JP4894562B2 - Communication apparatus and weight update method - Google Patents

Description

  The present invention relates to a communication device and a weight update method.

The multi-antenna technique is a technique for improving communication capacity, frequency utilization efficiency, power consumption, and the like by performing transmission / reception using a plurality of antennas in wireless communication. Even if the number of antennas on either the transmission side or the reception side is one, it is possible to improve the communication quality according to the number of antennas on the other side.
Moreover, there exists MIMO (Multiple Input Multiple Output) as a term regarding the multi-antenna technology. MIMO, when used as a communication term, often refers to a communication scheme in which both the transmission side and the reception side use a plurality of antennas, but may also be used to refer to general multi-antenna technology.

Advantages obtained by the multi-antenna signal processing algorithm include the following four.
(1) Spatial diversity
(2) Synthetic gain
(3) Interference mitigation (Interference Mitigation)
(4) Spatial Multiplexing

The space diversity is to reduce deterioration in communication quality due to the influence of multipath or the like by using spatially separated antennas.
The combined gain increases the ratio of received power and noise from the desired direction by applying a weight using the propagation path information (changes in amplitude and phase) to the signals on the receiving and transmitting antennas. It is to be.

In the interference wave removal, a received signal from each antenna is combined with a weight so as to cancel an incoming signal (interference signal) other than the desired signal. A number of interference signals smaller than the number of receiving antennas can be removed. If the propagation coefficient of the incoming signal is unknown, some learning algorithm must be used.
The spatial multiplexing is a method of establishing a plurality of communication paths simultaneously by applying interference wave cancellation. There are a method in which a single user transmits different signals from a plurality of antennas to increase the communication capacity, and a method in which a plurality of users simultaneously communicate to increase frequency utilization efficiency. The latter method is called SDMA (Space Division Multiple Access).

As a multi-antenna technique that has recently attracted attention, there is OFDM-MIMO using an OFDM (Orthogonal Frequency Division Multiplexing) scheme.
In the OFDM method, a plurality of carrier waves (subcarriers) are arranged on the frequency axis, and the plurality of carrier waves are partially overlapped to improve frequency use efficiency. OFDM is employed in transmission systems such as terrestrial digital broadcasting and wireless LAN.

One important technique in OFDM-MIMO is updating weights.
For example, in the case of the multi-antenna technique, when the ratio of the received power and the noise power from the desired wave direction is increased by the combined gain of (2) above in the multi-antenna technique and strong directivity is directed in the desired wave direction (beam forming) Used.
In beam forming, in addition to directing strong directivity in the desired wave direction, the influence of received signals other than the desired wave can be reduced.

  The weight is generated using the reference signal. For example, in OFDM, since a known signal (pilot signal) is inserted on the reception side and transmission side, the weight can be updated using this pilot signal as a reference signal.

  As weight update algorithms, there are LMS (Least Mean Square) and RLS (Recursive Last-Squares). When these operate properly, error energy is minimized, and all advantages (1) to (4) are provided. Can be obtained.

Since the OFDM pilot signals are arranged at predetermined intervals in the time axis direction, it is possible to sequentially update the weight each time the pilot signal is received.
In steady state (when there is no temporal change in the propagation coefficient), updating the weight more than a certain number of times can converge the weight calculation result and reduce the influence of interference signals and noise signals. it can.

The weight update method is described in Patent Document 1, for example.
FIG. 26 shows a signal arrangement diagram of FIG. This signal arrangement diagram is a signal arrangement of the digital terrestrial television broadcasting system based on the OFDM system. In the figure, the subcarrier arrangement in the carrier-symbol space is shown in which the vertical axis is the symbol direction (time axis direction) i and the horizontal axis is the carrier direction (frequency axis direction) k. In the figure, black circles indicate scattered pilot SP, and white circles indicate data signals (data subcarriers).
In the case of the signal arrangement shown in the figure, for the same SP carrier number kp, the SP signal is repeated at a cycle of 4 symbols.

Patent Document 1 describes a method of updating weights by applying an LMS algorithm.
According to this document, when there is a weight wb _kp (i) updated by using an SP signal at time i of a certain carrier number kp, the next weight update is performed 4 symbols after the same carrier number kp. The weight update value wb _kp (i + 4) is calculated using the SP signal (carrier number kp, time i + 4).
JP 2003-174427 A

  As described above, in Patent Document 1, the weight update is simply repeated in the time axis direction. However, in a communication method such as OFDMA (Orthogonal Frequency Division Multiple Access), one frame can be assigned to a plurality of users.

In OFDMA, a basic transmission frame has a downlink subframe and an uplink subframe, and each transmission subframe includes a burst.
Here, a burst is a block for data transmission allocated within a frame.

When one frame is assigned to a plurality of users, the propagation environment is different even for pilot signals in the same frame. For example, when viewed from the base station, the propagation environment between the user A terminal and the propagation environment between the user B terminal is different.
Therefore, switching from weight update using a pilot signal in a burst assigned to user A to weight update using a pilot signal in a burst assigned to user B (hereinafter referred to as “burst switching”). If this occurs, the beamforming directivity must be changed. Therefore, if weight updating is performed continuously with the burst switching between, the weight estimation accuracy decreases.

Moreover, even when there is no burst switching in the desired signal, burst switching may occur in the interference signal from the interfering station. When burst switching occurs in the interference signal, the interference signal to be canceled differs by beamforming. Therefore, it is necessary to change the directivity of beam forming, and the weight estimation accuracy is also lowered.
Moreover, unlike the desired signal, it is difficult to know the burst switching timing of the interference signal.

  Therefore, an object of the present invention is to suppress a decrease in weight estimation accuracy associated with burst switching during weight update as much as possible.

  The present invention provides a weight estimation value by updating a weight based on a pilot signal included in a received signal in a communication apparatus that performs communication using a communication method in which a burst region allocated to a user is included in a transmission frame. A weight updating unit, and an order control unit that controls the order of pilot signals used to update weights, wherein the order control unit updates all of a plurality of pilot signals existing in one burst region. After use, the order is controlled so as to perform weight update using a pilot signal existing in another burst region.

  According to the present invention, burst switching is unlikely to occur during weight updating performed sequentially, so that a decrease in weight estimation accuracy can be suppressed.

  The burst area is preferably a burst area in the OFDMA system. In the OFDAMA scheme, since frequency multiplexing is also possible as user multiplexing, burst switching is particularly likely to occur. However, according to the present invention, a decrease in weight estimation accuracy can be suppressed even in the OFDMA scheme.

  From another viewpoint, the present invention provides a communication apparatus that performs communication using a communication method that can allocate one transmission frame to a plurality of users, and performs weight updating based on a pilot signal included in the received signal. A weight update unit for obtaining an estimated value; and an order control unit for controlling the order of pilot signals used for updating the weight, wherein the order control unit exists in a region of a minimum unit of user allocation in the transmission frame The order is controlled so that all of the plurality of pilot signals to be used are used for weight update, and then weight update is performed using pilot signals existing in other user assigned minimum unit regions.

  According to the present invention, since many weights can be updated in the area of the minimum user allocation unit, which is an area where burst switching does not occur, it is possible to suppress a decrease in weight estimation accuracy.

  Preferably, the user allocated minimum unit area is a tile area in an uplink PUSC scheme of WiMAX or mobile WiMAX. The user allocated minimum unit area is preferably a cluster area in a WiMAX or mobile WiMAX downlink PUSC scheme. In WiMAX, since frequency multiplexing is also possible as user multiplexing, burst switching is particularly likely to occur. However, in the present invention, many weights can be updated in the area of the user allocated minimum unit, which is an area where burst switching does not occur. A decrease in weight estimation accuracy can be suppressed.

  It is preferable to include a weight smoothing unit that obtains a smoothed estimated value obtained by smoothing a weight estimated value obtained by a plurality of weight update operations. By smoothing the weight, the weight estimation accuracy is improved.

According to another aspect of the present invention, in a communication apparatus that performs communication by a communication method in which a burst region allocated to a user is included in a transmission frame, based on a pilot signal included in a received signal, the weight is updated, A weight updating unit for obtaining a weight estimation value;
A weight smoothing unit that obtains a smoothed estimated value obtained by smoothing a weight estimated value obtained by a plurality of weight update operations, and the weight smoothing unit includes a plurality of weight estimated values in burst area units. Smoothing is performed.

  According to the present invention, since the weight estimation value is smoothed in units of burst areas, smoothing can be performed without being affected by burst switching.

  The burst area is preferably a burst area in the OFDMA system. In OFDMA, frequency multiplexing is also possible as user multiplexing, so burst switching is particularly likely to occur. However, smoothing on a burst area basis reduces weight estimation accuracy even when burst switching is frequent. Can be suppressed.

  From another viewpoint, the present invention provides a communication apparatus that performs communication using a communication method that can allocate one transmission frame to a plurality of users, and performs weight updating based on a pilot signal included in the received signal. A weight updating unit that obtains an estimated value; and a weight smoothing unit that obtains a smoothed estimated value obtained by smoothing a plurality of weight estimated values obtained by weight update calculation, wherein the weight smoothing unit includes the user A plurality of weight estimation values are smoothed in the allocation minimum unit.

