JP2008109664A - Data transmission method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data transmission method that allows to resolve a pilot collision problem and improve resource utilization. <P>SOLUTION: The data transmission method includes step (a) for a base station to group mobile terminals when it obtains signal-to-noise ratio or signal power from the mobile terminal to the base station or a relay station and sends them from a different base station or relay station, step (b) to define an initial concurrent transmission mobile terminal group corresponding to each STF and the mobile terminals belonging to each initial concurrent transmission mobile terminal group, step (c) to adjust the mobile terminals in the initial concurrent transmission mobile terminal group and multiplex different mobile terminal groups to map to an OFDM sub-carrier symbols, step (d) to define weighting factors of the pilot and data in the employed pre-coding method, and step (e) to perform pre-coding and coordinated transmission with the data and pilot combined in the base station and the relay station and send the data to a target mobile terminal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a data transmission method, and more particularly to a data transmission method that can solve a pilot collision problem and belongs to the field of communication technology.

  The IEEE 802.16j network is an extension of the network coverage (Coverage Extension) and throughput (Throughput Enhancement) by introducing Mobile Multi-hop Relaying (MMR) to the IEEE 802.16 network. It is. The IEEE 802.16j network has the following technical requirements.

  (1) Based on the OFDMA system.

  (2) Compatible with IEEE 802.16-2004 and IEEE 802.16e mobile terminals, that is, the mobile terminals should not be changed.

  (3) Do not change the point-to-multi-points access link from the base station or relay station to the wireless terminal.

  When assigning downlink subcarriers in the IEEE 802.16-2004 standard and IEEE 802.16e standard, pilot subcarriers are assigned first, and then data subcarriers are assigned. In the IEEE 802.16 network, after a relay station that implements mobile multi-hop relay is introduced, a mobile terminal located in the coverage area between the base station and the relay station receives pilot signals from the base station and the relay station. When the mobile terminal receives a plurality of overlapping pilot signals at the same time, there is a case where the output estimated channel response does not match the actual data channel response. The phenomenon is a pilot collision. Pilot collision is a special problem that occurs after the introduction of a relay station in the network, and greatly reduces the bit error rate performance of the mobile terminal.

  In order to clearly explain the pilot collision problem, a communication system having two mobile terminals will be described as an example. FIG. 1 is a diagram illustrating subcarrier allocation between pilots and data subchannels of two mobile terminals in the system. Assume that the mobile terminal MS1 uses data subchannel 1 and the mobile terminal MS2 uses data subchannel 2. Data subchannel 1 and data subchannel 2 use different subcarriers, respectively, and the pilot subcarrier is shared by two data subchannels.

  Point-to-multipoint data transmission in a network without a conventional relay station such as an IEEE 802.16-2004 or IEEE 802.16e network is as shown in FIG. Base station BS transmits a pilot signal on pilot subcarriers, and transmits data to mobile terminal MS1 and mobile terminal MS2 on data subchannel 1 and data subchannel 2, respectively. Each of the mobile terminal MS1 and the mobile terminal MS2 performs channel estimation of the own data subchannel using the pilot signal. That is, the mobile terminal MS1 can correctly estimate the channel response H1, and the mobile terminal MS2 can correctly estimate the channel response H2, and can detect data using the estimated channel responses H1 and H2. . There is no pilot collision problem in such data transmission.

  Since relay stations have been introduced in the IEEE 802.16j network, data of some mobile terminals is transmitted to the mobile terminals via the relay stations. In the network, data transmission is as shown in FIG. 3, and RS is an introduced relay station. In order to maintain generality, it is assumed that the mobile terminal MS1 belongs to the relay station RS. After the introduction of the relay station RS, the base station BS transmits a pilot signal on the pilot subcarrier, transmits data on the data subchannel 2 to the mobile terminal MS2, and the relay station RS transmits the pilot on the pilot subcarrier. A signal is transmitted and data is transmitted on the data subchannel 1 to the mobile terminal MS1. At this time, the channel response from the base station BS to the mobile terminal MS1 is H1, the channel response to the mobile terminal MS2 is H3, and the channel response from the relay station to the mobile terminal MS1 is H2. According to FIG. 3, since the mobile terminal MS2 can only receive a pilot signal from the base station BS, both the estimated channel response H3 and the data detection performed using the output of the channel response H3 are correct. On the other hand, since there is a possibility that the mobile terminal MS1 receives the pilot signals of the base station BS and the relay station RS at the same time, it estimates “H1 + H2” of the wrong channel response when performing channel estimation. It will be. Actually, the data channel response from the relay station RS to the mobile terminal MS1 is H1. Therefore, when the mobile terminal MS1 performs data detection using an incorrect channel response output, the bit error rate performance of the mobile terminal becomes very poor.

  As shown in FIG. 4, the pilot collision problem is also encountered when the mobile terminal can receive signals from multiple relay stations. The channel responses from each of the relay station RS1 and the relay station RS2 to the mobile terminal MS1 are assumed to be H1 and H2, respectively. At this time, since the mobile terminal MS1 can simultaneously receive the pilot signals of the relay station RS1 and the relay station RS2, when performing channel estimation, an incorrect channel response “H1 + H2” is estimated. Similarly, when the mobile terminal MS1 performs data detection using an incorrect channel response output, the bit error rate performance of the mobile terminal becomes very poor.

  In order to solve the pilot collision problem, the following two solutions (for example, see Non-Patent Document 1) have been submitted.

  In the conventional method 1, as shown in FIG. 5, the base station MMR-BS and all the relay stations RS1, RS2, RS3, RS4 belonging to the base station MMR-BS transmit data at different times. At this time, since there are no two base stations, two relay stations, or one base station and one relay station transmitting signals at the same time, there is no pilot collision problem, and the mobile terminal has a relatively good bit. Error rate performance can be acquired. However, this method has the following obvious drawbacks. One is that there is no base station and relay station that can transmit simultaneously in all subcarriers, so that spatial reuse of resources (radio frequency) is not performed. Another disadvantage is that the data of one base station or relay station alone cannot occupy all subcarriers, and idle subcarriers are used by other base stations or relay stations. Because it is not possible, resources will not be fully utilized.

Conventional method 2, as shown in FIG. 6, the base station MMR-BS transmits data at t _1, all of the relay stations RS1, RS2 which the base station belongs, RS3, RS4 the data in all _{t 2} Send. At this time, since the base station and the relay station transmit data at different times, there is no pilot collision problem for mobile terminals belonging to the base station. However, this method has the following drawbacks. First, since a plurality of relay stations transmit data at the same time, if the distance between the two relay stations is relatively close, a pilot collision occurs and the performance of the mobile terminal is deteriorated. Another disadvantage is that simultaneous transmission is not possible between the base station and the relay station, so that the spatial reuse of resources between the two is insufficient. Furthermore, another drawback is that resources are not effectively utilized. For example, if the base station data cannot occupy all the subcarriers, idle subcarriers cannot be used by the relay station, so there is a waste of resources. Here, the number of base stations and relay stations that can transmit simultaneously is defined as a simultaneous transmission factor (STF) in the present invention. In method 1 STF is 1, the method 2 STF is 4 in 1, t ₂ at t _1.
Jaroslaw Sydir, Wendy C. Wong, Hyunjeong Lee, Kerstin Johnsson, IEEE C80216j-06_057, Proposal for requirement that RS transmit preamble, Jul. 2006.

