WO2010124729A1

WO2010124729A1 - Spectrum arrangement for co-channel interference reduction

Info

Publication number: WO2010124729A1
Application number: PCT/EP2009/055185
Authority: WO
Inventors: Hai Jiang; Ye Wu; Yi Wu; Dong Mei Zhang
Original assignee: Nokia Siemens Networks Oy
Priority date: 2009-04-29
Filing date: 2009-04-29
Publication date: 2010-11-04

Abstract

The described subject matter relates to a wireless communication system (100) with a first base station (102) serving a first cell which overlaps with a second cell of a second base station (108a-c). A second frequency spectrum (114) usable by the second base station (108a-c) overlaps with a shared spectrum part (116) of a first frequency spectrum (112) usable by the first base station (102). The remaining dedicated spectrum part (118) of the first frequency spectrum (112) is exclusively provided for communication of the first base station (102). For an user equipment (104a-f) which communicates with the first base station (102) a threat indicating quantity indicative of a threat of the user equipment (104a-f) of causing interference in the second cell is determined. The first base station (102) communicates with the user equipment (104a-f) by using only the dedicated spectrum part (118) if the threat indicating quantity indicates that the user equipment (104a-f) provides a threat of causing interference in the second cell.

Description

Spectrum arrangement for co-channel interference reduction

Field of the invention

The present invention relates to the field of wireless communication networks which include two base stations with overlapping cells and overlapping frequency spectrums .

Art background

Advanced wireless communication networks may include two types of base stations for serving a user equipment. For example, femto cells which are small, low cost cellular base stations are considered for improving indoor coverage. Femto cells are small cellular access points that connect to a mobile operator' s network using residential DSL or cable broadband connections. The concept of a femto cell provides a base station cheap enough to be deployed in high volume for residential use, connected to the core network via broadband. This could deliver a higher connection quality while allowing to use existing standard user equipments.

In order to mitigate interference, some wireless communication systems employ intracell orthogonality among users and mitigate intercell interference through fractional frequency reuse (e.g. LTE (long-term evolution) or WiMAX (worldwide interoperability of microwave access) ) .

In view of the above-described situation, there exists a need for a technique that provides improved characteristics regarding intercell interference. Summary of the invention

This need may be met by the subject-matter according to the independent claims. Advantageous embodiments of the herein disclosed subject-matter are described by the dependent claims .

According to a first aspect of the invention, there is provided a method of operating a first base station of a wireless communication system in which the first base station is configured for being capable of communicating with user equipments in a first region by using a first frequency spectrum. A second base station is configured for being capable of communicating with user equipments in a second region by using a second frequency spectrum. In this wireless communication system, the second region is at least partially located in the first region and the second frequency spectrum overlaps with a shared spectrum part of the first frequency spectrum. Hence, the first frequency spectrum comprises a dedicated spectrum part exclusively provided for communication of the first base station and the shared spectrum part usable by the first base station and the second base station. The method according to the first aspect comprises determining for an user equipment, which communicates with the first base station, a threat indicating quantity indicative of a threat of the user equipment of causing interference in the second region. Depending on the threat indicating quantity, the first base station communicates with the user equipment by using only the dedicated spectrum part.

For example, according to an embodiment, for a first state or range or value of the threat indicating quantity the first base station communicates with the user equipment by using only the dedicated spectrum part, while for different, second state or range or value of the threat indication quantity the first base station communicates with the user equipment by using the shared spectrum part or the whole first frequency spectrum. It should be noted that herein the terms "state", "range" or "value" are interchangeable. For example, embodiments which refer e.g. to a value of the threat indicating quantity are considered to implicitly disclose the reference to a range or state of the threat indicating quantity.

The first aspect of the invention is based on the idea that interference can be reduced by determining for each user equipment which communicates with the first base station whether the user equipment provides a threat of causing interference in the second region and communicating with such user equipments, which provide a threat of causing interference, only on the dedicated spectrum part which is exclusively provided for communication of the first base station and which is thus not used by the second base station .

According to an embodiment, the method comprises receiving from a network element, which is e.g. operated by an operator of the second base station, the frequency range of the second frequency spectrum.

According to an embodiment, the user equipments are categorized into user equipments which provide a threat of causing interference and user equipments which do not provide a threat of causing interference. According to a further embodiment, the user equipments which are categorized as providing a threat of causing interference are considered as belonging to an interference pool.

According to an embodiment, the first base station receives information about the second frequency spectrum from a network element of the wireless communication system, e.g. a network element operated by an operator.

According to an embodiment, the first base station is a macro base station which operates according to a particular wireless communication standard.

According to a further embodiment, the second base station has a coverage which is smaller than the coverage of the first base station, i.e. the first region is larger than the second region. For example, according to an embodiment, the second base station is a femto base station.

According to a further embodiment, the method according to the first aspect comprises comparing the threat indicating quantity with a predetermined threshold. In such a case, communicating with the user equipment by using only the dedicated spectrum part is performed depending on the relation of the threat indicating quantity to the predetermined threshold. For example, according to an embodiment the first base station communicates with the user equipment by using only the dedicated spectrum part if the threat indicating quantity is higher (or, according to another embodiment, lower) than a predetermined threshold. However, it should be understood that the action which is performed depending on the relation of the threat indicating quantity to the predetermined threshold depends on the nature of the threat indicating quantity.

