WO2009038395A2

WO2009038395A2 - Method and apparatus for allocating radio resources in a wireless communication system

Info

Publication number: WO2009038395A2
Application number: PCT/KR2008/005573
Authority: WO
Inventors: Hyung-Joon Jeon; Jae-Hyeong Kim; Jun-Seong Park; Jae-Hyun Ahn
Original assignee: Posdata Co., Ltd.
Priority date: 2007-09-19
Filing date: 2008-09-19
Publication date: 2009-03-26
Also published as: WO2009038395A3; KR20090029910A; KR100956182B1

Abstract

A method and apparatus is provided for allocating radio resource in a wireless communication system. The method includes, when a Mobile Station (MS), which sends a first Channel Quality Indicator (CQI) report through a CQI channel for a subchannel zone that uses a first frequency reuse factor, satisfies a predetermined condition, receiving from the MS a second CQI report even for a subchannel zone that uses a second frequency reuse factor; and deciding whether to allocate the subchannel zone that uses the second frequency reuse factor, based on the CQI reports. The present invention can properly allocate frequency resources to the MS using the frequency reuse factors thereby optimizing the entire capacity of the system.

Description

Description Method and apparatus for allocating radio resources in a wireless communication system Technical Field

[1] The present invention relates generally to a wireless communication system, and in particular, to a method and apparatus for allocating radio resources in a wireless communication system. Background Art

[2] Generally, in a cellular communication system, two spaced-apart zones use the same frequency resource to efficiently use the limited frequency resources. FIG. 1 schematically illustrates the frequency reuse concept in a general cellular communication system. As illustrated in FIG. 1, a frequency resource Fl used in a first cell 100 with a radius R is reused in another cell with a radius R, i.e., a second cell 150, which is spaced apart from the center of the first cell 100 by a distance D, and this is called frequency reuse . Meanwhile, a Frequency Reuse Factor (FRF) K is defined that one same frequency resource, or frequency band, is reused in units of K cells.

[3] In the case where each cell is composed of 3 sectors (not shown in the drawing), K=I is given when the sectors all are allocated the same Radio Frequency (RF) frequency, and K=3 can be defined when each sector is composed of 3 different subchannel sets in the entire RF frequency.

[4] Therefore, as the FRF is higher, the interference due to use of frequency resources between cells, or sectors, which use the frequency resources, decreases in the amount.

[5] A subchannel reuse pattern algorithm can be configured so that Mobile Stations

(MSs) having a high Signal to Interference and Noise Ratio (SINR) can operate in a zone where all subchannels are available (hereinafter referred to as an 'all-subchannel zone'. On the other hand, for MSs having a low SINR, each cell or sector operates in a zone where a fraction of subchannels are available (hereinafter referred to as a 'segmented zone'). With this configuration, the full-load frequency reuse K=I allows the high-SINR MSs to keep their maximum spectral efficiency, and the fractional frequency reuse is implemented for the low-SINR MSs to ensure connection quality and throughput.

[6] Although the above characteristics are not complex conceptually, the following matters should be considered actually. First, frequency allocation for Channel Quality Indicator (CQI) report should be updated according to the zone to which the MS belongs. For example, if the MS belongs to the all- subchannel zone, its Carrier to Interference and Noise Ratio (CINR) is measured based on FRF-I configuration, and if the MS belongs to the segmented zone, its CINR is measured based on FRF-3 configuration.

[7] Next, the start Orthogonal Frequency Division Multiple Access (OFDMA) symbol offset and the size of the segmented zone and/or all- subchannel zone should be synchronized between all neighbor Base Stations (BSs). It means that the dynamic zone allocation based on the number of MSs, network load and interference condition is not possible by a single BS without communication and synchronization with the neighbor BSs.

[8] The conventional subchannel reuse pattern algorithm sets a lower boundary or threshold to change the subchannel zone when CINR of MSs, to which the all- subchannel zone is allocated, is lower than or equal to the boundary or threshold; sets an upper boundary or threshold to change the subchannel zone when CINR of MSs, to which the segmented zone is allocated, is higher than or equal to the boundary or threshold; and checks if CINR of the MSs belonging to each zone is within the boundaries.

[9] If CINR of an MS in the all- subchannel zone is lower than or equal to a predetermined first threshold, the MS will be moved (switched) to the segmented zone. On the contrary, if CINR of an MS in the segmented zone is higher than or equal to a predetermined second threshold, the MS will be moved to the all-subchannel zone. When the zone to which the MS belongs is changed, the CINR measurement will also be changed according to the zone. If the MS moves from the all-subchannel zone to the segmented zone, its CINR is measured based on FRF-3 configuration. However, if the MS moves from the segmented zone to the all-subchannel zone, its CINR is measured based on FRF-I configuration. To this end, the BS sends a CQI Channel (CQICH) Allocation Information Element (IE) message to the MS.

[10] Since an MS that cannot be serviced in the FRF-I configuration due to a low CINR can be serviced through the segmented zone by applying the basic subchannel reuse pattern algorithm, the foregoing algorithm has the following two problems even though the cell coverage can be extended wider than that of the full FRF-I configuration.

[11] First, for synchronization in the subchannel reuse pattern, since the start OFDMA symbol offset and the size of each zone should be fixed for all neighbor BSs, one zone may waste the frequency resource whereas another zone may suffer from a lack of the resource.