  The present invention is a data transmission method submitted for the above-described problem in the prior art, and an object of the present invention is to provide a data transmission method capable of solving the pilot collision problem and improving the resource utilization rate.

  The present invention is realized by the following technical solution.

A data transmission method comprising:
When the base station acquires the signal-to-noise ratio or signal power from the mobile terminal to the base station or relay station and transmits from a different base station or relay station, the signal-to-noise ratio or signal power is Classifying mobile terminals based on (a),
The base station determines, based on the mobile terminal classification, an initial simultaneous transmission mobile terminal group corresponding to each STF and a mobile terminal belonging to each initial simultaneous transmission mobile terminal group;
The base station adjusting the mobile terminals of the initial simultaneous transmission mobile terminal group, multiplexing different mobile terminal groups and mapping to OFDM subcarrier symbols;
Step (d) in which the base station determines a weighting factor between pilot and data on the subcarrier of the mobile terminal in the precoding method to be employed based on the situation mapped to the OFDM symbol and the transmission situation of the base station or the relay station )When,
A step of transmitting data to the target mobile terminal by performing precoding and coordinated transmission in which the data and pilot are associated in the base station and the relay station based on the weighting factors of pilot and data in the determined precoding method ( e).

Further, in the step (a), the base station obtains a signal-to-noise ratio or signal power from the mobile terminal to the base station or the relay station,
In the relay station, monitor the ranging signal or pilot signal of the mobile terminal, report the signal-to-noise ratio or signal power from the mobile terminal to the relay station to the base station,
Also in the base station, it is realized by directly monitoring the ranging signal or pilot signal of the mobile terminal and acquiring the signal-to-noise ratio or signal power from the mobile terminal to the base station.

Further, in the step (a), the process of classifying the mobile terminal is as follows:
A mobile terminal that can receive one signal, or a mobile terminal that can receive multiple signals, but one of which has a signal-to-noise ratio or power that is much greater than the signal-to-noise ratio or power of another signal. Divided into one class
Mobile terminals capable of receiving a plurality of signals having a signal-to-noise ratio or a power close to being equal are classified into another class.

In addition, a mobile terminal that can receive one signal, or a mobile terminal that can receive multiple signals, but the signal-to-noise ratio or power of one signal is much larger than the signal-to-noise ratio or power of the other signal. Dividing terminals into a class further sets the signal-to-noise ratio or signal power threshold,
A mobile terminal having a signal-to-noise ratio or signal power from the mobile terminal to the base station or relay station that is larger than the set signal-to-noise ratio or signal power threshold is classified into one class. The mobile terminals whose signal-to-noise ratio or signal power is smaller than the set signal-to-noise ratio or signal power threshold are classified into another class.

Furthermore, the step (c)
The base station adjusting the data of mobile terminals belonging to different initial simultaneous transmission mobile terminal groups according to the amount of data of the mobile terminals and assigning OFDM subcarriers (c1);
When the OFDM subcarriers occupied by the adjusted simultaneous transmission mobile terminal group data do not occupy all the available OFDM subcarriers, the base station schedules transmission data of mobile terminals of other simultaneous transmission mobile terminal groups This is realized by the step (c2) that occupies all the idle OFDM subcarriers.

Further, in the step (d), the base station determines that the precoding method to be used is precoding used for multiplexing, and if the base station and the relay station do not know the channel response of the mobile terminal, the precoding is performed. The weighting factors for pilot and data on the subcarriers of the mobile terminal at

Of which

Is the pilot weighting factor of the nth subcarrier from the base station to the mobile terminal,

Indicates the data weighting factor of the nth subcarrier from the base station to the mobile terminal,

Indicates the pilot weighting factor of the nth subcarrier from the relay station i to the mobile terminal,

Indicates the data weighting coefficient of the nth subcarrier from the relay station i to the mobile terminal,
d and b _i are set based on the power of the system and the bit error rate.

Further, in the step (d), the base station determines the precoding method to be adopted as the precoding used for multiplexing, the base station and the relay station know the channel response of the mobile terminal, and the single mobile station If it is a terminal, the weighting factors of pilot and data on the subcarriers of the mobile terminal in the precoding are respectively

Of which

And

Indicates the channel response of the nth subcarrier from the base station to the mobile terminal,

Indicates the channel response of the nth subcarrier from the relay station to the mobile terminal,

Indicates the subcarrier number,

Indicates the value of the argument,

Is the pilot weighting factor of the nth subcarrier from the base station to the mobile terminal,

Indicates the data weighting factor of the nth subcarrier from the base station to the mobile terminal,

Is a pilot weighting factor of the nth subcarrier from the relay station to the mobile terminal,

Indicates the data weighting factor of the nth subcarrier from the relay station to the mobile terminal,
When the base station and the relay station know the channel response of the mobile terminal and are multi-mobile terminals, the weighting coefficients of pilot and data on the subcarriers of the mobile terminal in the precoding are respectively

Of which

And

From the base station to the mobile terminal

Shows the channel response of the nth subcarrier to

From the relay station to the mobile terminal

Shows the channel response of the nth subcarrier to

Indicates a subcarrier number and a mobile terminal number,

From the base station to the mobile terminal

Indicates the pilot weighting factor of the nth subcarrier to

From the base station to the mobile terminal

Indicates the data weighting factor of the nth subcarrier to

From the relay station to the mobile terminal

Indicates the pilot weighting factor of the nth subcarrier to

From the relay station to the mobile terminal

The data weighting coefficient of the n-th subcarrier is shown.

Further, in the step (d), the base station determines the precoding method to be adopted as precoding used for simultaneous transmission, and in the precoding used for simultaneous transmission, the pilot and data on the subcarriers of the mobile terminal Each of the weighting factors of

Of which

Indicates the channel response from the base station to the mobile terminal,

Is a relay station

Shows the channel response from to the mobile terminal,

Indicates the subcarrier number,

Indicates the value of the argument,
b and d _i are set based on the power of the system and the bit error rate, and i indicates the value of the relay station i.

