WO2010091713A1

WO2010091713A1 - Radio resource allocation for geran-lte co-existence and co-location

Info

Publication number: WO2010091713A1
Application number: PCT/EP2009/051472
Authority: WO
Inventors: Jari Yrjana Hulkkonen; Mikko Saily
Original assignee: Nokia Siemens Networks Oy
Priority date: 2009-02-10
Filing date: 2009-02-10
Publication date: 2010-08-19
Also published as: EP2396985A1

Abstract

The present invention relates to the field of radio resource allocation between fourth-generation Evolved Universal Terrestrial Radio Access Networks (E-UTRANs) and second-generation radio access networks according to the GSM/EDGE standard (herein also referred to as GERANs). More particularly, the invention proposes a method and mechanism which allows GERAN and LTE radio resource management to share the same spectrum allocation in both co-channels and adjacent channels.

Description

Radio Resource Allocation for GERAN-LTE Co-existence and Co- location

DESCRIPTION

The present invention relates to the field of radio resource allocation between fourth-generation Evolved Universal Terrestrial Radio Access Networks (E-UTRANs) and second- generation radio access networks according to the GSM/EDGE standard (herein also referred to as GERANs) . More particularly, the invention proposes a method and mechanism which allows GERAN and LTE radio resource management to share the same spectrum allocation in both co-channels and adjacent channels. Thereby, GERAN scalability and LTE flexibility in time/frequency allocation enables efficient frequency sharing between the systems. This shared portion of the spectrum allocation is driven by a GSM Base Station System (BSS) Mobile Allocation (MA) procedure. Since GSM frequency hopping is a deterministic process, the occupied frequencies in the following frames can be predicted. According to the invention, LTE utilizes this information from GSM in the shared frequency area and thus avoids allocation of the occupied resource blocks (in frequency domain) during the duration of the next transmit time interval (in time domain) .

BACKGROUND OF THE PRESENT INVENTION

The 3GPP Long Term Evolution (LTE) represents a major advance in cellular technology. LTE has been designed to meet carrier needs for high-speed data and media transport as well as high-capacity voice support well into the next decade. It encompasses high-speed data, multimedia unicast and multimedia broadcast services. To be more precise, LTE provides for an uplink speed of up to 50 megabits per second (Mbps) and a downlink speed of up to 100 Mbps . Aside therefrom, LTE will bring many technical benefits to cellular networks. Bandwidth will be scalable from 1.25 MHz to 20 MHz. This will suit the needs of different network operators that have different bandwidth allocations, and also allow operators to provide different services based on spectrum. LTE is also expected to improve spectral efficiency in 3G networks, allowing carriers to provide more data and voice services over a given bandwidth. Although technical specifications are not yet finalized, significant details are emerging.

E-UTRAN systems (sometimes also referred to as UTRAN LTE systems) aim at further reducing operator and end-user costs and improving service provisioning. Possible ways of reaching this target are to study ways to achieve reduced latency, to achieve higher user data rates, and to improve the system capacity and coverage. One of the main novelties introduced for E-UTRAN in order to achieve these targets is the introduction of a new physical layer which applies Orthogonal Frequency Division Multiplexing (OFDM) for the downlink, thus allowing data to be directed to or from multiple users on a subcarrier-by-subcarrier basis for a specified number of symbol periods, and Single Carrier - Frequency Division Multiple Access (SC-FDMA) for the uplink. These choices were made, e.g., to achieve greater spectrum flexibility and enabling deployment in various spectrum allocations, to achieve the possibility of frequency domain adaptation and enabling higher spectrum efficiency, to achieve enhanced efficiency for broadcast services in the downlink due to the inherent macro-diversity combining properties of OFDM and to achieve reduced receiver complexity, especially at high bandwidths and in conjunction with Multiple Input Multiple Output (MIMO) data transmission. An Evolved UTRAN system may either apply the frequency-division duplex (FDD) transmission mode or the time-division duplex (TDD) transmission mode. When applying the time-division transmission mode, the evolved UTRAN uses the same frequency band for both uplink and downlink communication. Thus, some time slots are reserved for the uplink while others are reserved for the downlink. This is typically configured by the network. One time slot is assigned mandatory for the downlink, e.g. the first time slot in a radio frame. By reading control information in this time slot, the user equipment (UE) then knows the configuration of the other time slots, uplink or downlink .