According to an embodiment, the threat indicating quantity is a user equipment moving speed. According to an embodiment, determining the threat indicating quantity comprises detecting a moving speed of the user equipment. For example, according to an embodiment, the threat of causing interference is judged as being low if a moving speed of the user equipment is above a predetermined threshold. Taking into account the moving speed of the user equipment allows the determination whether the user equipment provides a threat of causing interference or not with comparably low effort.

According to an embodiment, determining the threat indicating quantity comprises selectively determining a channel quality indicator for the shared spectrum part. For example, according to an embodiment, the absolute value of the channel quality indicator for the shared spectrum part is taken into account for determining the threat indicating quantity. According to other embodiments, the relative value of the channel quality indicator for the shared spectrum part is taken into account for determining the threat indicating quantity. For example, according to an embodiment, the difference between the channel quality indicator for the shared spectrum part and the channel quality indicator for the dedicated spectrum part is used as threat indicating quantity. According to other embodiments, the difference between the channel quality indicator for the shared spectrum part and the channel quality indicator for the whole spectrum is used as threat indicating quantity.

According to a further embodiment of the first aspect, determining the channel quality indicator comprises indicating to the user equipment the frequency range of the shared spectrum part. According to a further embodiment, indicating to the user equipment the frequency range of the shared spectrum part comprises indicating to the user equipment the mapping of the second frequency spectrum on the sub-bands of the first frequency spectrum. For example, according to a further embodiment, indicating to the user equipment the frequency range of the shared spectrum part comprises indicating to the user equipment the mapping of a femto spectrum on macro cell sub-bands.

Briefly speaking, an embodiment of the first aspect corresponds to a method of operating a first base station, wherein the first base station is configured for being capable of communicating by using a dedicated spectrum part, exclusively reserved for the first base station, and a shared spectrum part which is usable by the first base station and other base stations, and wherein the method comprises detecting the user equipments with potential threat of co- channel interference with the second base station. Further, according to an embodiment, the detected use equipment (s) , which have a potential threat of causing interference in the cell (s) spanned by the at least one second base station, are allocated with the dedicated spectrum part (clear part of the spectrum) which has no frequency overlap with the second base station (s) .

According to a further embodiment of the first aspect, the frequency range of the shared spectrum is indicated to the user equipment in a broadcasting message. For example, the user equipment can store the frequency range indication provided by the first base station in its memory and selectively report the channel quality indicator for the shared spectrum part automatically, e.g. without further indication of the shared spectrum part by the first base station. In such an embodiment, the user equipment needs to be aware of embodiments of the herein disclosed subject- matter .

According to a further embodiment, the frequency range of the shared spectrum is indicated to the user equipment in a request message requesting transmission of a channel quality indicator of the frequency range of the shared spectrum part. In this way, the user equipment can be any standard user equipment which is not aware of embodiments of the herein disclosed subject-matter.

According to a second aspect of the herein disclosed subject- matter, a method of operating a user equipment is provided, wherein the user equipment communicates with a first base station by using a first frequency spectrum. The method according to the second aspect further comprises receiving an indication of a second frequency range of a second frequency spectrum which is usable by a second base station. The second frequency spectrum overlaps with a shared part of the first frequency spectrum, such that the first frequency spectrum comprises a dedicated spectrum part and a shared spectrum part, wherein the dedicated spectrum part is exclusively provided for communication of the first base station and the shared spectrum part usable by the first base station and by the second base station. According to an embodiment, the method according to the second aspect comprises determining a channel quality indicator for the shared spectrum part. According to an embodiment of the second aspect, the channel quality indicator of the shared spectrum part is considered as a threat indicating quantity as used herein.

According to an embodiment, the method comprises determining a channel quality indicator for the first frequency spectrum. According to a further embodiment, the method comprises determining a channel quality indicator for the dedicated spectrum part.

According to an embodiment, the indication of the second frequency range is received from the first base station which is capable of communicating with user equipments by using the first frequency spectrum.

According to an embodiment, an indication of the first frequency range is received from the first base station. According to another embodiment, the user equipment comprises a measurement unit for determining the first frequency range.

According to an embodiment, the channel quality indicator for the shared spectrum part is determined by the user equipment upon request of the first base station or, according to another embodiment, upon receiving the indication of the second frequency range.

According to a third aspect of the herein disclosed subject- matter, a computer program is provided for determining and/or processing a physical object, namely a threat indicating quantity indicative of a threat of a user equipment of causing interference. According to an embodiment of the third aspect, the computer program, when being executed by a data processor, is adapted for controlling the method according to the first aspect or an embodiment thereof. According to a further embodiment of the third aspect, the computer program, when being executed by a data processor, is adapted for controlling the method according to the second aspect or an embodiment thereof.

According to an embodiment, the computer program is provided for determining the physical object. According to an embodiment, the computer program is provided for processing the physical object. According to a further embodiment, the computer program is provided for determining and processing the physical object.

According to a fourth aspect, a base station of a wireless communication system is provided. The wireless communication system comprises the base station as a first base station configured for being capable of communicating with a user equipment in a first region, e.g. a macro cell, by using a first frequency spectrum. The wireless communication system further comprises a second base station, for example a femto base station, configured for being capable of communicating with user equipments in a second region, e.g. a femto cell, by using a second frequency spectrum. The second region is at least partially located in the first region. Further, the second frequency spectrum overlaps with a shared spectrum part of the first frequency spectrum. Hence, the first frequency spectrum comprises a dedicated spectrum part exclusively provided for communication of the first base station and a shared spectrum part usable by the first base station and the second base station. The base station according to the fourth aspect comprises a controller for determining for a user equipment communicating with the first base station a threat indicating quantity, wherein the threat indicating quantity is indicative of a threat of the user equipment of causing interference in the second region.

