JP5574014B2 - Communication device - Google Patents

Description

  The present invention relates to a communication apparatus used in a broadband mobile radio communication system or the like.

In recent years, as a communication system that can cover a wide area wirelessly and provide a high-speed broadband service, for example, a so-called WiMAX (Worldwide Interoperability for Microwave Access) defined in IEEE 802.16 is a broadband mobile radio communication system. ,Attention has been paid.
In the WiMAX, a large number of base stations that set an area (cell) that covers communication with a mobile terminal are installed. A mobile terminal in a cell can communicate with a base station that sets the cell.

WiMAX employs an OFDMA scheme in which a frequency band of an OFDM signal is assigned to a plurality of mobile terminals (users).
A communication frame in WiMAX includes a downlink subframe that is a time transmitted by the base station apparatus and an uplink subframe that is a time transmitted by the mobile terminal. Among these, in the uplink subframe, the minimum unit to which each user is allocated for data transmission is called a tile. In this tile, the tile allocated for each user is randomly arranged on the uplink subframe. Sent.
The tile is composed of 4 subcarriers × 3 symbols. Pilot signals are arranged on the subcarriers located at the four corners of the tile, and data signals are arranged on the other subcarriers.

  Here, WiMAX defines a CSM (Collaborative Spatial Multiplexing) system in which a plurality of mobile terminals perform transmission using the same tile in order to improve frequency utilization efficiency (for example, Non-Patent Document 1). The CSM scheme improves the utilization efficiency of radio resources by sharing one tile among a plurality of mobile terminals.

In the CSM scheme, when two mobile terminals share the same tile, both mobile terminals transmit signals having structures as shown in FIGS. 4 (a) and 4 (b), respectively. In FIG. 4, the horizontal direction indicates the frequency axis (subcarrier), and the vertical direction indicates the time axis (symbol).
The pilot signals are transmitted in different arrangement patterns from each of the mobile terminals. That is, as shown in FIG. 4A, one mobile terminal arranges the transmission pilot signals P1 ′ and P2 ′ on a pair of diagonal subcarriers among the subcarriers at the four corners of the tile, Another pair of subcarriers in a diagonal relationship is null. As shown in FIG. 4 (b), the other mobile terminal arranges transmission pilot signals P3 ′ and P4 ′ on a pair of subcarriers so as to be in a different position from the one mobile terminal, and transmits the transmission pilot signal P1 ′. , P2 ′ is a null subcarrier.
Also, a plurality of first data signals (first data signal group D) included in the transmission signal of one mobile terminal and a plurality of second data signals (second data signal group) included in the transmission signal of the other mobile terminal. E) means that the same subcarrier is shared by being arranged on the same subcarrier.

  As described above, in the CSM scheme, data subcarriers in a tile are shared by two mobile terminals, and each of a plurality of pilot signals in the tile is allocated so that only one of the mobile terminals is used. It is done.

  Since the same subcarriers are assigned to the data signals of both mobile terminals, the base station apparatus that has received the spatially multiplexed signal including the data signal and the pilot signal as described above receives the data signals of both mobile terminals. As shown in FIG. 4 (c), it is received as a plurality of received data signals (received data signal group S) including the data signals of both mobile terminals. On the other hand, since the transmission pilot signals P1 ′ to P4 ′ are arranged and transmitted at different positions between the two mobile terminals, they correspond to the transmission pilot signals P1 ′ to P4 ′ without interfering with other pilot signals. Received by the base station apparatus as received pilot signals P1 to P4. For this reason, the base station apparatus can estimate the transmission path characteristics in the received pilot signals P1 to P4.

  The base station apparatus estimates the transmission path characteristic value of one mobile terminal in the reception data signal group S based on the transmission path estimation values of the reception pilot signals P1 and P2, and based on this transmission path estimation value, Demodulate the data signal transmitted by the terminal. Similarly, based on the transmission path estimation values of pilot signals P3 and P4, the transmission path characteristic value of the other mobile terminal is estimated and the data signal is demodulated. Thereby, the base station apparatus can acquire both data signals transmitted by both mobile terminals.

IEEE Std 802.16Rev2 / Dod, IEEE Standard for Local and metropolitan area networks, Part 16: Air Interface for Broadband Wireless Access Systems

In the base station apparatus, when the transmission path estimation value of each data signal included in the first data signal group D of one mobile terminal is obtained, a pair of received pilot signals arranged in subcarriers located at the corners of the tiles The estimation is performed based on the transmission path estimation value. At this time, the method for estimating the transmission path estimation value of each data signal from the transmission path estimation value of the pair of received pilot signals is defined in Non-Patent Document 1. Has not been made.
Therefore, for example, for the transmission channel estimation value of one mobile terminal, the average value of the transmission channel estimation values of the corresponding pair of received pilot signals is regarded as the transmission channel estimation value for each reception data signal, and each data signal It is conceivable to take a method such as demodulating

However, the WiMAX must be used in a severe communication environment in which the transmission path characteristics vary greatly. Under such a communication environment, as described above, if all the received data signals included in one tile are uniformly set to the same transmission path estimation value without considering the positional relationship with the pilot signal, the fluctuation varies greatly. There is a possibility that a large error is included in the estimated transmission path. As described above, even if the data signal is demodulated based on the transmission path estimation value that includes a large error, the demodulation characteristic is deteriorated.
The present invention has been made in view of such circumstances, and an object thereof is to provide a communication apparatus capable of improving demodulation characteristics in communication by cooperative spatial multiplexing.

