot channel of each channel is preferably a pseudo-random sequence, and more specifically, a portion of a predetermined code for each subcarrier is multiplied from a long code sequence such as a PN sequence or a Gold sequence. Further, in order to satisfy the spectrum mask between chips for each channel, chips corresponding to subcarriers that are not used are set. By setting a chip corresponding to a subcarrier that is not used, for example, when channel # 1 and channel # 2 are combined to form a wide bandwidth channel during system operation, data transmission is performed when the channel is used. In consideration of using unused subcarriers between channel # 1 and channel # 2 as subcarriers, chips corresponding to all subcarriers are prepared in advance.

  However, in a case where the system does not use subcarriers between channels, that is, in a system where the channel bandwidth is fixed, it is not always necessary to set a corresponding chip.

  In the mobile communication technique according to the first embodiment of the present invention, the cell search pilot channel of channel # 1 is multiplied by the number of chips equal to the number of subcarriers of channel # 1 from the beginning of the code, and then the channel The cell search pilot channel of channel # 2 is multiplied by the number of chips equal to the number of subcarriers of # 2. Similarly, with respect to channel # 3 and channel # 4, the pilot channel for cell search is similarly multiplied by the scrambling code.

  In this embodiment, the scrambling code, which is a long code, is assigned to each channel from the beginning of the sequence. However, the scrambling code assignment method does not necessarily have to be assigned from the first chip of the code. There is no need to assign each channel continuously. However, in any case, the mobile station needs to know the code sequence (scrambling code) and the allocation to each channel before performing the cell search operation. The chip positions of the scramble codes to be multiplied are the same.

  According to the above method, there is an advantage that it is possible to identify a scramble code by scanning one frame even for mobile stations that support different bandwidths.

  Next, an example of a scramble code assignment method for the data channel will be described with reference to FIG. The scramble code will be described by taking as an example the case of using the scrambling spreading code shown in FIG. 10, the horizontal axis represents time, and the vertical axis represents frequency. FIG. 10 is a diagram corresponding to FIG. One frame is shown on the time axis, and two channels are shown on the frequency axis.

  As shown in FIG. 10, a method of assigning and multiplying the head of the scramble code from the head symbol of the data channel after the cell search pilot channel 111 assigned in advance by the above-described method is used for the data channel. .

  That is, in one frame shown as a range with arrows at both ends, the cell search pilot channel 111 is sequentially scrambled from the origin side of the time axis, such as the CH1, CH2, CH3,... A code is assigned and a scramble code is multiplied in the direction indicated by the single arrow in each channel. In this way, one frame is formed. The areas 115, 117, and 121 where hatching is not performed are chips corresponding to unused subcarriers between the channels. In addition, although the data channel allocation method has been described with respect to the method of allocation for each frame, the data channel may be allocated for each time slot unit or for each frame division unit. In that case, it is desirable to repeat the scramble code multiplied by the data channel in units of time slots or in units of divided frames.

  Next, a cell search method when the mobile station receives a reception signal having the frame configuration shown in FIGS. 3 and 4 will be described with reference to FIG. When the process is started (step S1), in step S2, the mobile station performs symbol synchronization of the received signal. The symbol synchronization method can be performed, for example, by using the correlation characteristic of the guard interval.

  Second, the mobile station performs frame synchronization. Here, a frame synchronization method will be described below with reference to FIG. The method described in Non-Patent Document 1 described above is a three-stage fast cell search method using a common pilot channel (CPICH: Common Pilot Channel). In the first stage, symbol timing is detected using the correlation of the GI interval. In the second stage, frame timing and scramble code group detection are performed based on correlation detection between CPICHs by using a scramble code allocation in which the code length of the frequency axis is equal to the number of subcarriers and phase shift is performed for each symbol. Do. In the third stage, the scramble code of the target cell is identified by detecting the correlation of CPICH. Although the cell search including frame synchronization can be performed also by this first method, the method shown in FIG. 9 is scrambled in the second step so that subcarriers can be used effectively even in a limited bandwidth. A method is shown in which the ring code is not phase shifted. In the above non-patent document, a two-dimensional scramble code is realized by phase-shifting the scramble code for each symbol. However, in this embodiment, a long scramble code is multiplied over a plurality of symbols in one frame, so that the same effect Furthermore, when the pilot channel correlation is detected, the preceding and succeeding symbols are multiplied by one subcarrier, and therefore, surplus and deficiency occur between the subcarrier having the highest frequency and the lowest subcarrier in the band.

