KR101753399B1 - Apparatus and method for diversity in coordinated multi-point transmission of multi-beam satellite communication - Google Patents

Abstract

The present invention relates to a cooperative transmit diversity transmission method by a satellite apparatus in a multi-beam satellite communication system, comprising: determining a different one or more cyclic delay offsets; generating one or more beams delayed with the determined different cyclic delay offsets, To the user terminal.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a cooperative transmission diversity transmitting apparatus and method in a multi-beam satellite communication system,

The present invention relates to a satellite communication system, and more particularly, to a multi-beam based satellite communication system and method.

Most satellite communications systems currently in operation and under development provide multi-beam based services to increase the total system capacity and increase the Effective Isotropically Radiated Power (EIRP) in the satellite. In general, a multi-carrier based multi-beam satellite communication system including an Orthogonal Frequency Division Multiplexing (OFDM) or an Orthogonal Frequency Division Multiple Access (OFDMA) do. In providing such a multi-beam based service, a frequency reuse index greater than 1 is considered in order to avoid interference between adjacent beams, and a frequency reuse factor of 3 to 7 is usually considered.

On the other hand, due to an increase in requirements for providing high-quality multimedia services, satellite communication systems must also provide broadband services. However, the bandwidth currently allocated for satellite communication services is very limited. For example, in the satellite IMT-2000 band allocated by the ITU-R, the uplink 1980-2010 MHz band and the downlink 2170-2200 MHz band of 30 MHz are allocated. Therefore, in order to provide a broadband service, a wireless interface having a bandwidth of at least 10 MHz is considered, and it can be seen that the allocated frequency is very limited in implementing the frequency reuse index of 3 or 7 that has been considered so far.

That is, the frequency reuse 7 can not be implemented, and in the case of the frequency reuse factor 3, all the frequencies are allocated to one operator. Therefore, it is necessary to implement a satellite communication system having a frequency reuse index of 1 in order to provide a broadband service.

Meanwhile, in the CDMA-based satellite communication system, different spreading codes are used for a plurality of beams to reduce interference between adjacent beams. As a result, implementing the frequency reuse factor of 1 also produces the same effect. However, TDMA, FDMA, and OFDMA-based satellite communication systems, which are currently considered as IMT-Advanced wireless access technologies, are not easy to implement.

To achieve this, an OFDMA-based satellite communication system and its communication method have been proposed in order to satisfy frequency reuse factor 1 through partial frequency reuse. In the proposed method, the user equipment (UE) located at the beam center and the UE located at the beam boundary are separated from each other by a time interval for allocating resources. That is, all the subcarriers of the considered band may be used for the time interval for the UE located at the center of the beam. On the other hand, in a time interval for a UE located at a beam boundary, only a part of a plurality of subcarrier groups is used in consideration of interference between adjacent beams. This method can reduce the interference between the UEs in the beam boundary area while satisfying the frequency reuse factor 1. [

However, in this method, the UE located at the beam boundary receives the signal at a lower power than the UE located at the beam center. In addition, since the UE located at the beam boundary can not receive through all the sub-carriers and receives only a part of the sub-carriers, the maximum frequency efficiency is inferior to that of the UE located at the center of the beam.

Therefore, there is a need for a method that can improve the frequency efficiency of a UE located at a beam boundary and minimize the interference between adjacent beams in a satellite communication system using a frequency reuse ratio of 1, thereby resolving the digital divide between the beam center and the beam boundary. For this purpose, an interference mitigation technique has been proposed in an OFDMA based multi-beam satellite communication system, but this method can also increase the SNR of the signals of the UEs in the beam boundary region, but the diversity gain can not be obtained.

The present invention provides a cooperative transmit diversity apparatus and method in a multi-beam satellite communication system that can minimize interference at beam boundaries.

The present invention provides a cooperative transmit diversity apparatus and method in a multi-beam satellite communication system capable of enhancing frequency utilization efficiency in a user terminal located at a beam boundary.

The present invention relates to a cooperative transmit diversity apparatus and method in a multi-beam satellite communication system that enables diversity gain through cooperative transmission at beam boundaries.

The present invention relates to a satellite apparatus for performing communication with one or more user terminals in a multi-beam satellite communication system, the apparatus comprising: a transmitter for generating signals for one user terminal by a plurality of beams delayed by different circular offsets, And a cyclic delay offset determiner for determining a cyclic delay offset to be applied to each of the plurality of beams and outputting the cyclic delay offset to the transmitter.

