JP4882791B2 - 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. 14 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).
The updating method as described above is the same for any carrier number kp having an SP signal.

That is, the updating method of Patent Document 1 is the same for every carrier number kp as shown by the arrow in FIG. 15, and there is only one way of updating the weight.
JP 2003-174427 A

  Conventionally, no appropriate consideration has been given to the way of updating weights, and only a single weight updating method as described above has been assumed.

  Therefore, an object of the present invention is to provide a new technique for diversifying the way of updating weights.

  The present invention provides a communication apparatus that updates weights used for signal synthesis based on pilot signals included in a received signal, and includes a sequence control unit that controls the order of pilot signals used for weight updates, The control unit has a plurality of update order rules in which the order of pilot signals used for updating the weights is different.

  According to the present invention, since the order control unit can execute a plurality of update order rules, the way of updating weights can be diversified.

  It is preferable that signal synthesis is performed using a plurality of weights obtained by order control according to each of the plurality of update order rules. In this case, by performing signal synthesis using a plurality of weights obtained by a plurality of update order rules, it is possible to obtain a more appropriate output than in the case of a single update order rule.

  A weight combining unit that generates a combined weight by combining a plurality of weights obtained by order control according to each of the plurality of update order rules, a weight interpolation unit that interpolates a weight for a data signal from the combined weight, It is preferable that a weight multiplier for multiplying the received data signal by the weight for the data signal obtained by the weight interpolator to obtain an output signal is provided. In this case, an appropriate output signal can be obtained by a combined weight obtained by combining a plurality of weights.

  Preferably, the weight combining unit weights and combines a plurality of weights. In this case, it is possible to obtain a more appropriate composite weight.

  A plurality of weight interpolation units for interpolating data signal weights from a plurality of weights obtained by order control according to the plurality of update order rules, and a plurality of data signals obtained by the plurality of weight interpolation units. A plurality of weight multiplying units for multiplying each received weight by the received data signal to obtain a plurality of output signals, and an output combining unit for combining the plurality of output signals to obtain a combined output signal. It is preferable. In this case, an appropriate output signal can be obtained by combining a plurality of output signals.

  It is preferable that the output synthesis unit weights and synthesizes a plurality of output signals. In this case, a more appropriate combined output signal can be obtained.

  A weight interpolation unit that interpolates data signal weights using a plurality of weights obtained by order control according to each of the plurality of update order rules, and a data signal weight obtained by the weight interpolation unit. And a weight multiplying unit that multiplies the received data signal to obtain an output signal. In this case, appropriate weight interpolation can be performed from a plurality of weights.

  It is preferable that the weight interpolation unit weights and interpolates a plurality of weights used for weight interpolation for data signals. In this case, more appropriate weight interpolation can be performed.

  Another aspect of the present invention is a method for updating weights used for signal synthesis based on a pilot signal included in a received signal, and the order of pilot signals used for updating weights with respect to the received signal is A plurality of weights are obtained by applying a plurality of different update order rules.

  According to the update method, a plurality of weights can be obtained by a plurality of different update order rules.

  According to the present invention, it is possible to diversify how to update weights.

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 an OFDM subcarrier arrangement employed 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.

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 and pilot subcarriers excluding null subcarriers. 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, one tile structure is configured by a total of 12 subcarriers, 3 in the symbol direction (time axis direction) and 4 in the frequency axis direction. 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 functional blocks of the communication apparatus according to the present 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. 3, in addition to the mobile station (desired station) 2 with which the communication apparatus 1 is trying 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.
4 shows a filtering model showing the relationship between the desired signal, the output signal, and the received signal (strictly speaking, the signal from the FFT unit 13 corresponding to the antenna element 11 of the communication device 1) in FIG.

In FIG. 4, k indicates a symbol number, and l indicates a subcarrier number. M represents the number of desired signals and interference signals.
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. 4 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. 5 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 (combined weight) W (k, l) to synthesize the output signal Y (k, l) = W (k, l l) Output ^H X (k, l).

Further, the received signal (pilot subcarrier) X (k, l) of the first buffer 141 is given to the weight calculator 143 to be used for updating the weight. When the received signal stored in the first buffer 141 is not used by the weight multiplier 142 and the weight calculator 143, the received signal is erased as needed.
By accumulating received signals in the first buffer 41, it is possible to easily update the weights in various directions as in the present embodiment and perform a plurality of weight updates.

