JP2012182593A - Radio communication system, interference avoidance method, relay station, and radio communication terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently avoid interference between the same channels between systems without imposing a large burden on a terminal side in a heterogenous network.SOLUTION: A terminal communicating with a first cell estimates a first transfer function with a first base station and a second transfer function with a second cell by use of a preamble section of a signal from the second cell. In a data section where there is interference from the second cell, the first base station transmits a first desired signal to the terminal in a directivity of a reception signal at a relay station becoming null, and the relay station receives an interference signal from the second cell. In a data section where there is no interference from the second cell, the first base station transmits a second desired signal to the terminal, and the relay station transmits interference information about the interference signal to the terminal. The terminal estimates the second desired signal based on the reception signal, the interference information, and the first and second transfer functions.

Description

  The present invention relates to a technique for avoiding the influence of inter-channel interference between systems in an environment where systems of different service areas such as heterogeneous networks coexist, and in particular, such an interference avoiding method, The present invention relates to a configuration of a wireless communication system, a relay station, and a wireless communication terminal.

  In recent years, a heterogeneous network as shown in FIG. 1 has attracted attention (for example, see Non-Patent Document 1). FIG. 1 shows an application example in a cellular system. In a normal cellular system, a communication area such as a macro cell 101 for a service area of about several hundred meters to several kilometers is employed. On the other hand, in order to improve the communication capacity per unit frequency, the size of the cell has been reduced, and a method of arranging the pico cell 201 for a service area of about several tens of meters to a hundred meters in the macro cell 101 is adopted. ing. The femtocell 301 may be arranged as an indoor system. Further, the relay station 105 may be used to expand the service area and improve the quality.

  In general, not only in heterogeneous networks but also in wireless communication networks, interference at the area end (cell end) becomes a problem. Also, since the data size of the downlink is generally larger than that of the uplink, interference on the terminal side becomes serious.

  As means for removing interference, a zero forcing (ZF) method and an MMSE (Minimum Mean Square) method using an array antenna are generally known (see, for example, Non-Patent Document 2). By applying these methods and estimating the propagation channel for the interference signal, it is possible to remove the interference wave from the neighboring cells.

FIG. 2 shows interference cancellation when zero forcing is used. In FIG. 2, h _Si and h _Ii (i = 1 to 2) represent the channel response between the desired signal station and the receiving station and the channel response between the interference station and the receiving station, respectively. If the desired signal is S and the interference signal is I, the signals x1 and x2 received by the antennas # 1 and # 2 of the mobile terminal MS are given by the following equations.

ここで、ｎは熱雑音を表わす。式（１）、（２）を行列化すると以下の式で表される。

Here, n represents thermal noise. When formulas (1) and (2) are matrixed, they are represented by the following formulas.

式（３）において、雑音電力を無視すると、以下の式で干渉信号を推定できる。

If noise power is ignored in equation (3), the interference signal can be estimated by the following equation.

ここで、

here,

はそれぞれ所望信号の推定値と干渉信号の推定値である。以後、本明細書において上添え字（ハット）は、推定値を表わすものとする。式（４）により、ＺＦ法に基づいて所望信号を復元できることがわかる。このとき、干渉信号は完全に除去される。

Are the estimated value of the desired signal and the estimated value of the interference signal, respectively. Hereinafter, the superscript (hat) in this specification represents an estimated value. Equation (4) shows that the desired signal can be restored based on the ZF method. At this time, the interference signal is completely removed.

  However, it is known that the characteristics of the zero forcing (ZF) method due to interference removal are greatly deteriorated at the zone edge where the SNR is low (see, for example, Non-Patent Document 3). This is because the noise power is ignored when deriving the expression (4) from the expression (3). However, if the number of signals increases, the noise power cannot actually be ignored.

  Further, MLD (Maximum Likelihood Detection) in which nonlinear arithmetic processing is applied to the terminal side has been studied (for example, see Non-Patent Document 2 above). However, in this method, the calculation amount increases exponentially when the modulation scheme becomes multi-valued. When the interference signal is transmitted using multilevel modulation, the terminal must perform MLD considering the modulation scheme and multilevel modulation, which places a heavy burden on the terminal side. Basically, it is desirable that the terminal can operate with low power consumption.

Tanno et al., Heterogeneous Network at IMT-Advanced, IEICE Technical Report, RCS2009-317, March 2010 Daigane, MIMO system basics and elemental technology, antenna and propagation design and analysis method workshop, W29, 39 Nishimori et al., Effect of MIMO-ZF configuration using transmit selection diversity in indoor real environment, IEICE Society Conference Proposal, B-1-243

  When returning to the heterogeneous network, in addition to the deterioration of the interference cancellation characteristics at the zone edge described above and an increase in the computation load at the terminal, between the same channels between systems of different area sizes arranged in the same space Interference becomes a problem. In addition, since the macro cell 101, the pico cell 201, and the femto cell 301 have different transmission powers, there is a problem that the influence of the interference amount is different.

  3A and 3B are diagrams illustrating the influence of interference assumed when the pico cell 201 or the femto cell 301 coexists with the macro cell 101. FIG. FIG. 3A shows the influence of interference that the pico cell 201 gives to the macro cell terminal (M-UE) 120 when the pico cell 201 is located near the macro cell terminal (M-UE) 120. This is an example in which the interference wave i from the picocell base station (P-BS) 210 arrives while the macrocell terminal (M-UE) 120 is communicating with the macrocell base station (M-BS) 110. The reduction of interference in this case is set as problem 1.

  In FIG. 3B, the influence of the interference which the pico cell terminal (P-UE) 220 in communication with the pico cell 201 receives from the macro cell base station (M-BS) 110 becomes a problem. It is known that a base station generally transmits a signal with a larger transmission power than a terminal device. This indicates that there is a high probability that a terminal device communicating with the pico cell 201 or the femto cell (see FIG. 1) receives the interference wave i from the macro cell base station (M-BS) 110. The reduction of interference in this case is set as problem 2.

  In solving the problems 1 and 2, it is necessary to consider the characteristic deterioration due to the interference removal at the zone edge and the reduction of the burden on the terminal.

