WO2015084223A1

WO2015084223A1 - Controlling apparatus, method of allocating radio channels, program and storage medium

Info

Publication number: WO2015084223A1
Application number: PCT/SE2013/051442
Authority: WO
Inventors: Varun Joshi; Krishna MOHAN MENON; Rahul KRISHNA; Sai Karthik GINNI REDD; Venkat ANNAM RAEVANTH
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2013-12-04
Filing date: 2013-12-04
Publication date: 2015-06-11

Abstract

A controlling apparatus that allocates radio channels in a first radio communication system, and a method of allocating radio channels. The apparatus acquires information for distinguishing channels of a first type shared with a second radio communication system or shared by a control channel of the first system and determines, in accordance with the information, whether a first condition including that an occupation ratio of the one or more channels of the second type does not exceed a first threshold is satisfied. The apparatus allocates a channel of the second type when the first condition is satisfied, and a channel of the first type when the first condition is not satisfied.

Description

DESCRIPTION

CONTROLLING APPARATUS, METHOD OF ALLOCATING RADIO

CHANNELS, PROGRAM AND STORAGE MEDIUM

TECHNICAL FIELD

[0001] The present invention generally relates to a controlling apparatus, a method of allocating radio channels, a program, and a storage medium.

BACKGROUND

[0002] Increasing popularity of high-rate data service based applications for mobile devices has led to a rise in the high data-rate radio communication systems, such as those based on Wideband Code Division Multiple Access (WCDMA) and Long Term Evolution (LTE) , for example.

[0003] However, the global radio frequency

spectral resource is a limited resource that is already very crowded. As a result, a strategy for

accommodating high data-rate systems known as spectrum re-farming has been adopted. In spectrum re-farming, spectrum of an existing system such as, for example, a Global System for Mobile Communications (GSM) radio communication system, is "carved out" (reallocated to a high data-rate system) . Spectrum re-farming puts pressure on the carved out system, which become more susceptible to intra-system radio frequency interference due to the decrease in available spectral resource. Also, in many spectrum re-farming scenarios, the incoming high data-rate system will coexist with the carved out system. This may result in inter-system radio frequency interference (mutual interference) between the two systems (see " 3GPP TR 25.816 V2.0.0") . Intra-system interference, or inter-system interference may occur due to strategies for dealing with the

decrease in spectral resource such as sharing traffic channels for other purposes, for example, or sharing traffic channels with channels of the high data-rate system.

[0004] Therefore, there is a need for strategies for mitigating intra-system or inter-system

interference in situations where a system is put under pressure, such as when frequencies have been carved out in spectrum re-farming.

[0005] Adaptive channel allocation (ACA) has been proposed as one method for decreasing co-channel

interference in communications links caused by

subcarriers used in neighboring cells (see WO 98/24258) . In ACA, various measurements of signal quality and interference are made by a mobile terminal and reported to a network. The network uses these measurements to dynamically allocate channels having the highest

carrier to interference ratio. However, the

measurements used in ACA may not be available to the network, and there may be no provision for dynamic allocation in the network.

[0006] Another strategy for reducing radio

frequency interference for GSM radio communication systems is described in US 2005/0059403 Al . This technique makes use of Overlaid (OL) and Underlaid (UL) sub-cells. A GSM cell is divided into two coverage zones according to distance to the center (a smaller OL sub-cell and a larger UL sub-cell) . Channels having frequencies sensitive to interference are allocated to the OL sub-cell, whereas channels having frequencies insensitive to interference are allocated to the UL sub-cell. Interference is reduced by optimizing the combination of the OL and UL cells.

[0007] However, the technique described in US

2005/0059403 Al and WO 98/24258 does not consider intra-system or inter-system interference due to shared channels in cases of spectrum re-farming, for example.

SUMMARY

[0008] The present invention was conceived in view of the above circumstances, and it is an object thereof to provide a technique of radio channel allocation for reducing interference and improving quality in a radio communication system.

[0009] According to the first aspect of the present invention, there is provided a controlling apparatus capable of allocating radio channels for communication with a mobile station in a first radio communication system in which a spectral resource is divided into a plurality of channels. The controlling apparatus comprises an acquiring unit configured to acquire information for distinguishing, out of the plurality of channels, one or more channels of a first type and one or more channels of a second type. The one or more channels of the first type include at least one of a channel corresponding to a portion of the spectral resource shared with a second radio

communication system or a channel corresponding to a portion of the spectral resource shared by a control channel of the first radio communication system. The controlling apparatus also comprises a determining unit configured to determine, in accordance with the

information acquired by the acquiring unit, whether a first condition is satisfied, the first condition including that an occupation ratio of the one or more channels of the second type is less than a first

threshold and an allocating unit configured to allocate, for the communication with the mobile station, a

channel of the second type when the first condition is satisfied, and a channel of the first type when the first condition is not satisfied.