According to embodiments of the fourth aspect, the thread indicating quantity may be e.g. a user equipment moving speed, a difference of channel quality indicator values for the shared spectrum part and the dedicated spectrum part, etc.

The base station according to the fourth aspect, i.e. the first base station, is configured for communicating with the user equipment by using only the dedicated spectrum part depending on the threat indicating quantity.

According to a further embodiment, the controller of the base station according to the fourth aspect comprises a comparator for comparing the threat indicating quantity with a predetermined threshold and a spectrum selector for selecting only the dedicated spectrum part for communication with the user equipment depending on the comparison of the threat indicating quantity with the predetermined threshold.

According to a further embodiment, the controller of the base station according to the fourth aspect further comprises a speed determination unit for determining moving speed of the user equipment as the threat indicating quantity.

According to a further embodiment, the controller of a base station according to the fourth aspect comprises a channel quality determination unit for determining a channel quality indicator for the shared spectrum. For example, the channel quality determination unit may be configured for receiving the channel quality indicator from the user equipment.

According to a further embodiment, the controller of a base station according to the fourth aspect comprises the user equipment information unit for indicating to the user equipment the frequency range of the shared spectrum part. For example, according to an embodiment, indicating to the user equipment the frequency range of the shared spectrum part comprises indicating to the user equipment the mapping of the shared spectrum part on sub-bands of the first frequency spectrum. According to an embodiment, indicating to the user equipment the frequency range of the shared spectrum part comprises sending to the user equipment a message comprising a frequency range indicator which is indicative of the frequency range of the shared spectrum part.

According to a fifth aspect of the herein disclosed subject- matter, a user equipment for a wireless communication network is provided, the user equipment comprising a communication unit for communication with a first base station by using a first frequency spectrum and a receiving unit for receiving an indication of a frequency range of a second frequency spectrum which is usable by a second base station. According to the fifth aspect, the second frequency spectrum overlaps with a shared spectrum part of the first frequency spectrum, the first frequency spectrum thus comprising a dedicated spectrum part exclusively provided for communication of the first base station (e.g. with the user equipment) and the shared spectrum part which is usable by the first base station but is also usable by the second base station.

According to an embodiment of the fifth aspect, the user equipment comprises a channel quality determination unit for determining a channel quality indicator for the shared spectrum part. According to an embodiment, the channel quality determination unit is configured for measuring the channel quality of the shared spectrum part.

As used herein, reference to a computer program is intended to be equivalent to a reference to a program element and/or a computer-readable medium containing instructions for controlling a computer system to coordinate carrying out the method according to the first aspect or an embodiment thereof or to coordinate carrying out the method according to the second aspect or an embodiment thereof. The computer program may be implemented as computer-readable instruction code by use of any suitable programming language, such as, for example, JAVA, C++, etc. and may be stored on a computer-readable medium (removable disk, volatile or non- volatile memory, embedded memory/processor, etc.) . The instruction code is operable to program a computer or any other programmable device to carry out the intended function. The computer program may be available from a network, such as the WorldWideWeb, from which it may be downloaded. According to an embodiment, the computer program is a full release of software. According to other embodiments, the computer program is an update for an existing software.

Accordingly, the herein disclosed subject-matter or at least parts thereof may be realized by means of a computer program respectively software. However, the invention may also be realized by means of one or more specific electronic circuits respectively hardware. Furthermore, the invention may also be realized in a hybrid form, i.e. in a combination of software modules and hardware modules.

In the following, there will be described exemplary embodiments of the subject-matter disclosed herein with reference to a method of operating a first base station, a method for operating a user equipment, a base station and a user equipment. It has to be pointed out that of course any combination of features relating to different aspects of the herein disclosed subject-matter is also possible. In particular, some embodiments have been described with reference to apparatus type claims whereas other embodiments have been described with reference to method type claims. However, a skilled person will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one aspect also any combination between features relating to different aspects or embodiments, for example even between features of the apparatus type claims and features of the method type claims, as well as features of the base station related claims and features of the user equipment related claims is considered to be disclosed with this application.

The aspects and embodiments defined above and further aspects and embodiments of the herein disclosed subject-matter are apparent from the examples described hereinafter and are explained with reference to the drawings, but to which the herein disclosed subject-matter is not limited.

Brief description of the drawings

Fig. 1 illustrates a wireless communication system in accordance with embodiments of the herein disclosed subject- matter.

Fig. 2 shows a spectrum arrangement according to embodiments of the herein disclosed subject matter.

Fig. 3 shows a further wireless communication system in accordance with embodiments of the herein disclosed subject matter .

Fig. 4 illustrates frequency dependent scheduling for a macro base station without awareness of a femto cell.

Fig. 5 illustrates a femto cell aware spectrum arrangement for a macro base station according to embodiments of the herein disclosed subject-matter. Fig. 6 shows components of a wireless communication system according to embodiments of the herein disclosed subject matter.

Detailed description

The illustration in the drawings is schematic. It is noted that in different figures, similar or identical elements are provided with the same reference signs or with reference signs which are different from the corresponding reference signs only within the first digit or an appended character.