  Compared with the prior art, the present invention can arbitrarily arrange the positions of the base station and the plurality of relay stations in the system without being limited by the distance, under the situation where the mobile terminal is not changed. Even in this case, the pilot collision problem does not occur, thereby improving the bit error rate performance of the mobile terminal. In addition, since the present invention employs a precoding scheme designed to perform pilot and data simultaneously and to combine the pilot and data of the base station and the relay station, multiplexing of resources and spatial reuse are performed. It can be done more effectively.

  According to the data transmission method of the present invention, the pilot collision problem can be solved and the resource utilization rate can be improved.

  Hereinafter, the present invention will be further described with reference to the drawings and specific examples, but the present invention is not limited thereto.

  FIG. 7 shows a flow of a kind of data transmission method. The method includes the following steps.

  In step 101, the base station classifies the mobile terminals according to the transmission status from the base station or relay station based on the signal-to-noise ratio or signal power from the mobile terminal to the base station or relay station. That is, a mobile terminal that is affected by a pilot collision is distinguished from a mobile terminal that is not affected by a pilot collision.

First, each mobile terminal is defined as follows.

Is a mobile terminal that can receive only one signal, or can receive multiple signals, but the signal-to-noise ratio or power of one signal is much larger than the signal-to-noise ratio or power of the other signal Indicates a mobile terminal. Depending on the magnitude of the signal to noise ratio,

The

When

And can be further subdivided. When subdividing, a specific signal-to-noise ratio threshold is set first, and when the signal-to-noise ratio of the mobile terminal is larger than the threshold, the mobile terminal is

And vice versa

It is defined as The specific signal-to-noise ratio threshold setting is related to the transmission method employed in the actual system, for example, the encoding method, the adjustment method, etc., and can be determined based on the transmission method employed in the actual system. it can. For example, in the case of a system that does not encode, a mobile terminal that supports a signal-to-noise ratio of 64QAM and 16QAM

Or a mobile terminal whose signal-to-noise ratio supports QPSK and BPSK.

It is good. The specific signal-to-noise ratio threshold setting is a technique known to those skilled in the art, and will not be described in detail here.

Is

Because it can resist stronger interference, in the multiplexing of resources and the simultaneous transmission described later,

Is preferentially scheduled.

  Indicates a mobile terminal capable of receiving a plurality of signals having substantially the same signal-to-noise ratio or signal power.

In particular,

When

  It is necessary to explain which base station or relay station the mobile terminal is located between and which base station or relay station.

In the following, the following definitions were made.

Is

Belonging to

When

Between

Indicates.

Is

Belonging to

When

Between

  Indicates.

  In the simplified network model shown in FIG. 8, there are seven different cases in which data is transmitted from a base station or a relay station. Details are as follows.

  (A) The base station BS, the relay station RS1, and the relay station RS2 transmit data together.

  (B) The base station BS and the relay station RS1 transmit data together.

  (C) The base station BS and the relay station RS2 transmit data together.

  (D) The relay station RS1 and the relay station RS2 transmit data together.

  (E) The base station BS transmits data.

  (F) The relay station RS1 transmits data.

  (G) The relay station RS2 transmits data.

  Based on the above seven cases, mobile terminals are classified, and mobile terminals of the same type are divided into one group. Among them, the mobile terminal classification when the base station BS and the two relay stations RS1 and RS2 all transmit data is illustrated in FIG.

FIG. 9 shows another simplified network model. Among them, when the base station BS and the two relay stations RS1 and RS2 all transmit data,

Is

At the same time

And

Is

At the same time

  It is.

The following will be supplemented and described. In general, in the case of an arbitrarily arranged network, if the sum of the base station and the number of all relay stations is K, the different transmission statuses of the base station or the relay station can be calculated.

There are types. Specifically, the situation in which all base stations or relay stations all transmit is counted.

Kind,

The situation where all base stations or relay stations transmit

Kind,

The situation where all base stations or relay stations transmit

The situation where a single base station or relay station transmits is

It is a kind.

  Is a symbol of the number of combinations.

  In step 101, the base station obtains a signal-to-noise ratio or signal power from the mobile terminal to the base station or relay station by the following method.

  (I) The base station acquires the signal-to-noise ratio or signal power of the mobile terminal by a certain method in order to perform operations such as automatic power control, adaptive modulation / coding, and overhand, and the acquired signal-to-noise Use ratio or signal power directly.

  (Ii) The relay station monitors the ranging signal or pilot signal of the mobile terminal, reports the signal-to-noise ratio or signal power from the mobile terminal to the relay station to the base station, and the base station also reports the ranging signal of the mobile terminal. Alternatively, the pilot signal is directly monitored, the signal-to-noise ratio or signal power from the mobile terminal to the base station is obtained, and the difference value between the two signal-to-noise ratios or signal powers is used as the basis of the mobile terminal classification. .

  In step 102, based on the mobile terminal classification in step 101, the base station sequentially determines the initial simultaneous transmission mobile terminal group and the mobile terminals belonging to each initial simultaneous transmission mobile terminal group according to the size of the simultaneous transmission factor. . Here, the simultaneous transmission mobile terminal group is a group of mobile terminals belonging to different base stations or relay stations that can simultaneously transmit using the same resource.

  Taking the network model shown in FIG. 8 as an example, the initial simultaneous transmission mobile terminal group and each initial simultaneous transmission mobile terminal group based on the mobile terminal classification according to the seven different transmission situations of the base station or relay station obtained in step 101 How to determine the mobile terminal to which it belongs is explained. Details are as follows.

  (A) The base station BS, the relay station RS1, and the relay station RS2 transmit data together.

At this time, the base station BS, the relay station RS1, and the relay station RS2

Can configure a mobile terminal group for simultaneous transmission of STF = 3. That is,

  (B) The base station BS and the relay station RS1 transmit data together.

At this time, the base station BS and the relay station RS1

Can configure a mobile terminal group for simultaneous transmission of STF = 2. However, some mobile terminals have already

When

From the simultaneous transmission mobile terminal group,

When

It is necessary to exclude the mobile terminals belonging to, that is, the obtained simultaneous transmission mobile terminal group is as follows.

  (C) The base station BS and the relay station RS2 transmit data together.

At this time, similar to (b) above, a simultaneous transmission mobile terminal group with STF = 2 is obtained.

  (D) The relay station RS1 and the relay station RS2 transmit data together.

At this time, similar to (b) above, a simultaneous transmission mobile terminal group with STF = 2 is obtained.

  (E) The base station BS transmits data.

At this time, all mobile terminals belonging to the base station BS can form a STF = 1 simultaneous transmission mobile terminal group, but some mobile terminals have already

Therefore, it is necessary to remove all these mobile terminals from the simultaneous transmission mobile terminal group. That is,

  (F) The relay station RS1 transmits data.

At this time, a simultaneous transmission mobile terminal group of STF = 1 is obtained similar to (e).

  (G) The relay station RS1 transmits data.

At this time, a simultaneous transmission mobile terminal group of STF = 1 is obtained similar to (e).