[12] Second, as it takes time to get a reliable CINR measurement value from a CQI report, it is too late if the BS orders the MS to change the CINR measurement scheme after crossing the threshold by the CQICH Allocation IE, making it hard to decide an initial Modulation and Coding Scheme (MCS) level after switching the allocated zone of the MS. Disclosure of Invention

Technical Problem

[13] Therefore, the present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a radio resource allocation method and apparatus for reducing a loss of frequency resource due to synchronization of a frequency reuse pattern in a wireless communication system.

[14] It is another object of the present invention to provide a radio resource allocation method and apparatus for optimizing the entire capacity of the system by easily determining an initial MCS level.

[15] It is further another object of the present invention to provide a radio resource allocation method and apparatus for allocating a suitable OFDMA-based frequency reuse pattern. Technical Solution

[16] According to one aspect of the present invention, there is provided a method for allocating radio resource in a wireless communication system. The method includes, when a Mobile Station (MS), which sends a first Channel Quality Indicator (CQI) report through a CQI channel for a subchannel zone that uses a first frequency reuse factor, corresponds to a predetermined condition, receiving from the MS a second CQI report even for a subchannel zone that uses a second frequency reuse factor; and deciding whether to allocate the subchannel zone that uses the second frequency reuse factor, based on the CQI reports. Preferably, the predetermined condition corresponds to a case where when the first frequency reuse factor is 1, a Carrier to Interference and Noise Ratio (CINR) value of the first CQI report is less than a lower CINR threshold. Preferably, the predetermined condition corresponds to a case where when the first frequency reuse factor is 3, a CINR value of the first CQI report is greater than an upper CINR threshold. Preferably, the subchannel zone allocation is applied when the first frequency reuse factor and the second frequency reuse factor are used on a frame- by-frame basis, or used in each frame in a mixed manner.

[17] According to another aspect of the present invention, there is provided a method for allocating radio resource, comprising: when a Mobile Station (MS), which sends a first Channel Quality Indicator (CQI) report through a CQI channel for a first subchannel zone that uses a first frequency reuse factor, corresponds to a predetermined condition, receiving from the MS a second CQI report for a second subchannel zone that uses a second frequency reuse factor; and deciding whether to allocate the second subchannel zone from at least one of a spectral efficiency for each subchannel zone and a resource utilization of each subchannel zone based on the CQI reports. Preferably, the method further comprise deciding to change a current subchannel zone according to whether the current subchannel zone has available resource as a result of the decision. Preferably, the method further comprise, when the current subchannel zone has no available resource and another subchannel zone has available resource as a result of the decision, allocating the another subchannel zone to an MS having a low loss of the spectral efficiency.

[18] According to further another aspect of the present invention, there is provided a method for supporting allocation of radio resource, comprising: sending to a Mobile Station (MS), which sends a first Channel Quality Indicator (CQI) report through a first CQI channel for a subchannel zone that uses a first frequency reuse factor, a request for a second CQI report for a subchannel zone that uses a second frequency reuse factor, when a Carrier to Interference and Noise Ratio (CINR) of the first CQI report corresponds to a predetermined condition; and receiving from the MS the second CQI report through a second CQI channel and the first CQI report through the first CQI channel to decide whether to allocate the subchannel zone that uses the second frequency reuse factor; wherein the MS supports at least two CQI channels.

[19] According to still further another aspect of the present invention, there is provided a method for supporting allocation of radio resource, comprising: when a Mobile Station (MS) supporting at least two concurrent Channel Quality Indicator (CQI) channels sends a first CQI report through a first CQI channel for a subchannel zone that uses a first frequency reuse factor and a Carrier to Interference and Noise Ratio (CINR) of the first CQI report corresponds to a predetermined condition, receiving from a Base Station (BS) a request for a second CQI report for a subchannel zone that uses a second frequency reuse factor; and sending the second CQI report through a second CQI channel and the first CQI report through the first CQI channel to support the BS in deciding whether to switch the MS to the subchannel zone that uses the second frequency reuse factor.

[20] According to still further another aspect of the present invention, there is provided an apparatus for allocating radio resource in a wireless communication system. The apparatus includes a condition determiner for determining if a Carrier to Interference and Noise Ratio (CINR) value of a first Channel Quality Indicator (CQI) report received from a Mobile Station (MS) through a CQI channel for a subchannel zone that uses a first frequency reuse factor, corresponds to a predetermined condition; a CQI report requester for, when the CINR value corresponds to the predetermined condition, requesting the MS to send through the CQI channel a second CQI report for a subchannel zone that uses a second frequency reuse factor; and a zone decider for deciding whether to allocate the subchannel zone that uses the second frequency reuse factor, based on the CQI reports.

[21] According to still further another aspect of the present invention, there is provided an apparatus for allocating radio resource, comprising: a switching region setter for setting a zone switching region according to a Carrier to Interference and Noise Ratio (CINR) threshold difference between Modulation and Coding Scheme (MCS) levels for subchannel zone switching; a region determiner/Channel Quality Indicator (CQI) report requester for determining if a switching region corresponds to the set zone switching region based on a first CQI report received from a Mobile Station (MS) through a CQI channel for a first subchannel zone that uses a first frequency reuse factor, and if the switching region corresponds to the set zone switching region, sending to the MS a request for a second CQI report for a second subchannel zone that uses a second frequency reuse factor; and

[22] a zone decider for deciding whether to allocate the second subchannel zone from at least one of a spectral efficiency of each subchannel zone and a resource utilization of each subchannel zone based on the CQI reports.