The present invention relates to a cooperative transmit diversity transmission method by a satellite apparatus in a multi-beam satellite communication system, comprising: determining a different one or more cyclic delay offsets; generating one or more beams delayed with the determined different cyclic delay offsets, To the user terminal.

The present invention has the advantage that the capacity of the beam boundary region can be increased in order to eliminate the digital divide between the beam center and the boundary without reducing the capacity of the center of the beam.

1 is a diagram for explaining a communication method in a general multi-beam satellite communication system.
2 is a diagram for explaining a cooperative transmission method in a multi-beam satellite communication system.
3 is a diagram for explaining a method for managing frequency and resources for a user in a beam boundary region in a multi-beam satellite communication system.
4 is a schematic block diagram of a multi-beam satellite communication system according to a preferred embodiment of the present invention.
5 is a diagram illustrating a configuration of a transmitter for applying a cyclic delay offset in the time domain according to a preferred embodiment of the present invention.
FIG. 6 illustrates a structure of a transmitter for applying a cyclic delay offset in the frequency domain according to a preferred embodiment of the present invention.
7 is a diagram showing another embodiment of the structure of a transmitter of a satellite apparatus according to a preferred embodiment of the present invention.
FIG. 8 is a flowchart for explaining a multi-cooperation diversity transmission method in a satellite apparatus according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

The present invention applies a different cyclic delay offset value between signals transmitted to a user equipment (UE) located at the boundary of beams co-transmitted through multiple beams in an OFDM or OFDMA based multi-beam satellite system, And an apparatus and method for obtaining the same.

The present invention is advantageous in that a UE located at a beam boundary can gain a diversity gain and maximize a system capacity while maintaining commonality with a conventional OFDM-based terrestrial air interface. The present invention is applicable to a multi-carrier-based multi-beam satellite communication system including OFDM or OFDMA. It is also applicable to satellite communication systems in low frequency bands such as L and S bands or high frequency bands such as Ka and Ku bands. It is also applicable in mobile or fixed, broadcast satellite communication systems.

1 is a diagram for explaining a communication method in a general multi-beam satellite communication system.

Referring to FIG. 1, all UEs communicate through a target spot beam emitted from a satellite device 100. In case of UE1, since there is no interference from the adjacent beam, resource use of the target spot beam is easy. However, since UE2 is located at the boundary between Beam 1 and Beam 3, a frequency and resource plan considering interference between Beam 1 and Beam 3 is required. When the satellite device 100 uses the frequency reuse factor of 1, the beam 1 and the beam 3 serve through the same resource. Therefore, UE 2 will experience performance degradation due to severe interference from beam 3.

In case of UE3, since the strength of the signal received from beam 2 and beam 3 is similar to the strength of the signal received from beam 1, the problem due to interference is further increased. As a method for overcoming this, there is a method in which the satellite apparatus 100 partially uses resources in the beam boundary region. This reduces interference by not using the same resources between adjacent beams. However, such a scheme has a disadvantage in that the amount of resources that can be used in the beam boundary region is reduced.

A cooperative transmission method is proposed to overcome this disadvantage. The cooperative transmission method is a method for improving the communication service performance to the UE by forming a cooperative relationship with each other, rather than competing with each other, in order to provide communication service in the beam boundary region.

2 is a diagram for explaining a cooperative transmission method in a multi-beam satellite communication system.

Referring to FIG. 2, the satellite apparatus 100 can transmit a signal to the UE 1 located at the center of the beam through all the sub-carriers available in the transmission interval for the terminal located at the center of the beam. At this time, since the satellite apparatus 100 can interfere with the UE located at the center of the beam, it does not transmit signals to UE 2 and UE 3 which are not located at the center of the beam. Instead, the satellite device 100 transmits signals to the UE 2 and the UE 3 during the transmission interval for the UE located at the beam boundary.