Embodiments of the herein disclosed subject-matter deal with mitigation of interference of overlapping regions of coverage of a first and a second base station. In a case of absence of coordination between the base stations, for example between a macro base station and a femto base station, the intercell interference may be significant around the edge of the over- lap, e.g. around the edge of a femto cell located within a macro cell.

If the spectrum of the different base stations is totally separate from each other, the co-channel interference between the cells of the two base stations could be avoided. However, this kind of configuration reduces the efficiency of the spectrum usage and therefore it is expensive for the opera^¬ tors to reserve a particular frequency resource for a base station with a comparably small coverage region. An alterna- tive hereto is to let the base stations with small coverage (second base station) use the same spectrum as the base sta^¬ tions with large coverage (first base station) , wherein the co-channel interference could be tolerable due to the limited power of the base station with small coverage. However, the user equipment communicating with the base station of large coverage which is located around the edge of the cell of the base station with small coverage would lead to high interference on the cell of the base station with small coverage. To solve this problem, the partial co-channel configuration is proposed.

Fig. 1 shows a wireless communication system 100 according to embodiments of the herein disclosed subject-matter. A first base station 102 is configured for being capable of communicating with user equipments 104a-f in a first region 106 by using a first frequency spectrum.

At least one second base station 108a-c is configured for be^¬ ing capable of communicating with user equipments in a second region llOa-c by using a second frequency spectrum. The second region llOa-c is located at least partially in the first region 106 of the first base station 102.

The spectrum arrangement in frequency f for the first base station and the second base station according to embodiments of the herein disclosed subject-matter is illustrated in Fig. 2. The first frequency spectrum, indicated at 112 in Fig. 2, and the second frequency spectrum, indicated at 114 in Fig. 2 overlap to a certain extent, defining a shared spectrum part 106 of the first frequency spectrum 112. Hence, the first frequency spectrum 112 thus comprises a dedicated spectrum part 118 exclusively provided for communication of the first base station 102 and the shared spectrum part 116 usable by the first base station 102 and the second base station 108a- c. According to an embodiment, where two or more second base stations 108a-c are located such that their second regions (cells) overlap with the first region 106, these second base stations may operate on different second frequency spectrums or on the same second frequency spectrum.

Having now again regard to Fig. 1, an embodiment of a method of operating the first base station 102 comprises determining for a user equipment, e.g. the user equipment 104e, which communicates with the first base station 102, a threat indi^¬ cating quantity indicative of a threat of the user equipment 104e of causing interference in the second region 110a of the second base station 108a. Depending on the threat indicating quantity for the user equipment under consideration, i.e. 104e in the present case, the first base station 102 communicates with the user equipment 104e by using only the dedicated spectrum part 118.

According to an embodiment, the first base station 102 is a macro base station, e.g. a base station operating according to the LTE (long-term evolution) or WiMAX (worldwide interoperability for microwave access) . According to a further embodiment, the second base stations 108a-c are femto base sta^¬ tions, i.e. cellular access points that connect to a mobile operator's network using residential DSL or cable broadband connections. However, according to other embodiments, the first base station 102 as well as the second base station 108a-c operate according to other standards. In this sense, the herein disclosed subject-matter is applicable to any com- bmation of base stations which have an overlapping region of communication and overlapping frequency spectrums. According to an embodiment, the threat indicating quantity determined for a particular user equipment is compared with a predetermined threshold, wherein the first base station 102 communicates with this particular user equipment by using the dedicated spectrum part 118 depending on the relation of the threat indicating quantity to the predetermined threshold.

For example, according to an embodiment, the threat indicating quantity is a moving speed of the user equipment. Hence, according to an embodiment, the first base station 102 uses the knowledge of the user equipment moving speed as one criterion for estimating if the user equipment is a potential threat over the cell of the second base station 108a-c. The user equipment moving speed can be evaluated by Doppler fre- quency estimation of received reference signals. Also other mechanisms, such as handover may also need the information of the user equipment moving speed as an assistant, and, there^¬ fore, this may not be an increased burden for the base station functionality. By roughly estimating the moving speed of the user equipment, the base station can exclude those user equipments with high speed from being a potential threat of causing interference in the second region 110a of the second base station 110a.

According to an embodiment, the user equipments communicating with the first base station 102 are categorized into belonging to an interference pool or belonging not to the interfer^¬ ence pool. For example, those user equipments which represent a potential threat of causing interference in the second re- gion of a second base station, may be judged as belonging to the interference pool. Deciding whether a user equipment be^¬ longs to the interference pool or not may be done by compar- ing the threat indicating quantity of the user equipment with the above-mentioned predetermined threshold. For example, user equipments having a moving speed which is larger than a predetermined moving speed threshold may be judged as not be- longing to the interference pool. The interference pool is exemplarily indicated at 120 in Fig. 1. The reason, why user equipments having a high moving speed are excluded from the interference pool is that they are supposed not to be in or around the second region 110a for non-negligible time consid- ering the fact that the second region 110a is smaller than the first region 106 in an embodiment. For example, in the case that the second region is a femto cell, the size of the second region is about the size of a building and hence quite small compared to a cell of a first base station in the form of an LTE or WiMAX base station. In the exemplary example shown in Fig. 1, the user equipments 104b and 104d have a user equipment moving speed above a predetermined threshold, indicated by a moving vector 122 in Fig. 1.