[ 0010 ] According to the second aspect of the present invention, there is provided a method of allocating radio channels for communication with a mobile station in a first radio communication system in which a spectral resource is divided into a plurality of channels. The method comprises an acquiring step of acquiring information for distinguishing, out of the plurality of channels, one or more channels of a first type and one or more channels of a second type. The one or more channels of the first type include at least one of a channel corresponding to a portion of the spectral resource shared with a second radio

communication system or a channel corresponding to a portion of the spectral resource shared by a control channel of the first radio communication system. The method also comprises a first determining step of determining, in accordance with the information

acquired in the acquiring step, whether a first

condition is satisfied, the first condition including that an occupation ratio of the one or more channels of the second type is less than a first threshold and an allocating step of allocating, for the communication with the mobile station, a channel of the second type when the first condition is satisfied, and a channel of the first type when the first condition is not

satisfied.

[ 0011 ] By virtue of the above features, it is possible to reduce interference and improve quality in a radio communication system. [0012] Further features and advantages of the present invention will be apparent from the following description with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF DRAWINGS

[0013] Fig. 1 is an overall view illustrating coexisting first and second communication systems

according to some embodiments;

[0014] Fig. 2 is a functional block diagram of a base station controller of the first communication system according to some embodiments of the present invention;

[0015] Fig.s 3A, 3B and 3C are views illustrating the spectral resource available after spectrum re- farming according to some embodiments;

[0016] Fig. 4 is a chart showing a distribution of traffic channels (TCH) and broadcast control

channels (BCCH) before and after spectrum re-farming according to some embodiments;

[0017] Fig. 5 is a flowchart for describing

traffic channel allocation processing executed by a base station controller in the first communication system according to some embodiments;

[0018] Fig. 6 is a flowchart for describing

traffic channel allocation processing executed by a base station controller in the first communication system according to some embodiments; and

[0019] Fig. 7 is a flowchart for describing reconfiguration processing executed by a base station controller in the first communication system according to some embodiments.

DETAILED DESCRIPTION

[0020] Fig. 1 is an overall view illustrating embodiments of co-existing radio communication systems. Spectral re-farming has been performed, and frequencies of a first radio communication system 100 have been carved out for a second communication system 101.

Explanation will be given for embodiments in which the first communication system 100 is a GSM based system and the second communication system 101 is a UMTS based system. In other embodiments the second communication system 101 is a CDMA2000 based system or an LTE based system, for example.

[0021] The systems are divided into a plurality of cells. For simplicity, only three cells of each system are shown in Fig. 1. It should be understood that some embodiments will contain many more cells. The cells of the first communication system 100 physically overlap the cells in the second communication system 101. The cells of the first communication system 100 are

indicated by solid lines and the cells of the second communication system 101 are indicated by broken lines.

[0022] The first communication system 100 cells are each further divided into three sub-cells:

overlaid (OL) sub-cells; underlaid (UL) sub-cells; and interfered ( IL) sub-cells. The OL sub-cells are

indicated by dash-dot lines. Because the UL and IL sub-cells are the same size as the cells in the

embodiments according to Fig. 1, they are also shown by the solid lines that indicate the cells of the first communication system 100.

[0023] As shown in Fig. 1, the OL sub-cell has a smaller range, whereas the ranges of the UL and IL sub- cells are that of the entire cell. Transport channels of the cell are divided amongst these three sub-cells, based on uplink/downlink power strength, interference propensity, attenuation characteristics and the like. Detailed explanation of how the transport channels are divided amongst the sub-cells will be given below, with reference to Fig. 3A, Fig. 3B, Fig. 3C and Fig. 4.

[0024] Each of the cells of the first

communication system 100 has a corresponding base station (BS) 103 which contains equipment for

transmitting and receiving radio signals over a

plurality of radio frequencies. Similarly, each of the cells of the second communication system 101 has a corresponding base station (BS) 104. In Fig. 1, the BSs 103 and the BSs 104 are located in the center of the cells and communicate via omni-directional antennas. In other embodiments, the BSs 103 and/or the BSs 104 may be located at positions other than the center of the cells. In some embodiments the BSs 103 and/or the BSs 104 communicate with mobile stations 105 via

directional antennas. Fig. 1 illustrates embodiments where the BSs 103 and BSs 104 are co-located

(coordinated operation) . In other embodiments the BSs 103 and the BSs 104 are not co-located (uncoordinated operation), and have adjacent placement, for example.

[ 0025 ] The BSs 103 are controlled by a base

station controller (BSC) 200. In Fig. 1, all of the BSs 103 are controlled by one BSC 200. However, in other embodiments there may be multiple BSCs 200, each of which controls a subset of the BSs 103 in the system. The BSC 200 generally controls the BSs 103 and performs such tasks as radio channel allocation processing, for example. In some embodiments, the BSC 200 performs processing of measurement data received from mobile stations (MSs) 105 to determine a level of interference experienced by the mobile station 105, for example. In some embodiments, the functionality of the BSC 200 is implemented so as to have portions in multiple devices. In some embodiments functionality of the BSC 200 is incorporated into the BSs 103. In embodiments

according to Fig.l, the BSs 104 are controlled by a UMTS radio network controller (RNC) (not shown) , for example .