In the method shown in FIG. 1, since the adjacent beams use different resources, the UEs located at the beam boundary receive communication service from one of the adjacent beams. However, in the cooperative transmission method shown in FIG. 2, a UE located at a beam boundary is provided with communication services through all adjacent beams. For example, the satellite device 100 simultaneously transmits signals through the same resource to the UE 2 via beam 1 and beam 3. Thus, unlike the method shown in FIG. 1, the signal from beam 3 no longer interferes, but rather strengthens the signal of UE2. Therefore, the reception performance at the UE 2 can be improved. In addition, the satellite apparatus 100 can improve the reception performance of the UE 3 by transmitting the same signal to the UE 3 through the same resources simultaneously via the beam 1, the beam 2 and the beam 3.

Also, in the method shown in FIG. 1, the UE located at the beam boundary has a lower EIRP than the UE located at the center of the beam, and interference is present from the adjacent beam, so reception performance is greatly reduced. In addition, the maximum frequency efficiency is degraded because the UE located at the beam boundary can receive signals only through some of the subcarriers. On the other hand, in the case of the cooperative transmission method shown in FIG. 2, even if the UE is located in a beam boundary region, it receives its signal from multiple beams. Therefore, the signal-to-noise ratio can be increased in the UE in the beam boundary region, and interference can be avoided because the adjacent beam also transmits its own signal. In addition, if the number of UEs in the beam boundary region is small, the maximum frequency efficiency can be increased since the number of sub-carriers allocable to the UE increases.

However, even in the case of such a cooperative transmission method, the number of UEs capable of supporting communication can be reduced because the neighboring beams are cooperated with each other and communication is performed with one UE. For example, if beam 3 is not used for communication services with UE2, it may be used for communication with other UEs in the border area of beam 3.

However, this disadvantage can be overcome by managing the resource and frequency between multiple beams, and by increasing the capacity of the beam boundary region.

3 is a diagram for explaining a method for managing frequency and resources for a user in a beam boundary region in a multi-beam satellite communication system.

Referring to FIG. 3, seven beams are formed, and the beam can be divided into a beam center SCall and a beam boundary SC. The beam boundary SC further includes areas SC1 ', SC2', SC3 ', SC4', and SC5 'in which the two beams overlap each other and the three beams overlap each other (SC1, SC2, SC3, SC4, , SC6 ').

The satellite device verifies where the UE is located in the region delineated as shown in FIG. That is, it is checked whether the position of the UE is the beam center or the beam boundary. The satellite device separates the UE located at the beam center and the UE located at the beam center, respectively. And, the satellite device provides the service to the UE located at the center of the beam using all the subcarriers during the UE transmission period located at the center of the beam. This transmission interval is a period in which the service is provided with a frequency reuse ratio of 1.

The satellite device then services the UE located at the beam boundary during the transmission interval for the UE located at the beam boundary. For this purpose, the UE located at the beam boundary must monitor the number of beams capable of cooperative multi-point transmission at its own location and report the monitoring result to the satellite device. The satellite apparatus separates UEs capable of cooperative multipoint transmission using UEs capable of cooperative multipoint transmission using two neighboring beams and three adjacent beams using monitoring results transmitted from UEs located at a beam boundary. The satellite apparatus verifies the traffic information requested by the UEs capable of cooperative multi-point transmission using two adjacent beams. That is, the satellite apparatus calculates the total demand traffic amount of the UEs requesting the cooperative multi-point transmission using the beam 1 and the beam 2, and uses the beam 1 and the beam 3, the beam 4, the beam 5, the beam 6 and the beam 7 To calculate the aggregate demand traffic amounts of the UEs requesting cooperative multipoint transmission. The satellite device appropriately allocates the size of each subcarrier group for the UEs located at the boundary of satellite beam 1 according to the amount of traffic required between the calculated cooperating beams. For example, when the amount of traffic when the cooperative multipoint transmission is performed using the beam 1 and the beam 2 is very large, the satellite device allocates the largest number of subcarriers for the SC1. When a resource is allocated to a subcarrier group in this manner, the satellite apparatus can allocate a maximum number of subcarriers to the subcarrier group when traffic is not requested from other beams. Therefore, not only the maximum frequency efficiency of the UE located at the beam boundary is improved but also the resources can be flexibly allocated according to the traffic requirements of the UEs located at the beam boundary.

The satellite apparatus transmits the same signal to the UEs located at the boundaries of the beams using the same subcarriers in the adjacent beams that perform cooperative multipoint transmission on the subcarrier groups appropriately allocated according to the traffic requirements. The transmission of the signal takes place during the transmission interval for cooperative multipoint transmission using two beams during the transmission interval for the beam boundary area. This method can increase the signal-to-noise ratio of the UEs located at the beam boundary, and the neighboring beam also transmits its own signal, so interference can be greatly reduced.