The weight calculation unit 143 includes P (plural) weight calculation units 143-1 to 143-P that perform weight update independently.
Each of the weight calculation units 143-1 to 143-P updates the weight by an update process using pilot subcarriers included in the received signal. P weights W ₁ (k, l) to W _P (k, l) obtained by the respective weight calculation units 143-1 to 143-P are given to the weight combining unit 147.
Details of the weight calculation unit will be described later.

The weight combining unit 147 combines the plurality of weights W ₁ (k, l) to W _P (k, l) output from the respective weight calculation units 143-1 to 143-P to generate a combined weight W (k, l) is generated, and this combined weight W (k, l) is given to the second buffer 144.
Details of the weight combining unit 147 will also be described later.

  The second buffer (weight storage unit; combined weight storage unit) 144 sequentially stores the weight W (k, l) at the position of each pilot subcarrier combined by the weight combining unit 147. The update weight in the second buffer 144 is erased 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. The weight W (k, l) obtained by the interpolation is given to the weight multiplier 142.
FIG. 6 shows an example of weight interpolation. In the example of FIG. 6, linear interpolation is performed in tile units. Specifically, by performing the calculation shown in FIG. 6A 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 calculator]
Each of the weight calculation units 143-1 to 143-P of the present embodiment is configured to update the weights by the RLS algorithm. However, other algorithms such as an LMS algorithm or an SMI algorithm may be used.

Each weight calculation unit 143-1 to 143-P includes pilot subcarriers X (k, l) in the received signal, reference signals (pilot subcarriers) S (k, l) corresponding to the desired signals, and weight updates. The current weight W _i (k _prev , l _prev ) is updated to a new weight W _i (k, l) using the parameter P. Note that i is an integer from 1 to P.

The weight update arithmetic expression by the RLS algorithm is as the following expressions (3) and (4). Note that the weight calculation unit 143 also calculates an update value P _text of the parameter P _i used in the equation (4). Updating calculation formula for P _i are as the following formula (5).

FIG. 7 shows details of the weight calculation units 143-1 to 143-P. The configuration of the plurality of weight calculation units is common to each other.
As illustrated in FIG. 7, each of the weight calculation units 143-1 to 143-P includes a weight update unit 143a that performs weight update based on the above formulas (3) to (5). Of the values used in the above equations (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 143b and is given to the weight update unit 143a. The weight update parameter P _i (N × N matrix) is stored in the fourth buffer (weight update parameter storage unit) 143c, and the weight update unit 143a acquires the parameter P _i from the fourth buffer 143c. The parameter P _int updated by the weight updating unit 143a is updated and stored in the fourth buffer 143c and used as the parameter P _i at the next weight update.

  Moreover, (alpha) in said Formula (4) (5) is a forgetting factor, and takes the value between 0-1. 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.

The weights W _i (k, l) updated by the weight updating unit 143a according to the above equation (3) are sequentially stored in the third buffer (weight storage unit) 143d. The weight W _i (k, l) stored in the third buffer 143d is used for the next weight update by the weight update unit 143a. The weight W _i (k, l) stored in the third buffer 143d is used by the weight combining unit 147 to combine with another weight at the same pilot subcarrier position (k, l).

By storing a plurality of weights W ₁ (k, l) to W _P (k, l) by a plurality of third buffers 143d, the timing at which a weight at a certain pilot subcarrier position is obtained is a plurality of times. Even if different in the weight updating unit 143a, the weight combining unit 147 can easily combine the weights.
The weight stored in the third buffer 143d is deleted when it is no longer used in the weight combining unit 147.

[Weight update order control]
As described above, each weight updating unit 143a obtains a 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, the order control unit 146 controls the order of pilot subcarriers used by the plurality of weight update units 143a for weight update. Specifically, order control section 146 rearranges the separated pilot subcarriers in the order that each weight update section 143a uses for weight update. Then, the order control unit 146 gives the rearranged pilot subcarriers to the respective weight update units 143a in the rearranged order.

Here, order control section 146 has a plurality of pilot subcarrier rearrangement rules (hereinafter referred to as “update order rules”). The order control unit 146 can execute order control according to each rule.
The order control unit 146 includes a number (P) of rules corresponding to the number (P) of the weight update units 143a as the update order rules. These rules differ in how pilot subcarriers are rearranged. That is, each of the plurality of rules has a different update method.

