JP2005167401A - Radio communications system, radio communications device and radio communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communications system capable of controlling two-dimensional spread with high precision, by specifying a notch from the state of a transmission line. <P>SOLUTION: In the radio communications system performing radio communication while combining multicarrier modulation and two-dimensional spread, a first radio communication device comprises a means for estimating the state of a transmission line, based on a received signal, a means for determining an unused subcarrier corresponding to a notch occurring in the state of the transmission line, and a means for notifying information indicative of the unused subcarrier to a second radio communications device. The second radio communications device comprises a means for selecting a continuous subcarrier, except the unused subcarrier being specified by the information notified from the first radio communications device, and a means for controlling two-dimensional spread of a subcarrier selected by the selecting means, such that the product of spread length in the frequency direction and the time direction becomes constant. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wireless communication system, a wireless communication apparatus, and a wireless communication method that adaptively control two-dimensional spreading in the frequency direction and the time direction according to transmission path conditions and the like.

  Several multi-carrier CDMA transmissions that combine multi-carrier modulation and CDMA (Code Division Multiple Access) have been proposed, and those that perform two-dimensional spreading in the frequency direction and time direction have also been proposed (for example, Non-Patent Document 1 and (See Patent Document 1). In such a transmission technique, a wideband signal is divided into a plurality of relatively narrow-band carriers, and spreading on the frequency axis is performed in units of the divided carriers.

  In multi-carrier CDMA transmission, a carrier having a weak reception electric field strength may be generated among a plurality of carriers due to the influence of multipath. If despreading or demodulation is performed including such a carrier, the quality of the demodulated signal will deteriorate. When the multipath distortion is small, the transmission line state is relatively flat in the frequency direction. However, when the multipath distortion is large, the transmission line state includes a so-called notch (notch) having extremely low electric field strength in the frequency direction. This is because a significant phase rotation before and after the notch is seen as a feature of the multipath transmission line.If the spread signal is despread with the phases not uniform, the signal level after despreading is significantly reduced, and the communication quality is reduced. It causes deterioration.

  Patent Document 2 describes that the state of the transmission line is observed on the receiving side, and the spreading factor is changed according to the transmission line state in each of the frequency direction and the time direction. The gist of this is to suppress the deterioration of quality in a poor transmission path state by the spreading gain by increasing the spreading factor.

  Japanese Patent Application Laid-Open No. H10-228561 describes that quality measurement is performed on the receiving side, and transmission is performed by thinning out data assigned to a carrier having poor channel quality. By suppressing transmission on a line with poor quality, it is possible to reduce interference with other users on average.

  In Patent Document 4, quality measurement is performed on the receiving side, and transmission power is not allocated to carriers with poor quality as in Patent Document 3, and allocation is performed for carriers to which transmission power is allocated. It is described that power corresponding to the transmission power of a carrier that has not been allocated is allocated. What is disclosed in Patent Document 4 is different from Patent Document 3 in that deterioration on the receiving side can be suppressed. That is, the signal power lost by thinning out the carriers is compensated by increasing the power of other carriers.

As described above, conventionally, in multicarrier CDMA, transmission path estimation or the like is performed on the receiving side in order to prevent deterioration in communication quality due to notch influence in the transmission path state, and adaptively two-dimensionally on the transmitting side based on the information Controlling diffusion is performed.
JP 2003-46481 A JP 2003-46474 A JP 2002-190788 A JP 2003-32218 A IEICE technical report Spread spectrum SST2002-05 pp. 1-6 (2002)

  However, a fundamental solution to the problem that the phase rotates before and after the notch has not been made. For example, in Patent Document 1, this is dealt with by increasing the spreading factor in accordance with the deterioration of the transmission path state. Certainly, if the spreading factor is increased, a diffusion gain can be obtained and the performance may be improved. However, if this is diffusion across notches, sufficient quality is not always obtained because of the influence of a significant change in phase before and after the notches. Further, increasing the spreading factor is equivalent to decreasing the transmission rate, and is difficult to apply to communications that require a constant transmission rate.

  In Patent Document 2 and Patent Document 3, communication is performed while avoiding the corresponding carrier, and the avoided carrier is compensated by increasing the transmission power of another good carrier. Also in this case, the problem that the phase before and after the notch is rotated is unsolved, and it cannot be said that sufficient performance is achieved.

  The present invention has been made in view of such circumstances, and provides a wireless communication system, a wireless communication apparatus, and a wireless communication method capable of controlling a two-dimensional diffusion with high accuracy by specifying a notch from a transmission line state. For the purpose.