[0026] The BSs 103 communicate with mobile

stations 105 located in corresponding cells in

accordance with the GSM standard, for example.

Explanation will be given for embodiments in which mobile stations 105 communicate with the BSs 104 in accordance with a WCDMA (Wideband Code Division

Multiple Access) standard, for example. In other embodiments, this communication may be in accordance with CDMA2000, LTE or other standards.

[0027] A mobile station 105 in a cell is capable of performing communication, such as a telephone call, via a BS 103 corresponding to the cell. It should be understood that in some embodiments there will be many more mobile stations 105 than are illustrated in the exemplary Fig. 1. Mobile stations 105 may only be capable of communicating with the BSs 103, or may be capable of communicating with both the BSs 103 and the BSs 104. Other mobile stations that only communicate with the BSs 104 may exist in the system, but these are omitted from Fig. 1. Communication in the first communication system 100 may be realized through a connection to a mobile switching center (MSC) (not shown) connected to the public switched telephone network (PSTN) (not shown) , via a BS 103 and the BSC 200, for example. When a mobile station 105 makes or receives a call, the BSC 200 allocates a traffic channel, out of a plurality of channels into which a spectral resource of a corresponding BS 103 is divided, for communication with the mobile station 105.

[0028] Embodiments involve implementation of a method and apparatus for performing this traffic channel allocation in the first radio communication system 100. Using the IL sub-cell, interference can be reduced by allocating based on differing interference propensity with respect to intra-system or inter-system interference due to spectral re-farming, as will be explained in detail below. Also, using the OL and UL sub-cells, interference can be reduced by allocating in consideration of uplink/downlink power strength and anti-interference ability with respect to distance to the BS 103.

[0029] Fig. 2 is a functional block diagram of the

BSC 200 according to some embodiments of the present invention. The BSC 200 comprises a central processing unit (CPU) 201, a random access memory (RAM) 202, a read-only memory (ROM) 203, a storage unit 204, an acquiring unit 205, a determining unit 206, an

allocating unit 207, a reconfiguring unit 208, and a selecting unit 209.

[0030] The storage unit 204 is a device capable of storing data that the acquiring unit 205 is capable of acquiring. In some embodiments, the storage device is a built-in memory device, for example. [0031] In some embodiments, the functionality of the units 205-209 is implemented by the CPU 201

executing a software program stored in the ROM 203 using the RAM 202 as a work area. In other embodiments, the units 205-209 are implemented using dedicated hardware. In still other embodiments, the units 205- 209 are implemented using a combination of software and hardware. The detailed operation of the units 205-209 will be described later with reference to Fig.s 5-7.

[0032] Fig.s 3A, 3B and 3C are views illustrating the spectral resource available after the spectrum re- farming to the first communication system 100 and the second communication system 101 according to some embodiments. The horizontal axes represent frequency, whereas the vertical axes represent an amount of

electromagnetic radiation used in the corresponding frequencies. Note, that these diagrams are not to scale and are simplified for ease of explanation.

[0033] As can be seen from these figures, the frequency band of the first communication system 100 (GSM) is divided into a plurality of separate channels. On the other hand there is a smooth distribution of frequency usage spread across the frequency band

because this example corresponds to embodiments where the second communication system 101 is a WCDMA-based system.

[0034] Fig. 3A exemplifies embodiments in which an aggressive strategy is taken to minimize the carved out portion of the original frequency band of the first communication system 100. Frequencies are contiguously carved out of a central portion of the original frequency band of the first communication system 100 for the incoming second communication system 101. On either side of the carved out portion, there are frequencies which are available to both the first communication system 100 and the second communication system 101.

[0035] In other words, a BS 103 of the first communication system 100 will share channels

corresponding to a portion of its spectral resource with a BS 104 of the second communication system 101 corresponding to an overlapping cell of the second communication system 101. Such a strategy may be adopted because the amount of electromagnetic radiation due to communication in the second communication system 101 at the edges of the frequency band used by the second communication system 101 is less than that in the center of the band. Thus, even when the first communication system 100 and the second communication system 101 both use the same frequencies in the

overlapping portions, communication will be possible, albeit with higher levels of interference.

[0036] In other embodiments, a central portion of the original frequency band of the first communication system 100 is similarly carved out, but with less aggressive overlapping. In some embodiments a guard band is provided on one or both sides of the frequency band of the second communication system 101, which further reduces the remaining frequency band of the first communication system 100, but minimizes inter- system interference.