  An example in which the frame configuration as shown in FIG. 4 is set, that is, a cell search pilot channel of one symbol is set at the beginning and end of each frame will be described. Here, the basic chip sequence P of the pilot channel is defined as follows.

In the following description, Z is a cell-specific scrambling code (CSSC), that is, a cell-specific scramble code, C _ij is a CSSC group code, and x _i is a pilot chip.

In the above equation, Pn represents a value in the nth subcarrier of the pilot channel.
Next, a code sequence Ck having a number of chips J greater than the total number N of subcarriers is defined as follows.

  Here, Ck is a code sequence representing each group obtained by dividing the aforementioned scrambling code into one or more groups in order to shorten the time required for cell search, and the absolute value thereof is 1. k represents each group number. Similarly to the total number of subcarriers P described above, Ck is also assigned a code sequence of chips defined in advance for each subcarrier from a code sequence having a number of chips larger than the number N of subcarriers in all bands. Further, Ck representing a scrambling code group is set to such a value that the cross-correlation between the sequences is sufficiently low, so that the group can be discriminated more accurately.

Furthermore, as a Ck chip configuration, c _k2n (n is an integer of 0 or more) is a chip pattern common to all cells, and c _k2n-1 (n is an integer of 0 or more) is a code indicating a group. Thus, a faster cell search can be performed. More specifically, at the stage of calculating the cross-correlation with Ck, first, the correlation is calculated with the pattern common to all cells in one frame interval, and the correlation value with Ck indicating the group is detected in the symbol portion having the highest correlation value. This is a group detection method divided into two steps. However, the all-cell common chip pattern is not necessarily 2n, and a part of Ck only needs to be the all-cell common chip pattern.

  According to the allocation method according to the present embodiment, by assigning a predetermined portion of the code sequence to each channel from a sufficiently long chip sequence code sequence, the bandwidth is not dependent on the length of the chip sequence. It is possible to perform a cell search flexibly corresponding to the increase / decrease of the width. Further, since the allocation chip for each subcarrier is determined in advance, there is an advantage that cell search can be performed even in a partial band.

  Next, a scramble code for multiplying the pilot channel is defined as follows.

  Here, L is a value larger than the total number N of subcarriers. Z is a code sequence, and it is desirable to use a long code sequence such as a PN sequence or a Gold sequence that is a pseudo-random sequence. For example, a scramble code sequence used in W-CDMA can be used as it is, and furthermore, code assignment to each cell can be performed efficiently when the same cell arrangement expansion is performed. The pilot channel at the end of the frame multiplied by the scramble code in the above definition is set as follows.

  The pilot channel at the head of the frame is set as follows.

The difference from the pilot channel at the end of the frame is that Ck indicating a group of scramble code sequences is multiplied. With this setting, when the complex conjugate of P _E of the symbols before and after the frame boundary is multiplied by P _T , only the Ck term remains, and a scramble code group can be determined.

  Here, the arrangement of the pilot channel at the head and the pilot channel at the end of the frame can be interchanged.

  An example of pilot in channel # 1 with N1 subcarriers is shown below. The frame head pilot channel is expressed by the following equation.

  The frame tail pilot channel is expressed by the following equation.

  Similarly, for channel # 2 to channel # 4, a pilot channel is set by an arbitrary part of each code sequence.

  A method for detecting a frame boundary using the pilot channel of the frame head and tail set as described above will be described below.

  After performing symbol synchronization using the correlation characteristics of the guard interval, the mobile station performs processing for detecting a frame boundary in step S3. The frame boundary detection process is performed by multiplying a complex conjugate of a preceding symbol and a succeeding symbol by a complex symbol of a preceding symbol and a value of a code sequence representing a scramble code group possessed in the mobile station. It is performed by taking the correlation of The place where the peak value of the correlation value appears can be determined as the frame boundary (FIG. 8: Step S3).

Here, a specific procedure related to the correlation detection process will be described based on the operation at the frame boundary shown in FIG. FIG. 9 is a diagram showing the pilot channels of the #M frame and the next frame # M + 1 frame in two-dimensional coordinates defined by the frequency-time axis. As shown in FIG. 9, in this correlation detection method, first, symbol synchronization (window synchronization) is performed by the GI, and second, the complex conjugate of the symbol before the continuous symbol and the symbol after the multiplier 103-1. Scramble code group C _ki is identified based on the cross-correlation value between the result of multiplication by 5 and the code indicating the scramble code group in the mobile station (step S4), and thirdly, a pilot symbol multiplied by the scramble code The scramble code having the highest correlation value with the created pilot symbol replica is detected (step S5), and the process is terminated (step S6).