  Therefore, an object of the present invention is to provide a technique for avoiding inter-channel interference between different systems while reducing the load on the terminal side as much as possible in a heterogeneous network.

  In order to solve the above problems, a relay station that is usually used for improving a service area is used as a means for avoiding interference.

In a first aspect, a radio communication system capable of efficiently avoiding interference is provided. A wireless communication system includes: a first radio base station that provides a first cell; a second cell of a different type that spatially overlaps the first cell; and a relay station that is disposed in the first cell And a wireless communication terminal that communicates with the first cell,
The radio communication terminal uses a preamble section of a signal from the second cell, and uses a first transfer function between the first radio base station and a second cell between the second cell and the second cell. 2 estimate the transfer function,
In a first time of a data interval with interference from the second cell, the first radio base station has a directivity such that a received signal at the relay station becomes zero, and a first desired signal To the wireless communication terminal, and the relay station receives an interference signal from the second cell,
In a second time of a data interval without interference from the second cell, the first radio base station transmits a second desired signal different from the first desired signal to the radio communication terminal. The relay station transmits interference information related to the interference signal from the second cell to the wireless communication terminal,
The wireless communication terminal estimates the second desired signal based on the received signal at the second time, the interference information, and the first and second transfer functions.

  In this system, interference in the wireless communication terminal can be effectively avoided by using the relay station.

In a second aspect, an interference avoidance method in a wireless communication system is provided. This method
A radio communication system including a first radio base station that provides a first cell, a second cell of a different type that spatially overlaps the first cell, and a relay station that is used in the first cell In the wireless communication terminal that communicates with the first cell, using the preamble section of the signal from the second cell, a first transfer function with the first wireless base station, and Estimating a second transfer function to and from the second cell;
In the first time of the data interval with interference from the second cell, the directivity from the first radio base station to the radio communication terminal is such that the received signal at the relay station becomes zero. Transmitting a first desired signal and receiving an interference signal from the second cell at the relay station;
A second desired signal different from the first desired signal is transmitted from the first radio base station to the radio communication terminal in a second time of a data interval without interference from the second cell. And transmitting interference information related to the interference signal from the relay station to the wireless communication terminal,
In the wireless communication terminal, the second desired signal is estimated based on the received signal at the second time, the interference information, and the first and second transfer functions.

According to a third aspect, there is provided a relay station used in a radio communication system in which a first cell and a second cell of a different type from the first cell are spatially overlapped. The relay station is used in the first cell,
A receiving unit for receiving an interference signal in a data interval from the second cell;
A transfer function estimating unit that estimates a transfer function between the second cell and the relay station using a preamble section of a signal from the second cell;
An interference signal estimator that estimates the interference signal based on the estimated transfer function and the received signal in the data interval;
A transmission unit that transmits the estimated interference signal to a wireless communication terminal that communicates with the first cell.

According to a fourth aspect, there is provided a radio communication terminal used in a radio communication system in which a first cell and a second cell of a type different from the first cell are spatially overlapped. Wireless communication terminal
A first reception unit that receives a preamble signal from the first cell and a preamble signal from the second cell;
Estimating a first transfer function with the first cell using the preamble signal from the first cell, and using the preamble signal from the second cell, A transfer function estimator for estimating a second transfer function between
A first receiver for receiving a first desired signal from the first cell and an interference signal from the second cell at a first time when there is interference from the second cell;
In a second time without interference from the second cell, the second desired signal from the first cell and the second cell transmitted from the relay station arranged in the first cell A third receiving unit for receiving interference information about;
Based on the received signal at the second time, the interference information, and the first and second transfer functions, the second desired signal is estimated, the received signal at the first time, A signal estimation unit configured to estimate the first desired signal based on interference information and the first and second transfer functions;

  In a favorable configuration example, the wireless communication terminal further includes an interference decoding unit that decodes interference information about the second cell transmitted from the relay station. The interference decoding unit estimates the interference by approximating a ratio of the first transfer function to the second transfer function to zero.

  With the above-described technique and configuration, it is possible to avoid inter-channel interference between systems in a heterogeneous network without imposing a heavy burden on the terminal side.

It is a figure which shows the example of a heterogeneous network. It is a figure for demonstrating the interference removal method by a zero forcing (ZF) method. It is a figure which shows the problem 1 which should be solved in a heterogeneous network. It is a figure which shows the problem 2 which should be solved in a heterogeneous network. It is a figure which shows the structural example of the heterogeneous network to which this invention is applied. It is a flowchart which shows the interference avoidance procedure of an Example. It is a figure which shows an example of the transmission timing of a macrocell base station (M-BS) and a picocell base station (P-BS). It is a figure which shows the example of a setting of the signal transmission area for a transfer function estimation. FIG. 10 is a sequence diagram illustrating in detail the operation of procedure 2. In the radio | wireless communications system of an Example, it is the schematic which shows the communication state at the time of transmission timing t = t1. In the radio | wireless communications system of an Example, it is the schematic which shows the communication state at the time of transmission timing t = t2. It is a sequence diagram which shows operation | movement of the procedures 3-8. It is a figure which shows the transmission / reception timing of each station. It is a figure for demonstrating the signal processing by the interference composite in a macrocell terminal. It is a graph which shows the effect of the interference avoidance method of an Example. It is a figure which shows an example of the transmission timing between base stations in the case of performing the interference avoidance from a macrocell base station to a pico cell terminal. It is a schematic block diagram of the relay station used in an Example. It is a schematic block diagram of the radio | wireless communication terminal used in an Example.

  Hereinafter, specific embodiments will be described with reference to the drawings. The present invention can be applied to both the problem 1 shown in FIG. 3A and the problem 2 shown in FIG. 3B, but in the following, the situation of the problem 1 will be described as an example.

  FIG. 4 is a schematic diagram of a wireless communication system 1 to which the present invention is applied. In the radio communication system 1, a macro cell 11 provided by a macro cell base station (M-BS) 10 that is a first radio base station and a pico cell base station (P-BS) 40 that is a second radio base station are provided. The pico cell 41 is disposed so as to overlap spatially. In the macro cell 11, a macro cell relay station (M-RS) 30 is used to expand area coverage and improve quality. In FIG. 4, only the macro cell relay station (M-RS) 30 located closest to the macro cell terminal (M-UE) 20 is illustrated for convenience of illustration, but a plurality of macro cell relay stations (M -RS) (hereinafter simply referred to as “relay station (M-RS)”) 30 is disposed.