[0037] In other embodiments, the carved out portion is at one end of the original frequency band of the first communication system 100 as shown in Fig. 3B. In such cases as well, different degrees of

aggressiveness with respect to inter-system

interference due to overlapping may be taken.

[0038] In still other embodiments, in which the original first communication system 100 was a multi- band GSM network, an entire band is carved out for the second communication system 101, leaving only the other band for the first communication system 100 as shown in Fig. 3C.

[0039] Thus, in some embodiments, there will be channels that suffer from inter-system interference due to aggressive placement/overlapping of the second communication system 101. These may not simply include the channels corresponding to frequencies that directly overlap with frequencies of the second communication system 101. Channels of the first communication system 100 that are adjacent to frequencies of the second communication system 101 (as opposed to using directly overlapping frequencies) may also suffer from

interference due to the adjacency.

[0040] In addition, there are embodiments in which some channels will suffer from intra-system

interference. This may be because, due to the loss of channels to the spectral re-farming, it becomes

necessary for a BS 103 of the first communication system 100 to share a portion of its spectral resource between a traffic channel and a control channel such as a broadcast control channel (BCCH) , for example. This may be particularly pertinent in embodiments where spectral re-farming is performed with less aggressive frequency overlapping, because in such cases the reduction of the original spectral resource of the first communication system 100 due to the carving may be more severe.

[0041] The channels of the first communication system 100 that correspond to a portion of the spectral resource shared with the second communication system 101, or that correspond to a portion of the spectral resource shared by a control channel of the first communication system 100 can be identified

(predetermined) at the frequency planning stage. By allocating such channels in the IL sub-cell in

accordance with procedures explained in detail with reference to Fig. 5, Fig. 6 and Fig. 7 below, interference due to the spectral re-farming can be mitigated .

[0042] Fig. 4 is a chart showing a distribution of traffic channels (TCH) and broadcast control

channels (BCCH) of the first communication system 100 before and after spectrum re-farming, according to some embodiments. The chart of Fig. 4 corresponds to the carving scenario described above with reference to Fig. 3A, in which a central portion of the original spectrum of the first communication system 100 is carved out with overlapping.

[0043] Before the spectrum re-farming, the

spectral resource available is divided into contiguous channels (absolute radio-frequency channel number

(ARFCN) ) 75 through 125. Of these channels, ARFCN 75 to 92 were used for BCCH, and ARFCN 93 to 125 were used for TCH. In the spectrum re-farming, ARFCN 91 to 115 were carved out for the second communication system 101. ARFCN 91, 92, 114 and 115 are allowed to overlap

between the two systems 100 and 101. The channels available in the first communication system 100 after the carving are ARFCN 75 to 92 and 114 to 125. All of these channels are used for TCH. In addition, ARFCN 75 to 89 are shared between TCH and BCCH.

[0044] In this scenario, ARFCN 91, 92, 114 and 115 are predetermined to cause a certain level of inter- system interference when used as traffic channels in - li ^¬ the first communication system 100 because they are shared with the second communication system 101. Also, ARFCN 75 to 89 are predetermined to cause intra-system interference when used as traffic channels in the first communication system 100 because they are shared with control channels in the first communication system 100. So, these channels are categorized as "interfered channels". The remaining channels (ARFCN 116 to 125), which are not predetermined to cause the inter-system interference or intra-system interference, as described above, are categorized as "non-interfered channels".

[ 0045 ] In some embodiments, these "non-interfered channels" may be further divided into overlaid channels and underlaid channels in accordance with the power at which they are to be transmitted, anti-interference ability, propensity to attenuation, or the like. In some embodiments, the underlaid channels correspond to portions of the spectral resource in a first radio frequency band such as GSM900 for example, and the overlaid channels correspond to portions of the

spectral resource in a second radio frequency band such as GSM1800 for example. Note, the GSM1800 frequencies suffer more propagation attenuation than GSM900

frequencies. In some embodiments, the interfered channels correspond to frequencies in the lower

frequency band. In such cases, the GSM900 interfered channels and the GSM900 underlaid channels will have corresponding interference characteristics with respect to distance from the base station (propagation

attenuation characteristics, etc.), but differing interference characteristics due to channel sharing. Therefore, with such a configuration, allocation can be performed considering not only the band of a channel but also whether the channel is shared.

[0046] Information about the classification for distinguishing the types of the channels of the first communication system 100 is stored in the storage unit 204 of the corresponding BSC 200 of the first

communication system 100, for example. When the first communication system 100 is in operation, the BSC 200 acquires this information, and uses it to determine which channel to allocate for communication with a mobile station 105, as is described below in detail with reference to Fig. 5.

[0047] Fig. 5 is a flowchart for describing traffic channel allocation processing executed by a BSC 200 in the first communication system 100 according to some embodiments. This processing starts when a mobile station 105 in a cell corresponding to a BS 103

controlled by the BSC 200 either receives a call or initiates a call in the first communication system 100.