Finally, the satellite device confirms the traffic information requested by the UEs capable of cooperative multi-point transmission using three adjacent beams. For example, referring to FIG. 3, a satellite apparatus calculates the total amount of demand traffic of UEs requesting cooperative multi-point transmission using Beam 1, Beam 2 and Beam 3, Lt; RTI ID = 0.0 > UEs < / RTI > requesting point transmission. The satellite device appropriately allocates the size of each subcarrier group for the UEs located at the boundary of the beam 1 according to the amount of traffic required between the calculated cooperating beams. For example, when the amount of traffic is large when cooperative multi-point transmission is performed using Beam 1, Beam 2, and Beam 3, the subcarriers for SC2 'are allocated the most. When a resource is allocated to a subcarrier group in this manner, subcarriers can be allocated to the subcarrier group at a maximum when traffic is not requested from other beams. Therefore, not only the maximum frequency efficiency of the UE located at the beam boundary is improved, but also the resources can be flexibly allocated according to the traffic requirements of the UEs located at the beam boundary.

The satellite apparatus transmits the same signal to the UEs located at the boundaries of the beams using the same subcarriers in the adjacent beams in the cooperative multi-point transmission with the subcarrier groups appropriately allocated according to the traffic requirements. The transmission of the signal takes place in the transmission interval for cooperative multi-point transmission using three beams during the transmission interval for the beam boundary zone. In this way, not only the signal-to-noise ratio of the UEs located at the beam boundary is improved, but also the signals of the UEs located at the beam boundary are transmitted even in the adjacent beam.

The cooperative transmission method as described above can increase the reception SNR while reducing the interference generated at the UEs located at the beam boundary. Therefore, there is an advantage that the total system capacity is increased. However, in this cooperative transmission method, diversity gain can not be obtained between UE signals transmitted through a plurality of beams.

Accordingly, the present invention proposes an apparatus and method for applying a cyclic delay offset delay to a satellite transmitter to obtain a diversity gain between UE signals transmitted through a plurality of beams while having all the advantages of the cooperative transmission method described above . Through the embodiments of the present invention, compatibility with the existing satellite communication system can be maintained and diversity gain can be obtained without changing the structure and control signal of the UE

4 is a schematic block diagram of a multi-beam satellite communication system according to a preferred embodiment of the present invention.

Referring to FIG. 4, the satellite device 410 may transmit information to a user equipment (UE) 420 through a forward link channel. In addition, the satellite device 410 may receive information from the user terminal 420 over the reverse link channel.

According to an embodiment of the present invention, the satellite apparatus 410 includes a cooperative transmission control unit 411, a cyclic delay offset determination unit 412, and a transmission unit 413 in detail.

The transmitter 413 can transmit a signal based on the OFDMA-based air interface scheme. Also, a circular offset delay operation is performed according to a preferred embodiment of the present invention. Depending on whether the cyclic offset delay is performed in the frequency domain or the time domain, the transmitter 413 can implement two embodiments. Herein, since the UE located at the beam boundary can receive its own signal from two or three beams, in the embodiment of the present invention, a cyclic delay offset is applied to cooperative transmission from two or three beams Will be described. However, this is an embodiment of the present invention, but the present invention is not limited thereto. That is, the present invention can be applied to cooperative transmission from three or more beams.

5 is a diagram illustrating a configuration of a transmitter for applying a cyclic delay offset in the time domain according to a preferred embodiment of the present invention.

Referring to FIG. 5, the transmitter 413 has a structure for generating a plurality of beams for one user terminal and simultaneously transmitting the signals for a plurality of antenna groups. However, since the communication through the LOS (Line of Sight) is mostly performed between the multi-beam signals for the beam-edge user terminals cooperatively transmitted through the plurality of beams, the channel characteristics between each beam and the beam- flat) characteristics. Therefore, the frequency diversity gain obtainable in the OFDMA-based terrestrial system can not be obtained because the received signal from the multiple beams does not have frequency selective characteristics. Thus, according to a preferred embodiment of the present invention, the transmitter 413 applies a different cyclic delay offset to each of the multiple beam signals to generate frequency selective fading between the beam signals.