  The macro cell 11 includes a radio communication terminal (hereinafter referred to as “macro cell terminal (M-UE)”) 20 capable of communicating with the macro cell base station (M-BS) 10. On the other hand, a radio communication terminal (hereinafter referred to as a “pico cell terminal (P-UE)”) 50 capable of communicating with a pico cell base station (P-BS) 40 is provided in a pico cell 41 that spatially overlaps the macro cell 11. Exists.

  The macro cell terminal (M-UE) 20 receives desired waves such as data and control signals from the macro cell base station (M-BS) 40 in the downlink. At this time, the pico cell base station (P-BS) 40 may also transmit data, control signals, and the like to the pico cell terminal (P-UE) 50 in the pico cell 41 using the same communication channel. In this case, the signal transmitted by the picocell base station (P-BS) 40 becomes an interference wave for the macrocell terminal (M-UE) 20. The interference wave from the picocell base station (P-BS) 40 also reaches the macrocell relay station (M-RS) 30 located in the vicinity of the macrocell terminal (M-UE) 20.

  The relay station (M-RS) 30 is used in the vicinity of the macro cell terminal (M-UE) 20 for area expansion and communication quality improvement. In the embodiment, the relay station (M-RS) 30 receives from an interference station. The interference wave is positively used as interference avoidance means for the wireless communication terminal (M-UE 20 in the case of FIG. 3A).

FIG. 5 is a flowchart for explaining the procedure of the interference avoidance method according to the embodiment. Hereinafter, specific procedures will be described in order.
<Procedure 1>
In the procedure 1, the macro cell terminal (M-UE) 20 receives interference from the pico cell base station (P-BS) 40, and notifies the macro cell base station (M-BS) 10 and the macro cell relay station (M-RS). Notice. Upon receiving this notification, the interference avoidance method of the embodiment operates.

  For example, in the state of FIG. 4, it is assumed that the macro cell terminal (M-UE) 20 is receiving a signal from the macro cell base station (M-BS) 10 in the vicinity of the pico cell 41. At this time, when downlink data transmission to the pico cell terminal (P-UE) 50 occurs in the pico cell 41, the downlink signal transmitted by the pico cell base station (P-BS) 40 is the macro cell terminal (M-UE). 20 is an interference wave i.

FIG. 6 is a diagram illustrating an example of transmission timings of the macro cell base station (M-BS) 10 and the pico cell base station (P-BS) 40. In this example, the macro cell base station (M-BS) 10 uses the frequency division multiplexing (FDD) system and always performs downlink transmission using the frequency channel f1. On the other hand, the picocell base station (P-BS) 40 uses a time division multiplexing (TDD) system and uses the frequency channel f1 separately for uplink communication and downlink communication. As an example, the section t1 is used for transmission (downlink communication), and the section t2 is used for reception (uplink communication). For the macro cell terminal (M-UE) 20, the downlink interference from the pico cell base station (P-BS) becomes a problem in the section t1.
<Procedure 2>
In the procedure 2, transmission between the picocell base station (P-BS) 40 in each of the macrocell terminal (M-UE) 20 and the macrocell relay station (M-RS) 30 using the preamble section of the interference wave. Estimate the function. Further, in each of the macro cell terminal (M-UE) 20 and the relay station (M-RS) 30, a transfer function between the macro cell base station (M-BS) 10 is estimated. This process will be specifically described with reference to FIGS.

  FIG. 7 is a diagram illustrating a configuration example of a communication frame of the wireless communication system 1, and FIG. 8 is a macro cell base station (M-BS) 10, a relay station (M-RS) 30, a macro cell terminal (M-UE 20), and It is a sequence diagram which shows operation | movement of the picocell base station (P-BS) 40.

  As shown in FIG. 7, the signal is transmitted periodically. A signal section called a preamble or a unique word is provided at the head of the communication signal, and subsequently, a data section is set. The preamble and unique word are frame synchronization signals for establishing synchronization between the base station and the mobile terminal. Such a signal is generally called a training signal and is a unique signal determined by the system. In the procedure 2, a preamble section of the interference signal (a section in which a training signal is generated) is estimated, and channel estimation is performed using this section.

  In the example of FIG. 7, the preamble section of the interference signal is divided into sections 1 to 3. In section 1, there is no transmission from the macro cell base station (M-BS) 10, and the preamble is transmitted only in the interference signal. Section 2 is an interference wave preamble section and a preamble section from the macro cell base station (M-BS) 10 to the macro cell terminal (M-UE) 20. Section 3 overlaps with the preamble section from macro cell relay station (M-RS) 30 to macro cell terminal (M-UE) 20.

When the signal transmission section is set as described above, the operation of each communication station in the sections 1 to 3 in the wireless communication system 1 of the embodiment is as follows (a) to (e).
(A) In section 1, the M-BS 10 does not transmit and the M-RS 30 is in a receiving state.
(B) In section 2, the M-BS 10 performs preamble transmission and the M-RS 30 is in a receiving state.
(C) In section 3, the M-BS 10 does not transmit, and the M-RS 30 transmits a preamble.
(D) The macro cell terminal (M-UE) 20 is always receiving.
(E) The picocell base station (P-BS) 40 always transmits.

  A specific process of the procedure 2 will be described with reference to the sequence diagram of FIG. Since the interference signal arrives over all of the sections 1 to 3, first, in the preamble section 1, the macro cell relay station (M-RS) 30 and the macro cell terminal (M-UE) 20 respectively, the pico cell base which is an interference station. A transfer function with the station (P-BS) 40 is estimated (S101, S102).

Specifically, the macro cell terminal (M-UE) 20 determines a pico cell base station based on the received signal x _{P1, UE} actually received by the own terminal and the training signal i _P1 of the interference wave in the section 1. A transfer function h _PU with (P-BS) 40 is estimated (S102). The relay station (M-RS) 30 is connected to the picocell base station (P-BS) based on the received signal x _{P1, RS} actually received by the own station and the interference signal training signal i _P1 in section 1. _Is estimated. Processing at this time is expressed by the following equations (5) and (6).