The order control unit 146 performs rearrangement of pilot subcarriers to be given to each weight update unit 143a according to the rule. Therefore, each weight updating section 143a uses pilot subcarriers for weight updating in different orders.
Note that the update order rule can be dynamically changed according to the propagation environment.

  FIG. 8 shows an example of weight update when there are two update order rules, that is, when P = 2. In the example of FIG. 8, there are a first update order rule that is updated in the frequency axis direction and a second update order rule that is updated in the time axis direction.

  In the first update order rule, first, update in the direction D11 in FIG. 8 is performed. That is, a plurality of pilot subcarriers in the frequency axis direction at the same symbol (same time k = 1) are targeted (1, 1) to (1, L), and weight updating is performed using pilot subcarriers in ascending order of frequency. (Frequency axis direction update control D1). The movement width of the frequency axis direction control D11 is L (= 840) subcarriers.

  When the frequency axis direction update control D11 is performed and the pilot subcarrier (1, L) having the largest subcarrier number L is reached, update in the direction D12 in FIG. That is, it moves in the time axis direction from the position (1, L), and the next pilot subcarrier (3, L) in the time axis direction is used for weight update (time axis direction update control 1D2). Note that the movement width (pilot interval) for time axis direction update is two symbols.

  After the time axis direction update control D12, the update is performed in the direction D13 of 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 D13). In other words, weight update is performed in the opposite direction to the update control. Note that the movement width of the frequency axis direction update control D13 is L (= 840) subcarriers.

When the frequency axis direction update control D13 is performed and the pilot subcarrier (3, 1) having the smallest subcarrier number 1 is reached, the update is performed in the direction D14 in FIG. That is, it moves in the time axis direction from the position (3, 1), and the next pilot subcarrier (4, 1) as seen in the time axis direction is used for weight update (time axis direction update control D14). Note that the movement width (pilot interval) of the time axis direction update control D14 is one symbol.
After the time axis direction update control D14, the frequency axis direction update D11 is performed, and the above processes D11 to D14 are repeated.

  On the other hand, in the second update order rule, first, update in the direction D21 in FIG. 8 is performed. That is, in the same subcarrier (same subcarrier number = 1), a plurality of pilot subcarriers (1, 1) to (k, 1) existing in the time axis direction are targeted in order from the pilot subcarrier having the smallest symbol number. To update the weight (time axis direction update control D21).

Note that the movement width (movement width in the time direction) of one time axis direction update control D21 may be an arbitrary length, but may be, for example, a symbol length for one frame (subframe).
In WiMAX, one basic frame includes an uplink subframe and a downlink subframe, and the base station receives the uplink subframe. This uplink subframe is composed of 15 symbols. Therefore, it is preferable that the movement width in one time axis direction update control D21 is a maximum of 15 symbols.

  When the time axis direction update control D21 is performed and the pilot subcarrier (k, 1) of the predetermined symbol number = k is reached, the update in the frequency direction D22 is performed next. That is, it moves in the frequency axis direction from the position (k, 1), and the next pilot subcarrier (k, 4) in the frequency axis direction is used for weight update (frequency axis direction update control D2). Note that the movement width of the frequency axis direction update control D22 is equal to three subcarriers.

  After the frequency axis direction update control D22, the update is performed in the direction D23 of FIG. That is, in the same subcarrier (same subcarrier number = 4), a plurality of pilot subcarriers (k, 4) to (1, 4) existing in the time axis direction are targeted in order from the pilot subcarrier having the largest symbol number. To update the weight (time axis direction update control D23).

  Note that the movement width (movement width in the time direction) of one time axis direction update control D23 may be an arbitrary length, but the maximum symbol length (15 symbols) for one frame (subframe). preferable.

When the time axis direction update control D23 is performed and the pilot subcarrier (1, 4) having the smallest symbol number 1 is reached, the update is performed in the direction D24 in FIG. That is, it moves in the time axis direction from the position (1, 4), and the next pilot subcarrier (1, 5) in the frequency axis direction is used for weight update (frequency axis direction update control D24). Note that the movement width of the frequency axis direction update is one subcarrier.
After the frequency axis direction update control D24, the time axis direction update control D21 is performed, and the above processes D1 to D24 are repeated. If updating in the D4 direction cannot be performed, updating may be performed in the same manner using the next k symbols that are temporally after the symbol number k.

