KR20100098903A - Method for data transmission in a mobile communiation system with relay station and system thereof - Google Patents

Abstract

PURPOSE: A method and a system for transmitting data of mobile communication system using relay station are provided to supply service also in mobile station within a region which interference is severe, thereby maintaining a high MCS(Modulation and Coding Scheme) level. CONSTITUTION: A RS2 and a RS3 does not influence RS1 which is receiving data from a base station while RS2(Relay Station2) and the RS3 is performing transmission about each lower mobile station. The RS2 and the RS3 transmits data through same frequency resources with the base station to mobile stations in an interference section within coverage in T1 interval. The RS2 provides service to mobile stations in interference section 4. The RS3 provides service to mobile stations in interference section 5.

Description

METHOD FOR DATA TRANSMISSION IN A MOBILE COMMUNIATION SYSTEM WITH RELAY STATION AND SYSTEM THEREOF}

The present invention relates to the use of a downlink relay zone of an IEEE 802.16j transmission frame in a mobile communication system using a relay station to serve mobile stations.

IEEE 802.16j is a concept of a relay station (RS) in the existing IEEE 802.16e for improving throughput to a mobile station (MS) and extending transmission coverage of a base station (BS). Is an international standard specification.

1A shows a three-sector scheme topology of IEEE 802.16j.

Unlike IEEE 802.16e, where a base station was the only service station in a cell, IEEE 802.16j can know that multiple relay stations serve a mobile station together with a base station.

1B illustrates a frame structure of IEEE 802.16j.

The horizontal axis of the frame shown in FIG. 1B is the time axis, and the vertical axis is the frequency axis. One frame is divided into two subframes for downlink and uplink, and each subframe is divided into an access zone and a relay zone. The access zone is a transmission interval between a service station (i.e., base station and relay station) and mobile stations within the coverage of the service station, and the relay zone is a transmission interval between the base station and the relay station. The present invention focuses on the utilization of the downlink subframe.

Resource allocation schemes of service stations are largely divided into two schemes, an overlapped scheme and an orthogonal scheme, depending on the frequency resource usage scheme. The overlapping scheme is a scheme in which all the service stations serve the lower mobile stations using the same frequency band in the downlink access zone. The term "lower" means within the transmission coverage of the service station, and is used interchangeably in the specification of the present invention. In the orthogonal scheme, service stations divide frequency bands and use different bands.

2 illustrates a frequency band in a downlink access zone according to a resource allocation scheme.

2A illustrates resource allocation of a downlink access zone according to an overlap scheme.

In addition to the base station BS, the relay stations RS1, RS2, and RS3 also transmit using the same frequency band.

2B illustrates resource allocation of a downlink access zone according to an orthogonal scheme.

The base station BS and all the relay stations RS1, RS2, and RS3 transmit using different frequency bands.

IEEE 802.16j allows base stations and all relay stations in a cell to simultaneously service mobile stations in their own transmission coverage in the downlink access zone. In the overlapping scheme, since all the service stations (ie, base stations and relay stations) use the same frequency band, interference in the cell occurs. That is, if there is more than one serving relay station in the cell besides the base station, severe interference occurs in an area where transmission coverage overlaps between different serving stations. Interference in the cell degrades the MCS level (modulation and coding selection level, hereinafter referred to as the " MCS level ") of the mobile stations and may even result in service outage.

3 shows an MCS level distribution according to a resource allocation scheme.

In the orthogonal resource allocation, since different frequency bands are used between service stations, intra-cell interference does not occur. Therefore, the orthogonal scheme has a higher MCS level distribution than the overlap scheme, and there is no out of service area.

4 shows average throughput according to a resource allocation scheme.

Orthogonal resource allocation uses frequency bands between service stations so that the cell capacity is smaller than that of the overlapping method.