式中の上添え字〜（ハット）は推定値を表わし、実際の値と区別するために添えられている。また、n_{*} (*は下添え字)は雑音を表すが、伝播関数を推定する際、受信信号に対し十分小さいため，ここではこの項については無視をしている。以下も同様である。

The superscripts ~ (hats) in the formula represent estimated values and are added to distinguish them from actual values. Also, n _ {*} (* is a subscript) represents noise, but this term is ignored here because it is sufficiently small with respect to the received signal when estimating the propagation function. The same applies to the following.

In section 1, there is no signal transmission from the macro cell base station (M-BS) 10, and the macro cell terminal (M-UE) 20 and the relay station (M-RS) 30 interfere with each other from the pico cell base station (P-BS) 40. Using the preamble signal i _p1 , the channel response between the picocell base station (P-BS) 40 is estimated from Equation (5) and Equation (6), respectively.

Next, in section 2, since there is preamble transmission from the macro cell base station (M-BS) 10 (S103), the macro cell terminal (M-UE) 20 is connected to the macro cell base station (M-BS) 10 and its own terminal. A transfer function h _BU between the two is estimated (S106). The transfer function h _BU includes a reception signal x _P2 at interval 2, it is estimated using the training signal S _P output from the macrocell base station (M-BS) 10. However, since the interference signal from the pico cell 41 is also included in this section (S105), the estimation result in the section 1 (propagation function with the pico cell) as shown in the equation (7).

と、区間２で受信した干渉トレーニング信号ｉ_P2（Ｓ１０５）とを用いることで、マクロセル基地局（Ｍ−ＢＳ）１０とマクロセル端末（Ｍ−ＵＥ）２０の間の伝達関数を推定する（Ｓ１０６）。

And the interference training signal i _P2 (S105) received in section 2 is used to estimate the transfer function between the macrocell base station (M-BS) 10 and the macrocell terminal (M-UE) 20 (S106). .

他方、中継局（Ｍ−ＲＳ）３０も、区間２でマクロセル基地局（Ｍ−ＢＳ）１０からのプリアンブル信号Ｓ_Pと、ピコセル基地局（Ｐ−ＢＳ）４０からの干渉プリアンブル信号ｉ_P2を受信するので、同様に区間１の推定結果を用いて、マクロセル基地局（Ｍ−ＢＳ）１０との間の伝達関数推定する（Ｓ１０４）。Ｍ−ＢＳ１０とＭ−ＲＳ３０は、基地局と中継局の関係なので、両者の間の伝達関数はあらかじめ推定可能であり、この変動も小さいので、Ｓ１０４での推定は必須ではないが、中継局（Ｍ−ＲＳ）３０においても定期的に無線環境を推定するのが望ましい。

On the other hand, the relay station (M-RS) 30 also receives the preamble signal S _P from the macro cell base station (M-BS) 10 and the interference preamble signal i _P2 from the pico cell base station (P-BS) 40 in section 2. Therefore, similarly, using the estimation result of section 1, the transfer function with the macro cell base station (M-BS) 10 is estimated (S104). Since the M-BS 10 and the M-RS 30 are related to each other between the base station and the relay station, the transfer function between them can be estimated in advance, and since this fluctuation is small, the estimation in S104 is not essential, but the relay station ( (M-RS) 30 also desirably estimates the wireless environment periodically.

Next, in interval 3, the macrocell relay stations (M-RS) 30 transmits a preamble signal S _p to the macro-cell MT (M-UE) 20 (S107 ), the macro-cell MT (M-UE) 20 is the own terminal the transfer function h between the received signal x _p3, using the training signal S _p from the relay station (M-RS) 30, a relay station (M-RS) 30 and the macro-cell MT (M-UE) 20 in _RU is estimated (S109). However, since the interference signal from the picocell base station (P-BS) 40 is also included in this section (S108), the estimation result (propagation function with the picocell) in section 1 is

と、区間３で受信した干渉トレーニング信号ｉ_p3とを用いることで、次式（８）から、中継局（Ｍ−ＲＳ）３０とマクロセル端末（Ｍ−ＵＥ）２０との間の伝達関数を推定する。

And the interference training signal i _p3 received in the section 3, the transfer function between the relay station (M-RS) 30 and the macro cell terminal (M-UE) 20 is estimated from the following equation (8). To do.

このようにして、手順２では、干渉波のプリアンブル区間を利用して、P-BS→M-UEの伝達関数、P-BS→M-RSの伝達関数、M-BS→M-UEの伝達関数、及びM-BS→M-RSの伝達関数を推定する。

In this way, in the procedure 2, using the preamble section of the interference wave, the transfer function of P-BS → M-UE, the transfer function of P-BS → M-RS, and the transfer of M-BS → M-UE Estimate the function and the transfer function of M-BS → M-RS.

It should be noted that the timing of executing the processing of the procedure 2 is worst, but can be performed within the range of t1 in FIG. 6, but is performed at an arbitrary timing before t1.
<Procedure 3>
The procedure 3 is performed at the time t = t1 in FIG. FIG. 9 is a diagram for explaining procedure 3 performed at time t = t1. At time t = t1, the macro cell base station (M-BS) 10 is directed to the macro cell terminal (M-UE) 20 with directivity such that the received signal at the relay station (M-RS) 30 becomes zero. Signal S1 is transmitted. As a result, the relay station (M-RS) 30 exclusively receives the interference signal i from the pico cell 41 at time t1, and the interference signal estimation accuracy described later is improved. On the other hand, the macro cell terminal (M-UE) 20 receives the interference wave i from the pico cell 41 in addition to the desired wave S 1 from the macro cell base station (M-BS) 10. Specific processing at this time will be described with reference to FIGS. 11A and 11B.

  FIG. 11A is a sequence diagram showing the operation of each station at time t = t1 and subsequent time t = t2. FIG. 11B shows transmission / reception timings of the macro cell base station (M-BS) 10, the pico cell base station (P-BS) 40, the macro cell terminal (M-UE) 20, and the relay station (M-RS) 30 at times t1 and t2. FIG.