  In summary, all the initial simultaneous transmission mobile terminal groups of the network shown in FIG. 8 can be obtained. One set of simultaneous transmission mobile terminal groups with STF = 3, three sets of simultaneous transmission mobile terminal groups with STF = 2, and STF = 3 simultaneous transmission mobile terminal groups can be obtained.

Generally, in the case of an arbitrarily arranged network, if the sum of the number of base stations and all relay stations is K, the initial simultaneous transmission mobile terminal group

It becomes a piece. Specifically, STF = K simultaneous transmission mobile terminal group

Pieces, STF =

Simultaneous transmission mobile terminal group

Pieces, STF =

Simultaneous transmission mobile terminal group

, ..., STF = 1 simultaneous transmission mobile terminal group

  I have one. In particular, when determining mobile terminals belonging to a simultaneous transmission mobile terminal group having a low simultaneous transmission factor, it is necessary to exclude mobile terminals belonging to a simultaneous transmission mobile terminal group having a high simultaneous transmission factor.

  In step 103, the base station adjusts the mobile terminals of the initial simultaneous transmission mobile terminal group, multiplexes different mobile terminal groups, and maps them to OFDM subcarriers.

  In the initial simultaneous transmission mobile terminal group, it is necessary to continuously adjust the simultaneous transmission mobile terminal group according to the data length of the mobile terminal. The purpose of the adjustment is to finally determine the mobile terminals that make up the simultaneous transmission mobile terminal group, and the goal is to obtain as large a resource reuse rate and resource utilization rate as possible.

  This step is specifically realized by the following steps.

  In step 1031, the base station adjusts the mobile terminals belonging to different simultaneous transmission mobile terminal groups according to the data amount of the mobile terminal, thereby obtaining a resource reuse rate and a resource usage rate as large as possible.

Hereinafter, how to adjust the initial simultaneous transmission mobile terminal group will be described by taking as an example one cell of the Manhattan model including the base station BS and the four relay stations RS1, RS2, RS3, and RS4. Assume that after performing the processing of steps 101 and 102 for the mobile terminal of the cell, an initial simultaneous transmission mobile terminal group is obtained. Among them, the OFDM subcarriers occupied by the data of the mobile terminal groups with STF = 5, STF = 3, and STF = 1 are as shown in FIG. In order to improve the resource utilization rate, some mobile terminals of the relay station RS3 of STF = 5 group may be adjusted to STF = 4 group, and STF = 1 group may be merged into STF = 5 group. At this time, the mobile terminals in the STF = 1 group shown in FIG.

If so, the mobile terminal group of the part may be adjusted to RS2 and RS3 of STF = 5 group. In this way, not only can the resource utilization rate be greatly improved, but also the gain of the mobile terminal in that part can be improved, and the bit error rate of the mobile terminal in that part can be further reduced. The OFDM subcarriers occupied by the data of the mobile terminal group for simultaneous transmission of STF = 5, STF = 3 and STF = 1 adjusted by the above method are as shown in FIG.

  In step 1032, if the OFDM subcarriers occupied by the data of the simultaneous transmission mobile terminal group do not occupy all the OFDM subcarriers, the transmission data of appropriate mobile terminals of other groups are scheduled and allocated to the idle subcarriers. To improve resource utilization.

The above Manhattan model will be described as an example. Assume that the final STF = 5 simultaneous transmission mobile terminal group determined through steps 101, 102 and sub-step 1031 of step 103 is as shown in FIG. According to FIG. 12, the data transmitted from each relay station of STF = 5 group does not occupy all the OFDM subcarriers. Therefore, in order to improve the resource utilization as much as possible, it is necessary to multiplex with data of other simultaneous transmission mobile terminal groups and assign them to these idle OFDM subcarriers. An appropriate mobile terminal may be scheduled and allocated from the STF = 4 group shown in FIG. FIG. 13 is a diagram illustrating a process of multiplexing STF = 4 groups and STF = 5 groups. FIG. 14 is a diagram illustrating OFDM subcarriers occupied by the adjusted simultaneous transmission mobile terminal groups STF = 5 and STF = 1. Suitable from STF = 1 group

May be assigned to STF = 5 groups. FIG. 15 is a diagram illustrating a process of multiplexing STF = 5 groups and STF = 1 groups. FIG. 16 is a diagram showing OFDM subcarriers occupied by the adjusted simultaneous transmission mobile terminal groups STF = 5 and STF = 1. Furthermore, STF = 5 groups may be allocated using the third method. At this time, appropriate from STF = 1 group

And STF = 5 may be assigned. Where

  In order to allocate data to two relay stations, it is necessary to transmit data simultaneously from the two relay stations. FIG. 17 is a diagram illustrating OFDM subcarriers occupied by simultaneously transmitted mobile terminal groups STF = 5 and STF = 1 in the third method of multiplexing STF = 5 groups and STF = 1 groups.

  In general, in steps 1031 and 1032 described above, since it is necessary to perform processing based on the data of the mobile terminal, the specific implementation process each time is various. However, both are as high as possible by appropriately adjusting the terminals of the simultaneous transmission mobile terminal group according to the data amount of different simultaneous transmission mobile terminal groups and multiplexing a plurality of simultaneous transmission mobile terminal groups. It is to obtain resource reuse rate and resource utilization rate.

  The base station determines whether all OFDM subcarriers are occupied and which mobile terminal data is scheduled and allocated. In the IEEE 802.16-2004 and IEEE 802.16e standards, the number of usable data subcarriers is defined in each OFDM subcarrier. When the adjustment method and the coding method are determined, the number of data bits supported by these available subcarriers is also determined. When the number of data bits of the mobile terminals in the simultaneous transmission mobile terminal group is smaller than the number of data bits supported by the available subcarriers, it indicates that the OFDM subcarriers are not completely occupied, thereby improving the resource utilization rate. In addition, it is necessary for the base station to schedule and assign data of mobile terminals of other simultaneous transmission mobile terminal groups. Which mobile terminal data is scheduled and allocated is determined according to the data amount of the mobile terminal. The scheduled mobile terminal data should occupy all remaining OFDM subcarriers as much as possible. As shown in step 1032 above, a plurality of schemes may be used when allocating to obtain the highest possible resource utilization rate and the lowest possible bit error rate.

  In step 104, the base station determines a precoding scheme to be employed based on the situation mapped to the OFDM symbol and the transmission situation of the base station or the relay station, and weights of pilot and data in the selected precoding scheme. Optimize for

  According to step 103 above, there are a plurality of different multiplexing and simultaneous transmissions of simultaneous transmission mobile terminal groups. For example, in the case of the Manhattan model, STF = 5 group may be multiplexed with STF = 4 group, or may be multiplexed with STF = 1 group. Further, when multiplexing with STF = 1, there are three types of multiplexing as shown in FIG. 13, FIG. 15, and FIG. These different multiplexing and simultaneous transmission schemes all need to support a precoding scheme. That is, it is necessary to perform the multiplexing and simultaneous transmission using different precoding schemes so that pilot collision does not occur.