Advantageous Effects

[23] The present invention can reduce a loss of frequency resource due to synchronization of a frequency reuse pattern, thereby facilitating efficient frequency resource allocation. In addition, the present invention can easily decide the initial MCS level thereby optimizing the entire capacity of the system. Further, the invention can implement allocation of a suitable OFDMA-based frequency reuse pattern. Brief Description of the Drawings

[24] The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

[25] FIG. 1 is a diagram schematically illustrating the frequency reuse concept in a general cellular communication system;

[26] FIG. 2 is a block diagram illustrating a structure of a radio resource allocation apparatus according to an embodiment of the present invention;

[27] FIG. 3 is a flowchart illustrating a radio resource allocation method according to an embodiment of the present invention;

[28] FIG. 4 is a block diagram illustrating a structure of a radio resource allocation apparatus according to another embodiment of the present invention;

[29] FIG. 5 is a flowchart illustrating a radio resource allocation method according to another embodiment of the present invention;

[30] FIG. 6 is a flowchart illustrating a method for supporting radio resource allocation for frequency reuse by a BS according to an embodiment of the present invention;

[31] FIG. 7 is a flowchart illustrating a method for supporting radio resource allocation for frequency reuse by an MS according to an embodiment of the present invention; [32] FIG. 8 is a flowchart illustrating a dynamic frequency allocation method for network entry according to an embodiment of the present invention; and

[33] FIGs. 9 to 11 are flowcharts illustrating a radio resource allocation method in a normal operation after network entry according to an embodiment of the present invention. Mode for the Invention

[34] Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for clarity and conciseness.

[35] FIG. 2 is a block diagram illustrating a structure of a radio resource allocation apparatus according to an embodiment of the present invention. The radio resource allocation apparatus for frequency reuse according to the present invention includes a condition determiner 210, a CQI report requester 220 and a zone decider 230.

[36] The condition determiner 210 determines if a CINR value of a CQI report received from an MS corresponds to a predetermined condition. That is, the condition determiner 210 determines if a first CQI report value reported through a CQI channel for a subchannel zone that uses a first frequency reuse factor corresponds to a predetermined condition. For example, if the MS is allocated in a subchannel zone that uses FRF-I, the condition determiner 210 determines if a CINR value of a CQI report received through a CQI channel for the FRF-I corresponds to a predetermined condition. Herein, the predetermined condition represents the case where if the first frequency reuse factor is 1 or FRF-I, a CINR value of the first CQI report is less than a lower CINR threshold, and if the first frequency reuse factor is 3 or FRF-3, a CINR value of the first CQI report is greater than an upper CINR threshold. In addition, as to the predetermined condition, a CINR value of the first CQI report can fall within a CINR range which is set according to a predetermined MCS level table.

[37] The CQI report requester 220, when the CINR value corresponds to the predetermined condition, requests the MS to send through the CQI channel a second CQI report for a subchannel zone that uses a second frequency reuse factor. For example, when an MS is in the FRF-I subchannel zone and a CINR value of the CQI is less than the lower CINR threshold, the CQI report requester 220 requests the MS to send a CQI report for FRF-3 through a CQI channel.

[38] The zone decider 230 decides whether to allocate the subchannel zone that uses the second frequency reuse factor, based on the CQI reports. The subchannel zone allocation can be applied when it alternately uses the first frequency reuse factor and the second frequency reuse factor on a frame-by-frame basis, or uses them in each frame in a mixed manner.

[39] More specifically, the zone decider 230 checks if CINR of an MS belonging to an

FRF- 1 zone is in a predetermined range centered on a predetermined first threshold, or if CINR of an MS belonging to an FRF-3 zone is in a predetermined range centered on a predetermined second threshold. If it is checked that the CINR of the MS is in a predetermined range centered on the first threshold or the second threshold, the zone decider 230 allocates one more CQICH to the MS so that the MS can measure and report CINR for FRF-I and CINR for FRF-3. Thereafter, if a CINR value reported from the MS exceeds (crosses) the first threshold or the second threshold, the zone decider 230 moves the frequency reuse factor zone. The movement of the FRF-I and FRF-3 zones happens when CINR of an MS belonging to FRF-I is less than the first threshold, or happens when CINR of an MS belonging to FRF-3 is greater than the second threshold.

[40] FIG. 3 is a flowchart illustrating a radio resource allocation method according to an embodiment of the present invention. An operation of the radio resource allocation apparatus for frequency reuse, shown in FIG. 2, will be described with reference to FIG. 3.

[41] The radio resource allocation apparatus receives a first CQI report through a CQI channel for a subchannel zone that uses a first frequency reuse factor (Step S310). The radio resource allocation apparatus checks if an MS that is making the first CQI report satisfies a predetermined condition (Step S320). If the MS satisfies the predetermined condition, the radio resource allocation apparatus receives, from the MS, a second CQI report even for a subchannel zone that uses a second frequency reuse factor (Step S330). Based on the first CQI report and the second CQI report, if it is checked that a CINR value of the CQI report crosses a predetermined threshold (Step S340), the radio resource allocation apparatus allocates a subchannel zone that uses the second frequency reuse factor (Step S350).

