KR101508392B1 - Method for data transmission in a mobile communiation system with relay station and system thereof - Google Patents

Abstract

The present invention provides a data transmission method in a mobile communication system including 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, And transmitting data to a relay station in a corresponding sector in each of the divided sub-relay zones, the method comprising the steps of: dividing a relay zone for transmitting data into a sub- Method. According to the method and system proposed by the present invention, the relay station secures a sub-relay zone in which data is not received from the base station base and serves mobile stations under the interference occurrence area using the directional antenna characteristics of the base station, And a high transmission rate.

Base station, relay station, three sectors, directional antenna, downlink relay zone, overlap method, orthogonal method

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a data transmission method and a system for a mobile communication system using a relay station,

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

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

1A shows a 3-sector topology of IEEE 802.16j.

Unlike IEEE 802.16e, where a base station is the only service station in a cell, IEEE 802.16j knows that multiple relay stations, together with the base station, serve the mobile 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 a downlink and an uplink, and each of the subframes is divided into an access zone and a relay zone. The access zone is a transmission interval between a service station (i.e., a base station and a 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 aims at paying attention to utilization of the downlink subframe.

The resource allocation methods of the service stations are divided into two methods, that is, an overlapped method and an orthogonal method depending on the usage method of the frequency resource. The overlapping scheme is a scheme in which all service stations in the downlink access zone service the lower mobile stations using the same frequency band. The 'lower' refers to being within the coverage of the service station and is used interchangeably in the specification of the present invention. In the orthogonal method, service stations use different bands by dividing frequency bands.

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

2A shows resource allocation of a downlink access zone in accordance with an overlapping scheme.

Not only the base station BS but also the relay stations RS1, RS2 and RS3 transmit the same frequency band.

2B shows resource allocation of the downlink access zone in accordance with the orthogonal scheme.

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

IEEE 802.16j services mobile stations in their respective coverage areas simultaneously in the cell and all relay stations in the downlink access zone. In the case of the overlapping scheme, all the service stations (i. E., The base station and the relay stations) use the same frequency band, resulting in interference within the cell. That is, if there are more than one serving relay stations in a cell other than the base station, severe interference occurs in areas where transmission coverage overlaps between different service stations. Interference within a cell degrades the modulation and coding selection level (MCS level) of the mobile stations, and even a service outage may occur.

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

In the case of orthogonal resource allocation, intra-cell interference does not occur because service stations use different frequency bands. Therefore, the orthogonal scheme has a higher MCS level distribution than the overlap scheme, and there is no service disabled area.

FIG. 4 shows an average throughput according to a resource allocation scheme.

Since orthogonal resource allocation uses frequency bands among service stations, cell capacity is smaller than that of overlapping schemes.

In summary, in the case of the overlapping resource allocation, intra-cell interference occurs in service stations using the same frequency band, exhibits a lower MCS level distribution than the orthogonal scheme due to the interference, and some service disabled areas exist . On the other hand, the cell capacity is larger in the overlapping scheme as compared with the case of the orthogonal scheme.

Thus, there is a trade-off between cell capacity and intra-cell interference in the existing frame structure. Therefore, a new frame structure is required that can eliminate some service disabling areas that occur in the case of overlapping resource allocation and increase the MCS level while enabling a high average throughput.

In the mobile communication system using the relay station, overlapped resource allocation is performed, but service incompetence due to interference between service stations is eliminated.

In addition, the present invention has a higher average transmission rate than that of the conventional overlapping resource allocation while having a high MCS level as in the orthogonal resource allocation.

The present invention provides a data transmission method in a mobile communication system including 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, And transmitting data to a relay station in a corresponding sector in each of the divided sub-relay zones, the method comprising the steps of: dividing a relay zone for transmitting data into a sub- Method.

Further, in the mobile communication system according to the present invention, the entire service area is divided into at least three sectors by use of a directional antenna, the relay zone is divided into sub-relay zones by the number of sectors on the time axis, And a base station for transmitting data to a relay station in a corresponding sector in each relay zone.

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

Prior to the detailed description, a service station used in the specification of the present invention is a concept that includes a base station and an RS as a service providing service to a mobile station.

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

The shaded areas (1 to 6) inside the cell are regions where the service areas of the service stations overlap and severe interference occurs. There are six areas where interference is severe.

Alternatively, the severe interference region can be defined as an area where the maximum transmission power (PMAX) is less than twice the minimum transmission power (PMIN). That is, the interference region is expressed by the following equation.

P _MAX <2 * P _MIN

According to an embodiment of the present invention, a three sector topology is assumed in which three relay stations exist in different positions around a base station. The base station has three directional antennas each of which is divided into three sectors by the three relay stations. The directional antenna has been widely used for performance improvement from IEEE 802.16e. On the other hand, each relay station uses one omnidirectional antenna.