  A radio communication system according to an aspect of the present invention is a radio communication system that performs radio communication in which multicarrier modulation using a plurality of subcarriers and two-dimensional spreading in a frequency direction and a time direction are combined. The first wireless communication apparatus includes: an estimation unit that estimates a transmission path state based on a received signal; a determination unit that determines an unused subcarrier corresponding to a notch generated in the transmission path state; and Notification means for notifying the second wireless communication apparatus of the information to be expressed. The second wireless communication apparatus is selected by the selecting means for selecting consecutive subcarriers excluding unused subcarriers specified based on the information notified from the first wireless communication apparatus, and the selecting means. Control means for controlling the two-dimensional spreading so that the product of the spreading length in the frequency direction and the spreading length in the time direction is constant for the subcarriers.

  ADVANTAGE OF THE INVENTION According to this invention, the radio | wireless communications system, radio | wireless communication apparatus, and radio | wireless communication method which specify the notch which arose in the transmission-line state and control two-dimensional spreading | diffusion with high precision can be provided. In particular, according to the present invention, the communication operation is good even when the variation in the frequency direction due to multipath distortion is large.

(First embodiment)
FIG. 1 is a block diagram showing a configuration of a transmission unit applied to the radio communication system according to the first embodiment of the present invention, and FIG. 2 is another radio communication apparatus applied to the system. And it is a block diagram which shows the structure of the receiving part. In the following description, the wireless communication device 1 shown in FIG. 1 is described as a transmission side, and the wireless communication device 2 shown in FIG. Note that both of these wireless communication apparatuses 1 and 2 have the same function, and for simplification of illustration, the demodulation unit 111 of the wireless communication apparatus 1 has the configuration of the reception unit of the wireless communication apparatus 2 shown in FIG. On the other hand, the modulation unit 214 of the wireless communication device 2 is assumed to have the same configuration as the transmission unit of the wireless communication device 1.

  As shown in FIG. 1, in a wireless communication device 1 (hereinafter referred to as “communication device 1”), after data transmission is performed by a turbo encoding unit (Turbo encoder) 101 on data to be transmitted, a data modulation unit After performing modulation processing and data interleaving in 102, serial data is converted into parallel data by the S / P converter 103. Each data string of the parallel data corresponds to each carrier in multicarrier modulation. The two-dimensional spreading code is multiplied by the two-dimensional spreading unit 104 for the parallel data after the S / P conversion. The two-dimensional spreading code is generated from a two-dimensional code generator 105 controlled by the two-dimensional code data / code control unit 106. When spreading in the frequency direction is performed, the S / P converter 103 is controlled by the two-dimensional code data / code controller 106 so as to output the same data as parallel data. The two-dimensionally spread spread data is subjected to inverse Fourier transform by the IFFT unit 107 to become a multicarrier modulation signal, a guard interval is added by the GI unit 108, and then frequency converted to a radio frequency band by the radio unit 109. It is transmitted from the antenna 110.

  On the other hand, as shown in FIG. 2, in the wireless communication device 2 (hereinafter “communication device 2”), the wireless unit 202 converts the received signal received by the antenna 201 into a baseband signal. With this baseband signal as input, time symbol synchronization is established by a symbol timing detector 203. After the guard interval is removed by the GI unit 204, the FFT unit 205 performs Fourier transform, thereby extracting the signal component of each carrier. Each extracted carrier signal is subjected to transmission path correction based on transmission path information estimated using a pilot signal inserted in advance, and then subjected to two-dimensional despreading processing by a two-dimensional despreading unit 208 to obtain parallel data. Demodulated as a signal. The parallel data signal is converted into serial data by the P / S converter 211, and further, a deinterleaver and data demodulating process by the data demodulator 212 and a turbo decoding process by the turbo decoder 213 are performed to obtain an information signal.

  The communication device 2 includes a channel estimation unit 206 that estimates a transmission path state from the transmitted pilot signal. The channel estimation unit 206 is connected to a selection unit 207 that selects unused subcarriers based on the estimated transmission path state. The selection unit 207 transmits (notifies) information representing the selected unused subcarrier to the transmission-side communication device 1 via the modulation unit 214.

  FIG. 3 is a graph schematically showing a transmission format and a communication format when performing two-dimensional spreading in the frequency direction and the time direction. Each axis of the graph indicates a power, frequency axis, and time axis. As shown in FIG. 3A, the two-dimensional spreading unit 104 of the communication device 1 on the transmission side performs 8 code spreading (carriers f0 to f7) in the frequency direction and 1 code spreading in the time axis direction. The channel estimation unit 206 of the communication device 2 on the reception side measures the power (reception electric field strength) of each carrier. In the state shown in FIG. 3A, a substantially stable received electric field strength is obtained.