In order to achieve the above object, in order to share the minimum unit of user allocation in an OFDMA signal by a plurality of transmitters, each of a plurality of data signals in the minimum unit is shared by a plurality of transmitters. And a coordinated spatial multiplexing scheme in which each of the plurality of pilot signals within the minimum unit is assigned to each transmitter so that only one of the plurality of transmitters is used. A communication device capable of receiving a transmitted spatially multiplexed signal, comprising: a decoder unit that receives the spatially multiplexed signal and demodulates each signal transmitted by each transmitter; A first transmission line characteristic estimation unit that obtains a transmission line characteristic estimation value for each pilot signal based on a pilot signal included in the spatial multiplexing signal; A second transmission path for obtaining a transmission path characteristic estimation value of the one transmitter in each data signal within the minimum unit based on transmission path characteristic estimation values of a plurality of pilot signals allocated to the single transmitter A transmission line characteristic estimation value for each transmitter in the data signal, and a data signal transmitted by each transmitter is demodulated based on the transmission line estimation value for each transmitter in the data signal. Configured, the second transmission line characteristic estimation unit,
Within said minimum unit, channel characteristics from the channel estimation value of the first pilot signal allocated to the first transmitter of the plurality of transmitters, the data signal of the first transmitter has transmitted first estimated coefficients Bei example Rutotomoni used to calculate the estimated value, within said minimum unit, different from the second the first pilot signal allocated to the transmitter of the plurality of transmitters A second estimation coefficient used to calculate a transmission path characteristic estimation value of the data signal transmitted by the second transmitter from a transmission path characteristic estimation value of the second pilot signal ;
The first estimation coefficient is set for each of data signals included in a plurality of areas that divide the minimum unit into a plurality of areas, and the plurality of areas for which the first estimation coefficient is set includes at least one data signal And the second area including a plurality of the data signals, and the same first estimation coefficient is set for the data signals included in the same area, and the plurality of the plurality of data signals are included in the plurality of data signals. The first estimation coefficient is set for each area,
The second estimation coefficient is set for each data signal included in a plurality of areas that divide the minimum unit into a plurality of areas, and the plurality of areas for which the second estimation coefficient is set includes at least one data signal And a fourth area including a plurality of the data signals, and the same second estimation coefficient is set for the data signals included in the same area, and the plurality of the plurality of data signals are included in the plurality of data signals. The second estimation coefficient is set for each area,
The plurality of areas in which the first estimation coefficient is set and the plurality of areas in which the second estimation coefficient is set have the same minimum unit division method .

  According to the communication apparatus configured as described above, the second transmission line characteristic estimation unit calculates the estimation coefficient used to calculate the transmission line characteristic estimation value of one transmitter in each data signal within the minimum unit. Since each data signal is provided for each of a plurality of transmitters, transmission path characteristic estimation for each transmitter corresponding to each data signal is performed based on the estimation coefficient and the transmission path characteristic estimation values of the plurality of pilot signals. The value can be determined. As a result, the demodulation characteristics of each data signal can be improved.

The estimation coefficient is set to a value corresponding to the position of each data signal in the minimum unit by weighting each of the channel characteristic estimation values of a plurality of pilot signals allocated to the transmitter in which the estimation coefficient is used. It is preferable that
In this case, the second transmission line characteristic estimation unit can obtain an appropriate transmission line characteristic estimation value according to the difference in position of each data signal within the minimum unit by using the estimation coefficient. Therefore, it is possible to improve the estimation accuracy of the transmission path characteristic estimation value of each data signal, and to further improve the demodulation characteristics of each data signal.

  In the communication apparatus, for a data signal whose frequency direction position in the minimum unit is the same as any one of the allocated pilot signals, a pilot signal having the same frequency direction position is used. It is preferable that the weighting of the estimation coefficient with respect to the channel characteristic estimation value is set to be larger than that of other pilot signals. In this case, the estimation coefficient is set to a value that can effectively improve the estimation accuracy in the frequency axis direction. be able to.

Further, in the communication apparatus, for a data signal whose position in the frequency direction within the minimum unit is closer to any one of the allocated pilot signals, a transmission path of the pilot signal having the closer frequency The weighting of the estimation coefficient with respect to the characteristic estimation value may be set more than the weighting with respect to other pilot signals.
In this case, the estimation coefficient can be set to a value that can effectively increase the estimation accuracy in the frequency direction.

  The estimation coefficient is a pilot whose time direction position is the same for a data signal whose time direction position in the minimum unit is the same as any one of the assigned pilot signals. The weighting of the signal transmission path characteristic estimation value may be set larger than other pilot signals. In this case, in addition to the effect of improving the estimation accuracy in the frequency axis direction, the effect of improving the estimation accuracy in the time axis direction can also be obtained.

  As described above, according to the communication apparatus of the present invention, it is possible to improve the demodulation characteristics in communication by cooperative spatial multiplexing.