  According to the present invention, since the weight estimation value is smoothed by the minimum unit of user allocation, smoothing can be performed without being affected by the burst switching of the interference signal.

  Preferably, the user allocated minimum unit area is a tile area in an uplink PUSC scheme of WiMAX or mobile WiMAX. The user allocated minimum unit area is preferably a cluster area in a WiMAX or mobile WiMAX downlink PUSC scheme. In WiMAX, frequency switching is also possible as user multiplexing, so burst switching is particularly likely to occur. However, smoothing is performed in units of minimum user allocation, which reduces the weight estimation accuracy even when burst switching is frequent. Can be suppressed.

  The weight smoothing unit is configured to perform the smoothing based on information of a post-pilot signal used at the time of weight update performed after the weight update when the weight estimation value to be smoothed is obtained. It is preferable to obtain a conversion estimation value. In this case, information on the post pilot signal used for weight update performed later can be reflected in the smoothed estimation value. Accordingly, the smoothed estimated value reflects more information than the weight estimated value.

  The information of the post-pilot signal includes the post-pilot signal, a post-weight estimation value obtained by the weight update unit performing weight update using the post-pilot signal, or a smoothed estimation value of the post-weight estimation value, Is preferred. In addition to the post-pilot signal, the post-weight estimation value and the smoothed estimation value of the post-weight estimation value also reflect the information of the post-pilot signal. Therefore, using this information (one or more), smoothing is performed. Can be made.

  The weight smoothing unit smoothes a weight destination estimation value to be smoothed and a post-weight estimation value obtained by weight update performed after the weight update at the time of obtaining the weight estimation value. It is preferable to obtain a smoothed estimated value of the weighted destination estimated value by weighted synthesis of the normalized estimated value. In this case, the smoothed estimated value can be obtained by a simple calculation.

  The weight smoothing unit obtains weights obtained by weight update performed after the weight update by a pilot signal used in weight update when the weight estimation value to be smoothed is obtained. It is preferable to obtain the smoothed estimated value of the weight estimated value by updating the weight of the post estimated value. In this case, smoothing can be performed by a weight update algorithm.

  The weight smoothing unit performs fixed interval smoothing based on a post-pilot signal used at the time of weight update performed after the weight update when the weight estimation value to be smoothed is obtained. It is preferable to obtain a smoothed estimated value of the weight estimated value by performing. By using fixed interval smoothing, estimation can be performed with high accuracy.

  It is preferable that the weight smoothing unit includes a smoothing parameter adjusting unit that adjusts a parameter for performing smoothing. In this case, the smoothing parameter can be adjusted to perform appropriate smoothing.

  From another viewpoint, the present invention is a weight update method in a communication scheme in which a burst area allocated to a user is included in a transmission frame, and all of a plurality of pilot signals existing in one burst area are updated in weight. After use, weight update is performed using pilot signals existing in other burst regions.

  From another aspect, the present invention provides a weight update method in a communication scheme capable of assigning one transmission frame to a plurality of users, and a plurality of pilots existing in a minimum unit area of user assignment in the transmission frame. All of the signals are used for weight update, and then weight update is performed using pilot signals existing in other user assigned minimum unit areas.

  From another viewpoint, the present invention provides a weight update method in a communication system in which a burst area allocated to a user is included in a transmission frame, and performs a weight update operation based on a received pilot signal to perform a weight update operation. A weight update step for obtaining an estimated value; and a weight smoothing step for obtaining a smoothed estimated value obtained by smoothing a plurality of weight estimated values obtained by weight update calculation. In the weight smoothing step, A plurality of weight estimation values are smoothed in units.

  The present invention from still another aspect is a weight update method in a communication method capable of assigning one transmission frame to a plurality of users, and updates the weight based on a pilot signal included in the received signal, A weight update step for obtaining a weight estimate value, and a weight smoothing step for obtaining a smoothed estimate value obtained by smoothing a plurality of weight estimate values obtained by calculation of weight update. In the weight smoothing step, A plurality of weight estimation values are smoothed in a user allocation minimum unit.

  In another aspect of the present invention, the weight smoothing unit is performed after the weight destination estimation value to be smoothed and the weight update when the weight estimation value is obtained. The smoothed estimated value of the weighted destination estimated value is obtained by weighting and combining the smoothed estimated value of the post-weight estimated value obtained by the weight update.

  In the communication device, the weight smoothing unit may update the weight according to a pilot signal used when updating the weight when the weight estimation value to be smoothed is obtained. The smoothed estimated value of the weight estimated value is obtained by updating the weight of the post-weight estimated value obtained by the weight update performed later.

  In another aspect of the present invention, the weight smoothing unit is used for weight update performed after weight update when the weight estimation value to be smoothed is obtained. The smoothed estimated value of the weight estimated value is obtained by performing fixed interval smoothing based on the pilot signal that has been obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the weight estimation precision accompanying the burst switching at the time of weight update can be suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, WiMAX (Worldwide Interoperability for Microwave Access, IEEE 802.16) will be described as an example of a communication method.

  FIG. 1 shows a subcarrier arrangement of an OFDM system (WirelessMAN-OFDM) or an OFDMA system (WirelessMAN-OFDMA) adopted in WiMAX. OFDM is a type of frequency multiplexing method, and is a communication method in which digital information is transmitted by applying QAM modulation to a large number of carriers (subcarriers) arranged so as to be orthogonal on the frequency axis. In addition, OFDMA is a scheme in which the concept of logical subchannels configured by subsets of subcarriers is introduced into the OFDM scheme to expand the flexibility of radio resource allocation to user data.

There are three types of OFDM subcarriers: a data subcarrier (Data Sub-Carrier), a pilot subcarrier (Pilot Sub-Carrier), and a null subcarrier (Null Sub-Carrier).
The data subcarrier (data signal) is a subcarrier for transmitting data and a control message. The pilot subcarrier is a known signal (pilot signal) on the reception side and the transmission side, and is used for propagation coefficient estimation or as a reference signal for weight update.

  A null subcarrier is a subcarrier in which nothing is actually transmitted, and a guard subband on the low frequency side (guard subcarrier), a guard subband on the high frequency side (guard subcarrier), and a DC subcarrier ( Center frequency subcarrier).

FIG. 2 shows a two-dimensional arrangement of data subcarriers (data signals) and pilot subcarriers (pilot signals) excluding null subcarriers for OFDMA uplink PUSC (Partial Used SubChannel). In FIG. 2, the horizontal axis is the frequency axis, and the vertical axis is the time axis.
1 (1-L) on the horizontal axis in FIG. 2 indicates the subcarrier number. The subcarrier number is a number in which the subcarriers excluding the null subcarrier are numbered in ascending order of frequency. When the number of all subcarriers including null subcarriers is 1024, the total number L of data subcarriers and pilot subcarriers is 840.
K on the vertical axis in FIG. 2 indicates a symbol number. The symbol number is a number assigned to symbols in order of arrival time.

In FIG. 2, a total of 12 subcarriers, 3 in the symbol direction (time axis direction) × 4 in the frequency axis direction, are subdivided to form one tile structure. A tile is a minimum unit for user allocation.
Pilot subcarriers are arranged at the four corners of the tile, and the other subcarriers in the tile are data subcarriers.
As shown in FIG. 2, the tiles are regularly arranged in the time axis direction and the frequency axis direction. As a result, pilot subcarriers exist at a plurality of positions in the frequency axis direction and exist at a plurality of positions in the time axis direction.

  FIG. 3 shows the subcarrier arrangement of FIG. 2 in terms of subchannels and time slots. Here, the subchannel is a subset of four (plural) subcarriers. In addition, the time slot is a time slot for three (plural) symbols. That is, the above-mentioned tile is one subchannel and one slot.

  In OFDMA, it is possible to assign a subchannel to each user. Therefore, OFDMA allows multiple access that performs frequency division multiplexing (FDM) as well as time division multiplexing (TDM) employed in WirelessMAN-OFDM.

  OFDMA (uplink) user allocation is performed in units of tiles (minimum unit of user allocation). An area in which a plurality of tiles (minimum unit for user allocation) is combined is allocated to a user as a data area (burst area).

  FIG. 4 shows a transmission frame structure of OFDMA. One transmission frame (one basic frame) has a downlink subframe and an uplink subframe. A transmission / reception switching gap TTG (Transmit / Receive Transition Gap) is provided between the downlink subframe and the subsequent uplink subframe. Also, a reception / transmission switching gap RTG (Receive / Transmit Transition Gap) is provided between the upstream frame and the downstream subframe.

  The downlink subframe has a preamble first, followed by FCH (frame control header), DL-MAP (downlink allocation information), and UL-MAP (uplink allocation information). The downlink subframe further includes downlink burst #n (for example, n: 1 to 9) for transmitting downlink user data. The downlink burst area is a downlink data area assigned to a user, and user data combining TDM and FDM is multiplexed.