  Here, it is assumed that the reception state has changed with time and the state shown in FIG. Carriers f5 and f6 have extremely poor reception electric field strength due to the influence of multipath and the like, and a notch 30 is generated on the frequency axis as can be seen from FIG. The unused subcarrier selection unit 207 of the communication device 2 determines that f5 and f6 are poor quality carriers based on the transmission path state estimated by the channel estimation unit 206 (that is, the measurement result of the received electric field strength here). Then, the communication device 1 is notified of information for specifying these carriers as unused subcarriers.

  The communication device 1 that has received the notification performs spreading in the frequency axis direction using the carriers other than the unused subcarriers so that the spreading factor is the same as that before the change. Specifically, eight codes are spread in the frequency direction using f0 to f4 and f7 to f9 as shown in FIG.

  Here, the operation of the unused subcarrier selection unit 207 will be described with reference to FIG. The unused subcarrier selection unit 207 observes the signal power of each subcarrier from the channel estimation unit 206 and compares these values with a threshold value A0 (see FIG. 4C). The unused subcarrier selection unit 207 sets this subcarrier as a subcarrier with poor quality when the power level equal to or lower than the threshold value A0 falls below a predetermined time (for example, five measurement intervals).

  By allocating the spread for the subcarriers not used to other subcarriers, stable communication quality can be ensured even when the quality of a specific subcarrier deteriorates.

  In addition to adaptively disabling low quality subcarriers in this way, this embodiment further improves communication quality by controlling two-dimensional spreading as described below.

  For example, as shown in FIG. 5, when f5 and f6 are poor-quality carriers and the notch 30 is detected by the communication device 2, the communication device 1 is notified to make these not-used subcarriers. Upon receiving the notification, the communication device 1 controls the two-dimensional spreading in which the spreading length in the frequency direction is 8 and the spreading length in the time direction is 1, as shown in FIG. That is, the two-dimensional data / code control unit 106 of the communication device 1 is set so that the subcarriers with poor quality do not straddle and the spreading length in the frequency direction is set to 4, and the two-dimensional spreading length is constant. Thus, the two-dimensional diffusion unit 104 is controlled so as to expand the diffusion in the time direction to 2. The communication format obtained as a result is shown in FIG.

  When the notch 30 enters in the frequency direction, the phase rotation of the signal becomes severe before and after the frequency of the notch 30. In a conventional configuration in which diffusion and despreading are performed without avoiding such a notch 30, there may be a case where sufficient diffusion gain cannot be obtained. On the other hand, according to the embodiment of the present invention, spreading across the notch 30 in the frequency direction is avoided, and therefore extremely good communication characteristics can be obtained. In addition, since the two-dimensional diffusion length is constant, the diffusion gain is maintained constant, and stable communication can be ensured.

  FIG. 6 is a flowchart showing an operation procedure of the communication device 1 and the communication device 2. For convenience of explanation, it is assumed that the communication device 1 that determines the communication format is a “base station”. The communication device 2 that performs reception in the designated communication format is referred to as a “mobile station”. In the mobile station 2, the channel estimation unit 206 performs quality measurement for each subcarrier (step S1). It is detected that the subcarrier has fallen below a predetermined period threshold, and an unused subcarrier is selected (step S2). The selected unused subcarrier is transmitted (notified) to the base station 1 as an unused subcarrier request (step S3). The base station 1 determines an unused subcarrier according to the notified request (step S4). Then, subcarriers to be used excluding unused subcarriers and the two-dimensional spreading method (spreading length in the frequency direction / spreading length in the time direction / spreading code, etc.) at that time are determined (step S5). Thereafter, an unused subcarrier response indicating the determined subcarrier number, spreading parameter, time to change to the communication format, and the like is transmitted from the base station 1 to the mobile station 2 (step S6). Both the base station 1 and the mobile station 2 change to the new communication format at the designated time tch (step S7).

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. FIG. 7 shows a case where the quality of each subcarrier is generally poor. Of the eight subcarriers f0 to f7, there are three subcarriers below the threshold A0. That is, there are many subcarriers that are lower than the required quality, and the margin is very small even when the threshold value A0 is exceeded. When adaptive control as described in the first embodiment or the second embodiment is executed in this state, it is difficult to select a subcarrier or assign a spreading code, or to keep a required spreading length constant. It is possible to become.

  Therefore, in the second embodiment of the present invention, the reception quality of all the subcarriers is notified to the base station 1, or the reception quality of each subcarrier is notified to the base station 1 only for subcarriers having a quality lower than the threshold A0. The base station side is configured to determine unused subcarriers.