Other embodiments of determining a threat indicating quantity involve determination of a channel quality indicator for the shared spectrum part 116 of the first frequency spectrum 102. For example, according to an embodiment, when the sub-bands of the first base station are configured for channel quality indicator reporting (CQI reporting) , the first base station 102 makes sure that the second spectrum 114 of the second base station 108a-f does not span over any sub-band boundary of the first base station, so that the second spectrum 114 can be mapped to a subset of the sub-bands of the first base station 102. There are several alternative ways for the first base station 102 to distinguish the connected user equipments from being an interference threat for the second region of the second base stations, e.g. the femto cells: First, if the user equipment supports CQI reporting of all sub-bands, the first base station 102 can categorize the re^¬ porting user equipments 104 into the interference pool 120 if it is detected that the CQI values of the sub-bands belonging to the dedicated spectrum 118 of the first frequency spectrum 112 are comparably higher than those belonging to the second frequency spectrum 114. This can be understood by taking into account that in the case of co-channel interference between the first frequency spectrum 112 and the second frequency spectrum 114, the CQI value is lower for the shared spectrum part 116.

Second, if the user equipment reports CQI reporting of part of the sub-bands, according to an embodiment the user equipment selects a set of M sub-bands corresponding to the shared spectrum part 116 and reports a CQI value reflecting trans^¬ mission only over the M selected sub-bands. Additionally, the user equipment is further configured to also report the wide band CQI value, i.e. the CQI value for the whole first fre^¬ quency spectrum 112. Alternatively, according to a further embodiment, the user equipment is configured to report a CQI value for the dedicated spectrum part 118 instead of reporting a CQI value for the whole first frequency spectrum 112. Depending on the received CQI values, the first base station 102 detects that if the CQI value over the shared spectrum part 116 is lower than the wide band CQI value, the user equipment presents a threat of causing interference in the second region of the second base station 108a and categorizes the respective user equipment into the interference pool 120. For example, according to an embodiment, the first base station 102 categorizes the user equipment into the interference pool 120 if the CQI value over the shared spectrum part 116 is lower than the wide band CQI value over the whole first frequency spectrum 112 by a predetermined value. In this regard, being lower by a predetermined value includes being lower by a predetermined absolute value or being lower by a predetermined relative value, e.g. percentage.

The user equipment selected sub-band feedback can be done in two alternative ways:

First, the first base station 102 involves the mapping of the sub-bands to the shared spectrum part 116 and the dedicated spectrum 118 in a broadcasting system message and therefore the user equipment needs to be configured to store the mapping in its own memory and selectively report the M sub-bands automatically. In this way, the user equipment is aware of the method according to the herein disclosed subject-matter or an embodiment thereof. Making the user equipment aware of the matter according to the herein disclosed subject-matter can be done by e.g. a software update.

Second, the first base station 102 notifies the user equip^¬ ment to select the required M sub-bands by sending a higher layer message and the user equipment reports the channel quality information of the sub-bands according to the noti- fied required M sub-bands. Notifying the user equipment by the required M sub-bands can be performed by sending a sub- band index of the M sub-bands to the user equipment. In such an embodiment, the user equipment is not aware of methods according to the herein disclosed subject-matter and the lmple- mentation thereof is only required at the first base station 102. According to an embodiment, for the above comparisons between the CQI values of the shared spectrum part 116 and the dedicated spectrum part 118 (or the wide band spectrum 112 in another embodiment) , there is predefined a threshold in the first base station 102 as the criterion of detected interference between the cell 106 spanned by the first base station 102 and the cell 110a-c spanned by the second base station 108a-c, e.g. between the femto cell and macro cell. Whenever the CQI difference between the shared spectrum part 116 and the dedicated spectrum part 118 or the wide band spectrum 112 goes below the predetermined threshold, the first base station 102 excludes the reporting user equipment from the interference pool 120 immediately, since there is no danger of interference .

Since the first base station 102 can also measure the channel quality of the user equipment 104a-f in the uplink direction, the first base station can similarly distinguish the femto interfering user equipment 104e,f with the knowledge of sub- bands mapping to the shared spectrum part 116. Practically, the first base station 102 can make a decision of categoriz^¬ ing a user equipment 104e, f into the interference pool 120 based on both of the downlink CQI reports and the uplink channel measurements. However, it is noted that the downlink CQI reports are much more important than the uplink measure^¬ ments due to the fact that the downlink traffic is usually dominant in the cell of the second base station 108a-c and the user equipment communicating with the second base station (not shown in Fig. 1) may not be located near the edge of the second region 110a-c, i.e. the cell spanned by the second base station 108a-c. Therefore, even when the user equipment communicating with the first base station 102 is falling into an interference area where it is a threat of causing inter- ference in the second region, the first base station 102 may possibly not able to distinguish it from the channel quality measurements only in the uplink direction.

In accordance with embodiments mentioned before, the user equipments 104a-f in the example of Fig. 1, are categorized into belonging to the interference pool 120 and not belonging to the interference pool 120. In particular, for the exemplary situation shown in Fig. 1, user equipments 104e and 104f are categorized as belonging to the interference pool

120 and hence are categorized for communication only via the dedicated spectrum part 118. Further, user equipments 104a, 104b, 104c and 104d are categorized as not belonging to the interference pool 120 and hence are categorized for communi- eating via the dedicated spectrum part 118 plus the shared spectrum part 116.