The uplink frame has an uplink burst #m (for example, m: 1 to 3) for transmitting uplink user data in addition to the registering subchannel. The uplink burst area is an uplink data area allocated to a user, and is configured by a combination of one or a plurality of tile areas.
In FIG. 4, the uplink frame is only multiplexed by subchannel (FDM). However, multiplexing in slot units (TDM) may also be performed. That is, multiplexing similar to that of the downlink is possible.

  FIG. 5 shows a cluster structure that is a minimum unit of user allocation in downlink PUSC. Also in the case of downlink PUSC, a burst region is configured by a combination of clusters with the cluster structure as a minimum unit.

[First Embodiment]
FIG. 6 shows functional blocks of the communication apparatus according to the first embodiment. As this communication apparatus 1, a base station is mainly assumed. The communication device 1 includes a plurality of antenna elements 11 and configures an adaptive array antenna system in which a spatial filtering characteristic is adaptively controlled by a filtering processing unit 14.

The communication device 1 is provided with an RF (Radio Frequency) unit 12 and an FFT unit 13 corresponding to each antenna element 11. The RF unit 12 performs processing such as removal of guard intervals added at the transmission side and A / D conversion. The FFT unit performs processing such as serial / parallel conversion and discrete Fourier transform.
The output (multi-antenna signal) of each FFT unit 13 is given to the filtering processing unit 14. The filtering processing unit 14 adaptively obtains a spatial filtering characteristic corresponding to the propagation environment.

In FIG. 6, in addition to the mobile station (desired station) 2 with which the communication device 1 is to communicate, interference stations (mobile stations) 3 and 4 that are interference sources are shown. The total number of desired stations and interfering stations 3 and 4 is M.
The desired station 2 and the interfering stations 3 and 4 respectively perform IFFT units 21, 31, and 41 that perform processing such as parallel / serial conversion and inverse discrete Fourier transform, and processing such as addition of guard intervals and D / A conversion. RF units 22, 32 and 42 and antenna elements 23, 33 and 43 are provided.

  The propagation path between the transmission side communication apparatuses 2, 3, 4 and the reception side communication apparatus 1 is a fading propagation path. When the subcarrier passes through the fading propagation path, its amplitude and phase change. The amount of change varies depending on the position of the subcarrier (time axis direction position and frequency axis direction position).

The filtering processing unit 14 of the receiving-side communication device 1 combines an output signal from each FTT unit corresponding to each antenna element 11 by applying an appropriate weight, extracts a desired signal in each subcarrier, Output as an output signal.
FIG. 7 shows a filtering model showing the relationship between the desired signal, the output signal, and the received signal (strictly speaking, a signal from the FFT unit 13 corresponding to the antenna element 11 of the communication device 1) in FIG.

In FIG. 7, k indicates a symbol number, and l indicates a subcarrier number. M represents the number of desired signals and interference signals. Note that the symbol M may be used in another meaning in the following description.
The noise signal Z (k, l) is a complex N × 1 vector representing noise in each antenna element 11.
The received signal X (k, l) is a complex N × 1 vector composed of the output from the FFT unit corresponding to each antenna element 11.
The transfer function H _m (k, l) (m = 1 to M) is a complex N × 1 vector in which changes in amplitude and phase that each subcarrier of each signal receives in a fading propagation path with N antenna elements are arranged. is there.
The weight W (k, l) is an N × 1 vector in which complex conjugates of complex weights to be multiplied for each element of the received signal are arranged. In FIG. 4, the superscript H represents a complex conjugate transpose. In the following, the superscript T represents transposition.

The relationship between the signals in FIG. 7 is expressed as in equations (1) and (2).

The purpose of the filtering processing unit 14 is to estimate only the desired signal S ₁ (k, l) from the received signal X (k, l) affected by the interference signal.
FIG. 8 shows details of the filtering processing unit 14. The filtering processing unit 14 includes a first buffer (reception signal storage unit; reception pilot signal storage unit) 141 that sequentially stores the reception signal X (k, l). Received signal X (k, l) stored in first buffer 141 is applied to weight multiplier 142. The weight multiplying unit 142 multiplies the received signal (data subcarrier) X (k, l) by the weight W (k, l) and combines them to generate an output signal Y (k, l) = W (k, l) ^H X (K, l) is output.

In addition, the received signal (pilot subcarrier) X (k, l) of the first buffer 141 is given to the weight updating unit 143 because it is used to update the weight W (k, l). When the received signal stored in the first buffer 141 is not used by the weight multiplier 142 and the weight updater 143, it is erased as needed.
By accumulating received signals in the first buffer 141, it is possible to easily cope with diversifying weight update directions as in the present embodiment. It is also possible to cope with smoothing of the weight estimation value.

  Weight update section 143 updates the current weight estimated value by an update process (weight update step) using pilot subcarriers included in the received signal, and outputs the updated weight estimated value to second buffer 144. . Details of the update process will be described later.

The second buffer (weight estimated value storage unit) 144 is weight estimated value W (k, l) ((k, l) = (1, 1), (1, 4) at the position of the pilot subcarrier. .., (1, L),... Specifically, a plurality of weight estimation values obtained by weight updating using a plurality of pilot subcarriers in a predetermined region when the subcarriers are viewed in a two-dimensional arrangement of the time axis and the frequency axis are stored.
The weight estimation value in the second buffer 144 is deleted as needed when it is not used in the weight interpolation unit 145 described later.

The weight interpolation unit 145 interpolates the weight W (k, l) at the data subcarrier position using the weight at the pilot subcarrier position, and gives the weight W (k, l) to the weight multiplication unit 142. .
FIG. 9 shows an example of weight interpolation. In the example of FIG. 9, linear interpolation is performed in tile units. Specifically, by performing the calculation shown in FIG. 9A on the weights W ₁ , W ₄ , W ₉ , and W ₁₂ at the pilot subcarrier positions of the tile shown in FIG. Weights W ₂ , W ₃ , W ₅ , W ₆ , W ₇ , W ₈ , W ₁₀ , W ₁₁ at the subcarrier position are calculated.
By performing this calculation for all tiles, weights at all data subcarrier positions can be calculated.

[Weight update processing by weight update unit (weight update step)]
The weight update unit 143 according to the present embodiment is configured to update weights using the RLS algorithm. However, other algorithms such as an LMS algorithm or an SMI algorithm may be used.

The weight update unit 143 includes a pilot subcarrier X (k, l) in a received signal, a corresponding desired signal reference signal (pilot subcarrier) S (k, l), weight update parameters P and α, To update the current weight W (k _prev , l _prev ) to a new weight W (k, l).

The weight update arithmetic expression by the RLS algorithm is as the following expressions (3) and (4). Note that the weight update unit 143 also calculates an update value P _{next of the} parameter P used in Expression (4). The update calculation formula of P is as the following formula (5).

As shown in FIG. 8, among the values used in the above formulas (3) to (5), the pilot subcarrier X (k, l) is acquired from the first buffer 141 via the order control unit 146. . Further, the reference signal (pilot subcarrier) S (k, l) of the desired signal is generated by the reference signal generation unit 147 and given to the weight update unit 143. The weight update parameter P (N × N matrix) is stored in the third buffer (weight update parameter storage unit) 148, and the weight update unit 143 acquires the parameter P from the third buffer 148. The parameter P _next updated by the weight updating unit 143 is updated and stored in the third buffer 148 and used as the parameter P for the next weight update.

  The update parameter α in the above formulas (4) and (5) is a forgetting factor and takes a value between 0 and 1. By adjusting the value of α, it is possible to adjust the follow-up characteristic to the variation of the transfer function in the frequency axis direction and the time axis direction. Since the value of the parameter P is determined depending on α, the value of P can be adjusted by adjusting the value of α.

[Weight update order control]
As described above, the weight updating unit 143 acquires the received signal (pilot subcarrier) X (k, l) from the first buffer 141 via the order control unit 146.
The order controller 146 separates and extracts pilot subcarriers from the received signal stored in the first buffer 141.
Then, order control section 146 controls the order of pilot subcarriers used by weight update section 143 for weight update. Specifically, order control section 146 rearranges the separated pilot subcarriers in the order used for weight update. Then, order control section 146 provides the rearranged pilot subcarriers to weight update section 143 in the rearranged order.
The order control unit 146 has a rearrangement rule (update order rule) for one or a plurality of pilot subcarriers. Note that the rearrangement rule (update order) can be dynamically changed according to the propagation environment.

An example of the update order rule is shown in FIG. One basic policy of the update order rule here is to use all pilot subcarriers present in one burst region B1. Further, in this update order rule, weights using pilot subcarriers in the other burst regions B2, B3, and B4 until weight update using all pilot subcarriers existing in one burst region B1 is completed. Do not update.
In other words, in this update order rule, when the weight update in one burst area B1 is completed and the weight update in the other burst areas B2, B3, B4 is switched, then the original burst area B1 is restored. It will not return.

  In the update order rule of FIG. 10, first, a certain burst area B1 is updated in the direction D1 of FIG. That is, for a plurality of pilot subcarriers X (1, 1) to X (1, l) in the frequency axis direction for the same symbol (same time k = 1), the pilot subcarriers having the lowest frequency are used in order. Weight update is performed (frequency axis direction update control; frequency axis ascending direction update control D1).