  Overall, the precoding scheme has two purposes. One purpose is to multiplex data of different simultaneous transmission mobile terminal groups, and another purpose is to simultaneously transmit data of different simultaneous transmission mobile terminal groups. The precoding scheme of the present invention is different from the conventional precoding scheme in that the pilot and data are simultaneously performed and the pilot and data of the base station and the relay station are associated.

The weighting coefficient matrix shown in Table 1 may be adopted for precoding for multiplexing. At this time, precoding can be performed without requiring a channel response of the mobile terminal. The precoding weight coefficient matrix shown in Table 1 can also be applied to the case of a plurality of base stations or relay stations. That is, in precoding, the weighting factors of pilot and data in the subcarriers of the mobile terminal are as follows.

Of which

Is the pilot weighting factor of the nth subcarrier from the base station to the mobile terminal,

Indicates the data weighting factor of the nth subcarrier from the base station to the mobile terminal,

Indicates the pilot weighting factor of the nth subcarrier from the relay station i to the mobile terminal,

Indicates the data weighting coefficient of the nth subcarrier from the relay station i to the mobile terminal,
d and b _i are set based on the power of the system and the bit error rate.

In the network shown in FIG. 3, the subcarrier multiplexing process realized by precoding used for multiplexing is as shown in FIG. Of which
BS-> MS2 indicates that data and pilot are transmitted from the base station BS to the mobile terminal MS2.

  RS-> MS1 indicates that data and pilot are transmitted from the relay station RS to the mobile terminal MS1.

BS-> MS1, MS2, and RS-> MS1 indicate that the base station BS and the relay station RS perform coordinated transmission. Base station BS is a subcarrier

, The weighted data is transmitted to the mobile terminal MS2, and the base station BS and the relay station RS

, The weighted data is transmitted simultaneously to the mobile terminal MS1, and the base station BS and the relay station RS simultaneously transmit the weighted pilot signal in the pilot subcarrier.

  A specific subcarrier multiplexing process in combination with the weighting coefficient matrix of Table 1 will be described as follows.

The base station BS signals the pilot subcarriers, subcarriers

Signal and subcarrier to be transmitted to mobile terminal MS2 in

For the data signal transmitted to the mobile terminal MS1

Perform weighting with. At the same time, the relay station RS transmits the signal in the pilot subcarrier and the subcarrier.

For the data signal transmitted to the mobile terminal MS1

Perform weighting with. The relay station RS is a subcarrier

No signal is sent at.

The precoding weight coefficient matrix shown in Table 1 is used when the channel response of the mobile terminal is not known. When the base station BS and the relay station RS know the channel responses of the mobile terminals MS1 and MS2, the following optimal precoding weight coefficients may be adopted. At this time, not only can the pilot collision problem be solved and the same OFDM subcarrier can be multiplexed in different transmissions, but the spatial diversity gain can be acquired to reduce the bit error rate of the mobile terminal.

Of which

And

Indicates the channel response of the nth subcarrier from the base station to the mobile terminal,

Indicates the channel response of the nth subcarrier from the relay station to the mobile terminal,

Indicates the subcarrier number,

Indicates the value of the argument,

Is the pilot weighting factor of the nth subcarrier from the base station to the mobile terminal,

Indicates the data weighting factor of the nth subcarrier from the base station to the mobile terminal,

Is a pilot weighting factor of the nth subcarrier from the relay station to the mobile terminal,

  Indicates the data weighting coefficient of the nth subcarrier from the relay station to the mobile terminal.

Specifically, the base station BS transmits a signal in a pilot subcarrier,

Is used to weight the subcarrier

For the data signal transmitted to the mobile terminal MS2 by

Is used to weight the subcarrier

For the data signal transmitted to the mobile terminal MS1 by

Is used for weighting. At the same time, the relay station RS receives the signal in the pilot subcarrier,

Is used to weight the subcarrier

For the data signal transmitted to the mobile terminal MS1 by

The relay station RS uses subcarriers for weighting.

  No signal is sent at.

  In conventional transmission that does not employ precoding, for example, transmission from BS to MS2 and transmission from RS to MS1 cannot multiplex the same OFDM symbol. This is because if the same OFDM symbol is multiplexed, pilot collision occurs in MS1. When the cooperative precoding shown in Table 1 or the optimum precoding shown in the above formula is adopted, that is, the base station BS and the relay station RS perform weights respectively specified for the data and pilot transmitted by the base station BS and the relay station RS. In this case, the pilot collision problem can be avoided, and the same OFDM symbol can be multiplexed in different transmissions, so that the resource utilization rate can be improved.

For precoding used for simultaneous transmission, the weighting coefficient matrix shown in Table 2 may be adopted. The precoding at this time requires the channel response of the mobile terminal.

Of which

In the above formula,

Indicates the channel response from the base station to the mobile terminal,

Is a relay station

Shows the channel response from to the mobile terminal,

Indicates the subcarrier number,

  Indicates the value of the argument. Using the above formula, precoding coefficients for simultaneous transmission shown in Table 2 can be calculated.

The simultaneous transmission precoding method is also applied to a plurality of terminals. In this case, the pilot and data weighting factors in the subcarriers of the mobile terminal are as follows.

Of which

Indicates the channel response from the base station to the mobile terminal,

Is a relay station

Shows the channel response from to the mobile terminal,

Indicates the subcarrier number,

Indicates the value of the argument,
b and d _i are set based on the power of the system and the bit error rate, and d _i indicates the value of the relay station i.

  In the network shown in FIG. 19, the subcarrier multiplexing process realized by precoding for simultaneous transmission is as shown in FIG.

  BS-> MS0 indicates that the base station BS transmits data and pilot to the mobile terminal MS0.

  RS1-> MS1 & MS3 indicates that the relay station RS1 transmits data and pilot to the mobile terminals MS1, MS3.

  RS2-> MS2 indicates that the relay station RS2 transmits data and pilot to the mobile terminal MS2.

  BS-> MS0, BS, RS1-> MS1, BS, RS2-> MS2 and RS1, RS2-> MS3 indicate four types of transmission / coordinated transmissions performed simultaneously. That is, the base station BS transmits data and pilot to the mobile terminal MS0, the base station BS and the relay station RS1 transmit data and pilot in cooperation to the mobile terminal MS1, and the base station BS and the relay station RS2 Data and pilot are transmitted cooperatively to mobile terminal MS2, and relay station RS1 and relay station RS2 transmit data and pilot cooperatively to mobile terminal MS3.

Specifically, the base station BS transmits signals on pilot subcarriers.