It is a figure which shows the structure of the radio | wireless communications system containing the base station apparatus which is one Embodiment of this invention. It is a figure which shows the structure of the communication frame in WiMAX. FIG. 3 is a diagram illustrating a data arrangement structure in an uplink subframe in FIG. 2. In a CSM system, it is a figure which shows the structure of the signal of two MS which transmits a transmission signal using the same tile, (a) is the structure of the transmission signal of one MS, (b) is the other The structure of the MS transmission signal, (c) shows the structure of the reception signal received by the base station apparatus. It is a figure which shows the area which defines the estimation coefficient set with respect to the received data signal group S in a tile, (a) is a figure which shows the area which defines the estimation coefficient for calculating | requiring the transmission-line estimated value of one MS. (B) is a figure which shows the area which defines the estimation coefficient for calculating | requiring the transmission-line estimated value of the other MS. It is a figure which shows the variation of the area of the estimation coefficient for an estimation coefficient setting part for calculating | requiring the transmission line estimated value set with respect to the received data signal group in a tile. It is a graph which shows the evaluation result by Example 1, (a) is the setting 1 (Example 1-1), (b) is the setting 2 (Example 1-2), (c) is the setting 3 (Example 1-3), (d) shows the case of setting 4 (Example 1-4), and (e) shows the case of setting 5 (Example 1-5). It is a graph which shows the evaluation result by the said Example 2, (a) is the case of setting 1 (Example 2-1), (b) is the case of setting 2 (Example 2-2), (c) is a setting. 3 (Example 2-3), (d) shows the case of setting 4 (Example 2-4), and (e) shows the case of setting 5 (Example 2-5), respectively. It is a graph which shows the evaluation result by the said Example 3, (a) is the case of setting 1 (Example 3-1), (b) is the case of setting 2 (Example 3-2), (c) is a setting. 3 (Example 3-3), (d) shows the case of setting 4 (Example 3-4), and (e) shows the case of setting 5 (Example 3-5). It is a graph which shows the evaluation result by the said Example 4, (a) is the case of setting 1 (Example 4-1), (b) is the case of setting 2 (Example 4-2), (c) is a setting. 3 (Example 4-3), (d) shows the case of setting 4 (Example 4-4), and (e) shows the case of setting 5 (Example 4-5). It is a graph which shows the evaluation result by the said Example 5, (a) is the case of setting 1 (Example 4-1), (b) is the case of setting 2 (Example 4-2), (c) is a setting. 3 (Example 4-3), (d) shows the case of setting 4 (Example 4-4), and (e) shows the case of setting 5 (Example 4-5). It is a graph which shows the evaluation result by the said Example 6, (a) is the case of setting 1 (Example 6-1), (b) is the case of setting 2 (Example 6-2), (c) is a setting. 3 (Example 6-3), (d) shows the case of setting 4 (Example 6-4), and (e) shows the case of setting 5 (Example 6-5).

Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a configuration of a wireless communication system including a base station apparatus (communication apparatus) according to an embodiment of the present invention. This wireless communication system employs, for example, a communication system conforming to “WiMAX” defined in IEEE 802.16 that supports an orthogonal frequency division multiple access (OFDMA) system in order to realize broadband wireless communication. Base station apparatus (BS: Base Station) and a plurality of mobile terminals (MS: Mobile Station).
A plurality of base station apparatuses can communicate with mobile terminals in an area (cell) covered by each base station apparatus. In FIG. 1, one base station apparatus (BS1) and two mobile terminals (MS2, MS3) located in the area of BS1 are shown.
The BS 1 establishes communication with the MSs 2 and 3 and puts a data signal on a predetermined communication frame so that user data can be transmitted and received and connected to an external network. Therefore, the MSs 2 and 3 can enter the external network by transmitting and receiving user data to and from the BS 1. Thereby, BS1 can provide high-speed broadband service by wireless communication to MS2 and MS3.

  FIG. 2 is a diagram illustrating a configuration of a communication frame in WiMAX. In WiMAX, one basic frame has a downlink subframe DL (base station signal transmission time) and an uplink subframe UL (mobile terminal signal transmission time) arranged side by side in the time axis direction, and is TDD (time division). The communication system performs transmission and reception by duplex.

  FIG. 3 is a diagram showing a data arrangement structure in the uplink subframe in FIG. In FIG. 3, the horizontal axis is the frequency axis, and the vertical axis is the time axis. In FIG. 3, l (1 to L) on the horizontal axis indicates the subcarrier number. The subcarrier numbers are numbered in ascending order of frequency. K on the vertical axis indicates the symbol number. The symbol number is a number assigned to symbols in order of arrival time. In FIG. 3, white circles indicate data signals, and black circles indicate pilot signals.

  The uplink subframe of this embodiment is configured by arranging a large number of tiles T each including 12 subcarriers in total, 3 in the time axis direction and 4 in the frequency axis direction. The tile T is a minimum unit assigned to each user (mobile terminal) for transmitting data, and a plurality of tiles T are assigned to each user.

The subcarriers located at the four corners of the tile T are pilot subcarriers on which pilot signals are arranged, and the other subcarriers are data subcarriers on which data signals are arranged.
As shown in FIG. 3, the tiles T are regularly arranged in the time axis direction and the frequency axis direction, and each pilot signal and data signal are regularly arranged in the time axis direction and the frequency axis direction. . The tiles T are randomly arranged on the uplink subframe regardless of the assigned user.

Here, the MSs 2 and 3 have a function of performing communication by the above-described cooperative spatial multiplexing (CSM) method. As described above, the CSM scheme is a transmission mode in which two mobile terminals share the same tile T for transmission, and a signal composed of the tiles T shared by the two mobile terminals is used as a spatially multiplexed signal. By transmitting to a base station apparatus etc., the utilization efficiency of a radio | wireless resource is improved.
Here, the transmission signal transmitted by the MSs 2 and 3 is composed of a large number of tiles T assigned to the MSs 2 and 3, but in the following, only one tile T constituting the transmission signal will be described. .

  FIG. 4 is a diagram illustrating the tile structure of the MS2 and 3 signals that transmit the transmission signal using the same tile in the CSM system, where (a) is the structure of the transmission signal of MS2, (b) Shows the structure of the transmission signal of MS3. In FIG. 4, the horizontal direction indicates the frequency axis, and the vertical direction indicates the time axis.

As shown in FIG. 4A, the MS 2 transmits a transmission signal including transmission pilot signals P1 ′ and P2 ′ and the first data signal group D to the tile T.
The transmission pilot signals P1 ′ and P2 ′ are arranged on a pair of subcarriers having a diagonal relationship among the subcarriers at the four corners of the tile T. Null data is arranged on another pair of subcarriers in a diagonal relationship. The first data signal group D is composed of a plurality of first data signals d1 to d8 arranged on the remaining eight subcarriers in the tile T, respectively.