High-level E-UTRAN systems shall be able to support two distinct deployment scenarios: standalone deployment scenarios and integrated scenarios together with coexisting GERAN networks. In the first case, there may be an existing UTRAN/GERAN coverage, but for any reason there may not be any requirement for an interaction of these two networks. In the latter case, the operator is having GERAN coverage in the same geographical area. It may thereby be the case that both networks and thus the network services and data traffic to be transferred via these networks are assigned adjacent carriers (see Fig. Ia) or even that allocated GERAN carriers are used for transferring LTE traffic in case an LTE service is requested (see Fig. Ib) .

E-UTRA operates on a flexible spectrum with a useable bandwidth of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz or 20 MHz, both in the uplink and downlink and in a paired and unpaired spectrum. On TDD bands operating at a chip rate of 1.28 Mcps, a useable bandwidth of 1.6 MHz is intended. E-UTRA thereby supports co-existence (and co-location) with GERAN on adjacent channels, co-existence between operators on adjacent channels and co-existence on overlapping and/or adjacent spectrum at country borders. Thereby, all frequency bands should be allowed following release-independent frequency band principles.

For LTE, the minimum frequency allocation in current 3GPP scenarios is 1.4 MHz containing both common control and traffic. Evolved Universal Terrestrial Radio Access (E-UTRA), which is the air interface of 3GPP' s LTE upgrade path for mobile networks and represents the successor to High-Speed Downlink Packet Access (HSDPA) and High-Speed Uplink Packet Access (HSUPA) technologies specified in 3GPP releases 5, 6 and 7, operates on a flexible spectrum in 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz in both the uplink and downlink as well as in paired and unpaired spectrum. It has been agreed that the DL synchronization signals are transmitted on sub-carriers, which are centred with respect to the BCH sub-carrier (see 3GPP TS 36.211 V8.4.0 (2008-09) Technical Specification, E-UTRAN, Physical Channels and Modulation, Release 8) .

GERAN, on the other hand, which is an abbreviation for "GSM/EDGE Radio Access Network", is the radio part of GSM/EDGE together with the network that joins the base stations and base station controllers. The standards for GERAN are maintained by the 3GPP (Third Generation Partnership Project) . GERAN is a key part of GSM, and also of combined UMTS/GSM networks. The network represents the core of a GSM network through which phone calls and packet data are routed from and to the public switched telephone network (PSTN) and Internet to and from subscriber handsets. A mobile phone operator's network is comprised of one or more GERANs, coupled with UTRANs in the case of a UMTS/GSM network.

As prescribed by the associated 3GPP standard, GERAN networks can be operated on 200 kHz resolution, and minimum resource allocation in LTE is 180 kHz. Typical minimum frequency band allocation requirement to operate practical GERAN network is 5.0 to 7.5 MHz (or even 10 MHz), which at 5 MHz yields 12 carriers for the broadcast control channel BCCH (i.e., a BCCH reuse of 12) and 13 frequency hopping traffic carriers.

SUMMARY OF THE INVENTION

A severe problem consists in the fact that LTE specifies the co-existence and co-location with GERAN systems on adjacent channels (cf. 3GPP TR 25.913 V7.3.0 (2006-03) Technical Report, Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN), Release I)₁ which limits the inter-system capacity maximization and load balancing between GERAN and LTE (see Figs, la-c) .

More precisely, there is a high risk that the overall inter- system spectral efficiency is degraded when two different systems are allocated to the operator network with dedicated spectrum allocations.

When LTE is initially introduced into the operator network, there may not be sufficiently high penetration of LTE-capable user equipments. Still, the operator needs to invest to the minimum required capacity for expected Quality of Service

(QoS) to launch and operate LTE services. This extra capacity is not able to bring any revenue for the operator until the LTE user equipment penetration gets moderately high.

If the operator can not acquire a new frequency spectrum to operate LTE services, then LTE must be introduced to the same bandwidth with GERAN (see Fig. Ib) . In this case, a significant capacity loss is seen on the GERAN side. In practice, this is not acceptable, and in most of the cases the majority of the traffic (especially voice) will remain in the GERAN network until the LTE user equipment penetration is high .