[42] More specifically, if an MS belongs to an FRF- 1 zone, the radio resource allocation apparatus receives CINRl of the MS through the condition determiner 210 (Step S310), and checks if the CINR value is in a predetermined Range 1 centered on a predetermined first threshold (Step S320). That is, the radio resource allocation apparatus checks if the CINRl has arrived near the first threshold. This is to previously measure CINR for FRF-3 before performing zone switching, on the assumption that there is high possibility that the CINRl will arrive at the first threshold.

[43] If an MS belongs to FRF-3, the radio resource allocation apparatus receives CINR2 of the MS through the condition determiner 210 (Step S310), and checks if the CINR value is in a predetermined Range2 centered on a predetermined second threshold (Step S320). That is, the radio resource allocation apparatus checks if the CINR2 has arrived near the second threshold. Similarly, this is to previously measure CINR for FRF- 1 before performing zone switching, on the assumption that there is high possibility that the CINR2 will arrive at the second threshold.

[44] The radio resource allocation apparatus allocates CQICH to an MS whose CINR is in the Range 1 or the Range2, orders the MS to measure CINRl for FRF-I and CINR2 for FRF- 3 and to report the result to the BS, and receives the report by means of the CQI report requester 220 (Step S330). The measurement of CINRl and CINR2 can be performed by allocating one more CQICH to the MS.

[45] If the CINR value reported from the MS crosses a predetermined threshold (Step

S340), the radio resource allocation apparatus changes the current frequency reuse factor zone to another frequency reuse factor zone by means of the zone decider 230 (Step S350). That is, when CINRl of the MS belonging to FRF-I is less than the first threshold, the MS moves to the FRF-3 zone, and if CINR2 of the MS belonging to FRF-3 is greater than the second threshold, the MS moves to the FRF-I zone.

[46] In conclusion, if CINR approaches the threshold capable of changing the zone, since there is high possibility that the MS will change its zone, the radio resource allocation apparatus orders the MS to temporarily measure both of the two CQICHs. In this manner, even though the zone is changed, it is possible to reduce the time required for setting an MCS level to a proper value, and since the MS temporarily allocates CQICHs, it is possible to prevent a waste of CQICH resources as compared with a method of always allocating two CQICHs.

[47] As stated above, the subchannel zone allocation can be applied when it alternately uses the first frequency reuse factor and the second frequency reuse factor on a frame- by-frame basis, or uses them in each frame in a mixed manner. In addition, based on the CQI reports, the radio resource allocation apparatus can estimate frequency efficiency for each subchannel zone. Further, as to the predetermined condition, a CINR value of the first CQI report can fall within a CINR range which is set according to a predetermined MCS level table.

[48] FIG. 4 is a block diagram illustrating a structure of a radio resource allocation apparatus according to another embodiment of the present invention. The radio resource allocation apparatus for frequency reuse includes a switching region setter 410, a region determiner/CQI report requester 420, and a zone decider 430.

[49] The switching region setter 410 sets a zone switching region according to a CINR threshold difference between MCS levels for subchannel zone switching. More specifically, the switching region setter 410 sets, as a switching region, the interval where a difference in CINR threshold between MCS levels is small when the MS moves from the FRF- 1 zone to the FRF-3 zone. On the contrary, when the MS moves from the FRF-3 zone to the FRF-I zone, the switching region setter 410 sets, as a switching region, the interval where a difference in CINR threshold between MCS levels is large. The reasons are as follows. When the MS moves from the FRF-I zone to the FRF-3 zone, a CINR gain of about 8 dB is obtained on average. Therefore, if CINR thresholds for MCSs are close to each other, a high MCS level gain is obtained, and in the opposite case, the CINR thresholds should be separated far away from each other, in order to reduce the loss due to the MCS level.

[50] The region determiner/CQI report requester 420 determines if the region corresponds to the set region based on a first CQI report received from an MS through a CQI channel for a first subchannel zone that uses a first frequency reuse factor, and if the region corresponds to the set switching region, the region determiner/CQI report requester 420 requests a second CQI report for a second subchannel zone that uses a second frequency reuse factor. For example, if the MS belongs to an FRF-I zone, the region determiner/CQI report requester 420 determines if a CINR value of a CQI report for the channel received from the MS through a CQI channel for the zone belongs to the switching region. If it is determined that the CINR value belongs to the switching region, the region determiner/CQI report requester 420 allocates CQICH for a FRF-3 zone and requests a CQI report of the FRF-3 zone.

[51] The zone decider 430 decides based on the CQI reports whether to allocate the second subchannel zone from at least one of a spectral efficiency for each subchannel zone and a resource utilization of each subchannel zone. For example, assuming that a zone is decided depending on the spectral efficiency of each subchannel zone, if an MS is allocated in the FRF- 1 zone, the zone decider 430 calculates and compares spectral efficiencies for FRF-I and FRF-3. If the FRF-I zone is higher than the FRF-3 zone in the spectral efficiency as a result of the comparison, the MS is moved to the FRF-3 zone.