MS3 uses the same tile T as MS2, and transmits a transmission signal including transmission pilot signals P3 ′ and P4 ′ and a second data signal group E as shown in FIG. 4B. Transmission pilot signals P3 ′ and P4 ′ are arranged in a pair of subcarriers in which null data is arranged in MS2. For this reason, the transmission pilot signals P1 ′ to P4 ′ are used for only one of the MSs 2 and 3.
The second data signal group E is composed of a plurality of second data signals e1 to e8 respectively arranged on the remaining eight subcarriers in the tile T. Therefore, both data signal groups D and E are transmitted by sharing the same data subcarrier.

  As described above, in the transmission signals transmitted from the MSs 2 and 3 based on the CSM, the data subcarriers in the tile T are shared by the MSs 2 and 3, and among the plurality of transmission pilot signals in the tile T, Transmission pilot signals P1 ′ and P2 ′ are assigned to be used only for MS2, and transmission pilot signals P3 ′ and P4 ′ are assigned to be used only for MS3.

  Since both data signal groups D and E of MS 2 and 3 are assigned the same subcarrier, BS 1 that has received the spatial multiplexing signal including the data signal and pilot signal transmitted from MS 2 and 3 is , MS2 and MS2 are received as a received data signal group S including both MS2 and MS2 data signal groups D and E, as shown in FIG. 4C. The received data signal group S includes a signal obtained by multiplying the first data signals d1 to d8 by a transmission path characteristic value between BS1 and MS2, and a transmission path between BS1 and MS3 to the second data signals e1 to e8. The signal multiplied by the characteristic value is composed of received data signals s1 to s8 that overlap and interfere with each other in the same data subcarrier.

  On the other hand, the transmission pilot signals P1 ′ to P4 ′ transmitted together with the data signals are transmitted on the subcarriers different from each other between the MSs 2 and 3, and therefore do not interfere with each other. For this reason, BS1 receives transmission pilot signals P1 ′ to P4 ′ as reception pilot signals (pilot signals) P1 to P4 in a state where there is no interference with other pilot signals.

Returning to FIG. 1, the BS 1 receives the spatially multiplexed signal by the CSM system transmitted by both the MSs 2 and 3 and demodulates the received data signal group S to thereby convert the data signal groups D and E of the MS 2 and 3 respectively. It has a function to acquire individually.
BS 1 has an A / D converter 5 and an FFT unit 6 corresponding to each of a pair of antenna elements 4 for receiving a transmission signal from a mobile terminal, and each of these units 5 and 6 receives received signals. On the other hand, processing such as A / D conversion, serial / parallel conversion, and discrete Fourier transform is performed.
The BS 1 also includes a decoder unit 7 that performs processing related to CSM such as receiving outputs from the FFT units 6 and individually demodulating and acquiring the data signal groups D and E of the MSs 2 and 3 respectively.

The decoder unit 7 includes a first estimation unit 7a that obtains transmission path characteristic estimation values of the pilot signals P1 to P4 included in the received spatially multiplexed signal, and a pilot signal assigned to one of the MSs 2 and 3 in the tile T. A second estimation unit 7b for obtaining a transmission path estimation value of a target MS in each received data signal in the tile T based on a transmission path characteristic estimation value (hereinafter also referred to as a transmission path estimation value) of MS2, A demodulator 7c that obtains transmission path estimation values for each received data signal every three, and demodulates and acquires each of the data signal groups D and E from the received data signal group S based on these transmission path estimation values. And have.
Hereinafter, processing when BS 1 receives a signal transmitted from MS 2 and 3 as a received signal will be described focusing on one tile T.

The BS 1 transmits a transmission signal composed of the tiles T having the structure shown in FIGS. 4A and 4B from the MSs 2 and 3 to the pilot signals P1 to P4 and the received data signal as shown in FIG. 4C. Received as a spatially multiplexed signal including the group S.
When receiving the spatially multiplexed signal, BS1 causes the first estimating unit 7a to obtain transmission path estimation values hP1 to hP4 of the pilot signals _{P1 to P4} included in the spatially multiplexed signal. The first estimation unit 7a stores transmission pilot signals P1 ′ to P4 ′ in advance, and compares the pilot signals P1 to P4 included in the reception signal with each other to estimate the transmission path estimation value h _{P1 of the} pilot signals P1 to P4. ~ H _P4 can be determined.

When the first estimation unit 7a obtains the transmission path estimation values h _{P1 to} h _P4 of the pilot signals _{P1 to P4} , it outputs these to the second estimation unit 7b. The second estimator 7b that has received these calculates the channel estimation values of the MSs 2 and 3 in each received data signal based on the channel estimation values h _{P1 to} h _P4 of the pilot signals _{P1 to P4} .

More specifically, the second estimation unit 7b determines each received data signal in the tile T based on the transmission path estimation values h _P1 and h _P2 of the pilot signals P1 and P2 assigned to the MS 2 in the tile T. The following procedure is taken in order to obtain the transmission path estimation value of MS2 in FIG. That is, the second estimation unit 7b calculates the transmission path estimation value h _dn (n = 1 to 8) of the MS2 in each reception data signal s1 to s8 included in the reception data signal group S based on the following equation (1). Ask.
_{h dn = c P1 × h P1} + c P2 × h P2 ···· (1)

In the above formula (1), c _P1 and c _P2 are estimation coefficients for obtaining the transmission path estimation value h _dn of MS2. Further, the estimation coefficients c _P1 and c _P2 have the relationship of the following formula (2).
c _P1 + c _P2 = 1 (2)

As is apparent from the equations (1) and (2), the estimation coefficients c _P1 and c _P2 are obtained from the transmission path estimation values h _P1 and h _{P2 of} the pilot signals P1 and P2 assigned to the MS 2 in the tile T. This is used to calculate the transmission path estimation value h _dn of MS2 in each of the received data signals s1 to s8 in T. The estimation coefficients c _P1 and c _P2 are set to values corresponding to the positions in the tile T of the received data signals s1 to s8. This point will be described later.
The second estimation unit 7b stores estimation coefficients c _P1 and c _P2 corresponding to the reception data signals s1 to s8, and is used when obtaining the transmission path estimation value of the MS 2 in each reception data signal. The second estimation unit 7b also stores the estimation coefficient for obtaining the transmission path estimation value of the MS 3, and includes the estimation coefficient for each mobile terminal.

