TECHNICAL FIELD

Embodiments herein relate to a network node, a method therein, a computer program and a carrier comprising the computer program. In particular, they relate to mitigating interference in a first carrier of a first Radio Access Technology (RAT), during a transmission in a second carrier of a second RAT. BACKGROUND

Wireless devices or terminals for communication are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server, such as server providing video streaming service, via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.

Wreless devices may further be referred to as mobile telephones, cellular telephones, computers, or surf plates with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.

A cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNodeB (eNB), NodeB, B node, Base Transceiver Station (BTS), or AP (Access Point), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless devices within range of the base stations. The base stations and wireless devices involved in communication may also be referred to as transmitter-receiver pairs, where the respective transmitter and receiver in a pair may refer to a base station or a wireless device, depending on the direction of the communication. Two wireless devices involved in D2D communication may also be referred to as a transmitter-receiver pair. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to a wireless device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.

Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile

Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for communication with terminals. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.

In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.

With the rapid development of the telecommunication systems, new multi standard base stations, new features such as Voice services over Adaptive Multi-user channels on One Slot (VAMOS) and features such as Discontinuous Transmission (DTX) in GSM domain may be successfully combined to create even more efficient LTE deployments, than what is currently possible. VAMOS increases voice calls capacity supported by a GSM network. It is possible to use one time slot for four voice calls/services. It does not require any extra

transmit/receive hardware to achieve this and will provide similar voice quality as normal GSM handset (non VAMOS handset). With GSM full rate, 1 call per time slot is possible. With GSM Half rate, 2 calls per time slot is possible. Wth VAMOS in GSM half rate, 4 calls per time slot is achievable. VAMOS is one of the most important features added in 3GPP Release 9 as it has the potential to double the voice capacity in the GSM network. The new Adaptive

Quadrature Phase Shift Keying (AQPSK) modulation scheme in DL enables allocation of different power levels on the ln-phase (I) part and the quadrature (Q) phase part and in combination with new orthogonal training sequences, two voice users may share the same physical resource.

One or several GSM 200 kHz carriers, within or even relatively close to an LTE band, will in many cases greatly reduce cell efficiency of one or several LTE cells also referred to as LTE carriers. This is due to the high output power used for a GSM carrier, in a narrow band, generating a very potent co-channel interferer for part of the LTE cell. In an ideal world the GSM carrier would only degrade the part of the LTE cell that it is actually transmitting on, but in reality the consequence is often much worse. Also site solutions where the LTE eNodeB is equipped with extra filters to reduce interference only helps the eNodeB, not the UE. For a UE it is in in many cases not a feasible solution as it will need different filters and filter settings for different cells. With the vast number of GSM only devices in the world, operators are obliged to provide service for these, and with the rapid LTE deployment this conflict is growing. In practice this conflict costs either spectrum for LTE or(and) degraded cells, even if features such as frequency selective scheduling will detect the interferer and will improve the situation or filters, there is still a significant negative impact on the LTE cell. This is also due by that many LTE UEs have difficulties filtering out narrow band powerful disturbance sources and as result the performance of the entire cell is degraded, not just the primarily disturbed Resource Blocks.

There are some techniques for dynamic spectrum re-farming with overlay for legacy devices discussed, where GSM carriers are inserted into LTE cells, yet with significant LTE cell degradation and capacity loss due to its static nature, large part of this capacity loss is also often present even if the GSM carrier is not actually being used. This is based on the LTE cell detects the bursts from the GSM carriers and reacts and removed allocation of UEs on these. This means the LTE cell will often at the start of GSM channel transmission have its corresponding Physical Resource Blocks transmissions fail. The more discontinuous the GSM channels behave, the more they will fail bursts.

Another solution relating to Co-channel interference discusses geographical isolation zones that can be used to counter interference where different wireless networks use the same frequency bands. LTE network building will create more complex interference problems in the future and it is needed to eliminating interference caused by the coexistence of GSM, UMTS and LTE networks, and the co-channel and adjacent- channel interference between wireless networks. A solution discussed is to provide optimal anti-interference solutions through spatial isolation, equipment isolation, guard bands and other approaches but it costs intricate network planning and unnecessary use of limited spectrum to handle interference between GSM and LTE.

Another solution would be to focus on how to pack GSM and LTE side by side using less spectrum, good use of features and cell planning, but with likely large risk for significant interference.

Other prior art solutions relies on simple static allocations where the UE and the LTE cell has to fend for itself as good as possible.

SUMMARY

It is therefore an object of embodiments herein to further improve the performance of a wireless communications network using multiple overlapping or adjacent RAT carriers. According to a first aspect of embodiments herein, the object is achieved by a method performed by a network node, for mitigating interference in a first carrier of a first Radio Access Technology, RAT, during a transmission in a second carrier of a second RAT. The network node comprises a first part related to the first RAT, and a second part related to the second RAT. The first part acts as a first RAT base station and the second part act as a second RAT base station.