인 순환 지연 오프셋이 적용되고, 빔 2를 생성하는 순환 오프셋 지연기(532)들에는

인 순환 지연 오프셋이 적용되고, 빔 3를 생성하는 순환 오프셋 지연기(533)에는

인 순환 지연 오프셋이 적용된다. Referring to FIG. 5, inverse fast Fourier transforms (IFFT) 511, 512 and 513 perform IFFT on the physical layer data of the input multi-beam, (P / S) 521, 522, and 523, respectively. The parallel-to-serial (P / S) converter 521, 522, and 523 serial-converts the multi-beam signals output from the IFFTs 511, 512, The Cyclic Offset Delay (D) 531, 532, 533 may be used to differentiate the antenna feed signals for each of the multiple beams to different cyclic delay offsets Is applied. Circular offset delays 531, which produce beam 1,

And the circular offset delays 532, which produce beam 2,

And a circular offset delay unit 533 for generating beam 3

A circular delay offset is applied.

A guard interval inserter (G) 540 inserts a guard interval into a signal output from each of the circulation offset delays (D) 531, 532 and 533, DAC < / RTI > Herein, the guard interval is inserted in the OFDMA communication system in order to remove the interference between the current OFDM symbols to be transmitted between the current OFDM symbols in the OFDM symbol transmitted in the previous OFDM symbol time when transmitting the OFDM symbol in the OFDMA communication system. A cyclic prefix or a cyclic postfix. A digital analog converter (DAC) 550 analog-converts the signal output from the guard interval inserter 540 and outputs the analog signal. Then, a beamforming (B / F) unit 560 forms signals output from the analog converter (DAC) 550 as a beam, and outputs the beams to an antenna group composed of antenna feeds 1 to Ns. At this time, the beam 1 is transmitted through the beam former 1 561, the beam 2 is transmitted through the beam former 2 562, and the beam 3 is transmitted through the beam former 3 563. In addition, FIG. 5 is equally applicable to the case where beams 1, 2 and 3 are transmitted through one antenna feed group but beams 1, 2 and 3 are transmitted through another antenna feed group.

6 shows a structure of a transmitter for applying a cyclic delay offset in the frequency domain.

Referring to FIG. 6, the cyclic offset delay units 611, 612, and 613 and the beamformers 621, 622, and 623 are located before the IFFT 630 according to a preferred embodiment of the present invention. Therefore, unlike the embodiment in which the cyclic delay offset is applied in the time domain, the structure of the transmitter is simplified. In the following, the operation of the other components of the transmitter except for the circulation offset delay units 611, 612, and 613 and the beam formers 621, 622, and 623 is the same as that of FIG.

A k th subcarrier data vector for forming a multi-beam for one user terminal is input from the transmitter 413. The cyclic offset delay units 611, 612, and 613 apply a cyclic delay offset matrix Ri (i = 1, 2, 3) having a diagonal matrix to the data signal transmitted from the kth subcarrier in each beam. For example, the cyclic delay offset matrix R1 may be a diagonal matrix as shown in Equation (1) below.

,

,

은 빔 1, 2, 3의 협력 전송을 통해 신호를 수신하는 빔 경계 지역 UE의 다이버시티 이득을 극대화할 수 있도록 선택한다. 예를 들어, 0, 2pi/3, 4pi/3이 선택될 수 있다.The beam forming units 621, 622, and 623 multiply the beam forming matrix B1 by the data output from the circular offset delay units 611, 612, and 613 to form a target beam. The kth subcarrier signals of the beams 1, 2, and 3 output from the beamformers 621, 622, and 623 are mapped to kth subcarrier positions in the IFFT 630, and then transmitted independently from each antenna. Therefore, the signal x (k) for each antenna feed group applying the cyclic delay offset and applying the digital beam forming algorithm is mapped to the k < th > subcarrier signal for the IFFT of the antenna feed elements constituting the antenna group for beamforming, And then transmitted after RF processing. Here, the selected cyclic delay offset value

,

,

Is selected to maximize the diversity gain of the beam boundary area UE receiving the signal through the cooperative transmission of beams 1, 2, For example, 0, 2pi / 3, 4pi / 3 can be selected.