  As shown in FIG. 11A, after estimating the transfer function using the preamble section in step 2, the macro cell base station M-BS10 determines the relay station (M-RS) 30 at time t = t1. The signal S1 is transmitted to the macro cell terminal (M-UE) 20 so as to be null (S201). The null control can generate desired directivity using the transfer function between the macro cell base station (M-BS) 10 and the relay station (M-RS) 30 estimated in S104 of FIG. Alternatively, using a transfer function with the relay station 30 prepared in advance by the macrocell base station (M-BS) 10, directivity is generated such that the received signal at the relay station (M-RS) 30 becomes zero. May be.

At t = t1, the picocell base station (P-BS) 40 is also transmitting a signal (data interval) in the downlink, which becomes an interference signal i for the macrocell terminal (M-UE) 20 (S202). Therefore, the signal received by the macro cell terminal (M-UE) 20 is a combined signal of the desired signal S1 and the interference signal i (S203). The reception signal x _U, t1 of the macro cell terminal (M-UE) 20 at t = t1 in the data _period is expressed by the following equation (9).

このとき、中継局（Ｍ−ＲＳ）３０は、もっぱらピコセル基地局（Ｐ−ＢＳ）４０からの干渉信号ｉを受信しているので、データ区間でのｔ＝ｔ１における中継局（Ｍ−ＲＳ）３０の受信信号ｘ_{R, t1}は、次式（１０）で表わされる。

At this time, since the relay station (M-RS) 30 exclusively receives the interference signal i from the picocell base station (P-BS) 40, the relay station (M-RS) at t = t1 in the data interval. The 30 received signals x _{R, t1} are expressed by the following equation (10).

＜手順４＞
手順４では、中継局（Ｍ−ＲＳ）３０が、式（１０）により求めたデータ区間での受信信号と、手順２で得られたピコセル基地局（Ｐ−ＢＳ）４０との間の伝達関数

<Procedure 4>
In the procedure 4, the relay station (M-RS) 30 performs a transfer function between the received signal in the data section obtained by the equation (10) and the picocell base station (P-BS) 40 obtained in the procedure 2.

を用いて、データ区間の干渉信号を推定する（Ｓ２０５）。推定される干渉信号は式（１１）で表わされる。

Is used to estimate the interference signal in the data interval (S205). The estimated interference signal is expressed by equation (11).

＜手順５＞
手順５以降は、図１０に示すように、データ区間の干渉信号の到来がないｔ＝ｔ２での手順となる。手順５では、マクロセル基地局（Ｍ−ＢＳ）１０がマクロセル端末（Ｍ−ＵＥ）２０に所望信号Ｓ２を送信するとともに、中継局（Ｍ−ＲＳ）３０が、推定した干渉信号をマクロセル端末（Ｍ−ＵＥ）２０に送信する。干渉のない時間ｔ２で、干渉が生じていた時間ｔ１の干渉情報（推定された干渉）をマクロセル端末（Ｍ−ＵＥ）２０に送信する理由は、後述するように、時間ｔ１で受信した所望信号Ｓ１の推定を精度よく行なうためである。

<Procedure 5>
From step 5 onwards, as shown in FIG. 10, the procedure is at t = t2 where no interference signal arrives in the data section. In procedure 5, the macro cell base station (M-BS) 10 transmits the desired signal S2 to the macro cell terminal (M-UE) 20, and the relay station (M-RS) 30 transmits the estimated interference signal to the macro cell terminal (M -UE) 20. The reason why the interference information (estimated interference) at the time t1 when the interference has occurred at the time t2 when there is no interference is transmitted to the macro cell terminal (M-UE) 20 is that the desired signal received at the time t1, as will be described later. This is for the purpose of accurately estimating S1.

  Referring to FIG. 11A, at time t = t2, the macro cell base station (M-BS) 10 transmits a signal S2 different from the signal S1 transmitted at t = t1 to the macro cell terminal (M-UE) 20 (S206). ). Transmission at this time may be performed with directivity such that reception at the relay station (M-RS) 30 is zero, or may be transmitted without null control.

On the other hand, the relay station (M-RS) 30 transmits the interference information (interference signal expressed by Equation 11) estimated at time t = t1 to the macro cell terminal (M-UE) 20 (S207). Therefore, the signal received at the macro cell terminal (M-UE) 20 at time t2 is the desired signal S2 from the macro cell base station (M-BS) 10 and the interference signal (i from the relay station (M-RS) 30). ) And a combined signal (S208).
<Procedure 6>
In Procedure 6, the macro cell terminal (M-UE) 20 estimates an interference signal based on the received signal at t = t2 (received signal in S208) and the transfer function estimated in Procedure 2. The received signal of the macro cell terminal (M-UE) 20 at t = t2 is expressed by the following equation (12).

ここで、実施例では、マクロセル基地局（Ｍ−ＢＳ）１０とマクロセル端末（Ｍ−ＵＥ）２０の間と、中継局（Ｍ−ＲＳ）３０とマクロセル端末（Ｍ−ＵＥ）２０の間とでは、ＳＮＲが大きく異なることを利用する。上述のように、中継局（Ｍ−ＲＳ）３０は通信エリアを拡大するために使用され、無線通信端末の近傍に位置していることが予想される（無線通信端末（Ｍ−ＵＥ）は最も近くに位置する中継局（Ｍ−ＲＳ）を選択する）。その場合、中継局（Ｍ−ＲＳ）３０からマクロセル端末（Ｍ−ＵＥ）２０への信号のＳＮＲは、マクロセル基地局（Ｍ−ＢＳ）１０からマクロセル端末（Ｍ−ＵＥ）２０への信号のＳＮＲよりもはるかに大きくなると考えられる。すなわち、
SNR(M-RS→ M-UE) >> SNR(M-BS→ M-UE)
の関係が成り立つ。

Here, in the embodiment, between the macro cell base station (M-BS) 10 and the macro cell terminal (M-UE) 20 and between the relay station (M-RS) 30 and the macro cell terminal (M-UE) 20. , The fact that the SNR is greatly different is used. As described above, the relay station (M-RS) 30 is used to expand the communication area and is expected to be located in the vicinity of the wireless communication terminal (the wireless communication terminal (M-UE) is the most Select a nearby relay station (M-RS)). In that case, the SNR of the signal from the relay station (M-RS) 30 to the macro cell terminal (M-UE) 20 is the SNR of the signal from the macro cell base station (M-BS) 10 to the macro cell terminal (M-UE) 20. Will be much larger than. That is,
SNR (M-RS → M-UE) >> SNR (M-BS → M-UE)
The relationship holds.