The second part of the network node schedules a second RAT transmission in a second RAT carrier related to the second RAT. The second RAT carrier is allocated within or adjacent to a first RAT carrier related to the first RAT. The network node then transfers information from the second part to the first part. The information relates to the scheduled second RAT transmission. During the second RAT transmission, the first part of the network node mitigates interference, in a part of the first RAT carrier where the second RAT carrier is not allocated, based on said information.

According to a second aspect of embodiments herein, the object is achieved by a computer program comprising instructions, which when executed by at least one processor, cause the at least one processor to perform actions according to any of the actions above.

According to a third aspect of embodiments herein, the object is achieved by a carrier comprising the computer program. The carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer-readable storage medium.

According to a fourth aspect of embodiments herein, the object is achieved by a network node for mitigating interference in a first carrier of a first Radio Access

Technology, RAT, during a transmission in a second carrier of a second RAT. The network node comprises a first part related to the first RAT, and a second part related to the second RAT. The first part is configured to act as a first RAT base station and the second part is configured to act as a second RAT base station.

The network node is configured to:

-schedule by the second part, a second RAT transmission in a second RAT carrier related to the second RAT, which second RAT carrier is arranged to be allocated within or adjacent to a first RAT carrier related to the first RAT,

-transfer information from the second part to the first part, which information is arranged to relate to the scheduled second RAT transmission, and

-mitigate interference by the first part during the second RAT transmission, in a part of the first RAT carrier where the second RAT carrier is not allocated, based on said information. An advantage with embodiments herein is that overlapping use of spectrum between different RAT carriers is possible. Spectrum usage and spectrum planning are significantly simplified for different RATs sharing the same carrier/frequency band. End user performance is also improved, as the first RAT carrier is only affected when a second RAT carrier is actually transmitted, interference can be reduced during the transmission and there is no need to reserve guard periods in general for the second RAT as static solutions would require, thus general loss of capacity is removed.

Thus, the performance of a wireless communications network using multiple overlapping or adjacent RAT carriers is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments herein are described in more detail with reference to attached drawings in which:

Figure 1 is a schematic block diagram illustrating embodiments of a communications network.

Figure 2 is a flowchart depicting embodiments of a method in a network node.

Figure 3 is a schematic block diagram illustrating embodiments of a method.

Figure 4 is a schematic block diagram illustrating embodiments of a network node.

DETAILED DESCRIPTION

Figure 1 depicts an example of a wireless communications network 100 in which embodiments herein may be implemented. The wireless communications networklOO implementing embodiments herein relates to a multi-RAT network. The wireless communications networkl OO relates to at least two RATs, a first RAT and a second RAT. The multiple RATs in the wireless communications network 100 may relate to any one or more out of: LTE, GSM, GSM EDGE Radio Access Network (GERAN), Wi Fi, Wireless Local Area network (WLAN), WMax, Code Divisional Multiple Access (CDMA) 2000, LTE- NX, Massive Ml MO systems etc. EDGE is the abbreviation for Enhanced Data Rates for GSM Evolution, and NX LTE means next-generation 5G radio access technology.

A plurality of network nodes operate in the wireless communications network 100 whereof one, a network node 110 is depicted in Figure 1. Thus the network node 1 10 a comprises at least a first part 111 related to the first RAT, and a second part 112 related to the second RAT. According to embodiments herein network nodes or network units of different RATs share the same hardware, such as e.g. a GSM Base Transceiver Station and an LTE eNodeB share the same hardware within the network node 110. In one embodiments the network node 110 is represented by two, i.e. a first and a second not co-located nodes but with high speed communication in-between not necessarily sharing the same hardware. This embodiment is in Figure 1 symbolized as a dashed line. In that case the first part 1 1 1 is located in the first node and the second part 112 is located in the second node. This makes it possible to communicate in between the first part 1 11 and second part 112. The first part 1 11 acts as a first RAT base station, and the second part 1 12 acts as a second RAT base station. The base stations functionallity may for example refer to any type of network node functionallity such as e.g. Radio Base Station (RBS), eNodeB (eNB), NodeB, B node, Base Transceiver Station (BTS), or AP (Access Point), depending on the technology and terminology used, or any other network node functionallity capable to serve an electronic device such as a UE or a machine type communication device in a wireless communications network. The first part 1 11 may provide a first cell 115 and and the second part 112 may provide a second cell 116.

As said above it possible to communicate within the network node 110. Thus the first part 1 11 and the second part 1 12 are capable to communicate with each other such as for exchange information. The first part 1 11 is e.g. capable of scheduling first RAT transmissions in a first RAT carrier. The first RAT carrier is related to the first RAT. The second part 1 12 is e.g. capable of scheduling second RAT transmissions in a second RAT carrier. The second RAT carrier is related to the second RAT. Please note that the first RAT carrier and the second RAT carrier each may comprise one or more subcarriers.