Referring again to FIG. 4, the cooperative transmission control unit 411 outputs a signal for controlling the operations of the cyclic delay offset determination unit 412 and the transmission unit 413. The cooperative transmission control unit 411 determines whether or not the cooperative multipoint transmission is performed and inputs a control signal to generate and output a cyclic delay offset to the cooperative delay offset determination unit 412 in the case of the cooperative multipoint transmission, ) So that the cyclic offset delay is operated. Meanwhile, the cooperative transmission control unit 411 outputs different control signals according to the following two embodiments in cooperative multipoint transmission.

First, there is no distinction of the time period over which the cooperative multi-point transmission is applied in the entire frame, and the case where the cyclic delay offset delay is applied.

Secondly, the time frame to which the cooperative multi-point transmission is applied in the entire frame is divided.

In the first embodiment, since the cyclic delay offset delay is applied to all the frames, the operation of the transmitter is simplified. In the second embodiment, an optimum cyclic delay offset value can be independently selected for each of beam-border user terminals cooperatively transmitted from two beams and beam-boundary user terminals cooperatively transmitted from three beams, thereby obtaining an optimal diversity gain There is an advantage.

Meanwhile, the cyclic delay offset determiner 413 stores a predetermined cyclic delay offset list so that the user terminal located at the beam boundary obtains the maximum diversity gain. The cyclic delay offset determiner 413 determines a cyclic delay offset in the cyclic delay offset list according to the control signal output from the cyclic delay controller 411 and outputs the determined cyclic delay offset to the transmitter 413.

을 순환 지연 오프셋으로 출력하고, 빔 2를 생성하는 순환 오프셋 지연기(532)들에는

을 순환 지연 오프셋으로 출력하고, 빔 3를 생성하는 순환 오프셋 지연기(533)에는

을 순환 지연 오프셋으로 출력한다. 또한, 다중 빔 위성 장치는 3개의 순환 지연 오프셋 지연기를 인접한 빔들 간에 다른 순환 지연 오프셋 지연기를 선택하는 방식으로 재사용할 수 있다. Since the user terminal located at the beam boundary can receive signals from up to three beams according to the first embodiment, the cyclic delay offset determiner 412 can determine three cyclic delay offset values for obtaining the maximum diversity gain And outputs it to the transmitter 413. For example, referring to FIG. 5, the cyclic offset delays 531 that generate beam 1

And the circular offset delays 532, which produce beam 2,

To the circular delay delay 533 for generating the beam 3

As a cyclic delay offset. In addition, a multi-beam satellite device may reuse three cyclic delay offset retarders in a manner that selects other cyclic delay offset retarders between adjacent beams.

According to the second embodiment, the cooperative transmission control unit 411 outputs indication information indicating whether there are two beam cooperative transmission intervals or three beam cooperative transmission intervals to the cyclic delay offset determination unit 412 or the transmission unit 413.

Then, the cyclic delay offset determiner 412 may select and output different optimal cyclic delay offset values in the two beam cooperative transmission intervals or the three beam cooperative transmission intervals to the transmitter 413. In addition, the transmitter 413 can be operated differently in two beam cooperative transmission intervals or three beam cooperative transmission intervals. In the three beam cooperation transmission period, the transmission unit 413 is driven to transmit three beams so that three beams can be cooperatively transmitted as shown in FIG. 5 or 6.

On the other hand, in the section where cooperative transmission is performed from two beams, the transmitting section 413 is driven to transmit two beams so that two beams can be cooperatively transmitted as shown in FIG. 5, when a control signal of two beam transmission periods is input from the cooperative transmission control unit 411, the transmission apparatus for beam 3 may not be driven.

7 is a diagram showing another embodiment of the structure of a transmitter of a satellite apparatus according to a preferred embodiment of the present invention.

Referring to FIG. 7, cyclic offset delays 711 and 712 and beamformers 721 and 722 are located before IFFT 730 according to a preferred embodiment of the present invention. Operations of other components of the transmitter except for the circular offset delays 711 and 712 and the beam forming units 721 and 722 are the same as those in FIG.

A k'th subcarrier data vector for forming a multiple beam for one user terminal is input to the transmitter 413. The cyclic offset delay units 711, 712, and 713 apply a cyclic delay offset matrix Ri '(i = 1, 2) having a diagonal matrix to the data signal transmitted from the kth subcarrier in each beam. For example, the cyclic delay offset matrix R1 'may be a diagonal matrix as shown in Equation (2) below.