  In the first update order rule, 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.

  On the other hand, in the second update order rule, the update performed by moving in the time axis direction is performed more than the update performed by moving in the frequency 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 time axis direction is larger than the cross correlation in the frequency axis direction, an appropriate weight is given early. Is obtained.

[Relationship between cross-correlation of propagation coefficients and weight update]
The cross-correlation of propagation coefficients may be larger in the frequency axis direction and larger in the time axis direction. For example, when the mobile station that is the communication partner of the base station is moving at high speed, the propagation environment changes from moment to moment, so the cross-correlation in the time axis direction becomes lower and the cross-correlation in the frequency direction becomes relatively lower. Will be bigger.
On the other hand, when the mobile station is slow or stopped, there is almost no change in the propagation environment even if the time changes, so the cross-correlation becomes larger in the time axis direction.
This will be described in detail below.

FIG. 9 shows a two-dimensional arrangement of subcarriers of WiMAX Uplink PUSC. 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.

Further, the correlation coefficients ρ of the propagation coefficients h _n and h _m of the signal points (subcarriers) n and m shown in FIG. 10 are expressed by the following formulas when the time change model is the James model and the delay profile is the exponential decay delay profile. It is obtained like this.

Table 1 below shows calculation results of correlation coefficients between the propagation coefficient h _{A of} FIG. 9 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. That is, the second update order rule that performs many updates in the time axis direction is preferable.

On the other hand, 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. That is, the first update order rule that performs many updates in the frequency axis direction is preferable. When delay dispersion is large, it is desirable to preferentially update in the time axis direction.

  Since the order control unit 146 has a plurality of rules, it is possible to select and use one appropriate rule according to the propagation environment. However, here, weight updating is performed using a plurality of rules.

Now, by executing the order control according to the two update order rules, a plurality of pilot subcarriers (k, l) = (1, 1), (1, 4),... Included in k symbols. , (1, L), (3, 1), ..., (3, L), ..., (k-2, 1), ..., (k-2, L), ... , (K, 1),..., (K, L), two (plural) weights W ₁ (k, l) and W ₂ (k, l) are obtained.

Two weights W ₁ (k, l) and W ₂ (k, l) obtained by each rule are stored in the third buffers 143d and 143d, respectively. Since the weights of all pilot subcarriers included in the k symbol shown in FIG. 8 are stored in the third buffer 143d, weight combining described later can be easily performed.

[Weight composition]
In the weight combining unit 147, W ₁ (k, l), W ₂ (k, k) calculated by the weight updating units 143a and 143a of the respective weight calculation units 143-1 and 143-2 and stored in the third buffer 143d. l) is used to generate a combined weight W (k, l) at the pilot subcarrier (k, l) position.

An arithmetic expression for weight synthesis is as follows.

As in the above equation, the weight combining unit 147 performs weighted combining using weight combining weights (weights) β ₁ (k, l), β ₂ (k, l). The weight combining weights β ₁ (k, l) and β ₂ (k, l) are generated by the weight combining weight generation unit 148 (see FIG. 5) and given to the weight combining unit 147. The weight combining weight may be set in advance in the weight combining weight generation unit 148 or may be dynamically generated using an update order rule or the like.

The weight combining weights β ₁ (k, l) and β ₂ (k, l) are the number of updates of the weights W ₁ (k, l) and W ₂ (k, l) and the change of the transfer function in the time axis direction. It is determined in consideration of the degree, the change degree of the transfer function in the frequency direction, and the like.

For example, attention is paid to the weight W ₁ (3, 1) based on the first update order rule and the weight W ₂ (3, 1) based on the second update order rule in the pilot subcarrier (3, 1) in FIG.

The weight W ₁ (3, 1) based on the first update order rule is a result of updating the weight several hundred times through the update control D11, D12, D13, and the weight estimation accuracy is relatively high. .
On the other hand, the weight W ₂ (3, 1) according to the second update order rule is a result of the second weight update, and the weight estimation accuracy is relatively low.
Therefore, the weight combined weight β ₁ (3,1) of the weight W ₁ (3,1), which has a large number of weight update times, is increased, and the weight combined weight β ₂ (3,1) of the weight W ₂ (3,1) is increased. By reducing the value, the combined weight W (3, 1) can be updated a sufficient number of times and the weight W ₁ (3, 1) with high accuracy can be largely reflected.