Here, the estimation coefficients c _P1 and c _P2 will be described. As described above, the estimation coefficients c _P1 and c _P2 are set to values corresponding to the positions of the received data signals s1 to s8 in the tile T, and the transmission paths of the pilot signals P1 and P2 assigned to the MS 2 This is a coefficient for weighting the estimated values h _P1 and h _P2 .

FIG. 5 is a diagram showing areas for determining estimation coefficients set for the received data signals s1 to s8 in the tile T. FIG. 5A shows estimation coefficients for obtaining the transmission path estimation value of the MS2. The area to be defined is shown.
In the present embodiment, as shown in FIG. 5A, the second estimation unit 7b is configured to make the received data signal group S a first area A1 close to the pilot signal P1 and a second area close to the pilot signal P2. It is divided into area A2. Then, the second estimation unit 7b, to the received data signal s1, s3, s4, s7 contained in the first area A1, the estimated coefficient _{c P1} 0.7, and the estimated coefficients _{c P2} is 0.3 Configuration Is remembered. In addition, for the reception data signals s2, s5, s6, and s8 included in the second area A2, a setting in which the estimation coefficient _cP1 is 0.3 and the estimation coefficient _cP2 is 0.7 is stored.

In the present embodiment, the estimation coefficients c _P1 and c _P2 for each received data signal are set with different weights in the frequency axis direction with respect to the positions of the pilot signals P1 and P2. That is, the estimation coefficients c _P1 and c _P2 are set for each area (first area A1 and second area A2) that bisects the tile T in the frequency axis direction, and the first area closer to the pilot signal P1. The received data signal included in A1 is set such that the weight of pilot signal P1 is larger than the weight of pilot signal P2.
As a result, the estimation coefficients c _P1 and c _P2 are weighted to the transmission channel characteristic estimation value of the pilot signal for a data signal whose position in the frequency direction in the tile T is closer to either of the pilot signals P1 and P2. Is set to be greater than or equal to the weight for the other pilot signal.

As described above, the second estimation unit 7b calculates the transmission path estimation value h _dn of the MS 2 in each of the reception data signals s1 to s8 based on the above formula (1).

Furthermore, the second estimation unit 7b, for channel estimation value _h e1 _{to h e8} of MS3 in the received data signals s1~s8 included in the received data signal group S, as in the above formula (3), ( Obtained based on 4).
h _en = c _P3 x h _P3 + c _P4 x h _P4 (3)
c _P3 + c _P4 = 1 (4)

FIG. 5B is a diagram showing an area for determining an estimation coefficient for obtaining a transmission path estimation value of MS 3 set for each reception data signal s 1 to s 8 in tile T.
As shown in FIG. 5B, the second estimation unit 7b sets the estimation coefficient _cP3 to 0.3 and the estimation coefficient for the first area A1 in which the reception data signals s1, s3, s4, and s7 are arranged. c _Stores the setting with _P4 set to 0.7. In addition, for the second area A2 where the received data signals s2, s5, s6, and s8 are arranged, a setting in which the estimation coefficient _cP3 is 0.7 and the estimation coefficient _cP4 is 0.3 is stored.
The second estimation unit 7b bisects the tile T in the frequency axis direction with respect to the weighting in the frequency axis direction of the estimation coefficients c _P3 and c _P4 for each received data signal in the same manner as obtaining the transmission channel estimation value of the MS 2 It changes for every area, and it sets so that the weight of the pilot signal in the position nearer to a frequency axis direction may become large.
Specifically, the received data signal included in the first area A1 closer to the pilot signal P4 is set so that the weight of the pilot signal P4 is larger than the weight of the pilot signal P3.

The demodulator 7c uses the transmission channel estimation values of the MS2 and MS3 in the received data signals obtained by the second estimator 7b as described above, from the received data signal group S to the data signal groups D and E. Is demodulated.
Specifically, the respective received data signal s1~s8 included in the received data signal group S, the channel estimation value _h d1 _{to h d8} of MS2, by dividing for each same data subcarrier, the data signal group D the demodulated data signal d1~d8 contained, also, each respective received data signal s1 to s8, the channel estimation value _h e1 _{to h e8} of MS3, if the division into each of the same data subcarrier, the data signal Data signals e1 to e8 included in E are demodulated.

  According to the BS 1 configured as described above, the second estimation unit 7b estimates the estimation coefficient set to a value according to the position of each received data signal in the tile T, and the transmission path estimation of each pilot signal. Since the transmission path estimation value for each MS 2 and 3 in each received data signal is obtained based on the value, an appropriate value can be obtained according to the position difference in the tile T. Accordingly, it is possible to improve the estimation accuracy of the transmission path estimation value of each received data signal, and as a result, it is possible to improve the demodulation characteristics of the data signal groups D and E demodulated from the received data signal group S.

In the above embodiment, the estimation coefficient c _P1 , c _P2 (c _P3 , c _P4 ) for each received data signal has a position in the frequency direction within the tile T whichever of the pilot signals P1, P2 (P3, P4). For the received data signal that is the same, the weighting for the transmission channel characteristic estimation value of the pilot signal having the same position in the frequency direction is set larger than that of the other pilot signals.
Specifically, in FIG. 5 (a), when obtaining the channel estimation value h _d3 of the received data signal s3 is the same frequency as the pilot signal P1 is estimated coefficients c _P1 corresponding to this pilot signal P1 (= 0.7) is set to be larger than the estimation coefficient c _P2 (= 0.3) corresponding to the pilot signal P2 as another pilot signal. In this case, the estimation coefficient is set to an estimation coefficient that can effectively increase the estimation accuracy in the frequency axis direction.