In summary, in the case of the overlapping resource allocation, in-cell interference is generated by service stations using the same frequency band, and due to the interference, the MCS level distribution is lower than that of the orthogonal scheme, and some out of service areas exist. . On the other hand, the cell capacity of the overlapping method is larger than that of the orthogonal method.

As such, there is a trade off of cell capacity and intra-cell interference in the existing frame structure. Accordingly, there is a need for a new frame structure that eliminates some of the unserviceable areas that occur in the case of overlapping resource allocation and enables a high average transmission amount while increasing the MCS level.

The present invention solves the service unavailability in some regions due to interference between service stations while allocating overlapping resources in a mobile communication system using a relay station.

In addition, the present invention has a higher MCS level as in the case of orthogonal resource allocation, but has a higher average transmission amount than in the case of conventional overlapping resource allocation.

The present invention provides a data transmission method in a mobile communication system comprising a base station having a total service area divided into at least three sectors by use of a directional antenna, and relay stations existing in each of the sectors. Dividing a relay zone for transmitting data to a sub-relay zone by the number of sectors on a time axis, and transmitting data to a relay station in a corresponding sector in each of the divided sub relay zones. Suggest a method.

In addition, in the mobile communication system, the entire service area is divided into at least three sectors by use of a directional antenna, and the relay zone is divided into sub relay zones equal to the number of sectors on a time axis. A mobile communication system including a base station for transmitting data from a relay zone to a relay station in a corresponding sector is proposed.

When the new frame structure according to the present invention is applied to a mobile communication system using a relay station, even a frequency resource is allocated in an overlapping manner, a service can be provided to a mobile station located in a severe interference area. At the same time, a higher MCS level can be maintained than in the case of the conventional overlapping method, and a high average transmission amount can be maintained.

Prior to the detailed description, a service station used in the specification of the present invention is a subject that provides a service to a mobile station, and includes a base station and a relay station.

In FIG. 5, three relay stations are assumed in one cell to indicate an area where interference occurs.

The hatched areas 1 to 6 in the cell are areas in which the service areas of the service stations overlap and severe interference occurs. The areas where severe interference occurs are divided into six areas.

Optionally, the severe interference zone may be defined as an area where the highest transmit power (PMAX) is less than twice the lowest transmit power (PMIN). That is, the interference zone is represented by the following equation.

P _MAX <2 * P _MIN

According to an embodiment of the present invention, assume a three sector topology in which three relay stations exist in different locations around a base station. The base station has three directional antennas each responsible for three sectors divided by the three relay stations. The directional antenna has been widely used to improve performance since IEEE 802.16e. Each relay station, on the other hand, uses one omni-directional antenna.

6A and 6B are examples of a frame structure proposed by the IEEE 802.16j standard.

In the downlink relay zone, the base station allocates and transmits a burst to three relay stations. Depending on the burst allocation, relay stations may or may not have an idle section that neither transmits nor receives.

In the case of FIG. 6A, RS1 and RS3 have an idle section, while RS2 does not have an idle section.

In the case of FIG. 6B, all three relay stations have idle sections. However, RS1 has much larger idle intervals than RS2 and RS3.

7 shows an example burst allocation of a downlink relay zone in accordance with the present invention.

If the base station transmits to the relay stations in a time division multiplexing (TDM) scheme in the relay zone, an idle period is guaranteed as shown in FIG. 7. When allocating the same amount of resources to all the relay stations, each relay station will idle two-thirds of the relay zone. That is, if the relay zone is divided into sub relay zones by the number of sectors separated by the relay station on the time axis, and the base station transmits data to the relay station during the sub relay zone, idle periods for all relay stations are constant. Is guaranteed.

The present invention intends to use the idle interval, which is constantly guaranteed, as a new access interval.

In FIG. 7, the relay zone is divided into three parts. T1 is a section received by RS1, and T2 and T3 are sections received by RS2 and RS3, respectively.

8 shows transmission coverage in the T1 section.