  As shown in the flowchart of FIG. 8, the mobile station 2 measures the reception quality for each subcarrier (step S1), and selects one below the threshold A0 as a status report subcarrier (step S2). The reception status information of the selected subcarrier is transmitted to the base station 1 (step S3). The base station 1 determines unused subcarriers based on the notified reception state information (step S4). In the present embodiment, when, for example, 20% or more of the subcarriers used do not satisfy the quality, the subcarriers are generally poor (the amount of improvement in characteristics even if only specific subcarriers are excluded and diffusion is performed) Communication is continued without making the corresponding subcarrier unused. On the other hand, if 20% or less of the subcarriers are lower than the predetermined quality, the base station side determines unused subcarriers (step S4), and uses the subcarriers, spreading codes, etc. that are excluded from the unused subcarriers. Is determined (step S5), and the communication format is changed by notifying the mobile station 2 (step S6).

  According to the second embodiment, frequent format changes can be prevented by not performing format changes when the communication quality is generally poor. It is also possible to reliably improve the communication quality after the format change.

(Third embodiment)
In the present embodiment, the present invention is applied to VSF-OFCDM (Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing). FIG. 9 is a block diagram showing a configuration of a wireless communication apparatus according to the third embodiment of the present invention. The configuration is the same as that of the communication device 1 described in the first embodiment except that the two-dimensional code determination circuit 112 is provided.

  In this embodiment, the two-dimensional code determination circuit 112 of the communication device 1000 determines a two-dimensional code. A communication device (not shown) on the receiving side observes the output of the channel estimation unit (Channel estimator) to identify subcarriers below a predetermined threshold and select unused subcarriers.

  FIG. 10A shows a state of spreading using spreading codes (C0, C1, C2,... C15) having a spreading (code) length of 16 in the frequency direction. In the state of FIG. 10B, it is determined based on the threshold value that deterioration due to the transmission path occurs, and that the two locations of the frequencies f9 and f10 do not satisfy the required quality.

  FIG. 11 shows orthogonal spreading codes used for VSF-OFCDM. This code is a code hierarchically configured from SF = 1, and has the property of being orthogonal to each other if it is another branch on the code tree. For example, assuming that a user with SF = 16 (spreading length 16) and a user with SF = 8 (spreading length 8) communicate at the same time, the code numbers Cn16.1 and Cn8.1 have a hierarchical parent-child relationship. Because there is, can not be used at the same time. However, since Cn8.2 and Cn16.1 are not in a parent-child relationship (separated by Cn8.1 and Cn8.2), no interference occurs even if they are used simultaneously.

  In FIG. 10A, a user (user1) is communicating with a code (C0, C1, C2,... C15) of SF = 16, and at the same time, another user (user2) is using a code of SF = 8 (C '0, C'1,... C'7). The condition that the codes of SF = 16 and SF = 8 are orthogonal is that the base points of the codes match. That is, the condition is that the positions of C0 and C′0 are the same, and if C0 and C′1 are the same position, the orthogonality condition is broken and interference occurs.

  FIG. 12 is a flowchart showing an operation procedure of the two-dimensional code determination circuit. From the communication device 2, f9 and f10 are notified as unused subcarriers because of the transmission path as shown in FIG. The two-dimensional code determination circuit 112 first counts how many unused subcarriers are notified (step S1), and does not perform code change processing when subcarriers exceeding a predetermined threshold value are unused. (Step S2). This is because, for example, when there are 10 unused subcarriers for the spreading length 16, there is a high possibility that optimum code selection cannot be performed, and even if code selection is performed, an effective performance improvement effect cannot be obtained. It is.

  Here, f9 and f10 and the two subcarriers are reported as unused, the unused subcarrier number threshold is set to 8, for example, and the process proceeds to step S3. In step S3, the initial spreading length 16 in the frequency direction is set to ½ of 8, and it is determined whether or not eight consecutive subcarriers can be taken at positions satisfying the orthogonality in FIG. 10 (steps S4 and S5). . That is, here, it is determined whether a good subcarrier exists continuously in either f0-f7 or f8-f15. In this embodiment, since there are good carriers continuously in f0-f7, the spreading length in the frequency direction is set to 8 (step S6), and the spreading length in the time direction is set to 2 (step S7). A total of 8 × 2 = 16 diffusion lengths are obtained, and the same diffusion length is ensured, and stable quality communication can be continued. The communication format obtained as a result is shown in FIG.