  When the frequency axis ascending direction update control D1 is performed and the pilot subcarrier X (1, l) having the largest subcarrier number 1 in the burst region B1 is reached, update in the direction D2 in FIG. 10 is performed next. That is, the pilot subcarrier X (3, l), which moves from the position (1, l) in the time axis direction and is next in the time axis direction, is used for weight update (first time axis direction update control D2). Note that the movement width (pilot interval) for the first time axis direction update is two symbols.

  After the first time axis direction update control D2, the update is performed in the direction D3 in FIG. That is, it is used for weight update in order from the pilot subcarrier having the highest frequency in the same symbol (same time) (frequency axis direction update control; frequency axis descending direction update control D3). In other words, the weight update is performed in the opposite direction to the frequency axis ascending direction update control D1.

When the frequency axis descending direction update control D3 is performed and the pilot subcarrier X (3, 1) having the smallest subcarrier number 1 is reached, 107 is updated in the D4 direction. That is, it moves in the time axis direction from the position of X (3, 1), and uses pilot subcarrier X (4, 1) next in the time axis direction for weight update (second time axis direction update control D4). . Note that the movement width (pilot interval) of the second time axis direction update is one symbol.
After the second time axis direction update control D4, the frequency axis ascending direction update D1 is performed, and the above process is repeated until one burst region B1 ends. If the weight update in one burst area B1 is completed, the weight update may be performed in another burst area (for example, the next burst area B2 in terms of time).

  In the rule of FIG. 10, the control is a combination of four update controls: frequency axis ascending direction update control D1, first time axis direction update control D2, frequency axis descending direction update control D3, and second time axis direction update control D4. ing. In the update controls D1 to D4, the frequency axis direction update controls D1 and D3 and the time axis direction update controls D2 and D4 are combined.

  According to the above rules, the number of weight updates per symbol is performed a plurality of times when the symbols in which pilot subcarriers exist are observed. If the weight is updated only in the time axis direction, the weight is updated only once per symbol. However, according to the rule, the number of updates is dramatically increased. As a result, many updates can be performed even if the number of symbols is small, and it is easy to obtain an appropriate weight.

Further, according to the rule of FIG. 10, the update performed by moving in the frequency axis direction is performed more than the update performed by moving in the time axis direction. Therefore, when considering the cross-correlation of propagation coefficients at the position of each subcarrier, if the cross-correlation between subcarriers in the frequency axis direction is larger than the cross-correlation in the time axis direction, an appropriate weight is given early. Is obtained.
In an environment where the cross-correlation of propagation coefficients between subs and carriers in the time axis direction is larger, the number of updates performed by moving in the time axis direction may be increased.

Obtaining an appropriate weight at a high speed is particularly useful in a system that performs transmission with a mobile unit, such as mobile WiMAX (IEEE 802.16e).
Moreover, in the update order rule of this embodiment, since a plurality of directions are combined, the degree of freedom in the update order is high. Moreover, when the diagonal direction which moves simultaneously in a time-axis direction and a frequency-axis direction is included, a freedom degree becomes higher.

Moreover, in burst area B1 and other burst areas B2, 3, and 4, areas (resources) may be allocated to different users. Therefore, for example, if weight updating is performed from the burst area B1 in the frequency axis direction and the burst area B1 is entered to enter the burst area B3 and weight updating is performed, the first several weight estimations in the burst area B3 are performed. The value is less accurate. When returning from the burst area B3 to the burst area B2 again, the accuracy of the first several weight estimation values after returning to the burst area B1 also decreases.
As described above, when burst switching occurs, the weight estimation accuracy generally deteriorates in the vicinity of the boundary between the burst areas B1 and B3.

  Similarly, when burst switching occurs between the burst area B1 and the burst area B2, the weight estimation accuracy generally deteriorates near the boundary between the burst areas B1 and B2.

On the other hand, in the rule of FIG. 10, since all pilot signals in burst area B1 are used for weight update and then moved to other burst areas B2, B3, B4, one burst area B1 is changed to another burst area. Transition to B2, B3, and B4 (burst switching) occurs only once, so that burst switching does not occur frequently.
As a result, it is possible to suppress weight estimation accuracy deterioration due to burst switching.

  Note that burst switching may be performed in the time axis direction or may be performed in the frequency axis direction. Also, the order of pilot subcarriers used for weight update within one burst region can be set as appropriate.

FIG. 11 shows another example of the weight update order rule.
In the example of FIG. 11, the weight update is performed with reference to a tile that is a minimum unit of user allocation in the uplink PUSC. One basic policy of the update order rule of FIG. 11 is to use all pilot subcarriers present in one tile area T1. Further, in this update order rule, weight update using pilot subcarriers in other tile regions T2 to T6 is performed until weight update using all pilot subcarriers existing in one tile region T1 is completed. Not performed.
In other words, according to the update order rule of FIG. 11, when the weight update in one tile area T1 is completed and the weight update in the other tile areas T2 to T6 is switched, then the original tile area T1 is restored. It will not return.

  More specifically, in the example of FIG. 11, the weight update is performed as follows. First, the weight at the pilot subcarrier position at the upper left of the tile is W1, the weight at the pilot subcarrier position at the upper right of the tile is W4, the weight at the pilot subcarrier position at the lower left of the tile is W9, and the pilot subcarrier position at the lower right of the tile Is W12.

In this case, in FIG. 11, the weights are updated in the order of W1, W4, W12, and W9 for one tile, and the weights are updated in the same order for the subsequent tiles.
Movement D11 from W1 to W4 is frequency axis direction update control (ascending order), and movement D13 from W12 to W9 is also frequency axis direction update control (descending order). The movement D12 from W4 to W12 and the movement D14 from W9 to W1 of the next tile are time axis direction update control.
Also in the update controls D11 to D14, the frequency axis direction update controls D11 and D13 and the time axis direction update controls D12 and D14 are combined.

  In the rule of FIG. 11 as well, the number of weight updates per symbol is larger than the weight update only in the time axis direction. Moreover, since the weight can be updated four times per tile, there is a high possibility that an appropriate weight can be obtained by updating the weight within one tile.

  In addition, since the tile is a minimum unit for user allocation, there is a possibility that areas are allocated to different users in one tile area T1 and the other tile areas T2 to T6. On the other hand, one tile is not divided and assigned to a plurality of users.

In the example of FIG. 11 as well, in the same way as in the example of FIG. 10, there is a case where tile switching is performed in which weight is updated by switching from one tile T1 to another tile T2 to T6. However, since all pilot signals in the tile area T1 are used for weight update and then moved to the other tile areas T2 to T6, the transition from one tile area T1 to the other tile areas T2 to T6 (tile switching) Occurs only once and tile switching does not occur frequently.
As a result, it is possible to suppress weight estimation accuracy deterioration due to tile switching.

In addition, when sequentially updating weights in units of tiles as shown in FIG. 11, it is possible to suppress deterioration in weight estimation accuracy without considering how burst areas are set.
Furthermore, when the weight is sequentially updated in units of tiles as shown in FIG. 11, it is possible to avoid deterioration in weight estimation accuracy due to burst switching of interference signals. That is, since the interference signal is not a signal from the original communication partner (desired station), it is difficult for the communication device to grasp where burst switching occurs (unless it communicates with the interference station). However, since burst switching does not occur within a tile, deterioration of weight estimation accuracy can be suppressed by performing weight update in units of tiles as shown in FIG. 11 wherever interference signal burst switching occurs.

In addition, although the tile area T2 in the time axis direction is illustrated in FIG. 11 as a tile area used for weight update after one tile area T1, a tile T3 in the frequency direction may be used.
Also, the order of pilot subcarriers used for weight update within one tile region can be set as appropriate.
Further, even when the minimum unit of user allocation is the cluster structure shown in FIG. 5, the above update order rule can be applied. That is, the minimum unit for user allocation is not limited to tiles, and may be another minimum unit for user allocation.

[Relationship between cross-correlation of propagation coefficients and weight update]
Hereinafter, characteristics of the time axis direction update control and the frequency axis direction update control employed in the update order rules as shown in FIGS. 10 and 11 will be described.
FIG. 12 shows a two-dimensional array of uplink PUSC subcarriers. The correlation coefficients of the propagation coefficients h _A , h _B , h _C , h _D , h _E at each pilot sub carrier position on this sub carrier arrangement were calculated under the following conditions.
Center frequency: 2600MHz
Doppler frequency: (1) 7.2 Hz, (2) 288 Hz
Delay dispersion: (a) 0.37 μsec (b) 2.2 μsec

The Doppler frequency (1) 7.2 Hz corresponds to the case where the moving speed of the mobile station is 3 km / h, and the Doppler frequency (2) 288 Hz corresponds to the case where the moving speed of the mobile station is 120 km / h.
Delay dispersion (a) 0.37 μsec is determined by ITU-R M.I. 1225 Vehicular ch. This is the value of A and indicates the average delay dispersion. Delay dispersion (b) 2.2 μsec is calculated according to ITU-R M.D. 1225 Vehicular ch. The value of B indicates that there are many buildings and the delay dispersion is large.
The combination of (1) and (a) is an assumed average environment, and the combination of (2) and (b) is the worst case in the assumed environment.