The network node 110 e.g. provides overlapping use of spectrum between the first RAT carries and second RAT carriers. Thus the second RAT carrier is allocated within or adjacent to a first RAT carrier related to the first RAT. Within or adjacent here means that the frequency band allocated for the second RAT carrier is within or partly within the frequency band allocated for the first RAT carrier and consequently affects the first RAT carrier, or is allocated as adjacent to the frequency band or range within a frequency allocated for the first RAT carrier the that the second RAT carrier affects the first RAT carrier. It may also be referred to as the first RAT carrier is in the proximity of the second RAT carrier and thereby is affected.

According to an example scenario the first RAT is represented by LTE and the second RAT is represented by GSM. However any combination of RATs mentioned above may be used. According to the example scenario, the first part 1 1 1 is related LTE and acts as an LTE base station such as an eNodeB , and the second part 112 related to GSM and acts as a GSM base station such as a BTS. In some embodiments the network node 1 10 deploys LTE and GSM on the same frequency band or on adjacent frequency bands.

Embodiments herein are advantageously used in scenarios where the second RAT carrier is a narrowband carrier strongly affecting the first RAT carrier when being a broad band carrier such as e.g GSM affecting LTE and/or WCDMA. One or more UEs 121, 122, 123 are operable in the wireless communications network 100. The UE 121 is capable of being served by the first part 1 1 1 of the network node 1 10.

The UEs 122 and 123 are capable of being served by the second part 1 12 of the network node 110. The term UE when used herein may e.g. refer to a wireless device, a mobile wireless terminal or a wireless terminal, a mobile phone, a target device, a Device to Device (D2D) UE, a computer such as e.g. a laptop, a Personal Digital Assistants (PDAs) or an iPad, a tablet computer, sometimes referred to as a surf plate, with wireless capability, a smart phone, Laptop Embedded Equipment (LEE), Laptop Mounted

Equipment (LME), Universal Serial Bus (USB) dongles or any other radio network units capable to communicate over a radio link in a wireless communications network. Please note the term UE used in this document also covers other wireless devices such as Machine to machine (M2M) devices. According to embodiments herein, the knowledge of second RAT transmissions such as e.g. GSM transmissions is used to minimize the detrimental effects of affected first RAT carriers such as e.g. LTE carriers. Embodiments herein may use knowledge of the GSM upcoming transmission e.g. by sniffing the GSM Abis jitter buffer, enabling DTX/VAMOS/Half-rate features based on LTE traffic and in the eNodeB take appropriate scheduling actions. Additional use of GSM/LTE features will compound the effects superior to prior art.

GSM Abis is the interface between a Base Station Controller (BSC) and a Mobile switching center (MSC) in GSM.

Some embodiments herein are based on allocating spectrum for first RAT carriers, and on the border of this spectrum, within it, or adjacent to it, allocate second RAT carriers from second part 112 residing in the same network node 1 10 as the first part 1 11. When a second RAT transmission is allocated within the first RAT carrier the first part 11 1 mitigates interference i.e. the impact. This may be performed by e.g. ceasing transmission on affected part of first RAT carrier and selecting a more robust Modulation and Coding Scheme, a more protected mode of transmission on the remaining first RAT carrier for the duration of the second RAT transmission. An illustrative example of the above embodiments is based on allocating spectrum for LTE carriers, and on the border of this spectrum, within it, or adjacent to it, allocate carriers from a GSM BTS residing in the same baseband unit as an eNodeB. When the GSM BTS needs to transmit on a carrier within or adjacent to the LTE carriers, LTE 5 eNodeB part mitigates the impact by ceasing transmission on affected resource blocks and selecting a more robust Modulation and Coding Scheme (MCS), a more protected mode of transmission, on the remaining resource blocks in the cell 1 15 for the duration of the GSM transmission. By smart using of GSM services impact may also be reduced by using for instance VAMOS, with DTX and half rate channels, thus reducing the amount of 10 time GSM carriers are actually transmitted. Embodiments herein may in this example e.g. be referred to as Spectrum re-farming and network optimization when deploying LTE and GSM on the same frequency band, and/or LTE and GSM inband channel sharing.

15 A method for mitigating interference in a first carrier of the first RAT, during a

transmission in a second carrier of the second RAT is performed by the first network node 1 10. As an alternative, a Distributed Node (DN), such as the network node 118, and functionality, e.g. comprised in a cloud 119 may be used for performing the method.

20

Example embodiments of the method performed by the network node 1 10, 1 18 for mitigating interference in a first carrier of the first RAT during a transmission in a second carrier of the second RAT will be described with reference to a flowchart depicted in

Figure 2. As Mentioned above the network node 1 10 comprises the first part 11 1 related

25 to the first RAT, and the second part 112 related to the second RAT. The first part 11 1 acts as a first RAT base station and the second part 112 acting as a second RAT base station. In some embodiments, the first RAT is represented by LTE, and the second RAT is represented by GSM.