According to the applicant's knowledge, no prior-art solutions are known for GERAN-LTE radio resource allocation using both co-channels and adjacent channels as shared spectrum.

Conventional proposals according to the prior art are mainly concentrating on offering a dedicated spectrum for LTE-based services. This implies the disadvantage that carved GSM spectrum will impair the legacy voice capacity significantly.

It has also been proposed to increase LTE frequency allocation granularity (minimum allocation plus an integer multiple of 180 kHz) . This would improve flexibility for the allocation of a dedicated LTE spectrum, but the specification of this method would require a lot of effort in 3GPP and support from other companies, which is not considered feasible in 3GPP Release 8.

Aside therefrom, WCDMA will be also difficult to pair with LTE in limited operator spectrum allocations due to fixed 5 MHz spectrum allocation.

It is thus an object of the present invention to address problems that occur when more than one radio access network, e.g. GERAN and E-UTRAN, need to co-exist on the same frequency band.

In view of this object, a first exemplary embodiment of the present application refers to a method for allocating requested radio resources for at least two coexisting and co- located radio access networks sharing the same frequency spectrum in an active radio cell. In accordance with the invention, said method comprises the steps of predicting a deterministic frequency occupancy for the allocated frequency spectrum of at least one first radio access network for several frames in advance and allocating at least one frequency band from the residual, unoccupied parts of the shared frequency spectrum for at least one second radio access network according to bandwidth requirements of said at least one second radio access network.

In particular, said at least one first radio access network may be given by a second-generation radio access network which operates based on the GSM/EDGE standard, and said at least one second radio access network may e.g. be a fourth- generation radio access network which operates based on the E-UTRAN standard.

The claimed method may thereby begin with the steps of entering a channel request and controlling the active radio cell such as to avoid co-channel interference between the at least two co-existing and co-located radio access networks. It may further be provided that the at least one first radio access network executes a resource block allocation procedure for allocating those radio resources which are requested by said first radio access network, wherein carrier allocation is adaptively changed based on a deterministic frequency hopping scheme. According to the present invention, the at least one second radio access network then calculates the frequency occupancy for the allocated frequency spectrum of the at least one first radio access network for several frames in advance. In case a channel resource request is received from the at least one second radio access network, said method may then be continued with the step of performing a channel selection and activation based upon the predicted frequency occupancy for the allocated frequency spectrum of the at least one first radio access network.

When the channel resource request is received from the at least one second radio access network, it is looked for available active channels in the shared frequency spectrum and the resource allocation of the at least one first radio access network is predicted by calculating the deterministic frequency occupancy for the allocated frequency spectrum of said at least one first radio access network for several frames in advance. After that, the shared resource pool as given by the shared frequency spectrum is updated by indicating new occupied and restricted channels of said at least one first radio access network before a set of resources as requested by said at least one second radio access network is allocated. After correspondingly updating the shared resource pool by indicating the new occupied and restricted channels of said at least one second radio access network, a traffic channel using the allocated set of resources as requested by said at least one second radio access network can be activated.

A second exemplary embodiment of the present application relates to a base transceiver station for allocating requested radio resources for at least two coexisting and co- located radio access networks sharing the same frequency spectrum in an active radio cell. In accordance with the proposed invention, said base transceiver station may be configured for calculating a deterministic frequency occupancy for the allocated frequency spectrum of at least one first radio access network for several frames in advance and allocating at least one frequency band from the residual, unoccupied parts of the shared frequency spectrum for at least one second radio access network according to bandwidth requirements of said at least one second radio access network.

Finally, a third exemplary embodiment of the present application is directed to a computer program for executing a method as described above with reference to said first exemplary embodiment when being implemented and running on a base transceiver station as disclosed with reference to said second exemplary embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be elucidated by way of example with respect to the embodiments described hereinafter and with respect to the accompanying drawings.