The beam forming units 721 and 722 multiply the beam forming matrix B1 by the data output from the circular offset delay units 711 and 712 to form a target beam. The k'th subcarrier signals of the beams 1 and 2 output from the beamforming units 721 and 722 are mapped to k'th subcarrier positions in the IFFT 730 and then transmitted independently in each antenna. Accordingly, the signal x (k) for each antenna feed group applying the cyclic delay offset and applying the digital beam forming algorithm is mapped to the k'th subcarrier signal for the IFFT of the antenna feed elements constituting the antenna group for beamforming After IFFT, it is transmitted after RF processing. Here, the selected cyclic delay offset values? ₁ and? ₂ are selected so as to maximize the diversity gain of the user terminal located in the beam boundary region receiving the signal through the cooperative transmission of the beams 1 and 2. For example, you can choose 0, pi.

The diversity transmission method in the above-described satellite communication system will now be described.

8 is a flowchart for explaining a diversity transmission method in a satellite communication system according to a preferred embodiment of the present invention.

Referring to FIG. 8, in step 810, the satellite apparatus determines whether cooperative multipoint transmission is necessary. If it is determined in step 810 that the cooperative multi-point transmission is not required, the satellite apparatus terminates the operation without applying the cyclic delay offset in step 820.

However, if it is determined that the cooperative multipoint transmission is required, the satellite apparatus must determine a different circular offset value to be applied to the multiple beams. However, according to the present invention, two embodiments are possible depending on whether the same cyclic delay offset is performed in all frames or whether two beam cooperative transmission intervals or three beam cooperative transmission intervals are divided to perform a cyclic delay offset.

Thus, the satellite device determines whether to apply the same cyclic delay offset over all of the frames in step 830.

If it is determined in step 820 that the cyclic delay offset is applied to all the frames, the satellite apparatus calculates different cyclic delay offsets for each beam to be applied to all the frames as in the first embodiment as described above in step 840 And generates multiple beams delayed with the determined cyclic delay offset, respectively.

However, if it is determined in step 830 that the cyclic delay offset is not applied to all the frames, that is, if no cyclic delay offset is applied to all the frames, but there are two beam transmission periods or three beam transmission periods, The satellite apparatus determines in step 850 whether the current transmission interval is two beam transmission time intervals or three beam transmission intervals. As a result of the determination in step 850, in case of two beam transmission time intervals, the satellite apparatus selects and applies an optimal cyclic delay offset for two beams in step 860. [ However, if it is determined in step 850 that the beam transmission time interval is 3, the satellite apparatus selects and applies an optimum circular delay offset for the 3 beams in step 870.

Then, the satellite apparatus transmits one or more beams to which the cyclic delay offset is applied to one user terminal as described above.

Claims (18)