The signal points shown in FIG. 13 (subcarriers) n, the propagation coefficient of the m h _n, is ρ correlation coefficient h _m, time change model Jakes model, when the exponential decay delay profile a delay profile, the following formula It is obtained like this.

Table 1 below shows calculation results of correlation coefficients between the propagation coefficient h _A in FIG. 12 and other propagation coefficients h _B , h _C , h _D , and h _E.

As can be seen from Table 1, the correlation coefficient between the propagation coefficients _{h A} and propagation coefficients _{h B [h B: ρ]} and the correlation coefficient between the propagation coefficients _{h A} and propagation coefficients _{h C [h C:} With respect to ρ], when the moving speed of the mobile station is low [(1) (a), (1) (b)], the correlation coefficient is almost 1, which is large.
Therefore, in such a case, the time axis direction update control is preferable.

However, when the delay dispersion is average and the moving speed of the mobile station is high [(2) (a)], the correlation coefficient [h _D : between the propagation coefficient h _A and the propagation coefficient h _c : ρ] is smaller than [h _B : ρ] and [h _C : ρ].
Therefore, when the moving speed of the mobile station is high, it is preferable to perform frequency axis direction update control. When delay dispersion is large, it is desirable to preferentially update in the time axis direction.

[Simulation by update order rule of FIG. 11]
In the uplink PUSC subcarrier arrangement, simulation was performed under the following conditions for pattern A (comparative example) and pattern B (example: same as the rule of FIG. 11) shown in FIG. Pattern A is a time axis direction update control only, and pattern B is a combination of time axis direction update control and frequency axis direction update control.

(Simulation parameters)
Center frequency: 2.6 [GHz], sampling time 89.2 [ns], subcarrier interval 10.9 [kHz], number of antenna elements: 2, FFT size: 1024, guard interval length: 11.4 [μs] , Number of used subcarriers: 840, frame length: 5 [ms], Uplink subframe length: 1.5 [ms], modulation method: QPSK, used algorithm: RLS algorithm (forgetting factor 0.5)

(Propagation path model in simulation)
Number of incoming signals: 2 (desired signal and interference signal), propagation path model: equal power two-wave Rayleigh fading model, delay time difference: 8.92 × 10 ² [ns], maximum Doppler frequency: 288
[Hz] (equivalent to moving at 120 km / h), average received SNR: 20 [dB], average received SIR: 0 [dB]

The simulation results are shown in FIG. FIG. 15 shows a comparison of changes in interference signal removal characteristics (for each received symbol) with respect to the weight update pattern of FIG. 14 by MER (modulation error rate) in the data portion. The MER was calculated by MER = E [| Y (t) −W (t) ^H X (t) | ² ]. Further, the propagation path parameter was changed at random, 100 trials were performed, and the average value was calculated.

  As shown in the P1 part of FIG. 15, the MER drops significantly every 15 symbols. This is because there is a downstream frame section between the upstream frames of 15 symbols, and the propagation characteristics change greatly during the downstream frame section. It is.

As can be seen from FIG. 15, even when the MER drops significantly, the pattern B of the embodiment has a faster rise and a relatively good weight estimation value is obtained by updating the weights within one tile. This is because the number of updates per symbol is large (twice) (see P2 in FIG. 15).
Also, when the MER rises, the pattern B is larger by about 3 dB than the pattern A (see P3 and P4 in FIG. 15). Note that the demodulation characteristics change for each received symbol because the magnitude of the correlation of the propagation characteristics between pilots differs.

[Second Embodiment]
FIG. 16 illustrates the filtering processing unit 14 of the communication device according to the second embodiment. In the second and subsequent embodiments, the points that are not particularly described are the same as those in the first embodiment.

  The filtering processing unit 14 of the second embodiment is obtained by adding a weight smoothing unit 149, a fourth buffer 150, and a smoothing parameter adjusting unit 151 to the filtering processing unit 14 shown in FIG.

  Also in the second embodiment, the weight estimated value calculated by the weight updating unit 143 is accumulated in the second buffer 144. The weight estimation value in the second buffer 144 is deleted as needed when the weight interpolation unit 145 stops using it.

  The weight smoothing unit 149 performs a smoothing process on each of the plurality of weight estimation values stored in the second buffer 144 to calculate a weight smoothing estimation value (smoothing step). The weight smoothing estimated value calculated by the weight smoothing unit 149 is output to the fourth buffer 150. Details of the smoothing process will be described later.

  The fourth buffer (weight smoothed estimated value storage unit) 145 can store a plurality of smoothed estimated values. The smoothed estimated value in the fourth buffer 145 is deleted as needed when the weight interpolation unit 145 stops using it.

The weight interpolation unit 145 interpolates the weight W (k, l) at the data subcarrier position using the weight smoothing estimation value at the pilot subcarrier position), and the weight W (k, l). Is given to the weight multiplier 142.
In the present embodiment, since the weight is smoothed and the accuracy is improved, the weight at the data subcarrier position also has a high accuracy, and signal synthesis can be performed with high accuracy.

[Smooth processing of weight estimation value (smoothing step)]
Here, the weight update order by the order control unit 146 is assumed to be the order of FIG. 10 using all pilot subcarriers (M pilot subcarriers) in one burst region B1.
M (a plurality) weight estimation values, which are the result of all M weight updates performed in one burst region B1, are stored in the second buffer 144.
Here, one burst region B1 is set as one smoothing target region, and the weight smoothing unit 149 obtains a smoothed estimated value obtained by smoothing the M weight estimated values.

As shown by dotted arrows D1-S to D4-S in FIG. 17, the weight smoothing unit 149 performs smoothing in the order opposite to the weight update order.
If one of the weight update count of the burst region within B1 was m (m = 1~M), M pieces of weight estimation value _{W (k m, l} m) of the, most information (M pilots The subcarriers are reflected in W (k _M , l _M ) obtained by the last (m = Mth) weight update in the burst region B1.

  On the other hand, W (1,1) obtained by the first weight update in the burst region B1 which is the smoothing target region reflects only the least information (one pilot subcarrier). In general, the weight estimated using a lot of information (pilot subcarriers) is more accurate.

Therefore, in the smoothing processing here, most information is reflected _{W (k M, l} M) of the other of the weight _W of the smoothing target area _{(k m, l m) (} m = 1~ Reflected in M-1).

Specifically, the smoothing process performed by the weight smoothing unit 149 is as shown in FIG.
First, the smoothing unit 149 sends the weight estimated value W (k _M , l _M ) from the second buffer 144 to the fourth buffer 150 (step S1). The weight estimation value W (k _M , l _M ) reflects the most information and does not need to be further smoothed. Therefore, the smoothed estimation value W ^S (k _M , l _M ) = weight estimation value Let W (k _M , l _M ). Note that the processing in step S1 is also referred to as smoothing calculation processing as in step S5 described later, if necessary.

Subsequently, the weight smoothing unit 149 sets the counter m = M−1 (step S2). Then, the weight smoothing unit 149, the weight estimate from the second buffer _{144 W (k m, l m} ) acquires the (step S3), and the smoothed estimate previously obtained from the fourth buffer 0.99 ^W S ( k _{m + 1} , l _{m + 1} ) are acquired (step S4). Note that the weight smoothing unit 149 acquires the smoothing parameter β from the smoothing parameter adjustment unit 151.

Then, the weight smoothing unit 149 performs a smoothing calculation process according to the calculation formula of step S5. Step 5 of the smoothing processing weight estimation value obtained by the weight updating unit 143 is _{W (k} m, _{l m)} and the weight of the weight estimation value _{W (k} m, _{l m)} After obtaining the (immediately) combines the weight estimation obtained with the updated value _{W (k m + 1, l} m + 1) for smoothing the estimated value ^{_{W S (k m + 1,}} l m + 1) ( the parameters (weighted synthesis by weighting factor) beta), weight estimation values _{W (k m, l} m) smoothed estimate of ^{_{W S (k m, l m}} ) obtained.

Here, weight estimation value _{W (k m, l} m) is referred to as a "weight destination estimate", weight estimation value _W a _{(k m + 1, l m} + 1) will be referred to as "estimated value after the wait."
Weight destination estimate _{W (k} m, _{l m)} and the weight after the estimated value _{W (k m + 1, l} m + 1) are compared, and the weight after the estimated value _{W (k m + 1, l} m + 1) is the weight end estimation value W ( Since it is a value obtained by the weight update processing after (immediately after) k _m , l _m ), more information is reflected.
Each smoothing estimation value includes information on the weight estimation value W (k _M , l _M ) obtained by the last weight update in the smoothing region.
Therefore, the smoothed estimate obtained by the above synthesis _{^{W S (k m, l m}} ) is made shall smoothing previous weight estimation values W (k _{m, l m)} is more information than is reflected, The accuracy will be good.

Then, the weight smoothing unit 149 sends the calculated smoothed estimate ^{_{W S (k m, l m}} ) of the fourth buffer 150 (step S6).
Thereafter, the weight smoothing unit 149 determines whether m = 1 as an end determination of the repetition of the smoothing calculation (step S7). If m = 1 is not satisfied, m is decremented and steps S3 to S6 are performed again. If m = 1, the smoothing process ends.