Therein,

Figs, la-c show three schematic diagrams which illustrate three example of resource allocation between an LTE system and a GERAN system when introducing LTE services,

Fig. 2 shows the LTE time and frequency domain structure for the downlink and uplink case,

Fig. 3 shows the principle of a shared frequency resource area,

Fig. 4 shows a schematic diagram for illustrating GERAN-LTE coexistence using shared resources, Fig. 5 shows a schematic diagram for illustrating GERAN-LTE coexistence in the downlink,

Fig. 6 shows a schematic diagram for illustrating GERAN-LTE coexistence in the uplink,

Fig. 7 shows a schematic diagram for illustrating GERAN-LTE interference control in a shared spectrum,

Fig. shows the compatibility of GSM-LTE coexistence for the example of an LTE cell search,

Figs. 9a+b show two schematic diagrams for exemplarily illustrating GSM-LTE coexistence based on variable, non-overlapping bandwidths, and

Figs. 10a+b show two schematic diagrams for exemplarily illustrating GSM-LTE coexistence based on shared bandwidths with LTE variable bandwidths using GSM resources.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following sections, an exemplary embodiment of the claimed wireless dual-transceiver circuit according to the present invention will be explained in more detail, thereby referring to the accompanying drawings.

Figs, la-c illustrate the above-mentioned problems concerning resource allocation between co-existing LTE- and co-located GERAN-based networks for an example with original 5.0 MHz allocation . In Fig. Ia, a radio resource allocation scheme is shown where LTE-based services are assigned an additional frequency band (A) having a bandwidth of 2.5 MHz adjacent to a frequency band of 5.0 MHz which is provided for GERAN traffic with said 5.0 MHz band being sub-divided into 12 BCCH traffic carriers (referred to as "12 ARFN") and 13 other carriers (referred to as "13 ARFN") which can be used for frequency hopping purposes .

Another radio resource allocation scheme where only roaming GSM users using dedicated frequency bands for LTE-based services and GERAN traffic within said 5.0 MHz band are supported (scenario B) is shown in Fig. Ib. As can be seen from this figure, GERAN interference diversity is lost (as there is no dedicated hopping layer) , which means that the GERAN network is limited to the BCCH traffic.

According to a further alternative, a shared frequency band (C) for LTE-based services and GERAN traffic can be provided such as illustrated by the radio resource allocation scheme shown in Fig. Ic. Both systems implement mandatory common control channels. A balanced traffic load can only be achieved by using a flexible shared spectrum (such as proposed by the present invention) .

A schematic diagram showing the LTE time and frequency domain structure for the downlink and uplink case is depicted in Fig. 2. In LTE, resource blocks having a size of 1.0 ms X 180 kHz are used. For LTE services, partial radio frame allocation on GSM carriers would thus be possible.

As briefly mentioned above, the present invention proposes a method and mechanism which allows GERAN and LTE radio resource management to share the same spectrum allocation (see Figs. 3 and 4) in both co-channels and adjacent channels (see Figs. 5 and 6) . Aside therefrom, other coexistence strategies for GERAN and LTE systems using the same band may be foreseen. It may e.g. be provided that GSM drives slow radio resource allocation on a TDMA frame basis. Furthermore, both systems may have a common radio resource management (CRRM) - also referred to as "inter-system RRM" - by using an inter-system DFCA (dynamic frequency and channel allocation) .

Another coexistence strategy may be given by dynamic BCH offset assignment and dynamic BCH/BCCH allocation.

According to an embodiment of the present invention as described above, GERAN and LTE may be allocated to the same operator frequency bandwidth, e.g. to a bandwidth between 5 MHz and 10 MHz. Thus, a common shared portion of the overall spectrum is configured and available for the traffic channels. Both systems may thereby be provided with practical minimum dedicated bandwidth allocation for the broadcast control channel (BCCH) and the broadcast channel (BCH) . This shared portion of the spectrum allocation is driven by a GSM Base Station System (BSS) Mobile Allocation (MA) procedure. Since GSM frequency hopping is a deterministic process, the occupied frequencies in the following frames can be predicted. According to the invention, LTE utilizes this information from GSM in the shared frequency area and avoids allocation of the occupied resource blocks (in frequency domain) during the duration of the next transmit time interval (in time domain) .