[0048] In step S501, the acquiring unit 205 acquires information, stored in the storage unit 204. This information is for distinguishing which of the plurality of channels, into which the spectral resource of the BS 103 is divided, correspond to channels of the above described interfered channels (channels of a first type) and which correspond to the above described non-interfered channels (channels of a second type) which include overlaid channels and underlaid channels.

[ 0049 ] Next, in step S502, the determining unit

206 determines whether an occupation ratio of non- interfered channels is less than a non-interfered channel threshold in accordance with the information acquired by the acquiring unit 205 in step S501. The occupation ratio is a ratio of a number of time slots of the non-interfered channels out of a total number of time slots of the non-interfered channels that are currently allocated and thus occupied. The time slots of this occupation ratio may correspond to half-rate time slots so as to maximize the number of calls allocated on non-interfered channels before allocating on interfered channels. In some embodiments, this threshold is predetermined based upon a necessity to maintain a reserve of non-interfered channels of a predetermined size. Such a reserve is maintained in order to accommodate features such as conversion of TCH timeslots into standalone dedicated control channel

(SDCCH) timeslots in cases of high SDCCH traffic, for example. Note that in some embodiments the non- interfered channel threshold is 100% and no reserve is maintained .

[0050] In a case where the determining unit 206 determines that the occupation ratio of non-interfered channels is less than the non-interfered channel

threshold, the processing proceeds to step S503 and the allocating unit 207 allocates, for the communication with the mobile station 105, a non-interfered channel. This allocation may be for a half-rate time slot or for a full-rate time slot, depending on the state of the system.

[0051] In a case where the determining unit 206 determines that the occupation ratio of non-interfered channels is greater than or equal to the non-interfered channel threshold, the processing proceeds to step S504, and the determining unit 206 determines whether an occupation ratio of interfered channels is less than an interfered channel threshold in accordance with the information acquired by the acquiring unit 205 in step S501. The occupation ratio is a ratio of a number of time slots of the interfered channels out of a total number of time slots of the interfered channels that are currently allocated and thus occupied. The time slots may be full-rate time slots or half-rate time slots. In some embodiments, this threshold is

predetermined based upon a necessity to maintain a reserve of interfered channels of a predetermined size. Note that in some embodiments the interfered channel threshold is 100% and no reserve is maintained.

[0052] In a case where the determining unit 206 determines that the occupation ratio of interfered channels is less than the interfered channel threshold, the processing proceeds to step S505 and the allocating unit 207 allocates an interfered channel. In some embodiments, this allocation is for a full-rate time slot. This is because these channels suffer more interference, and so preferentially allocating full- rate channel results in higher quality of calls in IL channels. In such embodiments, the time slots in the occupation ratio in step S504 correspond to full-rate time slots.

[0053] In a case where the determining unit 206 determines that the occupation ratio of interfered channels is greater than or equal to the interfered channel threshold, the processing proceeds to step S506, and the determining unit 206 determines whether an available non-interfered channel exists. Specifically, the determining unit 206 determines whether or not there is a half-rate time slot or a full-rate time slot for a non-interfered channel that can be allocated for communication with the mobile station 105.

[0054] In a case where the determining unit 206 determines that there is a time slot for a non- interfered channel that can be allocated, the

processing proceeds to step S507 and the allocating unit 207 allocates the non-interfered channel for which the time slot can be allocated. This allocation may be for a half-rate time slot or for a full-rate time slot.

[0055] In a case where determining unit 206 determines that there is no time slot for a non- interfered channel that can be allocated, the

processing proceeds to step S508, and the determining unit 206 determines whether an available interfered channel exists. Specifically, the determining unit 206 determines whether or not there is a half-rate time slot or a full-rate time slot for an interfered channel that can be allocated for communication with the mobile station 105.

[0056] In a case where the determining unit 206 determines that there is a time slot for an interfered channel that can be allocated, the processing proceeds to step S509 and the allocating unit 207 allocates the interfered channel for which the time slot can be allocated. This allocation may be for a half-rate time slot or for a full-rate time slot.

[0057] In a case where the determining unit 206 determines that there is no time slot for an interfered channel that can be allocated, the processing proceeds to step S510 and the processing ends in a TCH block

(allocation failure) .

[0058] By embodiments according to Fig. 5, it is possible to mitigate inter-system or intra-system interference due to the interfered channels by

postponing their allocation. Furthermore a reserve of non-interfered channels for dynamically accommodating features such as dynamic SDCCH timeslot allocation can be maintained.

[0059] Fig. 6 is a flowchart for describing

traffic channel allocation processing executed by a BSC 200 in the first communication system 100 according to some embodiments. In such embodiments, separate

thresholds are kept for each of the three types of channels: interfered channels (first type); overlaid channels (second type); underlaid channels (third type) . This processing starts when a mobile station 105 in a cell corresponding to a BS 103 controlled by the BSC 200 either receives a call or initiates a call in the first communication system 100. Steps common to Fig. 5 are labeled with the same reference number, and

explanation of these is omitted.