The above smoothing process, the smoothing estimate ^{_{W S (k m, l m}} ) is, m = M, M-1 , obtained in the order of ... 2,1. That is, the smoothed estimation value is obtained in the reverse order of the weight update.

By performing the smoothing process, it is possible to obtain a good weight reflecting a lot of pilot signal information for a weight (unconverged weight) obtained by relatively initial weight update.
Specifically, for example, the weight estimated value W (1,1) is obtained based on one pilot signal and is usually an estimated value that has not converged, but the smoothed estimated value W ^S (1,1) reflects information on M pilot signals. The same applies to the other of the smoothed estimate _{^{W S (k m, l m}} ).
As a result, the accuracy of each weight is improved and weight interpolation is performed using the smoothed estimation value, so that the signal estimation is also improved as a whole.

In the above example, the smoothing calculation is performed in the reverse order of the weight update. However, the order in which the M weight estimation values are subjected to the smoothing calculation is limited to the above example. Absent. For example, the order may be m = M, 1, 2,..., M-2, M-1. That is, any order may be used as long as the weight estimated value obtained by the subsequent weight update can be reflected in the weight estimated value obtained by the previous weight update. That is, the order of smoothing calculations may be determined regardless of the weight update order.
In the above example, both the weight update unit and the smoothing unit are burst areas. However, if smoothing is performed, the weight update may not be performed in burst area units.

Since the smoothing process here uses the smoothing target area as a burst area unit, good smoothing can be performed. That is, since the burst area is a user allocation area, one burst area is allocated to the same user. For this reason, since the fluctuation of the propagation coefficient is relatively small within the burst region, if the smoothing process is performed in units of the burst region, a good weight can be obtained in the entire burst region.
The smoothing process is similarly performed for other burst regions.

[Adjustment of smoothing parameter β]
Now, as apparent from the equation at step 5 of FIG. 18, to what extent a by smoothing operation, the weight after the estimated value by the weight updating after information (smoothed estimate _{^{W S (k m + 1,}} l m + 1)) , smoothed estimate of the weight end estimation value _{W (k m, l m)} W S (k m, l m) is either reflected is up to the value of the smoothing parameter beta. Similar to the above-described weight update parameter α, by adjusting the value of β, it is possible to adjust the follow-up characteristic to the variation of the propagation coefficient in the frequency axis direction and the time axis direction.

Pilot subcarriers _{X (k m, l m)} X (k m + 1, l m + 1) between, the propagation coefficients when the cross-correlation is large, smooth estimate of the weight after the estimated value ^W S of _{(k m + 1, l m} + 1) Since more information should be used, the estimation accuracy of the smoothed estimated value of the weighted destination estimated value is improved by increasing the smoothing parameter β.
On the other hand, the pilot subcarrier _{X (k m, l m)} X (k m + 1, l m + 1) between the case cross-correlation of the propagation coefficient is small, the smoothed estimate of the weight after the estimated value ^{_{W S (k m + 1,}} l m + 1 ) Is less used, the follow-up characteristics to fluctuations in the propagation coefficient are improved. Therefore, in this case, the estimation accuracy of the smoothed estimated value of the weight destination estimated value is improved by reducing the smoothing parameter β.

Therefore, the smoothing parameter adjustment unit 151, a pilot subcarrier _{X (k m, l m)} X (k m + 1, l m + 1) the positional relationship (direction in subcarrier 2-dimensional arrangement (time axis direction and frequency axis direction) and (Or subcarrier spacing) is adjusted according to the cross-correlation of propagation coefficients.
Thereby, appropriate weight smoothing can be performed according to a smoothing direction (refer FIG. 17) and / or propagation environment, and a weight estimation precision can be improved.

[Third Embodiment]
19 and 20 illustrate a filtering processing unit 14 according to the third embodiment. Note that the third embodiment also includes the weight smoothing unit 149, and is the same as the second embodiment in that it is not specifically described in the third embodiment.

  The function of the weight smoothing unit 149 of the third embodiment has a weight update function substantially similar to the function of the weight update unit 143. However, the weight smoothing unit 149 here performs an update operation for smoothing in an order reverse to the update order of the weight update 143 (see the dotted arrow in FIG. 17).

Specifically, the smoothing process is performed according to the procedure shown in FIG. First, the smoothing unit 149 sends the weight estimated value W (k _M , l _M ) from the second buffer 144 to the fourth buffer 150 (step S11). That is, the weight estimated value W (k _M , l _M ) becomes the smoothed estimated value W ^S (k _M , l _M ) as it is.

Subsequently, the weight smoothing unit 149 sets the counter m = M−1 (step S12). Then, the weight smoothing unit 149, a pilot subcarrier _{X (k m, l} m) from the first buffer 141 obtains the (step S13), and the smoothed estimate previously obtained from the fourth buffer 0.99 ^W S ( k _{m + 1} , l _{m + 1} ) are acquired (step S14). Incidentally, the weight smoothing unit 149, the reference signal _{S (k m, l} m) to obtain a. In addition, the weight smoothing unit 149 obtains the parameter P for weight updating in the weight smoothing unit 149 from the fifth buffer 155 and the parameter α from the smoothing parameter adjustment unit (update parameter adjustment unit) 156.

In the third embodiment, the update parameter α in the weight update unit 143 can also be adjusted by the update parameter adjustment unit 153.
Further, the functions of the fifth buffer and the third buffer are the same, and the functions of the smoothing parameter adjustment unit 156 and the update parameter adjustment unit 153 are also the same.

Then, the weight smoothing unit 149 performs a smoothing calculation process (update calculation process) in accordance with the smoothing calculation formula shown below (step S15).

  The smoothing calculation formula is substantially the same as the weight update calculation formulas (3) to (5) described above except for the update order.

The smoothing processing in step 15, the immediately preceding on the obtained smoothed estimate ^{_{W S (k m + 1,}} l m + 1), based on the pilot subcarrier _{X (k m, l m)} , the weight updated by the calculation of the equation the estimated values obtained by, weight estimation value _{W (k m, l} m) of the smoothed estimate ^{_{W S (k m, l m}} ) is obtained as.

Well, again, weight estimation value _{W (k m, l} m) is referred to as a "weight destination estimate", the weight estimation value _{W (k m + 1, l} m + 1) will be referred to as "estimated value after the wait."
Weight destination estimate _{W (k m, l} m) and the weight after the estimated value _{W (k m + 1, l} m + 1) of the smoothed estimate ^{_{W S (k m + 1,}} l m + 1) are compared, and the smoothed estimate W ^{_{S (k m + 1, l}} m + 1) is intended to pilot subcarriers (rear pilot _{signal) X (k m + 1,} l m + 1) is calculated based on the weight end estimation value _{W (k m + 1, l} m + 1) obtained by smoothing So there is a lot of information reflected.

Therefore, as described above, the weight after the estimated value _{W (k m + 1, l} m + 1) of the smoothed estimate ^{_{W S (k m + 1,}} l m + 1), pilot subcarriers (previous pilot signal) _{X (k m, l} m ) on the basis of, by weight updating, based on the weight estimate _{W (k m, l} m) accurate smoothed estimate ^W S _(k m than, _{l m)} is obtained.

Then, the weight smoothing unit 149 sends the calculated smoothed estimate ^{_{W S (k m, l m}} ) of the fourth buffer 150 (step S16).
Thereafter, the weight smoothing unit 149 determines whether m = 1 as an end determination of the smoothing calculation (step S17). If m is not 1, m is decremented and the processes of steps S13 to S16 are performed again. If m = 1, the smoothing process ends.

The above smoothing process, the smoothing estimate ^{_{W S (k m, l m}} ) is, m = M, M-1 , obtained in the order of ... 2,1 (see FIG. 17).

Note that the parameter (forgetting factor) α is appropriately adjusted in the smoothing parameter adjustment unit 156 and / or the update parameter adjustment unit 153 in FIG.
Specifically, the forgetting factor α is small when the cross-correlation of the propagation coefficient is large between the pilot signal used for the previous weight update calculation (smoothing calculation) and the pilot signal to be used for weight update. Is preferred. On the other hand, when the cross correlation of the propagation coefficient is small between the pilot signal used for the previous weight update and the pilot signal to be used for the weight update, it is preferable that the forgetting coefficient α is large.
Therefore, in any update direction and / or pilot subcarrier interval, the estimation accuracy can be improved by adjusting the parameter α according to the update (smoothing) direction and / or pilot subcarrier interval. it can.

As the update algorithm of the weight smoothing unit 149 of the third embodiment, the RLS algorithm is adopted as in the case of the weight update unit 143, but other algorithms such as an LMS algorithm and an SMI algorithm may be used. good.
Further, the order of pilot signals used for smoothing is not limited to the above, and is arbitrary.

[Fourth Embodiment]
FIGS. 21-22 has shown the filtering process part 14 which concerns on 4th Embodiment. Note that points not specifically described in the fourth embodiment are the same as those described above.