As another example, the weight W ₁ (1, 4) according to the first update order rule and the weight W ₂ (1, 4) according to the second update order rule in the pilot subcarrier (1, 4) of FIG. Pay attention.

The weight W ₁ (1, 4) according to the first update order rule is a result of the second weight update, and the weight estimation accuracy is relatively low.
On the other hand, the weight W ₂ (1, 4) according to the second update order rule is a result of more weight updates, and the weight estimation accuracy is relatively high.
Therefore, the weight combined weight β ₂ (1,4) of the weight W ₂ (1,4), which has a large number of weight update times, is increased, and the weight combined weight β ₁ (1,4) of the weight W ₁ (1,4) is increased. Can be made to reflect the weight W ₂ (1, 4), which is updated a sufficient number of times and highly accurate, in the combined weight W (1, 4).

Note that the size of the weight combining weights β ₁ (k, l) and β ₂ (k, l) depends on each pilot subcarrier position (k, l).

As described above, by adjusting the weight combining weights β ₁ (k, l) and β ₂ (k, l) according to the number of weight updates, the weight of which pilot subcarrier position (k, l) is adjusted. Also, the update result updated a sufficient number of times can be reflected.

In addition, even if the number of weight updates by the first update order rule is the same as the number of weight updates by the second update order rule and the pilot subcarrier position (k, l), the weight combining weight β ₁ ( In some cases, it is better to vary k, l) and β ₂ (k, l).

For example, when the cross correlation of the propagation coefficients is large in the frequency axis direction, the weight W ₁ (k, l) based on the first update order rule having a large number of updates in the frequency axis direction has higher weight estimation accuracy. Therefore, it is better to make β ₁ (k, l) larger than β ₂ (k, l).
On the other hand, when the cross correlation of the propagation coefficients is large in the time axis direction, the weight W ₂ (k, l) based on the second update order rule having a large number of updates in the time axis direction has higher weight estimation accuracy. Therefore, it is better to make β ₂ (k, l) larger than β ₁ (k, l).

As described above, the weight estimation for the weight combining weights β ₁ (k, l) and β ₂ (k, l) is performed in consideration of the direction in which the cross correlation of the pilot subcarrier position, the number of weight updates, and the propagation coefficient is large. A weight combining weight may be determined so that a higher accuracy is more strongly reflected in the combined weight.
By taking such considerations, it becomes easy to deal with various propagation environments.

  When determining the composite weight, it is not necessary to use all P weights, and only some of the weights may be used.

[Second Embodiment]
FIG. 11 shows a modification (second embodiment) of the filtering processor 14. The points that are not particularly described in the second embodiment are the same as those shown in FIGS.

In the second embodiment, a plurality of weights W ₁ (k, l) to W _P (k, l) obtained by the plurality of weight calculation units 143-1 to 143-P are combined without being combined. A plurality of output signals Y ₁ (k, l) to Y _P (k, l) are obtained separately using W ₁ (k, l) to W _P (k, l). Then, a plurality of output signals Y ₁ (k, l) to Y _P (k, l) are synthesized to obtain a synthesized output Y (k, l).

  More specifically, in the second embodiment, the second buffers 144-1 to 144 -P, the weights correspond to the fact that there are P (a plurality of) weight calculation units 143-1 to 143 -P. P (multiple) interpolation units 145-1 to 145-P and weight multiplication units 142-1 to 142-P are also provided.

A plurality of output signals _Y 1 _(k, ^l) outputted from the P-number of weight multiplication unit ^{142-1~142-P = W 1 (k} , l) H X (k, l) ~Y P (k, l ) = W _P (k, l) ^H X (k, l) is stored in a plurality of fifth buffers (output signal storage units) 149-1 to 149 -P, respectively. By storing a plurality of output signals in the fifth buffers 149-1 to 149 -P, timings at which the plurality of output signals Y ₁ (k, l) to Y _P (k, l) are generated are different. However, the composite output signal can be easily generated.

Furthermore, in the second embodiment, an output combining unit 150 that combines a plurality of output signals Y ₁ (k, l) to Y _P (k, l) to generate a combined output signal Y (k, l) is provided. Yes.
When the update order rule number P = 2 as in the example shown in FIG. 8, an arithmetic expression for output synthesis is as follows.