[0060] Note that in the embodiments of Fig. 6, the information acquired in step S501 is for distinguishing which of the plurality of channels of the BS 103

correspond to channels of the above described

interfered channels (first type), which correspond to the above described overlaid channels (second type) and which correspond to the underlaid channels (third type) .

[0061] In step S601, the determining unit 206 determines whether an occupation ratio of overlaid channels is less than an overlaid channel threshold in accordance with the information acquired by the

acquiring unit 205 in step S501. The occupation ratio is a ratio of a number of time slots of the overlaid channels out of a total number of time slots of the overlaid channels that are currently allocated and thus occupied. These time slots of this occupation ratio may correspond to half-rate time slots so as to

maximize the number of calls allocated on overlaid channels before allocating on interfered channels. In some embodiments, this threshold is predetermined based upon a necessity to maintain a reserve of overlaid channels of a predetermined size. Such a reserve is maintained in order to accommodate features such as conversion of TCH timeslots to SDCCH timeslots, as described above with reference to Fig. 5. Note that in some embodiments the overlaid channel threshold is 100% and no reserve is maintained.

[0062] In a case where the determining unit 206 determines that the occupation ratio of overlaid channels is less than the overlaid channel threshold, the processing proceeds to step S602 and the allocating unit 207 allocates an overlaid channel. This

allocation may be for a half-rate time slot or for a full-rate time slot, depending on the state of the system.

[0063] In a case where the determining unit 206 determines that the occupation ratio of overlaid

channels is greater than or equal to the overlaid channel threshold, the processing proceeds to step S603, and the determining unit 206 determines whether an occupation ratio of underlaid channels is less than an underlaid channel threshold in accordance with the information acquired by the acquiring unit 205 in step S501. The occupation ratio is a ratio of a number of time slots of the underlaid channels out of a total number of time slots of the underlaid channels that are currently allocated and thus occupied. The time slots of this occupation ratio may correspond to half-rate time slots so as to maximize the number of calls

allocated on underlaid channels before allocating on interfered channels. In some embodiments, this

threshold is predetermined based upon a necessity to maintain a reserve of underlaid channels of a

predetermined size. Such a reserve is maintained in order to accommodate features such as conversion of TCH timeslots to SDCCH timeslots, as described above with reference to Fig. 5. Note that in some embodiments the underlaid channel threshold is 100% and no reserve is maintained .

[ 0064 ] In a case where the determining unit 206 determines that the occupation ratio of underlaid channels is less than the underlaid channel threshold, the processing proceeds to step S604 and the allocating unit 207 allocates an underlaid channel. This

[0065] In a case where the determining unit 206 determines that the occupation ratio of underlaid channels is greater than or equal to the underlaid channel threshold, the processing proceeds to step S504. From step S504 onwards, the flowchart of Fig. 6 is the same as that of Fig. 5, and so explanation is omitted.

[0066] By the embodiments according to Fig. 6, inter-system or intra-system interference due to the interfered channels is mitigated by postponing their allocation. Additionally reserves of overlaid channels and underlaid channels for dynamically accommodating features such as dynamic SDCCH timeslot allocation can be maintained. At the same time, interference is reduced by allocating overlaid channels before

underlaid channels. In other words, the embodiments of Fig. 6 reduce interference based on both the

predetermined propensity of channels to interference due to the channels being shared, and the properties of the channels (power/attenuation) with respect to

distance from the BS 103.

[0067] Fig. 7 is a flowchart for describing

reconfiguration processing executed by a BSC 200 in the first communication system 100 according to some embodiments. This process is periodically performed in order to reconfigure communication with a mobile station 105 from an interfered channel (first type) to a non-interfered channel (second type) . This process may start after an interfered channel is allocated as in step S505 and step S509 of Fig.s 5 and 6.

[0068] In step S701, the determining unit 206 determines whether an occupation ratio of non- interfered channels is less than a second non- interfered channel threshold in accordance with the information acquired by the acquiring unit 205 in step S501 of Fig. 5 or Fig. 6. In some embodiments, this threshold is predetermined based upon a necessity to maintain a reserve of non-interfered channels of a predetermined size as described above. In at least one embodiment, the threshold is made to be a hysteresis threshold, smaller than the non-interfered threshold described with reference to Fig. 5, in order to avoid performance degrading ping-pong effects.

[0069] In a case where the determining unit 206 determines that the occupation ratio of non-interfered channels is less than the second non-interfered channel threshold, the processing proceeds to step S702. In a case where the determining unit 206 determines that the occupation ratio of non-interfered channels is greater than or equal to the second non-interfered channel threshold, step S701 is repeated according to a predetermined periodicity of the process.