Furthermore, in the above embodiment, the estimation coefficients c _P1 , c _P2 (c _P3 , c _P4 ) are data whose position in the frequency direction within the tile T is closer to any of the pilot signals P1, P2 (P3, P4). For a signal, the weight of the pilot signal transmission channel characteristic estimation value is set to be higher than the weight of the other pilot signal.
That is, as shown in FIG. 5A, each received data signal included in the first area A1 is closer to the pilot signal P1 in terms of the frequency axis direction among the pilot signals P1 and P2. positioned. For this reason, when the transmission path estimation value for each received data signal included in the first area A1 is obtained, the estimation coefficient c _P1 (= 0.7) corresponding to the pilot signal P1 is used as another pilot signal. It is set to be larger than the estimation coefficient c _P2 (= 0.3) corresponding to the pilot signal P2.
Thereby, in obtaining the transmission path estimation values of MS2 and MS3 in each received data signal, the estimation coefficient for the frequency axis direction is set to an estimation coefficient that can be more effectively enhanced.

In the above embodiment, the second estimation unit 7b stores the setting shown in FIG. 5 for the weighting relationship of the estimation coefficients. However, for example, as shown in FIG.
FIG. 6 is a diagram showing variations in the area of the estimation coefficient for obtaining the transmission path estimation value set for the reception data signal group S in the tile T. FIG. 6 shows an area in the case of obtaining the transmission path estimation value of MS2. That is, the relationship between pilot signals P1, P2 assigned to MS2 and each received data signal is shown. Further, in the figure, the received data signal indicated by hatching by the vertical line is set such that the weight for the pilot signal P1 in the estimation coefficient is larger than that of the pilot signal P2, and the received data signal indicated by hatching by the horizontal line is It shows that the weighting for the pilot signal P2 is set larger than that of the pilot signal P1. Further, the reception data signal shown in white indicates that the weights for the pilot signals P1 and P2 are set to be the same (each 0.5).

FIG. 6A shows an area pattern shown in the above-described embodiment.
FIG. 6B shows a pattern in which a first area A1 close to the pilot signal P1 and a second area A2 close to the pilot signal P2 are set, and a third area A3 located between the two areas A1 and A2 is set. .
The reception data signals (s1, 2, 4, 5, 7, 8) located in the third area A3 have the same (0.5) estimation coefficients c _P1 and c _P2 for the pilot signals P1 and P2, respectively. Is set to In this case, only the received data signal whose position in the frequency direction is the same as that of the pilot signal P1 (P2) is set such that the weight for the pilot signal P1 (P2) in the estimation coefficient is larger than that of the pilot signal P2 (P1).

In FIG. 6C, in addition to the condition of (b), the position in the time direction is the same time as the pilot signal P1 (P2) and is adjacent to the pilot signal P1 (P2) in the frequency axis direction. For the received data signal (s1, s8), the weight of the estimation coefficient for the adjacent pilot signal P1 (P2) is set large.
In the case of this pattern, the third area A3 (received data signal s2) is set so that the estimation coefficients corresponding to the pilot signals P1 and P2 are the same between the first area A1 and the second area A2. , 4, 5, 7).

FIG. 6 (d) shows a modified pattern of (a). For a received data signal whose position in the time direction is the same as that of pilot signal P1 (P2), weighting of an estimation coefficient for pilot signal P1 (P2) is performed. It is set to be larger than the weighting of the estimation coefficient for the pilot signal P2 (P1).
In the case of this pattern, there is no third area A3 set so that the estimation coefficients corresponding to the pilot signals P1 and P2 are the same.

In FIG. 6E, in addition to the condition of (b), the pilot coefficient P1 (P2) is weighted with respect to the received data signal whose position in the time direction is the same as that of the pilot signal P1 (P2). It is set larger than the weighting of the estimation coefficient for the signal P2 (P1).
In the case of this pattern, the third area A3 (received data signals s4, 5) exists between the first area A1 and the second area A2.

In the patterns shown in FIGS. 6 (a), 6 (b), and 6 (c), for all the received data signals, the transmission path characteristic estimation of the pilot signal closer in the frequency direction to the pilot signal P1 or P2 is performed. The weight for the value is set to be greater than the weight for the other pilot signals.
Further, in the patterns shown in FIGS. 6D and 6E, the channel characteristics estimation of the pilot signal whose position in the frequency direction is closer to the pilot signal P1 or P2 in a part of the received data signal. The weight for the value is set to be greater than the weight for the other pilot signals.

  Further, as shown in FIGS. 6C, 6D, and 6E, with respect to a reception data signal whose position in the time direction in the tile T is the same as that of the pilot signal P1 (P2), the pilot signal When the weighting of the estimation coefficient for the transmission path estimation value of P1 (P2) is set to be greater than the weighting for the pilot signal P2 (P1), in addition to the effect of improving the estimation accuracy in the frequency axis direction, An effect of improving the estimation accuracy can also be obtained.

  FIG. 6F shows the weighting of the estimation coefficient corresponding to the pilot signal P1 (P2) for the reception data signals s1,2 (s7,8) whose position in the time direction is the same as that of the pilot signal P1 (P2). Is set larger than the weighting of the estimation coefficient corresponding to the pilot signal P2 (P1), and the received data signals (s3, 4, 5, 6) that are not the same as the time of both pilot signals P1, P2 are pilot signals P1, P2 The third area A3 is set such that the estimation coefficients corresponding to the respective areas are the same. Thus, in this pattern, the received data signals of the same time are all set to the same setting, and the weighting setting of the estimation coefficient is set to be different only in the time direction. For this reason, the improvement effect of the estimation precision with respect to a time-axis direction can be acquired.