To illustrate some features and advantages of the proposed scheme over that of the normal frequency dependent schedul- ing, reference is made to Fig. 3 which shows a wireless communication network 200 in accordance with embodiments of the herein disclosed subject-matter. According to an embodiment shown in Fig. 3, a first base station 202 provides an LTE FDD (long-term evolution frequency division duplex) cellular net- work providing a macrocell 206 overlapping with a femto cell 210. The macro user equipment 204, i.e. the user equipment which communicates with the first base station 202 spanning the macrocell 206, is assumed to be around the edge of the femto cell 210. Communication between the macro user equip- ment 204 and the first base station 202 is indicated at 230 in Fig. 3. Since the macro user equipment 204 is around the edge of the femto cell 210 and is not moving with a high ve- locity, it is considered as a potential co-channel threat on the performance of the femto user equipment 244, i.e. the user equipment which communicates with the second base station 208 (femto base station) spanning the femto cell 210. Communication between the femto user equipment 244 and the femto base station 208 is indicated at the 232 in Fig. 3.

Fig. 4 illustrates frequency dependent scheduling for the macro base station 202 in the case that the macro base sta- tion is not aware of the femto cell 210. As can be seen from Fig. 4, if the macro base station has no knowledge about the femto base station 208, the co-channel interference is hard to be avoided because resource allocation of the femto cell is unpredictable by the macro base station. In Fig. 4 the time slots involving co-channel interference for specific channel (along the frequency axis) are marked with a cross pattern .

In contrast, having regard to Fig. 5, when a method according to the herein disclosed subject-matter is employed for femto cell aware spectrum arrangement, as long as the macro user equipment 204 is detected to be a potential threat for femto co-channel interference, the allocated spectrum for the macro user equipment 204 is moved to the macro dedicated part 118. According to an embodiment, the allocated spectrum is moved to the dedicated spectrum part 118 both in downlink and uplink direction. Hence, the performance of the macro user equipment 204 is improved efficiently and also the potential threat on the femto cell 210 is avoided. In Fig. 5 the time slots involving co-channel interference for specific channel (along the frequency axis) are also marked with a cross pat^¬ tern . It should be noted that in the exemplary embodiment the co- channel interference occurring in the first time slot is due to a scheduling collision for the first time, i.e. if both the macro base station 202 and the femto base station 208 send data in the interference resource for the first time, it will not be detected and the first-time "collision" is un^¬ avoidable in this embodiment. However, as long as the interference is detected by the user equipment 204 and reported to the macro base station 202, the intercell interference will be avoided in the subsequent time slots.

Having regard to Fig. 6, some features of elements of the wireless communication network are discussed.

According to an embodiment shown in Fig. 6, the first base station 302 comprises a controller 350 for determining for a user equipment 304, which communicates with the first base station 302, a threat indicating quantity, e.g. a user equip- ment moving speed, a difference of CQI values for a shared spectrum part and a dedicated spectrum part, indicative of a threat of the user equipment of causing interference in the second region 210. The first base station 302 comprises a spectrum selector 352 selecting only the dedicated spectrum part (118 in Fig. 2) for communication with the user equipment 204 depending on the threat indicating quantity determined by the controller 350.

According to a further embodiment, the first base station 302 comprises a comparator 354 for comparing the threat indicating quantity with a predetermined threshold. According to an embodiment, the spectrum selector 352 is configured for se- lecting only the dedicated spectrum part (118 in Fig. 2) for communication with the user equipment 304 depending on the comparison of the threat indicating quantity with the predetermined threshold. According to a further embodiment, the base station 302 further comprises a speed determination unit 356 for determining a moving speed of the user equipment as the threat indicating quantity. Speed determination units for determining a moving speed of a user equipment are known in the art.

According to a further embodiment, the base station 302 comprises a receiving unit 357 for receiving (indicated at 353 in Fig. 6) from a network element 359 a frequency range (or a frequency range indicator) of the second frequency spectrum.

According to a further embodiment, the base station 302 comprises a channel quality determination unit 358 for determining a channel quality indicator for the shared spectrum. The shared spectrum may be determined from the frequency range of the second frequency spectrum and the frequency range of the first frequency spectrum, e.g. by a shared spectrum determination unit 355. For example, according to an embodiment, the shared spectrum determination unit 355 is configured for map^¬ ping subbands of the first frequency spectrum to the second frequency spectrum.

According to an embodiment, the channel quality determination unit 358 is configured for communicating with the user equipment for effecting the user equipment 304 to send a channel quality indicator (of at least one of the shared spectrum part 116, the dedicated spectrum part 118 or the whole first spectrum 112) to the first base station 302. Further, the channel quality determination unit 358 may be configured for receiving the channel quality indicator sent by the user equipment 304. According to other embodiments, the channel quality determination unit 358 is configured for measuring a channel quality in the uplink (from the user equipment to the base station) .

According to a further embodiment, the base station 302 comprises a user equipment information unit 360 for indicating to the user equipment the frequency range of the shared spec^¬ trum part (116 in Fig. 2) . For example, according to an embodiment, the user equipment information unit 360 is configured for indicating to the user equipment the mapping of the second frequency spectrum 114 (e.g. the femto spectrum) on the macro cell sub-bands, i.e. the sub-bands of the first base station 302.

Having regard to the user equipment 304, according to an embodiment the user equipment 304 comprises a communication unit 361 for communicating (indicated at 363 in Fig. 6) with the first base station 302 by using a first frequency spectrum.