Weighting using subcarrier

The data signal to be transmitted to the mobile terminal MS0 in

Weighting using subcarrier

No signal is sent at. At the same time, the relay station RS1 transmits the signal on the pilot subcarrier.

Weighting using subcarrier

A data signal to be transmitted to the mobile terminal MS1 in

Weighting using subcarrier

The data signal transmitted by the mobile terminal MS3 in

Is used for weighting. At the same time, the relay station RS2 transmits the signal on the pilot subcarrier.

Weighting using subcarrier

A data signal to be transmitted to the mobile terminal MS2 in

Weighting using subcarrier

The data signal transmitted by the mobile terminal MS3 in

  Is used for weighting.

In the precoding coefficients shown in Table 1 and Table 2,

Is selected according to the specific situation of the mobile terminal in multiplexing and simultaneous transmission, and needs to be selected based on the signal-to-noise ratio of the mobile terminal. The rules to be selected are (1) satisfying the bit error rate requirement of the mobile terminal and (2) minimizing the increase in transmission power.

By selecting the value of, optimal performance and power compromise can be obtained.

Once the value of is determined, the multiplexing shown in Table 1 can be performed, or

  When the value is calculated, the simultaneous transmission shown in Table 2 can be executed.

  If the base station and the relay station weight pilots and data using the cooperative precoding shown in Tables 1 and 2 before transmission, the pilot collision problem in the mobile terminal can be avoided. Hereinafter, an example will be described.

In conventional point-to-point transmission, first, a mobile terminal that is a receiver needs to perform channel estimation based on a pilot. And the estimated channel response

To use the weight for data detection

Is calculated. And the mobile terminal

Estimate the data by detecting the received signal using

To get. last,

Estimated transmission data can be acquired by performing a hard decision on. The specific process is as follows.

In the network structure shown in FIG. 3, when cooperative precoding is not performed, channel estimation and data detection processes in the mobile terminal MS1 are as follows.

According to the above process, the mobile terminal MS1 can receive the pilot signal of the base station and the pilot signal of the relay station at the same time.

  You will get Thus, interference occurs during data detection, and the bit error rate of the estimated data is greatly increased, resulting in a pilot collision problem.

If the precoding shown in Table 1 is performed in the base station and the relay station, the pilot collision problem can be solved. For convenience of explanation,

The channel estimation and data detection process in the mobile terminal MS1 is as follows.

  According to the above process, there is no extra interference when performing data detection in the cooperative precoding transmission between the base station and the relay station, so that there is no pilot collision problem and normal data detection can be performed. .

  In step 105, based on the selected precoding coefficient, the base station and the relay station perform precoding and coordinated transmission in which data and pilot are associated, and transmit the data to the target mobile terminal.

  The data transmission method of the present invention can be applied to any other network arrangement to improve the resource utilization rate of the network.

  Hereinafter, the transmission method will be described with more specific application examples.

  In an IEEE 802.16j network, a relay station is used for two purposes. One is an increase in the cover area, and the other is an improvement in throughput. Each example will be described below with examples.

Application Example 1: Application to Relay Station for “Expansion of Cover Area” FIG. 21 shows a coverage hole network arrangement used by a relay station for the purpose of expansion of the cover area. Of which, within the coverage of relay stations, a large amount

A terminal exists. In the conventional pilot collision avoidance method, since the base station BS and the relay station RS transmit data at different times, these mobile terminals

  The OFDM subcarrier resource occupied by is not reused. When data is transmitted using the data transmission method according to the present invention, the resource usage rate in the coverage / hole network arrangement can be clearly improved. The specific process is as follows.

  (A) The mobile terminal is classified based on the signal-to-noise ratio or signal power of the mobile terminal, (i) the base station and the relay station transmit together, (ii) the base station transmits, (iii) There are three cases where the relay station transmits.

(B) Determine initial simultaneous transmission mobile terminal groups and obtain three initial simultaneous transmission mobile terminal groups. That is,
1 group of STF = 2 groups

2 groups of groups with STF = 1

(C) Map to an OFDM symbol. The situation after mapping is shown in FIG. First, simultaneous transmission is performed on the same subcarrier for data of all mobile terminals in the mobile terminal group of STF = 2. Then, OFDM symbols that are not occupied are allotted. here,

When

Allocate using this data. FIG. 23 shows a resource utilization situation when data transmission is performed by the conventional method 2. According to FIGS. 22 and 23, the method according to the present invention is far superior to the method of transmitting data by the conventional method 2, can effectively implement the spatial reuse of resources, and greatly increase the resource usage rate. Can be improved.

  (D) Determine the cooperative precoding scheme. Using precoding coefficients shown in Tables 1 and 2, appropriate coefficient values are selected based on specific channel responses.

  (E) Based on the selected precoding coefficient, the base station and the relay station perform precoding and coordinated transmission in which data and pilot are associated, and transmit the data to the target mobile terminal.

  Application Example 2: Application to a relay station for the purpose of “throughput improvement”, two relay stations, and a network having a relatively long distance between relay stations.

  FIG. 24 shows a relay station for the purpose of “throughput improvement”, two relay stations, and a network having a relatively long distance between the relay stations. When data transmission is performed using the data transmission method according to the present invention, the resource usage rate in the network arrangement can be improved.

  (O) Classify mobile terminals. There are three cases: a) base station, relay station 1 and relay station 2 transmit together, b) relay station 1 and relay station 2 transmit together, c) base station transmit. In each case, mobile terminals may be classified based on signal-to-noise ratio or signal power.

(P) The initial simultaneous transmission mobile terminal groups are determined, and a total of three initial simultaneous transmission mobile terminal groups are obtained. That is,
One group of STF = 3

1 group of STF = 2 groups

One group of STF = 1

  (Q) Map to an OFDM symbol. The situation after mapping is shown in FIG. FIG. 26 shows a subcarrier resource usage situation of a mobile terminal in the conventional pilot collision resolution method 2. According to FIGS. 25 and 26, the conventional pilot collision resolution method 2 has a good resource utilization rate in the network arrangement, but the method according to the present invention has a better performance. In the method according to the present invention, there is simultaneous transmission of STF = 3, but the conventional pilot collision resolution method 2 has only simultaneous transmission of STF = 2 at most. Therefore, the present invention is more excellent.

  (R) Determine the cooperative precoding scheme. Using precoding coefficients shown in Tables 1 and 2, appropriate coefficient values are selected based on specific channel responses.

  (S) Based on the selected precoding coefficient, the base station and the relay station perform precoding and coordinated transmission in which data and pilot are associated, and transmit the data to the target mobile terminal.

  Application Example 3: Application to a relay station for the purpose of “throughput improvement”, two relay stations, and a network in which the distance between the relay stations is relatively short.