  FIG. 6G shows a comparative example with respect to the pattern as the above-described embodiment. As described in the above-described conventional example, the transmission paths of both pilot signals P1 and P2 are uniformly applied to all the received data signal groups S. The pattern in the case of setting a value (weighting is the same) obtained by averaging estimated values is shown.

Next, a description will be given of the test results evaluated by the present inventor regarding the demodulation characteristics when the CSM system communication is performed between the two MSs 2 and 3 using the BS 1 having the above configuration.
As an embodiment according to the present invention, BSs configured to demodulate received signals from MSs 2 and 3 using the five patterns shown in FIGS. did.
As comparative examples, BSs using the pattern shown in FIG.
In Examples 1 to 6 and Comparative Example 1, with respect to the received signal from MS3, the positional relationship between pilot signals P1 and P2 in the MS2 pattern shown in FIG. 6 and each received data signal Each pattern in FIG. 6 was set to a line-symmetric pattern with respect to the time axis so as to be the same.
For the estimation coefficients c _P1 , c _P2 , c _P3 and c _P4 , five types of settings 1 to 5 shown in Table 1 below were prepared.

In Table 1, the first area A1 is an area including a reception data signal in which the weighting of the estimation coefficient corresponding to the pilot signal P1 (P4) is set larger than that of the pilot signal P2 (P3) as described above. is there. The second area A2 is an area including a reception data signal in which the weight of the estimation coefficient corresponding to the pilot signal P2 (P3) is set larger than that of the pilot signal P1 (P4). The third area A3 is an area including reception data signals in which the weighting of the estimation coefficient is set to be the same.
Therefore, in this test, for each of Examples 1 to 6, five levels of settings 1 to 5 in Table 1 were evaluated.

As an evaluation method, BS1 is obtained in a high-speed moving environment (moving speed of MS2, 3: 120 km / h, multipath environment: number of main paths 6, number of subpaths 20 per main path) by simulation using a computer. Reproduce the case where the signals from MS2 and MS3 are received by CSM, give estimation coefficients c _P1 , c _P2 , c _P3 , c _P4 in BS 1, obtain the estimated channel values for each received data signal, MS 2, The demodulation characteristics when the received signal from 3 was demodulated were calculated.
Demodulation characteristics are evaluated by graphing the cumulative distribution of MER (Modulation Error Ratio) and the correlation with CDF (Cumulative Density Function) when demodulating based on the above simulation. evaluated.
MER is the ratio of the power of the signal point that should be originally and the error power of the demodulated signal, and it can be determined that the larger the value, the better the demodulation characteristics. The CDF is defined as the probability that the MER is equal to or less than that value.

  FIG. 7 is a graph showing the evaluation results according to Example 1, wherein (a) shows the case of setting 1 (Example 1-1), and (b) shows the case of setting 2 (Example 1-2). , (C) in the case of the setting 3 (Example 1-3), (d) in the case of the setting 4 (Example 1-4), and (e) in the case of the setting 5 (Example 1-5). ) Respectively. In these graphs, the horizontal axis represents the MER value, and the vertical axis represents the CDF value. In each graph, the results of the above examples are indicated by solid lines, and the results of Comparative Example 1 are indicated by broken lines.

  Referring to FIG. 7, in any case of setting 1 to setting 5 ((a) to (e)), the MER is improved and the demodulation characteristic is improved as compared with the comparative example 1. I can say that. In particular, in the case of Example 1-2, the improvement in demodulation characteristics was particularly noticeable.

FIG. 8 is a graph showing the evaluation results according to Example 2, where (a) shows the case of setting 1 (Example 2-1) and (b) shows the case of setting 2 (Example 2-2). , (C) in the case of the setting 3 (Example 2-3), (d) in the case of the setting 4 (Example 2-4), and (e) in the case of the setting 5 (Example 2-5). ) Respectively.
In any of the settings 1 to 5 ((a) to (e)) in the present embodiment, the MER is improved and the demodulation characteristics are improved as compared with the comparative example 1. In the case of the present embodiment, the demodulation characteristics are improved from setting 1 to setting 5, that is, as the difference in weighting of the estimation coefficients increases.

FIGS. 9A and 9B are graphs showing the evaluation results according to Example 3, where FIG. 9A shows the case of setting 1 (Example 3-1), and FIG. 9B shows the case of setting 2 (Example 3-2). , (C) in the case of setting 3 (Example 3-3), (d) in the case of setting 4 (Example 3-4), and (e) in the case of setting 5 (Example 3-5). ) Respectively.
Also in the third embodiment, as in each of the above embodiments, in any of the settings 1 to 5 ((a) to (e)), the MER is improved as compared with the first comparative example, and the demodulation characteristics are improved. Has improved. Also in the present embodiment, the demodulation characteristics improve as the difference in weighting of the estimation coefficients increases.

FIG. 10 is a graph showing the evaluation results according to Example 4, where (a) shows the case of setting 1 (Example 4-1) and (b) shows the case of setting 2 (Example 4-2). , (C) in the case of setting 3 (Example 4-3), (d) in the case of setting 4 (Example 4-4), and (e) in the case of setting 5 (Example 4-5). ) Respectively.
FIG. 11 is a graph showing the evaluation results according to Example 5, where (a) shows the case of setting 1 (Example 4-1), and (b) shows the case of setting 2 (Example 4-2). , (C) in the case of setting 3 (Example 4-3), (d) in the case of setting 4 (Example 4-4), and (e) in the case of setting 5 (Example 4-5). ) Respectively.
In each of Examples 4 and 5, as in each example, the MER was improved and the demodulation characteristics were improved as compared with Comparative Example 1.