[52] Assuming that a zone is decided depending on the resource utilization of each subchannel zone, even though the current zone is higher than another zone in the spectral efficiency, if resource of one zone is insufficient while resource of another zone is surplus, the zone decider 430 allocates MSs in another zone in ascending order of a loss of the spectral efficiency. That is, as the spectral efficiency appears to be high only for the MSs in the FRF-3 zone, the MSs are allocated only in the FRF-3 zone, and if no MSs are allocated in the FRF-I zone, the FRF-3 zone suffers from a lack of the resource and resource waste occurs in the FRF-I zone. In order to prevent this, even though the spectral efficiency is high in the FRF-3 zone, the zone decider 430 allocates MSs in the FRF-I zone to prevent the resource waste. In this case, the zone decider 430 allocates MSs in the FRF-I zone in ascending order of the spectral efficiency, and vice versa. [53] FIG. 5 is a flowchart illustrating a radio resource allocation method according to an embodiment of the present invention. An operation of the radio resource allocation apparatus for frequency reuse, shown in FIG. 4, will be described with reference to FIG. 5.

[54] To provide a frequency allocation method according to the present invention, the radio resource allocation apparatus sets a switching region by means of the switching region setter 410 (Step S500). For example, when an MS moves from an FRF-I zone to an FRF-3 zone, the radio resource allocation apparatus sets, as a switching region, the interval where a difference in CINR threshold between MCS levels is small. On the contrary, when the MS moves from the FRF-3 zone to the FRF-I zone, the radio resource allocation apparatus sets, as a switching region, the interval where a difference in CINR threshold between MCS levels is large.

[55] The radio resource allocation apparatus receives a first CQI report from the MS through a CQI channel for a first subchannel zone that uses a first frequency reuse factor (Step S505). For example, when the MS belongs to the FRF-I zone, the radio resource allocation apparatus receives CQI for the zone through a CQI channel. Thereafter, the radio resource allocation apparatus checks if the received CQI report value, or CINR value, belongs to a predetermined condition, for example, the set switching region, by means of the region determiner/CQI report requester 420 (Step S510).

[56] If the CINR value of the MS belongs to the set switching region, the radio resource allocation apparatus allocates a CQI channel to the MS for a second subchannel zone that uses a second frequency reuse factor, requests a second CQI report, and receives the second CQI report from the MS through the CQI channel (Step S515).

[57] Thereafter, the radio resource allocation apparatus compares spectral efficiency between MCS levels of the two zones (Step S520). That is, the radio resource allocation apparatus compares spectral efficiency SpEff 1 of the current frequency reuse factor zone with spectral efficiency SpEff2 of another frequency reuse factor zone.

[58] The radio resource allocation apparatus decides whether to allocate the second subchannel zone from at least one of the spectral efficiency for each subchannel zone and the resource utilization of each subchannel zone based on the CQI reports. If the spectral efficiency SpEff2 of another frequency reuse factor zone is higher than the spectral efficiency SpEff 1 of the current frequency reuse factor zone as a result of the comparison, the MS can move to the zone having the high frequency spectral efficiency.

[59] Meanwhile, if unbalance of resources is also considered together, the radio resource allocation apparatus checks if resource of one zone is insufficient while resource of another zone is surplus (Step S525). That is, if there is no available resource for the current subchannel zone and there is available resource for another subchannel zone, the radio resource allocation apparatus allocates MSs in the zone with available resource in ascending order of a loss of frequency spectral efficiency SpEff (Step S530). However, if there is no, or insignificant, resource unbalance in Step S525, the radio resource allocation apparatus moves the MS to the frequency reuse factor zone having a high frequency spectral efficiency SpEff2 (Step S535). In this manner, it is possible to optimize the entire capacity of the system.

[60] FIG. 6 is a flowchart illustrating a method for supporting radio resource allocation for frequency reuse by a BS. In the method for supporting radio resource allocation for frequency reuse, the BS receives a first CQI report from an MS through a first CQI channel for a subchannel zone that uses a first frequency reuse factor (Step S610). If a CINR value of the received CQI report corresponds to a predetermined condition (Step S620), the BS sends to the MS a request for a second CQI report for a subchannel zone that uses a second frequency reuse factor (Step S630). In order to decide whether to allocate the subchannel zone that uses the second frequency reuse factor, the BS concurrently receives, from the MS, the second CQI report through the second CQI channel and the first CQI report through the first CQI channel (Step S640). The MS supports at least two (concurrent) CQI channels.

[61] FIG. 7 is a flowchart illustrating a method for supporting radio resource allocation for frequency reuse by an MS. In the method for supporting radio resource allocation for frequency reuse, an MS supporting at least two concurrent CQI channels sends a first CQI report through a first CQI channel for a subchannel zone that uses a first frequency reuse factor (Step S710). If CINR of the first CQI report corresponds to a predetermined condition (Step S720), the MS receives, from a BS, a request for a second CQI report for a subchannel zone that uses a second frequency reuse factor (Step S730).

[62] In order to support the BS in deciding whether to make switching to the subchannel zone that uses the second frequency reuse factor, the MS concurrently sends the second CQI report through the second CQI channel and the first CQI report through the first CQI channel (Step S740).