Specifically, first, Ck is calculated only when the successive symbols are multiplied at the frame boundary. This is because, as mentioned above, each complex conjugate symbol of the frame head symbol and end symbol is composed of Z, P, P ^* , Z ^* , Ck, so if noise and interference components are ignored, only Ck is the multiplication result. Because it remains as. Therefore, when the mobile station correlates with Ck indicating the scramble code group, a high correlation value is obtained. That is, the time when the peak value is the highest is determined as the frame boundary, and the scramble code group used in the cell is determined from Ck indicating the peak. If it is not a frame boundary, it becomes noise even if it correlates with Ck, and no peak appears.

For other channels # 2 to # 4, each code sequence (Z, Z ^* , Ck) is assigned a specific location from the same long code sequence. It is possible to support all channels.

  Third, for all the scramble codes in the scramble code group determined in the second stage, the correlation between the pilot channel and the copy of the pilot channel created in the mobile station at the frame timing similarly determined in the second stage. I take the. The scramble code having the maximum correlation value is determined as the scramble code being used.

  By setting the pilot channel for cell search as described above, a spreading code can be effectively allocated even for a channel with a small number of subcarriers. Furthermore, since codes are assigned to each symbol on a one-to-one basis, it is possible to flexibly cope with changes in channel bandwidth or use of a plurality of channels.

Next, a mobile communication system according to the second embodiment of the present invention is described.
The present embodiment has the same processing and apparatus configuration as the first embodiment, but the differences will be described below.

  FIG. 6 is a diagram showing a scramble code multiplication method according to the present embodiment on the frame configuration in the multicarrier wireless communication system shown by the two-dimensional plane defined by the two axes of frequency and time. . FIG. 6 illustrates a case where the number of channels in the frequency axis direction is four channels, as in the first embodiment. FIG. 7 is a diagram illustrating an example of a scrambling code.

  As shown in FIG. 7, the scrambling code according to the present embodiment forms a scrambling code sequence configured as a set of a large number of chips following the direction indicated by the arrow. Each chip of the scrambling code is sequentially assigned to the frame configuration shown in FIG.

  For example, as shown in FIG. 6, as a channel configuration example 91 in a frame, each symbol before and after two consecutive frames is converted into cell search pilot channels (PLCH) 83, 85, 87, 91 and 93. , 95, 97, 101, and the other areas are data channels. As in the first embodiment, the above-described cell search pilot channels (PLCH) 83, 85, 87, 91 and 93, 95, 97, 101 are sequentially provided with the scrambling code sequences shown in FIG. You can see that it is assigned. The data channel allocation is performed by the same method (see FIG. 10) as in the first embodiment described above. However, for example, cell search pilot channels 83 and 93 are periodically allocated every two frames in channel # 1.

  In the mobile communication technique according to the present embodiment, as shown in FIG. 6, the multiplication method of the scramble code multiplied by the cell search pilot channel before and after the frame is multiplied so as to be one period in two frames. It is characterized by. That is, the frame boundary detection method and the scramble code group determination method in the second stage of the cell search in the first embodiment of the present invention complete the operation in one frame, whereas the second embodiment In the embodiment, the second stage processing is performed over two frames. This can improve the frame boundary detection system. That is, according to this method, the peak position of the frame boundary can be detected more accurately, and more reliable determination can be performed with respect to the determination of the scramble code group.

  In the frame configuration shown in FIG. 6, the spreading code sequence multiplied by the first and last pilot channels is repeated every two frames. Here, the basic chip sequence P of the pilot channel is defined as follows.

In the above formula, p _n denotes the chip in the n sub-carriers of the pilot channel. Here, in the above equation, p ₀ to p _N-1 and p _N to p _2N-1 can be used repeatedly. Next, a code sequence Ck having a number of chips J greater than twice the number of subcarriers N is defined as follows.

Here, as in the case of the first embodiment, C _k represents a code sequence representing a group obtained by dividing the scrambling code into several groups, and k represents the group number. In this embodiment, C _k is also assigned a code sequence of a portion defined in advance for each channel from a code sequence having a number of chips larger than 2N, which is twice the number of subcarriers in the entire band, as in P described above. .

  According to the present embodiment, by assigning the code sequence of the part determined for each channel from the code sequence of a sufficiently long chip sequence to two locations, frame synchronization can be performed more reliably than in the first embodiment. In addition, more accurate determination can be performed regarding the determination of the scramble code group. In addition, as in the first embodiment, cell search can be performed flexibly corresponding to increase / decrease in bandwidth, and since the allocation code of each subcarrier is determined in advance, the cell search can be performed even with only one channel. There is an advantage that can be done. Next, a scramble code for multiplying the pilot channel is defined as follows.