The best way to utilize the proposed inter-system RRM is to expand the existing GSM DFCA algorithm to cover and coordinate both systems for resource allocation, e.g. such as illustrated in Fig. 7. Optionally, an inter-system interference control may be provided which may be configured as an extension to the scaled inter-cell interference values of a common background interference matrix (BIM) . In this connection, Fig. 7 shows the shared spectrum between LTE and GERAN and illustrates an example for inter-cell interference management for a total bandwidth of 10 MHz where in two radio cells (cells 100 and 101) a bandwidth of 7.5 MHz is allocated to the GERAN system and a bandwidth of 2.5 MHz is allocated to the LTE system, whereas in two other radio cells (cells 110 and 111) a bandwidth of 5.0 MHz is allocated to the GERAN system and a bandwidth of 5.0 MHz is allocated to the LTE system. As can be seen from Fig. 7, this scenario requires the use of a shared spectrum and an effective inter-cell interference management between these two systems such as proposed in the scope of the present application.

Fig. 8 shows the compatibility of GSM-LTE coexistence for the example of an LTE cell search in a scenario where a 10-MHz user equipment (UE) is located in a 20-MHz cell site with mandatory BCH and SCH common control channels occupying an SCH (synchronization channel) bandwidth of 1.25 MHz and a BCH (broadcast channel) bandwidth of 1.25 MHz. Owing to GSM-LTE co-existence, said radio resource is multiplexed in frequency domain. While spectrum assignment comes from the GSM system, the LTE system has the freedom to allocate resources outside the current active GSM MA lists. First, a cell search (step a) is initiated using a synchronization channel SCH. As a result thereof, the associated 1.25 MHz spectrum around the center carrier frequency f_c of the overall spectrum is detected. In a next step (step b) , a BCH signal is received. After that, the UE shifts to the center carrier frequency assigned by the system and initiates a data transmission (step c) . In Figs. 9a+b, two schematic diagrams for exemplarily illustrating GSM-LTE coexistence based on variable, non- overlapping bandwidths are shown. If GSM voice quality is good, only GSM carriers 1 to 8 are used for frequency hopping (FH) . The remaining carriers of the spectrum can be used for LTE traffic. As can be seen from Fig. 9a, GSM data are allocated to the BCCH, and GSM voice data are allocated to the BCCH and GSM frequency hopping layer. GSM radio resource management thereby minimizes the usage of hopping frequencies. There are several ways to control the hopping list in GSM, e.g. by means of a DFCA algorithm or by using MAIO (mobile allocation index offset) parameters. By comparing Figs. 9a and 9b it can be seen that the LTE band can be varied based on GSM quality of service and traffic load conditions. Inside a cell, there is no overlap of the GSM and LTE spectrum (see Fig. 9b) .

Two schematic diagrams for exemplarily illustrating GSM-LTE coexistence based on shared bandwidths with LTE variable bandwidths using GSM resources are shown in Figs. 10a+b. As can be seen from Fig. 10a, GSM data are allocated to the BCCH, and GSM voice data are allocated to the BCCH and GSM frequency hopping layer such as in the scenario of Fig. 9a. As the LTE band is variable, all free resources from GSM can be used by LTE. From Fig. 10b it can be taken that LTE uses the carriers inside the GSM spectrum. If there is a free GSM carrier inside the GSM hopping list, LTE can use this resource (see Fig. 10b) .

In the following, implementation details and advantages of the present invention shall be described in more detail.

For GSM-LTE coexistence there are spectrum deployment requirements for LTE, which comprise co-existence in the same geographical area and co-location with GERAN/3G on adjacent channels. When these adjacent channels are part of the GSM bandwidth, it will be possible to also allocated co-channels. As a result, it will be possible to co-exist and co-site GSM and LTE transceivers which share the same bandwidth and are allocated on co-channel and adjacent carriers.

The network load for each system is monitored using RRM tools or key performance indicators. For example, average reception quality for wireless speech connections can indicate that the network on the GERAN side is not heavily loaded and less frequency resources are needed for GERAN such that LTE can gain more resources.

Radio Resource Allocation baseline procedure is based on the following baseline requirements: 1. GSM allocation and frequency reuse configured and available, 2. LTE bandwidth allocation excludes GSM BCCH, 3. LTE BCH bandwidth is dedicated to LTE, and 4. shared spectrum configured and available. Optionally, an inter-system interference control is configured and available.