Assuming that RS2 and RS3 transmit in the T1 section, they have transmission coverage as shown in FIG. 8. Although RS2 and RS3 transmit to their subordinate mobile stations, they have little effect on RS1 receiving data from the base station, which is due to the directional antenna characteristics of the base station. Accordingly, the RS2 and the RS3 can transmit data using the same frequency resources as those of the base station to the mobile stations in the interference generating area belonging to their coverage in the T1 section.

Each relay station has interference generating areas between two adjacent relay stations. The RS2 has interference zones 3 and 4 and the RS3 has interference zones 5 and 6. However, in the T1 section, the coverage of the base station by the directional antenna toward the RS1 has a significant effect on the interference areas 3 and 6. Accordingly, each relay station transmits data to a mobile station in an area where interference by data transmission of the base station is relatively low. That is, the RS2 serves the mobile stations in the interference zone 4 and the RS3 serves the mobile stations in the interference zone 5.

When the idle section overlaps with the idle section of another relay station, frequency resources are shared with the other relay station. If the RS2 and the RS3 transmit in the same frequency band, the interference of the interference zones 4 and 5 becomes severe. Thus, during the T1 period, the RS2 and RS3 divide the frequency band in half and transmit different bands to the downlink transmission to the lower mobile station. To use. Therefore, by using the directional antenna characteristics of the base station, the relay stations in the idle state can be reused without interference.

The above-described method is also applied to the time slots T2 and T3 in the relay zone.

9 illustrates a frame structure of a relay zone according to the method proposed by the present invention.

The downlink access zone is overlapped so that all service stations use the same frequency band. Mobile stations served by the access zone are limited to mobile stations that are not in the interference zone. Mobile stations in the interfering zone serve in six transmission intervals A to F newly allocated to the relay zone. The six sections are referred to as interference-free slots. As described above, since the area affected by the base station is different for each section, the service station that can serve each interference-free slot is different from the interference area.

However, only mobile stations in the interrupted service state in the interference zone are not accessed in the interference-free slot. For example, suppose that 10% of all mobile stations are in service outages and 15% of mobile stations are accessible in the interference-free slots. That is, 5% of mobile stations (which are in BPSK 1/2 state) will be accessed in an additional interference-free slot. This is because the interference-free slot has no interference between the relay station and the base station in the cell, so that the MCS level is improved than in the access zone.

Table 1 shows the service stations (relay stations) and the interference zones serviceable in each interference-free slot.

slot Transmit RS Serviceable Interference Area A RS2 4 B RS1 One C RS1 2 D RS3 5 E RS3 6 F RS2 3

The frame structure proposed by the IEEE802.16j standard establishes a trade-off relationship between cell capacity and intra-cell interference according to a resource allocation scheme. Service stations can increase cell capacity by using the same frequency band, but severe interference occurs within the cell. On the other hand, when the frequency is distributed in the orthogonal manner among the service stations, the intra-cell interference does not occur, but the cell capacity is greatly reduced.

The frame structure proposed by the present invention increases the cell capacity by utilizing an interval that is an idle state of the relay station in the directional antenna and the downlink relay zone of the base station.

10 shows an increase rate of the cell capacity according to the ratio of the access zone to the relay zone.

The increased cell capacity depends on the ratio of downlink access zones and relay zones. It can be seen that the larger the ratio of the relay zone, the larger the increase rate of the cell capacity according to the present invention. By using the increased cell capacity to service the mobile station located in the severe interference zone it is possible to solve both the cell capacity problem and the intra-cell interference problem at the same time.

Simulation results in a system using a frame structure according to the present invention show that 11.4% to 20.1% of all mobile stations located within the coverage of the service station serve in the interference-free slot of the relay zone.