As in the above equation, the output synthesis unit 150 performs weighted synthesis using output synthesis weights (weights) γ ₁ (k, l), γ ₂ (k, l). The weight combining weights γ ₁ (k, l) and γ ₂ (k, l) are generated by the output combining weight generating unit 151 and given to the output combining unit 150. The output composition weight may be preset in the output composition weight generation unit 151, or may be dynamically generated using an update order rule or the like.

Similarly to the weight synthesis weights β ₁ (k, l) and β ₂ (k, l), the output synthesis weights γ ₁ (k, l) and γ ₂ (k, l) are also updated in terms of the number of weight updates and the time axis. It is determined in consideration of the degree of change in the transfer function in the direction, the degree of change in the transfer function in the frequency direction, and the like.
That is, since the output accuracy at a certain data subcarrier position (k, l) varies depending on the update order rule, an output signal with high output accuracy is strongly reflected in the combined output signal Y (k, l). , A good combined output signal Y (k, l) can be obtained.

  Note that when generating the combined output signal, it is not necessary to use all the P output signals, and only a part of the output signals may be used.

[Third Embodiment]
FIG. 12 shows another modification (third embodiment) of the filtering processing unit 14. Note that points not particularly described in the third embodiment are the same as those shown in FIGS.

In the third embodiment, a plurality of weights W ₁ (k, l) to W _P (k, l) obtained by the plurality of weight calculation units 143-1 to 143-P are combined without being combined. Using W ₁ (k, l) to W _P (k, l), weight interpolation at the data subcarrier position is performed.

More specifically, in the third embodiment, a plurality of second buffers 144-1 to 144-P are provided in correspondence with the provision of P (a plurality) of weight calculation units 143-1 to 143-P. Is provided.
Then, the weight interpolation unit 145 obtains a plurality of weights W ₁ (k, l) to W _P (k, l) from the second buffers 144-1 to 144-P, and performs weight interpolation for the data subcarriers. I do.

FIG. 13 shows an example of weight interpolation in the third embodiment. As shown in FIG. 13B, the weights W ₁ ¹ , W ₄ ¹ , W ₉ ¹ , W ₁₂ ¹ at the pilot subcarrier positions are obtained for a certain tile according to the first update order rule, and the second It is assumed that the weights W ₁ ² , W ₄ ² , W ₉ ² , and W ₁₂ ² at the corresponding pilot subcarrier positions are obtained by the update order rule.

The weight interpolation unit 145 calculates the weights W ₂ , W ₃ , W ₅ , W ₆ , W ₇ , W ₈ , W ₁₀ , and W ₁₁ at the data subcarrier position of the tile as shown in FIG. To calculate.
The calculation in FIG. 13B is weighted linear interpolation with a plurality of weights obtained by each rule.

With the linear interpolation described in FIG. 6, when obtaining weights at a certain data subcarrier position, weights W ₁ , W ₄ , W ₉ , and W ₁₂ at four pilot subcarrier positions in one tile are used. It was.
On the other hand, in the case of the calculation of FIG. 13B, when obtaining a weight (for example, W ₆ ) at a certain data subcarrier position of a certain tile, W ₁ ¹ , W obtained by a plurality of update order rules for the tile. Weight interpolation can be performed using ₄ ¹ , W ₉ ¹ , W ₁₂ ¹ and W ₁ ² , W ₄ ² , W ₉ ² , W ₁₂ ² .

Then, by appropriately setting the value of δ in FIG. 6A, W ₁ ¹ , W ₄ ¹ , W ₉ ¹ , W ₁₂ ¹ and W ₁ ² , W ₄ ² , W ₉ ² , W ₁₂ ² Weight interpolation can be performed by preferentially using weights with high estimation accuracy (weighted interpolation).
That is, each of the values of δ in FIG. 6A corresponds to the weights W ₁ ¹ , W ₄ ¹ , W ₉ ¹ , W ₁₂ ¹ , W ₁ ² , W ₄ ² , W ₉ ² , W ₁₂ ² . This is an interpolation parameter (weight) indicating which weight is used preferentially.
The interpolation parameter δ is generated by the interpolation parameter generation unit 152 and given to the weight interpolation unit 145.