[63] The foregoing embodiments will be described below in more detail. The present invention, aimed to dynamically allocate frequencies, i.e., users or MSs, receives two separate CQI reports to alternately decide the zones on a frame-by-frame basis according to required Quality of Service (QoS) of each zone and spectral efficiencies of MSs so that the MSs can temporarily acquire information of both zones.

[64] For the dynamic frequency allocation, the MS is adapted to send multiple CQI reports. For example, Worldwide Interoperability for Microwave Access (WiMAX) Forum Mobile System Profile can mandate two concurrent CINR measurements and CQI reports, which simultaneously occur at the request of the MS, as shown in Table 1.

[65] [TABLE 1] [66]

[67] The BS can also know if the MS supports two concurrent CQI channels by 'OFDMA Subscribe Station (SS) CINR measurement capability' TLV in an SS Basic Capability (SBC)-REQ message. Table 2 is disclosed in "Draft IEEE Standard for Local and metropolitan area networks - Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems, Amendment2:Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1," IEEE P802. 16e-2005 February 2006.

[68] The BS can get the CQI reports of FRF-I based CINR measurement and FRF-3 based CINR measurement simultaneously by allocating two CQICHs or sharing a CQICH time division manner through two CQICH Allocation IEs.

[69] [TABLE 2] [70] Type Length Value Scope

Bit #O:Physical CINR measurement from the preamble SBC-REQ (see 6 3 2 3 23)

Bit #1 Physical CINR measurement for a permutation SBC-RSP (see 6 3 2 3 24) zone from pilot subcarriers

Bit #2:Physical CINR measurement for a permutation zone from data subcarriers

Bit #3:Effectιve CI NR measurement from the preamble

1 OU 1

Bit #4:Effective CI NR measurement for a permutation zone from pilot subcarriers

Bit #5: Effective CI NR measurement for a permutation zone from data subcarriers

Bit #6 Support for 2 concurrent CQ channels

Bit #7^' Frequency selectivity characterization report [71] The dynamic frequency allocation will be described below in more detail. First, network entry is achieved as follows. FIG. 8 is a flowchart illustrating a dynamic frequency allocation method for network entry, and a brief description of the network entry will be given below. If an MS is coincident with a Medium Access Control (MAC) address in an RNG-REQ message (Step S800), a BS allocates a Basic Connection Identifier (BCID) and a Primary Management CID (PMCID) (Step S810).

[72] After allocating the BCID, the BS can allocate CQICH with CQICH Allocation IE

(Step S 820). In Step S 820, Frame offset = ObOOl, Duration = ObI 11 (until explicit deallocation), Feedback type= ObOO (PCINR), Report type = ObI (zone), and Zone permutation = ObOOl (PUSC with use all SC =1).

[73] The MS measures CINR based on FRF-I configuration. The reason why CINR measurement is based on FRF- 1 configuration is because the expected spectral efficiency is usually higher in the all- subchannel zone rather than the segmented zone. The MS sends FRF-I configuration-based CQI report periodically (Step S830). The recommended report periodicity is every frame.

[74] The BS compares the reported CQI with a predefined FRF-I Exit threshold (Step

S840). The FRF-I Exit threshold is a threshold used in the all- subchannel zone. If the reported CQI is lower than the FRF- 1 Exit threshold for N consecutive reports or the spectral efficiency of segmented zone is expected to be higher than that of the all- subchannel zone, the BS updates the current CQICH allocation information for the CINR to be measured and reported based on the FRF-3 configuration (Step S850), and receives the CINR measured and reported based on the FRF-3 configuration (Step S860). In Step S850, Frame offset = ObOOl, Duration = ObI 11 (until explicit deallocation), Feedback type = ObOO (PCINR), Report type = ObI (preamble), and CINR preamble report type = ObI (FRF-3 configuration).

[75] The BS allocates a data grant for the SBC-REQ message before expiration of a T9 timer so that the MS can send the SBC-REQ message, and restores the 'OFDMA SS CINR measurement capability' information to check if the MS supports two concurrent CQICHs.

[76] If Steps S830 to S860 are completed, the BS sends the SBC-RSP message through the selected zone (Step S870). That is, if the current CQI report is based on FRF-I configuration, the BS sends the SBC-RSP message through the all- subchannel zone, and if the current CQI report is based on FRF-3 configuration, the BS sends the SBC-RSP message through the segmented zone.

[77] FIGs. 9 to 11 are flowcharts illustrating a radio resource allocation method in a normal operation after network entry. The proposed radio resource allocation method for a subchannel reuse pattern after network entry is as follows.

[78] The BS receives a first CQI report from the MS (Steps S900 and S950), restores the 'OFDMA SS CINR measurement capability' information of the MS (Step S915), and checks if the MS supports two concurrent CQICHs (Step S920). If the MS supports two concurrent CQICHs, the BS checks if the reported CQI crosses an FRF-I Exit candidate boundary downward or an FRF-3 Exit candidate boundary upward (Steps S905 and S955). If so, the BS allocates a new CQICH Allocation IE so that the MS sends a second CQI report (Steps S910 and S960).