The second part 1 12 has an upcoming second RAT transmission to e.g. the UE

30 123. To describe embodiments herein a specific example scenario wherein the first RAT is represented by LTE and the second RAT is represented by GSM, will be used to explain the different actions in the method. E.g., the GSM part has an upcoming GSM transmission. In the specific example, a logical GSM BTS is capable to communicate with its LTE counterpart in the eNodeB. The LTE eNodeB and the GSM BTS have high speed

35 links internally to communicate on making rapid sharing of information possible. The method comprises the following actions, which actions may be taken in any suitable order. Actions that are optional are presented in dashed boxes in Figure 2.

Action 201

The upcoming second RAT transmission is to be scheduled. It is a second RAT transmission and it will be scheduled in the second part 112. Thus the second part 112 schedules the second RAT transmission in the second RAT carrier related to the second RAT. The second RAT carrier is allocated within or adjacent to a first RAT carrier related to the first RAT. In the specific example, the GSM BTS schedules the GSM transmission in the GSM carrier. The GSM carrier is allocated within or adjacent to the LTE carrier.

Action 202

The first part 1 11 and the second part 1 12 need to exchange information about the scheduled second RAT transmission, so that the any overlap or proximity between the first RAT carrier and the second RAT carrier of interest, i.e. that is affected by the second RAT transmission can be detected. The second part 112 knows in advance when to send the second RAT transmission on the second RAT carrier, this is required to have time to inform the first part 11 1 about the second transmission to be able to mitigate interference of the affected part of the first carrier when the second RAT transmission starts and during the second RAT transmission. The second part 112 such as the GSM BTS knows when itself will transmit, but depending on service it may or may not know if the UE 123 will transmit, however the second part 112 still knows when the UE 123 is expected to transmit. This data may also be made available to the first part 1 11 such as the LTE eNodeB.

With the second RAT transmission being IP based transmission there is also an jitter buffer to mitigate effects of the jitter in the IP network the GSM BTS, i.e. to compensate for the jitter in the IP network so payload data reach the GSM BTS in time to be transmitted over the air interface to the UE 123.

In e.g. Voice over IP (VoIP) or for other data, a jitter buffer may be a shared data area where voice packets may be collected, stored, and sent to the voice processor in evenly spaced intervals. Variations in packet arrival time, called jitter, may occur because of network congestion, timing drift, or route changes. The jitter buffer, which is located at the receiving end of the voice connection, intentionally delays the arriving packets so that the end user experiences a clear connection with very little sound distortion. This buffering is configurable and leads to that the second part 1 12 such as the GSM BTS has configurable advance knowledge of the second RAT transmission to be sent over the second RAT transmission, which could be shared with the first part 1 11 such as the LTE eNodeB, giving the first part 11 1 time to act and send said information. For best performance the jitter buffer depth, also referred to as timing or average jitter delay setting, need a few extra milliseconds to allow the second part 1 11 enough time to inform the first part 1 12 in almost all cases, otherwise it may be a best effort approach.

Thus, in the network node 110, information is transferred from the second part 1 12 to the first part 1 11. The information relates to the scheduled second RAT transmission. The information may comprise any one or more out of frequency, modulation, power, start of and duration of the scheduled transmission.

In the specific example, the LTE eNodeB and the GSM BTS exchanges information about the scheduled GSM transmission such as e.g. about frequencies used for the GSM carriers, in GSM frequency hop are often used meaning that a connection regularly changes frequency or Absolute Radio Frequency Channel Number (ARFCN) within the band, so that the any overlap or proximity between GSM carrier and LTE carrier of interest can be detected. The GSM BTS know in advance when to send a burst on a carrier which is needed to have time to inform the eNodeB. ARFCN is a unique number given to each radio channel in GSM.

Action 203

In some embodiments the information is processed before it is possible to be used as a basis for mitigating the interference. It may also be used to decide whether or not to perform any interference mitigation at all. The first part 11 1 may need to convert information received such as e.g. frequency, modulation, power and start of and duration of the second RAT transmission into mitigating actions to take. In these embodiments the base station 11 1 e.g. the first part 11 1 , processes the information. This may be performed according to any one or more out of:

Calculating an expected degradation of the first RAT carrier related to the scheduled transmission.

Calculating Signal to Noise Ratio, SNR, and/or Signal to Interference plus Noise Ratio, SINR, based on the calculated an expected degradation of the first RAT carrier. This to see how affected the first RAT channel is.

SNR = S/N and SINR= S/(N+I) wherein S represents transmitted signal power, N represents noise power and I represent interference power. Calculating which subcarriers of the first RAT carrier that are affected by the scheduled transmission,

Deciding whether or not to schedule any data on the affected subcarriers of the first RAT carrier. The affected subcarriers of the first RAT carrier may e.g. be resource blocks in the LTE carrier.

Deciding whether or not to select a more robust modulation for any transmission e.g. to the UEs 121 and 122, on affected and unaffected subcarriers of the first RAT carrier for the duration of the scheduled second RAT transmission, based on said information and first RAT cell data such as e.g. UE reports Channel Quality Indication (CQI) and eNodeB internal measurement. This is performed by the first part 11 1.