[0070] In step S702, the selecting unit 209 selects a mobile station 105 from the plurality of mobile stations 105 for which an interfered channel has been allocated for communication based on a level of interference experienced by the mobile station 105. This level of interference is determined based on measurement information sent from the mobile stations 105 to the BS 103, for example. After the mobile station 105 is selected, the processing proceeds to step S703. Note, that in some embodiments, in step S702, the MS 105 is selected based on criteria other than the level of interference. For example, the MS 105 may be selected pseudo-randomly or based on a predetermined order.

[0071] In step S703, the reconfiguring unit 208 reconfigures the communication with the mobile station 105 selected in step S702 from the interfered channel to a non-interfered channel, and the processing returns to step S701.

[0072] By embodiments according to Fig. 7, inter- system or intra-system interference due to the

interfered channels is further reduced by reconfiguring communication over an interfered channel to a non- interfered channel. Furthermore, by selecting, for the reconfiguration, the mobile station 105 communicating over an interfered channel based on the level of interference experienced, the reduction in interference due to the reconfiguration is maximized.

[0073] As described above, according to the embodiments, a base station controller 200 of a first radio communication system 100 acquires information for distinguishing, out of a plurality of channels, which channels are interfered channels (i.e. which channels are shared with a second radio communication system 101 or with a control channel of the first radio

communication system 100) and which channels are non- interfered channels. The BSC 200 then uses this information to determine whether to allocate a non- interfered channel or an interfered channel, based upon an occupation ratio of the non-interfered channels.

[0074] Accordingly, these embodiments enhance performance by reducing interference in not only the first communication system 100, but also in the second radio communication system introduced in the spectrum re-farming. This results in lower rates of dropped calls, and higher quality and capacity of

communications .

[0075] The present invention is not limited to the above-described embodiments, and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to apprise the public of the scope of the present invention, the following claims are made.

Claims

1. A controlling apparatus (200) capable of

allocating radio channels for communication with a mobile station (105) in a first radio communication system (100) in which a spectral resource is divided into a plurality of channels, the controlling apparatus comprising :

an acquiring unit (205) configured to acquire information for distinguishing, out of the plurality of channels, one or more channels of a first type and one or more channels of a second type, the one or more channels of the first type including at least one of a channel corresponding to a portion of the spectral resource shared with a second radio

communication system (101) or

a channel corresponding to a portion of the spectral resource shared by a control channel of the first radio communication system;

a determining unit (206) configured to determine, in accordance with the information acquired by the acquiring unit, whether a first condition is satisfied, the first condition including that an occupation ratio of the one or more channels of the second type is less than a first threshold; and

an allocating unit (207) configured to allocate, for the communication with the mobile station, a channel of the second type when the first condition is satisfied, and a channel of the first type when the first condition is not satisfied.

2. The controlling apparatus according to claim 1, wherein the one or more channels of the second type comprise one or more overlaid channels and one or more underlaid channels.

3. The controlling apparatus according to claim 1, wherein :

the information further distinguishes, out of the plurality of channels, one or more channels of a third type,

the one or more channels of the second type comprise one or more overlaid channels, and

the one or more channels of the third type comprise one or more underlaid channels,

and wherein the determining unit is further configured to

determine whether or not a second condition is satisfied, the second condition including that an occupation ratio of the one or more channels of the third type is less than a second threshold,

and wherein the allocating unit is further configured to:

allocate, for the communication with the mobile station, a channel of the third type when the first condition is not satisfied and the second

condition is satisfied, and

the channel of the first type when neither the first condition nor the second condition is satisfied.

4. The controlling apparatus according to any one of claims 1 - 3, wherein:

the determining unit is further configured to determine whether or not a third condition is satisfied, the third condition including that the occupation ratio of the one or more channels of the second type is less than a third threshold; and further comprising

a reconfiguring unit (208) configured to

reconfigure the communication with the mobile station from the channel of the first type allocated by the allocating unit to a channel of the second type when the third condition is satisfied.

5. The controlling apparatus according to claim 4, wherein the third threshold is smaller than the first threshold .

6. The controlling apparatus according to claim 4 or 5, further comprising:

a selecting unit (209) configured to select, based on a level of interference, the mobile station from a plurality of mobile stations for which a channel of the first type has been allocated for communication, wherein the reconfiguring unit is further

configured to reconfigure the communication with the mobile station selected by the selecting unit.

7. The controlling apparatus according to any one of claims 1 - 6, wherein the determining unit is further configured to determine in accordance with the

information acquired by the acquiring unit:

whether or not a fourth condition is satisfied, the fourth condition including that an occupation ratio of the one or more channels of the first type is less than a fourth threshold;

whether or not a fifth condition is satisfied, the fifth condition including that an available channel of the second type exists; and

whether or not a sixth condition is satisfied, the sixth condition including that an available channel of the first type exists, and

wherein the allocating unit is further configured to allocate, for the communication with the mobile

station :

the channel of the first type when the first condition is not satisfied and the fourth condition is satisfied, a channel of the second type when neither the first condition nor the fourth condition is satisfied and the fifth condition is satisfied, and

a channel of the first type when neither the first condition, the fourth condition, nor the fifth condition is satisfied and the sixth condition is satisfied.