The number of mobile stations that can serve in the interference-free slots depends on the traffic situation of every frame. Basically, the more relay stations transmit data to subordinate mobile stations than the base station, the greater the percentage of mobile stations accessible in the interference-free slot. Since the area of the interference-free slot is proportional to the size of the relay zone, the larger the ratio of the relay zone is, the larger the area of the interference-free slot is, and the larger the percentage of mobile stations accessible in the interference-free slot. . Thus, the proportion of mobile stations that can be serviced varies according to traffic conditions that affect the ratio of the relay zone.

The performance in the case of applying the frame structure of the method proposed by the present invention to FIGS. 11 and 12 has been described in terms of MCS level and average transmission amount.

As a result of experimenting with the present invention, the MCS level distribution is increased compared to the overlapping resource allocation, and the service outage problem is solved (FIG. 11).

In addition, as a result of experimenting with the present invention, the average throughput per cell also increased by 35% compared to the overlapped resource allocation and 117% compared to the orthogonal resource allocation (FIG. 12).

1A is a schematic of a three-sector topology of IEEE 802.16j;

Figure 1b is a frame structure of IEEE 802.16j,

2A illustrates an example of frequency resource allocation of a downlink access zone in an overlap scheme;

2b illustrates an example of frequency resource allocation of a downlink access zone in an orthogonal scheme;

3 is an MCS level distribution diagram according to a resource allocation scheme;

4 is a comparison diagram of average transmission amount according to a resource allocation scheme;

5 is a diagram illustrating an interference occurrence area of a cell assuming three relay stations;

6A is an exemplary frame structure possible according to the IEEE 802.16j standard.

6B is an exemplary frame structure possible according to the IEEE 802.16j standard.

7 is an exemplary burst allocation diagram of a downlink relay zone according to the present invention;

8 is a diagram illustrating a structure of transmission coverage in a T1 section according to the present invention;

9 is a frame structure diagram of a relay zone according to the present invention;

10 is a comparison diagram of cell capacity according to a ratio of an access zone and a relay zone;

11 is an MCS level distribution diagram when the frame structure according to the present invention is applied;

12 is a comparison diagram of average transmission amounts when the frame structure according to the present invention is applied.

Claims (8)

A data transmission method in a mobile communication system comprising a base station in which an entire service area is divided into at least three sectors by use of a directional antenna, and relay stations existing in each of the sectors. Dividing, by the base station, a relay zone for transmitting data to the relay station into sub relay zones equal to the number of sectors on a time axis; and And transmitting data from each of the divided sub relay zones to a relay station in a corresponding sector. The method of claim 1, When the relay station selects a sub relay zone that does not receive data from the base station among the sub relay zones as an idle section and transmits data to the mobile station, when the idle section overlaps with an idle section of another relay station, And dividing the sub relay zone in the idle section on the frequency side and sharing the same with the other relay station. The method of claim 2, In the idle period, the relay station transmits data to a mobile station within an interference generating area where interference by data transmission of the base station is relatively low among the interference generating areas with two relay stations adjacent to the relay station. The method of claim 3, And wherein the interference generating area is an area where a maximum transmit power (PMAX) in a cell is less than twice the minimum transmit power (PMIN) in a cell. In the mobile communication system, The use of the directional antenna divides the entire service area into at least three sectors, divides the relay zone into sub-relay zones by the number of sectors on a time axis, and from each of the divided sub relay zones to a relay station in the corresponding sector. A mobile communication system comprising a base station for transmitting data. The method of claim 5, The relay station selects a sub relay zone that does not receive data from the base station among the sub relay zones as an idle section, and transmits data to the mobile station. When the idle section overlaps with an idle section of another relay station, And dividing the sub relay zone of the idle section on the frequency side to share with the other relay station. The method of claim 6, In the idle period, the RS transmits data to a mobile station in an interference generating area having relatively little interference due to data transmission of the base station among the interference generating areas with two RSs adjacent to the relay station. system. The method of claim 7, wherein The interference generating area is a mobile communication system, characterized in that the maximum transmit power (PMAX) in the cell is less than twice the minimum transmit power (PMIN) in the cell.

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