Action 204

In the network node 110 and during the second RAT transmission, the first part 11 1 mitigates interference in a part of, such as in one or more subcarriers of, the first RAT carrier where the second RAT carrier is not allocated, based on said information. This is to reduce the effect of the interference in the first RAT carrier during the second RAT transmission.

As soon as the second RAT transmission is over, the values used before the mitigation of interference can be used again and the part of the first RAT channel used for the second RAT transmission can be used again for first RAT transmissions.

In some embodiments where the action of processing the information is performed, the first part 1 11 may mitigate interference based on said information when processed.

In the specific example, the LTE eNodeB part mitigates the impact selecting a more robust MCS, a more protected mode of transmission, on the remaining resource blocks in the cell 1 15 for the duration of the GSM transmission.

The interference may further be mitigated by Inter Cell frequency load balancing in the first RAT carrier or when Inter Cell frequency load balancing is not possible using Inter Frequency offload or Inter RAT Off load from the first RAT carrier to WCDMA. This may be performed by counting interfered resource blocks as being partly or completely used to make the load balancing work on the effective capacity of the cell. Inter-frequency offload may be used for cases when Inter-frequency load balancing is not possible use e.g. when only S1 handover is supported. The feature avoids too high load in one frequency as long as capacity remains on another frequency.

The interference may yet further be mitigated by applying Inter-RAT Offload from the first RAT carrier to WCDMA. This may be performed by monitoring the load in the LTE cell and in case of load being above a threshold UEs are moved to WCDMA to offload the LTE cell. The load measure is the same as for Inter-frequency load balancing.

The interference may further be mitigated by adjustment of the cell capacity of the first part 11 1. This may be performed by adjusting the actual cell capacity in the cell load monitoring and applying a hysteresis on the reported interference.

One way of mitigating interference may be to not send any data where there is no chance that the receiver can hear over the disturber.

Thus according to some embodiments, the first part 11 1 performs the mitigating of the interference according to any one or more out of: selecting an adjusted mode of transmission, performing inter frequency Offload of the first RAT carrier, performing inter cell frequency load balancing of the first RAT carrier, adjusting the cell capacity of the first RAT carrier, and performing inter RAT off load from the first RAT carrier.

Then this makes the first RAT carrier more robust and less affected by interference.

Action 205

In some embodiments, and during the transmission in the second RAT carrier, the first part 1 11 ceases any transmission in a part of, such as in one or more subcarriers of, the first RAT carrier in which the second RAT carrier is allocated. When the first RAT carrier scheduler receives the information from Action 203 and expected interference from second RAT carrier, the too interfered subcarriers will be removed from scheduling for the duration of the second RAT carrier transmission. If the interferer in the second RAT is a GSM carrier, with the normal GSM cell feature for frequency hopping, the sudden change of frequency using another GSM carrier for the second RAT carrier may also be covered as the first RAT carrier would prior the frequency change receive the information as shown above.

In the specific example, the LTE eNodeB part mitigates the impact by ceasing transmission on affected LTE carriers such as LTE resource blocks a for the duration of the GSM transmission.

Action 206

In some embodiments, the first part 11 1 such as the LTE eNodeB also informs the second part 1 12 such as the GSM BTS if any second RAT carrier collides with sensitive parts of the first RAT carrier such as the LTE Carrier. Sensitive parts of the first RAT carrier may e.g. be Packet Data Channels (PDCH), Secondary Synchronization Channel (S-SCH) and Primary (P)-SCH so that these may be removed from the second RAT hopping set and any operator may be notified of the planning conflict. The RAT hopping set may comprise at least two parts, the first part is the ARCNs frequencies which to use or hop over, the second is the order to use them in. In addition, information of where in the sequence to start is preferably used so that both sender and receiver can follow the same sequence.

In GSM, a carrier may be divided into one or more hopping sets, e.g. 8 or 12, . If there are many transceivers such as Transceivers(TRXs) for a carrier, the second RAT carrier may e.g. be divided into two groups with 4 or 6 transmitters each, where one group uses frequencies within the first RAT carrier and the other group uses frequencies outside the first RAT carrier. It may be controlled by a second RAT controller such as e.g. by a BSC which of the two groups that shall start the second RAT transmission. For the second part 1 12 with information from the first part 11 1 , the second part 112 may remove a sensible frequency for the first RAT carrier from the frequency hop list based on the information from the first part 11 1. However, in case of a Broadcast Control Channel (BCCH), it must be chosen which carrier to be used.

Thus, the second information may be transferred from the first part 11 1 to the second part 112. The information relates to that the second RAT carrier collides with sensitive parts of the first RAT carrier.

According to some embodiments, second RAT carriers such as GSM carriers may be prioritized for larger cells by the second part 1 12 such as the BTS based on

information from the first part 1 1 1 such as the eNodeB to ensure that subcarriers within the first RAT carrier such as the LTE cells are used last.