According to a preferred embodiment of the present application, channel allocation and assignment may be carried out as follows: When a channel request is entered to the system (step Sl), free resource blocks in a shared area in frequency domain are available for both (GERAN- and LTE- based) systems. An inter-System Radio Resource allocation process then controls the own cell and avoids co-channel interference between co-locating systems (step S2) . After that, the GSM system drives the resource block allocation. Thereby, GSM channel activation or deactivation changes the mobile allocation adaptively depending on the load, quality and available resources (step S3) . The LTE system then calculates the GSM frequency occupancy for several frames in advance, and therefore avoids the carriers being occupied by GSM traffic channels in the own cell (step S4) . This step is followed by a channel selection and activation (step S5) when channel resource request is received. In case a resource is requested for the GSM system, a normal resource allocation is carried out (step S5a (i) ) , e.g. by physical layer parameters for mobile allocation. Thereby, GSM data are prioritized on a dedicated BCCH channel. After that, the shared resource pool as given by the shared frequency spectrum is updated by indicating new occupied and restricted channels (step S5a (ii) ) . In case a resource is requested for LTE system, available active channels are looked for in the shared resource area (step S5b (i) ) . After that, GSM Mobile Allocation for the next following transmit time intervals are predicted (step S5b (ii) ) and the shared resource pool indicating new occupied and restricted channels is updated (step S5b (iii) ) . The proposed method is then continued with the steps of allocating the set of resources as requested, e.g. according to quality of service (QoS) requirements (step S6) , Updating the shared resource pool indicating new occupied and restricted channels (step S7) and activating a traffic channel (step S8) .

Applying the proposed method according to the present invention thereby leads to the following advantages:

• High spectral efficiency of multi-mode systems operating on a same operator frequency allocation, thereby maintaining the requested quality of service for GSM users and maximizing the available spectrum for LTE.

• The operator frequency bandwidth can remain fully occupied after LTE roll-out, thus maximizing the multi- mode spectral efficiency and investment to the network and licensed spectrum.

• Minimal updates required for GSM. There is no need to make major changes or additional control in the GSM system because LTE controls and avoids allocation of the occupied resource.

• Capacity and traffic mix can be tuned between the systems .

• Capacity and traffic mix can be tuned for each sector and site independently, when the systems are co-sited.

• Capacity and traffic mix can be adaptively modified based on the network load, RRM QoS measurements, busy hour control, or some other criteria.

• It is possible to multiplex the two systems in frequency domain, and adaptively avoid collisions in time domain in co-channels. This is possible since the LTE transmit time interval can be adapted with the information from the GSM MA.

• The applied frequency hopping sequence is deterministic and defined at the channel allocation for both base station and mobile station. Therefore, LTE can be aware of the GSM resource allocations on a timeslot/frame basis .

• The proposed method is compatible with the LTE cell search algorithm and frame structure (both structure in time and frequency) and is also compatible with different LTE frequency band allocations.

• The proposed method is compatible with the downlink reference signal (s) (channel-quality measurements, channel estimation for coherent demodulation/detection at the UE, cell search and initial acquisition) . • Antenna line and installation can be shared between the systems, or dedicated antenna and radio equipment can be used.

• It is possible to manage the resources in GERAN by packing full rate traffic channels to half rate traffic channels with multiple sub-channels for an overall higher number of traffic channels. This can be done due to an improved link performance with shared spectrum in the high traffic loaded conditions. • Roll-out of LTE to GERAN frequency band (e.g. at 900 MHz, 1800 MHz, etc.) will be challenging in smaller bandwidth allocations without any shared band.

• GERAN is flexible, and frequencies can be allocated at 200 kHz accuracy.

In this context, it should also be noted that several use cases can be derived. For example, a service deployment can be configured where GSM is used as a coverage layer, and LTE makes a handover to GSM when there is a coverage problem. With this method the GSM coverage layer can be optimized, while LTE can maintain the best possible Quality of Service, since the bandwidth is not wasted for two adjacent systems.