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

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

In the case of FIG. 6A, RS1 and RS3 have an idle period, whereas RS2 has no idle period.

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

7 shows an example of burst allocation of the downlink relay zone according to the present invention.

If the base station transmits to the relay stations in the relay zone in a time division multiplexing (TDM) manner, the idle interval is guaranteed as shown in FIG. When allocating the same amount of resources to all the relay stations, each relay station leaves 2/3 of the relay zones in the idle state. That is, if the relay zone is divided into sub-relay zones by the number of sectors divided by the relay station on the time axis and the base station transmits data to the relay station during the sub-relay zone, .

The present invention intends to use the idle period which is guaranteed to be a new access period.

In Fig. 7, the relay zone is largely divided into three parts. T1 is a period in which RS1 receives, and T2 and T3 are periods in which RS2 and RS3 receive, respectively.

The transmission coverage in the T1 section is shown in FIG.

Assuming that the RS2 and the RS3 transmit in the T1 interval, the BS has the transmission coverage as shown in FIG. Even though RS2 and RS3 transmit to their respective lower 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. Therefore, the RS2 and the RS3 can transmit data to the mobile stations in the coverage area belonging to its coverage in the T1 interval using the same frequency resource as the base station.

Each of the relay stations has interference occurrence areas between two adjacent relay stations. The RS2 has the interference zones 3 and 4, and the RS3 has the interference zones 5 and 6. However, in the T1 interval, the coverage of the base station by the directional antenna toward the RS1 has a considerable influence on the interference areas 3 and 6. Therefore, each of the RSs transmits data to a mobile station in an area where interference due to data transmission of the BS is relatively small. That is, the RS2 makes the mobile stations in the interference area 4, and the RS3 makes the mobile stations in the interference area 5 serviced.

If the idle period is overlapped with the idle period of the other relay station, the relay station shares the frequency resource with the relay station. If the RS2 and the RS3 transmit in the same frequency band, the interference between the interference areas 4 and 5 becomes severe. Therefore, the RS2 and the RS3 divide the frequency band in half and transmit different bands to the downlink transmission To use. Thus, using the directional antenna characteristics of the base station, the relay stations in the idle state can reuse the frequency without interference.

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

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

The downlink access zone services all service stations using the same frequency band in an overlapping manner. The mobile station serviced by the access zone is limited to mobile stations that are not in the interference area. The mobile stations in the interference zone serve in six transmission intervals (A to F) newly assigned to the relay zone. The six intervals are referred to as interference-free slots. As described above, since the zones affected by the base station are different for each interval, the service station and the interference zone, which can service each interference-free slot, are different.

However, it does not access only the mobile stations in the service interruption state in the interference area in an interference-free slot. For example, if 10% of all mobile stations are in a service outage and 15% of the mobile stations are allowed to access in an interference-free slot, I.e., 5% of the MSs in the BPSK 1/2 state, are additionally accessed in the interference-free slot. This is because the interference-free slot has no interference between the relay station and the base station in the cell, and therefore the MCS level is improved in the access zone.

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

slot Transmission 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 IEEE 802.16j standard has a tradeoff relationship between the cell capacity and intra-cell interference according to the resource allocation scheme. Service stations can increase cell capacity by using the same frequency band, but severe interference in the cell occurs. On the other hand, when frequency is divided and used between service stations in an orthogonal manner, 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 the idle state of the relay station in the directional antenna of the base station and the downlink relay zone.

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

The increased cell capacity depends on the ratio of the access zone and the relay zone of the downlink. As the ratio of the relay zone is larger, the increase rate of the cell capacity according to the present invention increases. The cell capacity problem and the intra-cell interference problem can be solved at the same time by using the increased cell capacity to service the mobile station located in the severe interference area.

As a result of the simulation using the frame structure according to the present invention, 11.4% ~ 20.1% of all the mobile stations located within the coverage of the service station are served in the interference-free slot of the relay zone.

The number of mobile stations that can serve in the interference-free slot depends on the traffic condition of each frame. Basically, the more the relay stations transmit data to the lower mobile stations than the base station, the greater the proportion 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, the larger the area of the interference-free slot and the greater the proportion of mobile stations accessible in the interference- . Therefore, the ratio of the serviceable mobile stations changes according to the traffic situation affecting the ratio of the relay zone.

11 and 12 illustrate performance of the frame structure proposed by the present invention in terms of MCS level and average throughput.