  The network arrangement in this case is as shown in FIG. When data transmission is performed using the data transmission method according to the present invention, the resource usage rate in the network arrangement can be improved.

  (U) The mobile terminal is classified into five types of base stations or relay stations.

  1. The base station BS, the relay station RS1, and the relay station RS2 transmit together.

  2. Relay station RS1 and relay station RS2 transmit together.

  3. The base station BS transmits.

  4. The relay station RS1 transmits.

  5. Transmitted by relay station RS2.

  The mobile terminal classification in these five cases is performed.

(V) The initial simultaneous transmission mobile terminal groups are determined, and a total of five initial simultaneous transmission mobile terminal groups are obtained. That is,
1 group of STF = 3 groups

1 group of STF = 2 groups

3 groups of groups with STF = 1

  (W) Map to an OFDM symbol. FIG. 28 shows the subcarrier resource usage status of the mobile terminal after mapping. FIG. 29 shows a subcarrier resource usage situation of a mobile terminal in the conventional pilot collision resolution method 2. According to FIGS. 28 and 29, the conventional pilot collision resolution method 2 causes a pilot collision problem when simultaneous transmission is performed using the same resource in the network arrangement, so that the bit error rate performance of the mobile terminal is greatly reduced. Let On the other hand, since the scheme according to the present invention can solve the pilot collision problem by combining precoding, it is possible to obtain a bit error rate performance superior to the pilot collision resolution method 2.

  (X) Determine the cooperative precoding scheme. Using precoding coefficients shown in Tables 1 and 2, appropriate coefficient values are selected based on specific channel responses.

  (Y) Based on the selected precoding coefficient, the base station and the relay station perform precoding and coordinated transmission in which data and pilot are associated, and transmit the data to the target mobile terminal.

  In order to verify the effect of the method according to the invention, the bit error rate performance of the mobile terminal in data transmission according to the invention is simulated and compared with the prior art.

  The simulation settings are as follows.

  (1) The transmission method employs OFDMA, the subcarrier is 512, the cyclic prefix is 64 samples, the pilot is a cam pilot, and occupies a total of 64 subcarriers.

  (2) The modulation method is 16QAM.

  (3) The channel estimation algorithm employs LS (Least Square) and linear interpolation.

  (4) A 20-path multipath delay line model is adopted for the channel, and the channel response is unchanged in each OFDM symbol, but randomly changes in different OFDM symbols.

FIG. 30 shows a simulation diagram of the bit error rate performance of the mobile terminal during pilot collision and when there is no pilot collision. According to the figure, pilot collisions greatly reduce system performance. If there is a pilot collision problem and no processing is performed, the bit error rate performance of the mobile terminal is about

And cannot satisfy the requirements of the system. On the other hand, the performance when there is no pilot collision is much better than the performance when there is a pilot collision. Since the conventional pilot collision resolution method 2 does not solve the pilot collision problem during simultaneous transmission in the same resource, the performance of the mobile terminal is divided into performance without pilot collision and performance with pilot collision. All of the submitted algorithms

Has performance when there is no pilot collision.

FIG. 31 shows a simulation diagram of bit error rate performance of a mobile terminal when precoding and cooperative transmission schemes are adopted. According to the figure, when precoding and cooperative transmission schemes are adopted, the performance of the mobile terminal is similar to the performance when there is no pilot collision, and has a performance gain of about 3 db when there is a single user. All of the submitted algorithms

  Has a similar performance when there is no pilot collision.

  In addition, according to the above-described embodiment, the data transmission method according to the present invention can not only avoid pilot collision but also obtain a higher resource reuse rate and resource utilization rate than the conventional method.

FIG. 1 is a diagram illustrating subcarrier allocation between pilots and data subchannels of two mobile terminals in a communication system having two mobile terminals. FIG. 2 is a diagram illustrating data transmission in an IEEE 802.16-2004 or IEEE 802.16e network. FIG. 3 is a diagram illustrating data transmission of a system including one base station and one relay station in the IEEE 802.16j network. FIG. 4 is a diagram showing data transmission in a system composed of two relay stations in the IEEE 802.16j network. FIG. 5 is a diagram illustrating a method 1 for resolving pilot collision in the prior art. FIG. 6 is a diagram illustrating a method 2 for resolving pilot collision in the prior art. FIG. 7 is a flowchart of a data transmission method according to an embodiment of the present invention. FIG. 8 is a diagram illustrating a simplified network model in the embodiment according to the present invention. FIG. 9 is a diagram illustrating another simplified network model in the embodiment according to the present invention. FIG. 10 is a diagram illustrating OFDM subcarriers occupied by data of three groups (STF = 5, STF = 3 and STF = 1) after initializing a simultaneous transmission mobile terminal group in an embodiment according to the present invention. It is. FIG. 11 is a diagram illustrating OFDM subcarriers occupied by data of three groups (STF = 5, STF = 3 and STF = 1) after adjusting the simultaneous transmission mobile terminal groups in the embodiment according to the present invention. is there. FIG. 12 is a diagram illustrating OFDM subcarrier allocation after adjusting the simultaneous transmission mobile terminal groups when multiplexing STF = 4 groups and STF = 5 groups. FIG. 13 is a diagram illustrating OFDM subcarrier allocation after multiplexing simultaneous transmission mobile terminal groups when multiplexing STF = 4 groups and STF = 5 groups. FIG. 14 is a diagram illustrating OFDM subcarrier allocation after adjusting the simultaneous transmission mobile terminal groups when the STF = 5 group and the STF = 1 group are multiplexed in the first case. FIG. 15 is a diagram showing OFDM subcarrier allocation after multiplexing simultaneously transmitting mobile terminal groups when STF = 5 groups and STF = 1 groups are multiplexed in the first case. FIG. 16 is a diagram illustrating OFDM subcarrier allocation after adjusting the simultaneous transmission mobile terminal group when the STF = 5 group and the STF = 1 group are multiplexed in the second case. FIG. 17 is a diagram showing OFDM subcarrier allocation after multiplexing simultaneously transmitting mobile terminal groups when STF = 5 groups and STF = 1 groups are multiplexed in the second case. FIG. 18 is a diagram showing a subcarrier multiplexing process realized by precoding used for multiplexing in the network shown in FIG. FIG. 19 shows another type of data transmission network. FIG. 20 is a diagram showing a subcarrier multiplexing process realized by precoding used for multiplexing in the network shown in FIG. FIG. 21 is a diagram showing a network in application example 1 of the present invention. FIG. 22 is a diagram illustrating a subcarrier resource usage status of a mobile terminal after mapping when the method of the present invention is employed in Application Example 1 of the present invention. FIG. 23 is a diagram illustrating a subcarrier resource usage state of a mobile terminal after mapping when the method of the present invention is employed in Application Example 1 of the present invention. FIG. 24 is a diagram showing a network in application example 2 of the present invention. FIG. 25 is a diagram illustrating a subcarrier resource usage state of a mobile terminal after mapping when the method of the present invention is employed in Application Example 2 of the present invention. FIG. 26 is a diagram illustrating a subcarrier resource usage situation of a mobile terminal when adopting the conventional method 2 for resolving pilot collision in Application Example 2 of the present invention. FIG. 27 is a diagram showing a network in an application example 3 of the present invention. FIG. 28 is a diagram illustrating a subcarrier resource usage state of a mobile terminal after mapping when the method of the present invention is employed in Application Example 3 of the present invention. FIG. 29 is a diagram illustrating a usage state of subcarrier resources of a mobile terminal when adopting the conventional method 2 for resolving pilot collision in Application Example 3 of the present invention. FIG. 30 is a diagram illustrating the bit error rate performance of the mobile terminal when the pilot collision occurs and when there is no pilot collision in the simulation example of the present invention. FIG. 31 is a diagram illustrating the bit error rate performance of a mobile terminal when the precoding and the cooperative transmission scheme are employed in the simulation example of the present invention.