According to another embodiment, the user equipment 304 com- prises a receiving unit 362 for receiving from the first base station an indication of a second frequency range of a second frequency spectrum (114 in Fig. 2) which is used by a second base station (not shown in Fig. 6) . According to an embodiment the receiving unit 362 is configured for receiving the indication of the second frequency range, thereby providing to the user equipment 304 the knowledge about the frequency range of the second frequency spectrum which is used by the second base station, with which the user equipment 304 does not communicate at this time (and which is not shown in Fig. 6) . According to an embodiment, the receiving unit 362 is configured for receiving the indication of the second fre- quency range via the first frequency range, e.g. via the communication link 363 which uses the first frequency spectrum.

It should be noted that according to an embodiment, the user equipment 304 is capable of connecting to the second base station (not shown in Fig. 6) . For example, in case the user equipment 304 connects to the second base station, e.g. by handover, according to an embodiment the user equipment uses for communication with the second base station the same transceiver which is also used for communication with the first base station 302. In other words, according to this embodiment, a single transceiver of the user equipment is used for communication via the first frequency spectrum and the second frequency spectrum. This is advantageous since the second frequency spectrum overlaps the first frequency spec- trum according to embodiments discloses herein.

The user equipment 304 further comprises a channel quality determination unit 364 for determining a channel quality indicator for the second spectrum part (116 in Fig. 2) . Accord- ing to an embodiment, the channel quality determination unit 364 is further configured for determining a channel quality indicator of the first frequency spectrum or for the dedi^¬ cated spectrum part of the first frequency spectrum.

According to a further embodiment, the user equipment comprises a channel quality indicator reporting unit 366 for re- porting the channel quality indicator (s) to the first base station 302.

It should be understood that according to embodiments of the herein disclosed subject matter, the above mentioned components of the base station 302 are operatively coupled for performing and providing respective functions disclosed herein. Similarly, the above mentioned components of the user equipment 304 are operatively coupled for performing and pro- viding respective functions disclosed herein.

According to embodiments of the invention, any component of the wireless communication system, e.g. any component of the first base station or the second base station or the user equipment is provided in the form of respective computer pro^¬ gram products which enable a processor to provide the func^¬ tionality of the respective elements as disclosed herein. According to other embodiments, any component of the wireless communication system, e.g. components of the first base sta- tion, the second base station or the user equipment is provided in hardware. According to other - mixed - embodiments, some components are provided in software while other components are provided in hardware.

It should be noted that the term "comprising" does not ex^¬ clude other elements or steps and that "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be con- strued as limiting the scope of the claims. In order to recapitulate the above-described embodiments of the herein disclosed subject-matter, one can state:

A novel scheme of a second cell aware spectrum arrangement for co-channel interference reduction between a first cell, exemplarily referred to as a macro cell, and a second cell, exemplarily referred to as a femto cell, is provided. The scheme is applied to the partial co-channel configuration of the first and second cells as described above. By operator configuration, the macro base station may have knowledge of the shared frequency resource for the femto cells within its coverage. In this way, the macro base station divides its available spectrum into different parts: The dedicated spectrum part and the shared spectrum part. When managing user equipments, the macro base station is proposed to maintain an interference pool. The user equipments belonging to the in^¬ terference pool are supposed to have a potential threat of co-channel interference on the femto cells and therefore, there arranged frequency should be limitation to the dedi- cated spectrum part during scheduling. All the other user equipments outside the interference pool could be freely scheduled spanning the whole spectrum including the dedicated spectrum part and the shared spectrum part.

The described subject matter relates to a wireless communication system with a first base station serving a first cell which overlaps with a second cell of a second base station. A second frequency spectrum usable by the second base station overlaps with a shared spectrum part of a first frequency spectrum usable by the first base station. The remaining dedicated spectrum part of the first frequency spectrum is exclusively provided for communication of the first base station. For an user equipment which communicates with the first base station a threat indicating quantity indicative of a threat of the user equipment of causing interference in the second cell is determined. The first base station communicates with the user equipment by using only the dedicated spectrum part if the threat indicating quantity indicates that the user equipment provides a threat of causing interference in the second cell.

List of reference signs:

100, 200, 300 wireless communication system

102, 202, 302 first base station 104a-f, 204, 304 user equipment

106, 206 first region

108a-c, 208 second base station llOa-c, 210 second region

112 first frequency spectrum 114 second frequency spectrum

116 shared spectrum part

118 dedicated spectrum part

120 interference pool

122 moving vector 230 communication between a user equipment and the first base station

232 communication between a user equipment and the second base station

244 user equipment communicating with the second base station

350 controller

352 spectrum selector

354 comparator

355 shared spectrum determination unit 356 speed determination unit

357 receiving unit of 302

358 channel quality determination unit of 302

359 network element

360 user equipment information unit 362 receiving unit

364 channel quality determination unit of 304

366 reporting unit

Claims

CLAIMS :

1. Method of operating a first base station (102, 202, 302) of a wireless communication system (100, 200, 300), the wireless communication system comprising:

- the first base station (102, 202, 302) configured for being capable of communicating with user equipments in a first region (106, 206) by using a first frequency spec- trum (112) ;

- a second base station (108a-c, 208) configured for being capable of communicating with user equipments in a second region (llOa-c, 210) by using a second frequency spectrum (114) ; - the second region (llOa-c, 210) being at least partially located in the first region (106, 206) ; and

- the second frequency spectrum (114) overlapping with a shared spectrum part (116) of the first frequency spectrum (112), the first frequency spectrum (112) thus comprising a dedicated spectrum part (118) exclusively provided for communication of the first base station (102, 202, 302) and said shared spectrum part (116) useable by the first base station (102, 202, 302) and the second base station (108a-c, 208) ; the method comprising:

- determining for a user equipment (104a-f, 204, 304) commu^¬ nicating with the first base station (102, 202, 302) a threat indicating quantity indicative of a threat of the user equipment (104a-f, 204, 304) of causing interference in the second region (llOa-c, 210) ;

- communicating with the user equipment (104a-f, 204, 304) by using only the dedicated spectrum part (118) depending on the threat indicating quantity.