According to some embodiments, further improvements to enhance co-channel may be used.

In GSM Time Division Multiple Access (TDMA) channels are used, which time slices a 200 KHz carrier into 8 timeslots, thus enabling 1 timeslot gives a maximum of <12.5% of interference over time, with an estimated DTX rate of 40% giving an interference reduction to around 7.5% per timeslot over time. A Careful selection of features used on the conflicting second RAT carrier may also reduce negative impact on the first RAT carrier, such as using DTX VAMOS half rate, BCCH power save etc.

By using DTX in Uplink and Downlink of the second RAT carrier, the number of packages sent on an active second RAT carrier are reduced, which reduces negative impact on the first RAT carrier.

Using half rate speech channels or VAMOS half rate on the second RAT carrier when being a GSM carrier, gives more GSM speech service per timeslot used. This results in fewer GSM channels needed to serve the same number of erlangs in the second RAT carrier. An eriang is a unit of traffic density in a telecommunications system. Also on allocated speech channels with DTX there is even possible for the first RAT carrier to use or the same carrier that is active for a second RAT carrier. Such as the first RAT carrier for receiving information from the second RAT carrier that transmissions for next transmit window is not used by the second RAT carrier. This gives a significant advantage as as soon as DTX or any other feature causing the second RAT carrier to ceise transmission the first RAT carrier can use this temporary silence to transmit its own carrier. GSM has 8 timeslots per carrier, which may be used for signalling BCCH or Standalone Dedicated Control Channel (SDCCH), speech or data.

For speech, any of the following may be choosen: With GSM full rate, 1 call per time slot is possible meaning 100% occupation. With GSM Half rate, 2 calls per time slot is possible resulting in 50% occupation of GSM transmission and the other 50% may be used by the first RAT carrier for first RAT transmissions. Downlink Power Control and MS Power control may be used to reduce the actual power used in the transmission by the RAT carrier and UE 123.

For GSM Data services, many UEs may receive data on more timeslots than they can transmit. This may be used to reduce uplink disturbance caused by the second RAT carriers as fewer timeslots are needed and these timeslots may be shared between UEs of the second RAT.

Second RAT carriers such as Broadcast Control Channel (BCCH) configured GSM carriers should if feasible not be put within first RAT carriers such as the LTE used frequencies, but even if so the method herein will help mitigate such effects.

BCCH Power savings in the second RAT carrier when being a GSM carrier may also improve performance of the first RAT carrier if a BCCH carrier is placed close or within the first RAT carrier used frequencies such as LTE used frequencies. Using larger frequency set for the second RAT carrier such as the GSM carriers, but avoiding critical channels in the RAT cell such as the LTE cell, this also improves the performance of the second RAT channel such as the GSM carrier at no additional loss for the first RAT carrier such as LTE cell.

Assume 4 TRXs per second RAT carrier, here GSM carrier, and 10 MHz first RAT carrier, here LTE carrier, as long as critical parts of the LTE carrier is avoided, it does not matter wherein the LTE carrier the GSM carrier is located. So for the GSM more than one carrier may be used, maybe 10 carriers, but not more than 4 of these may be used for transmissions per time and since the first part 11 1 is informed, this will not decrease performance in the first RAT carrier.

Cell conflicts may be notified to the operator by the second part 1 12 such as the GSM BTS. Depending on severity it may be a notification to a network manager such as e.g. Encore Network Manager (ENM) to remove the offending frequency from the frequency hopping list of the second RAT channel or to disabling the second RAT carrier and issue an alarm.

Figure 3 illustrates embodiments wherein the first RAT is LTE and the second RAT is GSM. Figure 3 shows how communication between the first part 11 1 when being an eNodeB and the second part 112 when being a GSM BTS is set up and initial data exchanged, to establish if there are conflicts, remove critical conflicts and notify on north bound interfaces for GSM BTS to Operations Support Systems (OSS)/BSC. The interface between BTS and BSC is referred to as Abis. The OSS interface is referred to as Mu. A northbound interface is used to interface with higher level layers.

301. An assessment of the GSM carrier is performed by the GSM second part 1 12, here the GSM BTS, i.e. investigation of which frequencies are comprised in the GSM carrier of the second part 112 for communication. The GSM BTS communicates with the eNodeB and exchanges information relating to the upcoming GSM transmission in the GSM carrier.

302. Based on information from the second part 1 12, the eNodeB checks whether there are there any conflicts between the GSM carrier and the LTE carrier. If it is, move to

303, if not move to 307.

303. When it is a critical LTE impact, i.e. conflict move to 304. This means if the LTE carrier is affected by the GSM carrier. Critical impact here means that on for the LTE carrier critical frequency is disturbed and must be removed otherwise the LTE carrier will not work. An example is P-SCH. 304. The GSM BTS acts on the information from the LTE part and removes offending frequencies from GSM carriers hopping sequence. This may be performed with low speed communication, since it is cell data and not real time data. Then move either to 305 or 306.