8. The controlling apparatus according to claim 7, wherein

the occupation ratio of the one or more channels of the first type for the fourth condition is an

occupation ratio with respect the a full-rate time slot, and

the allocating unit is further configured to:

allocate a full-rate time slot when allocating the channel of the first type when the first condition is not satisfied and the fourth condition is satisfied, and allocate a half-rate time slot when

allocating the channel of the first type when neither the first condition, the fourth condition, nor the fifth condition is satisfied and the sixth condition is satisfied.

9. The controlling apparatus according to claim 3, wherein

the one or more underlaid channels correspond to portions of the spectral resource in a first radio frequency band and the one or more overlaid channels correspond to portions of the spectral resource in a second radio frequency band, no frequency of which is included in the first radio frequency band,

and wherein the one or more channels of the first type correspond to portions of the spectral resource in the first radio frequency band.

10. The controlling apparatus according to any one of claims 1 - 9 wherein:

the occupation ratio of the one or more channels of the second type is an occupation ratio of half-rate time slots of the one or more channels of the second type .

11. A method of allocating radio channels for

communication with a mobile station (105) in a first radio communication system (100) in which a spectral resource is divided into a plurality of channels, the method comprising:

an acquiring step (S501) of acquiring information for distinguishing, out of the plurality of channels, one or more channels of a first type and one or more channels of a second type, the one or more channels of the first type including at least one of

a channel corresponding to a portion of the spectral resource shared with a second radio

communication system (101) or

a first determining step (S502, S601) of

determining, in accordance with the information

acquired in the acquiring step, whether a first

condition is satisfied, the first condition including that an occupation ratio of the one or more channels of the second type is less than a first threshold; and

an allocating step (S503, S505, S507, S509, S602, S604) of allocating, for the communication with the mobile station, a channel of the second type when the first condition is satisfied, and a channel of the first type when the first condition is not satisfied.

12. The method according to claim 11, wherein the one or more channels of the second type comprise one or more overlaid channels and one or more underlaid channels .

13. The method according to claim 11, wherein:

and further comprising

a second determining step (S603) of

determining whether or not a second condition is satisfied, the second condition including that an occupation ratio of the one or more channels of the third type is less than a second threshold

wherein the allocating step comprises:

allocating, for the communication with the mobile station,

a channel of the third type when the first condition is not satisfied and the second

condition is satisfied, and

14. The method according to any one of claims 11 - 13, further comprising:

a third determining step (S701) of determining whether or not a third condition is satisfied, the third condition including that the occupation ratio of the one or more channels of the second type is less than a third threshold; and

a reconfiguring step (S703) of reconfiguring the communication with the mobile station from the channel of the first type allocated in the allocating step to a channel of the second type when the third condition is satisfied.

15. The method according to claim 14, wherein the third threshold is smaller than the first threshold.

16. The method according to claim 14 or 15, further comprising :

a selecting step (S702) of selecting, based on a level of interference, the mobile station from a plurality of mobile stations for which a channel of the first type has been allocated for communication,

wherein the reconfiguring step reconfigures the communication with the mobile station selected in the selecting step.

17. The method according to any one of claims 11 - 16, further comprising:

a fourth determining step (S504) of determining, in accordance with the information acquired in the acquiring step, whether or not a fourth condition is satisfied, the fourth condition including that an occupation ratio of the one or more channels of the first type is less than a fourth threshold;

a fifth determining step (S505) of determining whether or not a fifth condition is satisfied, the fifth condition including that an available channel of the second type exists; and

a sixth determining step (S506) of determining whether or not a sixth condition is satisfied, the sixth condition including that an available channel of the first type exists, and

wherein the allocating step comprises:

allocating, for the communication with the mobile station,

the channel of the first type when the first condition is not satisfied and the fourth

condition is satisfied,

a channel of the second type when neither the first condition nor the fourth condition is

satisfied and the fifth condition is satisfied, and

18. The method according to claim 17, wherein

occupation ratio with respect the a full-rate time slot, and

the allocating of the channel of the first type when the first condition is not satisfied and the fourth condition is satisfied includes allocating a full-rate time slot,

and the allocating of the channel of the first type when neither the first condition, the fourth condition, nor the fifth condition is satisfied and the sixth condition is satisfied includes allocating a half-rate time slot.

19. The method according to claim 13, wherein

20. The method according to any one of claims 11 - 19 wherein :

21. A program for causing a computer to execute the method according to any one of claims 11 - 20.

22. A non-transitory computer-readable storage medium storing a program for causing a computer to execute the method according to any one of claims 11 - 20.