  Transmission between the relay station (M-RS) 30 and the macro cell terminal (M-UE) 20 in which both sides of the received signal at the macro cell terminal (M-UE) 20 represented by the equation (12) are estimated in the procedure 2 Function (transfer function represented by equation (8))

で除算すると、次式（１２）'になる。

When dividing by, the following expression (12) ′ is obtained.

ここで、干渉信号のプリアンブル区間で推定された中継局（Ｍ−ＲＳ）３０とマクロセル端末（Ｍ−ＵＥ）２０との間の伝達関数（図８のＳ１０９参照）の推定精度はきわめて高いから、ｔ＝ｔ２における実際の伝達関数ｈ_RUと、プリアンブル区間での推定値とは近似し、式（１２）'の右辺の第２項、すなわち干渉成分ｉの係数は、ほぼ１となる。

Here, since the estimation accuracy of the transfer function (see S109 in FIG. 8) between the relay station (M-RS) 30 and the macro cell terminal (M-UE) 20 estimated in the preamble section of the interference signal is extremely high, The actual transfer function h _{RU at} t = t2 and the estimated value in the preamble section are approximated, and the second term on the right side of Equation (12) ′, that is, the coefficient of the interference component i is approximately 1.

On the other hand, for the first term on the right side of Equation (12) ′, that is, the coefficient of the desired signal S2, the macro cell base station (M-BS) 10 and the relay station (M-RS) 30 for the macro cell terminal (M-UE) 20 are used. From the positional relationship with
| H _RU | >> | h _BU |, | h _RU | >> | n _{U, t2} |
The relationship holds. Here, | h _RU | is the absolute value of the transfer function between the relay station (M-RS) 30 and the macro cell terminal (M-UE) 20, and | h _BU | is the macro cell base station (M-BS) 10 It is the absolute value of the transfer function with the macro cell terminal (M-UE) 20. As a result, the coefficient and the third term of the second term (desired signal S2) on the right side of Expression (12) ′ approximate to zero.

  Therefore, the interference signal represented by the following equation (13) is estimated from the equation (12) ′.

この処理は、図１１Ａのシーケンス図のＳ２０９に対応する。

This process corresponds to S209 in the sequence diagram of FIG. 11A.

  Thus, in the macro cell terminal (M-UE) 20, when the interference information from the relay station (M-RS) 30 is very large compared to the desired signal S2 from the macro cell base station (M-BS) 10, Only the interference signal can be decoded. The effect of this method is shown in FIG.

FIG. 12 is a graph showing the bit rate as a function of SIR (signal to interference ratio) when the interference signal is decoded. The simulation was performed by setting the average SNR between the macro cell base station (M-BS) 10 and the macro cell terminal (M-UE) 20 to 20 dB. As is apparent from FIG. 12, when the interference signal is decoded, a higher bit rate can be obtained as SIR [dB] becomes a negative region.
<Procedure 7>
In the procedure 7, the interference signal estimated in the procedure 6 is subtracted from the received signal of the macro cell terminal (M-UE) 20 at t = t2, and the desired signal S2 is estimated using the transfer function estimated in the procedure 2.

  More specifically, the interference signal of equation (13) estimated in step 6

と、式（１２）で表わされるｔ＝ｔ２での受信信号ｘ_{U, t2}と、手順２で得たチャネル情報

And the received signal x _{U, t2} at t = t2 represented by the equation (12) and the channel information obtained in the procedure 2

に基づいて、ｔ＝ｔ２にマクロセル基地局（Ｍ−ＢＳ）１０が送信した所望信号Ｓ２を、次式（１４）により推定することができる。

The desired signal S2 transmitted by the macro cell base station (M-BS) 10 at t = t2 can be estimated by the following equation (14).

この処理は、図１１Ａのシーケンス図のＳ２１０に対応する。
＜手順８＞
手順８では、ｔ＝ｔ１におけるマクロセル端末（Ｍ−ＵＥ）の受信信号から、手順６で推定した干渉信号を差し引き、手順２で推定した伝達関数を用いて、所望信号Ｓ１を推定する。

This process corresponds to S210 in the sequence diagram of FIG. 11A.
<Procedure 8>
In procedure 8, the interference signal estimated in procedure 6 is subtracted from the received signal of the macro cell terminal (M-UE) at t = t1, and the desired signal S1 is estimated using the transfer function estimated in procedure 2.

  That is, the interference signal of equation (13)

と、式（９）で表わされる受信信号ｘ_{U, t1}と、手順２で得たチャネル情報

And the received signal x _{U, t1} represented by equation (9) and the channel information obtained in step 2

に基づいて、マクロセル基地局（Ｍ−ＢＳ）１０がｔ＝ｔ１に送った信号Ｓ１を次式（１５）により推定することができる。

The signal S1 sent from the macrocell base station (M-BS) 10 at t = t1 can be estimated from the following equation (15).

このように、実施例の手法によれば、中継局を積極的に干渉回避に利用することで、無線通信端末のアンテナに高度な機能を持たせることなく、所望信号を推定することができる。

As described above, according to the method of the embodiment, the relay station is actively used for interference avoidance, so that a desired signal can be estimated without giving an advanced function to the antenna of the wireless communication terminal.

  3B, that is, downlink transmission data from the macro cell base station (M-BS) 110 is generated while the pico cell terminal (P-UE) 220 is communicating with the pico cell base station (P-BS) 210. In the lower case, the above-described procedures 1 to 8 can also be applied to avoid interference given to the pico cell terminal (P-UE) 220.

  4 and FIG. 5, when the pico cell terminal (P-UE) 50 detects interference from the macro cell base station (M-BS) 10, the macro cell base station (M-BS) 10 Is notified to the picocell base station (P-BS) 40 and a relay station (not shown) in the picocell 41.