By doing as described above, good weight interpolation can be performed with weights with high estimation accuracy.
In the weight interpolation, it is not necessary to use all the weights obtained by the P update order rules, and only the weights obtained by a part of the update order rules may be used.

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. For example, the present invention is not limited to WiMAX but can be applied to, for example, an apparatus for digital terrestrial broadcasting.
In the above embodiment, all the plurality of update order rules are executed. However, one of the plurality of rules may be selectively used.

Furthermore, a weight selection unit that selects one weight (a weight with good estimation accuracy) from a plurality of weights may be provided instead of the weight combining unit 147 of FIG.
Further, an output selection unit that selects one output signal (good output signal) from a plurality of output signals may be provided instead of the output synthesis unit 150 in FIG.
In addition, the weight interpolation unit 145 in FIG. 12 may perform weight interpolation by selecting a weight (weight with good estimation accuracy) obtained from one update order rule among a plurality of update order rules.

It is a figure which shows the subcarrier structure of OFDM. It is a frequency-time two-dimensional array of subcarriers. 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 a filtering process part. It is explanatory drawing of the weight interpolation method. It is a block diagram of a weight calculation part. It is a figure which shows several weight update order rules. 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 block diagram of the filtering process part which concerns on 2nd Embodiment. It is a block diagram of the filtering process part which concerns on 3rd Embodiment. It is a figure which shows the weight interpolation in 3rd Embodiment. It is a figure which shows the subcarrier arrangement | positioning in terrestrial digital broadcasting. It is a figure which shows the conventional weight update direction.

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 pilot signal storage unit) 142 : Weight multiplication unit 143: weight calculation unit 143 a: weight update unit 143 b: reference signal generation unit 143 c: fourth buffer (weight update parameter storage unit) 143 d: third buffer (weight storage unit) 144: second buffer (weight storage) 145: weight interpolation unit 146: sequence control unit 147: weight synthesis unit 149: fifth buffer (output signal storage unit) 150: output synthesis unit 151: output synthesis weight generation unit 152: interpolation parameter generation Part

Claims (9)

Regarding the weight of the reception beam in the communication apparatus constituting the multi-antenna system, the weight updated at the previous weight update is updated based on the pilot signal used for the update, thereby calculating the weight at the position of the pilot signal. In communication equipment,
An order control unit for controlling the order of pilot signals used for updating weights;
The communication apparatus according to claim 1, wherein the order control unit has a plurality of update order rules in which the order of pilot signals used for updating weights is different.   The communication apparatus according to claim 1, wherein the communication apparatus is configured to perform signal synthesis using a plurality of weights obtained by order control according to each of the plurality of update order rules. A weight combining unit that generates a combined weight by combining a plurality of weights obtained by order control according to each of the plurality of update order rules;
A weight interpolation unit for interpolating data signal weights from the combined weights;
A weight multiplication unit for multiplying the received data signal by the weight for the data signal obtained by the weight interpolation unit to obtain an output signal;
The communication apparatus according to claim 1, further comprising:   The communication apparatus according to claim 3, wherein the weight combining unit weights and combines a plurality of weights. A plurality of weight interpolation units for interpolating weights for data signals from a plurality of weights obtained by order control according to each of the plurality of update order rules;
A plurality of weight multiplication units for obtaining a plurality of output signals by multiplying the received data signals by the respective weights for the plurality of data signals obtained by the plurality of weight interpolation units;
An output combining unit that combines a plurality of output signals to obtain a combined output signal;
The communication apparatus according to claim 1, further comprising:   The communication apparatus according to claim 5, wherein the output combining unit weights and combines a plurality of output signals. A weight interpolation unit that interpolates weights for data signals using a plurality of weights obtained by order control according to each of the plurality of update order rules;
A weight multiplication unit for multiplying the received data signal by the weight for the data signal obtained by the weight interpolation unit to obtain an output signal;
The communication apparatus according to claim 1, further comprising:   8. The communication apparatus according to claim 7, wherein the weight interpolation unit weights and interpolates a plurality of weights used when weight interpolation for data signals is performed. A method of calculating a weight at a position of a pilot signal by updating a weight of a received beam in a multi-antenna system based on a pilot signal used for updating the weight updated in the previous weight update,
A weight update method, wherein a plurality of weights are obtained by applying a plurality of update order rules, each having a different order of pilot signals used for updating weights, to a received signal.

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