In the fourth embodiment, the weight updating unit 143 and the weight smoothing unit 149 are mainly different from those in the second and third embodiments.
The third buffer (updated parameter storage unit) 148 shown in FIG. 21, the parameter _{P (k} m, _{l m)} sent from the weight updating unit stores the. The third buffer 148 erases the _{P (k m, l} m) is no longer used in the weight update unit 143 and the weight smoothing unit 149. Further, the fifth buffer (smoothing parameter storage unit) 162 shown in FIG. 21 stores the parameter λ sent from the weight smoothing unit 149. Here, the initial value of λ is 0.

The weight update unit 143 of the fourth embodiment performs weight update according to the following procedure. The update processing procedure in the weight update unit 143 is basically the same as that of the above-described embodiment except for the update arithmetic expression.
Specifically, the update processing procedure is as follows. For M pilot signals in the burst region B1 that is the smoothing target region (see FIG. 17), the following procedures 2 to 3 are changed to M. Repeat until.
Step 1: m = 1
Procedure 2: Update calculation procedure Procedure 3: Return to Procedure 2 with m = m + 1

The update calculation process of the procedure 2 is performed according to the following formula.

When updating processing of step 2, the weight update unit 143 acquires the reference signal _{S (k m, l} m) from the reference signal generator 147, a pilot subcarrier _{X (k m, l} m) of the first Obtained from the buffer 141, and obtains the parameter P (km _-1 , lm _-1 ) from the third buffer.

According to the above equation, the weight estimate _{W (k m, l} m) is obtained in addition, it updates the parameter _{P (k m, l} m) is obtained. The obtained weight estimation values _{W (k m, l} m) is sent to the second buffer _{144, P (k m, l} m) is sent to the third buffer 148 are stored in respective buffers.

Note that the _{Q (k m, l} m), depending on the positional relationship between the pilot subcarriers _{X (k m, l m)} X (k m-1, l m-1), adjusted by updating the parameter adjuster 153 Is done.

The weight smoothing unit 149 of the fourth embodiment uses a fixed-interval smoother as a smoothing algorithm. Here, Fraser's algorithm is used as the fixed section smoother.
Specifically, the smoothing process is performed according to the procedure shown in FIG. First, the smoothing unit 149 sends the weight estimated value W (k _M , l _M ) from the second buffer 144 to the fourth buffer 150 (step S21). That is, the weight estimated value W (k _M , l _M ) becomes the smoothed estimated value W ^S (k _M , l _M ) as it is.

Subsequently, the weight smoothing unit 149 sets the counter m = M−1 (step S22). Then, the weight smoothing unit 149, a pilot subcarrier _X from the first buffer _{141 (k m + 1, l} m + 1) acquires the (step S23), weight estimation value of the smoothing target from the second buffer 144 ^W S (k _m , l _m ) is acquired (step S24).
Incidentally, the weight smoothing unit 149, the reference signal _{S (k m + 1, l} m + 1) acquired from the reference signal generator 160, the parameters obtained on the weight update computation _{P (k m, l} m) of the third buffer 148 and λ _{m + 1} is obtained from the fifth buffer 162.

Then, the weight smoothing unit 149 performs a smoothing calculation process according to the smoothing calculation formula shown below (step S25).

The smoothing processing in step 25, as shown in FIG. 17, weight estimation value obtained in the weight update unit _{143 W (k m, l m} ) was converted, smoothed by Fraser algorithms, smoothed estimate ^{_{W S (k m, l m}} ) are seeking.

Well, here, weight estimation value _{W (k m, l} m) is referred to as a "weight destination estimate", the weight estimation value _{W (k m + 1, l} m + 1) will be referred to as "estimated value after the wait." The wait end estimation value _{W (k m, l} m) pilot signal _{X (k m, l} m) used for obtaining a good and above pilot signal, the weight after the estimated value _W a _{(k m + 1, l m} + 1) It is assumed that the pilot signal X (k _{m + 1} , l _{m + 1} ) used for the determination is used.

In the above operation expression, as information of the rear pilot signal _{X (k m + 1, l} m + 1) is reflected, smoothing weights end estimation value _{W (k m, l m)} . Therefore, the weight end estimation value _{W (k m, l} m) of the smoothed estimate ^{_{W S (k m, l m}} ) is becomes the information of the rear pilot signal _{X (k m + 1, l} m + 1) is reflected .

Then, the weight smoothing unit 149 sends the calculated smoothed estimate ^{_{W S (k m, l m}} ) of the fourth buffer 150 (step S26). The weight smoothing unit 149 sends the updated λ _m to the fifth buffer 162, and the fifth buffer 162 stores λ _m for use in the next smoothing calculation process.

  Thereafter, the weight smoothing unit 149 determines whether m = 1 as an end determination of the repetition of the smoothing calculation (step S27). If m = 1 is not satisfied, m is decremented and steps S23 to S26 are performed again. If m = 1, the smoothing process ends.

The above smoothing process, the smoothing estimate ^{_{W S (k m, l m}} ) is, m = M, M-1 , obtained in the order of ... 2,1 (see FIG. 17).

  FIG. 23 shows another example of the smoothing target area. Here, the smoothing target area is not the burst area but the tile areas T1 to T6 which are the user allocation minimum units. Also, the weight update order is the same as the order shown in FIG. 11, and the smoothing order D13-S, D12-S, D11-S within one tile area is the reverse of the weight update order. . The smoothing process may be any of the second embodiment to the fourth embodiment. When the tile area is a smoothing target area, M in the smoothing process is “4”.

Since the tile area is a minimum user allocation unit, smoothing can be performed in an area where burst switching does not occur by performing smoothing in units of tile areas. That is, if a plurality of tile areas are set as one smoothing area, there is a possibility that smoothing processing is performed in an area to which a plurality of users are assigned. On the other hand, by estimating the weight at each time from a plurality of signals in an area to which the same user is assigned, it is possible to suppress the influence of a rapid change in the optimum weight due to user switching.
In addition, even for an interference signal for which it is difficult to grasp the occurrence of burst switching, burst switching does not occur in the tile area, so the influence of burst switching on the interference signal can be eliminated.

In the example of FIG. 23, both the weight update unit and the smoothing unit are tile areas. However, if smoothing is performed, the weight update may not be performed in tile area units. For example, the weight update may be performed in burst area units as shown in FIG. 10, and smoothing may be performed in tile area units.
Further, the weight update may be performed regardless of the burst area or the tile area, and may be performed so that burst switching occurs during continuous weight update, and smoothed in units of tiles.

[Smoothing simulation]
In the uplink PUSC subcarrier arrangement, the case of no smoothing shown in FIG. 24 (weight update by the update order rule of FIG. 11) and the case of smoothing (same as the weight update and smoothing of FIG. 23) are shown. Based on the configuration of the communication apparatus according to the second embodiment, the simulation was performed under the following conditions.

(Simulation parameters)
Center frequency: 2.6 [GHz], sampling time 89.2 [ns], subcarrier interval 10.9 [kHz], number of antenna elements: 2, FFT size: 1024, guard interval length: 11.4 [μs] , Number of used subcarriers: 840, frame length: 5 [ms], Uplink subframe length: 1.5 [ms], modulation method: QPSK, use algorithm of weight update unit: RLS algorithm (forgetting factor 0.5), Smoothing parameter β = 0.5

(Propagation path model in simulation)
Number of incoming signals: 2 (desired signal and interference signal), propagation path model: equal power two-wave Rayleigh fading model, delay time difference: 8.92 × 10 ² [ns], maximum Doppler frequency: 288
[Hz] (equivalent to moving at 120 km / h), average received SNR: 20 [dB], average received SIR: 0 [dB]

The simulation results are shown in FIG. FIG. 25 shows a comparison of changes in interference signal removal characteristics (for each received symbol) when smoothing is not performed on a tile-by-tile basis with MER (modulation error rate) in the data portion. The MER was calculated by MER = E [| Y (t) −W (t) ^H X (t) | ² ]. Further, the propagation path parameter was changed at random, 100 trials were performed, and the average value was calculated.

  As shown in the P5 part of FIG. 25, the MER drops significantly every 15 symbols. This is because there is a downstream frame section between the upstream frames of 15 symbols, and the propagation characteristics change greatly during the downstream frame section. It is. However, it can be seen that when smoothing is performed, the drop of every 15 symbols is small and the rising performance is improved.

  Further, as can be seen from the P6 portion of FIG. 25, it can be seen that the overall 1 dB characteristic is improved by smoothing. Further, in the tile structure (3 symbols), when the first symbol is k in time, the second symbol is k + 2, and the third symbol is k + 3, the weight improvement effect in the order of symbol k, symbol k + 2, and symbol k + 2. Is getting bigger.

  The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the spirit of the present invention.