A satellite apparatus for performing communication with one or more user terminals in a multi-beam satellite communication system,
A transmitter for generating a plurality of beams delayed by different circulation offsets and simultaneously transmitting signals for one user terminal,
A cyclic delay offset determining unit for determining a cyclic delay offset to be applied to each of the plurality of beams and outputting the determined cyclic delay offset to the transmitter,
And a cooperative transmission controller for determining whether or not to transmit the multi-cooperative point according to the position of the one user terminal and outputting a control signal for controlling the application of the cooperative delay offset to the cooperative delay offset determiner A multi-cooperative transmit diversity transmitter.
2. The apparatus of claim 1, wherein the transmitter
Wherein the plurality of beams are transmitted through at least one multi-antenna feed group.
2. The apparatus of claim 1, wherein the transmitter
Wherein the signal is transmitted based on a radio interface based on an orthogonal frequency division multiple access scheme.
2. The apparatus of claim 1, wherein the transmitter
And performs a cyclic delay offset operation in the time domain.
2. The apparatus of claim 1, wherein the transmitter
And performs a cyclic delay offset operation in the frequency domain.
2. The apparatus of claim 1, wherein the transmitter
A plurality of inverse fast Fourier transformers for receiving a plurality of physical layer data bits to be generated by a plurality of beams,
A plurality of parallel-to-serial converters for converting a parallel signal output from the plurality of inverse fast Fourier transformers into a serial signal,
A plurality of cyclic offset delays for delaying and outputting a plurality of signals output from the plurality of parallel-to-serial converters with different cyclic delay offsets,
A plurality of guard interval inserters for inserting guard intervals into the plurality of signals output from the plurality of cyclic offset delays,
A plurality of digital-to-analog converters for converting the signals output from the plurality of guard interval inserters into analog signals and outputting the analog signals,
And a plurality of beamformers for forming signals output from the plurality of digital-to-analog converters into beams and transmitting the beams through an antenna.
7. The apparatus of claim 6, wherein each of the plurality of cyclic offset retarders
And a cyclic offset delay component corresponding to each of the antenna components of the multiple antennas transmitting the beam.
2. The apparatus of claim 1, wherein the transmitter
A plurality of cyclic offset delays for multiplying different data vectors by a different cyclic delay offset matrix for each beam as a result of inputting a subcarrier data vector to be generated by a plurality of beams,
A plurality of beamformers for multiplying a signal output from the circulation offset delay unit by a beamforming matrix,
An inverse fast Fourier transformer for mapping the beam signal calculated by the beam former to a subcarrier position and outputting the result;
A guard interval inserter for inserting a guard interval into a signal output from the inverse fast Fourier transformer,
A digital-to-analog converter for converting a signal output from the guard interval inserter into an analog signal and outputting the analog signal,
And a radio processing unit for wirelessly processing signals output from the digital-to-analog converter and outputting the signals through multiple antennas.
The method of claim 8, wherein the cyclic delay offset matrix is
And the number of beams to be generated is a diagonal matrix having the number of rows and columns.
2. The apparatus of claim 1, wherein the cyclic delay offset determination unit
Stores a list of cyclic delay offsets capable of maximum diversity gain, selects a cyclic delay offset from the list, and outputs the cyclic delay offset to the transmitter.
The method according to claim 1,
In the case of the multi-cooperative point transmission,
The cyclic delay offset determination unit selects the cyclic delay offset according to the control signal output from the cooperative transmission control unit and outputs the cyclic delay offset to the transmission unit,
Wherein the transmission unit applies a cyclic delay offset output from the cyclic delay offset determination unit according to a control signal output from the cooperative transmission control unit.
The method according to claim 1,
In the case of the multiple cooperative point transmission, the cooperative transmission control unit determines whether or not to apply the same cyclic delay offset in all frames, outputs the determination result as a control signal,
The cyclic delay offset determination unit selects the cyclic delay offset according to the control signal output from the cooperative transmission control unit and outputs the cyclic delay offset to the transmission unit,
Wherein the transmission unit applies a cyclic delay offset output from the cyclic delay offset determination unit according to a control signal output from the cooperative transmission control unit.
2. The apparatus of claim 1, wherein the cyclic delay offset determination unit
And determines a different cyclic delay offset according to the two beam cooperative transmission time intervals or the three beam cooperative transmission time intervals, and outputs the determined cyclic delay offset to the transmission unit.
A cooperative transmit diversity transmission method by a satellite apparatus in a multi-beam satellite communication system,
Determining one or more different cyclic delay offsets;
Generating one or more beams delayed with the determined cyclic delay offset and transmitting the beams to one user terminal,
Wherein the determining comprises:
Determining whether to transmit multiple cooperation points according to a location of the one user terminal, and outputting a control signal for controlling whether or not to apply the cyclic delay offset.
delete 15. The method of claim 14, wherein determining
Further comprising determining whether to apply the same cyclic delay offset across all frames,
Wherein the optimal cyclic delay offset to be applied to all frames is determined when the same cyclic delay offset is applied to all frames.
15. The method of claim 14, wherein determining
Further comprising determining whether to apply the same cyclic delay offset across all frames,
Wherein the optimum cyclic delay offset is determined to correspond to the number of generated beams when a time interval for applying the cyclic delay offset is present as a result of the determination.
15. The method of claim 14, wherein the transmitting comprises:
Applying a different cyclic delay offset matrix for each beam to subcarrier data to be generated with a plurality of beams for one user terminal;
Applying a beamforming matrix to subcarrier data to which the cyclic delay offset matrix is applied;
Performing inverse fast Fourier transform on the signal to which the beamforming matrix is applied,
And performing wireless processing on the inverse fast Fourier transformed signal to transmit the inverse fast Fourier transformed signal.

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