  Here, L is a value larger than the total number N of subcarriers. The pilot at the end of the frame multiplied by the scramble code in the above definition is set as follows.

  Also, the pilot channel at the head of the frame is set as follows.

The difference between the pilot channel at the beginning of the frame and the pilot channel at the end of the frame is that Ck indicating a group of scramble code sequences is multiplied. As a result, when the complex conjugate of P _E and P _T are multiplied, only the Ck term remains, and the determination of the scramble code group becomes easy. Here, the pilot channel in channel 1 with N1 subcarriers is as follows. Since the structure of the pilot channel is 2-frame repetition, the first pilot channel of the first frame and the odd-numbered frame are expressed by the following equations, respectively.

  The tail pilot channels of the first frame and the odd-numbered frame are expressed by the following equations.

第2フレームおよび偶数番目フレームの先頭パイロットチャネルは以下の式で表される。

The first pilot channel of the second frame and the even-numbered frame is expressed by the following equation.

  The tail pilot channels of the second frame and the even-numbered frame are expressed by the following equations.

  Here, x is an arbitrary integer greater than or equal to N1. Similarly, for channel 2 to channel 4, a pilot channel is set by an arbitrary part of each code sequence.

  As shown in FIG. 6, the scramble code multiplied by the pilot channel according to the present embodiment uses a plurality of code sequences having the same number of chips as the number of subcarriers of each channel. The pilot channels set at the beginning and the end in the frame use different scramble code sequences.

  The method for detecting the frame boundary using the continuous pilot channel between frames and the method for determining the scramble code group are the same as in the first embodiment, but 2 for Ck indicating the scramble code group owned by the mobile station. By detecting the correlation over the frame, the frame boundary can be detected. At this time, more accurate detection can be performed by detecting portions corresponding to a plurality of pilot channels with respect to Ck.

  This point will be described with reference to FIG. 8 again. As a first stage, symbol synchronization is performed using the correlation of the guard interval (step S2). Second, frame boundary detection (step S3) and scramble code group determination (step S4) are performed.

  Hereinafter, a procedure for determining a scramble code to be multiplied by subcarrier N in three consecutive frames of frame M-1, frame M, and frame M + 1 will be described. First, the mobile station multiplies consecutive symbols as in the second procedure in the first embodiment, and obtains a correlation with a Ck sequence indicating a scramble code group. Only when the correlation between successive values of symbols at the boundary between the frame M-1 and the frame M is obtained, the correlation value increases, so that the boundary for two periods of the frame can be determined.

  Next, in order to detect the boundary between the frame M and the frame M + 1, a correlation value peak is detected for a Ck sequence consisting of another part. After the frame boundary and the scramble code group can be determined in this way, a scramble code that uses a scramble code that takes a maximum correlation value by creating a duplicate for each scramble code in the group and correlating with the pilot channel Judgment is made (step S5).

  By setting the pilot channel for cell search according to the procedure as described above, a spreading code can be effectively allocated even for a channel with a small number of subcarriers. Furthermore, since codes are assigned one-to-one with respect to each symbol, it is possible to flexibly cope with changes in channel bandwidth or use of a plurality of channels. Furthermore, since the correlation is detected over two frames in the second embodiment, there is an advantage that it is possible to make a more accurate determination regarding cell search than in the case of only one frame.

  The present invention can be used in mobile communication technology.

It is a figure which shows the example of a frame structure of the downlink used in the mobile communication system by the 1st Embodiment of this invention. It is a functional block diagram which shows the example of 1 structure of the transmitter (base station) among the radio | wireless communication apparatuses by this Embodiment. It is a functional block diagram which shows the example of 1 structure of the receiver (mobile station) among the radio | wireless communication apparatuses by this Embodiment. It is the figure which showed the multiplication method of the scramble code by this Embodiment on the frame structure in the said multicarrier radio | wireless communication system shown by the two-dimensional plane defined by the two axes of frequency and time. It is a figure which shows an example of a scrambling code. It is a figure which shows the structure by which the spreading | diffusion code series by which the head and the last pilot channel are multiplied is repeated every 2 frames by the 2nd Embodiment of this invention. It is a figure which shows an example of a scrambling code. It is a flowchart figure which shows the cell search method when a mobile station receives the received signal which has the frame structure by this Embodiment. It is a figure which shows the method of a frame synchronization. It is a figure which shows the allocation process of a data channel.