It is a figure which shows the subcarrier structure of OFDM. It is a frequency-time two-dimensional array of subcarriers. 2 is a two-dimensional array of subchannel-time slots of tiles. It is a figure which shows a transmission frame structure. It is a figure which shows a cluster structure. It is a block diagram of a communication apparatus. It is a figure which shows the simplified spatial filtering model. It is a block diagram of the filtering process part which concerns on 1st Embodiment. It is explanatory drawing of the weight interpolation method. It is a figure which shows the example of a weight update order rule. It is a figure which shows the other example of a weight update order rule. It is a figure which shows the propagation coefficient in each pilot subcarrier. It is a figure which shows the premise of the cross correlation calculation of a propagation coefficient. It is a figure which shows the weight update pattern in simulation. It is a figure which shows a simulation result. It is a block diagram of the filtering process part which concerns on 2nd Embodiment. It is a figure which shows a weight update order and a smoothing order. It is a flowchart of the smoothing process in 2nd Embodiment. It is a block diagram of the filtering process part which concerns on 3rd Embodiment. It is a flowchart of the smoothing process in 3rd Embodiment. It is a block diagram of the filtering process part which concerns on 4th Embodiment. It is a flowchart of the smoothing process in 4th Embodiment. It is a figure which shows the smoothing order of a tile unit. It is a figure which shows the weight update and smoothing order in simulation. It is a figure which shows a simulation result. It is a figure which shows the subcarrier arrangement | positioning in terrestrial digital broadcasting.

Explanation of symbols

1: Communication device (base station) 2: Desired station 3: Interfering station 4: Interfering station 11: Antenna element 12: RF unit 13: FFT unit 14: Filtering processing unit 141: First buffer (received signal storage unit) 142: Weight multiplication unit 143: Weight update unit 144: Second buffer (weight estimated value storage unit) 145: Weight interpolation unit 146: Order control unit 147: Reference signal generation unit 148: Third buffer (weight update parameter storage unit) 149: Weight smoothing unit 150: fourth buffer (weight smoothing estimated value storage unit) 151: smoothing parameter adjustment unit 153: update parameter adjustment unit 154: reference signal generation unit 155: fifth buffer (smoothing parameter storage unit) 156 : Smoothing (update) parameter adjustment unit 160: reference signal generation unit 161: smoothing parameter adjustment 162: fifth buffer (lambda storage unit)

Claims (13)

A burst region allocated to a user is included in a transmission frame, and pilot signals exist in a plurality of time-axis direction positions and a plurality of frequency-axis direction positions in the transmission frame. A plurality of minimum unit areas are arranged in the time axis direction and a plurality of frequency direction areas are arranged, and communication is performed by a communication method in which an area in which the minimum unit of user allocation is combined is assigned to a user as a burst area. In the communication device to perform
Based on a pilot signal included in the received signal, a weight update unit that calculates a weight estimation value by updating the weight of the received beam in the communication device that constitutes the multi-antenna system ;
An order controller for controlling the order of pilot signals used for updating weights;
With
The weight update unit obtains a weight estimated value at the position of the pilot signal by updating the weight updated in the previous weight update based on the pilot signal used for the update,
The order control unit uses all of a plurality of pilot signals existing in one burst region for weight update, and then performs weight update using pilot signals existing in another burst region. A communication device characterized by controlling.   The communication apparatus according to claim 1, wherein the burst area is a burst area in the OFDMA scheme. One transmission frame can be assigned to a plurality of users, and pilot signals are present in a plurality of time axis direction positions and a plurality of frequency axis direction positions in the transmission frame. In a communication device that performs communication by a communication method in which a plurality of areas of the minimum unit of allocation are arranged in the time axis direction and a plurality of areas are also arranged in the frequency direction ,
Based on a pilot signal included in the received signal, a weight update unit that calculates a weight estimation value by updating the weight of the received beam in the communication device that constitutes the multi-antenna system ;
An order controller for controlling the order of pilot signals used for updating weights;
With
The weight update unit obtains a weight estimated value at the position of the pilot signal by updating the weight updated in the previous weight update based on the pilot signal used for the update,
The sequence control unit uses all of a plurality of pilot signals existing in a minimum unit area of user allocation in the transmission frame for weight update, and then uses pilot signals existing in other minimum user allocation unit areas. The communication apparatus is characterized in that the order is controlled so as to perform weight update.   The communication apparatus according to claim 3, wherein the user allocated minimum unit area is a tile area in an uplink PUSC scheme of WiMAX or mobile WiMAX.   4. The communication apparatus according to claim 3, wherein the user allocated minimum unit area is a cluster area in a downlink PUSC scheme of WiMAX or mobile WiMAX. In a communication apparatus that performs communication by a communication method in which a burst region allocated to a user is included in a transmission frame,
Based on a pilot signal included in the received signal, a weight update unit that calculates a weight estimation value by updating the weight of the received beam in the communication device that constitutes the multi-antenna system;
An order controller for controlling the order of pilot signals used for updating weights;
A weight smoothing unit;
With
The weight update unit obtains a weight estimated value at the position of the pilot signal by updating the weight updated in the previous weight update based on the pilot signal used for the update,
The order control unit uses all of a plurality of pilot signals existing in one burst region for weight update, and then performs weight update using pilot signals existing in another burst region. Control
The weight smoothing unit, multiple weights updating communication apparatus you and obtains the smoothed estimate the weight estimation value obtained by smoothing obtained by calculation.   In a communication device that performs communication by a communication method that can assign one transmission frame to a plurality of users,
  Based on a pilot signal included in the received signal, a weight update unit that calculates a weight estimation value by updating the weight of the received beam in the communication device that constitutes the multi-antenna system;
  An order controller for controlling the order of pilot signals used for updating weights;
  A weight smoothing unit;
With
  The weight update unit obtains a weight estimated value at the position of the pilot signal by updating the weight updated in the previous weight update based on the pilot signal used for the update,
  The sequence control unit uses all of a plurality of pilot signals existing in a minimum unit area of user allocation in the transmission frame for weight update, and then uses pilot signals existing in other minimum user allocation unit areas. Control the order to update the weight
The weight smoothing unit obtains a smoothed estimated value obtained by smoothing a weight estimated value obtained by a plurality of weight update operations.
  A communication device. The weight smoothing unit
Obtaining the smoothed estimated value based on the information of the post-pilot signal used in the weight update performed after the weight update when the weight estimated value to be smoothed is obtained. The communication device according to claim 6 or 7, characterized in that The information of the post pilot signal is
The post pilot signal,
A post-weight estimation value obtained by the weight updating unit performing weight updating using the post-pilot signal, or a smoothed estimation value of the post-weight estimation value,
The communication device according to claim 8, wherein: A burst region allocated to a user is included in a transmission frame, and pilot signals exist in a plurality of time-axis direction positions and a plurality of frequency-axis direction positions in the transmission frame. A plurality of minimum unit areas are arranged in the time axis direction and a plurality of frequency direction areas are arranged, and the weight update in the communication method in which the area in which the minimum unit of user allocation is combined is assigned to the user as a burst area A method,
Based on the pilot signal included in the received signal, update the weight of the received beam in a multi-antenna system to obtain a weight estimate,
In the update of the weight, the weight updated in the previous weight update is updated based on the pilot signal used for the update, thereby obtaining a weight estimated value at the position of the pilot signal,
A weight update method comprising: using all of a plurality of pilot signals existing in one burst region for weight update, and then performing weight update using pilot signals existing in another burst region. One transmission frame can be assigned to a plurality of users, and pilot signals are present in a plurality of time axis direction positions and a plurality of frequency axis direction positions in the transmission frame. A weight update method in a communication method in which a plurality of areas of the minimum unit of allocation are arranged in the time axis direction and a plurality of areas are also arranged in the frequency direction ,
Based on the pilot signal included in the received signal, update the weight of the received beam in a multi-antenna system to obtain a weight estimate,
In the update of the weight, the weight updated in the previous weight update is updated based on the pilot signal used for the update, thereby obtaining a weight estimated value at the position of the pilot signal,
All of a plurality of pilot signals existing in the minimum unit area of user allocation in the transmission frame are used for weight update, and then weight update using pilot signals existing in other minimum user allocation unit areas is performed. The weight update method characterized by this.   A weight update method in a communication method in which a burst region allocated to a user is included in a transmission frame,
  Based on the pilot signal included in the received signal, update the weight of the received beam in a multi-antenna system to obtain a weight estimate,
  In the update of the weight, the weight updated in the previous weight update is updated based on the pilot signal used for the update, thereby obtaining a weight estimated value at the position of the pilot signal,
  Use all of the pilot signals that exist in one burst region for weight update, then perform weight update using pilot signals that exist in another burst region,
  Find a smoothed estimate by smoothing the weight estimate obtained by multiple weight update operations
  A weight update method characterized by the above.   A weight update method in a communication method capable of assigning one transmission frame to a plurality of users,
  Based on the pilot signal included in the received signal, update the weight of the received beam in a multi-antenna system to obtain a weight estimate,
  In the update of the weight, the weight updated in the previous weight update is updated based on the pilot signal used for the update, thereby obtaining a weight estimated value at the position of the pilot signal,
  Using all of a plurality of pilot signals present in the minimum unit area of user allocation in the transmission frame for weight update, then performing weight update using pilot signals existing in other user allocation minimum unit area,
  Find a smoothed estimate by smoothing the weight estimate obtained by multiple weight update operations
  A weight update method characterized by the above.

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