  As the relay station in the pico cell 41, for example, a wireless terminal apparatus that is not currently communicating in the pico cell 41 may be used as a relay station, or a fixed relay station may be arranged in the pico cell 41 in advance. . Procedures 2 to 8 are executed using a notification of interference detection from the picocell terminal (P-UE) 50 as a trigger.

  FIG. 14 is a diagram illustrating an example of transmission timings of the macro cell base station and the pico cell base station in this case. In the example of FIG. 14, both the macro cell base station and the pico cell base station are operating in FDD. The macro cell base station temporarily stops transmission at time t2 after time t1 of the data interval. At time t2 when there is no interference, the pico cell terminal (P-UE) 50 estimates the desired signal S2 at the time t2 from the pico cell base station and the desired signal S1 at the time t1.

  In procedure 2, the pico cell terminal (P-UE) 50 and the pico cell relay station (not shown) use the preamble section of the interference signal from the macro cell base station (M-BS) at an arbitrary time before t = t1. Then, a necessary channel transfer function is estimated.

  In procedure 3, at time t = t1, the pico cell base station (P-BS) 40 in FIG. 4 transmits a signal S1 to the pico cell terminal (P-UE) 50 with directivity that does not reach the pico cell relay station (not shown). (Data section) is transmitted. At this time, the pico cell relay station exclusively receives the interference wave from the macro cell base station (M-BS) 10. In procedure 4, the pico cell relay station estimates the interference signal using a transfer function between the received interference signal and the macro cell base station (M-BS) 10 estimated in procedure 2.

  At time t = t2 when the interference wave does not arrive in procedure 5 (see FIGS. 11A and 11B), the picocell base station (P-BS) 40 transmits a signal S2 to the picocell terminal (P-UE) 50, and the picocell The interference information (interference signal from the macro cell base station (M-BS) 10) estimated in the procedure 4 is transmitted from a relay station (not shown) to the pico cell terminal (P-UE) 50. Therefore, the pico cell terminal (P-UE) 50 receives the desired signal S2 from the pico cell base station (P-BS) 50 and the interference signal i from the relay station.

  In procedure 6, the pico cell terminal (P-UE) 50 estimates the interference signal i using the received signal of procedure 5 (t = t2) and the transfer function estimated in procedure 2. In this estimation, as described with reference to FIG. 11A, the estimation accuracy of the interference signal estimated by the relay station in the data section of procedure 4 is extremely high (the picocell base station performs null control of the relay station). The signal S1 is sent to the pico cell terminal below), and the transfer function between the pico cell relay station and the pico cell terminal (P-UE) 50 is the macro cell base station (M-BS) 10 and the pico cell terminal (P-UE) 50. Is very large compared to the transfer function between

  In procedure 7, the interference signal estimated in procedure 6 is subtracted from the received signal at t = t2, and the desired signal S2 at t = t2 is estimated using the transfer function of procedure 2. Further, at step 8, the interference signal estimated at step 6 is subtracted from the received signal at t = t1, and the desired signal S1 at t = t1 is estimated using the transfer function of step 2.

  In this way, even when inter-channel interference occurs when service areas of different sizes are spatially overlapped as in a heterogeneous network, the burden on the wireless communication terminal is not increased by using the relay station. Interference can be avoided.

  Note that the transmission timing as shown in FIG. 14 can be realized by cooperation between the macrocell base station (M-BS) 10 and the picocell base station (P-BS) 40. The pico cell 41 receives interference information from the relay station using t2 without interference from the macro cell 11, and estimates the desired signal S2 with high accuracy, and also estimates the desired signal S1 at time t = t1 when there is interference. can do.

  FIG. 15 is a schematic configuration diagram of a relay station used in the embodiment, for example, a macro cell relay station (M-RS) 30. In this figure, components that are not related to the invention, such as a filtering unit, an amplification unit, a frequency conversion unit, an encoding / decoding unit, and a modulation / demodulation unit are omitted.

  The relay station 30 includes a reception unit 31, a transfer function estimation unit 32, a transmission unit 33, and an interference signal estimation unit 34. The receiving unit 31 receives interference signals from different types of cells (picocells) that spatially overlap the macrocell to which the relay station 30 belongs. The transfer function estimation unit estimates the transfer function between the pico cell and the relay station 30 using the preamble section of the interference signal from the interference station (pico cell). The receiving unit 31 also receives the interference signal in the data interval from the pico cell at time t1 exclusively receiving the interference signal from the pico cell. The interference signal estimation unit 34 estimates an interference signal based on the received signal in the data section and the previously estimated transfer function. The transmission unit 33 transmits the estimated interference signal to the terminal (M-UE) 10 communicating with the macro cell at time t2 when there is no interference from the pico cell.

  In this way, the relay station 30 transmits the interference signal estimation result received at t1 as interference information to the wireless communication terminal at time t2 when there is no interference, so that the desired signal can be easily estimated at the wireless communication terminal. Make it accurate.

  FIG. 16 is a schematic configuration diagram of a radio communication terminal used in the embodiment, for example, a macro cell terminal (M-UE) 20. Also in this figure, components not related to the invention are omitted.

  The wireless communication terminal 20 includes a reception unit 21, a transfer function estimation unit 22, a transmission unit 23, an interference decoding unit 24, and a signal estimation unit 25. The receiving unit 21 includes first to third receiving units. The first reception unit receives a preamble signal from a macro cell (first cell) with which a radio communication terminal (M-UE) communicates and a preamble signal from a pico cell (second cell). The second receiving unit receives the first desired signal (S1) transmitted from the macro cell and the interference signal from the pico cell at a first time (data interval) in which there is interference from the pico cell. The third reception unit includes a second desired signal (S2) transmitted from the macro cell and a relay station (M-RS) arranged in the macro cell at a second time (data interval) without interference from the pico cell. The interference information about the picocell transmitted from is received.

  The transfer function estimation unit 23 estimates a first transfer function with the macro cell (macro cell base station M-BS) using the preamble signal from the macro cell, and uses the preamble signal from the pico cell to generate a pico cell (pico cell base station). P-BS) is estimated.

  The signal estimation unit 25 estimates the second desired signal S2 based on the received signal at the second time, the interference information from the relay station (M-RS), and the first and second transfer functions. . In addition, the first desired signal S1 is estimated based on the received signal at the first time, interference information from the relay station (M-RS), and the first and second transfer functions.