305. The GSM BTS raises alarm on GSM carriers that were removed.

306. The GSM BTS informs BSC of the active GSM carrier within the LTE carrier so these can be used last, such that if parts of the GSM carrier is located outside the LTE carrier, if allowed for the cell planning, allocating GSM UEs on this outside part of the LTE carrier first.

307. If there is a non-critical risk of conflicts between the GSM carrier and the LTE carrier in 302, i.e. if it is a part of the LTE carrier that is not used for signalling, only for payload. Move to 306 and/or move to 308

308. A fast communication is established between the GSM BTS and the eNodeB to exchange information relating to dynamic conflict data. Then move to any of 309, 313, and 316. Dynamic data is related to the active calls and use of timeslot per timeslot, 301 is on the other hand semi static data which frequencies are used where is BCCH etc.

309. The GSM BTS monitors incoming packages of the GSM transmission on conflicting carriers.

310. When a packet is found, go to 311.

311. Provide eNodeB with information about planned transmission data of the GSM transmission such as frequency, power, modulation and start/stop time in System Frame Number (SFN). A SFN is associated to each 10 ms frame counting from 0 to 1023 so that it can be reflected in the scheduling.

312. The eNodeB then mitigate conflict based on the information.

313. After 308, the GSM BTS checks whether there is any conflict also affecting Uplink such as feedback from the eNodeB. An LTE carrier comprises different frequency bands and may also use different modes Time Division Duplex (TDD) on a shared UL/DL frequency and Frequency Division Duplex (FDD) with separate UL/DL frequency.

314. If yes, move to 315.

315. The GSM BTS provides the eNodeB Cell with frequency, power and start/stop time (in SFN) when the UE 123 is allowed unscheduled channels such as RACH or expected to transmit and go to 312. 316. After 308, the GSM BTS checks if there are any filler carriers such as BCCH channels in conflict.

317. If yes, move to 311 and 312.

5

The actions according to an example embodiment wherein the first RAT is LTE and the second RAT is GSM and wherein the first part 11 1 is an eNodeB and the second part 1 12 is a GSM BTS will now be described. These actions relate to how the eNodeB uses the conflict data to minimize the impact of the GSM carrier on the LTE carrier. The 10 eNodeB preventatively acts on expected radio conditions for the duration of the GSM

transmission, as it already knows what the GSM carrier will have for frequency, power and duration based on the received information from the GSM BTS.

When the eNodeB shall decide whether or not to mitigate the conflict, i.e. the impact 15 of the GSM carrier on the LTE carrier, it starts to handle the conflict by assessing the severity of it. This may e.g. be performed by analyzing the information from the GSM BTS as mentioned in actions 204-205 and 31 1.

When the conflict is not within the LTE frequencies of the LTE carrier, i.e. outside 20 the LTE carrier but so adjacent to it that it causes a conflict, e.g. a higher noise ratio may be used based on data received from GSM carrier(s) when calculating SNR, than actually received from the UE 123 to determine which MCS to use for transmission to increase likelihood of successful reception.

25 When the conflict is within the LTE frequencies of the LTE carrier, i.e. inside the LTE carrier, no transmission shall be scheduled on severely affected LTE subcarriers, e.g. resource blocks. A higher interference ratio shall be used based on data received from GSM carrier(s) when calculating SNR/SINR, than actually received from the UE 123 to determine which MCS to use for transmission to increase likelihood of successful

30 reception.

The actions according to an example embodiment wherein the first RAT is LTE and the second RAT is GSM and wherein the first part 11 1 is an eNodeB and the second part 35 1 12 is a GSM BTS will now be describes. Abis Payload packages received in the GSM BTS enter the jitter buffer in the GSM

BTS.

The GSM BTS such as e.g. by means of a GSM carrier scheduler checks the jitter buffer for each timeslot for data to transmit.

When data is found, the GSM BTS such as e.g. by means of a GSM carrier scheduler performs GSM scheduling as normal according to prior art. According to embodiments herein, also a notification is sent to the eNodeB such as e.g. a scheduler in the eNodeB, with time, frequency, power, modulation of the coming GSM transmission.

The eNodeB such as e.g. the LTE scheduler takes mitigation action, as described above to reduce detrimental effect on the LTE carrier.

An advantage of embodiments herein is that overlapping use of spectrum between different RAT carriers such as GSM carriers and LTE carriers is possible, and negative prior art effects are significantly reduced.

Carrier usage and spectrum planning for carriers and/or cells are significantly simplified for GSM and LTE sharing the same frequency band. End user performance is also improved, as e.g. a LTE carrier is only affected when GSM carriers are actually transmitted, interference can be reduced during the transmission and no need to reserve guard PRBs in general for GSM as static solutions would require, and thus general loss of capacity is removed. As long as sensitive radio blocks are excluded, the GSM carriers may be injected anywhere within the LTE cells spectrum, and the GSM cells may use frequency hopping over many frequencies within the LTE cell without causing additional deterioration for the LTE carrier. If sensitive PRBs are in the hopping set the LTE eNodeB may inform the GSM BTS of the conflict and the GSM carrier that can remove them from hopping sequence and notify on north bound interface that there is a configuration conflict. The network node such as the GSM BTS may also report on the north bound interface which GSM carriers that are within an LTE carrier so these can be scheduled last for transmission, if there are GSM carriers available within the cell outside the spectrum of the LTE cell. It is also becoming more common for customers to share nodes, and this solution works regardless if the different carriers belong to different operators or not.