[79] In an alternative embodiment for radio resource allocation, the BS can check if a

CINR value of the CQI reported from the MS falls within a predetermined range, receive two CQI reports, and allocate radio resource. More specifically, the BS restores the 'OFDMA SS CINR measurement capability' information of the MS (Step S915), and checks if the MS supports two concurrent CQICHs (Step S920). If the MS supports two concurrent CQICHs, the BS checks if a CINR value of the CQI reported from the MS is in a switching region in a range centered on a threshold (Step S930), and if the CINR value is in the switching region, the BS allocates CQICH Allocation IE for another zone (Step S940).

[80] If the BS acquires CQI reports for both FRF-I and FRF-3 in this way (Step S945), it compares spectral efficiencies based on the two CQI reports (Step SlOlO). If the spectral efficiency SpEff(FRF-3) of the segmented zone is greater than or equal to 3 times the spectral efficiency SpEff(FRF-l) of the all- subchannel zone (Step S1015), the BS moves the MS to the segmented zone (Step S 1020), and otherwise, maintains the MS in the all- subchannel zone (Step S 1045). If the zone-changed MS is separated far away from the candidate boundary (Steps S 1025 and S 1050), the CQICH allocation based on another zone is cancelled (Steps S 1030 and S 1055).

[81] Meanwhile, the BS can compulsorily allocate the MS in a particular zone according to resource utilization of the zone. That is, when resource of one zone is insufficient and resource of another zone is surplus, i.e., when resource utilization of the all- subchannel zone is 100% and resource utilization of the segmented zone is less than 100% (Step Sl 100), or when resource utilization of the segmented zone is 100% and resource utilization of the all- subchannel zone is less than 100% (Step S 1125), the BS allocates MSs in another zone in ascending order of a loss of the spectral efficiency (Steps Sl 105, Sl 110, Sl 130 and Sl 135). If the zone-changed MS is separated far away from the candidate boundary (Steps Sl 115 and Sl 140), the CQICH allocation based on another zone is cancelled (Steps Sl 120 and Sl 145).

[82] For this, the BS knows the required CINR for each MCS level, as shown in Table 3.

[83] [TABLE 3]

[84]

[85] If the CINR gain of FRF- 3 over FRF-I is assumed to be about 8 dB, then followings could be guessed. If the CINR of MSl in all-subchannel zone is 20 dB, the highest MCS level applicable is 16QAM 1/2. If this MS is allocated in segmented zone, the CINR will be about 28 dB and the 64QAM 3/4 may be applicable. In this case, the achievable spectral efficiency of the MS in all- subchannel zone is 2 bps/subcarrier whereas the spectral efficiency in the segmented zone is 4.5 bps/subcarrier.

[86] If the CINR of MS2 in the all- subchannel zone is 2 dB, the highest MCS level applicable is QPSK 1/2 repetition 6. If the MS is allocated in the segmented zone, the CINR will be about 10 dB and the QPSK 1/2 repetition 4 may be applicable. In this case, the achievable spectral efficiency of the MS in the all- subchannel zone is 1/6 bps/ subcarrier whereas the spectral efficiency in the segmented zone 1/4 bps/subcarrier. If the subchannel zone is assumed to correspond to 1/3 of the all- subchannel zone, the spectral efficiency of the segmented zone corresponds to a value reduced to 1/3.

[87] Therefore, MS2 will be smaller than MSl in terms of the spectral efficiency lost by moving the corresponding MS from the all-subchannel zone to the segmented zone. It can deduced from above example that the greater the spectral efficiency gain - or the smaller the spectral efficiency loss - from the segmented zone to the all-subchannel zone might be, the greater the CINR difference between current MCS level and the lower MCS levels might be. On the contrary, the greater the spectral efficiency gain - or the smaller the spectral efficiency loss - from the all-subchannel zone to the segmented zone might be, the smaller the CINR difference between current MCS level and the lower MCS levels might be.

[88] As a result, the BS can define specific CINR ranges as recommended switching region for segmented zone and all-subchannel zone, respectively, and allocate CQICH for CINR measurement of another zone if the CINR of an MS belongs to this switching region.

[89] In sum, there is an interval where CINR thresholds for MCSs are close to each other and there is an interval where CINR thresholds for MCSs are separated far away from each other. When the MS moves from the all-subchannel zone to the segmented zone, it is preferred that the thresholds are closer to each other, and in the opposite case, it is preferred that the thresholds are separated far away from each other. The BS sets these intervals, and allows the MS belonging thereto to send CQICH even for another zone. The BS compares SpEff between MCS levels suitable to the two zones, and changes the zone if another zone is superior to the current zone. In addition, when one zone is insufficient in resource and another zone is surplus, the BS allocates MSs in another zone in ascending order of SpEff loss, thereby optimizing the entire capacity of the system.

[90] Meanwhile, functions used in an apparatus and a method disclosed in the present specification can be embodied in storage media that a computer can read as codes that the computer can read. The storage media that the computer can read, include all sorts of record devices in which data that can be read by a computer system is stored. Examples of the storage media that the computer can read, include ROMs, RAMs, CD- ROMs, magnetic tape, floppy discs, optic data storage devices, etc., and also, include things embodied in the form of carrier wave (e.g., transmission through the internet). Furthermore, the storage media that the computer can read is distributed in a computer system connected with networks. Then, the codes that the computer can read, are stored in the distributed storage media in a distribution scheme, and the codes can be executed in the distribution scheme.