  Thus, the radio communication terminal (M-UE) 20 extremely increases the amount of calculation by receiving the interference information of the interference station (P-BS) from the relay station (M-RS) located in the vicinity. Therefore, the desired signal can be estimated accurately.

  As described with reference to FIG. 12, the interference decoding unit 24 determines that the second transfer function between the relay station and the first transfer function with the macro cell base station is extremely large. Use this to estimate interference information. Further, at least the first desired signal is a signal transmitted from the macro cell with directivity such that the reception signal at the relay station becomes zero.

  In this way, by using the relay station (M-RS) 30 having the configuration of FIG. 15 in the heterogeneous network, it is possible to easily avoid interference at the wireless communication terminal. Further, by using the radio communication terminal (M-UE) 20 having the configuration of FIG. 16, a received signal, interference information from the relay station, and a transfer function estimated in advance (for example, using a preamble section) are used. Thus, the desired signal can be estimated with high accuracy.

  It can be applied to interference avoidance in heterogeneous networks.

10 Macrocell base station (M-BS)
11 Macrocell 20 Macrocell terminal (M-UE)
21 receiving unit 22 transmitting unit 23 transfer function estimating unit 24 interference decoding unit 25 signal estimating unit 30 macro cell relay station (M-RS)
31 Receiver 32 Transfer Function Estimator 33 Transmitter 34 Interference Signal Estimator 40 Picocell Base Station (P-BS)
41 Picocell 50 Picocell terminal (P-UE)

Claims (10)

A first radio base station that provides a first cell; a second cell of a different type that spatially overlaps the first cell; a relay station that is used in the first cell; In a wireless communication system including a wireless communication terminal that communicates with a cell,
The radio communication terminal uses a preamble section of a signal from the second cell, and uses a first transfer function between the first radio base station and a second cell between the second cell and the second cell. 2 estimate the transfer function,
In a first time of a data interval with interference from the second cell, the first radio base station has a directivity such that a received signal at the relay station becomes zero, and a first desired signal To the wireless communication terminal, and the relay station receives an interference signal from the second cell,
In a second time of a data interval without interference from the second cell, the first radio base station transmits a second desired signal different from the first desired signal to the radio communication terminal. The relay station transmits interference information related to the interference signal from the second cell to the wireless communication terminal,
The wireless communication terminal estimates the second desired signal based on the received signal at the second time, the interference information, and the first and second transfer functions;
A wireless communication system. In the second time, the wireless communication terminal estimates the first desired signal using the received signal in the first time, the interference information, and the first and second transfer functions. The wireless communication system according to claim 1. In the preamble period, the relay station estimates a third transfer function with the second cell;
In the second time, the relay station generates the interference information based on the received signal received by the relay station in the first time and the third transfer function, and transmits the interference information to the wireless communication terminal. The wireless communication system according to claim 1 or 2, wherein the transmission is performed. An interference avoidance method in a wireless communication system, comprising:
A radio communication system including a first radio base station that provides a first cell, a second cell of a different type that spatially overlaps the first cell, and a relay station that is used in the first cell In the wireless communication terminal that communicates with the first cell, using the preamble section of the signal from the second cell, a first transfer function with the first wireless base station, and Estimating a second transfer function to and from the second cell;
In the first time of the data interval with interference from the second cell, the directivity from the first radio base station to the radio communication terminal is such that the received signal at the relay station becomes zero. Transmitting a first desired signal and receiving an interference signal from the second cell at the relay station;
A second desired signal different from the first desired signal is transmitted from the first radio base station to the radio communication terminal in a second time of a data interval without interference from the second cell. And transmitting interference information related to the interference signal from the relay station to the wireless communication terminal,
In the wireless communication terminal, the second desired signal is estimated based on the received signal at the second time, the interference information, and the first and second transfer functions.
The interference avoidance method characterized by the above-mentioned. The wireless communication terminal further includes the step of estimating the first desired signal using the received signal at the first time, the interference information, and the first and second transfer functions. The interference avoidance method according to claim 4, wherein In the relay station, using the preamble section, estimate a third transfer function between the second cell,
Generating the interference information based on the third transfer function and the received signal received at the relay station at the first time, and transmitting the interference information to the wireless communication terminal;
The interference avoidance method according to claim 4 or 5, wherein In a wireless communication system in which a first cell and a second cell of a different type from the first cell are spatially overlapped, a relay station used in the first cell,
A receiving unit for receiving an interference signal in a data interval from the second cell;
A transfer function estimating unit that estimates a transfer function between the second cell and the relay station using a preamble section of a signal from the second cell;
An interference signal estimator that estimates the interference signal based on the estimated transfer function and the received signal in the data interval;
A relay station, comprising: a transmission unit that transmits the estimated interference signal to a wireless communication terminal that communicates with the first cell. A wireless communication terminal used in a wireless communication system in which a first cell and a second cell of a different type from the first cell are spatially overlapped,
A first reception unit that receives a preamble signal from the first cell and a preamble signal from the second cell;
Estimating a first transfer function with the first cell using the preamble signal from the first cell, and using the preamble signal from the second cell, A transfer function estimator for estimating a second transfer function between
A first receiver for receiving a first desired signal from the first cell and an interference signal from the second cell at a first time when there is interference from the second cell;
In a second time without interference from the second cell, the second desired signal from the first cell and the second cell transmitted from the relay station arranged in the first cell A third receiving unit for receiving interference information about;
Based on the received signal at the second time, the interference information, and the first and second transfer functions, the second desired signal is estimated, the received signal at the first time, A radio communication terminal comprising: a signal estimation unit that estimates the first desired signal based on interference information and the first and second transfer functions. An interference decoding unit for decoding interference information about the second cell transmitted from the relay station;
Further comprising
The radio communication terminal according to claim 8, wherein the interference decoding unit estimates the interference by approximating a ratio of the first transfer function to a second transfer function to zero.   10. The transmission station according to claim 8, wherein the transmission station receives the first desired signal transmitted from the first cell with directivity such that a reception signal at the relay station becomes zero. The wireless communication terminal described.

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