To perform the method actions for mitigating interference in a first carrier of the first RAT during a transmission in a second carrier of the second RAT, the network node 110, 1 18 may comprise the following arrangement depicted in Figure 4. As mentioned above, the network node 110, 118 comprises a first part 1 11 related to the first RAT, and a second part 112 related to the second RAT. The first part 1 11 is configured to act as a first RAT base station and the second part 1 12 is configured to act as a second RAT base 5 station. In some embodiments, the first RAT is configured to be represented by LTE, and the second RAT is configured to be represented GSM.

The network node 1 10, 1 18 is configured to, e.g. by means of a scheduling module 410 configured to, schedule by the second part 112, a second RAT transmission 10 in a second RAT carrier related to the second RAT. The second RAT carrier is arranged to be allocated within or adjacent to the first RAT carrier related to the first RAT.

The network node 1 10, 1 18 is further configured to, e.g. by means of a transferring module 420 configured to, transfer information from the second part 112 to the first part 15 1 11. The information is arranged to relate to the scheduled second RAT transmission.

In some embodiments, the information is adapted to comprise any one or more out of: frequency, modulation, power, start of and duration of the scheduled transmission.

The network node 110, 118 is further configured to, e.g. by means of an mitigating 20 interference module 430 configured to, mitigate interference by the first part 1 11 during the second RAT transmission, in a part of the first RAT carrier where the second RAT carrier is not allocated, based on said information.

The network node 110, 118 is further configured to, e.g. by means of an ceasing 25 module 440 configured to cease by the first part 1 11 during the transmission in the

second RAT carrier, any transmission in a part of the first RAT carrier in which the second RAT carrier is allocated.

The network node 1 10, 1 18 is further configured to, e.g. by means of a processing 30 module 450 configured to process the information according to any one or more out of:

calculating an expected degradation of the first RAT carrier related to the scheduled transmission,

calculating Signal to Noise Ratio, SNR, and/or Signal to Interference plus Noise Ratio, SINR, based on the calculated an expected degradation of the first RAT carrier, calculating which subcarriers of the first RAT carrier that are affected by the scheduled transmission,

deciding whether or not to schedule any data on the affected subcarriers of the first RAT carrier, and

deciding whether or not to select a more robust modulation for any transmission on affected and unaffected subcarriers of the first RAT carrier for the duration of the scheduled second RAT transmission, based on said information and first RAT cell data, In these embodiments, the network node 1 10, 1 18 is further configured to, e.g. by means of the mitigating interference module 430 configured to mitigate the interference by the first part 1 11 , based on said information when processed.

The network node 110, 118 may further be configured to, e.g. by means of the transferring module 420 configured to, transfer second information from the first part 1 11 to the second part 1 12. The second information is arranged to relate to that the second RAT carrier collides with sensitive parts of the first RAT carrier.

In some embodiments, the network node 110, 118 is further configured to, e.g. by means of the mitigating interference module 430 configured to mitigate the interference by any one or more out of: Selecting an adjusted mode of transmission, performing inter frequency Offload of the first RAT carrier, performing inter cell frequency load balancing of the first RAT carrier, adjusting the cell capacity of the first RAT carrier, and performing inter RAT off load from the first RAT carrier.

The embodiments herein may be implemented through one or more processors, such as a processor 460 in the network node 1 10, 1 18 depicted in Figure 4, together with computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the network node 1 10, 1 18. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the network node 110, 118. The network node 1 10 may further comprise a memory 470 comprising one or more memory units. The memory 470 comprises instructions executable by the processor 460.

The memory 470 is arranged to be used to store e.g. information relating to the scheduled second RAT transmission such as any one or more out of: frequency, modulation, power, start of and duration of the scheduled transmission, second information relating to that the second RAT carrier collides with sensitive parts of the first RAT carrier, data, configurations, and applications to perform the methods herein when being executed in the network node 1 10, 118.

In some embodiments, a computer program comprises instructions, which when executed by the at least one processor 460, cause the at least one processor 460 to perform actions according to any of the Actions 201-206. In some embodiments, a carrier comprises the computer program, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer- readable storage medium. Those skilled in the art will also appreciate that the modules in the network node 1 10, 1 18, described above may refer to a combination of analog and digital circuits, and/or one or more processors 460 configured with software and/or firmware, e.g. stored in the memory 470, that when executed by the one or more processors such as the processor 460 as described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuitry (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system- on-a-chip (SoC).