[91] While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

[1] A method for allocating radio resource, comprising: when a Mobile Station (MS), which sends a first Channel Quality Indicator (CQI) report through a CQI channel for a subchannel zone that uses a first frequency reuse factor, corresponds to a predetermined condition, receiving from the MS a second CQI report for a subchannel zone that uses a second frequency reuse factor; and deciding whether to allocate the subchannel zone that uses the second frequency reuse factor, based on the CQI reports.

[2] The method of claim 1, wherein the predetermined condition corresponds to a case where when the first frequency reuse factor is 1, a Carrier to Interference and Noise Ratio (CINR) value of the first CQI report is less than a predetermined range value centered on a lower CINR threshold.

[3] The method of claim 1, wherein the predetermined condition corresponds to a case where when the first frequency reuse factor is 3, a CINR value of the first CQI report is greater than a predetermined range value centered on an upper CINR threshold.

[4] The method of claim 1, wherein the first CQI report and the second CQI report are sent through a same CQI channel or different CQI channels.

[5] The method of claim 1, wherein the subchannel zone allocation is applied when the first frequency reuse factor and the second frequency reuse factor are used on a frame -by-frame basis, or used in each frame in a mixed manner.

[6] The method of claim 1, further comprising: estimating frequency efficiency for each of the subchannel zones based on the CQI reports.

[7] The method of claim 1, wherein the predetermined condition is satisfied when a

CINR value of the first CQI report falls within a CINR range which is set according to a predetermined Modulation and Coding Scheme (MCS) level table.

[8] A method for allocating radio resource, comprising: when a Mobile Station (MS), which sends a first Channel Quality Indicator (CQI) report through a CQI channel for a first subchannel zone that uses a first frequency reuse factor, corresponds to a predetermined condition, receiving from the MS a second CQI report for a second subchannel zone that uses a second frequency reuse factor; and deciding whether to allocate the second subchannel zone from at least one of a spectral efficiency for each subchannel zone and a resource utilization of each subchannel zone based on the CQI reports.

[9] The method of claim 8, wherein the first CQI report and the second CQI report are sent through a same CQI channel or different CQI channels.

[10] The method of claim 8, further comprising: deciding to change a current subchannel zone according to whether the current subchannel zone has available resource as a result of the decision.

[11] The method of claim 10, further comprising: when the current subchannel zone has no available resource and another subchannel zone has available resource as a result of the decision, allocating the another subchannel zone to an MS having a low loss of the spectral efficiency.

[12] A method for supporting allocation of radio resource, comprising: sending to a Mobile Station (MS), which sends a first Channel Quality Indicator (CQI) report through a first CQI channel for a subchannel zone that uses a first frequency reuse factor, a request for a second CQI report for a subchannel zone that uses a second frequency reuse factor, when a Carrier to Interference and Noise Ratio (CINR) of the first CQI report corresponds to a predetermined condition; and receiving from the MS the second CQI report through a second CQI channel and the first CQI report through the first CQI channel to decide whether to allocate the subchannel zone that uses the second frequency reuse factor; wherein the MS supports at least two CQI channels.

[13] A method for supporting allocation of radio resource, comprising: when a Mobile Station (MS) supporting at least two concurrent Channel Quality Indicator (CQI) channels sends a first CQI report through a first CQI channel for a subchannel zone that uses a first frequency reuse factor and a Carrier to Interference and Noise Ratio (CINR) of the first CQI report corresponds to a predetermined condition, receiving from a Base Station (BS) a request for a second CQI report for a subchannel zone that uses a second frequency reuse factor; and sending the second CQI report through a second CQI channel and the first CQI report through the first CQI channel to support the BS in deciding whether to switch the MS to the subchannel zone that uses the second frequency reuse factor.

[14] An apparatus for allocating radio resource, comprising: a condition determiner for determining if a Carrier to Interference and Noise Ratio (CINR) value of a first Channel Quality Indicator (CQI) report received from a Mobile Station (MS) through a CQI channel for a subchannel zone that uses a first frequency reuse factor, corresponds to a predetermined condition; a CQI report requester for, when the CINR value corresponds to the predetermined condition, requesting the MS to send a second CQI report for a subchannel zone that uses a second frequency reuse factor; and a zone decider for deciding whether to allocate the subchannel zone that uses the second frequency reuse factor, based on the CQI reports.

[15] The apparatus of claim 14, wherein the first CQI report and the second CQI report are sent through a same CQI channel or different CQI channels.

[16] An apparatus for allocating radio resource, comprising: a switching region setter for setting a zone switching region according to a Carrier to Interference and Noise Ratio (CINR) threshold difference between Modulation and Coding Scheme (MCS) levels for subchannel zone switching; a region determiner/Channel Quality Indicator (CQI) report requester for determining if a switching region corresponds to the set zone switching region based on a first CQI report received from a Mobile Station (MS) through a CQI channel for a first subchannel zone that uses a first frequency reuse factor, and if the switching region corresponds to the set zone switching region, sending to the MS a request for a second CQI report for a second subchannel zone that uses a second frequency reuse factor; and a zone decider for deciding whether to allocate the second subchannel zone from at least one of a spectral efficiency of each subchannel zone and a resource utilization of each subchannel zone based on the CQI reports.

[17] The apparatus of claim 16, wherein the first CQI report and the second CQI report are sent through a same CQI channel or different CQI channels.