Explanation of symbols

DESCRIPTION OF SYMBOLS A ... Transmission apparatus, 11 ... Transmission data generation part, 15 ... Multiplex part, 17 ... S / P conversion part, 23 ... Code multiplication part, 25 ... IFFT part, 27 ... GI insertion part, 31 ... D / A conversion part , 33 ... wireless transmission unit, 35 ... antenna unit, 37 ... code generation unit, B ... reception device, 41 ... antenna unit, 43 ... wireless reception unit, 45 ... A / D conversion unit, 47 ... GI removal unit, 51 ... Symbol boundary detection unit, 53... FFT unit, 55... Correlation detector, 57... Code multiplication unit, 61 ... Code generation unit, 65 ... P / S conversion unit, 67 ... Received data demodulation unit.

Claims (18)

A mobile communication system comprising a base station and a plurality of mobile stations, wherein the base station communicates with the mobile station using a plurality of frequency channels configured by a plurality of carriers for downlink wireless communication,
The base station
Means for transmitting a pilot channel at the beginning and end in the communication frame to detect a boundary of the communication frame;
Means for assigning a part of an arbitrary code sequence to the pilot channel;
Control information transmitting means for transmitting control information to the mobile station using the code sequence assigned to the pilot channel.   The assigning means assigns different portions of the first code sequence to a plurality of pilot channels of different frequency channels on the same time axis, and controls the control to either the first or last pilot channel in a frame The mobile communication system according to claim 1, wherein a second code sequence for transmitting information is assigned.   The mobile station, between pilot symbols transmitted in the time direction transmitted from the base station, a complex conjugate of one symbol of the consecutive pilot symbols, a multiplication result of the other symbol, and a code owned by the mobile station The mobile communication system according to claim 1 or 2, further comprising means for detecting a radio frame boundary by taking a cross-correlation with a sequence and identifying a code sequence group.   The mobile communication system according to any one of claims 1 to 3, wherein the first code sequence is a code sequence that is different for each cell.   5. The movement according to claim 1, wherein the second code sequence is a code sequence indicating a group obtained by dividing the first code sequence into several groups. 6. Communications system   The mobile communication system according to claim 1, wherein the control information is a code group used by the base station. A mobile communication system comprising a base station and a plurality of mobile stations, wherein the base station communicates with the mobile station using a plurality of frequency channels configured by a plurality of carriers for downlink wireless communication,
The mobile communication system, wherein the base station has means for assigning the same first code sequence to each data channel of a different frequency channel.   The means for assigning a code sequence to the data channel assigns the first code sequence to each frequency channel from the first symbol of the data channel in the frequency direction and repeatedly uses the first code sequence every frame or TTI (Transmission Time Interval). The mobile communication system according to claim 7, characterized in that:   The mobile communication system according to any one of claims 4 to 8, wherein the first code sequence is a cell-specific code sequence used in another communication method using the same frequency band.   The mobile communication system according to claim 9, wherein the first code sequence is a pseudo-random sequence.   The mobile communication system according to claim 9, wherein the first code sequence uses the same code sequence as that of a W-CDMA communication system.   The mobile communication system according to any one of claims 1 to 11, wherein the mobile communication system uses a part of divided frequency channels.   In the first and second code sequences, chips corresponding to subcarriers that are not used are set in order to satisfy the spectrum mask of each frequency channel between the chips used in the pilot channel of each frequency channel. The mobile communication system according to any one of claims 4 to 12, wherein the mobile communication system is characterized in that: A communication method comprising a base station and a plurality of mobile stations, wherein the base station communicates with the mobile station using a plurality of frequency channels configured by a plurality of carriers for downlink wireless communication,
The base station forming a pilot channel at the beginning and end of the communication frame to detect a frame boundary; allocating a part of an arbitrary code sequence to the pilot channel; and Transmitting the control information to the mobile station using the allocated code sequence.   In the communication frame, different portions of the first code sequence are allocated to a plurality of pilot channels of different frequency channels on the same time axis, and the pilots at the beginning and end of the frame are included in the communication frame The communication method according to claim 14, wherein a second code sequence for transmitting the control information is assigned to any of the channels.   Between the pilot symbols transmitted in the time direction transmitted from the base station by the mobile station, the complex conjugate of one symbol of the consecutive pilot symbols, the multiplication result of the other symbol, and the code owned by the mobile station 16. The communication method according to claim 14, further comprising a step of detecting a radio frame boundary by taking a cross-correlation with a sequence and a step of identifying a code sequence group.   The communication method according to claim 16, wherein the value of the cross-correlation is increased only in the case of a frame boundary.   The communication method according to claim 16, wherein the cross-correlation has a high correlation value only when a code sequence group is identified.

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