Explanation of symbols

MS ... mobile terminal, BS ... base station, RS ... relay station

Claims (8)

When the base station acquires the signal-to-noise ratio or signal power from the mobile terminal to the base station or relay station and transmits from a different base station or relay station, the signal-to-noise ratio or signal power is Classifying mobile terminals based on (a),
A base station determines, based on the mobile terminal classification, an initial simultaneous transmission mobile terminal group corresponding to each simultaneous transmission factor and a mobile terminal belonging to each initial simultaneous transmission mobile terminal group;
The base station adjusting the mobile terminals of the initial simultaneous transmission mobile terminal group, multiplexing different mobile terminal groups and mapping to OFDM subcarrier symbols;
A step in which the base station determines a weighting factor between pilots and data on subcarriers of each mobile terminal in a precoding method to be adopted based on the situation mapped to the OFDM symbol and the transmission situation of the base station or relay station ( d) and
A step of transmitting data to a target mobile terminal by performing precoding and coordinated transmission in which data and pilot are associated in a base station and a relay station based on a weighting factor between pilot and data in the determined precoding method ( a data transmission method comprising: e). In the step (a), the base station obtains a signal-to-noise ratio or signal power from the mobile terminal to the base station or the relay station,
In the relay station, the ranging signal or pilot signal from the mobile terminal is monitored, the signal-to-noise ratio or signal power from the mobile terminal to the relay station is reported to the base station, and the ranging signal from the mobile terminal or The method according to claim 1, characterized in that it is realized by directly monitoring the pilot signal and obtaining the signal to noise ratio or signal power from the mobile terminal to the base station. In the step (a), the classification for the mobile terminal is:
A mobile terminal that can receive one signal, or a mobile terminal that can receive multiple signals, but the power of one of the signals is much higher than the power of the other signals,
The method according to claim 1, characterized in that the mobile terminals that can receive a plurality of signals of nearly equal power are divided into another class. To classify a mobile terminal that can receive one signal, or a mobile terminal that can receive multiple signals, but whose power of one signal is much higher than the power of the other signal, is further improved by signal-to-noise. Set the ratio or signal power threshold,
The mobile terminals whose signal-to-noise ratio or signal power from the mobile terminal to the base station or relay station is larger than the set signal-to-noise ratio or signal power threshold are classified into one class. 4. The method according to claim 3, wherein the mobile terminals whose signal-to-noise ratio or signal power is less than the set signal-to-noise ratio or signal power threshold are classified into another class. The step (c) further includes a step (c1) in which the base station allocates OFDM subcarriers by adjusting data of mobile terminals belonging to different initial simultaneous transmission mobile terminal groups according to the amount of data of the mobile terminals.
When the OFDM subcarriers occupied by the data of the adjusted simultaneous transmission mobile terminal group do not occupy all the available OFDM subcarriers, the base station schedules the transmission data of the mobile terminals of other simultaneous transmission mobile terminal groups And (c2) occupying all of the idle OFDM subcarriers. In the step (d), the base station determines the precoding method to be employed as precoding to be used for multiplexing, and when the base station and the relay station do not know the channel response of the mobile terminal, The weighting factors for pilot and data on subcarriers of
Of which
Is the pilot weighting factor of the nth subcarrier from the base station to the mobile terminal,
Indicates the data weighting factor of the nth subcarrier from the base station to the mobile terminal,
Indicates the pilot weighting factor of the nth subcarrier from the relay station i to the mobile terminal,
Indicates the data weighting coefficient of the nth subcarrier from the relay station i to the mobile terminal,
The method of claim 1, wherein d and b _i are set based on system power and bit error rate. In the step (d), the base station determines the precoding method to be employed as precoding used for multiplexing, and the base station and the relay station know the channel response of the mobile terminal and are a single mobile terminal. The pilot and data weighting factors on the sub-carriers of the mobile terminal in the precoding, respectively,
Of which
And
Indicates the channel response of the nth subcarrier from the base station to the mobile terminal,
Indicates the channel response of the nth subcarrier from the relay station to the mobile terminal,
Indicates the subcarrier number,
Indicates the value of the argument,
Is the pilot weighting factor of the nth subcarrier from the base station to the mobile terminal,
Indicates the data weighting factor of the nth subcarrier from the base station to the mobile terminal,
Is a pilot weighting factor of the nth subcarrier from the relay station to the mobile terminal,
Indicates the data weighting factor of the nth subcarrier from the relay station to the mobile terminal,
When the base station and the relay station know the channel response of the mobile terminal and are multi-mobile terminals, the weighting coefficients of pilot and data on the subcarriers of the mobile terminal in the precoding are respectively
Of which
And
From the base station to the mobile terminal
Shows the channel response of the nth subcarrier to
From the relay station to the mobile terminal
Shows the channel response of the nth subcarrier to
Indicates a subcarrier number and a mobile terminal number,
From the base station to the mobile terminal
Indicates the pilot weighting factor of the nth subcarrier to
From the base station to the mobile terminal
Indicates the data weighting factor of the nth subcarrier to
From the relay station to the mobile terminal
Indicates the pilot weighting factor of the nth subcarrier to
From the relay station to the mobile terminal
The method according to claim 1, characterized in that the data weighting factor of the nth subcarrier to the is indicated. In the step (d), the base station determines the precoding method to be used as precoding to be used for simultaneous transmission, and in the precoding to be used for simultaneous transmission, a weighting factor between pilot and data on a subcarrier of a mobile terminal Respectively
Of which
Indicates the channel response from the base station to the mobile terminal,
Is a relay station
Shows the channel response from to the mobile terminal,
Indicates the subcarrier number,
Indicates the value of the argument,
8. The method according to claim 7, wherein b and d _i are set based on system power and bit error rate, and i indicates a value of relay station i.