FIGS. 12A and 12B are graphs showing the evaluation results according to Example 6, in which FIG. 12A shows the case of setting 1 (Example 6-1), and FIG. 12B shows the case of setting 2 (Example 6-2). , (C) in the case of setting 3 (Example 6-3), (d) in the case of setting 4 (Example 6-4), and (e) in the case of setting 5 (Example 6-5). ) Respectively.
The demodulation characteristics of the sixth embodiment are the same as or slightly deteriorated as compared with the first comparative example.
In the sixth embodiment, the reception data signals of the same time are all set to the same estimation coefficient for each reception data signal of the same time without considering the frequency when setting the estimation coefficient.
As described above, the communication environment set in this evaluation test assumes a high-speed movement environment (movement speed of MS 2 and 3: 120 km / h). Generally speaking, transmission path characteristics with respect to the time axis direction. It is thought that the fluctuation of is intense. For this reason, in the above test results, it can be expected that a high effect can be obtained with respect to improvement of the demodulation characteristics by setting the estimation coefficient as a pattern taking the time axis direction into consideration. However, on the contrary, the effect was not obtained remarkably, and conversely, when the estimation coefficient was set as a pattern considering the frequency axis direction, a result that the effect of improving the demodulation characteristic was obtained more significantly was obtained. .

Note that the time axis direction of the tile T has a time width of 3 symbols and a very short time width, and it can be considered that the change in the time axis direction is small with respect to the change in the frequency axis direction. For this reason, even when setting the estimation coefficient in consideration of only the change in the time axis direction as in the sixth embodiment, it is considered that the effect of improving the demodulation characteristics cannot be remarkably obtained.
Considering the above, in Example 6, it can be considered that the effect of improving the estimation accuracy in the time axis direction can be obtained in an environment where the change in the time axis direction is more severe than in this evaluation test.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Base station equipment (communication equipment)
2 Mobile terminal (transmitter)
3 Mobile terminal (transmitter)
7 Decoder unit 7a First estimation unit (first transmission line characteristic value estimation unit)
7b Second estimation unit (second transmission line characteristic value estimation unit)

Claims (5)

In order to share the smallest unit of user assignment in an OFDMA signal by multiple transmitters,
Each of a plurality of data signals within the minimum unit is shared by a plurality of transmitters; and
A coordinated spatial multiplexing scheme in which each of the plurality of pilot signals within the minimum unit is assigned to each transmitter so that only one of the plurality of transmitters is used;
A communication device capable of receiving a spatially multiplexed signal transmitted based on
A decoder unit that receives the spatially multiplexed signal and demodulates each signal transmitted by each transmitter;
The decoder unit
A first transmission line characteristic estimation unit for obtaining a transmission line characteristic estimation value in each pilot signal based on a pilot signal included in the received spatially multiplexed signal;
Based on transmission path characteristic estimation values of a plurality of pilot signals assigned to one transmitter in the minimum unit, a transmission path characteristic estimation value of the one transmitter in each data signal in the minimum unit is obtained. Two transmission path characteristics estimation unit;
The transmission path characteristic estimation value for each transmitter in the data signal is obtained, and configured to demodulate the data signal transmitted by each transmitter based on the transmission path estimation value for each transmitter in the data signal,
The second transmission path characteristic estimation unit is
Within said minimum unit, channel characteristics from the channel estimation value of the first pilot signal allocated to the first transmitter of the plurality of transmitters, the data signal of the first transmitter has transmitted first estimated coefficients Bei example Rutotomoni used to calculate the estimated value, within said minimum unit, different from the second the first pilot signal allocated to the transmitter of the plurality of transmitters A second estimation coefficient used to calculate a transmission path characteristic estimation value of the data signal transmitted by the second transmitter from a transmission path characteristic estimation value of the second pilot signal ;
The first estimation coefficient is set for each of data signals included in a plurality of areas that divide the minimum unit into a plurality of areas, and the plurality of areas for which the first estimation coefficient is set includes at least one data signal And the second area including a plurality of the data signals, and the same first estimation coefficient is set for the data signals included in the same area, and the plurality of the plurality of data signals are included in the plurality of data signals. The first estimation coefficient is set for each area,
The second estimation coefficient is set for each data signal included in a plurality of areas that divide the minimum unit into a plurality of areas, and the plurality of areas for which the second estimation coefficient is set includes at least one data signal And a fourth area including a plurality of the data signals, and the same second estimation coefficient is set for the data signals included in the same area, and the plurality of the plurality of data signals are included in the plurality of data signals. The second estimation coefficient is set for each area,
A plurality of areas in which the first estimation coefficient is set and a plurality of areas in which the second estimation coefficient is set have the same minimum unit division method. apparatus.   The estimation coefficient is set to a value corresponding to the position of each data signal in the minimum unit by weighting each of the channel characteristic estimation values of a plurality of pilot signals allocated to the transmitter in which the estimation coefficient is used. The communication device according to claim 1.   For a data signal in which the position in the frequency direction within the minimum unit is the same as any one of the assigned pilot signals, the channel characteristics estimation value of the pilot signal having the same position in the frequency direction The communication apparatus according to claim 2, wherein the weighting of the estimation coefficient with respect to is set larger than that of other pilot signals.   For a data signal whose position in the frequency direction within the minimum unit is closer to any one of the assigned pilot signals, the estimation coefficient for the channel characteristic estimation value of the pilot signal of the closer frequency The communication apparatus according to claim 2, wherein the weighting is set to be greater than the weighting for other pilot signals.   The estimation coefficient is determined based on a pilot signal having the same position in the time direction with respect to a data signal having the same position in the time direction within the minimum unit as any of the plurality of assigned pilot signals. 5. The communication apparatus according to claim 3, wherein the weighting for the transmission path characteristic estimation value is set to be greater than the weighting for other pilot signals.

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