The main disadvantage is that the LTE carrier spacing is 180 kHz, whereas in GERAN systems the carrier spacing is 200 kHz. Therefore, LTE is not able to fully utilize free resources in the shared band. This limitation can be overcome partly by sharing only those carriers which match with the different carrier spacing by a common factor (see Fig. 4) . In a GSM system, frequency reuse is applied. For example, in case of a reuse factor of 1/3, only every third GSM carrier is used in a cell. Furthermore, usage of GSM radio resources varies based on traffic load and requested quality of service. As exemplarily shown in Fig. 4, a cell may use GSM carriers 1,

4, 7 and 12 such that LTE can use resource blocks 1, 4, 5, 8 to 18 and 21 to 25. This means that LTE resource blocks 1, 4,

5, 8, 9, 17, 18 and 21 to 25 must be controlled in order to avoid that interference to (and from) neighboring GSM cells is too high.

Another disadvantage is that GSM and LTE are not fully compatible in time domain due to different numerology in the frame structures. TDMA frame and radio frame synchronization can not be achieved easily. This limitation can be overcome partly by having a radio resource management which keeps track on both frame structures using a common system clock.

Aside therefrom, a further disadvantage consists in the requirement of extra control logic in GERAN and LTE RRM to support adaptive capacity adaptation between the systems. However, this can be justified by capacity improvements and already existing traffic allocation functions between GERAN and WCDMA.

While the present invention has been illustrated and described in detail in the drawings and in the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, which means that the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. Furthermore, any reference signs in the claims should not be construed as limiting the scope of the invention.

Claims

1. A method for allocating requested radio resources for at least two coexisting and co-located radio access networks sharing the same frequency spectrum in an active radio cell, wherein said method comprises the steps of predicting (S5b (ii) ) a deterministic frequency occupancy for the allocated frequency spectrum of at least one first radio access network for several frames in advance and allocating (S6) at least one frequency band from the residual, unoccupied parts of the shared frequency spectrum for at least one second radio access network according to bandwidth requirements of said at least one second radio access network.

2. A method according to claim 1, wherein said at least one first radio access network is a second-generation radio access network which operates based on the GSM/EDGE standard.

3. A method according to claim 2, wherein said at least one second radio access network is a fourth-generation radio access network which operates based on the E-UTRAN standard.

4. A method according to claim 3, comprising the following steps : entering a channel request (Sl), controlling (S2) the active radio cell such as to avoid co- channel interference between the at least two co-existing and co-located radio access networks, said at least one first radio access network carrying out a resource block allocation procedure for allocating those radio resources which are requested by said first radio access network, wherein carrier allocation is adaptively changed based on a deterministic frequency hopping scheme (S3), said at least one second radio access network calculating the frequency occupancy for the allocated frequency spectrum of the at least one first radio access network for several frames in advance (S4), and, if a channel resource request is received from the at least one second radio access network, performing a channel selection and activation (S5) based upon the predicted frequency occupancy for the allocated frequency spectrum of the at least one first radio access network.

5. A method according to claim 4, wherein, - when the channel resource request is received from the at least one second radio access network, looking for available active channels in the shared frequency spectrum (S5b (i)),

- predicting the resource allocation of the at least one first radio access network by calculating the deterministic frequency occupancy for the allocated frequency spectrum of said at least one first radio access network for several frames in advance (S5b (ii) ) ,

- updating the shared resource pool as given by the shared frequency spectrum by indicating new occupied and restricted channels of said at least one first radio access network (S5b (iii) ) ,

- allocating a set of resources as requested by said at least one second radio access network (S6) , - correspondingly updating the shared resource pool by indicating the new occupied and restricted channels of said at least one second radio access network (S7), and - activating a traffic channel using the allocated set of resources as requested by said at least one second radio access network (S8) .

6. A base transceiver station for allocating requested radio resources for at least two coexisting and co-located radio access networks sharing the same frequency spectrum in an active radio cell, wherein said base transceiver station is configured for calculating a deterministic frequency occupancy for the allocated frequency spectrum of at least one first radio access network for several frames in advance and allocating at least one frequency band from the residual, unoccupied parts of the shared frequency spectrum for at least one second radio access network according to bandwidth requirements of said at least one second radio access network .

7. A computer program for executing a method according to anyone of claims 1 to 5 when being implemented and running on a base transceiver station according to claim 6.