As a result of experiments using the present invention, the MCS level distribution has risen compared to the resource allocation of the overlapping scheme, and the problem of service outage has been solved (FIG. 11)

As a result of experiments using the present invention, the average throughput per cell is also increased by 35% compared with the resource allocation of the overlapping method and by 117% as compared with the resource allocation of the orthogonal method (FIG. 12).

1A is a three-sector topology overview of IEEE 802.16j,

1B shows a frame structure structure of IEEE 802.16j,

2A is an exemplary frequency resource allocation of a downlink access zone in an overlapping scheme,

FIG. 2B is an exemplary frequency resource allocation of a downlink access zone in an orthogonal manner,

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

FIG. 4 is a diagram illustrating an average transmission amount comparison according to a resource allocation method,

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

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

6B is an exemplary frame structure diagram according to the IEEE 802.16j standard,

7 is a diagram illustrating an example of a burst allocation of a downlink relay zone according to the present invention,

FIG. 8 is a transmission coverage structure diagram in a T1 interval according to the present invention; FIG.

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

10 is a diagram showing a comparison of cell capacity according to the ratio of the access zone and the relay zone,

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

FIG. 12 is a view for comparing an average transmission amount when a frame structure according to the present invention is applied. FIG.

Claims (12)

A data transmission method in a mobile communication system including 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 a relay zone for transmitting data to the relay station into sub-relay zones corresponding to the number of sectors in a time axis; And transmitting data to a relay station in a corresponding sector in each of the sub-relay zones, Wherein the relay station selects a sub-relay zone in which data is not received from the base station among the sub-relay zones as an idle interval and transmits data to the mobile station, and when the idle interval overlaps with the idle interval of another relay station, Wherein the sub relay zone of the idle period is divided on the frequency axis and shared with the other relay station. delete The method according to claim 1, Wherein the relay station transmits data to the mobile stations in an interference occurrence area where interference due to data transmission of the base station is relatively small among interference occurrence areas with two relay stations adjacent to the relay station in the idle period. The method of claim 3, Wherein the interference occurrence region is a region in which the maximum transmission power (PMAX) in the cell is less than twice the minimum transmission power (PMIN) in the cell. In a mobile communication system, By using the directional antenna, the entire service area is divided into at least three sectors, the relay zone is divided into the sub-relay zones by the number of sectors in the time axis, and each relay station in the corresponding sector in each of the sub- Comprising: a base station for transmitting data, Wherein the relay station selects a sub relay zone in which data is not received from the base station among the sub relay zones as an idle interval and transmits data to the mobile station, and when the idle interval overlaps with the idle interval of another relay station, And divides the sub-relay zone of the idle period on the frequency axis so that the sub-relay zone is shared with the other relay station. delete 6. The method of claim 5, Wherein the relay station transmits data to a mobile station in an interference occurrence area where interference due to data transmission of the base station is relatively small among interference occurrence areas with two relay stations adjacent to the relay station in the idle period. system. 8. The method of claim 7, Wherein the interference occurrence region is a region in which the maximum transmission power (PMAX) in the cell is less than two times the minimum transmission power (PMIN) in the cell. A method of transmitting data in a relay station in a sector in a mobile communication system in which an entire service area is divided into at least three sectors by use of a directional antenna of a base station, Dividing a relay zone for receiving data from the base station into sub-relay zones by the number of sectors in a time axis; Receiving data in a sub-relay zone corresponding to the relay station among the sub-relay zones; And Selecting an idle interval for a sub-relay zone that does not receive data from the base station among the sub-relay zones, and transmitting data to the mobile station during the idle interval, Wherein when the idle period overlaps with the idle period of the other relay station, the sub relay zone corresponding to the idle period is divided on the frequency axis and shared with the other relay station. 10. The method of claim 9, The operation of transmitting data to the mobile station in the idle period includes: And transmitting data to a mobile station in an interference occurrence area where interference due to data transmission of the base station is relatively small among interference occurrence areas with two relay stations adjacent to the relay station in the idle period. A relay station existing in a sector in a mobile communication system in which an entire service area is divided into at least three sectors by use of a directional antenna of a base station, Wherein the relay station divides a relay zone for receiving data from the base station into a number of sub-relay zones corresponding to the number of sectors on a time axis, receives data from a sub-relay zone corresponding to the relay station among the sub- A sub relay zone which does not receive data from the base station among the sub relay zones is selected as an idle period and data is transmitted to the mobile station in the idle period, Wherein the relay station divides the sub relay zone corresponding to the idle period on the frequency axis and shares it with the other relay station when the idle period overlaps with the idle period of the other relay station. 12. The method of claim 11, Wherein the relay station transmits data to a mobile station in an interference occurrence area where interference due to data transmission of the base station is relatively small among interference occurrence areas with two relay stations adjacent to the relay station in the idle period.

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