  In order to ensure a certain diffusion length, it is also possible to skip codes with deteriorated quality and arrange the codes as shown in FIG. However, when a hierarchical code is used, another user uses the code of SF = 8 at f8-f15 (C′1, C′2,... C′7), and only one user has the code. If the position is changed, the orthogonality with other users is lost and interference occurs, which makes communication impossible. Therefore, this is not a problem when only one user is communicating, but when two or more users are simultaneously communicating by code multiplexing, first, a good spreading length continuous in the frequency direction is secured, Needs to match the code start position of the layered code. In the present embodiment, in consideration of these points, two-dimensional code allocation is performed that maintains the total diffusion length and keeps the quality constant while maintaining the orthogonality of the layered codes.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  The present invention can be used for all communication systems that perform spreading on the frequency axis, and is particularly effective for cellular communication systems.

1 is a block diagram showing a configuration of a transmission unit of a radio communication device applied to a radio communication system according to a first embodiment of the present invention. 1 is a block diagram showing a configuration of a receiving unit, which is a radio communication device applied to a radio communication system according to a first embodiment of the present invention. A graph that schematically shows the communication format when two-dimensional spreading is performed in the transmission path state and in the frequency and time directions The figure for demonstrating operation | movement of an unused subcarrier selection part. The figure for demonstrating the two-dimensional spreading | diffusion in 1st Embodiment The flowchart which shows the operation | movement procedure of the communication apparatus 1 and the communication apparatus 2 The figure for demonstrating 2nd Embodiment of this invention The flowchart which shows the operation | movement procedure of 2nd Embodiment. The block diagram which shows the structure of the radio | wireless communication apparatus which concerns on 3rd Embodiment of invention. The figure for demonstrating 3rd Embodiment The figure which shows the orthogonal spreading code used for VSF-OFCDM Flow chart showing operation procedure of two-dimensional code determination circuit Diagram showing the code arrangement to ensure a certain diffusion length

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wireless communication apparatus (communication apparatus) 101 ... Turbo encoding part, 102 ... Data modulation part, 103 ... S / P conversion part, 104 ... Two-dimensional spreading | diffusion part, 105 ... Two-dimensional code generator, 106 ... Two-dimensional Code data / code control unit, 107 ... IFFT unit, 108 ... GI (guard interval) unit, 109 ... radio unit, 110 ... antenna, 111 ... demodulation unit

Claims (5)

In a wireless communication system that performs wireless communication in which multicarrier modulation using a plurality of subcarriers and two-dimensional spreading in the frequency direction and time direction are combined,
The first wireless communication apparatus includes: an estimation unit that estimates a transmission path state based on a received signal; a determination unit that determines an unused subcarrier corresponding to a notch generated in the transmission path state; and Notification means for notifying the second wireless communication device of information to be represented,
The second radio communication apparatus selects a subcarrier that is continuous except for unused subcarriers specified based on information notified from the first radio communication apparatus, and the selection means selects the second radio communication apparatus. And a control means for controlling the two-dimensional spreading so that a product of the spreading length in the frequency direction and the spreading length in the time direction becomes constant for the subcarriers that are set. system. The radio communication system according to claim 1, wherein an orthogonal spreading code having a hierarchical structure is used for the two-dimensional spreading. In a wireless communication apparatus that performs wireless communication in which multicarrier modulation using a plurality of subcarriers and two-dimensional spreading in the frequency direction and time direction are combined,
Estimating means for estimating a transmission path state based on a received signal;
Determining means for determining unused subcarriers corresponding to notches generated in the transmission path state;
A wireless communication apparatus comprising: notification means for notifying information representing the unused subcarrier to another wireless communication apparatus. In a wireless communication apparatus that performs wireless communication in which multicarrier modulation using a plurality of subcarriers and two-dimensional spreading in the frequency direction and time direction are combined,
Receiving means for receiving information representing an unused subcarrier corresponding to a notch generated in a transmission path state from another wireless communication device;
Selecting means for selecting consecutive subcarriers excluding unused subcarriers identified based on the information;
Control means for controlling the two-dimensional spreading so that the product of the spreading length in the frequency direction and the spreading length in the time direction is constant for the subcarriers selected by the selection means. A wireless communication device. In a wireless communication method in which multicarrier modulation using a plurality of subcarriers and two-dimensional spreading in the frequency direction and the time direction are combined,
Estimating a transmission path state based on the received signal in the first wireless communication device;
Determining unused subcarriers corresponding to notches generated in the transmission path state;
Notifying the second wireless communication device of information representing the unused subcarriers;
Selecting, in the second wireless communication device, continuous subcarriers excluding unused subcarriers identified based on information notified from the first wireless communication device;
And controlling the two-dimensional spreading so that a product of the spreading length in the frequency direction and the spreading length in the time direction is constant for the continuous subcarriers. Method.

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