2. Method according to claim 1, the method comprising:

- comparing the threat indicating quantity with a predetermined threshold; - wherein said communicating with the user equipment (104a- f, 204, 304) by using only the dedicated spectrum part (118) is performed depending on the relation of said threat indicating quantity to said predetermined thresh- old.

3. Method according to claim 2, wherein determining said threat indicating quantity comprises detecting a moving speed of the user equipment (104a-f, 204, 304) .

4. Method according to one of claims 1 to 3, wherein determining said threat indicating quantity comprises selectively determining a channel quality indicator for said shared spectrum part.

5. Method according to claim 4, wherein determining said channel quality indicator comprises indicating to the user equipment (104a-f, 204, 304) the frequency range of the shared spectrum part (116) .

6. Method according to claim 5, wherein said frequency range of the shared spectrum is indicated to the user equipment (104a-f, 204, 304) in a broadcasting message.

7. Method according to claim 5, wherein said frequency range of the shared spectrum is indicated to the user equipment (104a-f, 204, 304) in a request message requesting transmis^¬ sion of a channel quality indicator of the frequency range of the shared spectrum part (116) .

8. Method of operating a user equipment (104a-f, 204, 304) communicating with a first base station (102, 202, 302) by using a first frequency spectrum, the method comprising:

- receiving from said first base station (102, 202, 302) an indication of a frequency range of a second frequency spectrum (114) which is usable by a second base station (108a-c, 208) ; - the second frequency spectrum (114) overlapping with a shared part of the first frequency spectrum (112) , the first frequency spectrum (112) thus comprising a dedicated spectrum part (118) exclusively provided for commu- nication of the first base station (102, 202, 302) and said shared spectrum part (116) useable by the first base station (102, 202, 302) and the second base station (108a-c, 208) ; and

- determining a channel quality indicator for said shared spectrum part from a communication with the first base station (102, 202, 302) .

9. A computer program for determining and processing a physical object, namely a threat indicating quantity indicative of a threat of the user equipment (104a-f, 204, 304) of causing interference, the computer program, when being executed by a data processor, is adapted for controlling the method as set forth in any one of the claims 1 to 8.

10. Base station of a wireless communication system (100, 200, 300), the wireless communication system comprising:

- said base station as a first base station (102, 202, 302) being configured for being capable of communicating with user equipments in a first region (106, 206) by using a first frequency spectrum (112) ;

- the second frequency spectrum (114) overlapping with a shared spectrum part (116) of the first frequency spectrum (112), the first frequency spectrum (112) thus comprising a dedicated spectrum part (118) exclusively provided for communication of the first base station (102, 202, 302) and said shared spectrum part (116) useable by the first base station (102, 202, 302) and the second base station (108a-c, 208) ; the first base station (102, 202, 302) :

- comprising a controller (350) for determining for a user equipment (104a-f, 204, 304) communicating with the first base station (102, 202, 302) a threat indicating quantity indicative of a threat of the user equipment (104a-f, 204, 304) of causing interference in the second region (llOa-c, 210) ; and - being configured for communicating with the user equipment (104a-f, 204, 304) by using only the dedicated spectrum part (118) depending on the threat indicating quantity.

11. Base station according to claim 10, said controller (350) further comprising:

- a comparator (354) for comparing the threat indicating quantity with a predetermined threshold;

- a spectrum selector (352) for selecting only the dedicated spectrum part (118) for communication with the user equip- ment (104a-f, 204, 304) depending on the comparison of said threat indicating quantity with said predetermined threshold.

12. Base station according to claim 10 or 11, said controller (350) further comprising a speed determination unit (356) for determining a moving speed of the user equipment (104a-f, 204, 304) as said threat indicating quantity.

13. Base station according to one of claims 10 to 12, said controller (350) comprising a channel quality determination unit (358) for determining a channel quality indicator for said shared spectrum.

14. Base station according to claim 13, wherein said control- ler (350) comprises a user equipment information unit (360) for indicating to the user equipment (104a-f, 204, 304) the frequency range of the shared spectrum part (116) .

15. User equipment (104a-f, 204, 304) for a wireless communi^¬ cation network, the user equipment comprising:

- a communication unit for communicating with a first base station (102, 202, 302) by using a first frequency spec- trum (112) ;

- a receiving unit for receiving from said first base sta^¬ tion (102, 202, 302) an indication of a second frequency range of a second frequency spectrum (114) which is used by a second base station (108a-c, 208) ; - the second frequency spectrum (114) overlapping with a shared part of the first frequency spectrum (112), the first frequency spectrum (112) thus comprising a dedicated spectrum part (118) exclusively provided for communication of the first base station (102, 202, 302) and said shared spectrum part (116) useable by the first base station (102, 202, 302) and the second base station (108a-c, 208) ;

- a channel quality determination unit (364) for determining a channel quality indicator for said shared spectrum part (116) .